EFFECT OF ATKOPINE ON THE RESPONSE OF NEWBORN LAMBS TO MASSIVE HEMORRHAGE

Top of pageAbstract We studied 30 spontaneously breathing newborn lambs who were bled to 50% their blood volume(measured with CsCl labeled red blood cells) in 30 min. time. In each case heart rate, blood pressure, pH, blood gases, hematocrit and coloidoncotic pressure were determined. Cardiac output (CO) and organ blood flow(Q) were determined by microsphere method. No volume was re--infused. In 19 lambs (Group I) there was severe hypotension and bradycardia at 20 min. during hemorrhage (HEM). Miocardic blood flow(QM) changed with changes in blood pressure, falling to 40% of baseline values. Eight lambs survived(Pediat.Res. 17:70-76, 83). In 6 lambs, atropine(0.2mg/Kg) was administered twice before and 3 times during HEM, every 10min. None developed bradycardia. Decreases in blood pressure and CO were similar to those observed in Group I. QM only decreased by 7%, Cerebral Q remained stable as in survivors from Group I. All 6 lambs survived. In 5 lambs, atropine was only administered during HEM, when bradycardia and hypotension had already developed. Brady oould not be reverted by repeating atropine or by increasing doses (0.4mg/Kg). Two lambs survived. We conclude that unanesthetized newborn lambs develop bradycardia during HEM. Bradycardia can be prevented by administering atropine before and during HEM. This treatment modifies physiologic responses especially QM. However, atropine cannot revert bradycardia once it has developed. This suggests that there are probably other issues involved in HEM induced bradycardia, other than vagal stimulation.