Incidence, therapy, and outcome in the management of chronic subdural hematoma in Switzerland: a population-based multicenter cohort study.

Background: Chronic subdural hematoma (cSDH) is a disease affecting mainly elderly individuals. The reported incidence ranges from 2.0/100,000 to 58 per 100,000 person-years when only considering patients who are over 70 years old, with an overall incidence of 8.2-14.0 per 100,000 persons. Due to an estimated doubling of the population above 65 years old between 2000 and 2030, cSDH will become an even more significant concern. To gain an overview of cSDH hospital admission rates, treatment, and outcome, we performed this multicenter national cohort study of patients requiring surgical treatment of cSDH. Methods: A multicenter cohort study included patients treated in 2013 in a Swiss center accredited for residency. Demographics, medical history, symptoms, and medication were recorded. Imaging at admission was evaluated, and therapy was divided into burr hole craniostomy (BHC), twist drill craniostomy (TDC), and craniotomy. Patients' outcomes were dichotomized into good (mRS, 0-3) and poor (mRS, 4-6) outcomes. A two-sided t-test for unpaired variables was performed, while a chi-square test was performed for categorical variables, and a p-value of <0.05 was considered to be statistically significant. Results: A total of 663 patients were included. The median age was 76 years, and the overall incidence rate was 8.2/100,000. With age, the incidence rate increased to 64.2/100,000 in patients aged 80-89 years. The most prevalent symptoms were gait disturbance in 362 (58.6%) of patients, headache in 286 (46.4%), and focal neurological deficits in 252 (40.7%). CSDH distribution was unilateral in 478 (72.1%) patients, while 185 presented a bilateral hematoma with no difference in the outcome. BHC was the most performed procedure for 758 (97.3%) evacuations. CSDH recurrence was noted in 104 patients (20.1%). A good outcome was seen in almost 81% of patients. Factors associated with poor outcomes were age, GCS and mRS on admission, and the occurrence of multiple deficits present at the diagnosis of the cSDH. Conclusion: As the first multicenter national cohort-based study analyzing the disease burden of cSDH, our study reveals that the hospital admission rate of cSDH was 8.2/100,000, while with age, it rose to 64.2/100,000. A good outcome was seen in 81% of patients, who maintained the same quality of life as before the surgery. However, the mortality rate was 4%.

Supratentorial cerebrospinal fluid diversion using image-guided trigonal ventriculostomy during retrosigmoid craniotomy for cerebellopontine angle tumors.

Background: Cerebellar contusion, swelling and herniation is frequently encoutered upon durotomy in patients undergoing retrosigmoid craniotomy for cerebellopontine angle (CPA) tumors, despite using standard methods to obtain adequate cerebellar relaxation. Objective: The aim of this study is to report an alternative cerebrospinal fluid (CSF)-diversion method using image-guided ipsilateral trigonal ventriculostomy. Methods: Single-center retro- and prospective cohort study of n = 62 patients undergoing above-mentioned technique. Prior durotomy, CSF-diversion was performed to the point where the posterior fossa dura was visibly pulsatile. Outcome assessment consisted of the surgeon's intra- and postoperative clinical observations, and postoperative radiological imaging. Results: Fifty-two out of n = 62 (84%) cases were eligible for analysis. The surgeons consistently reported successful ventricular puncture and a pulsatile dura prior durotomy without cerebellar contusion, swelling or herniation through the dural incision in n = 51/52 (98%) cases. Forty-nine out of n = 52 (94%) catheters were placed correctly within the first attempt, with the majority of catheter tips (n = 50, 96%) located intraventricularly (grade 1 or 2). In n = 4/52 (8%) patients, postoperative imaging revealed evidence of a ventriculostomy-related hemorrhage (VRH) associated with an intracerebral hemorrhage [n = 2/52 (4%)] or an isolated intraventricular hemorrhage [n = 2/52 (4%)]. However, these hemorrhagic complications were not associated with neurological symptoms, surgical interventions or postoperative hydrocephalus. None of the evaluated patients demonstrated radiological signs of upward transtentorial herniation. Conclusion: The method described above efficiently allows CSF-diversion prior durotomy to reduce cerebellar pressure during retrosigmoid approach for CPA tumors. However, there is an inherent risk of subclinical supratentorial hemorrhagic complications.

