Geoffrey Barker

Ventilatory predictors of pulmonary hypoplasia in congenital diaphragmatic hernia, confirmed by morphologic assessment

We carried out a prospective study in 66 infants with congenital diaphragmatic hernia within the first 6 hours of life to determine whether outcome is related to the degree of underlying pulmonary hypoplasia, as predicted by preoperative PaCO2, when correlated with an index of ventilation (VI = mean airway pressure X respiratory rate) and confirmed by postmortem analysis of the lung. Those infants with PaCO2 greater than 40 mm Hg before surgery had a 77% mortality; when PaCO2 reduction could be achieved only with VI greater than 1000, the mortality was still greater than 50%. After repair, however, the ability to hyperventilate to PaCO2 less than 40 mm Hg proved to be an important determinant of survival; only one of 31 infants in this group died, whereas only two of 27 infants with PaCO2 greater than 40 mm Hg survived. In 16 infants with PaCO2 greater than 40 mm Hg despite hyperventilation, high-frequency oscillatory ventilation was started. This resulted in a rapid fall in PaCO2, but 14 of the 16 infants had only temporary improvement in oxygenation, and died. In five of the infants who died, alveolar number was assessed by postmortem morphometric analysis; there was a severe reduction to less than 10% of published normal neonatal values. Pulmonary vascular changes of increased muscularization were less remarkable than those observed in infants with persistent pulmonary hypertension. Our findings suggest that the degree of pulmonary hypoplasia (which would not be influenced by surgical repair), rather than the pulmonary vascular abnormality, mainly determines survival. Consideration could therefore be given to an initial nonsurgical approach to congenital diaphragmatic hernia, with the expectation that pulmonary function might improve and pulmonary vascular resistance decrease.

Effect of surgical repair on respiratory mechanics in congenital diaphragmatic hernia

To determine whether surgical repair of congenital diaphragmatic hernia (CHD) results in improvement in respiratory mechanics, we measured respiratory system compliance in nine patients (five survivors and four nonsurvivors) before and after operation. In all nine infants, CHD was diagnosed within 6 hours of life, and surgical repair was through an abdominal approach after a period of stabilization. Measurements were made noninvasively, using the passive expiratory flow-volume technique. In only one of the nine infants did compliance immediately improve after surgical repair, and in another it showed no change. Both of these infants survived, with an uneventful postoperative course. In the remaining seven infants, however, postoperative compliance immediately decreased to 10% to 77% from the preoperative value. The four infants with more than 50% decrease in compliance died with increasing hypoxemia and acidosis. These results suggest that respiratory mechanics in CHD, far from improving, frequently deteriorate as a result of repair of the hernia. The role of urgent surgery in this malformation should be reevaluated.

Congenital diaphragmatic hernia—A tale of two cities: The Toronto experience☆

PURPOSEnThe optimal therapy for congenital diaphragmatic hernia (CDH) is evolving. This study analyzes the results of treatment of CDH in a large tertiary care pediatric center using conventional and high-frequency oscillatory ventilation (HFOV) without extracorporeal membrane oxygenation (ECMO) contrasting these with a parallel study from a similar large urban center using conventional ventilation with ECMO.nnnMETHODSnBetween 1981 and 1994, 223 consecutive neonates who had CDH diagnosed in the first 12 hours of life were referred for treatment before repair. Conventional ventilation was used with conversion to HFOV for refractory hypoxemia or hypercapnia, and a predicted near 100% mortality rate. ECMO was used in only three patients, all of whom died. A retrospective database was collected. Thirty-one clinical variables were tested for their association with the outcome. Common ventilatory and oxygenation indices were tested for their prognostic capability.nnnRESULTSnApgar scores, birth weight, right-sided defects, pneumothorax, total ventilatory time, and the use of high frequency oscillatory ventilation were the only variables associated with outcome. A modified ventilatory index and postductal A-aDo2 were strong prognostic indicators. From 1981 to 1984 surgery was performed on an emergency basis. Since 1985 surgery was deferred until stabilization had been achieved. This resulted in a shift in the mortality from postoperative to preoperative with no change in total survival. HFOV did not alter the overall survival. Results of autopsies performed (70%) showed significant pulmonary hypoplasia and barotrauma as the primary causes of death. The survival was 54.7%.nnnCONCLUSIONnConventional ventilation with HFOV produced equal survival to conventional ventilation with ECMO in two comparable series. Pulmonary hypoplasia was the principle cause of death. This continued high mortality at both centers suggests that new therapies are required to improve outcomes.

