Anthony A. Figaji
Anthony A. Figaji, Eugene Zwane, A. Graham Fieggen, Jonathan C. Peter and Peter D. Leroux
The goal of this paper was to examine the relationship between methods of acute clinical assessment and measures of secondary cerebral insults in severe traumatic brain injury in children.
Patients who underwent intracranial pressure (ICP), cerebral perfusion pressure (CPP), and brain oxygenation (PbtO2) monitoring and who had an initial Glasgow Coma Scale score, Pediatric Trauma Score, Pediatric Index of Mortality 2 score, and CT classification were evaluated. The relationship between these acute clinical scores and secondary cerebral insult measures, including ICP, CPP, PbtO2, and systemic hypoxia were evaluated using univariate and multivariate analysis.
The authors found significant associations between individual acute clinical scores and select physiological markers of secondary injury. However, there was a large amount of variability in these results, and none of the scores evaluated predicted each and every insult. Furthermore, a number of physiological measures were not predicted by any of the scores.
Although they may guide initial treatment, grading systems used to classify initial injury severity appear to have a limited value in predicting who is at risk for secondary cerebral insults.
Anthony A. Figaji, Eugene Zwane, A. Graham Fieggen, Andrew C. Argent, Peter D. Le Roux, Peter Siesjo and Jonathan C. Peter
Cerebral pressure autoregulation is an important neuroprotective mechanism that stabilizes cerebral blood flow when blood pressure (BP) changes. In this study the authors examined the association between autoregulation and clinical factors, BP, intracranial pressure (ICP), brain tissue oxygen tension (PbtO2), and outcome after pediatric severe traumatic brain injury (TBI). In particular we examined how the status of autoregulation influenced the effect of BP changes on ICP and PbtO2.
In this prospective observational study, 52 autoregulation tests were performed in 24 patients with severe TBI. The patients had a mean age of 6.3 ± 3.2 years, and a postresuscitation Glasgow Coma Scale score of 6 (range 3–8). All patients underwent continuous ICP and PbtO2 monitoring, and transcranial Doppler ultrasonography was used to examine the autoregulatory index (ARI) based on blood flow velocity of the middle cerebral artery after increasing mean arterial pressure by 20% of the baseline value. Impaired autoregulation was defined as an ARI < 0.4 and intact autoregulation as an ARI ≥ 0.4. The relationships between autoregulation (measured as both a continuous and dichotomous variable), outcome, and clinical and physiological variables were examined using multiple logistic regression analysis.
Autoregulation was impaired (ARI < 0.4) in 29% of patients (7 patients). The initial Glasgow Coma Scale score was significantly associated with the ARI (p = 0.02, r = 0.32) but no other clinical factors were associated with autoregulation status. Baseline values at the time of testing for ICP, PbtO2, the ratio of PbtO2/PaO2, mean arterial pressure, and middle cerebral artery blood flow velocity were similar in the patients with impaired or intact autoregulation. There was an inverse relationship between ARI (continuous and dichotomous) with a change in ICP (continuous ARI, p = 0.005; dichotomous ARI, p = 0.02); that is, ICP increased with the BP increase when ARI was low (weak autoregulation). The ARI (continuous and dichotomous) was also inversely associated with a change in PbtO2 (continuous ARI, p = 0.002; dichotomous ARI, p = 0.02). The PbtO2 increased when BP was increased in most patients, even when the ARI was relatively high (stronger autoregulation), but the magnitude of this response was still associated with the ARI. There was no relationship between the ARI and outcome.
These data demonstrate the influence of the strength of autoregulation on the response of ICP and PbtO2 to BP changes and the variability of this response between individuals. The findings suggest that autoregulation testing may assist clinical decision-making in pediatric severe TBI and help better define optimal BP or cerebral perfusion pressure targets for individual patients.