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The purpose of this study was to compare the water accumulation in 3 types of metered dose inhaler (MDI) spacer shapes in-line in a ventilator circuit, in 2 positions over 2-, 4-, and 6-hour time periods through the use of heated- and nonheated-wire ventilator circuits.The study design was prospective, quasiexperimental, and random assignment.The study was conducted in a university laboratory.Three brands of MDI spacers (OptiVent, ACE, AeroVent) were tested.Grams of water accumulation were measured.Distilled water accumulation was measured in 3 brands of MDI spacers in 0 degrees and 45 degrees positions at 2-, 4-, and 6-hour time intervals. Water accumulation was measured in each spacer by calculating the differences between pretest (dry) weights and posttest (wet) weights through the use of an analytical balance. A Marquest SCT-3000 servo-controlled humidifier with heated-wire ventilator circuit was used with a room temperature range of 21.7 degrees C-22.8 degrees C (71 degrees -73 degrees F) and a relative humidity range of 57%-65%.Multivariate repeated measures analysis demonstrated a difference between brands (P.001). The amount of water accumulated during 6 hours (time variable) was significantly different (P.001), as was the interaction between time and "spacer brand" (with Greenhouse-Geisser adjustment). The interaction of time and position was also significantly different (P =.001). Water accumulations at a 45 degrees angle were: AeroVent 0.765 +/- 0.152 g; OptiVent 1.894 +/- 0.228 g; and ACE 4.043 +/- 0.665 g through 6 hours of use.We found that water accumulation was a result of the type of spacer, position of the spacer, and time that the spacer was left in-line. All 3 brands of spacer collected less than 5 mL of water over 6 hours in either position. Heated-wire circuits accumulated less water than nonheated-wire circuits and may be safer when using MDI spacers.

To determine the use of ventilator circuit and secretion management strategies in France and Canada.Binational cross-sectional survey.Intensive care unit (ICU) directors in French and Canadian university hospitals.We compared responses between countries regarding the use of seven circuit and secretion strategies, the rationales against their use, decisional responsibility for these strategies, whether ventilator-associated pneumonia (VAP) practice was audited, and whether VAP prevention guidelines addressing these strategies were used.The response rate was 72/84 (85.7%) for French and 31/32 (96.9%) for Canadian ICUs. Endotracheal intubation was predominantly oral in both countries. Changing the ventilator circuits only for every new patient was more frequent in France than in Canada (p.0001). Heated humidifiers were used more in Canada than France (p = .0003). Closed endotracheal suctioning was used more frequently in Canada (p.0001). In both countries, subglottic secretion drainage and kinetic beds were rarely used. Semirecumbent positioning was reported more often by French than Canadian ICUs (p = .003). Reasons for nonuse of these strategies included adverse effects (heat and moisture exchangers), cost (kinetic beds), lack of convincing benefit (subglottic secretion drainage), and nurse inconvenience (semirecumbency). Decisional responsibility for each strategy differed among institutions. VAP prevention practice was periodically reviewed in 53% of French and 68% of Canadian ICUs (p = .20). VAP prevention guidelines were used in 64% and 30% of these ICUs, respectively (p = .002).Our study does not support the notion that published recommendations substantially impact reported use of several ventilator circuit and secretion management strategies. Based on the use of more frequent ventilator circuit changes, closed suctioning systems, heated humidifiers, and respiratory therapists, ventilator circuit and secretion management practice appears more costly in Canada than in France.

The aim of this in vitro study was to investigate the measuring range and accuracy of a miniaturized equipment for respiratory impedance (Zrs) measurements in newborns using jet-pulses. Brief flow pulses (peak flow=16 L x min(-1), width=10 ms) were generated by a jet-generator consisting of a solenoid valve and an injector, situated between pneumotachograph and outflow resistance. Serially arranged resistance-inertance-compliance (R-I-C) lung models (RM=1.3-6.4 kPa x L(-1) x s, CM=7.4-36.9 mL x kPa(-1), IM=1.5 Pa x L(-1) x s2) were used to measure the real and imaginary part of Zrs between 4 and 50 Hz and to determine R, C and I by means of the method of least squares. The median errors for R, C and I were -0.1 kPa x L(-1) x s (-2%), 2.4 mL x kPa(-1)(13%) and -0.2 Pa x L(-1) x s2 (-13%) for measurements without breathing signals and 0.11 kPa x L(-1) -s (3%), 3 mL x kPa(-1) (16%) and 0.28 Pa x L (-1) x s2 (19%) in mechanically ventilated models. During spontaneous breathing the influence of the breathing flow on Zrs was negligible. The equipment did not show any nonlinearity when different pulse amplitudes were used (Vmax=13-22 L x min(-1)). The investigations have shown that jet-pulses allow reliable measurements of respiratory impedance and have the potential to provide valuable information about lung mechanics in spontaneously breathing and mechanically ventilated newborns. The developed measuring head has a low apparatus dead space, is easy to disinfect, has standard connections and can be used as the T-piece in a ventilator circuit.

Objective: To assess the feasibility of expiratory flow-volume curves as a measurement of respiratory mechanics during ventilatory support: to what extent is the shape of the curve affected by the exhalation valve of the ventilator? Design: Prospective, comparative study. Setting: Medical intensive care unit of a university hospital. Patients: 28 consecutive patients with various conditions, mechanically ventilated with both the Siemens Servo 900C and 300 ventilators, were studied under sedation and paralysis. Interventions: The ventilator circuit was intermittently disconnected from the ventilator at end-inspiration in order to obtain flow-volume curves with and without the exhalation valve in place. Measurements and results: Peak flow (PEF) and the slope of the flow-volume curve during the last 50 % of expired volume (SF50) were obtained both with and without the exhalation valve in place. The exhalation valve caused a significant reduction in peak flow of 0.3 l/s (from 1.27 to 0.97 l/s) with the Siemens Servo 900 C ventilator and of 0.42 l/s (from 1.36 to 0.94 l/s) with the Siemens Servo 300 ventilator (p < 0.001). The SF50 was not affected. Conclusion: In mechanically ventilated patients, the exhalation valve causes a significant reduction in peak flow, but does not affect the SF50. This study further suggests that the second part of the expiratory flow-volume curve can be used to estimate patients' respiratory mechanics during ventilatory support.

