Cerebral autoregulation in children during sevoflurane anaesthesia

The Effect of Electroencephalography Abnormalities on Cerebral Autoregulation in Sedated Ventilated Children

Purpose: To determine the effects of non-ictal electroencephalogram (EEG) changes on cerebrovascular autoregulation (AR) using the cerebral oximetry index (COx). Materials and Methods: Mean arterial blood pressure (MAP), cerebral tissue oxygenation (CrSO2), and EEG were acquired for 96 h. From all of the EEG recordings, 30 min recording segments were extracted using the endotracheal suction events as the guide. EEG recordings were classified as EEG normal and EEG abnormal groups. Each 30 min segment was further divided into six 5 min epochs. Continuous recordings of MAP and CrSO2 by near-infrared spectroscopy (NIRS) were extracted. The COx value was defined as the concordance (R) value of the Pearson correlation between MAP and CrSO2 in a 5 min epoch. Then, an Independent-Samples Mann-Whitney U test was used to analyze the number of epochs within the 30 min segments above various R cutoff values (0.2, 0.3, and 0.4) in normal and abnormal EEG groups. A p-value < 0.05 was considered significant, and all analyses were two-tailed. Results: Among 16 sedated, mechanically ventilated children, 382 EEG recordings of 30 min segments were analyzed. The proportions of epochs in each 30 min segment above the R cutoff values were similar between the EEG normal and EEG abnormal groups (p > 0.05). The median concordance values for CSrO2 and MAP in EEG normal and EEG abnormal groups were similar (0.26 (0.17−0.35) and 0.18 (0.12−0.31); p = 0.09). Conclusions: Abnormal EEG patterns without ictal changes do not affect cerebrovascular autoregulation in sedated and mechanically ventilated children.

Response of internal carotid artery blood flow velocity to fluid challenge under general anesthesia in pediatric patients with moyamoya disease: A prospective observational study

BACKGROUND

Maintaining cerebral blood flow is important in intraoperative management of moyamoya disease patients.

AIMS

To access changes in the carotid artery blood flow velocity in response to fluid challenge, blood pressure, and cardiac output under general anesthesia in pediatric patients with moyamoya disease.

METHODS

This observational study included pediatric patients with moyamoya disease undergoing general anesthesia for encephaloduroarteriosynangiosis. Each patient underwent an ultrasound assessment thrice as follows: after anesthetic induction (T1), after fluid challenge (10 ml/kg, T2), and at the end of surgery (T3). The primary outcome was the change in the internal carotid artery blood flow velocity after fluid challenge and was assessed using a paired t-test. The secondary outcomes comprised changes in the internal, external, and common carotid artery blood flow peak velocities after fluid challenge and the factors influencing these changes.

RESULTS

We enrolled and analyzed 30 patients with a mean age of 7.2 years. After fluid challenge, the systolic (p = .003) and mean blood pressure (p = .017), stroke volume index (p = .008), and cardiac index (p = .140) were higher than those at T1. However, both internal carotid artery blood flow velocities did not change after fluid challenge (p = .798, mean difference and 95% confidence interval [CI], -1.1 and -10.3 to 8.0 for right, p = .164, mean difference and 95% CI, -5.2 and -12.7 to 2.2 for left). The internal carotid artery blood flow velocity was correlated with the cardiac index, stroke volume index, and mean and diastolic blood pressure, with low significance.

CONCLUSIONS

The internal carotid artery blood flow velocity did not increase in pediatric patients with moyamoya disease under general anesthesia, despite fluid challenge and corresponding changes in the blood pressure and cardiac output. Intraoperative hemodynamic management to improve the cerebral blood flow in these patients requires further investigation.

Age Difference of the Relationship Between Cerebral Oxygen Saturation and Physiological Parameters in Pediatric Cardiac Surgery with Cardiopulmonary Bypass: Analysis Using the Random-Effects Model

Recently, monitoring of cerebral oxygen saturation (ScO₂) has become widespread in pediatric cardiac surgery. Our previous study reported that mean blood pressure (mBP) was the major contributor to ScO₂ throughout cardiac surgery with cardiopulmonary bypass (CPB) in children weighing under 10 kg. We speculated that this result might be attributable to incomplete cerebral autoregulation in such young children. Accordingly, our hypothesis is that the relationship between ScO₂ and the physiological parameters may change according to the growth of the children. ScO₂ was measured with an INVOS 5100C (Somanetics, Troy, MI). Random-effects analysis was employed with ScO₂ as a dependent variable, and seven physiological parameters (mBP, central venous pressure, nasopharyngeal temperature, SaO₂, hematocrit, PaCO₂, and pH) were entered as independent covariates. The analysis was performed during the pre-CPB, CPB, and post-CPB periods by dividing the patients into two groups: infants (Infant Group) and children who were more than 1 year old (Child Group). The Infant and Child Groups consisted of 28 and 21 patients. In the random-effects analysis, mBP was the major contributor to ScO₂ during CPB in both groups. During the pre-CPB period, the effect of mBP was strongest in the Infant group. However, its effect was second to that of SaO₂ in the Child Group. During the post-CPB period, SaO₂ and mBP still affected ScO₂ in the Infant group. However, the dominant contributors were unclear in the Child Group. Cerebral autoregulation may be immature in infants. In addition, it may be impaired during CPB even after 1 year of age.

Cerebral autoregulation in infants during sevoflurane anesthesia for craniofacial surgery

BACKGROUND

Data on cerebral pressure-flow autoregulation in the youngest children are scarce. We studied the correlation between mean arterial pressure and cerebral tissue oxygen saturation (rSO₂ ) by near-infrared spectroscopy (NIRS) in patients undergoing nose, lip, and palate surgery.

