The Effects of Intermittent Positive Pressure Respiration on Occurrence of Air Embolism and Morality Following Primary Blast Injury

Abstract : Twenty beagle dogs were exposed in pairs to airblast on the endplate of a 42-inch diameter shock tube. One dog of each pair then was given intermittent positive pressure respiration (IPPR) for 2 hours with 100 percent oxygen, and the other dog was maintained on 100 percent oxygen for 4 hours in a hyperbaric chamber at a chamber pressure of 14 p.s.i.a., after which she was given IPPR with 100 percent oxygen for 2 hours. The mortality, time of death, and incidence of arterial air embolism in these two groups then were compared with those of 10 untreated control animals that previously had been exposed to airblast in the same way as those in the treatment groups. The mortality was 60 percent in the untreated control group, 80 percent in the immediate IPPR group, and 50 percent in the delayed IPPR treatment group. There was one case of air embolism (14-minute fatality) in the untreated control group, three cases of air embolism in the immediate IPPR group, and none in the delayed IPPR group. The mean survival time for the fatalities was 12.4 hours for the untreated control group, 2.3 hours for the immediate IPPR group, and 9.9 hours for the delayed IPPR group. Thus, the results indicate that the use of IPPR immediately following blast injury may result in an increase in the incidence of air embolism, increase in mortality, and a reduction in survival time; whereas, when used after a delay of 4 hours, IPPR resulted in neither an increase in incidence of air embolism nor in mortality but did result in a shortening of survival time.