Regional cerebral blood flow and intraventricular pressure in acute head injuries

Cerebral blood flow and metabolism in children with severe head injuries. Part 2: Cerebrovascular resistance and its determinants

It has been proposed that in children with severe head injuries the cerebral circulation does not respond appropriately to normal physiological control mechanisms, making children more susceptible than adults to low cerebrovascular resistance, increased cerebral blood flow (cerebral hyperaemia), and raised intracranial pressure. To investigate this issue, 122 serial measurements of cerebrovascular resistance in 17 children with severe head injuries have been performed and related to cerebral perfusion pressure, arterial CO2 (PaCO2), arterial oxygen content (AO2), and the cerebral metabolic rate of oxygen (CMRO2). Cerebrovascular resistance values (mean (SD) 1.54 (0.61) mm Hg.ml-1.100 g.min) were normal or raised in most cases; 71 values (58%) were within the normal range, 39 (32%) above the upper limit, and only 12 (10%) below the lower limit. There was a significant correlation between cerebral perfusion pressure and cerebrovascular resistance (r = 0.32, p = 0.0003), suggesting preservation of pressure autoregulation. This correlation was absent in four of the five children who died or survived with severe handicap. Analysis by multilevel modelling indicated that, as in normal subjects, CMRO2, CPP, AO2, PaCO2, and cerebrovenous pH were important independent determinants of cerebrovascular resistance. The results indicate that normal cerebrovascular reactivity is often preserved in children with severe head injuries but may be impaired in the most severely injured patients.

99mTc-HMPAO SPECT of the brain in mild to moderate traumatic brain injury patients: compared with CT--a prospective study

Single photon emission computed tomography (SPECT) with Technetium-99m hexamethyl propylenamine oxime (Tc-99m-HMPAO) was used in 20 patients with mild to moderate traumatic brain injury (TBI) to evaluate the effects of brain trauma on regional cerebral blood flow (rCBF). SPECT scan was compared with CT scan in 16 patients. SPECT showed intraparenchymal differences in rCBF more often than lesions diagnosed with CT scans (87.5% vs. 37.5%). In five of six patients with lesions in both modalities, the area of involvement was relatively larger on SPECT scans than on CT scans. Contrecoup changes were seen in five patients on SPECT alone, two patients with CT alone and one patient had contrecoup lesions on CT and SPECT. Of the eight patients (50%) with skull fractures, seven (43.7%) had rCBF findings on SPECT scan and five (31.3%) demonstrated decrease in rCBF in brain underlying the fracture. All these patients with fractures had normal brain on CT scans. Conversely, extra-axial lesions and fractures evident on CT did not visualize on SPECT, but SPECT demonstrated associated changes in rCBF. Although there is still lack of clinical and pathological correlation, SPECT appears to be a promising method for a more sensitive evaluation of axial lesions in patients with mild to moderate TBI.

The management of cerebral perfusion pressure and intracranial pressure after severe head injury

Neurosurgical intervention attempts to minimize secondary central nervous system injury after severe head injury through the evacuation of mass lesions with subsequent manipulation of cerebral perfusion pressure and intracranial pressure. The normal brain couples blood flow to metabolic demand through autoregulation of the cerebral vasculature. After severe head trauma and its attendant increase in intracranial pressure, marked alterations in cerebral blood flow and perfusion may occur. Currently, intervention is based on maintenance of coronary perfusion pressure and aggressive management of intracranial pressure. Both may be impacted by manipulation of ventilation, systemic blood pressure and volume status, administration of osmotic diuretics, and head elevation. Such therapy in the patient with severe head injury attempts to maintain coronary perfusion pressure and adequate oxygen delivery in a damaged central nervous system with altered hemodynamics and raised intracranial pressure.

Cerebral ischemia-reperfusion injury after severe head injury and its possible treatment with polyethyleneglycol-superoxide dismutase

Oxygen radical-mediated mechanisms play a role both in cerebral ischemia-reperfusion injury and in traumatic brain injury. Moreover, my work with measurements of cerebral blood flow with the 133Xe method and the stable xenon-computed tomography method and through measurements of arteriovenous difference of oxygen indicates that ischemia and ischemia-reperfusion are also part of traumatic brain injury but only in the first few hours after injury. The contributions of the research laboratories at the Medical College of Virginia, Richmond, to the understanding of the role of oxygen free radicals in traumatic brain injury are discussed. Finally, a trial of the oxygen radical scavenger polyethyleneglycol-superoxide dismutase in human beings with severe head injuries show that death and vegetative state occurred twice as often in the 26 patients receiving placebo compared with the group of 26 patients receiving a 10,000 U/kg bolus of polyethyleneglycol-superoxide dismutase (43%, respectively; 20% at three months; P < .03).

Measurements of cerebral blood flow and metabolism in severe head injury using the Kety-Schmidt technique

Global cerebral blood flow (CBF) was measured serially for up to 10 days after severe head injury, and related to outcome. Twenty-five of the patients had a reduced CBF, 47 had a normal CBF, and 30 had an elevated CBF. Patients with a reduced CBF had a poorer outcome than patients with a normal or elevated CBF. There were no differences in the type of injury, initial GCS, severity of intracranial hypertension in each CBF group. Systemic factors did not significantly contribute to the differences in CBF among the 3 groups. A logistic regression model of the effect of CBF on neurological outcome was developed. When adjusted of variables which were found to be significant confounders, including age, initial Glasgow Coma Score, hemoglobin, cerebral perfusion pressure, and cerebral oxygen consumption, a reduced CBF remained significantly associated with an unfavorable neurological outcome.

Xenon 133--CBF measurements in severe head injury and subarachnoid haemorrhage

The possibility of measuring cerebral blood flow by mobile bedside units with the intravenous 133-Xenon technique increased the interest to monitor haemodynamic changes after head injury and subarachnoid haemorrhage in intensive care. Time course of resting CBF after trauma is variable (reduced CBF, hyperemia) and there is no strong correlation to clinical outcome. Additional studies of CBF/CO2 reactivity show normal and impaired CO2 response in the acute stage after trauma (day 1-8). A permanently impaired CO2 reactivity correlates with severe brain damage and bad outcome (GOS 1,2). A normal or improving CO2 reactivity indicates a favourable outcome (GOS 3-5). There was no significant correlation between CBF and ICP, nor between CBF and CPP. A CPP of more than 70 mmHg did not guarantee a sufficient CBF in every case indicating the variability of the limits of autoregulation. As therapeutic hyperventilation may lead to ischemia, mannitol was preferred to reduce ICP and increased low CBF to normal values. This fact should be considered in the treatment of patients with low CBF and normal CO2 reactivity. Delayed ischemic neurological deficits ("vasospasm") are well-known as significant complications of the clinical course following SAH. Immediately postoperatively performed CBF measurements enable to detect ischemia and allow to start early antiischemic therapy. During "vasospasm" CBF showed a better correlation to the neurological status than blood flow velocity in the basal arteries measured by transcranial doppler sonography. Furthermore hyperemia after SAH could only be verified by CBF measurements.

