Shape mapping of the hippocampus in young children with autism spectrum disorder

BACKGROUND AND PURPOSE

We hypothesized the occurrence of characteristic hippocampal-shape alterations in young children with autistic spectrum disorder (ASD) who also exhibit deficits on neuropsychologic tests of medial temporal lobe (MTL) function.

MATERIALS AND METHODS

Coronal 3D MR images were acquired from 3- to 4-year-old children with ASD (n = 45) and age-matched children with typical development (n = 13). Children with ASD were further subclassified into those with autism disorder (AD, n = 29) or pervasive developmental disorder-not otherwise specified (PDD-NOS) (n = 16). Variations in hippocampal shape were evaluated by using large-deformation high-dimensional brain mapping.

RESULTS

Hippocampal shape measures distinguished children with ASD from those with typical development; within the ASD sample, children with AD were distinguished from those with PDD-NOS. Hippocampal-shape alterations in children with ASD were correlated with degree of mental retardation and performance deficits on tests of MTL function.

CONCLUSIONS

Children with ASD exhibited an alteration of hippocampal shape consistent with inward deformation of the subiculum. This pattern of hippocampal-shape deformations in the children with ASD was accentuated in the more severely affected subgroup of children with AD and was associated with deficits on neuropsychologic tests of MTL but not prefrontal function. Hippocampal-shape deformation in the children with ASD was observed to be similar to a pattern of hippocampal shape deformation previously reported in adults with MTL epilepsy. Although the children with ASD, and those with AD in particular, PDD-NOS are at high risk for epilepsy as they enter adolescence, the specificity and causal relationship of this pattern of hippocampal-shape deformation to the development of seizures is not yet known.

Gray matter abnormalities in autism spectrum disorder revealed by T2 relaxation

OBJECTIVE

To perform quantitative T2 relaxation measurements to evaluate cerebral water content in children with autism.

METHODS

Sixty 2- to 4-year-old children with autism spectrum disorder (ASD), 16 age-matched children with idiopathic developmental delay (DD), and 10 children with typical development (TD) were scanned on a 1.5 T GE MRI scanner to obtain dual-echo fast spin echo images (2.5 mm thick, 0-mm gap). Images were segmented into gray and white matter and used to mask regions of interest for calculating T2 for each tissue type. Analysis of variance, covarying for age and sex, was used to compare T2 between groups, and correlations were used to compare T2 to IQ measures.

RESULTS

Children with ASD had prolonged cortical gray matter T2, but white matter T2 was not significantly different, compared with the children with TD. T2 was prolonged in cortical gray matter and white matter in children with DD compared with children with ASD or TD. Significant interactions between T2 measures and IQ were not observed.

CONCLUSIONS

Prolonged gray and white matter T2 in the children with developmental delay likely represents a delay in neuronal development and maturation. Prolonged T2 in gray matter, but not white matter, observed in children with autism spectrum disorder may signify abnormal developmental processes specific to autism.

Cerebrospinal fluid dynamics and brain tissue composition following intravenous infusions of hypertonic saline in anesthetized rabbits

This study examined brain tissue, cerebrospinal fluid (CSF), and plasma composition following intravenous infusion of two doses of 3% saline to rabbits anesthetized with halothane. The low dose of 3% saline consisted of infusion for 10 min at 1.0 ml/min at 1.0 ml/min and then thereafter at 7.0 ml/h. Infusion of either dose caused no significant change in CSF pressure, brain tissue water content, the concentration of sodium in CSF, or the concentration of potassium in CSF or plasma. Brain tissue sodium and potassium concentrations increased (by 8.5 and 8.6%, respectively), and CSF and plasma osmolalities increased (by 11-18 mOsm/kg) following both doses of 3% saline. Resistance to reabsorption of CSF increased by 56 +/- 22% (mean +/- SD) with the low dose of 3% saline and plasma sodium concentration increased by 5-11 mEq/L with the high dose of 3% saline. Both doses decreased the rate of CSF formation from 0.010 +/- 0.002 to 0.007 +/- 0.002 ml/min. It is concluded that 3% saline may not favor reduction of cerebral edema or decrease CSF pressure if it is given while the CSF pressure is normal, in part because of the large volume load imposed (22 ml/kg).

Concentration-related changes in the rate of CSF formation and resistance to reabsorption of CSF during enflurane and isoflurane anesthesia in dogs receiving nitrous oxide

The rate of cerebrospinal fluid (CSF) formation (Vf) and resistance to reabsorption of CSF (Ra) were determined at four concentrations of enflurane (0.9, 1.8, 2.0, and 3.5% end-expired) or isoflurane (0.6, 1.1, 1.7, and 2.2% end-expired) in dogs receiving nitrous oxide (66%) in oxygen. At the two higher concentrations of enflurane, Vf was about 27% greater (38-40% greater when corrected for the effects of time) than at the two lower concentrations of enflurane. At the two lower concentrations of enflurane and at all doses of isoflurane, Vf did not differ between or within anesthetic groups (0.029-0.033 ml/min). The pattern of Ra data was more varied. Ra was elevated with the two lower concentrations of enflurane (by about 68%) and with isoflurane 1.1% (by about 33%), and reduced with the two higher concentrations of isoflurane (by about 14-17%). It is concluded that the effects of enflurane and isoflurane on CSF dynamics are concentration-related. All concentrations of enflurane studied favor CSF volume expansion, while high concentrations of isoflurane favor CSF volume contraction.

Regional brain chemical alterations in young children with autism spectrum disorder

OBJECTIVE

The authors evaluated regional brain chemistry for evidence of increased neuronal packing density in autism.

METHODS

Forty-five 3- to 4-year-old children with autism spectrum disorder (ASD), 13 children with typical development (TD), and 15 children with delayed development (DD) were studied using dual-echo proton echoplanar spectroscopic imaging (32 x 32 matrix-1 cm(3) voxels) to measure brain chemical concentrations and relaxation times. Chemical quantification was corrected for tissue partial volume and relative measures of chemical relaxation (T(2r)) were calculated from the paired echoes. Measures from averaged and individual regions were compared using analysis of variance corrected for multiple comparisons.

RESULTS

ASD subjects demonstrated reduced N-acetylaspartate (NAA) (-10%), creatine (Cre) (-8%), and myo-inositol (-13%) concentrations compared to TD controls and prolonged NAA T(2r) relative to TD (7%) and DD (9%) groups. Compared to DD subjects, children with ASD also demonstrated prolonged T(2r) for choline (10%) and Cre (9%). Regional analyses demonstrated subtle patterns of chemical alterations in ASD compared to the TD and DD groups.

CONCLUSIONS

Brain chemical abnormalities are present in ASD at 3 to 4 years of age. However, the direction and widespread distribution of these abnormalities do not support hypothesis of diffuse increased neuronal packing density in ASD.

Brain structural abnormalities in young children with autism spectrum disorder

OBJECTIVE

To explore the specific gross neuroanatomic substrates of this brain developmental disorder, the authors examine brain morphometric features in a large sample of carefully diagnosed 3- to 4-year-old children with autism spectrum disorder (ASD) compared with age-matched control groups of typically developing (TD) children and developmentally delayed (DD) children.

METHODS

Volumes of the cerebrum, cerebellum, amygdala, and hippocampus were measured from three-dimensional coronal MR images acquired from 45 children with ASD, 26 TD children, and 14 DD children. The volumes were analyzed with respect to age, sex, volume of the cerebrum, and clinical status.

RESULTS

Children with ASD were found to have significantly increased cerebral volumes compared with TD and DD children. Cerebellar volume for the ASD group was increased in comparison with the TD group, but this increase was proportional to overall increases in cerebral volume. The DD group had smaller cerebellar volumes compared with both of the other groups. Measurements of amygdalae and hippocampi in this group of young children with ASD revealed enlargement bilaterally that was proportional to overall increases in total cerebral volume. There were similar findings of cerebral enlargement for both girls and boys with ASD. For subregion analyses, structural abnormalities were observed primarily in boys, although this may reflect low statistical power issues because of the small sample (seven girls with ASD) studied. Among the ASD group, structural findings were independent of nonverbal IQ. In a subgroup of children with ASD with strictly defined autism, amygdalar enlargement was in excess of increased cerebral volume.

CONCLUSIONS

These structural findings suggest abnormal brain developmental processes early in the clinical course of autism. Research currently is underway to better elucidate mechanisms underlying these structural abnormalities and their longitudinal progression.

The importance of kinin antagonist treatment timing in closed head trauma

BACKGROUND

Giving LF 16-0687 Ms (a bradykinin B2 receptor antagonist) 1 hour after closed head trauma (CHT) previously was reported to decrease brain edema at 24 hours and improve neurologic severity score (NSS) at 7 days. It is not certain whether a greater benefit could be achieved by treatment sooner after CHT.

METHODS

To examine the latter possibility we studied a surrogate condition for the earliest possible administration of LF 16-0687 Ms after CHT, e.g., we examined brain edema and NSS when LF 16-0687 Ms was given 15 min before CHT in rats.

