NEONATAL SHOCK HYPOTENSION MEDICAL CARE

Medical Care:
Once shock is suspected in a newborn, appropriate supportive measures must be instituted as soon as possible. These include securing the airway and assuring its patency, providing supplemental oxygen and positive-pressure ventilation, achieving intravascular or intraosseous access, and infusing 20 mL/kg of colloid or crystalloid. Use of crystalloid or colloid solutions is appropriate, unless the source of hypovolemia has been hemorrhage, in which case whole or reconstituted blood is more appropriate.

Take the opportunity to sample blood for hematocrit, electrolytes, blood culture, and glucose as soon as vascular access is obtained. At this stage, attempt to determine the type of shock, eg, hypovolemic, cardiogenic, or maldistributive, because each requires a different therapeutic approach. In any neonate who is hypotensively compromised, the authors encourage the early use of a bladder catheter because hourly urine output is one of the few objective methods of evaluating specific organ failure and perfusion and it prevents the assumption that low urine output (which often happens in babies receiving narcotics) is always a problem.

Hypovolemic shock is the most common cause of shock in infancy, and the key to successful resuscitation is early recognition and controlled volume expansion with the appropriate fluid. The estimated blood volume of a newborn is 80-85 mL/kg of body weight. Clinical signs of hypovolemic shock depend on the degree of intravascular volume depletion, which is estimated to be 25% in compensated shock, 25-40% in uncompensated shock, and over 40% in irreversible shock. Initial resuscitation with 20 mL/kg of volume expansion should replace a quarter of the blood volume. If circulatory insufficiency persists, this dose should be repeated.

Once half of the blood volume has been replaced, further volume infusion should be titrated against central venous pressure (CVP), if possible, measured through an appropriately placed umbilical venous or other central catheter. This requires careful interpretation because of inherent technical difficulties. In the absence of CVP, titration against clinical parameters should be completed. Use of crystalloid or colloid solutions is appropriate, unless the source of hypovolemia has been hemorrhage, in which case whole or reconstituted blood is more appropriate. If blood is needed in an emergent situation, type-specific or type O (Rh negative) blood can be administered. Frequent and careful monitoring of the infant's vital signs with repeated assessment and reexamination are mandatory.

Cardiogenic shock usually occurs following severe intrapartum asphyxia, structural heart disease, or arrhythmias. Global myocardial ischemia reduces contractility and causes papillary muscle dysfunction with secondary tricuspid valvular insufficiency. Clinical findings suggestive of cardiogenic shock include peripheral edema, hepatomegaly, cardiomegaly, and a heart murmur suggestive of tricuspid regurgitation. Inotropic agents, with or without peripheral vasodilators, are warranted in most circumstances. Structural heart disease or arrhythmia often requires specific pharmacologic or surgical therapy. Excessive volume expansion may be potentially harmful.

The most common form of maldistributive shock in the newborn is septic shock, and it is a source of considerable mortality and morbidity. In sepsis, cardiac output may be normal or even elevated, but it still may be too small to deliver sufficient oxygen to the tissues because of the abnormal distribution of blood in the microcirculation, which leads to decreased tissue perfusion. In septic shock, cardiac function may be depressed (the left ventricle is usually affected more than the right).

The early compensated phase of septic shock is characterized by an increased cardiac output, decreased systemic vascular resistance, warm extremities, and a widened pulse pressure. If effective therapy is not provided, cardiovascular performance deteriorates and cardiac output falls. Even with normal or increased cardiac output, shock develops. The normal relationship between cardiac output and systemic vascular resistance breaks down, and hypotension may persist as a result of decreased vascular resistance.

Newborns, who have little cardiac reserve, often present with hypotension and a picture of cardiovascular collapse. These critically ill infants are a diagnostic and therapeutic challenge, and sepsis must be presumed and treated as quickly as possible. Survival from septic shock depends upon maintenance of a hyperdynamic circulatory state. In the early phase, volume expansion with agents that are likely to remain within the intravascular space is needed, whereas inotropic agents with or without peripheral vasodilators may be indicated later. In early-onset neonatal sepsis, ampicillin and either gentamicin or cefotaxime are the antimicrobials of choice until a specific infectious agent is identified.

