Phenobarbital as Anticonvulsant Prophylaxis in Patients With Traumatic Brain Injury at Risk for Alcohol Withdrawal Syndrome

Background: Anticonvulsant prophylaxis (ACP) for early post-traumatic seizures (PTS) is recommended in patients with traumatic brain injury (TBI). Phenobarbital (PB) may be used to prevent alcohol withdrawal syndrome (AWS) in at-risk patients. The dual-purpose use of PB in the TBI population would allow for consolidation of pharmacotherapy. Objective: The primary objective of this study was to determine the frequency of early PTS in TBI patients at risk of AWS treated with PB as ACP. Secondary objectives included determining rates of over sedation and endotracheal intubation. Methods: Patients received an intravenous (IV) loading dose of PB at 15-20 mg/kg followed by 1 mg/kg every 12 hours for 7 days with a goal level of 15-20 mcg/mL. Medication data, seizure frequency, and episodes of over sedation and endotracheal intubation were collected. Results: Eighty patients were treated with PB over a 1-year period. Thirty-nine patients were analyzed. Median loading dose was 19.9 (Interquartile Range 19.1-20.0) mg/kg with a median post load level of 21.7 mcg/mL (IQR 18.3-25.8) mcg/mL. One patient (2.6%) had electrographic evidence for early PTS. PB was discontinued in 4 (10.3%) patients out of concern for over sedation. One patient required endotracheal intubation after rapid PB loading. Conclusion: The frequency of early PTS was low when PB was used as primary ACP in patients with TBI at risk for AWS. Over sedation is a potential adverse effect that should be considered in the choice of ACP. No conclusions can be drawn as to the effectiveness of PB in preventing AWS.

Duration of cardiopulmonary resuscitation and phenotype of post-cardiac arrest brain injury

BACKGROUND

Patients resuscitated from cardiac arrest have variable severity of primary hypoxic ischemic brain injury (HIBI). Signatures of primary HIBI on brain imaging and electroencephalography (EEG) include diffuse cerebral edema and burst suppression with identical bursts (BSIB). We hypothesize distinct phenotypes of primary HIBI are associated with increasing cardiopulmonary resuscitation (CPR) duration.

METHODS

We identified from our prospective registry of both in-and out-of-hospital CA patients treated between January 2010 to January 2020 for this cohort study. We abstracted CPR duration, neurological examination, initial brain computed tomography gray to white ratio (GWR), and initial EEG pattern. We considered four phenotypes on presentation: awake; comatose with neither BSIB nor cerebral edema (non-malignant coma); BSIB; and cerebral edema (GWR ≤ 1.20). BSIB and cerebral edema were considered as non-mutually exclusive outcomes. We generated predicted probabilities of brain injury phenotype using localized regression.

RESULTS

We included 2,440 patients, of whom 545 (23%) were awake, 1,065 (44%) had non-malignant coma, 548 (23%) had BSIB and 438 (18%) had cerebral edema. Only 92 (4%) had both BSIB and edema. Median CPR duration was 16 [IQR 8-28] minutes. Median CPR duration increased in a stepwise manner across groups: awake 6 [3-13] minutes; non-malignant coma 15 [8-25] minutes; BSIB 21 [13-31] minutes; cerebral edema 32 [22-46] minutes. Predicted probability of phenotype changes over time.

CONCLUSIONS

Brain injury phenotype is related to CPR duration, which is a surrogate for severity of HIBI. The sequence of most likely primary HIBI phenotype with progressively longer CPR duration is awake, coma without BSIB or edema, BSIB, and finally cerebral edema.

Early risk stratification for progression to death by neurological criteria following out-of-hospital cardiac arrest

BACKGROUND

Some patients resuscitated from out-of-hospital cardiac arrest (OHCA) progress to death by neurological criteria (DNC). We hypothesized that initial brain imaging, electroencephalography (EEG), and arrest characteristics predict progression to DNC.

METHODS

We identified comatose OHCA patients from January 2010 to February 2020 treated at a single quaternary care facility in Western Pennsylvania. We abstracted demographics and arrest characteristics; Pittsburgh Cardiac Arrest Category, initial motor exam and pupillary light reflex; initial brain computed tomography (CT) grey-to-white ratio (GWR), sulcal or basal cistern effacement; initial EEG background and suppression ratio. We used two modeling approaches: fast and frugal tree (FFT) analysis to create an interpretable clinical risk stratification tool and ridge regression for comparison. We used bootstrapping to randomly partition cases into 80% training and 20% test sets and evaluated test set sensitivity and specificity.