Evaluation of regional cerebral blood flow in acute head injury by stable xenon-enhanced computerized tomography

Measurement of regional cerebral blood flow (rCBF) in head-injured patients is considered useful for understanding the cerebral hemodynamics of brain trauma and for determining the optimal therapy. Most data thus far obtained with 133Xe clearance techniques have made only relative contribution, due to limitations of the 133Xe method. More recently, is has become possible to measure rCBF by xenon-enhanced computerized tomography (Xe-CT), which obviates most problems inherent to the 133Xe method. On the other hand, computational errors and concerns regarding the safety of xenon inhalation have thwarted the clinical use of Xe-CT. Recent advances in CT technology, however, have largely eliminated these problems. Xe-CT CBF measurements in severe head injury demonstrate a good correlation between CBF values obtained with 133Xe and Xe-CT. By consistently applying these studies in conjunction with conventional CT, information on very early flow derangements (within 1 to 2 hours after injury) can be obtained, in relation to anatomical lesions. Preliminary data reveal higher incidences of global and focal ischaemia than found previously. Local ischaemia tends to evolve to hyperemia in the ensuing days.

Intracranial blood flow velocity after head injury: relationship to severity of injury, time, neurological status and outcome

Middle cerebral artery (MCA) blood flow velocity was measured daily by transcranial Doppler ultrasonography in 121 patients with severe (50), moderate (16) and minor (55) head injury during their hospital stay, and the results compared with findings in control subjects. Admission MCA velocity was significantly lower after severe 35.8 (31.9-39.7) cm/s, mean (95% confidence limits), moderate 45.5 (40.0-51.0) cm/s and minor 51.7 (47.9-55.5) cm/s head injury when compared with normal controls 60.1 (56.9-63.3) cm/s. Initial mean velocity in severe head injury was significantly lower than in moderate and minor injury. At discharge, MCA velocity in severe injury remained below normal 46.2 (43.2-49.0) cm/s, whereas, in moderate and minor injury flow velocity had returned to normal. Correlation (r = 0.46, p less than 0.01) was found between MCA velocity and Glasgow Coma Score (GCS) on admission but not on discharge. Persistently low flow velocity was found in all 10 patients who died within 72 hours (early deaths). An admission MCA velocity of less than 28 cm/s correctly predicted 80% of the early deaths. Patients who made a good recovery or had only moderate disability at six months showed a significant increase in velocity from admission 36.2 (31.5-41.2) cm/s to discharge 47.8 (43.7-51.9) cm/s in contrast to those who were severely disabled, in whom velocity generally remained low.

Relationships between dopamine infusions and intracranial hemodynamics in patients with raised intracranial pressure

Dopamine, 1-10 micrograms/kg body weight/min was infused in 6 patients suffering from cerebrovascular diseases with elevated intracranial pressure and a critical cerebral perfusion pressure. Dopamine decreased intracranial pressure in 3 and increased it moderately in the other 3 patients. In all patients, the dopamine-induced rise of mean arterial pressure led to an increase of cerebral perfusion pressure. Transcranial Doppler ultrasonographic recordings of the middle cerebral artery in patients whose intracranial pressure declined revealed a decrease of the pathologically elevated cerebrovascular resistance, and an augmentation of cerebral blood supply. In conclusion, dopamine infusions may improve cerebral hemodynamics in some patients with severe brain edema. Such patients can be identified by intracranial pressure and Doppler monitoring.

Cerebral blood flow, arteriovenous oxygen difference, and outcome in head injured patients

Cerebral blood flow (CBF) and other physiological variables were measured repeatedly for up to 10 days after severe head injury in 102 patients, and CBF levels were related to outcome. Twenty five of the patients had a reduced CBF [mean (SD) 0.29 (0.05) ml/g/min]; 47 had a normal CBF, (0.41 (0.10) ml/g/min); and 30 had a raised CBF (0.62 (0.14) ml/g/min). Cerebral arteriovenous oxygen differences were inversely related to CBF and averaged 2.1 (0.7) mumol/ml in the group with reduced CBF, 1.9 (0.5) mumol/ml in the group with normal CBF, and 1.6 (0.4) mumol/ml in the group with raised CBF. Patients with a reduced CBF had a poorer outcome than patients with a normal or raised CBF. Mortality was highest in patients with a reduced CBF, and was 32% at three months after injury, whereas only 21% of the patients with a normal CBF and 20% of the patients with a raised CBF died. There were no differences in the type of injury, initial score on the Glasgow Coma Scale, mean intracranial pressure (ICP), highest ICP, or the amount of medical treatment required to keep the ICP less than 20 mm Hg in each group. Systemic factors did not significantly contribute to the differences in CBF among the three groups. A logistic regression model of the effect of CBF on neurological outcome was developed. When adjusted for variables which were found to be significant confounders, including age, initial Glasgow Coma Score, haemoglobin concentration, cerebral perfusion pressure and cerebral metabolic rate of oxygen, a reduced CBF remained significantly associated with an unfavourable neurological outcome.

Cognitive recovery correlates with long-term increases of cerebral perfusion after head injury

Prospective measurements of cerebral blood flow (CBF) and Cognitive Capacity Screening Examination (CCSE) were obtained following head injury among 42 patients for a mean total follow-up interval of 10 years. Clinical data obtained at the time of injury and detailed neurological examinations at each follow-up visit were correlated with serial CBF and CCSE scores. Comparisons of the group of patients who cognitively improved (n = 32) were made with the group that did not (n = 10). Of the total group, 76% showed cognitive improvements for as long as 10 years after injury, with CBF increases toward normal. Predictors for long-term cognitive improvements include: higher initial Glasgow Coma Scales, earlier recovery from coma, absence of signs of brain stem injury, and improvements of cerebral perfusion and autoregulation. Failure to improve correlated with low initial Glasgow Coma Scales, signs of brain stem injury, and persistent impairments of cerebral perfusion.

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.

A bedside test for cerebral autoregulation using transcranial Doppler ultrasound

Although disorders of cerebral autoregulation are commonly seen in neurosurgical disease, there is currently no test of autoregulation in widespread use that may be performed safely at the bedside. The presence of autoregulation, however, can be seen in the brief hyperemic response in the middle cerebral artery distribution following a transient manual carotid artery compression in the neck. This transient hyperemic response (THR) is readily measured with transcranial Doppler techniques, and therefore might serve as a qualitative marker of cerebral autoregulation. To evaluate the THR as a clinical tool, carotid compressions were performed during 172 TCD studies on 79 patients with neurosurgical disorders and on 10 patients without cerebral disease. The results were correlated with clinical status (e.g., Hunt-Hess Grade for subarachnoid hemorrhage and Glasgow Coma Score for trauma). There were no complications arising from the compressions. A separate assessment of autoregulation was made from TCD recordings obtained intraoperatively during 16 procedures and correlated to the pre-operative THRs. Autoregulation was further assessed in 4 patients during a hypotensive challenge, and again compared to the THRs. A strong correlation was seen between the THR results and clinical status. The THR was also strongly correlated with the intraoperative assessments, and all 4 patients receiving hypotensive challenges had abnormal THRs and demonstrated evidence of poor autoregulation during the challenge. None of the control patients had abnormal THRs. The THR arising from transient artery compression is readily detected with TCD techniques and correlates well with clinical status and other indicators of autoregulatory ability.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of brain-stem dysfunction following severe fluid-percussion head injury to the cat

