AN EXPERIMENTAL COMPARISON IN DOGS OF EXPIRED AIR AND OXYGEN VENTILATION DURING EXTERNAL CARDIAC MASSAGE BY

A comparison has been made between the effects of ventilation with oxygen and expired air via a non-rebreathing circuit during manual external cardiac massage for 43-60 minutes in two groups of dogs. Ten of the eighteen dogs receiving expired air survived, as did six of the twenty which received oxygen. The Paco2 remained below 10 rnm Hg in the oxygen group and was about 28 mm Hg in the expired air group. In the expired air group the Pa ^ remained above 63 mm Hg. The calculated venous arterial admixtures in eight of the dogs were between 2.1 and 14.7 per cent. The importance of pupillary changes and the complications occurring during and after external cardiac massage are discussed. It is suggested that, when oxygen is not available, expired air ventilation combined with external cardiac massage may safely be encouraged during resuscitation in previously fit humans. Following the description of external cardiac mas-sage (e.c.m.) by Kouwenhoven and his colleagues in 1960 the technique has been widely and suc-cessfully applied in hospital practice, combined with positive pressure ventilation with oxygen (Sykes and Orr, 1966; Linko et al., 1967; Kirby and McNicol, 1967). It has been continued for as long as 75 minutes with full recovery despite a period of 45 minutes with dilated pupils (Shocket and Rosenblum, 1967). Studies on patients with heart disease, who required resuscitation by external cardiac massage accompanied by ventilation with oxygen have shown that deterioration of cardiac and pulmonary function may occur. It has been found that the cardiac output falls to about 20-35 per cent of its normal value during external cardiac massage both in human patients (Mackenzie et al., 1964; Cohn and Del Guerico, 1966; Oriol and Smith, 1968) and in dogs (Weiser, Adler and Kuhn