cmH2O Positive End-expiratory Pressure Research Articles

Effect of positive end-expiratory pressure during anaesthesia induction on non-hypoxic apnoea time in infants: A randomised controlled trial.

Hypoxaemia occurs frequently in infants during anaesthetic induction. We evaluated the effect of positive end-expiratory pressure during anaesthesia induction on nonhypoxic apnoea time in infants. Randomised controlled trial. Tertiary care children's hospital, single centre, from November 2018 to October 2019. We included patients under 1 year of age receiving general anaesthesia. We assigned infants to a 7 cmH2O or 0 cmH2O positive end-expiratory pressure group. Anaesthesia was induced with 0.02 mg kg-1 atropine, 5 mg kg-1 thiopental sodium and 3 to 5% sevoflurane, and neuromuscular blockade with 0.6 mg kg-1 rocuronium. Thereafter, 100% oxygen was provided via face mask with volume-controlled ventilation of 6 ml kg-1 tidal volume, and either 7 cmH2O or no positive end-expiratory pressure. After 3 min of ventilation, the infants' trachea was intubated but disconnected from the breathing circuit, and ventilation resumed when pulse oximetry reached 95%. The primary outcome was nonhypoxic apnoea time defined as the time from cessation of ventilation to a pulse oximeter reading of 95%, whereas the secondary outcome was the incidence of significant atelectasis (consolidation score ≥2) assessed by lung ultrasound. Sixty patients were included in the final analysis. Apnoea time in the 7 cmH2O positive end-expiratory pressure group (105.2 s) increased compared with that in the control group (92.1 s) (P = 0.011, mean difference 13.0 s, 95% CI, 3.1 to 22.9 s). Significant atelectasis was observed in all patients without positive end-expiratory pressure and 66.7% of those with 7 cmH2O positive end-expiratory pressure (P = 0.019, 95% CI, 1.7 to 563.1, odds ratio 31.2). Positive end-expiratory pressure during anaesthesia induction with face mask ventilation increased nonhypoxic apnoea time in infants. www.clinicaltrials.gov, NCT03540940.

Application of two different nasal CPAP levels for the treatment of respiratory distress syndrome in preterm infants\u2014\u201cThe OPTTIMMAL-Trial\u201d\u2014Optimizing PEEP To The IMMAture Lungs: study protocol of a randomized controlled trial

BackgroundNasal continuous positive airway pressure (CPAP) applies positive end-expiratory pressure (PEEP) and has been shown to reduce the need for intubation and invasive mechanical ventilation in very low birth weight infants with respiratory distress syndrome. However, CPAP failure rates of 50% are reported in large randomized controlled trials. A possible explanation for these failure rates is the application of insufficient low levels of PEEP during nasal CPAP treatment to maintain adequate functional residual capacity shortly after birth. The optimum PEEP level to treat symptoms of respiratory distress in very low birth weight infants has not been assessed in clinical studies. The aim of the study is to compare two different PEEP levels during nasal CPAP treatment in preterm infants.MethodsIn this randomized multicenter trial, 216 preterm infants born at 26 + 0–29 + 6 gestational weeks will be allocated to receive a higher (6–8 cmH2O) or a lower (3–5 cmH2O) PEEP during neonatal resuscitation and the first 120 h of life. The PEEP level within each group will be titrated throughout the intervention based on the FiO2 (fraction of inspired oxygen concentration) requirements to keep oxygenation within the target range. The primary outcome is defined as the need for intubation and mechanical ventilation for > 1 h or being not ventilated but reaching one of the two pre-defined CPAP failure criteria (FiO2 > 0.5 for > 1 h or pCO2 ≥ 70 mmHg in two consecutive blood gas analyses at least 2 h apart).DiscussionBased on available data from the literature, the optimum level of PEEP that most effectively treats respiratory distress syndrome in preterm infants is unknown, since the majority of large clinical trials applied a wide range of PEEP levels (4–8 cmH2O). The rationale for our study hypothesis is that the early application of a higher PEEP level will more effectively counteract the collapsing properties of the immature and surfactant-deficient lungs and that the level of inspired oxygen may serve as a surrogate marker to guide PEEP titration. Finding the optimum noninvasive continuous distending pressure during early nasal CPAP is required to improve CPAP efficacy and as a consequence to reduce the exposure to ventilator-induced lung injury and the incidence of chronic lung disease in this vulnerable population of very preterm infants.Trial registrationdrks.de DRKS00019940. Registered on March 13, 2020

Effect of positive end-expiratory pressure on functional residual capacity in two experimental models of acute respiratory distress syndrome.

