Capillary blood gases are comparable to arterial gases in COPD
Date First Published:
October 8, 2000
Last Updated:
April 18, 2001
Report by:
Ross Murphy, Senior Clinical Fellow (MRI)
Search checked by:
Magnus Harrison, MRI
Three-Part Question:
In [a patient with an acute exacerbation of COPD] is [a capillary blood sample as good as an arterial blood sample] at measuring [PaO2, PaCO2 and pH]?
Clinical Scenario:
A 60 year old man presents to the Emergency Department with an acute exacerbation of COPD. Analysis of his blood gases is required. You wonder whether a capillary blood sample will be as accurate as an arterial blood sample.
Search Strategy:
Medline 1966-11/00 using OVID interface.
Search Details:
{[Capillar$.mp AND (exp blood gas analysis OR blood gas$.mp)] AND [(exp arteries OR arter$.mp) AND (exp blood gas analysis OR blood gas$.mp)]} LIMIT to human AND english.
Outcome:
280 papers found of which 276 were irrelevant or of insufficient quality. The remaining 4 papers are shown in the table.
Relevant Paper(s):
| Study Title | Patient Group | Study type (level of evidence) | Outcomes | Key results | Study Weaknesses |
|---|---|---|---|---|---|
| Small blood samples from ear-lobe puncture. Langlands JH, Wallace WF. 1965, UK. | 14 patients under investigation for pulmonary disease and 2 normal patients. Arterial blood vs capillary blood from ear. |
Diagnostic test | PO2 | Mean difference 0.62 mm Hg (SD 4.1) NS | Small numbers No power calculation Do not know if any patients were suffering from COPD |
| PCO2 | Mean difference 1.05 mm Hg (SD 1.6) NS | ||||
| pH | Mean difference 0.006 (SD 0.01) NS | ||||
| Value of capillary blood gas analysis in the management of acute respiratory distress. Begin R, Racine T, Roy JC. 1975, USA. | 45 patients in acute respiratory distress without circulatory shock. 15 were below age 16. Arterial vs capillary blood from finger. |
Diagnostic test | PO2 | Mean difference 2.1 mm Hg (SD 4.4) r=0.97 | Small numbers No power calculation Do not know if any of these patients were suffering from COPD |
| PCO2 | Mean difference 1.4 mm Hg (SD 3.2) r=0.98 | ||||
| pH | Mean difference 0.006 (SD 0.016) r=0.98 | ||||
| Arterialised earlobe blood gas analysis: an underused technique. Pitkin AD, Roberts CM, Wedzicha JA. 1994, UK. | 40 patients with chronic lung disease and a variety of arterial blood gas tensions. 29 had COPD and bronchiectasis. Arterial blood vs capillary blood from ear. |
Diagnostic test | PO2 | Mean difference 0.17 kPa (CI -1.09 to +0.75) | Small numbers No power claculation Patients suffered from a variety of underlying illnesses. |
| PCO2 | Mean difference 0.21 kPa (CI -0.24 to +0.67) | ||||
| pH | Mean difference 0.007 (CI -0.008 to +0.022) | ||||
| Arterial versus capillary sampling for analysing blood gas pressures. Dar K, Williams T, Aitken R, et al. 1995, UK. | 55 patients requiring measurment of blood gases. 22 had exacerbations of COPD. Arterial vs capillary blood from ear. |
Diagnostic test | PO2 | Mean difference 0.09 kPa (SD 0.59) | Small numbers No power calculation |
| PCO2 | Mean difference 0.01 kPa (SD 0.3) | ||||
| pH | Mean difference 0.007 (SD 0.02) |
Author Commentary:
Different studies have given slightly different results. There have been no statistically significant differences identified. Moreover the differences that have been seen are clinically insignificant as well. Further research in patients with COPD would be useful.
Bottom Line:
Properly taken capillary blood samples accurately reflect arterial blood gas measures of PO2, PCO2 and pH.
References:
- Langlands JH, Wallace WF.. Small blood samples from ear-lobe puncture.
- Begin R, Racine T, Roy JC.. Value of capillary blood gas analysis in the management of acute respiratory distress.
- Pitkin AD, Roberts CM, Wedzicha JA.. Arterialised earlobe blood gas analysis: an underused technique.
- Dar K, Williams T, Aitken R, et al.. Arterial versus capillary sampling for analysing blood gas pressures.