Shock and Hypotension in the Newborn 

Updated: Nov 27, 2021
Author: Samir Gupta, MD, DM, FRCPCH, FRCPI; Chief Editor: Muhammad Aslam, MD 

Overview

Background

Shock is a complex clinical syndrome caused by an acute failure of circulatory function. It is characterized by an imbalance between tissue demand and the supply of substrates.[1] When this occurs, inadequate amounts of oxygen and nutrient substrate are delivered to body tissues, and removal of metabolic waste products is inadequate. This results in cellular dysfunction, which may eventually lead to cell death. Shock is an independent predictor of mortality, and survivors have a greater risk for neurologic impairment.[2, 3] Failure of perfusion may involve isolated organs or the entire organism.

Hypotension (ie, lower-than-expected blood pressure) frequently, but not always, accompanies shock. (See Pathophysiology and Etiology.) Preterm infants are particularly prone to injury related to hypoperfusion and hypoxemia owing to their immature cardiovascular system and impaired compensatory/autoregulatory mechanisms.[4] In addition, preterm infants also often have relative renal insufficiency.[3] In a study of the variation in the prevalence of hypotension among low–birth-weight infants, 16-52% received volume expansion and 4-39% received vasopressors.[5]

Patient education

Parents should be informed of the risk of mortality and morbidity in the form of neurodevelopmental problems as well as the need for intensive follow-up care for medical and neurologic problems. For patient education information, see Shock and Cardiopulmonary Resuscitation (CPR).

Physiology

Maintenance of adequate tissue perfusion depends on a combination of three major factors: (1) cardiac output; (2) integrity and maintenance of vasomotor tone of local vascular beds, including arterial, venous, and capillary; and (3) the ability of the blood to perform its necessary delivery of metabolic substrates and removal of metabolic wastes. (See Treatment and Medication.)

Cardiac output (CO) is the product of heart rate (HR) and stroke volume (SV) (CO = HR × SV). Neonatal cardiac output depends more on heart rate than stroke volume; therefore, very high (>180 beats per minute [bpm]) and very low (< 80 bpm) heart rates are likely to compromise cardiac output if prolonged. However, not all infants with subnormal heart rates have impaired perfusion. At higher rates, ventricular filling time and end-diastolic volume are diminished, and myocardial oxygen consumption is increased. Because myocardial perfusion occurs during diastole, further increases in heart rate may produce undesirable cardiac ischemia, leading to ventricular dysfunction.

Stroke volume, the other major determinant of cardiac output, is influenced by preload, afterload, and myocardial contractility, as follows:

  • Preload: Preload corresponds to the myocardial end-diastolic fiber length and is determined by the amount of blood filling the ventricles during diastole; increases in preload raise stroke volume up to a maximum value, beyond which stroke volume falls according to the Starling law.

  • Afterload: Afterload is the force that the myocardium is required to generate during ejection against systemic and pulmonary vascular resistances (for the left and right ventricles, respectively); reductions in afterload increase stroke volume if other variables remain constant.

  • Contractility: Contractility is a semi-quantitative measure of ventricular function, and an increase in contractility produces an increase in stroke volume if preload and afterload are unchanged; this is determined by the percentage of fractional shortening, which depends on the ventricular end diastolic and end-systolic diameter.

Clinically significant alterations in preload, afterload, and contractility may be achieved by the use of vasoactive pharmacologic agents, administration of inotropic agents, changes in blood volume, or a combination of these methods. Hypotension refers to a blood pressure lower than the expected reference range. Although the normal physiologic range for blood pressure (defined by the presence of normal organ blood flow) is not well studied in the newborn population, in clinical practice the reference range blood pressure limits are defined as the gestational age–dependent and postnatal age–dependent blood pressure values between the 5th (or 10th) and 95th (or 90th) percentiles.[6]

Blood pressure measurement is limited to assessing systemic blood flow. In the presence of physiologic shunts in newborns, the estimation of superior vena cava (SVC) flow is observed to correlate with low flow states rather than left ventricular output (LVO).

A linear relationship between blood pressure and both gestational age or birthweight and postnatal age is recognized; however, only preliminary data are available on the gestational age–dependent and postnatal age–dependent organ blood flow autoregulatory range and on the relation among blood pressure and systemic blood flow, cardiac output, and neonatal mortality and morbidity.