The multiple inert gas elimination technique (MIGET) is a robust tool to assess both ventilation-perfusion (V'A/Q') distributions and the role of extrapulmonary factors determining arterial oxygenation during spontaneous breathing and in mechanically ventilated patients. Mixed expired gas sampling used in the MIGET is most often obtained from a 10-L mixing box (10L-MB) placed in the expiratory side of the ventilator circuit. Consequently, a considerable increase in the compression volume (Vc) would be expected which, in turn, can give rise to potential errors in the estimation of the effective tidal volume delivered to the patient. The effects of the 10L-MB on the Vc were compared with those produced by a newly designed 1-L, mixing box (IL-MB). At a given peak pressure (Ppeak) within the ventilator circuit, the Vc generated by the 10L-MB was about six-times higher than that produced by the 1L-MB. At a Ppeak =50 cmH2O, the Vc were 377 mL (10L-MB) and 67 mL (1L-MB) (p

We report an incident involving a Fisher and Paykel “Three in One Respiratory Care System” (Fisher and Paykel Healthcare, Auckland, New Zealand). This is a new ventilator circuit designed to be adaptable to the needs of ventilator, intubated CPAP, and mask therapies. In this case the patient had received eight hours of CPAP therapy overnight, during which time the “Three in One” circuit had been broken down to the CPAP configuration. The expiratory limb heater element, normally disconnected, was inadvertently left connected to the heater base. Under the extreme conditions of heating under “no gas flow” mode, the heater element malfunctioned. As a result when the circuit was reconfigured to provide pressure-supported ventilation, in the high oxygen environment of the expiratory limb (FiO2 0.5), ignition and combustion of the respiratory circuit occurred. The case is reported because of the potentially serious consequences and because the incident prompted the manufacturer to redesign and change componentry in parts of the circuit implicated.

Nitric oxide (NO), in concentrations between 0 and 20 ppm, is currently being used as an inhaled agent to treat patients with post surgical complications and respiratory disorders. Because excessive levels of NO can be detrimental to the patient, NO must be monitored accurately and continuously. Currently available instruments have problems that limit their usefulness for this application. This paper discusses the development of an inexpensive, direct and continuous sensor for the measurement of inhaled nitric oxide. The sensor incorporates a 0.05 inch, gas permeable, flow-through liquid cell into a probe, which can be incorporated into a ventilator circuit. Sensor operation is based on the complexation reaction of NO with cytochrome-c, a biologically derived heme. The complex is monitored spectrophotometrically by measuring the absorbance in the visible region of the spectrum at 563 nm. The sensor is specific to NO in the presence of oxygen. This paper will address experiments to optimize sensitivity of the sensor. Increasing the flow rate and pressure of NO into the sensing chamber increased the optical absorbance at a high concentration of NO. Increasing the concentration of cytochrome-c increased the sensitivity of the sensor. The sensor is currently sensitive to a minimum concentration of 5 ppm and linear in the range of 5 to 175 ppm.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Objective: To evaluate the accuracy of physiologic deadspace (VD/VT) measurement, using a metabolic monitor. Design: Prospective collection of data. Setting: University-affiliated children's hospital with a 51-bed critical care area. Patients: Infants and children who were sedated and paralyzed and were receiving mechanical ventilation through a cuffed endotracheal tube. Interventions: None. Measurements and Main Results: Mlxed expired carbon dioxide tension (PECO 2 ) was measured. With the Douglas bag method, mixed expired gas was collected over 15 mins and was analyzed. With the metabolic monitor, FECO 2 was measured for 15 mins and the results were averaged. The PECO 2 was calculated by multiplying FECO 2 by the barometric pressure. The Paco 2 was measured simultaneously. The PECO 2 was corrected for the compressible volume in the ventilator circuit. All gas volumes were corrected for body temperature, pressure, and water vapor pressure. The physiologic deadspace/tidal volume ratio (VD/VT) was calculated for both techniques using the Enghoff modification of the Bohr equation. The accuracy of the VD/VT measured, by using the metabolic monitor, was assessed by comparing this measurement against the VD/VT measured by the Douglas bag method. This comparison was done by simple linear regression and correlation and by bias analysis (Bland and Altman method). The magnitude of compressible volume expressed as a fraction of the tidal volume delivered by the ventilator was compared with the error In VD/VT expressed as the difference between the uncorrected and corrected VD/VT. Sixteen paired measurements were made in 12 children. The VD/VT measured by the metabolic monitor correlated well with the VD/VT measured by the Douglas bag method (r 2 = .99; p

We examined the ability of a new combined nitric oxide (NO)/nitrogen dioxide (NO2) electrochemical analyser (PrinterNOx, Micro Medical Limited, Chatham, Kent, England) to measure NO and NO2 concentrations. The PrinterNOx was compared to a chemiluminescence analyser (42H, Thermo Environmental Instruments Inc, Franklin MA, U.S.A.). NO and NO2 were generated in a standard ventilator circuit using a paediatric ventilator (900C, Siemens Elema, Sweden) connected to an artificial lung (260li, TTL Test Lung, Michigan Instruments, MI, U.S.A.). Forty-four paired NO measurements ranging from 2.56 ppm to 74.6 ppm and 50 paired NO2 measurements ranging from 0.0 ppm to 5.39 ppm were obtained. For the measurement of NO the PrinterNOx showed a tendency to overestimate the chemiluminescence analyser. Regression analysis showed a close relationship between the two analysers with r2=0.9981 and a regression equation of y=1.1658 x +0.0197. In the more clinically important range of 0-25 ppm, r2 increased to 0.9996 with a regression equation of y=1.1984 x -0.4657. Conversely the PrinterNOx underestimated the chemiluminescence analyser for the measurement of NO2. The regression equation describing this relationship was y=0.879 x -0.0447 (r2=0.9993). We conclude that the PrinterNOx is of sufficient accuracy to be of clinical use in the administration of NO.

Objective To determine the risk of acquiring ventilator-associated pneumonia (VAP) and the impact on costs when extending ventilator circuit change intervals beyond 2 days to 7 and 30 days. Design Prospective 4-year review of mechanically ventilated patients. Setting The respiratory and medical ICUs of an 800-bed tertiary teaching Veterans Affairs hospital. Patients All adult patients receiving mechanical ventilation from January 1991 through December 1994. Interventions Ventilator circuits with active heated water humidifiers were changed at 2-day intervals during a 2-year control period, followed by 7-day and 30-day intervals (for 1 year each). Heated wire circuits were adopted with the 30-day interval. The rate of VAP per 1,000 ventilator days was calculated for each circuit change interval group. Survival analysis was used to model VAP with ventilator circuit change to determine risk. Results During the study period, 637 patients received mechanical ventilation. During the 2 years with 2-day change intervals, the VAP per 1,000 ventilator days was 11.88 (n=343), compared with 3.34 (n=137) and 6.28 (n=157) for 7-day and 30-day change intervals, respectively. The risk of acquiring a VAP for those with a circuit change every 2 days was significantly greater (relative risk, 3.1; p=0.0004; 95% confidence interval, 1.662, 5.812) than those with the 7- and 30-day circuit changes. Extending circuit change intervals reduced supply and labor costs averaging $4,231/yr for each ventilator in use. Conclusions Circuit change intervals of 7 and 30 days have lower risks for VAP than the 2-day intervals, yielding substantial reductions in morbidity as well labor and supply costs.

