Pulmonary hypertension in infants with bronchopulmonary dysplasia.

Seventeen children with oxygen-dependent bronchopulmonary dysplasia, right ventricular hypertrophy, and Doppler echocardiographic evidence of pulmonary hypertension were studied by cardiac catheterization. Fifteen of these patients had pulmonary hypertension when placed in room air; six of these 15 patients were shown to have large systemic-to-pulmonary collateral vessels. The hemodynamic responses to oxygen and hydralazine were evaluated. Five patients developed normal pulmonary artery pressure while receiving supplemental oxygen and were not studied further. Of the remaining ten patients, the six patients with large, hemodynamically significant collateral vessels all had deleterious reactions to hydralazine. Two of the four patients without collateral pulmonary circulation responded to hydralazine with further reductions in mean pulmonary artery pressure. Five of the ten patients who had persistent pulmonary hypertension while receiving oxygen have died. Cardiac catheterization and angiography may provide important diagnostic, therapeutic, and prognostic information in patients with pulmonary hypertension complicating bronchopulmonary dysplasia.

Ligation of the patent ductus arteriosus in newborn respiratory failure.

Patent ductus arteriosus (PDA) is commonly associated with respiratory disease in newborn infants and may require ligation. Surgical ligation of the PDA can be done in small infants with low operative risk and minimal complications. The outcome of patients after ligation depends primarily on the severity of the underlying pulmonary disease. One hundred fifty-one patients have undergone ligation in an eight-year period at this center. A simplified technique performed in the neonatal intensive care unit with the use of local anesthesia and conventional ventilator management is described.

Percutaneous transluminal angioplasty of congenital coarctation of the aorta.

Two cases of successful dilatation of congenital coarctation of the aorta using the Grüntzig technique are reported. In a 3-week-old boy and an 11-month-old girl, systolic gradients across the narrowed areas were lowered from 50 to 8 mm Hg and from 23 to 8 mm Hg. Although the femoral pulses later disappeared in the younger patient, surgery was avoided. The second patient's gradient has remained minimal for 8 months and no surgery has been performed.

Pseudoaneurysm of the thoracic aorta: a late complication of umbilical artery catheterization.

Pseudoaneurysm of the thoracic aorta developed in an infant eight months following neonatal catheterization of the umbilical artery. Infection and placement of a stiff polyvinyl chloride catheter in the thoracic aorta appear to be the etiological factors. Preoperative diagnosis was posterior mediastinal tumor, and pseudoaneurysm was not included in the differential. Dacron graft patch angioplasty repair using partial cardiopulmonary bypass was successful. Postoperatively the patient has done well with no pressure gradient. Pseudoaneurysm should be suspected whenever a mediastinal mass appears in children who have had thoracic placement of umbilical artery catheters.

An improved method for inducing hypothermia and rewarming.

A hypothermia and rewarming system combining body surface and ventilatory heat exchange is described. The method utilizes body surface heat exchange through conduction, convection, and black body radiation, and ventilatory heat exchange across the lung surface through conduction, convection, and water evaporation. The system consisted of a chamber in which the temperature was maintained at a desired level (+/- 2.5 degrees C) using a refrigeration-heat pump unit. Chamber temperatures during cooling and rewarming were -15.5 +/- 2.7 degrees C and 43.2 +/- 2.3 degrees C, respectively. Inhalate temperatures during cooling were -8.2 +/- 6.5 degrees C and during rewarming they were 41.5 +/- 0.3 degrees C. Helium (100%) was supplied to the chamber, while the animal was ventilated with 20% O2 + 80% He. Under these conditions, the cooling and rewarming rates were 0.33 +/- 0.06 degrees C/min and 0.20 +/- 0.04 degrees C/min, respectively, at 38--21 degrees C. The system provided for rapid cooling and rewarming with no evidence of any untoward effects.

Effect of inhalate thermal conductivity and high O2 in producing hypothermia.

