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hypovolemia (extracellular volume depletion)

Etiology: 1) acute hemorrhage 2) skin a) diaphoresis b) burns c) dermatitis (weeping) 3) interstitial fluid shifts (3rd space) a) crush injury b) pancreatitis c) peritonitis d) bowel obstruction e) bowel necrosis f) rhabdomyolysis g) non cardiac pulmonary edema 4) gastrointestinal a) vomiting b) nasogastric suction c) GI fistula d) diarrhea 5) renal a) solute diuresis 1] diuretics 2] urea 3] ketones 4] glucosuria 5] NaCl 6] RTA type II 7] hypoaldosteronism a] adrenal insufficiency b] interstitial nephritis b) water diuresis 1] diabetes insipidus 2] ethanol 3] mannitol 4] post-obstructive diuresis 5] diuretic phase of acute tubular necrosis 6) increased vascular capacity a) septic shock b) autonomic dysfunction c) pharmacologic agents Clinical manifestations: 1) mild volume depletion (< 5%, 1-2 liters) a) thirst b) fatigue c) dry mucosa, dry mouth d) concentrated urine e) capillary refill time may be increased 2) moderate volume depletion (5-10%, 2-4 liters) a) anorexia b) nausea c) cramps d) near syncope e) little to no tears & sweat f) tachycardia g) orthostatic hypotension h) decreased urine output 3) severe volume depletion (> 10% 4-6 liters) a) lethargy b) confusion c) hypothermia d) hypotension 4) moribund (> 20%, 8L) a) cool extremities b) vasoconstriction c) shock d) coma Laboratory: 1) urinalysis a) urine sodium 1] > 20 meq/L indicates renal Na+ loss, check serum HCO3- a] serum HCO3- < 23 meq/L 1] renal tubular acidosis 2] hyperaldosteronism 3] check serum K+ b] serum HCO3- normal suggests osmotic losses 1] glucose 2] mannitol c] serum HCO3- > 27 meq/L suggests diuretics 2] < 10 meq/L indicates non renal Na+ loss, check serum HCO3- a] serum HCO3- < 23 meq/L 1] diarrhea 2] GI fistula or shunt b] serum HCO3- normal suggests interstitial losses 1] intestinal edema 2] peritonitis 3] pancreatitis 4] rhabdomyolysis c] serum HCO3- > 27 meq/L 1] vomiting 2] gastric suctioning b) urine chloride 1] useful in the context of: a] metabolic alkalosis b] renal tubular acidosis type II 2] HCO3- secretion by the proximal tubules into the urine is accompanied by Na+, thus increasing Na+ in the urine 3] urine chloride may be used in the same algorithm as urine Na+ for evaluation of extracellular volume depletion b) osmolality > 500 (normal renal function) c) specific gravity increased (normal renal function) d) pH 2) serum a) electrolytes b) glucose c) osmolality d) increased urea nitrogen e) urea nitrogen/creatinine ratio > 20 f) increased creatinine with severe volume depletion g) hyperuricemia h) phosphate increased i) protein increased 3) fractional excretion of sodium (FENA) 4) complete blood count (CBC) a) hemoglobin increased b) hematocrit increased Indications: 1) congestive heart failure 2) cardiac tamponade 3) tension pneumothorax Management: 1) large bore peripheral IV for fluid resuscitation [8] - preferably 2 2) restore intravascular volume with normal saline or lactated Ringer's until patient is hemodynamically stable a) 4% albumin may be useful in septic patient (see SAFE study) b) avoid hydroxyethyl starch (Hespan) [3,5,6] 3) packed RBC transfusion to replace blood loss 4) stop or remove medications that contribute to symptoms a) diuretics b) antihypertensive agents c) sedatives d) transdermal patches 1] clonidine 2] nitrate patches 5) reassess volume status frequently & adjust accordingly 6) mild volume depletion may be replaced orally (Na+ & water)

Related

SAFE study

Specific

clinical dehydration hypovolemic shock

General

fluid imbalance; water imbalance

References

  1. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 682-84
  2. Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 267
  3. Myburgh JA et al. Hydroxyethyl starch or saline for fluid resuscitation in intensive care. N Engl J Med 2012 Oct 1 PMID: 23075127
  4. McGee S, Abernethy WB 3rd, Simel DL. The rational clinical examination. Is this patient hypovolemic? JAMA. 1999 Mar 17;281(11):1022-9. PMID: 10086438
  5. The NNT: Hydroxyethyl Starch for Acute Volume Resuscitation. http://www.thennt.com/nnt/hydroxyethyl-starch-for-acute-volume-resuscitation/ - Zarychanski R et al Association of Hydroxyethyl Starch Administration With Mortality and Acute Kidney Injury in Critically Ill Patients Requiring Volume Resuscitation. A Systematic Review and Meta-analysis. JAMA. 2013;309(7):678-688 PMID: 23423413 http://jama.jamanetwork.com/article.aspx?articleid=1653505
  6. FDA MedWatch. June 20, 2013 Hydroxyethyl Starch Solutions: FDA Safety Communication - Boxed Warning on Increased Mortality and Severe Renal Injury and Risk of Bleeding
  7. The NNT: Hypovolemia. Diagnostics and Likelihood Ratios, Explained. http://www.thennt.com/lr/hypovolemia/
  8. Medical Knowledge Self Assessment Program (MKSAP) 17, American College of Physicians, Philadelphia 2015