Use Of High Positive End-expiratory Pressure Research Articles

High PEEP with recruitment maneuvers versus Low PEEP During General Anesthesia for Surgery - a Bayesian individual patient data meta-analysis of three randomized clinical trials.

The influence of high positive end-expiratory pressure (PEEP) with recruitment maneuvers on the occurrence of postoperative pulmonary complications after surgery is still not definitively established. Bayesian analysis can help to gain further insights from the available data and provide a probabilistic framework that is easier to interpret. Our objective was to estimate the posterior probability that the use of high PEEP with recruitment maneuvers is associated with reduced postoperative pulmonary complications in patients with intermediate-to-high risk under neutral, pessimistic, and optimistic expectations regarding the treatment effect. Multilevel Bayesian logistic regression analysis on individual patient data from three randomized clinical trials carried out on surgical patients at Intermediate-to-High Risk for postoperative pulmonary complications. The main outcome was the occurrence of postoperative pulmonary complications in the early postoperative period. We studied the effect of high PEEP with recruitment maneuvers versus Low PEEP Ventilation. Priors were chosen to reflect neutral, pessimistic, and optimistic expectations of the treatment effect. Using a neutral, pessimistic, or optimistic prior, the posterior mean odds ratio (OR) for High PEEP with recruitment maneuvers compared to Low PEEP was 0.85 (95% Credible Interval [CrI] 0.71 to 1.02), 0.87 (0.72 to 1.04), and 0.86 (0.71 to 1.02), respectively. Regardless of prior beliefs, the posterior probability of experiencing a beneficial effect exceeded 90%. Subgroup analysis indicated a more pronounced effect in patients who underwent laparoscopy (OR: 0.67 [0.50 to 0.87]) and those at high risk for PPCs (OR: 0.80 [0.53 to 1.13]). Sensitivity analysis, considering severe postoperative pulmonary complications only or applying a different heterogeneity prior, yielded consistent results. High PEEP with recruitment maneuvers demonstrated a moderate reduction in the probability of PPC occurrence, with a high posterior probability of benefit observed consistently across various prior beliefs, particularly among patients who underwent laparoscopy.

Efficacy of Higher Positive End-Expiratory Pressure Ventilation Strategy in Patients With Acute Respiratory Distress Syndrome: A Systematic Review and Meta-Analysis.

Previous systematic reviews and meta-analyses assessing the pooled effects of higher positive end-expiratory pressure (PEEP) failed to show significantly reduced mortality in patients with acute respiratory distress syndrome (ARDS). Some new randomized controlled trials (RCTs) have been reported and an updated systematic review is needed to evaluate the use of higher PEEP in patients with ARDS.We searched MEDLINE, Cochrane Central Register of Controlled Trials (CENTRAL), EMBASE, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Igaku-Chuo-Zasshi, ICTRP, the National Institute of Health Clinical Trials Register, and the reference list of recent guidelines. We included RCTs to compare the higher PEEP ventilation strategy with the lower strategy in patients with ARDS. Two authors independently assessed the eligibility of the studies and extracted the data. The primary outcomes were 28-day mortality. The GRADE (Grading of Recommendations, Assessment, Development, and Evaluations) methodology was used to evaluate the certainty of the evidence.Among the 6530 screened records, 16 randomized trials involving 4150 patients were included in our meta-analysis. When comparing higher PEEP versus lower PEEP, the pooled risk ratio (RR) for 28-day mortality was 0.85 (15 studies, n=4108, 95% CI 0.72 to 1.00, I2=58%, low certainty of evidence). Subgroup analysis by study participants with a low tidal volume (LTV) strategy showed an interaction (P for interaction, 0.001).Our study showed that in patients with ARDS, the use of higher PEEP did not significantly reduce 28-day mortality compared to the use of lower PEEP.

