Open-lung PEEP Research Articles

Effect of recumbency and body condition score on open-lung positive end-expiratory pressure and respiratory system compliance following a stepwise lung recruitment manoeuvre in healthy dogs during general anaesthesia

The aim was to assess the effects of recumbency and body condition score (BCS) on open-lung positive end-expiratory pressure (OL-PEEP) and quasistatic respiratory system compliance (Crs) following stepwise lung recruitment manoeuvre (RM) in healthy dogs under general anaesthesia. Thirty-four dogs were anaesthetised and mechanically ventilated (tidal volume of 10 mL/kg) without PEEP for 1 min (baseline). A stepwise RM was then performed and the individual OL-PEEP was subsequently applied. The Crs was registered at baseline and every 10-min for 50 min after RM. Dogs were classified into either dorsal or lateral recumbency groups, and as normal (score 4–5/9) or high (≥6/9) BCS groups.The OL-PEEP was higher in lateral than in dorsal recumbency (P = .002), but differences were not observed between normal and high BCS (P = .865). The Crs was increased from baseline at all time points after RM in all groups. The Crs did not differ between dorsally and laterally recumbent dogs at any time point. However, the baseline Crs was significantly lower in dogs with a high BCS than in those with a normal BCS (P < .001); therefore, the absolute change from baseline was considered when comparing Crs after the RM and it was similar in both BCS groups. In conclusion, in anaesthetised healthy dogs the OL-PEEP following RM was lower when dogs were positioned in dorsal than in lateral recumbency. The Crs after RM remained unchanged regardless of the dogs' recumbency. A stepwise RM followed by OL-PEEP could compensate for the potential negative impact of moderately increased BCS on Crs.

Comparative effects of open-lung positive end-expiratory pressure (PEEP) and fixed PEEP on respiratory system compliance in the isoflurane anaesthetised healthy dog

This study was performed to assess the effects of open-lung positive end-expiratory pressure (OL-PEEP) following stepwise recruitment manoeuvre (RM) and those of a fixed PEEP of 5 cm H2O without previous RM on respiratory system compliance (Crs) and selected cardiovascular variables in healthy dogs under general anaesthesia. Forty-five healthy client-owned dogs undergoing surgery were anaesthetised and mechanically ventilated (tidal volume, VT = 10–12 mL/kg; PEEP = 0 cm H2O) for 1 min (baseline) and randomly allocated into zero positive end-expiratory pressure (ZEEP), PEEP (5 cm H2O) and OL-PEEP treatment groups. In the OL-PEEP group, a stepwise RM was performed and the individual OL-PEEP was subsequently applied. The Crs, heart rate (HR) and non-invasive mean arterial pressure (NIMAP) were registered at baseline and then every 10 min during 60 min.In the ZEEP group, Crs decreased from baseline. In the PEEP group, Crs was not different from either baseline or ZEEP group values. In the OL-PEEP group, Crs was higher than both baseline and ZEEP group values at all time points as well as of those in the PEEP group during at least 20 min after RM. There were no differences for HR and NIMAP between groups. A clinically relevant hypotension following RM was observed in 40% of dogs. Therefore, an individually set OL-PEEP following stepwise RM improved Crs in anaesthetised healthy dogs, although transient but clinically relevant hypotension was observed during RM in some dogs. Fixed PEEP of 5 cm H2O without previous RM did not improve Crs, although it prevented it from decreasing.

Multimodal non-invasive monitoring to apply an open lung approach strategy in morbidly obese patients during bariatric surgery

