The single most important principle of critical care transfer is that the patient must be optimally stabilised before departure. This means that all immediately reversible physiological derangements should be addressed, the airway should be definitively secured if there is any doubt about its safety, haemodynamic status should be as stable as achievable, and all invasive monitoring and infusion lines should be in place, functioning, and checked.

It can be tempting — particularly when a patient requires a specialist intervention available only at another centre — to rush the departure in the belief that the sooner the patient arrives, the better. In most cases, spending an additional 30–60 minutes on stabilisation before departure is far safer than departing prematurely and managing a deteriorating patient in the back of an ambulance. The exception is when the needed intervention is itself the stabilising treatment — for example, a patient with an expanding extradural haematoma who is deteriorating despite all available measures, where the only definitive treatment is surgical decompression.