Air leak syndromes (Pneumomediastinum, pneumothorax, and subcutaneous emphysema) in critically ill COVID-19 patients – Prevalence, risk factors, and outcome

Background: A high incidence of air leak syndromes (ALSs) has been reported in critically ill coronavirus disease 2019 (COVID-19) patients, which affects disease outcome. Objective: To evaluate the incidence, outcome, and risk factors associated with ALSs in critically ill COVID-19 patients receiving invasive or non-invasive positive pressure ventilation. Result: Out of 79 patients, 16 (20.2%) patients had ALS. The mean age of the ALS group was 48.6 ± 13.1 years as compared to 52.8 ± 13.1 (p = 0.260) years in the non-ALS group. The study group had a lower median body mass index (25.9 kg/m2 vs 27.6 kg/m2, P = 0.096), a higher D-dimer value (1179.5 vs 762.0, P = 0.024), lower saturation (74% vs 88%, P = 0.006), and a lower PF ratio (134 vs 189, P = 0.028) at presentation as compared to the non-ALS group. Patients with ALS had received a higher median positive end-expiratory pressure (PEEP) (10 cm vs 8 cm of water, P = 0.005). The pressure support, highest driving pressure, and peak airway pressure were not significantly different in the two groups. The ALS group had a significantly longer duration of hospital stay (17.5 vs 9 days, P = 0.003). Multiple logistic regression analyses indicated that patients who received inj. dexamethasone were less likely to develop ALS (OR: 12.6 (95% CI 1.6-95.4), P = 0.015). Conclusion: A high incidence of ALS is present in critically ill COVID-19 patients. High inflammatory parameters, severe hypoxia at presentation, and use of high PEEP are significant risk factors associated with ALS. The risk of developing ALS was lower in patients who received inj. dexamethasone.

Association of early positive end-expiratory pressure settings with ventilator-free days in patients with coronavirus disease 2019 acute respiratory distress syndrome: A secondary analysis of the Practice of VENTilation in COVID-19 study.

BACKGROUNDThere is uncertainty about how much positive end-expiratory pressure (PEEP) should be used in patients with acute respiratory distress syndrome (ARDS) due to coronavirus disease 2019 (COVID-19).OBJECTIVETo investigate whether a higher PEEP strategy is superior to a lower PEEP strategy regarding the number of ventilator-free days (VFDs).DESIGNMulticentre observational study conducted from 1 March to 1 June 2020.SETTING AND PATIENTSTwenty-two ICUs in The Netherlands and 933 invasively ventilated COVID-19 ARDS patients.INTERVENTIONSPatients were categorised retrospectively as having received invasive ventilation with higher (n=259) or lower PEEP (n=674), based on the high and low PEEP/FiO2 tables of the ARDS Network, and using ventilator settings and parameters in the first hour of invasive ventilation, and every 8 h thereafter at fixed time points during the first four calendar days. We also used propensity score matching to control for observed confounding factors that might influence outcomes.MAIN OUTCOMES AND MEASURESThe primary outcome was the number of VFDs. Secondary outcomes included distant organ failures including acute kidney injury (AKI) and use of renal replacement therapy (RRT), and mortality.RESULTSIn the unmatched cohort, the higher PEEP strategy had no association with the median [IQR] number of VFDs (2.0 [0.0 to 15.0] vs. 0.0 [0.0 to 16.0] days). The median (95% confidence interval) difference was 0.21 (−3.34 to 3.78) days, P = 0.905. In the matched cohort, the higher PEEP group had an association with a lower median number of VFDs (0.0 [0.0 to 14.0] vs. 6.0 [0.0 to 17.0] days) a median difference of −4.65 (−8.92 to −0.39) days, P = 0.032. The higher PEEP strategy had associations with higher incidence of AKI (in the matched cohort) and more use of RRT (in the unmatched and matched cohorts). The higher PEEP strategy had no association with mortality.CONCLUSIONIn COVID-19 ARDS, use of higher PEEP may be associated with a lower number of VFDs, and may increase the incidence of AKI and need for RRT.TRIAL REGISTRATIONPractice of VENTilation in COVID-19 is registered at ClinicalTrials.gov, NCT04346342.

