Pediatric and Neonatal Critical Care

Shock

Shock is the inability to provide adequate oxygen to the tissues that require it. The condition of shock depends on the balance of supply and demand of oxygen. Typically the body delivers excess oxygen to the tissues. Under periods of stress or illness there can be a decrease in supply caused by diminished blood flow or as decreased oxygen in blood. There can also be increased demand or oxygen extraction from the tissues. The content of oxygen is the blood is dependent on the amount bound to hemoglobin and the amount dissolved in plasma. Oxygen content (CaO ₂ ) (mL/dL) = (1.34g/dL) (SaO ₂ ) (Hb) + (PaO ₂ ) (0.003). The normal oxygen content is approximately 20 mL/dL. Delivery of oxygen to the tissues depends on oxygen content and cardiac output. Oxygen delivery ( $\dot{D}{\text{O}}_2$ ) (mL/min) = oxygen content (CaO ₂ ) × cardiac output (CO) × 0.01. Oxygen consumption ( $\dot{V}{\text{O}}_2$ ) is the demand portion of the equation. Oxygen consumption ( $\dot{V}{\text{O}}_2$ ) is independent of oxygen delivery ( $\dot{D}{\text{O}}_2$ ) above a critical threshold and over a wide range. Below this critical threshold $\dot{V}{\text{O}}_2$ is dependent on $\dot{D}{\text{O}}_2$ . For infants and young children, $\dot{V}{\text{O}}_2$ is estimated at 175 mL/min/m ² . Oxygen consumption is equal to oxygen delivery multiplied by oxygen extraction (O ₂ EX) by the body: $\dot{V}{\text{O}}_2=\dot{D}{\text{O}}_2\times {\text{O}}_2\text{EX}$ . Oxygen extraction O ₂ EX is equal to (CaO ₂ – CvO ₂ )/CaO ₂ . CaO ₂ is the oxygen content of arterial blood and CvO ₂ the oxygen content of venous blood. The difference between oxygen content of arterial and venous blood is predictably 4 to 6 mL/100 mL blood. Initially, as oxygen delivery decreases, the oxygen consumption can remain constant via increased extraction. Below a critical threshold in oxygen delivery, oxygen consumption becomes dependent on delivery. When oxygen to meet metabolic needs of the body cannot be met, nonessential metabolism is decreased or eliminated. Such metabolism includes growth, neurotransmitter synthesis, thermoregulation, and so forth. In this way the remaining oxygen can continue to be substrate for mitochondria. There are organs in the body, such as the kidney, skin, intestines, and skeletal muscle, that receive a high supply of blood relative to their metabolic needs. These organs also have a high proportion of sympathetic nerve innervations that allow for redistribution of blood flow to organs that with limited oxygen reserves such as the brain and heart.

Classification of Shock

There are several schemas which clinicians use to classify shock. Further within these classification schemas, disease states can fall into more than one category. One classification schema separates shock into the categories of hypovolemic, cardiogenic, distributive or vasogenic, and extracardiac obstructive.

Hypovolemic shock can be due to hemorrhage from trauma or gastrointestinal (GI) losses from internal bleeding. Nonhemorrhagic hypovolemic shock can be due to external losses of fluid from vomiting, diarrhea, polyuria, and poor fluid intake. Fluid redistribution in cases of burns, trauma, and anaphylaxis can also be a cause.

Cardiogenic shock may be myopathic due to decreased heart function. For adults this may commonly follow myocardial infarction. For children, myocarditis or cardiomyopathy are more common. Other causes of cardiogenic shock include mechanical failure such as valvular regurgitation or obstruction. Significant arrhythmias may result in cardiogenic shock when contractions are so asynchronous they decrease cardiac output.

Extracardiac obstructive shock results from a physical obstruction that prevents adequate forward circulatory flow. Causes include inadequate preload secondary to mediastinal masses, increased intrathoracic pressure from tension pneumothorax, constrictive pericarditis, and cardiac tamponade from pericardial effusions. Pulmonary hypertension, pulmonary embolus, and aortic dissection can cause obstruction to systolic contraction.

Distributive shock is caused by a decrease in SVR and the maldistribution of end-organ blood flow. Cardiac output may be increased in distributive shock, however, blood pressure may remain low due to a very low SVR. Septic causes of distributive shock can be related to bacterial, fungal, viral or rickettsial infections or toxins produced from these infections. Toxic shock syndrome would be an example of toxin-mediated hypotension. Anaphylactic or anaphylactoid reactions are a type of distributive shock. Systemic inflammatory response syndrome (SIRS) may present with distributive shock. Spinal shock can result in distributive shock on a neurogenic basis. Adrenal insufficiency with low circulating hormones results in distributive shock decreased SVR.

