Cerebral venous oxygen content as a measure of brain energy metabolism with increased intracranial pressure and hyperventilation

The early effect of Voluven, a novel hydroxyethyl starch (130/0.4), on cerebral oxygen supply and consumption in resuscitation of rabbit with acute hemorrhagic shock

BACKGROUND

Voluven (hydroxyethyl starch [HES] 130/0.4), a new generation of HES product with low molecular weight, has been widely used for the treatment of traumatic and hemorrhagic shock in clinics. However, no data are available whether it affects the balance of cerebral oxygen supply and consumption when applied to resuscitate hemorrhagic shock. The purpose of this study was to address this question in rabbits subjected to a severe hemorrhagic shock.

METHODS

In New Zealand rabbits, an acute hemorrhagic shock was induced by withdrawing 45% to 50% of total blood volume from the femoral vein in 10 minutes when the mean arterial pressure was reduced to 60% of the baseline level. Thirty minutes after the hemorrhage, animals were infused with either an equal amount of Voluven (group V) or a tripled amount of lactated Ringer's solution (group R). The saturation of oxygen was obtained in arterial (Sao2) and venous (SjvO2) blood samples from the femoral artery and jugular bulb, respectively. Arterial oxygen content (Cao2), jugular oxygen content (CjvO2), arteriovenous oxygen difference (AVDO2), and cerebral oxygen extraction rate (CERO2) were calculated accordingly to evaluate the oxygenation state in the brain.

RESULTS

Levels of SjvO2 and CjvO2 were decreased after hemorrhagic shock, and there were increases in AVDO2 and CERO2 values. After resuscitation, the SjvO2, AVDO2, and CERO2 levels in group V were quickly recovered to the basal levels, whereas the values in group R remained in the abnormal levels (p < 0.05). There were significant differences between the groups in their SjvO2 and CERO2 levels at 30 minutes after resuscitation. In addition, the mean arterial pressure was restored to the basal levels in group V but not in group R after resuscitation (p < 0.05).

CONCLUSION

We conclude that early infusion of Voluven is beneficial for maintenance of the hemodynamic stability and for the balance of cerebral oxygen supply and consumption during the resuscitation of acute hemorrhagic shock.

Effect of Graded Hyperventilation on Cerebral Metabolism in a Cisterna Magna Blood Injection Model of Subarachnoid Hemorrhage in Rats

In subarachnoid hemorrhage (SAH) with cerebrovascular instability, hyperventilation may induce a risk of inducing or aggravating cerebral ischemia. We measured cerebral blood flow (CBF) and cerebral metabolic rates of oxygen (CMRO2), glucose (CMRglc), and lactate (CMRlac) at different PaCO2 levels after experimental SAH in rats (injection of 0.07 mL of autologous blood into the cisterna magna). Four groups of Sprague-Dawley male rats were studied at predetermined PaCO2 levels: group A: normocapnia (5.01-5.66 kPa [38.0-42.0 mm Hg]); group B: slight hyperventilation (4.34-5.00 kPa [32.5-37.5 mm Hg]); group C: moderate hyperventilation (3.67-4.33 kPa [27.5-32.4 mm Hg]); group D: profound hyperventilation (3.00-3.66 kPa [22.5-27.4 mm Hg]). Each of the four groups included eight rats with SAH and eight sham-operated controls. CBF was determined by the intracarotid Xe method; CMRo2, CMRglc, and CMRlac were obtained by cerebral arteriovenous differences. In both SAH rats and controls, hyperventilation decreased CBF in proportion to the decrement in PaCO2 without affecting either CMRO2, CMRglc, or CMRlac. In groups C and D, CBF decreased by 20%-35%, but CMRs were maintained by a compensatory increase in oxygen extraction fraction (OEF). The results show that even profound hyperventilation in this model of SAH is associated with an adequate increase in OEF so that CMRs of oxygen, glucose, and lactate remain similar to levels observed in normocapnic conditions.

Is the renal production of erythropoietin controlled by the brain stem?

Although the structure and function of erythropoietin (Epo) are well documented, the mechanisms of the regulation of the renal synthesis of Epo are still poorly understood. Especially, the description of the localization and function of the O(2)-sensitive sensor regulating the renal synthesis of Epo is insufficient. A body of evidence suggests that extrarenal O(2)-sensitive sensors, localized particularly in the brain stem, play an important role in this connection. To support this concept, high cerebral pressure with consecutive hypoxia of the brain stem was generated by insufflation of synthetic cerebrospinal fluid into the catheterized cisterna magna of rats. When the cerebral pressure of the rats was above the level of their mean arterial blood pressure or the high cerebral pressure persisted for a longer period (>/=10 min), the Epo plasma concentration increased significantly. Bilateral nephrectomy or hypophysectomy before initiation of high intracranial pressure abolished this effect. Systemic parameters (heart rate, blood pressure, Pa(O(2)), Pa(CO(2)), arterial pH, renal blood flow, glucose concentration in blood) were not affected. Other stressors, like restricting the mobility of the rats, had no effect on Epo production. Hence, the effect of high cerebral pressure on renal synthesis of Epo seems to be specific. Increasing cerebral hydrostatic pressure leads to increased renal synthesis of Epo. Obviously, during hypoxia, cerebral O(2)-sensitive sensors release humoral factors, triggering the renal synthesis of Epo. The structure and function of these "Epo-releasing-factors" will have to be characterized in future experiments.

