Authors: Yasmeen Elsawaf; Linda Papa, MD (Orlando, FL)
Capnography is a fast, non-invasive technique that is easily administered and accurately measures exhaled ETCO2 concentration. ETCO2 levels respond to changes in ventilation, perfusion, and metabolic state, alteration of which is well documented following a traumatic brain injury. This study examined the relationship between ETCO2 levels and severity of TBI as measured by injury severity indicators including Glasgow Coma Scale (GCS) score, Computerized Tomography (CT) findings, and requirement of neurosurgical intervention.
This prospective cohort study enrolled adult patients presenting to a Level 1 trauma center following a MMTBI defined by blunt head trauma followed by loss of consciousness, amnesia, or disorientation and a GCS 9-15. ETCO2 measurements were recorded from the prehospital and emergency department records and compared to indicators of TBI severity.
Of the 46 patients enrolled, 21 (46%) had a normal ETCO2 level and 25 (54%) had an abnormal ETCO2 level. The mean age of enrolled patients was 40 (range 19-70) and 32 (70%) were male. Mechanisms of injury included motor vehicle collision in 19 (41%), motor cycle collision in 9 (20%), fall in 8 (17%), bicycle/pedestrian struck in 8 (17%) and other in 2 (4%). Eight (17%) patients had a GCS 9-12 and 38 (83%) had a GCS 13-15. Of the 11 (24%) patients with intracranial lesions on CT, 10 (91%) had an abnormal ETCO2 level (p=0.006). Of the 5 (11%) patients who required a neurosurgical intervention 100% had an abnormal ETCO2 level (p=0.05).
Abnormal levels of ETCO2 were significantly associated with clinical measures of brain injury severity, in particular, the need for neurosurgical intervention. Future applications of ETCO2 levels include integration of noninvasive vital signs to predict the extent of injury. Further research with a larger sample of TBI patients will be required to better understand and validate these findings.