Pre-operative screening for sleep disordered breathing: obstructive sleep apnoea and beyond

Simplified schematic illustration of the load–capacity ratio of the respiratory muscle pump. The central efferent output, neural respiratory drive, needs to increase to account for an elevated load on the respiratory muscle pump (e.g. obesity, obstructive sleep apnoea), or with diminished capacity (e.g. neuromuscular conditions, kyphoscoliosis). However, sleep inhibits central efferent output and an imbalance in the load–capacity ratio results in sleep disordered breathing with the development of respiratory failure and nocturnal hypoventilation. These conditions are replicated under sedation or with use of centrally active drugs (e.g. opioids). CNS: central nervous system.