On-line monitoring of global cerebral hypoxia in acute brain injury. Relationship to intracranial hypertension

Transcranial, Non-Invasive Evaluation of Potential Misery Perfusion During Hyperventilation Therapy of Traumatic Brain Injury Patients

Hyperventilation (HV) therapy uses vasoconstriction to reduce intracranial pressure (ICP) by reducing cerebral blood volume. However, as HV also lowers cerebral blood flow (CBF), it may provoke misery perfusion (MP), in which the decrease in CBF is coupled with increased oxygen extraction fraction (OEF). MP may rapidly lead to the exhaustion of brain energy metabolites, making the brain vulnerable to ischemia. MP is difficult to detect at the bedside, which is where transcranial hybrid, near-infrared spectroscopies are promising because they non-invasively measure OEF and CBF. We have tested this technology during HV (∼30 min) with bilateral, frontal lobe monitoring to assess MP in 27 sessions in 18 patients with traumatic brain injury. In this study, HV did not lead to MP at a group level (p > 0.05). However, a statistical approach yielded 89 events with a high probability of MP in 19 sessions. We have characterized each statistically significant event in detail and its possible relationship to clinical and radiological status (decompressive craniectomy and presence of a cerebral lesion), without detecting any statistically significant difference (p > 0.05). However, MP detection stresses the need for personalized, real-time assessment in future clinical trials with HV, in order to provide an optimal evaluation of the risk-benefit balance of HV. Our study provides pilot data demonstrating that bedside transcranial hybrid near-infrared spectroscopies could be utilized to assess potential MP.

Brain Tissue Oxygenation-Guided Therapy and Outcome in Traumatic Brain Injury: A Single-Center Matched Cohort Study

Brain tissue oxygenation (PbtO2)-guided therapy can improve the neurological outcome of traumatic brain injury (TBI) patients. With several Phase-III ongoing studies, most of the existing evidence is based on before-after cohort studies and a phase-II randomized trial. The aim of this study was to assess the effectiveness of PbtO2-guided therapy in a single-center cohort. We performed a retrospective analysis of consecutive severe TBI patients admitted to our center who received either intracranial pressure (ICP) guided therapy (from January 2012 to February 2016) or ICP/PbtO2-guided therapy (February 2017 to December 2019). A genetic matching was performed based on covariates including demographics, comorbidities, and severity scores on admission. Intracranial hypertension (IH) was defined as ICP > 20 mmHg for at least 5 min. Brain hypoxia (BH) was defined as PbtO2 < 20 mmHg for at least 10 min. IH and BH were targeted by specific interventions. Mann−Whitney U and Fisher’s exact tests were used to assess differences between groups. A total of 35 patients were matched in both groups: significant differences in the occurrence of IH (ICP 85.7% vs. ICP/PbtO2 45.7%, p < 0.01), ICU length of stay [6 (3−13) vs. 16 (9−25) days, p < 0.01] and Glasgow Coma Scale at ICU discharge [10 (5−14) vs. 13 (11−15), p = 0.036] were found. No significant differences in ICU mortality and Glasgow Outcome Scales at 3 months were observed. This study suggests that the role of ICP/PbtO2-guided therapy should await further confirmation in well-conducted large phase III studies.

Current Status and Recommendations in Multimodal Neuromonitoring

Every patient in neurocritical care evolves through two phases. Acute pathologies are addressed first. These include trauma, hemorrhagic or ischemic stroke, or neuroinfection. Soon after, the concentration shifts to identifying secondary pathologies like fever, seizures, and ischemia, which may exacerbate the brain injury. Frequent bedside examinations are not sufficient for timely detection and prevention of secondary brain injury (SBI) as per the International Multidisciplinary Consensus Conference on Multimodality Monitoring in Neurocritical Care. Multimodality monitoring (MMM) can help in tailoring treatment decisions to prevent such a brain injury. Multimodal neuromonitoring involves data-guided therapeutic interventions by employing various tools and data integration to understand brain physiology. Monitors provide real-time information on cerebral hemodynamics, oxygenation, metabolism, and electrophysiology. The monitors may be invasive/noninvasive and global/regional. We have reviewed such technologies in this write-up. Novel themes like bioinformatics, clinical research, and device development will also be discussed.

Brain Multimodality Monitoring: A New Tool in Neurocritical Care of Comatose Patients

Neurocritical care patients are at risk of developing secondary brain injury from inflammation, ischemia, and edema that follows the primary insult. Recognizing clinical deterioration due to secondary injury is frequently challenging in comatose patients. Multimodality monitoring (MMM) encompasses various tools to monitor cerebral metabolism, perfusion, and oxygenation aimed at detecting these changes to help modify therapies before irreversible injury sets in. These tools include intracranial pressure (ICP) monitors, transcranial Doppler (TCD), Hemedex™ (thermal diffusion probe used to measure regional cerebral blood flow), microdialysis catheter (used to measure cerebral metabolism), Licox™ (probe used to measure regional brain tissue oxygen tension), and continuous electroencephalography. Although further research is needed to demonstrate their impact on improving clinical outcomes, their contribution to illuminate the black box of the brain in comatose patients is indisputable. In this review, we further elaborate on commonly used MMM parameters, tools used to measure them, and the indications for monitoring per current consensus guidelines.

