of modern intensive care units in hospitals (Figure 2). In 1952, an epidemic of poliomyelitis struck Copenhagen, overwhelming the supply of negative pressure ventilators. Dr Bjørn Ibsen proposed positive pressure ventilation as asubstitute, and hundreds of medical students provided the manpower for manual ventilation via a tracheostomy tube and a rubber bag (Figure 3). Necessity overturned conventional practice, and endotracheal positive pressure ventilation became the standard of care and was routinely implemented in intensive care units, which were first formed in the 1960s.22