The cyanotic infant--heart disease or lung disease

Pulse oximetry in neonates at high altitudes: a modified Colorado protocol

Pulse oximetry for detecting critical CHD produces more false positive tests at high altitudes than at sea level, because at altitude the average resting saturation is lower and the variability is higher. This increases diagnostic difficulties, especially in small isolated communities without paediatric echocardio-graphy, and requires expensive transport to a regional medical centre. One way of reducing diagnostic errors is to measure arterial oxygen saturation while the infant is breathing 100% oxygen. In the absence of right-to-left shunting through the heart, the ductus, or the lungs, arterial oxygen tension will exceed 150 mmHg and arterial oxygen saturation will be 100%. With right-to-left shunting, arterial oxygen tension will be <100 mmHg, and thus <96% (usually much lower).

False negative diagnoses of critical congenital heart disease with screening neonatal pulse oximetry

BACKGROUND

False negative pulse oximeter results occur in new born infants with critical congenital heart disease who have an oximeter saturation ≥95%. Some of these infants have abnormal physical findings but others do not.

OBJECTIVES

To determine the causes of false negative results.

METHODS

Mathematical analysis of determinants of arterial oxygen saturation and discussion of oximeter bias.

RESULTS

False negative oximeter results are not rare; the sensitivity of pulse oximetry screening for critical congenital heart disease is about 80%. The high saturation may be due to a very small right-to-left shunt at the time of study, a relatively high cardiac output and mixed venous saturation, or to positive bias in oximeter readings. It may also be due to some critical congenital heart lesions that do not show desaturation at the time of testing.

CONCLUSIONS

A diagnosis of a normal heart based on a negative oximeter test is presumptive, and requires careful follow-up for 1-2 weeks after birth.

Refractory neonatal hypoxemia: diagnostic evaluation and pharmacologic management

Hypoxemia refractory to oxygen administration and assisted ventilation is found in many clinical conditions and results from a variety of pathophysiologic disorders. Recent clinical and laboratory experience has demonstrated that the choice of therapy for an infant with refractory hypoxemia depends upon identification of the underlying etiologic and pathophysiologic conditions. The ideal therapies for many of these conditions have not yet been defined. We have provided, based on our experience, guidelines for selection of the most appropriate of the currently available therapies for many of these patients.

A practical approach to diagnosis and immediate care of the cyanotic neonate. Stabilization and preparation for transfer to level III nursery

The diagnostic and therapeutic strategies described above have been presented sequentially for the sake of clarity, but in practice should be performed as quickly as possible in any infant who remains cyanotic despite receiving 100% oxygen. The practitioner must proceed with emergent stabilization of the infant with specific therapies for identified problems and nonspecific therapies for suspected problems, recognizing that the coexistence of two or more pathophysiologic entities is not uncommon. By the time of transport, the practitioner may have laid the groundwork for further diagnostic procedures and therapies by having already classified the infant into one of four primary pathophysiologic categories, as outlined in Table 4. Although congenital heart disease may be highly suspected, confirmation may not be possible without echocardiography. The practitioner, however, should not be discouraged by failure to achieve a specific etiologic diagnosis, despite careful analysis of all the information obtained from diagnostic evaluations prior to transport. Hypoxemia refractory to oxygen administration and assisted ventilation is found in many clinical conditions and results from a variety of pathophysiological disorders. The pediatrician caring for such an infant has primary responsibility for stabilization and preparation for transport of the infant to a Level III facility, and for communicating information about diagnostic procedures and therapeutic maneuvers that might facilitate extended resuscitative efforts by the neonatologist accepting responsibility for the transport and subsequent care of the infant.

Influence of lipid infusion (0.4 g/kg/hr) and positive end expiratory pressure (8 cm H2O) on pulmonary function and hemodynamics in healthy anesthetized pigs

Fat emulsions are used increasingly for parenteral nutrition in premature infants suffering from various disorders, including respiratory insufficiency necessitating artificial ventilation with positive end expiratory pressure (PEEP). Both PEEP and lipid infusions (LI) may alter pulmonary hemodynamics. The simultaneous effect of LI and PEEP were therefore investigated. Five adult anesthetized Göttinger minipigs were infused with a 20% LI at a high rate of 0.4 g/kg/hr for 30 min, followed by PEEP of 8 cm H2O for 15 min. Catheters were inserted into the upper vena cava, the pulmonary artery, the right and left atrium, and the aorta, and pressures recorded continuously. Ventilation volume, respiratory fractional gas concentrations of O2 and CO2 (mass spectrometer), and blood gases were measured. The following parameters were calculated: total peripheral resistance, pulmonary arteriolar resistance, right-to-left shunt (QS/QT) dead space ventilation (VD/VT) and effective compliance. Total peripheral resistance remained unchanged. Pulmonary arteriolar resistance increased significantly during PEEP, PEEP + LI, but not during LI alone. QS/QT increased significantly during LI and returned to normal when PEEP was applied. VD/VT and effective compliance did not change during LI. The increased right to left shunt, caused by LI, is reduced by means of PEEP, while the pulmonary arteriolar resistance increased with PEEP and LI.

