gms | German Medical Science

Objective: The pulsatility index (PI) of the transcranial dopppler sonography (TCD) offers a non-invasive method of estimating intracranial pressure. We examined the influence of additional haemodynamic parameters in order to improve the prediction of the PI.

Methods: A prospective study was designed. In the intensive care unit, comatous patients with an intraparenchymatous or fluid coupled pressure monitor were routinely examined using TCD and the PI was calculated. Patients with a known cardiovascular abnormality or vasospasm (Vmean > 100cm/s) were excluded. A model with multiple additional parameters was used to improve the prediction of the ICP by PI. These parameters were: simultanous measurement of PI, hematocrite, mean arterial blood pressure (MAP), heart rate and arterial CO₂ pressure (paCO₂). A co-variance and a regression analysis of the different parameters was performed. Additionally, the Shapiro-Wilk test as a Goodness-of-Fit test was used.

Results: Fourty nine patients were examined in the age group of 18 – 81 years (mean age 49,5 years). The intracranial pathologies of the patients included head injury (18), intracranial hemmorrhage (10), subarachnoid hemmorrhage (10), other (11). 88 simultanous measurements of all parameters were undertaken. The additional use of the hematocrite (values 25–47%) and the heart rate (p=0,043) did not improve the prediction of ICP. When autoregulation was impaired, the MAP improved outcome prediction (p=0,027). This could be used as additional parameter. Although the paCO₂ is regarded as one of the main factors of vasoregulation, in our model its influence on the PI showed no significant improvement.

Conclusions: Using a model with multiple additional haemodynamic parameters, the predictable value of the PI regarding ICP was slightly improved. However, according to our data, the ICP-prediction using PI is still not reliable.