The IMPROVE group’s trial on Intraoperative Low-Tidal-Volume Ventilation in Abdominal Surgery published in NEJM are supporting lung protective ventilation (LPV). Just as was found in the JAMA 2012 meta-analysis. The IMPROVE trial emphasises that it’s not just low tidal volumes, but also PEEP and regular recruitment maneuvers that help the lungs through the operation and beyond. Lung protective ventilation is a whole package.
It seems the medical research community is finally running out of fancy acronyms. So, to clarify, no, we’re not talking about that IMPROVE trial, but this IMPROVE trial: Intraoperative PROtective Ventilation.
Anyway, the study is a French multicenter, double blinded (sort of), randomised trial recruiting patients over the age of 40 and a risk of pulmonary complications >2 having open or laparoscopic abdominal surgery.
The whole package
The thing here is the whole package. The intervention group received not only low tidal volume ventilation (6-8ml/kg IBW), but also PEEP 6-8 cmH2O and recruitment maneuvers every 30 minutes. I think of it as:
• Low tidal volumes – to avoid shearing stress on alveoli
• PEEP – to keep alveoli open
• Recruitment maneuvers – to open alveoli that might have closed anyway
The control group got high tidal volume ventilation (10-12ml/kg IBW), and no PEEP or recruitment unless the anesthetist found it clinically indicated during surgery. (According to the tables in the article, they never did).
It is also worth noting this is IBW – ideal body weight. Much too often in the OR I’ve seen that the ventilator is set after the patient’s actual body weight. In this day and age, that usually means unnecessary high tidal volumes.
Primary outcome was major pulmonary and extrapulmonary complications occurring within the first seven days after surgery. This occurred in 10% of the LPV group vs 27% in the control group. In the same period, 5% assigned to LPV required noninvasive ventilation or intubation for acute respiratory failure, compared with 17% in the control group.
This outtake from the comparison table shows how lung compliance already at baseline, straight after intubation, is much worse in the control group (1st column) compared to the LPV group (2nd column). And towards the end of the surgery the control group had worsened, while the LPV group had kept their baseline lung compliance.
This compares well with what we wrote on atelectasis prevention with the use of PEEP, recruitment and low FiO2 levels here.
The results are convincing, and in line with most other studies, including this meta-analysis from JAMA we wrote about here.
It might be practical in a trial setting to have a set PEEP, but in clinical practice the PEEP value should be set to fit the patient to optimise the effect. If there is a clinical need for recruitment, the PEEP is usually too low. Still, some alveoli will collapse, and recruitment will help open them. So regular recruitment might be good.
Lung protective ventilation is good for your patient. And lung protective ventilation is not just low tidal volumes, but the whole package: Low tidal volume, PEEP and recruitment maneuvers.