An interesting technicality in the use of the PERC rule to rule out pulmonary embolism is the tachycardia component — it asks not whether the patient is tachycardic at the time of the application of the rule, or whether tachycardia was sustained throughout the emergency department stay, but instead whether the patient had (as described by Jeff Kline in his great review article on PE diagnosis and risk stratification): “3. Pulse <100 beats/min during entire stay in ED”. Meaning, even transient tachycardia may suggest a life-threatening diagnosis, even if it resolves while the patient is in the emergency department, and we’re probably PERCing out a whole bunch of patients inappropriately, at least according to Kline (who, notably, testifies a whole bunch as an expert witness in cases of missed pulmonary emboli).
I recently had a handful of patients in whom concerning blood pressures were measured and documented, which then resolved when vital signs were re-checked or after a small quantity of fluid or repositioning. I was wondering whether anyone had looked at the prognostic significance of ED hypotension, and whether these momentary dips in blood pressure should be something that concerns me. I did a quick search and found two studies that addressed this question in two different populations:
First we have, from the Rick Bukata school of title writing: “Emergency department hypotension predicts sudden unexpected in-hospital mortality: A prospective cohort study.” This study, by Alan Jones and Jeff Kline out of (and formerly out of) Carolinas, prospectively enrolled 4,790 adult ED patients admitted to the hospital for reasons other than trauma. Patients were divided into those with and without systolic BPs below 100 mmHg at any time during their ED visit and followed through their hospitalization for the primary outcome of in-hospital mortality. Secondary outcomes included “sudden and unexpected death”, the relationship between the degree and the duration of hypotension measured and mortality, and the test characteristics of hypotension as a test for predicting in-hospital mortality.
Their conclusions are illustrated well in this graph:
As they concisely summarize in the article’s conclusion:
Patients exposed to hypotension had a threefold increased risk of in-hospital death and a 10-fold increased risk of sudden, unexpected in-hospital death. Patients with any one SBP < 80 mm Hg had a sixfold-increased incidence of in-hospital death, and patients with a SBP < 100 mm Hg for > 60 min had almost a threefold-increased incidence of in-hospital death.
The second article from the same group echoes this conclusion in a different population of patients. This article, “The significance of non-sustained hypotension in emergency department patients with sepsis” is a secondary analysis of the above data set which looks specifically at the prognostic value of non-sustained hypotension defined as one or more occurrence of SBP < 100 mmHg in patients with sepsis as defined by the receipt of antibiotics in the ED + at least two SIRS criteria.
774 patients met their inclusion criteria for sepsis, and after 74 were excluded for “overt shock” (sustained hypotension or use of pressors). They examined the remaining patients for a primary outcome of in-hospital death. They found, as one might expect, that hypotension predicts worse outcomes in this sub-population of patients — including when patients had non-sustained hypotension. Again, there seemed to be a “dose-dependent” relationship, with an inverse relationship between the nadir of the ED SBP and the frequency of in-hospital death, as shown here:
Another important finding (though taken in context of a fairly small sample) was the statistically similar incidence of the primary outcome in both the groups with transient and sustained hypotension. Both groups of patients had a 2.5-3x higher risk of in-hospital mortality when compared to patients without any hypotension.
Without belaboring the point, these two studies underscore the prognostic significance of even transient hypotension in the undifferentiated emergency department patient, and (as is better known to have implications in terms of severity) in patients diagnosed with sepsis. Like the previous post regarding lactate, or the well-known pearl about tachycardia at discharge, this is a number that should get your attention and which demands evaluation and possible intervention / escalation of care.