Search

BACKGROUND: Intrinsic PEEP during mechanical ventilation occurs when there is insufficient time for expiration to functional residual capacity before the next inspiration, resulting in air trapping. Increased expiratory resistance (RE), too rapid of a patient or ventilator breathing rate, or a longer inspiratory to expiratory time ratio (TI/TE) can all be causes of intrinsic PEEP. Intrinsic PEEP can result in increased work of breathing and patient-ventilator asynchrony (PVA) during patient-triggered breaths. We hypothesized that the difference between intrinsic PEEP and ventilator PEEP acts as an inspiratory load resulting in trigger asynchrony that needs to be overcome by increased respiratory muscle pressure (Pmus). METHODS: Using a Servo lung model (ASL 5000) and LTV 1200 ventilator in pressure control mode, we developed a passive model demonstrating how elevated RE increases intrinsic PEEP above ventilator PEEP. We also developed an active model investigating the effects of RE and intrinsic PEEP on trigger asynchrony (expressed as percentage of patient-initiated breaths that failed to trigger). We then studied if trigger asynchrony could be reduced by increased Pmus. RESULTS: Intrinsic PEEP increased significantly with increasing RE (r = 0.97, P = .006). Multivariate logistic regression analysis showed that both RE and negative Pmus levels affect trigger asynchrony (P < .001). CONCLUSIONS: A passive lung model describes the development of increasing intrinsic PEEP with increasing RE at a given ventilator breathing rate. An active lung model shows how this can lead to trigger asynchrony since the Pmus needed to trigger a breath is greater with increased RE, as the inspiratory muscles must overcome intrinsic PEEP. This model will lend itself to the study of intrinsic PEEP engendered by a higher ventilator breathing rate, as well as higher TI/TE, and will be useful in ventilator simulation scenarios of PVA. The model also suggests that increasing ventilator PEEP to match intrinsic PEEP can improve trigger asynchrony through a reduction in RE. [ABSTRACT FROM AUTHOR]

Abstract Background Tidal expiratory flow limitation (EFLT) promotes intrinsic PEEP (PEEPi) in patients with chronic obstructive pulmonary disease (COPD). Applying non-invasive ventilation (NIV) with an expiratory positive airway pressure (EPAP) matching PEEPi improves gas exchange, reduces work of breathing and ineffective efforts. We aimed to evaluate the effects of a novel NIV mode that continuously adjusts EPAP to the minimum level that abolishes EFLT. Methods This prospective, cross-over, open-label study randomized patients to one night of fixed-EPAP and one night of EFLT-abolishing-EPAP. The primary outcome was transcutaneous carbon dioxide pressure (PtcCO2). Secondary outcomes were: peripheral oxygen saturation (SpO2), frequency of ineffective efforts, breathing patterns and oscillatory mechanics. Results We screened 36 patients and included 12 in the analysis (age 72 ± 8 years, FEV1 38 ± 14%Pred). The median EPAP did not differ between the EFLT-abolishing-EPAP and the fixed-EPAP night (median (IQR) = 7.0 (6.0, 8.8) cmH2O during night vs 7.5 (6.5, 10.5) cmH2O, p = 0.365). We found no differences in mean PtcCO2 (44.9 (41.6, 57.2) mmHg vs 54.5 (51.1, 59.0), p = 0.365), the percentage of night time with PtcCO2 > 45 mm Hg was lower (62(8,100)% vs 98(94,100)%, p = 0.031) and ineffective efforts were fewer (126(93,205) vs 261(205,351) events/hour, p = 0.003) during the EFLT-abolishing-EPAP than during the fixed-EPAP night. We found no differences in oxygen saturation and lung mechanics between nights. Conclusion An adaptive ventilation mode targeted to abolish EFLT has the potential to reduce hypercapnia and ineffective efforts in stable COPD patients receiving nocturnal NIV. Trial registration: ClicalTrials.gov, NCT04497090. Registered 29 July 2020—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04497090 .

Abstract Background Quantification of intrinsic PEEP (PEEPi) has important implications for patients subjected to invasive mechanical ventilation. A new non-invasive breath-by-breath method (etCO2D) for determination of PEEPi is evaluated. Methods In 12 mechanically ventilated pigs, dynamic hyperinflation was induced by interposing a resistance in the endotracheal tube. Airway pressure, flow, and exhaled CO2 were measured at the airway opening. Combining different I:E ratios, respiratory rates, and tidal volumes, 52 different levels of PEEPi (range 1.8–11.7 cmH2O; mean 8.45 ± 0.32 cmH2O) were studied. The etCO2D is based on the detection of the end-tidal dilution of the capnogram. This is measured at the airway opening by means of a CO2 sensor in which a 2-mm leak is added to the sensing chamber. This allows to detect a capnogram dilution with fresh air when the pressure coming from the ventilator exceeds the PEEPi. This method was compared with the occlusion method. Results The etCO2D method detected PEEPi step changes of 0.2 cmH2O. Reference and etCO2D PEEPi presented a good correlation (R 2 0.80, P