RESULTS

LF 16-0687 Ms decreased brain water content (80.0 +/- 1.4%, mean +/- SD) at 24 hours and improved NSS (2 +/- 3, median +/- range) at 7 days after CHT in comparison to that with CHT + saline (82.9 +/- 1.3% and 8 +/- 4).

CONCLUSION

Similarity of the present results to those previously reported indicates that the benefit of giving LF 16-0687 Ms 1 hour after CHT appears to represent the maximal benefit afforded by this drug.

The effect of treatment with albumin, hetastarch, or hypertonic saline on neurological status and brain edema in a rat model of closed head trauma combined with uncontrolled hemorrhage and concurrent resuscitation in rats

In rats subjected to closed head trauma (CHT) plus uncontrolled hemorrhage, giving 0.3 mL of 0.9% saline per 0.1 mL of blood lost did not restore mean arterial blood pressure (MAP) or improve neurological severity score (NSS). In CHT without hemorrhage, giving 20% albumin or 10% hetastarch improved NSS. We hypothesized that these latter treatments would also improve NSS after CHT plus uncontrolled hemorrhage. Rats were randomly assigned to one of seven groups. Experimental conditions were CHT (yes or no), uncontrolled hemorrhage (yes or no), and fluid given to replace blood loss (none; 10% hetastarch, 20% albumin, or 3% saline [0.1 mL per 0.1 mL of blood lost]; or 0.9% saline [0.3 mL per 0.1 mL of blood lost]). NSS (0--25 scale, where 0 = no impairment) was determined at 1, 4, and 24 h, and brain water content was determined at 24 h after CHT. NSS (median +/- range) at 24 h was 11 +/- 6 when no fluid was given; 16 +/- 5 with 10% hetastarch; 14 +/- 5 with 20% albumin; 12 +/- 4 with 3% saline; and 13 +/- 4 with 0.9% saline given (not significant). In addition, brain water content and MAP did not differ among the groups receiving CHT with or without uncontrolled hemorrhage. In our model of CHT plus uncontrolled hemorrhage in rats, giving 10% hetastarch, 20% albumin, 3% saline, or 0.9% saline failed to improve NSS, brain water content, or MAP.

IMPLICATIONS

In previous studies of closed head trauma (CHT) without hemorrhage, giving 20% albumin or 10% hetastarch improved neurological severity scores (NSSs). We hypothesized that these treatments also might be beneficial in CHT plus uncontrolled hemorrhage. We found that giving 10% hetastarch, 20% albumin, 3% saline, or 0.9% saline failed to improve NSS, brain water content, or mean arterial blood pressure.

The effect of treatment with albumin, hetastarch, or hypertonic saline on neurological status and brain edema in a rat model of closed head trauma combined with uncontrolled hemorrhage and concurrent resuscitation in rats

In rats subjected to closed head trauma (CHT) plus uncontrolled hemorrhage, giving 0.3 mL of 0.9% saline per 0.1 mL of blood lost did not restore mean arterial blood pressure (MAP) or improve neurological severity score (NSS). In CHT without hemorrhage, giving 20% albumin or 10% hetastarch improved NSS. We hypothesized that these latter treatments would also improve NSS after CHT plus uncontrolled hemorrhage. Rats were randomly assigned to one of seven groups. Experimental conditions were CHT (yes or no), uncontrolled hemorrhage (yes or no), and fluid given to replace blood loss (none; 10% hetastarch, 20% albumin, or 3% saline [0.1 mL per 0.1 mL of blood lost]; or 0.9% saline [0.3 mL per 0.1 mL of blood lost]). NSS (0--25 scale, where 0 = no impairment) was determined at 1, 4, and 24 h, and brain water content was determined at 24 h after CHT. NSS (median +/- range) at 24 h was 11 +/- 6 when no fluid was given; 16 +/- 5 with 10% hetastarch; 14 +/- 5 with 20% albumin; 12 +/- 4 with 3% saline; and 13 +/- 4 with 0.9% saline given (not significant). In addition, brain water content and MAP did not differ among the groups receiving CHT with or without uncontrolled hemorrhage. In our model of CHT plus uncontrolled hemorrhage in rats, giving 10% hetastarch, 20% albumin, 3% saline, or 0.9% saline failed to improve NSS, brain water content, or MAP.

IMPLICATIONS

In previous studies of closed head trauma (CHT) without hemorrhage, giving 20% albumin or 10% hetastarch improved neurological severity scores (NSSs). We hypothesized that these treatments also might be beneficial in CHT plus uncontrolled hemorrhage. We found that giving 10% hetastarch, 20% albumin, 3% saline, or 0.9% saline failed to improve NSS, brain water content, or mean arterial blood pressure.

Probenecid-inhibitable efflux transport of valproic acid in the brain parenchymal cells of rabbits: a microdialysis study

Delivery of valproic acid (VPA) to the human brain is relatively inefficient as reflected by a low brain-to-unbound plasma concentration ratio (< or =0.5) at steady state. Previous pharmacokinetic studies suggested that the unfavorable brain-to-plasma gradient is maintained by coupled efflux transport processes at both the brain parenchymal cells and blood-brain barrier (BBB); one or both of the efflux transporters are inhibitable by probenecid. The present study in rabbits utilized microdialysis to measure drug concentration in the brain extracellular fluid (ECF) of the cerebral cortex during steady-state i.v. infusion with VPA alone or with VPA plus probenecid. Probenecid co-infusion elevated VPA concentration in the brain tissue surrounding the tip of the microdialysis probe to a greater extent than in the ECF (230% versus 47%). Brain intracellular compartment (ICC) concentration was estimated. In control rabbits, the ICC concentration was 2.8+/-0.28 times higher than the ECF concentration. Probenecid co-infusion elevated the ICC-to-ECF concentration ratio to 4.2+/-0.44, which confirms the existence of an efflux transport system in brain parenchymal cells. The ECF-to-unbound plasma concentration ratio was well below unity (0.029), indicating an uphill efflux transport of VPA across the BBB. Co-infusion of probenecid did not have a significant effect on VPA efflux at the BBB as evidenced by a minimal change in the ECF-to-unbound plasma concentration ratio. This study suggests the presence of distinctly different organic anion transporters for the efflux of VPA at the parenchymal cells and capillary endothelium in the brain.

NPS 1506: a novel NMDA receptor antagonist: neuroprotective effects in a model of closed head trauma in rats

We examined whether NPS 1506, a novel uncompetitive N-methyl-D-aspartate receptor antagonist, influences neurological outcome following closed head trauma (CHT) in rats. One hundred ten rats were divided into 11 groups: CHT (yes/no), treatment with NPS 1506 (yes/no), and time of euthanization (24 h/48 h). The dose of NPS 1506 was 1 mg/kg IV at 1 and 4 hours following CHT or sham operation. Closed head trauma induced the following changes in the injured hemisphere: Decreased specific gravity (sg) (1.036 +/- 0.006) and magnesium (Mg) (0.042 +/- 0.005 microg/mg) at 24 hours, and potassium (K) at 24 (1.145 +/- 0.376 microg/mg) and 48 hours, and increased water content (W) (84.9 +/- 2.5%) and sodium (Na) (2.135 +/- 0.699 microg/mg) at 24 hours, and calcium (Ca) at 24 (0.543 +/- 0.157 microg/mg) and 48 hours. These were reversed by NPS 1506; sg of 1.043 +/- 0.004, Mg of 0.077 +/- 0.009 microg/mg, K of 1.930 +/- 0.238 microg/mg, W of 81.5 +/- 1.9%, Ca of 0.043 +/- 0.023 microg/mg, and Na of 0.688 +/- 0.110 microg/mg. In groups not given NPS 1506, a nonsignificant decrease in neurological severity score (NSS) occurred at 24 and 48 hours as compared to NSS at 1 hour after CHT. In groups given NPS 1506, NSS at 24 and 48 hours decreased significantly (improved) compared to NSS at 1 hour, but not compared to NSS at 24 and 48 hours in groups not given NPS 1506. NPS 1506 caused no significant change in ischemic tissue volume or hemorrhagic necrosis volume in the injured hemisphere at 24 hours or 48 hours. These findings indicate that NPS 1506 improved measures of brain tissue edema (at 24 hours but not at 48 hours) and ion homeostasis, and this improvement was not related to other measures of outcome.

Concentrations of lidocaine and monoethylglycine xylidide in brain, cerebrospinal fluid, and plasma during lidocaine-induced epileptiform electroencephalogram activity in rabbits: the effects of epinephrine and hypocapnia

When injecting lidocaine into tissues, the mean toxic dose of lidocaine may be increased by adding epinephrine to lidocaine and by decreasing the PaCO(2). In contrast, when lidocaine is introduced directly into an artery or vein, adding epinephrine to lidocaine may decrease the mean toxic dose of lidocaine. Less is known about the effects of decreased PaCO(2) on intravascular lidocaine toxicity. We infused lidocaine in 24 rabbits at 4 mg. kg(-1). min(-1) with/without epinephrine and with/without hypocapnia. We measured the time to onset of lidocaine-induced seizures, total dose of lidocaine at the time of seizures, and concentrations of lidocaine and monoethylglycine xylidide (MEGX), a metabolite of lidocaine, in plasma, brain, and cerebrospinal fluid. Epinephrine decreased onset time by 11% with hypocapnia and by 21% with normocapnia, and it increased plasma MEGX by 1 microg/mL with hypocapnia and 2 microg/mL with normocapnia. Hypocapnia increased onset time by 18% without epinephrine and by 33% with epinephrine, and it increased whole-brain MEGX by 10 microg/mL without epinephrine and by 14 microg/mL with epinephrine. We conclude that, when lidocaine is given intravascularly, hypocapnia increases onset time and lidocaine dose required for seizures. These effects occur with no change in the concentration of lidocaine in plasma or the brain.

