Moderate Positive End-expiratory Pressure Research Articles

Lung-Protective Mechanical Ventilation in Patients with Severe Acute Brain Injury: A Multicenter Randomized Clinical Trial (PROLABI).

Rationale: Lung-protective strategies using low Vt and moderate positive end-expiratory pressure (PEEP) are considered best practice in critical care, but interventional trials have never been conducted in patients with acute brain injuries because of concerns about carbon dioxide control and the effect of PEEP on cerebral hemodynamics. Objectives: To test the hypothesis that ventilation with lower VT and higher PEEP compared to conventional ventilation would improve clinical outcomes in patients with acute brain injury. Methods: In this multicenter, open-label, controlled clinical trial, 190 adult patients with acute brain injury were assigned to receive either a lung-protective or a conventional ventilatory strategy. The primary outcome was a composite endpoint of death, ventilator dependency, and acute respiratory distress syndrome (ARDS) at Day 28. Neurological outcome was assessed at ICU discharge by the Oxford Handicap Scale and at 6 months by the Glasgow Outcome Scale. Measurements and Main Results: The two study arms had similar characteristics at baseline. In the lung-protective and conventional strategy groups, using an intention-to-treat approach, the composite outcome at 28 days was 61.5% and 45.3% (relative risk [RR], 1.35; 95% confidence interval [CI], 1.03-1.79; P = 0.025). Mortality was 28.9% and 15.1% (RR, 1.91; 95% CI, 1.06-3.42; P = 0.02), ventilator dependency was 42.3% and 27.9% (RR, 1.52; 95% CI, 1.01-2.28; P = 0.039), and incidence of ARDS was 30.8% and 22.1% (RR, 1.39; 95% CI, 0.85-2.27; P = 0.179), respectively. The trial was stopped after enrolling 190 subjects because of termination of funding. Conclusions: In patients with acute brain injury without ARDS, a lung-protective ventilatory strategy, as compared with a conventional strategy, did not reduce mortality, percentage of patients weaned from mechanical ventilation, or incidence of ARDS and was not beneficial in terms of neurological outcomes. Because of the early termination, these preliminary results require confirmation in larger trials. Clinical trial registered with www.clinicaltrials.gov (NCT01690819).

Maintaining moderate versus lower PEEP after cardiac surgery: a propensity-scored matched analysis

BackgroundSetting positive end-expiratory pressure (PEEP) at around 5 cm H2O in the early postoperative period seems a common practice for most patients. It remains unclear if the routine application of higher levels of PEEP confers any meaningful clinical benefit for cardiac surgical patients. The aim of this study was to compare moderate versus conventional lower PEEP on patient-centered outcomes in the intensive care unit (ICU).MethodsThis is a single-center retrospective study involving patients receiving cardiac surgery from June 2022 to May 2023. Propensity-score matching (PSM) was used to balance the baseline differences. Primary outcomes were the duration of mechanical ventilation and ICU length of stay. Secondary outcomes included PaO2/FiO2 ratio at 24 h and the need for prone positioning during ICU stay.ResultsA total of 334 patients were included in the study, 102 (31%) of them received moderate PEEP (≥ 7 cm H2O) for the major time in the early postoperative period (12 h). After PSM, 79 pairs of patients were matched with balanced baseline data. The results showed that there was marginal difference in the distribution of mechanical ventilation duration (p = 0.05) and the Moderate PEEP group had a higher extubation rate at the day of T-piece trial (65 [82.3%] vs 52 [65.8%], p = 0.029). Applying moderate PEEP was also associated with better oxygenation. No differences were found regarding ICU length of stay and patients requiring prone positioning between groups.ConclusionIn selective cardiac surgical patients, using moderate PEEP compared with conventional lower PEEP in the early postoperative period correlated to better oxygenation, which may have potential for earlier liberation of mechanical ventilation.

Positive end-expiratory pressure limits inspiratory effort through modulation of the effort-to-drive ratio: an experimental crossover study

