Increased mortality associated with after-hours and weekend admission to the intensive care unit: a retrospective analysis

To the Editor: We read with interest the recent cover article by Bhonagiri and colleagues detailing increased standardised mortality rates for patients admitted to Australian intensive care units (ICUs) out of hours.1 Have the authors considered a secondary analysis controlling for night-time staffing ratios? Aside from staffing levels, human factors such as the effects of fatigue and sleepiness due to circadian rhythm misalignment and sleep deprivation should be considered and further investigated.