14.3 Burn Injury in Pregnancy: Maternal Physiology, Resuscitation, and Fetal Surveillance
Key Takeaways
- Fetal outcome tracks maternal outcome, so the best fetal resuscitation is an aggressive maternal resuscitation; treatment is rarely withheld from the mother because she is pregnant.
- Plasma volume expands 40-50% in pregnancy, so hypotension appears late and fetal distress on the monitor is often the earliest objective sign of maternal hypovolemia.
- Aortocaval compression after roughly 20 weeks requires left lateral tilt of 15-30 degrees or manual left uterine displacement, which is compatible with spinal precautions using a wedge.
- Fetal hemoglobin binds carbon monoxide more avidly than maternal hemoglobin, so the hyperbaric oxygen threshold falls to a carboxyhemoglobin level above 15% in pregnancy versus above 25% in the non-pregnant adult.
- Silver sulfadiazine is avoided near term because sulfonamides displace bilirubin and raise kernicterus risk, and systemic NSAIDs are avoided after 20 weeks and contraindicated after 30 weeks.
14.3 Burn Injury in Pregnancy: Maternal Physiology, Resuscitation, and Fetal Surveillance
Core Knowledge: The BCEN content outline lists "Pregnant patients" as its own lettered topic under Special Populations — a domain worth 18 of the 150 scored items. Pregnancy changes almost every number you use during resuscitation: circulating volume, oncatic pressure, functional residual capacity, arterial blood gases, and the interpretation of vital signs. The single organizing principle for the exam is that the best fetal resuscitation is an aggressive maternal resuscitation; fetal outcome tracks maternal outcome almost linearly, and treatments are rarely withheld from the mother because she is pregnant.
Why Pregnancy Changes the Burn Assessment
Burns complicating pregnancy are uncommon in high-income countries but carry disproportionate mortality. Two facts drive every exam item:
- Fetal survival is dependent on maternal survival. Maternal mortality rises with %TBSA, and fetal loss rises faster still — largely from uteroplacental hypoperfusion, hypoxemia, sepsis, and preterm labour rather than from direct thermal injury to the uterus.
- Normal pregnancy masks shock. Plasma volume expands 40–50% by the third trimester, so a pregnant patient can lose a substantial volume before classic hypotension appears. Fetal distress on the monitor is frequently the earliest objective sign of maternal hypovolemia — the uterus is a non-essential organ from the body's perspective, so uteroplacental flow is sacrificed first.
Physiologic Changes That Alter Burn Management
| System | Change in Pregnancy | Consequence for the Burn Nurse |
|---|---|---|
| Hematologic | Plasma volume ↑ 40–50%; red-cell mass ↑ ~20% → dilutional (physiologic) anemia; hypercoagulable state | Hemoglobin of 10–11 g/dL may be normal; shock is masked until late; VTE prophylaxis is a higher priority |
| Cardiovascular | Cardiac output ↑ 30–50%; heart rate ↑ 15–20 bpm; systemic vascular resistance ↓; aortocaval compression after ~20 weeks | Baseline tachycardia is expected — do not dismiss it, but do not treat it as the sole shock trigger; supine positioning can drop cardiac output sharply |
| Oncotic pressure | Serum albumin and colloid oncotic pressure fall | Greater interstitial edema and higher pulmonary edema risk for the same crystalloid volume |
| Respiratory | Minute ventilation ↑ ~50%; functional residual capacity ↓ 20–25%; chronic compensated respiratory alkalosis (PaCO₂ ~28–32 mmHg) | Rapid desaturation during any apneic period; a "normal" PaCO₂ of 40 mmHg signals impending respiratory failure; airway edema and mucosal friability make intubation harder |
| Gastrointestinal | Delayed gastric emptying; lower esophageal sphincter tone ↓ | Elevated aspiration risk at induction; early enteral access still indicated |
| Renal | GFR ↑ ~50%; baseline creatinine falls to ~0.4–0.6 mg/dL | A creatinine of 1.0 mg/dL may already represent acute kidney injury |
| Abdominal | Gravid uterus raises baseline intra-abdominal pressure | Circumferential trunk burns reach abdominal compartment syndrome thresholds sooner; escharotomy decisions come earlier |
Assessment and Resuscitation Priorities
1. Burn size estimation. Use the same primary and secondary survey, but recognize that the Rule of Nines was validated on the non-gravid adult. At term the anterior trunk surface enlarges relative to the standard 18%, so a strict Rule of Nines tends to underestimate trunk involvement. Lund–Browder is age-adjusted, not pregnancy-adjusted. Use the palmar method (the patient's own palm plus fingers ≈ 1% TBSA) for scattered burns and document the estimating method used, because fluid volumes are computed from it.
