Warming Prior to Heel Stick: Blood Sample Quality and Infant Comfort—A Randomized Controlled Trial

BACKGROUND: Capillary blood sampling (heel stick) in infants is commonly performed in neonatal care units. Before the procedure, warming the infant's heel is often a customary practice, but no consensus exists on the most effective heel-warming method. PURPOSE: To compare the effects of routinely used warming methods (glove, gel pack, or blanket) applied prior to heel stick on blood sample quality and infant's comfort. METHODS: This prospective, double-blind, randomized controlled trial conducted in the neonatal intensive care unit included infants (postmenstrual age of ≥28 + 0 weeks and ≤43 + 6 weeks) who were computer-randomized to 1 of 3 warming methods. The primary outcome was blood flow velocity at sampling. Secondary outcomes were hemolysis index, infant COMFORTneo score, and frequency of postprocedure skin injuries. In addition, irrespective of the warming method used, the correlation between heel skin temperature and postprocedure heel skin injury was analyzed. RESULTS: A total of 176 heel warmings were successfully randomized, and 173 were analyzed. Despite a significant difference in obtained heel skin temperature after warming between the 3 warming methods (P = .001), no difference in blood flow velocity (P = .91), hemolysis index (P = .99), or COMFORTneo score (P = .76) was found. Baseline skin temperatures above 37.0°C were associated with higher incidences of skin injury, and skin temperatures after warming were significantly higher in skin-injured heels (P = .038). IMPLICATIONS FOR PRACTICE AND RESEARCH: All 3 warming methods had similar effects on blood sample quality and infant's comfort. However, excessive warming of the heel should be avoided to prevent skin injuries.