AIM

We tested the hypothesis that cerebral pressure-flow autoregulation is impaired in children less than 1 year undergoing surgery and general anesthesia with sevoflurane under controlled mechanical ventilation.

METHOD

After approval from the Ethical board, 15 children aged <1 year were included. Before anesthesia induction, a NIRS sensor (INVOS^TM , Medtronic, Minneapolis, USA) was placed over the cerebral frontal lobe. Frontal rSO₂ , a surrogate for cerebral perfusion, mean arterial pressure, end-tidal CO₂ - and sevoflurane concentration, and arterial oxygen saturation were sampled every minute after the induction. A repeated measures correlation analysis was performed to study correlation between mean arterial pressure and cerebral rSO₂ , and the repeated measures correlation coefficient (r_rm ) was calculated.

RESULTS

Fifteen patients, aged 7.7 ± 1.9 months, were studied. rSO₂ showed a positive correlation with mean arterial pressure ([95% CI: 9.0-12.1], P < 0.001) with a moderate to large effect size (r_rm  = 0.462), indicating an impaired cerebral pressure-flow autoregulation. The slopes of the rSO₂ -mean arterial pressure correlations were steeper in patients who were hypotensive (mean arterial pressure <50 mm Hg) compared to patients having a mean arterial pressure ≥50 mm Hg, indicating that at lower mean arterial pressure, the cerebral pressure dependence of cerebral oxygenation is even more pronounced.

CONCLUSION

During sevoflurane anesthesia in the youngest pediatric patients, cerebral perfusion is pressure-dependent, suggesting that the efficiency of the cerebral blood flow autoregulation is limited.

Does hypertension at initial presentation adversely affect outcomes in pediatric traumatic brain injury?

BACKGROUND

Adults with traumatic brain injury (TBI) who present hypertensive suffer worse outcomes and increased mortality compared to normotensive patients. The purpose of this study is to determine if age-adjusted hypertension on presentation is associated with worsened outcomes in pediatric TBI.

METHODS

A retrospective chart review was conducted on pediatric patients with severe TBI admitted to a single system pediatric tertiary care center. The primary outcome was mortality. Secondary outcomes included length of stay, need for neurosurgical intervention, duration of mechanical ventilation, and the need for inpatient rehabilitation.

RESULTS

Of 150 patients, 70% were hypertensive and 30% were normotensive on presentation. Comparing both groups, no statistically significant differences were noted in mortality (13.3% for both groups), need for neurosurgical intervention (51.4% vs 48.8%, p = 0.776), length of stay (6 vs 8 days, p = 0.732), duration of mechanical ventilation (2 vs 3 days, p = 0.912), or inpatient rehabilitation rates (48.6% vs 48.9%, p = 0.972). In comparing just the hypertensive patients, there was a trend toward increased mortality in the 95th and 99th percentile groups at 15.8% and 14.1%, versus the 90th percentile group at 6.7% but the difference was not statistically significant (p = 0.701).

CONCLUSIONS

Contrary to the adult literature, pediatric patients with severe TBI and hypertension on presentation do not appear to have worsened outcomes compared to those who are normotensive. However, a trend toward increased mortality did exist at extremes of age adjusted hypertension. Larger scale studies are needed to validate these findings.

STUDY TYPE

Retrospective cohort study LEVEL OF EVIDENCE: III.

Effect of dexmedetomidine on dynamic cerebral autoregulation and carbon dioxide reactivity during sevoflurane anesthesia in healthy patients

BACKGROUND

There are conflicting opinions on the effect of dexmedetomidine on cerebral autoregulation. This study assessed its effect on dynamic cerebral autoregulation (dCA) using a transcranial Doppler (TCD).

METHODS

Thirty American Society of Anesthesiologists physical status I and II patients between 18 and 60 years, who underwent lumbar spine surgery, received infusions of dexmedetomidine (Group D) or normal saline (Group C), followed by anesthesia with propofol and fentanyl, and maintenance with oxygen, nitrous oxide and sevoflurane. After five minutes of normocapnic ventilation and stable bispectral index value (BIS) of 40-50, the right middle cerebral artery flow velocity (MCAFV) was recorded with TCD. The transient hyperemic response (THR) test was performed by compressing the right common carotid artery for 5-7 seconds. The lungs were hyperventilated to test carbon dioxide (CO2) reactivity. Hemodynamic parameters, arterial CO2 tension, pulse oximetry (SpO2), MCAFV and BIS were measured before and after hyperventilation. Dexmedetomidine infusion was discontinued ten minutes before skin-closure. Time to recovery and extubation, modified Aldrete score, and emergence agitation were recorded.

RESULTS

Demographic parameters, durations of surgery and anesthesia, THR ratio (Group D: 1.26 ± 0.11 vs. Group C: 1.23 ± 0.04; P = 0.357), relative CO2 reactivity (Group D: 1.19 ± 0.34 %/mmHg vs. Group C: 1.23 ± 0.25 %/mmHg; P = 0.547), blood pressure, SpO2, BIS, MCAFV, time to recovery, time to extubation and modified Aldrete scores were comparable.

CONCLUSIONS

Dexmedetomidine administration does not impair dCA and CO2 reactivity in patients undergoing spine surgery under sevoflurane anesthesia.

Early changes in cerebral autoregulation among youth hospitalized after sports-related traumatic brain injury

OBJECTIVE

To examine early cerebral haemodynamic changes among youth hospitalized with sports-related traumatic brain injury (TBI).

STUDY DESIGN

Youth 0-18 years admitted to a level one trauma centre with sports-related TBI were enrolled. Daily measures included clinical symptoms and Glasgow Coma Scale (GCS) score. Using Transcranial Doppler (TCD) ultrasonography and tilt testing, we measured middle cerebral artery flow velocity (Vmca) and cerebral autoregulation index (ARI).