BackgroundHow assisted spontaneous breathing should be used during acute respiratory distress syndrome is questioned. Recent evidence suggests that high positive end-expiratory pressure (PEEP) may limit the risk of patient self-inflicted lung injury (P-SILI). The aim of this study was to assess the effects of PEEP on esophageal pressure swings, inspiratory drive, and the neuromuscular efficiency of ventilation. We hypothesized that high PEEP would reduce esophageal pressure swings, regardless of inspiratory drive changes, by modulating the effort-to-drive ratio (EDR). This was tested retrospectively in an experimental animal crossover study. Anesthetized pigs (n = 15) were subjected to mild to moderate lung injury and different PEEP levels were applied, changing PEEP from 0 to 15 cmH2O and back to 0 cmH2O in steps of 3 cmH2O. Airway pressure, esophageal pressure (Pes), and electric activity of the diaphragm (Edi) were collected. The EDR was calculated as the tidal change in Pes divided by the tidal change in Edi. Statistical differences were tested using the Wilcoxon signed-rank test.ResultsInspiratory esophageal pressure swings decreased from − 4.2 ± 3.1 cmH2O to − 1.9 ± 1.5 cmH2O (p < 0.01), and the mean EDR fell from − 1.12 ± 1.05 cmH2O/µV to − 0.24 ± 0.20 (p < 0.01) as PEEP was increased from 0 to 15 cmH2O. The EDR was significantly correlated to the PEEP level (rs = 0.35, p < 0.01).ConclusionsHigher PEEP limits inspiratory effort by modulating the EDR of the respiratory system. These findings indicate that PEEP may be used in titration of the spontaneous impact on ventilation and in P-SILI risk reduction, potentially facilitating safe assisted spontaneous breathing. Similarly, ventilation may be shifted from highly spontaneous to predominantly controlled ventilation using PEEP. These findings need to be confirmed in clinical settings.

Impact of a positive end-expiratory pressure strategy on oxygenation, respiratory compliance, and hemodynamics during laparoscopic surgery in non-obese patients: a systematic review and meta-analysis of randomized controlled trials

BackgroundHigher positive end-expiratory pressure (PEEP) during laparoscopic surgery may increase oxygenation and respiratory compliance. This meta-analysis aimed to compare the impact of different intraoperative PEEP strategies on arterial oxygenation, compliance, and hemodynamics during laparoscopic surgery in non-obese patients.MethodsWe searched RCTs in PubMed, Cochrane Library, Web of Science, and Google Scholar from January 2012 to April 2022 comparing the different intraoperative PEEP (Low PEEP (LPEEP): 0–4 mbar; Moderate PEEP (MPEEP): 5–8 mbar; high PEEP (HPEEP): >8 mbar; individualized PEEP - iPEEP) on arterial oxygenation, respiratory compliance (Cdyn), mean arterial pressure (MAP), and heart rate (HR). We calculated mean differences (MD) with 95% confidence intervals (CI), and predictive intervals (PI) using random-effects models. The Cochrane Bias Risk Assessment Tool was applied.Results21 RCTs (n = 1554) met the inclusion criteria. HPEEP vs. LPEEP increased PaO2 (+ 29.38 [16.20; 42.56] mmHg, p < 0.0001) or PaO2/FiO2 (+ 36.7 [+ 2.23; +71.70] mmHg, p = 0.04). HPEEP vs. MPEEP increased PaO2 (+ 22.00 [+ 1.11; +42.88] mmHg, p = 0.04) or PaO2/FiO2 (+ 42.7 [+ 2.74; +82.67] mmHg, p = 0.04). iPEEP vs. MPEEP increased PaO2/FiO2 (+ 115.2 [+ 87.21; +143.20] mmHg, p < 0.001). MPEEP vs. LPEP, and HPEEP vs. MPEEP increased PaO2 or PaO2/FiO2 significantly with different heterogeneity. HPEEP vs. LPEEP increased Cdyn (+ 7.87 [+ 1.49; +14.25] ml/mbar, p = 0.02). MPEEP vs. LPEEP, and HPEEP vs. MPEEP did not impact Cdyn (p = 0.14 and 0.38, respectively). iPEEP vs. LPEEP decreased driving pressure (-4.13 [-2.63; -5.63] mbar, p < 0.001). No significant differences in MAP or HR were found between any subgroups.ConclusionHPEEP and iPEEP during PNP in non-obese patients could promote oxygenation and increase Cdyn without clinically significant changes in MAP and HR. MPEEP could be insufficient to increase respiratory compliance and improve oxygenation. LPEEP may lead to decreased respiratory compliance and worsened oxygenation.Prospero registrationCRD42022362379; registered October 09, 2022.

Mechanical ventilation in patients with acute brain injury: a systematic review with meta-analysis

