Comparison of accuracy of optic nerve ultrasound for the detection of intracranial hypertension in the setting of acutely fluctuating vs stable intracranial pressure: post-hoc analysis of data from a prospective, blinded single center study

Abstract

IntroductionOptic nerve sheath diameter (ONSD) measurement with bedside ultrasound has been shown in many studies to accurately detect high intracranial pressure (ICP). The accuracy of point-in-time ONSD measurement in the presence of ongoing fluctuation of ICP between high and normal is not known. Recent laboratory investigation suggests that reversal of optic nerve sheath distension may be impaired following bouts of intracranial hypertension. Our objective was to compare the accuracy of ONSD measurement in the setting of fluctuating versus stable ICP.MethodsThis was a retrospective analysis of data from prospective study comparing ONSD to invasive ICP. Patients with invasive ICP monitors in the ICU underwent ONSD measurement with simultaneous blinded recording of ICP from the invasive monitor. Three measurements were made in each eye. Significant acute ICP fluctuation (SAIF) was defined in two different ways; as the presence of ICP both above and below 20 mmHg within a cluster of six measurements (Definition 1) and as a magnitude of fluctuation >10 mmHg within the cluster (Definition 2). The accuracy of point-in-time ONSD measurements for the detection of concurrent ICP >20 mmHg within clusters fulfilling a specific definition of SAIF was compared to the accuracy of ONSD measurements within clusters not fulfilling the particular definition by comparison of independent receiver operating characteristic (ROC) curves.ResultsA total of 613 concurrent ONSD-ICP measurements in 109 clusters were made in 73 patients. Twenty-three (21%) clusters fulfilled SAIF Definition 1 and 17 (16%) SAIF Definition 2. For Definition 1, the difference in the area under the curve (AUC) of ROC curves for groups with and without fluctuation was 0.10 (P = 0.0001). There was a fall in the specificity from 98% (95% CI 96 to 99%) to 74% (63 to 83%) and in the positive predictive value from 89% (80 to 95%) to 76% (66 to 84%) with fluctuation. For Definition 2, also, there was a significant difference between the AUC of ROC curves of groups with fluctuation-magnitude >10 mmHg and those with fluctuation-magnitude 5 to 10 mmHg (0.06, P = 0.04) as well as <5 mmHg (0.07, P = 0.01).ConclusionsSpecificity and PPV of ONSD for ICP >20 mmHg are substantially decreased in patients demonstrating acute fluctuation of ICP between high and normal. This may be because of delayed reversal of nerve sheath distension.

Ultrasonographic measured optic nerve sheath diameter as an accurate and quick monitor for changes in intracranial pressure

“…7 This was demonstrated in the retrospective study by Rajajee et al in which a delayed reversal of ONSD after ICP fluctuations was shown. 16 However, in our study, changes in ICP were reflected by immediate changes in ONSD. In all cases ONSD reverted to baseline levels simultaneous with a decrease in ICP, directly after tracheal manipulation was stopped.…”

“…Bilateral ocular trauma can make it impossible to perform ONSD measurement, but this is uncommon in head trauma patients. 16 In ICU settings, invasive, continuous ICP measurement with the ICP probe remains superior to this noninvasive, intermittent ONSD ultrasonography because it delivers continuous values and requires no additional skills from the attending ICU nurse. However, in emergency care and prehospital conditions ONSD measurement may be useful to distinguish between normal or elevated ICP in comatose patients.…”

“…This might compromise the specificity of ONSD. 16,17 Therefore, in this study, we performed dynamic measurements in patients with TBI to examine whether changes in ICP and not papilledema causes changes in ONSD. Changes in ONSD are directly caused by ICP changes and are not influenced by papilledema.…”

“…9,14,17 All previous studies on the relationship between ICP and optic nerve sheath diameter (ONSD) were performed crosssectionally. [9][10][11][12][13][14][15][16][17][18][19] ONSD distension was correlated to the ICP measured at the same moment. However, it remains unclear whether these changes in ONSD resulted only from ICP changes or from papilledema as well.…”

Sonography of the optic nerve sheath beyond the hyperacute stage of intracerebral hemorrhage

“…However, in the literature there are very little data on ONSD changes in patients with increased ICP secondary to ICH beyond the hyperacute or acute stage [6]. We performed serial US studies to measure ONSD in four patients with extensive hypertensive ICH followed longitudinally beyond the hyperacute and acute stage.…”