Mean blood pressure, rather than systolic pressure, is usually used to judge the normality of data obtained from indwelling arterial lines. Mean blood pressure is thought to be free of artifacts caused by resonance, thrombi, and air bubbles, but this may not always be true. Based on published data, the statistically defined lower limits of mean blood pressure during the first day of life are approximately numerically similar to the gestational age reference range of the infant. However, most preterm infants, even at 24-26 weeks' gestation, have a mean blood pressure of 30 mmHg or greater by the third day of life. The systolic blood pressure correlates with the gestational age reference range 4-24 hours after birth; only 3% of babies with the normal long-term outcome have systolic blood pressures below the reference range for the gestational age.[7]

A low upper body blood flow is common in the first day of life in preterm infants younger than 30 weeks' gestation; this has a strong correlation with periventricular or intraventricular hemorrhage. The presence of fetal shunts in premature babies, such as patent ductus arteriosus (PDA) and patent foramen ovale (PFO), further affects the systemic and pulmonary blood flow. Depending on the size of these predominantly systemic pulmonary shunts, there may be volume overloading of the left side of the heart, which could lead to cardiac failure and other complications, including low blood pressure. Shock unresponsive to inotropes in the first few days of life in preterm babies can be caused by a large PDA. Furthermore, it has been observed that estimations of blood pressure (mean and systolic) have poor correlation with cardiac output in babies with a PDA.[8]

Blood flow to tissues and organs is influenced by their vascular beds, which are under the control of central and local vasoregulation, also referred to as autoregulation. This provides different organs with the ability to maintain internal blood flow over a wide range of arterial blood pressure fluctuations. When autoregulation is lost, blood flow becomes pressure passive; this may lead to ischemic or hemorrhagic consequences. The biochemical mediators of vasomotor tone for each vascular bed are different, and their complex interactions are not yet fully understood.

The ability of blood to impart delivery of oxygen and nutrients and to remove metabolic excretory products is largely determined by adequate lung ventilation and perfusion, oxygen-carrying capacity, and oxygen extraction by the tissues.

Hemoglobin content

Although each gram of hemoglobin can bind 1.36 mL of oxygen, fetal hemoglobin binds oxygen more tightly than adult hemoglobin and, thus, has a relatively reduced oxygen-unloading capacity at the tissue level. This results in a leftward shift of the oxygen-hemoglobin dissociation curve. Other factors that may cause a significant leftward shift of this curve frequently accompany shock and include hypothermia and hypocarbia. Under these circumstances, oxygen extraction by tissues may be decreased despite adequate oxygen delivery. Oxygen delivery to tissues is influenced by cardiac output and blood flow more so than blood pressure; hence, values of blood pressure that are statistically abnormal are not necessarily pathologic. This is true for systolic, diastolic, and mean arterial blood pressures. Similarly, hypotension is not synonymous with shock but may be associated with the later stages of shock. Determinants of cardiac function and oxygen delivery to tissues are shown in the image below.

Shock and Hypotension in the Newborn. Determinants Shock and Hypotension in the Newborn. Determinants of cardiac function and oxygen delivery to tissues. Adapted from Strange GR. APLS: The Pediatric Emergency Medicine Course. 3rd ed. Elk Grove Village, Ill: American Academy of Pediatrics; 1998:34.

 

Pathophysiology

Shock is a progressive disorder, but it can generally be divided into three phases: compensated, uncompensated, and irreversible.

Compensated shock

In compensated shock, perfusion to vital organs, such as the brain, heart, and adrenal glands, is preserved by sympathetic reflexes, which increase systemic arterial resistance. Derangement of vital signs, such as heart rate, respiratory rate, blood pressure, and temperature, may be absent or minimal.

Increased secretion of angiotensin and vasopressin allows the kidneys to conserve water and salt. The release of catecholamines enhances myocardial contractility, whereas decreased spontaneous activity reduces oxygen consumption.

Clinical signs at this time include pallor, tachycardia, cool peripheral skin, and prolonged capillary refill time. As these homeostatic mechanisms are exhausted or become inadequate to meet the metabolic demands of tissues, the uncompensated stage ensues.

Uncompensated shock

During uncompensated shock, delivery of oxygen and nutrients to tissues becomes marginal or insufficient to meet demands. Anaerobic metabolism becomes the major source of energy production, and lactic acid production increases significantly, resulting in metabolic acidosis. Acidosis reduces myocardial contractility and impairs its response to catecholamines.

Numerous chemical mediators, enzymes, and other substances are released, including histamine, cytokines (especially tumor necrosis factor and interleukin-1), xanthine oxidase (which generates oxygen free radicals), platelet-aggregating factor, and bacterial toxins (in the case of septic shock). This cascade of metabolic changes further reduces tissue perfusion and oxidative phosphorylation.