The degree of brain-stem dysfunction associated with high-level fluid-percussion injury (3.0 to 3.8 atm) was investigated in anesthetized cats. Measurements were made of the animals' intracranial pressure (ICP) pressure-volume index (PVI), far-field brain-stem auditory evoked responses (BAER's), and cerebral blood flow (CBF). The animals were classified into two groups based on the severity of neuropathological damage to the brain stem after trauma: Group 1 had mild intraparenchymal and subarachnoid hemorrhages and Group 2 had severe intraparenchymal and subarachnoid hemorrhages. The ICP values in Group 1 were insignificantly lower than those in Group 2, while the PVI values in Group 2 were clearly lower (p less than 0.05). Immediately after the injury, peaks II, III, and IV of the BAER's demonstrated a transitory and marked suppression. One Group 1 and two Group 2 animals showed the disappearance of peak V. In Group 1, the latencies of peak II, III, and IV gradually increased until 60 to 150 minutes postinjury, then returned to 95% of baseline value at 8 hours; however, the animals in Group 2 showed poor recovery of latencies. Two hours after brain injury, the CBF decreased to 40% of the preinjury measurement in both groups (p less than 0.001). In contrast to Group 2, the CBF in Group 1 returned to 86.8% of the preinjury measurement by 8 hours following the injury. Changes in PVI, BAER, and CBF correlated well with the degree of brain-stem injury following severe head injury. These data indicate that high-level fluid-percussion injury (greater than 3.0 atm) is predominantly a model of brain-stem injury.

Cerebral vasoreactivity and the prediction of outcome in severe traumatic brain lesions

Mean hemispheric blood flow (CBF) was studied in 38 comatose, severely brain-injured patients following intravenous administration of xenon-133. Repeated measurements were performed in order to evaluate cerebral vasoreactivity following a decrease in PaCO2. Simultaneously, arterial-venous oxygen differences (AVDO2) and intracranial pressure (ICP) were measured. An impaired CBF response to hyperventilation (delta CBF/delta PaCO2 less than 1.0) was obtained in 22 patients. Three of 16 patients with preserved CO2-reactivity died because of their brain injuries and 12 patients reached good recovery/moderate disability. In the group of patients with impaired vasoreactivity 11 of 22 patients died and only three patients reached good recovery/moderate disability. The study documents that in patients with severe traumatic brain lesions measurements of cerebral vasoreactivity to hyperventilation give prognostic information that is not obtained by clinical observations or CT-scanning.

Continuous monitoring of cerebral oxygenation in acute brain injury: injection of mannitol during hyperventilation

Global cerebral oxygenation, perfusion pressure, and expired pCO2 were continuously monitored in 10 adults with acute severe closed head trauma. Cerebral oxygenation was monitored by fiberoptic catheter oximetry, which allowed simultaneous measurements of arterial and jugular bulb oxyhemoglobin saturation. Intracranial pressure levels over 20 mm Hg were recorded several times in all patients, in spite of sedation, muscle paralysis, and profound hyperventilation. Intracranial hypertension was frequently associated with oligemic cerebral hypoxia, identified as abnormally low jugular oxygen saturation in the presence of normal arterial oxygenation. Intracranial hypertension was then managed with intravenous administration of mannitol boluses, which yielded simultaneous decreases in intracranial pressure and increases in cerebral oxygenation to highly statistically significant levels. Monitoring cerebral oxygenation was clinically useful because it allowed identification of impaired cerebral oxygenation even when cerebral perfusion pressure was normal. It is therefore proposed as a new monitoring technique, to supplement conventional monitoring of cerebral perfusion pressure.

Relationship of early cerebral blood flow and metabolism to outcome in acute head injury

Cerebral blood flow (CBF) measurements were obtained acutely in 96 comatose patients with closed head injury, using the intravenous 133Xe technique. Arteriojugular venous oxygen differences and cerebral metabolic rate for oxygen (CMRO2) were determined in a subgroup of 66 patients. The relationship between each of these variables and outcome at 6 months was analyzed, using the Glasgow Outcome Scale. The CMRO2 was significantly depressed in patients who subsequently died or remained in a vegetative state, whereas higher values were obtained in patients who later regained consciousness. Although CBF was not predictive of outcome in the total sample, omission of patients with acute hyperemia resulted in a significant relationship that paralleled the metabolic findings. Follow-up studies in the survivors revealed a correlation between CBF and degree of functional recovery, the lowest blood flows being obtained among patients with severe disability. Age, initial Glasgow Coma Scale score, and occurrence of intracranial hypertension were each found to be predictive of outcome, thus confirming previous reports. When these variables were combined with CMRO2 in a logistic regression analysis, the probability of recovery was correctly predicted in 82% of the cases. The CMRO2 was relatively independent of the other prognostic indicators and, next to age, contributed most to the prediction.

Measurements of CO2 reactivity and barbiturate reactivity in patients with severe head injury

In nine patients with severe head injury subjected to continuous hyperventilation and barbiturate coma treatment with pentobarbitone, the regional cerebral blood flow was measured as initial slope index (ISI) with a 32 channel Cerebrograph, and cerebral metabolic rate of oxygen (CMRO2) was calculated as the product of mean global CBF and the arterio-venous oxygen content difference. CBF was measured at strategic intervals either to follow the treatment (hyperventilation and/or pentobarbitone), or to determine whether these principles of treatment should be intensified or reduced. During the flow measurements the CO2 reactivity and the reactivity to a bolus injection of thiopentone 5 mg/kg were calculated globally and regionally. The global CO2 reactivity was calculated as relative (%change CBF/delta PaCO2 mmHg) and absolute (deltaCBF/deltaPaCO2 mmHg), and the reactivity to barbiturate was calculated globally as delta CMRO2, and regionally as %change rCBF. The absolute and relative global CO2 reactivities correlated positively with the mean CBF values before hyperventilation, and the global barbiturate reactivity was dependent on the CMRO2 value obtained before hyperventilation. However, at low levels of CMRO2 ranging between 1.0 and 1.1 ml O2 the barbiturate reactivity was abolished. The regional studies of CBF, CMRO2, CO2 reactivity and barbiturate reactivity gave important information, when decisions concerning therapeutic regimes with special reference to hyperventilation and sedation with pentobarbitone were necessary.

Does acute hyperventilation provoke cerebral oligaemia in comatose patients after acute head injury?

