THE STANDARDIZATION OF STRESS IN THE PRODUCTION OF HEMORRHAGIC SHOCK: THE RELATION OF THE DURATION OF STRAIN AND THE RESISTANCE OF THE ANIMAL TO THE ONSET OF IRREVERSIBLE SHOCK

When hemorrhagic shock is produced by bleeding from an artery into a reservoir at a height fixed to provide a constant level of hypotension, compensatory vasoconstriction eventually fails and the blood in the reservoir spontaneously reinfuses into the animal. The value of the onset of this spontaneous reinfusion as a criterion for the production of a standardized and irreversible hemorrhagic shock has been investigated in the rat. The animal was bled into the reservoir until the arterial pressure fell to 30 mm. Hg, which was maintained until a reduction of the volume of blood in the reservoir at three successive 2-minute intervals signified that spontaneous reinfusion had just begun. Reinfusion of the remainder of the blood was quickly completed by raising the reservoir. The animal was observed for 48 hours.A good correlation between the volume of blood forced into the reservoir early in hypotension and the duration of hypotension until the occurrence of spontaneous reinfusion was observed. With a regression equation of time (expressed as percentage of the total hypotensive period) against the volume of blood in the reservoir at various times it was possible to predict from early bleeding volumes, with fair accuracy, the duration of hypotension necessary to produce spontaneous reinfusion. In general, animals forcibly reinfused before this predicted spontaneous reinfusion survived while those exposed to the total duration died. Spontaneous reinfusion under these conditions appears to be closely associated in time with the onset of irreversible shock. The prediction from early bleeding volumes of duration to spontaneous reinfusion should permit the determination of the effect of various treatments on the resistance to hemorrhagic hypotension without the necessity for sacrifice of the animal.