Tracheal gas insufflation (TGI) is the continuous or phasic insufflation of fresh gas into the central airways for the purpose of improving the efficiency of alveolar ventilation andJor minimizing the ventilatory pressure requirement. TGI usually employs modest flow rates of 2 to 15 L/min. Two mechanisms are responsible for improving the efficacy of conventional tidal breaths during TGI (1-3). First, fresh gas introduced by the catheter during expiration can dilute the CO2 stored in the series (anatomic) deadspace compartment proximal to its tip. Second, at high catheter flow rates, turbulence generated at the tip of the catheter can enhance gas mixing in regions distant to the catheter tip, thereby contributing to carbon dioxide removal. TGI is unlikely to be very effective when the alveolar as opposed to the series compartment dominates the total physiologic deadspace; yet at small tidal volumes (whenever series deadspace is especially high) or when alveolar ventilation is very low, TGI should be helpful (10). Many investigators have attempted to combine flow through an intratracheal catheter with conventional mechanical ventilation (CMV) techniques (5-13) as well as high frequency jet (14) and oscillatory (15) ventilation. This approach takes advantage of improved ventilatory efficiency due to anatomic deadspace washout as well as enhanced mixing due to catheter turbulence generated to permit reduction in tidal volume (VT)(11). Combining small tidal volumes with constant flow ventilation, delivers fresh gas further down the airways from the catheter site above the carina, bypassing the high-resistance central zone to achieve eucapnia at low flow rates (16). Furthermore, fresh gas introduced by the catheter improves the “efficacy” of each tidal breath.

Although the use of inhaled nitric oxide (NO) is currently still experimental, it is being used increasingly during mechanical ventilation to treat diseases characterized by hypoxemia and pulmonary hypertension [1–10]. Numerous approaches have been designed by researchers to administer NO via the mechanical ventilator [7–36] (Table 1), however few of these experimental approaches are capable of providing accurate, precise and consistent concentrations of inhaled NO without the potential for the formation of nitrogen dioxide (NO2) at concentrations up to 80 ppm NO and during all modes of ventilatory support regardless of their being assist or control [37]. In this chapter, information is presented regarding the technical limitations (precision/bias) and measurement capabilities of current commercially available NO/NO2 analyzers, as well as a detailed analysis of the various NO delivery systems in use, both developed by researchers and commercially available.

To determine the dose of inhaled budesonide suspension in the treatment of preterm infants with ventilator-dependent lung disease, we measured the dose of nebulized budesonide delivered through an endotracheal tube (ETT), using a test lung and filters. The effect of delivering the nebulized aerosol to two different locations in the same ventilatory circuit was evaluated. In addition, a new synchronized jet nebulizer was tested. The median drug delivery to the test lung was 0.3% (range, 0–0.4%) of the nominal dose when the nebulizer activated by continuous gas flow was inserted into the inspiratory line of the circuit. Drug delivery could be increased to 0.7% (range, 0.5–0.8%) by delivering the nebulizer output directly to the ETT. When using the synchronized jet nebulizer, drug delivery was 1.1% (range, 0.8–1.6%). The particle size of aerosol emerging from the ETT was 2.14 μm. The nebulization time with the synchronized nebulizer set-up was 38 min, while the other set-ups delivered an equal volume of solution in 6–7 min. Drug delivery of 0.3–1.1% to the test lung illustrates the problems encountered in aerosol treatment of intubated neonates. We conclude that the delivery of budesonide to the test lung can be increased by delivering the nebulizer output to the ETT directly. Using synchronized nebulization during inspiration only can achieve further increases in drug delivery, and wastage of drug during expiration is decreased. Synchronized nebulization may, therefore, have an important place in the delivery of expensive aerosolized drugs. Pediatr. Pulmonol. 1997;24:282–286. © 1997 Wiley-Liss, Inc.

Simultaneous measurements of nitric oxide (NO) (0-80 ppm) using a chemiluminescence monitor and two electrochemical monitors were performed during simulated paediatric mechanical ventilation. The mean difference (bias) between the chemiluminescence (Model 42H Thermo Environmental Instruments Inc) and an electrochemical monitor (Pulmonox Research and Development Corp) was 0.52±6.52 ppm (SD). The 95% confidence limits of the mean difference were 3.00 to −1.96 ppm and the limits of agreement between the two techniques were 13.56 to −12.52 ppm. The mean difference between the chemiluminescence monitor and another electrochemical monitor (NOxBox, Bedfont Scientific Inc) was −7.27±4.29 ppm. The 95% confidence limits of the mean difference were −9.02 to −5.56 ppm and limits of agreement of the two techniques were −16.13 to 1.55 ppm. These results suggest that electrochemical monitors may be used to guard against potentially toxic concentrations of NO (greater than 20 ppm). However they do not suggest that either of the electrochemical monitors may be used with confidence in lieu of the chemiluminescence monitor to regulate NO at low clinical NO levels (1-5 ppm).

Objectives Mechanical ventilation in patients with obstructive airway disease (OAD) is associated with the development of dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEPi). One of the effects of this form of PEEPi is to act as an inspiratory threshold load that can produce ineffective breath triggering, dyspnea, and muscle fatigue. Recently it has been shown that applying PEEP in the ventilator circuit can reduce this imposed triggering load. We wished to investigate this further by studying patients with OAD being weaned with pressure support (PS) ventilation. Our first objective was to determine the prevalence and magnitude of this form of PEEPi in OAD patients who were clinically judged to be capable of triggering mechanical ventilatory breaths. Our second objective was to attempt to reduce the triggering load by applying circuit PEEP and then observe the response of patient-ventilator interactions during the patient-triggered, pressure-limited PS breath. Design Thirteen random patients with OAD who were receiving PS ventilation were studied by measuring airway pressures, airway gas flow, baseline esophageal pressure, esophageal pressure time products (PTP), and esophageal pressure changes before ventilator gas delivery began (APes taken to represent PEEPi). Measurements were made at baseline and after stepwise increases in circuit PEEP up to the PEEPi. Results We found measurable PEEPi in all patients (average ±SD of 9.54±4.3 cm H 2 O) and it was > 10 cm H 2 O in seven patients. As would be predicted, we observed progressive reductions in PEEPi as applied PEEP was given. We also observed that the component of patient effort (PTP) related to overcoming PEEPi also decreased, but the PTP related to tidal volume (VT) did not. The VT associated with the set PS thus did not change with application of PEEP, nor did the breathing frequency. Conclusion PEEPi is common in OAD patients receiving mechanical ventilatory support. The imposed triggering load from PEEPi can be offset to large extent by circuit PEEP approaching the baseline PEEPi. Although total patient effort substantially falls with applied PEEP, the patient effort that combine with PS to effect VT does not.

