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. 1999 Mar 13;318(7185):734.

Arterial blood gases and acid-base balance

Knowledge of bicarbonate concentrations is needed to assess respiratory failure

Peter C Matthews 1
PMCID: PMC1115159  PMID: 10074029

Editor—Williams has not emphasised the importance of looking at the bicarbonate concentration in patients presenting with respiratory failure.1 Depressingly often, intensive care doctors are presented with patients rendered unnecessarily hypoxic by the casualty or medical teams: any patients with a raised arterial carbon dioxide concentration are immediately starved of oxygen in case they stop breathing. The teams should look at the bicarbonate concentration. If it is normal this virtually proves that the respiratory failure is of acute onset, metabolic compensation having not had time to occur; it is then safe to give a high inspired oxygen concentration. If the bicarbonate concentration is abnormally raised this suggests that the patient has long term carbon dioxide retention; then a more cautious approach to oxygen treatment is justified.

References

  • 1.Williams AJ. ABC of oxygen. Assessing and interpreting arterial blood gases and acid-base balance. BMJ. 1998;317:1213–1216. doi: 10.1136/bmj.317.7167.1213. . (31 October.) [DOI] [PMC free article] [PubMed] [Google Scholar]
BMJ. 1999 Mar 13;318(7185):734.

Allen’s test is not routinely used before radial arterial puncture

Adrian Steele 1

Editor—In his article on arterial blood gas analysis Williams repeats the common advice to perform a modified Allen’s test before attempting radial artery puncture.1-1 My impression is that this advice is never carried out in practice, and a survey of anaesthetist colleagues confirmed that none of six specialist registrars and eight consultants (with a combined experience of several thousand radial artery punctures) used the test routinely.

Allen’s test has a poor sensitivity and specificity for complications after radial artery cannulation. In a series of 1699 patients undergoing arterial cannulation for coronary artery surgery, 16 of 411 who had an Allen’s test had abnormal results. None of these 16 had complications from radial arterial cannulation.1-2 Mandel and Dauchot have reported serious complications in 2 of 982 patients who had a normal result of an Allen’s test before radial arterial cannulation.1-3

The available evidence does not support the routine use of Allen’s test before radial artery puncture. Nevertheless, because of the rare incidence of serious complications, common sense suggests that all patients should have regular clinical observation of their hand and finger blood supply after arterial puncture or cannulation.

References

  • 1-1.Williams AJ. ABC of oxygen. Assessing and interpreting arterial blood gases and acid-base balance. BMJ. 1998;317:1213–1216. doi: 10.1136/bmj.317.7167.1213. . (31 October.) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 1-2.Slogoff S, Keats AS, Arlund C. On the safety of radial artery cannulation. Anesthesiology. 1983;59:42–47. doi: 10.1097/00000542-198307000-00008. [DOI] [PubMed] [Google Scholar]
  • 1-3.Mandel MA, Dauchot PJ. Radial artery cannulation in 1000 patients: precautions and complications. J Hand Surg. 1977;2:482–485. doi: 10.1016/s0363-5023(77)80030-0. [DOI] [PubMed] [Google Scholar]

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