Recovery of cardiovascular function in newborn lambs after thoracotomy

Knowledge of the quality and speed of recovery after thoracotomy is crucial for studies of the early changes in cardiovascular function in the neonatal period. We studied the early recovery period after thoracotomy with pericardiotomy, but without ventriculotomy, in 21 lambs operated on between 2-24 days after birth. In 15 lambs, we measured resting pH,, PaO2, PaCO2, O2 consumption, cardiac output, heart rate, and aortic and pulmonary arterial pressures, before and after thoracotomy, daily for 1 wk. We found that, except for PaO2 (82 versus 87 torr), all variables returned to normal by the third day after thoracotomy. Four lambs were exposed to hypoxia (FIO2 0.09 for 1 h) before and 3 days after thoracotomy; hypoxia-induced changes were not different at the two different periods. Six other lambs, undergoing thoracotomy within the first 3 days after birth and exposed to hypoxia on the third postoperative day, had hypoxia-induced responses similar to six age-matched nonthoracotomized lambs. These findings indicate recovery of cardiovascular function by 48-72 h after thoracotomy. We believe, therefore, that reliable studies of the circulation in lambs are possible as early as 3-4 days after birth, even if thoracotomy is required for making measurements.