Cerebral autoregulation derived blood pressure targets in elective neurosurgery.

Poor postoperative outcomes may be associated with cerebral ischaemia or hyperaemia, caused by episodes of arterial blood pressure (ABP) being outside the range of cerebral autoregulation (CA). Monitoring CA using COx (correlation between slow changes in mean ABP and regional cerebral O2 saturation-rSO2) could allow to individualise the management of ABP to preserve CA. We aimed to explore a continuous automated assessment of ABPOPT (ABP where CA is best preserved) and ABP at the lower limit of autoregulation (LLA) in elective neurosurgery patients. Retrospective analysis of prospectively collected data of 85 patients [median age 60 (IQR 51-68)] undergoing elective neurosurgery. ABPBASELINE was the mean of 3 pre-operative non-invasive measurements. ABP and rSO2 waveforms were processed to estimate COx-derived ABPOPT and LLA trend-lines. We assessed: availability (number of patients where ABPOPT/LLA were available); time required to achieve first values; differences between ABPOPT/LLA and ABP. ABPOPT and LLA availability was 86 and 89%. Median (IQR) time to achieve the first value was 97 (80-155) and 93 (78-122) min for ABPOPT and LLA respectively. Median ABPOPT [75 (69-84)] was lower than ABPBASELINE [90 (84-95)] (p < 0.001, Mann-U test). Patients spent 72 (56-86) % of recorded time with ABP above or below ABPOPT ± 5 mmHg. ABPOPT and ABP time trends and variability were not related to each other within patients. 37.6% of patients had at least 1 hypotensive insult (ABP < LLA) during the monitoring time. It seems possible to assess individualised automated ABP targets during elective neurosurgery.

MicroRNA cerebrospinal fluid profile during the early brain injury period as a biomarker in subarachnoid hemorrhage patients.

Introduction: Delayed cerebral ischemia (DCI) is a dreadful complication present in up to 30% of patients with spontaneous subarachnoid hemorrhage (SAH). Indeed, DCI is one of the main causes of long-term disability in SAH, yet its prediction and prevention are troublesome in poor-grade SAH cases. In this prospective study, we explored the potential role of micro ribonucleic acid (microRNA, abbreviated miRNAs)-small non-coding RNAs involved in clue gene regulation at the post-transcriptional level-as biomarkers of neurological outcomes in SAH patients. Methods: We analyzed the expression of several miRNAs present in the cerebrospinal fluid (CSF) of SAH patients during the early stage of the disease (third-day post-hemorrhage). NanoString Technologies were used for the characterization of the CSF samples. Results: We found an overexpression of miRNAs in the acute stage of 57 SAH in comparison with 10 non-SAH controls. Moreover, a differential expression of specific miRNAs was detected according to the severity of clinical onset, but also regarding the development of DCI and the midterm functional outcomes. Conclusion: These observations reinforce the potential utility of miRNAs as prognostic and diagnostic biomarkers in SAH patients. In addition, the identification of specific miRNAs related to SAH evolution might provide insights into their regulatory functions of pathophysiological pathways, such as the TGF-ß inflammatory pathway and blood-brain barrier disruption.

Minimally Invasive Surgery for Spontaneous Intracerebral Hematoma. Real-Life Implementation Model and Economic Estimation.

Objective: Spontaneous intracerebral hemorrhage is characterized by high fatality outcomes, even under best medical treatment. Recently, minimally invasive surgical (MIS) evacuation of the hematoma has shown promising results and may soon be implemented in the clinical practice. Hereby, we intended to foresee the logistic requirements for an early hematoma evacuation protocol, as well as to evaluate in a real-life implementation model the cost-utility of the two main MIS techniques for hemorrhagic stroke (catheter evacuation plus thrombolysis and neuroendoscopic aspiration). Methods: Data were obtained from the pool of hemorrhagic-stroke patients admitted to our institution during an annual period (2020-2021) and contrasted to the reported results in published trials of MIS techniques. Potential candidates for surgical treatment were identified according to the inclusion/exclusion criteria established in these trials. Then, a cost-utility analysis was performed, which explored the incremental cost per unit of health gained with a given treatment. The treatment effect was measured by differences in modified Rankin Score, and subsequently converted to quality-adjusted life years (QALY). Results: Of the 137 patients admitted to our center with supratentorial spontaneous intracerebral hemorrhage in a 1-year period, 17 (12.4%) were potential candidates for the catheter evacuation plus thrombolysis technique (Minimally Invasive Surgery with Thrombolysis in Intracerebral Hemorrhage Evacuation trial, MISTIE III criteria) and 59 (43.0%) for the neuroendoscopic aspiration technique (Dutch Intracerebral Hemorrhage Surgery Trial Pilot Study, DIST criteria). The incremental cost-utility ratio was € 76,533.13 per QALY for the catheter-based evacuation and € 60,703.89 per QALY for the endoscopic-based technique. Conclusion: Around 12-43% of patients admitted to hospital with spontaneous hemorrhagic stroke could be potential candidates to MIS early evacuation of the cerebral hematoma. In our real-life implementation model, the cost-utility analysis favored the neuroendoscopic evacuation over the catheter aspiration technique. Further studies are advisable as new data from the ongoing randomized trials becomes available.

