Booked inpatient admissions and hospital capacity: Mathematical model misses the point

EDITOR—Gallivan et al report a mathematical model of variability of length of stay in an intensive care unit after cardiac surgery.1 The programmes of the NHS modernisation agency use quality improvement methods adapted to health care in England.2 The cornerstones of the approach are patient centredness; mapping the whole process; analysis of true demand and capacity; and redesign through innovation, experimentation, and incremental implementation. The methods are underpinned by the science of complex adaptive systems.3 The NHS is the epitome of a complex adaptive system. Data on the variability of length of stay are valuable but reflect activity, not demand. Activity is limited by capacity throughout the process. Gallivan et al assumed that length of stay was an independent variable, but length of stay in cardiac intensive care will be affected by a patient's clinical condition and the availability of beds for care afterwards. The dependency of other patients may affect the care given and influence length of stay. Gallivan et al assumed …