Mortality rates among adult critical care patients with unusual or extreme values of vital signs and other physiological parameters: a retrospective study

Abstract

Background: We evaluated relationships of vital signs and laboratory-tested physiological parameters with in-hospital mortality, focusing on values that are unusual or extreme even in critical care settings.

Methods: We retrospectively studied Philips Healthcare-MIT eICU data (207 U.S. hospitals, 20142015), including 166,959 adult-patient critical care admissions. Analyzing most-deranged (worst) value measured in the first admission day, we investigated vital signs (body temperature, heart rate, mean arterial pressure, and respiratory rate) as well as albumin, bilirubin, blood pH via arterial blood gas (ABG), blood urea nitrogen, creatinine, FiO2 ABG, glucose, hematocrit, PaO2 ABG, PaCO2 ABG, sodium, 24-hour urine output, and white blood cell count (WBC).

Results: In-hospital mortality was ≥50% at extremes of low blood pH, low and high body temperature, low albumin, low glucose, and low heart rate. Near extremes of blood pH, temperature, glucose, heart rate, PaO2 , and WBC, relatively. Small changes in measured values correlated with several-fold mortality rate increases. However, high mortality rates and abrupt mortality increases were often hidden by the common practice of thresholding or binning physiological parameters. The best predictors of in-hospital mortality were blood pH, temperature, and FiO2 (scaled Brier scores: 0.084, 0.063, and 0.049, respectively).

Conclusions: In-hospital mortality is high and sharply increasing at extremes of blood pH, body temperature, and other parameters. Common-practice thresholding obscures these associations. In practice, vital signs are sometimes treated more casually than laboratory-tested parameters. Yet, vitals are easier to obtain and we found they are often the best mortality predictors, supporting perspectives that vitals are undervalued.

Keywords: acidosis; body temperature; fever; hypothermia; physiological parameters; vital signs.

Figure 1.

Physiological parameters in the first 24 hours and their associations with in-hospital death, as evaluated in the Philips Healthcare – MIT eICU database for 166,959 critical care admissions. Analyses of the exact values of physiological parameters (continuous analysis, blue lines) show that extreme values physiological parameters are often associated with high rates of in-hospital mortality. For example, in-hospital mortality rates reach at least 50% in patients who have unusual values of blood pH, body temperature, albumin level, and several other physiological parameters. However, common practice is to evaluate binned (i.e., categorized) values of physiological parameters, and when this is done (quintile-binned analysis, red lines), most of the elevations in mortality rates are hidden at unusual physiological parameter values. Confidence bands are 95% and are sometimes too narrow to be visible.