Background: PEEP decreases intrinsic PEEP (PEEPi) in COPD patients. However, the best PEEP for someone with COPD is unclear. Methods: Ten COPD patients who received invasive mechanical ventilation were enrolled. Before PEEP titration, subjects were sedated and received mandatory ventilation. PEEP increased from 0 to 15 cmH2O. At each PEEP, peak pressure (Ppeak), plateau pressure (Pplat), PEEPi, and other variables were recorded. Increment of Pplat (ΔPplat) and PEEPi were plotted against PEEP applied. The best PEEP was recorded at the cross of the two curves. Results: From PEEP = 0 cmH2O to best PEEP, Ppeak (37.4 ± 5.1 vs. 38.4 ± 4.9 cmH2O) and Pplat (18.7 ± 3.3 vs. 20.4 ± 3.2 cmH2O) increased slightly, resistance (28.1 ± 5.6 vs. 26.6 ± 5.0 cmH2O/l/s) decreased slightly, and PEEPi (7.9 ± 2.3 vs. 1.5 ± 0.4 cmH2O) decreased sharply. Compliance, heart rate, blood pressure, and SpO2 did not change. However, from best PEEP to PEEP = 15 cmH2O, Ppeak (38.4 ± 4.9 vs. 44.9 ± 4.3 cmH2O) and Pplat (20.4 ± 3.2 vs. 27.6 ± 3.3 cmH2O) increased sharply, and systolic blood pressure (116 ± 13 vs. 99 ± 14 mmHg) and compliance (46.1 ± 18.1 vs. 37.7 ± 10.6 mL/cmH2O) decreased sharply. At the same time, PEEPi (1.5 ± 0.4 vs. 0.7 ± 0.8 cmH2O) decreased only slightly, and resistance, heart rate, and SpO2 did not change. Conclusions: It is feasible to use Pplat as a simple way of determining the best PEEP in COPD patients. [ABSTRACT FROM AUTHOR]

JUSTIFICATIVA E OBJETIVOS: Em ventilação mecânica invasiva e não-invasiva, o conhecimento da fisiologia da mecânica respiratória, é imprescindível para tomada de decisões e no manuseio eficiente dos ventiladores modernos. A monitorização dos parâmetros da mecânica pulmonar é recomendada nos trabalhos de revisão e de pesquisas clínicas. O objetivo deste estudo foi rever os conceitos de mecânica pulmonar e os métodos utilizados para obtenção de medidas à beira do leito, enfatizando três parâmetros: resistência, complacência e PEEP intrínseca. MÉTODO: Foi realizada revisão bibliográfica através dos bancos de dados LILACS, MedLine e PubMed, no período de 1996 a 2006. RESULTADOS: Esta revisão abordou os parâmetros de resistência, complacência pulmonar e PEEP intrínseca como fundamentais na compreensão da insuficiência respiratória aguda e suporte ventilatório mecânico, principalmente na doença pulmonar obstrutiva crônica (DPOC) e na síndrome da angústia respiratória aguda (SARA). CONCLUSÕES: A monitorização da mecânica pulmonar em pacientes sob ventilação mecânica em unidade de terapia intensiva (UTI) pode fornecer dados relevantes e deve ser implementada de forma sistemática e racional.BACKGROUND AND OBJECTIVES: In mechanical ventilation, invasive and noninvasive, the knowledge of respiratory mechanic physiology is indispensable to take decisions and into the efficient management of modern ventilators. Monitoring of pulmonary mechanic parameters is been recommended from all the review works and clinical research. The objective of this study was review concepts of pulmonary mechanic and the methods used to obtain measures in the bed side, preparing a rational sequence to obtain this data. METHODS: It was obtained bibliographic review through data bank LILACS, MedLine and PubMed, from the last ten years. RESULTS: This review approaches parameters of resistance, pulmonary compliance and intrinsic PEEP as primordial into comprehension of acute respiratory failure and mechanic ventilatory support, mainly in acute respiratory distress syndrome (ARDS) and in chronic obstructive pulmonary disease (COPD). CONCLUSIONS: Monitoring pulmonary mechanics in patients under mechanical ventilation in intensive care units gives relevant informations and should be implemented in a rational and systematic way.