RESULTS

We included 1,569 patients, of whom 147 (9%) had diagnosed DNC. Across bootstrap samples, >99% of FFTs included three predictors: sulcal effacement, and in cases without sulcal effacement, the combination of EEG background suppression and GWR ≤ 1.23. This tree had mean sensitivity and specificity of 87% and 81%. Ridge regression with all available predictors had mean sensitivity 91 % and mean specificity 83%. Subjects falsely predicted as likely to progress to DNC generally died of rearrest or withdrawal of life sustaining therapies due to poor neurological prognosis. Two of these cases awakened from coma during the index hospitalization.

CONCLUSIONS

Sulcal effacement on presenting brain CT or EEG suppression with GWR ≤ 1.23 predict progression to DNC after OHCA.

Protocol for a randomised trial of an interprofessional team-delivered intervention to support surrogate decision-makers in ICUs

INTRODUCTION

Although shortcomings in clinician-family communication and decision making for incapacitated, critically ill patients are common, there are few rigorously tested interventions to improve outcomes. In this manuscript, we present our methodology for the Pairing Re-engineered Intensive Care Unit Teams with Nurse-Driven Emotional support and Relationship Building (PARTNER 2) trial, and discuss design challenges and their resolution.

METHODS AND ANALYSIS

This is a pragmatic, stepped-wedge, cluster randomised controlled trial comparing the PARTNER 2 intervention to usual care among 690 incapacitated, critically ill patients and their surrogates in five ICUs in Pennsylvania. Eligible subjects will include critically ill patients at high risk of death and/or severe long-term functional impairment, their main surrogate decision-maker and their clinicians. The PARTNER intervention is delivered by the interprofessional ICU team and overseen by 4-6 nurses from each ICU. It involves: (1) advanced communication skills training for nurses to deliver support to surrogates throughout the ICU stay; (2) deploying a structured family support pathway; (3) enacting strategies to foster collaboration between ICU and palliative care services and (4) providing intensive implementation support to each ICU to incorporate the family support pathway into clinicians' workflow. The primary outcome is surrogates' ratings of the quality of communication during the ICU stay as assessed by telephone at 6-month follow-up. Prespecified secondary outcomes include surrogates' scores on the Hospital Anxiety and Depression Scale, the Impact of Event Scale, the modified Patient Perception of Patient Centredness scale, the Decision Regret Scale, nurses' scores on the Maslach Burnout Inventory, and length of stay during and costs of the index hospitalisation.We also discuss key methodological challenges, including determining the optimal level of randomisation, using existing staff to deploy the intervention and maximising long-term follow-up of participants.

ETHICS AND DISSEMINATION

We obtained ethics approval through the University of Pittsburgh, Human Research Protection Office. The findings will be published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT02445937.

Reliability of the Telemedicine Examination in the Neurologic Diagnosis of Death

Objective

To determine whether telemedicine technology can be used to reliably determine the neurologic diagnosis of death (NDD) in patients with catastrophic brain injury (CBI).

Methods

We included a convenience sample of patients with CBI at a single academic medical center from November 2016 through June 2018. We simultaneously performed brain death evaluation at the bedside and remotely via telemedicine. Remote examiners were neurointensivists who were experienced and knowledgeable in the NDD. In addition to standard clinical examination, we used quantitative pupillometry to evaluate pupil size and reactivity. We determined the proportion of agreement for each NDD examination element and the overall diagnosis of brain death between bedside and remote examiners.

Results

Twenty-nine patients with mean age 46 ± 18 years underwent 30 paired NDD examinations. Twenty-eight (97%) patients met the NDD criteria and were pronounced dead. One patient did not meet the NDD criteria and died after withdrawal of life support. With the exception of qualitative assessment of pupillary reactivity, we observed excellent agreement (97%-100% across NDD examination elements) between bedside and remote examiners and 97% agreement on the overall diagnosis of brain death. Unlike qualitative pupillary assessment, quantitative pupillometry was consistently interpretable by remote examiners.