Pneumonia is the major infectious cause of mortality and morbidity in the mechanically ventilated, critically ill patient, yet the condition remains difficult to treat successfully and currently available preventive strategies are, at best, only moderately effective.

Objective: To assess whether paralysis alters pulmonary deposition of albuterol delivered by metered dose inhaler and spacer to small animals. Design: A parallel group study of intubated and ventilated rabbits. Interventions: Animals in group 1 (n = 7) were paralyzed with intravenous pancuronium, and ventilated at a rate of 30 breaths/min. The animals in group 2 (n = 6) were ventilated at a rate of 10 breaths/min under light anesthesia without paralysis. In this latter group, spontaneous respiration continued at a rate of 40 to 50 breaths/min. Both groups were maintained at Paco 2 of 35 to 40 torr (4.7 to 5.3 kPa), and other ventilatory settings were identical. Measurements and Main Results: Technetium-99m labeled albuterol aerosol was delivered by metered dose inhaler via a spacer device to both groups. Pulmonary deposition of the aerosol, determined by measuring the radioactivity in the lung tissues at autopsy, was expressed as percent of the total radioactivity dispensed by the metered dose inhaler. Group 2 showed significantly greater lung deposition than group 1 (0.510 ± 0.076 [SEM] % vs. 0.226 ± 0.054%, p =.0094). Deposition in the airway, the endotracheal tube, and the ventilator circuit did not differ significantly. Conclusion: Metered dose inhaler delivery of aerosolized medications to ventilated rabbits is significantly enhanced if respiration is not controlled. This observation might have implications for the delivery of therapeutic aerosols to newborns and young infants receiving slow, intermittent, mandatory ventilation.

BACKGROUND: Ventilator-associated pneumonia (VAP) is a significant complication in critically ill, intubated pediatric patients. While there are data demonstrating effective interventions in decreasing the incidence of VAP in adults, there is little data regarding interventions to decrease VAP in the pediatric population. We describe a multidisciplinary approach to decrease VAP in a pediatric intensive care unit (PICU). METHODS: The PICU at St. Louis Children's Hospital is a 26-bed multidisciplinary unit. In September 2003, education regarding the pathophysiology and risk factors of VAP was given to PICU physicians, nurses, and respiratory therapists in the form of educational flyers, a self-study module, and lectures. VAP was defined according to CDC NNIS definitions, and the rate expressed as number of VAP episodes per 1000 ventilator (vent) days. In January 2004, a PICU team consisting of management, an intensivist, an infection control practitioner, an advanced practice nurse, staff nurses, and respiratory therapists was assembled to identify and implement strategies to decrease the incidence of VAP. Interventions known to affect the incidence of VAP in adults were targeted. These included: elevation of head of bed (HOB) 30 degrees, use of in-line suction (minimizing breaks into the system), wearing gloves while draining the ventilator condensate away from the patient, and emphasizing hand hygiene before and after handling the ventilator/ventilator circuit. VAP rates for the PICU were shared with physicians, nurses, and respiratory therapists on a monthly basis and posted in areas accessible to staff. Pre- and post-intervention VAP rates were compared using chi square. RESULTS: The baseline VAP rate in 2002, pre intervention, was 9.1 (41 VAP/4509 vent days). In 2003, the rate was 8.8 (33 VAP/3741 vent days). In 2004, the rate decreased to 3.3 (14 VAP/4202 vent days). This represents a decrease of 42% from 2003 (p=0.001). CONCLUSION: A multidisciplinary team approach with focused interventions, including educational programs, can decrease VAP in the PICU. Similar to findings in adult populations, elevating the HOB 30 degrees, avoiding interruption of the ventilator circuit, and wearing gloves when handling ventilator condensate can decrease the incidence of VAP. It is especially important to involve members of the patient care team in addition to infection control in order to implement and monitor interventions.

Inhaled NO has become widely used for diagnosis and therapy of pulmonary hypertension. The potential hazards of NO inhalation include the formation of methemoglobin, formation of NO2, and generation of free radicals in the presence of humidity and oxygen. Careful monitoring of NO and NO2 concentration, and titration of the dose according to a patient's clinical response is essential to minimize toxicity. This paper describes a formula and method that permits calculation and precise control of NO concentration in the inspired gas. The accuracy of the delivery system was assessed by a comparison of calculated and measured NO and NO2 concentrations in a continuous flow ventilator circuit. A comparison of electrochemical detector (ECD) versus chemiluminescence detector (CLD) monitoring techniques showed agreement between the instruments within ∼2 ppm, with the ECD averaging a higher reading than the calculated or CLD measured values. We deemed a 2 ppm discrepancy between instruments clinically acceptable, and concluded that the instruments could be used interchangeably for clinical purposes to measure NO, and that the ECD was preferable to CLD for measuring NO2. Details about the equipment are given and techniques are discussed to avoid the risk of inhalation of toxic concentrations of NO and NO2. This method provides the possibility of using inhaled NO with appropriate safety precautions in the range 0–60 ppm in a variety of continuous flow respiratory devices. Pediatr Pulmonol. 1996; 22:182–187. © 1996 Wiley-Liss, Inc.

Objective : To evaluate a portable scavenging system for nitric oxide and its oxides, designed for use on neonatal transport. Design : A prospective evaluation of the nitric oxide scavenging system, using a neonatal transport incubator ventilator and a test lung. Setting : Laboratory of a tertiary care children's hospital. Interventions : The scavenging system was tested, using a neonatal transport Incubator with attached ventilator, ventilator circuit, and a neonatal test lung. Nitric oxide was administrated on the inspiratory limb, and nitric oxide and its oxides were measured in the expiratory gas after passing through the scavenger. Measurements and Main Results : A modified scrubber assembly was filled with 50% activated charcoal and 50% aluminas potassium permanganate pellets (3). Three wire meshes were placed before, in between, and after the two chemicals to facilitate gas flow. Using the maximum FIO 2 , with a nitric oxide concentration of 120 parts per million (ppm), the test lung continuous flow ventilation (FIO 2 of 0.86, peak inspiratory pressure of 30 cm H 2 O, positive end-expiratory pressure of 6 cm H 2 O, and respiratory rate of 60 breaths/min) was performed for 4 hrs with each of four freshly prepared scavenging systems. A fifth scavenging system was tested for a 12-hr period. The mean composition of the exhaled gases for 4 hrs were : nitric oxide 0.01 ± 0.03 (SD) ppm, nitric dioxide 0.06 ± 0.06 ppm, and other oxides 0.05 ± 0.09 ppm. After 12 hrs of 120 ppm of inhaled nitric oxide, the fifth scavenger system had undetectable nitric oxide, nitric dioxide, and other oxides in the exhaled gas. Normal room air contained between 0.0 and 0.03 ppm of nitric oxide, 0.0 and 0.02 ppm of nitric dioxide, and 0.0 and 0.02 ppm of other oxides. Conclusion : Nitric oxide, nitric dioxide, and other dioxides can be safely scavenged by this portable scavenging system, allowing safe administration of nitric oxide free from environmental contamination with nitric oxide and its oxides.

