The Journal of Thoracic and Cardiovascular Surgery, Vol 93, 647-657, Copyright © 1987 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Nitroprusside abolishes the deleterious effects of surface cooling- induced hypothermia on immature pigs with ventricular septal defects
JP Gott, S Cox and C Mavroudis
The efficacy of systemic hypothermia in combination with cardiopulmonary
bypass for the repair of congenital cardiac malformations is established.
Surface cooling in infants with ventricular septal defects as a prebypass
adjunct has been associated with visceral ischemic complications. Surface
cooling in infant pigs with ventricular septal defects results in increased
systemic vascular resistance and unchanged pulmonary vascular resistance
with increased left-to-right shunting and a maldistribution of blood flow
away from the viscera and kidneys. This study was to determine whether
nitroprusside ameliorates the deleterious effects of increased systemic
vascular resistance during hypothermia in infant pigs with ventricular
septal defects. Nine neonatal pigs (4 weeks, 4 kg) had experimental
ventricular septal defects resulting in a 2.3 +/- 0.3: 1 shunt. Systemic
and pulmonary vascular resistances were determined by the flow probe and
microsphere techniques. Systemic and pulmonary blood flow distributions
were measured by the microsphere technique. Left-to-right shunt ratios were
determined by oximetry, flow probe, and microsphere. The pigs were cooled
to 28 degrees C and measurements were made at 37 degrees, 32 degrees, and
28 degrees C. We found that nitroprusside abolishes the deleterious effects
of surface cooling by blocking the rise of systemic vascular resistance
without significant changes in aortic pressure. As a result, the animals
maintained control pulmonary- to-systemic flow levels and maintained
control levels of oxygen delivery while showing a decline in oxygen
consumption. Additionally, the vasodilatory effect allowed the animals to
cool twice as fast as animals without nitroprusside. Regional blood flow
distribution as percent cardiac output and absolute tissue flow were
protected during surface cooling. This technique may have a role in cardiac
operations on infants with left-to-right shunts.