Anaerobic metabolism further results in failure of the energy-dependent sodium-potassium pump, which maintains a normal homeostatic environment for cell function. The integrity of the capillary endothelium is disrupted, and plasma proteins leak, with the resultant loss of oncotic pressure and extravasation of intravascular fluids into the extravascular space.

Sluggish flow of blood and chemical changes in small blood vessels lead to platelet adhesion and activation of the coagulation cascade, which may eventually produce a bleeding tendency and further deplete blood volume.

Clinically, patients with uncompensated shock present with falling blood pressure, very prolonged capillary refill time, tachycardia, cold skin, rapid breathing (to compensate for the metabolic acidosis), and reduced or absent urine output. If effective intervention is not promptly instituted, progression to irreversible shock follows.

Irreversible shock

In the setting of irreversible shock, major vital organs, such as the heart and brain, are so extensively damaged that death occurs despite adequate restoration of the circulation. Early recognition and effective treatment of shock are crucial in preventing progression to this stage.

Etiology

Many conditions and pathophysiologic disturbances are associated with shock and hypotension. Causes of neonatal shock include the following:

  • Hypovolemic shock: Caused by acute blood loss or fluid and electrolyte losses

  • Distributive shock: Caused by sepsis, vasodilators, myocardial depression, or endothelial injury

  • Cardiogenic shock: Caused by cardiomyopathy, heart failure, arrhythmias, or myocardial ischemia

  • Obstructive shock: Caused by tension pneumothorax or cardiac tamponade

  • Dissociative shock: Caused by profound anemia or methemoglobinemia

  • Mixed shock: Can occur in various disease conditions like sepsis, where there may be distributive shock to begin with and then cardiogenic shock develops later 

Risk factors

Risk factors for neonatal shock include the following:

  • Umbilical cord accident

  • Placental abnormalities

  • Fetal or neonatal hemolysis

  • Fetal or neonatal hemorrhage

  • Maternal infection

  • Maternal anesthesia, maternal hypotension

  • Intrauterine asphyxia, intrapartum asphyxia

  • Neonatal sepsis

  • Pulmonary air leak syndromes

  • Lung overdistention during positive pressure ventilation

  • Cardiac arrhythmias

Prognosis

Shock remains a major cause of neonatal morbidity and mortality, although—because it accompanies other primary conditions—specific figures for the frequency of shock in this population are unavailable. Prognosis following neonatal shock is related to the underlying cause (eg, sepsis, heart disease) and the injuries sustained during the period of inadequate perfusion. Early recognition and treatment is essential to maximizing outcome in neonatal shock. Morbidity as a consequence of end-organ injury and organ dysfunction is similar. Frequent sequelae include pulmonary, renal, endocrine, gastrointestinal (GI), and neurologic dysfunction. Delayed diagnosis and treatment can lead to permanent neurologic sequelae such as cerebral palsy, epilepsy, and mental retardation.

Complications

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. (See Pathophysiology.)

The liver and bowel may be damaged by shock, leading to GI bleeding and increasing the risk for necrotizing enterocolitis, particularly in the premature infant.

The extent of irreversible brain damage is probably the most anxiously monitored following shock, because the brain is so sensitive to hypoxic-ischemic injury once compensation fails. (See Pathophysiology.)

 

Presentation

History and Physical Examination

History

Newborns may present with signs of infections such as lethargy, poor feeding, and—rarely—with fever. A gistory of acute blood loss or fluid loss may be present in hypovolemic shock.

Physical examination

Clinical manifestations of hypotension include prolonged capillary refill time, tachycardia, mottling of skin, cool extremities, and decreased urine output. Carefully observe heart sounds, peripheral pulses, and breath sounds. If hypotension is left untreated, neurologic signs with altered sensorium and signs of other organ damage may ensue.

The physical examination should accurately assess blood pressure, existence of any heart murmurs, and presence of the femoral pulses. Measurement of neonatal blood pressure can be completed directly through invasive techniques or indirectly through noninvasive techniques. Invasive methods include direct manometry using an arterial catheter or the use of an in-line pressure transducer and continuous monitor. Noninvasive methods include manual oscillometric techniques and automated Doppler techniques.

A good correlation is observed between the systolic blood pressure measured by Doppler, and pressure as assessed by direct manometry using an intra-arterial catheter.

Hypovolemic shock

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 more than 40% in irreversible shock.

Cardiogenic shock

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.