Pulse oximetry in pediatric intensive care: Comparison with measured saturations and transcutaneous oxygen tension

We evaluated a new pulse oximeter designed to monitor beat-to-beat arterial oxygen saturation (SaO2) and compared the monitored SaO2 with arterial samples measured by co-oximetry. In 40 critically ill children (112 data sets) with a mean age of 3.9 years (range 1 day to 19 years), SaO2 ranged from 57% to 100%, and PaO2 from 27 to 128 mm Hg, heart rates from 85 to 210 beats per minute, hematocrit from 20% to 67%, and fetal hemoglobin levels from 1.3% to 60%; peripheral temperatures varied between 26.5 degrees and 36.5 degrees C. Linear correlation analysis revealed a good agreement between simultaneous pulse oximeter values and both directly measured SaO2 (r = 0.95) and that calculated from measured arterial PaO2 (r = 0.95). The device detected several otherwise unrecognized drops in SaO2 but failed to function in four patients with poor peripheral perfusion secondary to low cardiac output. Simultaneous measurements with a tcPO2 electrode showed a similarly good correlation with PaO22 (r = 0.91), but the differences between the two measurements were much wider (mean 7.1 +/- 10.3 mm Hg, range -14 to +49 mm Hg) than the differences between pulse oximeter SaO2 and measured SaO2 (1.5% +/- 3.5%, range -7.5% to -9%) and were not predictable. We conclude that pulse oximetry is a reliable and accurate noninvasive device for measuring saturation, which because of its rapid response time may be an important advance in monitoring changes in oxygenation and guiding oxygen therapy.

Gastric-outlet obstruction induced by prostaglandin therapy in neonates

BACKGROUNDnAn infusion of prostaglandin E1 is widely used to maintain patency of the ductus arteriosus in neonates with congenital heart disease. After gastric-outlet obstruction was recognized in several infants who received prostaglandin E1, we studied the association between the drug and this complication.nnnMETHODSnWe evaluated all neonates who received prostaglandin E1 in our hospital between October 1, 1989, and September 30, 1991, for clinical, radiologic, or pathological evidence of acute gastric-outlet obstruction.nnnRESULTSnOf the 74 neonates evaluated, 65 had no signs of gastric obstruction and were considered normal; 5 had clinical and radiologic or pathological evidence of gastric obstruction consistent with the presence of antral mucosal hyperplasia. The remaining four neonates had clinical signs of gastric obstruction, but no radiologic or pathological examinations were performed. The 5 neonates with antral hyperplasia had received prostaglandin E1 for longer periods (mean [+/- SD] duration, 569 +/- 341 hours) than the 65 normal neonates (54 +/- 58 hours, P less than 0.001) or the 4 neonates with clinical signs of gastric obstruction (119 +/- 60 hours, P less than 0.05). The cumulative dose of prostaglandin E1 was higher in the neonates with antral hyperplasia (2982 +/- 1392 micrograms per kilogram of body weight) than in the normal neonates (279 +/- 270 micrograms per kilogram, P less than 0.001) or the neonates with signs of gastric obstruction (528 +/- 306 micrograms per kilogram, P less than 0.01). In two neonates with antral hyperplasia, the cessation of therapy lessened the gastric-outlet obstruction.nnnCONCLUSIONSnThe administration of prostaglandin E1 to neonates can cause gastric-outlet obstruction due to antral hyperplasia. Neonates who receive prostaglandin E1 at recommended doses for more than 120 hours should be closely monitored for evidence of antral hyperplasia.

Intravenous salbutamol in the treatment of status asthmaticus in children.

