Noninvasive Monitoring of Cerebrovascular Reactivity with Near Infrared Spectroscopy in Head-Injured Patients
Academic Neurosurgical Unit, University of Cambridge Clinical School, Cambridge, United Kingdom.Journal of neurotrauma (Impact Factor: 3.71). 11/2010; 27(11):1951-8. DOI: 10.1089/neu.2010.1388
Monitoring of cerebrovascular pressure reactivity (PRx) has diagnostic and prognostic value in head-injured patients, but requires invasive monitoring of intracranial pressure (ICP). Near infrared spectroscopy (NIRS) is a noninvasive method that is suitable for continuous detection of cerebral blood volume changes. We compared a NIRS-based index of cerebrovascular reactivity, called total hemoglobin reactivity (THx), against standard measurements of PRx in a prospective observational study. Forty patients with closed-head injury were monitored daily with arterial blood pressure (ABP), ICP, and a NIRS-based total hemoglobin index. PRx and THx were calculated as the moving correlation coefficients using 5-min time windows between 10-sec averaged values of ICP and ABP, and total hemoglobin index and ABP, respectively. A total of 120 recordings were performed between the median first (IQR 0.75-2) and fourth (IQR 2-6) day after head injury, giving a total duration of 1760 hours. PRx and THx demonstrated a significant association across averaged individual recordings (r = 0.49, p < 0.0001), and across patients (r = 0.56, p = 0.0002). Assessment of optimal cerebral perfusion pressure (CPP) and ABP using THx was possible in about 50% of recordings, and showed a significant agreement with the optimal CPP and ABP assessed with PRx. THx may be of diagnostic value to optimize therapy oriented toward restoration and continuity of cerebrovascular reactivity, especially in patients for whom direct ICP monitoring is not feasible.
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- "In patients with neuronal injury, the knowledge of the status of cerebrovascular autoregulation can help to optimize the management of the CPP. NIRS shows promise for the continuous assessment of cerebrovascular reactivity and cerebral autoregulation in adults. NIRS-based index of cerebrovascular reactivity, called total hemoglobin reactivity (THx) was found to have significant correlation with standard measurements of PRx which requires invasive ICP monitoring. "
ABSTRACT: Traumatic brain injury (TBI) consists of varied pathophysiological consequences and alteration of intracranial dynamics, reduction of the cerebral blood flow and oxygenation. In the past decade more emphasis has been directed towards optimizing cerebral perfusion pressure (CPP) in patients who have suffered TBI. Injured brain may show signs of ischemia if CPP remains below 50 mmHg and raising the CPP above 60 mmHg may avoid cerebral oxygen desaturation. Though CPP above 70 mmHg is influential in achieving an improved patient outcome, maintenance of CPP higher than 70 mmHg was associated with greater risk of acute respiratory distress syndrome (ARDS). The target CPP has been laid within 50-70 mmHg. Cerebral blood flow and metabolism are heterogeneous after TBI and with regional temporal differences in the requirement for CPP. Brain monitoring techniques such as jugular venous oximetry, monitoring of brain tissue oxygen tension (PbrO2), and cerebral microdialysis provide complementary and specific information that permits the selection of the optimal CPP. This review highlights the rationale for use CPP directed therapies and neuromonitoring to identify optimal CPP of head injured patients. The article also reviews the evidence provided by various clinical trials regarding optimal CPP and their application in the management of head injured patients.Journal of Anaesthesiology Clinical Pharmacology 07/2014; 30(3):318-27. DOI:10.4103/0970-9185.137260
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- "Furthermore, a non-invasive alternative for continuous determination of cerebrovascular reactivity and CPPopt may be the near-infrared spectroscopy based index THx. The index has been evaluated in TBI patients . However, the applicability of THx in the setting of high brain compliance has not been addressed. "
ABSTRACT: Current guidelines for spontaneous intracerebral hemorrhage (ICH) recommend maintaining cerebral perfusion pressure (CPP) between 50-70 mmHg, depending on the state of autoregulation. We continuously assessed dynamic cerebral autoregulation and the possibility of determination of an optimal CPP (CPPopt) in ICH patients. Assocations between autoregulation, CPPopt and functional outcome were explored. Intracranial pressure (ICP), mean arterial pressure (MAP) and CPP were continuously recorded in 55 patients, with 38 patients included into the analysis. The pressure reactivity index (PRx) was calculated as moving correlation between MAP and ICP. CPPopt was defined as the CPP associated with the lowest PRx values. CPPopt was calculated using hourly updating 4 hour windows. The modified Rankin score (mRS) was assessed at 3 months and associations between PRx, CPPopt and outcomes were explored using Pearson correlation and Fisher's exact test. Multivariate stepwise logistic regression models were calculated including standard outcome predictors along with percentage of time with PRx > 0.2 and percentage of time within the CPPopt range. An overall PRx indicating impairment of pressure reactivity was found in 47% (n = 18). The mean PRx and the time spent with a PRx > 0.2 significantly correlated with mRS at 3 months (r = 0.50, P = 0.002; r = 0.46, P = 0.004). CPPopt was calculable during 57% of the monitoring time. The median CPP was 78 mmHg, the median CPPopt 83 mmHg. Mortality was lowest in the group of patients with a CPP close to their CPPopt. However, for none of the CPPopt variables a significant association to outcome was found. The percentage of time with impaired autoregulation and hemorrhage volume were independent predictors for acceptable outcome (mRS 1-4) at three months (OR 0.94, 95% CI 0.90-1.00). Failure of pressure reactivity seems common following severe ICH and is associated with unfavorable outcome. Real-time assessment of CPPopt concept is feasible in ICH and might provide a tool for an autoregulation-oriented CPP management. A larger trial is needed to explore if a CPPopt management results in better functional outcomes.Critical care (London, England) 03/2014; 18(2):R51. DOI:10.1186/cc13796 · 4.48 Impact Factor
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- "Specifically, cerebral tissue oxygen saturation (TOS) and total haemoglobin have been applied as surrogates of CBF and CBV, respectively. When correlated with ABP these indices agree with well-established indices of CVPR [4, 5]. "
ABSTRACT: Understanding changes in cerebral oxygenation, haemodynamics and metabolism holds the key to individualised, optimised therapy after acute brain injury. Near-infrared spectroscopy (NIRS) offers the potential for non-invasive, continuous bedside measurement of surrogates for these processes. Interest has grown in applying this technique to interpret cerebrovascular pressure reactivity (CVPR), a surrogate of the brain's ability to autoregulate blood flow. We describe a physiological model-based approach to NIRS interpretation which predicts autoregulatory efficiency from a model parameter k_aut. Data from three critically brain-injured patients exhibiting a change in CVPR were investigated. An optimal value for k_aut was determined to minimise the difference between measured and simulated outputs. Optimal values for k_aut appropriately tracked changes in CVPR under most circumstances. Further development of this technique could be used to track CVPR providing targets for individualised management of patients with altered vascular reactivity, minimising secondary neurological insults.Advances in Experimental Medicine and Biology 03/2013; 765:87-93. DOI:10.1007/978-1-4614-4989-8_13 · 1.96 Impact Factor
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