To evaluate the use of non-invasive variables for monitoring an open-lung approach (OLA) strategy in bariatric surgery. Twelve morbidly obese patients undergoing bariatric surgery received a baseline protective ventilation with 8 cmH2O of positive-end expiratory pressure (PEEP). Then, the OLA strategy was applied consisting in lung recruitment followed by a decremental PEEP trial, from 20 to 8 cmH2O, in steps of 2 cmH2O to find the lung's closing pressure. Baseline ventilation was then resumed setting open lung PEEP (OL-PEEP) at 2 cmH2O above this pressure. The multimodal non-invasive variables used for monitoring OLA consisted in pulse oximetry (SpO2), respiratory compliance (Crs), end-expiratory lung volume measured by a capnodynamic method (EELVCO2), and esophageal manometry. OL-PEEP was detected at 15.9 ± 1.7 cmH2O corresponding to a positive end-expiratory transpulmonary pressure (PL,ee) of 0.9 ± 1.1 cmH2O. ROC analysis showed that SpO2 was more accurate (AUC 0.92, IC95% 0.87-0.97) than Crs (AUC 0.76, IC95% 0.87-0.97) and EELVCO2 (AUC 0.73, IC95% 0.64-0.82) to detect the lung's closing pressure according to the change of PL,ee from positive to negative values. Compared to baseline ventilation with 8 cmH2O of PEEP, OLA increased EELVCO2 (1309 ± 517 vs. 2177 ± 679mL) and decreased driving pressure (18.3 ± 2.2 vs. 10.1 ± 1.7 cmH2O), estimated shunt (17.7 ± 3.4 vs. 4.2 ± 1.4%), lung strain (0.39 ± 0.07 vs. 0.22 ± 0.06) and lung elastance (28.4 ± 5.8 vs. 15.3 ± 4.3 cmH2O/L), respectively; all p < 0.0001. The OLA strategy can be monitored using noninvasive variables during bariatric surgery. This strategy decreased lung strain, elastance and driving pressure compared with standard protective ventilatory settings.Clinical trial number NTC03694665.

The Effects of an Open-Lung Approach During One-Lung Ventilation on Postoperative Pulmonary Complications and Driving Pressure: A Descriptive, Multicenter National Study

Thoracic surgical procedures are associated with an increased risk of postoperative pulmonary complications (PPCs), which seem to be related directly to intraoperative driving pressure. The authors conducted this study to describe the incidence of PPCs in patients in whom an individualized open-lung approach was applied during one-lung ventilation. This was a prospective, multicenter, national descriptive study. Thoracic surgery patients undergoing one-lung ventilation. Eligible participants were included consecutively from October 1, 2016, to September 30, 2017. A total of 690 patients were included. An individualized open-lung approach that consisted of an alveolar recruitment maneuver followed by a positive end-expiratory pressure adjusted to best respiratory system compliance was performed in all patients. Preoperative and intraoperative data were recorded; the primary outcome was a description of the incidence of PPCs in these patients during the first 7 postoperative days. The patients were mainly male, and half of them had a high risk of PPCs (ARISCAT score exceeding 44). Eleven percent of participants developed a PPC within the first postoperative week. The mean open lung positive end-expiratory pressure was 8 ± 3 cmH2O. When compared with pre-open lung approach values, the open-lung approach significantly decreased the driving pressure (14±4 cmH2O v 11±3 cmH2O; p<0.001) and increased dynamic compliance (30±10 mL/cmH2O v 43 ±15 mL/cmH2O; p <0.001). The low incidence of PPCs in patients who underwent an open-lung approach during one-lung ventilation compared with that reported for other thoracic surgery series and the decrease in the driving pressure in these patients justify an additional randomized controlled trial to compare the open-lung approach with the standard protective strategy of low tidal volume and low positive end-expiratory pressure.

Open lung approach versus standard protective strategies: Effects on driving pressure and ventilatory efficiency during anesthesia - A pilot, randomized controlled trial.

BackgroundLow tidal volume (VT) during anesthesia minimizes lung injury but may be associated to a decrease in functional lung volume impairing lung mechanics and efficiency. Lung recruitment (RM) can restore lung volume but this may critically depend on the post-RM selected PEEP. This study was a randomized, two parallel arm, open study whose primary outcome was to compare the effects on driving pressure of adding a RM to low-VT ventilation, with or without an individualized post-RM PEEP in patients without known previous lung disease during anesthesia.MethodsConsecutive patients scheduled for major abdominal surgery were submitted to low-VT ventilation (6 ml·kg-1) and standard PEEP of 5 cmH2O (pre-RM, n = 36). After 30 min estabilization all patients received a RM and were randomly allocated to either continue with the same PEEP (RM-5 group, n = 18) or to an individualized open-lung PEEP (OL-PEEP) (Open Lung Approach, OLA group, n = 18) defined as the level resulting in maximal Cdyn during a decremental PEEP trial. We compared the effects on driving pressure and lung efficiency measured by volumetric capnography.ResultsOL-PEEP was found at 8±2 cmH2O. 36 patients were included in the final analysis. When compared with pre-RM, OLA resulted in a 22% increase in compliance and a 28% decrease in driving pressure when compared to pre-RM. These parameters did not improve in the RM-5. The trend of the DP was significantly different between the OLA and RM-5 groups (p = 0.002). VDalv/VTalv was significantly lower in the OLA group after the RM (p = 0.035).ConclusionsLung recruitment applied during low-VT ventilation improves driving pressure and lung efficiency only when applied as an open-lung strategy with an individualized PEEP in patients without lung diseases undergoing major abdominal surgery.Trial registrationClinicalTrials.gov NCT02798133

How much esophageal pressure-guided end-expiratory transpulmonary pressure is sufficient to maintain lung recruitment in lavage-induced lung injury?

