Emmanuel Futier

Protective Mechanical Ventilation during General Anesthesia for Open Abdominal Surgery Improves Postoperative Pulmonary Function

Background:The impact of intraoperative ventilation on postoperative pulmonary complications is not defined. The authors aimed at determining the effectiveness of protective mechanical ventilation during open abdominal surgery on a modified Clinical Pulmonary Infection Score as primary outcome and postoperative pulmonary function. Methods:Prospective randomized, open-label, clinical trial performed in 56 patients scheduled to undergo elective open abdominal surgery lasting more than 2 h. Patients were assigned by envelopes to mechanical ventilation with tidal volume of 9 ml/kg ideal body weight and zero-positive end-expiratory pressure (standard ventilation strategy) or tidal volumes of 7 ml/kg ideal body weight, 10 cm H2O positive end-expiratory pressure, and recruitment maneuvers (protective ventilation strategy). Modified Clinical Pulmonary Infection Score, gas exchange, and pulmonary functional tests were measured preoperatively, as well as at days 1, 3, and 5 after surgery. Results:Patients ventilated protectively showed better pulmonary functional tests up to day 5, fewer alterations on chest x-ray up to day 3 and higher arterial oxygenation in air at days 1, 3, and 5 (mmHg; mean ± SD): 77.1 ± 13.0 versus 64.9 ± 11.3 (P = 0.0006), 80.5 ± 10.1 versus 69.7 ± 9.3 (P = 0.0002), and 82.1 ± 10.7 versus 78.5 ± 21.7 (P = 0.44) respectively. The modified Clinical Pulmonary Infection Score was lower in the protective ventilation strategy at days 1 and 3. The percentage of patients in hospital at day 28 after surgery was not different between groups (7 vs. 15% respectively, P = 0.42). Conclusion:A protective ventilation strategy during abdominal surgery lasting more than 2 h improved respiratory function and reduced the modified Clinical Pulmonary Infection Score without affecting length of hospital stay.

Noninvasive Ventilation and Alveolar Recruitment Maneuver Improve Respiratory Function during and after Intubation of Morbidly Obese Patients A Randomized Controlled Study

Background:Morbid obesity predisposes patients to lung collapse and hypoxemia during induction of anesthesia. The aim of this prospective study was to determine whether noninvasive positive pressure ventilation (NPPV) improves arterial oxygenation and end-expiratory lung volume (EELV) compared with conventional preoxygenation, and whether NPPV followed by early recruitment maneuver (RM) after endotracheal intubation (ETI) further improves oxygenation and respiratory function compared with NPPV alone. Methods:Sixty-six consecutive patients (body mass index, 46 ± 6 kg/m2) were randomized to receive 5 min of either conventional preoxygenation with spontaneous breathing of 100% O2 (CON), NPPV (pressure support and positive end-expiratory pressure), or NPPV followed by RM (NPPV+RM). Gas exchange was measured in awake patients, at the end of preoxygenation, immediately after ETI, and 5 min after the onset of mechanical ventilation. EELV was measured immediately after ETI and 5 min after mechanical ventilation. The primary endpoint was arterial oxygenation 5 min after the onset of mechanical ventilation. Results are presented as mean ± SD. Results:At the end of preoxygenation, Pao2 was higher in the NPPV and NPPV+RM groups (382 ± 87 mmHg and 375 ± 82 mmHg, respectively; both P < 0.001) compared with the CON group (306 ± 51 mmHg) and remained higher after ETI (225 ± 104 mmHg and 221 ± 110 mmHg, in the NPPV and NPPV+RM groups, respectively; both P < 0.01 compared with the CON group [150 ± 50 mmHg]). After the onset of mechanical ventilation, Pao2 was 93 ± 25 mmHg in the CON group, 128 ± 54 mmHg in the NPPV group (P = 0.035 vs. CON group), and 234 ± 73 mmHg in the NPPV+RM group (P < 0.0001 vs. NPPV group). After ETI, EELV was higher in the NPPV group compared with the CON group (P < 0.001). Compared with NPPV alone, RM further improved gas exchange and EELV (all P < 0.05). A significant correlation was found between Pao2 obtained 5 min after mechanical ventilation and EELV (R2 = 0.41, P < 0.001). Conclusion:NPPV improves oxygenation and EELV in morbidly obese patients compared with conventional preoxygenation. NPPV combined with early RM is more effective than NPPV alone at improving respiratory function after ETI.

