++
PATIENT 
Ms. P is a 75-year-old woman with weakness and hypotension.
What is the differential diagnosis of hypotension? How would you frame the differential?
+++
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.
++
PATIENT
Ms. P has a past medical history of coronary artery disease (CAD), hypertension, and diabetes. She complains of weakness, anorexia, nausea, and vomiting. Her initial vital signs demonstrate a pulse of 110 bpm and BP of 85/55 mm Hg. She is having difficulty staying awake during the interview.
At this point, what is the leading hypothesis, and what are the active alternatives? What other tests should be ordered?
+++
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 following:
++
Significantly decreased BP
Typically systolic BP < 90 mm Hg
A patient may be in shock with a “normal” BP; comparison to prior BPs is necessary.
BP should be measured with a manual cuff. BPs measured with automatic BP cuffs may be inaccurate at lower BPs, especially the pulse pressure.
The pulse pressure should be calculated: pulse pressure = systolic BP – diastolic BP. Wide pulse pressures suggest high cardiac output, whereas narrow pulse pressures suggest low cardiac output (ie, septic shock vs cardiogenic shock).
Tachycardia
Increased respiratory rate
Alteration of mental status
Decreased urinary output
Increased venous lactate
++
The first pivotal diagnostic step is to differentiate septic shock from cardiogenic or hypovolemic shock. Hypovolemic shock is often obvious due to a history of ...