Association between preoperative serum lactate concentrate with tumor cell proliferative index in primary brain tumor.

BACKGROUND: Elevated preoperative lactate levels have been reported in patients admitted for resection of brain tumors. As histologic type and tumor grade have also been linked to lactate concentration, we hypothesized that preoperative lactate concentration in patients with brain tumors may be associated with tumor proliferation. We describe the relationship between preoperative plasma lactate levels, and the cell proliferation marker Ki-67 in brain tumor surgery. METHODS: In this cross-sectional study, records of patients who underwent craniotomy between June 2017 and February 2018 at our Hospital were reviewed to select glioma and meningioma cases in which lactate concentrations in plasma and degree of cell proliferation were registered. Bivariable and linear regression analyses were used to assess the association between lactate concentrations and the Ki-67 Index. RESULTS: Lactate concentrations in plasma and Ki-67 Index were available in 55 patients. Meningioma cases had a mean concentration of 1.2 (0.1) mmol/L compared to diffuse astrocytic and oligodendroglial tumors cases with 1.7 (0.1) mmol/L (P<0.01). Both variables had a low positive correlation in meningiomas (Spearman's r, 0.29; 95% CI, -0.10-0.61; P=0.13) and a high correlation in gliomas (Spearman's r, 0.64; 95% CI, 0.33-0.82; P<0.01). The pooled analysis showed a high correlation index (Spearman's r, 0.61; 95% CI, 0.40-0.76; P<0.01). A linear regression model showed that the Ki-67 Index explained 43% of the variation in lactate (P<0.01). CONCLUSIONS: Brain tumors with higher rates of cell proliferation have higher plasma lactate levels. In this scenario, lactate concentrations may not only reflect systemic perfusion.

Venous tortuosity as a novel biomarker of rupture risk in arteriovenous malformations: ARI score.

BACKGROUND: Risk of rupture in arteriovenous malformations (AVMs) varies considerably among series. Hemodynamic factors, especially within the venous side of the circuit, seem to be responsible but are not yet well defined. We analyzed tortuosity in the draining vein as a potential new marker of rupture in AVMs, and propose a simple index to predict AVM bleeding. METHODS: A retrospective analysis of the venous angioarchitecture of brain AVMs was carried out at our center from 2013 to 2021, with special attention to venous tortuosity. After univariate analysis, the features of interest were combined to construct several predictive models using multivariate logistic regression. The best model proposed was the new AVM rupture index (ARI), which was then validated in an independent cohort. RESULTS: 68 AVMs were included in the first step and 32 in the validation cohort. Venous tortuosity, expressed as at least one curve >180°, was a significant predictor of rupture (p=0.023). The proposed bleeding index consisted of: venous tortuosity (any curve of >180°), single draining vein, and paraventricular/infratentorial location. It seems to be a robust evaluation tool, with an area under the receiver operating characteristic (AUROC) curve of 0.806 (95% CI 0.714 to 0.899), consistently replicated in the independent sample (AUROC 0.759 (95% CI 0.607 to 0.911)), and with an inter-rater kappa coefficient of 0.81 . CONCLUSIONS: Venous tortuosity may serve as a predictor of bleeding in AVMs that warrants further investigation. This likely new marker was one of the three elements of the proposed ARI. ARI outperformed the predictive accuracy of previous scores, and remained consistent in an independent cohort.

Hemodynamic Response, Coughing and Incidence of Cerebrospinal Fluid Leakage on Awakening with an Endotracheal Tube or Laryngeal Mask Airway in Place after Transsphenoidal Pituitary Surgery: A Randomized Clinical Trial.

