Intramuscular atropine sulfate in children: comparison of injection sites

In children undergoing inhaled induction of anesthesia with halothane who suffer bradycardia, submental glossal injection of atropine may result in more rapid onset of vagolysis than traditional intramuscular sites. We compared the intervals between injection and onset of heart rate acceleration (tHR increases) after intramuscular injection of atropine into the deltoid, vastus lateralis, and glossa in children between 1 mo and 10 yr of age scheduled for elective surgery. The tHR increases was determined by measuring the interval between atropine injection and the time point at which the slope of the heart rate curve initially became positive. To ensure that the drug had taken effect before surgical stimulation, heart rate observation was continued until it increased at least 5% above baseline with evidence of continuing acceleration. Anesthesia was induced in all subjects by mask with nitrous oxide and halothane. After tracheal intubation, constant inspired concentrations of the anesthetics were administered for 3 min. While heart rate was monitored, atropine (0.02 mg/kg) was injected into one of the three sites. Each patient's end-tidal anesthetic concentrations were recorded, and minimum alveolar anesthetic concentrations (MAC) were subsequently calculated and adjusted for age. The tHR increases was recorded and averaged for each group. The study groups did not differ by age, weight, end-tidal anesthetic concentrations, age-adjusted MAC, or heart rate at the time atropine was administered. After submental glossal injection (n = 11), tHR increases increase was fastest (3.0 +/- 1.1 min) and was significantly faster than that found with deltoid injection (n = 16; 4.4 +/- 1.1 min) or vastus lateralis injection (n = 8; 6.4 +/- 2.4 min) (P < 0.05 compared with both). The tHR increases also differed significantly between the deltoid and the vastus lateralis (P < 0.05). We conclude that submental glossal injection of atropine results in a more rapid onset of vagolysis than injection at traditional intramuscular sites.