The management of status asthmaticus using a continuous iv infusion of salbutamol was studied in 14 children with a total of 16 episodes of respiratory failure, unresponsive to conventional bronchodilator therapy. The mean Paco2 at the start of the infusion was 60 ± 6 torr. A loading dose of 1 μg/kg · mm body weight was given over 10 min, followed by an infusion of 0.2 μg/kg · min which was increased in 0.1-μg/kg steps according to response. The maximum dose was 4 μg/kg · min. On 11 (69%) occasions a sustained reduction in Paco2 was achieved within 4 h of starting the infusion. In 5 (11%) instances no reduction in Paco2 was seen and mechanical ventilation was instituted because of increasing respiratory distress and CO2 retention. Mean heart rate during the infusion increased from 161 to 183 beat/min. Comparison with previous data from 30 pediatric patients (40 infusions) receiving iv isoproterenol showed less effect on heart rate and a more sustained fall in Paco2 without the recurrence of bronchospasm. We found salbutamol to be a safe and effective bronchodilator capable of reversing severe bronchospasm in most children who would otherwise require mechanical ventilation. Its greater specificity for beta2-receptors may make it preferable to isoproterenol.

Evaluation of pulmonary function in muscular dystrophy patients requiring spinal surgery

Scoliosis associated with muscular dystrophy frequently necessitates surgical stabilization of the spine. The timing of surgery usually is based on the degree of spinal angulation. Pulmonary function, which deteriorates with age in children with muscular dystrophy, should also be an important consideration in this timing. In a retrospective study of 48 patients who underwent spinal stabilization, preoperative respiratory function tests were correlated with postoperative respiratory complications. The percentage of predicted vital capacity provided the best indicator of outcome and values of <30% were associated with major rtspiratory complications. Spinal fixation failed to arnst the decline in respiratory function in these patients, but it seemed to slow the rate of deterioration compared with preoperative changes. Evaluation of pulmonary function should play a major role in the timing of surgical intervention in muscular dystrophy.

Outcome of children with hematologic malignancy who are admitted to an intensive care unit.

Sixty-four (48%) of 133 children with hematologic malignancy who were admitted to three pediatric ICUs died. Children who required management because of airway obstruction or after general anesthesia had the best outlook (mortality rate of 7% or less); those children who required major circulatory support or mechanical ventilation for hypoxemia did poorly (mortality rate of 84% or greater). Certain conditions in children with hematologic malignancy that require intensive care are associated with a mortality rate of approximately 75%. These include the following: suspected sepsis, interstitial pneumonitis, encephalopathy due to sepsis or hemorrhage. In children with these life-threatening conditions, therapy must be improved because at this stage, the patients do not benefit from admission to the ICU.

Effects of mechanical ventilation on cardiopulmonary function in children after open-heart surgery.

The reduction in functional residual capacity (FRC) after anesthesia and thoracic surgery may result in atelectasis, hypoxia, and respiratory failure. Mechanical ventilation reverses the FRC reduction but may also decrease cardiac output and increase the pulmonary vascular resistance index (PVRI) in some patients.The cardiopulmonary effects of stopping mechanical ventilation after open-heart surgery were studied in 17 children. FRC, arterial pH, and Pao2 were significantly reduced, while Paco2, oxygen consumption, and right ventricular stroke work index significantly increased. Mean FRC on spontaneous respiration was below normal despite continuous positive airway pressure. PVRI increased significantly in patients whose FRC fell below 22 ml/kg on spontaneous respiration. The PVRI increase was most marked in patients with pre-existing pulmonary vascular disease. These results confirm the value of appropriate mechanical ventilation in the early postoperative management of children undergoing open-heart surgery, particularly those with pulmonary vascular disease.

Hemodynamic effects of dobutamine after cardiopulmonary bypass in children.

The synthetic inotropic agent, dobutamine, has reportedly increased cardiac output in adults after cardiopulmonary bypass with minimal side effects. Its use in children, after surgical correction of congenital heart disease, was tested by infusing the drug at 1, 4, 7, and 10 μg/kg min in 11 children. While significant increases in cardiac index above control (23, 23, and 16% at 4, 7, and 10 μg/kg min, respectively) were observed, this was achieved at the expense of significant increases in heart rate (15, 24, and 10%). This increase in heart rate (47% in one child) necessitated discontinuing the infusion in 4 subjects. There were also significant increases in systolic and mean blood pressure with no change in stroke volume or peripheral vascular resistance.The authors conclude that in children, dobutamine is an effective inotropic agent acting principally by stimulating β1-receptors in the myocardium producing a predominantly chronotropic effect without significant changes in peripheral vascular resistance. Given the intrinsically higher heart rate of children, the levels of tachycardia produced by the drug in some instances reach unacceptable levels and as such, may make dobutamine unsuitable for use in children after cardiopulmonary bypass.