We aimed to compare systemic and cerebral hemodynamics and coughing during emergence after pituitary surgery after endotracheal tube (ETT) extubation or after replacing ETT with a laryngeal mask airway (LMA). Patients were randomized to awaken with an ETT in place or after replacing it with an LMA. We recorded mean arterial pressure (MAP), heart rate, middle cerebral artery (MCA) flow velocity, regional cerebral oxygen saturation (SrO2), cardiac index, plasma norepinephrine, need for vasoactive drugs, coughing during emergence, and postoperative cerebrospinal fluid (CSF) leakage. The primary endpoint was postoperative MAP; secondary endpoints were SrO2 and coughing incidence. Forty-five patients were included. MAP was lower during emergence than at baseline in both groups. There were no significant between-group differences in blood pressure, nor in the number of patients that required antihypertensive drugs during emergence (ETT: 8 patients (34.8%) vs. LMA: 3 patients (14.3%); p = 0.116). MCA flow velocity was higher in the ETT group (e.g., mean (95% CI) at 15 min, 103.2 (96.3-110.1) vs. 89.6 (82.6-96.5) cm·s-1; p = 0.003). SrO2, cardiac index, and norepinephrine levels were similar. Coughing was more frequent in the ETT group (81% vs. 15%; p < 0.001). CSF leakage occurred in three patients (13%) in the ETT group. Placing an LMA before removing an ETT during emergence after pituitary surgery favors a safer cerebral hemodynamic profile and reduces coughing. This strategy may lower the risk for CSF leakage.

Intraoperative magnetic resonance imaging for cerebral cavernous malformations: When is it maybe worth it?

OBJECTIVE: Intraoperative magnetic resonance imaging (iMRI) can be useful for cerebral cavernous malformations (CCM) surgery. However, literature on this topic is scarce. We aim to investigate its clinical utility and propose criteria for the selection of patients who may benefit the most from iMRI. METHODS: From 2017 to 2019, all patients with CCMs who required surgery assisted with iMRI were included in the study. Clinical and radiological features were analyzed. Outcome measures included the need for an immediate second-look resection and clinical course in early post-surgery -Timepoint 1- (Tp1) and at the 6-to-12-month follow-up -Timepoint2- (Tp2). RESULTS: Out of 19 patients with 20 CCMs, 89% had bleeding in the past, and in 75% the CCM affected an eloquent area. According to the iMRI results, an immediate second-look resection was needed in 16% of them. In one patient, a remnant was not seen on iMRI. The mRS worsened in the immediate post-surgical exam (median, 1; IQR, 1) with improvements on the 6-month visit (median, 1; IQR, 2), (p = 0.018). When comparing the outcome of patients with and without symptoms at baseline, the latter fared better at Tp2 (p = 0.005). CONCLUSIONS: iMRI is an intraoperative imaging tool that seems safe for CCM surgery and might reduce the risk of lesion remnants. In our series, it allowed additional revision for further resection in 16% of the patients. In our experience, iMRI may be especially useful for lesions in eloquent areas, those with a significant risk of brain shift and for large CCMs.

Effects on cerebral blood flow of position changes, hyperoxia, CO2 partial pressure variations and the Valsalva manoeuvre: A study in healthy volunteers.

