Normal saline wound dressing--is it really normal?

Gauze swabs soaked in normal saline are frequently used as dressing on open wounds. Their exact mechanism of action is not known. This study was designed to assess the hypothesis that normal saline dressings act in part as an osmotic dressing. Ten patients had skin ulcers (n = 10) dressed with normal saline soaked sponges. Acting as controls (n = 10) identical sponges were placed upon intact skin. The sponge fluid osmolarity and electrolyte concentrations were serially assayed to test our hypothesis. In the control group, the osmolarity, sodium and chloride concentrations increased with time as a result of evaporation, altering it from an isotonic to a hypertonic dressing. However, in the ulcer group, the osmolarity, sodium and chloride concentrations in the sponge fluid remained relatively isotonic with time. This result is statistically significant (P< 0.05). We postulate that, as a result of evaporation, the sponge dressing increases its tonicity. This draws fluid from the wound into the dressing so that a dynamic equilibrium occurs and the sponge dressing regains isotonicity. The dressing remains functional provided that the wound fluid is absorbed freely from the wound. This process is terminated when either the dressing completely absorbs the wound fluid or the dressing dries out. The latter often occurs prematurely in a contaminated wound or in a wound where exudate forms a non-permeable barrier which prevents osmosis and allows the remaining water in the dressing to evaporate completely. This correlates with the observation in clinical practice that for maximum efficacy the dressing should be changed regularly.