Aortic cannulation.

In heart-lung bypass the arterial blood can be returned to the patient by a variety of methods; these differ in the type of cannula used, the site of insertion, and the technique of insertion. 'Cannulae' have been fashioned from both biological (homograft aorta; Dodrill, Marshall, Nyboer, Hughes, Derbyshire, and Stearns, 1957) and synthetic materials (metal and plastic; Nuniez and Bailey, 1959). The infusion sites commonly used are the femoral artery and the ascending arch of the aorta, with a growing preference in recent years for the latter site. There is little in the literature about the complications of aortic cannulation, compared with that found in ilio-femoral cannulation (Jones, Vetto, Winterscheid, Dillard, and Merendino, 1960; Elliott and Roe, 1965). However, death from cerebral haemorrhage, attributable to imperfect aortic arch perfusion, has been reported (Kulkarni, 1968), and, in a recent paper on aortic cannulation, some disadvantages of the site are briefly mentioned by Borman and Milwidsky (1968). To these must be added the post-perfusion death, where imperfect perfusion of the aortic arch is suspected, especially when this is associated with the small aortic arch of a child. Unfortunately, imperfect perfusion of the head will not normally be evident during bypass, may only be suspected when the patient fails to regain consciousness, and will often be undetectable even at post-mortem examination. It is prudent to point out that, during heart-lung bypass, a low radial artery pressure, associated with a very high line pressure unrelated to the resistance in the actual line, implies inadequate aortic arch perfusion. Concern about the possible dangers of aortic arch cannulation, as currently practised, and experimental evidence of the better haemodynamics of perfusion via the femoral artery, prompted this study of the factors involved, and led to the developmnent of an improved method of aortic cannulation.