Does using heat with eutectic mixture of local anesthetic cream shorten analgesic onset time? A randomized,...

We determine whether the addition of heat to topical eutectic mixture of local anesthetic (EMLA) cream shortens the onset time to effective analgesia. We hypothesized that applying EMLA cream for 20 minutes with an external heat pack would be as effective as the standard 60-minute application time.

In this prospective, double-blind study using adult volunteers, research subjects were randomized into groups undergoing either 20 minutes or 60 minutes of EMLA cream application time. Each research subject underwent randomized cream application over both hands and wrists in the following manner: EMLA cream with heat, EMLA cream without heat, placebo with heat, and placebo without heat. Research subjects then underwent a single attempt at intravenous catheterization over each of the 4 sites and scored the degree of pain using a 100-mm visual analog scale.

Seventy-six research subjects were enrolled: 39 were randomized to the 20-minute group, and 37 were randomized to the 60-minute group. EMLA cream applied for 20 minutes with heat (adjusted mean visual analog scale score of 31.9 mm) provided statistically and clinically significantly greater analgesia compared with that seen in the placebo groups with or without heat (46.6 and 46.1 mm, respectively), with estimated differences of -14.6 (95% confidence interval [CI] -21.2 to -8.1) and -14.1 (95% CI -20.8 to -7.3), respectively. However, applying EMLA cream for 60 minutes without heat (16.6 mm) provided better analgesia compared with that seen after 20 minutes of EMLA cream with heat (31.9 mm; estimated difference of -15.4 [95% CI -25.1 to -5.6]).

Applying EMLA cream for 20 minutes with heat provides intermediate analgesia for intravenous catheter placement, although 60 minutes of application time remains superior.