Conclusions

Our results suggest that remote telemedicine technology can be used to verify the findings of bedside examiners performing NDD examinations when a pupillometer is used to assess pupillary reactivity. When performed by neurocritical care experts, the telemedicine NDD examination has potential to facilitate timely and accurate certification of brain death in patients with CBI.

Classification of Evidence

This study provides Class IV evidence on the concordance of neurologic diagnosis of death by telemedicine and bedside examiners.

A Randomized Trial of a Family-Support Intervention in Intensive Care Units

BACKGROUND

Surrogate decision makers for incapacitated, critically ill patients often struggle with decisions related to goals of care. Such decisions cause psychological distress in surrogates and may lead to treatment that does not align with patients' preferences.

METHODS

We conducted a stepped-wedge, cluster-randomized trial involving patients with a high risk of death and their surrogates in five intensive care units (ICUs) to compare a multicomponent family-support intervention delivered by the interprofessional ICU team with usual care. The primary outcome was the surrogates' mean score on the Hospital Anxiety and Depression Scale (HADS) at 6 months (scores range from 0 to 42, with higher scores indicating worse symptoms). Prespecified secondary outcomes were the surrogates' mean scores on the Impact of Event Scale (IES; scores range from 0 to 88, with higher scores indicating worse symptoms), the Quality of Communication (QOC) scale (scores range from 0 to 100, with higher scores indicating better clinician-family communication), and a modified Patient Perception of Patient Centeredness (PPPC) scale (scores range from 1 to 4, with lower scores indicating more patient- and family-centered care), as well as the mean length of ICU stay.

RESULTS

A total of 1420 patients were enrolled in the trial. There was no significant difference between the intervention group and the control group in the surrogates' mean HADS score at 6 months (11.7 and 12.0, respectively; beta coefficient, -0.34; 95% confidence interval [CI], -1.67 to 0.99; P=0.61) or mean IES score (21.2 and 20.3; beta coefficient, 0.90; 95% CI, -1.66 to 3.47; P=0.49). The surrogates' mean QOC score was better in the intervention group than in the control group (69.1 vs. 62.7; beta coefficient, 6.39; 95% CI, 2.57 to 10.20; P=0.001), as was the mean modified PPPC score (1.7 vs. 1.8; beta coefficient, -0.15; 95% CI, -0.26 to -0.04; P=0.006). The mean length of stay in the ICU was shorter in the intervention group than in the control group (6.7 days vs. 7.4 days; incidence rate ratio, 0.90; 95% CI, 0.81 to 1.00; P=0.045), a finding mediated by the shortened mean length of stay in the ICU among patients who died (4.4 days vs. 6.8 days; incidence rate ratio, 0.64; 95% CI, 0.52 to 0.78; P<0.001).

CONCLUSIONS

Among critically ill patients and their surrogates, a family-support intervention delivered by the interprofessional ICU team did not significantly affect the surrogates' burden of psychological symptoms, but the surrogates' ratings of the quality of communication and the patient- and family-centeredness of care were better and the length of stay in the ICU was shorter with the intervention than with usual care. (Funded by the UPMC Health System and the Greenwall Foundation; PARTNER ClinicalTrials.gov number, NCT01844492 .).

Concepts of the Strong Ion Difference Applied to Large Volume Resuscitation

The occurrence of acidosis following trauma or other clinical conditions that require large volumes of resuscitation fluid may be modified by manipulation of the physical chemistry properties of substances within plasma. These include the strong ion difference, modification of hydrogen ion production through control of alveolar ventilation, and protection/provision of protein and phosphate-based weak acids. An understanding of these principles as an alternative method to analyze/anticipate acid-base abnormalities is important during resuscitation. Loss of protein-based weak acids may often occur after trauma or other conditions requiring large-volume resuscitation. These losses may potentially be replaced with albumin-based colloid solutions. Large quantities of normal saline should be avoided so as to avoid hyperchloremia-induced metabolic acidosis. Ringer's lactate solution is preferred. Alveolar ventilation must be adjusted so as to eliminate further hydrogen ion production caused by hypercarbia. The serum base excess and/or hyperlactemia have only limited value in diagnosing acidosis and guiding resuscitation. Current experimental data and reviews of this topic were obtained from a Medline literature search. In addition, the personal experience and investigations of the authors in critically ill and injured patients were used to formulate recommendations.

