Theye, Richard A.

Measurements were made of O2 uptake, CO2 output and CO2 tension of arterial and mixed venous blood and expired alveolar gas in 28 anesthetized and paralyzed dogs ventilated with air at a constant rate. Retention of CO2 was not observed in the lateral decubitus position with either closed or open thorax. Induction of open pneumothorax resulted in an unexplained metabolic alteration characterized by an increase in O2 uptake and CO2 elimination and a decrease in plasma buffer base. Small amounts of CO2 were eliminated from exposed pleura. The left pulmonary artery was occluded (after left thoracotomy) and 1 hour later the left bronchus also was occluded—or the order was reversed. CO2 retention of major degree was observed after initial occlusion of the artery and retention of minor degree after occlusion of the bronchus. During the 2nd hour (after additional occlusion) the previously retained CO2 was eliminated. The results suggest that the ventilatory requirements are not influenced specifically by effects of lateral position, open pneumothorax, or small right-to-left shunts, but rather are determined to a large degree by the metabolic production of CO2 and the degree to which ventilation is distributed to perfused alveoli. Submitted on December 3, 1958

The distribution of tidal air and nonshunted blood flow to each lung, the elimination of CO2 from each lung, and Paco2 were measured in ten anesthetized and paralyzed dogs during intermittent positive-pressure breathing in the supine position and before and after thoracotomy in the lateral decubitus position. Ventilation via a divided tracheal airway (Wright-Lategola) at a constant rate and a constant volume (±5%) with 65% oxygen in nitrogen was provided by a Bird ventilator. Reduction of total CO2 elimination and increase of ratio of total physiologic dead space to tidal volume were observed after thoracotomy. Mean percentages of total ventilation and blood flow to, and CO2 elimination from, the right lung were about 58% in the supine position. When the right or left lung became dependent in the lateral decubitus position, its proportional ventilation and CO2 elimination decreased. After thoracotomy was made on the superior nondependent side, further reductions were noted and blood flow to the dependent lung also decreased. Proportional CO2 elimination was more dependent on alveolar ventilation than on the ratio of ventilation to perfusion.

Cardiac output and related variables were measured in patients after open intracardiac surgery. Factors affecting cardiac performance during this period were the original anatomic lesions, the details of the operative procedure, ventricular-outflow resistance, transfusion of blood, the stage of convalescence, and digitalis. In postoperative patients, metabolic rate, level of hemoglobin, and level of oxygen in arterial blood varied more widely and acutely than in nonsurgical patients, resulting in a less predictable relation between cardiac output and oxygen saturation of mixed venous blood. Therapeutic applications of these observations were discussed.

Physiologic studies have been carried out during the first 3 days after intracardiac repair of tetralogy of Fallot. All patients survived. The ratio between systolic pressure in right ventricle and a systemic artery was 0.7 or less in all cases and did not vary significantly during the period of study. Residual left-to-right shunts of moderate degree were demonstrated in three patients (repaired with Teflon prostheses). In one of these three, no definite evidence of shunt could be found 2 weeks after operation. Additional abnormal circulatory pathways exist in these patients. Clear evidence was obtained of left-to-right shunting through aorticopulmonary collateral connections in one case. Systemic index was usually below normal or in the low normal range. It was usually lower on the second and third postoperative days than on the first postoperative day. Left atrial pressure was sometimes strikingly higher than right atrial pressure 30 minutes after repair, but not thereafter. Pulmonary vascular resistance was normal or slightly elevated. Gas exchange and management were adequate to maintain normal or near normal oxygen and carbon dioxide levels in arterial blood. Mild metabolic acidosis existed on the first 2 days, but had generally cleared by the third day. The implications of these data are discussed relative to ventricular function and performance, adequacy and technic of surgical repair, administration of blood after operation, and the state of preparedness in the lung and left ventricle in patients with tetralogy of Fallot.

Sixteen patients were studied immediately and for 3 days following surgical closure of ventricular septal defect. In eight patients with absent or mild pulmonary vascular disease, convalescence was uneventful and only small deviations from normal in cardiac output, blood gas levels, and acid-base profile were observed. The remaining eight patients had pre-existing moderate or severe pulmonary vascular disease. Values for cardiac output were abnormally low at some time in the postoperative period in all but two of these eight patients. Failure to survive was clearly related to a low cardiac output in four of the five nonsurvivors. Reduction in cardiac output observed in this group of patients is believed to be based in major part on the pre-existing increased resistance to blood flow through the pulmonary vascular bed and also to impaired right ventricular function following operation. No evidence was obtained to suggest that major changes in pulmonary vascular resistance occurred in the immediate postoperative period in patients with moderate or severe pulmonary vascular disease following closure of ventricular septal defect. Right ventricular function following atriotomy or transverse ventriculotomy was less impaired than after vertical ventriculotomy.

Physiologic observations were made on eight patients following repair of atrial septal defect or total anomalous pulmonary venous connection. A pattern of changes in cardiac output and atrial pressures during the first 3 postoperative days was noted. Cardiac output was abnormally low in some patients with obstructive pulmonary vascular disease or low atrial pressures. Transfusion of whole blood was effective in elevating cardiac output in the operating room and after operation. Left atrial pressure was higher than right atrial pressure in the operating room. Postoperatively left and right atrial pressures tended to become equal in some patients, and the levels were slightly elevated. Heart rate did not seem to be directly related to cardiac output. Ventilation was adequate with regard to elimination of carbon dioxide. Arterial oxygen saturation was maintained at 93 per cent or more by the use of oxygen-enriched mixtures. The difference in arteriovenous oxygen content was inversely related to cardiac output. Acidemia was present 2 to 4 hours after operation, but in general the pH of arterial blood had returned to normal by day 2. Some mechanisms possibly related to the observations are discussed.