EDEMA

LINDA L. BROWN, MD, MSCE

Edema is defined as the abnormal swelling of tissues from the accumulation of fluid in the extravascular space. This fluid may appear as generalized or localized swelling. Frequently in pediatrics, edema occurs as a localized response to injury or inflammation and, in this setting, is often benign and self-limited. However, it is important to recognize that edema may be the result of a variety of causes and the initial presentation of generalized edema may be quite subtle. When significant edema is present, collections of fluid may be visualized as pericardial or pleural effusions, or as ascites. When edema is profound and generalized, the patient is described as having anasarca. The completion of a careful history and a thorough physical examination will not only help to identify these patients early, but may also lead to a definitive diagnosis in some cases.

PATHOPHYSIOLOGY

The occurrence of edema in healthy individuals is usually prevented by the balance of oncotic and hydrostatic pressures between the intravascular and interstitial spaces, as well as the normal function of the lymphatic system. Any imbalance in this system may lead to increased interstitial fluid and eventual tissue swelling. Edema may occur as a result of decreased intravascular oncotic pressure, increased vascular permeability, increased hydrostatic pressure, lymphatic dysfunction, or a combination of these factors.

Tightly controlled levels of circulating proteins, especially albumin, maintain normal intravascular oncotic pressure. Hypoalbuminemia may arise from the decreased production of proteins caused by hepatic disease, as a result of protein malnutrition or, more commonly, from losses of protein through gastrointestinal, renal, or dermal conditions. When the albumin level is less than 2.5 g per dL, the oncotic pressure in the vascular space is reduced enough for fluid to move freely into the soft tissues and, if not corrected, generalized edema may result.

Edema can also result from changes in vascular (capillary) permeability, mediated by intrinsic cytokines and other inflammatory factors. This is seen most commonly in patients with burns, sepsis, or hypersensitivity reactions. In certain cases, the swelling may be rapid, localized, and potentially life-threatening. In patients with a severe allergic reaction, such as that associated with anaphylaxis, this edema may involve the tissues adjacent to the airway leading to potential airway compromise.

When intravascular albumin levels are within the normal range and vascular permeability is preserved, edema can result from increased hydrostatic pressures that overcome the oncotic pressure, forcing fluid out of the vascular space. This can occur as a result of changes in sodium and water retention from cardiac failure, renal failure or estrogen–progesterone excess, or from venous obstruction. Lymphatic dysfunction, either congenital or acquired, can also result in edema.

DIFFERENTIAL DIAGNOSIS

A myriad of disease processes can result in either localized or generalized edema (Table 20.1). Localized edema in children is often caused by an allergic reaction, with the most severe reactions resulting from exposure to nuts, shellfish, or hymenoptera venom. Idiopathic nephrotic syndrome, although rare (occurring in just 2 to 3 of every 100,000 children annually), is the most common cause of generalized edema (Table 20.2). Overall, most children who develop edema will have a benign diagnosis and a self-limited course. However, potentially life-threatening conditions (Table 20.3) causing edema can also occur, including severe allergic reactions, sepsis (see Chapter 102 Infectious Disease Emergencies), venous thrombosis, and kidney, liver, or cardiac disease.

EVALUATION

When evaluating the child with edema it is necessary to obtain a thorough history and perform a complete physical examination, including the assessment of vital signs. It is important to remember that the onset of symptoms is often gradual and subtle for causes of generalized edema. In fact, a 10% to 15% weight gain may be accumulated, with symptoms existing for weeks to months, before a patient presents for medical care. It is, therefore, essential to inspect for edema around the eyes, scrotum or labia, as well as the distal extremities, as these areas may be the only locations with perceptible swelling.

It is also helpful to classify the swelling as localized or generalized (Fig. 20.1)

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