Hyperventilation in head injury: a review

The aim of this review was to consider the effects of induced hypocapnia both on systemic physiology and on the physiology of the intracranial system. Hyperventilation lowers intracranial pressure (ICP) by the induction of cerebral vasoconstriction with a subsequent decrease in cerebral blood volume. The downside of hyperventilation, however, is that cerebral vasoconstriction may decrease cerebral blood flow to ischemic levels. Considering the risk-benefit relation, it would appear to be clear that hyperventilation should only be considered in patients with raised ICP, in a tailored way and under specific monitoring. Controversy exists, for instance, on specific indications, timing, depth of hypocapnia, and duration. This review has specific reference to traumatic brain injury, and is based on an extensive evaluation of the literature and on expert opinion.

Metabolic crisis without brain ischemia is common after traumatic brain injury: a combined microdialysis and positron emission tomography study

Brain trauma is accompanied by regional alterations of brain metabolism, reduction in metabolic rates and possible energy crisis. We hypothesize that microdialysis markers of energy crisis are present during the critical period of intensive care despite the absence of brain ischemia. In all, 19 brain injury patients (mean GCS 6) underwent combined positron emission tomography (PET) for metabolism of glucose (CMRglu) and oxygen (CMRO(2)) and cerebral microdialysis (MD) at a mean time of 36 h after injury. Microdialysis values were compared with the regional mean PET values adjacent to the probe. Longitudinal MD data revealed a 25% incidence rate of metabolic crisis (elevated lactate/pyruvate ratio (LPR) > 40) but only a 2.4% incidence rate of ischemia. Positron emission tomography imaging revealed a 1% incidence of ischemia across all voxels as measured by oxygen extraction fraction (OEF) and cerebral venous oxygen content (CvO(2)). In the region of the MD probe, PET imaging revealed ischemia in a single patient despite increased LPR in other patients. Lactate/pyruvate ratio correlated negatively with CMRO(2) (P < 0.001), but not with OEF or CvO(2). Traumatic brain injury leads to a state of persistent metabolic crisis as reflected by abnormal cerebral microdialysis LPR that is not related to ischemia.

Subcortical White Matter Metabolic Changes Remote from Focal Hemorrhagic Lesions Suggest Diffuse Injury after Human Traumatic Brain Injury

OBJECTIVE:

We used positron emission tomographic studies to prospectively examine the relationship between glucose and oxidative metabolism in the subcortical white matter (WM) acutely after traumatic brain injury (TBI). The objective was to determine the nature, extent, and degree of metabolic abnormalities in subcortical brain regions remote from hemorrhagic lesions.

METHODS:

Sixteen normal volunteers and 10 TBI patients (Glasgow Coma Scale score, 4–10; age, 17–64 yr; 6 with focal and 4 with diffuse injury) were studied. Each subject underwent dynamic positron emission tomographic studies using [15O]CO, 15O2, [15O]H2O, and fluorodeoxyglucose plus a magnetic resonance imaging scan acutely after TBI. Parametric images of the metabolic rate of oxygen and metabolic rate of glucose were generated, and a molar oxygen-to-glucose utilization ratio was calculated. Data from gray matter and WM remote from hemorrhagic lesions, plus whole brain, were analyzed.

RESULTS:

There was a significant reduction in the subcortical WM oxygen-to-glucose utilization ratio after TBI compared with normal values (3.99 ± 0.77 versus 5.37 ± 1.00; P &lt; 0.01), whereas the mean cortical gray matter and whole-brain values remained unchanged. WM metabolic changes, which were diffuse throughout the hemispheres, were characterized by a reduction in the metabolic rate of oxygen without a concomitant drop in the metabolic rate of glucose.

CONCLUSION:

The extent and degree of subcortical WM metabolic abnormalities after moderate and severe TBI suggest that diffuse WM injury is a general phenomenon after such injuries. This pervasive finding may indicate that the concept of focal traumatic injury, although valid from a computed tomographic imaging standpoint, may be misleading when considering metabolic derangements associated with TBI.

Defining ischemic burden after traumatic brain injury using 15O PET imaging of cerebral physiology

Whereas postmortem ischemic damage is common in head injury, antemortem demonstration of ischemia has proven to be elusive. Although 15O positron emission tomography may be useful in this area, the technique has traditionally analyzed data within regions of interest (ROIs) to improve statistical accuracy. In head injury, such techniques are limited because of the lack of a priori knowledge regarding the location of ischemia, coexistence of hyperaemia, and difficulty in defining ischemic cerebral blood flow (CBF) and cerebral oxygen metabolism (CMRO2) levels. We report a novel method for defining disease pathophysiology following head injury. Voxel-based approaches are used to define the distribution of oxygen extraction fraction (OEF) across the entire brain; the standard deviation of this distribution provides a measure of the variability of OEF. These data are also used to integrate voxels above a threshold OEF value to produce an ROI based upon coherent physiology rather than spatial contiguity (the ischemic brain volume; IBV). However, such approaches may suffer from poor statistical accuracy, particularly in regions with low blood flow. The magnitude of these errors has been assessed in modeling experiments using the Hoffman brain phantom and modified control datasets. We conclude that this technique is a valid and useful tool for quantifying ischemic burden after traumatic brain injury.