BACKGROUND: Maintaining adequate blood pressure to ensure proper cerebral blood flow (CBF) during surgery is challenging. Induced mild hypotension, sitting position or unavoidable intra-operative circumstances such as haemorrhage, added to variations in carbon dioxide and oxygen tensions, may influence perfusion. Several of these circumstances may coincide and it is unclear how these may affect CBF. OBJECTIVE: To describe the variation in transcranial Doppler and regional cerebral oxygen saturation (rSO2), as a surrogate of CBF, after cardiac preload and gravitational positional changes. DESIGN: Observational study. SETTING: Operating room at Hospital Clínic de Barcelona. VOLUNTEERS: Ten healthy volunteers, white, both sexes. INTERVENTIONS: Measurements were performed in the supine, sitting and standing positions during hyperoxia, hypocapnia and hypercapnia protocols and after a Valsalva manoeuvre. MAIN OUTCOME MEASURES: Cardiac index (CI), haemodynamic and respiratory variables, maximal and mean velocities (Vmax, Vmean) (transcranial Doppler) and rSO2 were acquired. Results were analysed using a generalised estimating equation technique. RESULTS: CI increases more than 16% after a preload challenge were not accompanied by differences in rSO2 or Vmax - Vmean. With positional changes, Vmean decreased more than 7% (P = 0.042) from the supine to the seated position. Hyperoxia induced a cerebral rSO2 increase more than 6% (P = 0.0001) with decreases in Vmax, Vmean and CI values more than 3% (P = 0.001, 0.022 and 0.001) in the supine and standing position. During hypocapnia, CI rose more than 20% from supine to seated and standing (P = 0.0001) with a 4.5% decrease in cerebral rSO2 (P = 0.001) and a decrease of Vmax - Vmean more than 24% in all positions (P = 0.001). Hypercapnia increased cerebral rSO2 more than 17% (P = 0.001), Vmax - Vmean more than 30% (P = 0.001) with no changes in CI. After a Valsalva manoeuvre, rSO2 decreased more than 3% in the right hemisphere in the upright position (P = 0.001). Vmax - Vmean decreased more than 10% (P = 0.001) with no changes in CI. CONCLUSION: CBF changes in response to cerebral vasoconstriction and vasodilatation were detected with rSO2 and transcranial Doppler in healthy volunteers during cardiac preload and in different body positions. Acute hypercapnia had a greater effect on recorded brain parameters than hypocapnia.

Estimation of pulsatile cerebral arterial blood volume based on transcranial doppler signals.

OBJECTIVE: Mathematical modeling of cerebral hemodynamics by descriptive equations can estimate the underlying pulsatile component of cerebral arterial blood volume (CaBV). This way, clinical monitoring of changes in cerebral compartmental compliances becomes possible. Our aim is to validate the most adequate method of CaBV estimation in neurocritical care. APPROACH: We retrospectively reviewed patients with severe traumatic brain injury (TBI) [admitted from 1992-2012] and continuous transcranial Doppler (TCD) monitoring of cerebral blood flow velocity (FV) displaying either plateau waves of intracranial pressure (ICP), episodes of controlled, mild hypocapnia, or vasopressor-induced increases in arterial blood pressure (ABP). Each cohort was analyzed with continuous flow forward (CFF, pulsatile blood inflow and steady blood outflow) or pulsatile flow forward (PFF, both blood inflow and outflow are pulsatile) modeling approaches for estimating the pulse component of CaBV. Spectral pulsatility index (sPI, the first harmonic of the FV pulse/mean FV) can be estimated using the compliance of the vascular bed (Ca) and the cerebrovascular resistance (CVR - here, Ra). We compared three possible methods of assessing Ca (C1: the CFF model, C2 and C3: the PFF models based on ABP or cerebral perfusion pressure (CPP) pulsations, respectively) and combined them with three possible methods of assessing Ra (Ra1= ABP/FV, Ra2= the resistance area product, and Ra3= CPP/FV). Linear regression techniques were applied to describe the strength of each CaBV estimator (a combination of Ca and Ra) against sPI. MAIN RESULTS: The combination of C1 and Ra3 (PI_C1Ra3) was the superior descriptor of CaBV as approximated by sPI for both the plateau waves and the hypocapnia cohorts (r = 0.915 and r = 0.955, respectively). The combination of C1 and Ra1 (PI_C1Ra1) was nearly as robust in the vasopressors cohort (r = 0.938 and r = 0.931, respectively). SIGNIFICANCE: TCD-based estimation of CaBV pulsations seems to be feasible when employing the CFF modeling approach.

Relationship Between Brain Pulsatility and Cerebral Perfusion Pressure: Replicated Validation Using Different Drivers of CPP Change.