ObjectiveTo describe the potential effects of ventilatory strategies on the outcome of acute brain-injured patients undergoing invasive mechanical ventilation.DesignSystematic review with an individual data meta-analysis.SettingObservational and interventional (before/after) studies published up to August 22nd, 2022, were considered for inclusion. We investigated the effects of low tidal volume Vt < 8 ml/Kg of IBW versus Vt > = 8 ml/Kg of IBW, positive end-expiratory pressure (PEEP) < or > = 5 cmH2O and protective ventilation (association of both) on relevant clinical outcomes.PopulationPatients with acute brain injury (trauma or haemorrhagic stroke) with invasive mechanical ventilation for ≥ 24 h.Main outcome measuresThe primary outcome was mortality at 28 days or in-hospital mortality. Secondary outcomes were the incidence of acute respiratory distress syndrome (ARDS), the duration of mechanical ventilation and the partial pressure of oxygen (PaO2)/fraction of inspired oxygen (FiO2) ratio.ResultsThe meta-analysis included eight studies with a total of 5639 patients. There was no difference in mortality between low and high tidal volume [Odds Ratio, OR 0.88 (95%Confidence Interval, CI 0.74 to 1.05), p = 0.16, I2 = 20%], low and moderate to high PEEP [OR 0.8 (95% CI 0.59 to 1.07), p = 0.13, I2 = 80%] or protective and non-protective ventilation [OR 1.03 (95% CI 0.93 to 1.15), p = 0.6, I2 = 11]. Low tidal volume [OR 0.74 (95% CI 0.45 to 1.21, p = 0.23, I2 = 88%], moderate PEEP [OR 0.98 (95% CI 0.76 to 1.26), p = 0.9, I2 = 21%] or protective ventilation [OR 1.22 (95% CI 0.94 to 1.58), p = 0.13, I2 = 22%] did not affect the incidence of acute respiratory distress syndrome. Protective ventilation improved the PaO2/FiO2 ratio in the first five days of mechanical ventilation (p < 0.01).ConclusionsLow tidal volume, moderate to high PEEP, or protective ventilation were not associated with mortality and lower incidence of ARDS in patients with acute brain injury undergoing invasive mechanical ventilation. However, protective ventilation improved oxygenation and could be safely considered in this setting. The exact role of ventilatory management on the outcome of patients with a severe brain injury needs to be more accurately delineated.

Does tidal volume challenge improve the feasibility of pulse pressure variation in patients mechanically ventilated at low tidal volumes? A systematic review and meta-analysis

BackgroundPulse pressure variation (PPV) has been widely used in hemodynamic assessment. Nevertheless, PPV is limited in low tidal volume ventilation. We conducted this systematic review and meta-analysis to evaluate whether the tidal volume challenge (TVC) could improve the feasibility of PPV in patients ventilated at low tidal volumes.MethodsPubMed, Embase and Cochrane Library inception to October 2022 were screened for diagnostic researches relevant to the predictability of PPV change after TVC in low tidal volume ventilatory patients. Summary receiving operating characteristic curve (SROC), pooled sensitivity and specificity were calculated. Subgroup analyses were conducted for possible influential factors of TVC.ResultsTen studies with a total of 429 patients and 457 measurements were included for analysis. The predictive performance of PPV was significantly lower than PPV change after TVC in low tidal volume, with mean area under the receiving operating characteristic curve (AUROC) of 0.69 ± 0.13 versus 0.89 ± 0.10. The SROC of PPV change yielded an area under the curve of 0.96 (95% CI 0.94, 0.97), with overall pooled sensitivity and specificity of 0.92 (95% CI 0.83, 0.96) and 0.88 (95% CI 0.76, 0.94). Mean and median cutoff value of the absolute change of PPV (△PPV) were 2.4% and 2%, and that of the percentage change of PPV (△PPV%) were 25% and 22.5%. SROC of PPV change in ICU group, supine or semi-recumbent position group, lung compliance less than 30 cm H2O group, moderate positive end-expiratory pressure (PEEP) group and measurements devices without transpulmonary thermodilution group yielded 0.95 (95%0.93, 0.97), 0.95 (95% CI 0.92, 0.96), 0.96 (95% CI 0.94, 0.97), 0.95 (95% CI 0.93, 0.97) and 0.94 (95% CI 0.92, 0.96) separately. The lowest AUROCs of PPV change were 0.59 (95% CI 0.31, 0.88) in prone position and 0.73 (95% CI 0.60, 0.84) in patients with spontaneous breathing activity.ConclusionsTVC is capable to help PPV overcome limitations in low tidal volume ventilation, wherever in ICU or surgery. The accuracy of TVC is not influenced by reduced lung compliance, moderate PEEP and measurement tools, but TVC should be cautious applied in prone position and patients with spontaneous breathing activity.Trial registration PROSPERO (CRD42022368496). Registered on 30 October 2022.

