Version May 2024
INTRODUCTION — Shock is a dynamic and unstable pathophysiologic state characterized by inadequate tissue perfusion. Although the effects of inadequate perfusion are reversible initially, prolonged hypoperfusion and tissue hypoxia can disrupt critical biochemical processes, which if not addressed result in cell death, end-organ failure, and, possibly, death.
The classification and underlying mechanisms of neonatal shock are the same as those seen in pediatric and adult shock. However, the etiology, clinical manifestations, and initial management of neonatal shock differ somewhat from shock in other populations. (See "Initial evaluation of shock in children" and "Definition, classification, etiology, and pathophysiology of shock in adults".)
The etiology, clinical presentation, and evaluation of neonatal shock will be reviewed here. Management of neonatal shock is discussed separately. (See "Neonatal shock: Management".)
DEFINITION
●Shock – Shock, or circulatory failure, is defined as a physiologic state characterized by tissue hypoxia due to reduced oxygen delivery and/or increased oxygen consumption or inadequate oxygen utilization. It is manifested by physical findings of tissue hypoperfusion (eg, cold extremities, acrocyanosis, and poor capillary refill), hypotension, and metabolic acidosis. Shock is often initially reversible, but must be recognized and treated immediately to prevent progression to irreversible organ dysfunction.
It is important to recognize that hypotension, which is commonly used to define shock states in adults, is generally a late finding of shock in neonates.
●Hypotension – In older infants and children, hypotension is commonly defined by a numeric threshold such as blood pressure (BP) below the 5th percentile for age. However, characterizing a neonate's BP as "normal" or "abnormally low" using a numerical definition is challenging because BP values vary considerably depending on birth weight, gestational age, and postnatal age (figure 1 and figure 2). For these reasons, low BP should not be the sole criteria for therapeutic intervention (see 'Vital signs abnormalities' below). In addition, extremely preterm (EPT) infants may maintain adequate perfusion despite numerically low BP values. The definition of hypotension (low blood pressure) in EPT infants is discussed in greater detail separately. (See "Assessment and management of low blood pressure in extremely preterm infants", section on 'Definitions'.)
PATHOPHYSIOLOGY — Shock, a state of cellular and tissue hypoxia, is due to reduced oxygen delivery, increased oxygen consumption, and/or inadequate oxygen utilization [1-3]. Cellular hypoxia results in a switch to anaerobic metabolism and accumulation of lactic acid. Increasing levels of lactic acid causes metabolic acidosis, which interferes with cell and organ function and, if not addressed, cell death. Tissue hypoperfusion also leads to endothelial dysfunction, stimulation of inflammatory and anti-inflammatory cascades, and activation of local humoral processes that disrupt the microcirculation, resulting in further tissue injury. If untreated, these processes result in circulatory collapse, major organ failure, and death.
Shock is classified based on the underlying pathophysiologic mechanism:
●Hypovolemic (see 'Hypovolemic shock' below)
●Distributive (see 'Distributive shock' below)
●Cardiogenic (see 'Cardiogenic shock' below)
●Obstructive (see 'Obstructive shock' below)
●Multifactorial (see 'Multifactorial shock' below)
When the underlying mechanism is unclear or unknown, the term "undifferentiated shock" is used.
The pathophysiology of shock is discussed in greater detail separately. (See "Pathophysiology and classification of shock in children".)
ETIOLOGIC CLASSIFICATION — Shock can be classified based on the underlying pathogenesis: hypovolemic, distributive, cardiogenic, and obstructive shock (table 1). However, these processes are not mutually exclusive, and neonates with circulatory failure may have a combination of more than one form of shock (multifactorial shock). When the underlying mechanism is unclear or unknown, the term "undifferentiated shock" is used.
Hypovolemic shock — Hypovolemic shock occurs due to insufficient circulating blood volume, resulting in a reduction in cardiac output and reduced oxygen delivery. Neonatal shock due to hypovolemia is most commonly due to hemorrhage [4].
Causes of hemorrhagic shock in the neonate include:
●Fetomaternal hemorrhage (see "Spontaneous massive fetomaternal hemorrhage")
●Acute hemorrhage from umbilical cord prolapse or rupture associated with abnormal presentation (vasa previa) or insertion (velamentous cord) (see "Umbilical cord prolapse" and "Velamentous umbilical cord insertion and vasa previa")
●Acute bleeding into the subgaleal space (subgaleal hemorrhage) following a vacuum-assisted delivery (see "Neonatal birth injuries", section on 'Subgaleal hemorrhage' and "Neonatal birth injuries")
●Massive internal bleeding in the gastrointestinal (GI) tract, brain, lungs, or other major organ (see "Germinal matrix and intraventricular hemorrhage (GMH-IVH) in the newborn: Risk factors, clinical features, screening, and diagnosis" and "Neonatal necrotizing enterocolitis: Clinical features and diagnosis")
●Tumor-associated acute hemorrhage (eg, sacral coccygeal teratoma) (see "Sacrococcygeal teratoma")
In addition, acute blood transfusion between monochorionic twins may result in hypovolemic shock. (See "Twin-twin transfusion syndrome: Screening, prevalence, pathophysiology, and diagnosis".)
