The effects of normal and hypertonic saline on regional blood flow and oxygen delivery

Boluses of crystalloids are frequently given to patients to optimize vital organ perfusion. However, their effect on regional blood flow and oxygen delivery in the normal mammalian circulation has not been studied. We compared the effects of normal or hypertonic (3%) saline or control on regional blood flow and oxygen delivery in normal animals.

We conducted a randomized, controlled animal study in seven merino cross-ewes. We implanted chronic flow probes around aorta, coronary, renal, and mesenteric arteries. We randomized animals to three different interventions: observation (control), normal saline (1 L over 15 min), or 3% saline (300 mL over 15 min). We continuously measured central hemodynamics and organ blood flow for 210 min.

Both fluids increased heart rate, cardiac output, central venous pressure, peripheral conductance, coronary and mesenteric blood flow, and conductance in the first hour (P < 0.05). In the second and third hour, both maintained a greater cardiac output, total peripheral conductance, and mesenteric blood flow (P < 0.05) than control, but the difference decreased. In contrast, renal blood flow was unaffected and, because of hemodilution, renal oxygen delivery was decreased in the first hour (P < 0.05). Simultaneously, urine output and creatinine clearance increased (P < 0.05) in both groups. Finally, 3% saline significantly, but transiently, increased serum sodium and osmolarity.

Normal and hypertonic saline have similar systemic and regional hemodynamic effects. They also have no effect on renal blood flow and initially decrease renal oxygen delivery while increasing urine output.