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Three Part Question

In [patients who require non-urgent arterial blood gas analysis] does [topical anesthetic] reduce [pain and discomfort]?

Clinical Scenario

A 56 year old man presents to the emergency department with a 2 day history of pleuritic chest pain and shortness of breath. Pulse oximetry reveals oxygen saturations of 92%, although he does not appear to be acutely short of breath. The patient has had routine blood samples sent to the laboratory but is hesitant to agree to any other blood tests. You wonder therefore, if prior to taking an arterial blood gas sample, application of a topical local anesthetic, would reduce pain and discomfort.

Search Strategy

Medline 1966-12/04 using the OVID interface.
[(exp lidocaine OR lidocaine.mp OR exp topical, administration OR exp anesthetics, local OR exp anesthesia, local OR emla.mp OR ametop.mp OR tetracaine OR lignocaine.mp OR prilocaine OR amethocaine.mp) AND (exp arterial puncture.mp OR exp blood gas analysis OR exp blood specimen collection OR arterial blood.mp) NOT (BestBETs paediatric filter)] LIMIT to English language AND human

Search Outcome

Altogether 431 papers were identified of which 429 were found not to answer the question directly, the remaining 2 papers were found to be relevant.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Tran NQ et al, 2002, Australia	Topical use of 4% amethocaine gel applied for 30 mins prior to arterial puncture for blood gas analysis 81 adult patients. 42 recieved amethocaine gel and 39 received a placebo gel	RCT	Primary outcome was pain experienced (measured on a visual analogue scale, 0-100)	Amethocaine group-mean score 16.0 (SD 23.3).Placebo group-mean score 20.7 (SD 18.5)	Amethocaine can cause blanching to the skin, which may affect blinding by introducing bias, though this was not commented on in the paper as one of the reported side effects Women of "child bearing potential" were excluded from the study. Does this mean that all pre-menopausal women were not included, and if so why?
			Number of passes through the skin	These differences were not statistically significant
			Heart rate before, during and after arterial puncture	These differences were not statistically significant
			Side effects of the gel	Small number of minor irritations reported in both groups
Aaron SD et al, 2003 Canada	Fifty patients randomised, 24 to recieve tetracaine and 26 placebo, 45 minutes prior to elective radial arterial puncture.	RCT	Patient's perception of pain (visual analogue scale, 0-100).	Tetracaine group-mean score 26.2+/-32.6 The placebo group-mean score 23.8+/-27.4 (P=0.78)
			Mean time from skin puncture to procurement of 1ml of arterial blood.	Tetracaine group-mean time 70+/-103 seconds. Placebo group-mean time 49+/-48 seconds. (P=0.40)
			Difficulty performing the test (graded scale).	Identical for both groups (P=0.86).

Comment(s)

Previous studies looking at the use of EMLA in pain reduction with venepuncture have highlighted that an application time of 60-90 minutes is necessary for adequate anaesthesia; the manufacturers of tetracaine recommend 45mins application prior to venepuncture. It may be necessary that longer application times are needed for deeper structures.

Clinical Bottom Line

The papers found in this search provide little evidence for the effectiveness of topical analgesia in reducing the pain and discomfort of arterial puncture. Further studies with longer application times would be useful.

References

1. Tran NQ, Pretto JJ, Worsnop CJ. A randomized trial of the effectiveness of topical amethocaine in reducing pain during arterial puncture. Chest 2002;122(4):1357-60.
2. Aaron SD, Vandemheen KL, Sheila NA et al. Topical tetracaine prior to arterial puncture: a randomized, placebo-controlled trial. Respiratory Medicine 2003;97:1195-1199.