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Background In ARDS patients, changes in respiratory mechanical properties and ventilatory settings can cause incomplete lung deflation at end-expiration. Both can promote dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEP). The aim of this study was to investigate, in a large population of ARDS patients, the presence of intrinsic PEEP, possible associated factors (patients’ characteristics and ventilator settings), and the effects of two different external PEEP levels on the intrinsic PEEP. Methods We made a secondary analysis of published data. Patients were ventilated with a tidal volume of 6–8 mL/kg of predicted body weight, sedated, and paralyzed. After a recruitment maneuver, a PEEP trial was run at 5 and 15 cmH2O, and partitioned mechanics measurements were collected after 20 min of stabilization. Lung computed tomography scans were taken at 5 and 45 cmH2O. Patients were classified into two groups according to whether or not they had intrinsic PEEP at the end of an expiratory pause. Results We enrolled 217 sedated, paralyzed patients: 87 (40%) had intrinsic PEEP with a median of 1.1 [1.0–2.3] cmH2O at 5 cmH2O of PEEP. The intrinsic PEEP significantly decreased with higher PEEP (1.1 [1.0–2.3] vs 0.6 [0.0–1.0] cmH2O; p

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 < 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., CIBERES CB06/06/0009-2015; Arnoldo Santos has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 796721

RATIONALE The use of extra-positive end-expiratory pressure (PEEP) at a level of 80% intrinsic-PEEP (iPEEP) to improve ventilation in severe asthma patients with control ventilation remains controversial. Electrical impedance tomography (EIT) may provide regional information for determining the optimal extra-PEEP to overcome gas trapping and distribution. Moreover, the experience of using EIT to determine extra-PEEP in severe asthma patients with controlled ventilation is limited. PATIENTS CONCERNS A severe asthma patient had 12-cmH2O iPEEP using the end-expiratory airway occlusion method at Zero positive end-expiratory pressures (ZEEP). How to titrate the extra-PEEP to against iPEEP at bedside? DIAGNOSES AND INTERVENTIONS An incremental PEEP titration was performed in the severe asthma patient with mechanical ventilation. An occult pendelluft phenomenon of the ventral and dorsal regions was found during the early and late expiration periods when the extra-PEEP was set to

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

Intrinsic positive end-expiratory pressure (PEEP) and gas trapping are recognised hazards during ventilation of patients with airflow obstruction. Demonstration of these phenomena on conventional lung models using realistic ventilation settings is difficult. We describe an Intrinsic PEEP Model that is able to demonstrate dynamic gas trapping and intrinsic PEEP at realistic ventilation settings, and demonstrate its ability to develop intrinsic PEEP in a timeframe useful for teaching. The model uses a Heimlich valve to permit a lower resistance on inspiration than expiration. The model was tested using a series of typical ventilation settings which, when applied in a clinical setting on patients with airflow obstruction issues, would result in prolonged low expiratory flow and the development of intrinsic PEEP of 10 to 20 cmH2O, and ultimately significant gas trapping. The IPM can be used to demonstrate this effect and the ventilator adjustments required to minimise these problems.

Typical modern mechanical ventilators offer the clinician the possibility of automatically performing end-inspiratory occlusion maneuvers. The static conditions induced by such maneuvers are indeed favorable to estimating patient's respiratory mechanics in terms of total resistance (R) and elastance (E). These are parameters of wide clinical interest. However, in the presence of intrinsic PEEP, the standard formula used to compute E via the occlusion maneuver is known to be inaccurate. In this paper we propose an alternative method for the estimation of E via the occlusion maneuver that eliminates the bias by leveraging concepts derived from physiological modeling of the respiratory system dynamics. The proposed method is also capable of accounting for respiratory efforts triggering the breath, and hence can be applied in both passive and spontaneously breathing conditions.