Other causes of hypovolemic shock include third spacing (ie, movement of intracellular fluid into the extravascular space), as can occur with perinatal distress, and acute intestinal injury (eg, volvulus, necrotizing enterocolitis, intestinal perforation). Less common causes include excess GI fluid loss from congenital chloridorrhea, polyuria due to congenital diabetes insipidus, and neonatal nephrotic syndrome.
Distributive shock — Distributive shock is characterized by severely reduced systemic vascular resistance (SVR) and abnormal vascular tone, which results in maldistribution of blood flow within the microcirculation and regional and global hypoperfusion. The following are causes of neonatal distributive shock:
●Sepsis – In neonates, sepsis is the most common cause of distributive shock. Sepsis releases vasoactive mediators that depress autonomic nervous system regulation of the systemic circulations resulting in diffuse vasodilation and impaired perfusion. However, the mechanisms by which this occurs and the impact of altered autonomic nervous system function are different in septic newborn infants compared with older patients. Sepsis may also cause myocardial dysfunction (cardiogenic shock). (See "Pathophysiology of sepsis", section on 'Circulation' and "Clinical features, evaluation, and diagnosis of sepsis in term and late preterm neonates".)
●Disseminated herpes simplex virus (HSV) infection – The mechanisms underlying shock in neonates with disseminated HSV infection are similar to those seen in bacterial sepsis. Disseminated HSV infection should be suspected in infants with a sepsis-like illness with a maternal history of genital herpes lesions. However, most neonates with HSV infection are born to asymptomatic women with no known history of HSV infection. Evaluation and treatment of neonatal HSV is discussed in greater detail separately. (See "Neonatal herpes simplex virus infection: Clinical features and diagnosis", section on 'Disseminated disease' and "Neonatal herpes simplex virus infection: Management and prevention".)
●Adrenal insufficiency – Shock due to adrenal insufficiency is due to impaired synthesis or release of adrenocortical hormones. This is most commonly associated with congenital adrenal hyperplasia. (See "Clinical manifestations and diagnosis of adrenal insufficiency in children", section on 'Adrenal crisis'.)
●Other rare conditions resulting in distributive shock include toxic shock syndrome and hydrops fetalis (the latter more often is multifactorial) [5]. (See "Staphylococcal toxic shock syndrome" and 'Multifactorial shock' below.)
Cardiogenic shock — Cardiogenic shock is characterized by reduced cardiac output due to ventricular dysfunction or rhythm disturbance. Cyanosis and hypoxemia are common manifestations when there is also inadequate pulmonary blood flow. Cardiogenic shock in the neonate can be caused by a variety of conditions, including the following [4]:
●Myocardial ischemia/hypoxemia can lead to myocardial damage resulting in poor contractility. Myocardial injury and dysfunction may be complications associated with intrapartum asphyxia, systemic bacterial infection, and chronic fetal hypoxemia.
●Congenital heart disease (CHD) – Some infants with critical CHD may present in the early neonatal period in cardiogenic shock as the ductus arterious closes and systemic perfusion decreases. Most commonly, this is seen in infants with unsuspected critically obstructive left heart lesions (table 2), including:
•Hypoplastic left heart syndrome (HLHS) (figure 3) (see "Hypoplastic left heart syndrome: Anatomy, clinical features, and diagnosis")
•Critical aortic valve stenosis (see "Valvar aortic stenosis in children", section on 'Critical aortic stenosis')
•Critical coarctation of the aorta (figure 4) (see "Clinical manifestations and diagnosis of coarctation of the aorta")
•Interrupted aortic arch (figure 5)
Infants with total anomalous pulmonary venous connection (TAPVC) (figure 6) most commonly present with cyanosis and tachypnea. However, if there is significant obstruction at the atrial communication, systemic perfusion will be impaired. (See "Identifying newborns with critical congenital heart disease", section on 'Shock'.)
●Cardiac arrhythmias
•Complete congenital heart block due to maternal antibodies in neonates born to mothers with systemic lupus erythematosus or Sjögren syndrome. (See "Neonatal lupus: Epidemiology, pathogenesis, clinical manifestations, and diagnosis", section on 'Heart block'.)
•Supraventricular tachycardia. (See "Clinical features and diagnosis of supraventricular tachycardia (SVT) in children".)