ObjectiveMeasurement of positive end-expiratory pressure (PEEP)-induced recruitment lung volume using passive spirometry is based on the assumption that the functional residual capacity (FRC) is not modified by the PEEP changes. We aimed to investigate the influence of PEEP on FRC in different models of acute respiratory distress syndrome (ARDS).MethodsA randomized crossover study was performed in 12 pigs. Pulmonary (n = 6) and extra-pulmonary (n = 6) ARDS models were established using an alveolar instillation of hydrochloric acid and a right atrium injection of oleic acid, respectively. Low (5 cmH2O) and high (15 cmH2O) PEEP were randomly applied in each animal. FRC and recruitment volume were determined using the nitrogen wash-in/wash-out technique and release maneuver.ResultsFRC was not significantly different between the two PEEP levels in either pulmonary ARDS (299 ± 92 mL and 309 ± 130 mL at 5 and 15 cmH2O, respectively) or extra-pulmonary ARDS (305 ± 143 mL and 328 ± 197 mL at 5 and 15 cmH2O, respectively). The recruitment volume was not significantly different between the two models (pulmonary, 341 ± 100 mL; extra-pulmonary, 351 ± 170 mL).ConclusionsPEEP did not influence FRC in either the pulmonary or extra-pulmonary ARDS pig model.

Protective Lung Ventilation in Children at Low Risk: Is it Necessary?

Background: Protective ventilation is often used to reduce pulmonary complications and we tested the benefit in paediatrics at low risk during general anaesthesia. Methods: In this randomised controlled trial, we recruited patients who were planned for nonabdominal surgery. Eligible participants were randomly assigned (1:1:1) to receive non-protective ventilation (control group) or low tidal volume with 5 cmH2O positive end-expiratory pressure (PEEP group) or low tidal volume with 5 cmH2O PEEP and recruitment manoeuvres (recruitment group). Lung ultrasonography was undertaken at eight predefined time points. Primary outcome was the difference in lung ultrasonography score and incidence of atelectasis among groups by 24 hours after extubation; a lower score indicates better lung aeration. Findings: Between 25 July 2019-10 January 2020, 90 eligible patients were randomly assigned and included in the final analysis. Atelectasis was the most common pulmonary complication. Patients in the PEEP and recruitment manoeuvre groups showed lower LUS score after the surgical procedure (H = 57.8, P=0.0001) and immediately after extubation (time point T3) (H =18.2, P=0.0001) compared with patients in the control group; However, this difference did not persist 15 min after extubation. Recruitment maneuvers can lead to hemodynamic instability. Interpretation: Aeration loss developed most severe immediately after extubation. Then aeration loss gradually improved and disappeared 3 hours after extubation despite ventilatory strategy. Drawing conclusions regarding the importance of an intraoperative protective ventilation strategy for patients at lower risk of atelectasis is challenging. Trial Registration: This study is registered with the Chinese Clinical Trial Registry (#ChiCTR1800018912). Funding Statement: None. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: The study was approved by the research ethics boards of Shanghai Children's Hospital (protocol number: 2019R044-F01, 24July 2019. Written informed consent was obtained from all participants.

Comparison of the efficacy of two ventilatory strategies in improving arterial oxygen tension and content in anaesthetized sheep

ObjectiveTo compare F-shunt and oxygen content indices in sheep ventilated with a positive end-expiratory pressure (PEEP) of 5 cmH2O alone or preceded by a stepwise alveolar recruitment manoeuvre (ARM). Study designRandomized crossover design. AnimalsA total of six nonpregnant Brogna ewes weighing 34–47 kg, undergoing thoracolumbar magnetic resonance scan. MethodsIn medetomidine-sedated sheep, anaesthesia was induced with propofol and maintained with isoflurane 1.1% ± 0.1% and an inspired oxygen fraction (FiO2) of 0.4. Animals were placed in left lateral recumbency and, after 10 minutes of spontaneous breathing, mechanically ventilated with 5 cmH2O of PEEP with (group ARM) or without (group PEEP) a stepwise recruitment manoeuvre. Maintaining a fixed driving pressure of 15 cmH2O, PEEP was increased from 0 to 20 cmH2O every 3 minutes in 5 cmH2O increments. In each sheep, arterial blood samples were collected to measure arterial gases and to calculate F-shunt, PaO2/alveolar oxygen partial pressure (PAO2) and PaO2/FIO2 during spontaneous breathing before mechanical ventilation (T0), after 20 minutes of ventilation (T20) and during spontaneous breathing at extubation (Text). ResultsBoth ventilatory strategies improved the arterial oxygen content although four animals in group PEEP showed oxygen content compatible with hypoxia compared with group ARM. F-shunt values were not statistically different at any time point in sheep that underwent only PEEP ventilation while they decreased at T20 and Text compared with T0 in group ARM. At extubation F-shunt was statistically lower in sheep that underwent an ARM. Mechanical ventilation improved PaO2/PAO2 and PaO2/FIO2 but they did not differ between groups. Conclusionsand clinical relevance The stepwise ARM evaluated in this study improved oxygenation indices and decreased F-shunt. This effect was maintained at extubation compared with sheep that were ventilated with only PEEP 5 cmH2O.