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

To the Editor: In an interesting study recently published in Respiratory Care, Natalini et al[1][1] analyzed in 186 subjects receiving mechanical ventilation (settings chosen by the attending physician) several potential causes of dynamic hyperinflation and intrinsic PEEP (auto-PEEP). Both

Background: In clinical practice, patients have different inspiratory behaviors during noninvasive pressure support ventilation (PSV): some breathe quietly, others actively help PSV by an additional effort, and others even resist the inspiratory pressure of PSV. Objective: What is the influence of patient collaboration (inspiratory behavior) on the efficiency of PSV? Methods: We ventilated 10 normal subjects with nasal PSV (inspiratory/expiratory: 10/0 and 15/5 cm H2O) and measured their flow and volume with a pneumotachograph and their esophageal and gastric pressures during three different respiratory voluntary behaviors: relaxed inspiration, active inspiratory work and resisted inspiration. Results: When compared with relaxed inspiration with 10/0 cm H2O PSV: (1) an active inspiratory effort increased tidal volume (from 789 ± 356 to 1,046 ± 586 ml; p = 0.006), minute ventilation (from 10.40 ± 4.45 to 15.77 ± 7.69 liters/min; p < 0.001), transdiaphragmatic work per cycle (from 0.55 ± 0.33 to 1.72 ± 1.40 J/cycle; p = 0.002) and inspiratory work per cycle (from 0.14 ± 0.20 to 1.26 ± 1.01 J/cycle; p = 0.003); intrinsic positive end-expiratory pressure (PEEPi) increased from 1.23 ± 1.02 to 3.17 ± 2.30 cm H2O; p = 0.002); (2) a resisted inspiration decreased tidal volume (to 457 ± 230 ml; p = 0.007), minute ventilation (to 6.93 ± 3.04 liters/min; p = 0.028) along with a decrease in transdiaphragmatic work but no change in PEEPi. Data obtained during a bilevel PSV of 15/5 cm H2O were similar to those obtained with the 10/0 cm H2O settings. Conclusions: Active inspiratory effort increases ventilation during PSV at the expense of an increased breathing work and PEEPi. Resisted inspiration inversely decreases inspiratory work and ventilation with no air trapping. These differences between inspiratory behaviors could affect the expected beneficial effects of PSV in acutely ill patients.

In spontaneously breathing (SB) patients expiratory muscle contraction leads to an overestimation of dynamic intrinsic PEEP (PEEP(i),dyn). To quantify this overestimation, PEEP(i),dyn measured with the esophageal balloon technique was corrected for the increase in Pga over the course of expiration (Pga,exp rise), for the whole decay of Pga during inspiration (Pga,total decay) or for the part of Pga decay restricted between the onset of inspiratory effort and the point of zero flow (Pga,zf decay). Corrections were compared with the reference PEEP(i),dyn (PEEP(i),dyn ref ), calculated by using the Campbell diagram. In 15 ventilator-dependent, SB, and actively expiring patients, we found that the difference PEEP(i),dyn - Pga, total decay (mean +/- SD, 5.7 +/- 1.9 cm H(2)O) was quite similar to PEEP(i),dyn ref (5.3 +/- 1.9 cm H(2)O). Their mean difference was 0. 37 cm H(2)O with limits of agreement -0.09 to 0.83 cm H(2)O, indicating strong agreement between these methods. PEEP(i),dyn - Pga, exp rise (6.0 +/- 2.1 cm H(2)O) was also similar to PEEP(i),dyn ref. Their mean difference was 0.72 cm H(2)O with limits of agreement -1. 69 to 3.13 cm H(2)O, indicating good agreement. In contrast, mean difference of PEEP(i),dyn - Pga,zf decay and PEEP(i),dyn ref was 3. 14 cm H(2)O with limits of agreement -0.46 to 6.74 cm H(2)O, indicating lack of agreement. The error in measurement due to the subtraction of Pga,zf decay from PEEP(i),dyn (i.e., [PEEP(i),dyn - Pga,zf decay] - PEEP(i),dyn ref ) was proportional to the intensity of expiratory muscle contraction, as expressed by the Pga,exp rise (r = 0.903, p < 0.001). We conclude that in actively expiring patients an adequate correction of PEEP(i),dyn for the overestimation caused by expiratory muscle contraction can be made by subtracting either Pga,total decay or Pga,exp rise from PEEP(i), dyn, the former achieving the best performance.

Our personal opinion, reached without the support of data meeting the criteria for evidence-based medicine, is that monitoring the flow, pressure, and volume curves, at least in the first few hours of ventilation, is one of the keys to the success of NIV. The analysis of these signals in real time is particularly useful for evaluating the interaction between the patient and the machine.