Emergency Surgical Airways Following Activation of a Difficult Airway Management Team in Hospitalized Critically Ill Patients: A Case Series

INTRODUCTION

An emergency surgical airway (ESA) is widely recommended for securing the airway in critically ill patients who cannot be intubated or ventilated. Little is known of the frequency, clinical circumstances, management methods, and outcomes of hospitalized critically ill patients in whom ESA is performed outside the emergency department or operating room environments.

METHODS

We retrospectively reviewed all adult patients undergoing ESA in our intensive care units (ICUs) and other hospital units from 2008 to 2012 following activation of our difficult airway management team (DAMT).

RESULTS

Of 207 DAMT activations for native airway events, 22 (10.6%) events culminated in an ESA, with 59% of these events occurring in ICUs with the remainder outside the ICU in the context of rapid response team activations. Of patients undergoing ESA, 77% were male, 63% were obese, and 41% had a history of a difficult airway (DA). Failed planned or unplanned extubations preceded 61% of all ESA events in the ICUs, while bleeding from the upper or lower respiratory tract led to ESA in 44% of events occurring outside the ICU. Emergency surgical airway was the primary method of airway control in 3 (14%) patients, with the remainder of ESAs performed following failed attempts to intubate. Complications occurred in 68% of all ESAs and included bleeding (50%), multiple cannulation attempts (36%), and cardiopulmonary arrest (27%). Overall hospital mortality for patients undergoing ESA was 59%, with 38% of deaths occurring at the time of the airway event.

CONCLUSION

An ESA is required in approximately 10% of DA events in critically ill patients and is associated with high morbidity and mortality. Efforts directed at early identification of patients with a difficult or challenging airway combined with a multidisciplinary team approach to management may reduce the overall frequency of ESA and associated complications.

Abnormalities in Fluids, Electrolytes, and Metabolism of Organ Donors

Abnormal serum concentrations of electrolytes, hormones, and glucose are common throughout donor care. The organ procurement coordinator must properly interpret and plan treatment for these changes to prevent intracellular dysfunction in donor organs. This article describes abnormalities in magnesium, phosphorous, calcium, sodium, potassium, and glucose levels; polyuria; and thyroid and pituitary changes. Their potential consequences are discussed, and recommendations for treatment options are presented.

Recommendations for Mechanical Ventilation during Donor Care

The organ procurement coordinator usually directs adjustments to the mechanical ventilator during donor care. It is often difficult to achieve optimal oxygen uptake and carbon dioxide removal while avoiding barotrauma or undesirable effects on the cardiac output. Interrelationships among a variety of ventilator parameters must be understood in order to achieve the desired goal of providing the best organs possible. These recommendations review the key ventilator parameters of tidal volume; positive end-expiratory pressure; auto–positive end-expiratory pressure; fraction of inspired oxygen; and flowrate and frequency and their interactions in controlling peak, plateau, and mean and end-expiratory airway pressures.

Management of Variations in Blood Pressure during Care of Organ Donors

The organ procurement coordinator commonly must correct and maintain the arterial blood pressure during donor care. This article reviews considerations in the accurate measurement of the blood pressure, causes of hypertension and hypotension, and desirable standards to use in order to provide adequate organ perfusion. Recommendations are presented for treatment of hypotension in a titrated response of intravenous fluids, inotropic support, and vasopressor infusion to maintain the mean arterial pressure above 65 mm Hg. Collaborative interaction between the coordinator and physician consultant remains important throughout management of blood pressure changes during donor care.

Proposed Treatment Guidelines for Donor Care

The complex care of the organ donor during preparation for organ removal and provision of the best organs for transplantation is often the responsibility of the organ procurement coordinator. To assist in that process the following clinical problem-based guidelines have been developed. A standard order set is recommended to initiate treatment and to provide a continuing laboratory database. As clinical concerns arise from that database, past medical history, or ongoing donor care, section of these guidelines may serve as references for specific interventions. Physician consultation and collaboration with other bedside care providers are encouraged throughout.

