Perioperative CGM was accurate for most readings, but less so during hypoperfusion

Design

Prospective observational validation study

Population

58 adults with diabetes undergoing surgery or ICU admission

Primary outcome

Agreement between CGM and point-of-care glucose (MARD)

Effect

MARD 10.9%; 98% of readings in error grid zones A-B; +4.5% MARD in hypoperfusion

Continuous glucose monitors are increasingly worn into hospital. This prospective study compared a Dexcom G7 sensor with point-of-care glucose in 58 people with diabetes on glucose-lowering drugs who were having surgery or were in intensive care.

The median absolute relative difference was 10.9%, and 98% of 1,212 paired readings fell in clinically acceptable error grid zones. The mean difference was -1 mmol/L, but limits of agreement were wide (-5.6 to 3.4 mmol/L). Error was 4.5 percentage points higher during hypoperfusion — MAP below 65, vasopressors or low perfusion index. No hypoglycaemia occurred, so accuracy at low values was not tested.

The data support CGM as a trend monitor around surgery, with point-of-care confirmation for decisions, especially when perfusion is poor or glucose is low.

• 98% of paired CGM and point-of-care readings were within acceptable error.
• Accuracy was worse during hypotension, vasopressor use or poor peripheral perfusion.
• Accuracy in hypoglycaemia was not tested; no low values occurred.
• Confirm with a capillary or arterial sample before treating a CGM reading.
• Record whether the patient wears a CGM at preoperative assessment.

Why it matters

Patients arrive wearing sensors, and teams need to know how far to trust them under anaesthesia.

Don't overread it

No hypoglycaemia occurred, so this says nothing about CGM accuracy at low glucose.

The statistics, in plain English

A MARD of about 11% means a typical reading sits about 11% from the reference. Limits of agreement of -5.6 to 3.4 mmol/L mean individual readings can be much further off.

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