Role of tissue fluid hyperosmolality in the pathogenesis of post-traumatic fluid loss

The changes in interstitial fluid osmolality in the injured tissues during and after bilateral hind-limb ischaemia have been studied in young rabbits. There was a marked tissue fluid hyperosmolality which was directly related to the period of ischaemia. The increase in osmolality could be attributed to increases in lactate and potassium concentration. The interstitial fluid hyperosmolality disappeared rapidly after restoration of the circulation to the hind-limbs and would therefore only be of importance in the earliest stages of the pathogenesis of post-ischaemic fluid loss. Although the tissue fluid hyperosmolality is so short-lasting 56% of the fluid loss, measured 1 h after a 4-h period of ischaemia, occurs during the first 10 min following removal of the tourniquets. The lactate concentration in ischaemic skeletal muscle of the newborn rabbit was higher than that in the older animal and if this is reflected in an increased tissue fluid hyperosmolality it may be a factor in the greater post-ischaemic fluid loss characteristic of the neonate.