Sex differences in the diagnostic value of optic nerve sheath diameter for assessing intracranial pressure.

The optic nerve sheath diameter (ONSD) can predict elevated intracranial pressure (ICP) but it is not known whether diagnostic characteristics differ between men and women. This observational study was performed at the Karolinska University Hospital in Sweden to assess sex differences in diagnostic accuracy for ONSD. We included 139 patients (65 women), unconscious and/or sedated, with invasive ICP monitoring. Commonly used ONSD derived measurements and associated ICP measurements were collected. Linear regression analyses were performed with ICP as dependent variable and ONSD as independent variable. Area under the receiver operator characteristics curve (AUROC) analyses were performed with a threshold for elevated ICP ≥ 20 mmHg. Analyses were stratified by sex. Optimal cut-offs and diagnostic characteristics were estimated. The ONSD was associated with ICP in women. The AUROCs in women ranged from 0.70 to 0.83. In men, the ONSD was not associated with ICP and none of the AUROCs were significantly larger than 0.5. This study suggests that ONSD is a useful predictor of ICP in women but may not be so in men. If this finding is verified in further studies, this would call for a re-evaluation of the usage and interpretation of ONSD to estimate ICP.

Optic nerve sheath diameter in intracranial hypertension: Measurement external or internal of the dura mater?

BACKGROUND AND PURPOSE: Optic nerve sheath diameter (ONSD) is a promising metric to estimate intracranial pressure (ICP). There is no consensus whether ONSD should be measured external (ONSDext) or internal (ONSDint) of the dura mater. Expert opinion favors ONSDint, though without clear evidence to support this. Adjustments of ONSD for eye diameter (ED) and optic nerve diameter (OND) have been suggested to improve precision. We examined the diagnostic accuracy of ONSDext and ONSDint for estimating ICP, unadjusted as well as adjusted for ED and OND. METHODS: We performed an observational cohort study, measuring ONSDext and ONSDint in patients with invasive ICP monitoring at Karolinska University Hospital in Stockholm, Sweden. We used ONSDext and ONSDint unadjusted as well as adjusted for ED and for OND. We compared the area under the receiver operator characteristics curve (AUROC) for these methods. Thresholds for elevated ICP were set at ≥20 and ≥22 mmHg, respectively. RESULTS: We included 220 measurements from 100 patients. Median ONSDext and ONSDint were significantly different at 6.7 and 5.2 mm (p = .00). There was no significant difference in AUROC for predicting elevated ICP between ONSDext and ONSDint (.67 vs. .64, p = .31). Adjustment for ED yielded better diagnostic accuracy (AUROC, cutoff, sensitivity, specificity) for ONSDext/ED (.76, .29, .81, .62) and ONSDint/ED (.71, .24, .5, .89). CONCLUSIONS: ONSDext and ONSDint differ significantly and are not interchangeable. However, there were no significant differences in diagnostic accuracy between ONSDext and ONSDint. Adjustment for ED may improve diagnostic accuracy of ONSD.

Optic nerve sheath diameter is associated with outcome in severe Covid-19.

Neurological symptoms are common in Covid-19 and cerebral edema has been shown post-mortem. The mechanism behind this is unclear. Elevated intracranial pressure (ICP) has not been extensively studied in Covid-19. ICP can be estimated noninvasively with measurements of the optic nerve sheath diameter (ONSD). We performed a cohort study with ONSD ultrasound measurements in severe cases of Covid-19 at an intensive care unit (ICU). We measured ONSD with ultrasound in adults with severe Covid-19 in the ICU at Karolinska University Hospital in Sweden. Patients were classified as either having normal or elevated ONSD. We compared ICU length of stay (ICU-LOS) and 90 day mortality between the groups. 54 patients were included. 11 of these (20.4%) had elevated ONSD. Patients with elevated ONSD had 12 days longer ICU-LOS (95% CI 2 to 23 p = 0.03) and a risk ratio of 2.3 for ICU-LOS ≥ 30 days. There were no significant differences in baseline data or 90 day mortality between the groups. Elevated ONSD is common in severe Covid-19 and is associated with adverse outcome. This may be caused by elevated ICP. This is a clinically important finding that needs to be considered when deciding upon various treatment strategies.

