Does modification of the Innsbruck and the Glasgow Coma Scales improve their ability to predict functional outcome?
M. N. Diringer and D. F. Edwards
Department of Neurology, Washington University School of Medicine, St Louis, Mo., USA. diringerm@neuro.wustl.edu
BACKGROUND: The accurate prediction of functional outcome requires the
development of multivariate models. To enhance their contribution to such
models, the predictive power of each component must be optimized.
OBJECTIVES: To improve the predictive power of coma scales as the first
step in building more sophisticated multivariate models to predict specific
levels of functional outcome. DESIGN: Prospective descriptive study.
SETTING: Neurology and neurosurgery intensive care unit (NNICU) in a
tertiary care academic center. PATIENTS: Eighty-four patients with acute
traumatic brain injury, intracerebral hemorrhage, subarachnoid hemorrhage,
or ischemic stroke. INTERVENTIONS: None. MAIN OUTCOME MEASURES: The Glasgow
Coma Scale (GCS) and Innsbruck Coma Scale (ICS) were administered within 24
hours of admission to the NNICU and then at 48-hour intervals until
discharge of the patient from the NNICU. The assessments were performed by
3 occupational therapy graduate students working under the supervision of
the medical director of the NNICU. The functional outcome at 3 months after
discharge from the hospital was assessed by telephone by the same nurse
using the following categories: (1) dead, (2) receiving nursing home or
custodial care, (3) home with help, or (4) independent. Cronbach's alpha
estimates of reliability for each scale were computed using all scores
obtained during the study. The analyses indicated that the verbal response
item of the GCS and the oral automatisms item of the ICS were less reliable
in this patient population. The scales were modified by deleting those
items, and predictive validity for the original and modified scales was
computed using a discriminant function of the admission scores. RESULTS:
Before modification, both scales were best at predicting independence (GCS
and ICS, 71% correct) and mortality (GCS, 60% correct; ICS, 56% correct).
The modifications produced a modest improvement in the ability of both
scales to better predict levels of outcome (modified GCS: home with help,
33% correct, independent, 71% correct; modified ICS: home with help, 0%
correct, independent, 74% correct). CONCLUSIONS: By deleting items with low
reliability from the ICS and the GCS we achieved improved reliability and
predictive validity. The improvement in predictive power, however, was
inadequate to accurately predict functional outcome. Combining clinical
scales with other demographic, physiological, functional, and radiographic
data will be needed to achieve useful predictions of functional outcome.
