Dehydration: excessive loss of body fluid

Volume deficit (Hypovolemia)

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Volume deficit (Hypovolemia)

Fluid volume deficit (also known as deficient fluid volume or hypovolemia) describes the loss of extracellular fluid from the body. Extracellular fluid is the body fluid not contained within individual cells. It constitutes about 20% of our body weight and includes blood plasma, lymph, spinal cord fluid, and the fluid between cells. Importantly, this fluid isn’t just water—it also contains electrolytes and other essential solutes.

Extra cellular fluid (ECF) volume deficit is the most common fluid volume disorder in the surgical patient. The lost fluid is not water alone, but water and electrolytes in approximately the same proportion as they exist in normal extra cellular fluid.

Causes

  • Losses of gastro-intestinal fluids: e.g. vomiting, gastric tube, diarrhea and enterocutaneous fistulas
  • Sequestration or loss of fluid in soft tissue injuries and infections such as burns
  • Intra-abdominal and retroperitoneal inflammatory processes such as peritonitis, intestinal obstruction, etc.

Types of Fluid Volume Deficit

While fluid volume deficit refers to the loss of both water and solutes from the body, there are three major types of fluid volume deficit:

  • Isotonic: Caused by losing fluids and solutes about equally; solute concentration in the remaining extracellular fluid then remains relatively unchanged
  • Hypertonic: Caused by losing more fluids than solutes, leading to increased solute concentration in the remaining fluid.
  • Hypotonic: Caused by losing more solutes than fluid leading to decreased solute concentration in remaining fluid. This is the rarest type.

The type of fluid volume deficit (as determined through lab work) may inform care, especially what fluids are offered to the patient to replace the lost fluid/solutes.

Clinical feature

  • Alterations in mental state
  • Patient complaints of weakness and thirst that may or may not be accompanied by tachycardia or weak pulse
  • Weight loss (depending on the severity of fluid volume deficit)
  • Concentrated urine, decreased urine output
  • Dry mucous membranes, sunken eyeballs
  • Weak pulse, tachycardia
  • Decreased skin turgor
  • Decreased blood pressure, hemoconcentration
  • Postural hypotension

Consequences of hypovolemia

Reduction in circulating blood volume leads to lower venous return irrespective of its cause and, when hypovolemia is sufficiently severe, arterial hypotension. Compensatory systemic release of catecholamines promotes peripheral vasoconstriction, increased cardiac contractility and tachycardia. Systemic blood pressure may therefore remain stable in the face of continuing hypovolemia. Tachycardia promotes increased myocardial oxygen demand that, in conjunction with reduced tissue perfusion, may result in myocardial failure. Finally, anerobic metabolism occurring in response to reduced perfusion may produce acidosis and, together with myocardial dysfunction, contribute to multi-organ failure.

Hypovolemia and hypotension exert differential effects on organ function. In the splanchnic organs, α-adrenergic activity is relatively high, and the splanchnic region is highly vulnerable in patients with hypovolemic shock and hypotension. Ischemia develops with diminished GI perfusion, especially in the mucosal layer of the gut. Mucosal integrity may be compromised. Impaired gut barrier function may allow translocation of bacteria and endotoxins, precipitating a systemic inflammatory response as a consequence of shock. In cases of severe hypovolemia, due for instance to trauma, these pathophysiologic processes may ultimately lead to the development of sepsis.

Treatment

Placement of extra cellular loss with fluid of similar composition:

  • Blood loss: Replace with Ringer’s Lactate, Normal Saline or Blood, if needed
  • Extra cellular fluid: Replace with Ringer’s Lactate, Normal Saline

Rate of fluid replacement

The Rate depends on the degree of dehydration. It should be fast until the vital signs are corrected and adequate urine output is achieved. One liter over 30 minutes to one hour can be given for severe dehydration.

Monitoring

The general condition and the vital signs of the patient should be followed. The urine out put should be monitored hourly. Auscultate the chest to follow overload especially in children and the elderly.

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