Metered-dose inhalers (MDIs) provide several advantages over nebulizers, including ease of administration, decreased cost, reliability of dosing, and freedom from contamination. However, this method of aerosol delivery has been considered ineffective in mechanically-ventilated patients because most of the aerosol deposits in the endotracheal tube and ventilator circuit. A smaller amount of aerosol from a MDI is deposited in the lower respiratory tract of mechanically-ventilated patients than in ambulatory patients, although recent studies show that a significant bronchodilator effect can still be achieved. When employed optimally, significant bronchodilation occurs with as little as 4 puffs of a sympathomimetic aerosol. Multiple factors influence the efficacy of MDIs in mechanically-ventilated patients. The method of connecting the MDI canister to the ventilator circuit has a marked effect on aerosol delivery, and other factors include the timing of MDI actuation, ventilator mode, tidal volume, circuit humidity, and duty cycle. With a proper technique of administration, a MDI serves as an effective, convenient, and safe method for delivering bronchodilator aerosols in mechanically-ventilated patients.

BACKGROUND: Jet nubulisers and metered dose inhalers are widely used to deliver aerosolised drugs to the lungs of intubated patients in adult intensive care units. Drug delivery using these systems has been shown to be inefficient and both forms of delivery have the potential to induce paradoxical bronchoconstriction in patients with reactive airways disease. METHODS: Experiments were carried out to determine whether it was possible to deliver drug from a dry powder delivery system through an endotracheal tube. A 200 micrograms budesonide Turbohaler was enclosed in a chamber which allowed it to be inserted into a ventilator circuit. Experiments were performed with a multistage liquid impinger in which drug was drawn through the Turbohaler and endotracheal tube at 60 l/min providing an index of the maximum drug delivery achievable via this route. A second series of experiments was performed in which the Turbohaler was placed in a ventilator circuit using a Servo 900C volume cycled ventilator. Drug delivered from the Turbohaler during the inspiratory phase was collected on a filter placed between the end of a 9 mm endotracheal tube and a model lung. A tidal volume of 500 ml and inspiratory time of 0.5 seconds was used. Budesonide was assayed using an ultraviolet spectrophotometric assay. RESULTS: Thirty percent of the nominal dose passed through the endotracheal tube and was collected in the multistage liquid impinger. Mean drug delivery to the filter in the ventilator circuit was 20%. CONCLUSIONS: This in vitro study indicates that drugs from dry powder inhalers (in this case the Turbohaler) can be satisfactorily delivered through endotracheal tubes and that clinical evaluation of this technique is now indicated.

The purpose of this study was to verify whether, compared with the introduction of the NO-N2 mixture at the air inlet of the ventilator (classical method), a direct injection of NO-N2 into the inspiratory line of the ventilator circuit with a new injection device (new method), would reduce NO2 formation by reducing contact time between O2 and NO. The effect of two FIO2(0.21 and 0.90) and NO concentrations on NO2 production was determined. In the classical method, NO and O2 were mixed with an air/oxygen blender before the gas mixture entered the ventilator. In the new method, NO was injected directly into the respiratory line with the injection system. Nitric oxide and nitrogen dioxide gases were measured using a chemiluminescence analyzer. For a FI02 of 0.90 and 90 ppm of NO2, the amount of NO2 produced was decreased from 8.9 +/- 0.8 ppm (mean +/- SD) with the classical injection system to 4.4 +/- 0.2 ppm with the new injection system (P = 0.0039, Mann-Whitney test), and NO2 production was decreased from 4.5 +/-0.2 ppm to 2.1 +/- 0.4 ppm (P = 0.02) at 60 ppm of NO. However, at a FIO2, no difference was found in the amount of NO2 produced. We conclude that, compared with the classical method of NO administration, the new NO injection system reduces considerably the concentration of inhaled NO2 when a high FIO2 and a high concentration of NO are used.

To investigate whether a new flow-triggered (FT) system can reduce the patient's inspiratory effort compared to a traditional pressure-triggered (PT) system during weaning from mechanical ventilation. Prospective study. Intensive care unit of a General Hospital. 10 mechanically ventilated patients, without chronic airway disease, ready to wean. Minute ventilation, breathing pattern, lung mechanics, inspiratory work of breathing (WI) and pressure time product (PTP) of Ppl were obtained in two conditions: 1) unsupported spontaneous breathing through the ventilator circuit (SB); 2) spontaneous breathing with continuous positive airway pressure set at 5 cmH2O (CPAP). Two triggering systems, namely PT and FT, were used in each condition. Though there was no change in breathing pattern, minute ventilation, and lung mechanics, the magnitude of the inspiratory effort decreased significantly with FT compared to PT in both instances. The added resistance (total flow resistance minus pulmonary resistance) decreased by 37% on average when FT replaced PT. PTP decreased, on average, 27% and 15% during SB and CPAP, respectively, with FT compared to PT (p

BACKGROUND: Detrimental physiologic effects of shivering in the cardiac surgery patient have been well documented. Rewarming techniques have been compared, with noted differences in the incidence of shivering. Ventilator circuits have not been examined independently from other rewarming variables. OBJECTIVE: To compare heated wire humidification circuits with heat and moisture exchanger circuits on the incidence of shivering and speed and pattern of rewarming in mechanically ventilated patients. METHODS: A prospective, descriptive, correlational study was done on 140 adult cardiac surgery patients in a university teaching medical center. All subjects underwent cardiac surgical procedures with hypothermic cardiopulmonary bypass. Subjects were randomized to humidified, heated wire circuits (n = 70) or heat and moisture exchanger circuits (n = 70). Heated water blankets were used on all patients. RESULTS: Mean intensive care unit admission temperature was 35.28 degrees C. No statistical differences were found in preoperative, demographic, or operative course data between treatment and control groups. Shivering was more common in the heat and moisture exchanger group than in the heated wire group. In our analysis, the only variable associated with shivering was the type of ventilator circuit. Patients using heated wire systems rewarmed more rapidly and had significantly higher temperatures than did patients using heat and moisture exchangers. CONCLUSION: These data suggest that use of heated wire humidified ventilator circuits with heated water blankets in adult cardiac surgery patients significantly reduces the incidence of shivering and results in a more rapid return to normothermia.