Because of limitations of the esophageal balloon technique, the value of using esophageal pressure (Pes)-guided end-expiratory transpulmonary pressure (PL-exp) to maintain lung recruitment in adult respiratory distress syndrome is controversial. This study aimed to investigate whether tailoring PL-exp to greater than 0 was enough to maintain lung recruitment. Ten pigs with severe lavage-induced lung injury were mechanically ventilated in a decremental positive end-expiratory pressure (PEEP) trial that was reduced from 20 to 6 cm H2O after full-lung recruitment. Respiratory mechanics, blood gases, hemodynamic data, and whole-lung computed tomography scans were recorded at each PEEP level. Open-lung PEEP (OL-PEEP) was determined by computed tomography, while Pes-guided PEEP (Pes-PEEP) was to maintain PL-exp greater than 0. OL-PEEP was higher than Pes-PEEP, which induced a higher PL-exp at OL-PEEP than at Pes-PEEP (4.6 [1.6] cm H2O vs. 1.2 [0.6] cm H2O, p < 0.001). Compared with OL-PEEP, the nonaerated lung region was significantly increased at Pes-PEEP. Superimposed pressure (SP) of the lung tissue between the esophageal plane and the dorsal level was higher at Pes-PEEP than at OL-PEEP, whereas PL-exp at the dorsal level was lower at Pes-PEEP than at OL-PEEP (-1.5 [0.7] cm H2O vs. 2.5 [1.5] cm H2O, p < 0.001). The SP correlated with PL-exp at the dorsal level and the nonaerated lung region. In this surfactant-depleted model, maintaining PL-exp just greater than 0 using Pes was unable to maintain lung recruitment; this was partly caused by a lack of compensation for the increased SP between the esophageal plane and the dorsal level.

Stress index for positive end-expiratory pressure titration in prone position: a piglet study.

Prone position ventilation is an important treatment for acute respiratory distress syndrome (ARDS), but chest wall elastance increases in prone position ventilation, and stress index may not reflect the changes in lung mechanics. We therefore investigated the effects of stress index guided PEEP titration on pulmonary mechanics and hemodynamics in the prone position in a piglet acute lung injury model. Ten piglets with severe lavage-induced lung injury were mechanically ventilated in a decremental PEEP trial after full lung recruitment in the prone position. Stress-index PEEP was the level at which the airway pressure stress index was 1, and open-lung PEEP was the level at which it was required to keep the lung open according to computed tomography (CT) scans. Respiratory mechanics, blood gases, hemodynamics, and whole-lung CT were recorded at the two PEEP levels. Respiratory system elastance and lung elastance were improved in the prone position but the ratio of chest wall elastance and respiratory system elastance was higher in the prone position. There was no significant difference between open-lung and stress-index guided PEEPs in the prone position (P = 0.46). There was no significant difference between collapsed lung volume (P = 0.07) and hyperinflation lung volume (P = 0.76) in the two groups. Similarly, there was no significant difference between open-lung and stress-index guided PEEPs in terms of oxygenation index (P = 0.95) and PaCO2 (P = 0.42). Stress index can be used to titrate PEEP in the prone position in a surfactant-depleted lung injury model.

Effects of lipopolysaccharide-induced inflammation on initial lung fibrosis during open-lung mechanical ventilation in rats

This study aimed to assess the impact of pulmonary inflammation on early fibrotic response in rats challenged with increasing doses of lipopolysaccharide (LPS). Twenty-four rats were randomized and infused with three different increasing doses of continuous LPS infusion (n=8/group) while being ventilated with low tidal volumes and open-lung positive end-expiratory pressure. Another eight animals served as uninjured control group. Hemodynamics, gas exchange, respiratory system mechanics, lung histology, α-smooth muscle actin, plasma cytokines, and mRNA expression of cytokines and type I and III procollagen in lung tissue were assessed. We found impaired hemodynamics and gas exchange as well as higher histological lung injury scores and α-smooth muscle actin expressions in the medium LPS dose compared to control and the lower LPS dose. The highest LPS dose did not cause further aggravation of these findings. In all LPS groups type I and III procollagen decreased compared to controls and there was a negative correlation between type III procollagen-RNA expression and proinflammatory mediators.