2. Fluid resuscitation. Formulas are unchanged: the ABA consensus starting point of 2 mL × kg × %TBSA of lactated Ringer's over 24 hours, half in the first 8 hours from the time of injury, using the patient's current weight. Titrate to the standard adult urine output of 0.5 mL/kg/hr — maternal urine output remains the practical surrogate for uteroplacental perfusion. Because colloid oncotic pressure is already low, over-resuscitation produces pulmonary edema faster than in the non-pregnant patient, so hourly titration discipline matters more, not less.
3. Positioning. After roughly 20 weeks' gestation, place the patient in left lateral tilt of 15–30° or apply manual left uterine displacement to relieve aortocaval compression. This is compatible with spinal precautions using a wedge under the backboard.
4. Oxygenation and carbon monoxide. Target SpO₂ ≥ 95% and generous supplemental oxygen. Fetal hemoglobin binds carbon monoxide with higher affinity than maternal hemoglobin, fetal carboxyhemoglobin peaks later than maternal levels, and its elimination half-life is roughly twice as long. Consequently the threshold for hyperbaric oxygen referral falls to a COHb > 15% in pregnancy (versus > 25% in the non-pregnant adult), and normobaric 100% oxygen is continued considerably longer than maternal levels alone would suggest — commonly for several times the duration required to clear the mother.
5. Fetal surveillance. Obtain obstetric consultation early. Continuous electronic fetal monitoring is indicated once the fetus is potentially viable (generally ≥ 23–24 weeks); before viability, monitoring is limited to documenting fetal heart tones. Antenatal corticosteroids are given between 24 and 34 weeks when preterm delivery is anticipated. Preterm labour is common after major burns, and delivery may be indicated for maternal deterioration or for a viable fetus in a mother with an extensive burn. In maternal cardiac arrest, perimortem cesarean delivery is begun within 4 minutes of arrest to improve both maternal and fetal survival.
Medication and Wound-Care Considerations
- Silver sulfadiazine is a sulfonamide. Avoid it near term because sulfonamides displace bilirubin from albumin and raise kernicterus risk in the newborn; it is also avoided in known G6PD deficiency.
- Mafenide acetate is a carbonic anhydrase inhibitor that produces a metabolic acidosis. Pregnancy already runs a compensated respiratory alkalosis with reduced buffering reserve, so large-surface mafenide use requires closer acid–base monitoring.
- Systemic NSAIDs are avoided after 20 weeks (oligohydramnios) and are contraindicated after 30 weeks (premature ductus arteriosus constriction). Acetaminophen, opioids, and ketamine remain the practical analgesic backbone.
- Tetanus toxoid is safe and indicated. Necessary radiographs are not withheld — shield the abdomen where feasible, but a diagnostic film that changes maternal management is always justified.
- Nutrition requirements add roughly 300 kcal/day for pregnancy on top of the calculated burn requirement.
Do Not Forget the Screening Obligation
Intimate partner violence increases during pregnancy. A burn pattern inconsistent with the reported history in a pregnant patient triggers the same non-accidental trauma pathway used in pediatrics, including confidential interviewing away from accompanying persons and referral to Adult Protective Services or the institutional violence-response team.
A woman at 30 weeks gestation sustains a 35% TBSA flame burn. Four hours into resuscitation her blood pressure is 108/64 mmHg, heart rate 118/min, and urine output has been 0.4 mL/kg/hr for two hours. The electronic fetal monitor now shows recurrent late decelerations. Which interpretation should guide the nurse’s next action?
A pregnant patient at 26 weeks gestation is rescued from a house fire. She is alert with a mild headache, and co-oximetry shows a carboxyhemoglobin level of 18%. Which management decision is most consistent with current practice?
Which wound-care and analgesic plan is most appropriate for a patient at 36 weeks gestation with partial-thickness burns to both lower extremities?