IMPLICATIONS

Hypocapnia increases the toxic dose of lidocaine given IV without altering lidocaine concentrations in blood, brain, or cerebrospinal fluid. Whole-brain monoethylglycine xylidide concentration is greater during hypocapnia than during normocapnia, and the addition of epinephrine to lidocaine increases the concentration of monoethylglycine xylidide in plasma.

Inhibition of cyclooxygenase 2 by nimesulide decreases prostaglandin E2 formation but does not alter brain edema or clinical recovery after closed head injury in rats

Recently, the enzyme cyclooxygenase (COX) has been recognized to exist as constitutive (COX-1) and inducible isoforms (COX-2). In previous studies, drugs that were inhibitors of both COX-1 and COX-2 failed to decrease brain edema formation or improve Neurological Severity Score (NSS) after closed head trauma (CHT), although some did decrease prostaglandin-E2 (PGE2) formation. The present study examined whether or not a specific inhibitor of COX-2 (nimesulide) exerts a beneficial effect after CHT in rats. Halothane-anesthetized rats (n = 8 in each group) were randomly assigned to one of four groups: surgery, no CHT, no drug (group 1); surgery, no CHT, nimesulide 30 mg/kg intraperitoneally (IP) (group 2); surgery, CHT, no drug (group 3); and surgery, CHT, nimesulide 30 mg/kg IP (group 4). NSS was determined at 1 and 24 h, and brain tissue PGE2 concentration and water content were determined after killing at 24 h. Treatment with nimesulide did not improve NSS (NSS at 24 h = 11+/-6 [median +/- range] in group 3 and 12+/-4 in group 4) or edema formation (brain water content at 24 h = 84.3+/-1.8% [mean +/- SD] in group 3 and 83.8+/-1.9% in group 4). However, nimesulide did decrease cortical and hypothalamic PGE2 formation by 41% and 47%, respectively during the first hour of incubation after brain tissue sampling. The authors conclude that although nimesulide does reduce tissue PGE2 formation, it does not exert a beneficial effect on brain tissue edema or functional activity after CHT in rats.

Rate of CSF formation and resistance to reabsorption of CSF during sevoflurane or remifentanil in rabbits

Information on the effects of sevoflurane on the rate of cerebrospinal fluid (CSF) formation (Vf) and resistance to reabsorption of CSF (Ra) is incomplete, and no such information is available for remifentanil. The present study examined the dose-related effects of sevoflurane and remifentanil on Vf and Ra in rabbits. Eight rabbits were studied during isoflurane 1.4% (baseline) and sevoflurane 1.4%, 2.5%, and 3.7%, and eight were studied during isoflurane 1.4% (baseline) and remifentanil 0.30, 0.67, and 1.00 microg x kg(-1) x min(-1) in randomized order. Ventriculocisternal perfusion at two CSF pressure states for each experimental condition was used to determine Vf and Ra. There was no dose-response relation for Vf (10.4+/-2.5, 9.0+/-2.0, and 10.0+/-3.0 microl x min(-1)) or Ra (0.81+/-0.33, 1.35+/-0.54, and 0.84+/-0.27 cm H2O x microl(-1) x min) between the three sevoflurane concentrations. There also was no dose-response relation for Vf (7.8+/-1.2, 8.8+/-3.0, and 6.5+/-2.3 microl x min(-1)) or Ra (1.07+/-0.54, 1.23+/-0.50, and 1.13+/-0.51 cm H2O x microl(-1) x min) between the three remifentanil doses. Vf and Ra during either sevoflurane or remifentanil were not significantly different from Vf and Ra during the two isoflurane baseline conditions (Vf = 8.5+/-2.5 and 9.8+/-1.3 microl x min(-1), and Ra = 0.97+/-0.36 and 1.38+/-0.55 cm H2O x microl(-1) x min, mean +/- SD). Vf and Ra are of interest because they influence CSF volume, intracranial pressure, and/or intracranial elastance. In our model, sevoflurane or remifentanil did not significantly alter Vf or Ra.

Albumin or hetastarch improves neurological outcome and decreases volume of brain tissue necrosis but not brain edema following closed-head trauma in rats

The present study examined whether hemodilution with 20% human serum albumin (HSA) or 10% hydroxyethyl starch (HES) improved the outcome from closed-head trauma (CHT) in rats. Rats anesthetized with halothane were given one of three hemodilution solutions (i.e., 20% HSA, 10% HES, or control [0.9% saline]) after CHT or sham surgery. CHT was delivered using a weight drop impact of 0.5 J onto the closed cranium. The hemodilution solution (volume = 1% of body weight) was given just after determining the neurological severity score (NSS) at 1 hour following CHT. The NSS was determined again at 24, 48, and 72 hours following CHT. At 72 hours, brains were removed, and brain edema and brain tissue necrosis volume were determined. Solutions of 20% HSA and 10% HES significantly improved brain tissue necrosis volume (143 +/- 72 mm3 and 104 +/- 53 mm3 as compared to 271 +/- 65 mm3 in controls, mean +/- SD) and NSS (12 +/- 2 and 9 +/- 2 as compared to 15 +/- 2 in controls at 72 hours, median +/- range) but not brain edema. The hematocrit decreased similarly in all groups during hemodilution. Hemodilution with 20% HSA and 10% HES following CHT in rats did not decrease brain edema but did decrease brain tissue necrosis volume and NSS (improved neurological function), suggesting that the beneficial effect of hemodilution resulted not from decreased edema formation but rather from effects not measured in this study such as improved perfusion of the salvageable brain tissue surrounding the core injury.

Treatments to support blood pressure increases bleeding and/or decreases survival in a rat model of closed head trauma combined with uncontrolled hemorrhage

Hemorrhagic hypotension may aggravate the detrimental effects of head trauma on neurologic outcome. Our study examined whether using phenylephrine or large volumes of saline IV to increase mean arterial blood pressure (MAP) to 70, 80, or 90 mm Hg during the combination of head trauma and uncontrolled hemorrhage would improve neurologic outcome. Rats were assigned to one of 17 groups. In Groups 1-5, the variables were head trauma (yes/no), hemorrhage (yes/no), 0 or 3 mL saline per milliliter of blood lost, and no target MAP. In Groups 6-11, hemorrhage was or was not combined with head trauma, and large volumes of saline were given IV to achieve target MAPs of 70, 80, or 90 mm Hg. Groups 12-17 were similar to Groups 6-11 except that phenylephrine was used rather than saline to achieve target MAPs. Saline increased blood loss at 2 h to approximately 16 and 25 mL at a MAP of 80 and 90 mm Hg respectively, increased (worsened) the neurodeficit score but not cerebral edema at 24 h, and decreased survival rate at 2 and 24 h. Because phenylephrine was fatal for 62 of 63 rats, group mean values for blood loss, neurodeficit score, and brain tissue specific gravity could not be calculated. We conclude that supporting MAP with either phenylephrine or large volumes of saline worsened the neurodeficit score and/or survival and did not affect cerebral edema formation in our rat model of head trauma combined with hemorrhage.

IMPLICATIONS

The results of this study indicate that maintaining mean arterial blood pressure at 70, 80, or 90 mm Hg with either phenylephrine or large volumes of saline worsened the neurodeficit score and/or survival and did not affect cerebral edema formation in our rat model of head trauma combined with hemorrhage.

Trabecular outflow facility and formation rate of aqueous humor during anesthesia with sevoflurane-nitrous oxide or sevoflurane-remifentanil in rabbits

In the present study, we examined the effect of sevoflurane and remifentanil on intraocular pressure (IOP) and fluid dynamics. Twenty-eight rabbits were anesthetized with halothane, and IOP was measured via a 25-gauge needle in the anterior chamber. Rabbits were then assigned to one of four groups, and halothane was replaced with sevoflurane 1% (n = 7), 2% (n = 7), 3% (n = 7), or 1% + remifentanil 0.65 microg kg(-1) x min(-1) i.v. (n = 7). In all groups, a series of intraocular infusions was made into the anterior chamber, and IOP, trabecular outflow facility, the rate of aqueous humor formation, and intraocular compliance were determined. With sevoflurane only, intraocular compliance decreased (55 +/- 14, 39 +/- 22, 31 +/- 17 nL/mm Hg; P < 0.05) as the concentration of sevoflurane increased. With sevoflurane 1% + remifentanil, intraocular compliance was significantly increased (100.1 +/- 30.5 nL/mm Hg; P < 0.05) compared with sevoflurane 1%, 2%, or 3%. Trabecular outflow facility, rate of aqueous humor formation, and IOP did not differ among groups, and IOP was similar to values obtained during halothane anesthesia.