BACKGROUND: Determination of relationships between transcranial Doppler (TCD)-based spectral pulsatility index (sPI) and pulse amplitude (AMP) of intracranial pressure (ICP) in 2 groups of severe traumatic brain injury (TBI) patients (a) displaying plateau waves and (b) with unstable mean arterial pressure (MAP). METHODS: We retrospectively reviewed patients with severe TBI and continuous TCD monitoring displaying either plateau waves or unstable MAP from 1992 to 1998. We utilized linear and nonlinear regression techniques to describe both cohorts: cerebral perfusion pressure (CPP) versus AMP, CPP versus sPI, mean ICP versus ICP AMP, mean ICP versus sPI, and AMP versus sPI. RESULTS: Nonlinear regression techniques were employed to analyze the relationships with CPP. In plateau wave and unstable MAP patients, CPP versus sPI displayed an inverse nonlinear relationship (R 2 = 0.820 vs. R 2 = 0.610, respectively), with the CPP versus sPI relationship best modeled by the following function in both cases: PI = a + (b/CPP). Similarly, in both groups, CPP versus AMP displayed an inverse nonlinear relationship (R 2 = 0.610 vs. R 2 = 0.360, respectively). Positive linear correlations were displayed in both the plateau wave and unstable MAP cohorts between: ICP versus AMP, ICP versus sPI, AMP versus sPI. CONCLUSIONS: There is an inverse relationship through nonlinear regression between CPP versus AMP and CPP versus sPI display. This provides evidence to support a previously-proposed model of TCD pulsatility index. ICP shows a positive linear correlation with AMP and sPI, which is also established between AMP and sPI.

Laryngeal Mask Ventilation During Lumbar Spine Neurosurgery in Knee-Chest Position is Feasible.

BACKGROUND: This study describes our experience with laryngeal mask (LM) inserted after anesthetic induction in patients already in knee-chest position for lumbar neurosurgery. METHODS: Airway management (need for LM repositioning, orotracheal intubation because of failed LM insertion), anticipated difficult airway, and airway complications were registered. Statistics were compared between groups with the t test or the χ test, as appropriate. RESULTS: A total of 358 cases were reviewed from 2008 to 2013. Tracheal intubation was performed in 108 patients and LM was chosen for 250 patients (69.8%). Intubated patients had a higher mean age and rate of anticipated difficult airway; duration of surgery was longer (P<0.001, all comparisons). LM insertion and anesthetic induction proved effective in 97.2% of the LM-ventilated patients; 7 patients (2.8%) were intubated because of persistent leakage. Incidences with airway management were resolved without compromising patient safety. CONCLUSION: LM airway management during lumbar neurosurgery in knee-chest position is feasible for selected patients when the anesthetist is experienced.

Experience with "Fast track" postoperative care after deep brain stimulation surgery.

BACKGROUND: A 24-h-stay in the post-anesthesia care unit (PACU) is a common postoperative procedure after deep brain stimulation surgery (DBS). OBJECTIVE: We evaluated the impact of a fast-track (FT) postoperative care protocol. METHODS: An analysis was performed on all patients who underwent DBS in 2 periods: 2006, overnight monitored care (OMC group), and 2007-2013, FT care (FT group). RESULTS: The study included 19 patients in OMC and 95 patients in FT. Intraoperative complications occurred in 26.3% patients in OMC vs. 35.8% in FT. Post-operatively, one patient in OMC developed hemiparesis, and agitation in 2 patients. In FT, two patients with intraoperative hemiparesis were transferred to the ICU. While on the ward, 3 patients from the FT developed hemiparesis, two of them 48h after the procedure. Thirty eight percent of FT had an MRI scan, while the remaining 62% and all patients of OMC had a CT-scan performed on their transfer to the ward. One patient in OMC had a subthalamic hematoma. Two patients in FT had a pallidal hematoma, and 3 a bleeding along the electrode. CONCLUSIONS: A FT discharge protocol is a safe postoperative care after DBS. There are a small percentage of complications after DBS, which mainly occur within the first 6h.

ProSeal Laryngeal Mask Airway Attenuates Systemic and Cerebral Hemodynamic Response During Awakening of Neurosurgical Patients: A Randomized Clinical Trial.

