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Howells, Timothy
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Publications (10 of 15) Show all publications
Donald, R., Howells, T., Piper, I., Enblad, P., Nilsson, P., Chambers, I., . . . Stell, A. (2019). Forewarning of hypotensive events using a Bayesian artificial neural network in neurocritical care. Journal of clinical monitoring and computing, 33(1), 39-51
Open this publication in new window or tab >>Forewarning of hypotensive events using a Bayesian artificial neural network in neurocritical care
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2019 (English)In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 33, no 1, p. 39-51Article in journal (Refereed) Published
Abstract [en]

Traumatically brain injured (TBI) patients are at risk from secondary insults. Arterial hypotension, critically low blood pressure, is one of the most dangerous secondary insults and is related to poor outcome in patients. The overall aim of this study was to get proof of the concept that advanced statistical techniques (machine learning) are methods that are able to provide early warning of impending hypotensive events before they occur during neuro-critical care. A Bayesian artificial neural network (BANN) model predicting episodes of hypotension was developed using data from 104 patients selected from the BrainIT multi-center database. Arterial hypotension events were recorded and defined using the Edinburgh University Secondary Insult Grades (EUSIG) physiological adverse event scoring system. The BANN was trained on a random selection of 50% of the available patients (n = 52) and validated on the remaining cohort. A multi-center prospective pilot study (Phase 1, n = 30) was then conducted with the system running live in the clinical environment, followed by a second validation pilot study (Phase 2, n = 49). From these prospectively collected data, a final evaluation study was done on 69 of these patients with 10 patients excluded from the Phase 2 study because of insufficient or invalid data. Each data collection phase was a prospective non-interventional observational study conducted in a live clinical setting to test the data collection systems and the model performance. No prediction information was available to the clinical teams during a patient's stay in the ICU. The final cohort (n = 69), using a decision threshold of 0.4, and including false positive checks, gave a sensitivity of 39.3% (95% CI 32.9-46.1) and a specificity of 91.5% (95% CI 89.0-93.7). Using a decision threshold of 0.3, and false positive correction, gave a sensitivity of 46.6% (95% CI 40.1-53.2) and specificity of 85.6% (95% CI 82.3-88.8). With a decision threshold of 0.3, > 15min warning of patient instability can be achieved. We have shown, using advanced machine learning techniques running in a live neuro-critical care environment, that it would be possible to give neurointensive teams early warning of potential hypotensive events before they emerge, allowing closer monitoring and earlier clinical assessment in an attempt to prevent the onset of hypotension. The multi-centre clinical infrastructure developed to support the clinical studies provides a solid base for further collaborative research on data quality, false positive correction and the display of early warning data in a clinical setting.

Keywords
Traumatic brain injury, Neuro-intensive care, Bayesian prediction, Clinical study results
National Category
Anesthesiology and Intensive Care
Identifiers
urn:nbn:se:uu:diva-374422 (URN)10.1007/s10877-018-0139-y (DOI)000454820400007 ()29799079 (PubMedID)
Funder
EU, Horizon 2020, IST-2007-217049
Available from: 2019-01-29 Created: 2019-01-29 Last updated: 2019-01-29Bibliographically approved
Abu Hamdeh, S., Marklund, N., Lewén, A., Howells, T., Raininko, R., Wikström, J. & Enblad, P. (2019). Intracranial pressure elevations in diffuse axonal injury: association with nonhemorrhagic MR lesions in central mesencephalic structures. Journal of Neurosurgery, 131(2), 604-611
Open this publication in new window or tab >>Intracranial pressure elevations in diffuse axonal injury: association with nonhemorrhagic MR lesions in central mesencephalic structures
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2019 (English)In: Journal of Neurosurgery, ISSN 0022-3085, E-ISSN 1933-0693, Vol. 131, no 2, p. 604-611Article in journal (Refereed) Published
Abstract [en]

Objective: Increased intracranial pressure (ICP) in patients with severe traumatic brain injury (TBI) with diffuse axonal injury (DAI) is not well defined. This study investigated the occurrence of increased ICP and whether clinical factors and lesion localization on MRI were associated with increased ICP in patients with DAI.