Acute kidney injury (AKI) in patients with Covid-19 infection is associated with ventilatory management with elevated positive end-expiratory pressure (PEEP)

BackgroundAcute kidney injury (AKI) in Covid-19 patients admitted to the intensive care unit (ICU) is common, and its severity may be associated with unfavorable outcomes. Severe Covid-19 fulfills the diagnostic criteria for acute respiratory distress syndrome (ARDS); however, it is unclear whether there is any relationship between ventilatory management and AKI development in Covid-19 ICU patients.PurposeTo describe the clinical course and outcomes of Covid-19 ICU patients, focusing on ventilatory management and factors associated with AKI development.MethodsSingle-center, retrospective observational study, which assessed AKI incidence in Covid-19 ICU patients divided by positive end expiratory pressure (PEEP) tertiles, with median levels of 9.6 (low), 12.0 (medium), and 14.7 cmH2O (high-PEEP).ResultsOverall mortality was 51.5%. AKI (KDIGO stage 2 or 3) occurred in 38% of 101 patients. Among the AKI patients, 19 (53%) required continuous renal replacement therapy (CRRT). In AKI patients, mortality was significantly higher versus non-AKI (81% vs. 33%, p < 0.0001). The incidence of AKI in low-, medium-, or high-PEEP patients were 16%, 38%, and 59%, respectively (p = 0.002). In a multivariate analysis, high-PEEP patients showed a higher risk of developing AKI than low-PEEP patients (OR = 4.96 [1.1–21.9] 95% CI p < 0.05). ICU mortality rate was higher in high-PEEP patients, compared to medium-PEEP or low-PEEP patients (69% vs. 44% and 42%, respectively; p = 0.057).ConclusionThe use of high PEEP in Covid-19 ICU patients is associated with a fivefold higher risk of AKI, leading to higher mortality. The cause and effect relationship needs further analysis.Graphic abstract

Higher PEEP for acute respiratory distress syndrome: a Bayesian meta-analysis of randomised clinical trials

Objective: Benefit or harm of higher positive end expiratory pressure (PEEP) for acute respiratory distress syndrome (ARDS) is controversial. We aimed to assess the impact of higher levels of PEEP in patients with ARDS under a Bayesian framework. Design: Systematic review and Bayesian meta-analysis of randomised clinical trials comparing higher to lower PEEP in adult patients with ARDS. Data sources: MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials from 1996 to 1 March 2020. Review methods: We extracted data from high quality randomised clinical trials comparing higher to lower levels of PEEP in adult patients, using low tidal volume in both arms, and conducted a Bayesian meta-analysis using aggregate data from these studies. Results: Eight clinical trials including 3703 patients (n = 1833 for higher PEEP, n = 1870 for lower PEEP) were included. Under a minimally informative prior, the posterior probability of benefit with higher PEEP was 65% (relative risk, 0.97 [95% credible interval, 0.78-1.14]). In patients with moderate-to- severe ARDS, the posterior probability of benefit with higher PEEP was 77% (relative risk, 0.94 [95% credible interval, 0.77-1.13]). Down-weighting studies that employed a maximum recruitment strategy by 100% increased the posterior probability of benefit to 92% under a minimally informative prior. Conclusions: The probability of benefit or harm from routine use of higher PEEP for patients with ARDS ranges from 27% to 86%, and from 14% to 73% depending on one's prior, suggesting continued uncertainty and equipoise regarding the benefit of PEEP If data from trials using a maximum recruitment strategy is discounted to some extent because of uncertainty over the appropriateness of this approach, the available evidence suggests that higher PEEP could be beneficial for moderate-to-severe ARDS. However, well powered randomised clinical trials are needed to confirm these findings.