Incidence and mechanisms of cerebral ischemia in early clinical head injury

Antemortem demonstration of ischemia has proved elusive in head injury because regional CBF reductions may represent hypoperfusion appropriately coupled to hypometabolism. Fifteen patients underwent positron emission tomography within 24 hours of head injury to map cerebral blood flow (CBF), cerebral oxygen metabolism (CMRO2), and oxygen extraction fraction (OEF). We estimated the volume of ischemic brain (IBV) and used the standard deviation of the OEF distribution to estimate the efficiency of coupling between CBF and CMRO2. The IBV in patients was significantly higher than controls (67 +/- 69 vs. 2 +/- 3 mL; P < 0.01). The coexistence of relative ischemia and hyperemia in some patients implies mismatching of perfusion to oxygen use. Whereas the saturation of jugular bulb blood (SjO2) correlated with the IBV (r = 0.8, P < 0.01), SjO2 values of 50% were only achieved at an IBV of 170 +/- 63 mL (mean +/- 95% CI), which equates to 13 +/- 5% of the brain. Increases in IBV correlated with a poor Glasgow Outcome Score 6 months after injury (rho = -0.6, P < 0.05). These results suggest significant ischemia within the first day after head injury. The ischemic burden represented by this "traumatic penumbra" is poorly detected by bedside clinical monitors and has significant associations with outcome.

Correlation between cerebral blood flow, substrate delivery, and metabolism in head injury: a combined microdialysis and triple oxygen positron emission tomography study

Microdialysis continuously monitors the chemistry of a small focal volume of the cerebral extracellular space. Conversely, positron emission tomography (PET) establishes metabolism of the whole brain, but only for the duration of the scan. The objective of this study was to apply both techniques to head-injured patients simultaneously to assess the relation between microdialysis (glucose, lactate, lactate/pyruvate [L/P] ratio, and glutamate) and PET (cerebral blood flow [CBF], cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen) parameters. Microdialysis catheters were inserted into the frontal cerebral cortex and adipose tissue of the anterior abdominal wall of 17 severely head-injured patients. Microdialysis was performed during PET scans, with regions of interest defined by the location of the microdialysis catheter membrane. An intervention (hyperventilation) was performed in 13 patients. The results showed that combining PET and microdialysis to monitor metabolism in ventilated patients is feasible and safe, although logistically complex. There was a significant relation between the L/P ratio and the OEF (Spearman r = 0.69, P = 0.002). There was no significant relation between CBF and the microdialysis parameters. Moderate short-term hyperventilation appeared to be tolerated in terms of brain chemistry, although no areas were sampled by microdialysis where the OEF exceeded 70%. Hyperventilation causing a reduction of the arterial carbon dioxide tension by 0.9 kPa resulted in a significant elevation of the OEF, in association with a reduction in glucose, but no significant elevation in the L/P ratio or glutamate.

Increased Intracerebral Pressure Following Stroke

Increased intracerebral pressure with lethal herniation still accounts for high mortality rates in patients with massive strokes. Patients that are likely to develop increased intracranial pressure can often be identified within the first few hours after stroke onset. Although medical management seems to fail in most of these patients, early hemicraniectomy and induced moderate hypothermia (32;C to 33;C) represent two novel therapeutic approaches to improve neurologic outcomes and decrease mortality rates.

Transcranial Doppler monitoring compared with invasive monitoring of intracranial pressure during acute intracranial hypertension

OBJECTIVE

To determine whether a simple transcanial Doppler waveform variable-pulsatility difference (systolic - diastolic blood flow velocity) can serve as a measure of critical changes in cerebral perfusion.

METHODS

Thirteen pigs were anesthetized (anesthesia maintained with halothane) and ventilated to maintain normoxia and normocarbia. To measure mean arterial pressure, hemoglobin, and blood gases, the right carotid artery was cannulated. The right intracranial lateral ventricle was cannulated to measure and increase intracranial pressure; the right internal jugular vein was cannulated in 8 of 13 pigs to measure jugular venous oxygen saturation and to calculate cerebral arteriovenous oxygen content difference. Intracranial pressure was also monitored continuously with a subdural bolt in the contralateral frontal region, and blood flow velocity in the middle cerebral artery was measured with a transcranial Doppler probe on the right orbital region. Intracranial pressure was increased in increments of 10 to 20 mmHg by infusing saline through the ventriculostomy catheter until the transcranial Doppler indicated that blood flow velocity had ceased, at which point all variables were allowed to return to baseline. If mean arterial pressure failed to return to baseline, epinephrine, 0.01 to 0.1 microg/kg/min, was infused. Useful data were obtained from 8 pigs and were analyzed separately for pigs that received epinephrine (n = 4) and those that did not (n = 4).