The effect of an increase in inhalate thermal conductivity and the fraction of inspiratory O2 (FIO2) on the rate of cooling and rewarming using a surface-inhalate heat exchange method was evaluated. Male New Zealand White rabbits were divided into three groups: those ventilated with air, those with 20% O2 + 80% He, and those with 100% O2. All animals were cooled to an esophageal temperature of 22.5 degrees C (or for 180 min maximum). Following a 15-min exposure to room air, the animals were connected to the humidifying and warming system. He-O2 had the highest thermal conductivity and the animals ventilated with it had the fastest cooling rate. One hundred percent O2 and room air had similar thermal conductivities, but the animals ventilated with 100% O2 had significantly lower cooling rates. These data indicate that, while maintaining a constant surface heart exchange, the rate of heat exchange across the lung can be modified by altering the thermal conductivity of the inhalate gas mixture. Total heat exchange can also be modified by hyperoxemia-induced hemodynamic changes.

Pulmonary artery pressure monitoring in persistent fetal circulation (PFC).

The use of the Swan-Ganz catheter to monitor pulmonary artery pressure in adults with cardiopulmonary failure has become commonplace. Our meager experience was with four neonates diagnosed as having persistent fetal circulation monitored by the use of this PA catheter. Tolazoline was infused directly into the pulmonary circulation via the catheter. Pulmonary artery pressure was temporarily reduced by tolazoline administration, with a marked increase in PaO2. More experience is required to define the role of the Swan-Ganz catheter in neonatal physiologic monitoring.

Tissue oxygen available as a criterion for the effectiveness of continuous positive pressure breathing.

As little as 3-5 cm H2O increase in proximal airway pressure applied to normal lung reduces cardiac output. It is postulated that decreased pulmonary compliance in respiratory distress syndrome (RDS) acts as a barrier thus offsetting this effect. Since cardiac output is not routinely measured, severe reduction in it could accompany regression of disease while maintaining the same airway pressure. This study was undertaken to determine whether tissue oxygen available (O2a) could be used to detect changes in perfusion during continuous positive pressure breating (CPPB). CPPB was evaluated in 10 normal rabbits (CL = 9.5 +/- 1.8 cc/g at 25 cm H2O) and in 10 pulmonary-damaged rabbits (CL = 5.5 +/- 1.4 cc/g at 25 cm H2O) produced by subjecting them to 100% O2. Airway pressure was increased from 0-15 cm H2O in 3 cm H2O increments at 10-min intervals. O2a and PaO2 were monitored continuously. In the normal group, O2a decreased at 3 cm H2O airway pressure, reaching 22% of control at 12 cm H2O, at which pressure PaO2 decreased. Breathing 100% O2 at this airway pressure increased PaO2 to 408 mm Hg, whereas O2a returned to 45% of control. In the experimental group, O2a decreased at 9 cm H2O airway pressure, at 12 cm H2O it was 36% of control at which pressure PaO2 decreased slightly. Breathing 100% O2 at this airway pressure increased PaO2 to 316 mm Hg, and increased O2a to 200% of control. These data indicate that with excessive airway pressure, muscle hypoxia may exist during systemic hyperoxemia and that a low compliance lung exerts a protective effect on O2a. Since changes in cardiac output during CPPB are compliance dependent, and since O2a is perfusion dependent, tissue oxygen available could provide a means of selecting optimal airway pressure during CPPB.

Electrochemical sensor for continuous transcutaneous PCO2 measurement.

A sensor suitable for continuous transcutaneous PCO2 measurements is described. The sensor consists of an antimony-antimony oxide electrode in combination with a silver-silver chloride reference electrode, bathed in an electrolyte and covered by a Teflon membrane. A servo-controlled heater unit was used to maintain the sensor's temperature and to produce local hyperemia. The resulting oxidation-reduction potential under constant temperature is a linear function of the logarithm PCO2. Response time (95%) to step changes in PCO2 from 27 to 70 mmHg was 2.7 +/- 0.3 min. Following a 12-h "aging" time, the electrode exhibited a minimal drift of 5.2 +/- 2.2 mV for 16 h, representing an average PCO2 drift of 0.5 mmHg/h. This sensor was applied on three rabbits and on five human volunteers, and found satisfactory under normal physiological conditions.

Arterial prosthesis of microporous expanded polytetrafluoroethylene for construction of aorta-pulmonary shunts.