Methods: Fifty-two patients with severe TBI (median age 24 years, range 9–61 years), who had undergone ICP monitoring and had DAI on MRI, as determined using T2*-weighted gradient echo, susceptibility-weighted imaging, and diffusion-weighted imaging (DWI) sequences, were enrolled. The proportion of good monitoring time (GMT) with ICP > 20 mm Hg during the first 120 hours postinjury was calculated and associations with clinical and MRI-related factors were evaluated using linear regression.

Results: All patients had episodes of ICP > 20 mm Hg. The mean proportion of GMT with ICP > 20 mm Hg was 5%, and 27% of the patients (14/52) spent more than 5% of GMT with ICP > 20 mm Hg. The Glasgow Coma Scale motor score at admission (p = 0.04) and lesions on DWI sequences in the substantia nigra and mesencephalic tegmentum (SN-T, p = 0.001) were associated with the proportion of GMT with ICP > 20 mm Hg. In multivariable linear regression, lesions on DWI sequences in SN-T (8% of GMT with ICP > 20 mm Hg, 95% CI 3%–13%, p = 0.004) and young age (−0.2% of GMT with ICP > 20 mm Hg, 95% CI −0.07% to −0.3%, p = 0.002) were associated with increased ICP.

Conclusions: Increased ICP occurs in approximately one-third of patients with severe TBI who have DAI. Age and lesions on DWI sequences in the central mesencephalon (i.e., SN-T) are associated with elevated ICP. These findings suggest that MR lesion localization may aid prediction of increased ICP in patients with DAI.

Abbreviations: ADC = apparent diffusion coefficient; CPP = cerebral perfusion pressure; DAI = diffuse axonal injury; DWI = diffusion-weighted imaging; EVD = external ventricular drain; GCS = Glasgow Coma Scale; GMT = good monitoring time; GOSE = Glasgow Outcome Scale–Extended; ICC = intraclass correlation coefficient; ICP = intracranial pressure; MAP = mean arterial blood pressure; NICU = neurointensive care unit; SN-T = substantia nigra and mesencephalic tegmentum; SWI = susceptibility-weighted imaging; TBI = traumatic brain injury; T2*GRE = T2*-weighted gradient echo.

Keywords
diffuse axonal injury, MRI, elevated ICP, intracranial pressure, TBI, traumatic brain injury, diffusion-weighted imaging, trauma
National Category
Neurology Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-362207 (URN)10.3171/2018.4.JNS18185 (DOI)000478642100036 ()30215559 (PubMedID)
Note

Correction in: JOURNAL OF NEUROSURGERY, Volume: 131, Issue: 2, Pages: 637-638, DOI: 10.3171/2018.10.JNS18185a

Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2019-10-18Bibliographically approved
Svedung-Wettervik, T., Howells, T., Hillered, L., Nilsson, P., Engquist, H., Lewén, A., . . . Rostami, E. (2019). Mild hyperventilation in traumatic brain injury - relation to cerebral energy metabolism, pressure autoregulation and clinical outcome. World Neurosurgery, 133, e567-e575
Open this publication in new window or tab >>Mild hyperventilation in traumatic brain injury - relation to cerebral energy metabolism, pressure autoregulation and clinical outcome
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2019 (English)In: World Neurosurgery, ISSN 1878-8750, E-ISSN 1878-8769, Vol. 133, p. e567-e575Article in journal (Refereed) Published
Abstract [en]

OBJECTIVE: Hyperventilation is a controversial treatment in traumatic brain injury (TBI). Prophylactic severe hyperventilation below 3.3 kPa/25 mm Hg) is generally avoided, due to the risk of cerebral ischemia. Mild hyperventilation (arterial pCO2 within 4.0-4.5 kPa/30-34 mm Hg) in cases of intracranial hypertension is commonly used, but its safety and benefits are not fully elucidated. The aim of this study was to evaluate the use of mild hyperventilation and its relation to, cerebral energy metabolism, pressure autoregulation and clinical outcome in TBI.

