Pulse oximetry and pulmonary oedema.

A case is reported where reduced oxygen saturationwas detected bya pulse oximeter before clinical signs of pulmonary oedema appeared. A 45 years old, 82 kilogram lady presented for emergency surgery with subacute intestinal obstruction. She had no previous history of any cardiovascular, respiratory or metabolic disorder. She underwent partial colectomy and colostomy. Two days later she was again brought to the operating room for revision of colostomy. On pre-opcrative examination she was conscious and orientated, afebrile, heart rate of 135 beats/minute and a respiratory rate of 45/minute. She was in a positive balance of + 1350 mls over the last 24 hours. On chest auscultation, she had only left basal crcpitations. The preoperative arterial blood gases showed a P02 of 90.6mm of Hg and oxygen saturation of 97.3% on 8 L of oxygen per minute via MC mask. The patient was preoxygenated through the Magill's circuit and a pulse oximeter probe (Ohmedia Biox 3700) was attached to her forefinger which showed an oxygen saturation of 98%. Anaesthesia was induced with a sleep dose of thiopentone, and 100mgs of suxamethonium. She was intubated with cricoid pressure and anaesthesia maintained with fifty per cent nitrous oxide and oxygen, pancuronium and pethidine. Intraoperatively she remained stable and her oxygen saturation remained at 96%. The patient was reversed with atropine and neostigmine. After reversal, but before extubation she was noticed to have difficulty in breathing and the oxygen saturation dropped to 87% on 8L/min-ute of oxygen. The ventilation was thereafter assisted and the saturation showed very slight improvement to 89%. Chest auscultation at this stage did not reveal any new findings. Nerve stimulator showed a fully reversed block. Arterial blood gases showed a pH of 7.38, pCO2 of 46.4 mm of Hg, P02 of 55 mm of Hg, bicarbonate 24, base excess 2.2 and oxygen saturation 87.8%. She was transferred to the Intensive Care Unit with an endotracheal tube in situ and connected to a T piece circuit on 12 L/minute humidified oxygen. Her oxygen saturation was monitored continuously and was 90%. A chest x-ray was done. On endotracheal tube suctioning slightly pinkish tinged secretions were observed. Chest auscultation at that stage did not reveal any new findings. She was given frusemide 40 mgs I.V stat’ and her oxygen saturation improved dramatically to 96-97% after diuresis. Her chest x-ray when received supported the findings of early pulmonary oedema. She was extubated one hour later.