A Prospective Randomized Study of Brain Tissue Oxygen Pressure-Guided Management in Moderate and Severe Traumatic Brain Injury Patients

The purpose of this study was to compare the effect of PbtO₂-guided therapy with traditional intracranial pressure- (ICP-) guided treatment on the management of cerebral variables, therapeutic interventions, survival rates, and neurological outcomes of moderate and severe traumatic brain injury (TBI) patients. From 2009 to 2010, TBI patients with a Glasgow coma scale <12 were recruited from 6 collaborative hospitals in northern Taiwan, excluding patients with severe systemic injuries, fixed and dilated pupils, and other major diseases. In total, 23 patients were treated with PbtO₂-guided management (PbtO₂ > 20 mmHg), and 27 patients were treated with ICP-guided therapy (ICP < 20 mmHg and CPP > 60 mmHg) in the neurosurgical intensive care unit (NICU); demographic characteristics were similar across groups. The survival rate in the PbtO₂-guided group was also significantly increased at 3 and 6 months after injury. Moreover, there was a significant correlation between the PbtO₂ signal and Glasgow outcome scale-extended in patients from 1 to 6 months after injury. This finding demonstrates that therapy directed by PbtO₂ monitoring is valuable for the treatment of patients with moderate and severe TBI and that increasing PaO₂ to 150 mmHg may be efficacious for preventing cerebral hypoxic events after brain trauma.

Update on intensive neuromonitoring for patients with traumatic brain injury: a review of the literature and the current situation

Intracranial pressure (ICP) measurements are fundamental in the present protocols for intensive care of patients during the acute stage of severe traumatic brain injury. However, the latest report of a large scale randomized clinical trial indicated no association of ICP monitoring with any significant improvement in neurological outcome in severely head injured patients. Aggressive treatment of patients with therapeutic hypothermia during the acute stage of traumatic brain injury also failed to show any significant beneficial effects on clinical outcome. This lack of significant results in clinical trials has limited the therapeutic strategies available for treatment of severe traumatic brain injury. However, combined application of different types of neuromonitoring, including ICP measurement, may have potential benefits for understanding the pathophysiology of damaged brains. The combination of monitoring techniques is expected to increase the precision of the data and aid in prevention of secondary brain damage, as well as assist in determining appropriate time periods for therapeutic interventions. In this study, we have characterized the techniques used to monitor patients during the acute severe traumatic brain injury stage, in order to establish the beneficial effects on outcome observed in clinical studies conducted in the past and to follow up any valuable clues that point to additional strategies for aggressive management of these patients.

Moderate and severe traumatic brain injury: pathophysiology and management

Traumatic brain injury (TBI) is a serious disorder that is all too common. TBI ranges in severity from mild concussion to a severe life-threatening state. Across this spectrum, rational therapeutic approaches exist. Early identification that TBI has occurred in a patient is paramount to optimal outcome. Proper clinical management should be instituted as soon as possible by appropriately trained medical providers. More seriously injured patients must be triaged to advanced care centers. It is only through this rational approach to TBI that patients may expect to achieve optimal clinical and functional outcome.

Monitoring cerebral oxygenation in traumatic brain injury

Ischemia is a common problem after traumatic brain injury (TBI) that eludes detection with standard monitoring. In this review we will discuss four available techniques (SjVO2, PET, NIRS and PbrO2) to monitor cerebral oxygenation. We present technical data including strengths and weaknesses of these systems, information from clinical studies and formulate a vision for the future.

Continuous regional cerebral blood flow monitoring in the neurosurgical intensive care unit

The aim of this study was to examine the intracranial pressure (ICP) and regional cerebral blood flow (rCoBF) changes during the acute stage of severe head injury and to improve outcome by modifying treatment modalities using real-time ICP and rCoBF data. Twenty patients with moderate or severe head injury that were monitored in our neurosurgical intensive care unit were included in this study. The changes in ICP, rCoBF and the relationship of ICP/rCoBF were observed. In patients with high ICP and low rCoBF, mannitol improves the rCoBF and decreases the ICP of these patients. When low rCoBF exists, hyperventilation may lead to a rapid further decline of rCoBF, however, some hyperemic brains respond well to hyperventilation treatment. Triple-H therapy is suitable for those with low rCoBF without significantly high ICP, which is an abnormal condition considered to be caused by vasospasm.

Arterio-Jugular Difference of Oxygen Content and Outcome After Head Injury

This study investigated AJDO2 (arterio-jugular difference of oxygen content) in a large sample of severely head-injured patients to identify its pattern during the first days after injury and to describe the relationship of AJDO2 with acute neurological severity and with outcome 6 mo after trauma. In 229 comatose head-injured patients, we monitored intracranial pressure, cerebral perfusion pressure, and AJDO2. Outcome was defined 6 mo after injury. Jugular hemoglobin oxygen saturation (SjO2) averaged 68%. The mean AJDO2 was 4.24 vol% (SD, 1.3 vol%). There were 80 measurements (4.6%) with SjO2 <55% and 304 (17.6%) with saturation >75%. AJDO2 was higher than 8.7 vol% in 8 measurements (0.4%) and was lower than 3.9 vol% in 718 (42%) measurements. AJDO2 was higher during the first tests and decreased steadily over the next few days. Cases with a favorable outcome had a higher mean AJDO2 (4.3 vol%; SD, 0.3 vol%) than patients with severe disability or vegetative status (3.8 vol%; SD, 1.3 vol%) and patients who died (3.6 vol%; SD, 1 vol%). This difference was significant (P < 0.001). We conclude that low levels of AJDO2 are correlated with a poor prognosis, whereas normal or high levels of AJDO2 are predictive of better results.