Septic shock

The most common form of maldistributive shock in the newborn is septic shock; this is a source of considerable mortality and morbidity. In sepsis, cardiac output may be normal or even elevated, but it may still be too small to deliver sufficient oxygen to the tissues because of the abnormal distribution of blood in the microcirculation, leading to decreased tissue perfusion.[9] In septic shock, cardiac function may be depressed (the left ventricle is usually affected more than the right ventricle).

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, and peripheral vasoconstriction leads to cold shock. 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 represent a diagnostic and therapeutic challenge, and sepsis must be presumed and treated as quickly as possible.

As previously stated, shock is a progressive disorder and can generally be divided into three phases: compensated, uncompensated, and irreversible. Each phase has characteristic clinicopathologic manifestations and outcomes; however, in the neonatal setting, distinguishing them may be impossible. It is therefore important to initiate aggressive treatment in all cases where shock is suspected.

 

DDx

 

Workup

Approach Considerations

Attempt to determine the type of shock (eg, hypovolemic, cardiogenic, maldistributive) to guide the therapeutic approach. In neonates who are hypotensively compromised, the authors encourage the early use of a bladder catheter. Hourly urine output is one of the few objective methods of evaluating hypoperfusion that leads to specific organ failure, and its accurate objective measurement can augment clinical decision making.

Obtain the hematocrit, electrolyte levels, blood cultures, blood gases (for acid/base status), and glucose level as soon as vascular access is attained. Among laboratory investigations, data supporting the diagnosis of shock include metabolic acidosis on an arterial blood specimen in the face of reasonable oxygenation.

An elevated plasma lactate level with a normal pyruvate result (infrequently measured) suggests anaerobic metabolism triggered by tissue hypoxia-ischemia.

Other pertinent tests include the following:

  • Automated Doppler: Provides blood pressure readings through a noninvasive method

  • Manual oscillometric techniques: Used for noninvasive blood pressure testing

  • Infant blood pressure testing: Invasive methods include direct manometry using an arterial catheter and the use of an in-line pressure transducer and continuous monitor

Specific studies must be performed to determine the cause (eg, sepsis, cardiac lesions, anemia) and sequelae (eg, renal, hepatic, endocrine) of shock.

Echocardiography can provide useful insight into the pathophysiology involved in the hemodynamic instability as well as aid in therapeutic strategies. Newer modalities such as functional magnetic resonance imaging (MRI) are being evaluated to assess cardiac function. This technology is promising, but it is limited to research findings and is subject to the availability of an MRI scanner. It also has the limitation of an inability to perform repeated longitudinal measurements at the point of care, whereas this can be done with bedside echocardiography.

Noninvasive hemodynamic monitoring

With advances in technology, newer noninvasive hemodynamic monitoring devices such as Near-InfraRed Spectroscopy (NIRS) and electrical cardiometry are being used in many centers across the world. Both devices have the limitations of availability, cost and accuracy, and being noninvasive.

NIRS works on a principle similar to that of pulse oximetry, but it uses the NIR light of frequency ranging between 730 nm and 810 nm. It can be applied on the forehead for cerebral saturations on either side and also on the flanks for renal saturation or over the abdomen for splanchnic saturations. In the presence of shock, NIRS can help in early diagnosis and management. Cerebral NIRS measures cerebral regional oxgen saturations (CrSO2) in the watershed areas (anterior cerebral artery [ACA] and middle cerebral artery [MCA]) with a normal CrSO2 of 60-80%. In shock, these levels drop far below 50% and show improvement with fluid management, ionotropic support, and blood transfusion depending on the underlying pathology. Mesenteric NIRS measures splanchnic regional oxygen saturations (SrSO2) , where there is variable flow and lower extraction, thus splanchnic saturations are generally in the range of 5-20% more than CrSO2. Similarly, renal  circulation (RrSO2) is also of variable flow and higher extraction, ranging 5-20% more than CrSO2. In the presence of shock, regional saturations drop significantly and, especially in hypovolemic shock, these organs may be significantly affected due to the brain-sparing redistribution of blood.

Electrical cardiometry (EC) or noninvasive cardiac output monitoring devices work on the principle of measuring changing electrical impedance over that area of the thorax in relationship with blood flow during various phases of the cardiac cycle. It is a novel technique that noninvasively provides continuous bedside information on various parameters, such as cardiac output, systemic vascular resistance, cardiac contractility, and fluid status in the body. EC can help to differentiate various types of shock as well as monitor response to therapy.