Wound closure with a mesh and liquid tissue adhesive (Dermabond Prineo) system in pediatric spine surgery: a prospective single-center cohort study incorporating parent-reported outcome measures.

OBJECTIVE: Wound healing can be challenging in children undergoing spine surgery for neurological conditions due to a high risk of cerebrospinal fluid (CSF) leakage and wound infection. In adults, use of the Dermabond Prineo (DP) skin closure system, which consists of both tissue adhesive glue and a self-adhesive mesh, for wound closure of medium-length surgical incisions has been reported. The aim of this study was to investigate the efficiency and cosmetic outcome of DP for wound closure in extra- and intradural pediatric neurological spine surgery. METHODS: In this prospective cohort study, 47 children underwent 50 spine procedures using DP for wound closure between 2018 and 2022 at a single institution. Patient demographic and surgical data were collected. The primary outcome was revision surgery for wound healing disorders, while secondary outcomes were infections, minor wound healing disorders, and both physician and parental satisfaction (parent-reported outcome measures [PROMs]) at last follow-up. RESULTS: Among 50 spinal (45 intra- and 5 extradural) interventions, 1 patient (2%) underwent revision surgery for a cutaneous CSF fistula and pseudomeningocele. Minor wound healing disorders occurred after 16 surgeries, which did not require surgical wound revision and resolved completely. No allergic reactions to DP or surgical site infections within 30 days were observed. The parents and the medical team described wound care as significantly facilitated since wound dressing changes were not needed. Three families (6.4%) encountered difficulties in wound care, and 46 (97.9%) were satisfied with DP. The cosmetic outcome based on PROMs was excellent, with a mean score of 8 (IQR 2) on a scale from 1 to 10. At long-term follow-up, a mean of 11.3 ± 10.7 months after surgery, physicians rated the cosmetic outcome on the visual analog scale (median score 9, IQR 1) and Hollander scale (median score 6, IQR 1). The outcomes were similar among the different pathologies and age groups and did not differ in patients with and without syndromic malformations. CONCLUSIONS: The application of DP is simple, enables good patient comfort, facilitates both professional and parental wound care, and leads to excellent cosmetic results. DP possibly aids in the reduction of postoperative CSF leakage and infections after pediatric neurological spine surgery.

Perioperative Complications of Patients with SARS-CoV-2 Infection in Neurosurgery.

BACKGROUND: The outbreak of coronavirus disease 2019 (COVID-19) has been rapidly evolving, resulting in a pandemic, with 270,031,622 infections according to the World Health Organization. Patients suffering from COVID-19 have also been described to suffer from neurologic and coagulopathic symptoms apart from the better-known flu-like symptoms. Some studies showed that patients suffering from COVID-19 were likely to developed intracranial hemorrhages. To our knowledge, only a few studies have investigated postoperative complications in COVID-19-positive neurosurgical patients and investigated the perioperative complications, either thrombotic or hemorrhagic, in patients with SARS-CoV-2 undergoing a neurosurgical intervention. METHODS: We conducted a retrospective cohort study including patients from March 2020 to March 2021 undergoing neurosurgical interventions and suffering from COVID-19. Our primary outcome parameter was a hemorrhagic or thrombotic complication within 30 days after surgery. These outcomes were compared to those for a COVID-19-negative cohort of patients using propensity score matching. RESULTS: We included ten COVID-19-positive patients with a mean age of 56.00 (±14.91) years. Twelve postoperative complications occurred in five patients. Three thrombotic complications (30%) were observed, with two cerebral sinus vein thromboses and one pulmonary embolus. Two patients suffered from a postoperative hemorrhagic complication (20%). The mean postoperative GCS was 14.30 (±1.57). COVID-19-positive patients showed a significantly higher rate of overall postoperative complications ((6 (60.0%) vs. 10 (19.2%), p = 0.021), thrombotic complications (3 (30.0%) vs. 1 (1.9%), p = 0.009), and mortality (2 (20.0%) vs. 0 (0.0%), p = 0.021) compared to the matched cohort of COVID-19-negative patients, treated at our institute before the SARS-CoV-2 pandemic. CONCLUSION: Patients undergoing neurosurgical operations with concomitant COVID-19 infection have higher rates of perioperative complications.

