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Department of Anesthesiology and Critical Care; binsaiims{at}sify.com (Biswas, Singh, Agarwal, Prasad, Chaturvedi) Department of Gynecology & Obstetrics; B. P. Koirala Institute of Health Sciences; Dharan, Nepal (Banerjee)
To the Editor:
A 47-year-old woman (weight 52 kg, height 154 cm) with uncontrolled hyperthyroidism (goiter and clinical features for 20 and 7 yr, respectively) underwent emergency lower-abdominal laparotomy under lumber epidural block.
We inserted an epidural catheter at the L3–4 inter-vertebral space and administered 2 mL of 0.5% bupivacaine through it to exclude subarachnoid placement. After incremental administration of 14 mL of 0.5% bupivacaine, the patient developed difficulty in breathing (jerky paradoxical breathing) and oxygen desaturation. We ventilated her lungs with 100% oxygen through a Bain circuit using positive pressure via a face mask. Her hemodynamic variables were within the normal range. Her lungs were clear to auscultation.
The sensory block (pinprick method) was at the T5 level. The laparotomy proceeded under mask ventilation, which yielded arterial blood gas values of Po2 170.5 mm Hg, Pco2 60.2 mm Hg, pH 7.27, HCO3– 26.9 mmol/L, and base deficit 1 mmol/L. After 30 min of manual ventilation, the patient developed synchronized thoraco-abdominal movement accompanied by an increase in tidal volume. After 45 min, mask ventilation was no longer required. The surgical procedure took 90 min. Her postoperative arterial blood gas values were within the normal range.
Normal tidal volume is generated by the synchronized actions of lower intercostal muscles and the diaphragm. Thoracic epidural block extending even up to the T2 level does not alter resting ventilation and blood gases significantly in healthy persons (1). However, hyperthyroidism can cause myopathy, skeletal muscle dysfunction, diaphragmatic weakness, and ineffective cardiorespiratory function, leading to decreased lung capacity and volume and capacity-impaired dynamic function (2,3). We presume that our patient developed respiratory failure because of preexisting myopathy of her respiratory muscles. Even a differential epidural block may have produced intense paralysis of her intercostal muscles, which, in conjunction with diaphragmatic weakness, failed to generate adequate tidal volume. Thus, mechanical respiratory failure developed.
In appropriate situations, regional anesthesia has been recommended as an excellent alternative to general anesthesia for hyperthyroid patients (4). However, anesthesiologists should be aware that in the background of prolonged, uncontrolled hyperthyroidism, neuraxial block with local anesthetics can unmask the weakness of the respiratory muscles and result in a life-threatening situation such as respiratory failure.
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