Chapter 25-8: Hypovolemic Shock

Typically, a patient with hypovolemic shock will have an obvious source of bleeding, a drop in hematocrit, or recognizable gastrointestinal fluid or renal losses.

DISEASE HIGHLIGHTS

1. Patients who are hypovolemic have 1 of 2 clinical conditions:

   1. Volume depletion due to vomiting, diarrhea, inadequate oral intake, or excessive diuresis (from diuretics or uncontrolled diabetes)

   2. Hemorrhage (due to trauma, gastrointestinal or intra-abdominal hemorrhage)

2. Hospitalizations related to gastrointestinal hemorrhage are common, 150/100,000 population per year, and have a case fatality rate of 3–10%.

3. Degree of bleeding is often difficult to assess.

   1. Melena can occur with massive hemorrhage or as little as 100 mL of blood loss.

   2. Admission hematocrit correlates poorly with degree of blood loss and mortality.

4. Hypovolemia secondary to dehydration sufficiently severe to cause hypovolemic shock disproportionately affects the elderly. Common risk factors include:

   1. Female sex

   2. Age > 85

   3. Greater than 4 chronic medical conditions

   4. Taking 4 or more medications

   5. Being confined to bed

EVIDENCE-BASED DIAGNOSIS

1. In a review of physical exam findings in hypovolemia, abnormal vital signs are relatively specific but not sensitive (Table 25-4).

   1. Orthostatic vital signs, particularly an increase in pulse are more sensitive than supine vital signs. Orthostatic hypotension can occur immediately or be delayed.

      1. When measuring orthostatic vital signs, wait 3 minutes before measuring supine vitals and wait 1 minute after patient stands to measure upright vitals.

      2. Helpful physical findings include:

         1. Severe postural dizziness (unable to measure upright vital signs due to dizziness).

         2. Postural pulse increment of 30 beats/min or more.

   2. Dry axilla supports hypovolemia in the elderly (sensitivity, 50%; specificity, 82%; LR+ 2.8; LR–, 0.61).

   3. Poor skin turgor has no proven diagnostic value in adults.

2. Laboratory evidence is often more revealing.

   1. Hematocrit

      1. Decreased in hemorrhage if bleeding has been ongoing

      2. However, in acute bleeding, blood loss prior to hemodilution (from IV or oral fluid repletion) may result in a normal hematocrit.

         Patients may have a normal hematocrit despite massive hemorrhage.

      3. The hematocrit is often elevated in patients with nonhemorrhagic hypovolemia.

   2. Other laboratory findings typically seen in hypovolemic patients include:

      1. An elevated BUN/Cr ratio > 20 (see Chapter 28, Acute Kidney Injury)

      2. A low urine sodium concentration < 30 mEq/L and a Fe_Na < 1%

      3. In patients taking diuretics, the Fe_urea < 35% may be more accurate (see Evidence Based Diagnosis)

3. A brisk BP response to a 500 mL bolus given over 10 minutes supports hypovolemia (but may also be seen in sepsis).