IMPLICATIONS

The dose-related effects of sevoflurane on intraocular compliance did not produce significant intraocular pressure differences. Adding remifentanil to sevoflurane increased intraocular compliance. Sevoflurane or sevoflurane + remifentanil causes a decrease in intraocular pressure compared with the average of previously reported values in awake rabbits, and the magnitude of the decrease is similar to that previously reported in rabbits anesthetized with ethyl urethane, pentobarbital, or halothane alone or in combination with propofol, cocaine, or lidocaine.

Human brain metabolic response to caffeine and the effects of tolerance

OBJECTIVE

Since there is limited information concerning caffeine's metabolic effects on the human brain, the authors applied a rapid proton echo-planar spectroscopic imaging technique to dynamically measure regional brain metabolic responses to caffeine ingestion. They specifically measured changes in brain lactate due to the combined effects of caffeine's stimulation of glycolysis and reduction of cerebral blood flow.

METHOD

Nine heavy caffeine users and nine caffeine-intolerant individuals, who had previously discontinued or substantially curtailed use of caffeinated products because of associated anxiety and discomforting physiological arousal, were studied at baseline and then during 1 hour following ingestion of caffeine citrate (10 mg/kg). To assess state-trait contributions and the effects of caffeine tolerance, five of the caffeine users were restudied after a 1- to 2-month caffeine holiday.

RESULTS

The caffeine-intolerant individuals, but not the regular caffeine users, experienced substantial psychological and physiological distress in response to caffeine ingestion. Significant increases in global and regionally specific brain lactate were observed only among the caffeine-intolerant subjects. Reexposure of the regular caffeine users to caffeine after a caffeine holiday resulted in little or no adverse clinical reaction but significant rises in brain lactate which were of a magnitude similar to that observed for the caffeine-intolerant group.

CONCLUSIONS

These results provide direct evidence for the loss of caffeine tolerance in the human brain subsequent to caffeine discontinuation and suggest mechanisms for the phenomenon of caffeine intolerance other than its metabolic effects on elevating brain lactate.

Renal effects of sevoflurane during conditions of possible increased risk

In 32 published reports in surgical patients, the preponderance of evidence from standard clinical measures of renal function (BUN and Cr) indicates the absence of renal toxicity following sevoflurane anesthesia. Studies of surgical patients receiving intermediate-duration sevoflurane with high or low fresh gas flow and long-duration sevoflurane with high fresh gas flow included sensitive measures of renal function and/or injury, which also indicate the absence of renal toxicity following sevoflurane anesthesia. Studies of surgical patients receiving long-duration sevoflurane with low fresh gas flow did not include sensitive measures. Seven studies in volunteers are not directly relevant to clinical practice but do raise the issue of whether it is important to apply sensitive measures of renal function and/or injury such as urine concentrations and/or excretion of NAG, beta 2M, alpha 1M, AAP, alpha GST, pi GST, gamma GTP, albumin, protein, and glucose and Cr clearance. Two studies of volunteers receiving prolonged sevoflurane anesthesia with fresh gas flow no greater than 2 L/min concluded that the potential for adverse renal effects of sevoflurane may exist. The other studies of volunteers did not. In 14 published reports of surgical patients in special conditions, the preponderance of evidence from standard clinical measures of renal function indicates the absence of renal toxicity. Studies with sensitive measures have been reported for some conditions where the kidney may be at increased risk (e.g., sevoflurane-induced hypotension, advanced age, and renal insufficiency and failure), are incomplete in others (e.g., hypertension and ischemic heart disease), and are missing in others (e.g., morbid obesity). Studies with sensitive measures of renal function and/or injury are also missing in an important group where the kidney may not be at increased risk--pediatric patients. Studies of other risk conditions, such as temporary ischemia, hemorrhagic hypotension, nephrotoxic antibiotics, kidney transplantation, and diabetes may provide additional information about the renal effects of sevoflurane.

Posttreatment with propofol terminates lidocaine-induced epileptiform electroencephalogram activity in rabbits: effects on cerebrospinal fluid dynamics

There are no controlled studies to determine whether propofol given after the onset of lidocaine-induced seizures (posttreatment) stops lidocaine-induced seizures. In this study, we determined whether posttreatment with propofol abolishes lidocaine-induced epileptiform electroencephalogram (EEG) activity as effectively as does midazolam, and cerebrospinal fluid (CSF) dynamics during lidocaine-induced epileptiform EEG activity and its treatment. EEG activity and CSF dynamics were determined in two groups of anesthetized rabbits at each of four experimental conditions: baseline, lidocaine-induced epileptiform activity, treatment with midazolam (n = 6) or propofol (n = 6), and return to baseline. The analog EEG signal was converted into a set of digital parameters using aperiodic analysis, and CSF dynamics were determined using ventriculocistemal perfusion. Propofol (3.8 +/- 1.3 mg/kg) stopped epileptiform activity, as did midazolam (2.0 +/- 1.7 mg/kg). The rates of CSF formation or reabsorption and resistances to CSF reabsorption or flow at the arachnoid villi did not differ among conditions or between groups. Our results indicate that propofol and midazolam both terminate epileptiform activity without changing CSF dynamics.

IMPLICATIONS

Propofol may be an alternative to benzodiazepines for treating lidocaine-induced epileptiform electroencephalogram activity in patients.

Phenylephrine-induced hypertension does not improve outcome after closed head trauma in rats

Phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) is reported to increase cerebral perfusion pressure and collateral flow to ischemic areas of the brain in a rat model of focal cerebral ischemia. In the present study, we examined whether phenylephrine-induced hypertension of similar magnitude and duration was beneficial in a rat model of closed head trauma (CHT). Forty-eight rats were randomized into four experimental conditions: CHT at time 0 min (yes/no), plus phenylephrine-induced hypertension (increase of 30-35 mm Hg for 15 min) at 65 min (yes/no). CHT was delivered using a weight-drop device (0.5 J). Outcome measures were neurological severity score (NSS) at 1, 4, and 24 h, and brain tissue specific gravity (microgravimetry) and injury volume (2,3,5-triphenyltetrazoium chloride) at 24 h. After CHT, NSS at 24 h (median +/- range) and brain tissue specific gravity (mean +/- SD, injured hemisphere) were 7+/-2 and 1.033+/-0.007 without phenylephrine and 8+/-2 and 1.035+/-0.005 with phenylephrine (P = 0.43), respectively. Tissue injury volume (mean +/- SD) was 335+/-92 mm3 without phenylephrine and 357+/-154 mm3 with phenylephrine (P > 0.62). The results of our study indicate that postinjury treatment with 15 min of phenylephrine-induced hypertension does not attenuate brain edema, reduce tissue injury volume, or improve neurological outcome after CHT in rats.

IMPLICATIONS

Phenylephrine-induced hypertension is reported to increase cerebral perfusion pressure and blood flow in a rat model of focal cerebral ischemia. In our study, phenylephrine-induced hypertension did not decrease brain edema or tissue injury volume or improve neurological outcome in a rat model of closed head trauma.

Labetalol-induced hypotension decreases blood loss during uncontrolled hemorrhage

In a model of uncontrolled hemorrhagic hypotension (UCHH) in rats, we examined whether blood loss or blood chemistry were affected by (1) deliberate, controlled hypotension induced with labetalol (L) or sodium nitroprusside (SNP) and (2) intravenous (iv) fluid therapy. Two hours of UCHH was induced by resecting the distal 25% of the tail. L or SNP was infused with the aim of decreasing MAP to 50 mmHg. In the groups receiving iv fluid, 3 ml of 0.9% saline was given for each 1 ml of blood loss. L decreased blood loss (2.8+/-2.0 and 3.0+/-1.9 ml, respectively, in the groups not receiving and receiving iv fluid) compared to the groups not given hypotensive drugs (6.3+/-4.1 and 13.5+/-6.6 ml). SNP did not decrease blood loss (5.7+/-4.7 and 11.0+/-6.2 ml), increased serum potassium (5.0+/-0.6 and 5.8+/-0.4 mEq l(-1)), and with accompanying iv fluid administration decreased hematocrit, worsened acidosis, and increased mortality. In this model of 2 h of UCHH in rats, hypotension to MAP of 50 mmHg with L but not with SNP decreased blood loss.

0.45% saline and 5% dextrose in water, but not 0.9% saline or 5% dextrose in 0.9% saline, worsen brain edema two hours after closed head trauma in rats

In this study, we examined the effect of four i.v. fluids (250 mL/kg) on blood glucose and osmolality and brain tissue specific gravity after closed head trauma (CHT) in rats. CHT was delivered at Time 0; blood was sampled at 60 min; fluid infusion began at 75 min and ended at 105 min. Blood was again sampled at 105 and 120 min, and brain tissue specific gravity was determined at 120 min. Five groups (one control and four fluid-treated groups) received CHT, and five other groups (one control and four fluid-treated) did not (n = 9 in each group). 0.45% saline (1/2 NS) and 5% dextrose in water (D5W) accentuated the decrease of brain tissue specific gravity (1.0366 +/- 0.0025 and 1.0368 +/- 0.0028, respectively; mean +/- SD) caused by CHT (1.0395 +/- 0.0036), but 5% dextrose in 0.9% saline (D5NS) and 0.9% saline (NS) did not (1.0431 +/- 0.0042 and 1.0389 +/- 0.0049, respectively). In addition, 1/2 NS decreased blood osmolality (248 +/- 6 mOsm/L), D5W increased blood glucose (1095 +/- 173 mg/dL), D5NS increased blood osmolality (350 +/- 5 mOsm/L) and glucose (1695 +/- 76 mg/dL), and NS caused no significant change. We conclude that administering hypoosmolar i.v. fluids after CHT causes a significant worsening of cerebral edema 2 h after CHT.