Intrinsic positive end-expiratory pressure (PEEPi) is routinely determined under static conditions by occluding the airway at end-expiration (PEEPi,stat), the resulting plateau pressure representing the average PEEPi present within a nonhomogeneous lung. In contrast, PEEPi can also be evaluated dynamically (PEEPi,dyn) by recording the change in pressure required to initiate lung inflation. It has been suggested that PEEPi,dyn reflects the lowest regional PEEPi, and therefore underestimates PEEPi,stat in the presence of heterogenous mechanical properties. The purposes of this study were (1) to compare PEEPi obtained with these two methods in mechanically ventilated patients with significant airway obstruction (AWO) and those without (non-AWO), and (2) to relate any discrepancies observed with other indices of respiratory mechanics. PEEPi,stat, PEEPi,dyn, and respiratory mechanics were measured during controlled mechanical ventilation in 22 sedated, paralyzed patients. PEEPi,dyn was significantly less than PEEPi,stat in AWO, averaging 3.0 +/- 0.5 (SEM) and 9.3 +/- 1.1 (SEM) cm H2O, respectively (p0.0001). In contrast, these values were more comparable in non-AWO, averaging 4.6 +/- 0.8 and 5.4 +/- 1.0 cm H2O (p0.05). As a result, the ratio of PEEPi,dyn to PEEPi,stat amounted to 0.36 +/- 0.06 for AWO compared with 0.87 +/- 0.05 in non-AWO (p0.005). Maximal (Rmax) and minimal (Rmin) respiratory resistance were greater in AWO whereas respiratory compliance (Crs) was no different between groups. PEEPi,dyn/PEEPi,stat was inversely related to delta P, the pressure losses attributable to time constant inequalities and viscoelastic tissue properties (r = 0.64, p0.005). No correlation was found between this ratio and Rmax, Rmin, or Crs.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic measurements of intrinsic positive end-expiratory pressure (PEEPi,dyn) considerably underestimate values obtained under static conditions (PEEPi,stat) in patients with severe airway obstruction. This may be related to regional differences in respiratory system mechanical properties and/or viscoelastic behavior. To evaluate this concept, PEEPi,stat and PEEPi,dyn were compared in six anesthetized paralyzed cats during dynamic hyperinflation produced by inverse ratio ventilation (IRV) and aerosolized methacholine (MCh). PEEPi,stat did not differ between IRV and MCh, averaging 2.70 +/- 0.33 (SE) and 2.70 +/- 0.25 cmH2O, respectively. PEEPi,dyn was significantly less with MCh (0.25 +/- 0.05 cmH2O) than IRV (2.05 +/- 0.28 cmH2O) (P < 0.0001), resulting in a lower PEEPi,dyn/PEEPi,stat ratio for MCh (0.10 +/- 0.02) than for IRV (0.76 +/- 0.03) (P < 0.0001). Compared with control values (33.5 +/- 3.7 cmH2O.l-1.s), maximum resistance (Rmax) was unchanged during IRV (29.1 +/- 2.1 cmH2O.l-1.s) but increased considerably with MCh (288.8 +/- 18.4 cmH2O.l-1.s) (P < 0.0001). Similar changes in minimum resistance (Rmin) and delta R (Rmax-Rmin) were noted. There was a strong inverse relationship between delta P, an index of time constant inequalities and viscoelastic pressure losses and PEEPi,dyn/PEEPi,stat ratio. No correlation was found between this ratio and Rmax, Rmin, delta R, or compliance. In conclusion, PEEPi,dyn considerably underestimates PEEPi,stat in acute nonhomogeneous airway obstruction with MCh in contrast to IRV, where the magnitude and distribution of mechanical properties remain unaltered. These findings support the concept that the difference between PEEPi,dyn and PEEPi,stat is related to regional time constant inequalities and/or increased viscoelastic pressure losses.