RESULTS

Six previously healthy males age 14 (IQR 12-16) years with headache and abnormal head CT were admitted with median admission GCS 15. Six patients underwent 12 TCD examinations between hospital days 0-9. Low Vmca occurred in 3/6 patients and on the side of TBI, whereas high Vmca occurred in 2/6 patients. Five patients had at least one measurement of impaired and five patients had absent cerebral autoregulation of at least one hemisphere; all these five patients had GCS 15 and headache during TCD examinations. Three patients were discharged with absent cerebral autoregulation. Five (83%) patients were discharged to home and one patient was discharged to a rehabilitation facility.

CONCLUSION

Headache, abnormal Vmca and impaired cerebral autoregulation occur after sports-related TBI, despite normal GCS. Headache may signal underlying neurovascular abnormality in sports-related TBI.

Anterior cerebral blood velocity and end-tidal CO2 responses to exercise differ in children and adults

Little is known about the response of the cerebrovasculature to acute exercise in children and how these responses might differ with adults. Therefore, we compared changes in middle cerebral artery blood velocity (MCAV_mean), end-tidal Pco₂ ([Formula: see text]), blood pressure, and minute ventilation (V̇e) in response to incremental exercise between children and adults. Thirteen children [age: 9 ± 1 (SD) yr] and thirteen sex-matched adults (age: 25 ± 4 yr) completed a maximal exercise test, during which MCAV_mean, [Formula: see text], and V̇e were measured continuously. These variables were measured at rest, at exercise intensities specific to individual ventilatory thresholds, and at maximum. Although MCAV_mean was higher at rest in children compared with adults, there were smaller increases in children (1-12%) compared with adults (12-25%) at all exercise intensities. There were alterations in [Formula: see text] with exercise intensity in an age-dependent manner [F(2.5,54.5) = 7.983, P < 0.001; η² = 0.266], remaining stable in children with increasing exercise intensity (37-39 mmHg; P > 0.05) until hyperventilation-induced reductions following the respiratory compensation point. In adults, [Formula: see text] increased with exercise intensity (36-45 mmHg, P < 0.05) until the ventilatory threshold. From the ventilatory threshold to maximum, adults showed a greater hyperventilation-induced hypocapnia than children. These findings show that the relative increase in MCAV_mean during exercise was attenuated in children compared with adults. There was also a weaker relationship between MCAV_mean and [Formula: see text] during exercise in children, suggesting that cerebral perfusion may be regulated by different mechanisms during exercise in the child.NEW & NOTEWORTHY These findings provide the first direct evidence that exercise increases cerebral blood flow in children to a lesser extent than in adults. Changes in end-tidal CO₂ parallel changes in cerebral perfusion in adults but not in children, suggesting age-dependent regulatory mechanisms of cerebral blood flow during exercise.

Cerebral Blood Flow Autoregulation and Dysautoregulation

This article provides a review of cerebral autoregulation, particularly as it relates to the clinician scientist experienced in neuroscience in anesthesia and critical care. Topics covered are biological mechanisms; methods used for assessment of autoregulation; effects of anesthetics; role in control of cerebral hemodynamics in health and disease; and emerging areas, such as role of age and sex in contribution to dysautoregulation. Emphasis is placed on bidirectional translational research wherein the clinical informs the study design of basic science studies, which, in turn, informs the clinical to result in development of improved therapies for treatment of central nervous system conditions.

Monitoring of cerebral blood flow autoregulation in adults undergoing sevoflurane anesthesia: a prospective cohort study of two age groups

Autoregulation of blood flow is a key feature of the human cerebral vascular system to assure adequate oxygenation and metabolism of the brain under changing physiological conditions. The impact of advanced age and anesthesia on cerebral autoregulation remains unclear. The primary objective of this study was to determine the effect of sevoflurane anesthesia on cerebral autoregulation in two different age groups. This is a follow-up analysis of data acquired in a prospective observational cohort study. One hundred thirty-three patients aged 18-40 and ≥65 years scheduled for major noncardiac surgery under general anesthesia were included. Cerebral autoregulation indices, limits, and ranges were compared in young and elderly patient groups. Forty-nine patients (37 %) aged 18-40 years and 84 patients (63 %) aged ≥65 years were included in the study. Age-adjusted minimum alveolar concentrations of sevoflurane were 0.89 ± 0.07 in young and 0.99 ± 0.14 in older subjects (P < 0.001). Effective autoregulation was found in a blood pressure range of 13.8 ± 9.8 mmHg in young and 10.2 ± 8.6 mmHg in older patients (P = 0.079). The lower limit of autoregulation was 66 ± 12 mmHg and 73 ± 14 mmHg in young and older patients, respectively (P = 0.075). The association between sevoflurane concentrations and autoregulatory capacity was similar in both age groups. Our data suggests that the autoregulatory plateau is shortened in both young and older patients under sevoflurane anesthesia with approximately 1 MAC. Lower and upper limits of cerebral blood flow autoregulation, as well as the autoregulatory range, are not influenced by the age of anesthetized patients. Trial registration ClinicalTrials.gov (NCT00512200).

Mechanisms and consequences of acquired brain injury during development

The brain of the infant and young child is a developing, dynamic, structure subject to functional remodelling under the influence of factors responsible for optimal neuronal development and synaptogenesis. It exhibits age dependent variation in metabolic rate, blood flow, and ability to tolerate oxidative stress. It is also characterized by an exuberance of neurotransmitter activity, particularly in the first few years of life. The dynamic evolution and adaptability of early brain function permits the organization of neuronal networks to be influenced by environmental stimulation, and, to reduce the functional impact of injury. However, these same processes may also exacerbate the harm sustained by the brain following an acquired brain injury (ABI). The developing neurons are susceptible to excitotoxicity, oxidative stress, and, inflammation, often leading to cellular necrosis and apoptosis. Despite being immunologically privileged via the blood brain barrier, the developing brain is susceptible to injury from systemic inflammation through alteration of normally protective cerebrovascular endothelial cell function. Finally, many of the therapeutic agents currently employed in post-ABI hospital care may also compromise ABI outcome via non-intended pharmacological effects. These agents include analgesic, sedative and anti-convulsant medications. This review emphasizes those physiological considerations in the developing brain which may impact the outcome after ABI, including, the cellular mechanisms of neuronal and cerebrovascular endothelial cell injury, ABI outcome and future therapeutic directions.