RESULTS

Transcranial Doppler measurements correlated more closely with cerebral perfusion pressure = (mean arterial pressure - intracranial pressure) than with intracranial pressure. In the range of 30 to 60 mmHg, cerebral perfusion pressure correlated linearly with the pulsatility difference. The closest nonlinear correlation (third order polynomial relationship) was noted between cerebral perfusion pressure and pulsatility difference (r = 0.8, P < 0.001, n = 217), for the animals that did not receive epinephrine. When a cerebral perfusion pressure < 60 mmHg and a cerebral arteriovenous oxygen content difference > 6.5 vol% were used to define limits of abnormal, pulsatility difference was a sensitive and specific indicator of abnormality in either variable. Pulsatility difference of > 70 cm/sec had > 77.1% and 86.7% positive accuracy rate, and < 0% and 14.3% negative accuracy rate for abnormal cerebral perfusion pressure (CPP) and cerebral arterio-venous O2 (C[a-v]O2), respectively.

CONCLUSIONS

In pigs with induced diffuse intracranial hypertension, noninvasive transcranial Doppler waveform monitoring of pulsatility difference can identify increased cerebral oxygen extraction and dangerously decreased cerebral perfusion pressure.

Cerebral oxygenation during warming after cardiopulmonary bypass

OBJECTIVES

To evaluate jugular venous oxygen saturation (SjVO2), measured with a fiberoptic oximetry catheter, and brain tissue oxygen saturation, measured by near-infrared spectroscopy (NIRSO2), as monitors of cerebral oxygenation during cardiopulmonary bypass surgery.

DESIGN

Prospective, clinical study.

SETTING

Operating room of a Veterans Administration Hospital.

PATIENTS

Nineteen patients undergoing moderate hypothermic cardiopulmonary bypass surgery.

INTERVENTIONS

SjvO2 and NIRSO2 were monitored in the patients during the surgical procedure.

MEASUREMENTS AND MAIN RESULTS

Moderate hypothermic cardiopulmonary bypass surgery had two distinct cerebral hemodynamic phases. While the patients were hypothermic, SjvO2 averaged 80 +/- 7% and none of the patients had an increase in cerebral lactate production. During the rewarming period, however, reductions in SjvO2 to < 50% occurred in 16 (84%) patients and increased cerebral anaerobic metabolism developed in 11 (58%) patients. SjvO2 during rewarming was dependent on mean arterial pressure, with 60 mm Hg appearing to be a critical value. Two other factors appeared to also contribute to the jugular desaturation, a low hematocrit and a rapid warming time. The SjvO2 catheter had excellent performance during the surgery. The average difference between paired measurements of SjvO2 by the catheter and in blood samples was -0.4 +/- 4.25%, and the correlation between the two measurements was highly significant (r2 = .93; p < .001). The NIRSO2 trended with the SjvO2 in most patients (r2 = .63; p < .001).

CONCLUSIONS

The study confirms other studies showing that jugular venous desaturation can occur during rewarming after cardiopulmonary bypass surgery. Presently, SjvO2 appears to be a better monitor of cerebral oxygenation than NIRSO2. However, NIRSO2 has promise as a noninvasive monitor of cerebral oxygenation if future developments allow more quantitative measurements of oxygen saturation.

Cerebral arteriovenous oxygen difference: a predictor of cerebral infarction and outcome in patients with severe head injury

Jugular bulb oxygen monitoring can be used to estimate the adequacy of cerebral blood flow to support cerebral metabolism after severe head injury. In the present study, the authors studied the cerebral arteriovenous oxygen difference (AVDO[2]) before and after treatment in 32 head-injured patients (Glasgow Coma Scale scores < or = 8) to examine the relationships among AVDO and cerebral perfusion pressure (CPP), delayed cerebral infarction, and outcome. Fifteen patients (Group A) underwent craniotomy for hematoma evacuation and 17 (Group B) received mannitol for sustained intracranial hypertension (intracranial pressure > 20 mm Hg, > 10 minutes). Radiographic evidence of delayed cerebral infarction was observed in 14 patients. Overall, 17 patients died or were severely disabled. Cerebral AVDO(2) was elevated before craniotomy or mannitol administration; the mean AVDO(2) for all patients before treatment was 8.6 +/- 1.8 vol%. Following craniotomy or mannitol administration, the AVDO(2) decreased in 27 patients and increased in five patients (mean AVDO(2) 6.2 +/- 2.1 vol% in all patients; 6 +/- 1.9 vol% in Group A; and 6.4 +/- 2.4 vol% in Group B). The mean CPP was 75 +/- 9.8 mm Hg and no relationship with AVDO(2) was demonstrated. Before treatment, the AVDO(2) was not associated with delayed cerebral infarction or outcome. By contrast, a limited improvement in elevated AVDO(2) after craniotomy or mannitol administration was significantly associated with delayed cerebral infarction (Group A: p < 0.001; Group B: p < 0.01). Similarly, a limited improvement in elevated AVDO(2) after treatment was significantly associated with an unfavorable outcome (Group A: p < 0.01; Group B: p < 0.001). In conclusion, these findings strongly indicate that, despite adequate cerebral perfusion, limited improvement in elevated cerebral AVDO(2) after treatment consisting of either craniotomy or mannitol administration may be used to help predict delayed cerebral infarction and poor outcome after traumatic brain injury.

