Applied physiology of patient transfer: DipIMC practice questions

Answer: C

Blood shifts towards the feet, cutting venous return; fill the patient first and drive smoothly

With the patient supine and head towards the direction of travel, forward acceleration effectively forces blood towards the feet, decreasing venous return, cardiac output and blood pressure. The critically ill often cannot mount the normal baroreceptor and vasoconstrictor response, so the fall is exaggerated in the hypovolaemic and blunted in the well-filled — hence the workbook's teaching that 'full' patients travel better: resuscitate before setting off, and go slowly and steadily, with rarely any need for blue lights. The direction matters: it is the feet, not the head, that blood moves towards. Movement can disturb an arterial trace, but a fall that follows each acceleration and recovers at steady speed is the physiology described above; and swapping to the cuff makes things worse, because vibration interferes with non-invasive readings and the ICS guidance calls intermittent non-invasive measurement unreliable in a moving vehicle. Passive cooling is a real transfer hazard but does not produce a pressure that tracks the throttle.

Answer: A

Its fraction is unchanged but its partial pressure falls

By Dalton's law the total barometric pressure is the sum of the partial pressures of the constituent gases. As an aircraft climbs, barometric pressure falls; the percentage of oxygen in air stays constant (about 21%), so the partial pressure of oxygen falls in proportion, and with it alveolar and arterial oxygen tension. A patient whose gas exchange is already borderline — acute illness or injury such as chest trauma, or chronic lung disease — will desaturate. The ABC (Table 32.5, Flight physiology) therefore advises supplemental oxygen for all patients being transported. The ABC summarises the effects of increasing altitude as colder, less oxygen, and expansion of gas volumes; the last is Boyle's law, which affects air-filled body cavities and equipment such as tracheal tube cuffs. A pressurised fixed-wing cabin reduces these effects, whereas a helicopter flies unpressurised.