Open lung approach with low tidal volume mechanical ventilation attenuates lung injury in rats with massive brain damage

IntroductionThe ideal ventilation strategy for patients with massive brain damage requires better elucidation. We hypothesized that in the presence of massive brain injury, a ventilation strategy using low (6 milliliters per kilogram ideal body weight) tidal volume (VT) ventilation with open lung positive end-expiratory pressure (LVT/OLPEEP) set according to the minimal static elastance of the respiratory system, attenuates the impact of massive brain damage on gas-exchange, respiratory mechanics, lung histology and whole genome alterations compared with high (12 milliliters per kilogram ideal body weight) VT and low positive end-expiratory pressure ventilation (HVT/LPEEP).MethodsIn total, 28 adult male Wistar rats were randomly assigned to one of four groups: 1) no brain damage (NBD) with LVT/OLPEEP; 2) NBD with HVT/LPEEP; 3) brain damage (BD) with LVT/OLPEEP; and 4) BD with HVT/LPEEP. All animals were mechanically ventilated for six hours. Brain damage was induced by an inflated balloon catheter into the epidural space. Hemodynamics was recorded and blood gas analysis was performed hourly. At the end of the experiment, respiratory system mechanics and lung histology were analyzed. Genome wide gene expression profiling and subsequent confirmatory quantitative polymerase chain reaction (qPCR) for selected genes were performed.ResultsIn NBD, both LVT/OLPEEP and HVT/LPEEP did not affect arterial blood gases, as well as whole genome expression changes and real-time qPCR. In BD, LVT/OLPEEP, compared to HVT/LPEEP, improved oxygenation, reduced lung damage according to histology, genome analysis and real-time qPCR with decreased interleukin 6 (IL-6), cytokine-induced neutrophil chemoattractant 1 (CINC)-1 and angiopoietin-4 expressions. LVT/OLPEEP compared to HVT/LPEEP improved overall survival.ConclusionsIn BD, LVT/OLPEEP minimizes lung morpho-functional changes and inflammation compared to HVT/LPEEP.

Dead Space Fraction Changes During PEEP Titration Following Lung Recruitment in Patients With ARDS

Elevated dead space fraction (the ratio of dead space to tidal volume [V(D)/V(T)]) is a feature of ARDS. PEEP can partially reverse atelectasis, prevent alveoli recollapse, and improve lung compliance and gas exchange in patients with ARDS. However, whether V(D)/V(T) variables have a close relationship with PEEP and collapse alveolar recruitment remains under recognized. Meanwhile, few clinicians titrate PEEP in consideration of changes in V(D)/V(T). Therefore, we performed the study to evaluate V(D)/V(T), arterial oxygenation, and compliance changes during PEEP titration following lung recruitment in ARDS patients. Twenty-three ARDS patients ventilated in volume-controlled mode were enrolled in the study. Sustained inflation (40 cm H₂O, 30 s) was used as a recruitment maneuver, followed by decremental PEEP changes from 20 to 6 cm H₂O, in steps of 2 cm H₂O, and then to 0 cm H₂O. V(D)/V(T), pulmonary mechanics parameters, gas exchange parameters, and hemodynamic parameters were recorded after 20 min at each PEEP step. Compared with V(D)/V(T) at the PEEP levels of 20 cm H₂O and 0 cm H₂O, V(D)/V(T) was significantly lower at 12 cm H₂O (P = .02), and compliance of the static respiratory system (C(RS)) was significantly higher at pressure step 12/10 cm H₂O (P < .001). Compared with P(aCO₂) at the PEEP level of 20 cm H₂O, P(aCO₂) was significantly lower at 12 cm H₂O (P < .001). Arterial oxygenation values and functional residual capacity were reduced gradually during PEEP, decreasing from 20 cm H₂O to 0 cm H₂O. A significant change of V(D)/V(T), compliance and arterial oxygenation could be induced by PEEP titration in subjects with ARDS. Optimal PEEP in these subjects was 12 cm H₂O, because at this pressure level the highest compliance in conjunction with the lowest V(D)/V(T) indicated a maximum amount of effectively expanded alveoli. Monitoring of V(D)/V(T) was useful for detecting lung collapse and for establishing open-lung PEEP after a recruitment maneuver.