Successful use of the new high-dose mannitol treatment in patients with Glasgow Coma Scale scores of 3 and bilateral abnormal pupillary widening: a randomized trial

OBJECT

The authors evaluated long-term clinical outcomes in selected acutely comatose patients with severe diffuse brain swelling and recent clinical signs of impending brain death who received a novel high-dose mannitol treatment compared with those who received conventional-dose mannitol in the emergency room.

METHODS

Forty-four adult patients with traumatic, nonmissile-inflicted, acute, severe diffuse brain swelling were prospectively and randomly evaluated. All patients were selected based on the presence of recent clinical signs of impending brain death on the first emergency room evaluation. These signs included bilateral abnormal pupillary widening and lack of motor responses to painful stimulation (Glasgow Coma Scale score of 3). The study group (23 patients) received ultra-early and fast intravenous high-dose mannitol treatment (approximately 1.4 g/kg), whereas the control group (21 patients) received half that dose (approximately 0.7 g/kg). Ultra-early improvement of bilateral abnormal pupillary widening was significantly more frequent in the high-dose mannitol group than in the conventional-dose group (p < 0.02). High-dose mannitol treatment in the emergency room was also associated with significantly better 6-month clinical outcomes (p < 0.02); the best rate of favorable outcomes was 43.5%, compared with only 9.5% in the conventional-dose mannitol group. The two groups of patients were well matched with respect to all emergency room and head computerized tomography findings, as well as the timing of initial mannitol treatment (approximately 80-90 minutes after the first evaluation at the scene of the injury). Comparative evaluation of bilateral pupillary widening between the scene of the injury and the emergency room showed no significant differences between groups, whereas mannitol dose dependence was statistically significant (p < 0.05), insofar as early pupillary improvement in the emergency room was concerned.

CONCLUSIONS

Ultra-early high-dose mannitol administration in the emergency room is the first known treatment strategy significantly to reverse recent clinical signs of impending brain death, and also to contribute directly to improved long-term clinical outcomes for these patients who have previously been considered unsalvageable.

Brain tissue oxygen guided treatment supplementing ICP/CPP therapy after traumatic brain injury

OBJECTIVE

To evaluate the effects of a brain tissue oxygen (P(ti)O(2)) guided treatment in patients with traumatic brain injury.

METHODS

P(ti)O(2) was monitored in 93 patients with severe traumatic brain injury. Forty patients admitted from 1993 to 1996 were treated with intracranial pressure/cerebral perfusion pressure (ICP/CPP) management alone (ICP < 20 mm Hg, CPP > 70 mm Hg). Fifty three patients admitted from 1997 to 2000 were treated using ICP/CPP management, but in this second group CPP was also increased as individually required to raise the P(ti)O(2) above 1.33 kPa (10 mm Hg) (P(ti)O(2) guided group).

RESULTS

Cerebral hypoxic phases with P(ti)O(2) values below 1.33 kPa occurred significantly less often in the P(ti)O(2) guided group. P(ti)O(2) values were higher over the whole monitoring period. No statistical differences could be observed in outcome at six months, despite a positive trend in the P(ti)O(2) guided group.

CONCLUSIONS

Cerebral hypoxic events can be reduced significantly by increasing cerebral perfusion pressure as required. To show a clear beneficial effect of P(ti)O(2) guided cerebral perfusion pressure management on outcome, a multicentre randomised trial needs to be undertaken.

Diagnosis and monitoring of hemorrhagic shock during the initial resuscitation of multiple trauma patients: a review

The initial management of the multiple trauma victim requires evaluation for potential hemorrhage and ongoing monitoring to assess the efficacy of resuscitation and avoid complications related to hemorrhagic shock. A variety of strategies exist to assess circulatory status, including hemodynamic monitoring, tissue perfusion measurement, and use of serum markers of metabolism. We review available technologies used to assess fluid status and tissue perfusion in patients with blood loss or hemorrhagic shock, discuss how these methods can be used effectively and efficiently during initial trauma resuscitation to guide therapy and disposition, and suggest directions for future research to improve outcomes by providing more appropriate and timely care and avoiding unnecessary complications.

Brain tissue oxygen monitoring for assessment of autoregulation: preliminary results suggest a new hypothesis

Brain tissue oxygen monitoring (P(ti)O2 (Neurotrend, Codman, Germany) was employed in addition to standard intracranial pressure (ICP) and cerebral perfusion pressure (CPP) monitoring in seven patients with severe neuronal damage of heterogeneous etiology. The correlation between P(ti)O2 changes and CPP fluctuations during periods of 30 minutes were analyzed, when CPP was above 70 mmHg and lower than 100 mmHg. A new ratio, the CPP-oxygen-reactivity (COR) index was calculated as COR=delta p(ti)O2 %/delta CPP%. The patient COR values were compared to those found in the brain of six noninjured anesthetized piglets. The analysis was performed to determine the significance of synchronous fluctuations of CPP and P(ti)O2, when CPP is above the lower threshold of autoregulation. The correlation between CPP variations and p(ti)O2 variations was found to be strong (R(mean)) = 0.74 +/- 0.17) in the patients and was weak in the uninjured animals (R(mean)) =0.38 +/- 0.43). The COR (mean) was 2.05 +/- 0.57 in patients and 0.78 +/- 0.6 in the animals. In the injured brain of our patients, we observed an unexpectedly close correlation between P(ti)O2 and CPP variations when CPP levels were within a therapeutically targeted range (70 to 100 mmHg). In a porcine model, we could not find this relationship in the noninjured brain. We speculate that an increased COR might be indicative for an impaired local pressure autoregulation. The preliminary data suggest that COR values above "1" might be pathologic. However, the reported sample sizes are too small to provide sufficient statistical power to justify inferential statistical analyses. As such, results are presented with descriptive statistics only, and should be regarded as a hypothesis.

