Interaction of sodium and volume in fluid resuscitation after hemorrhage.

Some measures of the efficacy of fluid resuscitation after hemorrhage are blood volume restitution (BVR) and attenuation of the neuroendocrine response. We compared the effectiveness of resuscitation with 0.9% NaCl and 3.0% NaCl in chronically prepared awake dogs after 30% hemorrhage. Each dog was bled on four occasions and resuscitated by four protocols: 1) full resuscitation (infusion to return and maintain mean arterial pressure (MAP) at control +/- 10 mm Hg) with 3.0% NaCl (HS); 2) full resuscitation with 0.9% NaCl (NS); 3) under-resuscitation with a volume of 0.9% NaCl equal to the subject's previous 3.0% NaCl requirement (SV); and 4) no fluid therapy (NR). Approximately three times more volume was needed to restore MAP with NS vs. HS, and thus the amount of Na administered was not different in these groups. Net volume balance was positive in the NS and SV groups but negative in the HS group due to marked saline diuresis. Net Na balance was positive in all three fluid-treated groups, but significantly higher in the HS group (p less than 0.01). MAP remained below baseline in the SV and NR groups (p less than 0.05). BVR exceeded 100% in NS and HS early in resuscitation, but BVR was not sustained in the HS group. Total plasma protein increased in all three fluid treated groups. Responses of all hormones were completely attenuated in the NS group. ACTH, cortisol, and AVP responses were promptly attenuated in the HS group, but remained greater than control. In the SV group, all hormone levels except renin returned to control values, but more slowly than the other groups. ACTH and cortisol correlated best with BVR; AVP, PRA, and aldosterone correlated with MAP restoration. In summary, resuscitation with either HS or NS can achieve similar MAP restoration. Hypertonic saline produces a more rapid increase in BVR and MAP, but the BVR improvement is transient. Resuscitation with HS incurs an intracellular water debt which is aggravated by a saline diuresis. Hormonal attenuation is linked either to BVR (ACTH, cortisol) or to MAP restoration (renin, AVP). Thus the optimal resuscitation regimen may consist of initial infusion of hypertonic saline followed by sufficient hypotonic solution to restore interstitial fluid volume and normal cellular hydration.