IMPLICATIONS

We previously reported worse neurological outcome and/or mortality after closed head trauma in rats when 5% dextrose in water or 0.45% saline was given i.v. compared with 0.9% saline or 5% dextrose in 0.9% saline. The present results and our previous findings indicate that worsening of outcome after closed head trauma in rats may be caused more by edema formation than by hyperglycemia.

Neuroprotective effects of NPS 846, a novel N-methyl-D-aspartate receptor antagonist, after closed head trauma in rats

OBJECT

The authors sought to determine whether 3,3-bis (3-fluorophenyl) propylamine (NPS 846), a novel noncompetitive N-methyl-D-aspartate receptor antagonist, alters outcome after closed head trauma in rats.

METHODS

The experimental variables were: presence or absence of closed head trauma, treatment with NPS 846 or no treatment, and time at which the rats were killed (24 or 48 hours). The NPS 846 (1 mg/kg) was administered intraperitoneally at 1 and 3 hours after closed head trauma or sham operation. Outcome measures were the neurological severity score (NSS), ischemic tissue volume, hemorrhagic necrosis volume, and specific gravity, water content, and concentrations of calcium, sodium, potassium, and magnesium in brain tissue. The following closed head trauma-induced changes in the injured hemisphere (expressed as the mean +/- the standard deviation) were reversed by NPS 846: decreased specific gravity of 1.035 +/- 0.006 at 24 hours was increased to 1.042 +/- 0.004; the decreased potassium level of 0.583 +/- 0.231 mg/L at 48 hours and at 24 hours was increased to 2.442 +/- 0.860 mg/L; the increased water content of 84.7 +/- 2.6% at 24 hours was decreased to 79.8 +/- 2%; the increased calcium level of 0.592 +/- 0.210 mg/L at 24 hours was decreased to 0.048 +/- 0.029 mg/L; and the increased sodium level of 2.035 +/- 0.649 mg/L was decreased to 0.631 +/- 0.102 mg/L. Administration of NPS 846 also lowered the NSS (improved neurological status) at 48 hours (7 +/- 3) and caused no significant changes in ischemic tissue or hemorrhagic necrosis volumes in the injured hemisphere at 24 or 48 hours.

CONCLUSIONS

In this model of closed head trauma, NPS 846 improved neurological outcome, delayed the onset of brain edema, and improved brain tissue ion homeostasis.

Effects of closed head trauma and lipopolysaccharide on body temperature, brain tissue water content, and PGE2 production in rats

Closed head trauma (CHT) increases brain tissue prostaglandin E2 (PGE2) concentration, and that increase is associated with cerebral edema formation and worsening of the neurologic severity score (NSS). Injection of the bacterial endotoxin lipopolysacharride (LPS) increases cerebral and hypothalamic PGE2, and the hypothalamic increase is associated with increased body temperature. The present study determined (a) whether LPS-induced increase of PGE2 causes brain edema or worsens NSS and (b) whether CHT increases hypothalamic PGE2 and thereby increases body temperature. Halothane-anesthetized rats were divided into four groups: group 1 = surgery with no CHT and no LPS (n = 8); group 2 = surgery with LPS and no CHT (n = 8); group 3 = surgery with CHT and no LPS (n = 8); and group 4 = surgery with CHT plus LPS (n = 8). NSS was determined at 1 and 24 h after injury, and brain tissue PGE2 and edema were determined when animals were killed 24 h after injury. As compared with group 1, LPS alone, but not CHT or CHT plus LPS, increased rectal temperature. CHT and CHT plus LPS, but not LPS alone increased brain water content and worsened NSS. LPS, CHT, and CHT plus LPS all increased hypothalamic and cerebral PGE2 production. We conclude that although LPS and CHT increased PGE2 levels, LPS alone did not affect neurologic status or brain edema, CHT did not increase rectal temperature, and addition of LPS to CHT did not aggravate the sequelae of CHT.

Combined hemodilution and hypotension monitored with jugular bulb oxygen saturation, EEG, and ECG decreases transfusion volume and length of ICU stay for major orthopedic surgery

STUDY OBJECTIVE

To assess the efficacy and safety of hemodilution combined with induced hypotension during surgery.

DESIGN

Randomized, nonblinded, controlled study.

SETTING

Operating room suite and intensive care unit (ICU) at a university hospital.

PATIENTS

16 ASA physical status I and II patients who underwent general or general plus epidural anesthesia for major orthopedic surgery.

INTERVENTIONS

In Group 1 (n = 10), mean arterial blood pressure (MAP) was decreased to 50 mmHg by increasing the inspired concentration of isoflurane and injecting 75 mg of 0.5% bupivacaine into the epidural catheter. Hematocrit was decreased to 20% by phlebotomy and simultaneous infusion of crystalloid and colloid. In Group 2 (n = 6), isoflurane was adjusted to maintain MAP within 20% of baseline values, and no phlebotomy or hemodilution was used.

MEASUREMENTS AND MAIN RESULTS

Efficacy of hemodilution combined with induced hypotension (Group 1) was compared to standard management of blood volume and pressure (Group 2) by measuring transfusion volume and length of ICU stay. Safety of hemodilution/hypotension was determined by measuring the electroencephalogram, internal jugular venous oxygen saturation, the electrocardiogram, and central venous oxygen saturation. In Group 1, both the volume of homologous blood (225 +/- 150 ml) and total blood (1440 +/- 286 ml) was significantly less than the volume of homologous blood transfused in Group 2 (2650 +/- 878 ml). No patients in Group 1, but all patients in Group 2 required ICU admission (3.5 +/- 1.6 days) for treatment to prevent sequelae from, or progression of, moderate-severe tissue edema and metabolic acidosis. Cerebral and myocardial measures were not significantly different between groups.

CONCLUSIONS

Hemodilution combined with induced hypotension was safe and may reduce the need for transfusion and ICU admission.

Effects of probenecid on brain-cerebrospinal fluid-blood distribution kinetics of E-Delta 2-valproic acid in rabbits

E-Delta 2-valproic acid (E-Delta 2-VPA), a major active metabolite of VPA, has been proposed as an alternative to VPA because it is less hepatotoxic and is nonteratogenic. In rodents, VPA and E-Delta 2-VPA have a brain tissue/free plasma concentration ratio less than unity, which suggests rapid removal of the alkanoate anticonvulsants from the central nervous system. This study in rabbits employed a simultaneous iv infusion-ventriculocisternal (VC) perfusion technique to investigate the steady-state kinetics of E-Delta 2-VPA transport at the blood-brain barrier, the blood-cerebrospinal fluid (CSF) barrier, and the neural cell membrane. Probenecid (PBD) was coadministered to probe the mediation of transport by organic anion transporter(s). Rabbits in the control group (N = 6) received an iv infusion of E-Delta 2-VPA to achieve a steady-state plasma concentration of 50 to 60 microg/ml. Blood and cisternal outflow of mock CSF perfusate were continuously sampled. Midway through the experiment, the VC perfusate was switched to one containing [3H]E-Delta 2-VPA. At 225 min, the rabbits were sacrificed, and each brain was removed and dissected into ten regions. Rabbits in the PBD group (N = 9) received an iv infusion and VC perfusion as in the control group as well as concomitant iv infusion of the inhibitor. The mean steady-state VC extraction ratio for [3H]E-Delta 2-VPA did not differ between the control and PBD groups (63.7 +/- 8.3% vs. 60. 6 +/- 9.6%), indicating the lack of a significant PBD-sensitive transport at the choroidal epithelium. Coadministration of PBD elevated brain concentration of cold E-Delta 2-VPA in the absence of a significant change in total or free steady-state plasma concentration. Mean E-Delta 2-VPA brain tissue/free plasma concentration ratios in the various brain regions were 3.5- to 5.2-fold higher in PBD-treated animals than in the controls. Significant increases (3.0- to 4.5-fold) in the mean brain tissue/cisternal perfusate concentration ratios were also observed. Compartmental modeling of the steady-state distribution data suggested that clearance of E-Delta 2-VPA from the brain parenchyma is governed jointly by efflux transporters at the neural cell membrane and brain capillary endothelium. Moreover, PBD-induced elevation of E-Delta 2-VPA tissue concentrations is attributed primarily to inhibition of E-Delta 2-VPA efflux transport at the neural cell membrane, resulting in both intracellular trapping and greater tissue retention of E-Delta 2-VPA.