Advanced monitoring in the intensive care unit: brain tissue oxygen tension

Cerebral monitoring of patients with acute intracranial disorders generally focuses on intracranial pressure and cerebral perfusion pressure monitoring. Over the past few years, several new techniques have become available for more detailed routine monitoring of cerebral oxygenation and metabolism. Brain tissue oxygen pressure measurement is increasingly being used for evaluation of cerebral oxygenation. This article discusses brain tissue oxygen pressure measurement in regards to its technical aspects, safety, reliability, and value relative to other techniques for evaluation of cerebral oxygenation. Published experimental and clinical data are considered, and the current status of the clinical use and indications of the technique are summarized. Monitoring may be performed in relatively undamaged parts of the brain or, preferably, in the penumbra region of an intracerebral lesion. Pathophysiologic evidence warrants targeting therapy for patients with traumatic brain injury and subarachnoid hemorrhage toward improvement of cerebral oxygenation guided by continuous monitoring of brain tissue oxygen tension.

Improving clinical outcomes from acute subdural hematomas with the emergency preoperative administration of high doses of mannitol: a randomized trial

OBJECTIVE

To evaluate clinical outcomes and postoperative physiological findings for comatose patients with acute subdural hematomas who received preoperative high-dose mannitol (HDM) versus conventional-dose mannitol treatment.

METHODS

One hundred seventy-eight adult patients with non-missile, traumatic, acute, subdural hematomas were prospectively and randomly assigned to receive emergency, preoperative, intravenous HDM treatment (91 patients), compared with a control group treated with a lower preoperative mannitol dose (87 patients).

RESULTS

Preoperative improvement of abnormal pupillary widening was significantly more frequent in the study group than in the control group of patients (P < 0.0001). Preoperative HDM treatment was also associated with significantly better clinical outcomes at 6-month follow-up evaluations (P < 0.01). Postoperative physiological findings revealed statistically significant between-group differences, with higher intracranial pressure and lower cerebral extraction of oxygen (relative cerebral hyperperfusion) in the control group, compared with the HDM group. Postoperative global brain ischemia (abnormally low arteriojugular lactate difference values) was rare and was detected in 2.2 and 3.4% of the patients in the study and control groups, respectively.

CONCLUSION

Emergency preoperative HDM administration was associated with improved clinical outcomes for patients with acute subdural hematomas. Preoperative improvement of abnormal pupillary widening and better postoperative control of intracranial hypertension and associated relative cerebral hyperperfusion seemed to be relevant factors associated with improved outcomes.

The relation between acute physiological variables and outcome on the Glasgow Outcome Scale and Disability Rating Scale following severe traumatic brain injury

The relation between outcome and duration of adverse physiological events was studied, using suggested critical physiological values. Subjects were 184 patients with severe traumatic brain injury who received continuous monitoring of intracranial pressure (ICP), mean arterial pressure (MAP), cerebral perfusion pressure (CPP), and jugular venous oxygen saturation. Longer durations of adverse physiological events were significantly related to Glasgow Outcome Scale (GOS) scores and Disability Rating Scale (DRS) scores for all variables at all timepoints postinjury. When analyses excluded patients who died, the relation between adverse physiological events and GOS was nonsignificant; however, duration of ICP, MAP, and CPP still accounted for a significant portion of the variance in DRS scalres. The relative sensitivity of the GOS and DRS is discussed.

Estimation of cerebral oxygenation and hemodynamics in cerebral vasospasm using indocyaningreen dye dilution and near infrared spectroscopy: a case report

Changes in cerebral hemodynamics and oxygenation patterns in cerebral vasospasm might be underestimated if transcranial doppler sonography and angiography findings are considered singularly. This report describes preliminary findings in further development of a noninvasive method that estimates regional cerebral oxygenation and perfusion. A 50-year-old patient suffering from cerebral vasospasm after subarachnoid hemorrhage before and after superselective papaverine infusion was examined. Measurements were taken by using a technique combining indocyaningreen dye dilution and near infrared spectroscopy. Our first results suggest that the technique could be suitable for estimation of cerebral hemodynamics. This noninvasive technique can be performed at the bedside and in special environments, such as neurocritical care units. It seems to be safe, easy to perform, and less time-consuming than conventional techniques. Combination of indocyaningreen dye dilution and near infrared spectroscopy might become a powerful tool in the detection and treatment of cerebral vasospasm causing delayed cerebral ischemic deficit. Further larger-scale investigations are necessary to evaluate the diagnostic accuracy of this technique. Our preliminary observations however, based on measurements before and after superselective papaverine infusion in vasospastic vessels, helped to clarify the influence of extracerebral contamination on the cerebral near infrared spectroscopy signal in the adult head.