BACKGROUND: Artificial airway resistance as provided by small-lumen tracheal tubes or catheters increases the risk of intrinsic PEEP (PEEPi). We hypothesized that by active expiration assistance, larger minute volumes could be generated without causing PEEPi compared with conventional mechanical ventilation when using small-lumen tracheal tubes or a cricothyrotomy catheter. METHODS: We investigated the active expiration assistance in a physical model of the respiratory system and estimated its hypothetical performance in terms of maximal flow generated with endotracheal tubes ranging from 3.0 to 8.0 mm inner diameter (ID); with microlaryngeal tubes of 4.0, 5.0, and 6.0 mm ID; and with a cricothyrotomy catheter. Furthermore, we determined the minute volumes that could be achieved without generating PEEPi by ventilating a physical lung model using conventional mechanical ventilation or using active expiration assistance. RESULTS: The inspiratory and expiratory flow during active expiration assistance increased with increasing supply flow and decreased with decreasing ID of the connected endotracheal tubes (both P < .001). With small-lumen tracheal tubes, the active expiration assistance generated similar or higher minute volumes than conventional ventilation. Conventional mechanical ventilation with PEEPi <1 cm H2O was not achievable via a microlaryngeal tube of 4.0 mm ID and smaller lumen tubes. CONCLUSIONS: For mechanical ventilation via small-lumen tubes or thin catheters, active compensation of airway resistance might be a necessary means to generate adequate minute ventilation without causing PEEPi. Active expiration assistance can generate reasonable respiratory minute volumes via small-lumen tubes or thin catheters. [ABSTRACT FROM AUTHOR]

Study Objective: To assess the safety of mechanical ventilation and effectiveness of extrinsic positive end-expiratory pressure (PEEP) (PEEPe) in improving peripheral oxygen saturation (SpO2) during direct microlaryngeal laser surgery; to assess the incidence, amount, and nature (dynamic hyperinflation or airflow obstruction) of ensuing intrinsic PEEP (PEEPi); and to find a surrogate PEEPi indicator.Design: Quasiexperimental.Setting: S. Raffaele Hospital (Milano), November 2009 to December 2010.Patients: Fifty-two adults scheduled for direct microlaryngeal laser surgery. Exclusion criterion is pregnancy.Interventions: Twenty-one percent O2 mechanical ventilation through 4.5- to 5.5-mm internal diameter endotracheal tubes; in 29 patients, after measurement of PEEPi, an identical amount of PEEPe was added; and PEEPi.Measurements: SpO2, peak (Pawpeak) and plateau (Pawplateau) airway pressure, and end-expiratory carbon dioxide were measured every 5 minutes. Respiratory compliance (Crs) was computed. PEEPi was measured (end-expiratory occlusion method).Main Results: PEEPi ≥5 cm H2O occurred in 14 patients (27%) after intubation, in 16 (30%) at the beginning, and in 14 (27.3%) at the end of surgery. Thirty-one patients (59.4%) exhibited PEEPi ≥5 cm H2O on at least 1 time point. PEEPi at the beginning of surgery was positively correlated with Pawplateau, Crs, tidal volume, and body mass index. Body mass index was the only predictor for the occurrence of PEEPi ≥5 cm H2O. At the beginning of surgery, the Pawplateau receiver operating characteristic curve predicting PEEPi ≥5 cm H2O had area under the receiver operating characteristic curve of 0.85; best cutoff value of 15.5 cm H2O (sensitivity, 88.9%; specificity, 75%; correctly classified cases, 86.1%). When PEEPe was applied, in 23 cases (82.1%), total PEEP equaled PEEPe+ PEEPi; in 3 (10.7%), it was lower; and in 2 (7.1%), it was higher. Application of PEEPe increased SpO2 (P< .05) and Crs (P< .05).Conclusions: During ventilation through small endotracheal tubes, PEEPi (mostly due to dynamic hyperinflation) is common. Hemodynamic complications, barotrauma, and O2 desaturation (reversible with PEEPe) are rare. Pawplateau provided by ventilators is useful in suspecting and monitoring the occurrence of PEEPi and allows detection of lung overdistension as PEEPe is applied. [ABSTRACT FROM AUTHOR]

Background: Double-lumen tubes (DLT) are routinely used to enable one-lung-ventilation (OLV) during thoracic anaesthesia. The flow-dependent resistance of the DLT's bronchial limb may be high as a result of its narrow inner diameter and length, and thus potentially contribute to an unintended increase in positive end-expiratory pressure (auto-PEEP). We therefore studied the impact of adult sized DLTs on the dynamic auto-PEEP during OLV.Methods: In this prospective clinical study, dynamic auto-PEEP was determined in 72 patients undergoing thoracic surgery, with right- and left-sided DLTs of various sizes. During OLV, air trapping was provoked by increasing inspiration to expiration ratio from 1:2 to 2:1 (five steps). Based on measured flow rate, airway pressure (Paw) and bronchial pressure (Pbronch), the pressure gradient across the DLT (ΔPDLT) and the total auto-PEEP in the respiratory system (i.e. the lungs, the DLT and the ventilator circuit) were determined. Subsequently the DLT's share in total auto-PEEP was calculated.Results: ΔPDLT was 2.3 (0.7) cm H2O over the entire breathing cycle. At the shortest expiratory time the mean total auto-PEEP was 2.9 (1.5) cm H2O (range 0-5.9 cm H2O). The DLT caused 27 to 31% of the total auto-PEEP. Size and side of the DLT's bronchial limb did not impact auto-PEEP significantly.Conclusions: Although the DLT contributes to the overall auto-PEEP, its contribution is small and independent of size and side of the DLT's bronchial limb. The choice of DLT does not influence the risk of auto-PEEP during OLV to a clinically relevant extent.Clinical Trial Registration: DRKS00005648. [ABSTRACT FROM AUTHOR]