Relationship between regional lung compliance and ventilation homogeneity in the supine and prone position

The prone position (PP) improves ventilation homogeneity in acute respiratory distress syndrome. The aim of this study was to investigate whether the alleviation of ventilation inhomogeneity in PP was due to changes in regional lung compliance. Ten lung-lavaged piglets were mechanically ventilated in supine position (SP) and in PP. In each position, positive end-expiratory pressure (PEEP) was reduced from 20 to 6 cmH(2)O in steps of 2 cmH(2)O every 10 min after full lung recruitment. Respiratory mechanics, blood gas, haemodynamic data and whole-lung computed tomography scans were recorded at each PEEP. The compliances of normally aerated (C(normal)) and newly recruited (C(recruited)) lung regions were calculated. Open lung PEEP (OL-PEEP) was defined as the lowest PEEP to maintain full lung recruitment. At OL-PEEP, PP significantly increased normally aerated lung regions, decreased poorly aerated and hyperinflated lung regions and decreased tidal recruitment and hyperinflation. C(normal) was significantly reduced in PP compared with SP (12.8 ± 4.2 ml/cmH(2)O vs. 20.1 ± 6.2 ml/cmH(2)O, P < 0.001), whereas C(recruited) was increased in PP (13.9 ± 3.9 ml/cmH(2)O vs. 9.4 ± 2.4 ml/cmH(2)O, P < 0.001). C(normal) was correlated with hyperinflated lung regions at end-expiration (rho = 0.67) and end-inspiration (rho = 0.56) at OL-PEEP. C(recruited) was correlated with normally (r(2) = 0.36) and poorly aerated lung regions (rho = -0.58) at OL-PEEP. This surfactant-depleted model shows that the improvement of ventilation homogeneity in PP is related to an increase in C(recruited) and a decrease in C(normal).

Volume-Independent Elastance

A decremental positive end-expiratory pressure (PEEP) trial after full lung recruitment allows for the adjustment of the lowest PEEP that prevents end-expiratory collapse (open-lung PEEP). For a tidal volume (Vt) approaching zero, the PEEP of minimum respiratory system elastance (PEEP(minErs)) is theoretically equal to the pressure at the mathematical inflection point (MIP) of the pressure-volume curve, and seems to correspond to the open-lung PEEP in a decremental PEEP trial. Nevertheless, the PEEP(minErs) is dependent on Vt and decreases as Vt increases. To circumvent this dependency, we proposed the use of a second-order model in which the volume-independent elastance (E1) is used to set open-lung PEEP. Pressure-volume curves and a recruitment maneuver followed by decremental PEEP trials, with a Vt of 6 and 12 mL/kg, were performed in 24 Wistar rats with acute lung injury induced by intraperitoneally injected (n = 8) or intratracheally instilled (n = 8) Escherichia coli lipopolysaccharide. In 8 control animals, the anterior chest wall was surgically removed after PEEP trials, and the protocol was repeated. Airway pressure (Paw) and flow (F) were continuously acquired and fitted by the linear single-compartment model (Paw = Rrs·F + Ers·V + PEEP, where Rrs is the resistance of the respiratory system, and V is volume) and the volume-dependent elastance model (Paw = Rrs·F + E1 + E2·V·V + PEEP, where E2·V is the volume-dependent elastance). From each model, PEEPs of minimum Ers and E1 (PEEP(minE1)) were identified and compared with each respective MIP. The accuracy of PEEPminE1 and PEEPminErs in estimating MIP was assessed by bias and precision plots. Comparisons among groups were performed with the unpaired t test whereas a paired t test was used between the control group before and after chest wall removal and within groups at different Vts. All P values were then corrected for multiple comparisons by the Bonferroni procedure. In all experimental groups, PEEPminErs, but not PEEPminE1, tended to decrease as Vt increased. The difference between MIP and PEEPminE1 exhibited a lower bias compared with the difference between MIP and PEEPminErs (P < 0.001). The PEEPminE1 was always significantly higher than the PEEPminErs (7.7 vs 3.8, P < 0.001) and better approached MIP (7.7 vs 7.3 cm H2O with P = 0.04 at low Vt, and 7.8 vs 7.1 cm H2O with P < 0.001 at high Vt). PEEPminE1 better identifies the open-lung PEEP independently of the adjusted Vt, and may be a practical, more individualized approach for PEEP titration.