[Transcranial Doppler ultrasound, bispectral index, and electroencephalographic monitoring of entropy during pediatric total intravenous anesthesia]

BACKGROUND AND OBJECTIVE

Transcranial Doppler ultrasound is a noninvasive technique for monitoring the velocity of blood flow in the main intracranial arteries, particularly those in the circle of Willis. Our aim was to assess whether changes in cerebral arterial blood flow in anesthetized pediatric patients detected by pulsed Doppler ultrasound correlate with changes in the bispectral (BIS) index and electroencephalographic state and response entropy (ES and ER, respectively).

MATERIAL AND METHODS

Prospective, blinded observational study of 36 pediatric patients (age range, 5 to 11 years) under total intravenous anesthesia for minor surgical procedures. Propofol and fentanyl were used for induction; propofol and remifentanil in continuous perfusion and a single dose of cisatracurium were used for maintenance. In all patients we monitored hemodynamic and respiratory patterns, gases, temperature, and hypnosis (BIS, ES and ER) as well as cerebral blood flow estimated by pulsed Doppler ultrasound in the middle cerebral artery. Raw data were subjected to statistical smoothing. The resistance index, pulsatility index, mean velocity, and estimated baseline cerebral blood flow were calculated from the Doppler sonogram. We then studied the correlations between the Doppler-derived values and BIS, ES, ER, fraction of end-tidal carbon dioxide, and temperature. The variables were entered into logistic regression.

RESULTS

The pattern at induction indicated high resistance (low mean velocities and high pulsatility indexes) until the lowest BIS and ES values of 31 and 29, respectively, were reached. During maintenance, the Doppler sonogram pattern was slower (normalization of the pulsatility index, the resistance index, and mean velocity). Changes in flow and absolute entropy and BIS values were statistically correlated (Pearson's r values > or = 0.91); there was 95.6% agreement between Doppler values and BIS and agreement between BIS and ES values of 35-45. On awakening, flow velocities approached baseline values when BIS and ES rose to between 90 and 98. The estimated cerebral blood flow underwent fluctuations coinciding with an approximately concomitant increase or decrease in BIS (r > 0.95); the response of BIS was slightly delayed by no more than a minute but there was no corresponding response of entropy measurements.

CONCLUSIONS

We report Doppler ultrasound patterns during anesthesia with propofol. Systems for monitoring hypnosis could be considered indirect measurements of cerebral blood flow; BIS measurements are more sensitive to flow change. Transcranial Doppler ultrasound facilitates the observation of changes in blood flow that occur at different levels of hypnosis during anesthesia.

[Transcranial Doppler ultrasound, bispectral index, and electroencephalographic monitoring of entropy during sevoflurane anesthesia in children]

BACKGROUND AND OBJECTIVE

Transcranial Doppler ultrasound is a noninvasive technique for monitoring the velocity of blood flow in the main intracranial arteries, particularly those in the circle of Willis. Our aim was to assess whether changes in cerebral arterial blood flow in pediatric patients under sevoflurane anesthesia demonstrated by pulsed Doppler ultrasound correlate with changes in the bispectral (BIS) index and electroencephalographic state and response entropy (ES and ER, respectively).

MATERIAL AND METHODS

Prospective, blinded observational study of 36 pediatric patients (age range, 5 to 11 years; ASA physical status classification, 1-2) under sevoflurane anesthesia for minor surgical procedures. Anesthesia was induced with sevoflurane and maintained with 2.5% sevoflurane in an inspired oxygen fraction of 50% in air. A continuous perfusion of remifentanil was provided for analgesia. In all patients we monitored hemodynamic and respiratory patterns, gases, temperature, and hypnosis (BIS, ES and ER) as well as cerebral blood flow estimated by pulsed Doppler ultrasound in the middle cerebral artery. The resistance index, pulsatility index, mean velocity, and estimated baseline cerebral blood flow were calculated from the Doppler sonogram. Correlations (Pearson's r) were calculated between BIS, ES, ER, the pulsatility index, resistance index, mean flow velocity, estimated cerebral blood flow, fraction of end-tidal carbon dioxide, and temperature. A regression model was constructed.

RESULTS

Induction caused a pattern of high velocity (elevated mean velocity and normal or reduced pulsatility index) until the lowest BIS and ES values of 31 and 29, respectively, were reached. During maintenance, the Doppler sonogram pattern was slower (normalization of the pulsatility index, the resistance index, and mean velocity). Changes in flow and absolute entropy and BIS values were statistically correlated (Pearson's r values > or = 0.91); there was 95.6% agreement between Doppler values and BIS and agreement between BIS and ES values of 35 to 45. On awakening, flow velocities approached baseline values when BIS and ES rose to between 90 and 98. The estimated cerebral blood flow underwent fluctuations coinciding with an approximately concomitant increase or decrease in BIS (r > 0.95); the BIS response occurred with a slight delay of no more than a minute. The entropy measurements did not reflect the fluctuations.

CONCLUSIONS

We show Doppler ultrasound patterns during anesthetic induction with sevoflurane. Systems for monitoring hypnosis could be considered indirect measurements of cerebral blood flow; BIS measurements are more sensitive to change. Transcranial Doppler ultrasound facilitates the observation of changes in blood flow that occur at different levels of hypnosis during anesthesia.

