Optimal Positive End-Expiratory Pressure Obtained with Titration of Fraction of Inspiratory Oxygen: A Randomized Controlled Clinical Trial

Background Optimal intraoperative positive end expiratory pressure (PEEP) improves patient outcomes. The pulse-oximetry has been used to determine the lung opening and closing pressures. Therefore, we hypothesized that intraoperative optimal PEEP obtained by titrating inspiratory oxygen fraction (FiO2) guided with pulse-oximetry could improve perioperative oxygenation. Methods Forty-six males undergoing elective robotic assisted laparoscopic prostatectomy were randomly assigned to either optimal PEEP (Group O, n=23) or control with fixed PEEP of 5 cmH2O (Group C, n=23). Optimal PEEP, defined as the PEEP with lowest FiO2 or 0.21 to maintain SpO2≥ 95%, was obtained in both groups after placing the patients in Trendelenburg position and peritoneal insufflation. Patients in Group O maintained the optimal PEEP and in Group C maintained PEEP of 5cmH2O intraoperatively. Both groups were extubated in a sitting position once the extubation criteria met. The primary outcome was the partial arterial oxygen pressure (PaO2)/inspiratory oxygen fraction (FiO2) prior to extubation. Secondary outcome was the incidence of postoperative hypoxemia (SpO2༜92% on room-air after extubation) in post-operative care unit. Results The median optimal PEEP was 16 cm H2O [inter-quartile range, 12-18]. The PaO2/FiO2prior to extubation was significantly higher in Group O than that in Group C (77.0±4.9kPa vs.60.6±5.9kPa, p=0.04); PaO2/FiO2 was also significantly higher in Group O 30minutes after extubation (57.6±1.9 vs. 46.6±1.8kPa, p=0.01). The incidence of hypoxemia on room air in the post-operative care unit was significantly lower in the Group O than in the Group C (1/23, or 4.3% vs. 7/23 or 30.4%, p =0.02). Conclusions Intraoperative optimal PEEP can be achieved by titration of FiO2 guided with SpO2. Maintaining intraoperative optimal PEEP improves intraoperative oxygenation and reduces the incidence of post-operative hypoxemia. Trial registration : Chinese Clinical Trial Registry identifier: ChiCTR2100051010. Prospectively registered on 10 September, 2021

Intraoperative Fractions of Inspiratory Oxygen Are Associated With Recurrence-Free Survival After Elective Cancer Surgery

Background: Choice of the fraction of inspiratory oxygen (FiO2) is controversial. The objective of this analysis was to evaluate whether intraoperative FiO2 was associated with recurrence-free survival after elective cancer surgery.Methods and Analysis: In this single-center, retrospective study, we analyzed 1,084 patients undergoing elective resection of pancreatic (n = 652), colorectal (n = 405), or hepatic cancer (n = 27) at Heidelberg University Hospital between 2009 and 2016. Intraoperative mean FiO2 values were calculated. For unstratified analyses, the study cohort was equally divided into a low- and a high-FiO2 group. For cancer-stratified analyses, this division was done within cancer-strata. The primary outcome measure was recurrence-free survival until the last known follow-up. Groups were compared using Kaplan–Meier analysis. A stratified log rank test was used to control for different FiO2 levels and survival times between the cancer strata. Cox-regression analyses were used to control for covariates. Sepsis, reoperations, surgical-site infections, and cardiovascular events during hospital stay and overall survival were secondary outcomes.Results: Median FiO2 was 40.9% (Q1–Q3, 38.3–42.9) in the low vs. 50.4% (Q1–Q3, 47.4–54.7) in the high-FiO2 group. Median follow-up was 3.28 (Q1–Q3, 1.68–4.97) years. Recurrence-free survival was considerable higher in the high-FiO2 group (p < 0.001). This effect was also confirmed when stratified for the different tumor entities (p = 0.007). In colorectal cancer surgery, increased FiO2 was independently associated with increased recurrence-free survival. The hazard for the primary outcome decreased by 3.5% with every 1% increase in FiO2. The effect was not seen in pancreatic cancer surgery and we did not find differences in any of the secondary endpoints.Conclusions: Until definite evidence from large-scale trials is available and in the absence of relevant clinical conditions warranting specific FiO2 values, perioperative care givers should aim for an intraoperative FiO2 of 50% in abdominal cancer surgery as this might benefit oncological outcomes.

Individualized versus Fixed Positive End-expiratory Pressure for Intraoperative Mechanical Ventilation in Obese Patients: A Secondary Analysis

Background General anesthesia may cause atelectasis and deterioration in oxygenation in obese patients. The authors hypothesized that individualized positive end-expiratory pressure (PEEP) improves intraoperative oxygenation and ventilation distribution compared to fixed PEEP. Methods This secondary analysis included all obese patients recruited at University Hospital of Leipzig from the multicenter Protective Intraoperative Ventilation with Higher versus Lower Levels of Positive End-Expiratory Pressure in Obese Patients (PROBESE) trial (n = 42) and likewise all obese patients from a local single-center trial (n = 54). Inclusion criteria for both trials were elective laparoscopic abdominal surgery, body mass index greater than or equal to 35 kg/m2, and Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score greater than or equal to 26. Patients were randomized to PEEP of 4 cm H2O (n = 19) or a recruitment maneuver followed by PEEP of 12 cm H2O (n = 21) in the PROBESE study. In the single-center study, they were randomized to PEEP of 5 cm H2O (n = 25) or a recruitment maneuver followed by individualized PEEP (n = 25) determined by electrical impedance tomography. Primary endpoint was Pao2/inspiratory oxygen fraction before extubation and secondary endpoints included intraoperative tidal volume distribution to dependent lung and driving pressure. Results Ninety patients were evaluated in three groups after combining the two lower PEEP groups. Median individualized PEEP was 18 (interquartile range, 16 to 22; range, 10 to 26) cm H2O. Pao2/inspiratory oxygen fraction before extubation was 515 (individual PEEP), 370 (fixed PEEP of 12 cm H2O), and 305 (fixed PEEP of 4 to 5 cm H2O) mmHg (difference to individualized PEEP, 145; 95% CI, 91 to 200; P < 0.001 for fixed PEEP of 12 cm H2O and 210; 95% CI, 164 to 257; P < 0.001 for fixed PEEP of 4 to 5 cm H2O). Intraoperative tidal volume in the dependent lung areas was 43.9% (individualized PEEP), 25.9% (fixed PEEP of 12 cm H2O) and 26.8% (fixed PEEP of 4 to 5 cm H2O) (difference to individualized PEEP: 18.0%; 95% CI, 8.0 to 20.7; P < 0.001 for fixed PEEP of 12 cm H2O and 17.1%; 95% CI, 10.0 to 20.6; P < 0.001 for fixed PEEP of 4 to 5 cm H2O). Mean intraoperative driving pressure was 9.8 cm H2O (individualized PEEP), 14.4 cm H2O (fixed PEEP of 12 cm H2O), and 18.8 cm H2O (fixed PEEP of 4 to 5 cm H2O), P < 0.001. Conclusions This secondary analysis of obese patients undergoing laparoscopic surgery found better oxygenation, lower driving pressures, and redistribution of ventilation toward dependent lung areas measured by electrical impedance tomography using individualized PEEP. The impact on patient outcome remains unclear. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New