Neurologic outcome with hemorrhagic hypotension after closed head trauma in rats: effect of early versus delayed conservative fluid therapy

OBJECTIVE

This study examined (1) whether two previously reported, well-established models in rats, one a model of hemorrhagic hypotension and the other a model of closed head trauma, could be combined to evaluate neurologic outcome when hemorrhage occurs subsequent to head injury, and (2) the ability of the traditional, conservative approach to fluid therapy (3 mL of intravenous fluid for 1 mL of blood loss) to reverse the detrimental effects of hemorrhagic hypotension after closed head trauma. In addition, two strategies of fluid therapy (early and delayed) were examined.

METHODS

Fifty-six Sprague-Dawley male rats were divided into five groups with head injury at time 0 in groups 3 to 5, hemorrhage at 1 hour in groups 1, 2, 4, and 5, and intravenous fluid at 15 minutes (groups 2 and 5) or 60 minutes (groups 1 and 4) after hemorrhage. Head injury was delivered using a weight-drop impact of 0.5 J onto the closed cranium. Neurologic Severity Score (NSS) was determined at 1 hour (just before hemorrhage) and at 4 hours.

RESULTS

NSS at 1 hour did not differ between groups 3 to 5 (15.5 (9-24) to 16 (2-21), median (range)). The amount of bleeding did not differ between groups during the first 15 minutes of hemorrhage (2.8 +/- 0.8 to 3.7 +/- 2.0 mL, mean +/- SD). After 60 minutes, cumulative blood loss in the delayed fluid therapy groups was less (3.1 +/- 1.13 mL in group 1 and 4.25 +/- 2.39 mL in group 4) than in the early fluid therapy groups (7.73 +/- 4.41 mL in group 2 and 6.85 +/- 2.36 mL in group 5) (analysis of variance, p < 0.01). The NSS of group 3 (head injury only) improved at 4 hours after injury (12 (5-20)), whereas the NSS of groups 4 and 5 (head injury followed by hemorrhage) deteriorated (24 (17-25) and 19.5 (9-25), respectively) (Kruskal-Wallis test,p < 0.05). In all the hemorrhage groups, fluid therapy failed to restore blood pressure to prehemorrhage levels.

CONCLUSION

It is concluded that the two individual models of hemorrhagic hypotension and closed head trauma in rats can be combined to evaluate outcome when hemorrhage occurs subsequent to head injury. Furthermore, traditional, conservative fluid therapy, whether early or delayed, failed to restore blood pressure or to improve NSS when hemorrhage occurred after head injury. Blood loss was greater with early fluid therapy whether or not head injury was present.

Intracranial pressure, middle cerebral artery flow velocity, and plasma inorganic fluoride concentrations in neurosurgical patients receiving sevoflurane or isoflurane

This study examined the concentration-related effects of sevoflurane and isoflurane on cerebral physiology and plasma inorganic fluoride concentrations. Middle cerebral artery flow velocity (Vmca), intracranial pressure (ICP), electroencephalogram (EEG) activity, and jugular bulb venous oxygen saturation were measured, and cerebral perfusion pressure (CPP) and estimated cerebral vascular resistance (CVRe) were calculated at baseline and at 0.5, 1.0, and 1.5 minimum alveolar anesthetic concentration (MAC) sevoflurane (n = 8) or isoflurane (n = 6). Mannitol 0.5-0.75 g/kg was given before dural incision, and blood was sampled for plasma inorganic fluoride during surgery and for up to 72 h postoperatively. Both sevoflurane and isoflurane decreased Vmca (to 31 +/- 12 - 36 +/- 14 cm/s, mean +/- SD), did not significantly alter ICP (13 +/- 9 - 15 +/- 11 mm Hg), and did not cause epileptiform EEG activity. With sevoflurane, decreased Vmca was accompanied by decreased CPP and unchanged CVRe at 0.5 MAC, and unchanged CPP and increased CVRe at 1.0 and 1.5 MAC. Plasma inorganic fluoride was 39.0 +/- 12.9 microM at the end of anesthesia (3.2 +/- 2.0 MAC hours) with sevoflurane, similar to the value (36.2 +/- 3.9 microM) for 3.7 +/- 0.1 MAC hours sevoflurane in patients not receiving mannitol. Decreased Vmca during sevoflurane presumably results from decreased cerebral metabolic rate, with CVRe changing secondarily in accord with CPP. Plasma inorganic fluoride does not seem to be altered by mannitol-induced diuresis.

IMPLICATIONS

In neurosurgical patients, sevoflurane decreased middle cerebral artery flow velocity and caused no epileptiform electroencephalogram activity and no increase of intracranial pressure or plasma inorganic fluoride. These effects are suitable for neurosurgery. Two other possible effects of sevoflurane, i.e., increased cerebrospinal fluid volume and/or intracranial elastance, may not be suitable for neurosurgery and warrant further study.

In vivo measurement of regional brain metabolic response to hyperventilation using magnetic resonance: proton echo planar spectroscopic imaging (PEPSI)

A new rapid spectroscopic imaging technique with improved sensitivity and lipid suppression, referred to as Proton Echo Planar Spectroscopic Imaging (PEPSI), has been developed to measure the 2-dimensional distribution of brain lactate increases during hyperventilation on a conventional clinical scanner equipped with a head surface coil phased array. PEPSI images (nominal voxel size: 1.125 cm3) in five healthy subjects from an axial section approximately 20 mm inferior to the intercommissural line were obtained during an 8.5-min baseline period of normocapnia and during the final 8.5 min of a 10-min period of capnometry-controlled hyperventilation (end-tidal PCO2 of 20 mmHg). The lactate/N-acetyl aspartate signal increased significantly from baseline during hyperventilation for the insular cortex, temporal cortex, and occipital regions of both the right and left hemisphere, but not in the basal ganglia. Regional or hemispheric right-to-left differences were not found. The study extends previous work using single-voxel MR spectroscopy to dynamically study hyperventilation effects on brain metabolism.

The influence of acute and chronic alcohol treatment on brain edema, cerebral infarct volume and neurological outcome following experimental head trauma in rats

The aim of this study was to determine the influence of acute and chronic ethanol treatment on neurological outcome following head trauma in rats. Eight-two Sprague-Dawley rats were divided into 10 groups. Four groups received sham head trauma (surgical incision of the scalp but no trauma) and were treated with (A) nothing, (B) chronic ethanol (6% ethanol in drinking water for 40 days), (C) acute ethanol 1.5 g/kg, intraperitoneally (IP) and (D) acute ethanol 3 g/kg IP. Four groups (E-H) received the same treatment; in addition, head trauma was delivered using a weight-drop device to the left cranium (2 h after ethanol treatment in the acute ethanol groups). To assess the influence of acute plus chronic alcohol and whether the glutamate antagonist ketamine can modify the neurologic outcome following head trauma, two additional head trauma groups were studied: group I received both acute and chronic ethanol treatment and group J received acute ethanol (1.5 g/kg) IP plus ketamine (180 mg/kg). Neurologic assessment was performed at 1, 2, 4, 8, 10, and 24 hours after head trauma or sham trauma in all animals who survived the treatment (omitted in group J animals while still under the anesthetic influence of ketamine). At the end of 24 hours, or at the time of death, the animals were decapitated. Specific gravity was determined from brain tissues adjacent to the injury and the contralateral hemispheres and the volume of hemorrhagic necrosis was quantified. None of the rats in the sham trauma groups died or had neurologic deficits. Of the head trauma groups, the mortality in animals that received 3 g/kg of ethanol and the animals that received acute plus chronic ethanol treatment was 100% before the end of 24 hours. Fifty percent of the animals receiving low-dose acute ethanol treatment (1.5 g/kg) died before 24 hours. In contrast, the mortality in the other groups was only 30% (p < 0.05). The neurologic severity score was significantly higher (greater neurological deficit) in the surviving animals that received acute ethanol treatment at 10 and 24 hours than in rats receiving no ethanol or chronic ethanol treatment. Specific gravity was also lower in the acute ethanol-treated groups compared with no ethanol, chronic ethanol, and acute ethanol plus ketamine groups (p < 0.03). Based on these observations, we conclude that in this rat head trauma model acute ethanol treatment increases mortality, neurological deficit, hemorrhagic necrosis volume, and brain edema. On the other hand, chronic ethanol treatment has no apparent effect and ketamine treatment does not counteract the effect of acute ethanol treatment.

Furosemide decreases cerebrospinal fluid formation during desflurane anesthesia in rabbits

Previous studies suggest that desflurane may increase cerebrospinal fluid (CSF) formation rate (Vf) and volume, particularly during conditions of hypocapnia combined with elevated CSF pressure. The present study was designed to determine whether treatments routinely used in patients during anesthesia for neurological surgery would decrease Vf during desflurane anesthesia in rabbits. Three groups of six rabbits each were examined at four experimental conditions. Condition 1 was the combination of isoflurane, normocapnia, and normal CSF pressure (baseline, all groups). Condition 2 was the combination of isoflurane (group 1) or desflurane (groups 2 and 3), hypocapnia, and elevated CSF pressure (27 and 33 cm H2O). Conditions 3 and 4 were the same as condition 2 with the addition of furosemide, dexamethasone, mannitol, or fentanyl in groups 2 and 3. Vf, resistance to reabsorption of CSF (Ra), and systemic values were determined at each experimental condition, and brain water content was determined at the end of the study. Mean baseline Vf was 9.8 +/- 2.6 microliters.min-1. During the combination of desflurane, hypocapnia, and elevated CSF pressure, furosemide decreased Vf to 3.2 +/- 1.7 microliters.min-1, mannitol increased plasma osmolality and decreased plasma sodium concentration, and fentanyl decreased heart rate and increased plasma potassium concentration. Values for Ra and brain water content did not differ between groups. Of the four treatments examined, only furosemide decreased Vf during the combination of desflurane, hypocapnia, and elevated CSF pressure.