Severe Intraabdominal Hypertension in Critically Ill COVID-19 Patients With Acute Kidney Injury

Severe Intraabdominal Hypertension in Critically Ill COVID-19 Patients With Acute Kidney Injury

Mechanical ventilation of the healthy lungs: lessons learned from recent trials.

Although there is clear evidence for benefit of protective ventilation settings [including low tidal volume and higher positive end-expiratory pressure (PEEP)] in patients with acute respiratory distress syndrome (ARDS), it is less clear what the optimal mechanical ventilation settings are for patients with healthy lungs. Use of low tidal volume during operative ventilation decreases postoperative pulmonary complications (PPC). In the critically ill patients with healthy lungs, use of low tidal volume is as effective as intermediate tidal volume. Use of higher PEEP during operative ventilation does not decrease PPCs, whereas hypotension occurred more often compared with use of lower PEEP. In the critically ill patients with healthy lungs, there are conflicting data regarding the use of a higher PEEP, which may depend on recruitability of lung parts. There are limited data suggesting that higher driving pressures because of higher PEEP contribute to PPCs. Lastly, use of hyperoxia does not consistently decrease postoperative infections, whereas it seems to increase PPCs compared with conservative oxygen strategies. In patients with healthy lungs, data indicate that low tidal volume but not higher PEEP is beneficial. Thereby, ventilation strategies differ from those in ARDS patients.

Determination of adequate positive end‐expiratory pressure level required for carbon dioxide homeostasis in an animal model of infant laparoscopy

Capnoperitoneum provides a ventilatory challenge due to reduction in end-expiratory lung volume and peritoneal carbon dioxide absorption in both children and adults. The primary aim of this controlled interventional trial was to determine the positive end-expiratory pressure (PEEP) level needed to ensure for adequate carbon dioxide clearance and preservation of carbon dioxide homeostasis in an experimental model of infant laparoscopy. The secondary aim was to evaluate potential effects on cardiac output of PEEP and abdominal pressure level variations in the same setting. Eight chinchilla bastard rabbits were anesthetized and mechanically ventilated. Intra-abdominal pressures were randomly set to 0, 6, and 12mmHg by carbon dioxide insufflation. Carbon dioxide clearance using volumetric capnography, arterial blood gas data, and cardiac output was recorded, while PEEP 3, 6, and 9 cmH2 O were applied in a random order. A PEEP of 9 cmH2 O showed restoration of carbon dioxide clearance without causing changes in arterial partial pressure of carbon dioxide and bicarbonate and with no associated deterioration in cardiac output. The results promote a PEEP level of 9 cmH2 O in this model of infant capnoperitoneum to allow for adequate carbon dioxide removal with subsequent preservation of carbon dioxide homeostasis. The use of high PEEP was not associated with any decrease in cardiac output.

Analysis of different levels of positive end-expiratory pressure during lung retrieval for transplantation: an experimental study.

Atelectasis and inadequate oxygenation in lung donors is a common problem during the retrieval of these organs. Nevertheless, the use of high positive end-expiratory pressure (PEEP) is not habitual during procedures of lung retrieval. Twenty-one Sprague-Dawley male consanguineous rats were used in the study. The animals were divided into 3 groups according to the level of PEEP used: low (2 cmH2O), moderate (5 cmH2O), and high (10 cmH2O). Animals were ventilated with a tidal volume of 6 mL/kg. Before lung removal, the lungs were inspected for the presence of atelectasis. When atelectasis was detected, alveolar recruitment maneuvers were performed. Blood gasometric analysis was performed immediately. Finally, the lungs were retrieved, weighed, and submitted to histological analysis. The animals submitted to higher PEEP showed higher levels of oxygenation with the same tidal volumes PO2=262.14 (PEEP 2), 382.4 (PEEP 5), and 477.0 (PEEP 10). The occurrence of atelectasis was rare in animals with a PEEP of 10 cmH2O, which therefore required less frequent recruitment maneuvers (need for recruitment: PEEP 2=100%, PEEP 5 =100%, and PEEP 10=14.3%). There was no change in hemodynamic stability, occurrence of pulmonary edema, or other histological injuries with the use of high PEEP. The use of high PEEP (10 cmH2O) was feasible and probably a beneficial strategy for the prevention of atelectasis and the optimization of oxygenation during lung retrieval. Clinical studies should be performed to confirm this hypothesis.