Physiological response to prone positioning in intubated adults with COVID-19 acute respiratory distress syndrome: a retrospective study

BackgroundCOVID-19 related acute respiratory distress syndrome (ARDS) has specific characteristics compared to ARDS in other populations. Proning is recommended by analogy with other forms of ARDS, but few data are available regarding its physiological effects in this population. This study aimed to assess the effects of proning on oxygenation parameters (PaO2/FiO2 and alveolo-arterial gradient (Aa-gradient)), blood gas analysis, ventilatory ratio (VR), respiratory system compliance (CRS) and estimated dead space fraction (VD/VT HB). We also looked for variables associated with treatment failure.MethodsRetrospective monocentric study of intubated COVID-19 ARDS patients managed with an early intubation, low to moderate positive end-expiratory pressure and early proning strategy hospitalized from March 6 to April 30 2020. Blood gas analysis, PaO2/FiO2, Aa-gradient, VR, CRS and VD/VT HB were compared before and at the end of each proning session with paired t-tests or Wilcoxon tests (p < 0.05 considered as significant). Proportions were assessed using Fischer exact test or Chi square test.ResultsForty-two patients were included for a total of 191 proning sessions, median duration of 16 (5–36) hours. Considering all sessions, PaO2/FiO2 increased (180 [148–210] vs 107 [90–129] mmHg, p < 0.001) and Aa-gradient decreased (127 [92–176] vs 275 [211–334] mmHg, p < 0.001) with proning. CRS (36.2 [30.0–41.8] vs 32.2 [27.5–40.9] ml/cmH2O, p = 0.003), VR (2.4 [2.0–2.9] vs 2.3 [1.9–2.8], p = 0.028) and VD/VT HB (0.72 [0.67–0.76] vs 0.71 [0.65–0.76], p = 0.022) slightly increased. Considering the first proning session, PaO2/FiO2 increased (186 [165–215] vs 104 [94–126] mmHg, p < 0.001) and Aa-gradient decreased (121 [89–160] vs 276 [238–321] mmHg, p < 0.001), while CRS, VR and VD/VT HB were unchanged. Similar variations were observed during the subsequent proning sessions. Among the patients who experienced treatment failure (defined as ICU death or need for extracorporeal membrane oxygenation), fewer expressed a positive response in terms of oxygenation (defined as increase of more than 20% in PaO2/FiO2) to the first proning (67 vs 97%, p = 0.020).ConclusionProning in COVID-19 ARDS intubated patients led to an increase in PaO2/FiO2 and a decrease in Aa-gradient if we consider all the sessions together, the first one or the 4 subsequent sessions independently. When considering all sessions, CRS increased and VR and VD/VT HB only slightly increased.

Influence of positive end-expiratory pressure on arterial blood pressure in mechanically ventilated trauma patients in the field: a retrospective cohort study.

Ventilation with positive end-expiratory pressure (PEEP) may result in decreased venous return to the heart and therefore decrease cardiac output. We evaluated the influence of PEEP ventilation on arterial blood pressure in the field in 296 posttraumatic intubated patients being treated by a helicopter emergency medical service in a retrospective cohort study. Initial systolic blood pressure on the scene, upon hospital admission and their mean difference were compared between patients being ventilated with no/low PEEP (0–0.3 kPa) and moderate PEEP (0.3–1 kPa). In a subgroup analysis of initially hemodynamic unstable patients (systolic blood pressure < 80 mmHg), systolic blood pressure was compared between patients being ventilated with no/low or moderate PEEP Further, the mean difference between initial systolic blood pressure and upon hospital admission was correlated with the chosen PEEP. Systolic arterial blood pressure of patients being ventilated with no/low PEEP improved from 105 ± 36 mmHg to 112 ± 38 mmHg, and that of patients being ventilated with moderate PEEP improved from 105 ± 38 mmHg to 119 ± 27 mmHg. In initially unstable patients being ventilated with no/low PEEP systolic blood pressure improved from initially 55 ± 36 mmHg to 78 ± 30 mmHg upon hospital admission, and in those being ventilated with moderate PEEP, the systolic blood pressure improved from 43 ± 38 mmHg to 91 ± 27 mmHg. There was no significant correlation between the chosen PEEP and the mean difference of systolic blood pressure (Pearson’s correlation, r = 0.07, P = 0.17). Ventilation with moderate PEEP has no adverse effect on arterial systolic blood pressure in this cohort of trauma patients requiring mechanical ventilation. Initially unstable patients being ventilated with moderate PEEP tend to be hemodynamically more stable.

Anesthetic management of a severely obese patient (body mass index 70.1 kg/m2) undergoing giant ovarian tumor resection: a case report

BackgroundGiant ovarian tumors are rarely seen with severe obesity. There are few reports of perioperative management of giant ovarian tumors and severe obesity. Here, we report the perioperative management of physiological changes in massive intraabdominal tumors in a patient with severe obesity.Case presentationA 46-year-old Japanese woman (height 166 cm, weight 193.2 kg; body mass index 70.1 kg/m2) was scheduled to undergo laparotomy for a giant ovarian tumor. The patient was placed in the ramp position. Preoxygenation was performed using a high-flow nasal cannula, and awake tracheal intubation was performed using a video laryngoscope. Mechanical ventilation using a limited tidal volume with moderate positive end-expiratory pressure was applied during the surgical procedure. The aspiration speed for 15 L of tumor aspirate was set to under 1 L/minute, and the possibility of reexpansion pulmonary edema was foreseen by conventional monitoring.ConclusionsWe successfully completed anesthetic management in a patient with concomitant severe obesity and giant ovarian tumors.

