Influence of Infection on the Hematological Effects and Mortality Following Mid-Lethal Roentgen Irradiation

Abstract

In many studies of the mortality following exposure to lethal amounts of ionizing radiation, bacterial infection has been regarded as playing a major role. Very little data can be found, however, on the incidence of bacterial infection, or its nature, and the resulting effect on radiation morbidity or mortality. Warren and Whipple (1) studied the blood and tissue of dogs sacrificed two, three, and four days following massive dosages of x-radiation to the abdomen. The dosage used was lethal in three to six days and caused extensive destruction of the intestinal epithelium. In these animals the incidence of positive bacterial cultures was higher than in controls, but no evidence of an overwhelming sepsis could be demonstrated. These findings were extended by Chrom (2) and by Lawrence and Tennant (3), who obtained a high incidence of positive cultures for enteric organisms from the blood and tissues of mice during the second week after lethal dosages of x-rays or neutrons. Miller and associates (4) demonstrated a bacteremia in mice during the second week after lethal whole body irradiation. The organisms isolated were predominantly the gram-negative bacilli normally present in the lower intestinal tract of the mouse. In the study to be reported here blood cultures of 54 dogs receiving whole body irradiation with mid-lethal doses of 350 to 450 r were examined. Positive cultures of many types of organisms were obtained during the period of survival. Positive cultures of gram-negative organisms appeared to be closely related to the terminal state. Some correlation was demonstrated between the leukocyte counts and the mortality. In dying animals a consistent relationship between infection and anemia was noted. Methods Dogs used in this experiment were healthy mongrels, six months to two years of age. All were being used in various studies of vitamin P compounds given three times daily before and after irradiation (5). Whole body dosage of 350 r, the mid-lethal level for this laboratory (6), was used for most experiments. A few animals received 450 r. The irradiation factors were 250 kv., 15 ma., filtration-aluminum parabolic (9 inches in diameter and 0.56 inches at center) + 0.5 mm. copper, half-value layer 2.15 mm. copper, target-skin distance 40 inches, intensity 7.0 r per minute. Complete hematological studies were performed prior to irradiation and three times weekly following irradiation. Bacteriological studies were carried out at the same time, the cultures being taken from the jugular vein following surgical preparation by shaving, soap and water scrubbing, and application of zephiran. Four-milliliter samples of blood were obtained, half of which were placed in Douglas broth and half in deep meat broth. Aerobic cultures were kept five days and anaerobic cultures seven days. All organisms noted were identified by standard bacteriologic technics.