Hypovolemia

A decrease in intravascular extracellular fluid volume (esp. plasma volume) due to loss of salt and water (e.g., hemorrhage, GI/renal losses) or maldistribution/third spacing (burns, pancreatitis, sepsis). Not the same as dehydration, which is a pure water deficit causing hypernatremia and intracellular water loss. In practice, both can coexist.

• Hypovolemia is a leading cause of shock, prerenal azotemia/AKI, and perioperative/trauma morbidity. Early recognition and targeted resuscitation (right fluid, right amount, right timing) are life‑saving and heavily tested across exams and OSCEs.

• Common causes: hemorrhage (trauma, GI bleed, postpartum), GI loss (vomiting/diarrhea), renal loss (diuretics, osmotic diuresis), burns, pancreatitis or bowel obstruction (third spacing), sepsis (capillary leak), endocrine salt loss (adrenal insufficiency).
• Early signs (compensated): thirst, anxiety, tachycardia, cool clammy skin, delayed capillary refill, flat neck veins/low JVP, oliguria; BP may be normal (narrow pulse pressure).
• Late signs (decompensated): hypotension, altered mental status, anuria, lactic acidosis, mottled skin.
• Orthostatics: ↓SBP ≥20 mmHg or ↓DBP ≥10 mmHg within 3 min standing suggests volume depletion if clinically appropriate.
• Pediatrics: hypotension is late; look for tachycardia, prolonged capillary refill, sunken eyes/fontanelle, absent tears, lethargy.
• Hemorrhagic shock classes (ATLS): I (<15%), II (15–30%), III (30–40%), IV (>40%) blood loss with progressively worse tachycardia, narrow pulse pressure, mental status change, oliguria, hypotension.

1. Start with ABCs; place two large‑bore IVs (or IO), give oxygen, put on monitor; obtain point‑of‑care glucose.
2. History/Exam: focus on losses (bleeding, GI, urine, burns) and third spacing; check JVP, skin, mucosae, capillary refill, peripheral perfusion, mental status, urine output.
3. Initial labs: CBC (Hgb/Hct), BMP (BUN/Cr), lactate, type & cross if bleeding, VBG/ABG, coagulation panel; consider cortisol if adrenal crisis suspected.
4. AKI pattern for prerenal volume depletion: BUN/Cr >20:1, FeNa <1% (or FEUrea <35% if on diuretics), urine Na <20 mEq/L, urine osmolality >500—interpret in clinical context.
5. Dynamic assessment of fluid responsiveness: passive leg raise (PLR) with stroke volume/cardiac output monitoring; bedside echo/IVC variation (interpret with caution: ventilation mode, RV function).
6. Imaging as indicated: FAST exam/CT for trauma; bedside ultrasound for IVC/cardiac function; CXR if pulmonary edema suspected.
7. Classify the driver: hemorrhagic vs non‑hemorrhagic (dehydration/third spacing/sepsis/endocrine). Treat the cause in parallel with resuscitation.

1. All patients (initial): ABCs; 2 large‑bore IV/IO; oxygen; monitor; obtain labs, type & cross if bleeding; bedside ultrasound.
2. Fluids: Start isotonic crystalloid. For sepsis/hypoperfusion, give ~30 mL/kg within 3 hours, then reassess with dynamic measures (PLR, stroke volume, echo) and lactate. Prefer balanced crystalloids (LR/Plasma‑Lyte) when available.
3. Hemorrhage: Immediate bleeding control (direct pressure, tourniquet, hemostasis), early MTP with ~1:1:1 plasma:platelets:RBC; limit crystalloids. Give TXA 1 g IV over 10 min, then 1 g over 8 h within 3 h of injury. Consider permissive hypotension until hemostasis if no TBI.
4. Transfusion thresholds (non‑bleeding): in hemodynamically stable adults, consider RBC transfusion when Hb <7 g/dL (individualize by comorbidities).
5. Burns: Estimate fluids (historically Parkland 4 mL/kg/%TBSA; recent ABA suggests ~2 mL/kg/%TBSA to reduce "fluid creep"); use LR and titrate to urine output ≥0.5 mL/kg/hr; adjust for inhalation injury/large burns; consider albumin in larger burns per ABA CPG.
6. Pediatrics: Bolus 20 mL/kg isotonic crystalloid over 5–10 min; repeat to 40–60 mL/kg if needed while reassessing. If hemorrhagic, transition early to blood products (PRBC 10 mL/kg).
7. If fluid‑refractory shock: start norepinephrine (first‑line in septic shock) and address etiology (antibiotics, source control; endocrine support if adrenal crisis).
8. Monitoring/targets: mental status, MAP (≥65 mmHg in septic shock), capillary refill, urine output, serial lactate, point‑of‑care ultrasound; stop fluids when no longer fluid responsive or if signs of overload appear.