METHOD: This retrospective study was based on 120 patients with severe TBI treated at the neurointensive care unit, Uppsala university hospital, Sweden, 2008-2018. Data from cerebral microdialysis (glucose, pyruvate and lactate), arterial pCO2 and pressure reactivity index (PRx55-15) were analyzed for the first three days post-injury.

RESULTS: Mild hyperventilation 4.0-4.5 kPa (30-34 mm Hg) was more frequently used early and the patients were gradually normoventilated. Low pCO2 was associated with slightly higher intracranial pressure and slightly lower cerebral perfusion pressure (p-value < 0.01). There was no univariate correlation between low pCO2 and worse cerebral energy metabolism. Multiple linear regression analysis showed that mild hyperventilation was associated with lower PRx55-15 day 2 (p-value = 0.03), suggesting better pressure autoregulation. Younger age and lower ICP were also associated with lower PRx55-15.

CONCLUSIONS: These findings support the notion that mild hyperventilation is safe and may improve cerebrovascular reactivity.

Keywords
Traumatic brain injury, cerebral energy metabolism, clinical outcome, hyperventilation, neurointensive-care, pressure reactivity
National Category
Surgery
Research subject
Neurosurgery
Identifiers
urn:nbn:se:uu:diva-395237 (URN)10.1016/j.wneu.2019.09.099 (DOI)000503993700118 ()31561041 (PubMedID)
Available from: 2019-10-15 Created: 2019-10-15 Last updated: 2020-01-22Bibliographically approved
Svedung-Wettervik, T., Howells, T., Enblad, P. & Lewén, A. (2019). Temporal Neurophysiological Dynamics in Traumatic Brain Injury: Role of Pressure Reactivity and Optimal Cerebral Perfusion Pressure for Predicting Outcome. Journal of Neurotrauma, 36(11), 1818-1827
Open this publication in new window or tab >>Temporal Neurophysiological Dynamics in Traumatic Brain Injury: Role of Pressure Reactivity and Optimal Cerebral Perfusion Pressure for Predicting Outcome
2019 (English)In: Journal of Neurotrauma, ISSN 0897-7151, E-ISSN 1557-9042, Vol. 36, no 11, p. 1818-1827Article in journal (Refereed) Published
Abstract [en]

Intracranial pressure (ICP), cerebral perfusion pressure (CPP), and the pressure reactivity index (PRx) have been shown to correlate with outcome after traumatic brain injury (TBI), but their temporal evolution is less studied. Optimal CPP (CPPopt; i.e., the CPP with the lowest [optimal] PRx value) has been proposed as a dynamic, individualized CPP target. Our aim was to map the temporal course of these parameters and their relation to outcome, in particular the extent and impact of CPP insults based both on fixed CPP thresholds and on divergence from CPPopt. Data from 362 TBI patients with ICP-monitoring treated at the neurointensive care unit of Uppsala University Hospital, Uppsala, Sweden, between 2008-2016 were retrospectively analyzed for the temporal course of ICP, mean arterial blood pressure, CPP, PRx, PRx55-15 (a variant of PRx), and CPPopt the first 10 days post-injury. PRx and PRx55-15 showed significantly lower/better values for those with favorable outcome, most pronounced on Days 2 to 5. PRx55-15 gave better separation between the two groups. In the univariate analysis, CPP insults (both fixed and CPPopt-thresholds) were significantly correlated with outcome on these days. Multi-variate logistic regression showed that age, Glasgow Coma Score Motor, pupillary abnormality at admission, CPP > CPPopt, and PRx55-15 were significant independent outcome predictors. PRx was significant when PRx55-15 was excluded. High PRx55-15 and high grade of monitoring time with CPP > CPPopt, but not the traditional fixed CPP thresholds, were strong predictors for worse clinical outcome. The study supports the concept that CPPopt is an important parameter in TBI management.