BACKGROUND: Extubation and emergence from anesthesia may lead to systemic and cerebral hemodynamic changes that endanger neurosurgical patients. We aimed to compare systemic and cerebral hemodynamic variables and cough incidence in neurosurgery patients emerging from general anesthesia with the standard procedure (endotracheal tube [ETT] extubation) or after replacement of the ETT with a laryngeal mask airway (LMA). MATERIALS AND METHODS: Forty-two patients undergoing supratentorial craniotomy under general anesthesia were included in a randomized open-label parallel trial. Patients were randomized (sealed envelopes labeled with software-generated randomized numbers) to awaken with the ETT in place or after its replacement with a ProSeal LMA. We recorded mean arterial pressure as the primary endpoint and heart rate, middle cerebral artery flow velocity, regional cerebral oxygen saturation, norepinephrine plasma concentrations, and coughing. RESULTS: No differences were found between groups at baseline. All hemodynamic variables increased significantly from baseline in both groups during emergence. The ETT group had significantly higher mean arterial pressure (11.9 mm Hg; 95% confidence interval [CI], 2.1-21.8 mm Hg) (P=0.017), heart rate (7.2 beats/min; 95% CI, 0.7-13.7 beats/min) (P=0.03), and rate-pressure product (1045.4; 95% CI, 440.8-1650) (P=0.001). Antihypertensive medication was administered to more ETT-group patients than LMA-group patients (9 [42.9%] vs. 3 [14.3%] patients, respectively; P=0.04). The percent increase in regional cerebral oxygen saturation was greater in the ETT group by 26.1% (95% CI, 9.1%-43.2%) (P=0.002), but no between-group differences were found in MCA flow velocity. Norepinephrine plasma concentrations rose in both groups between baseline and the end of emergence: LMA: from 87.5±7.1 to 125.6±17.3 pg/mL; and ETT: from 118.1±14.1 to 158.1±24.7 pg/mL (P=0.007). The differences between groups were not significant. The incidence of cough was higher in the ETT group (87.5%) than in the LMA group (9.5%) (P<0.001). CONCLUSIONS: Replacing the ETT with the LMA before neurosurgical patients emerge from anesthesia results in a more favorable hemodynamic profile, less cerebral hyperemia, and a lower incidence of cough.

[Diagnostic yield and postoperative management of patients submitted to brain biopsy in a university hospital]. / Eficacia diagnóstica y manejo posoperatorio de los pacientes sometidos a biopsia cerebral en un hospital universitario.

OBJECTIVE: To assess the diagnostic yield and the incidence of perioperative complications in patients undergoing an open or closed cerebral biopsy and to determine the length of intensive care monitoring, for early diagnosis and fast management of perioperative complications. MATERIAL AND METHOD: This was a retrospective analysis of all the patients that underwent brain biopsy between January 2006 and July 2012. We recorded demographic data, comorbidities, modality of biopsy, intraoperative clinical data, histological results, computed tomography scanning findings and occurrence, and type of perioperative complications and moment of appearance. RESULTS: Seventy-six brain biopsies in 75 consecutive patients (51 closed and 25 open) were analysed. Diagnostic yield was 98% for closed biopsies and 96% for open biopsies. Mortality related to the procedures was 3.9 and 4%, respectively. The incidence of major complications was 3.9% for closed biopsies and 8% for open biopsies; half of these appeared within the first 24 postoperative hours, during patient stay in the Intensive Care Unit. Age was the only risk factor for complications (P=.04) in our study. No differences in morbimortality were found between the studied groups. CONCLUSIONS: Diagnostic yield was very high in our series. Because the importance of early diagnosis of complications for preventing long-term sequelae, we recommend overnight hospital stay for observation after open or closed brain biopsy.

Critical closing pressure during intracranial pressure plateau waves.

BACKGROUND: Critical closing pressure (CCP) denotes a threshold of arterial blood pressure (ABP) below which brain vessels collapse and cerebral blood flow ceases. Theoretically, CCP is the sum of intracranial pressure (ICP) and arterial wall tension (WT). The aim of this study is to describe the behavior of CCP and WT during spontaneous increases of ICP, termed plateau waves, in order to quantify ischemic risk. METHODS: To calculate CCP, we used a recently introduced multi-parameter method (CCPm) which is based on the modulus of cerebrovascular impedance. CCP is derived from cerebral perfusion pressure, ABP, transcranial Doppler estimators of cerebrovascular resistance and compliance, and heart rate. Arterial WT was estimated as CCPm-ICP. The clinical data included recordings of ABP, ICP, and transcranial Doppler-based blood flow velocity from 38 events of ICP plateau waves, recorded in 20 patients after head injury. RESULTS: Overall, CCPm increased significantly from 51.89 ± 8.76 mmHg at baseline ICP to 63.31 ± 10.83 mmHg at the top of the plateau waves (mean ± SD; p < 0.001). Cerebral arterial WT decreased significantly during plateau waves by 34.3% (p < 0.001), confirming their vasodilatatory origin. CCPm did not exhibit the non-physiologic negative values that have been seen with traditional methods for calculation, therefore rendered a more plausible estimation of CCP. CONCLUSIONS: Rising CCP during plateau waves increases the probability of cerebral vascular collapse and zero flow when the difference: ABP-CCP (the "collapsing margin") becomes zero or negative.