Relationship between regional cerebral blood flow and electrocorticographic activities under sevoflurane and isoflurane anesthesia

The aims of this study are (1) to assess the effects of volatile anesthetics on regional cerebral blood flow (rCBF) and electrocorticography (ECoG), and (2) to investigate the relationship between rCBF and ECoG influenced by volatile anesthetics. The authors measured rCBF using laser Doppler flowmetry and ECoG simultaneously and continuously from the same cortex during craniotomy, using the specially arranged probe. Patients received intravenous anesthetics with nitrous oxide until craniotomy, and after opening of dura, volatile anesthetic, either isoflurane or sevoflurane, was started and was gradually increased for the measurement. Four of the nine cases (44.4%) of the sevoflurane group showed no change both in rCBF and ECoG. In three cases (33.3%), rCBF increased as the frequency of the paroxysmal activities increased. In two cases (22.2%), decreased rCBF was accompanied by slow waves. In 12 cases of the isoflurane group, no apparent rCBF and ECoG changes were seen, except a case with decreased rCBF and slow waves. This is the first report of simultaneous recordings of regional CBF and neuronal activity under general anesthesia. During sevoflurane and isoflurane anesthesia <2.5 minimum alveolar anesthetic concentration, rCBF is affected by ECoG activities rather than pharmacologic action of inhalational anesthetics.

Cerebrovascular physiology in perinates with congenital hydrocephalus

PURPOSE

This study investigated changes in regional cerebral blood flow (rCBF), autoregulation (AR), and mean CO(2) reactivity (CO(2)r) in nine neonates, who underwent cerebrospinal fluid (CSF) diversion for congenital hydrocephalus.

METHODS

During shunt insertion, a thermal diffusion probe inserted adjacent to the ventricular catheter in the right parietal region recorded rCBF. Changes in rCBF, mean arterial pressure, intracranial pressure (ICP), and expired CO(2) tension were recorded before and after removing CSF.

RESULTS

Mean baseline rCBF for the entire group was 19.5 mL/100 g/min (range 8.4-44.8), with a mean ICP of 9.9 mmHg (range 4-20). Following CSF removal, the rCBF increased significantly in two patients. Three patients demonstrated AR throughout their studies; one infant showed AR after CSF removal. One infant without AR during shunt insertion showed an increase in rCBF and AR during a revision 5 months later. Baseline CO(2)r varied considerably but was greater than two in two patients and increased in three other children after CSF removal. Mean follow-up was 23.6 months. One child, with severe developmental delay, died. Death or severe delay was associated with the absence of AR and a negative CO(2)r in three children. Normal or mild developmental delay was associated with AR and a neutral or positive CO(2)r in five patients.

CONCLUSIONS

Baseline levels of rCBF were not associated with developmental prognosis. AR and a positive CO(2)r were necessary but insufficient factors for normal development. The absence of AR and a negative CO(2)r were associated with poor prognosis.

Sevoflurane inside and outside the operating room

BACKGROUND

Sevoflurane is often presented as a near-perfect anaesthetic. After 10 years in the operating room, new uses are emerging outside.

OBJECTIVE

To remind readers of the principal characteristics of sevoflurane, to affirm its usefulness for day-case anaesthesia and to consider the recent new uses.

METHODS

The discussion of the physical properties, pharmacokinetics, metabolism, mechanisms of action and clinical effects is based on classic, essential papers. Recent literature concerning emerging utilizations of sevoflurane was analysed.

RESULTS

Sevoflurane presents many benefits with minimum inconvenience. It allows rapid inhalation induction, maintenance and rapid recovery. It has little toxicity and its haemodynamic and respiratory depressive effects are moderate and well tolerated. It is already widely use for sedation for magnetic resonance imaging in children. Its use in paediatric or adult intensive care could improve the management of pain and sedation.

Impact of anesthetic agents on cerebrovascular physiology in children

The role of the pediatric neuroanesthetist is to provide comprehensive care to children with neurologic pathologies. The cerebral physiology is influenced by the developmental stage of the child. The understanding of the effects of anesthetic agents on the physiology of cerebral vasculature in the pediatric population has significantly increased in the past decade allowing a more rationale decision making in anesthesia management. Although no single anesthetic technique can be recommended, sound knowledge of the principles of cerebral physiology and anesthetic neuropharmacology will facilitate the care of pediatric neurosurgical patients.

Cerebral blood flow and autoregulation after pediatric traumatic brain injury

Traumatic brain injury is a global health concern and is the leading cause of traumatic morbidity and mortality in children. Despite a lower overall mortality than in adult traumatic brain injury, the cost to society from the sequelae of pediatric traumatic brain injury is very high. Predictors of poor outcome after traumatic brain injury include altered systemic and cerebral physiology, including altered cerebral hemodynamics. Cerebral autoregulation is often impaired after traumatic brain injury and may adversely impact the outcome. Although altered cerebrovascular hemodynamics early after traumatic brain injury may contribute to disability in children, there is little information regarding changes in cerebral blood flow and cerebral autoregulation after pediatric traumatic brain injury. This review addresses normal pediatric cerebral physiology and cerebrovascular pathophysiology after pediatric traumatic brain injury.

Early childhood gender differences in anterior and posterior cerebral blood flow velocity and autoregulation

OBJECTIVE

We aimed to describe gender differences in blood flow velocity and autoregulation of the anterior and posterior cerebral circulations in prepubertal children.

METHODS

A prospective observational cohort study was performed at Harborview Medical Center's Cerebrovascular Laboratory after institutional review board approval, consent, and assent procedures. Children underwent measurement of middle cerebral and basilar artery flow velocities and cerebral autoregulation testing of the middle cerebral and basilar arteries. Cerebral autoregulation was quantified using the autoregulatory index, and estimated cerebrovascular resistance was calculated. Autoregulatory index <0.4 reflects impaired cerebral autoregulation. Data are presented as mean +/- SD. Patients were healthy 4- to 8-year-old children.