The effect of cerebrospinal fluid drainage on cerebral perfusion in traumatic brain injured adults

Cerebrospinal fluid drainage is a first line treatment used to manage severely elevated intracranial pressure (> or = 20 mm Hg) and improve outcomes in patients with acute head injury. There is no consensus regarding the optimal method of cerebrospinal fluid removal. The purpose of this investigation was to determine whether cerebrospinal fluid drainage decreases intracranial pressure and improves cerebral perfusion and to identify factors that impact treatment effectiveness. This study involved 31 severely head injured patients. Intracranial pressure and other indices of cerebral perfusion (cerebral perfusion pressure, cerebral blood flow velocity, and regional cerebral oximetry) were measured before, during, and after cerebrospinal fluid drainage. Arterial and jugular venous oxygen content was measured before and after cerebrospinal fluid drainage. Patients underwent three randomly ordered cerebrospinal fluid drainage protocols that varied in the volume of cerebrospinal fluid removed (1 mL, 2 mL, and 3 mL) for a total of 6 mL of cerebrospinal fluid removed. There was a significant change in the intracranial pressure from a mean at baseline of 26.1 mm Hg (SD = 4.4) to 22.1 mm Hg immediately after drainage. One third of patients experienced a decrease in the intracranial pressure below 20 mm Hg; in two patients the intracranial pressure dropped less than 1 mm Hg. The following factors predicted 61.5% of the variance in the responsiveness of intracranial pressure to drainage: vecuronium hypothermia, baseline cerebral perfusion pressure and acuity of illness. Cerebrospinal fluid drainage provides a transient decrease in intracranial pressure without a measurable improvement in other indices of cerebral perfusion.

[Uses and abuses of hyperventilation in severe traumatic brain injury]

A critical evaluation was done about the guidelines and effects of the hyperventilation maneuver on prevention and treatment of increased intracranial pressure (ICP) that follows severe traumatic brain injury (TBI). The prophylactic use of hyperventilation should be avoided after severe TBI acute phase, unless high venous O2 values are recorded at jugular bulb blood (SjO2), or to allow time when there are evidences of neurologic deterioration with posturing. The lack of cerebrovascular response to hyperventilation to low the ICP means that the blood brain barrier (BBB) function is extensively impaired. Then, hyperventilation may be used as a screening therapeutic test in acute severe TBI, since BBB impairment is the pointer that other available clinical procedures for high ICP control (sedation, paralysis and osmotic diuretics) are not workable. A new pathogenetic hypothesis about traumatic brain edema and its therapeutic approach is presented.

The Brain Trauma Foundation. The American Association of Neurological Surgeons. The Joint Section on Neurotrauma and Critical Care. Hyperventilation

Chronic prophylactic hyperventilation therapy should be avoided during the first 5 days after severe TBI and particularly during the first 24 h. CBF measurements in patients with severe TBI demonstrate that blood flow early after injury is low and strongly suggest that in the first few hours after injury the absolute values approach those consistent with ischemia. These findings are corroborated by AVdO2 and SjO2 and brain tissue O2 measurements. Hyperventilation will reduce CBF values even further, but will not consistently cause a reduction of ICP and may cause loss of autoregulation. The cerebral vascular response to hypocapnia is reduced in those with the most severe injuries (subdural hematomas and diffuse contusions), and there is substantial local variability in perfusion. While the CBF level at which irreversible ischemia occurs has not been clearly established, ischemic cell change has been demonstrated in 90% of those who die following TBI, and there is PET evidence that such damage is likely to occur when CBF drops below 15-20 cc/100 g/min. A prospective randomized clinical trial has determined that outcomes are worse when TBI patients are treated with chronic prophylactic hyperventilation therapy. Within the standard, guideline, and options, specific paCO2 thresholds have been described that are different for each of the three parameters. These individual thresholds were selected based on the preponderance of literature supporting those thresholds in the contexts of the statements which included them. With the exception of the threshold included for the standard in this guideline, it is emphasized that the paCO2 threshold is not as important as the general concept of hyperventilation. The preponderance of the physiologic literature concludes that hyperventilation during the first few days following severe traumatic brain injury, whatever the threshold, is potentially deleterious in that it can promote cerebral ischemia.

Effect of hypocapnea on CBF and extracellular intermediates of secondary brain injury

We examined the metabolic response of the brain underlying subdural hematomas or surrounding contusions to hyperventilation and looked for evidence of ischemia. Twelve consecutive patients with severe traumatic brain injury (TBI) (GCS < 8) who required surgery for evacuation of subdural hematoma or hemorrhagic contusion were studied. At surgery, a microdialysis catheter was placed into the cortex in a gyrus adjacent to the contusion or underlying the subdural hematoma. A thermal diffusion flow probe was placed on the cortex directly above the dialysis catheter. On days 1 and 3 post injury, two trials of hyperventilation were performed which dropped the patients' pCO2 10 mm Hg for 30 minutes. Monitoring of CBF and collection of dialysis fluid continued throughout each hyperventilation trial. Data was analyzed for a three hour window surrounding each hyperventilation. Brief periods of hyperventilation did not cause a significant elevation of the extracellular lactate/pyruvate ratio or glutamate level in areas of the brain likely to be the most vulnerable to secondary injury. In spite of hyperventilation leading to a significant decline in local CBF in 20% of the trials, there was no evidence of ischemia or excitatory amino acid release associated with hyperventilation.