Tension Pneumomediastinum: A life-threatening condition in patients with COVID-19.

Tension pneumomediastinum (TPM) is a rare but potentially fatal clinical entity. TPM leads to the leakage of air into the mediastinal cavity and increased pressure in thoracic vessels, respiratory tract, and the heart. Herein, this report presents a series of five cases of coronavirus disease-2019 (COVID-19) that caused acute respiratory distress syndrome (ARDS) and TPM. All patients were male who had severe ARDS with a secondary lung infection that required invasive ventilation and had moderate positive-end expiratory pressure. All patients required vasopressors to maintain hemodynamics, and two patients needed decompression with chest drains. One patient received extracorporeal membrane oxygenation therapy. Three patients had cardiac arrest, and two patients died; thus, the mortality rate was 40%. Patients with COVID-19 pneumonia with ARDS required invasive ventilation and prone positioning. Secondary lung infection can cause TPM, and TPM may cause cardiac arrest. Management should be prompt recognition and decompression with the insertion of drains, and conservative treatment is required in stable cases. Protocols for the management of pneumomediastinum and TPM may enable early detection, earlier management, and prevention of TPM.

Неинвазивная вентиляция легких (лекция)

В лекции освещены вопросы step by step респираторной терапии у больных с острой дыхательной дисфункцией (ОДД). Первым шагом в лечении больных с ОДД (при отсутствии показаний к инвазивной механической вентиляции легких) является использование высокопоточной оксигенации (ВПО) и неинвазивной вентиляции легких (НИВЛ). По сравнению с инвазивной механической вентиляцией легких эти технологии имеют определенные преимущества. Они не приводят к вентилятор-ассоциированному повреждению легких, вентилятор-ассоциированной диафрагмальной дисфункции и не вызывают вентилятор-ассоциированной пневмонии. НИВЛ обеспечивает определенная концентрация кислорода на вдохе (FiO2) в сочетании с умеренным давлением в конце выдоха (РЕЕР)/постоянным положительным давлением в дыхательных путях (СРАР) и инспираторным давлением. В отличие от оксигенации через лицевую маску или носовые канюли она уменьшает возможность экспираторного закрытия мелких дыхательных путей, предупреждает коллапс альвеол и возможность возникновения ателектазов. Преимуществом НИВЛ в сравнении со стандартной оксигенотерапией через лицевую маску/носовые канюли можно считать то, что она обеспечивает умеренный уровень РЕЕР/СРАР, который уменьшает пред- и постнагрузку левого желудочка. Это имеет особенное значение у больных с острой левожелудочковой недостаточностью или отеком легких. Главным условием успешного проведения НИВЛ является наличие адекватного сознания у больного. В основе клинической эффективности ВПО лежит возможность создания большой скорости потока газа (до 60 л/мин). Такая скорость потока (которая равна или даже больше скорости потока при вдохе больного) минимизирует «примешивание» комнатного воздуха и разрешает поддерживать на вдохе высокую FiO2. Принципиально важно наличие возможности методом step by step регулировать скорость потока и температуры, точное измерение FiO2. Современные системы ВПО имеют специальные контуры из полупроницаемых материалов, которые не допускают образования конденсата и имеют оригинальные носовые или трахеостомические канюли.

Effect of open-lung ventilation strategy on oxygenation-impairment during laparoscopic colorectal cancer resection