•Ventricular tachycardia. (See "Causes of wide QRS complex tachycardia in children".)
●Myocarditis may occur as an isolated illness or as a component of a systemic illness. In the newborn, myocarditis is usually due to viral infection, most commonly coxsackievirus. (See "Clinical manifestations and diagnosis of myocarditis in children".)
●Congenital cardiomyopathy is a rare cause of cardiac dysfunction that typically presents with hydrops fetalis.
Obstructive shock — Obstructive shock occurs when extracardiac diseases lead to impaired cardiac output. Obstructive shock is categorized as either pulmonary vascular (eg, pulmonary embolism, severe pulmonary hypertension) or mechanical (eg, tension pneumothorax, pericardial tamponade, constrictive pericarditis). Pneumothorax and pulmonary hypertension are potential complications of severe neonatal respiratory disease (eg, respiratory distress syndrome, meconium aspiration). Pulmonary embolism and cardiac tamponade rarely cause neonatal shock. (See "Pulmonary air leak in the newborn", section on 'Pneumothorax' and "Persistent pulmonary hypertension of the newborn (PPHN): Clinical features and diagnosis".)
Multifactorial shock — Neonatal multifactorial shock may be observed in the following clinical settings. It is important to identify the multiple etiologies in order to guide treatment decisions.
●Sepsis – As noted above, sepsis is typically classified as distributive shock. However, patients may exhibit cardiogenic shock due to myocardial depression and hypovolemic shock due to capillary leak and third spacing (movement of intracellular fluid into the extravascular space). (See "Clinical features and diagnosis of bacterial sepsis in preterm infants <34 weeks gestation", section on 'Severe sepsis and septic shock'.)
●Severe intestinal injury – Patients with severe intestinal injury (eg, Stage III necrotizing enterocolitis [NEC] or malrotation with midgut volvulus) may develop circulatory collapse due to hypovolemic shock from third spacing and distributive shock caused by sepsis. (See "Neonatal necrotizing enterocolitis: Clinical features and diagnosis" and "Intestinal malrotation in children", section on 'Clinical presentation'.)
●Pulmonary hypertension – Pulmonary hypertension is typically classified as obstructive shock. However, patients with severe disease commonly have biventricular dysfunction leading to cardiogenic shock. (See "Persistent pulmonary hypertension of the newborn (PPHN): Clinical features and diagnosis".)
●Hydrops fetalis ‒ Hydrops fetalis is defined as abnormal fetal fluid collection in a minimum of two anatomic locations caused by dysregulation of the net fluid movement between the vascular and interstitial spaces. The etiology of hydrops fetalis is broad, and neonatal shock is a common manifestation of an affected infant at birth. Distributive shock occurs in all patients with hydrops fetalis due to capillary leak, but neonates with hydrops fetalis and shock frequently may exhibit hypovolemic shock (eg, third spacing), cardiogenic shock (eg, congenital cardiac disease), and obstructive shock (eg, congenital obstructive lymphatic abnormality). (See "Nonimmune hydrops fetalis in the neonate: Causes, presentation, and overview of neonatal management".)
CLINICAL MANIFESTATIONS
Vital signs abnormalities — Vital sign abnormalities are a hallmark of shock and may include:
●Abnormal heart rate (HR) – Tachycardia (HR >180 beats per minute) is a common but nonspecific finding in neonatal shock. Increasing the HR is the neonate's chief compensatory mechanism to maintain cardiac output when there is a limited capacity to increase stroke volume (SV) [6]. Variability of HR may be another early sign of septic shock [7]. In term infants, bradycardia (HR <90 beats per minute) is often a terminal finding, whereas in preterm infants, bradycardia can occur at any time.
●Hypotension – Low blood pressure (BP) (hypotension) is generally a late finding of shock, and ideally shock is diagnosed prior to the onset of hypotension [6]. BP below the 5th percentile for GA and postnatal age is cause for concern and warrants additional investigation. If low BP is accompanied by clinical signs of poor perfusion, treatment should be initiated. (See "Neonatal shock: Management".)
Definitions of hypotension are based on normative BP values, which vary somewhat depending on gestational and postnatal age:
•Full-term infants (figure 7)
•Preterm infants – Gestational age (GA) 28 to 36 weeks (figure 2)
•Extremely preterm (EPT) infants – GA <28 weeks (figure 1)
Of note, BP in very preterm (VPT) infants correlates poorly with systemic blood flow such that BP alone is an imperfect measure to detect early shock, especially in EPT infants [8-10]. EPT infants may have low BP and still have adequate perfusion and may not need further interventions. This is discussed in greater detail separately. (See "Assessment and management of low blood pressure in extremely preterm infants".)