In 27 comatose patients with acute head injury, 45 paired studies of regional cerebral blood flow (rCBF) were performed before and after hyperventilation. In total 676 regions were studied, and rCBF was calculated as initial slope index using the intracarotid washout technique of 133 Xe. The tests were applied from one day to three weeks after the acute trauma. In total hyperventilation from PaCO2 averaging 4.8 to 3.5 kPa increased the frequency of regions with oligaemia defined CBF less than 20 ml/100 g/min from 5 to 16%. Before hyperventilation oligaemia was observed in 11 of 45 studies (9 of 27 patients); after hyperventilation the frequency increased to 21 studies (15 patients). The frequency of severe oligaemia (CBF less than 15 ml) increased from 0.1 to 3% of all regions, or from 2 to 8 of all studies (from 2 to 9 patients). The increased frequency of oligaemia after hyperventilation was correlated to a poor outcome (dementia, vegetative survival or death), where it was observed in 21% of all regions, in 16 of 26 studies and 11 of 15 patients, whereas the frequency in patients with a good recovery was found to be 7% of all regions and observed in 5 of 19 studies (4 of 12 patients). The high frequency of oligaemia after hyperventilation was associated to a low hemispheric CBF before hyperventilation, but not to the level of PaCO2, the level of intracranial pressure, cerebral perfusion pressure or CSF-pH or lactate.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral blood flow and metabolism in severely head-injured children. Part 1: Relationship with GCS score, outcome, ICP, and PVI

The literature suggests that in children with severe head injury, cerebral hyperemia is common and related to high intracranial pressure (ICP). However, there are very few data on cerebral blood flow (CBF) after severe head injury in children. This paper presents 72 measurements of cerebral blood flow ("CBF15"), using the 133Xe inhalation method, with multiple detectors over both hemispheres in 32 children aged 3 to 18 years (mean 13.6 years) with severe closed head injury (average Glasgow Coma Scale (GCS) score 5.4). In 25 of the children, these were combined with measurements of arteriojugular venous oxygen difference (AVDO2) and of cerebral metabolic rate of oxygen (CMRO2). In 30 patients, the first measurement was taken approximately 12 hours postinjury. In 18 patients, an indication of brain stiffness was obtained by withdrawal and injection of ventricular cerebrospinal fluid and calculation of the pressure-volume index (PVI) of Marmarou. The CBF and CMRO2 data were correlated with the GCS score, outcome, ICP, and PVI. Early after injury, CBF tended to be lower with lower GCS scores, but this was not statistically significant. This trend was reversed 24 hours postinjury, as significantly more hyperemic values were recorded the lower the GCS score, with the exception of the most severely injured patients (GCS score 3). In contrast, mean CMRO2 correlated positively with the GCS score and outcome throughout the course, but large standard deviations preclude making predictions based on CMRO2 measurements in individual patients. Early after injury, there was mild uncoupling between CBF and CMRO2 (CBF above metabolic demands, low AVDO2) and, after 24 hours, flow and metabolism were completely uncoupled with an extremely low AVDO2. Consistently reduced flow as found in only four patients; 28 patients (88%) showed hyperemia at some point in their course. This very high percentage of patients with hyperemia, combined with the lowest values of AVDO2 found in the literature, indicates that hyperemia or luxury perfusion is more prevalent in this group of patients. The three patients with consistently the highest CBF had consistently the lowest PVI: thus, the patients with the most severe hyperemia also had the stiffest brains. Nevertheless, and in contrast to previous reports, no correlation could be established between the course of ICP or PVI and the occurrence of hyperemia, nor was there a correlation between the levels of CBF and ICP at the time of the measurements. The authors argue that this lack of correlation is due to: 1) a definition of hyperemia that is too generous, and 2) the lack of a systematic relationship between CBF and cerebral blood volume

Cerebral blood flow and metabolism in severely head-injured children. Part 2: Autoregulation

Autoregulation of cerebral blood flow ("CBF15") was tested in a series of 26 pediatric patients (mean age 13.2 years) with severe head injury (average Glasgow Coma Scale (GCS) score 5.5) in the acute stage. A baseline 133Xe CBF measurement was performed and then repeated, after blood pressure was increased by 29% with intravenous phenylephrine or decreased by 26% with intravenous trimethaphan camsylate. Correlations were made between CBF and clinical condition, outcome, time after injury, intracranial pressure (ICP), and pressure-volume index (PVI) changes, and the site of injury (hemispheres, diencephalon, or brain stem). The site of injury was determined with multimodality evoked potential measurements. Autoregulation was intact in 22 (59%) of 37 measurements. There was no correlation with GCS score, outcome, time after injury, site of injury, or way of testing (decreasing or increasing blood pressure). Autoregulation was statistically significantly more often impaired when CBF was either below normal -2 standard deviations (SD) (reduced flow) or above normal +2 SD (absolute hyperemia). In cases with intact autoregulation, mean ICP decreased from 17.5 to 15.0 mm Hg with higher blood pressure and increased from 19.0 to 21.3 mm Hg with lower blood pressure. When PVI was measured during the blood pressure manipulations, it was found to change in a direction opposite to the ICP change. The consequences of these findings in the management of ICP problems with blood pressure control are discussed.

Intracranial blood velocity in head injury. A transcranial ultrasound Doppler study

We report our experience monitoring head-injured patients by means of transcranial Doppler sonography. Cerebral velocity measurements and waveforms change in a consistent pattern with the existence of intracranial pressure, and it is possible to discriminate low versus high flow states. The technique, in contrast to cerebral blood flow measurement, is reliable, atraumatic, and repeatable so that diagnostic assessments can be made and the patient can be followed for therapeutic efficacy.

The effect of hypoxia on traumatic head injury in rats: alterations in neurologic function, brain edema, and cerebral blood flow

We evaluated the effects of early posttraumatic hypoxia on neurologic function, magnetic resonance images (MRI), brain tissue specific gravities, and cerebral blood flow (CBF) in head-injured rats. By itself, an hypoxic insult (PaO2 40 mm Hg for 30 min) had little effect on any measure of cerebral function. After temporal fluid-percussion impact injury, however, hypoxia significantly increased morbidity. Of rats subjected to impact (4.9 +/- 0.3 atm) plus hypoxia, 71% had motor weakness contralateral to the impact side 24 h after injury, while only 29% of rats subjected to impact alone had demonstrable weakness (p less than 0.05). Lesions observed on MR images 24 h after injury were restricted to the impact site in rats with impact injury alone, but extensive areas with longer T1 relaxation times were observed throughout the ipsilateral cortex in rats with impact injury and hypoxic insult. Brain tissue specific gravity measurements indicated that much more widespread and severe edema developed in rats with impact injury and hypoxia. [14C]Iodoantipyrine autoradiography performed 24 h after injury showed that there was extensive hypoperfusion of the entire ipsilateral cortex in rats with impact injury and hypoxia. These results show that large areas of impact-injured brain are extremely vulnerable to secondary insults that can irreparably damage neural tissue, and provide experimental evidence for the observed adverse effects of hypoxia on outcome after human head injury.

