You are caring for a 3 year old with vomitting and diarrhea. The child's pulses are palpable but faint, and the child is now lethargic. The HR is variable (range, 44/min to 62/min). You begin bag-mask ventilation with 100% oxygen. When the HR does not improve, you begin chest comnpressions. The rhythm shown here is seen on the cardiac monitor (bradycardia). ____________would be the most appropriate therapy to consider next