A MAP alarm set at 72 mmHg matched the Hypotension Prediction Index

Design

Single-centre blinded randomised non-inferiority trial

Population

143 adults having moderate- or high-risk elective non-cardiac surgery with arterial lines

Primary outcome

Area under MAP 65 mmHg

Effect

Median 3.75 vs 4.00 mmHg·min; log difference 0.03 (95% CI -0.24 to 0.29)

The Hypotension Prediction Index (HPI) is a proprietary algorithm meant to warn of hypotension before it happens. It correlates strongly with mean arterial pressure, and observational data suggested a simple MAP alarm at 72 mmHg might perform similarly.

This single-centre blinded trial randomised adults having moderate- or high-risk elective non-cardiac surgery with continuous arterial monitoring to a MAP alarm below 72 mmHg or an HPI alarm above 85. In 143 patients, the area below MAP 65 was similar: median 3.75 vs 4.00 mmHg·min, with the log-transformed difference well within the non-inferiority margin (0.03, 95% CI -0.24 to 0.29). No differences were seen in other haemodynamic measures, alarm burden, kidney or myocardial injury, mortality, length of stay, vasopressor or fluid use.

The trial was small and not powered for organ injury. Both groups had very little hypotension, which may reflect attentive care in a trial setting.

For units without HPI, or weighing its cost, this supports setting an early MAP alarm, around 72 mmHg, on the arterial line as a pragmatic alternative.

• Set the arterial-line MAP alarm higher than 65 — around 72 mmHg — to prompt earlier action.
• A MAP alarm at 72 was non-inferior to the HPI for time below MAP 65.
• Vasopressor and fluid use did not differ between strategies.
• The trial was not powered to show differences in kidney or myocardial injury.
• Consider the alarm approach where HPI is unavailable or its cost is a barrier.

Why it matters

If an alarm setting on any monitor does the same job, the case for a costly proprietary algorithm becomes much harder to make.

Don't overread it

With 143 patients, the trial cannot show the two approaches are equivalent for organ injury.

The statistics, in plain English

Non-inferiority means the MAP alarm was not worse than HPI by more than a pre-agreed margin. The lower confidence limit (-0.24) stayed above that margin (-0.4), so the claim holds for the primary outcome.

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