The contribution of ventilator circuit bacterial contamination to the occurrence of ventilator-associated pneumonia remains controversial. In a previous study, we found that the incidence of pneumonia was identical with ventilator circuit changes every 48 h and with no ventilator circuit changes. The present study prospectively assessed whether keeping ventilator circuits clean with a heat and moisture exchanger exhibiting antimicrobial barrier properties affects patient colonization and the incidence of nosocomial pneumonia in patients receiving mechanical ventilation for more than 48 h. Consecutive patients were randomly allocated to humidification with either a heat and moisture exchanger (Group 1, n = 61) or a heated humidifier (Group 2, n = 70). In both groups, no circuit changes were performed throughout ventilatory support. Duration of mechanical ventilation was identical in both groups (10 +/- 8.6 d (range: 2 to 47) in Group 1 and 12.5 +/- 14.2 d [range: 2 to 85] in Group 2). The incidence of pneumonia (positive quantitative culture of protected brush specimen) was similar in both groups (6/61 and 8/70 in Groups 1 and 2, respectively; p = 0.8), as was duration of ventilation prior to pneumonia (9 +/- 5.9 versus 8.2 +/- 5.7 d; p = 0.8). Ventilator tubing contamination was considerably reduced with the use of a heat and moisture exchanger. In contrast, bacterial colonization of the pharynx and trachea was identical in both groups. These results suggest that circuit colonization plays little or no role in the occurrence of ventilator-associated pneumonia, provided usual maintenance precautions are applied.(ABSTRACT TRUNCATED AT 250 WORDS)

Introduction PPHN is treated with inhaled nitric oxide (iNO). A novel ventilator circuit connector (NVCC, AFECTAIR®, Discovery Laboratories, Inc., Warrington, PA) has been developed to simplify the delivery of aerosols to patients receiving ventilatory support. We hypothesized that use of the NVCC for iNO delivery would substantially reduce NO consumption. Aim To compare the NVCC with the SoC in the delivery of iNO under simulated neonatal ventilator conditions. Material and Methods A pediatric/neonatal test system with Babylog® VN-500 with various inspiratory pressures, test lung, and ASL-5000 lung simulator were used. For SoC measurements, using a standard wye connector, the iNO was delivered per the manufacturer’s instructions. With the NVCC, iNO was administered by introducing the NO via a tube attached directly to the NVCC. NO concentrations were measured with a NOxBOX®+ analyzer and NO flow was recorded by Electronic Nitric Oxide flow controller abd titrated to 20 ppm at the patient interface. Results Compared with SoC, there was a 2 to 3 fold decrease in NO flow requirements to achieve desired iNO concentration with the NVCC. The delivery of O2 was not different between the study conditions. NO2 levels were slightly higher for the NVCC group, but never higher than 1.13 ppm. Conclusion The NVCC significantly decreased the NO flow required for targeted delivery of 20 ppm. The NVCC allows for simplified therapeutic gas delivery with reduced NO utilization. These results warrant further study of NVCC on compatibility assessment with various modes of ventilation and delivery of other medical gases.

Background Bronchoscopic bronchoalveolar lavage (BAL) in mechanically ventilated patients requires a large endotracheal tube, physician expertise, expensive equipment, and support staff. Methods The Ballard BAL catheter is a disposable coude tip 16F device that can be attached to the endotracheal tube and ventilator circuit without loss of positive end-expiratory pressure (PEEP) and also allows supplemental delivery of oxygen between the 12F inner and outer catheters. The catheter is directed into the selected bronchus. The inner catheter with mushroom tip is then advanced until it wedges by feel. Thirteen patients at a tertiary care, university hospital, had BAL performed through both the bronchoscope and Ballard BAL catheter using five aliquots of 20 mL of normal saline solution each. The return was quantified and submitted for blinded, paired laboratory investigations, including Gram stain and quantitative culture, and special stains and cultures as clinically appropriate. Results The procedure was well tolerated in all patients with no difference between devices in oxygen saturations; however, air leaks occurred in patients undergoing bronchoscopy and compromised safety in one. Two patients required reintubation to facilitate passage of the bronchoscope. The bronchoscopic BAL return averaged 49 mL (range, 5 to 85 mL) while BAL catheter averaged 37 mL (range, 18 to 70 mL) both being sufficient for all desired investigations except one patient who had undergone bronchoscopy. All were of excellent quality based on microscopy. The BAL results were concordant in nine patients: two Pneumocystis carinii , one Candida, one Streptococcus agalactiae , one Streptococcus pneumoniae , and no infection in four. Diagnoses of tuberculosis and Enterococcus (confirmed by blood culture) were obtained by the Ballard BAL catheter only. Kaposi's sarcoma and metastatic histiosarcoma were visualized by bronchoscope only. Two patients had compassionate plea use of the Ballard BAL catheter because of a small endotracheal tube. Hemorrhage secondary to lupus was documented in one and nosocomial infection was excluded in the other. Conclusions The Ballard BAL catheter allows easy, safe BAL, without loss of diagnostic yield, when visualization is not required in mechanically ventilated patients. The Ballard BAL catheter allows maintenance of PEEP when used with the supplied adapter and can be used with small endotracheal tubes.

Subject objective To assess the hemodynamic effects of manual lung hyperinflation in mechanically ventilated patients and to measure the different inspiratory pressures and tidal volumes generated by different operators. Design Measurements of aortic blood flow (by esophageal Doppler ultrasonography), systemic blood pressure, tidal volumes (by respirometry), and inspiratory pressures in the ventilator circuit were measured on the ventilator, during six intended manual hyperinflations (tidal volume > 150% that delivered by ventilator) using a 2-L rebreathing bag, and at 1,5,10, and 15 min after reconnection to the ventilator. Setting Intensive care unit. Patients Eighteen mechanically ventilated patients with normovolemia and stable circulatory status were assessed on a total of 20 occasions. Interventions Patients were disconnected from the ventilator to enable six manual hyperinflations to be given. Measurements were made before and at 5-min intervals until no further hemodynamic changes were seen. Measurements and results: Hyperinflation (50% increase in tidal volume) was achieved only in 10 of 20 studies. Large variations were seen in percentage change in peak inspiratory pressure (—30% to +250%) and tidal volume (—33% to +127%) generated. Falls in cardiac output correlated to the increase in tidal volume but not to the increase in peak inspiratory pressure and took up to 15 min to recover to baseline values. Changes in cardiac output were independent of lung compliance and concurrent vasoactive drug support. No consistent change was noted in either blood pressure or heart rate. Conclusions Lung hyperinflation is frequently not achieved by the manual technique. Significant changes in cardiac output can occur and appear to be related to the tidal volume rather than pressure generated.

to determine and compare the microbial retention efficiency of 3 types of heat and moisture exchange (HME) filters.randomised prospective study.Intensive Care Unit at the Middlesex Hospital and the microbiology laboratory of the Department of Academic Microbiology, University College London Medical School.An aerosol challenge to each filter using a suspension containing. S. marcescens and the bacteriophage MS2. In total 45 filters of 3 types were tested, 15 previously unused and 30 that had been used in ventilator circuits of 30 patients. The 3 types of filter generally had microbial retention efficiencies of99.99% for both S. marcescens and the bacteriophage MS2.The 3 types of HME filter were effective microbial filters and comparable in their microbial retention.