Can Quantitative Pupillometry be used to Screen for Elevated Intracranial Pressure? A Retrospective Cohort Study.

BACKGROUND: Elevated intracranial pressure (ICP) is a serious complication in brain injury. Because of the risks involved, ICP is not monitored in all patients at risk. Noninvasive screening tools to identify patients with elevated ICP are needed. Anisocoria, abnormal pupillary size, and abnormal pupillary light reflex are signs of high ICP, but manual pupillometry is arbitrary and subject to interrater variability. We have evaluated quantitative pupillometry as a screening tool for elevated ICP. METHODS: We performed a retrospective observational study of the association between Neurological Pupil index (NPi), measured with the Neuroptics NPi-200 pupillometer, and ICP in patients routinely monitored with invasive ICP measurement in the intensive care unit. We performed a nonparametric receiver operator curve analysis for ICP ≥ 20 mm Hg with NPi as a classification variable. We performed a Youden analysis for the optimal NPi cutoff value and recorded sensitivity and specificity for this cutoff value. We also performed a logistic regression with elevated ICP as the dependent variable and NPi as the independent variable. RESULTS: We included 65 patients with invasive ICP monitoring. A total of 2,705 measurements were analyzed. Using NPi as a screening tool for elevated ICP yielded an area under receiver operator curve of 0.72. The optimal mean NPi cutoff value to rule out elevated ICP was ≥ 3.9. The probability of elevated ICP decreased with increasing NPi, with an odds ratio of 0.55 (0.50, 0.61). CONCLUSIONS: Screening with NPi may inform high stakes clinical decisions by ruling out elevated ICP with a high degree of certainty. It may also aid in estimating probabilities of elevated ICP. This can help to weigh the risks of initiating invasive ICP monitoring against the risks of not doing so. Because of its ease of use and excellent interrater reliability, we suggest further studies of NPi as a screening tool for elevated ICP.

Optic nerve sheath diameter measurement by ultrasound: Evaluation of a standardized protocol.

BACKGROUND AND PURPOSE: Treatment of elevated intracranial pressure (ICP) is central to neurocritical care, but not all patients are eligible for invasive ICP-monitoring. A promising noninvasive option is ultrasound measurement of the optic nerve sheath diameter (ONSD). However, meta-analyses of ONSD for elevated ICP show wide confidence intervals. This might be due to baseline variations, inter-rater variability, and varying measurement methods. No standardized protocol has been validated. Corrections for eyeball diameter (ED) and optic nerve diameter (OND) may compensate for baseline variations. We evaluated a protocol and compared two different measurement methods for ONSD ultrasound. METHODS: Two operators, blinded to each other's measurements, measured ONSD, ED, and OND twice in 20 patients. ONSD was measured with two different methods in use: internal (ONSDint) or external (ONSDext) of the dura mater. Intra-class correlation (ICC) was calculated for inter-rater and intra-rater reliability. RESULTS: ICCs for inter-rater reliability of ONSDext and ONSDint (95% confidence interval) were 0.96 (0.93, 0.98) and 0.88 (0.79, 0.94), respectively. ICCs for intra-rater reliability of ONSDext and ONSDint were 0.97 (0.94, 0.99) and 0.93 (0.87, 0.96), respectively. There was no significant bias or difference in intra-rater reliability between operators. CONCLUSIONS: ONSD can be measured with an excellent inter- and intra-rater reliability and low risk of inter-rater bias, when using this protocol. ONSDext yields a higher inter- and intra-rater reliability than ONSDint. Corrections for ED and OND can be performed reliably.