Arterial versus capillary blood gases: A meta-analysis

Department of Anesthesia, McGill University Health Center, Montreal, Quebec, Canada. <>
Respiratory Physiology & Neurobiology (Impact Factor: 1.97). 03/2007; 155(3):268-79. DOI: 10.1016/j.resp.2006.07.002
Source: PubMed


A meta-analysis determined whether capillary blood gases accurately reflect arterial blood samples. A mixed effects model was used on 29 relevant studies obtained from a PubMed/Medline search. From 664 and 222 paired samples obtained from the earlobe and fingertip, respectively, earlobe compared to fingertip sampling shows that the standard deviation of the difference is about 2.5x less (or the precision is 2.5x better) in resembling arterial PO(2) over a wide range of arterial PO(2)'s (21-155 mm Hg ). The lower the arterial PO(2), the more accurate it is when predicting arterial PO(2) from any capillary sample (p<0.05). However, while earlobe sampling predicts arterial PO(2) (adjusted r(2)=0.88, mean bias=3.8 mm Hg compared to arterial), fingertip sampling does not (adjusted r(2)=0.48, mean bias=11.5 mm Hg compared to arterial). Earlobe sampling is slightly more accurate compared to fingertip sampling in resembling arterial PCO(2) (arterial versus earlobe, adjusted r(2)=0.94, mean bias=1.9 mm Hg ; arterial versus fingertip, adjusted r(2)=0.95, mean bias=2.2 mm Hg compared to arterial) but both sites can closely reflect arterial PCO(2) (880 total paired samples, range 10-114 mm Hg ). No real difference between sampling from the earlobe or fingertip were found for pH as both sites accurately reflect arterial pH over a wide range of pH (587 total paired samples, range 6.77-7.74, adjusted r(2)=0.90-0.94, mean bias=0.02). In conclusion, sampling blood from the fingertip or earlobe (preferably) accurately reflects arterial PCO(2) and pH over a wide range of values. Sampling blood, too, from earlobe (but never the fingertip) may be appropriate as a replacement for arterial PO(2), unless precision is required as the residual standard error is 6 mm Hg when predicting arterial PO(2) from an earlobe capillary sample.

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Available from: Gerald Stanley Zavorsky, Jan 05, 2014
    • "Gasometric analyses of the arterialized capillary blood sampled from the earlobe were performed at 0, 10 and 20 min during each procedure. This method was chosen because this procedure is less painful and harmful than arterial sampling, and arterialized earlobe blood accurately reflects arterial paCO 2 and is appropriate as a replacement for arterial paO 2 (Zavorsky et al., 2007). Heart rate and blood pressure were also recorded. "
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    ABSTRACT: The aims of this study were to examine selected respiratory and gasometric parameters during hyperventilation with and without isocapnia and to identify the possible mechanism by which isocapnic hyperventilation might be useful in the elimination of volatile substances, including CO. Ten healthy non-smoking volunteers were studied, and each underwent two procedures. During one session, CO2 was added to the respiratory circuit, and during the other session, only 100% O2 was used. The volunteers were coached to hyperventilate until the appearance of side effects. Isocapnic hyperventilation significantly increased alveolar minute ventilation and partial pressure of oxygen in arterialized capillary blood (paO2); to the best of our knowledge, these findings have not previously been reported. Isocapnic hyperventilation was associated with only mild side effects, such as dyspnea, increased respiratory effort and headache, in 30% of subjects. Side effects, including vertigo, paresthesias and muscle tremor, were present in 70% of the volunteers during hyperventilation with 100% O2, and these side effects forced them to limit their respiratory rates and tidal volumes. These increases in alveolar ventilation and the partial pressure of oxygen in the blood may play crucial roles in decreasing the half-time of carboxyhemoglobin, which is the primary goal of the treatment of CO poisoning.
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    • "However, studies in healthy subjects and patients have shown contradictory results on the accuracy of this technique, which has limited its implementation in current clinical practice [2-8]. As suggested in a recent meta-analysis [9], arterial gasometrical values could be estimated from EL capillary samples and may be useful for clinical practice. However, limited precision was reported, which was attributed to arterio-venous capillary gas differences and a lack of standardized sampling procedures. "
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    • "Thus, there are limitations with using PETCO 2 as a prediction of PaCO 2 that need to be considered when interpreting CPET data. Arterialized blood can also be used to predict PaCO 2 with reasonable accuracy [34] [35] but is practically more difficult as compared to PETCO 2 . "
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