Perihemorrhagic ischemia occurs in a volume-dependent manner as assessed by multimodal cerebral monitoring in a porcine model of intracerebral hemorrhage.

BACKGROUND: Changes in the perihemorrhagic zone (PHZ) of intracerebral hemorrhage (ICH) are variable. Different mechanisms contribute to secondary neuronal injury after ICH. This multimodal monitoring study investigated early changes in the PHZ of ICH. METHODS: Twenty-four swine were anesthetized, ventilated, and underwent monitoring of vital parameters. Next to an intracranial pressure-probe (ICP), microdialysis (MD), thermodiffusion cerebral blood flow (td-CBF), and oxygen probes (PbrO2) were placed into the gray white matter junction for 12 h of monitoring. ICH was induced using the autologous blood injection model. Pre-defined volumes were 0 ml (sham), 1.5 ml ipsilateral (1.5 ml), 3.0 ml ipsilateral (3.0 ml), and 3.0 ml contralateral (3.0 ml contra). RESULTS: ICP equally increased in all groups after ICH. In the 3.0 ml group tissue oxygenation decreased to ischemic values of 9 ± 7 mmHg early after 6 h of monitoring. This decrease was associated with a significant perfusion reduction from 36 ± 8 ml/100 g/min to 20 ± 10 ml/100 g/min. MD correlated with a threefold lactate/pyruvate ratio increase. Measurements in all other groups were unchanged. CONCLUSION: Multimodal monitoring demonstrates volume-dependent changes of tissue oxygenation, blood flow, and ischemic MD markers in the PHZ independent of increased ICP suggesting early moderate ischemia. No evidence was found for the existence of a perihemorrhagic ischemia in the small hematoma groups.

Intracranial pressure telemetry: first experience of an experimental in vivo study using a new device.

OBJECTIVE: To test two new telemetric intracranial pressure (ICP) probes (NEUROVENT(®)-P-tel, NEUROVENT(®)-S-tel) in a porcine model. We aimed to intraoperatively correlate the telemetric probes to parenchymal ICP probes and study their reliability in the first hours after implantation. The experimental set-up, new telemetric technology and first data will be presented. METHODS: We implanted a right parietal (parenchymal) and left parietal (subdural) telemetric ICP probe in 13 Göttingen mini-pigs under general anaesthesia. Through the left parietal burr hole a parenchymal ICP probe (Neurovent(®) ICP) was introduced. Intraoperatively, the head position was changed to provoke ICP changes every 10 min. The telemetric probes were left in situ and finally the parenchymal ICP probe was removed. We correlated mean differences between each telemetric probe and the conventional ICP measurement and Bland-Altman plots were generated for statistical analysis. RESULTS: We present first data containing intraoperative measurements of 26 telemetric probes after implantation. Intraoperatively, mean differences of 2.48 ± 1.52 mmHg SD (NEUROVENT(®)-P-tel) and 2.64 ± 1.79 mmHg (NEUROVENT(®)-S-tel) were observed. The Bland-Altman plot demonstrates good correlation of the telemetric probes compared with parenchymal ICP probes. CONCLUSION: We present a new telemetric technology that was experimentally compared with a parenchymal ICP probe. We provide data that the new telemetric probes will comparably measure ICP vs an external ICP probe. This stand-alone ICP tool may allow permanent measurement of ICP in hydrocephalus patients. Further continuation of our study will demonstrate whether this system guarantees acceptable long-term reliability.

Evidence of spreading depolarizations in a porcine cortical intracerebral hemorrhage model.

OBJECTIVES: To evaluate whether cortical spreading depolarizations (CSD) occur in the early stage after cortical intracerebral hemorrhage (ICH). METHODS: Ten anesthetized male swine were examined over 19 h. Two cerebral probes were inserted around the ICH (microdialysis and thermodiffusion cerebral blood flow), ICP was monitored contralaterally and up to two electrocorticographic grid electrodes were positioned over the hemisphere after hemicraniectomy and dural opening. A right frontal autologous, arterial ICH (3.0 mL) was induced in all the animals studied. RESULTS: Using a modified injection technique an 80% success rate in ICH formation could be achieved. Eight animals with cortical ICH could be analyzed finally. After induction of ICH, ICP increased non-significantly. Overall, six out of eight animals had CSDs, of either single type or clusters. In one animal a CSD occurred as early as 2 h after ICH; in all other animals the first CSD did not occur before 5 h after onset. CONCLUSION: CSD's occur in cortical experimental ICH. As ICP remained stable owing to the hemicraniectomy we cannot argue in favor of ICP-related triggering of CSD. Modifications of the experimental setup avoiding hemicraniectomy may better describe the pathophysiology of CSD related to ICH in future studies.