Reliability of the blood flow velocity pulsatility index for assessment of intracranial and cerebral perfusion pressures in head-injured patients.

BACKGROUND: It has been postulated that the Gosling pulsatility index (PI) assessed with transcranial Doppler (TCD) has a diagnostic value for noninvasive estimation of intracranial pressure (ICP) and cerebral perfusion pressure (CPP). OBJECTIVE: To revisit this hypothesis with the use of a database of digitally stored signals from a cohort of head-injured patients. METHODS: We analyzed prospectively collected data of patients admitted to the Cambridge Neuroscience critical care unit who had continuous recordings of arterial blood pressure, ICP, and cerebral blood flow velocities (FVs) using TCD. PI was calculated (FVsys-FVdia)/FVmean over each recording session. Statistical analysis was performed using Spearman rank correlation, receiver-operator-characteristics methods, and modeling of a nonlinear PI-ICP/CPP graph. RESULTS: Seven hundred sixty-two recorded daily sessions from 290 patients were analyzed with a total recording time of 499.9 hours. The correlation between PI and ICP was 0.31 (P<.001) and for PI and CPP -0.41 (P<.001). The 95% prediction interval of ICP values for a given PI was more than ±15 mm Hg and for CPP more than ±25 mm Hg. The diagnostic value of PI to assess ICP area under the curve ranged from 0.62 (ICP>15 mm Hg) to 0.74 (ICP>35 mm Hg). For CPP, the area under the curve ranged from 0.68 (CPP<70 mm Hg) to 0.81 (CPP<50 mm Hg). Probability charts for elevated ICP/lowered CPP depending on PI were created. CONCLUSION: Overall, the value of TCD-PI to assess ICP and CPP noninvasively is very limited. However, extreme values of PI can still potentially be used in support of a decision for invasive ICP monitoring.

The relationship between cerebral blood flow autoregulation and cerebrovascular pressure reactivity after traumatic brain injury.

BACKGROUND: Cerebrovascular pressure reactivity is the principal mechanism of cerebral autoregulation. Assessment of cerebral autoregulation can be performed by using the mean flow index (Mx) based on transcranial Doppler ultrasonography. Cerebrovascular pressure reactivity can be monitored by using the pressure reactivity index (PRx), which is based on intracranial pressure monitoring. From a practical point of view, PRx can be monitored continuously, whereas Mx can only be monitored in short periods when transcranial Doppler probes can be applied. OBJECTIVE: To assess to what degree impairment in pressure reactivity (PRx) is associated with impairment in cerebral autoregulation (Mx). METHODS: A database of 345 patients with traumatic brain injury was screened for data availability including simultaneous Mx and PRx monitoring. Absolute differences, temporal changes, and association with outcome of the 2 indices were analyzed. RESULTS: A total of 486 recording sessions obtained from 201 patients were available for analysis. Overall a moderate correlation between Mx and PRx was found (r = 0.58; P < .001). The area under the receiver operator characteristic curve designed to detect the ability of PRx to predict impaired cerebral autoregulation was 0.700 (95% confidence interval: 0.607-0.880). Discrepancies between Mx and PRx were most pronounced at an intracranial pressure of 30 mm Hg and they were significantly larger for patients who died (P = .026). Both Mx and PRx were significantly lower at day 1 postadmission in patients who survived than in those who died (P < .01). CONCLUSION: There is moderate agreement between Mx and PRx. Discrepancies between Mx and PRx are particularly significant in patients with sustained intracranial hypertension. However, for clinical purposes, there is only limited interchangeability between indices.

Ultrasound-guided popliteal sciatic block with a single injection at the sciatic division results in faster block onset than the classical nerve stimulator technique.

