The Influence of Positive End-Expiratory Pressure on Leakage and Oxygenation Using a Laryngeal Mask Airway
A Randomized Trial
November 2022 by Dr Liam O'Doherty
An RCT of adult patients undergoing surgery (urology, gynaecology, peripheral) with mandatory ventilation via a Proseal LMA mask randomised to PEEP 8.2 cmH2O (PEEP group) or PEEP 0 cmH2O (ZEEP group). Does this result in a higher incidence of gas leakage?
Adult ASA I/II patients were anaesthetised with Proseal LMA placed then given a mandatory ventilation protocol with no spontaneous breathing for the first 30 minutes of the case.
527 patients randomised: 174 ZEEP vs 208 PEEP
Excluded: increased risk aspiration, BMI >30, GORD, pregnancy, prone position, lateral position, laparoscopic surgery.
Intervention: 8.2 cmH2O PEEP (PEEP) or zero PEEP (ZEEP) on positive pressure ventilation.
Primary outcome: Detection of gas leakage (from ventilator, oral CO2 detection, audible leak)
Secondary outcomes: SpO2 at 25 mins; PIP, Vt, dynamic compliance and ETCO2 at 30 mins; number of desaturations occurring in the post anaesthetic care unit (PACU).
Incidence of gas leakage did not differ between groups: (ZEEP 13.2% vs PEEP 20.2%; P=0.07).
Incidence of severe gas leak requiring either new placement of LMA or intubation was higher in the PEEP group: (ZEEP 3.4%; PEEP 19.5%; p=0.025). This difference was primarily due to having to adjust the LMA positioning in the PEEP group.
Incidence of gas leak requiring intubation not different between the groups: (ZEEP 1.1% vs PEEP, 3.4%; p=0.190).
Mean SpO2 at 25 mins was higher in PEEP than ZEEP (ZEEP 98.0% vs PEEP 98.5%).
PIP at 30 mins was higher in PEEP than ZEEP (ZEEP 12 cmH2O vs PEEP 16 cmH2O).
Dynamic compliance at 30 mins was higher in the PEEP group (ZEEP 49 ml/mbar vs PEEP 57 ml/mbar).
No difference in duration of surgery or duration of anaesthesia.
No difference in mild or severe desaturations in the PACU.
No difference in PACU length of stay.
No aspirations in either group.
Take Home Message
The PEEP value used is higher than what would be used in usual practice with an LMA. The PEEP level was chosen “pragmatically” without any further reasoning. With this degree of PEEP, they were more likely to need to adjust the LMA due to gas leak. In usual clinical practice, with an LMA, PEEP levels would be set lower initially and if any leak occurs PEEP and PIP can be reduced.
The presence of PEEP seemed to have no clinically significant impact on any other outcomes. Aspiration is uncommon thus these numbers cannot determine if a difference is present.
This is not a paediatric study and given differences in LMA sizing and easier gastric insufflation in smaller age groups, this study cannot be generalised to all paediatric age groups, but may be applicable to older paediatric patients.