Optic Nerve Sheath Measurements Are Associated With Other Morbidity Factors Besides Intracranial Pressure

ABSTRACT Background and Purpose Measurement of the optic nerve sheath diameter (ONSD) is a non‐invasive and cost‐effective method to estimate intracranial pressure (ICP). ONSD has previously shown an association with intensive care unit length of stay (ICU‐LOS) in Covid‐19 patients. This association has prompted hypotheses that elevated ICP may be a feature of severe Covid‐19 cases. This study aimed to determine if any of the optic nerve sheath (ONS) compartments are correlated with ICU‐LOS, independent of ICP. Methods We performed a post‐hoc analysis of data from 138 ICU patients with invasive ICP monitoring at the Karolinska University Hospital in Sweden. The ONSD, the optic nerve diameter, the thickness of the perioptic subarachnoid space, and the thickness of the perioptic dura mater were all measured with ultrasound at the bedside and concomitant ICP was noted. The association between ICU‐LOS, ICP, and ONS compartments was assessed with multiple regression. Due to non‐normal distributions, we used quantile regression. Results The thickness of the dura mater was the only variable independently associated with ICU‐LOS. The ICP was the only variable independently associated with mortality. Conclusions The finding of this study suggests that the ONS, besides ICP, also is affected by other pathological processes in the brain that are associated with ICU‐LOS. Changes in ONSD may thus not only be caused by changes in ICP but be driven by other morbidity factors. This may have clinical implications for the reliability of ONSD as a non‐invasive estimate of ICP.