Protective versus Conventional Ventilation for Surgery: A Systematic Review and Individual Patient Data Meta-analysis.

Background:Recent studies show that intraoperative mechanical ventilation using low tidal volumes (VT) can prevent postoperative pulmonary complications (PPCs). The aim of this individual patient data meta-analysis is to evaluate the individual associations between VT size and positive end–expiratory pressure (PEEP) level and occurrence of PPC. Methods:Randomized controlled trials comparing protective ventilation (low VT with or without high levels of PEEP) and conventional ventilation (high VT with low PEEP) in patients undergoing general surgery. The primary outcome was development of PPC. Predefined prognostic factors were tested using multivariate logistic regression. Results:Fifteen randomized controlled trials were included (2,127 patients). There were 97 cases of PPC in 1,118 patients (8.7%) assigned to protective ventilation and 148 cases in 1,009 patients (14.7%) assigned to conventional ventilation (adjusted relative risk, 0.64; 95% CI, 0.46 to 0.88; P < 0.01). There were 85 cases of PPC in 957 patients (8.9%) assigned to ventilation with low VT and high PEEP levels and 63 cases in 525 patients (12%) assigned to ventilation with low VT and low PEEP levels (adjusted relative risk, 0.93; 95% CI, 0.64 to 1.37; P = 0.72). A dose–response relationship was found between the appearance of PPC and VT size (R2 = 0.39) but not between the appearance of PPC and PEEP level (R2 = 0.08). Conclusions:These data support the beneficial effects of ventilation with use of low VT in patients undergoing surgery. Further trials are necessary to define the role of intraoperative higher PEEP to prevent PPC during nonopen abdominal surgery.

Conservative vs restrictive individualized goal-directed fluid replacement strategy in major abdominal surgery: A prospective randomized trial.

OBJECTIVES To compare the influence of 2 volumes of fluid, integrated with goal-directed fluid therapy, on hypovolemia (a key trigger of tissue hypoperfusion) and central venous oxygen saturation (Scvo₂) and to assess their relationships with postoperative morbidity. DESIGN, SETTING, AND PATIENTS A prospective, randomized trial of 70 consecutive patients undergoing major abdominal surgery. INTERVENTIONS Patients were randomly assigned to 6 mL/kg/h of crystalloid (a restrictive fluid strategy) or 12 mL/kg/h of crystalloid (a more conservative fluid strategy). In both groups, a fluid bolus was administered when respiratory variation in peak aortic flow velocity (ΔPV) was greater than 13%. Data on hypovolemia (ΔPV > 13%), Scvo₂, and postoperative complications were recorded for all patients. MAIN OUTCOME MEASURES Overall incidence of postoperative complications, especially anastomotic leak and sepsis. RESULTS Overall incidence of complications, including postoperative anastomotic leak and sepsis, was higher in the restrictive group than in the conservative group (all P < .05). The number of patients with hypovolemia increased significantly in the restrictive group compared with the conservative group (P < .001). The perioperative mean Scvo₂ (P = .02) and mean minimum Scvo₂ (P = .04) were significantly lower in the restrictive group than in the conservative group. Multivariate analysis showed that both hypovolemia and mean minimum Scvo₂ were independently associated with anastomotic leak and sepsis. CONCLUSIONS Excessive fluid restriction increased the level of hypovolemia, leading to reduced Scvo₂ and thereby increased incidence of postoperative complications. Excessive fluid restriction should be applied cautiously in surgical patients. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00852449.