Place, publisher, year, edition, pages
MARY ANN LIEBERT, INC, 2019
Keywords
cerebral autoregulation, CPPopt, neurointensive care, traumatic brain injury
National Category
Neurosciences
Identifiers
urn:nbn:se:uu:diva-387934 (URN)10.1089/neu.2018.6157 (DOI)000470007600012 ()30595128 (PubMedID)
Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-06-27Bibliographically approved
Svedung Wettervik, T., Lenell, S., Nyholm, L., Howells, T., Lewén, A. & Enblad, P. (2018). Decompressive craniectomy in traumatic brain injury: usage and clinical outcome in a single centre. Acta Neurochirurgica, 160(2), 229-237
Open this publication in new window or tab >>Decompressive craniectomy in traumatic brain injury: usage and clinical outcome in a single centre
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2018 (English)In: Acta Neurochirurgica, ISSN 0001-6268, E-ISSN 0942-0940, Vol. 160, no 2, p. 229-237Article in journal (Refereed) Published
Abstract [en]

Background: Two randomised controlled trials (RCTs) of decompressive craniectomy (DC) in traumatic brain injury (TBI) have shown poor outcome, but there are considerations of how these protocols relate to real practice. The aims of this study were to evaluate usage and outcome of DC and thiopental in a single centre.

Method: The study included all TBI patients treated at the neurointensive care unit, Akademiska sjukhuset, Uppsala, Sweden, between 2008 and 2014. Of 609 patients aged 16 years or older, 35 treated with DC and 23 treated with thiopental only were studied in particular. Background variables, intracranial pressure (ICP) measures and global outcome were analysed.

Results: Of 35 DC patients, 9 were treated stepwise with thiopental before DC, 9 were treated stepwise with no thiopental before DC and 17 were treated primarily with DC. Six patients received thiopental after DC. For 23 patients, no DC was needed after thiopental. Eighty-eight percent of our DC patients would have qualified for the DECRA study and 38% for the Rescue-ICP trial. Favourable outcome was 44% in patients treated with thiopental before DC, 56% in patients treated with DC without prior thiopental, 29% in patients treated primarily with DC and 52% in patients treated with thiopental with no DC.

Conclusions: The place for DC in TBI management must be evaluated better, and we believe it is important that future RCTs should have clearer and less permissive ICP criteria regarding when thiopental should be followed by DC and DC followed by thiopental.

Place, publisher, year, edition, pages
SPRINGER WIEN, 2018
Keywords
Traumatic brain injury, Neurointensive care, Standardised treatment protocol, Decompressive craniectomy, Thiopental
National Category
Neurology Surgery
Identifiers
urn:nbn:se:uu:diva-341558 (URN)10.1007/s00701-017-3418-3 (DOI)000419961200003 ()29234973 (PubMedID)
Available from: 2018-02-13 Created: 2018-02-13 Last updated: 2018-08-24Bibliographically approved
Rostami, E., Engquist, H., Howells, T., Johnson, U., Ronne-Engström, E., Nilsson, P., . . . Enblad, P. (2018). Early low cerebral blood flow and high cerebral lactate: prediction of delayed cerebral ischemia in subarachnoid hemorrhage. Journal of Neurosurgery, 128(6), 1762-1770
Open this publication in new window or tab >>Early low cerebral blood flow and high cerebral lactate: prediction of delayed cerebral ischemia in subarachnoid hemorrhage
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2018 (English)In: Journal of Neurosurgery, ISSN 0022-3085, E-ISSN 1933-0693, Vol. 128, no 6, p. 1762-1770Article in journal (Refereed) Published
Abstract [en]