Our goal was to evaluate the accuracy of a prediction equation that estimates the minimal level of pressure support (PS) required to overcome the resistance of the ventilator circuit and the endotracheal tube during mechanical ventilation. We calculated the minimal PS (PSmin) by means of the relationship between airway resistance and peak inspiratory flow rate during mechanical ventilation. Measurements of breathing pattern, flow rates, work of breathing (WOB), pressure time product (PTP), and PEEPi were made during several modes of ventilation (PSmin, PSmin + 25 percent, PSmin-25 percent, flow by, CPAP 0 cm H2O) and while breathing through an endotracheal tube (ETT) and spontaneous breathing (EXT). The WOB was significantly higher during EXT than PSmin, PSmin-25 percent, and ETT (1.04 vs 0.45, 0.54, and 0.74 J/L, respectively, p0.05). An unexpected finding was a higher WOB and PTP during EXT as compared with ETT in six of seven of our patients (1.04 vs 0.74 J/L). Examination of breathing pattern and flow volume loops in these two breathing modes raises the possibility that the post-EXT pathology increases in WOB is related to upper airway abnormality. Because of this, our predicted PSmin underestimated the WOB required for spontaneous breathing immediately post EXT.

Objective: To determine the influence of nebulizer types and nebulization modes on bronchodilator delivery in a mechanically ventilated pediatric lung model. Design: In vitro, laboratory study. Setting: Research laboratory of a university hospital. Interventions: Using albuterol as a marker, three nebulizer types (jet nebulizer, ultrasonic nebulizer, and vibrating-mesh nebulizer) were tested in three nebulization modes in a nonhumidified bench model mimicking the ventilatory pattern of a 10-kg infant. The amounts of albuterol deposited on the inspiratory filters (inhaled drug) at the end of the endotracheal tube, on the expiratory filters, and remaining in the nebulizers or in the ventilator circuit were determined. Particle size distribution of the nebulizers was also measured. Measurements and Main Results: The inhaled drug was 2.8% ± 0.5% for the jet nebulizer, 10.5% ± 2.3% for the ultrasonic nebulizer, and 5.4% ± 2.7% for the vibrating-mesh nebulizer in intermittent nebulization during the inspiratory phase (p < 0.01). The most efficient nebulizer was the vibrating-mesh nebulizer in continuous nebulization (13.3% ± 4.6%, p < 0.01). Depending on the nebulizers, a variable but important part of albuterol was observed as remaining in the nebulizers (jet and ultrasonic nebulizers), or being expired or lost in the ventilator circuit (all nebulizers). Only small particles (range 2.39-2.70 μm) reached the end of the endotracheal tube. Conclusions: Important differences between nebulizer types and nebulization modes were seen for albuterol deposition at the end of the endotracheal tube in an in vitro pediatric ventilator-lung model. New aerosol devices, such as ultrasonic and vibrating-mesh nebulizers, were more efficient than the jet nebulizer.

This study was to determine whether the PconCO2 and PconO, which collect in the expiratory trap of a ventilator circuit are equivalent to PĒCO2 and PĒO2. Fifty studies were performed in 34 mechanically ventilated male patients. Five milliliters of condensate fluid were collected and PĒCO2 and PĒO2 were measured. Exhaled gases were collected simultaneously with condensate fluid for 5 min in a meteorologic balloon and FĒCO2 and FĒO2 were measured; PĒCO2 and PĒO2 were then calculated. The mean PĒCO2 was not significantly different from PconCO2 nor was the PconO2 significantly different from the condensate PconO2. There was a high correlation between mixed expired PĒCO2 and PconCO2 as well as PĒO2 and PconO2. These data indicate expiratory PconCO2 and PconO2 provide a valid reflection of PĒCO2 and PEO2. The PconCO2 and PconO, measured in a clinical blood gas analyzer are accurate and may be used in calculation of Vd/Vt and in metabolic assessments.

OBJECTIVE To evaluate a new and simple method for the measurement of intrinsic positive end-expiratory pressure during controlled and assisted modes of mechanical ventilation. DESIGN Prospective study. SETTING Three university hospital medical ICUs. PATIENTS A total of 13 intubated, mechanically ventilated patients with severe airway obstruction. INTERVENTIONS Airway occlusions reproducibly timed to occur coincidently with end-expiration were obtained by: a) manipulation of a three-way manual valve placed in the inspiratory limb of the external ventilator circuit (manual valve method) and b) activation of the expiratory pause hold function of the mechanical ventilator (Siemens 900C). MEASUREMENTS AND MAIN RESULTS Airway pressure, flow, and volume were recorded during controlled and assisted modes of mechanical ventilation. Intrinsic positive end-expiratory pressure was determined from the plateau in airway pressure, which was developed during end-expiratory occlusions. For controlled mechanical ventilation, intrinsic positive end-expiratory pressure averaged 11.42 +/- 0.77 (SEM) cm H2O with the manual valve method, compared with 11.38 +/- 0.70 cm H2O, using the ventilator expiratory pause hold function. There was close correlation between results over the wide range of intrinsic positive end-expiratory pressure observed, which varied from approximately 5 to 22 cm H2O (y = 1.08x - 0.92; r2 = .99). Values of intrinsic positive end-expiratory pressure were comparable for the two methods during assist-control ventilation, pressure support ventilation, and spontaneous breathing through the ventilator circuit. The manual valve method was also effective when tested with different mechanical ventilators using a mechanical lung model. CONCLUSIONS The manual valve method can be used to determine intrinsic positive end-expiratory pressure during controlled and assisted modes of ventilatory support with current ventilators. The availability of such an approach should facilitate the routine monitoring of intrinsic positive end-expiratory pressure in mechanically ventilated patients, thereby aiding clinical decision-making and management in these critically ill individuals.

Ventilator equipment maintenance includes cleaning, sterilization, adjustment, servicing, and repair. There are two ways of doing this: 1. All maintenance procedures can be performed by a biomedical central service unit in charge of the ventilators of the whole hospital. The principal problem here is the possible lack of cooperation between the technical and medical staff, leading to what might be called a “technical desert.” 2. Maintenance can be carried out between the various ICUs. The biomedical service center does only essential repairs, with or without the assistance of outside after-sales service engineers. In this case, maintenance work is available only if there is a small specialized team responsible for preventive maintenance inside the ICU. Its main responsibilities are to ensure optimal utilization, constant surveillance, detection and correction of minor faults, and instruction of the users.

