There is provided a method and apparatus for early detection of subacute,potentially catastrophic illness in a patient. This can be used to diagnoseillnesses such as, but not limited to, sepsis, necrotizing enterocolitis,pneumonia and meningitis, as well as noninfectious illnesses. In particular,there is provided a method and apparatus for early detection of subacute,potentially catastrophic illness in a patient. The method comprises: (a)monitoring the patients RR intervals (b) generating a normalized data set ofthe RR intervals (c) calculating one or more of (i) moments of the data setselected from the second and higher moments, including the standard deviation(ii) percentile values of the data set, (iii) sample entropy, and (iv) sampleassymetry and (d) identifying an abnormal heart rate variability associatedwith the illness based on one or more of the moments, the percentile values,sample entropy, and sample assymmetry analysis.