OBJECTIVE Delayed cerebral ischemia (DCI) following subarachnoid hemorrhage (SAH) is one of the major contributors to poor outcome. It is crucial to be able to detect early signs of DCI to prevent its occurrence. The objective of this study was to determine if low cerebral blood flow (CBF) measurements and pathological microdialysis parameters measured at the bedside can be observed early in patients with SAH who later developed DCI. METHODS The authors included 30 patients with severe SAH. The CBF measurements were performed at Day 0-3 after disease onset, using bedside xenon-CT. Interstitial glucose, lactate, pyruvate, glycerol, and glutamate were measured using microdialysis. RESULTS Nine of 30 patients developed DCI. Patients with DCI showed significantly lower global and regional CBF, and lactate was significantly increased in these patients. A high lactate/pyruvate ratio was also detected in patients with DCI. CONCLUSIONS Early low CBF measurements and a high lactate and lactate/pyruvate ratio may be early warning signs of the risk of developing DCI. The clinical value of these findings needs to be confirmed in larger studies.

Keywords
CBF, CBF = cerebral blood flow, CPP = cerebral perfusion pressure, DCI, DCI = delayed cerebral ischemia, GCS, GCS-M = Glasgow Coma Scale, GCS-motor, GOSE = Glasgow Outcome Scale–Extended, ICP = intracranial pressure, L/P = lactate/pyruvate, MD = microdialysis, NIC = neurointensive care, ROI = region of interest, SAH, SAH = subarachnoid hemorrhage, Xe-CT = xenon-CT, cerebral blood flow, delayed cerebral ischemia, lactate, lactate/pyruvate ratio, subarachnoid hemorrhage, vascular disorders, vasospasm, xenon-CT
National Category
Neurosciences
Identifiers
urn:nbn:se:uu:diva-330940 (URN)10.3171/2016.11.JNS161140 (DOI)000440653000023 ()28574309 (PubMedID)
Available from: 2017-10-07 Created: 2017-10-07 Last updated: 2018-10-12Bibliographically approved
Abu Hamdeh, S., Marklund, N., Lannsjö, M., Howells, T., Raininko, R., Wikström, J. & Enblad, P. (2017). Extended anatomical grading in diffuse axonal injury using MRI: Hemorrhagic lesions in the substantia nigra and mesencephalic tegmentum indicate poor long-term outcome. Journal of Neurotrauma, 5(34), 341-352
Open this publication in new window or tab >>Extended anatomical grading in diffuse axonal injury using MRI: Hemorrhagic lesions in the substantia nigra and mesencephalic tegmentum indicate poor long-term outcome
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2017 (English)In: Journal of Neurotrauma, ISSN 0897-7151, E-ISSN 1557-9042, Vol. 5, no 34, p. 341-352Article in journal (Refereed) Published
Abstract [en]

Clinical outcome after traumatic diffuse axonal injury (DAI) is difficult to predict. In this study, three magnetic resonance imaging (MRI) sequences were used to quantify the anatomical distribution of lesions, to grade DAI according to the Adams grading system, and to evaluate the value of lesion localization in combination with clinical prognostic factors to improve outcome prediction. Thirty patients (mean 31.2 years ±14.3 standard deviation) with severe DAI (Glasgow Motor Score [GMS] <6) examined with MRI within 1 week post-injury were included. Diffusion-weighted (DW), T2*-weighted gradient echo and susceptibility-weighted (SWI) sequences were used. Extended Glasgow outcome score was assessed after 6 months. Number of DW lesions in the thalamus, basal ganglia, and internal capsule and number of SWI lesions in the mesencephalon correlated significantly with outcome in univariate analysis. Age, GMS at admission, GMS at discharge, and low proportion of good monitoring time with cerebral perfusion pressure <60 mm Hg correlated significantly with outcome in univariate analysis. Multivariate analysis revealed an independent relation with poor outcome for age (p = 0.005) and lesions in the mesencephalic region corresponding to substantia nigra and tegmentum on SWI (p  = 0.008). We conclude that higher age and lesions in substantia nigra and mesencephalic tegmentum indicate poor long-term outcome in DAI. We propose an extended MRI classification system based on four stages (stage I—hemispheric lesions, stage II—corpus callosum lesions, stage III—brainstem lesions, and stage IV—substantia nigra or mesencephalic tegmentum lesions); all are subdivided by age (≥/<30 years).