Cerebral arteriovenous oxygen difference: a predictor of cerebral infarction and outcome in patients with severe head injury

Jugular bulb oxygen monitoring can be used to estimate the adequacy of cerebral blood flow to support cerebral metabolism after severe head injury. In the present study, the authors studied the cerebral arteriovenous oxygen difference (AVDO2) before and after treatment in 32 head-injured patients (Glasgow Coma Scale scores ¾ 8) to examine the relationships among AVDO2 and cerebral perfusion pressure (CPP), delayed cerebral infarction, and outcome. Fifteen patients (Group A) underwent craniotomy for hematoma evacuation and 17 (Group B) received mannitol for sustained intracranial hypertension (intracranial pressure > 20 mm Hg, > 10 minutes). Radiographic evidence of delayed cerebral infarction was observed in 14 patients. Overall, 17 patients died or were severely disabled. Cerebral AVDO2 was elevated before craniotomy or mannitol administration; the mean AVDO2 for all patients before treatment was 8.6 ± 1.8 vol%. Following craniotomy or mannitol administration, the AVDO2 decreased in 27 patients and increased in five patients (mean AVDO2 6.2 ± 2.1 vol% in all patients; 6 ± 1.9 vol% in Group A; and 6.4 ± 2.4 vol% in Group B). The mean CPP was 75 ± 9.8 mm Hg and no relationship with AVDO2 was demonstrated. Before treatment, the AVDO2 was not associated with delayed cerebral infarction or outcome. By contrast, a limited improvement in elevated AVDO2 after craniotomy or mannitol administration was significantly associated with delayed cerebral infarction (Group A: p < 0.001; Group B: p < 0.01). Similarly, a limited improvement in elevated AVDO2 after treatment was significantly associated with an unfavorable outcome (Group A: p < 0.01; Group B: p < 0.001). In conclusion, these findings strongly indicate that, despite adequate cerebral perfusion, limited improvement in elevated cerebral AVDO2 after treatment consisting of either craniotomy or mannitol administration may be used to help predict delayed cerebral infarction and poor outcome after traumatic brain injury.

[Measurement of arteriovenous oxygen difference in the monitoring of patients with subarachnoid hemorrhage due to cerebral aneurysm]

The arterious venous oxygen difference (AVDO2) due to the close relationship with cerebral metabolic rate of oxygen and cerebral blood flow shows metabolic alterations that occur in some pathological situations in the brain including subarachnoid haemorrhage. The AVDO2 was calculated by the Fick equation and the results evaluated by the Glasgow outcome scale. Measurements of arteriojugular oxygen difference were carried out in 30 patients with subarachnoid haemorrhage due to rupture of intracranial aneurysms, as an attempt to monitor the relationship between changes in AVDO2, clinical picture, and evolution of the patients. The subarachnoid haemorrhage was diagnosed by CT scan in 17 patients and by lumbar punction in 13 and the diagnosis of arterial vasospasm was carried out by clinical evaluation and confirmed by four vessels angiogram in only eight patients. Eighteen patients were admitted with Hunt & Hess (H&H) I/II, seven with H&H III and five with H&H IV/V. Nineteen patients had AVDO2 normal and this group had three deaths; five patients had AVDO2 continuously low with three deaths; and six patients had AVDO2 continuously high with two deaths. The patients with normal AVDO2 had better prognosis and clinical evolution than the patients with abnormal values of AVDO2. In conclusion, AVDO2 measurements could not be correlated with the diagnosis of vasospasm, but was useful in the early identification of metabolic changes that occur after subarachnoid haemorrhage and could be used as an supplementary monitoring in the clinical evaluation of patients with this pathology.

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.

The use of hyperventilation and its impact on cerebral ischemia in the treatment of traumatic brain injury

Traumatic brain injury is a common occurrence in the United States, leading to approximately 190,000 deaths or long-term disabilities. Following the primary insult, secondary disturbances in cerebral blood flow (CBF) and metabolism may have deleterious effects on potentially viable neurons. Recent studies evaluating CBF immediately following head injury have revealed flows low enough to produce cerebral ischemia. Hyperventilation is used routinely to lower suspected increased intracranial pressure (ICP). Aggressive hyperventilation produces a marked reduction in CBF, which may give rise to or exacerbate cerebral ischemia, thus enhancing rather than reducing secondary injury. This article reviews the role of hyperventilation in the treatment of increased ICP and its impact on cerebral ischemia following traumatic brain injury.

Intraoperative jugular desaturation during surgery for traumatic intracranial hematomas

Traumatic intracranial hematomas which are present on hospital admission or which develop during the hospital course are associated with a worse neurological outcome than diffuse injuries. The purpose of this study was to monitor jugular venous oxygen saturation (Sjvo2) during surgery for evacuation of traumatic intracranial mass lesions, to determine the incidence and the causes of jugular venous desaturation, and to assess the usefulness of Sjvo2 monitoring in this setting. Twenty-five severely head injured patients were monitored during 27 surgical procedures. At the start of the surgical procedure, the median Sjvo2 was 47% (range 25%-89%). Seventeen (63%) of the patients had a Sjvo2 less than 50%. Five patients had extremely low Sjvo2 values (< or = 30%). Upon evacuation of the intracranial hematoma, there was a significant (P < 0.001) increase in the median Sjvo2 to 65% (range 50%-88%). Intracranial hypertension was the primary cause of the low Sjvo2, as confirmed by the response to surgical evacuation. Hypotension (mean arterial pressure < 80 mm Hg) was a contributing factor in seven of the cases of jugular desaturation. The definitive treatment of a traumatic intracranial hematoma is surgical evacuation. However, during the period prior to evacuation of the hematoma, jugular venous desaturation was common, suggesting that monitoring Sjvo2 might provide useful information about the adequacy of cerebral perfusion.