Diagnosis of Shock

Maintaining a high index of suspicion is important to rapidly identify shock in pediatric patients. Volume losses may be readily apparent from the history of present illness. Fever, rash and irritability may point to infection. However, cardiogenic shock may present with vague reports of decreased activity and level of alertness. In addition, if the patient’s shock is currently compensated, changes in physical findings may be limited. A child in shock may present initially with tachycardia, cold extremities, and poor capillary refill. Further, in distributive shock, the child may be warm with just an isolated tachycardia. A brief pertinent physical exam should evaluate level of alertness, peripheral perfusion, mucous membranes, pulse rate and quality, respiratory effort, urine output, and blood pressure. In children, blood pressure may be preserved until the degree of shock has progressed. Hypotension is a sign of late and decompensated shock in children. Metabolic acidosis may not be present on the initial laboratory tests.

Compensatory Mechanisms

The body applies compensatory mechanisms with the onset of shock to maintain adequate tissue perfusion for as long as possible. There is redistribution of fluid from the intracellular and interstitium to the vascular space. There is a decrease in glomerular filtration to limit renal fluid losses. Renal fluid losses are also limited by the release of aldosterone and vasopressin. There is an increase in sympathetic activity and release of epinephrine. This results in decreased venous capacitance and some preservation of blood pressure. HR is increased as the body tries to maintain cardiac output. There is an increase in cardiac contractility through circulating catecholamines and adrenal stimulation. Increase in sympathetic nerve stimulation shunts blood away from nonvital organs. At the tissue level, transfer of oxygen from hemoglobin is increased by increased red blood cell (RBC) 2, 3-diphosphoglycerate, fever, and tissue acidosis.

Therapy and Outcomes

Aggressive therapy to treat pediatric septic shock appears to have resulted in improved outcomes. Therefore therapy for septic shock appears to be a good model for the treatment of shock in general. The overall goal of therapy in shock is to treat the underlying cause, return adequate oxygen delivery to the tissues, and remove metabolic products that developed during anaerobic metabolism. It appears the faster the body returns to adequate perfusion, the better the overall outcome. Many hospitals have developed sepsis pathways based on the data presented as follows that act as guidelines for resuscitation and are readily available to all care providers ( Fig. 79.1 ).

In 1991 Carcillo et al. described a population of 34 children that presented with septic shock to an emergency department. Shock was diagnosed based on hypotension for age, with decreased perfusion, poor peripheral pulses, cool extremities, and tachycardia. Sepsis was defined as a positive blood or tissue culture. Remarkably, within 6 hours of presentation, all the patients had a pulmonary artery catheter placed. The overall mortality for the group was 47%. However, in the nine patients who received more than 40 mL/kg of fluids in the first hour, there was only one death (mortality 11%). The authors point out this patient died with a second episode of sepsis 2 weeks later. In this study, the rapid fluid administration was not associated with an increase in cardiogenic pulmonary edema or ARDS.

In 2001 Rivers et al. published a study in adult patients with septic shock showing early, aggressive, goal directed therapy in the first 6 hours of care improved mortality. There were 263 adults were enrolled; 133 received standard therapy based on clinician discretion. The 130 patients randomized to early goal-directed therapy followed protocols treating hypovolemia and supporting blood pressure with vasoactive agents if necessary. The baseline characteristics of the two groups were similar. The in-hospital mortality was 46.5% in the standard therapy group and 30.5% in early goal-directed therapy group ( P < .01). Although in adults, this demonstrated the need for early aggressive intervention.

Following the Rivers publication, a task force was formed by members of the Society of Critical Care Medicine to address shock in children. Their work was published in 2002 as “Clinical Practice Parameters for Hemodynamic Support of Pediatric and Neonatal Patients in Septic Shock.” Their guidelines were incorporated into the American Heart Association’s (AHA) Pediatric Advanced Life Support (PALS) Provider Manual. Their guidelines were translated into Spanish and Portuguese and disseminated widely. The effectiveness of these interventions as well as an 2007 update was published by the same group in 2009. They highlighted significant improvements in mortality in dengue shock syndrome, malaria, and septic shock treated by community physicians using early goal directed therapy. The guidelines include rapid recognition of shock and early antibiotic administration and early administration of intravenous (IV) crystalloid. The initial resuscitation should include 20 mL/kg of isotonic saline or colloid pushed as a bolus to over 60 mL/kg until there is an improvement in the patient’s perfusion or rales or hepatomegaly develops. The goal is for the initial fluid resuscitation to occur in the first 15 minutes of therapy, and therapy should be initiated even if peripheral IV cannulation attempts fail, by placing and intraosseous (IO) device ( Fig. 79.2 ). The guidelines target therapeutic end points of normal pulses with no difference between peripheral and central; capillary refill ≤ 2 seconds; warm extremities, normalization of blood pressure for age, mental status, glucose concentration, ionized calcium concentration; and urine output greater than 1 mL/kg/h. If central venous access is not readily obtained, consideration should be given for placement of an IO line. Cold shock (cold mottled extremities with prolonged capillary refill) should be treated with dopamine up to 10 μg/kg/min and then epinephrine 0.05 to 0.3 μg/kg/min if there is no improvement. Warm shock (brisk capillary refill) should be treated with NE. Arrangements should be made early to admit the child to an ICU. If shock is not reversed with the inotropic support, hydrocortisone should be considered for catecholamine resistant shock. Recommendations for stabilization in the ICU following the first hour of therapy include monitoring central venous pressure, central venous saturation, and cardiac output. Persistent shock that is resistant to catecholamines should prompt the clinician to rule out pericardial tamponade, pneumothorax, or significantly elevated intra-abdominal pressure that may be compromising circulation. In the absence of a correctible condition, extracorporeal membrane oxygenation (ECMO) should be considered.