Flow/volume (F/V) spirometry is routinely used for assessing the type and severity of lung disease. Forced vital capacity (FVC) and timed vital capacity (FEV1) provide the best estimates of airflow obstruction in patients with asthma, chronic obstructive pulmonary disease (COPD) and emphysema. Computerized spirometers are now available for early home recognition of asthma exacerbation in high risk patients with severe persistent disease, and for recognition of either infection or rejection in lung transplant patients. Patients with severe COPD may exhibit expiratory flow limitation (EFL) on tidal volume (VT) expiratory F/V (VTF/V) curves, either with or without applying negative expiratory pressure (NEP). EFL results in dynamic hyperinflation and persistently raised alveolar pressure or intrinsic PEEP (PEEPi). Hyperinflation and raised PEEPi greatly enhance dyspnea with exertion through the added work of the threshold load needed to overcome raised pleural pressure. Esophageal (pleural) pressure monitoring may be added to VTF/V loops for assessing the severity of PEEPi: 1) to optimize assisted ventilation by mask or via endotracheal tube with high inspiratory flow rates to lower I : E ratio, and 2) to assess the efficacy of either pressure support ventilation (PSV) or low level extrinsic PEEP in reducing the threshold load of PEEPi. Intraoperative tidal volume F/V loops can also be used to document the efficacy of emphysema lung volume reduction surgery (LVRS) via disappearance of EFL. Finally, the mechanism of ventilatory constraint can be identified with the use of exercise tidal volume F/V loops referenced to maximum F/V loops and static lung volumes. Patients with severe COPD show inspiratory F/V loops approaching 95% of total lung capacity, and flow limitation over the entire expiratory F/V curve during light levels of exercise. Surprisingly, patients with a history of congestive heart failure may lower lung volume towards residual volume during exercise, thereby reducing airway diameter and inducing expiratory flow limitation. [ABSTRACT FROM AUTHOR]

Objective: Dynamic intrinsic PEEP (PEEPi-dyn) is the airway pressure required to overcome expiratory flow and is considered to represent the lowest regional PEEPi. However, there are few data to validate this assumption. We investigated if PEEPi-dyn represents the lowest PEEPi.Setting: The animal laboratory at the Osaka University Medical School.Measurements and Results: We compared static PEEPi (PEEPi-stat) and PEEPi-dyn in healthy animals. Five adult white rabbits (2.77+/-0.05 kg) were anesthetized, tracheostomized, and intubated with several different sizes of endotracheal tubes (ETT) (2.0, 2.5, 3.0, 3.5, or 4.0 mm i.d.). The animals were paralyzed and ventilated (Siemens Servo 900C). Baseline ventilator settings were at a rate of 50/min, inspiratory:expiratory (I:E) ratio of 2:1 or 4:1, and minute ventilation was manipulated to create 3 or 5 cm H2O PEEPi-stat. PEEPi-stat was measured using the expiratory hold button of the ventilator. PEEPi-dyn showed large variations. In all ventilator settings, PEEPi-dyn was higher than PEEPi-stat (p<0.001). The larger the ETT, the higher the PEEPi-dyn at an I:E ratio of 2:1 (p<0.05). The higher the minute ventilation, the greater the difference between PEEPi-stat and PEEPi-dyn. The tidal volume and the difference showed a significant correlation (r2 = 0.514, p<0.001).Conclusions: The value of PEEPi-dyn was dependent on ventilatory settings, and PEEPi-dyn does not necessarily represent the lowest regional PEEPi within the lungs. [ABSTRACT FROM AUTHOR]