Comparative effects of hypothermia, barbiturate, and osmotherapy for cerebral oxygen metabolism, intracranial pressure, and cerebral perfusion pressure in patients with severe head injury

In order to select the optimal neurointensive treatment for patients with severe head injury and intracranial hypertension, the effects of hypothermia (HT), barbiturates (BT), and osmotic agents (OT) on focal and diffuse cerebral oxygen metabolism were evaluated by means of continuous monitoring of bifrontal regional oxygen saturation (rSO2), jugular bulb oxygen saturation (SjO2), jugular bulb temperature (Tjb), intracranial pressure (ICP), and cerebral perfusion pressure (CPP).

PATIENTS AND METHODS

Cerebral oxygen metabolism in SjO2 and rSO2, ICP, CPP, and Tjb were continuously monitored in severe head injury patients with Glasgow Coma Scale < 8, ages 10-62: 13 with focal and 10 with diffuse injuries. The effects of BT (n = 6), HT (n = 9), and OT (n = 8) on these parameters (ICP/CPP, SjO2, and rSO2) were compared. Evaluations were performed in terms of: a) Percentage of abnormal values based on normal control values; ICP < 20 mm Hg, CPP > 60 mm Hg, SjO2 55-75%, and rSO2 60-80% were calculated, b) Effects of pentobarbital dose (mg/kg/h) for the parameters compared among < 1.0, 1.1-2.0, 2.1-3.0, and > 3.1. c) Effects of Tjb (degree C) on parameters compared among hyperthermia (> 38 degrees C), normothermia (36-37.9 degrees C), mild hypothermia (34-35.9 degrees C) and moderate hypothermia (< 33.9 degrees C).

RESULTS

a) Abnormal data differed significantly among the three treatment groups. rSO2 showing ischemia on the affected side was more marked in BT than in HT or OT. b) ICP decreases and CPP increases correlated significantly with the pentobarbital dose. c) ICP decreases and CPP increases correlated significantly with decreased Tjb.

CONCLUSION

The therapeutic effects of hypothermia, barbiturates, and osmotherapy on cerebral oxygen metabolism and ICP/CPP are different according to the underlying pathological lesions of patients with severe head injury.

Cerebral oxidative metabolism and evoked potential deterioration after severe brain injury: new evidence of early posttraumatic ischemia

BACKGROUND

We commonly observe progressive deterioration in somatosensory evoked potentials (SSEPs) after severe head injury. We had previously been unable to relate this deterioration to raised intracranial pressure but had noted a relationship with decreasing transcranial oxygen extraction (arteriovenous oxygen difference [AVDO2]). The purpose of this study was twofold: to prove the hypothesis that deterioration in SSEP values is associated with decreasing AVDO2 and to test the subsidiary hypotheses that deteriorating SSEPs were the result of either ischemia/reperfusion injury or failure of oxygen extraction/utilization.

METHODS

Monitoring of 97 patients with severe traumatic brain injury (Glasgow Coma Scale scores of < or = 8 after resuscitation) included twice daily AVDO2 measurement and hourly SSEP recording for an average of 5 days. The last 51 patients also underwent 12-hourly measurement of cerebral blood flow (CBF), with calculation of the cerebral metabolic rate of oxygen. Cluster analysis was used to classify patients based on initial AVDO2 values and subsequent SSEP trends. The time courses of CBF, SSEPs, AVDO2, and cerebral metabolic rate of oxygen were examined in the groups defined by the cluster analysis. The clinical outcomes considered were survival or nonsurvival and the Glasgow Outcome Scale scores obtained at 3 months or more after injury.

RESULTS

Cluster analysis confirmed the association between high initial AVDO2 values and subsequent SSEP deterioration. Patients in this category initially had significantly higher AVDO2, lower CBF, and higher cerebral metabolic rates of oxygen but recovered to adequate levels within 24 to 36 hours after injury. SSEP values were initially identical in the patients with normal AVDO2 values and those with elevated AVDO2 but differed significantly at 60 hours after injury and beyond.

CONCLUSION

The findings of increased oxygen utilization and lowered CBF in the patients with deteriorating SSEPs strongly imply that early ischemia rather than failure of O2 extraction or utilization is responsible for the associated SSEP deterioration. This issue of defining thresholds for ischemia based on AVDO2 is confounded by the dependency of CBF and AVDO2 values on the time after injury.

Accuracy of continuous jugular bulb oximetry in the intensive care unit

OBJECTIVE

To address the accuracy of a bedside jugular bulb oxygen saturation (SjO2) catheter monitor (Baxter-Edwards, Santa Ana, CA) versus in vitro co-oximetry measurements in the intensive care unit (ICU).

METHODS

By prospective protocol, we compared blood gas measurements with simultaneously recorded continuous bedside oximetric monitor values for 31 ICU patients with traumatic brain injury undergoing jugular bulb catheter monitoring. For suboptimal fiberoptic light signal quality indices, the catheter was repositioned, flushed, or both before drawing the sample for in vitro measurement. Laboratory and bedside monitor data were examined for association using the chi2 and paired t tests and a linear regression model.

