Effects of hypertonic and isotonic fluid infusion on the flash evoked potential in rats: hemorrhage, resuscitation, and hypernatremia.

In resuscitation from hemorrhagic shock, very small volumes of hypertonic saline (HS) improve blood pressure while reducing intracranial pressure and edema formation. The effects of hypertonic resuscitation fluids and hypernatremia on electrophysiologic brain function have not been studied. The present study was done in two parts. First we examined the effects of hemorrhagic shock and resuscitation with either 7.5% HS or lactated Ringer's (LR) solution on the flash evoked potential (FEP). Rats were bled to a mean arterial pressure (MAP) of 35 mm Hg for 1 hour, then resuscitated with HS (n = 10) or LR (n = 10) to a MAP of 80 mm Hg for another hour. Resuscitation required 3.8 +/- 0.5 mL/kg HS and 42.9 +/- 7.5 mL/kg LR (p < 0.05). During hemorrhage, FEP latencies increased and amplitudes decreased. During resuscitation, these variables returned toward baseline values. There were no significant differences between groups, although HS tended to restore the FEP better than LR. We next examined the effects on the FEP of hypernatremia and hyperosmolarity produced by two different hyperosmotic fluids. Over a 1-hour period, 16 mL/kg HS (n = 8), 16 mL/kg IsoSal (4.5% saline, 5.9% glucose, 6.4% mixed amino acids; n = 8), or 40 mL/kg LR (n = 8) was infused into normovolemic rats. Plasma sodium levels increased in both hyperosmotic groups (baseline = 145.2 +/- 0.7 mEq/L; after infusion, HS = 202.4 +/- 9.8 mEq/L, IsoSal = 163.3 +/- 4.2 mEq/L; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)