Autophagy Protects Against Developing Increased Lung Permeability and Hypoxemia by Down Regulating Inflammasome Activity and IL-1β in LPS Plus Mechanical Ventilation-Induced Acute Lung Injury

Targeting inflammasome activation to modulate interleukin (IL)-1β is a promising treatment strategy against acute respiratory distress syndrome and ventilator-induced lung injury (VILI). Autophagy is a key regulator of inflammasome activation in macrophages. Here, we investigated the role of autophagy in the development of acute lung injury (ALI) induced by lipopolysaccharide (LPS) and mechanical ventilation (MV). Two hours before starting MV, 0.2 mg/kg LPS was administered to mice intratracheally. Mice were then placed on high-volume MV (30 ml/kg with 3 cmH2O positive end-expiratory pressure for 2.5 h without additional oxygen application). Mice with myeloid-specific deletion of the autophagic protein ATG16L1 (Atg16l1fl/fl LysMCre) suffered severe hypoxemia (adjusted p < 0.05) and increased lung permeability (p < 0.05, albumin level in bronchoalveolar lavage fluid) with significantly higher IL-1β release into alveolar space (p < 0.05). Induction of autophagy by fasting-induced starvation led to improved arterial oxygenation (adjusted p < 0.0001) and lung permeability (p < 0.05), as well as significantly suppressed IL-1β production (p < 0.01). Intratracheal treatment with anti-mouse IL-1β monoclonal antibody (mAb; 2.5 mg/kg) significantly improved arterial oxygenation (adjusted p < 0.01) as well as lung permeability (p < 0.05). On the other hand, deletion of IL-1α gene or use of anti-mouse IL-1α mAb (2.5 mg/kg) provided no significant protection, suggesting that the LPS and MV-induced ALI is primarily dependent on IL-1β, but independent of IL-1α. These observations suggest that autophagy has a protective role in controlling inflammasome activation and production of IL-1β, which plays a critical role in developing hypoxemia and increased lung permeability in LPS plus MV-induced acute lung injury.

Effects of Trendelenburg position and increased airway pressure on hepatic regional blood flow of normal and resected liver.

High portal venous blood flow (Qpv) may contribute to posthepatectomy liver failure. Both Trendelenburg position (TP) and elevated airway pressure (Paw) increase backpressure to venous return and may thereby reduce Qpv. The aim of this study was to evaluate the effects of TP and increased Paw on hepatosplanchnic hemodynamics before and after major liver resection. Arterial and venous blood pressures, Qpv, extrasplanchnic inferior vena cava (Qivc), superior mesenteric (Qsma), hepatic (Qha), and carotid artery blood flows (Qca) were measured in 14 anesthetized and mechanically ventilated pigs in supine and 30° TP during end-expiratory hold at 5 cmH2O positive end-expiratory pressure (PEEP) and during inspiratory hold with Paw of 15, 20, 25, and 30 cmH2O. After major liver resection, the interventions were repeated in seven randomly selected animals. At baseline, TP increased right atrial pressure (Pra) and Qpv but not Qivc or Qsma. With increased Paw in the supine position, Pra increased and all regional blood flows decreased. TP during increasing Paw attenuated the decrease in Qpv, Qsma, and Qivc but not in Qha or Qca. After liver resection, the effects of TP during increasing Paw remained, albeit at higher portal vein pressures. However, TP alone did not increase IVC venous return. Increasing Paw in supine position reduces Qpv and all other regional flows, while the reduction in Qpv is attenuated in TP, suggesting partly preserved liver waterfall or decreased intrahepatic resistance. Liver resection, despite resulting in major intrahepatic blood flow changes, does not fundamentally influence the interaction of increasing Paw and TP on regional perfusion.NEW & NOTEWORTHY In Trendelenburg position (TP), liver blood flow is the only contributor to increased venous return measured in the inferior vena cava (IVC), which attenuates the decreased IVC venous return induced by increasing airway pressure. After liver resection, TP similarly attenuated effects of increasing airway pressure.