Intensivist-led management of brain-dead donors is associated with an increase in organ recovery for transplantation

The disparity between the number of patients in need of organ transplantation and the number of available organs is steadily rising. We hypothesized that intensivist-led management of brain dead donors would increase the number of organs recovered for transplantation. We retrospectively analyzed data from all consented adult brain dead patients in the year before (n = 35) and after (n = 43) implementation of an intensivist-led donor management program. Donor characteristics before and after implementation were similar. After implementation of the organ donor support team, the overall number of organs recovered for transplantation increased significantly (66 out of 210 potentially available organs vs. 113 out of 258 potentially available organs, p = 0.008). This was largely due to an increase in the number of lungs (8 out of 70 potentially available lungs vs. 21 out of 86 potentially available lungs; p = 0.039) and kidneys (31 out of 70 potentially available kidneys vs. 52 out of 86 potentially available kidneys; p = 0.044) recovered for transplantation. The number of hearts and livers recovered for transplantation did not change significantly. Institution of an intensivist-led organ donor support team may be a new and viable strategy to increase the number of organs available for transplantations.

Comparison of semi-quantitative endotracheal aspirates to quantitative non-bronchoscopic bronchoalveolar lavage in diagnosing ventilator-associated pneumonia

BACKGROUND

Current strategies for diagnosing ventilator-associated pneumonia (VAP) favor the use of quantitative methods; however, semi-quantitative cultures of endotracheal aspirates are still commonly used.

METHODS

The microbiological results of patients with suspected VAP who had both quantitative cultures with non-bronchoscopic bronchoalveolar lavage (BAL) and semi-quantitative cultures of endotracheal aspirate obtained within 24 hours of each other were retrospectively reviewed and compared, using a quantitative threshold of >or=10(4) colony-forming units/mL as a reference standard.

RESULTS

256 patients with paired cultures were identified. Concordance between endotracheal aspirate (any growth of pathogens) and non-bronchoscopic BAL was complete in 58.2% and completely discordant in 23.8%. The sensitivity and specificity of endotracheal aspirate were 65.4% and 56.1%, which improved to 81.2% and 61.9% when antibiotic management decisions were considered in the analysis. Twenty-six patients had endotracheal aspirate cultures that were falsely negative for pathogens, with 61.5% of these patients demonstrating growth of non-fermenting Gram-negative rods or methicillin-resistant Staphylococcus aureus (MRSA) on non-bronchoscopic BAL. Overall, 45 patients (17.5%) among the entire cohort had false positive endotracheal aspirate cultures, with 19 of these patients (42.2%) demonstrating growth of non-fermenting Gram-negative rods or MRSA.

CONCLUSIONS

Semi-quantitative cultures of endotracheal aspirate are poorly concordant with quantitative cultures obtained via non-bronchoscopic BAL. Although the performance of endotracheal aspirate improves when antibiotic treatment is considered, guiding therapy on the basis of semi-quantitative cultures may still result in failure to identify potentially multiple-drug-resistant pathogens, and would also tend to promote excessive antibiotic usage. Our data support the use of quantitative cultures in diagnosing VAP.

Levetiracetam versus phenytoin for seizure prophylaxis in severe traumatic brain injury

OBJECT

Current standard of care for patients with severe traumatic brain injury (TBI) is prophylactic treatment with phenytoin for 7 days to decrease the risk of early posttraumatic seizures. Phenytoin alters drug metabolism, induces fever, and requires therapeutic-level monitoring. Alternatively, levetiracetam (Keppra) does not require serum monitoring or have significant pharmacokinetic interactions. In the current study, the authors compare the EEG findings in patients receiving phenytoin with those receiving levetiracetam monotherapy for seizure prophylaxis following severe TBI.

METHODS

Data were prospectively collected in 32 cases in which patients received levetiracetam for the first 7 days after severe TBI and compared with data from a historical cohort of 41 cases in which patients received phenytoin monotherapy. Patients underwent 1-hour electroencephalographic (EEG) monitoring if they displayed persistent coma, decreased mental status, or clinical signs of seizures. The EEG results were grouped into normal and abnormal findings, with abnormal EEG findings further categorized as seizure activity or seizure tendency.

