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Anesthetic Management of a Parturient with Argininosuccinolyase Deficiency
Abstract Number: F3C-10
Abstract Type: Case Report/Case Series
Argininosuccinolyase deficiency (ASLD), the second-most common urea cycle disorder, is an inborn error of hepatic metabolism affecting 1 in 70,000 births. The inability to detoxify waste nitrogen products may cause life-threatening hyperammonemia with longterm neurocognitive defects, hepatic disease, or systemic hypertension. Successful pregnancies without evidence of teratogenicity have been reported in ASLD patients. However, guidelines for the anesthetic management of these patients are lacking.
A 30yo G1 with ASLD diagnosed in infancy presented at 39w1d gestation in labor. Her pregnancy had been uncomplicated. Epidural anesthesia was initiated uneventfully on request. The patient was initially maintained on her home low protein diet, then transitioned to clears with supplemental D10 infusion to promote anabolism. Ammunol® (an IV mixture of the nitrogen scavengers sodium benzoate and sodium phenylacetate) was available in case of hyperammonemia. The patient was monitored for ammonia levels and encephalopathy in labor. The patient delivered a baby boy, Apgars 8,9. Postpartum, the patient resumed a low protein (45g daily) diet with serum ammonia monitoring every 6 hours for 72 hours.
Mainstays of ASLD management include dietary nitrogen restriction to limit the buildup of urea cycle substrates, arginine supplementation to increase nitrogen excretion via the urea cycle, and avoidance of prolonged fasting to prevent protein catabolism. Treatment of hyperammonemia includes nitrogen scavenging therapy and hemodialysis to prevent neurologic damage.
To prevent peripartum catabolism, added metabolic stressors (e.g. infection, pain) must be managed aggressively. Exogenous glucocorticoids are discouraged. Benefits of fasting prior to anesthetic induction should be weighed against the risks to these patients. In our case, we interpreted npo guidelines liberally to shorten the anticipated fasting time in labor; this, combined with continuous dextrose infusion and frequent lab checks, led to a safe outcome for the patient.
We recommend perioperative serum electrolyte and ammonia levels for early detection of subclinical imbalances. In particular, hyponatremia or hyperosmolarity may result from D10W infusion, with altered mental status masquerading as hyperammonemic encephalopathy. Hypokalemia induces renal ammoniagenesis and may increase the risk of hyperammonemia.
Fatal hyperammonemia from enflurane has been reported in ASLD. Hepatotoxic medications should be avoided. If general anesthesia is needed, desflurane or isoflurane are preferred for their minimal hepatic metabolism; intraoperative D10 infusion should be given and frequent ammonia levels checked. The minimal systemic effects and blockade of the stress response make regional anesthesia ideal for ASLD patients in the absence of contraindications.
1.Genet Med 2012;14:501-7
2.J Inherit Metab Dis 1996;19:621-3
3.Eur J Pediatr 1998;157:169-70