Ultrasonographic evaluation of the effect of recruitment maneuvers and positive end-expiratory pressure on diaphragmatic functions in obese patients undergoing laparoscopic sleeve gastrectomy: A randomized controlled study

ABSTRACT Purpose The aim of this study was to evaluate the effect of recruitment maneuvers (RMs) and positive end expiratory pressure (PEEP) on diaphragmatic function and atelectasis areas during pneumoperitoneum and the trendelenburg position in laparoscopic sleeve gastrectomy (LSG) patients. Methods This prospective double-blinded randomized clinical study was conducted on 69 obese patients undergoing LSG. Patients were randomly allocated to one of the three groups, Group I (control group) patients were mechanically ventilated without PEEP or RM, Group II received PEEP of 5 cmH2O, and Group III received 5 cmH2O PEEP, and intermittent four times RM consisting of maintaining airway pressure 40 cmH2O for 40 s. Primary outcome was diaphragmatic excursion (DE). Secondary outcomes were atelectasis area, Forced Vital Capacity (FVC), Forced Expiratory Volume in 1 s (FEV1), Peak Inspiratory Pressure (PIP), and any complications. Results DE decreased in all investigated groups after anesthesia induction till the end of procedure compared to pre-induction values, and it was statistically significant lower in control group compared to the two interventional groups with no significant difference between PEEP and PEEP+RM groups. Atelectasis volume according to lung aeration score was significantly increased in control group compared to the other two groups, while there was no statistical significant difference in PEEP+RM compared to PEEP in all the times except before induction of anesthesia there was no significant difference among the three groups. Conclusion The application of RM and PEEP are helpful for preserving DE and improving lung aeration during laparoscopic sleeve gastrectomy.

Low-pressure support vs automatic tube compensation during spontaneous breathing trial for weaning

BackgroundDuring spontaneous breathing trial, low-pressure support is thought to compensate for endotracheal tube resistance, but it actually should provide overassistance. Automatic tube compensation is an option available in the ventilator to compensate for flow-resistance of endotracheal tube. Its effects on patient effort have been poorly investigated. We aimed to compare the effects of low-pressure support and automatic tube compensation during spontaneous breathing trial on breathing power and lung ventilation distribution.ResultsWe performed a randomized crossover study in 20 patients ready to wean. Each patient received both methods for 30 min separated by baseline ventilation: pressure support 0 cmH2O and automatic tube compensation 100% in one period and pressure support 7 cmH2O without automatic tube compensation in the other period, a 4 cmH2O positive end-expiratory pressure being applied in each. Same ventilator brand (Evita XL, Draeger, Germany) was used. Breathing power was assessed from Campbell diagram with esophageal pressure, airway pressure, flow and volume recorded by a data logger. Lung ventilation distribution was assessed by using electrical impedance tomography (Pulmovista, Draeger, Germany). During the last 2 min of low-pressure support and automatic compensation period breathing power and lung ventilation distribution were measured on each breath. Breathing power generated by the patient’s respiratory muscles was 7.2 (4.4–9.6) and 9.7 (5.7–21.9) J/min in low-pressure support and automatic tube compensation periods, respectively (P = 0.011). Lung ventilation distribution was not different between the two methods.ConclusionsWe found that ATC was associated with higher breathing power than low PS during SBT without altering the distribution of lung ventilation.

Dynamic hyperinflation and intrinsic positive end-expiratory pressure in ARDS patients

BackgroundIn 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.MethodsWe 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.ResultsWe 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 < 0.001). The applied tidal volume was significantly lower (480 [430–540] vs 520 [445–600] mL at 5 cmH2O of PEEP; 480 [430–540] vs 510 [430–590] mL at 15 cmH2O) in patients with intrinsic PEEP, while the respiratory rate was significantly higher (18 [15–20] vs 15 [13–19] bpm at 5 cmH2O of PEEP; 18 [15–20] vs 15 [13–19] bpm at 15 cmH2O). At both PEEP levels, the total airway resistance and compliance of the respiratory system were not different in patients with and without intrinsic PEEP. The total lung gas volume and lung recruitability were also not different between patients with and without intrinsic PEEP (respectively 961 [701–1535] vs 973 [659–1433] mL and 15 [0–32] % vs 22 [0–36] %).ConclusionsIn sedated, paralyzed ARDS patients without a known obstructive disease, the amount of intrinsic PEEP during lung-protective ventilation is negligible and does not influence respiratory mechanical properties.

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.

