Individualized positive end-expiratory pressure in obese patients during general anaesthesia: a randomized controlled clinical trial using electrical impedance tomography

Abstract

Background

General anaesthesia leads to atelectasis, reduced end-expiratory lung volume (EELV), and diminished arterial oxygenation in obese patients. We hypothesized that a combination of a recruitment manoeuvre (RM) and individualized positive end-expiratory pressure (PEEP) can avoid these effects.

Methods

Patients with a BMI ≥35 kg m⁻² undergoing elective laparoscopic surgery were randomly allocated to mechanical ventilation with a tidal volume of 8 ml kg⁻¹ predicted body weight and (i) an RM followed by individualized PEEP titrated using electrical impedance tomography (PEEP_IND) or (ii) no RM and PEEP of 5 cm H₂O (PEEP₅). Gas exchange, regional ventilation distribution, and EELV (multiple breath nitrogen washout method) were determined before, during, and after anaesthesia. The primary end point was the ratio of arterial partial pressure of oxygen to inspiratory oxygen fraction (PaO₂/FiO₂).

Results

For PEEP_IND (n=25) and PEEP₅ (n=25) arms together, PaO₂/FiO₂ and EELV decreased by 15 kPa [95% confidence interval (CI) 11–20 kPa, P<0.001] and 1.2 litres (95% CI 0.9–1.6 litres, P<0.001), respectively, after intubation. Mean (sd) PEEP_IND was 18.5 (5.6) cm H₂O. In the PEEP_IND arm, PaO₂/FiO₂ before extubation was 23 kPa higher (95% CI 16–29 kPa; P<0.001), EELV was 1.8 litres larger (95% CI 1.5–2.2 litres; P<0.001), driving pressure was 6.7 cm H₂O lower (95% CI 5.4–7.9 cm H₂O; P<0.001), and regional ventilation was more equally distributed than for PEEP₅. After extubation, however, these differences between the arms vanished.

Conclusions

In obese patients, an RM and higher PEEP_IND restored EELV, regional ventilation distribution, and oxygenation during anaesthesia, but these differences did not persist after extubation. Therefore, lung protection strategies should include the postoperative period.

Clinical trial registration

German clinical trials register DRKS00004199, http://ift.tt/2gfFcmy.

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