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Correspondence |
John Radcliffe Hospital, Oxford, UK, E-mail: r_mihai99{at}hotmail.com
To the Editor:
A 115-kg 65-yr-old female presented with symptomatic primary hyperparathyroidism (plasma calcium 2.9 mmol·L–1, PTH 10.5 pmol·L–1). She had type II diabetes, hypertension, hyperthyroidism and depression and was taking mixtard insulin, metformin, ramipril, atenolol, aspirin, simvastatin, paroxetine, and carbimazole. Sestamibi and magnetic resonance imaging scans demonstrated a retrosternal parathyroid adenoma. Surgery was planned for a morning operating list.
General anesthesia was induced with midazolam 2 mg iv, fentanyl 150 µg iv, and propofol 200 mg iv, followed by rocuronium 50 mg iv and endotracheal intubation. Anesthesia was maintained with 50% nitrous oxide in oxygen and 1% end-tidal isoflurane. At the request of the surgeon, the patient received 200 mg iv methylene blue (
1.75 mg·kg–1). The operation was completed uneventfully within 75 min, and her vital signs were stable throughout. No anticholinesterase or anticholinergic drugs were administered.
In the recovery room, oxygen saturation was 98% on facemask oxygen and her airway remained patent. The patient appeared agitated and restless. Blood pressure was 150/60 mmHg and blood sugar 11.6 mmol·L–1. Arterial blood gases revealed pH 7.44, pO2 85.9 mmHg, pCO2 37.3 mmHg. Eye opening was spontaneous with normal pupillary reflexes. She moved all four limbs, but she was unable to speak and she did not respond to verbal command. There was no limb weakness, her plantar responses were down-going, and there were no focal neurological signs.
The patient’s agitation failed to settle after two hours, and the unenhanced computed tomography (CT) scan done at that time demonstrated no intracranial abnormality. She was reintubated and ventilated due to concerns of airway safety. The following day she obeyed commands but remained drowsy and confused (Glasgow coma score of 11, E4M6V1). Serum calcium had normalized (2.25 mmol·L–1), methemoglobin levels were < 1%, the electrocardiogram and troponin-I were normal. The patient’s trachea was extubated successfully two days post-surgery. Her mental state slowly improved, and she was discharged home on day seven. There were no residual neurological symptoms at eight week follow-up.
Methylene blue (MB) infusion has been used by endocrine surgeons for over 30 years to aid intraoperative parathyroid localization. Adverse effects are rare, commonly limited to "pseudocyanosis" that may cause spuriously low readings on pulse oximetry. Pain at the infusion site, nausea/vomiting and bradycardia may sometimes occur. In recent years, there have been five case reports of anomalous recovery after parathyroidectomy in patients who received MB (Table
).1–5 Although many factors might be responsible for an abnormal emergence from anesthesia, MB toxicity was considered a likely cause. Hypoxia, hypovolemia, or biochemical/metabolic disturbances were discounted in all these patients. Their neurological presentations might suggest a cerebrovascular event since they had risk factors for cerebrovascular disease (diabetes, hypertension and overweight), but no patient developed limb weakness, specific neurological signs or CT abnormalities.
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In conclusion, the patient described may have suffered an adverse reaction to MB at a far lower dose (1.75 mg·kg–1) than reported in other cases. Methylene blue toxicity remains a diagnosis of exclusion. Whether such uncommon but serious side-effects should limit the use of MB during parathyroid surgery requires further debate.
Footnotes
Accepted for publication October 11, 2006.
References
1 Martindale SJ, Stedeford JC. Neurological sequelae following methylene blue injection for parathyroidectomy. Anaesthesia 2003; 58: 1041–2.[Medline]
2 Bach KK, Lindsay FW, Berg LS, Howard RS. Prolonged postoperative disorientation after methylene blue infusion during parathyroidectomy. Anesth Analg 2004; 99: 1573–4.
3 Majithia A, Stearns MP. Methylene blue toxicity following infusion to localize parathyroid adenoma. J Laryngol Otol 2006; 120: 138–40.[Medline]
4 Mathew S, Linhartova L, Raghuraman G. Hyperpyrexia and prolonged postoperative disorientation following methylene blue infusion during parathyroidectomy. Anaesthesia 2006; 61: 580–3.[Medline]
5 Patel AS, Singh-Ranger D, Lowery KA, Grinnion JN. Letter to the Editor. Head Neck 2006; 28: 567–8.[Medline]
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