Objective: After general anesthesia and mechanical ventilation for laparoscopic colorectal cancer resection, about 90% of patients would have different degrees of atelectasis. Authors speculated that an open-lung strategy (OLS) comprising moderate positive end-expiratory pressure (PEEP) and intermittent recruitment maneuvers (RM) can reduce atelectrauma and thus reduce the incidence of oxygenation-impairment during low-tidal-volume ventilation for laparoscopic colorectal cancer resection. The purpose of this study was to verify this hypothesis and provide a better intraoperative ventilation scheme for laparoscopic colorectal cancer resection. Methods: This was a prospectively randomized controlled clinical trial which was approved by the Ethics Committee of the Sixth Affiliated Hospital, Sun Yat-sen University (2017ZSLYEC-002), and registered at the ClinicalTrials.gov (NCT03160144). From January to July 2017, patients who underwent laparoscopic colorectal cancer resection, with age > 40 years, estimated pneumoperitoneum time ≥ 1.5 h, pulse oxygen saturation ≥ 92%, and risk grade for postoperative pulmonary complications ≥ 2 were prospectively enrolled. The patients with American Society of Anesthesiologists physical status ≥ IV, body mass index ≥ 30 kg/m(2), pneumonia, acute respiratory failure or sepsis within 1 month, severe chronic obstructive pulmonary disease, pulmonary bullae and progressive neuromuscular diseases, and those participating in other interventional clinical trials were excluded. The enrolled patients were randomly assigned (1:1) to the OLS group (with a PEEP of 6-8 cm H(2)O and intermittent RM), and the NOLS group (without using PEEP and RM). Partial pressure of arterial oxygen (PaO(2)) /fraction of inspired oxygen (FiO(2)) and shunt fraction (Q(S)/Q(T)) were calculated via arterial and central venous blood gas analysis performed at 0.5 h (T(1)), 1.5 h (T(2)) after pneumoperitoneum induction and at 20 min after admission to the recovery room. Driving pressure immediately before pneumoperitoneum induction (T(0)) and at T(2) were calculated via monitoring data. The primary outcome was oxygenation-impairment (PaO(2)/FiO(2) ≤ 300 mmHg) during mechanical ventilation. Results: In each group, 48 patients under general anesthesia and low-tidal-volume ventilation were included in the final analysis. During ventilation, the oxygenation-impairment occurred in 7 patients (14.6%) of OLS group and in 17 patients (35.4%) of NOLS group, whose difference was statistically significant between two groups (χ(2)=5.556, RR=0.31, 95%CI: 0.12 to 0.84, P=0.033). During ventilation, the patients in the OLS group had higher PaO(2)/FiO(2) [T(1): (427±103) mmHg vs. (366±109) mmHg, t=-2.826, P=0.006; T(2): (453±103) mmHg vs. (388±122) mmHg, t=-2.739, P=0.007], lower Q(S)/Q(T) [ T(1): (9.2±6.5) % vs. (12.6±7.7) %, t=2.322, P=0.022; T(2): (7.0±5.8)% vs.(10.9±9.2)%, t=2.408, P=0.019], and lower driving pressure [T(0): (6±3) cm H(2)O vs. (10±2) cm H(2)O, t=7.421, P<0.001; T(2): (13±3) cm H(2)O vs. (17±4) cm H(2)O, t=5.417, P<0.001] than those in the NOLS group, with stratistical differences in all comparisons. In recovery room, though PaO(2)/FiO(2) [(70.3±9.4) mmHg vs. (66.8±9.4) mmHg, P=0.082] was still higher and Q(S)/Q(T) [(18.6±8.3)% vs. (21.8±8.4)%, P=0.070] was still lower in the OLS group as compared to the NOLS group, the differences were not statistically significant (both P>0.05). Conclusion: The application of such an OLS during low-tidal-volume ventilation can greatly reduce the incidence of oxygenation-impairment in laparoscopic colorectal cancer resection, and such effect may last to the period of emergence from anesthesia.

Role of Positive End-Expiratory Pressure and Regional Transpulmonary Pressure in Asymmetrical Lung Injury.

Rationale: Asymmetrical lung injury is a frequent clinical presentation. Regional distribution of Vt and positive end-expiratory pressure (PEEP) could result in hyperinflation of the less-injured lung. The validity of esophageal pressure (Pes) is unknown.Objectives: To compare, in asymmetrical lung injury, Pes with directly measured pleural pressures (Ppl) of both sides and investigate how PEEP impacts ventilation distribution and the regional driving transpulmonary pressure (inspiratory - expiratory).Methods: Fourteen mechanically ventilated pigs with lung injury were studied. One lung was blocked while the contralateral one underwent surfactant lavage and injurious ventilation. Airway pressure and Pes were measured, as was Ppl in the dorsal and ventral pleural space adjacent to each lung. Distribution of ventilation was assessed by electrical impedance tomography. PEEP was studied through decremental steps.Measurements and Results: Ventral and dorsal Ppl were similar between the injured and the noninjured lung across all PEEP levels. Dorsal Ppl and Pes were similar. The driving transpulmonary pressure was similar in the two lungs. Vt distribution between lungs was different at zero end-expiratory pressure (≈70% of Vt going in noninjured lung) owing to different respiratory system compliance (8.3 ml/cm H2O noninjured lung vs. 3.7 ml/cm H2O injured lung). PEEP at 10 cm H2O with transpulmonary pressure around zero homogenized Vt distribution opening the lungs. PEEP ≥16 cm H2O equalized distribution of Vt but with overdistension for both lungs.Conclusions: Despite asymmetrical lung injury, Ppl between injured and noninjured lungs is equalized and esophageal pressure is a reliable estimate of dorsal Ppl. Driving transpulmonary pressure is similar for both lungs. Vt distribution results from regional respiratory system compliance. Moderate PEEP homogenizes Vt distribution between lungs without generating hyperinflation.