New indicators, Oxygen Cost of Breathing (ΔVO2), Work of Breathing (WOBp), intrapreural Pressure Time Product (PTP) and P0.1 were clinically examined to determine which of these indicators is the most specific and sensitive for predicting the outcome of weaning from mechanical ventilation. Twenty-three weanings were attempted and divided into a successful weaning group (Group-S) and a failed weaning group (Group-F). There were significant differences in Minute Volume, ΔVO2, ΔVCO2, WOBp, P0.1, PTP, Lung Compliance and Intrinsic PEEP between the groups. ΔVO2 and P0.1 in particular, were statsitically significantly different in the two groups (ΔVO2: 14.4±11.7 in Group-F VS. -7.7±9.6% in Group-S P

Modern ventilators are complicated electronic instruments with microprocessors and software, with the possibility of technical errors and problems such as autocycling. Despite autocycling being recognized as a problem in textbooks and reviews, there are few reports about autocycling in the literature. We report a case where a sudden increase in respiratory frequency due to autocycling resulted in a dangerous increase in intrinsic positive end-expiratory pressure (intrinsic PEEP, PEEPi). We think our case illustrates that autocycling does occur, but that the exact underlying mechanism may be hard to document and understand for clinicians. To remedy this situation, we suggest that manufacture-independent technical expertise should be established to evaluate incidents and suggest improvements.

Facing a patient who presents with respiratory functional impairment, the physician is left with the task of conducting tests to determine whether there is a mechanical component to the illness. One abnormality that must be considered is intrinsic positive end-expiratory pressure (PEEPi). PEEPi [1,2] is the difference between alveolar pressure and the pressure at the airway opening at the end of expiration. It has also been termed auto-PEEP [3], occult PEEP [3], inadvertent PEEP [4], endogenous PEEP, and internal PEEP. Although not difficult to accomplish, precise determination of PEEPi and subsequent interpretation of the results demand a thorough awareness of the pertinent theoretical and methodological concepts [5,6].

In treating a patient presenting respiratory functional impairment, the physician is left with the task of running tests to determine whether there is a mechanical component to the illness. One abnormality that must be sought is the intrinsic positive end-expiratory pressure (PEEPi).

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 (r 2 = 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.

Schuessler, Thomas F., Stewart B. Gottfried, and Jason H. T. Bates. A model of the spontaneously breathing patient: applications to intrinsic PEEP and work of breathing. J. Appl. Physiol. 82(5): 1694–1703, 1997.—Intrinsic positive end-expiratory pressure (PEEPi) and inspiratory work of breathing (Wi) are important factors in the management of severe obstructive respiratory disease. We used a computer model of spontaneously breathing patients with chronic obstructive pulmonary disease to assess the sensitivity of measurement techniques for dynamic PEEPi(PEEPi dyn) and Wi to expiratory muscle activity (EMA) and cardiogenic oscillations (CGO) on esophageal pressure. Without EMA and CGO, both PEEPi dynand Wi were accurately estimated ( r = 0.999 and 0.95, respectively). Addition of moderate EMA caused PEEPi dynand Wi to be systematically overestimated by 141 and 52%, respectively. Furthermore, CGO introduced large random errors, obliterating the correlation between the true and estimated values for both PEEPi dyn( r = 0.29) and Wi( r = 0.38). Thus the accurate estimation of PEEPi dynand Wi requires steps to be taken to ameliorate the adverse effects of both EMA and CGO. Taking advantage of our simulations, we also investigated the relationship between PEEPi dynand static PEEPi(PEEPi stat). The PEEPi dyn/PEEPi statratio decreased as stress adaptation in the lung was increased, suggesting that heterogeneity of expiratory flow limitation is responsible for the discrepancies between PEEPi dynand PEEPi statthat have been reported in patients with severe airway obstruction.

We conducted a study to assess the validity of the occlusion pressure (P0.1) measured during activation of the trigger mechanism (P0.1(aw)trig) in patients showing variable levels of PEEPi during pressure-support ventilation. We first compared P0.1(aw)trig and P0.1 measured with the conventional method (i.e., the airway pressure drop after the first 100 ms of an occluded inspiration) in 16 patients with chronic obstructive pulmonary disease (COPD). We observed good agreement and a highly significant correlation (r = 0.99; bias = 0.3 +/- 0.5 cm H20) between the two methods. In a second part of the study, we compared, in 17 patients, P0.1(aw)trig with (P0.1(es)), measured as the depression generated on the esophageal pressure tracing in the first 100 ms of the inspiratory negative swing, and with P0.1 measured on the P(es) tracing simultaneously with P(aw)trig (P0.1(es-synchro)). Our results showed a good correlation and good agreement between P(aw)trig and P0.1(es) (r = 0.92; bias = 0.3 +/- 0.5 cm H20); P(aw)trig and P0.1(es-synchro) (r = 0.97; bias = 0.1 +/- 0.2 cm H20); and P0.1(es) and P0.1(es-synchro) (r = 0.95, bias = 0.2 +/- 0.4 cm H20), respectively. This study suggests that reliable measurements of inspiratory drive can be obtained easily, on a breath-by-breath basis, from airway pressure tracings during pressure-support ventilation in patients with variable levels of PEEPi.