Severe head injury in the United Kingdom and Ireland: a survey of practice and implications for management

OBJECTIVE

To study the current intensive care management of patients with severe head injury (defined as a Glasgow Coma Scale score of < or = 8) in neurosurgical referral centers in the United Kingdom (UK) and ireland.

DATA COLLECTION

A questionnaire was sent to the directors of the 44 neurosurgical referral units identified from the UK Medical Directory. After 4 wks, a copy of the questionnaire was sent to all nonresponders, with a cover letter urging them to respond. The aim was to collect data regarding the characteristics of the intensive care units (ICU), sedation, monitoring modalities used, the treatment of intracranial hypertension, and general care of severely head-injured patients.

DATA EXTRACTION

Forty completed questionnaires were returned. Only 35 (88%) centers provided care for the severely head-injured as defined in the questionnaire. Patients were managed in specialized neurosurgical ICUs in 66% of centers and in general ICUs in the remainder of the centers. The ICUs were coordinated by an anesthesiologist in 66% of instances and by a neurosurgeon in 23%. The mean number of beds per units was 7.9 (range 4 to 16), with 1:1 nurse/bed ratio and 5.5 nurses per bed (total number of nursing staff per bed) (range 2.75 to 8). Annual caseload varied between units with the majority of units (49%) receiving between 25 and 50 patients with severe head injury, 23% receiving between 50 and 100 patients with severe head injury, and 29% receiving > 100 patients with severe head injury. There was considerable variability in both the nature of monitoring and therapy between centers. Although blood and central venous pressures were invasively monitored in > 50% of the patients in 94% and 77% of the centers, respectively, intracranial pressure was only monitored routinely in 57% of the centers. Jugular venous bulb oximetry, transcranial Doppler ultrasonography, electroencephalography, and near-infrared spectroscopy were rarely used. Nearly all centers used propofol and midazolam for sedation, with morphine, fentanyl, and alfentanil as the main analgesics. Muscle relaxation was commonly used, with 40% of the centers employing it in 100% of their patients. Atracurium and vecuronium were the most commonly used agents. Only 68% of the centers had a protocol for the treatment of intracranial hypertension. Although hyperventilation to a Paco2 of 26 to 30 torr (3.5 to 4.0 kPa) was the norm in the majority of centers (56%), two centers aimed for Paco2 values < 26 torr (< 3.5 kPa). A quarter of the units did not aim for a cerebral perfusion pressure of > 60 mm Hg. Mild hypothermia was rarely used and 14% of the centers continued to use corticosteroids for the treatment of intracranial hypertension as a result of head trauma.

CONCLUSION

We conclude that there are wide variations in the management of the severely head-injured patient in the UK and Ireland. Some of the therapies employed are not supported by available research findings. Rationalization (using rational management, i.e., based on good evidence) of the intensive care management of severe head injury with the development of widely accepted guidelines may result in an improvement in the quality of care of the head-injured patient.

Early discovery of a traumatic carotid-cavernous sinus fistula by jugular venous oxygen saturation monitoring. Case report

This report describes the early diagnosis, due to an acute increase of jugular venous oxygen saturation occurring 20 hours after trauma, of a traumatic carotid-cavernous sinus fistula after severe head injury. Hyperemia in severe head injury should be treated only after an intracerebral arteriovenous communication has been excluded.

Cerebral edema and intracranial pressure monitoring

With the wide acceptance of liver transplantation as a therapeutic alternative in fulminant hepatic failure (FHF), the successful management of patients with this syndrome has acquired a new urgency. Topping the list of medical problems is the development of brain swelling. Two decades after the recognition of its importance, brain edema and intracranial hypertension still constitute a major cause of death in these patients. In a more recent classification of FHF, brain edema was especially prominent in those subjects with "hyperacute failure," in whom a period of 7 days or less elapsed between the development of jaundice and encephalopathy. The goal of this review is to discuss two aspects of this clinical problem. On one hand, elucidation of its pathogenesis should lead to a more rational therapeutic approach; such an information would also be valuable to understand the relationship between hepatic encephalopathy and brain edema, a source of controversy. Studies of pathogenic mechanisms are difficult to perform in humans and animal models of FHF have proven valuable, as brain swelling can be detected with some regularity. On the other hand, an increasing array of techniques is now available in the intensive care setting to monitor patients with FHF. Of these, intracranial pressure monitoring has received the most critical attention. However, concerns with the risks of craniotomy and the need to acquire more dynamic information has led several groups to explore non-invasive methods that evaluate the consequences of intracranial hypertension. Their role, though potentially exciting, is still uncertain.