RESULTS

We assessed 195 samples (median, 5 per patient; range, 1-14) who were monitored an average of 3.4 (range, 1-6) days. The in vivo monitor (range, 32-94%) and in vitro co-oximetry (range, 38-93%) values had acceptable correlation (y = 0.94x + 4.4, r2 = 0.80). For bedside monitor detection of jugular bulb desaturation (SjO2 < 50% for 10 min), the kappa statistic was 0.35, the sensitivity was 45 to 50%, and the specificity was 98 to 100%.

CONCLUSION

Continuous ICU SjO2 monitoring correlates significantly with in vitro values, but less so than previously described during intracranial surgery. Although sensitivity of the bedside monitor to detect confirmed desaturations remains an issue, the high specificity indicates that it is less of a concern that patients may be misdiagnosed as having desaturations resulting in unnecessary interventions. Nonetheless, suspected jugular bulb desaturation should be verified before taking therapeutic actions.

The first decade of continuous monitoring of jugular bulb oxyhemoglobinsaturation: management strategies and clinical outcome

OBJECTIVE

To comparatively assess outcome of patients undergoing monitoring and management of cerebral extraction of oxygen along with cerebral perfusion pressure vs. outcome of patients undergoing monitoring and management of cerebral perfusion pressure alone in severe acute brain trauma.

DESIGN

Prospective, interventional study.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Adults (n = 353) with severe acute brain trauma. A group of 178 patients underwent continuous monitoring and management of cerebral extraction of oxygen and cerebral perfusion pressure, while a control group of 175 patients underwent monitoring and management of cerebral perfusion pressure only.

INTERVENTIONS

Routine neuroemergency procedures.

MEASUREMENTS AND MAIN RESULTS

The two groups of patients were matched with regard to age, postresuscitation Glasgow Coma Scale scores, rates of acute surgical intracranial hematomas and brain swelling, pupillary abnormalities, early hypotensive events (before intensive care monitoring), as well as initial levels of intracranial pressure and cerebral perfusion pressure. Outcome at 6 months post injury was significantly better (p < .00005) in the 178 patients undergoing monitoring and management of cerebral extraction of oxygen along with cerebral perfusion pressure, than in the control group of 175 patients undergoing monitoring and management of cerebral perfusion pressure alone.

CONCLUSION

In patients with severe acute brain trauma and intracranial hypertension associated with compromised cerebrospinal fluid spaces, monitoring and managing cerebral extraction of oxygen in conjunction with cerebral perfusion pressure result in better outcome than when cerebral perfusion pressure is managed alone.

Importance of textual data in multimodality monitoring

OBJECTIVES

The use of multimodality monitoring of patients in the intensive care unit (ICU) and the subsequent collection and analysis of such data are increasing. The aim of this work was to assess the importance of recording complementary textual data referring to patient care maneuvers, calibrations, and other incidents, in addition to the raw numerical values.

DESIGN

A retrospective analysis of multimodality monitoring data, which included comments entered concurrently at the bedside, collected from head-injured patients admitted to an ICU.

PATIENTS

One hundred forty-seven patients with a postresuscitation Glasgow Coma Scale score of < or = 12 were monitored for a total of nearly 1 million minutes on up to eight commonly used channels.

MEASUREMENTS AND MAIN RESULTS

Approximately 13,000 comments were added to the raw data at the time of collection. The data were subsequently validated using these comments as indicators of artifactual values. The comments were classified into a surprisingly small number of important categories, with the most frequent referring to monitor calibrations and regular ICU care maneuvers. The difference between validated and unvalidated data on the quantity of secondary insult observed was in some cases nearly 50%.

CONCLUSIONS

This work demonstrates that such textual information should be recorded concurrently with the raw monitoring values to ensure proper interpretation of the data in any retrospective analysis. Furthermore, it also suggests that a small number of prespecified categories could be used in the on-line validation of such data.

Continuous monitoring of cerebral substrate delivery and clearance: initial experience in 24 patients with severe acute brain injuries

OBJECTIVE

Current neuromonitoring techniques in severe human head injury often fail to detect the causes of clinical deterioration. A sensor is now available for continuous monitoring of brain oxygen tension, carbon dioxide tension, and pH values. In this study, brain tissue oxygen tension was used to differentiate patients at risk for brain ischemia and to predict outcome.

METHODS

The multiparameter sensor was inserted into brain tissue, along with a standard ventriculostomy catheter and a microdialysis probe, in 24 patients. Lactate and glucose were measured by high-pressure liquid chromatography in hourly dialysate samples.

RESULTS

Patients who experienced a good recovery (n = 8) sustained a mean brain partial oxygen pressure of 39 +/- 4 mm Hg, brain partial carbon dioxide pressure (PCO2) of 50 +/- 8 mm Hg, and a brain pH of 7.14 +/- 0.12. Patients with moderate to severe disability (n = 6) sustained a mean brain partial oxygen pressure of 31 +/- 5 mm Hg, brain PCO2 of 47 +/- 2 mm Hg, and a brain pH of 7.11 +/- 0.12. Ten patients who died or remained vegetative sustained a mean brain partial oxygen pressure of 19 +/- 8 mm Hg, a brain PCO2 of 64 +/- 21 mm Hg, and a brain pH of 6.85 +/- 0.41. Mean brain PCO2 levels of 90 to 150 mm Hg were consistently observed after cerebral circulatory arrest or brain death. Dialysate lactate and glucose were less clearly correlated to outcome than brain oxygen tension. Dialysate glucose was extremely low in all patients and zero in most patients who died.

