Relative, not absolute, intra-operative hypotension tracked postoperative pneumonia

Design

Retrospective multicentre cohort study; subdistribution hazard modelling of competing risks

Population

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

Primary outcome

Postoperative pneumonia within 30 days

Effect

≥20% baseline fall associated (hazard ratio 1.108, 1.068–1.149); absolute thresholds not consistently associated

Intra-operative hypotension is defined inconsistently, and whether it raises pulmonary risk has been unclear. This multicentre cohort of 151,036 adults having non-cardiac surgery under general anaesthesia tested 12 hypotension metrics across nine thresholds against postoperative pneumonia within 30 days.

Pneumonia occurred in 2.3%. A relative fall of 20% or more from the patient's own baseline mean arterial pressure was consistently associated with pneumonia — both the presence and the number of episodes — whereas fixed absolute thresholds lost their association after adjustment. Risk rose steeply at low exposure and then plateaued across 20–40% reductions.

The practical implication is to think in terms of each patient's baseline rather than a single number for everyone. A mean arterial pressure of 65 mmHg may be benign in one patient and a 30% drop in another; the latter is what tracked pulmonary risk here. It supports individualised, baseline-anchored blood-pressure targets intra-operatively, though as an observational study it cannot prove that preventing those falls prevents pneumonia.

• A ≥20% fall from baseline mean arterial pressure was associated with postoperative pneumonia (subdistribution hazard ratio 1.108 for its presence, 95% CI 1.068–1.149).
• The number of such relative-hypotension episodes also tracked pneumonia (hazard ratio 1.079 per episode, 1.050–1.109).
• Fixed absolute thresholds (e.g. <65 mmHg) were not consistently associated after adjustment.
• Anchor intra-operative blood-pressure targets to each patient's baseline rather than a single universal number.

Why it matters

It challenges the habit of chasing one universal pressure number and points to baseline-anchored targets.

Don't overread it

This was observational — it shows association, not that actively preventing relative hypotension prevents pneumonia.

The statistics, in plain English

A subdistribution hazard ratio of about 1.1 is a small relative increase per patient, but across a common exposure it adds up. The key message is comparative: the baseline-relative definition stayed associated with pneumonia after adjustment while absolute cut-offs did not.

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