There were several new recommendations in the 2007 guidelines that addressed changes in the literature between 2002 and 2007. It was identified that the availability of skilled practitioners to place central venous access could delay the initiation of inotropic support. Therefore, the 2007 guidelines recommended the use of a peripheral IV dopamine or epinephrine if there was delay in obtaining central venous access. Ongoing monitoring of the access site should be performed. It was not recommended to use NE in a peripheral IV, due to risk of extravasation. In the 2002–2007 interval there were several pediatric and adult studies indicating adrenal suppression and increased severity of illness adjusted mortality with the use of etomidate. The 2007 guidelines do not recommend the use of etomidate unless it is in the format of a randomized controlled trial. Ketamine with atropine was recommended for sedation for invasive procedures in infants and children. However, due to limited experience, ketamine could not be recommended for the newborn population.

The 2007 guidelines recommend titrating therapy to cardiac output and indicate that there are several methods by which cardiac output can be measured. The use of pulmonary arterial catheters has decreased in pediatrics over time, but other methods are available. A good review of monitoring techniques was published by Mtaweh et al. in 2013. Cardiac output can be monitored by newer techniques analyzing the arterial pulse wave, transpulmonary thermodilution, carbon dioxide rebreathing, echocardiography, bio-impedance of the thorax, and ultrasound continuous-wave Doppler. These techniques are less invasive than pulmonary artery catheters. However, many still require validation studies in pediatric, and they may not be available at all centers.

One additional area to be addressed in the 2007 guidelines is in the area of fluid removal. A study published by Goldstein et al. in 2005 in pediatric patients with multiorgan failure, including acute renal failure requiring continuous renal replacement therapy (CRRT), showed improved survival in the group that had a lower percentage of fluid overload at the initiation of CRRT. While supporting the primary premise of fluid resuscitation, the 2007 guidelines offered new recommendation for fluid removal in patients with fluid overload and multiorgan failure. They recommended the use of diuretics, peritoneal dialysis, or CRRT in patients who had been adequately fluid resuscitated but were not able to maintain an even fluid balance through native urine output. Again, it should be noted that peritoneal dialysis and CRRT for pediatric patients may not be available at all centers. However, the association between fluid overload and mortality with acute renal failure has been seen in other studies and will likely be an ongoing issue in pediatric ICU care.

The concern for possible adrenal insufficiency during septic shock needs to be addressed by the clinician caring for the patient. There are certain instances where limited function of the adrenal axis is anticipated. This would include patients who have recently received glucocorticosteroids, ketoconazole, or etomidate. Further, patients with disease states such as purpura fulminans or those affecting the hypothalamus, pituitary, or adrenal glands will be at increased risk. Patients with adrenal insufficiency need supplemental corticosteroids. However, for children with septic shock but without these factors, it is not clear whether the risk of relative adrenal insufficiency or treatment with systemic steroids alter outcome. Dr. Zimmerman reviewed the adult and limited pediatric literature in 2007 for therapeutic steroid use in sepsis. He highlighted adult studies showing high dose short courses of steroids are associated with decreased survival. Further, data from the CORTICUS trial indicated that low dose steroids as a physiologic replacement during periods of vasopressor resistant shock resolve shock more quickly but there was no change in mortality. In turn, the 2007 guidelines were unchanged from 2002. Hydrocortisone treatment was only recommended for patients with absolute adrenal insufficiency or adrenal-pituitary axis failure and catecholamine-resistant shock. Absolute adrenal insufficiency was defined as peak cortisol concentration of less than 18 μg/dL obtained after corticotropin stimulation.