Should we titrate ventilation based on driving pressure? Maybe not in the way we would expect

Mechanical ventilation maintains adequate gas exchange in patients during general anaesthesia, as well as in critically ill patients without and with acute respiratory distress syndrome (ARDS). Optimization of mechanical ventilation is important to minimize ventilator induced lung injury and improve outcome. Tidal volume (VT), positive end-expiratory pressure (PEEP), respiratory rate (RR), plateau pressures as well as inspiratory oxygen are the main parameters to set mechanical ventilation. Recently, the driving pressure (∆P), i.e., the difference of the plateau pressure and end-expiratory pressure of the respiratory system or of the lung, has been proposed as a key role parameter to optimize mechanical ventilation parameters. The ∆P depends on the VT as well as on the relative balance between the amount of aerated and/or overinflated lung at end-expiration and end-inspiration at different levels of PEEP. During surgery, higher ∆P, mainly due to VT, was progressively associated with an increased risk to develop post-operative pulmonary complications; in two large randomized controlled trials the reduction in ∆P by PEEP did not result in better outcome. In non-ARDS patients, ∆P was not found even associated with morbidity and mortality. In ARDS patients, an association between ∆P (higher than 13-15 cmH2O) and mortality has been reported. In several randomized controlled trials, when ∆P was minimized by the use of higher PEEP with or without recruitment manoeuvres, this strategy resulted in equal or even higher mortality. No clear data are currently available about the interpretation and clinical use of ∆P during assisted ventilation. In conclusion, ∆P is an indicator of severity of the lung disease, is related to VT size and associated with complications and mortality. We advocate the use of ∆P to optimize individually VT but not PEEP in mechanically ventilated patients with and without ARDS.

Basis function identification of lung mechanics in mechanical ventilation for predicting outcomes of therapy changes: A first virtual patient

Mechanical ventilation is a primary therapy for patients with acute respiratory failure. However, incorrect ventilator settings can cause further lung damage with inter- and intra- patient heterogeneity an issue. Lung protective ventilator settings include titrating positive end-expiratory pressure (PEEP) to the point of minimum elastance. However, predicting minimum elastance can be difficult, and use of high PEEP can lead to ventilator induced lung injury. In this study, a basis function elastance and resistance model is developed to allow use of information available at a lower PEEP level to identify patient-specific mechanics and predict lung mechanics at a higher PEEP. Accurate prediction of pressure and PEEP to within 5% over 8 recruitment manoeuvres validates the functionality of this virtual patient modelling and system identification approach.

Higher PEEP versus Lower PEEP Strategies for Patients with Acute Respiratory Distress Syndrome. A Systematic Review and Meta-Analysis.

