GENERAL PEDIATRIC EMERGENCIES

PEDIATRIC EMERGENCIES

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GENERAL PEDIATRIC EMERGENCIES Acute Pulmonary Edema Tetsu Uejima, MD

Acute pulmonary edema occurs less frequently in children because of the absence of coronary artery disease. The pathophysiologic mechanism behind any form of pulmonary edema, however, is based on the variables of the Starling equation44:

Q

=

k[(Pcap- Pint) - u(mcap -

mint)]

The resulting interactions of the pulmonary capillary hydrostatic pressure (Pcap),the interstitial hydrostatic pressure (Pint),the plasma the interstitial oncotic pressure (mint),the protein oncotic pressure (rcap), reflection coefficient (a),and the fluid filtration coefficient (k) determine net filtration (Q), which ultimately determines the nature of the pulmonary edema. Under normal circumstances, Q is slightly positive, resulting in a net positive fluid flux into the interstitium. This fluid is drained into the vascular system as lymph. The lymphatic system can accommodate a 300% increase in flow before fluid accumulates in the Cardiogenic pulmonary edema occurs when Pcap,which can be measured as the pulmonary capillary wedge pressure, is excessively high, resulting in a large Q. The resulting edema fluid in this situation is low in protein content. Noncardiogenic pulmonary edema occurs in the presence of a normal pulmonary capillary wedge pressure with a high protein content in the alveolar fluid signifying capillary leak. Clinically, this mathematic view of pulmonary edema is simplistic, but allows a better understand-

From the Department of Anesthesia, Children’s Memorial Hospital, Northwestern University Medical School, Chicago, Illinois

ANESTHESIOLOGY CLINICS OF NORTH AMERICA VOLUME 19 NUMBER 2 * TUNE 2001

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ing of the pathophysiology. This article focuses on three types of acute pulmonary edema in children: negative-pressure pulmonary edema, neurogenic pulmonary edema, and cardiogenic pulmonary edema. NEGATIVE-PRESSURE PULMONARY EDEMA

Negative-pressure pulmonary edema, also known as postobstructive pulmonary edema, occurs secondary to upper airway obstruction, and is a rare but well-recognized phenomenon. The true incidence is unknown. Various types of airway obstruction, including croup, epiglottitis, laryngospasm after tonsillectomy, hanging, and tumors have been reported to cause negative-pressure pulmonary edema.3,15, zo* 45, 47 Negative-pressure pulmonary edema also can occur with aspirated foreign bodies, esophageal foreign bodies, and after biting of a laryngeal mask airway.1z,17, 33 Unilateral pulmonary edema and negative-pressure-induced pulmonary hemorrhage also have been reported.', 4, 38 One recent paper reported negative-pressure pulmonary edema in a burn patient with a patent airway secondary to pulmonary emb01i.l~ The exact mechanism by which negative-pressure pulmonary edema occurs is unknown, although it is most likely multifactorial in 32 Large, negative intrapleural pressures are the pathophysiologic hallmark of negative-pressure pulmonary edema. These pressures increase lymph flow and interstitial edema, causing pulmonary edema.8,42 Hemodynamic changes associated with severe intrapleural pressures include increased venous return to the right circulation and pooling of blood in the pulmonary venous circulation during inspiration.28In negativepressure pulmonary edema, the Starling equation states that increases in fluid flux are related directly to differences in hydrostatic pressure. Left ventricular end diastolic pressures increase with negative pleural pressurezz,34 because of increased venous return to the right ventricle, causing right ventricular distention, and a leftward shift of the interventricular septum, causing decreased left ventricular compliance.z8,z9 HYPoxia and the CNS may play a role in negative-pressure pulmonary edema. In high-altitude pulmonary edema, hypoxia increases pulmonary vascular re~istance.~~ Hypoxia also can precipitate a massive CNS-induced adrenergic response similar to that seen in neurogenic pulmonary edema.18,z5 Clinically, negative-pressure pulmonary edema is characterized by its rapid onset and short-lived course. Pulmonary edema often occurs once the obstruction is relieved. Onset is usually within minutes, but may occasionally be hours. Treatment is symptomatic because the course is self-limited. Airway patency must be maintained. Most patients require endotracheal intubation with continuous positive airway pressure or positive end-expiratory pressure. Mask continuous positive airway pressure (CPAP) may be considered in patients requiring small amounts of CPAP who are not in ventilatory failure. Inspired oxygen can be titrated to a desired oxygen saturation, usually more than 90%. Inotropic

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support, diuretics, and invasive hemodynamic monitoring usually are not required if the diagnosis is clearly negative-pressure pulmonary edema. Symptoms commonly resolve within 12 to 24 hours. If symptoms persist, pulmonary aspiration and cardiogenic causes of pulmonary edema should be considered. Caution should be used regarding the use of intramuscular succinylcholine. Intramuscular succinylcholinehas been implicated in precipitating acute pulmonary edema and pulmonary hemorrhage in the absence of obvious upper airway obstruction." The exact mechanism of this phenomenon is unknown.