Objective: To determine whether nebulized salbutamol improves the respiratory mechanics of patients with adult respiratory distress syndrome (ARDS). We also assessed the mechanisms that contribute to high respiratory system resistances during this disease. Patients and setting: Eleven consecutive patients with ARDS without clinical evidence of chronic obstructive pulmonary disease, admitted to a polivalent intensive care unit, and mechanically ventilated with Siemens Elema Servo C ventilator at constant inspiratory flow. Method: Peak airway pressure (Ppeak), airway pressure immediately after end inspiratory occlusion (P1), plateau pressure (P2) and intrinsic positive end-expiratory pressure (PEEPi) were measured at baseline condition and then 5, 15, and 30 min after 1 mg of salbutamol had been administered via a nebulizer through the endotracheal tube. Partial pressure of arterial oxygen (PaO2), heart rate (HR) and mean blood pressure (BP) were monitored and minimal respiratory system resistances (Rrs, m), additional resistances (DRrs) and static compliance (Cst) were computed Results: Between baseline and post-salbutamol, we observed changes in Ppeak, P1, P2, PEEPi and Rrs, m. As there were no significant differences between values at the different intervals during post administration, the results are described comparing baseline and 15 min post-salbutamol administration values. We found a significant decrease in Ppeak (4.9±0.8 cmH2O), P1 (3±0.6 cmH2O), P2 (2.1±0.6 cmH2O), PEEPi (1.9±0.5 cmH2O) and Rrs, m (1.9±0.3 cmH2O/1 s-1); DR, rs decreased in five patients, did not change in four and increased in two. HR, PaO2 and BP did not change. Conclusions: a) Salbutamol administered through the endotracheal tube by a nebulizer device lessens respiratory system resistances and airway and alveolar pressures, and therefore could decrease the risk of barotrauma and alveolar damage; b) high respiratory system resistances in ARDS have an increased smooth muscle tone component that can be reversible with salbutamol. [ABSTRACT FROM AUTHOR]

Objectives: Prolongation of inspiratory time is used to reduce lung injury in mechanical ventilation. The aim of this study was to isolate the effects of inspiratory time on airway pressure, gas exchange, and hemodynamics, while ventilatory frequency, tidal volume, and mean airway pressure were kept constant.Design: Randomized experimental trial.Setting: Experimental laboratory of a University Department of Anesthesiology and Intensive Care.Animals: Twelve anesthetised piglets.Interventions: After lavage the reference setting was pressure-controlled ventilation with a decelerating flow; I:E was 1:1, and PEEP was set to 75% of the inflection point pressure level. The I:E ratios of 1.5:1, 2.3:1, and 4:1 were applied randomly. Under open lung conditions, mean airway pressure was kept constant by reduction of external PEEP.Measurements and Results: Gas exchange, airway pressures, hemodynamics, functional residual capacity (SF6 tracer), and intrathoracic fluid volumes (double indicator dilution) were measured. Compared to the I:E of 1:1, PaCO2 was 8% lower, with I:E 2.3:1 and 4:1 (p < or = 0.01) while PaO2 remained unchanged. The decrease in inspiratory airway pressure with increased inspiratory time was due to the response of the pressure-regulated volume-controlled mode to an increased I:E ratio. Stroke index and right ventricular ejection fraction were depressed at higher I:E ratios (SI by 18% at 2.3:1, 20% at 4:1; RVEF by 10% at 2.3:1, 13% at 4:1; p < or = 0.05).Conclusion: Under open lung conditions with an increased I:E ratio, oxygenation remained unaffected while hemodynamics were impaired. [ABSTRACT FROM AUTHOR]

Objective: To investigate effects of ventilator triggering systems (pressure and flow triggering: PT and FT) on measurement of dynamic intrinsic PEEP (PEEPidyn) and patient-ventilator interaction in patients with chronic obstructive pulmonary disease during weaning from mechanical ventilation.Design: Prospective study.Setting: Medical/surgical intensive care unit of an academic hospital.Patients and Participants: 6 COPD patients with acute respiratory failure ready to wean.Measurements: We measured flow, airway opening, esophageal and gastric pressures. Minute ventilation, breathing pattern and pressure time product (PTP) of the respiratory muscles and of the diaphragm were obtained during spontaneous ventilation through a mechanical ventilator (Puritan-Bennett 7200ae). Two triggering systems, namely PT and FT, were evaluated.Results: The inspiratory muscles effort necessary to overcome the triggering system overestimated PEEPidyn measurement of an amount equal to 49 +/- 2 and 58 +/- 3% during respectively pressure and flow triggering. FT increased tidal volume and minute ventilation and decrease PTP/b and PTP/min of the respiratory muscles and diaphragm.Conclusions: To correctly measure PEEPidyn, the inspiratory effort produced to overcome PEEPi and to trigger the ventilator must be discriminated. Application of flow triggering requires less effort to initiate inspiration and provide a positive end-expiratory pressure level that is able to unload the respiratory muscles by reducing PEEPi. With flow triggering higher minute ventilation are obtained in COPD patients during the weaning phase. [ABSTRACT FROM AUTHOR]