Cerebrovascular response to intracranial hypertension

Pial arterial and venous calibre changes during intracranial hypertension were studied in 11 cats under barbiturate- and nitrous oxide-anaesthesia by using a closed cranial window technique and multichannel videoangiometry. Intracranial pressure was elevated from a normal mean level of 6.4 mm Hg by cisternal infusion of mock CSF in steps to 20, 30, 40, 50 mm Hg and finally to the level of systolic pressure. Pial arteries dilated significantly, small ones more than large ones, by 42 +/- 5.6% and 33 +/- 3%, respectively at ICP 50. With a further elevation of ICP up to systolic pressure, dilatation diminished to 28 +/- 10% in small, and to near resting calibres in large arteries. Pial veins remained unreactive on the average. Grouping into veins smaller and larger than 100 microns of resting size revealed, however, minor though statistically significant 5-10% dilatation of small, and a 5-10% diminution of large veins. Blood flow stopped, when cerebral perfusion pressure was zero, however, neither arteries nor veins collapsed. The present data support the hypothesis that CBF during acute elevation of CSF pressure depends on perfusion pressure rather than local vascular compression.

The predictive value of cerebral anaerobic metabolism with cerebral infarction after head injury

Cerebral ischemia is a common mechanism of secondary brain injury following severe head injury. The cerebral metabolic rate of oxygen (CMRO2) and of lactate (CMRL), as well as cerebral blood flow (CBF) were measured daily for 5 days after head injury in 44 comatose head-injured patients to determine if metabolic changes could identify the patients who would develop cerebral infarction. Of 41 patients whose CBF remained at levels regarded as adequate to prevent infarction (CBF greater than or equal to 0.2 ml/gm/min), the six who showed a cerebral infarction on computerized tomography (CT) scans exhibited characteristic cerebral metabolic patterns: a CMRO2 of less than 0.6 mumol/gm/min on one or more of the days monitored, and markedly elevated cerebral lactate production (CMRL less than -0.06 mumol/gm/min) on Days 1 and/or 2 after injury. Patients who had no areas of infarction on serial CT scans typically had a CMRO2 and CMRL can be obtained at the bedside and can indicate the presence of an evolving ischemic infarct after head injury.

Prognostic significance of ventricular CSF lactic acidosis in severe head injury

Brain-tissue acidosis inferred by cerebrospinal fluid (CSF) lactic acidosis is considered to play an important role in the clinical course of severe head injury. Ventricular CSF lactate concentration was studied in 19 patients during the first 5 days after severe head injury. All patients were intubated, paralyzed, and artificially ventilated so that PaCO2 was kept at 33.2 +/- 5.0 mm Hg and PaO2 at 122 +/- 18 mm Hg (mean +/- standard deviation). The mean Glasgow Coma Scale score on admission was 5.73 +/- 2.42. The first CSF sample was drawn within 18 hours after head injury. Over the first 4 days postinjury, patients with a poor outcome had significantly higher ventricular CSF lactate levels than did those with moderate disabilities or a good outcome. Patients showing favorable outcome had a significant decrease in ventricular CSF lactate levels 48 hours after injury. This decrease was not observed in patients with a poor outcome. Increased ventricular CSF lactate concentration was also reliably associated with increased intracranial pressure (ICP). Ventricular CSF lactate levels did not correlate with the magnitude of intraventricular bleeding. Arterial and jugular venous blood lactate levels, although high after head injury, were usually lower than the levels in the ventricular CSF and reached a normal range by the 3rd day following head trauma. At that time, the ventricular CSF lactate concentration was still above normal in patients with a poor outcome but had decreased to normal in patients with moderate disabilities or a good outcome. Ventricular CSF pH did not generally correlate with the ventricular CSF lactate concentration in patients under controlled ventilation; however, in a few patients close to death or with ventricular infection, a correlation was noted. Ventricular CSF lactate levels were not related to cerebral blood flow. In this study, profiles of ventricular CSF lactate concentration are defined in relation to the patients' clinical course and outcome. High ventricular CSF lactate concentration is present within 18 hours after severe head injury. Its decrease to normal in the following 48 hours is a reliable sign of clinical improvement; however, ventricular CSF lactate levels that are persistently high or that increase over time indicate the patient's deterioration. Serial assessment of ventricular CSF for acid-base status and metabolites in head-injured patients with a ventricular catheter already placed for ICP monitoring is useful in the evaluation of prognosis and clinical course.

Effects of fluid-percussion brain injury on regional cerebral blood flow and pial arteriolar diameter

The effects of two levels of fluid-percussion brain injury on cerebral blood flow (CBF) and pial arteriolar diameter were investigated in cats. Regional CBF was measured using the radioactive microsphere technique. Experimental brain injury resulted in changes in arterial blood pressure, CBF, and pial arteriolar diameter that were related to the severity of the injury. Low-level injury (1.88 +/- 0.11 atm, mean +/- standard error of the mean) resulted in a slight transient increase in CBF which had returned to preinjury levels by 30 minutes. High-level injury (2.68 +/- 0.19 atm) resulted in larger, statistically significant (p less than 0.01) increases in whole-brain CBF, decreases in cerebrovascular resistance, and increases in pial arteriolar diameter 1 minute postinjury. One hour after injury, CBF had returned to preinjury levels while cerebral perfusion pressure was significantly (p less than 0.01) reduced. There was no evidence of reduced CBF in any region studied. Pial arterioles dilated during the posttraumatic hypertensive period and then returned to control diameters within 1 hour after injury. Changes in the diameter of pial arterioles were significantly correlated with posttraumatic changes in CBF.

Cerebral hemodynamics in patients with acute severe head trauma

Mean hemispheric cerebral blood flow (CBF) was studied in 11 comatose brain-injured patients following intravenous administration of xenon-133. Repeated measurements were performed in order to evaluate cerebral vasoreactivity following a decrease in PaCO2. In addition, the effect of induced barbiturate coma was evaluated in patients with intracranial hypertension. The cerebral vasoreactivity and the CBF response following induction of barbiturate coma varied. In patients with normal CO2 reactivity, barbiturate treatment was accompanied by a considerable decrease in CBF as compared to patients with decreased or abolished CO2 response. During barbiturate treatment the intracranial pressure (ICP) became normal in three of four patients with preserved CO2 response, but reached normal levels in only one of five patients with impaired CO2 reactivity. Patients whose ICP became normal recovered. The data suggest a positive correlation between CO2 reactivity and the effect of barbiturate treatment. Furthermore, preserved cerebral vasoreactivity after severe head injury may be of prognostic value.

CBF in head injury

In the last few years the possibility of measuring CBF by means of intravenous isotop injection technique and portable monitor has made the use of measuring CBF in the clinical setting of the brain injured patient of current interest. However, knowledge about the hemodynamics of the head trauma is inevitable for the interpretation of the CBF results. In this communication a short outline of the results obtained during the last decades studies about the hemodynamic of the damaged brain is given. The essence of these studies seems to be: The local level of CBF do not indicate the severity of the brain injury, as low as well as high flow may be seen initially in severely injured brain tissue. The oxygen uptake (CMRO2) is related to the severity of the brain trauma, as low CMRO2 correlate to poor clinical condition. In severely damaged brain tissue the autoregulation may appear normal (false autoregulation) whereas the autoregulation in moderately damaged tissue may appear impaired for weeks. The carbon dioxide response (CO2) is only impaired if the brain tissue is severely damaged. Thus, low CMRO2 and dissociation between apparently normal autoregulation and impaired CO2 response seem to predict poor outcome.