To study the ability of different ventilatory approaches to keep the lung open.Different ventilatory patterns were applied in surfactant deficient lungs with PEEP set to achieve pre-lavage PaO2.Experimental laboratory of a University Department of Anaesthesiology and Intensive Care.15 anaesthetised piglets.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).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.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.

In 1954, Mcllroy and Christie [1] observed that the mechanical work of breathing (WOB) was increased in stable COPD patients which they attributed to increased airway and “viscous” resistance of the lung. In later studies, it was suggested that in COPD patients there is an increase of (WOB) also as a result of a) time constant inequality within the lung which causes an increase of effective dynamic pulmonary elastance and flow resistance [2], and b) intrinsic PEEP (PEEPi) [3].

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.Prospective controlled study.Intensive care unit of a university hospital.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.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.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 (p0.0001). Mean values +/- SD: PEEPSCASSinspir 7.1 +/- 4.3 cmH2O; PEEPSCASSexpir 7.1 +/- 4.5 cmH2O; PEEPEEO 7.1 +/- 4.2 cmH2O.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.

In spontaneously breathing (SB) patients expiratory muscle contraction leads to an overestimation of dynamic intrinsic PEEP (PEEPi,dyn). To quantify this overestimation, PEEPi,dyn measured with the esophageal balloon technique was corrected for the increase in Pga over the course of expiration (Pga,exp rise), for the whole decay of Pga during inspiration (Pga,total decay) or for the part of Pga decay restricted between the onset of inspiratory effort and the point of zero flow (Pga,zf decay). Corrections were compared with the reference PEEPi,dyn (PEEPi,dyn ref ), calculated by using the Campbell diagram. In 15 ventilator-dependent, SB, and actively expiring patients, we found that the difference PEEPi,dyn − Pga,total decay (mean ± SD, 5.7 ± 1.9 cm H2O) was quite similar to PEEPi,dyn ref (5.3 ± 1.9 cm H2O). Their mean difference was 0.37 cm H2O with limits of agreement − 0.09 to 0.83 cm H2O, indicating strong agreement between these methods. PEEPi,dyn − Pga,exp rise (6.0 ± 2.1 cm H2O) was also similar to ...

Dynamic pulmonary hyperinflation and intrinsic PEEP (PEEPi) are known to play an important role in causing acute respiratory failure in COPD patients. In the present study, we have explored (1) the prevalence and magnitude of PEEPi in stable COPD patients, and (2) the correlation of PEEPi with respiratory mechanics and PaCO2. In 96 stable COPD patients with varying degrees of airway obstruction, we measured pulmonary flow resistance (RL), dynamic lung compliance (CLdyn), breathing pattern, arterial blood gases, and dynamic PEEPi. Dynamic PEEPi was determined as a negative deflection in esophageal pressure from the start of inspiratory effort to the onset of inspiratory flow. A significant correlation was found between dynamic PEEPi and FEVi (% predicted; r = -0.56, p less than 0.001), between PEEPi and RL (r = 0.69, p less than 0.001), and between PaCO2 and PEEPi (r = 0.6, p less than 0.001). These results indicate that increased severity of airway obstruction promotes PEEPi and concomitant dynamic hyperinflation. This implies increased inspiratory work in the face of decreased effectiveness of the inspiratory muscles as pressure generators. The present results suggest that dynamic hyperinflation may play a role in causing chronic hypoventilation in COPD patients.

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.

Mechanically ventilated COPD patients frequently present dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEPi), which usually goes unrecorded and, as a result, unrecognized.