Respiratory and hemodynamic changes during lung recruitment maneuvering through progressive increases and decreases in PEEP level

ObjectiveTo evaluate the respiratory and hemodynamic changes during lung recruitment maneuvering (LRM) through stepwise increases and decreases in PEEP level. Design and settingA retrospective study in a 17-bed ICU was carried out. PatientsTwenty-one patients with acute respiratory failure and bilateral pulmonary infiltration. InterventionLRM was carried out, consisting of stepwise increases in PEEP (4cmH2O every 3min), with fixed ventilation pressure, until reaching a maximal value of 36cmH2O PEEP (ascending branch), followed by progressive decreases in PEEP (2cmH2O every 3min) until establishing the open-lung PEEP at the value associated to maximum respiratory compliance (Crs) (descending branch). Continuous hemodynamic monitoring was performed using an esophageal echodoppler probe. ResultsCrs gradually decreased in the ascending branch of the LRM, and progressively increased surpassing the initial value after establishing the open-lung PEEP in the descending branch, reducing the ventilation pressure and increasing the SpO2/FiO2 ratio. Hemodynamic changes primarily consisted of a fall in cardiac output and left ventricular preload, together with an increased heart rate and cardiac contractility. At comparable levels of PEEP and mean airway pressure, these changes were more pronounced during the descending branch of the LRM. Conclusions(1) LRM increased Crs, improving oxygenation and decreasing ventilation pressure; (2) the main hemodynamic consequence was the drop in cardiac output and left ventricular preload; and (3) the unequal hemodynamic derangement in both branches, at the same level of PEEP and mean airway pressure, showed that, along with intrathoracic pressure, other factors such as Crs and hypercapnia may have influenced the hemodynamic consequences of this type of LRM.

Cambios respiratorios y hemodinámicos durante una maniobra de reclutamiento pulmonar mediante incrementos y decrementos progresivos de PEEP

ObjectiveTo evaluate the respiratory and hemodynamic changes during lung recruitment maneuvering (LRM) through stepwise increases and decreases in PEEP level. Design and settingA retrospective study in a 17-bed ICU was carried out. PatientsTwenty-one patients with acute respiratory failure and bilateral pulmonary infiltration. InterventionLRM was carried out, consisting of stepwise increases in PEEP (4cmH2O every 3minutes), with fixed ventilation pressure, until reaching a maximal value of 36cmH2O PEEP (ascending branch), followed by progressive decreases in PEEP (2cmH2O every 3minutes) until establishing the open-lung PEEP at the value associated to maximum respiratory compliance (Crs) (descending branch). Continuous hemodynamic monitoring was performed using an esophageal echodoppler probe. ResultsCrs gradually decreased in the ascending branch of the LRM, and progressively increased surpassing the initial value after establish the open-lung PEEP in the descending branch, reducing the ventilation pressure and increasing the SpO2/FiO2 ratio. Hemodynamic changes primarily consisted of a fall in cardiac output and left ventricular preload, together with an increased heart rate and cardiac contractility. At comparable levels of PEEP and mean airway pressure, these changes were more pronounced during the descending branch of the LRM. Conclusions1) LRM increased Crs, improving oxygenation and decreasing ventilation pressure; 2) the main hemodynamic consequence was the drop in cardiac output and left ventricular preload; and 3) the unequal hemodynamic derangement in both branches, at the same level of PEEP and mean airway pressure, showed that, along with intrathoracic pressure, other factor such as Crs and hypercapnia may have influenced the hemodynamic consequences of this type of LRM.

Lung aeration during ventilation after recruitment guided by tidal elimination of carbon dioxide and dynamic compliance was better than after end-tidal carbon dioxide targeted ventilation: A computed tomography study in surfactant-depleted piglets*

To test the hypothesis that tidal elimination of carbon dioxide and dynamic compliance guided lung recruitment and positive end-expiratory pressure titration in surfactant-depleted piglets result in improved aeration (repeated computed tomography scans) and reduced ventilation pressures compared to those of a control group with conventional end-tidal carbon dioxide targeted ventilation. Prospective animal investigation. Clinical physiology research laboratory. Seventeen saline-lavaged piglets. The piglets were initially ventilated at an end-inspiratory pressure of 20 cm H2O, a positive end-expiratory pressure of 5 cm H2O, and a tidal volume of 10 mL kg for an end-tidal carbon dioxide target of 30-45 torr followed by 5 mins of ventilation without positive end-expiratory pressure. After this, the control group was ventilated for the same end-tidal carbon dioxide target during the study period. In the recruitment group, the protocol started with an increase of the positive end-expiratory pressure to 15 cm H2O. The end-inspiratory pressure was then increased in steps of 3 cm H2O to a tidal elimination of carbon dioxide peak/plateau in one recruitment group and further increased in two steps in a second recruitment group. A downward positive end-expiratory pressure titration was followed by continuous dynamic compliance monitoring. The "open lung positive end-expiratory pressure" was set 2 cm H2O above the positive end-expiratory pressure at the first dynamic compliance decline and used for a final "open lung ventilation" period. The recruitment groups showed better aeration, lower ventilatory pressure amplitude, and better dynamic compliance than the control group at the end of the study. Recruitment using airway pressures above the tidal elimination of carbon dioxide peak/plateau did not improve aeration. Using end-tidal carbon dioxide targeted ventilation in the control group restored aeration after the ventilation without positive end-expiratory pressure, but no recruitment or improvement of dynamic compliance was measured. Aeration was significantly better after recruitment and positive end-expiratory pressure titration than in a control group managed by "conventional" end-tidal carbon dioxide targeted ventilation. An increase of the end-inspiratory pressure above the tidal elimination of carbon dioxide peak/plateau did not result in an increased amount of normally aerated lung. A recruitment maneuver resulted in a lower ventilatory amplitude for achieving a target tidal volume and better dynamic compliance at the end of the study period compared to those of the control group.

