Mp. Preziosi et al., METABOLIC ACIDEMIA WITH HYPOXIA ATTENUATES THE HEMODYNAMIC-RESPONSES TO EPINEPHRINE DURING RESUSCITATION IN LAMBS, Critical care medicine, 21(12), 1993, pp. 1901-1907
Objective: To examine the effects of metabolic acidemia and hypoxia on
the hemodynamic responses to epinephrine in an intact neonatal animal
model. Design: Multi-experiment, randomized, controlled trial. Settin
g: Animal research laboratory of a university hospital. Subjects: Sixt
een lambs, ranging in age hom 2 to 14 days. Interventions: The lambs w
ere chronically catheterized; the ductus arteriosus was ligated; and a
pulmonary arterial flow probe was inserted to measure cardiac output,
blood pressure (BP), and heart rate. In the first protocol, hemodynam
ic responses to epinephrine during pure metabolic acidemia or metaboli
c alkalosis were studied in eight lambs. Each lamb was studied on four
different days at a different arterial pH: 6.9, 7.1, 7.4, and 7.6. Ve
ntilation was controlled to maintain Pco(2) at 35 to 45 torr(4.66 to 5
.99 kPa). Acidemia was induced by the infusion of lactic acid and alka
losis by the infusion of sodium bicarbonate. When the appropriate arte
rial pH was achieved, 10 mu g/kg of epinephrine was administered intra
venously. In a second protocol, hemodynamic responses to epinephrine d
uring metabolic acidemia or alkalosis plus hypoxia were studied in eig
ht lambs. When the appropriate arterial pH was achieved, hypoxia was i
nduced until cardiac output decreased to 40% of baseline. Epinephrine
bolus was given, and after 90 secs, the lambs were resuscitated with o
xygen. Measurements and Main Results: Epinephrine administered during
uncompromised hemodynamics led to hypertension, bradycardia, and decre
ased cardiac output that were unaffected by arterial pH values between
6.9 and 7.6. Acidemia with hypoxia compromised hemodynamics with decr
eases in heart rate and cardiac output. Epinephrine administered durin
g this compromised condition did not improve cardiac output, heart rat
e, or BP before resuscitation with oxygen at any arterial pH studied.
Resuscitation with epinephrine and oxygen during hemodynamically compr
omised states led to increases in heart rate, BP, sued cardiac output
with significant attenuation of these hemodynamic responses during met
abolic acidemia at pH values of 6.9 and 7.1.