Objectives: To study the ability of different ventilatory approaches to keep the lung open.Design: Different ventilatory patterns were applied in surfactant deficient lungs with PEEP set to achieve pre-lavage PaO2.Setting: Experimental laboratory of a University Department of Anaesthesiology and Intensive Care.Animals: 15 anaesthetised piglets.Interventions: One volume-controlled mode (L-IPPV201:1.5) and two pressure-controlled modes at 20 breaths per minute (bpm) and I:E ratios of 2:1 and 1.5:1 (L-PRVC202:1 and L-PRVC201.5:1), and two pressure-controlled modes at 60 bpm and I:E of 1:1 and 1:1.5 (L-PRVC601:1 and L-PRVC601:1.5) were investigated. The pressure-controlled modes were applied using "Pressure-Regulated Volume-Controlled Ventilation" (PRVC).Measurements and Results: Gas exchange, airway pressures, hemodynamics, FRC and intrathoracic fluid volumes were measured. Gas exchange was the same for all modes. FRC was 30% higher with all post-lavage settings. By reducing inspiratory time MPAW decreased from 25 cmH2O by 3 cmH2O with L-PRVC201.5:1 and L-PRVC601:1.5. End-inspiratory airway pressure was 29 cmH2O with L-PRVC201.5:1 and 40 cmH2O with L-IPPV201:1.5, while the other modes displayed intermediate values. End-inspiratory lung volume was 65 ml/kg with L-IPPV201:1.5, but it was reduced to 50 and 49 ml/kg with L-PRVC601:1 and L-PRVC601:1.5. Compliance was 16 and 18 ml/cmH2O with L-PRVC202:1 and L-PRVC201.5:1, while it was lower with L-IPPV201:1.5, L-PRVC601:1 and L-PRVC601:1.5. Oxygen delivery was maintained at pre-lavage level with L-PRVC201.5:1 (657 ml/min.m2), the other modes displayed reduced oxygen delivery compared with pre-lavage.Conclusion: Neither the rapid frequency modes nor the low frequency volume-controlled mode kept the surfactant deficient lungs open. Pressure-controlled inverse ratio ventilation (20 bpm) kept the lungs open at reduced end-inspiratory airway pressures and hence reduced risk of barotrauma. Reducing I:E ratio in this latter modality from 2:1 to 1.5:1 further improved oxygen delivery. [ABSTRACT FROM AUTHOR]

Lung volume and alveolar pressure were assessed using inductance plethysmography, airway occlusion and pneumotachography in a child with severe adult respiratory distress syndrome during both conventional mechanical and combined high-frequency ventilation (HFJV). The results suggest that improved oxygenation during combined HFJV is associated with higher end-expiratory lung volume and lower peak and mean lung volume and alveolar pressure. [ABSTRACT FROM AUTHOR]

Objective: Evaluation of new computer-controlled occlusion procedure for determination of intrinsic PEEP in mechanically ventilated patients and comparison with the standard end-expiratory occlusion method.Design: Prospective controlled study.Setting: Intensive care unit of a university hospital.Patients: 16 patients with acute respiratory failure of different degree and etiology. All patients were mechanically ventilated, heavily sedated and muscle paralyzed (non-depolarising relaxants). The type of ventilator, the inspiration/expiration ratio, FIO2 and PEEP were selected by the attending clinicians according to the patients' need and independently from the study.Interventions: Static compliance of the respiratory system (Cstat) was determined at varying external end-expiratory pressure settings: ZEEP (= ambient pressure), PEEP of 5 cmH2O and 10 cmH2O. All other ventilator settings were kept constant during the entire procedure.Measurements and Results: A computer-controlled occlusion method (SCASS) was used for determination of Cstat. Intrinsic PEEP was determined by SCASS as the extrapolated zero-volume intercept of the regression line of multiple pressure/volume data pairs (PEEPSCASSinspir and PEEPSCASSexpir). Directly thereafter intrinsic PEEP in this particular ventilatory setting was determined by end-expiratory occlusions (PEPPEEO). The intrinsic PEEP values of the different methods were nearly identical with a significant correlation (p < 0.0001). Mean values +/- SD: PEEPSCASSinspir 7.1 +/- 4.3 cmH2O; PEEPSCASSexpir 7.1 +/- 4.5 cmH2O; PEEPEEO 7.1 +/- 4.2 cmH2O.Conclusion: Since no significant difference between PEEPi values measured by the inspiratory and expiratory occlusion method (SCASS) was seen, this indicates that no alveolar recruitment occurred during the respiratory cycle. This study demonstrates that the automated occlusion method for measuring Cstat system can also be used with high accuracy for determination of intrinsic PEEP in mechanically ventilated patients. [ABSTRACT FROM AUTHOR]