Dopamine

Dopamine is the most commonly infused inotrope in pediatric patients. Dopamine is the metabolic precursor of both NE and epinephrine. Its effects are dose dependent, with dopaminergic activity at low doses (although these low-dose dopamine effects have not been demonstrated in critically ill children); β-adrenergic activity with intermediate doses 5 to 10 μg/kg/min exhibiting chronotropic and inotropic effects; and some α-adrenergic activity at higher doses, with 10 to 20 μg/kg/min exhibiting peripheral vasoconstriction. Young children require higher doses of dopamine than adults do to produce the same effect. In one study, an infusion of 15 μg/kg/min was required to increase cardiac output above control levels after cardiac surgery. This may reflect the decreased releasable myocardial stores of NE in immature ventricles. Therefore, in the sick preterm infant there can be decreased dopamine clearance with a much greater vasopressor response than expected.

Vasopressin

Vasopressin is a pituitary peptide hormone with method of action on the kidney and vasculature. In the kidney, vasopressin controls water reabsorption in the renal tubules, and in the vasculature, it causes vasoconstriction by stimulating smooth muscle V1 receptors. Its clinical applications include GI hemorrhage, central diabetes insipidus (DI), and as a second- or third-line agent to treat hypotension.

Isoproterenol

Isoproterenol is a synthetic, potent, nonselective β-agonist with strong chronotropic effects with very low affinity to α-adrenergic receptors, and is usually well tolerated in children. However, high doses of isoproterenol can cause myocardial ischemia. Isoproterenol also induces vasodilation that is responsive to acute volume administration. It is often used for increasing HR in complete heart block, in the immediate postoperative period after cardiac transplantation to improve cardiac output by increasing HR in the denervated donor heart, and as a potent pulmonary vasodilator during pulmonary hypertensive crisis via β2-adrenergic receptor activity.

Dobutamine

Dobutamine provides positive inotropy and afterload reduction, β and α receptors. Its function is primarily as a inotropic agent but with less vasopressor activity compared with dopamine. It is only used as a continuous infusion of 5 to 20 μg/kg/min, and in some studies may increase myocardial oxygen In children but not in adults it causes tachycardia.

Norepinephrine

NE, a drug with strong α- and β-agonist effects, has had a resurgence of use in infants and children. Children with nearly normal cardiac function and marked peripheral vasodilation have good responses to this drug. It is especially useful in instances of warm septic shock, anaphylaxis, liver failure, and sympathetic blockade with regional anesthesia. It will increase SVR, but also limits mesenteric blood flow, including hepatic perfusion.

Milrinone

Milrinone is a selective phosphodiesterase III inhibitor that increases cyclic adenosine monophosphate by inhibiting breakdown. Milrinone has both inotropic and vasodilator effects, without acting on α and β receptors. This drug has improved the outcome of children who have low cardiac output syndrome after cardiac surgery. The loading dose of milrinone is 25 to 75 μg/kg administered over a period of 10 minutes; the maintenance infusion rate is 0.25 to 0.75 μg/kg/min. Loading doses are often avoided in the ICU setting because of resultant hypotension. Renal failure significantly increases the elimination half-life of this drug. Outside the cardiac ICU, milrinone is used for vasoconstricted septic shock and may have a role in the treatment of pulmonary hypertension.

Levosimendan

Levosimendan is a novel agent that increases the sensitivity of the contractile apparatus to calcium increasing inotropy by binding to cardiac myocyte troponin C. This agent will increase cardiac ejection fraction, while reducing catecholamine dose with minimal effects on blood pressure and HR. In children, the most common indications have been for cardiac failure or post–cardiac surgery, with a loading does of 612 μg/kg followed by an infusion of 0.1 to 0.2 μg/kg/min.

Nesiritide

Nesiritide is a recombinant form of the human B-type natriuretic peptide, the hormone release from the cardiac ventricles in response to volume overload and increasing mechanical wall stress. The action is on guanylate cyclase with resulting venous and arterial vasodilation. In addition, B-type natriuretic peptide leads to myocardial relaxation (lusitropy) and natriuresis. In children, it has been used to decrease central venous pressure and increase urinary output. Usual dosing suggestions for children and adults: initial 2 μg/kg bolus followed by a continuous infusion of 0.005 to 0.01 μg/kg/min.

Digitalis

Digitalis is useful for the long-term treatment of myocardial failure in children but may not be effective in neonates. Because of its long half-life and unpredictability, digitalis should be administered cautiously to children who have changing levels of serum potassium, calcium, and pH. In these cases, it is more appropriate to use rapid-acting, titratable inotropic agents.