Higher positive end-expiratory pressure (PEEP) levels may reduce atelectrauma, but increase over-distention lung injury. Whether higher PEEP improves clinical outcomes among patients with acute respiratory distress syndrome (ARDS) is unclear. To compare clinical outcomes of mechanical ventilation strategies using higher PEEP levels versus lower PEEP strategies in patients with ARDS. We performed a systematic review and meta-analysis of clinical trials investigating mechanical ventilation strategies using higher versus lower PEEP levels. We used random effects models to evaluate the effect of higher PEEP on 28-day mortality, organ failure, ventilator-free days, barotrauma, oxygenation, and ventilation. We identified eight randomized trials comparing higher versus lower PEEP strategies, enrolling 2,728 patients with ARDS. Patients were 55 (±16) (mean ± SD) years old and 61% were men. Mean PEEP in the higher PEEP groups was 15.1 (±3.6) cm H2O as compared with 9.1 (±2.7) cm H2O in the lower PEEP groups. Primary analysis excluding two trials that did not use lower Vt ventilation in the lower PEEP control groups did not demonstrate significantly reduced mortality for patients receiving higher PEEP as compared with a lower PEEP (six trials; 2,580 patients; relative risk, 0.91; 95% confidence interval [CI] = 0.80-1.03). A higher PEEP strategy also did not significantly decrease barotrauma, new organ failure, or ventilator-free days when compared with a lower PEEP strategy (moderate-level evidence). Quality of evidence for primary analyses was downgraded for precision, as CIs of outcomes included estimates that would result in divergent recommendations for use of higher PEEP. Secondary analysis, including trials that did not use low Vt in low-PEEP control groups, showed significant mortality reduction for high-PEEP strategies (eight trials; 2,728 patients; relative risk, 0.84; 95% CI = 0.71-0.99), with greater mortality benefit observed for high PEEP in trials that did not use lower Vts in the low-PEEP control group (P = 0.02). Analyses stratifying by use of recruitment maneuvers (P for interaction = 0.69), or use of physiological targets to set PEEP versus PEEP/FiO2 tables (P for interaction = 0.13), did not show significant effect modification. Use of higher PEEP is unlikely to improve clinical outcomes among unselected patients with ARDS.

Perioperative complications of obese patients.

The perioperative care of obese patients can often be challenging, as the presence of comorbidities is common in this patient population. In this article, we present recent data on perioperative complications of obese patients and discuss relevant details for daily practice, including drug dosing, airway management, and mechanical ventilation. The volatile agent desflurane reduces extubation time, without major effects on postoperative anesthesia care unit discharge time, incidence of postoperative nausea and vomiting, or postoperative pain scores compared with other volatile anesthetics. Lean body weight is the most appropriate dosing scalar for most drugs used in anesthesia, including opioids and anesthetic induction agents. Compared with the operational theatre, airway complications occur 20-fold more often in the ICU, with poor outcome. Individual titration of positive end-expiratory pressure (PEEP) after lung recruitment improves gas exchange and lung mechanics intraoperatively, but data on patient outcome are lacking. Intensive care physicians who treat obese patients need to be trained in the management of the difficult airway. The application of PEEP and the use of recruitment maneuvers may lead to improved intraoperative oxygenation, but current data do not allow recommending the use of high PEEP combined with lung recruitment maneuvers in this population.

Effect of high positive end-expiratory pressure for mechanical ventilation in the treatment of neurological pulmonary edema