During and following restoration of circulation, varying degrees of organ damage may remain and should be actively sought out and managed. For example, acute tubular necrosis may be a sequela of uncompensated shock. Once hemodynamic parameters have improved, consider fluid administration according to urine output and renal function as assessed by serum creatinine and electrolytes and blood urea nitrogen concentrations. Despite adequate volume restoration, myocardial contractility may still be a problem as a consequence of the prior poor myocardial perfusion, in which case inotropic agents and intensive monitoring may need to be continued.

During the process of shock, production of chemical mediators may initiate disseminated intravascular coagulopathy (DIC), which requires careful monitoring of coagulation profiles and management with fresh frozen plasma, platelets, and/or cryoprecipitate. The liver and bowel may be damaged by shock, leading to gastrointestinal bleeding and increasing the risk for necrotizing enterocolitis, particularly in the premature infant. However, the extent of irreversible brain damage is probably most anxiously monitored following shock because the brain is so sensitive to hypoxic-ischemic injury once compensation fails.

In circumstances where volume expansion and vasoactive/inotropic agents have been unsuccessful, glucocorticoids, such as dexamethasone or hydrocortisone, have been shown to be effective. The findings that steroids rapidly up-regulate cardiovascular adrenergic receptor expression and serve as hormone replacement therapy in cases of adrenal insufficiency explain their effectiveness in stabilizing the cardiovascular status and decreasing the requirement for pressure support in the critically ill newborn with volume- and pressure-resistant hypotension.

Surgical Care:
Structural heart disease or arrhythmias often require specific pharmacologic or surgical therapy. The liver and bowel may be damaged by shock, leading to gastrointestinal bleeding and increasing the risk for necrotizing enterocolitis, particularly in the premature infant. Consultations: Depending upon the type of shock, potential consultants might include the following pediatric subspecialists: neonatologist, cardiologist, nephrologist, infectious disease specialist, and hematologist. Diet: Infants in shock should not be fed, and feedings should not be resumed until gastrointestinal function has recovered. Initiate total parenteral nutrition as soon as possible.

Drug Category: Adrenergic agonists -- Cardiovascular performance deteriorates and cardiac output falls if effective therapy is not administered. These agents improve the hemodynamic status by increasing myocardial contractility and heart rate, resulting in increased cardiac output. They also increase peripheral resistance by causing vasoconstriction. Increased cardiac output and increased peripheral resistance lead to increased blood pressure.

Drug Category: Volume expanders -- Use of crystalloid or colloid solutions is appropriate, unless the source of hypovolemia is hemorrhage, in which case whole or reconstituted blood is more appropria

Drug Category: Antimicrobials -- In early-onset neonatal sepsis, ampicillin and either gentamicin or cefotaxime are the antimicrobials of choice, until a specific infectious agent is identified.

Further Inpatient Care:
Infants recovering from neonatal shock are at risk for multiple sequelae and should be intensively screened for neurodevelopmental abnormalities, using brain imaging and brainstem audiometric evoked responses. Other tests are determined by the clinical course and complications.

Further Outpatient Care:
Outpatient care should include neurodevelopmental follow-up testing and other studies as indicated by the neonatal course.

Transfer:
Infants presenting with evidence of shock should be transferred immediately to a full-service neonatal intensive care unit with adequate support, personnel, and expertise.

Deterrence/Prevention:
Early recognition and treatment is essential to maximizing outcome in neonatal shock.

Complications:
Complications of neonatal shock are related to both the underlying cause (eg, sepsis, heart disease) and the injury sustained during the period of inadequate tissue perfusion. Frequent sequelae include pulmonary, renal, endocrine, gastrointestinal, and neurologic dysfunction

Prognosis:
Prognosis following neonatal shock is also related to both the underlying cause (eg, sepsis, heart disease) and the injuries sustained during the period of inadequate perfusion.

Patient Education:
Parents should be informed of the risk for neurodevelopmental handicaps as well as the need for intensive follow-up care of both medical and neurologic problems.