Brain edema, hemorrhagic necrosis volume, and neurological status with rapid infusion of 0.45% saline or 5% dextrose in 0.9% saline after closed head trauma in rats

We previously reported that in rats with closed head trauma (CHT), intravenous (IV) administration of 0.25 mL/g of 5% dextrose solution (D5W) increased blood glucose (G), decreased blood sodium (Na), caused no change in blood osmolality (Osm), increased brain edema (BE), and worsened neurological severity score (NSS) and mortality rate (MR). D5W in 0.9% saline (D5NS) is isonatremic and hyperosmolar with respect to blood and may avoid the problems reported with D5W. The present study compared the effects of 0.25 mL/g of D5NS or 0.45% saline (0.45 S) after CHT in rats. In 11 groups of rats, the three experimental variables were CHT (yes or no), IV fluid (none, D5NS, or 0.45 S), and time of death (4 or 24 h). D5NS or 0.45 S was given IV at 1 h after surgical preparation with or without CHT, and experimental values were determined at 1, 2, 4, and 24 h. D5NS decreased BE at 4 h compared with the untreated group, increased Osm (380 +/- 2 mOsm/kg) and G (1278 +/- 199 mg/dL), decreased Na (131 +/- 2 mEq/L) in blood, and caused no significant change in hemorrhagic necrosis volume (HNV), NSS, or MR. 0.45 S increased MR (50%) at 24 h, decreased Osm (270 +/- 5 mOsm/kg) and Na (123 +/- 1 mEq/L) in blood, and caused no significant change in G, BE, HNV, or NSS. We conclude that after CHT in rats, D5NS decreased BE without changing NSS or MR. 0.45 S increased MR and significantly altered blood chemistries.

Intravenous lidocaine decreases but cocaine does not alter the rate of cerebrospinal fluid formation in anesthetized rabbits

Considering that adrenergic stimulation was reported to decrease the rate of cerebrospinal fluid (CSF) formation (Vf), it was hypothesized that cocaine might exert a similar effect. Accordingly, the present study was designed to examine the effects of low, moderate, and high doses of cocaine on Vf and resistance to reabsorption of CSF (Ra). Because cocaine possesses both adrenergic-stimulating and local anesthetic properties, the present study examined the effects of lidocaine, a local anesthetic without adrenergic-stimulating properties, as a comparison treatment to cocaine. New Zealand white rabbits (n = 17) weighing 3.5-4.3 kg were anesthetized with halothane. A needle was inserted into the left lateral cerebral ventricle and a catheter was inserted into the cisterna magna to permit ventriculocisternal perfusion with mock CSF labeled with blue dextran. A1 each of four experimental conditions, control and three doses of cocaine or lidocaine, fluid volumes and concentrations of blue dextran in timed samples of cisternal outflow were used to determine Vf and the rate of reabsorption of CSF (Va). In turn, Va at normal and elevated CSF pressures (+6 cmH2O) were used to determine Ra. For both the cocaine group (n = 9) and the lidocaine group (n = 8) the three drug doses were 0.5 mg.kg-1 followed by 1.0 microgram.kg-1.min-1, 1.5 mg.kg-1 followed by 3.0 micrograms.kg-1.min-1, and 4.5 mg.kg-1 followed by 9.0 micrograms.kg-1.min-1 i.v. Cocaine caused no significant change of Vf or Ra. In the lidocaine group there was a dose/time-related decrease of Vf (although the slope relating Vf to dose/time was not significantly different from that in the cocaine group), but no significant change of Ra. It is concluded that during halothane anesthesia cocaine does not decrease Vf, a finding not consistent with previous reports that adrenergic stimulation decreases Vf. Decrease of Vf with lidocaine is consistent with previous reports of similar dose-related effects of thiopental, etomidate, midazolam, and fentanyl on Vf.

Influence of closed head injury on isoflurane MAC in the rat

We designed the present study to determine whether the minimum alveolar concentration (MAC) for isoflurane is decreased after closed head trauma (CHT) in rats and, if so, whether the decrease of MAC is related to the severity of neurological impairment following CHT. Isoflurane MAC was determined in 36 Sprague-Dawley rats. Then, at time = 0 h, animals were grouped. Group 1 (n = 8) received no CHT, group 2 (n = 14) received moderate CHT, and group 3 (n = 14) received severe CHT. Neurological severity score (NSS, 0 = no deficit and 25 = maximal impairment) and MAC were determined at 1, 4, 24, and 48 h. In groups 1 and 2, isoflurane MAC at 1, 2, 24, and 48 h (1.0-1.1 +/- 0.8-1.2%, median +/- range) was not significantly different from baseline (1.0-1.1 +/- 1.0-1.1%). In group 3, isoflurane MAC at 1, 2, 24, and 48 h (0.4 +/- 0.2-0.5%) was decreased as compared to baseline (1.1 +/- 1.0-1.1%). In group 2, NSS at 1 h was 18 +/- 11-21 and improved by 48 h to 9 +/- 4-15. In group 3, NSS at 1 h was 24 +/- 22-25 and was not significantly different from NSS at 48 h (24 +/- 24-25). Thus, moderate CHT does not significantly alter isoflurane MAC, whereas severe CHT equivalent to a Glasgow Coma Scale score of 3 to 6 significantly decreases isoflurane MAC.

Effect of magnesium given 1 hour after head trauma on brain edema and neurological outcome

Excitatory amino acids (EAA), mainly glutamate and aspartate, are released in excessive amounts from terminals of ischemic or traumatically injured neurons. These excessive levels of EAAs initiate a cascade of events believed to lead to secondary delayed damage to the surrounding brain. The N-methyl-D-aspartate receptor antagonists MK-801 and ketamine are reported to suppress excessive EAA release and to attenuate the development of focal brain edema following neuronal injury. Magnesium is also reported to work at the postsynaptic receptor to reduce the neurotoxic effect of glutamate. The present study was undertaken to examine the effect of postinjury treatment with Mg++ on brain edema and neurological outcome after traumatic brain injury. Sixty-nine rats that survived halothane anesthesia and closed head trauma (CHT) were randomly assigned to one of seven experimental groups: sham, CHT, and CHT with administration of Mg++ 1 hour postinjury. At 48 hours, brain tissue Mg++ concentration (calculated from optical density using a standard curve) was significantly increased compared to baseline levels (10.06 +/- 2.44 mg/g vs. 6.83 +/- 0.81 mg/g, p < 0.01 calculated by one-way analysis of variance). Also at 48 hours postinjury, brain tissue specific gravity in the contused hemisphere of Mg(++)-treated rats was significantly greater than that in the contused hemisphere of untreated rats, indicating attenuation of brain edema formation by Mg++. The neurological severity score (NSS) of rats treated with Mg++ improved significantly at both 18 and 48 hours, compared to baseline values obtained 1 hour after CHT but prior to administration of Mg++ (11.2 +/- 2.5 vs. 15.2 +/- 4.1, p = 0.03; and 12.3 +/- 6.1 vs. 17.3 +/- 3.6, p = 0.004, respectively). In the untreated groups, the NSS at 18 and 48 hours was not significantly different from baseline values (that is, no neurological improvement). The present study indicates that postinjury treatment with Mg++ attenuates brain edema formation and improves neurological outcome after experimental CHT.

Effect of para-aminohippurate on the efflux of valproic acid from the central nervous system of the rabbit

Recently we investigated the mechanisms mediating the transport of valproic acid (VPA) between blood and brain. In one study efflux of valproic acid (VPA) from rabbit brain was inhibited by probenecid. Efflux of VPA decreased when probenecid was given intravenously but not when probenecid was given by ventriculocisternal (VC) perfusion indicating that the major site of probenecid-sensitive transport was at the brain capillary endothelium and not at the choroid plexus. In another study VPA transport into rat brain was inhibited by para-aminohippurate (PAH). The purpose of the present study were to determine (a) if the efflux of VPA from rabbit brain was also inhibited by PAH, and (b) whether efflux of VPA could occur at the choroid plexus via an PAH-selective transport system. Six control rabbits received VPA by intravenous infusion and tracer concentrations of [3H]VPA and [14C]PAH by VC perfusion. Rabbits in the PAH group (n = 6) received identical treatment with VPA, tracer concentrations of [3H]VPA and [14C]PAH and, in addition, received 20 mM PAH by VC perfusion. PAH had no effect on the VC extraction ratio of [3H]VPA or the steady-state brain concentration of intravenously administered VPA. It is concluded that the efflux of VPA at the rabbit blood-brain barrier is mediated by a transporter different from the PAH-like transporter responsible for the uptake of VPA into rat brain. In addition, the finding that VC perfusion with PAH had no effect on the VC extraction of [3H]VPA provides further evidence that the choroid plexus plays a negligible role in removal of VPA from the CNS.

