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Three Part Question

In [patients with DKA] can [capillary blood be used as an alternative to arterial puncture] for [guiding appropriate therapy]?

Clinical Scenario

A patient attends the Emergency Department with diabetic ketoacidosis. They have had previous similar attendances and are reluctant to have arterial blood gases taken; you wonder if capillary blood can be used as an alternative to arterial puncture.

Search Strategy

Medline using the OVID interface 1966-07/2007
Embase using the Dialog Datastar interface 1974-07/2007
Medline: [exp capillaries/ OR capillary.mp] AND [exp blood gas analysis/ OR blood gas.mp] AND [exp diabetes mellitus/ OR diabetes.mp].
Embase: [capillary ADJ blood ADJ gas] AND [diabetes ADJ mellitus].

Search Outcome

25 papers were found by the Medline search, of which 1 was relevant to the question (table). 61 papers were identified by the Embase search, but none of these were relevant to the question

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Hale PJ 1988 UK	20 patients admitted to hospital with DKA	Prospective observational	Correlation between simultaneously drawn radial or femoral arterial blood and capillary blood taken from a fingertip. The samples were taken 2 hours after the initiation of treatment.	There was good correlation: pH r = 0.98, pCO2 r = 0.89, bicarb r = 0.97 - all p<0.001 Range of values measured: pH 6.77-7.29, pCO2 1.5-5.4kPa, bicarb 2-15mmol/l	1. Small study. 2. Few clinical details, such as severity of illness, duration of acidosis prior to treatment, and blood pressure.

Comment(s)

This paper suggested that capillary blood might be a useful alternative to arterial puncture for early assessment of acid-base balance in DKA. However, it was a small study and not enough clinical details were given to assess the influence of confounding factors; in particular, the patients' blood pressures were not described. There are theoretical concerns that hypotension might lead to hypoperfusion of the capillary beds and this would lead to capillary blood becoming more like venous and less like arterial blood.

Clinical Bottom Line

There is insufficient evidence to recommend the use of capillary blood in the assessment of acid-base status in patients with diabetic ketoacidosis; more research is needed to answer this question.

References

1. Hale PJ and Nattrass M. A comparison of arterial and non-arterialized capillary blood gases in diabetic ketoacidosis. Diabetic Medicine. 1988; 5; 76-78.