Calcium

When serum ionized calcium levels are below normal, administration of calcium produces a positive inotropic effect. If the patient’s ionized calcium levels are normal, less marked inotropic effects occur. Low ionized calcium levels most commonly occur in patients with DiGeorge’s syndrome, when large volumes of citrate-containing blood products are rapid administered, and in neonates with relatively unstable calcium metabolism. Calcium also has effects on the cardiac conduction system. Rapid administration of calcium can cause severe bradycardia or asystole. This effect may be exaggerated in hypokalemic children or in those receiving digitalis. The vasomotor effects of calcium are controversial, but most reports show an increase in both SVR and PVR when the drug is administered.

Bicarbonate Therapy

Severe acidosis decreases myocardial function and tissue perfusion. Correction of acidosis with 1 to 2 mEq/kg of sodium bicarbonate is indicated for a pH below 7.20 if ventilation is adequate (PCO ₂ <40 mm Hg if possible). Treatment is necessary because the circulatory system is refractory to sympathomimetic amines when the pH is less than 7.00. After initial correction of pH, persistence or reappearance of metabolic acidosis suggest a continuing underperfused state and the need for further therapy. Administration of sodium bicarbonate is only a stopgap measure to improve the response to drugs. Repeat infusions of sodium bicarbonate can cause hypernatremia and hyperosmolarity. Every 50 mEq of bicarbonate administered produces 1250 mL of CO ₂ when the bicarbonate is fully reacted with acid. Consequently, adequate ventilation must be ensured while the drug is administered to avoid worsening the acidosis. Trishydroxymethylaminomethane (THAM) is an alternative to sodium bicarbonate, but larger volumes of THAM are required to produce the same amount of acid-base correction, which may be a problem in patients who have CHF. THAM does not increase PaCO ₂ .

Vasodilators

Vasodilators are used to control systemic hypertension, increase cardiac output by decreasing afterload, control pulmonary hypertension, and control cardiac shunting. Vasodilators are an effective treatment of systemic hypertension and increase cardiac output in children with CHF. Treatment of pulmonary hypertension and intracardiac shunting with vasodilators has met with limited success because they decrease both PVR and SVR, which may increase extrapulmonary right-to-right shunting and further reduce pulmonary blood flow.

Nicardipine

Nicardipine is a dihydropyridine calcium channel-blocking agent used as an IV infusion that has powerful, antihypertensive effects in children. Studies have shown that the rapid onset of action is usually within 1 minute, adding to the profile appropriate for treating severe hypertension. Flynn et al. reports that nicardipine is an effective anti-hypertensive medication in children ranging in age from 2 to 18 years. In our institution, nicardipine is the drug of choice for hypertensive crisis. Infusion ranges: 0.5 to 1.0 μg/kg/min up to 3.0 μg/kg/min.

Sodium Nitroprusside

Sodium nitroprusside relaxes arteriolar and venous smooth muscle, which decreases afterload and preload. The half-life of sodium nitroprusside is only minutes, making it safe to titrate the drug to a desired effect. Nitroprusside is commonly used to control severe systemic hypertension, to provide controlled hypotension to reduce blood loss, and to increase cardiac output in children with low cardiac output syndromes (myocarditis, post–cardiac surgery status). Sodium nitroprusside can generally be used for days without problems, although cyanide and thiocyanate poisoning develops in some children, especially those with renal failure or reduced renal perfusion. Serum thiocyanate levels of 10 mg/dL are associated with weakness, hypoxia, nausea, muscle spasms, and disorientation. When these symptoms occur, nitroprusside administration should be discontinued immediately.

Hydralazine

Hydralazine is used to control systemic hypertension because it relaxes arterial smooth muscle more than it relaxes veins. Administration of the drug can cause headache, nausea, dizziness, sweating, and tremors. The most important acute side effect is tachycardia, which may increase cardiac output; labetalol, a β-antagonist, can counteract this effect.

Tolazoline and Phentolamine

These competitive α-adrenergic blockers have had varied success in the treatment of pulmonary hypertension. However, they are effective in treating the symptoms of pheochromocytoma preoperatively. Serious side effects of these drugs include tachycardia, ventricular arrhythmias, hypotension, and tissue edema.

Prostaglandin E ₁

PGE ₁ acts directly on vascular smooth muscle and has greatly improved the care of neonates with heart disease. At infusion rates of of 0.1 μg/kg/min, patency of the ductus arteriosus is maintained and a closed ductus reopens in some neonates. The drug is indispensable in the care of patients with ductus-dependent cardiac lesions, such as interrupted aortic arch, critical aortic stenosis, or hypoplastic left heart syndrome, where systemic blood flow is supplied through the ductus arteriosus. It is equally important for the care of patients who have pulmonary atresia or critical pulmonic stenosis. Apnea, fever, and hypotension are common side effects of this drug.

