‘Treatment profile’: a new concept that must be considered when comparing data obtained from physiological severity of illness scores

Most of the physiological derangements that contribute to critical care outcome prediction models are responsive to direct therapy to correct them. For example K⁺ infusions for serum K⁺ levels; and inotropes for blood pressure changes. The total physiological score attained by a patient is therefore a product of the patient's illness and also the degree of physiological control that is achieved by critical care therapy. Differences in therapeutic culture between critical care units (and indeed the same critical care units over time) may therefore have a major influence on the final/score outcome prediction. We have assessed the percentage of patients in each score band of high abnormal range (+4), normal (0) and low abnormal range (+4) for each physiological variable for APACHE II [1] having treatment specifically targeted to correct that variable to normal, in order to define a treatment profile for our ICU.

Method

The notes, treatment cards and clinical observations for 100 consecutive patients were reviewed to find the most deranged of 11 physiological variables using the APACHE II methodology (i.e. the most deranged variable within the first 24 hours of ICU admission), and the occurrence of treatment specifically targeted to correct any derangement. Analysis of Glasgow Coma Scale was not included.

Results

The results for individual parameters are shown in the Table and for combined results in the Figure. Most parameters have more treatment the further the value from the 'normal' range, but the converse is true for respiratory rate. Within the group of patients who fall into the zero score band for physiological derangement, 30% (see Fig.) are being actively treated to maintain that parameter within that band. Zero percent to 100% of patients (see Table) are being actively treated depending on the physiological parameter.

Figure

Summary data showing the mean percentage of patients in each score band being treated for the physiological derrangement.

Table The patients falling into each APACHE II scoring band being actively treated for each physiological parameter (% [n])

Conclusion

We have described the 'treatment profile' for our ICU with regard to management of physiological parameters used in the APACHE II score. We speculate that different ICUs will have different treatment profiles. Possibilities to explain this include variations in targets of treatment in different ICUs (e.g. Haematocrit) or in the expediency that deviations from a defined range are treated. We suggest that the way patients are treated on different ICUs is unlikely to be the same altering the physiological score obtained in different ICUs. These variations may or may not be reflected in changes in mortality. This precludes meaningful comparisons between ICUs using data obtained from physiological scoring systems without also comparisons of 'treatment profile'.