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Emerg Med J. 2007 October; 24(10): 723–725.
PMCID: PMC2658444

Effect of warming local anaesthetics on pain of infiltration

Effect of warming local anaesthetics on pain of infiltration

Report by J Sultan, ST1 Accident and Emergency

Checked by Andrew J Curran, Consultant Accident and Emergency

Lancashire Teaching Hospitals NHS Foundation Trust, UK


A short cut review was carried out to establish whether warming local anaesthetic solution reduced the pain of infiltration. A total of 720 papers were found using the reported searches, of which 11 presented the best evidence to answer the clinical question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these best papers are presented in table 22.. It is concluded that warmed local anaesthetic solution is less painful than that at room temperature.

Table thumbnail
Table 2

Three‐part question

In [patients requiring local anaesthetic infiltration] is [infiltration of warmed or room temperature solution] [less painful]?

Clinical scenario

A 40‐year‐old man attends the emergency department, having sustained a 2 cm laceration to his left forearm. There is no tendon/neurovascular damage. He tells you that he has a real phobia of needles and asks if you can make sure it doesn't hurt when you inject the local anaesthetic. You consider saying that that's what the injection is for—but hold yourself back. Afterwards you discuss the matter with a dental colleague who tells you that warming the solution is quite a good way of reducing pain. You outwardly deride his opinion (what do dentists know about pain reduction!) but inwardly wonder whether he might be right.

Search strategy

Medline 1950 to July week 4 2007 using the OVID interface (limited to Humans and English Language): {[ or exp Lidocaine or or or exp Bupivacaine or or exp Prilocaine or or or exp Anesthetics, Local or exp Anesthesia, Local or] AND [ or exp Heat or or hot$.mp. or temperature$.mp. or exp Temperature or exp Body Temperature] AND [pain$.mp. or exp Pain or exp Pain Measurement]}

The Cochrane Library Issue 3 2007: MeSH descriptor Lidocaine explode all trees AND MeSH descriptor Temperature explode trees 2 and 3–61 none relevant.


A total of 720 papers were found, of which only 11 were relevant (table 22).).


Eight papers were double‐blinded and three were single‐blinded. All were randomised trials. All had small sample sizes ranging from 20–45 patients. Apart from two, all studied healthy volunteers; the two studied infiltration of traumatic wounds, and infiltration of facial lesions before excision. Six studied subcutaneous infiltration, three studied intradermal infiltration, one studied dental procedures, and one studied digital nerve blocks. All studied lignocaine except one studying bupivacaine.

The most relevant paper to wound closure in the emergency department was one that studied pain on infiltrating traumatic wounds. It had the largest sample (45 patients), and concluded that warming reduced pain on infiltration (p<0.05). It was, however, single‐blinded and did not determine the exact site or size of the wounds. Five more double‐blinded studies (on healthy volunteers) supported the result that warming reduces pain.

Two papers showed that warming and buffering have a synergistic effect in reducing infiltration pain. Another paper, however, concluded that only buffering reduces pain, and that warming a buffered solution does not reduce the pain any further.

Only one paper included children; however, it looked at pain of local anaesthetic injections in dental procedures, and a topical local anaesthetic was used before injections. It concluded that warming did not reduce the pain of infiltration.

Clinical bottom line

Overall the evidence suggests that warming local anaesthetics, either alone or in combination with buffering, significantly reduces pain of local infiltration.


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