The American Academy of Pediatrics recommends pain control for venipuncture “whenever possible,” and numerous modalities are effective even within the time constraints of the ED.11 Topical anesthetics (e.g., prilocaine, lidocaine, tetracaine) stop sodium transmission, raising the action potential threshold so the fast pain impulse cannot be conducted. All local anesthetics contain hydrophilic and hydrophobic ends, the former being repelled by the oil layer of intact skin. Three common anesthetic formulations that overcome the skin barrier are eutectic mixture of local anesthetics (EMLA) (Astra-Zeneca, Wilmington, DE), LMX-4 (Eloquest, Ferndale, MI), and tetracaine (e.g., Ametop Gel, Smith & Nephew Healthcare, Hull, UK; Synera, Galen US, Inc; Endo Pharmaceuticals, Malvern, PA).12
Eutectic mixture of local anesthetics is the first and most studied topical cream: prilocaine 2.5% and lidocaine 2.5%. Evidence supports reduction of pain with intravenous (IV) catheter insertion when applied for a minimum of 45 minutes.3,8,13 EMLA can be left on up to 4 hours with a depth of penetration up to 6 mm. Numbness lasts an hour after removal. EMLA causes vasoconstriction, which theoretically can decrease venipuncture success but this is contrary to study outcomes. Venipuncture success improves the longer EMLA is in place, up to 92% when left on for 2 to 3 hours.14 Methemoglobinemia is a rare side effect more likely in preterm infants lacking the enzyme necessary for its reduction. Current recommendations limit EMLA to infants of at least 37 weeks gestational age. A purpuric rash of presumed toxic origins has been described in 1% to 2%, particularly in atopic patients.
LMX-4 (previously called ELA-Max) places a 4% lidocaine preparation into liposomes for rapid absorption. Effective in 30 minutes, it works as well as EMLA for venipuncture pain.15 Rapid dissipation of the drug results in diminishing anesthesia approximately 40 to 60 minutes after application. LMX-4 improves cannulation success on the first attempt (74% vs. 55%) when compared with placebo, and lowers time of insertion and pain scores.16 LMX-4 does not require a prescription and does not carry the risk of methemoglobinemia. Several products enhance absorption of LMX-4 to make it more rapidly effective, including ultrasound devices and lasers.
Tetracaine gel, formerly known as amethocaine (Ametop Gel, Smith & Nephew Healthcare, Hull, UK), is available alone and compounded with lidocaine. The 4% formulation works in 30 to 45 minutes, and lasts 4 to 6 hours with an efficacy similar to EMLA.17
For venipuncture, tetracaine and lidocaine mixture (7%/7%) is available in a self-contained patch. Synera® (ZARS Pharma, Salt Lake City, UT) in the United States and Rapydan™ (Souderton, PA) in the European Union are designed to look like a child's bandage and recommended for children aged 3 years and older. The patch contains a heating element that decreases absorption time and causes local vasodilation. This mixture was tested to show good topical anesthesia and pain control when applied for less time than EMLA or placebo.15,18
Lidocaine Devices and Techniques
Iontophoresis uses a low-voltage electrical current to drive the positively charged end of lidocaine through the epidermis. As the current flows to the negative reservoir, lidocaine is carried from the positive side into the skin. The current flow is noxious to some children. Time of application is at a minimum of 10 minutes. In contrast, a simple injection of buffered lidocaine using a small gauge needle prior to venipuncture is rapid and well tolerated.19 Use of this method is inexpensive, depending on bundled hospital charges for the extra supplies.
The J-tip (National Medical Products, Irvine, CA) puts lidocaine under the skin via a jet of compressed carbon dioxide. Studies have found the J-tip less painful for IV cannulation than EMLA cream.20 In addition, this method was found to be most cost-effective compared with other topical agents for IV cannulation.21
COLD SPRAY AND VIBRATION DEVICES
Buzzy® (MMJ Labs, Atlanta, GA), combining cold spray and vibration and placed proximal to the site of cannulation, decreased pain by half compared with cold spray and increased IV success.22 Applying vapocoolant spray (Pain Ease, ethyl chloride, Gebauer, Cleveland, OH) to the penetration site has been used in hospitals for needle sticks but the cold spray may cause veins to shrink making cannulation difficult. Placebo-controlled randomized trials have produced varying results for venipuncture. It may be more effective for children older than 8 years. Cannulation on first attempt was more often successful with the use of vapocoolant spray (85.0%) than with placebo (62.5%) and the number needed to treat to prevent 1 cannulation failure was 5 (95% CI 3–32).23 Figure 13-3 provides an algorithm for balancing optimal pain control with time available.
Options for venipuncture pain (in order of increasing cost).