A comparison of methods to identify open-lung PEEP

A comparison of methods to identify open-lung PEEP

VTCO2 and dynamic compliance-guided lung recruitment in surfactant-depleted piglets: A computed tomography study

Using computed tomography (CT) as reference, our primary objectives were to test if maximal tidal elimination of carbon dioxide (VTCO2) could be used as a marker of "optimal recruitment," indicating maximal available lung tissue for gas exchange and if a decrease in dynamic compliance (Cdyn) indicated the beginning of lung collapse during a downward positive end-expiratory pressure (PEEP) titration. Prospective laboratory animal investigation. Clinical physiology research laboratory. Six piglets undergoing lung lavage. Saline-lavaged piglets were initially ventilated without PEEP at a tidal volume (VT) of 10 mL/kg followed by baseline ventilation at end-inspiratory pressure (EIP) 25 cm H2O and PEEP 6 cm H2O. PEEP was increased to 12 or 15 cm H2O. Then EIP was increased in steps of 5 cm H2O and the EIP where VTCO2 peaked or leveled off was assumed to define optimally recruited lungs. A downward PEEP titration followed from 12 or 15 to 4 cm H2O in steps of 1 cm H2O. First decline of Cdyn was assumed to define onset of lung collapse. VTCO2 and Cdyn were continuously recorded and CT scans iterated for each change of ventilation. "Open-lung PEEP" was set 2 cm H2O above PEEP at the first Cdyn decline and was used for a final period of "open-lung ventilation." CT images showed recruited lungs at peak VTCO2 and that a minimal amount of normally aerated lung was added by further increase in EIP. Cdyn declined just before CT scans indicated lung collapse. Compared with baseline, the target VT of 10 mL/kg was achieved at lower EIP and pressure amplitude (EIP-PEEP) during the final open-lung ventilation with more normally aerated and fewer collapsed lungs. Cdyn was doubled after recruitment. The lung recruitment maneuver was effective and lungs optimally recruited at maximal VTCO2. A fall in Cdyn indicated lung collapse during downward PEEP titration as confirmed by CT.

A comparison of methods to identify open-lung PEEP

Many methods exist in the literature for identifying PEEP to set in ARDS patients following a lung recruitment maneuver (RM). We compared ten published parameters for setting PEEP following a RM. Lung injury was induced by bilateral lung lavage in 14 female Dorset sheep, yielding a PaO(2) 100-150 mmHg at F(I)O(2) 1.0 and PEEP 5 cmH(2)O. A quasi-static P-V curve was then performed using the supersyringe method; PEEP was set to 20 cmH(2)O and a RM performed with pressure control ventilation (inspiratory pressure set to 40-50 cmH(2)O), until PaO(2) + PaCO(2) > 400 mmHg. Following the RM, a decremental PEEP trial was performed. The PEEP was decreased in 1 cmH(2)O steps every 5 min until 15 cmH(2)O was reached. Parameters measured during the decremental PEEP trial were compared with parameters obtained from the P-V curve. For setting PEEP, maximum dynamic tidal respiratory compliance, maximum PaO(2), maximum PaO(2) + PaCO(2), and minimum shunt calculated during the decremental PEEP trial, and the lower Pflex and point of maximal compliance increase on the inflation limb of the P-V curve (Pmci,i) were statistically indistinguishable. The PEEP value obtained using the deflation upper Pflex and the point of maximal compliance decrease on the deflation limb were significantly higher, and the true inflection point on the inflation limb and minimum PaCO(2) were significantly lower than the other variables. In this animal model of ARDS, dynamic tidal respiratory compliance, maximum PaO(2), maximum PaO(2) + PaCO(2), minimum shunt, inflation lower Pflex and Pmci,i yield similar values for PEEP following a recruitment maneuver.