Cerebral blood flow in minor cerebral contusion

Seventeen patients with minor cerebral contusion were selected from a series of patients with head injuries of various severity, who had undergone repeat evaluations of the regional cerebral blood flow. The mean global flow (expressed as mean global initial slope index) on early examination was found to be significantly lower, compared with that recorded in healthy volunteers. A tendency towards the recovery of higher flow values was apparent in repeat evaluations that were performed several weeks after the injury. Interhemispheric asymmetries of flow were a common occurrence, with lower perfusion and reduced attenuation values on computed tomography scans being, however, in good agreement only in approximately half of the cases.

Cerebral blood flow decrements in chronic head injury syndrome

Global and regional cerebral blood flow (CBF) has been reported to be decreased immediately after head injury. Since neuropsychological deficits in patients with chronic head injury syndrome persist long after the initial trauma, we studied CBF, which reflects cerebral metabolism and activity, and evaluated the results of neuropsychological tests in 12 alert, responsive patients aged 18-26, both 2-13 months after head injury and 1-12 months after they regained consciousness. Global CBF was significantly decreased in patients with head injury relative to age-matched normal controls. Four patients had well-localized injury; in three of these, CBF over the affected region was significantly decreased relative to the same region in the opposite hemisphere and relative to the same region in an age-matched normal control. In one patient with right frontal injury, cognitive improvement on repeat testing was associated with a relative increase in right frontal CBF. The remaining eight patients had diffuse bilateral injury. Asymmetry ratios (larger value of mean hemispheric CBF divided by the smaller) were significantly higher for the group with localized dysfunction (1.2 +/- 0.08 vs. 1.0 +/- 0.01, p less than 0.01), suggesting homolateral decrease in CBF in this group. Three patients with diffuse injury underwent repeat studies 5-14 weeks later; all improved on psychological tests, and two had a significant increase in global CBF. These results suggest that the chronic sequelae of head injury include decreased CBF, presumably reflecting decreased cerebral metabolism, which correlates with the neuropsychological impairment.

Effect of mannitol on ICP and CBF and correlation with pressure autoregulation in severely head-injured patients

In a previous paper, the authors showed that mannitol causes cerebral vasoconstriction in response to blood viscosity decreases in cats. The present paper describes the changes in intracranial pressure (ICP) and cerebral blood flow (CBF) after mannitol administration in a group of severely head-injured patients with intact or defective autoregulation. The xenon-133 inhalation method was used to measure CBF. Autoregulation was tested by slowly increasing or decreasing the blood pressure by 30% and measuring CBF again. Mannitol was administered intravenously in a dose of 0.66 gm/kg; 25 minutes later, CBF and ICP were measured once again. In the group with intact autoregulation, mannitol had decreased ICP by 27.2%, but CBF remained unchanged. In the group with defective autoregulation, ICP had decreased by only 4.7%, but CBF increased 17.9%. One of the possible explanations for these findings is based on strong indications that autoregulation is mediated through alterations in the level of adenosine in response to oxygen availability changes in cerebral tissue. The decrease in blood viscosity after mannitol administration leads to an improved oxygen transport to the brain. When autoregulation is intact, more oxygen leads to decreased adenosine levels, resulting in vasoconstriction. The decrease in resistance to flow from the decreased blood viscosity is balanced by increased resistance from vasoconstriction, so that CBF remains the same. This might be called blood viscosity autoregulation of CBF, analogous to pressure autoregulation. Vasoconstriction also reduces cerebral blood volume, which enhances the effect of mannitol on ICP through dehydration of the brain. When autoregulation is not intact there is no vasoconstriction in response to increased oxygen availability; thus, CBF increases with decreased viscosity. With the lack of vasoconstriction, the effect on ICP through dehydration is not enhanced, so that the resulting decrease in ICP is much smaller. Such a mechanism explains why osmotic agents do not change CBF but decrease ICP in normal animals or patients with intact vasoconstriction, but do (temporarily) increase CBF in the absence of major ICP changes after stroke.

Cerebral blood flow and metabolism in comatose patients with acute head injury. Relationship to intracranial hypertension

Cerebral blood flow (CBF) measurements were made in 75 adult patients with closed head injuries (mean Glasgow Coma Scale score 6.2) using the xenon-133 intravenous injection method with eight detectors over each hemisphere. All patients were studied acutely within 96 hours of trauma, and repeatedly observed until death or recovery (total of 361 examinations). Arteriojugular venous oxygen differences (AVDO2) were obtained in 55 of the patients, which permitted assessment of the balance between metabolism and blood flow, and provided estimates of cerebral metabolic rate for oxygen (CMRO2). Based on mean regional CBF, the patients were classified into two groups: those who exhibited hyperemia on one or more examinations, and those who had a consistently reduced flow during their acute illness. "Hyperemia" was defined as a normal or supernormal CBF in the presence of coma, a definition that was independently confirmed by narrow AVDO2's indicative of "luxury perfusion". During coma, all patients showed a significant depression in CMRO2. Forty-one patients (55%) developed an acute hyperemia with an average duration of 3 days, while 34 patients (45%) consistently had subnormal flows. Although more prevalent in younger patients, hyperemia was found at all age levels (15 to 85 years). There was a highly significant association between hyperemia and the occurrence of intracranial hypertension, defined as an intracranial pressure above 20 mm Hg. Patients with reduced flow showed little or no evidence of global cerebral ischemia, but instead revealed the expected coupling of CBF and metabolism. The CBF responses to hyperventilation were generally preserved, with the hyperemic patients being slightly more reactive. In 10 patients with reduced flow, hyperventilation resulted in wide AVDO2's suggestive of ischemia.

Cerebral oxygen metabolism and blood flow in human cerebral ischemic infarction

Fifteen patients with acute cerebral hemispheric infarcts have been studied with positron emission tomography and the oxygen-15 steady-state inhalation technique. Thirteen follow-up studies were also performed. The values of cerebral oxygen metabolism (CMRO2), cerebral blood flow (CBF), and oxygen extraction ration (OER) have been calculated for the infarcted regions, their borders, the symmetrical regions in contralateral cerebral hemispheres, and the cerebellar hemispheres. This study demonstrates that in the completed stroke there are thresholds for regional CMRO2 and regional CBF below which the general clinical outcome of the patients is usually poor. The ischaemic lesions invariably produce an uncoupling between the greatly decreased metabolic demand and the less affected blood supply, with very frequent instances of relative hyperperfusion. Remote effects of the hemispheric infarcts have been demonstrated, such as crossed cerebellar diaschisis and contralateral transhemispheric depression. The level of consciousness correlates with oxygen uptake and blood flow both in the posterior fossa and in the contralateral cerebral hemispheres. The follow-up studies of individual patients underline the high variability of metabolism-to-flow balance during the acute phase of the illness, and stress the need for more studies focused on repeated assessments of homogeneous patient populations.