Two patients with refractory hypoxemia due to unilateral lung atelectasis were treated with differential lung ventilation (DLV) through a Robertshaw-type, double-lumen tracheostomy tube. DLV was applied using two non-synchronized ventilators and maintained for 6 and 3 days, respectively. Ventilator settings were chosen in accord to the clinical, laboratory and chest X-rays results. Particularly, tidal volume and PEEP were set to avoid excessively high alveolar pressure and to obtain the highest possible value of compliance. We investigated the mechanical properties of the two lungs separately by measuring airway pressure and compliance of each lung before the beginning of DLV and at 0, 5, 24, and 48 h after. Initially we observed in both patients very low values of compliance (7-9 cm H2O/l) and a significant level of PEEPi (12-8 cm H2O) of the diseased lung, whereas PEEPi in the healthy lung was negligible. The clinical improvement was assessed by sequential chest X-rays and by significant improvement of arterial blood gas and PaO2/FiO2 ratios and was associated with a progressive increase of compliance (24-22 cm H2O/l) and by a fall of PEEPi levels (5-4 cm H2O) of the diseased lung. We also observed an improvement of SvO2, O2AVI, PVRI and Qva/Qt values (Case 1). The tracheostomy tube used to apply DLV was very reliable, allowing easy nursing care and selective bronchial aspirations. We conclude that DLV is a very useful technique in unilateral lung pathology, and it can be a life saving procedure in selected patients, by supplying volume and PEEP more efficiently to the affected lung. [ABSTRACT FROM AUTHOR]

We have studied 28 patients mechanically ventilated for acute respiratory failure at different levels of externally applied positive end-expiratory pressure (PEEPe). We describe and compare a computed method of measuring "effective" elastance of the total respiratory system (Ers,eff) with the static values of elastance of the total respiratory system (Ers,st), obtained with the end-inflation occlusion technique. Ers,eff was computed by an original device (Heres, R.P.A., Belgium), also the effective resistance of the total respiratory system was calculated. At zero end-expiratory pressure set by the ventilator (ZEEP). Ers,eff averaged 29.5 +/- 13.5 cm H2O x L-1 while Ers,st non-corrected for intrinsic PEEP (PEEPi) averaged 36.4 +/- 15.1 cm H2O x L-1 and Ers,st corrected for PEEPi averaged 28.2 +/- 13.4 cm H2O x L-1. The small difference between Ers,eff and Ers,st corrected for PEEPi was statistically significant and these two values were highly correlated (r = 0.98). This significant difference disappeared rapidly with PEEPe and probably reflects a frequency-dependance due to pendelluft. We also observed that PEEPi was present in 21 of 27 patients at ZEEP. Our results also indicate that low levels of PEEP may improve Ers in hyperinflated COPD patients, without inducing further hyperinflation. In conclusion, values of Ers,eff are very similar to static values corrected for PEEPi and permit an accurate and rapid approach to the management of ventilated patients. [ABSTRACT FROM AUTHOR]

To investigate the dose-response relationship and the time course of the effects of fenoterol (a selective β-adrenergic agonist) on respiratory function in mechanically ventilated patients with acute respiratory failure due to exacerbation of chronic airflow obstruction (CAO), seven consecutive acutely ill patients were studied within 3 days of the onset of mechanical ventilation. Airflow, airway pressure, and changes in lung volume were measured with the transducers of the 900 C Servo Ventilator, the last by electronic integration. The end-expiratory lung volume (EELV), the intrinsic positive end-expiratory pressure (PEEP), the static respiratory compliance (Cst), maximum and minimum respiratory resistance (Rrs and Rrs), and arterial oxygen tension (PaO), were measured under control conditions (all patients were receiving aminophylline infused at a constant rate) 5, 15, and 30 min after administration of 4 ml aerosolized saline solution and 5, 15, and 30 min after inhalation of 0.4, 0.8, and 1.2 mg fenoterol. After the last dose, measurements were repeated at 60, 120, and 180 min. We found that, on average, while saline did not cause any significant change in respiratory mechanics, a low dose (0.4 mg) of inhaled fenoterol was followed by a rapid (5 min) and significant decrease in Rrs (−33%), Rrs (−28%), EELV (−34%), and PEEP (−44%), with a slight but not significant further fall with higher doses. However, changes were short-lasting, and by 2h after the end of administration were no longer significant. PaO dropped significantly on average, with a maximum mean fall of 15 mmHg. We conclude that low doses of aerosolized fenoterol have a powerful and rapid but short-acting bronchodilating effect in mechanically ventilated patients with chronic airflow obstruction, bringing about a marked decrease in the dynamic pulmonary hyperinflation. These changes in respiratory mechanics can be easily and safely measured at the patient's bedside. [ABSTRACT FROM AUTHOR]

We studied the influence of ventilatory frequency (1-5 Hz), tidal volume, lung volume and body position on the end-expiratory alveolar-to-tracheal pressure difference during high-frequency jet ventilation (HFJV) in Yorkshire piglets. The animals were anesthetized and paralysed. Alveolar pressure was estimated with the clamp off method, which was performed by a computer controlled ventilator and which had been extensively tested on its feasibility. The alveolar-to-tracheal pressure difference increased with increasing frequency and with increasing tidal volume, the common determinant appearing to be the mean expiratory flow. The effects in prone and in supine position were similar. Increasing thoracic volume decreased the alveolar-to-tracheal pressure difference indicating a dependence of this pressure difference on airway resistance. We concluded that the main factors determining the alveolar-to-tracheal pressure difference (ΔP) during HFJV are expiratory flow (V′) and airway resistance (R), ΔP≃V′×R. [ABSTRACT FROM AUTHOR]

