Influence of hypertonic saline solution 7.2% on different hematological parameters in awake and anaesthetized ponies

The influence of hypertonic NaCl 7.2% infusion (4 ml/kg of body weight [BWT]) on plasma (PV) and blood (BV) volumes, sodium (Na), chloride (Cl), potassium (K) plasma concentrations, osmolality (Osm), total protein content (TP), packed cell volume (PCV) and red blood cell count (RBC) was studied in five standing and anaesthetized ponies (standard halothane anaesthesia). Arterial blood gases were followed in the anaesthetized ponies. Isotonic NaCl 0.9% (4 ml/kg of BWT) was used as a placebo in the standing ponies. Isotonic solution in the standing ponies induced few changes: only small decreases in K, TP, PCV and RBC were observed. Na, Cl and Osm increased significantly after the NaCl 7.2% infusions in the standing and anesthetized ponies. Significant decreases in PCV, RBC and TP after the administration of hypertonic solutions were determined and were in both groups clear indications of an occurring hemodilution although no significant increase in PV and BV could be demonstrated. An increase in diuresis characterized by numerous micturitions was observed in the standing ponies and during the recovery period after anaesthesia. Apparently, the occurring fluid shift towards the intravascular compartment was partly compensated by an increase in diuresis. The decreases in PCV, RBC and TP were less severe in the anaesthetized ponies compared to the changes observed in the standing ponies. Stress responses during anaesthesia might explain this finding. K increased abnormally at the end of anaesthesia, probably due to minimal muscle damage induced by the dorsal recumbent position. Arterial blood gases did not change after the administration of NaCl 7.2% solution during anaesthesia. No specific clinical side-effects related to the use of hypertonic solution could be observed in the standing and anaesthetized ponies. Further studies are necessary to investigate the effects of hypertonic NaCl solution in horses with a disturbed fluid balance (hypovolemia).