ABSTRACT
BACKGROUND: The pain of venous puncture for the cannulation of peripheral veins is disturbing to many patients. This is the first clinical trial of the efficacy of local anesthesia in comparison to placebo (no pretreatment) in a control group, as a function of the size of the cannula. METHODS: A randomized, controlled trial of fully factorial design was performed to study pain during venipuncture after local anesthesia either with intra - dermally injected lidocaine or with a vapocoolant spray, in comparison to placebo. A standardized protocol was used for structured communication with the patient to provide the greatest feasible degree of patient blinding (trial registration number DRKS00010155). The primary endpoints were the subjective discomfort of the patient during preparation and puncture of a vein of the dorsum of the hand, assessed on a numerical rating scale (NRS) from 0 (no discomfort) to 10 (unbearable discomfort), and the rate of unsuccessful puncture. RESULTS: The intention-to-treat analysis of all 450 patients revealed that the reported degree of pain during venipuncture depended to a large extent on the caliber of the chosen venous cannula. For a 17-gauge (17G) cannula, both the vapocoolant spray (NRS = 2.6 ± 1.3) and lidocaine (NRS = 3.5 ± 2.2) lessened the discomfort due to venipuncture compared to control treatment (5.0 ± 1.5). The effect of vapocoolant spray compared to the control was both clinically relevant and statistically significant (p < 0.0001). When a smaller 20G cannula was used, however, vapocoolant spray improved discomfort by only 0.8 NRS points, which, though still statistically significant (p = 0.0056), was no longer clinically relevant. The rate of unsuccessful puncture was higher after lidocaine pretreatment (12.7%) than after either vapocoolant spray (4.7%; p = 0.0066) or no pretreatment (4.0%; p = 0.0014). CONCLUSION: Local anesthesia can be recommended before venipuncture only if a large cannula is used (e.g., ≥ 17G). Vapocoolant spray may be at least as useful as lidocaine injection; it prevents pain to a similar extent and is associated with a lower rate of unsuccessful puncture.
