Abstract
BackgroundThe invasive nature of the current methods for monitoring of intracranial pressure (ICP) has prevented their use in many clinical situations. Several attempts have been made to develop methods to monitor ICP non-invasively. The aim of this study is to assess the relationship between ultrasound-based non-invasive ICP (nICP) and invasive ICP measurement in neurocritical care patients.Methods and findingsThis was a prospective, single-cohort observational study of patients admitted to a tertiary neurocritical care unit. Patients with brain injury requiring invasive ICP monitoring were considered for inclusion. nICP was assessed using optic nerve sheath diameter (ONSD), venous transcranial Doppler (vTCD) of straight sinus systolic flow velocity (FVsv), and methods derived from arterial transcranial Doppler (aTCD) on the middle cerebral artery (MCA): MCA pulsatility index (PIa) and an estimator based on diastolic flow velocity (FVd). A total of 445 ultrasound examinations from 64 patients performed from 1 January to 1 November 2016 were included. The median age of the patients was 53 years (range 37–64). Median Glasgow Coma Scale at admission was 7 (range 3–14), and median Glasgow Outcome Scale was 3 (range 1–5). The mortality rate was 20%. ONSD and FVsv demonstrated the strongest correlation with ICP (R = 0.76 for ONSD versus ICP; R = 0.72 for FVsv versus ICP), whereas PIa and the estimator based on FVd did not correlate with ICP significantly. Combining the 2 strongest nICP predictors (ONSD and FVsv) resulted in an even stronger correlation with ICP (R = 0.80). The ability to detect intracranial hypertension (ICP ≥ 20 mm Hg) was highest for ONSD (area under the curve [AUC] 0.91, 95% CI 0.88–0.95). The combination of ONSD and FVsv methods showed a statistically significant improvement of AUC values compared with the ONSD method alone (0.93, 95% CI 0.90–0.97, p = 0.01). Major limitations are the heterogeneity and small number of patients included in this study, the need for specialised training to perform and interpret the ultrasound tests, and the variability in performance among different ultrasound operators.ConclusionsOf the studied ultrasound nICP methods, ONSD is the best estimator of ICP. The novel combination of ONSD ultrasonography and vTCD of the straight sinus is a promising and easily available technique for identifying critically ill patients with intracranial hypertension.
Highlights
Intracranial hypertension is a frequent and harmful complication of brain injury; it is an important contributing factor for secondary brain injury, and its severity and duration have been correlated with a fatal outcome [1,2].A recent trial comparing an invasive intracranial pressure (ICP) monitoring protocol with a protocol based on imaging and clinical examination found no significant differences in patient outcome [3]
Patients with brain injury requiring invasive ICP monitoring were considered for inclusion. non-invasive ICP (nICP) was assessed using optic nerve sheath diameter (ONSD), venous transcranial Doppler of straight sinus systolic flow velocity (FVsv), and methods derived from arterial transcranial Doppler on the middle cerebral artery (MCA): MCA pulsatility index (PIa) and an estimator based on diastolic flow velocity (FVd)
ONSD and FVsv demonstrated the strongest correlation with ICP (R = 0.76 for ONSD versus ICP; R = 0.72 for FVsv versus ICP), whereas middle cerebral artery pulsatility index (PIa) and the estimator based on FVd did not correlate with ICP significantly
Summary
Intracranial hypertension is a frequent and harmful complication of brain injury; it is an important contributing factor for secondary brain injury, and its severity and duration have been correlated with a fatal outcome [1,2].A recent trial comparing an invasive intracranial pressure (ICP) monitoring protocol with a protocol based on imaging and clinical examination found no significant differences in patient outcome [3]. The best accuracy for a non-invasive method reported in the literature [14,15] has been demonstrated by 2-depth high-resolution transcranial Doppler insonation of the ophthalmic artery This method does not need calibration and is based on the measurement of the balance point when the measured parameters of blood flow velocity waveforms in the intracranial segment of the ophthalmic artery (which reflect ICP) are identical to extracranial segments (which are mechanically compressed by an externally applied pressure). Other authors [16,17] have proposed different methods for continuous nICP monitoring based on the waveform analysis of cerebral blood flow velocity from the middle cerebral artery (MCA) and arterial pressure Despite these promising results, non-invasive techniques remain of insufficient accuracy and temporal resolution to replace invasive ICP monitoring [18,19]. The aim of this study is to assess the relationship between ultrasound-based non-invasive ICP (nICP) and invasive ICP measurement in neurocritical care patients
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