Effects of small tidal volume and positive end-expiratory pressure on oxygenation in pressure-controlled ventilation-volume guaranteed mode during one-lung ventilation

Introduction The purpose of this study was to investigate whether tidal volume (TV) of 8 mL/kg without positive end-expiratory pressure (PEEP) and TV of 6 mL/kg with or without PEEP in pressure-controlled, ventilation-volume guaranteed (PCV-VG) mode can maintain arterial oxygenation and decrease inspiratory airway pressure effectively during one-lung ventilation (OLV). Methods The study enrolled 27 patients undergoing thoracic surgery. All patients were ventilated with PCV-VG mode. During OLV, patients were initially ventilated with TV 8 mL/kg (group TV8) without PEEP. Ventilation was subsequently changed to TV 6 mL/kg with PEEP (5 cmH2O; group TV6+PEEP) or without (group TV6) in random sequence. Peak inspiratory pressure (Ppeak), mean airway pressure (Pmean), and arterial blood gas analysis were measured 30 min after changing ventilator settings. Ventilation was then changed once more to add or eliminate PEEP (5 cmH2O), while maintaining TV 6 mL/kg. Thirty min after changing ventilator settings, the same parameters were measured once more. Results The Ppeak was significantly lower in group TV6 (19.3±3.3 cmH2O) than in group TV8 (21.8±3.1 cmH2O) and group TV6+PEEP (20.1±3.4 cmH2O). PaO2 was significantly higher in group TV8 (242.5±111.4 mmHg) than in group TV6 (202.1±101.3 mmHg) (P = 0.044). There was no significant difference in PaO2 between group TV8 and group TV6+PEEP (226.8±121.1 mmHg). However, three patients in group TV6 were dropped from the study because PaO2 was lower than 80 mmHg after ventilation. Discussion It is postulated that TV 8 mL/kg without PEEP or TV 6 mL/kg with 5 cmH2O PEEP in PCV-VG mode during OLV can safely maintain adequate oxygenation.

Variable Ventilation Is Equally Effective as Conventional Pressure Control Ventilation for Optimizing Lung Function in a Rabbit Model of ARDS.

BackgroundIntroducing mathematically derived variability (MVV) into the otherwise monotonous conventional mechanical ventilation has been suggested to improve lung recruitment and gas exchange. Although the application of a ventilation pattern based on variations in physiological breathing (PVV) is beneficial for healthy lungs, its value in the presence of acute respiratory distress syndrome (ARDS) has not been characterized. We therefore aimed at comparing conventional pressure-controlled ventilation with (PCS) or without regular sighs (PCV) to MVV and PVV at two levels of positive end-expiratory pressure (PEEP) in a model of severe ARDS.MethodsAnesthetised rabbits (n = 54) were mechanically ventilated and severe ARDS (PaO2/FiO2 ≤ 150 mmHg) was induced by combining whole lung lavage, i.v. endotoxin and injurious ventilation. Rabbits were then randomly assigned to be ventilated with PVV, MVV, PCV, or PCS for 5 h while maintaining either 6 or 9 cmH2O PEEP. Ventilation parameters, blood gas indices and respiratory mechanics (tissue damping, G, and elastance, H) were recorded hourly. Serum cytokine levels were assessed with ELISA and lung histology was analyzed.ResultsAlthough no progression of lung injury was observed after 5 h of ventilation at PEEP 6 cmH2O with PVV and PCV, values for G (58.8 ± 71.1[half-width of 95% CI]% and 40.8 ± 39.0%, respectively), H (54.5 ± 57.2%, 50.7 ± 28.3%), partial pressure of carbon-dioxide (PaCO2, 43.9 ± 23.8%, 46.2 ± 35.4%) and pH (−4.6 ± 3.3%, −4.6 ± 2.2%) worsened with PCS and MVV. Regardless of ventilation pattern, application of a higher PEEP improved lung function and precluded progression of lung injury and inflammation. Histology lung injury scores were elevated in all groups with no difference between groups at either PEEP level.ConclusionAt moderate PEEP, variable ventilation based on a pre-recorded physiological breathing pattern protected against progression of lung injury equally to the conventional pressure-controlled mode, whereas mathematical variability or application of regular sighs caused worsening in lung mechanics. This outcome may be related to the excessive increases in peak inspiratory pressure with the latter ventilation modes. However, a greater benefit on respiratory mechanics and gas exchange could be obtained by elevating PEEP, compared to the ventilation mode in severe ARDS.

A challenge with 5 cmH2O of positive end-expiratory pressure predicts fluid responsiveness in neurosurgery patients with protective ventilation: an observational study.