Respiratory and haemodynamic changes during decremental open lung positive end-expiratory pressure titration in patients with acute respiratory distress syndrome

IntroductionTo investigate haemodynamic and respiratory changes during lung recruitment and decremental positive end-expiratory pressure (PEEP) titration for open lung ventilation in patients with acute respiratory distress syndrome (ARDS) a prospective, clinical trial was performed involving 12 adult patients with ARDS treated in the surgical intensive care unit in a university hospital.MethodsA software programme (Open Lung Tool™) incorporated into a standard ventilator controlled the recruitment (pressure-controlled ventilation with fixed PEEP at 20 cmH2O and increased driving pressures at 20, 25 and 30 cmH2O for two minutes each) and PEEP titration (PEEP lowered by 2 cmH2O every two minutes, with tidal volume set at 6 ml/kg). The open lung PEEP (OL-PEEP) was defined as the PEEP level yielding maximum dynamic respiratory compliance plus 2 cmH2O. Gas exchange, respiratory mechanics and central haemodynamics using the Pulse Contour Cardiac Output Monitor (PiCCO™), as well as transoesophageal echocardiography were measured at the following steps: at baseline (T0); during the final recruitment step with PEEP at 20 cmH2O and driving pressure at 30 cmH2O, (T20/30); at OL-PEEP, following another recruitment manoeuvre (TOLP).ResultsThe ratio of partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FiO2) increased from T0 to TOLP (120 ± 59 versus 146 ± 64 mmHg, P < 0.005), as did dynamic respiratory compliance (23 ± 5 versus 27 ± 6 ml/cmH2O, P < 0.005). At constant PEEP (14 ± 3 cmH2O) and tidal volumes, peak inspiratory pressure decreased (32 ± 3 versus 29 ± 3 cmH2O, P < 0.005), although partial pressure of arterial carbon dioxide (PaCO2) was unchanged (58 ± 22 versus 53 ± 18 mmHg). No significant decrease in mean arterial pressure, stroke volume or cardiac output occurred during the recruitment (T20/30). However, left ventricular end-diastolic area decreased at T20/30 due to a decrease in the left ventricular end-diastolic septal-lateral diameter, while right ventricular end-diastolic area increased. Right ventricular function, estimated by the right ventricular Tei-index, deteriorated during the recruitment manoeuvre, but improved at TOLP.ConclusionsA standardised open lung strategy increased oxygenation and improved respiratory system compliance. No major haemodynamic compromise was observed, although the increase in right ventricular Tei-index and right ventricular end-diastolic area and the decrease in left ventricular end-diastolic septal-lateral diameter during the recruitment suggested an increased right ventricular stress and strain. Right ventricular function was significantly improved at TOLP compared with T0, although left ventricular function was unchanged, indicating effective lung volume optimisation.

A decremental PEEP trial for determining open‐lung PEEP in a rabbit model of acute lung injury

A positive end-expiratory pressure (PEEP) above the lower inflection point (LIP) of the pressure-volume curve has been thought necessary to maintain recruited lung volume in acute lung injury (ALI). We used a strategy to identify the level of open-lung PEEP (OLP) by detecting the maximum tidal compliance during a decremental PEEP trial (DPT). We performed a randomized controlled study to compare the effect of the OLP to PEEP above LIP and zero PEEP on pulmonary mechanics, gas exchange, hemodynamic change, and lung injury in 26 rabbits with ALI. After recruitment maneuver, the lavage-injured rabbits received DPTs to identify the OLP. Animals were randomized to receive volume controlled ventilation with either: (a) PEEP = 0 cm H2O (ZEEP); (b) PEEP = 2 cm H2O above OLP (OLP + 2); or (c) PEEP = 2 cm H2O above LIP (LIP + 2). Peak inspiratory pressure and mean airway pressure were recorded and arterial blood gases were analyzed every 30 min. Mean blood pressure and heart rate were monitored continuously. Lung injury severity was assessed by lung wet/dry weight ratio. Animals in OLP + 2 group had less lung injury as well as relatively better compliance, more stable pH, and less hypercapnia compared to the LIP + 2 and ZEEP groups. We concluded that setting PEEP according to the OLP identified by DPTs is an effective method to attenuate lung injury. This strategy could be used as an indicator for optimal PEEP. The approach is simple and noninvasive and may be of clinical interest.