By contrast, the finding of hypotension in a neonate with hypovolemic shock may signal a need for massive volume resuscitation. This is because hypotension does not occur as a manifestation of hypovolemic shock until the neonate has lost 30 to 40 percent of its blood volume. (See "Neonatal shock: Management", section on 'Acute blood loss'.)
●Abnormal body temperature – Fever is often present with neonatal sepsis. However, infants with shock due to any etiology (including sepsis) may have impaired autonomic nervous system function, which can result in hypothermia.
Decreased peripheral perfusion — Signs of decreased peripheral perfusion include:
●Cool extremities, acrocyanosis, and pallor are initial signs of decreasing cardiac output, as vasoconstrictive mechanisms compensate for decreased tissue perfusion by redirecting blood from the periphery to the vital organs (eg, coronary, cerebral, and adrenal perfusion). These signs may be difficult to differentiate from findings in the normal neonate whose hands and feet are often cool to the touch with varying degrees of acrocyanosis. Pallor may also be an indication of anemia.
●Delayed capillary refill >4 seconds is suggestive of neonatal shock especially in combination with other findings indicative of poor peripheral perfusion (ie, low BP, weak pulses, cool extremities, and abnormal neurologic signs) [8,9]. As an isolated finding, the predictive value of capillary refill is poor, and it is not a reliable physical finding alone to either confirm the diagnosis of shock or to assess response to therapy in newborns [8,11,12].
Neurologic findings — In the initial stages of shock, nonspecific neurologic findings may include lethargy, irritability, poor feeding, and poor tone. In the later stages, there is progression to stupor or coma. Other neurologic findings include decreased spontaneous movements of the extremities, diminished deep tendon reflexes, and absence of primitive reflexes (eg, palmar grasp reflex, Moro reflex, and rooting reflex). However, the differential diagnosis of abnormal neurological findings in a neonate is broad, and shock should not be presumed to be the underlying cause. (See "Neurologic examination of the newborn".)
Respiratory findings — The following nonspecific respiratory findings may be seen in neonatal shock:
●Tachypnea is generally seen in infants with septic or cardiogenic shock as a compensatory response to metabolic acidosis due to lactate production from poorly perfused tissue.
●Other signs of respiratory distress, such as grunting, retractions, nasal flaring, and gasping, often accompany tachypnea. These are observed especially in patients with primary pulmonary disease (eg, pneumonia) or cardiopulmonary compromise with pulmonary edema.
●Periodic breathing and apnea are usually centrally mediated and are more likely to be associated with decreased cerebral perfusion or significant metabolic acidosis that impairs cerebral function. As a result, these findings can present in all forms of neonatal shock.
●Hypoxemia may be present in infants with shock due to cardiac dysfunction or obstructed blood flow, but isolated hypoxemia is rare. Hypoxemia associated with neonatal shock may be due to persistent pulmonary hypertension that may accompany bacterial infections, especially those caused by group B streptococcus (GBS), cyanotic congenital heart disease (CHD), and severe anemia. (See "Cardiac causes of cyanosis in the newborn" and "Persistent pulmonary hypertension of the newborn (PPHN): Clinical features and diagnosis".)
Other findings
●Renal – There is a strong correlation between low urinary output (oliguria) and low systemic blood flow. However, there is often a time delay between the development of circulatory compromise and the recognition of oliguria [13].
●Gastrointestinal (GI) – The following nonspecific GI findings may be seen in patients with neonatal shock:
•Poor feeding due to lethargy and/or respiratory distress.
•Vomiting as a manifestation of decreased motility that results from non-mechanical disruption of the normal coordinated propulsive motor activity of the GI tract, which may progress to paralytic ileus. Bilious emesis is uncommon, and when present it should prompt an investigation into intra-abdominal causes of shock (eg, malrotation with midgut volvulus or necrotizing enterocolitis). (See "Intestinal malrotation in children" and "Neonatal necrotizing enterocolitis: Clinical features and diagnosis".)
•Abdominal distension as a manifestation of ileus.
Laboratory findings — The most common laboratory feature characteristic of neonatal shock is metabolic acidosis with decrease in serum/plasma bicarbonate and an increase in lactate due to increased anaerobic metabolism (increased lactate production) and decreased clearance of lactate.
Other less common laboratory features include:
●Anemia due to blood loss observed in hemorrhagic hypovolemic shock [14,15] or hemolysis in septic shock.
●Prolonged prothrombin time (PT)/international normalized ratio (INR) and partial thromboplastin time (PTT) tests can occur with consumptive coagulopathy, which may be present in infants with septic shock or complications from pregnancy, including fetal anoxia/birth asphyxia (distributive shock) and placental abruption (hypovolemic shock). Coagulopathy can also occur as a consequence of hepatic dysfunction. (See "Disseminated intravascular coagulation in infants and children", section on 'Other etiologies in neonates'.)