Frontoethmoidal Osteoma with Secondary Intradural Mucocele Extension Causing Frontal Lobe Syndrome and Pneumocephalus: Case Report and Review of Literature.

BACKGROUND: Paranasal sinus osteoma is a common, asymptomatic, histologically benign, slow-growing tumor. However, it can give rise to secondary pathologies such as a mucocele in about 50% of the cases. Rarely, intracranial and orbital extension is present, leading to rhinoliquorrhea, pneumocephalus, or neurologic and visual impairment, which might be potentially life-threatening. CASE DESCRIPTION: A 49-year-old man presented with an acute frontal lobe syndrome and rhinoliquorrhea. Cranial magnetic resonance tomography showed a suspected frontoethmoidal osteoma with a mucocele expanding intradurally into the left frontal lobe. It was accompanied by pneumocephalus and showed communication with the left lateral ventricle. Through a bifrontal craniotomy, in toto resection of the frontoethmoidal bony tumor and the intradural mucocele was performed, while thereafter the frontal sinus was cranialized using a pedunculated periosteal flap. Postoperative recovery was uneventful with complete resolution of the tension pneumocephalus and rhinoliquorrhea and led to an improvement of the frontal lobe syndrome. CONCLUSIONS: We present a rare case of pneumocephalus caused by a frontoethmoidal osteoma associated with an intradural mucocele. A review of the literature, focusing on the surgical strategies in such cases, is provided.

Continuous Autoregulatory Indices Derived from Multi-Modal Monitoring: Each One Is Not Like the Other.

We assess the relationships between various continuous measures of autoregulatory capacity in a cohort of adults with traumatic brain injury (TBI). We assessed relationships between autoregulatory indices derived from intracranial pressure (ICP: PRx, PAx, RAC), transcranial Doppler (TCD: Mx, Sx, Dx), brain tissue-oxygenation (ORx), and spatially resolved near infrared spectroscopy (NIRS resolved: TOx, THx). Relationships between indices were assessed using Pearson correlation coefficient, Friedman test, principal component analysis (PCA), agglomerative hierarchal clustering (AHC) and k-means cluster analysis (KMCA). All analytic techniques were repeated for a range of temporal resolutions of data, including minute-by-minute averages, moving means of 30 samples, and grand mean for each patient. Thirty-seven patients were studied. The PRx displayed strong association with PAx/RAC across all the analytical techniques: Pearson correlation (r = 0.682/r = 0.677, p < 0.0001), PCA, AHC, and KMCA in the grand mean data sheet. Most TCD-based indices (Mx, Dx) were correlated and co-clustered on PCA, AHC, and KMCA. The Sx was found to be more closely associated with ICP-derived indices on Pearson correlation, PCA, AHC, and KMCA. The NIRS indices displayed variable correlation with each other and with indices derived from ICP and TCD signals. Of interest, TOx and THx co-cluster with ICP-based indices on PCA and AHC. The ORx failed to display any meaningful correlations with other indices in neither of the analytical method used. Thirty-minute moving average and minute-by-minute data set displayed similar results across all the methods. The RAC, Mx, and Sx were the strongest predictors of outcome at six months. Continuously updating autoregulatory indices are not all correlated with one another. Caution must be advised when utilizing less commonly described autoregulation indices (i.e., ORx) for the clinical assessment of autoregulatory capacity, because they appear to not be related to commonly measured/establish indices, such as PRx. Further prospective validation is required.