Effect of two levels of induced hypocapnia on cerebral autoregulation in the acute phase of head injury coma

In eight unconscious and artificially ventilated patients with severe head injury, cerebral autoregulation (CA) was tested during angiotensin infusion, before and after a reduction of Paco2. Intracranial pressure (ICP) and systemic arterial pressure (SAP) were continuously recorded. Regional cerebral blood flow (rCBF) was measured by the intracarotid Xe133 washout technique as initial slope index, stochastic and compartmental analysis. In contradistinction to previous human studies, we found a preserved CA during moderate hypocapnia (mean Paco2 34.2 mmHg) while the CA after a further decrease in Paco2 (mean value 23.1 mmHg) was lost. The apparently preserved CA may be a "false phenomenon" due to a regional increase in ICP. After a decrease in Paco2, an association between high CO2 reactivity and rCBF increase during angiotensin was disclosed, while a decreased or unchanged rCBF was observed in regions with inverse steal or abolished CO2 reactivity. The study indicates that the interpretation of CA is facilitated by performing the test during two levels of Paco2, but the presence of impaired autoregulation in the acute phase of head injury indicates that deliberate increase in SAP may be dangerous, as it may provoke an increase of regional ICP and brain oedema.

Cerebral blood flow in the acute phase after head injury. Part 2: Correlation to intraventricular pressure (IVP), cerebral perfusion pressure (CPP), PaCO2, ventricular fluid lactate, lactate/pyruvate ratio and pH

In 40 comatose patients with severe head injury, cerebral blood flow (CBF) studies were performed with the 133Xenon washout technique over the most severely injured hemisphere. All patients were mildly sedated with diazepam, chlorpromazine and meperidine and subjected to respiratory support. Simultaneously with the CBF study, intraventricular pressure (IVP), systemic arterial pressure (SAP) and ventricular fluid (VF) lactate, pyruvate and pH were measured. The results indicate a positive correlation between CBF and lactate in patients with a good recovery, irrespective of the time after the trauma, and a positive correlation irrespective of outcome, if the measurements were performed more than 3 days after the trauma. In patients with mainly supratentorial lesions without signs of brain-stem lesions, CBF and CPP were positively correlated, while CBF and ICP were negatively correlated (lost autoregulation). In contradistinction, CBF was positively correlated to ICP and PaCO2 in patients with diffuse brain injury. In some cases of repeated dynamic studies, the clinical course seemed to be related to changes in the measured parameters.

Frequency of primary brain stem lesions after head injuries. A CT scan analysis from 186 cases of severe head trauma

Analysis of level of brain stem dysfunction, evolution, and CT scan profile was made on 76 cases of head injuries with prolonged unconsciousness and without hemispheric focal lesion and midline shift on CT scan. Eleven cases were considered normal on CT scan. The CT scan aspect of primary brain stem lesion was identified in 31.5% of these series, and in 14.5% of all severe head traumas (186 cases), from which this series is taken. Primary and secondary CT scan profiles were observed whatever the clinical level of dysfunction and its evolution. Pontine lesions were mainly associated with haemorrhage in the brain stem and diffuse brain swelling; but minimal signs (cortical level) and benign outcome can also be related to axial haemorrhage. These results emphasize the frequency of primary brain stem lesions and the value of CT scan in head injuries.

Cerebral blood flow in the acute phase after head injury. Part 1: Correlation to age of the patients, clinical outcome and localisation of the injured region

In 40 comatose patients with severe head injury, a total of 114rCBF studies were performed with the intraarterial 133xenon washout technique over the most severely injured hemisphere. All patients were subjected to respirator treatment, and mildly sedated with diazepam, chlorpromazine or meperidine. The average values of the regional flow were corrected for changes in PaCO2 by simultaneous measurements of CO2 reactivity. A PaCO2 value of 30 mmHg (4 kPa) was chosen as the reference value. The results indicate that hyperaemia following head injury is a common phenomenon, especially in young victims with supratentorial cortical lesions. The hyperaemic phase can last from some days to several weeks and is of no prognostic significance. In elderly patients with supratentorial cortical lesions, and in patients with mainly brain-stem lesions or diffuse brain lesions a persistent low flow state was observed in the acute phase (first 1-3 days after the injury). This low flow state was also observed 1-2 weeks after the injury if loss of consciousness persisted, but it was of no prognostic significance, as CBF values between 15 and 20 ml/100 g/min were associated with a good recovery.

Local cerebral blood volume in head-injured patients. Determination by emission computed tomography of 99mTc-labeled red cells

Local cerebral blood volume (CBV) was mapped in 10 normal subjects and in 30 patients after head injury. In normal subjects, the mean CBV was 4.34 ml/100 gm. The coefficient of variation was 12% for the group mean, and 3% for values obtained in duplicate studies of individuals. Patients with head injuries were divided into three groups according to the stage of their illness: acute illness, early recovery, and later recovery. Averages of mean CBV were within one standard deviation of normal. In contrast, consistent changes were found in serial studies of the mean CBV in the same patient. Compared to recovery values, levels of mean CBV measured soon after injury were reduced, largely at the expense of the gray-matter compartment. In five adults with predominantly unilateral lesions, there was an average early reduction in mean CBV and cerebral blood flow of 15% and 36%, respectively. In three children with diffuse brain swelling, there was an average early mean CBV reduction of 12%; a single child had early increased mean CBV at a time when intracranial pressure was high. Greater changes were seen in local CBV on individual sections. There were mixed zones of hypervolemia and hypovolemia in regions of infarction and intracerebral hematoma. Subdural hematomas had consistent medial margins of increased local CBV, representing dilated blood vessels of the underlying cortex. The presence and displacement of this hypervolemic zone were sensitive indicators of persistent subdural collection and mass effect, even when the collection was lucent to x-ray computed tomography.

Relation of cerebral blood flow to neurological status and outcome in head-injured patients

Noninvasive studies of regional cerebral blood flow (CBF) were performed on 36 head-injured patients in varying degrees of coma, using the intravenous xenon-133 method. Serial examinations, averaging four per patient, were begun during the acute phase of illness and continued until death of recovery of normal consciousness. Comparison of the initial and final studies revealed that CBF declined to very low levels in all nine patients who died, and remained subnormal in a patient with persistent vegetative state. In contrast, 25 of 26 patients who recovered consciousness showed increases in blood flow. Because of the presence of both reduced and elevated blood flows on the initial study, CBF was not predictive of outcome. Absolute or relative hyperemia, observed in nine acute cases, was associated with either diffuse cerebral swelling (observed on computerized tomography) or recovery from systemic shock. Cerebral metabolic studies in hyperemic patients yielded a very low oxygen uptake and arteriovenous oxygen difference, indicating that the high blood flow was a true "luxury perfusion." When instances of presumed luxury perfusion were excluded, CBF was positively correlated with level of consciousness, assessed on a four-point coma scale.

