Hypovolemic shock resuscitation with hyperosmotic 7.5% NaCl: effects on respiratory system mechanics.

The infusion of the hypertonic 7.5% NaCl solution stimulates the afferent vagal innervation of the lungs. In order to verify if this reflex elicits any respiratory mechanical alterations, normovolemic (n = 18) and hypovolemic (n = 18) (20 ml of shed blood/kg) guinea pigs were studied. The animals were assigned to groups of nine receiving either isotonic 0.9% NaCl or hypertonic 7.5% NaCl solutions (4 ml/kg body weight). Passive respiratory system elastance (Ers) and the maximal value of the resistance (Rrsmax) were measured. The latter was further partitioned into its minimal value (Rrsu) using the constant flow inflation method. Ers, Rrsmax, Rrsmin, and Rrsu were measured before and at 0, 2, 5, 10, and 15 minutes following the infusion. The results showed that both isotonic and hypertonic solutions, at the given volume rate, caused no significant alterations of respiratory mechanics in normovolemic and hypovolemic animals.