Safety, efficacy, and cost of surgery for patients with unruptured aneurysms deemed unsuitable for endovascular therapy.

BACKGROUND: Open surgery is a frequent option given to patients with unruptured intracranial aneurysms (UIAs) unsuitable for endovascular repair. Since the risk of rupture of UIAs is generally low, we determined whether the risks and costs of surgery in this patient subset are warranted. METHODS: The safety, efficacy, and costs of minimally invasive surgery by minicraniotomy were evaluated in 102 consecutive patients with anterior circulation UIAs deemed unsuitable for endovascular repair by an interdisciplinary conference of surgeons and neurointerventionalists. Data from 107 UIA patients treated by endovascular means in the same period were used as the standard. RESULTS: Surgical patients comprised a different subset of aneurysms, with more MCA and fewer paraophthalmic aneurysms (54 vs. 6, p < 0.0001 and 4 vs. 60, p < 0.0001, for minicraniotomy and endovascular, respectively). However, surgery incurred shorter anesthesia time (197.7 vs. 149.3 min, p < 0.0001), higher rates of complete aneurysm obliteration (94.57 vs. 66.67 %, p < 0.0001), and lower overall hospital costs ($8,287 CAD vs. $17,732 CAD, p < 0.0001) than the endovascular cohort. There were no treatment-related surgical deaths, but one patient had an mRS of 3 after 6 months due to temporal lobe epilepsy and memory problems. This compared favorably with the endovascular cohort in which two patients died due to treatment (mRS = 6) and one suffered a severe stroke (mRS = 5 at 6 months). CONCLUSIONS: For patients counseled to undergo treatment but have UIAs unsuitable for endovascular repair, surgery is safe, effective, and cost-efficient.

Postoperative Copeptin Concentration Predicts Diabetes Insipidus After Pituitary Surgery.

CONTEXT: Copeptin is a stable surrogate marker of vasopressin release; the peptides are stoichiometrically secreted from the neurohypophysis due to elevated plasma osmolality or nonosmotic stress. We hypothesized that following stress from pituitary surgery, patients with neurohypophyseal damage and eventual diabetes insipidus (DI) would not exhibit the expected pronounced copeptin elevation. OBJECTIVE: The objective was to evaluate copeptin's accuracy to predict DI following pituitary surgery. DESIGN: This was a prospective multicenter observational cohort study. SETTING: Three Swiss or Canadian referral centers were used. PATIENTS: Consecutive pituitary surgery patients were included. MEASUREMENTS: Copeptin was measured postoperatively daily until discharge. Logistic regression models and diagnostic performance measures were calculated to assess relationships of postoperative copeptin levels and DI. RESULTS: Of 205 patients, 50 (24.4%) developed postoperative DI. Post-surgically, median [25th-75th percentile] copeptin levels were significantly lower in patients developing DI vs those not showing this complication: 2.9 [1.9-7.9] pmol/L vs 10.8 [5.2-30.4] pmol/L; P < .001. Logistic regression analysis revealed strong association between postoperative copeptin concentrations and DI even after considering known predisposing factors for DI: adjusted odds ratio (95% confidence interval) 1.41 (1.16-1.73). DI was seen in 22/27 patients with copeptin <2.5 pmol/L (positive predictive value, 81%; specificity, 97%), but only 1/40 with copeptin >30 pmol/L (negative predictive value, 95%; sensitivity, 94%) on postoperative day 1. LIMITATIONS: Lack of standardized DI diagnostic criteria; postoperative blood samples for copeptin obtained during everyday care vs at fixed time points. CONCLUSIONS: In patients undergoing pituitary procedures, low copeptin levels despite surgical stress reflect postoperative DI, whereas high levels virtually exclude it. Copeptin therefore may become a novel tool for early goal-directed management of postoperative DI.