NEUROGENIC PULMONARY EDEMA

Shanahan first reported neurogenic pulmonary edema in 1908 in a series of 11 patients who had epileptic seizures.39Battle-related head injuries were associated with neurogenic pulmonary edema during World War IZ6and during the Vietnam War.40Since then, neurogenic pulmonary edema has been recognized as a form of pulmonary edema that most commonly occurs after CNS injuries associated with a rise in the intracranial pressure. Various CNS conditions, including open and 35, 40 subarachnoid 36 cerebral hemorclosed head 39 and cervical spine injuries31have rhage? meningiti~;~ postictal been reported to cause neurogenic pulmonary edema. The exact cause of neurogenic pulmonary edema is unknown. Experimental evidence in animals has isolated certain areas of the CNS most likely to be responsible for neurogenic pulmonary edema. These include the A, and A, areas of the medulla, the nuclei of solitary tract, the area postrema, and the hypothalamus.1° Two avenues of speculation have arisen regarding the cause of neurogenic pulmonary edema: increased capillary hydrostatic pressure and increased capillary permeability. Increased capillary hydrostatic pressure is the so-called blast theory.46 The blast theory hypothesizes that a CNS injury triggers a massive adrenergic response, causing severe pulmonary and systemic hypertension accompanied by an increase in venous return. The increase in Pcap causes an increase in net filtration and pulmonary edema.2,48 After the blast, capillary permeability increases because of barotrauma, unknown neurogenic mechanisms, or not yet identified mediators, allowing protein to leak, and more pulmonary edema despite normal pulmonary pressures. Neurogenic pulmonary edema also can occur with normal pulmonary pressures, suggesting increased capillary permeability as a cause.6,23 In this theory, u increases because of neuronal influences or by damage to the capillary endothelium, which causes leakage of protein into the interstitial and alveolar spaces, causing pulmonary edema. Analysis of alveolar fluid in neurogenic pulmonary edema reveals a high protein content, suggesting capillary leak as the primary cause.14More careful

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analysis of edema fluid protein to plasma protein ratios, however, do not support this theory consistently? l4 A diagnosis of neurogenic pulmonary edema should be considered in any patient with a history of head trauma or intracranial pathology. The incidence of neurogenic pulmonary edema is believed to be significantly lower in children than in adults. Onset is usually with a few hours, but some patients may not manifest symptoms until 12 hours to a few days after the insult.10Initial signs and symptoms are indistinguishable from other forms of pulmonary edema. Chest radiography may mimic adult respiratory distress syndrome.16 The treatment of neurogenic pulmonary edema is primarily supportive. Primary therapy should be directed at treating the CNS problem. Supplemental oxygen should be administered. Airway patency and adequacy of ventilation must be ensured because most patients have underlying CNS pathology and increased intracranial pressure. Patients with a Glasgow Coma Scale score of 8 or less should be intubated as quickly as p0ssib1e.l~Positive-pressure ventilation with hypocarbia may be required to decrease intracranial pressure. Positive end-expiratory pressure (PEEP) may be required to maintain oxygenation. Although the effect of high levels of PEEP on intracranial pressure in patients with head injury is controversial, intracranial pressure monitoring is probably appropriate if PEEP exceeds 10 cm H,O. Ventilatory settings should be adjusted to minimize hypotension and increases in airway pressure because they may be harmful to patients with CNS pathology. Neurogenic pulmonary edema usually resolves within 24 to 48 hours. Persistent pulmonary edema should prompt an examination for other causes, such as aspiration or cardiogenic pulmonary edema. CARDIOGENIC PULMONARY EDEMA

Cardiogenic pulmonary edema develops when Pcapis excessively high, overwhelming the ability of the lymphatic system to resorb fluid. In the adult, anesthesiologists are familiar with the patient with heart failure and cardiogenic pulmonary edema. In children, cardiogenic pulmonary edema occurs most often with congenital heart disease. Cardiogenic pulmonary edema can be iatrogenic and solely attributable to fluid overload in caretakers unfamiliar with fluid administration in children. More commonly, cardiogenic pulmonary edema can occur with large left-to-right shunting lesions, such as a patent ductus arteriosus or a ventricular septa1 defect. Cardiogenic pulmonary edema also can occur when there is a problem with left ventricular filling or emptying and with left ventricular function, as in congenital critical aortic stenosis and endomyocardial fibroelastosis. Lesions that obstruct normal emptying of the pulmonary veins, as in total anomalous pulmonary venous return, can cause cardiogenic pulmonary edema.7 Cardiogenic pulmonary edema usually occurs within the first 6 months of life. It rarely occurs after then without a concomitant medical

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problem, such as an arrhythmia, a cardiomyopathy, infective endocarditis, pneumonia, or high output states, such as severe anemia.30Chronologically, cardiogenic pulmonary edema presenting in the first week of life is often coincident with closure of the ductus arteriosus, the socalled ductal-dependent lesions. These infants often have critical obstructions to systemic arterial flow, as seen in preductal coarctation of the aorta. Early presentation also is seen in lesions causing pulmonary venous obstruction to ventricular filling, as in cor triatriatum. In the next few weeks, pulmonary vascular resistance decreases, allowing left-toright shunting lesions to become more evident. This scenario most commonly is seen with a ventricular septal defect. Infants with cardiogenic pulmonary edema are in severe respiratory distress, with tachycardia, tachypnea, grunting, pallor, and diaphoresis. Parents often report poor feeding, irritability, and poor weight gain. Some congenital lesions are associated with left-to-right shunting and mixing of venous and arterial blood, as in complete atrioventricular canal and transposition of the great vessels with a large ventricular septal defect. These infants present with signs and symptoms of congestive heart failure and cyanosis. Treatment requires definitive or palliative treatment of the underlying lesion. In ductal-dependent lesions, prostaglandin El administration maintains ductal patency, and helps to relieve vascular congestion. Treatment, otherwise, is directed at decreasing oxygen consumption and improving oxygenation and cardiac function. As in adults with cardiogenic pulmonary edema, medical management includes the use of supplemental oxygen, fluid restriction, diuretics, digoxin, inotropes, and systemic unloading agents.

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Address reprint requests to Tetsu Uejima, MD Department of Anesthesia Children’s Memorial Hospital Northwestern University Medical School 2300 Children’s Plaza Chicago, 1L 60614