Hypovolemic Shock

Hypovolemic shock is circulatory failure from loss of intravascular volume that is not due to hemorrhage. Preload falls, so stroke volume and cardiac output fall, and the body compensates with tachycardia and intense vasoconstriction.

Causes by mechanism

• Gastrointestinal losses: severe diarrhea (cholera can cause 1 L/h), vomiting and high-output fistula
• Renal and endocrine losses: diabetic ketoacidosis, hyperosmolar state, adrenal crisis, osmotic diuresis and diabetes insipidus
• Skin and heat loss: burns, severe sweating and heat stroke
• Third-space losses: pancreatitis, bowel obstruction, peritonitis, crush injury and capillary leak

Children are especially vulnerable because of a high ratio of surface area to weight and small reserve. Adults can lose about 15% of blood volume (about 750 mL) with few signs, and shock appears after 30% (about 1.5 L). Hypotension is a late sign in children, who preserve pressure until about 25% of volume is lost.

Untreated shock produces lactic acidosis, acute kidney injury, ischemic bowel and multiorgan failure. Prognosis depends on speed of correction and cause. Complications: acute tubular necrosis, electrolyte disturbance, hypothermia and cardiovascular collapse.

• Thirst, dry mucous membranes, reduced skin turgor, sunken eyes (and sunken fontanelle in infants)
• Tachycardia, weak thready pulse, cool pale extremities, delayed capillary refill (over 3 seconds)
• Postural drop in systolic pressure over 20 mmHg, then supine hypotension
• Oliguria under 0.5 mL/kg/h, low jugular venous pressure and confusion
• Cause-specific signs: rice-water stool (cholera), fruity breath and Kussmaul respiration (diabetic ketoacidosis), burns, abdominal distension
• Red flags: systolic pressure under 90 mmHg, lethargy, anuria, lactate over 4 mmol/L, and children who are limp or unrousable

1. Clinical diagnosis from the history of loss and the examination.
2. Bedside ultrasound: a small collapsing inferior vena cava, hyperdynamic collapsed ventricle and absent B-lines. Response to a passive leg raise (a rise of over 10% in stroke volume or pulse pressure) predicts fluid responsiveness.
3. Laboratory tests: lactate, urea, creatinine, sodium, potassium, bicarbonate, glucose, ketones, osmolality, hematocrit, blood gases, and cortisol if adrenal crisis is possible.
4. ECG, urinalysis and urine output measurement with a catheter.
5. Search for the cause: stool studies, amylase and lipase, abdominal imaging and burn surface area assessment.

Differentials: cardiogenic, obstructive and distributive shock, hemorrhage, and adrenal crisis.

1. Fluid resuscitation: warmed balanced crystalloid (Ringer lactate or Plasma-Lyte) 500 to 1000 mL IV over 15 minutes in adults, repeated by response up to 30 mL/kg. Children: 20 mL/kg IV or intraosseous over 10 to 20 minutes, repeated up to 60 mL/kg, then reassess. Neonates: 10 mL/kg.
2. Reassess after each bolus: heart rate, blood pressure, capillary refill, urine output, and lung examination for crackles. Stop boluses at overload.
3. Moderate dehydration without shock: oral rehydration solution 75 mL/kg over 4 hours in children, with ongoing replacement of 10 mL/kg for each loose stool.
4. Burns (over 15% of body surface in adults, over 10% in children): Ringer lactate 2 to 4 mL/kg for each percent of burned surface over 24 hours (half in the first 8 hours from the time of injury), adjusted to urine output of 0.5 mL/kg/h (1 mL/kg/h in children).
5. Specific causes:
   • Adrenal crisis: hydrocortisone 100 mg IV once then 50 mg IV every 6 hours (children 50 to 100 mg/m2 then 50 to 100 mg/m2 a day divided every 6 hours).
   • Diabetic ketoacidosis: 0.9% saline 1 L over 1 hour, then insulin 0.1 units/kg/h IV once potassium is over 3.3 mmol/L.
   • Cholera: Ringer lactate 100 mL/kg over 3 hours (30 mL/kg in the first 30 minutes in adults) and doxycycline 300 mg orally once.
   • Cirrhosis with paracentesis or hepatorenal risk: albumin 20 to 25% 1 g/kg IV (maximum 100 g).
   • Pancreatitis: Ringer lactate 5 to 10 mL/kg/h for the first 24 hours, adjusted to response.
6. Electrolytes: replace potassium (10 to 20 mmol/h IV maximum with monitoring) and magnesium. Correct sodium slowly: not over 8 mmol/L in 24 hours.
7. Vasopressors only briefly for life-threatening hypotension during fluid loading: norepinephrine 0.05 to 0.5 micrograms/kg/min IV.
8. Avoid hypotonic fluids, starch solutions and rapid sodium correction.
9. Endpoints: urine output 0.5 to 1 mL/kg/h, normalizing lactate, capillary refill under 2 seconds and mental clearing.

Follow-up: creatinine and electrolytes at 24, 48 and 72 hours, nutritional rehabilitation after diarrheal illness (zinc 20 mg orally daily for 10 to 14 days in children), and counseling on early oral rehydration.