Nitric Oxide

NO is an endothelium-derived relaxing factor that selectively vasodilates the pulmonary vasculature. When administered by inhalation to patients with pulmonary hypertension, NO reduces PVR. It improves the survival of neonates who have reactive pulmonary hypertension. This compound is inactivated by hemoglobin before it reaches the systemic circulation. On rare occasions, NO causes systemic vasodilation or clinically significant methemoglobinemia when administered at 5 to 80 ppm.

Disorders of Cardiac Rhythm

Sinus tachycardia or an elevated HR for age is not considered an arrhythmia. However, patients with a significantly increased HR may be the most critically ill in the ICU. Causes of tachycardia include hypovolemia, fever, pain, anxiety, CHF, myocardial disease and dysfunction and thyrotoxicosis. With all of these causes, the goal is to treat the underlying disease state and not the tachycardia. For children without underlying heart disease, temporary increases in HR up to 180 to 200 beats/min is well tolerated. This is also not uncommon; children cannot increase their stroke volume so they increase their cardiac output by increasing their HR. Again, the goal is not to specifically control an elevated HR but to treat the cause of the tachycardia. Sinus arrhythmia is a phasic acceleration and slowing of the HR that occurs with respiration. This is not an uncommon finding. It indicates that the patient has a vagal tone greater than sympathetic tone and it can indicate that there is good cardiac reserve. A slow HR or sinus bradycardia is another relatively common heart rhythm seen in the ICU. It is an unremarkable finding in an older teenage patient who is relatively fit. Other potential causes can include increased intracranial pressure (ICP), hyperkalemia, hypothermia, profound hypoxia, and hypothyroidism. These causes should also be investigated. A slow HR is being seen more commonly with the increased of Dexmedetomidine but can also occur with beta blockers or Digoxin use. Sinus node dysfunction can occur following repair of congenital heart disease in children. Temporary slowing may be treated with the transcutaneous pacemaker placed during surgery. In the absence of myocardial pacing, if there is complete heart block or a very slow ventricular escape rate, a pacemaker may be needed shortly after the cardiac surgery. Otherwise, some amount of time is given to see if this will resolve.

Normal cardiac conduction starts in the sinus node. The electrical activity propagates through the internodal pathways in the atrium, is delayed in the AV node, it travels though the bundle of His, and then is conducted to the ventricles through the left and right bundle branches. Supraventricular tachycardia (SVT) is an elevated HR occurring at the level of the atrium, the AV node, or both. SVT typically has a narrow QRS morphology. Sinus tachycardia is therefore not a type of SVT but an acceleration of the normal conduction pathways. SVT includes reentrant and non-reentrant tachycardias.

The reentrant tachycardias include AV node reentrant tachycardia (AVNRT), orthodromic reciprocating tachycardia (ORT), and atrial flutter. AVNRT is what is classically thought of as pediatric SVT. The reentrant tachycardias occur due to the presence of an accessory conduction pathway that allows for abnormal electrical conduction in the heart. The presence of the abnormal pathway may be apparent on a standard ECG such as the case of Wolf-Parkinson-White (WPW). Alternatively the abnormal pathway may not appear on an ECG and is described as a concealed pathway. Concealed pathways are non-WPW ORT. In AVNRT, the AV node itself is the area in which the reentrance occurs. In atrial flutter there is a micro-reentrant circuit within the atrial tissue itself. In children, the circuit is typically near the tricuspid valve. In atrial flutter, after the reentrant circuit in the atria, the conduction proceeds through the AV node, where it is slowed. The reentrant circuit is small, and the rates of atrial flutter can be very high. As the conduction is slowed in the AV node, these high rates are not usually conducted to the ventricle. However, if atrial flutter or fibrillation occurs in a patient with WPW, the accessory pathway can allow conduction of the electrical impulse at a rate much greater than through the AV node. This can lead to ventricular tachycardia or fibrillation and can cause sudden death.

The non-reentrant causes of SVT occur due to abnormal automaticity of myocardial tissue. Causes of abnormal automaticity include atrial fibrillation and ectopic atrial tachycardia (EAT). In non-reentrant SVT, the elevated atrial rate is slowed as conduction goes through the AV node. In children, atrial fibrillation is caused by disorganized circuits typically near the pulmonary veins. This rhythm is described as irregularly irregular. EAT is rapid atrial beats that are consecutive and occur without sinus morphology. There can be one focus of the rapid atrial beats. Alternatively, in multifocal or chaotic atrial tachycardia, there can be several different atrial origins. Brief periods of EAT usually do not cause much sequel but can lead to cardiomyopathy if it is prolonged.