RESULTS

Forty-eight children (24 boys and 24 girls) 4 to 8 years of age (mean: 6 +/- 2 years) were enrolled. Middle cerebral artery flow velocity was higher than basilar artery flow velocity (96 +/- 13 vs 65 +/- 11 cm/s). Girls had higher middle cerebral artery flow velocity (99 +/- 11 vs 91 +/- 13 cm/s) and basilar artery flow velocity (70 +/- 10 vs 61 +/- 9 cm/s) than boys. Cerebral autoregulation was intact in all children. There was no gender difference in autoregulation between the middle cerebral artery (boys: 0.97 +/- 0.07; girls: 0.94 +/- 0.11) or basilar artery (boys: 0.94 +/- 0.13; girls: 0.94 +/- 0.11).

CONCLUSIONS

Similar to older children and adults, girls between 4 and 8 years of age had higher middle cerebral and basilar artery flow velocity than age-matched boys. This difference may reflect inherent differences in cerebral metabolic rate and/or estimated cerebrovascular resistance between the genders.

Inhalational or intravenous anesthetics for craniotomies? Pro inhalational

PURPOSE OF REVIEW

In neurosurgery, anesthesiologists and surgeons focus on the same target - the brain. The nature of anesthetics is to interact with brain physiology, leading to favorable and adverse effects. Research in neuroanesthesia over the last three decades has been dedicated to identifying the optimal anesthetic agent to maintain coupling between cerebral blood flow and metabolism, keep cerebrovascular autoregulation intact, and not increase cerebral blood volume and intracranial pressure.

RECENT FINDINGS

Sevoflurane is less vasoactive than halothane, enflurane, isoflurane, or desflurane. The context sensitive half-life is short and similar to that of desflurane, which translates into fast on and offset. Compared with propofol, sevoflurane decreases cerebral blood flow to a lesser extent, while cerebral metabolism is suppressed to the same degree. Sevoflurane does not increase intracranial pressure, while propofol decreases intracranial pressure.

SUMMARY

In neurosurgical patients with normal intracranial pressure, sevoflurane might be a good alternative to propofol. In patients with reduced intracranial elastance, caused by space occupying lesions, with elevated intracranial pressure or complex surgical approaches, propofol should remain first choice.

The Effect of Sevoflurane on Cerebral Autoregulation in Young Children as Assessed by the Transient Hyperemic Response

The transient hyperemic response (THR) test is a simple, noninvasive technique to evaluate cerebral autoregulation using transcranial Doppler. It has not yet been used in studies involving children. In this study we evaluated this response in children undergoing general anesthesia using sevoflurane. Twenty ASA physical status I children undergoing elective urological surgery sequentially received sevoflurane at 0.5, 1.0, and 1.5 MAC in a randomized order. Analgesia was solely provided by caudal anesthesia. The right middle cerebral artery flow velocities before (F1), during (F2), and after (F3) a 10-s ipsilateral carotid artery compression were recorded. The THR ratios (THRR) (+/- sd) for 0.5 MAC, 1.0 MAC, and 1.5 MAC were 1.24 +/- 0.11, 1.16 +/- 0.09, and 1.13 +/- 0.07, respectively. The THRR was significantly different between 0.5 MAC versus 1.0 and 1.5 MAC, respectively (P < 0.05). However, no difference was detected between 1.0 and 1.5 MAC. A THRR of more than 1.09 has previously been accepted as the lower limit of a positive response. The results in this study suggest that THR is affected by sevoflurane in a dose-dependent fashion but is maintained at up to 1.5 MAC. This suggests cerebral autoregulation is preserved in children anesthetized with up to 1.5 MAC sevoflurane.

The Effect of Sevoflurane on Dynamic Cerebral Blood Flow Autoregulation Assessed by Spectral and Transfer Function Analysis

Sevoflurane reduces autonomic neural control, which plays a significant role in cerebral autoregulation. Therefore, we hypothesized that sevoflurane influences cerebral autoregulation. We investigated the effects of sevoflurane on dynamic cerebral blood flow (CBF) autoregulation by using spectral and transfer function analysis between blood pressure variability and CBF velocity variability. Eleven healthy male subjects received 0.5%, 1.0%, and 1.5% sevoflurane via facemask. Dynamic cerebral autoregulation was evaluated by transfer function gain, phase, and coherence between CBF velocity in the middle cerebral artery measured by transcranial Doppler, and blood pressure in the radial artery. Coherence in the very low-frequency range (0.02-0.07 Hz) increased above 0.5 during administration of 0.5% and 1.0% sevoflurane. Transfer function gain in this frequency range (0.02-0.07 Hz), as an index of dynamic cerebral autoregulation, increased significantly with 0.5% and 1.0% sevoflurane. Transfer function gain and coherence in the low- and high-frequency ranges, however, remained unchanged during administration of sevoflurane. These results suggest that sevoflurane impairs dynamic cerebral autoregulation in the very-low-frequency range even with small concentrations, whereas dynamic cerebral autoregulation in the low- and high-frequency ranges remained unchanged.

