Burns in pregnancy
How is burn in pregnancy different from conventional cases? how are they managed? Does it affect fetus?
@poli Pregnant women rarely are burned seriously, but when they are, they have unique medical problems. The mother and fetus are at great risk for fluid loss, hypoxemia, and sepsis. The overall fetal and neonatal mortality rate is greater than 50% when the mother is burned over more than 60% of her body. Fluid replacement, respiratory support, and initial wound care are the emergency management goals in pregnant burn patients. The loss of fluid through the denuded surface can be massive, and the amount often is underestimated in pregnant patients.
On arrival to the hospital and after the vital signs of the mother and fetus (monitor) are evaluated, a large-bore (ie, 18-gauge) intravenous line is started. In cases in which the burn covers more than 20% of the surface area, a central venous or Swan-Ganz catheter provides a better guide to fluid replacement. Lactated Ringer solution is started at 200 mL/h until the fluid replacement volume is calculated. Insert a nasogastric tube for burns involving more than 20% of body surface area.
Hospital admission is recommended for smoke inhalation, electrical burns, burns of both hands or both feet, partial-thickness burns that cover more than 10% of the surface area, or full-thickness burns on more than 2% of the surface area. The depth of the injury is estimated by appearance and sensation. Partial-thickness (ie, intradermal) injury appears red or pink, with blister formation. Full-thickness injury may be charred or marble gray in color, dry, and anesthetic. Partial-thickness burns also may be anesthetic because of neurapraxias of skin nerve endings in the burn area. Thus, pain response to stimulation is valuable only to indicate a partial-thickness burn.
A general estimate of the body surface area involved by a burn is determined by the rule of nines: head and neck, 9%; upper extremities, 9% each; anterior torso, 18%; posterior trunk, 18%; lower extremities, 18% each; and genitalia, 1%. Another method is to equate the number of palmar surfaces the burn entails, each palmar surface being equal to 1.25% of body surface. During late pregnancy, 5% is added if the anterior abdomen is involved. The fluid requirements for the first 24 hours after a burn injury are calculated as follows: body surface area burned (%) multiplied by 2-4 mL/kg body weight. For example, a 20% burn is calculated as 20 X 3 mL X 70 kg = 4200 mL.
Fluid requirements are met with lactated Ringer solution. The free-water requirement (ie, 500 mL) is supplied with 5% dextrose in water. Fifty percent of the replacement fluid is administered in the first 8 hours and the remainder during the next 16 hours. In the second 24 hours, colloids (albumin) are administered to maintain the serum albumin greater than 3 g/100 mL.
Fluid replacement is monitored by clinical and laboratory means. Systolic blood pressure should be greater than 110 mm Hg, maternal heart rate less than 120 beats per minute, temperature less than 38°C, and respiratory rate should be 12-24 breaths per minute. Central venous pressure should be approximately 10 cm H2 O, and urine output should be greater than 0.5 mL/kg/h. The initial laboratory workup should include a complete blood count and determination of blood levels of electrolytes, glucose, albumin, urea nitrogen, and serum creatinine. Monitor these parameters on a serial basis (eg, q4-8h).
Smoke inhalation is a major cause of morbidity and mortality in burn patients. In pregnancy, the fetus is at special risk because of its relatively hypoxic state (ie, normal umbilical vein PaO2 = 27 mm Hg). The pathophysiology of inhalation injury relates to impaired maternal ventilation (eg, upper airway obstruction from edema), increased diffusion distance (eg, interstitial alveolar edema), and acute functional anemia from carbon monoxide poisoning. Carbon monoxide binds more efficiently to hemoglobin than does oxygen. In addition to displacing oxygen, carbon monoxide impairs the release of oxygen from oxyhemoglobin. Very little carbon monoxide is needed to cause serious hypoxia. One part carbon monoxide per 1500 parts air can result in blood concentrations of carboxyhemoglobin of 5-10%. Car exhaust is 5-7% carbon monoxide. Carboxyhemoglobin values less than 15% usually are well tolerated, whereas values greater than 30% cause severe maternal syncope and fetal death.
Inhalation injury should be suspected among patients who have a history of closed-space fire, facial injury, carbonaceous material in the oropharynx, or respiratory symptoms. Interstitial edema on chest x-ray film, a carboxyhemoglobin level greater than 10%, or abnormal arterial blood gas levels also aid in establishing the diagnosis of inhalation injury. Initial treatment of any burn patient should include an arterial blood sample for gases and carboxyhemoglobin, as well as a chest radiograph. Patients should be placed on 100% oxygen by mask for at least 3 hours or until the carboxyhemoglobin level is known. They should receive vigorous chest physiotherapy. Intubation and mechanical ventilation should be used early in the presence of upper airway obstruction or oxygenation failure.
Sepsis is another major risk for the fetus and mother. Initial wound care can be instrumental in the prevention of these complications. On admission, the wound is cleaned with bland soap and water, and all dirt and loose devitalized tissue are removed. Blisters should be left intact if they are smaller than 5 cm in diameter. When burns involve the scalp, axilla, or pubic area, the hair should be clipped short until an adequate margin of unburned skin is obtained. After cleaning and debridement, a topical agent is applied with a bulky dressing. Silver sulfadiazine cream is used most commonly, but the consideration in pregnant patients is that this drug can be absorbed. The sulfa derivative crosses the placenta and displaces bilirubin. Should delivery ensue, hyperbilirubinemia is a risk for the neonate. Silver nitrate (0.5%) also is used, but this agent requires continuous soaking (ie, q2h) and a bulky dressing. Tetanus toxoid (0.5 mL) should be administered to all patients with burns.
After the initial management of a severely burned patient, her care requires a team approach with the obstetrician acting as a consultant. Pregnant women with severe burns are best cared for in centers geared both to managing severe burns and to the possibilities of early delivery. The major long-term problems are healing, sepsis prevention, scar complications, nutritional support, and rehabilitation. The various methods and problems of long-term care are beyond the scope of this article.