Keywords
adult brain injury, axonal injury, head trauma, MRI, susceptibility weighted imaging
National Category
Clinical Medicine Neurology
Identifiers
urn:nbn:se:uu:diva-309038 (URN)10.1089/neu.2016.4426 (DOI)000391754800009 ()27356857 (PubMedID)
Available from: 2016-12-01 Created: 2016-12-01 Last updated: 2018-07-13Bibliographically approved
Nyholm, L., Howells, T. & Enblad, P. (2017). Predictive Factors That May Contribute to Secondary Insults With Nursing Interventions in Adults With Traumatic Brain Injury. Journal of Neuroscience Nursing, 49(1), 49-55
Open this publication in new window or tab >>Predictive Factors That May Contribute to Secondary Insults With Nursing Interventions in Adults With Traumatic Brain Injury
2017 (English)In: Journal of Neuroscience Nursing, ISSN 0888-0395, E-ISSN 1945-2810, Vol. 49, no 1, p. 49-55Article in journal (Refereed) Published
Abstract [en]

Background: Nursing interventions pose risks and benefits to patients with traumatic brain injury at a neurointensive care unit. Objectives: The aim of this study was to investigate the risk of inducing high intracranial pressure (ICP) related to interventions and whether intracranial compliance, baseline ICP, or autoregulation could be used as predictors. Methods: The study had a quantitative, prospective, observational design. Twenty-eight patients with TBI were included, and 67 interventions were observed. The definition of a secondary ICP insult was ICP of 20 mm Hg or greater for 5 minutes or more within a continuous 10-minute period. Results: Secondary ICP insults related to nursing interventions occurred in 6 patients (21%) and 8 occasions (12%). Patients with baseline ICP of 15 mm Hg or greater had 4.7 times higher risk of developing an insult. The predictor with the best combination of sensitivity and specificity was baseline ICP. Conclusions: Baseline ICP of 15 mm Hg or greater was the most important factor to determine the risk of secondary ICP insult related to nursing intervention.

Keywords
neurointensive care, nursing implications, nursing interventions, secondary insults
National Category
Neurology Nursing
Identifiers
urn:nbn:se:uu:diva-316018 (URN)10.1097/JNN.0000000000000260 (DOI)000392410200012 ()28060220 (PubMedID)
Funder
Swedish Research Council
Available from: 2017-02-24 Created: 2017-02-24 Last updated: 2017-11-29Bibliographically approved
Rostami, E., Engquist, H., Howells, T., Ronne-Engström, E., Nilsson, P., Hillered, L. T., . . . Enblad, P. (2017). The Correlation between Cerebral Blood Flow Measured by Bedside Xenon-CT and Brain Chemistry Monitored by Microdialysis in the Acute Phase following Subarachnoid Hemorrhage. Frontiers in Neurology, 8, Article ID 369.
Open this publication in new window or tab >>The Correlation between Cerebral Blood Flow Measured by Bedside Xenon-CT and Brain Chemistry Monitored by Microdialysis in the Acute Phase following Subarachnoid Hemorrhage
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2017 (English)In: Frontiers in Neurology, ISSN 1664-2295, E-ISSN 1664-2295, Vol. 8, article id 369Article in journal (Refereed) Published
Abstract [en]

