woogy. . .think about this. why does any fluid move about in the body? it goes where osmotic pressure pulls it. going back to the basic principle of osmosis, fluids are going to go wherever they feel pulled to. they are always going to go to places where the mixture of fluids and electrolytes will be in equal concentrations. lr is what is called a balanced solution that very closely resembles plasma. once lr enters the veins, and assuming the patient is not suffering from any electrolyte balances, think of it as having found it's equal, in a manner of speaking. (ok. i can live with this!) it's going to be happy to hang out there keeping it's fluid content, thus increasing circulating fluid volume which is it's desired effect.
a solution such a normal saline, on the other hand, while it may be isotonic, finds itself in an environment of ever so subtle unequal electrolyte concentration. so, by diffusion, it's water content is lost to the interstitial spaces very rapidly. (i'm outta here!) now, this is ok if that is what is desired, but in the case of a post-op gi patient, the physician specifically wants to boost the circulating volume. so, isotonic saline just doesn't quite fit the bill.
regarding fluid loss in surgical patients, i just found this very interesting passage in fluid & electrolyte balance: nursing considerations, fourth edition by norma m. metheny, page 49, fluid volume imbalances: "varying degrees of third-spacing occur in surgical procedures and are related to tissue manipulation and injury. the amount of fluid lost from the extracellular space varies with the extent and nature of the surgical undertaking. minor operative procedures (such as appendectomy) are associated with considerably less fluid sequestration than are major operative procedures (such as extensive retroperitoneal dissection). for example, a simple laparotomy with a total small bowel exploration can result in 700 ml of ecf distributional loss, whereas an extensive colon resection can cause as much as 2 to 3 liters of ecf to sequester into the peritoneal cavity in 2 to 4 hours. after abdominal surgery, particularly pelvic surgery, fluid accumulates in the peritoneum, bowel wall, and other traumatized tissues, formation of a third-space after nonthermal traumatic injury occurs immediately and is maximal by 5 to 6 hours. in the surgical patient, it is difficult to assess fluid loss due to sequestration into the interstitial compartment. such unrecognized deficits of ecf during the early postoperative period are manifested primarily as circulatory instability."
if your patient had some inflammation process already going on prior to the appendectomy there would have been some tissue trama already with some fluid sequestration, no doubt. it would be hard to know the extent. with fluid already confined to tissues in this area in unknown amounts, the physician definitely would not want to contribute to that by giving an iv solution of isotonic saline since the saline is going to go where? the interstitial space.
clear as mud, now? :behindpc: