Third spacing of fluids
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Overview
In human physiology, extracellular fluids are distributed between the interstitial compartment (i.e. tissue) and intravascular compartment (i.e. plasma) in an approximately 75%-25% ratio. Third spacing is the physiological concept that body fluids may collect in a "third" body compartment that isn't normally perfused with fluids.
Symptoms
The patient will manifest symptoms of volume depletion and will be hypovolemic and dehydrated due to a shift of fluid from the intravascular compartment to the third space. Other symptoms include:
- Hypovolemia
- Dehydration
- Fall in blood pressure
- Reflex Tachycardia
- Decreased urine output
- Low central venous pressure
Differential diagnosis of causes of thrid spacing
For example, with severe burns, fluids may pool in the burn site and cause depletion of the fluids in the first and second compartments. With pancreatitis, fluids may "leak out" into the peritoneal cavity, also causing depletion of the first and second compartments. Sepsis syndrome may also cause third spacing. Other causes include viral and bacterial infections and gastrointestinal surgery. The underlying causes however are mainly trauma and inflammation.
Treatment
Clinically, the extent of "third spacing" is usually unknown, and therefore it serves more as a theoretical concept for problem-solving rather than a concrete value that requires repletion. In general third spacing is dealt with treating the underlying disturbance or illness rather than giving more fluids to correct the electrolyte and protein imbalances, since that will only help relieve the symptoms in the short term. While the patient may be edematous and is total body fluid overloaded, it should be realized that the patient is paradoxically often "dehydrated" or under filled in their intravascular space. For this reason, aggressive diuresis should be avoided to avoid pre renal azotemia. Diuresis should be performed at a rate that is commensurate with the mobilization of fluid from the third space into the intravascular space.
References
Redden M, Wotton K (2002). "Third-space fluid shift in elderly patients undergoing gastrointestinal surgery: Part 1: Pathophysiological mechanisms". Contemporary nurse : a journal for the Australian nursing profession. 12 (3): 275–83. PMID 12219956. |access-date= requires |url= (help)