Relative, not absolute, hypotension was linked to postoperative pneumonia

Design

Retrospective multicentre cohort, competing-risk analysis

Population

151,036 adults having non-cardiac surgery under general anaesthesia, China

Primary outcome

Postoperative pneumonia within 30 days

Effect

≥20% MAP fall: sHR 1.108 (95% CI 1.068–1.149); per episode sHR 1.079 (1.050–1.109)

A retrospective cohort at three Chinese hospitals included 151,036 adults having non-cardiac surgery under general anaesthesia. Intraoperative hypotension was defined 12 ways across nine thresholds, from absolute mean arterial pressures below 50–70 mmHg to relative falls of 20–50% from baseline. The outcome was pneumonia within 30 days, which occurred in 2.3%.

Relative falls were more consistently associated with pneumonia than absolute thresholds. With hypotension defined as a 20% fall from baseline, its presence was associated with pneumonia (subdistribution HR 1.11, 95% CI 1.07–1.15), and each additional episode added risk (sHR 1.08). Absolute thresholds were not consistently associated after adjustment. Risk rose steeply with the first exposure and then levelled off.

This is observational, and the per-patient effect is modest. But it aligns with the argument for individualised blood pressure targets, especially in patients whose usual pressure is high, for whom a 'normal' MAP of 65 may already be a large fall. It does not show that treating the falls prevents pneumonia.

• Consider setting intraoperative blood pressure targets relative to each patient's own baseline.
• Be particularly alert in hypertensive patients, for whom a fixed MAP threshold may hide a large relative fall.
• Treat repeated dips as well as sustained ones; episode count was linked to risk.
• Keep absolute floors in place as well; this study does not argue for abandoning them.

Why it matters

Many departments still define hypotension by a single fixed number, which may miss the falls that matter.

Don't overread it

Observational — it cannot show that preventing relative falls reduces pneumonia.

The statistics, in plain English

A subdistribution hazard ratio of 1.11 means about an 11% higher rate of pneumonia, accounting for death as a competing outcome. On a 2.3% baseline risk that is a small absolute increase per patient, but across many operations it adds up.

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