Low systemic vascular resistance: differential diagnosis and outcome

Analysis of consecutive patients over a 5-year period; retrospective review.Medical intensive care unit of a large university hospital.Fifty-five patients with unexplained hypotension and a SVR less than 800 dynes × s/cm5.There are minimal data in the medical literature determining the frequency or outcome of patients with a low SVR that is unrelated to sepsis or the sepsis syndrome. We retrospectively reviewed and analyzed all hemodynamic data in a large university hospital over a 5-year period to determine the frequency and prognosis of the various causes of low SVR. Fifty-five patients with unexplained hypotension and a SVR less than 800dynes×s/cm5were identified.Twenty-two patients (Groups 1 and 2) met the criteria for sepsis syndrome. The mean SVR for this group was 445 ± 168 dynes×s/cm5 with an associated mortality of 50%. Group 3 contained 20 patients with possible sepsis. Thirteen patients (Group 4) were nonseptic. The mean SVR of this group was 435 ± 180 dynes × s/cm5 with an associated mortality of 46%. Extremely low SVR (below 450 dynes × s/cm5) was associated with a significantly higher mortality regardless of the etiology.At least a quarter of patients with hypotension and a low SVR have nonseptic etiologies. The patients with nonseptic etiologies have a similar mortality to septic patients. Clinicians should be aware of the wide spectrum of conditions that induce a low SVR.As initially described by Poiseuille's law, resistance to flow is that resistance provided by a vessel or circulatory bed which permits a given pressure differential to produce a unit flow. Transcribed to human hemodynamics, systemic vascular resistance (SVR) can be measured from the differential pressure between the mean arterial pressure (MAP) and the central venous pressure (CVP) divided by the flow, ie cardiac output (CO). Although many clinical conditions can cause a low SVR, septic shock remains the most common cause and usually results in a severe decrease in SVR. In more than