To explore the effect of high positive end-expiratory pressure (PEEP) for the treatment of neurological pulmonary edema (NPE) in patients undergoing mechanical ventilation, and to look for the best mechanical ventilation strategy to improve the prognosis. A prospective study was conducted, and 120 patients with NEP admitted to Department of Critical Care Medicine of the First Affiliated Hospital of Guangxi Traditional Chinese Medical University from January 2010 to August 2013 were enrolled and divided into two groups according to random number table (n=60 in each group). The patients in two groups were given empiric treatment for the disease, and they underwent mechanical ventilation. In the normal PEEP group PEEP was 3-10 cmH2O (1 cmH2O=0.098 kPa), and in the high PEEP group PEEP was 11-30 cmH2O, and all the rest parameters were the same. Clinical indices before and 7 days after treatment, and 28-day morality rate were compared between two groups. The 28-day morality rate in high PEEP group was obviously lower than that in the normal PEEP group [25.0% (15/60) vs. 65.0% (39/60), χ(2)=6.465, P=0.011]. The clinical signs in both groups were improved after treatment. Compared with the normal PEEP group, the clinical indices in high PEEP group were more significantly improved. There were significant differences in body temperature (37.4±0.5 centigrade vs. 38.5±0.6 centigrade), respiratory rate (18.3±3.1 times/min vs. 23.3±3.5 times/min), heart rate (94.7±8.5 beats/min vs. 113.5±8.0 beats/min), white blood cell count (WBC: 12.5±2.1 ×10(9)/L vs. 17.1±1.7 ×10(9)/L), acute physiology and chronic health evaluation II (APACHEII) score (15.6±3.2 vs. 19.8±3.7), Glasgow coma score (GCS: 12.5±2.1 vs. 8.5±2.9), gastrointestinal dysfunction score (3.9±3.0 vs. 3.6±2.4), oxygenation index (PaO2/FiO2: 196.5±45.1 mmHg vs. 134.1±22.3 mmHg), serum creatinine (SCr: 86.5±35.6 μmol/L vs. 98.5±37.7 μmol/L), total bilirubin (TBil: 39.7±23.5 μmol/L vs. 41.5±16.2 μmol/L), C-reacting protein (CRP: 53.7±21.4 mmol/L vs. 108.4±26.3 mmol/L), prothrombin time (PT: 15.0±2.1 s vs. 20.4±2.2 s), activated partial thromboplastin time (APTT: 37.3±4.9 s vs. 56.7±13.6 s), international normalized ratio (INR: 2.52±0.64 vs. 4.01±0.77), extra vascular lung water index (EVLWI: 7.53±1.21 mL/kg vs. 15.85±3.41 mL/kg), pulmonary vascular permeability index (PVPI: 6.07±0.89 vs. 9.47±1.26), mean arterial pressure (MAP: 87.3±10.9 mmHg vs. 98.7±13.6 mmHg), cardiac output (CO: 7.15±1.42 L/min vs. 5.65±1.82 L/min), systemic vascular resistance index (SVRI: 112.4±9.5 KP vs. 136.5±11.9 KP), and blood lactate (2.53±1.23 mmol/L vs. 5.81±2.17 mmol/L) between high PEEP group and normal PEEP group (P<0.05 or P<0.01). Prognosis can be improved in NPE patients with the use of high PEEP in mechanical ventilation.

The Impact of Preload Alteration on the Myocardial Performance Index through Implementing Positive End Expiratory Pressure

Load independent methods should be used for the assessment of ventricular function. Debate still exists regarding whether tissue Doppler imaging (TDI) indices are influenced by preload. Here, we evaluated the effect of positive end expiratory pressure (PEEP) related preload reduction on both conventional pulsed Doppler (PD) and TDI myocardial performance index (MPI). Thirty-eight mechanically ventilated patients of 3 months to 12 years old (mean ± SD age of 30 ± 11 months) without overt heart disease were enrolled. Doppler mitral inflow velocities, isovolumetric contraction and relaxation times and aortic ejection time in addition to TDI peak systolic, early and late diastolic velocities from the basal segment of left ventricular lateral wall were determined for each patient before and after applying high PEEP (10 cmH(2) O).PD-MPI was load dependent (0.61 ± 0.22 vs. 0.78 ± 0.25, P = 0.002). However, TDI-MPI did not significantly change after the use of high PEEP declining the left ventricular volume loading (0.78 ± 0.21 vs. 0.84 ± 0.22, P = 0.23). Hence, regarding various interfering pathophysiologic factors particularly preload reduction, it seems that TDI-MPI would be a more reliable index for the assessment of ventricular function.

Clinical management of severely hypoxemic patients

To describe a physiopathological-based approach to clinical management of severely hypoxemic patients that integrates the most recent findings on the use of rescue therapies. Several techniques are available to improve oxygenation in severely hypoxemic patients. Survival benefits have not been proved for most of these techniques. In a recent randomized trial, centralization of acute respiratory distress syndrome patients to a specialized center able to provide extracorporeal membrane oxygenation showed better survival as compared to conventional treatment. Randomized trials failed to prove survival benefits with the use of high levels of positive end-expiratory pressure (PEEP) or prone positioning. However, pooled data from two meta-analyses showed significant higher survival in the most severe patients both with the use of higher PEEP and prone positioning. Treatment of severely hypoxemic patients should aim to improve oxygenation while limiting ventilator-induced lung injury. A physiopathological approach that accounts for the underlying mechanisms of hypoxemia, and physiological and clinical effects of different treatments is likely the best guide we have to treat severely hypoxemic patients.

