Hypovolemic States

Etiology: results from deficit in total body Na+ content.

• Renal losses of Na and water loss:

  • Diuretics

  • Osmotic diuresis

  • Hypoaldosteronism

  • Salt-wasting nephropathies

• Extrarenal losses of Na from ECF:

  • GI tract

    • vomiting, diarrhea, NG suctioning, fistula drainage, diarrhea.

  • Resp losses

  • Skin losses (insensible losses, sweat, burns)

  • H'ge

  • Third spacing of fluid in critical illness

• Renal water loss

  • DI (CDI or NDI)

• ECF volume normal or expanded

  • Decreased CO: myocardial, valvular, or pericardial disease

  • Redistribution: hypoalbuminemia (hepatic cirrhosis, nephrotic syndrome)

  • Capillary leak (acute pancreatitis, ischemic bowel, rhabdomyolysis)

• Increased venous capacitance: sepsis.

Dx:

• Sx: thirst, fatigue, weakness, muscle cramps, orthostatic syncope, dizziness

• Si: orthostatic hypotension, no JVD, postural tachycardia, absence of axillary sweat, dry mucous membrane, dry tongue, diminished skin turgor, mental status changes, oliguria, hypovolemic shock.

• Orthostatic: SBP drops >15 mmHg or HR increases >20 bpm from lying to sitting after 2 minutes. Look at skin turgor, mucosal hydration.

• Labs:

  • Electrolytes, BUN, glucose, Osm, UA.

  • Specific gravity: <1.015 suggests a renal concentration defect. >1.030 = moderate dehydration, >1.035 = sever.

  • Urine Na+ is a marker of Na avidity in kidney.

  • Urine Na+ <15 mEq is consistent with volume depletion.

  • FeNa <1% (Una/Ucr) x (Pcr/Pna) x 100

  • Concomitant metabolic alkalosis may increase urine Na excretion despite volume depletion due to obligate excretion of Na to accompany the bicarbonate anion. In such case Urine chloride <20 mEq is often helpful to confirm volume contraction.

  • Uosm and Sr. HCO3- levels are elevated.

  • Hct and Sr. albumin may be increased from hemoconcentration.

Tx:

• • Discontinue diuretics.

  • Calculate deficit:

    • Total deficit = (old wt - new wt) or = 0.35 (old wt) (1 - old Hct/new Hct).

  • Empiric therapy, requiring frequent assessments of volume status while resuscitation is under way.

  • Mild vol contraction correct PO.

  • IV therapy if PO not possible, hemodynamic instability, Sx fluid loss.

  • Replenish IV volume with Na-based solutions, since Na will be retained in the ECF.

    • 0.9% NaCl (Na: 154 mEq/L). Initial fluid of choice.

    • 0.45% NaCl (Na: 77 mEq/L). Half of this solution will stay in ECF, and half will flow the predicted distribution of water.

    • Pts with sx vol depletion, give 1 - 2 L bolus, with careful reassessment of Pt's vol status.

    • Pts with H'ge, give blood transfusion for vol expansion and correction of anemia.

    • Boluses can be repeated if necessary with attention to volume overload. Smaller boluses are used for patient with poor cardiac reserve or edema.

Holiday-Segar's

• • First 10 kg of total body wt = 100 ml/kg/day or 4 ml/kg/hr

  • Second 10 kg of total body wt = 50 ml/kg/day or 2 ml/kg/hr

  • Above 20 kg of total body wt = 20 ml/kg/day or 1 ml/kg/hr.