Treatment of reentrant SVT is based on whether the patient is clinically unstable or stable. The abnormal reentrant circuit can be interrupted with synchronized cardioversion or other methods. If the patient is unstable, reentrant SVT is treated with synchronized cardioversion with a dose of 0.5 to 1 J/kg. If the patient is stable, there is time to try other therapies. Therapies that increase vagal tone such as ice to the eyes or a Valsalva maneuver may interrupt the reentrant circuit. The medication adenosine will temporarily block conduction through the AV node. Adenosine can be used to interrupt episodes of reentrant SVT that have a reentrant circuit using the AV node. If the reentrant circuit does not include the AV node adenosine might not stop the tachycardia, but it may be helpful with diagnosis. Following administration of adenosine, there will be a period of sinus pause. Adenosine is metabolized by erythrocytes so it is a short acting medication. Equipment to perform cardioversion should be immediately available when adenosine is given. The initial dose is 0.1 mg/kg, and the dose should be given quickly with a sufficient flush. It is more effective when given centrally if available. If it is not effective at the dose of 0.1 mg/kg, the second dose can be increased to 0.2 mg/kg. Higher doses than this are not likely to be more effective, and if the SVT persists, other medications such as amiodarone, procainamide, or verapamil may be necessary. Amiodarone can block an accessory pathway as well as the AV node. If given too quickly, amiodarone will decrease the blood pressure. For both amiodarone and procainamide, continuous infusions may be necessary after the loading dose. Verapamil will block the AV node for a much longer period of time than adenosine. However, in younger patients (<2 years), verapamil may induce other life-threatening arrhythmias. If a patient has SVT, a cardiology consult should be obtained. This is because an echocardiogram may be beneficial, and depending on the cause, there may be a need for long-term follow-up.

Junctional ectopic tachycardia is caused by abnormal automaticity in an area around the atrioventricular junction. This is not a common pediatric arrhythmia but can occur following repair of congenital heart disease. The most common lesion with which this occurs is tetralogy of Fallot.

Wide complex tachycardias are assumed to arise from the ventricle until proven otherwise. SVT can cause a wide complex tachycardia if there is aberrancy of the conduction through the pathways in the ventricle. However, given the risk of delaying therapy, all wide complex tachycardias should initially be treated as ventricular tachycardia. If there is no pulse, initiate CPR, defibrillate, and follow PALS guidelines. If the patient has a pulse and stable blood pressure, there may be time to consider other therapies. These therapies are cardioversion or use of medications such as adenosine, amiodarone, or procainamide. Ventricular fibrillation is treated with CPR, defibrillation, and then medications following PALS guidelines. Ventricular rhythms should be quickly examined for the possibility of Torsades de Pointes, as giving magnesium will be especially helpful.

In the course of following the continuous rhythm strip of all children in the PICU, common abnormalities may be noted. A prolongation of the PR interval or first degree heart block can occur in otherwise normal children. Typically, these children are asymptomatic. Second-degree heart block occurs as Mobitz Type I and Mobitz Type II. Mobitz Type I is also known as Wenckebach . This is a gradual prolongation of the PR interval until a QRS is not seen and then the cycle restarts. This occurs due to delay of the electrical signal in the AV node, and it can be a benign phenomenon. Mobitz Type II is less likely to be a benign phenomenon. The PR interval remains constant, but intermittently there is no QRS or ventricular beat. This phenomenon is evidence of disease of the His-Purkinje fibers and can progress to complete heart block. Mobitz Type II occurs much less frequently in children as compared with adults. Complete heart block or third-degree AV block is the complete dissociation of atrial and ventricular activity. In complete heart block, the atria contract at a rate greater than the ventricle. Ventricular contraction occurs through ventricular escape. Congenital complete heart block can occur in infants born to mothers who have an autoimmune disorder such as lupus. When there is damage to the conduction pathway during surgery for congenital heart disease, complete heart block can occur. As immediate treatment of complete heart block, the ventricular rate may be increased with IV isoproterenol. When this is ineffective, transthoracic or transvenous pacing will be necessary until definitive therapy can be arranged.

Premature beats are also seen quite frequently in a PICU setting. Premature atrial contractions are usually benign and are caused by automaticity of atrial tissue other than the sinus node. Premature ventricular contractions (PVC) are usually benign with a few considerations. The presence of a central venous catheter touching the heart may cause increased PVCs, and if present, the catheter should be pulled back. Electrolyte abnormalities; typically of potassium, magnesium, and calcium, may cause PVCs. The frequency of PVCs may improve as the electrolytes are corrected. Exogenous catecholamines may cause PVCs, and the frequency of PVCs may improve if the catecholamines can be decreased. Endogenous catecholamines may cause PVCs, and the frequency may be decreased if pain or anxiety is treated.

