A middle aged thirty seven and half weeks pregnant dwarf with sever thoracic kyphoscoliosis presented for elective caesarean section in view of cephalopelvic disproportion. She had an anticipated anatomical difficult airway. Investigations revealed bilateral basal lung atelectasis, tricuspid regurgitation and mild pulmonary hypertension. low dose spinal anaesthesia with supplemental epidural anaesthesia allowed successful performance of surgery. Supplemental oxygen via face mask was provided but a steady rise in end tidal carbon dioxide appeared to indicate an impending airway disaster. The only corrective measure necessary was to change oxygen delivery device to low flow nasal prongs. This physiological difficult airway is attributable to the Haldene effect and hypoxic pulmonary vasoconstriction. Supplemental oxygen should be provided with caution in chronic restrictive lung cases to avoid maternal respiratory failure and subsequent foetal harm.