High Positive End-expiratory Pressure and Mortality in Acute Respiratory Distress Syndrome

Servicio de Anestesia-Reanimación, Residencia General, Hospital Universitario La Paz, Madrid, Spain. dpestana.hulp@salud.madrid.orgIn acute lung injury and acute respiratory distress syndrome (ARDS), the aim of positive end-expiratory pressure (PEEP) is to recruit lung tissue preventing the cyclic opening and closing of alveoli (atelectrauma).1However, PEEP is associated to deleterious pulmonary (overdistension of healthy tissue) and hemodynamic (decreased venous return, abnormalities in organ blood flow) effects.2–4In recent years, several studies have attempted to answer the question of which PEEP should be used in acute lung injury and ARDS. Two strategies may be used: the setting of a “low” PEEP to minimize its secondary effects or a “high” PEEP to maximize lung recruitment and gas exchange (open lung strategy). In their recent meta-analysis, Phoenix et al. 5observed that, in ARDS patients, the use of a high-PEEP strategy showed a trend toward improved mortality and increased risk of barotrauma, although these changes were not statistically significant. However, the authors stated that “the benefits [of this strategy] far outweigh potential risks” and considered that “current evidence supports the use of high PEEP in unselected groups of patients.”A major limitation in these studies is the lack of definition of high PEEP. Protocols include two strategies in which one of the groups is randomly assigned to receive a higher level of PEEP than the other. The selection of the PEEP level is rather arbitrary, based on oxygenation criteria, and always limiting the plateau pressure. The PEEP is never individualized according to the primary cause (pulmonary vs. extrapulmonary) or severity of ARDS. Results are not conclusive, because every group includes patients who require different levels of PEEP. Therefore, the potential benefits of a specific strategy in some of the patients in a group are likely neutralized by the deleterious effects on the rest of the patients. Another reason that may explain the lack of conclusive results is the limitation of the plateau pressure in all patients, which plays a major role in outcome and may be more important that the level of PEEP in unselected cases.The results from the meta-analysis are in accord with recent literature questioning the decrease in mortality in ARDS in the past decade despite the implementation of new ventilatory strategies.6–8In the ARDSNet trial,9a significant reduction in mortality was observed when a “protective strategy,” based on a low tidal volume (6 ml/kg), was used. But we may speculate that patients were actually being protected from an “aggressive strategy” (tidal volume 12 ml/kg in the control arm). It is likely that the application of a high PEEP in the initial phase of severe ARDS, with an expected important lung edema and inflammation, is justified.10Even accepting this approach, it remains unanswered for how long the PEEP should be “high.” The lack of clear benefits in unselected patients is probably related to the absence of objective tests that help in the individual titration of the ventilatory parameters. Several techniques have been proposed, such as the plotting of pressure–volume curves,11the stress index12(actually a sort of dynamic pressure–volume curve), or the electrical impedance tomography.13Interestingly, in the three smaller studies included in the meta-analysis by Phoenix et al. 5but finally excluded for the conclusions, PEEP was set according to the pressure–volume curve. Of note is the apparent major benefit observed with a high PEEP level in these studies. Until recruitment/derecruitment and hyperinflation are not estimated repeatedly in individual ARDS patients as their lung injury evolves, it is unlikely that any attempt to demonstrate the superiority of a ventilatory strategy will be conclusive.Servicio de Anestesia-Reanimación, Residencia General, Hospital Universitario La Paz, Madrid, Spain. dpestana.hulp@salud.madrid.org

Helium/Oxygen Breathing Improved Hypoxemia After Cardiac Surgery

Helium/Oxygen Breathing Improved Hypoxemia After Cardiac Surgery