●Glucose levels may be elevated or decreased during neonatal shock. The glucose level varies depending upon catecholamine release during the body's stress response (which affects insulin release and peripheral utilization of glucose) and the body stores of glucose and glycogen. (See "Neonatal hyperglycemia" and "Pathogenesis, screening, and diagnosis of neonatal hypoglycemia".)
●Hyperkalemia is a result of release of intracellular potassium stores due to acidosis, tissue injury, and cell death. It may be further exacerbated by renal impairment. Hyperkalemia may also be a manifestation of congenital adrenal hyperplasia, an important though rare cause of neonatal shock. (See "Neonatal acute kidney injury: Pathogenesis, etiology, clinical presentation, and diagnosis", section on 'Presentation due to other laboratory abnormalities' and "Clinical manifestations and diagnosis of adrenal insufficiency in children", section on 'Adrenal crisis'.)
●Serum bilirubin levels and liver enzymes may be elevated due to hepatic injury and dysfunction.
●Serum creatinine and blood urea nitrogen (BUN) may be elevated due to acute kidney injury.
DIAGNOSIS — The diagnosis of shock is clinically based on a constellation of clinical, biochemical, and hemodynamic features. These include physical findings of tissue hypoperfusion (eg, cold extremities, acrocyanosis, and poor capillary refill), and metabolic acidosis. Patients in the early stages of shock may present with tachycardia, peripheral vasoconstriction (eg, cold extremities and acrocyanosis), and normal blood pressure (BP) (ie, compensated shock). Hypotension typically occurs in the late stages of shock. Bradycardia is usually observed in the terminal stage in term infants, but may occur at any time in preterm infants. (See 'Clinical manifestations' above.)
INITIAL STABILIZATION — Stabilization of the patient's hemodynamic status takes precedence over the diagnostic evaluation. Resuscitation should not be delayed to obtain history, perform a physical examination, or obtain laboratory tests. However, during the initial stabilization, a focused evaluation to determine the etiology should occur concomitantly in order to best direct subsequent therapy. The goals of the initial stabilization and evaluation include rapid recognition and correction of circulatory compromise and other life-threatening conditions.
The approach to initial stabilization is summarized in the figure and is discussed in greater detail separately (algorithm 1). (See "Neonatal shock: Management", section on 'Initial stabilization'.)
It generally includes the following interventions:
●Provide respiratory support as needed. (See "Overview of mechanical ventilation in neonates".)
●Obtain vascular access. (See "Vascular (venous) access for pediatric resuscitation and other pediatric emergencies", section on 'Umbilical vein access'.)
●Administer initial fluid bolus – An initial fluid bolus of 10 to 20 mL/kg isotonic crystalloid is appropriate for most neonates presenting in shock. However, fluid boluses should be administered cautiously in extremely preterm infants (gestational age <28 weeks) or if there is suspicion for a cardiac etiology of shock. The initial fluid resuscitation in neonatal shock is discussed in greater detail separately. (See "Neonatal shock: Management", section on 'Fluid resuscitation'.)
●Administer empiric antibiotics, and, if there is clinical suspicion for herpes simplex infection, acyclovir. (See "Management and outcome of sepsis in term and late preterm neonates", section on 'Initial empiric therapy' and "Neonatal herpes simplex virus infection: Management and prevention", section on 'Initial antiviral therapy'.)
●Address any correctable abnormalities noted on the initial evaluation. (See "Neonatal shock: Management", section on 'Other interventions'.)
DIAGNOSTIC EVALUATION — For neonates presenting with clinical signs of shock, a focused diagnostic evaluation to determine the underlying cause should occur in concert with initial stabilization. The type and cause of shock can generally be determined from the history, physical examination, and basic diagnostic studies, which may guide management (algorithm 1) [6]. (See "Neonatal shock: Management", section on 'Ongoing goal-directed therapy'.)
History — The newborn history, including review of maternal health issues, antenatal screening, and pregnancy and delivery complications, often can identify the underlying cause of shock.
