In terms of adverse events, there was a suggestion that people aged 75 years and older receiving NP monitoring may be more likely to develop hyperkalaemia and hypotension, although there was no clinically significant difference in the incidence of renal failure. However, the committee emphasised the very wide confidence intervals around all of these estimates of effect, which in many cases ranged from a clinically important benefit to a clinically important harm. The committee agreed that while there was no clear evidence of benefit in people aged 75 and over, there was also no clear evidence of harm. Because of the uncertainty around the impact of NP monitoring in people 75 years of age and older, the committee decided to make no recommendation for this age group. The committee discussed at length the stratification of the recommendation by age, including the biological plausibility of the finding that NP monitoring had a differential effect depending on age. The committee suggested that the metabolism of NPs may change with age, and this could make NP monitoring less useful in older patients. The committee also agreed that age could be a surrogate for comorbidity, and this could explain the benefit of a more aggressive NP monitoring strategy in younger people (i.e. with fewer comorbidities). Supporting this hypothesis, one of the existing meta-analyses conducted a post-hoc analysis suggesting that the reduced mortality associated with NP monitoring was primarily seen in patients without previous cerebrovascular accident/transient ischemic attack, diabetes or COPD, and that the benefit of NP monitoring was absent in patients with any one of those comorbidities 55 . Peripheral vascular disease was also found to be a relevant comorbidity explaining some of the association between the treatment affect and age. 