Why is this important?

Although we have moved beyond routinely using high tidal volumes in favour of ’protective ventilation strategies’ the specifics of what is protective and what improves outcomes is controversial. Previous trials have struggled to demonstrate post-operative respiratory benefits from protective strategies.

What did they do?

In this small randomised controlled trial, Généreux et al. investigated whether intraoperative PEEP (7 cmH₂O) and recruitment manoeuvres (RM) q30min would reduce atelectasis post-extubation. Using ultrasound to measure intraoperative and post-operative atelectasis gives their study greater flexibility than other studies using CT scanning, generally considered the gold standard for atelectasis measurement.

And they found...

Among 34-85 yo women undergoing open gynae-oncology surgery >2h duration, there was no post-extubation difference in atelectasis whether receiving PEEP/RM or zero PEEP.

Not so fast

There was however less intraoperative atelectasis among the protective ventilation group, supporting the common use of PEEP and RM to improve oxygenation during surgery. Additionally, they specifically excluded morbidly obese women (BMI > 40 kg/m²), an increasingly common demographic at risk of ventilation challenges.

Nonetheless this study adds to the evidence that current protective ventilation strategies do not actually reduce post-operative respiratory complications.

Be smart

One interesting observation was the large amount of inter-patient variability, the researchers noting:

“...this heterogeneity highlights the need to dynamically monitor lung aeration changes and personalise our delivery of mechanical ventilation in the perioperative setting.”

As with many perioperative interventions, the benefits may in fact lie in the personalisation of our care for each individual patient.

summary

• Vincent Généreux, Michaël Chassé, François Girard, Nathalie Massicotte, Carl Chartrand-Lefebvre, and Martin Girard.
• Department of Anaesthesiology, Centre Hospitalier de l'Université de Montréal, Montreal, QC, Canada.
• Br J Anaesth. 2020 Jan 1; 124 (1): 101-109.

BackgroundDuring general anaesthesia, most patients develop atelectasis, which promotes postoperative pulmonary complications. RCTs that investigated perioperative lung protection have failed to reduce postoperative pulmonary complications consistently. Ultrasound imaging could help confirm the effects of different protective ventilatory strategies, but this has not been tested in trials. The objective of this study was to use ultrasonography to evaluate whether lung-protective ventilation measures reduce perioperative atelectasis.MethodsWe conducted a prospective, randomised patient- and assessor-blinded controlled trial in women undergoing open gynaecological surgery. Subjects were randomised to either lung protection or zero end-expiratory pressure (ZEEP; with no recruitment manoeuvres [RMs]). Lung protection entailed PEEP (7 cm H2O) and RMs every 30 min. Lung ultrasonography was undertaken at five predefined time points. The primary outcome was the difference in lung ultrasonography score (LUS) between groups before emergence; a lower LUS indicates better lung aeration.ResultsWe recruited 45 women (34-85 yr old). Women randomised to lung protection had lower mean (standard deviation) LUS before emergence (6.1 [3.7]), compared with women randomised to ZEEP (11.7 [3.9]; 95% confidence interval for the difference between group means [-7.9 to -3.2]; P<0.0001). This difference did not persist after extubation, with similar mean LUSs in women who had received intraoperative lung protection (7.0 [4.1]), compared with women randomised to receive ZEEP (7.7 [3.1]).ConclusionsAs assessed by lung ultrasonography, intraoperative PEEP/RMs decreased aeration loss during general anaesthesia. However, similar degrees of aeration loss were observed after tracheal extubation regardless of intraoperative ventilatory strategy.Clinical Trial RegistrationNCT02055807.Copyright © 2019 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.

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