Continuous monitoring of jugular bulb oxygen saturation in comatose patients--therapeutic implications

Comatose patients run a high risk of developing cerebral ischaemia which may considerably influence final outcome. It would therefore be extremely useful if one could monitor cerebral blood flow in these patients. Since there is a close correlation between the arteriovenous difference of oxygen and cerebral blood flow, it was a logical step to place a fiberoptic catheter in the jugular bulb for continuous measurement of cerebrovenous oxygen saturation. We have monitored cerebral oxygenation in 54 patients, comatose because of severe head injury, intracerebral haemorrhage or subarachnoid haemorrhage. Normal jugular venous oxygen saturation (SJVO2) ranges between 60 and 90%. A decline to below 50% is considered indicative of cerebral ischaemia. Spontaneous episodes of desaturation (SJVO2 < 50% for at least 15 min) were frequent during the acute phase of these insults. Many of these desaturation episodes could be attributed to hyperventilation, even though considered moderate. Likewise, insufficient cerebral perfusion pressure and severe vasospasm were found to be important causes of desaturation episodes. In many instances, tailoring of ventilation or induced hypervolaemia and hypertension were capable of reversing these low flow states. The new method of continuous cerebrovenous oximetry is expected to contribute to a better outcome by enabling timely detection and treatment of insufficient cerebral perfusion.

[Is there still a place for routine deep hypocapnia in intracranial surgery?]

Deliberate hypocapnia during the anaesthetic management of the patient undergoing craniotomy has become an accepted standard of care. However there has been a resurgence of interest, in how hypocapnia should be applied in intra- and extra-operative settings. There are three possible therapeutic effects of hypocapnia, namely, (a) reduction of brain bulk through a reduction in cerebral blood volume, with a decrease cerebral blood flow; (b) developing an "inverse steal" by redistribution of blood from normal to ischaemic regions and (c) acting to offset cerebral acidosis by increasing pH in the extracellular space. In anaesthetic intraoperative practice, hypocapnia is used as a specific treatment of, or prophylaxis against, intracranial hypertension during induction of anaesthesia and the period before dural exposure. More commonly, hypocapnia is used for intraoperative brain relaxation (intracranial pressure = 0). Severe hypocapnia (< 20 mmHg) may result in cerebral production of lactate; however no studies have shown that a Paco2 in the range of 23-28 mmHg has deleterious effects. Recent studies in head-injured patients suggest that routine long-term hyperventilation, without an objective index of cerebral flow/metabolism coupling, may place the brain at risk for adverse outcome. The few data available for intraoperative management suggest that Paco2 figures of 30-35 mmHg result in acceptable operating conditions. Unless otherwise specifically indicated by surgical conditions or cerebral flow/metabolism coupling (e.g. jugular O2 saturation), routine application of profound (Paco2 < 28-30 mmHg) hyperventilation should probably be avoided and its use needs reevaluation.

Concurrent changes in intracranial pressure, cerebral blood flow velocity, and brain energy metabolism in rabbits with acute intracranial hypertension

The relationship between intracranial pressure or cerebral perfusion pressure (CPP), cerebral blood flow, and brain energy failure is unpredictable throughout the development of acute intracranial hypertension. The purpose of the present study was to correlate intracranial pressure with cerebral blood flow velocities and brain energy metabolism in adult rabbits. The acute intracranial hypertension was achieved by pressure transmission. Transcranial Doppler wave-forms were obtained from the basilar artery for monitoring cerebral blood flow velocities. 31P-Magnetic resonance spectroscopy was used to assess brain energy metabolism. The diastolic blood flow velocity began to decrease significantly (34.5%) when the intracranial pressure was equal to half the diastolic arterial pressure for a CPP of 36 +/- 18 mmHg. Circulatory cerebral resistances increased significantly (55%) for the same value of CPP. Diastolic frequency was near zero when intracranial pressure approached diastolic arterial pressure (51 +/- 12 mmHg), corresponding to a CPP of 30 +/- 15 mmHg. At the same time, only a tendency for brain energy metabolism to decrease was observed. Consequently, transcranial Doppler sonography could be proposed for the follow-up of intracranial hypertension. Magnetic resonance spectroscopy could help to monitor these patients and could be especially proposed in case of high intracranial pressure (near diastolic arterial pressure). The joint use of these two methods would help in making appropriate therapeutic decision in humans.

Continuous monitoring of jugular bulb oxygen saturation as a measure of the shunt flow of cerebral arteriovenous malformations

Jugular bulb oxygen saturation (SjO2) was monitored during preoperative embolization procedures in a consecutive series of 15 patients with large supratentorial arteriovenous malformations (AVM's) in order to test the hypothesis that changes in the shunt flow ratio can be continuously evaluated from the SjO2. A fiberoptic catheter was placed at the dominant jugular bulb. The SjO2 measured using jugular blood withdrawn before embolization was significantly higher than the SjO2 measured at the end of the final embolization procedure (mean +/- standard deviation 84.1% +/- 12.7% vs. 74.2% +/- 10.9%, p < 0.0001), showing a positive correlation with the AVM volume (r = 0.66, p < 0.001). Continuous monitoring of SjO2 via the fiberoptic catheter revealed a progressive decrease in association with the embolization procedures. Microsurgical resection of the AVM was performed at 1 to 2 weeks after the final embolization. Cases in which postoperative hemispheric deformation was revealed on computerized tomography demonstrated a higher SjO2 at the end of embolization compared to that in the remaining cases (81.6% +/- 8.6% vs. 67.8% +/- 8.4%, p < 0.008). Hemispheric deformation was observed in all cases in which the SjO2 did not decline to a level below 90% following embolization. The risk of severe hyperemic complications appeared to be greatly diminished when the SjO2 fell to below 80%. Assuming that the oxygen saturation of the perfusion flow (SjpO2) ranges from 50% to 75%, the ratio of the shunt flow to total flow at an SjO2 of 90% was estimated to be 0.6 to 0.8 based on the following equation: shunt flow/(perfusion flow + shunt flow) = (SjO2 - SjpO2)/(arterial oxygen saturation - SjpO2). These results suggest that monitoring the SjO2 provides real-time information concerning the progress of embolization and helps to determine whether the embolization has progressed sufficiently to avoid postoperative hyperemic complications.