CONCLUSION

Brain oxygen pressure, brain carbon dioxide pressure, and brain pH measurements, as well as a microdialysis probe for glucose and lactate analysis, may optimize the management of comatose neurosurgical patients by allowing a fuller understanding of the dynamic factors affecting brain metabolism.

Thrombotic, infectious, and procedural complications of the jugular bulb catheter in the intensive care unit

OBJECTIVE

An assessment of the thrombotic, infectious, and technical complications of continuous jugular bulb catheter monitoring in the intensive care unit (ICU) was made.

METHODS

Over a 1-year period, 44 patients suffering from traumatic brain injury, subarachnoid hemorrhage, or stroke received jugular bulb catheter monitoring in the ICU. They were followed for catheter insertion complications and the development of bacteremia. In 20 patients chosen randomly, an ultrasonographic evaluation was performed after removal of the catheter for an assessment of internal jugular vein thrombosis.

RESULTS

Of the 44 patients, 1 became bacteremic; the source was identified as a thoracostomy site. Among the complications related to the 44 catheter insertions, there were 2 instances of carotid artery puncture (4.5%), 1 misplaced catheter (thoracic placement), and 1 clinically insignificant hematoma. Of the 20 patients investigated with ultrasonography, 8 (40%) had nonobstructive, subclinical internal jugular vein thrombi after jugular bulb catheter monitoring (95% confidence interval, 19-61%). The median monitoring duration was 3 days (range, 1-6 d). No clinical factor was identified to be associated with thrombus formation.

CONCLUSION

We conclude the following: 1) the risk of bacteremia related to the jugular bulb catheter was negligible; 2) complications related to catheter insertion were rare and clinically insignificant; and 3) the incidence of subclinical internal jugular vein thrombosis after jugular bulb catheter monitoring is considerable. Although it is worthy to note this complication, no patient with a thrombus became symptomatic in the present series. The risk-benefit assessment of this monitoring technique must include consideration of subclinical thrombosis.

Monitoring of cerebral hemodynamics with jugular bulb catheters

Jugular venous oxygen saturation (SjvO2) monitoring is useful for detecting episodes of cerebral hypoxia/ischemia in patients with head injury, patients undergoing neurosurgical procedures, and patients undergoing cardiopulmonary bypass. The use of SjvO2 monitoring can direct the treatment of ischemic episodes and identify the optimal level of cerebral perfusion pressure and PCO2 for the individual patient.

Monitoring of cerebral oxygenation in patients with severe head injuries: brain tissue PO2 versus jugular vein oxygen saturation

Monitoring of cerebral oxygenation is considered to be of great importance in minimizing secondary hypoxic and ischemic brain damage following severe head injury. Although the threshold for cerebral hypoxia in jugular bulb oximetry (measurement of O2 saturation in the jugular vein (SjvO2)) is generally accepted to be 50% oxygen saturation, a comparable value in brain tissue PO2 (PtiO2) monitoring, a new method for direct assessment of PO2 in the cerebral white matter, has not yet been established. Hence, the purpose of this study was to compare brain PtiO2 with SjvO2 in severely head injured patients during phases of reduced cerebral perfusion pressure (CPP) to define a threshold in brain PtiO2 monitoring. In addition, the safety and data quality of both SjvO2 and brain PtiO2 monitoring were studied. In 15 patients with severe head injuries, SjvO2 and brain PtiO2 were monitored simultaneously. For brain PtiO2 monitoring a polarographic microcatheter was inserted in the frontal cerebral white matter, whereas for SjvO2 measurements were obtained by using a fiberoptic catheter placed in the jugular bulb. Intracranial pressure was monitored by means of an intraparenchymal catheter. Mean arterial blood pressure, CPP, end-tidal CO2, and arterial oxygen saturation (pulse oximetry) were continuously recorded. All data were simultaneously stored and analyzed using a multimodal computer system. For specific analysis, phases of marked deterioration in systemic blood pressure and consecutive reductions in CPP were investigated. There were no complications that could be attributed to the PtiO2 catheters, that is, no intracranial bleeding or infection. The "time of good data quality" was 95% in brain PtiO2 compared to 43% in SjvO2; PtiO2 monitoring could be performed twice as long as SjvO2 monitoring. During marked decreases in CPP, SjvO2 and brain PtiO2 correlated closely. A significant second-order regression curve of SjvO2 versus brain PtiO2 (p < 0.01) was plotted. At a threshold of 50% in SjvO2, brain PtiO2 was found to be within the range of 3 to 12 mm Hg, with a regression curve "best fit" value of 8.5 mm Hg. There was a close correlation between CPP and oxygenation parameters (PtiO2 and SjvO2) when CPP fell below a breakpoint of 60 mm Hg, suggesting intact cerebral autoregulation in most patients. This study demonstrates that monitoring brain PtiO2 is a safe, reliable, and sensitive diagnostic method to follow cerebral oxygenation. In comparison to SjvO2, PtiO2 is more suitable for long-term monitoring. It can be used to minimize episodes of secondary cerebral maloxygenation after severe head injury and may, hopefully, improve the outcome in severely head injured patients.