Efek Perbedaan Ventilasi Mekanik Positive End Expiratory Pressure (PEEP) Low dan Moderate terhadap Rasio PaO2/FiO2 Pascabedah pada Kraniotomi Elektif

Background and Objective: Elective craniotomy is associated with high incidence of postoperative pulmonary complications (PPC, 25%) and mortality (10%). We determined to study the effect of Positive End Expiratory Pressure (PEEP) 5 cmH2O and 8 cmH2O to postoperative PaO2 / FiO2 ratio (PF ratio) in elective craniotomy. Subject and Methods: This randomized clinical trial was at a university hospital in Indonesia. Fifty two elective craniotomy patients (ages 17–55 years, surgical duration&gt; 4 hours, normal lung) were randomized into 2 intervention groups: perioperative mechanical ventilation with low PEEP (5 cmH2O) or moderate PEEP (8 cmH2O). The hypothesis of this study is that the ratio of PaO2 / FiO2 in the moderate PEEP group is higher than low PEEP. Blood gas analysis was performed 24 hours post induction. Results: This study did not show a significant difference in the PaO2/FiO2 ratio between the low PEEP and moderate PEEP groups. The PaO2 / FiO2 ratios of the low PEEP and moderate PEEP groups were respectively: at 24 hours post induction, 429.34 ± 72.25 mmHg and 458.59 ± 71.11mmHg (p = 0.147). Conclusions: Comparison of low PEEP and moderate PEEP in perioperative mechanical ventilation did not result in a significant difference in the value of the PaO2/FiO2 ratio at 24 hours post induction

Individualized lung protective ventilation vs. conventional ventilation during general anesthesia in laparoscopic total hysterectomy.

Laparoscopic total hysterectomy is performed by carbon dioxide insufflation, Trendelenburg position and mechanical ventilation of patients under general anesthesia. However, this may induce pulmonary atelectasis and/or hyperdistention of the lungs. Multiple studies have indicated that mechanical ventilation with the use of low tidal volumes, moderate positive end-expiratory pressure (PEEP) and regular alveolar recruitment maneuvers may improve post-operative outcomes. However, the benefits of an individualized level of PEEP have not been clearly established. In the present study, it was hypothesized that a moderate fixed PEEP may not suit all patients and an individually-titrated PEEP during anesthesia may improve the peri-operative pulmonary oxygenation function. The aim of the present study was to compare the pulmonary oxygenation function and post-operative pulmonary complications (PPCs) in patients receiving individualized lung-protective mechanical ventilation (LPV) vs. conventional ventilation (CV) during laparoscopic total hysterectomy. The present study was a randomized double-blinded clinical trial on 87 patients who were randomly divided to receive CV or protective ventilation (PV). An optimal individualized PEEP value was determined using a static pulmonary compliance-directed PEEP titration procedure. Pulmonary oxygenation function, serum inflammatory factors, including interleukin-8 and Clara cell protein 16, the incidence of PPCs and the post-operative length of stay were also determined. Patients in the PV group exhibited improved pulmonary oxygenation function during and after the operation. The total percentage of PPCs during the first 7 days after surgery was significantly lower in the PV group compared with those in the CV group. In conclusion, as compared to CV, intra-operative individualized LPV significantly improved pulmonary oxygenation function and reduced the incidence of PPCs during the first 7 days after laparoscopic total hysterectomy (Clinical trial registration no. ChiCTR1900027738).

This Month in Anesthesiology.

This Month in Anesthesiology.

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.

Exploring the intraoperative lung protective ventilation of different positive end-expiratory pressure levels during abdominal laparoscopic surgery with Trendelenburg position.

The intraoperative lung protective effect of mechanical ventilation of different positive end-expiratory pressure (PEEP) levels on patients undergoing abdominal laparoscopic surgery with the steep Trendelenburg position remains undefined. The purpose of the study was to explore the optimal PEEP. Sixty patients scheduled for abdominal laparoscopic surgery were randomized to four groups including: PEEP 0, 4, 8 and 12 cmH2O. The pulmonary dynamic compliance (Cdyn), dead space to tidal volume ratio (VD/VT), and intrapulmonary shunt ratio (QS/QT) were measured after anesthesia induction (T0), 5 min after pneumoperitoneum (PNP) with position change (T1), 30 (T2) and 60 min (T3) after PEEP, and end of surgery (T4). Cdyn increased when different levels of PEEP (including the 4, 8, and 12 cmH2O) were used vs. no PEEP (P<0.05). The VD/VT in PEEP 8 and 12 cmH2O were significantly improved than no PEEP (P<0.05). Meanwhile, the QS/QT in PEEP 12 cmH2O was higher than others during the procedures. A moderate PEEP level (8 cmH2O) with low tidal volume was sufficient to improve Cdyn and to decrease VD/VT without increasing QS/QT, which was suggested to be a good choice of intraoperative lung protective ventilation during abdominal laparoscopic surgery with Trendelenburg position.