A new arterial prosthesis made of polytetrafluoroethylene (OTFE) was evaluated in 10 infants with complex cyanotic congenital heart disease. All grafts used were 4 mm. in diameter and varied in length from 0.8 to 6 cm. The grafts were anastomosed to the main pulmonary artery or its bifurcation in 8 infants and to the right and left pulmonary arteries in one each. There were two early deaths, one of which was related to shunt failure. The advantages of a shunt to the main pulmonary artery are obvious, and the intraoperative procedure is facilitated with the prosthesis. Follow-up averages 9 months in the 8 survivors, and the patients have nearly doubled their preoperative weight. A shunt murmur is present in each case and the children have mild-to-moderate cyanosis at rest. Repeat aortograms in 2 patients, 8 and 10 months postoperatively, show a smooth graft without luminal narrowing. The aortic oxygen saturations were 73 per cent. The PTFE graft and/or anastomoses will not grow with the growth of the child and therefore may not accommodate growth by increased flow. This may prove to be a limiting factor in its long-term use in fants. We reserve the use of these grafts for infants with complex cyanotic defects undergoing emergency surgery or in older children in whom a conventional shunt is not possible or a previous shunt has failed.

Microporous expanded polytetrafluoroethylene arterial prosthesis for construction of aortopulmonary shunts: experimental and clinical results.

A new microporous, expanded polytetrafluoroethylene arterial prosthesis was evaluated in dogs. The material appears to produce an adequate prosthesis for aortopulmonary anastomosis in animals and can conduct a high rate of blood flow. The graft has been used in 3 patients with pulmonary atresia aged 2 days, 2 months, and 6 months. Thus far all patients are well, growing, and have a loud shunt murmur. The desirable features of this type of anastomosis are presented.

Hypothermia and rewarming by peritoneal dialysis and temperature-controlled inhalate.

In 12 rabbits hypothermia and rewarming were induced with temperature-controlled circulating peritoneal dialysis in combination with temperature-controlled hypoxic and hypercapnic gas mixtures. The average cooling time necessary for the esophageal temperature to decrease from 37.7 degrees +/- 0.7 to 20.6 degrees +/- 1.0 degrees C was 81 +/- 34 minutes with a range of 41 to 150 minutes. The average warming time for esophageal temperature to increase from 20.6 degrees +/- 1.0 degrees C to 35.2 degrees +/- 1.8 degrees C was 90 +/- 35 minutes. Time of cooling was related to the proportions of inspired carbon dioxide and oxygen. In contrast to surface and bypass methods, esophageal and muscular temperatures agreed very closely, suggesting an absence of regional temperature gradients.

Subclavian artery patch angioplasty. Treatment of infants and young children with aorta coarctation.

Repair of thoracic aorta coarctation in infants has had a high recurrence rate in most series. Recurrence is the result of several factors, but the type and growth of anastomosis are of primary importance. Subclavian artery patch angioplasty was used consecutively in eight children under the age of 5 years. There are six long-term survivors who have been observed for an average of 22 months. Body surface area during this time increased from a mean of 0.22 sq m preoperatively to a mean of 0.54 sq m at present. Blood pressure in the arms and legs were recorded at recent examination using an ultrasound pressure recorder. Only one patient had a substantial gradient (30 mm Hg). All survivors are asymptomatic. Use of the subclavian artery appears to allow for growth at the repair site.

Hypothermia and rewarming induced by surface and He-O2 inhalate temperature control.

Hypothermia and rewarming were induced by a combination of temperature-controlled surface and inhalate methods in rabbits. To facilitate respiratory heat exchange, inhalate-respiratory tract temperature and humidity gradients and thermal conductivity were increased. In addition, the upper respiratory tract was bypassed by an endotracheal tube. To aid in maintaining satisfactory circulatory dynamics, hypercapnia and hypoxia were induced. The combined surface and inhalate method produced a markedly more effective rate of cooling than surface temperature-controlled method alone. Animals survived core temperatures as low as 20.9 degrees C with no complications. The noninvasive simplicity of this method suggests its potential applicability in many clinical situations.

Cardiopulmonary changes following 24-36 hours of hyperoxia.

Cardiopulmonary variables were studied in rabbits breathing room air following 24-36 h of 100 percent 0-2 exposure. Initially, arterial pH and P-co-2 remained within normal limits while arterial P-0-2 decreased significantly. Cardiac output and oxygen consumption increased significantly. Static lung compliance was decreased, and histologic examination showed pulmonary hemorrhage, atelectasis, and adema. Myocardial function under these conditions was restored, and the myocardium was able to produce a compensatory increase in cardiac output. Therefore, changes in myocardial function, as related to oxygen toxicity, are reversable phenomena.