Distribution of ventilation and oxygenation in surgical obese patients ventilated with high versus low positive end-expiratory pressure

Abstract

BACKGROUNDIntra-operative ventilation using low/physiological tidal volume and positive end-expiratory pressure (PEEP) with periodic alveolar recruitment manoeuvres (ARMs) is recommended in obese surgery patients.OBJECTIVESTo investigate the effects of PEEP levels and ARMs on ventilation distribution, oxygenation, haemodynamic parameters and cerebral oximetry.DESIGNA substudy of a randomised controlled trial.SETTINGTertiary medical centre in Geneva, Switzerland, between 2015 and 2018.PATIENTSOne hundred and sixty-two patients with a BMI at least 35 kg per square metre undergoing elective open or laparoscopic surgery lasting at least 120 min.INTERVENTIONPatients were randomised to PEEP of 4 cmH2O (n = 79) or PEEP of 12 cmH2O with hourly ARMs (n = 83).MAIN OUTCOME MEASURESThe primary endpoint was the fraction of ventilation in the dependent lung as measured by electrical impedance tomography. Secondary endpoints were the oxygen saturation index (SaO2/FIO2 ratio), respiratory and haemodynamic parameters, and cerebral tissue oximetry.RESULTSCompared with low PEEP, high PEEP was associated with smaller intra-operative decreases in dependent lung ventilation [-11.2%; 95% confidence interval (CI) -8.7 to -13.7 vs. -13.9%; 95% CI -11.7 to -16.5; P = 0.029], oxygen saturation index (-49.6%; 95% CI -48.0 to -51.3 vs. -51.3%; 95% CI -49.6 to -53.1; P < 0.001) and a lower driving pressure (-6.3 cmH2O; 95% CI -5.7 to -7.0). Haemodynamic parameters did not differ between the groups, except at the end of ARMs when arterial pressure and cardiac index decreased on average by -13.7 mmHg (95% CI -12.5 to -14.9) and by -0.54 l min-1 m-2 (95% CI -0.49 to -0.59) along with increased cerebral tissue oximetry (3.0 and 3.2% on left and right front brain, respectively).CONCLUSIONIn obese patients undergoing abdominal surgery, intra-operative PEEP of 12 cmH2O with periodic ARMs, compared with intra-operative PEEP of 4 cmH2O without ARMs, slightly redistributed ventilation to dependent lung zones with minor improvements in peripheral and cerebral oxygenation.TRIAL REGISTRATIONNCT02148692, https://clinicaltrials.gov/ct2

Individualized Positive End-expiratory Pressure Titration Strategies in Superobese Patients Undergoing Laparoscopic Surgery: Prospective and Nonrandomized Crossover Study

“…[27][28][29] Transpulmonary pressures, respiratory mechanics, and Lung Volumes Individualizing PEEP may be necessary to homogenize regional ventilation, limit alveolar collapse, and preserve hemodynamics; however, the optimal levels of PEEP differ between patients and surgical conditions. 3,10,14,30,31 To date, the optimal intraoperative PEEP strategy for superobese patients is unclear, 9,32 and the physiologic effects of different bedside PEEP strategies have not been compared in the subgroup of superobese patients. In our study, a fixed level of empirical PEEP (PEEP Empirical ) led to negative end-expiratory transpulmonary pressures that were influenced by surgical positioning and were associated with a reduction in end-expiratory lung volume, resulting in higher respiratory system and transpulmonary driving pressures.…”

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“…Obese patients undergoing surgery require the effective removal of residual neuromuscular blockade (NMB) and the precise administration of muscle relaxation to guarantee the safety and efficacy of the surgical procedure. [6,7] The controlled administration of muscle relaxation is critical for safeguarding the lungs and preventing post-operative respiratory complications, as obese patients face a fourfold increased risk compared to individuals with normal body weights. [8] Excess body weight can lead to a multitude of health issues, including metabolic syndrome, venous thrombosis, and obstructive sleep apnea.…”

Setting positive end-expiratory pressure by using electrical impedance tomography

“…An experimental investigation studied the effect of different PEEP values on the homogeneity of ventilation during neurally-adjusted assisted ventilation using the dorsal fraction of ventilation to identify the PEEP value leading to the highest degree of ventral-dorsal balance [5]. The same parameter was applied in obese surgery patients and identified less dependent collapse at 12 than 4 cmH 2 O of PEEP [6]. A well designed prospective clinical study in postcardiac surgery patients determined PEEP by analyzing a decremental PEEP trial with EIT with the aim of avoiding ventilation loss in the dependent regions [7 ▪▪ ].…”