Intraoperative recruitment maneuver reverses detrimental pneumoperitoneum-induced respiratory effects in healthy weight and obese patients undergoing laparoscopy.

Background:Pulmonary function is impaired during pneumoperitoneum mainly as a result of atelectasis formation. We studied the effects of 10 cm H2O of positive end-expiratory pressure (PEEP) and PEEP followed by a recruitment maneuver (PEEP+RM) on end-expiratory lung volume (EELV), oxygenation and respiratory mechanics in patients undergoing laparoscopic surgery. Methods:Sixty consecutive adult patients (30 obese, 30 healthy weight) in reverse Trendelenburg position were prospectively studied. EELV, static elastance of the respiratory system, dead space, and gas exchange were measured before and after pneumoperitoneum insufflation with zero end-expiratory pressure, with PEEP alone, and with PEEP+RM. Results are presented as mean ± SD. Results:Pneumoperitoneum reduced EELV (healthy weight, 1195 ± 405 vs. 1724 ± 774 ml; obese, 751 ± 258 vs. 886 ± 284 ml) and worsened static elastance and dead space in both groups (in all P < 0.01 vs. zero-end expiratory pressure before pneumoperitoneum) whereas oxygenation was unaffected. PEEP increased EELV (healthy weight, 570 ml, P < 0.01; obese, 364 ml, P < 0.01) with no effect on oxygenation. Compared with PEEP alone, EELV and static elastance were further improved after RM in both groups (P < 0.05), as was oxygenation (P < 0.01). In all patients, RM-induced change in EELV was 16% (P = 0.04). These improvements were maintained 30 min after RM. RM-induced changes in EELV correlated with change in oxygenation (r = 0.42, P < 0.01). Conclusion:RM combined with 10 cm H2O of PEEP improved EELV, respiratory mechanics, and oxygenation during pneumoperitoneum whereas PEEP alone did not.

Central venous O2 saturation and venous-to-arterial CO2 difference as complementary tools for goal-directed therapy during high-risk surgery

IntroductionCentral venous oxygen saturation (ScvO2) is a useful therapeutic target in septic shock and high-risk surgery. We tested the hypothesis that central venous-to-arterial carbon dioxide difference (P(cv-a)CO2), a global index of tissue perfusion, could be used as a complementary tool to ScvO2 for goal-directed fluid therapy (GDT) to identify persistent low flow after optimization of preload has been achieved by fluid loading during high-risk surgery.MethodsThis is a secondary analysis of results obtained in a study involving 70 adult patients (ASA I to III), undergoing major abdominal surgery, and treated with an individualized goal-directed fluid replacement therapy. All patients were managed to maintain a respiratory variation in peak aortic flow velocity below 13%. Cardiac index (CI), oxygen delivery index (DO2i), ScvO2, P(cv-a)CO2 and postoperative complications were recorded blindly for all patients.ResultsA total of 34% of patients developed postoperative complications. At baseline, there was no difference in demographic or haemodynamic variables between patients who developed complications and those who did not. In patients with complications, during surgery, both mean ScvO2 (78 ± 4 versus 81 ± 4%, P = 0.017) and minimal ScvO2 (minScvO2) (67 ± 6 versus 72 ± 6%, P = 0.0017) were lower than in patients without complications, despite perfusion of similar volumes of fluids and comparable CI and DO2i values. The optimal ScvO2 cut-off value was 70.6% and minScvO2 < 70% was independently associated with the development of postoperative complications (OR = 4.2 (95% CI: 1.1 to 14.4), P = 0.025). P(cv-a)CO2 was larger in patients with complications (7.8 ± 2 versus 5.6 ± 2 mmHg, P < 10-6). In patients with complications and ScvO2 ≥71%, P(cv-a)CO2 was also significantly larger (7.7 ± 2 versus 5.5 ± 2 mmHg, P < 10-6) than in patients without complications. The area under the receiver operating characteristic (ROC) curve was 0.785 (95% CI: 0.74 to 0.83) for discrimination of patients with ScvO2 ≥71% who did and did not develop complications, with 5 mmHg as the most predictive threshold value.ConclusionsScvO2 reflects important changes in O2 delivery in relation to O2 needs during the perioperative period. A P(cv-a)CO2 < 5 mmHg might serve as a complementary target to ScvO2 during GDT to identify persistent inadequacy of the circulatory response in face of metabolic requirements when an ScvO2 ≥71% is achieved.Trial registrationClinicaltrials.gov Identifier: NCT00852449.