Research is ongoing for other markers of septic shock, such as mannose-binding lectin,[10] vasopressin,[11] and the use of electrical cardiometry.[12]

Blood Gases

Mixed venous blood gases may be more helpful than arterial measurements, because mixed venous blood gases reflect oxygen extraction and waste products at the tissue level. Conversely, arterial blood reflects lung function and the gas composition of blood before it is delivered to the tissues.

Comparison of simultaneous arterial and mixed venous blood gas determinations may be more useful in assessing cardiac output, tissue oxygenation, and acid-base balance.

The value of capillary blood gas determinations is limited, because they may only reflect diminished perfusion to the periphery and not reflect central perfusion.

Echocardiography and Doppler Flow Velocimetry

Echocardiography and Doppler flow velocimetry may provide semi-quantitative and semi-qualitative noninvasive analysis of preload, myocardial function, and afterload. This may help in understanding the underlying pathophysiology for hemodynamic instability. In conjunction with other clinical parameters and monitoring tools, echocardiographic assessment can be used in selecting fluid resuscitation therapy or appropriate inotropic or vasopressor/vasodilator therapy.

Assessment of left ventricular output (LVO)

In the setting of a low LVO and an underfilled left ventricle (LV), volume expansion is the first-line management. With a normal LVO but impaired LV contractility, dobutamine or epinephrine may be the initial choice. A low LVO with paradoxical movement of the interventricular septum would benefit from dobutamine administration. If blood pressure is low despite normal or high LVO and patent ductus arteriosus (PDA) is not evident, a vasopressor (eg, dopamine or epinephrine) can initially be instituted. In case of a hemodynamically significant PDA, additional treatment for pharmacologic PDA closure maybe considered.

Assessment of superior vena cava (SVC) flow

SVC flow in newborn infants is reported to be a novel marker of systemic blood flow, as it is not affected by the presence of any persistent fetal shunts like PDA and patent foramen ovale (PFO).[13] Low SVC flow (< 41 mL/kg/min) has been used to diagnose hypotension and to predict poor long-term outcomes.[14] SVC Doppler is also used as a surrogate for LVO in the presence of a PDA.[15, 16]

Assessment of the preload inferior vena cava (IVC) size and collapsibility index are useful parameters for assessing right heart filling pressure in spontaneously breathing infants, and they have the potential to inform fluid responsiveness in neonates with septic shock.[15, 16]

Cardiac function can be further assessed using various functional echocardiography parameters that are used for measuring systolic and diastolic function.[16, 17]  A detailed description of these is beyond the scope of this article.

Patent ductus arteriosus

PDA is a significant cause of hypotension in preterm infants. Although the increase in LVO and other compensatory mechanisms may initially offset the effects of ductal shunt on systemic circulation, effective LVO is reduced over time. This can lead to organ hypoperfusion, and treatment of shock in such situations should be directed toward closing the PDA.

 

Treatment

Approach Considerations

In relatively recent years, there has been a movement away from defining hypotension in the newborn purely based on blood pressure lower than the infant's gestational age.[4, 18, 19] Rather, infants with hemodynamic instability require an individualized approach, in which the underlying pathophysiologic mechanisms should be stratified and management is adapted for appropriate intervention.[4, 18, 20]

Once shock is suspected in a newborn, appropriate supportive measures must be instituted as soon as possible.[3] These include securing the airway and assuring its patency, providing supplemental oxygen and positive-pressure ventilation, achieving intravascular or intraosseous access, and infusing 10 mL/kg of colloid or crystalloid solution (to repeat the same volume if needed). Use of crystalloid or colloid solutions is appropriate unless the source of hypovolemia is hemorrhage, in which case whole or reconstituted blood is more appropriate.

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.

Varying degrees of renal, myocardial, gastrointestinal (GI), hepatic, and brain damage may occur during shock as elaborated in Complications.

Surgical care

Structural heart disease and arrhythmias often require specific pharmacologic or surgical therapy. The liver and bowel may be damaged by shock, leading to GI bleeding and increasing the risk for necrotizing enterocolitis, particularly in the premature infant.

Diet

Infants in shock should not be fed via the oral route, and feedings should not be resumed until GI function has recovered. Initiate total parenteral nutrition as soon as possible.

Consultations

Depending on the type of shock, potential consultants include the following pediatric subspecialists: neonatologist, cardiologist, nephrologist, surgeon, infectious disease specialist, and hematologist.

Transfer

If deemed safe, infants presenting with evidence of shock should be transferred immediately to a full-service neonatal intensive care unit with adequate support, personnel, and expertise.