Epinephrine

The primary medication used in the resuscitation of a newborn is epinephrine, and should be given if the infant’s HR is less than 60 bpm, 45 to 60 seconds after the initiation of PPV and chest compressions. The recommended dose is 0.1 to 0.3 mL/kg of 1:10,000 concentration; (0.01-0.03 mg/kg), followed by a 1 mL flush of saline. While IV administration is preferable, if venous access is not obtained, it is appropriate to give epinephrine via the ETT. In this instances the practitioner, should give a higher dose of Epinephrine: 0.5 to 1 mL/kg of 1:10,000 concentration; (0.05-0.1 mg/kg). Epinephrine can be repeated every five minutes, as needed, while re-evaluating HR every 45 to 60 seconds.

Naloxone

Naloxone (Narcan) is not recommended as an initial response to respiratory distress in neonatal resuscitation. Neonates should be supported on PPV, even in women who have received narcotics less than four hours prior to delivery. However, if respiratory depression continues, naloxone can be considered. In addition, naloxone should be avoided in an infant whose mother has a history of narcotic dependence due to the risk of seizures from withdrawal.

Airway-Breathing-Circulation or Circulation-Airway-Breathing

For OHCA victims, “compression-only” CPR has been associated with improved outcomes. This is now the recommended modality for emergency medical service dispatcher instructing bystander CPR. In a recent Japanese study, children with OHCA due to a primary cardiac etiology displayed an equivalent survival rate between compression-only CPR and classic CPR with rescue breaths. However, only 29% of patients had a cardiac cause of OHCA. Those with noncardiac etiology in the overall cohort had a significantly worse survival rate with compression-only CPR, as compared with classic CPR with rescue breaths. Additionally, in another nationwide Japanese OHCA registry study, compression-only CPR was superior to no bystander CPR at all but not to conventional CPR. In a recent American OHCA registry study, children who received conventional bystander CPR with chest compressions and rescue breaths had improved rates of overall survival and survival with favorable outcomes as compared with those who did not receive CPR, whereas those receiving compression-only CPR did not fare any better than children not receiving CPR. Thus compression-only CPR is not recommended for children in either the inpatient or out-of-hospital setting, except in situations in which “rescuers are unwilling or unable to deliver breaths.”

Regardless, the prioritization of initial interventions during CPR has shifted from airway-breathing-circulation (“A-B-C”) to circulation-airway-breathing (“C-A-B”) in order to prevent harmful delays in the initiation of chest compressions and due to the relative complexity of the tasks involved in providing assisted ventilation. This is endorsed by both the 2010 and 2015 AHA BLS Guidelines. However, a 2015 International Liaison Committee on Resuscitation consensus statement identified a paucity of pediatric-specific evidence to support this recommendation. In our opinion, the approach is physiologically sound, especially given the association of delayed chest compression initiation with poor outcomes. With that said, the pediatric provider must consider the predominance of asphyxia and hypoxemia as precursors to cardiac arrest. This is especially true in the ICU and operating room, where personnel and other resources frequently allow for simultaneous circulatory support with high-quality chest compressions as well as the provision of assisted ventilations by experienced personnel.

In order to improve outcomes from pediatric cardiac arrest, it is imperative to shorten the no-flow phase of untreated cardiac arrest. To that end, it is important to monitor high-risk patients to allow early recognition of the cardiac arrest and prompt initiation of basic and advanced life support. Effective CPR optimizes coronary perfusion pressure (by elevating aortic diastolic pressure relative to RAP) and cardiac output to critical organs to support vital organ viability (by elevating mean aortic pressure) during the low flow phase. Important tenets of basic life support are push hard, push fast, allow full chest recoil between compressions, and minimize interruptions of chest compression . The myocardium receives blood flow from the aortic root, mainly during diastole, via the coronary arteries. When the heart arrests and no blood flows through the aorta, coronary blood flow ceases. However, during chest compressions, aortic pressure rises at the same time as RAP and with the subsequent decompression phase of chest compressions, the RAP falls faster and lower than the aortic pressure, which generates a pressure gradient that perfuses the heart with oxygenated blood. Therefore, full elastic recoil (release) is critical to create a pressure difference between the aortic root and the right atrium. A CPP below 15 mm Hg during CPR is a poor prognostic factor for ROSC. Achieving optimal coronary perfusion pressure, exhaled carbon dioxide concentration, and cardiac output during the low flow phase of CPR is consistently associated with an improved chance for return of spontaneous circulation (ROSC) and improved short- and long-term outcome in mature animal and human studies. There is a critical need for research evaluating goal directed CPR, both in immature animal models and pediatric patients. Other measures essential for truncating the no-flow phase during VF and pulseless VT are rapid detection and prompt defibrillation. Clearly, CPR alone is inadequate for successful resuscitation from these arrhythmias. For cardiac arrests resulting from asphyxia and/or ischemia, provision of adequate myocardial perfusion and myocardial oxygen delivery are the critical elements for ROSC.