Noninvasive assessment of intracranial pressure using ocular sonography in neurocritical care patients

Introduction

Invasive devices are the 'gold standard' for measurement of intracranial pressure (ICP). Their placement, however, can be challenging (coagulation disorders, lack of surgical availability). Noninvasive sonography of the optic nerve sheath diameter (ONSD) has been proposed to detect elevated ICP [1, 2]. However, this method needs further validation. This study was performed to assess the relationship between the ONSD and ICP in neurocritical care patients.

Methods

After approval from the local ethics committee, 37 adult patients with severe traumatic brain injury (n = 22), subarachnoidal hemorrhage (n = 6), intracranial hematoma (n = 8) and stroke (n = 1) requiring sedation and ICP monitoring (intraparenchymal probe in the frontal lobe; Codman, Johnson & Johnson) were included. For each optic nerve, two measurements of ONSD were made using a 7.5 MHz linear probe (HP Sonos 5500^®; Hewlett Packard) (2D mode, 3 mm behind the globe, one measure in the sagittal and one in the transverse plane). The mean value for both eyes was retained. The ONSD and ICP were measured simultaneously once a day during the first 2 days after ICP probe placement and in cases of important changes in ICP.

Results

There was a significant linear relationship between the ONSD and ICP (Spearman correlation ρ = 0.75, P < 0.0001; Figure 1a). Changes in ICP (delta) were also significantly correlated with ONSD variations (ρ = 0.78, P < 0.001; Figure 1b). The ONSD cutoff for detecting ICP > 20 mmHg was 5.8 mm (area under ROC curve = 0.91). The negative likelihood ratio of this cutoff was 0.07.

Figure 1

Relationship between intracranial pressure (ICP) and the optic nerve sheath diameter (ONSD).

Conclusion

There is a significant relationship between the ONSD and ICP in neuro-ICU patients. Changes in ICP are accurately detected by the ONSD. The probability of having high ICP when the ONSD is below 5.8 mm is very low. This noninvasive method could be used to check the absence of raised ICP.