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.