Determination of the correlation between invasive intracranial pressure values measured via external ventricular drainage catheters and non-invasive intracranial pressure values measured by transcranial doppler USG in patients with increased intracranial pressure in intensive care units

Objective: We aim to determine the correlation between the invasively measured intracranial pressure and the non-invasively calculated intracranial pressure using transcranial doppler ultrasonography in patients with external ventricular drainage catheters in neuro-intensive care units. Materials and Methods: A total of 905 simultaneous invasive and non- invasive intracranial pressure (ICP) measurements, collected from 50 patients between February 1, 2023, and August 1, 2025, at the Intensive Care Units of Istanbul University-Cerrahpaşa, Cerrahpaşa Faculty of Medicine, Department of Anesthesiology and Reanimation, were evaluated prospectively and observationally. Results: A statistically insignificant and very weak correlation was found between invasive ICP and non-invasive ICP measurements (r = 0.012, p = 0.710). The mean difference (bias) between the two measurements was calculated as -17.12 mmHg. The limits of agreement were found to be considerably wide (-62.83 to +28.58 mmHg). This indicates high individual variability between the two methods and a lack of clinical consistency. While a moderate, positive, and significant correlation was observed between non-invasive ICP and mean arterial pressure (r = 0.476, p = 0.000), a weak and negative correlation was found between invasive ICP and mean arterial pressure. Conclusion: These findings suggest that transcranial Doppler ultrasonography parameters are not an alternative to invasive methods for monitoring intracranial pressure. However, they may be utilized solely as a supportive monitoring method in cases where invasive measurement is unfeasible or carries high risk Keywords: intracranial pressure, transcranial doppler ultrasonography, external ventricular drainage, resistive index, pulsatility index