Gender differences in cerebral blood flow velocity and autoregulation between the anterior and posterior circulations in healthy children

There is little information on gender differences in cerebral autoregulation. The purpose of this study was to compare autoregulation of the anterior and posterior circulations using the tilt test method in healthy boys and girls who were 10-16 y of age. Transcranial Doppler was used to measure middle cerebral artery and basilar artery flow velocities (Vmca and Vbas). Cerebral autoregulation (ARI) of the middle cerebral (ARImca) and basilar arteries (ARIbas) was examined using the tilt test method. An ARI <0.4 indicates impaired autoregulation. Among the 13 boys and 13 girls, Vmca and Vbas were higher in girls. All children demonstrated intact autoregulation, but boys had higher ARImca than girls, whereas girls had higher ARIbas than boys. Girls demonstrated greater autoregulation in the basilar artery, whereas boys demonstrated greater autoregulation in the middle cerebral artery. Girls had higher flow velocities in both vessels. This study provides normative data on cerebral autoregulation of the posterior circulation in healthy, awake boys and girls.

Sevoflurane effects on retrobulbar arteries blood flow in children

BACKGROUND

Measure of blood flow velocity in retrobulbar vessels is performed to determine the severity of ophthalmic pathologies as glaucoma. In children, this measure is usually performed under general anaesthesia. Sevoflurane is known to not modify cerebral blow flow velocities. However, its effect on retrobulbar circulation is not known. This study was designed to evaluate the effect of sevoflurane on retrobulbar circulation flow velocity in children undergoing examination for ocular disorders under general anaesthesia.

METHODS

Thirteen mechanically ventilated children (Fi(O2))=1) were included. Blood flow velocities of central retinal artery, ophthalmic artery, and middle cerebral artery were measured by Doppler ultrasound during 1 and 2 age-adjusted minimal alveolar concentration (MAC) sevoflurane anaesthesia. Intra-ocular pressure and non-invasive haemodynamic parameters were also measured. End-tidal carbon dioxide tension was controlled during all the study period.

RESULTS

Mean arterial pressure decreased from 1 to 2 age-adjusted MAC sevoflurane (58 [12] vs 54 [12] mm Hg, P=0.01). In the ophthalmic artery, end diastolic velocity (EDV) decreased significantly at 2 MAC (1 MAC: 4.4 [4] cm s(-1) vs 2 MAC: 1.4 [2.4] cm s(-1); P=0.04) and resistivity index (RI) increased significantly (1 MAC: 0.83 [0.11] vs 2 MAC: 0.93 [0.09]; P=0.007). Systolic velocity, EDV, and RI remained constant in the central retinal artery and in the middle cerebral artery.

CONCLUSION

High alveolar concentration of sevoflurane decreased blood flow velocity in the ophthalmic artery, but not in the central retinal and the middle cerebral arteries in children ventilated in hyperoxic condition. This effect was related to a decrease in mean arterial pressure. This vessel-dependent effect may be explained by the different autoregulatory mechanisms of these arteries. In the present hyperoxic conditions, the vascular effect of sevoflurane may have been limited in the central retinal artery and not in the ophthalmic artery.

The effect of remifentanil on cerebral blood flow velocity in children anesthetized with propofol

BACKGROUND

Cerebrovascular stability and rapid anesthetic emergence are desirable features of a neuroanesthetic regimen. In this randomized crossover study the effect of a low-dose remifentanil infusion on cerebral blood flow velocity (CBFV) in children anesthetized with propofol was evaluated.

METHODS

Twenty healthy children aged 1-6 years undergoing urological surgery were enrolled. Following face mask induction with sevoflurane, anesthesia was maintained with a standardized propofol infusion. Rocuronium was used to facilitate tracheal intubation and normothermia, and normocapnia were maintained. All children received a caudal epidural block, and a transcranial Doppler probe was placed to measure middle cerebral artery blood flow velocity (Vmca). Each patient received a remifentanil regimen of 0.5 microg x kg(-1) followed by 0.2 microg x kg(-1) x min(-1) in a predetermined order of remifentanil + propofol or propofol alone. Vmca, mean arterial pressure (MAP) and heart rate (HR) were recorded simultaneously at equilibrium with and without remifentanil.

RESULTS

The combination of remifentanil and propofol caused an 8.1% decrease in MAP (P = 0.0005) and an 11.8% decrease in HR (P < 0.0001) compared with propofol alone. Vmca was not different between the two groups (P = 0.4041).

CONCLUSION

The addition of remifentanil to propofol anesthesia in children causes a reduction in MAP and HR without affecting CBFV. This may imply that cerebral blood pressure autoregulation is preserved in children under propofol and remifentanil anesthesia.

Cerebral ischaemia during cardiac surgery in children detected by combined monitoring of BIS and near-infrared spectroscopy

BACKGROUND

Children frequently suffer transient cerebral ischaemia during cardiac surgery. We measured cerebral ischaemia in children during cardiac surgery by combining two methods of monitoring.

METHODS

We studied 65 children aged between 5 months and 17 yr having surgery to correct non-cyanotic heart disease using hypothermic cardiopulmonary bypass (CPB). During surgery, we measured the Bispectral Index (BIS) and regional cerebral haemoglobin oxygen saturation (SrO2) with near-infrared spectroscopy (NIRS). Cerebral ischaemia was diagnosed if both SrO2 and BIS decreased abruptly when acute hypotension occurred. In each patient, the relationship between SrO2 and arterial blood pressure (AP) was indicated by a plot of mean SrO2 against simultaneous mean AP.

RESULTS

We noted 72 episodes of cerebral ischaemia in 38 patients. Sixty-three ischaemic events were during CPB. Cerebral ischaemia was less frequent in older patients. Cerebral ischaemia was more common and more frequent in children under 4 yr old. Haematocrit during CPB was lower and SrO2 was more dependent on AP in children under 4 yr.

CONCLUSIONS

Children less than 4 yr of age are more likely to have cerebral ischaemia caused by hypotension during cardiac surgery. Ineffective cerebral autoregulation and haemodilution during CPB may be responsible.

Cerebral autoregulation in pediatric traumatic brain injury

OBJECTIVE

The aims of this study were to document the incidence of impaired cerebral autoregulation in children with traumatic brain injury using transcranial Doppler ultrasonography and to examine the relationship between autoregulatory capacity and outcome in children following traumatic brain injury.