Continuous time-domain monitoring of cerebral autoregulation in neurocritical care.

Integration of various brain signals can be used to determine cerebral autoregulation in neurocritical care patients to guide clinical management and to predict outcome. In this review, we will discuss current methodology of multimodal brain monitoring focusing on secondary 'reactivity indices' derived from various brain signals which are based on a 'moving correlation coefficient'. This algorithm was developed in order to analyze in a time dependent manner the degree of correlation between two factors within a time series where the number of paired observations is large. Of the various primary neuromonitoring sources which can be used to calculate reactivity indices, we will focus in this review on indices based on transcranial Doppler (TCD), intracranial pressure (ICP), brain tissue oxygenation (PbtO2) and near infrared spectroscopy (NIRS). Furthermore, we will demonstrate how reactivity indices can show transient changes of cerebral autoregulation and can be used to optimize management of arterial blood pressure (ABP) and cerebral perfusion pressure (CPP).

Endonasal endoscopic release of a delayed tension pneumocephalus after craniofacial resection of a tumor of the anterior skull base.

Tension pneumocephalus is a rare complication that can occur after craniofacial resection of lesions of the anterior skull base. Early diagnosis is important to avoid potential serious neurologic deficits, including death. It has been associated with the perioperative placement of a lumbar drainage and with esthesioneuroblastoma. Therapy consists of evacuation of the intracranial air as well as conservative measures. Here we report a case of a patient with an ethmoidal esthesioneuroblastoma who underwent a traditional microsurgical craniofacial resection and developed a delayed epidural tension pneumocephalus. This was treated by performing an incision in the pericranial flap covering the anterior cranial base defect using an endonasal endoscopic approach. To our knowledge, this particular treatment technique has not been reported before in this context.

Sinonasal carcinomas: epidemiology, pathology, and management.

Sinonasal carcinomas are uncommon neoplasms accounting for approximately 3% to 5% of all upper respiratory tract malignancies. Sinonasal malignancies in most cases do not cause early symptoms and present in an advanced stage of disease. Exact staging necessitates a clinical and endoscopic examination with biopsy and imaging. Tumor resection using an open or endoscopic approach is usually considered the first treatment option. In general, sinonasal carcinomas are radiosensitive, so adjuvant or neoadjuvant radiation treatment may be indicated in advanced disease. Multidisciplinary surgical and medical oncologic approaches, including ablation and reconstruction, have enhanced the survival outcome over the past few decades.

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.

Near infrared spectroscopy as possible non-invasive monitor of slow vasogenic ICP waves.

We aimed to study synchronisation between ICP and near infrared spectroscopy (NIRS) variables induced by vasogenic waves of ICP during an infusion study in hydrocephalic patients and after TBI. Nineteen patients presenting with hydrocephalus underwent a diagnostic intraventricular constant-flow infusion test. The original concept of the methodology, presented in the current paper, was derived from this material. Then the method was applied in 40 TBI patients, with results reported in an observational manner. During monitoring, NIRS deoxygenated and oxygenated haemoglobin (Hb, HbO(2)) were recorded simultaneously with ICP. Moving correlation coefficient (6 min) between Hb and HbO(2) was tested as a marker of the slow vasogenic waves of ICP.During infusion studies ICP increased from 10.7 (5.1) mmHg to a plateau of 18.9 (7.6) mmHg, which was associated with an increase in the power of slow ICP waves (p = 0.000017). Fluctuations of Hb and HbO(2) at baseline negatively correlated with each other, but switched to high positive values during periods of increased ICP slow-wave activity during infusion (p < 0.001). Similar behaviour was observed in TBI patients: baseline negative Hb/HbO(2) correlation changed to positive values during peaks of ICP of vasogenic nature.Correlating changes in Hb and HbO(2) may be of use as a method of non-invasive detection of vasogenic ICP waves.

