Radial lines under-read the cuff by over 11 mmHg in one in five patients on vasopressors

Design

Prospective multicentre observational study

Population

303 adult ICU patients on vasoactive drugs with radial arterial lines, 13 Polish ICUs

Primary outcome

Brachial-to-radial mean pressure gradient >11 mmHg

Effect

18.4% had a significant gradient; vasopressor dose OR 1.68 (95% CI 1.12–2.52)

This prospective study at 13 Polish ICUs compared invasive radial mean arterial pressure with non-invasive brachial cuff pressure in 303 adults receiving vasoactive drugs. A third had septic shock.

The median gradient was 4.5 mmHg, but 18% had a brachial pressure more than 11 mmHg above the radial reading. Those patients were on higher noradrenaline-equivalent doses (0.23 vs 0.10 µg/kg/min), had higher lactate and longer capillary refill, and more died in the ICU (48% vs 30%). Only the vasopressor dose remained independently associated with a large gradient.

Intense peripheral vasoconstriction can make the radial artery read lower than central pressure. If the team titrates to a radial target, a patient may be given more vasopressor than the central pressure needs.

This study shows the gradient exists and tracks with illness severity; it did not test whether acting on it changes outcomes. Mortality differences reflect sicker patients, not the gradient itself.

• Compare the radial line with a brachial cuff reading in patients on rising vasopressor doses.
• Suspect radial under-reading when doses climb without other signs of worsening shock.
• Consider a femoral or brachial arterial line when a large gradient persists on high-dose vasopressors.
• Check the arterial trace for damping and the transducer level before changing doses.

Why it matters

Titrating vasopressors to a radial number may push doses higher than the patient needs.

Don't overread it

This was observational; it does not show that switching line site improves outcomes.

The statistics, in plain English

An odds ratio of 1.68 per unit of vasopressor dose means higher doses were linked to greater odds of a large gradient after adjusting for other factors. The mortality difference is unadjusted and reflects illness severity; it does not show the gradient causes death.

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