Capillary blood gases as an alternative to arterial puncture in acute asthma

Report By: Simon FJ Clarke - Consultant in Emergency Medicine
Search checked by Andrew Parfitt - Consultant in Emergency Medicine
Institution: St Thomas' Hospital, London
Date Submitted: 22nd February 2005
Last Modified: 22nd February 2005
Status: Blue (submitted but not checked)

Three Part Question

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

Clinical Scenario

A patient attends the Emergency Department with an acute exacerbation of asthma. 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 1966-04/2004
[exp capillaries/ OR capillary.mp] AND [exp blood gas analysis/ OR blood gas.mp] AND [exp asthma/ OR asthma.mp

Search Outcome

10 papers were found of which 1 was relevant to the question

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Davis et al 1975 USA	19 samples taken on 16 patients. 13 children (1-13 years) and 3 adults. 1. Status asthmaticus (11 children) 2. Pneumonia (others)	Prospective observational	Correlation between blood drawn simultaneously from the radial artery and from the earlobe (massaged for 3 mins with nicotinate paste)	Good correlation. pO2 (r 0.965). pCO2 (r 0.972). pH (r 0.987). All p<0.005. Ranges over which samples were measured:pO2 25-125 mmHg, pC02 10-60 mmHg, pH 7.25-7.8.	Small study. No definition of status asthmaticus. No note of duration of illness and treatment given before the bloods were taken. Mostly single sample taken per patient, so no comment can be made on the utility of capillary blood for repeat measurements. No data on adults.

Comment(s)

Although there seems to be good correlation between capillary and arterial gases in the children in this paper, the study was small and insufficient clinical details were given to be able to rule out potential confounding factors. At most, the study acts as a guide for future research.

Clinical Bottom Line

There is insufficient evidence to recommend the use of capillary blood in the assessment of blood gas values in patients with acute asthma; more research is needed to answer this question.

References

Davis RH, Beran AV and Galant SP. Capillary pH and blood gas determinations in asthmatic children. J Allergy Clin Immunol. 1975; 56; 33-38.