title: Clinical implications of temperature curve complexity in critically ill patients.
abstract: OBJECTIVE
  In certain physiologic systems, disease is associated with a loss of complexity in system's output. We test the hypothesis that, in critically ill patients, there is an inverse relation between the complexity of the temperature curve and the clinical status. We also consider whether complexity analysis of the temperature curve may have prognostic value.
  
  
  METHODS
  Prospective, observational study.
  
  
  METHODS
  Intensive care unit of a general hospital in Madrid, Spain.
  
  
  METHODS
  Twenty-four successive patients admitted in the intensive care unit with multiple organ failure.
  
  
  METHODS
  Skin temperature was measured every 10 mins from inclusion in the study until discharge or death (median length of stay 18.8 days, interquartile range 86).
  
  
  METHODS
  From the temperature time series, hourly approximate entropy measurements were obtained. Clinical status was evaluated using the Sequential Organ Failure Assessment (SOFA) score.
  
  
  RESULTS
  A significant inverse relationship between approximate entropy and the attributed SOFA score was observed in 89% of the patients considered. Both mean and minimum approximate entropy were significantly lower in patients who died than in patients who survived (mean approximate entropy, 0.47 vs. 0.61; minimum approximate entropy, 0.24 vs. 0.40; in both cases p < .001). To evaluate the prognostic value of both mean and minimum approximate entropy, we fitted logistic regression models against survival. An increase in 0.1 units in minimum or mean approximate entropy increased 15.4- and 18.5-fold the odds of surviving, respectively.
  
  
  CONCLUSIONS
  The clinical status of patients suffering multiple organ failure is inversely correlated to the complexity of the temperature curve expressed as approximate entropy. Reduced complexity has dismal prognostic implications. Its assessment is noninvasive and inexpensive and allows for real-time continuous monitoring of clinical status.
authors.affiliation: Servicio de Medicina Interna, Hospital de Móstoles, Madrid, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Varela
authors.forename: Marta
authors.initials: M
authors.lastname: Calvo
authors.forename: Miriam
authors.initials: M
authors.lastname: Chana
authors.forename: Ivan
authors.initials: I
authors.lastname: Gomez-Mestre
authors.forename: Rosa
authors.initials: R
authors.lastname: Asensio
authors.forename: Pedro
authors.initials: P
authors.lastname: Galdos
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001833:Body Temperature Regulation / Q000502:physiology*; D003422:Critical Care / Q000379:methods*; D019277:Entropy; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D008297:Male; D008875:Middle Aged; D009102:Multiple Organ Failure / Q000175:diagnosis / Q000401:mortality / Q000503:physiopathology*; D011379:Prognosis; D012044:Regression Analysis; D012720:Severity of Illness Index; D012881:Skin Temperature / Q000502:physiology*; D013030:Spain; D015996:Survival Rate