Objective: In mechanical ventilation, the assessment of pulmonary mechanics, mainly of total compliance (Crs), total resistance (Rrs), and intrinsic positive end-expiratory pressure (PEEPint), is clinically important. By using airway pressure (Paw) and flow (V'aw), the least squares fit (LSF) method allows the continuous calculation of these parameters. The objective of this work was to study the influence of imprecise breath detection, phase shift between airway pressure and flow signals, and noise on the determination of Crs, Rrs, and PEEPint.Methods: Paw and V'aw were mathematically simulated as well as recorded in mechanically ventilated patients. Crs, Rrs, and PEEPint were computed off-line using the LSF method. The boundaries of the breath data window and the phase relationship between Paw and V'aw signals were manipulated and noise was superimposed.Results: Both simulated and patient data gave similar results. Crs and Rrs were not sensitive to imprecise breath detection. If the first portion of the breath was missed, the mean relative error on PEEPint was 20% or 53% when the exact beginning of inspiration was missed by 0.1 or 0.3 sec, respectively. Paw lag of 66 ms with respect to V'aw yielded a relative error of -15 +/- 4% (mean +/- SD) for Rrs, -5 +/- 2% for Crs, and +13 +/- 16% for PEEPint. Paw lead of 66 ms with respect to V'aw yielded a relative error of +5 +/- 4% for Rrs, +7 +/- 3% for Crs, and +14 +/- 18% for PEEPint. Noise had very little impact on the accuracy of Crs, Rrs, and PEEPint.Conclusions: We conclude that the LSF method allows the assessment of Crs, Rrs, and PEEPint even with high levels of noise in patients with normal lungs provided that Paw and V'aw signals are precisely synchronised and a reliable breath detection algorithm is used. [ABSTRACT FROM AUTHOR]

Measurements of pressure swings in the esophagus (Pes can be used to estimate variables of clinical importance, e.g., intrinsic positive end-expiratory pressure (PEEPi. Unfortunately, cardiogenic oscillations frequently corrupt Pes and complicate further analysis. Due to significant band overlap with the respiratory component of Pes, cardiogenic oscillations cannot be suppressed adequately using standard filtering techniques. In this article, we present an adaptive filter that employs the electrocardiogram to identify and suppress the cardiogenic oscillations. This filter was tested using simulated data, where the variance accounted for relative to the simulated respiratory pressure swings increased from as low as 55% for the unfiltered Pes signal to over 95% when the adaptive filter was used. In patient data, the adaptive filter reduced the apparent cardiogenic oscillations without noticeably distorting the sharp deflections in Pes due to respiration. Furthermore, the filter suppressed peaks in the Fourier transform of Pes at integer multiples of the heart rate, while the remaining frequencies remained largely unchanged. During stable breathing, the standard deviation of PEEPi was reduced by between 44% and 71% in these four patients when the filter was used. We conclude that our filter removes a significant fraction of the cardiogenic oscillations that corrupt records of Pes. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8430Vn [ABSTRACT FROM AUTHOR]

Background: Quantification of intrinsic PEEP (PEEPi) has important implications for patients subjected to invasive mechanical ventilation. A new non-invasive breath-by-breath method (etCO2D) for determination of PEEPi is evaluated.Methods: In 12 mechanically ventilated pigs, dynamic hyperinflation was induced by interposing a resistance in the endotracheal tube. Airway pressure, flow, and exhaled CO2 were measured at the airway opening. Combining different I:E ratios, respiratory rates, and tidal volumes, 52 different levels of PEEPi (range 1.8-11.7 cmH2O; mean 8.45 ± 0.32 cmH2O) were studied. The etCO2D is based on the detection of the end-tidal dilution of the capnogram. This is measured at the airway opening by means of a CO2 sensor in which a 2-mm leak is added to the sensing chamber. This allows to detect a capnogram dilution with fresh air when the pressure coming from the ventilator exceeds the PEEPi. This method was compared with the occlusion method.Results: The etCO2D method detected PEEPi step changes of 0.2 cmH2O. Reference and etCO2D PEEPi presented a good correlation (R2 0.80, P < 0.0001) and good agreement, bias - 0.26, and limits of agreement ± 1.96 SD (2.23, - 2.74) (P < 0.0001).Conclusions: The etCO2D method is a promising accurate simple way of continuously measure and monitor PEEPi. Its clinical validity needs, however, to be confirmed in clinical studies and in conditions with heterogeneous lung diseases. [ABSTRACT FROM AUTHOR]