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

Global cerebral oxygenation, perfusion pressure, and expired CO2 tension were continuously monitored in 69 adults with acute severe closed brain trauma. Cerebral oxygenation was assessed by continuous fiberoptic monitoring of jugular bulb oxyhemoglobin saturation, in conjunction with continuous monitoring of arterial oxyhemoglobin saturation. Jugular desaturation associated with arterial desaturation (hypoxemic cerebral hypoxia) was evaluated and managed. A total of 121 episodes of combined arterial and jugular desaturation were documented, 76 in the presence of gross abnormalities identified on chest roentgenograms. Prolonged episodes that did not respond promptly to treatment occurred 32 times in 12 patients, usually after the initial 72 hours posttrauma. The remaining 89 episodes promptly responded to treatment and occurred predominantly within the initial 72 hours. Profound but brief desaturation was not associated with neurological deterioration, while profound and prolonged desaturation was accompanied by significant decreases in Glasgow Coma Scale scores, even though intracranial pressure levels were not significantly different in these two groups. Global cerebral hypoxia that does not respond promptly to treatment appears to be independently deleterious to neurological function in severely head-injured patients.

Monitoring of jugular venous oxygen saturation in comatose patients with subarachnoid haemorrhage and intracerebral haematomas

To prevent secondary cerebral ischemia in comatose patients it would be of great importance to assess cerebral blood flow. Recently monitoring of the jugular venous oxygen saturation (SJVO2) has been shown to continuously evaluate cerebral oxygenation and to estimate cerebral blood flow. While most of these studies have dealt with severely head injured patients, we investigated cerebral oxygenation in 50 comatose patients due to an intracerebral haematoma (n = 14), subarachnoid haemorrhage (n = 12) and severe head injury (n = 24). In these groups of patients, the reaction of SJVO2 to hyperventilation and to lowering of blood pressure was studied. Moderate hyperventilation from 35 to 28 mmHg resulted in a significant decrease of SJVO2 in all groups. A critical SJVO2 between 50 and 55% was found in one half of the patients studied, a pathological SJVO2 below 50% was seen in 23% of the cases. Lowering of arterial blood pressure within the limits of autoregulation resulted in decreases of SJVO2 in patients with intracerebral haematomas only. 55% of these patients showed signs of insufficient cerebral oxygenation. Furthermore the frequency of spontaneous desaturation episodes was studied retrospectively and comparison made between the different groups. These episodes were found more frequently in patients with intracerebral haematomas compared to patients with severe head injury. In conclusion, monitoring of jugular venous oxygen saturation is a valuable tool for detecting and treating insufficient cerebral oxygenation in comatose patients following intracerebral haemorrhage, subarachnoid haemorrhage and severe head injury.

Cerebral circulation and metabolism after severe traumatic brain injury: the elusive role of ischemia

Although experimental and pathological studies suggest an important role for ischemia in the majority of fatal cases of traumatic brain injury, ischemia has been a rare finding in most clinical studies of cerebral blood flow (CBF) in head-injured patients. The hypothesis of the present study was that cerebral ischemia occurs in the first few hours after injury, but that CBF measurements have not been performed early enough. Early measurements of CBF (by the 133Xe intravenous method) and arteriovenous oxygen difference (AVDO2) were obtained in 186 adult head-injured patients with a Glasgow Coma Scale score of 8 or less, and were correlated with neurological status and outcome. During the first 6 hours after injury, CBF was low (22.5 +/- 5.2 ml/100 gm/min) but increased significantly during the first 24 hours. The AVDO2 followed the opposite course; the decline of AVDO2 was most profound in patients with low motor scores, suggesting relative hyperemia after 24 hours. A significant correlation between motor score and CBF was found in the first 8 hours after injury (Spearman coefficient = 0.69, p less than 0.001), but as early as 12 hours postinjury this correlation was lost. A similar pattern was found for the relationship between CBF and outcome. Cerebral blood flow below the threshold for infarction (CBF less than or equal to 18 ml/100 gm/min) was found in one-third of the studies obtained within 6 hours, the incidence rapidly decreasing thereafter. A low CBF after 24 hours was not generally associated with a high AVDO2, and was probably a reflection of low oxidative metabolism rather than frank ischemia. In 24 patients, a CBF of 18 ml/100 gm/min or less was found at some point after injury; the mortality rate was significantly higher in this subgroup, and survivors did worse. In some cases, ischemia was successfully treated by reducing hyperventilation or inducing arterial hypertension. These results support the above hypothesis, and suggest that early ischemia after traumatic brain injury may be an important factor determining neurological outcome. Moreover, these data indicate that early hyperventilation or lowering of blood pressure to prevent brain edema may be harmful.