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LETTER TO THE EDITOR

Glycine Encephalopathy and Delayed Emergence from Anesthesia

Department of Anaesthesiology; National Taiwan University Hospital; Taipei, Taiwan; shouzen{at}gmail.com

To the Editor:

Glycine encephalopathy or nonketotic hyperglycinemia (NKH) is a metabolic disorder of the glycine cleavage enzyme system that results in high brain concentrations of the inhibiting transmitter, glycine (1,2). We report a case of delayed recovery from anesthesia in a 3-year-old girl diagnosed with NKH at 1 mo of age by a 30-fold increased cerebrospinal fluid/plasma glycine ratio (3).

The patient suffered from episodic bronchiolitis, pneumonia, seizure, poor sleep, and apnea. Her twin sister, who had also been diagnosed with NKH, died at 3 mo from airway complications. The patient required bronchoscopy to evaluate her spells of apnea and airway obstruction. Before the procedure, we noted good muscle power, normal body movement, spontaneous eye opening, and normal skin color and respiration. The patient also suffered from mental retardation, poor feeding, and lethargy. Her motor examination showed active movement against gravity and resistance. The movement of intercostal and diaphragmatic muscles was normal without using the accessory muscles.

We elected to perform the bronchoscopy under general anesthesia with sevoflurane. We did not administer premedication, neuromuscular blocking drugs, IV anesthetics, or opioids during or after the procedure period. We maintained the patient’s body temperature throughout the procedure.

The patient did not awaken when the sevoflurane was turned off at the end of the procedure. Forty-five minutes after the discontinuance of the sevoflurane, with the end-tidal gas monitor showing no trace of anesthetic and the end-tidal CO₂ concentration more than 50 mm Hg, she began to have slow but weak spontaneous respirations. IV aminophylline (5 mg/kg) was ineffective at increasing respiration and activity. We assisted ventilation by facemask for another hour. The patient was then transferred to the postanesthetic care unit for further observation. Her neurological examination revealed lethargy and moderate hypotonia. Her motor examination expressed active movement, but not against gravity and resistance. The use of accessory muscles of respiration was also noted.

Factors that frequently prolong recovery include premedication, intraoperative muscle relaxant, opioids, and hypothermia. None of these applied to our patient. The interaction between glycine and trace anesthetics likely accounted for her slow emergence (4).

Glycine, like -aminobutyric acid, serves as a neuroinhibitory modulator in the central nervous system. Glycine is a simple amino acid. When released into a synapse, glycine binds to a receptor which makes the postsynaptic membrane more permeable to chloride ion, hyperpolarizing the cell membrane, and inhibiting conduction of action potentials (5–8). Excess chronic inhibitory tone from glycine must have interacted with the inhibitory effects of sevoflurane to produce the delayed recovery observed in our patient.

REFERENCES

1. Applegarth DA, Toone JR. Glycine encephalopathy (nonketotic hyperglycinemia): review and update. J Inherit Metab Dis 2004;27:417–22.[Medline]
2. Toone JR, Applegarth DA, Coulter-Mackie MB. Biochemical and molecular investigations of patients with nonketotic hyperglycinemia. Mol Genet Metab 2000;70:116–21.[Web of Science][Medline]
3. Applegarth DA, Toone JR. Nonketotic hyperglycinemia (glycine encephalopathy): laboratory diagnosis. Mol Genet Metab 2001;74:139–46.[Web of Science][Medline]
4. Hoover-Fong JE, Shah S, Van Hove JLK. Natural history of nonketotic hyperglycinemia in 65 patients. Neurology 2004;63: 1847–53.[Abstract/Free Full Text]
5. Krasowski D. Intravenous anesthesia differentially modulate ligand-gated ion channels. Anesthesiology 2000;92:141.
6. Miller KW. The nature of site of general anesthetic action. Br J Anaesth 2002;89: 17–31.[Web of Science][Medline]
7. Sloan TB. Anesthesia and the brain. Anesthesiol Clin North America 2002;20: 265–92.[Medline]
8. Yamakura T, Bertaccini E, Trudell JR. Anesthesia and ion channels. Molecular models and sites of action. Annu Rev Pharmacol Toxicol 2001;41:232–51.

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