Positive end-expiratory pressure (PEEP) increment induces a decrease in Stroke Volume Index (SVI). We hypothesized that the magnitude of SVI reduction due to a 5 cmH2O increase in PEEP could predict fluid responsiveness during low tidal volume ventilation. Forty-eight patients completed the study. Heart rate, mean arterial pressure, SVI, pulse pressure variation (PPV) and stroke volume variation (SVV) were recorded before short-time low PEEP (SLPC) challenge (applied additional 5 cmH2O PEEP to patients for 30 seconds), during SLPC and before and after 500 mL fluid loading. Patients whose SVI increased more than 15% after the fluid loading were defined as volume responders. Twenty-one (44%) patients were volume responder. Decrease percentage in SVI during SLPC was 17.4±3.6% and 9.9±3.1% in responders and non-responders respectively (P<0.001). A strong correlation was found between decrease percentage in SVI during SLPC and increase percentage in SVI after fluid loading (R2=0.680, P<0.001). The area under receiver operating curves generated to predict fluid responsiveness for decrease percentage in SVI during SLPC (0.944, 95% CI: 0.836-0.990) was significantly higher than that for PPV (0.777, 95% CI: 0.634-0.884, P=0.025) and SVV (0.773, 95% CI: 0.630-0.882, P=0.022). Best cut-off values of decrease percentage in SVI during SLPC was -14.2 with 95% sensitivity and 89% specificity. SVI change percentage during SLPC can predict fluid responsiveness better than PPV and SVV in neurosurgery patients ventilated with low tidal volume.

Different contributions from lungs and chest wall to respiratory mechanics in mice, rats, and rabbits.

Changes in lung mechanics are frequently inferred from intact-chest measures of total respiratory system mechanics without consideration of the chest wall contribution. The participation of lungs and chest wall in respiratory mechanics has not been evaluated systematically in small animals commonly used in respiratory research. Thus, we compared these contributions in intact-chest mice, rats, and rabbits and further characterized the influence of positive end-expiratory pressure (PEEP). Forced oscillation technique was applied to anesthetized mechanically ventilated healthy animals to obtain total respiratory system impedance (Zrs) at 0, 3, and 6 cmH2O PEEP levels. Esophageal pressure was measured by a catheter-tip micromanometer to separate Zrs into pulmonary (ZL) and chest wall (Zcw) components. A model containing a frequency-independent Newtonian resistance (RN), inertance, and a constant-phase tissue damping (G) and elastance (H) was fitted to Zrs, ZL, and Zcw spectra. The contribution of Zcw to RN was negligible in all species and PEEP levels studied. However, the participation of Zcw in G and H was significant in all species and increased significantly with increasing PEEP and animal size (rabbit > rat > mice). Even in mice, the chest wall contribution to G and H was still considerable, reaching 47.0 ± 4.0(SE)% and 32.9 ± 5.9% for G and H, respectively. These findings demonstrate that airway parameters can be assessed from respiratory system mechanical measurements. However, the contribution from the chest wall should be considered when intact-chest measurements are used to estimate lung parenchymal mechanics in small laboratory models (even in mice), particularly at elevated PEEP levels. NEW & NOTEWORTHY In species commonly used in respiratory research (rabbits, rats, mice), esophageal pressure-based estimates revealed negligible contribution from the chest wall to the Newtonian resistance. Conversely, chest wall participation in the viscoelastic tissue mechanical parameters increased with body size (rabbit > rat > mice) and positive end-expiratory pressure, with contribution varying between 30 and 50%, even in mice. These findings demonstrate the potential biasing effects of the chest wall when lung tissue mechanics are inferred from intact-chest measurements in small laboratory animals.

Assessment of PEEP-Ventilation and the Time Point of Parallel-Conductance Determination for Pressure-Volume Analysis Under β-Adrenergic Stimulation in Mice.