DESIGN

Prospective cohort study.

SETTING

Harborview Medical Center (level I pediatric trauma center) in Washington state.

PATIENTS

Thirty-six children <15 yrs old with traumatic brain injury: Glasgow Coma Scale score <9 (n = 12, group 1), Glasgow Coma Scale score 9-12 (n = 12, group 2), and Glasgow Coma Scale score 13-15 (n = 12, group 3).

INTERVENTIONS

Cerebral autoregulation testing was conducted during extracranial surgery. Mean middle cerebral artery flow velocities were measured using transcranial Doppler as mean arterial pressure was increased to whichever variable was greater: 20% above baseline or a set value (80 mm Hg for <9 yrs and 90 mm Hg for 9-14 yrs). Autoregulatory capacity was quantified by the Autoregulatory Index. Autoregulatory Index <0.4 was considered impaired cerebral autoregulation. Discharge outcome using the Glasgow Outcome Scale score was considered good if the Glasgow Outcome Scale score was > or =4.

MEASUREMENTS AND MAIN RESULTS

Twenty-four (67%) of 36 children had an Autoregulatory Index > or =0.4. The incidence of impaired cerebral autoregulation was 42% (five of 12) in group 1, 42% (five of 12) in group 2, and 17% (two of 12) in group 3. Ten (42%) of the 24 children with intact cerebral autoregulation had a good outcome compared with only one of 12 (8%) children with impaired cerebral autoregulation (p =.04). Six of 12 (50%) children with impaired cerebral autoregulation had hyperemia compared with one of 24 (4%) children with intact cerebral autoregulation (p <.01). Hyperemia was associated with poor outcome (p =.01).

CONCLUSIONS

The incidence of impaired cerebral autoregulation was greatest following moderate to severe traumatic brain injury. Impaired cerebral autoregulation was associated with poor outcome. Hyperemia was associated with impaired cerebral autoregulation and poor outcome.

Les nouveaux agents volatils halogénés en neuro-anesthésie : quelle place pour le sévoflurane ou le desflurane ?

The effects on cerebral circulation and metabolism of sevoflurane and desflurane are largely comparable to isoflurane. Both induce a direct vasodilation of the cerebral vessels, resulting in a less pronounced decrease in cerebral blood flow compared to the decrease in cerebral metabolism. This direct vasodilation seems to be dose-dependent and more pronounced for desflurane > isoflurane > sevoflurane. Many reports suggest luxury perfusion at high concentrations of desflurane. Sevoflurane maintains intact cerebral autoregulation up to 1.5 MAC. Desflurane induces a significant impairment in autoregulation, with a completely abolished autoregulation at 1.5 MAC. Both sevoflurane and desflurane (up to 1.5 MAC) maintain normal CO(2) regulation. As to their effect on final intracranial pressure (ICP), both sevoflurane and desflurane revealed no increases in ICP. However, compared to intravenous hypnotics, subdural ICP is higher with volatiles because of their tendency to increase cerebral swelling after dura opening (isoflurane > sevoflurane). Several case reports have noted seizure-like movements, as well as EEG recorded seizures during induction of sevoflurane anesthesia. Especially, in children during inhalational induction with hyperventilation at a high sevoflurane concentration, severe epileptiform EEG with a hyperdynamic response were observed, which urges for caution using inhalational sevoflurane induction in children for neurosurgical procedures. Neuroprotective properties (reduced neuronal death either by necrosis or apoptosis) have been attributed to all volatile agents. However, these neuroprotective effects have been described in experimental or animal models, so their possible effect on humans remains to be proven.

The Lower Limit of Cerebral Autoregulation in Children During Sevoflurane Anesthesia

In adults, the lower limit of cerebral autoregulation (LLA) is generally considered to be a mean arterial pressure (MAP) of 60 mmHg. The LLA in healthy children has not been identified. The aim of this report is to describe the LLA in anesthetized children and relate it to age. Static cerebral autoregulation testing was performed in children 6 months to 14 years of age during <1 MAC sevoflurane anesthesia. Mean middle cerebral artery flow velocities (Vmca) were continuously measured using transcranial Doppler ultrasonography. MAP was increased with infusion of intravenous phenylephrine incrementally titrated to the greater of either: 1) 20% above baseline MAP or 2) 80 mmHg (<9 years), 90 mmHg (9-14 years). The LLA was defined by the point where the two linear regression lines fitting the Vmca/MAP crossed. The lower limit reserve (LLR) and autoregulatory reserve (ARR%) were defined as follows: LLR=Baseline MAP-LLA; ARR (%)=(LLR/Baseline MAP)x100. There were 13 subjects <2 years of age (group 1), 13 subjects 2 to 5 years of age (group 2), 14 subjects 6 to 9 years of age (group 3), and 13 subjects 10 to 14 years of age (group 4). Older children (groups 3 and 4) had a higher baseline MAP compared with younger children (groups 1 and 2) (82 +/- 10 mmHg vs. 70 +/- 10 mmHg, respectively; P=0.0001). However, there was no difference in LLA (59 +/- 17 mmHg vs. 60 +/- 8 mmHg; P=0.6) between older and younger children. Consequently, the LLR was greater in older children compared with younger children (25 +/- 12 mmHg vs. 12 +/- 10 mmHg, respectively; P=0.0007). Similarly, the ARR was significantly higher in older children compared with younger children (30% +/- 16% vs. 16% +/- 12%; P=0.002). In this study, we found no age-related differences in the LLA. Older children had a greater LLR and ARR compared with young children. The baseline MAP in young children may rest close to the LLA. These findings may have implications for managing hemodynamics in anesthetized children at risk for secondary brain injury.