Perioperative anesthetic management of children having Inborn errors of metabolism.

Sir,

Inborn errors of metabolism (IEM) are biochemical disorders result from the absence or abnormality of an enzyme or its cofactor, leading to either accumulation or deficiency of a specific metabolite.[1] More than 600 described IEMs have a clear phenotype.[2] However, occasionally a clinical and biochemical phenotype is not completely explained based on known disorder. A clear diagnosis is not always possible for children presenting with ketotic hypoglycemia, which is one of the predominant biochemical findings in a number of IEM including glycogen storage disorders, defects in gluconeogenesis, fatty acid oxidation defects, organic acidemias and oxidative phosphorylation defects.[3] Ketotic hypoglycemia, also known as “accelerated starvation” is the common cause of clinically significant nondiabetic hypoglycemia among children between 1 and 5 years of age. Originally described by Colle and Ulstrom in 1964, it is defined by periodic episodes of hypoglycemia, associated with ketonuria, usually occurring after food deprivation.[4] The hypoglycemia is associated with raised ketone bodies, free fatty acids with suppressed insulin levels and elevated lactic acid.[5]

An 8-year-old boy, weighing 35 kg, having undiagnosed IEM for past 5 years and asthma since childhood, was scheduled for extraction of multiple decayed teeth as a day case surgery. The child presented first time with nausea, vomiting, and severe acidotic breathing at the age of 3 years following an acute viral illness. He was not comatose and had no hepatomegaly on physical examination. Initial biochemical workup revealed a high anion gap severe metabolic acidosis (pH 7.06, base excess 16), ketonuria (>7.8 mmol/l), lactic acidosis (8.1 mmol/l), and hypoglycemia (riparian buffer strips [RBS] 43 g/dl). Urine for toxicology, organic acid, and plasma acylcarnitine were normal. The patient had five episodes of metabolic decompensation from the first presentation, which clinically responded to intravenous fluids with high calories achieved through dextrose. The biochemical abnormalities present even during well-state were lactic acidosis and intermittent ketonuria. In view of the recurrent ketotic hypoglycemia, high anion gap metabolic acidosis with persistent lactic acidosis and intermittent ketonuria even during well state and absence of hepatomegaly, he was evaluated for glycogen synthetase defect. However, the GYS2 gene sequencing plus deletion and duplication was negative. Thus, so far a clear biochemical diagnosis has not been established in this patient.

The child visited the preoperative anesthesia clinic before the dental extraction surgery. After reviewing his case in consultation with the metabolic physician, it was decided to admit him a day before procedure to avoid fasting, anesthesia, and surgery-related risk for metabolic decompensation.[5] On admission, the child was kept on intravenous fluids, which was increased to 1.5 times maintenance providing 65 kcal/kg/day through dextrose and age appropriate electrolyte solution after which he was made nothing per oral before surgery. Baseline biochemical workup included assessment of acid-base status, electrolytes, RBS, serum lactic acid, and ketonuria. His baseline lactic acid before surgery was 4.2 mmol/l, whereas all other biochemical parameters were normal. These were then monitored every 4 hourly till he was allowed orally.

In view of asthma, use of atracurium for endotracheal intubation was avoided. Succinylcholine was not considered because of his mildly raised serum K+ (5.3 mEq/l). Rocuronium has a variable effect on muscle relaxation and sometimes its duration is more than an hour in our experience. After application of standard American Society of Anesthesiologists monitoring (electrocardiography, noninvasive blood pressure, SPO2, ETCO2), we did an induction of anesthesia with fentanyl 3 µg/kg, propofol 2 mg/kg, and sevoflurane 4–6% in 100% oxygen. The child was intubated using cuffed ring; Adair and Elwyn size 6.0 mm endotracheal tube without using muscle relaxant. The same maintenance fluid (half strength normal saline with 12.5% dextrose) was continued in intraoperative period. Blood glucose was monitored intra- and post-operatively to ensure normoglycemia. Surgery went uneventful, the patient remained hemodynamically stable, and his postoperative biochemical profiles were normal, so he was discharged a day after surgery.

In conclusion, children with IEM presenting for anesthesia and surgery can be best managed by multidisciplinary approach to ensure safe management of these patients.[6]

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Conflicts of interest

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