Monitoring

Infants recovering from neonatal shock are at risk of multiple sequelae and should be intensively screened for neurodevelopmental abnormalities using brain imaging and brainstem audiometric evoked responses. Other tests are determined by the individual infant's clinical course and complications.

Outpatient care should include neurodevelopmental follow-up and assessment, as indicated by the neonatal course.

Hypovolemic Shock

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 more than 40% in irreversible shock.

If blood loss is confirmed, initial resuscitation with 20 mL/kg of volume expansion should replace a quarter of the blood volume. Blood transfusion is preferred, but in an emergency, colloids or crystalloids can be used. If circulatory insufficiency persists, this dose can be repeated.

Once the first 10 mL/kg of blood volume is replaced, a decision to provide any further volume expansion should prompt the clinician to ascertain the cause of the hypotension and to evaluate the circulatory status. Information regarding central venous pressure (CVP) values in stable, ventilated newborns is limited; therefore, interpretation of readings in ill neonates is challenging. Its role in the management of systemic hypotension is uncertain, but serial measurements through an appropriately placed umbilical venous or other central venous catheter may help to guide volume expansion in suspected hypovolemia.[21] In the absence of CVP, titration against clinical parameters should be completed. Frequent and careful monitoring of the infant's vital signs with frequently repeated assessments and reexamination is mandatory. The use of crystalloid or colloid solutions is appropriate, unless the source of hypovolemia is hemorrhage, in which case whole or reconstituted blood is more appropriate. Commonly used agents include the following:

  • Isotonic sodium chloride solution: A low-cost, readily available alternative

  • Albumin: Useful for plasma volume expansion and the maintenance of cardiac output

  • Lactated Ringer solution

Each fluid is essentially isotonic and has equivalent volume-restorative properties. Although some differences between metabolic changes are observed with the administration of large quantities of either fluid, for practical purposes and in most situations, the differences are clinically irrelevant. Importantly, there is no demonstrable difference in hemodynamic effect, morbidity, or mortality with resuscitation.

Cardiogenic Shock

Inotropic agents, with or without peripheral vasodilators, are warranted in most circumstances of cardiogenic shock. Structural heart disease or arrhythmia often requires specific pharmacologic or surgical therapy. Excessive volume expansion may be potentially harmful. Table 1 summarizes the appropriate use of inotropes, lusitropes, or vasopressors in this situation (see Pharmacologic Therapy).

Septic Shock

Newborns, who have little cardiac reserve, often present with hypotension and a picture of cardiovascular collapse. These critically ill infants represent a diagnostic and therapeutic challenge, and sepsis must be presumed and treated as quickly as possible. Survival from septic shock depends on the 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, combined aminoglycoside and expanded-spectrum penicillin antibiotic therapy are the empiric antimicrobials of choice until a specific infectious agent is identified. Cephalosporins and vancomycin are often the antibiotics of choice in late-onset sepsis. Howver, concerns have been raised about the routine use of cephalosporins. In the face of renal failure, which may accompany shock, serum levels of gentamicin and vancomycin should be closely monitored to minimize iatrogenic renal toxicity.

Pharmacologic Therapy

The selection of drug for medical management of shock depends on the underlying cause. Table 1, below, lists agents commonly used in the treatment of neonatal shock.

Table 1. Agents Used to Treat Neonatal Shock (Open Table in a new window)

Agent Type

Agent

Initial Dosage

Additional Factors

Volume expanders

Isotonic sodium chloride solution

10-20 mL/kg intravenous (IV)

Inexpensive, available

Albumin (5%)

10-20 mL/kg IV

Expensive

Plasma

10-20 mL/kg IV

Expensive

Lactated Ringer solution

10-20 mL/kg IV

Inexpensive, available

Isotonic glucose

10-20 mL/kg IV

Inexpensive, available

Whole blood products

10-20 mL/kg IV

Limited availability

Reconstituted blood products

10-20 mL/kg IV

Use type O negative

Vasoactive drugs

Dopamine

5-20 mcg/kg/min IV

Never administer intra-arterially

Dobutamine

5-20 mcg/kg/min IV

Never administer intra-arterially

Epinephrine

0.05-1 mcg/kg/min IV

Never administer intra-arterially

Hydralazine

0.1-0.5 mg/kg IV every 3-6 h

Afterload reducer

Isoproterenol

0.05-0.5 mcg/kg/min IV

Never administer intra-arterially

Nitroprusside

0.5-8 mcg/kg/min IV

Afterload reducer

Norepinephrine

0.05-1 mcg/kg/min IV

Never administer intra-arterially

Phentolamine

1-20 mcg/kg/min IV

Afterload reducer

Milrinone

22.5-45 mcg/kg/h continuous IV infusion (ie, 0.375-0.75 mcg/kg/min)