RESULTS

Fifteen of 32 patients in the levetiracetam group warranted EEG monitoring. In 7 of these 15 cases the results were normal and in 8 abnormal; 1 patient had seizure activity, whereas 7 had seizure tendency. Twelve of 41 patients in the phenytoin group received EEG monitoring, with all results being normal. Patients treated with levetiracetam and phenytoin had equivalent incidence of seizure activity (p = 0.556). Patients receiving levetiracetam had a higher incidence of abnormal EEG findings (p = 0.003).

CONCLUSIONS

Levetiracetam is as effective as phenytoin in preventing early posttraumatic seizures but is associated with an increased seizure tendency on EEG analysis.

Therapeutic hypertension: principles and methods

The aspects of cardiovascular physiology important for the safe and effective implementation and titration of hypertensive therapy among neurosurgical patients with neurological or neurosurgical illness/injury are reviewed. Therapeutic hypertension may be an appropriate treatment for some neurological or neurosurgical conditions, e.g., vasospasm or support of cerebral perfusion pressure. Initiation and maintenance of hypertension should be done safely to avoid complications and/or undesired side effects. Accurate measurement of the arterial and central vascular pressures, the limitations of those methods, and alternative estimates of intravascular volume are reviewed. Hypertensive therapy is accomplished by modifying cardiac output and systemic vascular resistance, the principal physiological determinants of blood pressure. The goals of hypertensive therapy can be achieved by proper evaluation and manipulation of the four components of cardiac output, preload, afterload, heart rate and contractility. Measurement or calculation of estimates of these parameters is important in the selection of proper medications or supplemental fluid administration.

Abnormalities in fluids, electrolytes, and metabolism of organ donors

Abnormal serum concentrations of electrolytes, hormones, and glucose are common throughout donor care. The organ procurement coordinator must properly interpret and plan treatment for these changes to prevent intracellular dysfunction in donor organs. This article describes abnormalities in magnesium, phosphorous, calcium, sodium, potassium, and glucose levels; polyuria; and thyroid and pituitary changes. Their potential consequences are discussed, and recommendations for treatment options are presented.

Management of variations in blood pressure during care of organ donors

The organ procurement coordinator commonly must correct and maintain the arterial blood pressure during donor care. This article reviews considerations in the accurate measurement of the blood pressure, causes of hypertension and hypotension, and desirable standards to use in order to provide adequate organ perfusion. Recommendations are presented for treatment of hypotension in a titrated response of intravenous fluids, inotropic support, and vasopressor infusion to maintain the mean arterial pressure above 65 mm Hg. Collaborative interaction between the coordinator and physician consultant remains important throughout management of blood pressure changes during donor care.

Recommendations for mechanical ventilation during donor care

The organ procurement coordinator usually directs adjustments to the mechanical ventilator during donor care. It is often difficult to achieve optimal oxygen uptake and carbon dioxide removal while avoiding barotrauma or undesirable effects on the cardiac output. Interrelationships among a variety of ventilator parameters must be understood in order to achieve the desired goal of providing the best organs possible. These recommendations review the key ventilator parameters of tidal volume; positive end-expiratory pressure; auto-positive end-expiratory pressure; fraction of inspired oxygen; and flowrate and frequency and their interactions in controlling peak, plateau, and mean and end-expiratory airway pressures.

Current considerations in the issue of brain death

Brain death is an anatomically and physiologically complex process. The societal and psychological implications of brain death and organ donation are equally complex, and they have profound ramifications. Because the vast majority of organ donors die as a consequence of catastrophic intracranial processes, neurosurgeons are in a unique position to positively influence the supply of transplantable organs. Enhanced knowledge of the physiology of evolving brain death will improve the care of potential organ donors and increase the probability of successful transplantation. Likewise, better information about patient and family directives, beliefs, grieving, concurrent exposure to other health care workers, and experiences in the hospital environment will assist the neurosurgeon in providing the family with the opportunity for donation. Neurosurgeons can also play a leading role in the multidisciplinary approach required to support the families of potential organ donors during the transition from neurointerventional therapy to somatic support. New federal regulations on organ donation and a review of the literature about the "art of asking" are presented.