Aim: Cardiac pressure-volume (PV loop) analysis under β-adrenergic stimulation is a powerful method to simultaneously determine intrinsic cardiac function and β-adrenergic reserve in mouse models. Despite its wide use, several key approaches of this method, which can affect murine cardiac function tremendously, have not been experimentally investigated until now. In this study, we investigate the impact of three lines of action during the complex procedure of PV loop analysis: (i) the ventilation with positive end-expiratory pressure, (ii) the time point of injecting hypertonic saline to estimate parallel-conductance, and (iii) the implications of end-systolic pressure-spikes that may arise under β-adrenergic stimulation.Methods and Results: We performed pressure-volume analysis during β-adrenergic stimulation in an open-chest protocol under Isoflurane/Buprenorphine anesthesia. Our analysis showed that (i) ventilation with 2 cmH2O positive end-expiratory pressure prevented exacerbation of peak inspiratory pressures subsequently protecting mice from macroscopic pulmonary bleedings. (ii) Estimations of parallel-conductance by injecting hypertonic saline prior to pressure-volume recordings induced dilated chamber dimensions as depicted by elevation of end-systolic volume (+113%), end-diastolic volume (+40%), and end-diastolic pressure (+46%). Further, using this experimental approach, the preload-independent contractility (PRSW) was significantly impaired under basal conditions (−17%) and under catecholaminergic stimulation (−14% at 8.25 ng/min Isoprenaline), the β-adrenergic reserve was alleviated, and the incidence of ectopic beats was increased >5-fold. (iii) End-systolic pressure-spikes were observed in 26% of pressure-volume recordings under stimulation with 2.475 and 8.25 ng/min Isoprenaline, which affected the analysis of maximum pressure (+11.5%), end-diastolic volume (−8%), stroke volume (−10%), and cardiac output (−11%).Conclusions: Our results (i) demonstrate the advantages of positive end-expiratory pressure ventilation in open-chest instrumented mice, (ii) underline the perils of injecting hypertonic saline prior to pressure-volume recordings to calibrate for parallel-conductance and (iii) emphasize the necessity to be aware of the consequences of end-systolic pressure-spikes during β-adrenergic stimulation.

RETRACTED ARTICLE: The effects of a recruitment manoeuvre with positive end-expiratory pressure on lung compliance in patients undergoing robot-assisted laparoscopic radical prostatectomy

The effects of a recruitment manoeuvre (RM) with positive end-expiratory pressure (PEEP) on lung compliance (CLUNG) are not well characterised in robot-assisted laparoscopic radical prostatectomy (RARP). Patients were allocated to group R (n = 10; with an RM) or C (n = 9; without an RM). An RM involved sustained inflation of 30 cmH2O for 30 s. The lungs were ventilated with volume-controlled ventilation with tidal volume of 7 mL kg−1 of predicted body weight and fraction of inspired oxygen of 0.5. End-tidal carbon dioxide pressure was maintained at normocapnia. Patients were in the horizontal lithotomy position (pre-op). After pneumoperitoneum, patients underwent RARP in a steep Trendelenburg lithotomy position at a PEEP level of 0 cmH2O (RARP0). An RM was used in the R group but not in the C group. Patients were then ventilated with 5 cmH2O PEEP for 1 h after RARP0 (RARP5.1) and 2 h after RARP0 (RARP5.2). Oesophageal pressure and airway pressure were measured for calculating CLUNG and chest wall compliance. CLUNG significantly decreased from pre-op to RARP0 and did not significantly increase from RARP0 to RARP5.1 and RARP5.2 in either group. CLUNG differed significantly between groups at RARP5.1 and RARP5.2 (103 ± 30 vs. 68 ± 11 mL cm−1 H2O and 106 ± 35 vs. 72 ± 9 mL cm−1 H2O; P < 0.05). In patients undergoing RARP, with the addition of RM, the CLUNG was effectively increased from the horizontal lithotomy position to the steep Trendelenburg lithotomy position under pneumoperitoneum.

Effects of small tidal volume and positive end-expiratory pressure on oxygenation in pressure-controlled ventilation-volume guaranteed mode during one-lung ventilation.

BackgroundThe purpose of this study was to investigate whether tidal volume (TV) of 8 mL/kg without positive end-expiratory pressure (PEEP) and TV of 6 mL/kg with or without PEEP in pressure-controlled ventilation-volume guaranteed (PCV-VG) mode can maintain arterial oxygenation and decrease inspiratory airway pressure effectively during one-lung ventilation (OLV).MethodsThe study enrolled 27 patients undergoing thoracic surgery. All patients were ventilated with PCV-VG mode. During OLV, patients were initially ventilated with TV 8 mL/kg (group TV8) without PEEP. Ventilation was subsequently changed to TV 6 mL/kg with PEEP (5 cmH2O; group TV6+PEEP) or without (group TV6) in random sequence. Peak inspiratory pressure (Ppeak), mean airway pressure (Pmean), and arterial blood gas analysis were measured 30 min after changing ventilator settings. Ventilation was then changed once more to add or eliminate PEEP (5 cmH2O), while maintaining TV 6 mL/kg. Thirty min after changing ventilator settings, the same parameters were measured once more.ResultsThe Ppeak was significantly lower in group TV6 (19.3±3.3 cmH2O) than in group TV8 (21.8±3.1 cmH2O) and group TV6+PEEP (20.1±3.4 cmH2O). PaO2 was significantly higher in group TV8 (242.5±111.4 mmHg) than in group TV6 (202.1±101.3 mmHg) (p=0.044). There was no significant difference in PaO2 between group TV8 and group TV6+PEEP (226.8±121.1 mmHg). However, three patients in group TV6 were dropped from the study because PaO2 was lower than 80 mmHg after ventilation.ConclusionIt is postulated that TV 8 mL/kg without PEEP or TV 6 mL/kg with 5 cmH2O PEEP in PCV-VG mode during OLV can safely maintain adequate oxygenation.