• Hypovolemia ≠ dehydration: hypovolemia = ECF (plasma) deficit of salt+water; dehydration = water deficit → hypernatremia/ICF contraction.
• Adults: target urine output ≥0.5 mL/kg/hr (children ≥1 mL/kg/hr) as one bedside marker of adequate perfusion.
• Balanced crystalloids (LR/Plasma‑Lyte) are preferred to large volumes of normal saline to lower risk of hyperchloremic acidosis and renal events.
• In hemorrhage, avoid large crystalloid loads; activate massive transfusion protocol early with plasma:platelets:RBC ≈ 1:1:1 and control bleeding.
• Trauma pearl: consider permissive hypotension (e.g., SBP ~80–90 mmHg) until hemostasis if no TBI; in suspected TBI keep SBP ≥100–110 mmHg.
• Peds shock: give 20 mL/kg isotonic crystalloid bolus over 5–10 min; reassess; repeat as needed while watching for signs of overload.
• Prerenal markers (FeNa, BUN/Cr) are decision‑support, not absolute—interpret with the clinical picture, diuretics, CKD, and sepsis.

• Altered mental status, SBP <90 mmHg or rapidly falling, HR >120 with cool extremities, anuria, lactate ≥4 mmol/L
• Suspected aortic aneurysm rupture, massive GI bleed, postpartum hemorrhage, or tension pneumothorax/tamponade
• Burns ≥20% TBSA with hypotension/oliguria
• Child with shock signs (hypotension is late)—treat immediately

1. Suspect hypovolemia → ABCs, monitors, 2 large‑bore IV/IO, oxygen.
2. Focused history/exam for losses (bleeding, GI, urine) or third spacing; bedside ultrasound (FAST/IVC/cardiac) as available.
3. Send labs (CBC, BMP, lactate, VBG/ABG, type & cross, coags; ± cortisol). Start isotonic crystalloid immediately if hypoperfusion.
4. If bleeding → activate MTP, apply hemorrhage control, consider TXA; limit crystalloids, consider permissive hypotension if no TBI.
5. If sepsis/other non‑hemorrhagic → give ~30 mL/kg crystalloid promptly; reassess using PLR/echo and lactate clearance; start norepinephrine if fluid‑refractory.
6. Reassess perfusion: mental status, cap refill, urine output target ≥0.5 mL/kg/hr (adults); avoid over‑resuscitation.
7. Address cause (source control, stop diuretics, treat adrenal crisis, manage burns/pancreatitis), and de‑escalate fluids once not fluid responsive.

• Trauma: Young adult after MVC with tachycardia, cool extremities, narrow pulse pressure, FAST positive. Management asks for MTP (1:1:1), TXA within 3 hours, hemorrhage control; avoid excessive crystalloids; permissive hypotension if no TBI.
• Sepsis with volume loss: Elderly patient with vomiting/diarrhea, lactate 5 mmol/L, BUN/Cr 40/1.6, FeUrea 25%. Best initial step: 30 mL/kg crystalloid promptly, then guide by dynamic measures and lactate clearance; norepinephrine if persistent hypotension.
• Burns: Adult with ~30% TBSA burns—asks for initial fluid estimate and titration target (urine output ≥0.5 mL/kg/hr). Know that many exams still reference Parkland 4 mL/kg/%TBSA (½ in first 8 h), but new ABA guidance supports ~2 mL/kg/%TBSA with titration to endpoints.