A new locus (vsp417-4) belonging to the tsa417-like subfamily of variant-specific surface protein genes in Giardia intestinalis

A new variant-specific surface protein gene locus (vsp417-4) of Giardia intestinalis is described. Vsp417-4 represents the fourth member of a gene subfamily that is based on a previously described gene, tsa417 ( =vsp417-1). The new locus was detected by characterising DNA amplified in polymerase chain reactions from the 3' ends of divergent homologues (vsp417-4(A-I), vsp417-4(A-II)) found respectively in isolates belonging to the genetic Assemblage A/Group I ('A-I') and Assemblage A/Group II ('A-II') subtypes of G. intestinalis. The complete vsp417-4(A-I) gene was isolated on a 6.2-kb HindIII fragment by screening a genomic DNA library prepared from a type A-I isolate, Ad-1/C7. The deduced polypeptide (VSP417-4(A-I); 709 amino acids, Mr 72662) has properties characterising it as a Giardia variant-specific surface protein, namely a high cysteine content (11.85 mol%), 29 copies of the four amino-acid 'CXXC' motif, and conserved N-terminal signal peptide and C-terminal hydrophobic (membrane-spanning) segments--the latter terminating with the invariant, hydrophilic motif '-CRGKA'. An extended polyadenylation signal sequence (CTTAGRTAGTAAAY), which appears to be a characteristic feature of VSP genes in Giardia, is situated immediately beyond the stop codon. VSP417-4(A-I) shares 87% sequence identity with VSP417-4(A-II) over its C-terminal 235 amino acids, but only 57-58% identity with VSP417-1, VSP417-2 and VSP417-3 which are encoded by other vsp417 family genes identified in these genotypes. Southern hybridisations, using probes derived from the 5' segment of vsp417-4(A-I), indicated the presence of at least five to six closely related loci in both type A-I and type A-II isolates.

Giardia intestinalis: conservation of the variant-specific surface protein VSP417-1 (TSA417) and identification of a divergent homologue encoded at a duplicated locus in genetic group II isolates

The stability of the gene encoding TSA417, a 72-kDa variant-specific surface protein (VSP) produced by trophozoites of Giardia intestinalis isolate WB-C6, was investigated in isolates of similar (Assemblage A / Group I) or distinct (Assemblage A / Group II) genotype. Using primers specific for the WB-C6 tsa417 gene, DNA amplified in polymerase chain reactions from genomic DNA indicated the presence, in every isolate, of an intact coding sequence possessing conserved restriction sites diagnostic for this locus (herein designated vsp417-1). Sequence analysis of the DNA amplified from the genomes of genetic Group I ("A-I") isolates revealed complete identity with the published WB-C6 tsa417 (vsp417-1(A-I)) sequence. Equivalent products, amplified from the genomes of genetic Group II ("A-II") isolates, similarly yielded an invariant and apparently allelic 2142-bp coding sequence (designated vsp417-1(A-II)) possessing 79% nucleotide identity with vsp417-1(A-I) and polymorphisms unique to Group II organisms. The encoded polypeptides (VSP417-1(A-I) and VSP417-1(A-II)) are identical at 75% of amino acid positions. Substitutions are concentrated within the N-terminal portions of the proteins, but the overall structure of VSP417-1 has changed little during the evolution of the Group I and Group II genotypes from their common clonal ancestor. An additional 0.7-kb DNA, representing a separate locus (vsp417-5) encoding a 22.3-kDa VSP, was amplified from genetic Group II genomes exclusively but only using particular primer combinations. The vsp417-5(A-II) gene exhibits >85% sequence identity with the 5' and 3' segments of vsp417-1(A-I) and vsp417-1(A-II) but it lacks a 1482-bp segment that comprises the central portion of the vsp417-1 locus. Excision of this segment seems to have occurred by intragenic recombination, possibly initiated by a stem loop formed between palindromic sequences which border the 1482-bp segment within vsp417-1 but which are contiguous in vsp417-5(A-II). The detection by Southern hybridization of additional genomic sequences that share homology with these genes reveals the existence in these two genotypes of a distinctive "vsp417" gene subset.

