25: Hypotension

CHIEF COMPLAINT

CONSTRUCTING A DIFFERENTIAL DIAGNOSIS

When a patient presents with hypotension, the important question is whether or not the patient is in shock. Shock is present if there is evidence of multisystem organ hypoperfusion. This may manifest itself as tachycardia, tachypnea, diaphoresis, poorly perfused skin and extremities, altered mental status, or decreased urinary output. In addition, it is not necessary for a patient to have overt hypotension to be in shock since a marked reduction in a patient’s usual BP may cause shock (but still be in the low-normal range in previously hypertensive patients). Given the life-threatening nature of shock, hemodynamic stabilization must be prompt and cannot wait for a long series of investigations to be completed.

Therefore, a rational, rapid approach to hypotension is necessary. The 3 main etiologies of shock include distributive (low total peripheral resistance, usually septic), cardiogenic (low cardiac output despite adequate intravascular volume), and hypovolemic (low cardiac output due to low intravascular volume). In terms of epidemiology, septic shock is by far and away the most common. In a trial of over 1600 patients with shock, 62% had septic shock, 16% had hypovolemic shock, and 16% had cardiogenic shock.

Differential Diagnosis of Shock

1. Distributive shock

   1. Septic shock

   2. Hepatic failure

   3. Pancreatitis

   4. Anaphylactic shock

   5. Adrenal insufficiency

   6. Neurogenic shock

   7. Arteriovenous shunts

2. Hypovolemic shock

   1. Hemorrhage

      1. Trauma

      2. Gastrointestinal hemorrhage

      3. Postsurgical, postprocedural bleeding

      4. Intra-abdominal (eg, abdominal aortic aneurysm, ruptured ectopic pregnancy)

   2. Volume depletion

      1. Vomiting

      2. Diarrhea

      3. Excessive diuresis (from diuretics or uncontrolled diabetes)

3. Cardiogenic shock

   1. Poor contractility

      1. Left ventricular (LV) failure

         • (1) Myocardial infarction (MI)

         • (2) Myocarditis

         • (3) Metabolic derangements (eg, profound acidosis, hypophosphatemia, hypocalcemia)

         • (4) Depressant drugs (beta-blockers, calcium-channel blockers)

         • (5) Miscellaneous causes of heart failure (HF) (eg, alcoholic cardiomyopathy, adriamycin-related cardiomyopathy, dilated cardiomyopathy)

      2. Right ventricular (RV) failure

         • (1) MI

         • (2) Pulmonary vascular disease

         • (3) Hypoxic pulmonary vasoconstriction

   2. Outflow obstruction

      1. Aortic stenosis

      2. Hypertrophic cardiomyopathy

      3. Malignant hypertension

      4. Pulmonary embolism (PE)

   3. Arrhythmogenic

      1. Significant bradycardia

      2. Significant tachycardia

   4. Backflow

      1. Acute mitral regurgitation – papillary muscle rupture or dysfunction

      2. Rupture septum or free wall

      3. Acute aortic regurgitation

   5. Reduced filling

      1. Constrictive pericarditis

      2. Tension pneumothorax

      3. Mitral stenosis

RANKING THE DIFFERENTIAL DIAGNOSIS

The first step in approaching patients with hypotension and shock is recognition. Is there evidence of decreased perfusion? This may be manifest by any 1 or more of the ...