The following historical findings may help identify the underlying mechanism of shock (table 1) (see 'Etiologic classification' above):
●Hypovolemic shock:
•Significant blood loss from placental anomalies, maternal bleeding, or umbilical cord abnormalities (see "Placenta previa: Epidemiology, clinical features, diagnosis, morbidity and mortality")
•Internal bleeding due to traumatic vacuum-assisted delivery (eg, subgaleal bleed) (see "Neonatal birth injuries")
●Septic shock (see "Clinical features, evaluation, and diagnosis of sepsis in term and late preterm neonates", section on 'Maternal risk factors'):
•Prolonged rupture of membrane
•Maternal chorioamnionitis
•Maternal fever during labor
•Group B streptococcal (GBS) bacteriuria during the pregnancy
•Previous delivery of an infant affected by GBS disease
•Maternal history of herpes genital lesions may be indicative of shock due to disseminated herpes simplex virus (HSV) infection (see "Neonatal herpes simplex virus infection: Clinical features and diagnosis", section on 'Transmission')
●Cardiogenic shock:
•Maternal history of systemic lupus erythematosus or Sjögren's disease resulting in neonatal heart block (see "Neonatal lupus: Epidemiology, pathogenesis, clinical manifestations, and diagnosis")
•Antenatal asphyxia with abnormal heart rate (HR) pattern (see "Perinatal asphyxia in term and late preterm infants", section on 'Cardiovascular manifestations')
•Congenital heart disease (CHD) detected by prenatal ultrasound or newborn screening (see "Congenital heart disease: Prenatal screening, diagnosis, and management" and "Newborn screening for critical congenital heart disease using pulse oximetry")
●Hydrops fetalis is generally characterized by distributive shock but frequently is associated with multifactorial shock. (See "Nonimmune hydrops fetalis in the neonate: Causes, presentation, and overview of neonatal management".)
In some cases, fetuses with an increased risk of requiring resuscitation at birth can be identified prior to delivery. In such cases, the neonatal team should be alerted so that preparations for resuscitation can be set up in the delivery room. (See "Neonatal resuscitation in the delivery room", section on 'High-risk delivery'.)
Physical examination — The physical examination is important to assess the severity of shock and to monitor the response to therapeutic interventions. (See "Neonatal shock: Management", section on 'Monitoring'.)
Physical findings in neonatal shock are generally nonspecific and include decreased peripheral perfusion (cold extremities, acrocyanosis, delayed capillary refill) and poor vigor. (See 'Clinical manifestations' above.)
However, certain findings may point to a specific etiology. These include:
●Pathologic murmurs and/or gallop rhythm may raise suspicion of a cardiac cause. However, some forms of critical CHD may not have an appreciable murmur (eg, hypoplastic left heart syndrome [HLHS]). Murmurs commonly occur in some non-cardiac causes of neonatal shock (eg, tricuspid regurgitation murmur in birth asphyxia). (See "Approach to the infant or child with a cardiac murmur" and "Common causes of cardiac murmurs in infants and children".)
●Weak or absent lower extremity pulses (particularly in comparison to upper extremity pulses) might suggest cardiogenic shock due to critical coarctation of the aorta. (See "Clinical manifestations and diagnosis of coarctation of the aorta", section on 'Neonates'.)
●Chest asymmetry and absent breath sounds on one side might suggest tension pneumothorax. (See "Pulmonary air leak in the newborn", section on 'Pneumothorax'.)
●Abdominal distension might suggest necrotizing enterocolitis and sepsis. (See "Neonatal necrotizing enterocolitis: Clinical features and diagnosis", section on 'Clinical presentation'.)
●Ambiguous genitalia should raise suspicion for the possibility of adrenal insufficiency (table 3). (See "Causes of primary adrenal insufficiency in children", section on 'Congenital adrenal hyperplasia' and "Clinical manifestations and diagnosis of adrenal insufficiency in children", section on 'Adrenal crisis'.)
●Skin findings might suggest an infectious etiology (cellulitis, vesicles [herpes simplex virus]). (See "Neonatal herpes simplex virus infection: Clinical features and diagnosis", section on 'Neonatal HSV'.)
●Rash comprising erythematous annular lesions or arcuate macules located primarily on the scalp and periorbital area is one of the physical diagnostic findings of neonatal lupus, which can present with shock due to congenital heart block. (See "Neonatal lupus: Epidemiology, pathogenesis, clinical manifestations, and diagnosis", section on 'Rash'.)
Laboratory and imaging tests
Initial routine testing — The following tests may help identify the cause, assess the severity, and guide the initial treatment.
●Arterial blood gas – The arterial blood gas measures the degree of acidosis and hypoxemia, which are important factors in the assessment and management of patients with shock. The blood gas does not help to distinguish between different types of shock but rather confirms shock and assesses its severity. Blood gases are also an important to assess the effectiveness of interventions. (See "Neonatal shock: Management", section on 'Monitoring'.)
•Metabolic acidosis is observed in most cases primarily due to accumulation of lactate.
•Respiratory acidosis may be seen, particularly in patients with apnea or primary pulmonary disease (eg, pneumonia).
•Hypoxemia is often, but not always, observed depending on the degree of respiratory compromise and underlying etiology (eg, cyanotic CHD and primary pulmonary disorders are likely to present with hypoxemia).
Some point-of-care blood gas analyzers permit simultaneous measurement of electrolytes and lactate, which provides additional useful information.