Afterload reducer in cardiac dysfunction; reduce the dose in the setting of renal impairment

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

 

Medication

Medication Summary

In premature infants younger than 30 weeks' gestation, poor cardiac contractility is common; patients benefit from early institution of dobutamine. Other agents often used to manage hypotension in preterm infants include dopamine, epinephrine, norepinephrine, vasopressin, and milrinone; clinicians should closely monitor these infants for side effects of these medications.[19]

Patients with septic shock benefit from dopamine as first-line management; it has been found to be more effective than dobutamine and albumin in correcting blood pressure for short-term treatment in these situations; however, the effect of these drugs on long-term outcome is unknown.

Although adrenaline is used for cardiovascular compromise, its effect on mortality and morbidity has not yet been evaluated.

No evidence suggests that milrinone is beneficial in prevention of low systemic blood flow in ill, very-preterm neonates during the first postnatal day.

Evidence for using various inotropes or vasopressors is mainly derived from the adult or child population as not many trials have been published in neonatal population. It is thus generally advisable to manage newborns with shock using a physiologic-based approach with support of functional echocardiography. The first-line management in many scenarios is administration of normal saline boluses, but evidence does not support that it always increases blood pressure[22] or superior vena cava (SVC) flow.[23] Moreover, the majority of hypotensive preterm infants are not hypovolemic; hence, overzealous fluid administration is to be avoided.[24] However, when there is definitive evidence of volume loss in hypovolemic shock and also in redistributive shock, then volume expansion with saline or colloids can be considered.

Over the last couple of decades, practices in managing shock and hypotension in the newborn have changed but without significant change in mortality. The use of dopamine and dobutamine has shown a decreasing trend, along with a concomitant increase in use of epinephrine and hydrocortisone.[25] Additionally, trials that had been planned in the last decade regarding the use of inotropes, such as the Hypotension in Preterm Infants (HIP) trial (dopamine), Dobutamine for NEOnatal CIRCulatory failure (NeoCirc) trial (dobutamine guided by SVC flow), and Treatment of Hypotension of Prematurity (TOHOP) trial (intervention guided by compromised tissue perfusion), were not completed; thus, there are no substantive data to guide the use of inotrope/vasopressor agents in this population.

There are multiple challenges in performing trials in neonates on the use of various inotropes. These trials are difficult to initiate, and multi-site studies require interaction with multiple agencies. Additionally, enrollment can be challenging, with timely informed consent being a major factor. Also, lack of clinician equipoise and the unwillingness to enroll patients have been identified as key obstacles.

Thus, the choice of inotropes or vasopressors for medical management of shock is physiology based rather than evidence based, and it is increasingly guided by functional echocardiographic findings.

Cardiovascular drugs and their effects

The image below demonstrates presumed effects of cardiovascular drugs commonly used in neonatology.[17] The right side denotes more vasodilatory effects, whereas the left side shows more vasoconstrictory effects. On the Y-axis (inotropic properties), higher positions indicate more inotropic characteristics. The larger the size of the (semi-)circle, the more chronotropic effects.

Shock and Hypotension in the Newborn. Presumed eff Shock and Hypotension in the Newborn. Presumed effects of commonly used cardiovascular drugs in neonatal intensive care. X-axis (effect on vascular tone): The more to the right, the more vasodilatory effects; the more to the left, the more vasoconstrictory effects. Y-axis (inotropic properties): The higher on the Y-axis, the more inotropic characteristics. The larger the size of the (semi-)circle, the more chronotropic effects. It should be noted that the effect on vascular tone depends on the used dosage that determines which adrenergic receptors are activated (e.g., dopamine and epinephrine). Courtesy of Springer Nature [de Boode WP et al. The role of neonatologist performed echocardiography in the assessment and management of neonatal shock. Pediatr Res. 2018 Jul;84(suppl 1):57-67. Online at: https://www.nature.com/articles/s41390-018-0081-1. PMID: 30072807.].

Alpha/Beta Adrenergic Agonists

Class Summary

Cardiovascular performance deteriorates and cardiac output falls if effective therapy is not administered. Adrenergic antagonists improve the patient’s 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.