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.

Growth hormone and outcome in patients with intracerebral hemorrhage: a pilot study.

BACKGROUND: Endocrine alterations of the hypothalamic-pituitary-axis are one of the first measurable physiological changes in cerebral insults. During acute stress, human growth hormone (GH) is stimulated and has shown to have a prognostic value in various diseases. Within this pilot study, we evaluated the prognostic value of GH in patients with acute intracerebral hemorrhage (ICH). METHODS: In a prospective observational study in 40 consecutive patients with ICH, GH was measured on admission. The prognostic value of GH to predict 30-day mortality and 90-day functional outcome was assessed. Favorable functional outcome was defined as Barthel Index score >85 points and Modified Rankin Scale <3 points. RESULTS: GH levels were increased in patients who died within 30 days as compared to survivors (0.45 (IQR 0.20-1.51) vs. 1.51 (IQR 0.91-4.08) p = 0.03), and in patients with an unfavorable functional outcome as compared to patients with a favorable functional outcome after 90 days 0.28 (IQR 0.16-0.61) vs. 0.78 (IQR 0.31-1.99) p = 0.03). For mortality prediction, receiver-operating-characteristics revealed an area under the curve (AUC) on admission for GH of 0.78 (95% CI 0.60-0.96), which was in the range of the Glasgow Coma Score (GCS) (AUC 0.82 (95% CI 0.59-1.00) p = 0.80). For functional outcome prediction, GH had an AUC of 0.71 (95% CI 0.54-0.87), which was statistically not different from the GCS (AUC 0.81 (95% CI 0.68-0.94) p = 0.36). CONCLUSIONS: In our small cohort of patients with acute ICH, elevated GH level were associated with increased mortality and worse outcome. If confirmed in a larger study, GH levels may be used as an additional prognostic factor in ICH patients. (ClincalTrials.gov number NCT00390962).

The limitations of near-infrared spectroscopy to assess cerebrovascular reactivity: the role of slow frequency oscillations.

BACKGROUND: A total hemoglobin reactivity index (THx) derived from near-infrared spectroscopy (NIRS) has recently been introduced to assess cerebrovascular reactivity noninvasively. Analogously to the pressure reactivity index (PRx), THx is calculated as correlation coefficient with arterial blood pressure (ABP). However, the reliability of THx in the injured brain is uncertain. Although slow oscillations have been described in NIRS signals, their significance for assessment of autoregulation remains unclear. In the current study, we investigated the role of slow oscillations of total hemoglobin for NIRS-based cerebrovascular reactivity monitoring. METHODS: This study was based on a retrospective analysis of data that were consecutively recorded for a different project published previously. Thirty-seven patients with traumatic brain injury and admitted to Addenbrooke's Neurosciences Critical Care Unit between June 2008 and June 2009 were included. After artifact removal, we performed spectral analysis of the tissue hemoglobin index (THI, a measure of oxy- and deoxygenated hemoglobin) and intracranial pressure (ICP) signal. PRx and THx were calculated as moving correlations between ICP and ABP, and THI and ABP, respectively. The agreement between PRx and THx as a function of normalized power of slow oscillations (0.015-0.055 Hz) contained in the input signals was assessed performing between-subject and within-subject correlation analyses. Furthermore, the correlation between the THx values derived from the right and left sides was analyzed. RESULTS: The agreement between PRx and THx depended on the power of slow oscillations in the input signals. Between-subject comparisons revealed a significant correlation between THx and PRx (r = 0.80, 95% confidence interval 0.53-0.92, P < 0.01) for patients with normalized slow wave activity >0.4 in the THI signal, compared with r = 0.07 (95% confidence interval -0.40 to 0.51, P = 0.79) in the remaining files. Furthermore, within-subject comparisons suggested that THx may be used as a substitute for PRx only when there is an at least moderate agreement (r = 0.36) between the THx values derived from the right and left sides. CONCLUSIONS: Our results suggest that the NIRS-based cerebrovascular reactivity index THx can be used as a noninvasive substitute for PRx, but only during phases with sufficient slow wave power in the input signal. Furthermore, a good agreement between the THx measures on both sides seems to be a prerequisite for comparison of a global (PRx) versus the more local (THx) index. Nevertheless, noninvasive assessment of cerebrovascular reactivity may be desirable in patients without ICP monitoring and help to guide ABP management in these patients.