BACKGROUND: For successful, fast-onset sciatic popliteal block (SPB), either a single injection above the division of the sciatic nerve, or 2 injections to block the tibial nerve (TN) and common peroneal nerve (CPN) separately have been recommended. In this study, we compared the traditional nerve stimulator (NS)-guided SPB above the division of the sciatic nerve with the ultrasound (US)-guided block with single injection of local anesthetic (LA) between the TN and CPN at the level of their division. We hypothesized that US-SPB with a single injection between TN and CPN would result in faster block onset than a single-injection NS-SPB. METHODS: Fifty-two patients were randomized to receive either an NS-SPB or a US-SPB. For both blocks, a single injection of 20 mL mepivacaine 1.5% was given using an automated injection pump while controlling for injection force. For NS-SPB, a TN response below 0.5 mA was sought 7 cm above the popliteal fossa crease (and proximal to the divergence of the TN and peroneal nerves). For US-SPB, the injection was made after a US-guided needle was inserted between the TN and CPN at the level of their separation. Motor response was not actively sought but registered if present. The location and spread of LA were evaluated by US in both groups. Onset of motor and sensory blocks was serially assessed in 5-minute intervals in the TN and CPN divisions and compared between the groups. RESULTS: All patients in both groups had successful block at 30 minutes after the injection, defined as sensory block to allow surgery without supplementation. A higher proportion of patients in the US-SPB group had a complete sensory (80% vs 4%, P < 0.001) and motor block (60% vs 8%, P < 0.001), defined as anesthesia and paralysis in all nerve territories, at 15 minutes after injection. US signs of intraepineural injection were present in 19 patients (73%) in the NS-SPB group and 25 patients (100%) in the US-SPB group (P < 0.001). CONCLUSIONS: A single injection of LA in US-SPB with needle insertion at the separation of the TN and CPN results in a similar success rate at 30 minutes; however, more patients in the US-SPB group than in the NS-SPB group had complete block at 15 minutes.

Transcranial Doppler pulsatility index: what it is and what it isn't.

BACKGROUND: Transcranial Doppler (TCD) pulsatility index (PI) has traditionally been interpreted as a descriptor of distal cerebrovascular resistance (CVR). We sought to evaluate the relationship between PI and CVR in situations, where CVR increases (mild hypocapnia) and decreases (plateau waves of intracranial pressure-ICP). METHODS: Recordings from patients with head-injury undergoing monitoring of arterial blood pressure (ABP), ICP, cerebral perfusion pressure (CPP), and TCD assessed cerebral blood flow velocities (FV) were analyzed. The Gosling pulsatility index (PI) was compared between baseline and ICP plateau waves (n = 20 patients) or short term (30-60 min) hypocapnia (n = 31). In addition, a modeling study was conducted with the "spectral" PI (calculated using fundamental harmonic of FV) resulting in a theoretical formula expressing the dependence of PI on balance of cerebrovascular impedances. RESULTS: PI increased significantly (p < 0.001) while CVR decreased (p < 0.001) during plateau waves. During hypocapnia PI and CVR increased (p < 0.001). The modeling formula explained more than 65% of the variability of Gosling PI and 90% of the variability of the "spectral" PI (R = 0.81 and R = 0.95, respectively). CONCLUSION: TCD pulsatility index can be easily and quickly assessed but is usually misinterpreted as a descriptor of CVR. The mathematical model presents a complex relationship between PI and multiple haemodynamic variables.

Pressure inside the neuroendoscope: correlation with epidural intracranial pressure during neuroendoscopic procedures.

BACKGROUND: During neuroendoscopic procedures, pressure inside the neuroendoscope (PIN) monitored through the irrigation channel correlates with the occurrence of postoperative complications. Our aim was to analyze the reliability of PIN measurement as a surrogate for intracranial pressure (ICP) by comparing PIN with simultaneously epidural ICP measurement as the standard. METHODS: Seventeen consecutive patients undergoing neuroendoscopy were studied prospectively. Type and length of procedure and PIN and epidural ICP values during neuroendoscopy were recorded. Lin's concordance coefficient and Bland-Altman analysis of agreement were used to assess correspondence between the 2 systems. RESULTS: A consistent relation between PIN and epidural ICP waveforms was observed during neuroendoscopic navigation. A strong Pearson correlation between PIN and epidural ICP data were found in 15 patients. Epidural ICP values were systematically higher than PIN values in 15 patients. Lin concordance coefficients showed moderate global agreement between the 2 methods, at 0.58 (95% confidence interval, 0.577-0.592). In 6 cases (35.2%) concordance was good according to this analysis, in 7 cases (41.2%) agreement was moderate/fair, and in 4 cases (23.5%) agreement was poor. The Bland-Altman analysis of patient data showed good agreement between the PIN and epidural ICP measurements for most patients, although discrepancies were greater at higher ICP values for 11 patients. Bland-Altman analysis of the complete dataset, after the normalization of individual's measurements, showed good overall agreement. CONCLUSIONS: PIN measurement seems useful for evaluating ICP changes related to neuroendoscopic procedures and seems to be more consistent than epidural ICP at high pressures.