Association between driving pressure and development of postoperative pulmonary complications in patients undergoing mechanical ventilation for general anaesthesia: a meta-analysis of individual patient data.

BACKGROUND Protective mechanical ventilation strategies using low tidal volume or high levels of positive end-expiratory pressure (PEEP) improve outcomes for patients who have had surgery. The role of the driving pressure, which is the difference between the plateau pressure and the level of positive end-expiratory pressure is not known. We investigated the association of tidal volume, the level of PEEP, and driving pressure during intraoperative ventilation with the development of postoperative pulmonary complications. METHODS We did a meta-analysis of individual patient data from randomised controlled trials of protective ventilation during general anesthaesia for surgery published up to July 30, 2015. The main outcome was development of postoperative pulmonary complications (postoperative lung injury, pulmonary infection, or barotrauma). FINDINGS We included data from 17 randomised controlled trials, including 2250 patients. Multivariate analysis suggested that driving pressure was associated with the development of postoperative pulmonary complications (odds ratio [OR] for one unit increase of driving pressure 1·16, 95% CI 1·13-1·19; p<0·0001), whereas we detected no association for tidal volume (1·05, 0·98-1·13; p=0·179). PEEP did not have a large enough effect in univariate analysis to warrant inclusion in the multivariate analysis. In a mediator analysis, driving pressure was the only significant mediator of the effects of protective ventilation on development of pulmonary complications (p=0·027). In two studies that compared low with high PEEP during low tidal volume ventilation, an increase in the level of PEEP that resulted in an increase in driving pressure was associated with more postoperative pulmonary complications (OR 3·11, 95% CI 1·39-6·96; p=0·006). INTERPRETATION In patients having surgery, intraoperative high driving pressure and changes in the level of PEEP that result in an increase of driving pressure are associated with more postoperative pulmonary complications. However, a randomised controlled trial comparing ventilation based on driving pressure with usual care is needed to confirm these findings. FUNDING None.

Response to recruitment maneuver influences net alveolar fluid clearance in acute respiratory distress syndrome.

Background:Alveolar fluid clearance is impaired in the majority of patients with acute respiratory distress syndrome (ARDS). Experimental studies have shown that a reduction of tidal volume increases alveolar fluid clearance. This study was aimed at assessing the impact of the response to a recruitment maneuver (RM) on net alveolar fluid clearance. Methods:In 15 patients with ARDS, pulmonary edema fluid and plasma protein concentrations were measured before and after an RM, consisting of a positive end-expiratory pressure maintained 10 cm H2O above the lower inflection point of the pressure–volume curve during 15 min. Cardiorespiratory parameters were measured at baseline (before RM) and 1 and 4 h later. RM-induced lung recruitment was measured using the pressure–volume curve method. Net alveolar fluid clearance was measured by measuring changes in bronchoalveolar protein concentrations before and after RM. Results:In responders, defined as patients showing an RM-induced increase in arterial oxygen tension of 20% of baseline value or greater, net alveolar fluid clearance (19 ± 13%/h) and significant alveolar recruitment (113 ± 101 ml) were observed. In nonresponders, neither net alveolar fluid clearance (−24 ± 11%/h) nor alveolar recruitment was measured. Responders and nonresponders differed only in terms of lung morphology: Responders had a diffuse loss of aeration, whereas nonresponders had a focal loss of aeration, predominating in the lower lobes. Conclusion:In the absence of alveolar recruitment and improvement in arterial oxygenation, RM decreases the rate of alveolar fluid clearance, suggesting that lung overinflation may be associated with epithelial dysfunction.