Changes in cerebral compartmental compliances during mild hypocapnia in patients with traumatic brain injury.

The benefit of induced hyperventilation for intracranial pressure (ICP) control after severe traumatic brain injury (TBI) is controversial. In this study, we investigated the impact of early and sustained hyperventilation on compliances of the cerebral arteries and of the cerebrospinal (CSF) compartment during mild hyperventilation in severe TBI patients. We included 27 severe TBI patients (mean 39.5 ± 3.4 years, 6 women) in whom an increase in ventilation (20% increase in respiratory minute volume) was performed during 50 min as part of a standard clinical CO(2) reactivity test. Using a new mathematical model, cerebral arterial compliance (Ca) and CSF compartment compliance (Ci) were calculated based on the analysis of ICP, arterial blood pressure, and cerebral blood flow velocity waveforms. Hyperventilation initially induced a reduction in ICP (17.5 ± 6.6 vs. 13.9 ± 6.2 mmHg; p < 0.001), which correlated with an increase in Ci (r(2) = 0.213; p = 0.015). Concomitantly, the reduction in cerebral blood flow velocities (CBFV, 74.6 ± 27.0 vs. 62.9 ± 22.9 cm/sec; p < 0.001) marginally correlated with the reduction in Ca (r(2) = 0.209; p = 0.017). During sustained hyperventilation, ICP increased (13.9 ± 6.2 vs. 15.3 ± 6.4 mmHg; p < 0.001), which correlated with a reduction in Ci (r(2) = 0.297; p = 0.003), but no significant changes in Ca were found during that period. The early reduction in Ca persisted irrespective of the duration of hyperventilation, which may contribute to the lack of clinical benefit of hyperventilation after TBI. Further studies are needed to determine whether monitoring of arterial and CSF compartment compliances may detect and prevent an adverse ischemic event during hyperventilation.

Effect of hyper- and hypocapnia on cerebral arterial compliance in normal subjects.

BACKGROUND: Changes in partial pressure of carbon dioxide (PaCO2) are associated with a decrease in cerebral blood flow (CBF) during hypocapnia and an increase in CBF during hypercapnia. However, the effects of changes in PaCO2 on cerebral arterial compliance (Ca) are unknown. METHODS: We assessed the changes in Ca in 20 normal subjects using monitoring of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV). Cerebral arterial blood volume (CaBV) was extracted from CBFV. Ca was defined as the ratio between the pulse amplitudes of CaBV (AMPCaBV ) and ABP (AMPABP). All parameters were recorded during normo-, hyper-, and hypocapnia. RESULTS: During hypocapnia, Ca was significantly lower than during normocapnia (.10±.04 vs. .17±.06; P<.001) secondary to a decrease in AMPCaBV (1.3±.4 vs. 1.9±.5; P<.001) and a concomitant increase in AMPABP (13.8±3.4 vs. 11.6±1.7 mmHg; P<.001). During hypercapnia, there was no change in Ca compared with normocapnia. Ca was inversely correlated with the cerebrovascular resistance during hypo- (R2=0.86; P<.001), and hypercapnia (R2=0.61; P<.001). CONCLUSION: Using a new mathematical model, we have described a reduction of Ca during hypocapnia. Further studies are needed to determine whether Ca may be an independent predictor of outcome in pathological conditions.