Brain edema and neurological status with rapid infusion of lactated Ringer's or 5% dextrose solution following head trauma

Rapid infusion of 0.25 ml/g of 0.9% saline over 30 minutes has been shown to have no effect on electrolyte balance, neurological severity score (NSS), or brain edema, following closed head trauma (CHT). Rapid infusion of the same volume of 5% dextrose solution decreased blood sodium concentration, increased edema, and decreased NSS following CHT. In the present study the authors examined the effect of rapid infusion (30 minutes) of smaller volumes of 5% dextrose (0.08 ml/g and 0.16 ml/g) and of 0.25 ml/g lactated Ringer's solution on blood electrolyte concentrations, plasma osmolality, brain edema, and NSS. The purposes of this study were to determine whether rapid infusion of a large volume of lactated Ringer's solution could be given after CHT without increasing mortality or brain edema or producing electrolyte disturbances, and whether small volumes of 5% dextrose could be infused with few or none of the deleterious effects expected from large volumes of 5% dextrose. One hundred eighteen rats, which survived halothane anesthesia and CHT, were randomly assigned to one of 15 experimental groups. Fluids were administered beginning 1 hour after scalp incision or CHT. The NSS, extent of edema, blood electrolyte concentrations, and plasma osmolality in the groups treated with lactated Ringer's solution were not significantly different from those values in the nontreated groups. In addition, the mortality rate after CHT was not increased by administration of lactated Ringer's solution. The groups treated with 5% dextrose solution showed a significantly higher mortality rate, but the NSSs of the surviving rats were not different from controls. None of the groups treated with 0.16 ml/g 5% dextrose solution survived 24 hours. Although blood glucose concentration increased to 1126 +/- 102 g% (mean +/- standard deviation) and 1568 +/- 283 g% and blood sodium concentration decreased to 110.4 +/- 4.6 mEq/L and 92.0 +/- 5.2 mEq/L in the groups treated with 0.08 ml/g and 0.16 ml/g of 5% dextrose solution, respectively, plasma osmolality was normal and no significant difference could be found between the brain tissue specific gravity of animals in the nontreated and 5% dextrose treatment groups. It is concluded that in the CHT model used in this study, the large volume of lactated Ringer's solution did not affect blood electrolyte concentration, neurological outcome, or formation of brain edema, whereas smaller volumes of 5% dextrose solution increased blood glucose and decreased blood sodium concentrations, did not affect plasma osmolality, and had a deleterious effect on neurological outcome.

Rate of anterior chamber aqueous formation, trabecular outflow facility, and intraocular compliance during desflurane or halothane anesthesia in dogs

The present study examined the effects of desflurane on intraocular pressure (IOP), the rate of anterior chamber aqueous formation, trabecular outflow facility, and intraocular compliance. The effects of desflurane were compared to those of halothane because the effects of halothane on intraocular fluid dynamics are well known. Twenty-two dogs were anesthetized for surgical preparation. Pancuronium was given intravenously to produce neuromuscular blockade, and the lungs were mechanically ventilated through a tracheal tube. After surgical preparation, anesthesia was maintained in Group 1 (n = 12) with halothane (0.8% expired) and in Group 2 (n = 10) with desflurane (7.0% expired). In both groups a series of intraocular infusions was made via a 30-gauge needle in the anterior chamber and IOP, aqueous formation, outflow facility, and intraocular compliance were determined. In Group 1 (halothane) IOP was 9.4 +/- 2.8 mm Hg (mean +/- SD), aqueous formation was 1.45 +/- 0.45 microL/min, outflow facility was 0.091 +/- 0.054 microL.min-1.mm Hg-1, and compliance was 377 +/- 282 nL/mm Hg. In Group 2 (desflurane) IOP was 11.3 +/- 3.8 mm Hg, aqueous formation was 1.61 +/- 0.56 microL/min, outflow facility was 0.097 +/- 0.062 microL.min-1.mm Hg-1, and compliance was 432 +/- 238 nL/mm Hg. These values did not differ between groups. It is concluded that in dogs aqueous humor dynamics during desflurane anesthesia are similar to those during halothane anesthesia.

Application of a novel fiber-optic biosensor in situ to investigate the metabolic effect of lactate infusion

Recently developed biosensor technology, which allows near real-time measurement in situ of gas tension (pCO2 and pO2) and of pH, was applied to arterial blood, cerebrospinal fluid (CSF), and brain parenchyma during intravenous lactate infusion in monkeys. Comparison of simultaneous biosensor measurements and discrete arterial blood sampling for traditional blood gas analyses indicated a high level of correlation for pCO2, pO2, and pH. Arterial pO2 and pH values were significantly higher and pCO2 significantly lower than corresponding CSF and brain parenchyma values at baseline, during and following lactate infusion. There was a divergence between arterial and brain parenchyma pH and pO2 measurements. Lactate infusion was associated with progressive arterial pH rises, consistent with the production of a metabolic alkalosis. Cerebrospinal fluid pCO2 remained unchanged during and following lactate infusion. Brain parenchyma exhibited a complex pattern of response characterized by a trend for pO2 and pH to decrease during lactate infusion, which reversed following completion of the infusion. These observations are suggestive of a transient hypoxia from decreased cerebral blood flow and/or reduced oxyhemoglobin dissociation during lactate infusion, but verification of these results is required.

Proton magnetic resonance spectroscopy investigation of hyperventilation in subjects with panic disorder and comparison subjects

OBJECTIVE

The purpose of this study was to investigate differential effects of hyperventilation on brain lactate in patients with panic disorder and comparison subjects as a possible mechanism for explaining previous observations of an excess rise in brain lactate among panic disorder subjects during lactate infusion.

METHOD

Seven treatment-responsive patients with panic disorder and seven healthy comparison subjects were studied with proton magnetic resonance spectroscopy to measure brain lactate during controlled, voluntary hyperventilation over a period of 20 minutes. Hyperventilation was regulated with the use of capnometry to maintain end-tidal PCO2 at approximately 20 mm Hg during the period of hyperventilation. Blood lactate was measured prior to and at the end of hyperventilation.

RESULTS

At baseline the two groups had similar brain lactate levels. Panic disorder subjects exhibited significantly greater rises in brain lactate than comparison subjects in response to the same level of hyperventilation. Blood lactate levels before and after 20 minutes of hyperventilation were not significantly different between groups.

CONCLUSIONS

Controlled hyperventilation increases brain lactate and does so disproportionately in subjects with panic disorder. This increase in brain lactate may result from decreased cerebral blood flow due to hypocapnia, and individuals with panic disorder may have greater sensitivity to this regulatory mechanism.

Role of choroid plexus epithelium in the removal of valproic acid from the central nervous system

Previous experiments suggest the primary route of valproic acid (VPA) removal from the rabbit central nervous system (CNS) is by probenecid-sensitive transporters at the blood-brain barrier but not at the choroid plexus. The purpose of this study was to determine if other transport mechanisms at the choroid plexus played a significant role in the removal of VPA from the CNS. In six rabbits, silicone oil was perfused into both cerebral ventricles and out through the cisterna magna to physically block exchange of VPA between cerebrospinal fluid (CSF) and blood and between brain and CSF. In six control rabbits, perfusion was performed with mock CSF. Both groups received a loading dose followed by continuous intravenous infusion of VPA for 210 min. Ventriculocisternal perfusion with silicone oil had no significant effect on the steady-state brain concentrations or brain-to-plasma concentration ratios of VPA, further confirming that efflux of VPA at the choroid plexus is negligible.

Brain edema and neurologic status with rapid infusion of 0.9% saline or 5% dextrose after head trauma

We previously reported that intravenous (i.v.) administration of large volumes (0.2 ml/g) of either an isotonic dextrose-free solution or 5% dextrose solution given over 18 h after closed head trauma (CHT) in rats did not significantly affect neurological severity score or brain tissue specific gravity. However, it is possible that with more rapid administration, isotonic or 5% dextrose i.v. solutions may alter neurological outcome after CHT. Our study examined whether neurological severity score, brain tissue specific gravity and water content, and blood composition were significantly altered when 0.25 ml/g of either 0.9% saline or 5% dextrose was given i.v. over 0.5 h (rather than over 18 h) after CHT. Eight-four rats that survived ether anesthesia and CHT were randomly assigned to one of 11 experimental groups. Saline- and dextrose-treated rats were evaluated at 4 and 48 h after CHT and were compared to rats without CHT and to untreated rats at 4 and 48 h after CHT. There were no statistically significant differences in neurologic outcome and brain edema between the untreated and the saline-treated groups. However, 5% dextrose i.v. increased mortality (group 6 and 11, 50 and 0% survivors, respectively), decreased specific gravity in the noncontused hemisphere, and worsened neurologic outcome with and without CHT. Blood osmolality remained stable in comparison to the baseline value of 291.9 +/- 7.4 mOsm/kg (mean +/- SD).(ABSTRACT TRUNCATED AT 250 WORDS)