●Lactate – Serum lactate is a marker of tissue perfusion and is used to measure the severity of shock (lactate levels increase as the severity increases). Lactate is obtained at baseline and can be serially measured to follow the response to therapy. (See "Neonatal shock: Management", section on 'Monitoring'.)
●Complete blood count (CBC) with differential – Abnormalities of any of the three cell lines may occur in neonatal shock; however, these are nonspecific findings and may not be useful in diagnosing the underlying cause:
•Both elevated (>20,000/mm3) and depressed (<5000/mm3) total white blood cell (WBC) counts are associated with systemic bacterial infection, which may result in septic shock. However, neither is a reliable marker for bacterial infection. (See "Clinical features, evaluation, and diagnosis of sepsis in term and late preterm neonates", section on 'Complete blood count'.)
•Thrombocytopenia may be suggestive of disseminated intravascular coagulation due to complications from pregnancy including fetal anoxia/birth asphyxia (distributive shock) or placental abruption (hypovolemic shock), or neonatal septic shock [16]. (See "Disseminated intravascular coagulation in infants and children", section on 'Other etiologies in neonates'.)
•Anemia is seen in neonatal shock due to massive blood loss or hemolysis from overwhelming sepsis.
●Blood chemistries – Basic chemistry tests include electrolytes, glucose, renal (blood urea nitrogen [BUN], and creatinine) and liver function studies:
•As noted above, hyperkalemia and both hypo- and hyperglycemia may occur in neonatal shock.
•Serum bicarbonate is depressed as an indication of metabolic acidosis.
•Baseline renal and liver function studies should be obtained, and levels should be monitored to detect any abnormalities indicating end-organ damage and recovery.
•Hyponatremia and hyper- and hypoglycemia are typical manifestations of distributive shock due to adrenal insufficiency.
●Blood cultures – Blood cultures should be obtained in any infant who may have septic shock or shock without an identifiable cause.
●Viral testing – If there is concern for HSV, appropriate samples should be collected and sent for polymerase chain reaction and viral culture. Evaluation for HSV infection should be performed if the neonate had perinatal exposure to HSV, has physical findings consistent with HSV (mucocutaneous vesicles (picture 1A-C)), and/or has cerebrospinal fluid pleocytosis. In addition, the diagnosis should be considered in neonates with concerning findings that are otherwise unexplained. These may include seizures, focal neurologic signs, abnormal neuroimaging, sepsis-like illness (fever or hypothermia, irritability, lethargy, respiratory distress, apnea, abdominal distension, hepatomegaly, ascites), thrombocytopenia, or elevated liver transaminases. The evaluation of suspected HSV infection in neonates is discussed in greater detail separately. (See "Neonatal herpes simplex virus infection: Clinical features and diagnosis", section on 'Evaluation and diagnosis'.)
●Type and cross – Blood type, antibody screen, and crossmatching should be performed for infants with hypovolemic shock due to blood loss who will require red blood cell transfusion. (See "Red blood cell transfusion in infants and children: Selection of blood products", section on 'Newborns and young infants' and "Red blood cell (RBC) transfusions in the neonate", section on 'Acute blood loss'.)
●Chest radiograph – Chest radiography can be useful for neonates with respiratory distress or an abnormal cardiopulmonary examination. An abnormal chest radiograph may indicate pulmonary disease (eg, tension pneumothorax, pneumonia) or may suggest a cardiac abnormality (eg, cardiomegaly, abnormal pulmonary vascular markings, pulmonary venous congestion).
Additional selective testing — Additional testing, which is based upon the findings of the initial evaluation and the infant's response to initial interventions (see "Neonatal shock: Management", section on 'Interventions for suspected etiologies') may include:
●Echocardiography – Echocardiography should be performed if there is suspicion for a cardiac etiology of shock. Cardiac disease may be suspected on the basis of any of the following:
•Physical findings (eg, murmur, gallop, weak or absent femoral pulses)
•Cyanosis that does not improve with administration of 100 percent oxygen
•Differential in pre- and postductal oxygen saturation
•Clinical deterioration with fluid administration
•Abnormal electrocardiogram
•Abnormal chest radiograph (eg, cardiomegaly, pulmonary edema)
Consultation with a pediatric cardiologist is suggested if a cardiac etiology is suspected. Echocardiography provides detailed assessment of the cardiac anatomy, and it is the test of choice for diagnosing congenital heart disease (CHD). In addition, it provides an assessment of cardiac function and it can identify other potential etiologies of shock (eg, persistent pulmonary hypertension of the newborn, tamponade). Thus, it is reasonable to perform echocardiography in infants with persistent or severe shock even in the absence of the above findings. (See "Diagnosis and initial management of cyanotic heart disease in the newborn", section on 'Echocardiography'.)
