Pulmonary complications after muscle relaxants

Post-anaesthesia complications after use of muscle relaxants (POPULAR): a multicentre, prospective observational study

E Kirmeier et al, Lancet Respir Med. 2019 Feb;7(2):129-140

Take Home Message

Whilst this does provide some evidence that neuromuscular blockers may increase postoperative pulmonary complications in some groups, particularly those who are at a low baseline risk, we would not change practice based on this study, and think future studies looking at a narrower aspect of this question, with potential for randomisation, may be helpful. 

Background

There is increasing evidence that neuromuscular blockers (NMBs) can increase postoperative pulmonary complications (PPCs), and there is some evidence that adequate reversal and neuromuscular monitoring reduces this effect. However, this is mostly from retrospective data.

Aim

Conduct a prospective study that looks at whether use of NMBs increases risk of PPCs.

Design

  • Prospective multicenter observational cohort study 
  • 211 European hospitals over 2 weeks, 22,803 patients recruited
  • Inclusions: ≥ 18 years, receiving GA for any in-hospital procedure
  • Exclusions: remote site surgery, D/C within 12 hours, already intubated, planned ICU admission, surgery/anaesthesia within 7 days, cardiac surgery, surgery > 6 hours
  • 5 subcohorts to be analysed: GA, GA + NMB, GA + NMB + qualitiative monitoring, GA + NMB + quantitative monitoring, GA + NMB  + reversal agent used

Methodology

  • Data collected from anaesthetic charts and medical notes on patient characteristics, surgical details, anaesthetic including NMB use, and PPCs. 
  • PPCs were determined based on a bedside visit by an anaesthetist collecting data for the study or by analysis of patient notes. 
  • Logistic regression and propensity scoring used to account for differences between subcohorts – 40 risk factors for PPCs looked at

Outcomes

Incidence of PPCs from time of discharge from recovery area to day 28 post op

Results

  • NMBs are a risk factor for PPCs. They study found a PPC incidence of 3.3% without NMBs, and 8.6% when NMBs were used. This gave an OR of 1.86 (1.53 – 2.26), p < 0.0001
  • Subgroups with increased likelihood of receiving NMBs had increased risk of PPC irrespective of their treatment with NMBs, and almost all patients in subgroups known to be at high risk of PPCs had NMBs
  • Use of neuromuscular monitoring and reversal of neuromuscular blockade was not associated with decreased risk of PPC – both in fact associated with increased risk of PPCs

Study Limitations

  • Whilst a large number of confounding factors were taken into account when looking at differences between the groups, there will be factors that have not been taken account of 
  • No data on ventilation was collected, which is a significant factor in development PPCs. 
  • Not a randomised study 
  • There is a wide variation in practice relating to NMB use and monitoring, and there was little detail on this with ‘expected duration of action’ used in place of detail on drug given, dose given, and timing of administration.

Discussion

  • Positive points are this is a multicenter prospective study which recruited large numbers. 
  • Analysis suggests that PPCs are increased by NMBs in certain groups – strongest evidence is for those groups that have a low baseline risk of PPCs
  • Looks at actual clinical practice as opposed to a protocolized/limited subset of NMB use
  • Question they have asked is incredibly broad, and they look at a very broad range of surgeries, patients and practices – in future studies it may be useful to look at a narrower question, e.g. only in patients undergoing general emergency surgery, to remove more confounding factors 

Summary by Dr Jenny Hunter

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