Dopamine

Dopamine stimulates adrenergic and dopaminergic receptors. Its hemodynamic effect is dependent on the dose. Lower doses predominantly stimulate dopaminergic receptors that, in turn, produce renal and mesenteric vasodilation. Cardiac stimulation and peripheral vasoconstriction is produced by higher doses.

Dobutamine

Dobutamine produces vasodilation and increases the inotropic state. At higher dosages, it may cause increased heart rate, exacerbating myocardial ischemia.

Epinephrine (Adrenalin)

Epinephrine elicits alpha-agonist effects that include increased peripheral vascular resistance, reversed peripheral vasodilatation, systemic hypotension, and vascular permeability. The drug's beta-agonist effects include bronchodilatation, chronotropic cardiac activity, and positive inotropic effects.

Isoproterenol (Isuprel)

Isoproterenol possesses beta1- and beta2-adrenergic receptor activity. It binds to beta receptors of the heart, smooth muscle of the bronchi, skeletal muscle, vasculature, and alimentary tract. Isoproterenol elicits positive inotropic and chronotropic actions.

Norepinephrine (Levophed)

Norepinephrine is used to treat protracted hypotension following adequate fluid-volume replacement. It stimulates beta1- and alpha-adrenergic receptors, increasing cardiac muscle contractility and heart rate, as well as vasoconstriction; this results in systemic blood pressure and coronary blood flow increases. After obtaining a response, the rate of flow should be adjusted and maintained at a low-normal blood pressure, such as 80-100 mmHg systolic, sufficient to perfuse vital organs.

Vasodilators

Class Summary

Preload reduction with vasodilators is thought to be helpful in acute decompensated heart failure by reducing congestion and minimizing cardiac oxygen demand. Afterload reduction is also thought to be helpful in some patients with acute decompensated heart failure by decreasing myocardial oxygen demand and improving forward flow.

Hydralazine

Hydralazine decreases systemic resistance through direct vasodilation of arterioles.

Nitroprusside (Nitropress)

Nitroprusside produces vasodilation and increases inotropic activity of the heart. At higher dosages, it may exacerbate myocardial ischemia by increasing heart rate.

Inotropic agents

Class Summary

Inotropic agents increase cardiac contractility and may reduce vascular tone by vasodilatation.

Phentolamine (Oraverse)

Phentolamine has positive inotropic and chronotropic effects on the heart. Phentolamine is an alpha1- and alpha2-adrenergic blocking agent that blocks circulating epinephrine and norepinephrine action, reducing hypertension resulting from catecholamine effects on alpha receptors.

Milrinone

Milrinone is a bi-pyridine positive inotrope and vasodilator with little chronotropic activity. Its mode of actions differs from that of digitalis glycosides and catecholamines. Milrinone selectively inhibits phosphodiesterase type III (PDE III) in cardiac and smooth vascular muscle, resulting in reduced afterload and preload and increased inotropy.

Volume Expanders

Class Summary

The use of crystalloid or colloid solutions is appropriate, unless the source of hypovolemia is hemorrhage, in which case whole or reconstituted blood is more appropriate.

Sodium chloride hypertonic, ophthalmic

Isotonic sodium chloride solution is a low-cost alternative that is readily available.

Albumin (Albuminar, Buminate)

Albumin is useful for plasma volume expansion and the maintenance of cardiac output.

Lactated Ringer solution with isotonic sodium chloride

Each fluid is essentially isotonic and has equivalent volume restorative properties. Although some differences between metabolic changes are observed with the administration of large quantities of either fluid, for practical purposes and in most situations, the differences are clinically irrelevant. Importantly, there is no demonstrable difference in hemodynamic effect, morbidity, or mortality with resuscitation.

Antibiotics, Other

Class Summary

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

Ampicillin

Ampicillin has bactericidal activity against susceptible organisms.

Cefotaxime (Claforan)

Cefotaxime is a third-generation cephalosporin that possesses antimicrobial effects on a predominantly gram-negative spectrum. Its efficacy against gram-positive organisms is lower.

Gentamicin

Gentamicin is an aminoglycoside antibiotic for gram-negative coverage. It is used in combination with an agent against gram-positive organisms and one that covers anaerobes. Dosing regimens are numerous; adjust the dose based on creatinine clearance (CrCl) and changes in the volume of distribution. The drug may be administered intravenously or intramuscularly.

Follow each regimen by at least a trough level drawn on the third dose (0.5 h before dosing). Peak levels may be drawn 0.5 hour after a 30-minute infusion. If the trough level is greater than 2 mg/L, increase the dosing interval.