Pressure reactivity index correlates with metabolic dysfunction in a porcine model of intracerebral hemorrhage.

OBJECTIVE: We correlated oxygen, flow, and pressure indices of cerebrovascular reactivity (CR) with extracellular cerebral metabolite concentrations in a porcine model of intracerebral hemorrhage (ICH). METHODS: Continuous advanced multimodal monitoring including microdialysis, cerebral blood flow and P(br)O(2) probes were placed 1 cm in front of the coronal suture in the grey/white matter junction. Following a period of 1 h of monitoring, an autologous arterial ICH with defined volumes (3 mL) was induced. Pressure-, oxygen-, and flow-related autoregulation indices (PRx, ORx, and FRx) were simultaneously calculated and correlated hourly with extracellular cerebral metabolites, including glucose, lactate, pyruvate, and glutamate. RESULTS: Seventeen swine were monitored on average 12 continuous hours per animal. FRx correlated highly with ORx (0.96, P = <0.001), but values of both FRx and ORx > 0.2 did not correlate with any microdialysis metabolite. Values of PRx > 0.2 correlated highly (0.65, P < 0.001) with the lactate/pyruvate ratio, values of PRx > 0.3 correlated with glutamate (0.67, P < 0.05), the lactate/pyruvate ratio (0.60, P < 0.01), and P(br)O(2) (-0.65, P < 0.01). CONCLUSIONS: We found evidence for impaired CR in a porcine model of ICH. The findings suggest that, among other parameters of CR, positive PRx coefficients have the highest significance and could be associated with microdialysis alterations during hypoxic events.

Evaluation of a novel brain tissue oxygenation probe in an experimental swine model.

BACKGROUND: Cerebral microdialysis, cerebral blood flow, and cerebral oxygenation (PbrO2) measurements using intraparenchymal probes are widely accepted as invasive diagnostic monitoring for early detection of secondary ischemia. OBJECTIVE: To evaluate a novel PbrO2 probe for continuous and quantitative oxygenation assessment compared with the existing gold standard PbrO2 probe. METHODS: In 9 pigs, 2 PbrO2 probes (Neurovent-TO vs Licox) were implanted into the subcortical white matter. An intracranial pressure probe was inserted contralaterally. The PbrO2 probes were tested during (1) baseline measurements followed by (2) hyperoxygenation (fraction of inspired oxygen [Fio2]=1.0), medically induced (3) hypo- and (4) hypertension, (5) hyperventilation, (6) tris-hydroxymethylaminomethane application, and (7) hypoxygenation (Fio2<0.05). For statistical analyses, Bland-Altman plots were used. RESULTS: The Neurovent-TO probe is easy to handle and does not need a specific storage or calibration. Bland-Altman analyses revealed good comparability of both technologies under baseline conditions (meandiff 2.09 mm Hg, standard deviation 0.04 mm Hg, range 1.98-2.20 mm Hg), but measurement dynamics during hyperoxygenation (Fio2=1.0) revealed significantly different profiles, eg Neurovent-TO probe reached up to 1.53-fold higher PbrO2 values than the Licox probe. During hypoxygenation (Fio2<0.05), the Neurovent-TO probe detected the hypoxic level of 8.5 mm Hg 1.5 minutes earlier than did the Licox probe. All other maneuvers showed similar responses in both technologies. CONCLUSION: The Neurovent-TO PbrO2 device comparably measures PbrO2 under most conditions tested compared with the Licox device. The Neurovent-TO is more sensitive to rapid Fio2 changes. Further studies are necessary to clarify these differences. It is questionable whether existing knowledge of Licox tissue oxygenation, ie, hypoxic threshold, can be directly transferred to the Neurovent-TO.