●Electrocardiogram (ECG) – ECG should be performed if an abnormal rhythm is noted on examination or cardiac monitoring or if CHD is suspected. (See "Diagnosis and initial management of cyanotic heart disease in the newborn", section on 'Electrocardiogram'.)
●Abdominal imaging – Abdominal radiographs may be useful in the evaluation of infants with a suspected abdominal source for sepsis or shock (eg, necrotizing enterocolitis [NEC] or volvulus). Abdominal ultrasonography can be used to detect bleeding into the abdomen or kidney. (See "Neonatal necrotizing enterocolitis: Clinical features and diagnosis", section on 'Radiologic evaluation'.)
●Head ultrasonography (HUS) – HUS is appropriate to evaluate for intracranial hemorrhage, which may be suspected based on clinical findings (eg, abnormal neurologic examination) or because of evidence of acute blood loss without a clear source. (See "Germinal matrix and intraventricular hemorrhage (GMH-IVH) in the newborn: Risk factors, clinical features, screening, and diagnosis", section on 'Cranial ultrasound'.)
●Lumbar puncture (LP) – LP is a routine part of the evaluation for suspected bacterial sepsis in neonates and for suspected herpes simplex virus infection. However, many neonates with shock are too unstable to safely undergo LP, and therefore this testing is often deferred until the neonate is clinically stable. (See "Clinical features, evaluation, and diagnosis of sepsis in term and late preterm neonates", section on 'Lumbar puncture'.)
●Kleihauer-Betke assay – The Kleihauer-Betke assay is a method for quantifying fetal cells in maternal blood. A positive test is indicative of fetomaternal hemorrhage, which may be a cause for hypovolemic shock [17]. (See "Spontaneous massive fetomaternal hemorrhage", section on 'Kleihauer-Betke assay'.)
SUMMARY AND RECOMMENDATIONS
●Shock is a dynamic and unstable pathophysiologic state characterized by inadequate tissue perfusion due to reduced oxygen delivery and/or increased oxygen consumption or inadequate oxygen utilization. If untreated it leads to tissue/cellular damage that results in end-organ failure and, in some cases, death. (See 'Definition' above and 'Pathophysiology' above.)
●The causes of neonatal shock are classified into four pathophysiologic mechanisms (table 1). However, neonatal shock may be the result of more than one of these processes (multifactorial shock) (see 'Etiologic classification' above):
•Hypovolemic shock is characterized by impaired cardiac output due to significant fluid losses (eg, fetomaternal bleeding). (See 'Hypovolemic shock' above.)
•Distributive shock is characterized by abnormal vascular tone, which results in maldistribution of blood flow within the microcirculation and regional and global hypoperfusion. Sepsis is the most common cause of distributive shock. (See 'Distributive shock' above.)
•Cardiogenic shock is characterized by reduced cardiac output due to ventricular dysfunction or arrhythmia. (See 'Cardiogenic shock' above.)
•Obstructive shock is caused by extracardiac disorders (eg, tension pneumothorax) that result in decreased cardiac output. (See 'Obstructive shock' above.)
●Regardless of the etiology, neonates with shock typically present with signs of poor perfusion (cool extremities, acrocyanosis, pallor), tachycardia, and metabolic acidosis. Late signs of shock include bradycardia and hypotension. (See 'Clinical manifestations' above.)
●Stabilization of the patient's hemodynamic status takes precedence over the diagnostic evaluation, and resuscitation should not be delayed. However, a focused diagnostic evaluation is conducted in concert with resuscitative efforts (algorithm 1):
•Key elements of the initial resuscitation include (see 'Initial stabilization' above):
-Stabilization of the airway and respiratory status
-Vascular access
-Initial fluid resuscitation
-Administration of empiric antibiotics
-Use of specific interventions based on the underlying etiology as determined by the concurrent diagnostic evaluation
•Key elements of the initial diagnostic evaluation include (see 'Diagnostic evaluation' above):
-Brief review of the history (see 'History' above)
-Focused physical examination (see 'Physical examination' above)
-Basic laboratory tests (electrolytes, blood gas, complete blood count, lactate, blood culture, renal and liver function tests, and type and cross) (see 'Initial routine testing' above)
-Chest radiograph if there are respiratory symptoms or findings
●Additional testing, which is based upon the findings of the initial evaluation and the infant's response to initial interventions, may include (see 'Additional selective testing' above):
•Echocardiography
•Electrocardiogram
•Abdominal imaging
•Head ultrasonography
•Lumbar puncture
•Testing for fetal cells in maternal blood (Kleihauer-Betke assay)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Lisa Adcock, MD, who contributed to an earlier version of this topic review.
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