Volumetric but Not Time Capnography Detects Ventilation/Perfusion Mismatch in Injured Rabbit Lung.

Whereas time capnography (Tcap) is routinely displayed during mechanical ventilation, the volumetric representation (Vcap) is seldom used. We compared the diagnostic value of indices derived from Tcap and Vcap following ventilation to perfusion ratio () mismatch subsequent to experimentally induced acute respiratory distress syndrome (ARDS), and alveolar recruitment by elevating the positive end-expiratory pressure (PEEP). Lung injury was induced by iv lipopolysaccharide, whole lung lavage and injurious ventilation in anesthetized, mechanically ventilated rabbits (n = 26). Mainstream Tcap and Vcap were performed to assess normalized phase 2 (Sn2T, Sn2V) and phase 3 slopes (Sn3T, Sn3V) in the time and volumetric domains. Vcap was also used to estimate Enghoff’s physiological dead space (VDE). Lung oxygenation index (PaO2/FiO2) and intrapulmonary shunt (Qs/Qt) were derived from arterial and central venous blood gas samples. All measurements were made under baseline conditions, and, following lung injury, under moderate (6 cmH2O) and high PEEP levels (9 cmH2O). Lung injury deteriorated the PaO2/FiO2 (baseline vs. injured 466 ± 10.2 [95% confidence interval] vs. 77.3 ± 17.1 mmHg, p < 0.05) and compromised all mechanical parameters significantly, whereas Tcap parameters exhibited contradictory or inconsistent changes. Conversely, Vcap indices exhibited consistent changes and provided excellent diagnostic value in detecting lung-function deterioration subsequent to lung injury [area under the receiver operating characteristic (ROC) curve of 1.0 ± 0.0, 0.87 ± 0.22 and 0.86 ± 0.22 for VDE, Sn3V and Sn3V/Sn2V, respectively]. Elevated PEEP increased PaO2/FiO2 and decreased Qs/Qt, which was reflected only in the Vcap slope ratio (Sn3V/Sn2V, p < 0.05). Our findings demonstrate the limited value of Tcap to detect ventilation to perfusion ratio () mismatch, following severe lung injury. Conversely, indices derived from Vcap proved to be sensitive for detecting lung volume loss and alveolar recruitment. Therefore, promotion of Vcap is of paramount importance as a real-time, non-invasive, bedside monitoring modality to detect the development of and to follow-up the progression of lung injury in a model of ARDS.

High-Flow Nasal Oxygen Therapy in Immunocompromised Patients With Acute Hypoxemic Respiratory Failure

Acute respiratory failure (ARF) is common in immunocompromised patients. Low/intermediate-flow oxygen devices have several drawbacks, such as insufficient humidification and warming of the inspired gas or limited FiO2, which imply suboptimal therapeutic management. Compared with unselected patients, immunocompromised patients are at higher risk of ARF, and ARF is associated with a 2-fold increase in intensive care unit or hospital mortality. As a consequence, decreasing the need for intubation by the improvement of oxygenation and ventilation techniques has become a major goal of care in this population. Besides noninvasive ventilation, high-flow therapy (HFT), which can deliver up to 60 to 70 L/min of an FiO2 controlled, heated and humidified oxygen, seems to be a promising alternative. Various mechanisms explain the benefit of HFT, including dead space washout, reduction in oxygen dilution, and nasopharyngeal resistance, more reliable FiO2 delivering, moderate positive end-expiratory pressure effect that may generate alveolar recruitment, and reduction of the work of breathing. To date, the retrospective and prospective studies conducted in immunocompromised patients suggest that HFT is well tolerated, alleviates symptoms of respiratory distress, and improves oxygenation. In addition, it might be associated with a reduction in intubation and mortality when compared with noninvasive ventilation. Finally, HFT seems to be a safe alternative to noninvasive ventilation to prevent respiratory symptoms and subsequent intubation during fiberoptic bronchoscopy and bronchoalveolar lavage. These promising benefits of HFT in immunocompromised patients need to be confirmed by large prospective randomized controlled trials performed specifically in immunocompromised patients.