A 4-day-old, full-term neonate is brought to the ER by his parents for poor feeding and lethargy. His vital signs are as follows: temperature 36.2 °C, heart rate (HR) 192 beats per minute, respiratory rate (RR) 63 breaths per minute, and blood pressure (BP) 62/37 mmHg with oxygen saturation (SpO2) of 92% on room air.
On examination, the baby appears lethargic with cool extremities and capillary refill time of 4 s. He has nasal flaring with intercostal retractions. Liver edge is palpable 3 cm below the right costal margin. The saturations improve to 97% on 100% oxygen.
Repeat vital signs after initiation of oxygen administration show a HR of 212 beats per minute, RR of 75 breaths per minute, and a right upper extremity BP of 54/23 mmHg.
A chest radiograph demonstrates pulmonary edema and cardiomegaly (). An initial arterial blood gas (ABG) demonstrates pH 7.15, PCO2 28 mmHg, PaO2 94 mmHg, bicarbonate 10 mEq/L, and lactate 12 mmol/L.
List problems in this hild
Shock
Hyperlactatemia
Metabolic acidosis
What are the practi al consideration in this child?
Ductal-dependent lesions should be a consideration in all neonates presenting in shock and/or cyanosis in the neonatal period. Alprostadil (PGE1) infusion may be lifesaving if instituted even prior to an established diagnosis. FO-dependent lesions (TGV, obstructed TAPVR) may need balloon atrial septostomy. All patients with suspected CCHD should be promptly transferred to tertiary care centers.
Oxygen administration, which is a common intervention for life-threatening pediatric emergencies, may have deleterious consequences in certain cardiac lesions. Elevated PaO2 results in constriction of DA and pulmonary vasodilation.
In left-sided obstructive lesions of the heart, constriction of DA would result in worsening of systemic hypoperfusion, shock, and lactic acidosis. Pulmonary vasodilation in single ventricle physiology (e.g., Norwood surgery for hypoplastic left heart syndrome) may result in a greater proportion of cardiac output going to the lungs (Qp) at the expense of the rest of the body (Qs). Also, in left-to-right shunts, pulmonary overcirculation resulting from vasodilation may worsen pulmonary edema.
Oxygen administration in such situations must be carefully monitored to maintain SaO2 around 75–80% in single ventricle physiology and around 90% in left-to-right shunts. Administration of albuterol in a child whose respiratory symptoms are secondary to myocardial dysfunction will lead to increased oxygen demands on an already compromised heart.
Excessive fluid resuscitation for decreased cardiac output and apparent dehydration in a situation with a failing heart will have similar adverse consequences. Early identification of cardiac etiology as the underlying mechanism of life-threatening manifestations is of utmost importance.
Discussion
The neonate in this vignette has signs of shock, severe metabolic acidosis, and marked hyperlactatemia. The etiology of shock in an infant needs to be determined and lifesaving measures employed rapidly.
Cardiogenic shock should be suspected in all such infants in addition to hypovolemia and sepsis. In this infant presenting with shock in the first week of life, there are no historical findings to account for hypovolemia, hypotension, and poor perfusion. Therefore treatment for an underlying ductal-dependent cardiac disease is imperative.
Obstructive lesions of the left side of the heart such as HLHS, critical aortic stenosis, coarctation of the aorta, and interrupted aortic arch are at the top of the list of differential diagnosis. The infant may appear relatively normal at birth as long as the DA remains open, and thepostobstructive systemic circulation is maintained by the right ventricle through the pulmonary artery and DA.
Symptoms appear when closure of the DA leads to systemic hypoperfusion. These children are not cyanotic but rather appear ashen gray because of hypoperfusion and increased peripheral oxygen extraction.
In order to maintain ductal patency and establish systemic blood flow, alprostadil infusion must be started. Since alprostadil is a systemic vasodilator, judicious intravenous fluid expansion may be necessary to maintain normal blood pressure for age.
The use of oxygen in a child with shock due to a left-sided obstructive lesion can be of particular harm as oxygen itself is a potent DA constrictor which may further limit blood flow through a compromised DA.
Ductal patency is a major factor that determines the difference between survival and death in a child dependent on the DA for systemic blood flow.
Unlike the infant in the vignette, a child with right-sided obstructive lesions (pulmonary atresia, tricuspid atresia,) or independent circuits (TGA) will present with central cyanosis and often has PaO2 ~40 and oxygen saturations ~75%. In cyanotic infants, the hyperoxia test may be utilized as a clinical tool to differentiate between pulmonary and cardiac disease. The test is based on the principle that 100% oxygen will increase alveolar PO2, leading to an increase in systemic arterial PO2 in the absence of a fixed cardiac shunt.
In cyanotic congenital heart disease, little or no rise in PaO2 would be expected after breathing 100% O2. An arterial blood gas analysis done both before and after the administration of 100% O2 demonstrating an increase in PaO2 to more than 100 mmHg would suggest a respiratory disease, while an increase of PaO2 of less than 80 mmHg would require evaluation for cyanotic CHD.
Thus, persistent hypoxia refractory to 100% oxygen supply would indicate cyanotic CHD rather than a primary pulmonary disease. It should be noted that the hyperoxia test should be utilized only in cyanotic infants to differentiate cyanosis from pulmonary vs. cardiac etiology. It should not be used in infants who are in shock and therefore appear gray but have SpO2 above 90%. These patients shouldbe suspected of ductal-dependent left-sided obstructive lesion in whom 100% oxygen administration could be detrimental.
The most important first step in managing a neonate presenting within the first week of life with either shock or cyanosis necessitates that the ED physician considers a ductal-dependent cardiac lesion and initiates the administration of an alprostadil drip to improve patency of the DA.
Superintendent, ICH.