Continuous positive airway pressure: modes of action in relation to clinical applications

Some physical effects of CPAP are discussed, as are the various devices used for CPAP in infants. Some of the controversies about CPAP may be related to the unsuitability of certain techniques. Use in hyaline membrane disease, extrathoracic and intrathoracic airway obstruction, congestion of overperfusion of the lungs in diseases of the heart and great vessels, apnea repetens of immaturity, and phrenic nerve palsy is presented.

Usefulness of continuous positive airway pressure in differential diagnosis of cardiac from pulmonary cyanosis in newborn infants

Differential diagnosis of cyanosis in the neonate is difficult and cardiac catheterisation may be required for a correct diagnosis. It has been suggested that the response of PaO2 to continuous positive airway pressure (CPAP) with 100% oxygen may be useful. The purpose of this study was to test further this hypothesis by studying all neonates investigated for cyanosis with a PaO2 less than or equal to 50 torr in 0-8 to 1-0 F1O2. Arterial blood samples were obtained in an F1O2 of 0-21-0-4 and 0-8-1-0, and in an F1O2 of 0-8-1-0 with 8-10 cm CPAP, and were analysed for PaO2, PaCO2, and pH, bicarbonate being calculated. The final diagnoses were congenital heart disease (CHD) 21 cases, pulmonary parenchymal disease (PD) 10 cases, and persistent fetal circulation (PFC) 3 cases. No significant difference in pH, bicarbonate, or PaCO2 was observed among the three groups or with CPAP. In the CHD and PFC infants CPAP produced no significant change in PaO2. In the PD babies PaO2 increased by an average of 33 torr (P less than 0-05). Despite thus attaining statistical significance 2 PD infants had no increase in PaO2 with CPAP. An increase of PaO2 greater than 10 torr with CPAP suggests PD, and a nonsignificant increase in PaO2 does not rule out PD. Irrespective of initial PaO2, final PaO2 in 0-8-1-0 F1O2 with CPAP greater than 50 torr suggests PD, and less than 50 torr suggests CHD. The results indicate that CPAP may be used as an adjunct in differentiating cardiac from pulmonary disease.

Increased hypoxemia in neonates secondary to the use of continuous positive airway pressure

Five neonates are presented who, while receiving continuous transpulmonary pressure, developed increased systemic arterial hypoxemia, which was relieved when this therapeutic modality was decreased or discontinued. Three of the five had chest radiographs consistent with hyaline membrane disease: the other two had atypical radiographs. None had evidence of air leaks. Levels of positive airway pressure utilized when the hypoxemia was noted ranged from 5 to 15 cm H2O. Calculated shunt fractions (Qs/Qt) improved from a mean of 73% to 37% when the continuous positive airway pressure was lowered. The site of shunting in these infants could have been in the lung or through anatomic extrapulmonary shunts. Improvement in total cardiac output may also have contributed to the improved oxygenation. This paradoxical effect of continuous transpulmonary pressure appears to be mediated through changes in the pulmonary vascular resistance brought about by the continuous transpulmonary pressure.

Arterial oxygen tension and response to oxygen breathing in differential diagnosis of congenital heart disease in infancy

Arterial oxygen tension was measured from radial artery samples in 276 infants referred for cardiological investigation. Values obtained during air breathing in infants with congenital heart disease showed considerable overlap between 'cyanotic' and 'acyanotic' groups, and are of limited diagnostic use. By contrast, values obtained while breathing oxygen in concentrations of over 80%, measured in 182 infants, allowed clear differentiation between these groups. All infants with acyanotic, but only 2 of 109 with cyanotic lesions, achieved an arterial oxygen tension of more than 150 mmHg. In the cyanotic group the response to oxygen breathing was significantly greater in common mixing situations and in the hypoplastic left heart syndrome than with either pulmonary outflow tract obstruction or transposition of the great arteries. Infants with transposition had a significantly lower mean arterial oxygen tension in air than infants with other forms of cyanotic congenital heart disease. Of 23 infants whose final diagnosis was primary lung disease but in whom cyanotic congenital heart disease had been suspected, 7 achieved arterial oxygen tensions of more than 150 mmHg during oxygen breathing, and on this basis cardiac catheterization was not performed. We therefore conclude that measurement of the arterial oxygen tension while breathing high concentrations of oxygen should be routinely performed in the initial assessment of sick infants with suspected congenital heart disease.

Continuous positive airway pressure breathing (CPAP). Apparatus for use in neonates or adults

CPAP is a technique of respiratory care which was originally described in the management of the respiratory distress syndrome of the newborn and later in the post operative management of the cardiac infant following surgery. It has potential value in the respiratory management of older children and adults. Apparatus is described suitable for the application of continuous airway pressure during spontaneous ventilation via endotracheal tube in either neonates or adults. The inspired oxygen content is adjustable and the fresh gas warmed and humidified. High and low pressure alarms are not considered necessary. A head-harness is described for the application of CPAP in neonates via twin nasal or nasopharyngeal tubes. This equipment may be obtained from Messrs. Lusterlite Products Limited, 56 Devon Road, Leeds 2.