Effect of ventilation with different positive end-expiratory pressures on intracranial pressure in patients undergoing gynecological laparoscopic surgery

Objective To evaluate the effect of ventilation with different positive end-expiratory pressures (PEEPs) on intracranial pressure in the patients undergoing gynecological laparoscopic surgery. Methods Sixty American Society of Anesthesiologists physical status Ⅰor Ⅱ patients, aged 25-55 yr, with body mass index of 18-27 kg/m2, scheduled for elective gynecological endoscopic surgery, were divided into 3 groups (n=20 each) using a random number table method: routine ventilation group (group A), 4 cmH2O PEEP group (group B) and 8 cmH2O PEEP group (group C). The patients were mechanically ventilated with PEEP 4 or 8 cmH2O at 5 min of head-down tilt after start of pneumoperitoneum in group B and group C. The patients were mechanically ventilated in volume-controlled mode, with tidal volume 7 ml/kg, inspired oxygen concentration 50% and inspiratory/expiratory ratio 1∶2.Blood samples were collected from the radial artery for measurement of PaCO2 and PaO2 at 5 min after tracheal intubation (T0), 5, 15 and 30 min of head-down tilt (T1-3), and 5 min of the supine position after the end of pneumoperitoneum (T4). The peak airway pressure (Ppeak) was recorded, dynamic pulmonary compliance (Cdyn) was calculated, and optic nerve sheath diameter was measured using an ultrasonic apparatus at T0-4.Cognitive function was assessed at 1 day before surgery and 7 days after surgery using Mini-Mental State Examination. Results Compared with group A, Ppeak was significantly increased at T1-4, and PaO2 was increased at T2 in group B, and Ppeak and PaO2 were increased at T1-4, and Cdyn was increased at T1, 2 in group C (P 0.05). No patients developed cognitive dysfunction at 7 days after surgery in three groups. Conclusion Ventilation with different PEEPs causes no increase in intracranial pressure of the patients undergoing gynecological laparoscopic surgery. Key words: Positive-pressure respiration; Intracranial pressure; Laparoscopy; Gynecologic surgical procedures

Driving-pressure-independent protective effects of open lung approach against experimental acute respiratory distress syndrome

BackgroundThe open lung approach (OLA) reportedly has lung-protective effects against acute respiratory distress syndrome (ARDS). Recently, lowering of the driving pressure (ΔP), rather than improvement in lung aeration per se, has come to be considered as the primary lung-protective mechanism of OLA. However, the driving pressure-independent protective effects of OLA have never been evaluated in experimental studies. We here evaluated whether OLA shows protective effects against experimental ARDS even when the ΔP is not lowered.MethodsLipopolysaccharide was intratracheally administered to rats to establish experimental ARDS. After 24 h, rats were mechanically ventilated and randomly allocated to the OLA or control group. In the OLA group, 5 cmH2O positive end-expiratory pressure (PEEP) and recruitment maneuver (RM) were applied. Neither PEEP nor RM was applied to the rats in the control group. Dynamic ΔP was kept at 15 cmH2O in both groups. After 6 h of mechanical ventilation, rats in both groups received RM to inflate reversible atelectasis of the lungs. Arterial blood gas analysis, lung computed tomography, histological evaluation, and comprehensive biochemical analysis were performed.ResultsOLA significantly improved lung aeration, arterial oxygenation, and gas exchange. Even after RM in both groups, the differences in these parameters between the two groups persisted, indicating that the atelectasis-induced respiratory dysfunction observed in the control group is not an easily reversible functional problem. Lung histological damage was severe in the dorsal dependent area in both groups, but was attenuated by OLA. White blood cell counts, protein concentrations, and tissue injury markers in the broncho-alveolar lavage fluid (BALF) were higher in the control than in the OLA group. Furthermore, levels of CXCL-7, a platelet-derived chemokine, were higher in the BALF from the control group, indicating that OLA protects the lungs by suppressing platelet activation.ConclusionsOLA shows protective effects against experimental ARDS, even when the ΔP is not decreased. In addition to reducing ΔP, maintaining lung aeration seems to be important for lung protection in ARDS.