Adoption of Lung Protective ventilation IN patients undergoing Emergency laparotomy: the ALPINE study. A prospective multicentre observational study

Watson X, Chereshneva M, Odor PM et al. for Pan-London Perioperative Audit and Research Network (PLAN)

British Journal of Anaesthesia. Article in Press (Editorial decision May 2018)

Background

• Postoperative pulmonary complications (PPCs) are the second most common surgical complication
• Emergency abdominal surgery is associated with a high risk, in up to 40% patients, of postoperative pulmonary complications
  • Lung-protective ventilation (LPV) is a well-established strategy of care in ventilated patients with ARDS in ITUs
• LPV definition:
  • use of tidal volumes <8 ml / kg of ideal body weight (IBW)
  • PEEP of >5 cm H₂O
  • recruitment manoeuvres (30 seconds of 30 cm H₂O CPAP every 30min)
  • maintenance of plateau pressure <30 cm H₂O
• Could LPV reduce PPCs?

Hypothesis

The majority of patients are not ventilated using an LPV strategy, but its implementation may lead to a reduced occurrence of PPCs

Primary Endpoint

To determine whether patients undergoing emergency laparotomy surgery are ventilated using a lung-protective ventilation

Secondary Aim

To investigate the association between ventilation factors as below and the occurrence of PPCs:

• lung-protective ventilation strategy
• intraoperative FiO₂
• peak inspiratory pressure

Design and Location

Prospective, multicentre, observational study undertaken  (31 10 2016-31 03 2017) with 28 hospitals in collaboration with the National Emergency Laparotomy Audit (NELA) and delivered by the Pan-London Perioperative Audit and Research Network (PLAN)

Methodology

• Cohort: data were collected prospectively from 568 patients
• Inclusion criteria: all patients over the age of 18 who underwent expedited, urgent, or emergency, open laparotomy or laparoscopic surgery as per NELA guidelines were included
• Data for each ventilation parameter were recorded manually by the anaesthetist onto a pro forma by recording the most documented value from the anaesthetic chart for each whole procedure
• The development of PPCs was recorded on a daily basis until Day 7 postoperatively by reviewing the patient’s notes
• PPCs were defined according to the European Perioperative Clinical Outcome definition: respiratory failure, respiratory infection, atelectasis, bronchospasm, pneumothorax, and aspiration pneumonia

Results

• The preferred mode of ventilation was pressure control ventilation-volume guaranteed in 185/568 patients (33%) with volume control accounting for 30% of cases followed by pressure control (18%)
• The median tidal volume among all patients observed was 500ml, corresponding to a median tidal volume of 8 ml / kg ideal body weight
• A lung-protective ventilation strategy was employed in 4.9% of patients and was not protective against the occurrence of PPCs
• Out of a total of 568 patients, 275 (48%) patients developed a PPC within 7 days. Out of these 275 patients, 55% (n=175) developed at least two PPCs within 7 days. Postoperative respiratory failure was the most common PPC (n=197; 35%) followed by atelectasis (n=182; 32%)
• A peak inspiratory pressure of <30cm H₂O was protective against the development of PPCs
• The median FiO₂was 0.5 and an increase in FiO₂ by 5% increased the risk of developing a PPC by 8%

Conclusions

• Both intraoperative peak inspiratory pressure and FiO₂are independent factors significantly associated with the development of a PPC emergency laparotomy patients
• Further studies are required to identify their causality effect and to demonstrate if their manipulation could lead to better clinical outcomes

Evaluation:

– Pros

• Prospective study
• The first study to explore the ventilator strategies employed in emergency abdominal surgery
• Large economic PPCs burden; the more data, the better practice

– Cons

• The most significant limitation of the study was that authors were unable to adjust the results of the multivariable analysis for the likelihood of developing a PPC using the ARISCAT score, the most well-known and externally validated risk assessment tool for the development of PPCs (out of the seven variables included in the ARISCAT tool, authors were unable to collect data on previous respiratory infections in the last month and on the presence of preoperative anaemia)
• Whilst it was observational in nature, the fact that it was both voluntary and prospective may have had an impact on the delivery of the ventilation by the anaesthetist and influenced the ventilator strategies employed
• The ventilator parameters were recorded as the ‘most frequently documented’, and so, although they are more than likely to be reflective of true practice, it is possible that the peak pressures and tidal volumes used varied throughout the procedure, and thus, they may not be wholly representative
• As the data were only collected as part of routine standard care, the authors were limited to collecting data on PPCs on the patients who had the information readily available, as they we were unable to order any additional investigations to confirm the diagnosis
• <10% of patients actually received a recruitment manoeuvre
• Relatively small cohort given it was an observational study – study lasted just 5 months

Summary

• Emergency abdominal surgery is associated with a high risk of PPCs, but the use of ‘protective’ ventilation is uncertain
• In this prospective observational study, 48% of patients developed a PPC after emergency laparotomy
• PPCs were associated with:
  • increased age
  • use of high fractional inspired oxygen concentration
  • high peak inspiratory airway pressures
• Lung-protective ventilation was used in <5% of patients, and had no effect on the incidence of PPCs

Discussion from Journal Club Meeting

• Most patient already have pre-existing respiratory conditions (aspiration, raised diaphragm, atelectasis etc) and/or respiratory failure the study dis not evaluate this factor
• Most of the time anaesthetists are using higher FiO2, Peep and driving pressures due to compromised oxygenation/saturation or difficulty to ventilate patient during emergency laparotomy due pre-existing respiratory problems prior or related to the surgical pathology
• Difficult to trust collected data (patient ventilation settings in Theatre and ITU most of the time are not documented well)
• It is a very relevant/important topic – needs a separate trial for which the ventilation data would be collected
• Would be better if a third party would collect ventilation related parameters for more objectivity

Summary by Dr V Peciuliene. Journal Club Meeting 12 July 2018.