Nonvolumetric methods of detecting impaired intracranial compliance or reactivity: pulse width and wave form analysis

The authors have attempted to find a clinically reliable method of measuring intracranial pressure (ICP) compliance or reactivity that does not require volumetric manipulation. An analysis was undertaken of ICP, pulse widths and of the presence or absence of B waves, both experimentally in dogs and clinically in postoperative human patients. In both dogs and humans, ICP pulse width generally increased with increasing ICP and with increasing intracranial mass, and definitely increased with systolic arterial blood pressure. Nonetheless, ICP pulse width commonly failed to increase with increasing cerebral reactivity, and low ICP pulse width measurements were at times recorded in distinctly pathological situations. From the clinical study it was found that B waves were encountered more commonly in patients with increased ICP or increased ICP pulse width. However, the correlation between B waves alone or in combination with increased ICP or ICP pulse width and quantitative measurements of ICP reactivity was not significant. Mean reactivity and the range of reactivity measurements were almost identical in patient groups with and without B waves. For the time being the "ICP reserve test" remains the most accurate, the safest, and the most clinically useful method of quantitating ICP reserve.

Pressure passive cerebral blood flow and breakdown of the blood-brain barrier in experimental fetal asphyxia

Cerebral blood flow (CBF) was studied in non-exteriorized near-term sheep fetuses using the radioactive microsphere technique. By partially occluding the umbilical vessels for a period of 1--1 1/2 hours a progressive and severe asphyxia with a final arterial pH of 6.90 was achieved. Varying the mean arterial blood pressure in the fetuses by blood withdrawal or infusion in this state, CBF was measured at different perfusion pressures (mean arterial blood pressure (MABP) minus central venous pressure (CVP)). A passive flow/pressure relationship--loss of autoregulation--was found, with hyperemia reaching CBF values up to 6 times normal at normal MABP of about 60 to 70 mmHg, and severe ischemia reaching CBF values close to zero in large cortical areas at MABP of 30 mmHg. CVP remained essentially unchanged at 10--15 mmHg. The severe and prolonged asphyxia rendered the blood-brain barrier leaky to the albumin tracer Evans blue. In four other fetuses umbilical cord clamping was omitted. However, only in one of these cases was acidosis completely avoided, and CBF autoregulation maintained. The three other fetuses were acidotic at the end of the surgical procedure and had impaired autoregulation.

Cerebral autoregulation in unconscious patients with brain injury

In 18 unconscious patients with traumatic brain injury, the cerebral autoregulation was tested during the first 2-3 weeks after the acute trauma. Regional cerebral blood flow (rCBF) was measured by the intra-arterial 133xenon washout method before and after an increase of about 20% in the mean arterial blood pressure (MABP) by angiotensin. The difference between MABP and intraventricular pressure (IVP) was used as cerebral perfusion pressure (PP). Simultaneously, ventricular fluid pH, lactate and pyruvate were measured. Regional loss of autoregulation indicated by a 20% flow increase was observed in 29 out of 35 studies (83%), while hemispheric loss of autoregulation was observed in only one study. The results of the autoregulation tests were unrelated to the clinical outcome, the presence of brain-stem lesion, and the ventricular fluid pH, lactate and lactate/pyruvate ratio. In repeated studies, a gradual normalization of the autoregulation was observed about 5 days after the acute trauma.

Cerebral metabolic rate of oxygen (CMRO2) in the acute phase of brain injury

In 22 comatose patients with acute brain injury, the cerebral metabolic rate of oxygen (CMRO2) was calculated as the product of the hemispheric cerebral blood flow (CBF) and the arteriovenous oxygen content difference. All patients were subjected to moderate sedation without barbiturates, normothermia and respiratory treatment. The CBF was calculated by the 133xenon washout method as the average of 16 regions. The results indicate high jugular venous oxygen tension and, in some studies, very low oxygen consumption. A critical, low CMRO2 was not found, and values of about 0.4 ml/100 g/min were compatible with restitution of intellectual function. The CMRO2 was unrelated to the clinical outcome and to the time after the trauma. In bilateral studies, the lowest values were measured in the most severely injured hemisphere.

Autoregulation and CO2 responses of cerebral blood flow in patients with acute severe head injury

Regional cerebral blood flow (rCBF), cerebral intraventricular pressure (IVP), systemic arterial blood pressure, and cerebral ventricular fluid (CSF) lactate and pH were studied repeatedly in 23 patients during the acute phase of severe brain injury lasting from 3 to 21 days after the trauma. Cerebrovascular autoregulation was tested repeatedly by means of angiotensin infusion in 21 of the patients, and CO2 response in 14 by means of passive hyperventilation. The pressure in the brain ventricles was measured continuously in all patients and kept below 45 mm Hg during the study. If the IVP increased more than 10 mm Hg during the angiotensin infusion (as in one case), the autoregulation test was considered contraindicated and the angiotensin infusion was discontinued. Dissociation between cerebrovascular autoregulation and CO2 response was a common phenomenon. Typically, autoregulation appeared preserved in the most severely injured areas of the cerebral cortex when the patient was deeply comatose, but deteriorated concomitantly with recovery; by the time the patient became alert, the autoregulation was always impaired. The CO2 response was impaired only in patients who were deeply comatose and had attacks of decerebrate rigidity; during recovery the CO2 response became normal. Thus, preserved autoregulation associated with imparied CO2 response indicated very severe brain damage, whereas impaired autoregulation associated with preserved CO2 response suggested moderate or severe brain damage in recovery. These paradoxical observations raise the question whether the preserved autoregulation seen in severely injured brain tissue is a true autoregulation caused by an active vasoconstrictor response to an increase in blood pressure.

Correlation of cerebral blood flow with outcome in head injured patients

In order to determine the relationship of cerebral blood flow (CBF) to the clinical outcome of head injury, serial determinations of CBF were performed by the intravenous Xenon technique in 24 patients. The patients were of mixed injury severity and were classified into four groups depending on the neurological exam at the time of each CBF study. All eight patients who were lethargic on admission demonstrated increases in their minimally depressed CBF as they improved to normal status. Eleven patients in deep stupor or coma ultimately recovered. Ten of these patients initially had moderate to profound decreases in CBF which improved as recovery occurred. The single exception was an adolescent whose initial CBF was high but became normal at recovery. Five comatose patients died. In four of these, already depressed CBF fell even lower, while one adolescent with initially increased CBF developed very low CBF preterminally. The data presented in this report demonstrated a good correlation between CBF and clinical outcome. In every one of the adult survivors, depressed CBF increased as the patient recovered to normal status. All adults who died showed a deterioration of CBF as the neurological status worsened. The only exceptions were two adolescents who initially showed high CBF values. In the adolescent who died, CBF dropped to low levels while in the survivor a normal CBF was achieved. Thus in adults a traumatic brain injury was associated with depressed CBF which increased with recovery or decreased further with deterioration while the reaction to injury was quite different in the younger brain.