Adaptive support ventilation prevents ventilator-induced diaphragmatic dysfunction in piglet: an in vivo and in vitro study.

Background:Contrary to adaptive support ventilation (ASV), prolonged totally controlled mechanical ventilation (CMV) results in the absence of diaphragm activity and causes ventilator-induced diaphragmatic dysfunction. Because main-taining respiratory muscles at rest is likely a major cause of ventilator-induced diaphragmatic dysfunction, ASV may prevent its occurrence in comparison with CMV. The aim of our study was to compare the effects of ASV with those of CMV on both in vivo and in vitro diaphragmatic properties. Methods:Two groups of six anesthetized piglets were ventilated during a 72-h period. Piglets in the CMV group (n = 6) were ventilated without spontaneous ventilation, and piglets in the ASV group (n = 6) were ventilated with spontaneous breaths. Transdiaphragmatic pressure was measured after bilateral, supramaximal transjugular stimulation of the two phrenic nerves. A pressure–frequency curve was drawn after stimulation from 20 to 120 Hz of the phrenic nerves. Diaphragm fiber proportions and mean sectional area were evaluated. Results:After 72 h of ventilation, transdiaphragmatic pressure decreased by 30% of its baseline value in the CMV group, whereas it did not decrease in the ASV group. Although CMV was associated with an atrophy of the diaphragm (evaluated by mean cross-sectional area of both the slow and fast myosin chains), atrophy was not detected in the ASV group. Conclusion:Maintaining diaphragmatic contractile activity by using the ASV mode may protect the diaphragm against the deleterious effect of prolonged CMV, as demonstrated both in vitro and in vivo, in healthy piglets.

Soluble form of the receptor for advanced glycation end products is a marker of acute lung injury but not of severe sepsis in critically ill patients

Objectives:Levels of the soluble form of the receptor for advanced glycation end products (sRAGE) are elevated during acute lung injury. However, it is not known whether this increase is linked to its involvement in alveolar epithelium injury or in systemic inflammation. Whether sRAGE is a marker of acute lung injury and acute respiratory distress syndrome, regardless of associated severe sepsis or septic shock, remains unknown in the intensive care unit setting. Design:Prospective, observational, clinical study. Setting:Intensive care unit of an academic medical center. Patients:A total of 64 consecutive subjects, divided into four groups: acute lung injury/acute respiratory distress syndrome (n = 15); acute lung injury/acute respiratory distress syndrome plus severe sepsis/septic shock (n = 18); severe sepsis/septic shock (n = 16); and mechanically ventilated controls (n = 15). Interventions:None. Measurements and Main Results:Plasma sRAGE levels were measured at baseline and on days 3, 6, and 28 (or at intensive care unit discharge, whichever occurred first). Baseline plasma levels of sRAGE were significantly higher in patients with acute lung injury/acute respiratory distress syndrome, with (median, 2951 pg/mL) or without (median, 3761 pg/mL) severe sepsis, than in patients with severe sepsis (median, 488 pg/mL) only and in mechanically ventilated controls (median, 525 pg/mL). Levels of sRAGE were correlated with acute lung injury/acute respiratory distress syndrome severity and decreased over time but were not associated with outcome. Lower baseline plasma sRAGE was associated with focal loss of aeration based on computed tomography lung morphology. Conclusions:sRAGE levels were elevated during acute lung injury/acute respiratory distress syndrome, regardless of the presence or absence of severe sepsis. The plasma level of sRAGE was correlated with clinical and radiographic severity in acute respiratory distress syndrome patients and decreased over time, suggesting resolution of the injury to the alveolar epithelium. Further study is warranted to test the clinical utility of this biomarker in managing such patients and to better understand its relationship with lung morphology during acute lung injury/acute respiratory distress syndrome.