Cerebral microdialysis (MD) may be used in patients suffering from subarachnoid hemorrhage (SAH) to detect focal cerebral ischemia. The cerebral MD catheter is usually placed in the right frontal lobe and monitors the area surrounding the catheter. This generates the concern that a fall in cerebral blood flow (CBF) and ischemic events distant to the catheter may not be detected. We aimed to investigate if there is a difference in the association between the MD parameters and CBF measured around the MD catheter compared to global cortical CBF and to CBF in the vascular territories following SAH in the early acute phase. MD catheter was placed in the right frontal lobe of 30 SAH patients, and interstitial glucose, lactate, pyruvate, glycerol, and lactate/pyruvate ratio were measured hourly. CBF measurements were performed during day 0-3 after SAH. Global cortical CBF correlated strongly with CBF around the microdialysis catheter (CBF-MD) (r = 0.911, p ≤ 0.001). This was also the case for the anterior, middle, and posterior vascular territories in the right hemisphere. A significant negative correlation was seen between lactate and CBF-MD (r = -0.468, p = 0.009). The same relationship was observed between lactate and CBF in anterior vascular territory but not in the middle and posterior vascular territories. In conclusion, global CBF 0-3 days after severe SAH correlated strongly with CBF-MD. High lactate level was associated with low global CBF and low regional CBF in the right anterior vascular territory, when the MD catheter was placed in the right frontal lobe.

Keywords
Xenon-CT, cerebral blood flow, lactate, microdialysis, subarachnoid hemorrhage
National Category
Neurosciences
Identifiers
urn:nbn:se:uu:diva-330939 (URN)10.3389/fneur.2017.00369 (DOI)000407574600001 ()28824527 (PubMedID)
Available from: 2017-10-07 Created: 2017-10-07 Last updated: 2018-01-13Bibliographically approved
Howells, T., Johnson, U., McKelvey, T., Ronne-Engström, E. & Enblad, P. (2017). The effects of ventricular drainage on the intracranial pressure signal and the pressure reactivity index. Journal of clinical monitoring and computing, 31(2), 469-478
Open this publication in new window or tab >>The effects of ventricular drainage on the intracranial pressure signal and the pressure reactivity index
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2017 (English)In: Journal of clinical monitoring and computing, ISSN 1387-1307, E-ISSN 1573-2614, Vol. 31, no 2, p. 469-478Article in journal (Refereed) Published
Abstract [en]

In subarachnoid hemorrhage (SAH) patients intracranial pressure (ICP) is usually monitored via an extraventricular drain (EVD), which can produce false readings when the drain is open. It is established that both the ICP cardiac pulse frequency and long term trends over several hours are often seriously corrupted. The aim of this study was to establish whether or not the intermediate frequency bands [respiratory, Mayer wave and very low frequency (VLF)] were also corrupted. The VLF range is of special interest because it is important in cerebral autoregulation studies. Using a pattern recognition algorithm we retrospectively identified 718 cases of EVD opening in 80 SAH patients. An analysis of differences between closed and open-drain periods showed that ICP amplitude decreased significantly in all of the three lower frequency bands when the EVD was open. A similar analysis of systemic arterial pressure signal revealed similar changes in the same frequency bands that were positively correlated with the ICP changes. Therefore we concluded that the changes in the ICP signal represented real, physiological changes and not artifact. Pressure reactivity index (PRx) values were also computed during closed and open-drain periods. We found a small but statistically significant decrease during open-drain periods. Based on analysis of the change in the PRx distribution during open drainage we concluded that this decrease also represented physiological changes rather than artifact. In summary the ICP respiratory, Mayer wave, and VLF frequency bands are not corrupted when the EVD is open, and it safe to use these for autoregulation studies.

Keywords
Intracranial pressure, Subarachnoid hemorrhage, Cerebral autoregulation, Vascular pressure reactivity, Clinical monitoring
National Category
Surgery
Identifiers
urn:nbn:se:uu:diva-321426 (URN)10.1007/s10877-016-9863-3 (DOI)000396348800028 ()26987656 (PubMedID)
Available from: 2017-05-16 Created: 2017-05-16 Last updated: 2017-05-16
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