Background Perfluorocarbon (PFC) vapour in the expired gases during partial liquid ventilation should be prevented from entering the atmosphere and recovered for potential reuse. This study aimed to determine how much PFC liquid could be recovered using a conventional humidified neonatal ventilator with chilled condensers in place of the usual expiratory ventilator circuit and whether PFC liquid could be recovered when using the chilled condensers at the ventilator exhaust outlet. Methods Using a model lung, perfluorocarbon vapour loss during humidified partial liquid ventilation of a 3.5 kg infant was approximated. For each test 30 mL of FC-77 was infused into the model lung. Condensers were placed in the expiratory limb of the ventilator circuit and the amounts of PFC (FC-77) and water recovered were measured five times. This was repeated with the condensers placed at the ventilator exhaust outlet. Results When the condensers were used as the expiratory limb, the mean (± SD) volume of FC77 recovered was 16.4 mL (± 0.18 mL). When the condensers were connected to the ventilator exhaust outlet the mean (± SD) volume of FC-77 recovered was 7.6 mL (± 1.14 mL). The volume of FC-77 recovered was significantly higher when the condenser was used as an expiratory limb. Conclusion Using two series connected condensers in the ventilator expiratory line 55% of PFC liquid (FC-77) can be recovered during partial liquid ventilation without altering the function of the of the ventilator circuit. This volume of PFC recovered was just over twice that recovered with the condensers connected to the ventilator exhaust outlet.

192 Investigations of The F & P Neonatal Dry Ventilator Circuit in High Frequency Mode on the Drager 8000 Plus Ventilator

During invasive mechanical ventilation due to the dryness of medical gases is necessary to provide an adequate level of conditioning. The hot water humidifiers (HWH) heat the water, thus allowing the water vapor to heat and humidify the medical gases. In the common HWH there is a contact between the medical gases and the sterile water, thus increasing the risk of patient's colonization and infection. Recently to avoid the condensation in the inspiratory limb of the ventilator circuit, new heated ventilator circuits have been developed. In this in vitro study we evaluated the efficiency (absolute/relative humidity) of three HWH: (1) a common HWH without a heated ventilator circuit (MR 730, Fisher & Paykel, New Zeland), (2) the same HWH with a heated ventilator circuit (Mallinckrodt Dar, Italy) and (3) a new HWH (DAR HC 2000, Mallinkckrodt Dar, Italy) with a heated ventilator circuit in which the water vapor reaches the medical gases through a gorotex membrane, avoiding any direct contact between the water and gases. At a temperature of 35°C and 37°C the HWH and heated tube were evaluated. The absolute humidity (AH) and relative humidity (RH) were measured by a psychometric method. The minute ventilation, tidal volume respiratory rate and oxygen fraction were: 5.8 ± 0.1 l/min, 740 ± 258 ml, 7.5 ± 2.6 bpm and 100%, respectively. Ventilator settings were maintained constant for all the study period. The measurements were taken after 60 min of continuous use. At 35°C the output of the MR 730 with a heated tube was insufficient to provide adequate levels of conditioning, while at 37°C all the three devices were satisfactory. Table 1 Results as mean ± SD

Suctioning of artificial airways is a necessary procedure but is not without risk. Hypoxaemia is a recognised complication. Several small studies have suggested that closed suction catheters offer benefits over open suction because disconnection from the ventilator circuit is not required [1], thereby maintaining ventilation, FIO2 and PEEP. Other studies have sought to prove the maintenance of lung volume and cardiovascular stability with closed suction [2]. There is little evidence that closed suction systems offer clinical advantage over open suction in terms of arterial oxygenation. No published study had compared changes in PaO2/FIO2 post suction. We performed a study in critically ill adults to identify any differences in PaO2/FIO2 between closed and open suction for a given PEEP.

Objective.—Ventilator-associated pneumonia (VAP) is a serious complication of critical illness, conferring increased morbidity and mortality. Many interventions have been studied to reduce the risk of VAP. We systematically reviewed the influence of airway management on VAP in critically ill patients.Data Sources.—Studies were identified through searching MEDLINE and EMBASE from 1980 through July 1997 and by searching SCISEARCH, the Cochrane Library, bibliographies of primary and review articles, personal files, and contact with authors of the randomized trials.Study Selection.—We selected randomized trials evaluating ventilator circuit and secretion management strategies on the rate of VAP.Data Extraction.—Two investigators independently abstracted key data on design features, the population, intervention, and outcome of the studies.Data Synthesis.—The frequency of ventilator circuit changes and the type of endotracheal suction system do not appear to influence VAP rates (3 trials, none with significant difference; range of relative risks [RRs], 0.84-0.91). However, lower VAP rates may be associated with avoidance of heated humidifiers and use of heat and moisture exchangers (5 trials, only 1 showing a significant difference; range of RRs, 0.34-0.86), use of oral vs nasal intubation (1 trial; RR, 0.52; 95% confidence interval, 0.24-1.13), subglottic secretion drainage vs standard endotracheal tubes (2 trials, 1 showing a significant difference; range of RRs, 0.46-0.57), and kinetic vs conventional beds (5 trials, only 1 showing a significant difference; range of RRs, 0.35-0.78).Conclusions.—Some ventilator circuit and secretion management strategies may influence VAP rates in critically ill patients. Whether these strategies are adopted in practice depends on several factors such as the magnitude and precision of estimates of benefit and harm, as well as access, availability, and costs.

Background Mechanical ventilator circuits are commonly changed at 48-h intervals. This frequency may be unnecessary because ventilator-associated pneumonia often results from aspiration of pharyngeal secretions and not from the ventilator circuit. We compared the ventilator-associated pneumonia rates and costs associated with 48-h and 7-day circuit changes. Methods Ventilator circuits were changed at 48-h intervals during the control period (November 1992 to April 1993) and at 7-day intervals during the study period (June 1993 to November 1993). Nosocomial pneumonias were prospectively identified using the criteria of the Centers for Disease Control and Prevention. The annual cost difference of changing circuits at 48-h and 7-day intervals was calculated using the distribution of ventilator days for the control and study periods. Results There were 1,708 patients, 9,858 ventilator days, and a pneumonia rate of 9.64 per 1,000 ventilator days in the control group (48-h circuit changes). There were 1,715 patients, 9,160 ventilator days, and 8.62 pneumonias per 1,000 ventilator days when circuits were changed at 1-week intervals (study group). Using a logistic regression model, there were significantly greater odds of developing a ventilator-associated pneumonia in surgical patients (odds ratio 1.77, P = 0.02) and patients in critical care units (odds ratio 1.54, P = 0.05), but no significant risk of ventilator-associated pneumonia in patients in whom circuits were changed at 1-week intervals (odds ratio 0.82, P = 0.22). Changing circuits at 7-day intervals resulted in a 76.6% ($111,530) reduction in the annual cost for materials and salaries. Conclusions We found no difference in pneumonia rates with ventilator circuit changes at 48-h and 7-day intervals. Ventilator circuits can be safely changed at weekly intervals, resulting in large cost savings.