Comparison of tsa417-like variant-specific surface protein (VSP) genes in Giardia intestinalis and identification of a novel locus in genetic group II isolates

A gene (vsp417-3A-II) encoding a new member of the variant-specific surface protein (VSP) family of Giardia is described. Vsp417-3A-II is detected exclusively in isolates belonging to the genetic Assemblage A/Group II sublineage of G. intestinalis, and it is closely related to a previously characterized VSP gene (tsp11, herein renamed vsp417-2A-I) found in Group I isolates of G. intestinalis. Analysis of DNA amplified from the genomes of Group II isolates using consensus primers also revealed products corresponding to the vsp417-2 locus (vsp417-2A-II allele), indicating that vsp417-2A-II and vsp417-3A-II represent separate loci in these organisms. Southern hybridizations revealed a single genomic copy of vsp417-3A-II in Group II isolates, but efforts to detect this locus in Group I organisms were unsuccessful. Together with the vsp417-1 (tsa417) locus that was first identified in the genetic Group I isolate WB and which has been detected since in all tested genetic Group I isolates (as vsp417-1A-I) and in genetic Group II isolates (as vsp417-1A-II), vsp417-3A-II represents a third member of a stable subset of tsa417-like VSP genes in genetic Group II G. intestinalis. The encoded polypeptide, VSP417-3A-II (667 residues, predicted M(r) 69120) possesses a high cysteine content (12.1 mol%), 28 copies of the metal-binding -CXXC- motif, and a highly conserved C-terminal hydrophobic domain--similar to all other characterized Giardia VSP. A revised nomenclature for Giardia VSP genes is proposed, prompted by the need to describe the homologues found in the various major genotypes of the species complex, G. intestinalis.

Utilization and diagnostic yield of blood cultures in a surgical intensive care unit

OBJECTIVE

To evaluate the diagnostic yield of blood cultures obtained in a surgical intensive care unit (ICU) and to assess factors potentially influencing yield.

DESIGN

Retrospective, descriptive study.

SETTING

Surgical ICU in a university hospital.

SUBJECTS

All patients who had a blood culture obtained during their admission to the trauma/neurosurgical ICU of Presbyterian University Hospital from January 1, 1993 to December 31, 1993.

MEASUREMENTS AND MAIN RESULTS

Blood culture isolates were categorized as pathogens or contaminants and overall diagnostic yield was determined. Blood cultures were positive for pathogens in 4.6% of all culture episodes, while contaminants were isolated in 5.5% of all culture episodes. A total of 23 true bacteremias were identified in 21 patients, for an overall rate of bacteremia of 3.6 per 100 admissions (5.9 per 1,000 patient days). Concurrent antibiotics were being used at the time of blood culture in 65.3% of all culture episodes. The yield for pathogens was significantly lower (2.2%) when cultures were obtained on antibiotics compared with culture episodes obtained off antibiotics (6.4%) (p < .05). Single-set blood culture episodes were obtained in approximately 32% of all culturing episodes with the overall yield for pathogens of these culturing episodes lower (2.9%) than that of multiple-set culture episodes (5.3%) (p = NS).

CONCLUSIONS

Blood culture yield in this surgical ICU was relatively low in comparison with other published studies. The data further suggest that concurrent use of systemic antibiotics and inappropriate or excessive culturing may negatively influence blood culture yield.

Compartmentation of whole brain blood flow and oxygen and glucose metabolism in monkeys

The cerebral metabolic rate of oxygen (CMRO2) has been functionally compartmentalized using the barbiturate thiopental into active CMRO2, associated with electroencephalographic (EEG) activity, and the balance, basal CMRO2, associated with the maintenance of neuronal viability. Previous measurements of these CMRO2 compartments were made in anesthetized animals. Our aim was to determine whether the same proportions for these compartments applied in unanesthetized monkeys. The active: basal distribution of the cerebral metabolic rate of glucose (CMRG) and cerebral flood flow (CBF) were also determined. Three measurements of whole-brain CBF (H2 clearance), CMRO2, and CMRG were made in six unanesthetized rhesus monkeys (Macaca mulatta). Thereafter, thiopental anesthesia was induced and maintained until an isoelectric EEG was obtained. Three additional measurements of CBF, CMRO2, and CMRG were made. Arterial blood pressure, end-tidal CO2, and arterial blood gas were measured with each set of measurements. Thiopental-induced isoelectric EEG resulted in a 47% reduction in CMRO2 from 5.95 +/- 0.54 to 3.10 +/- 0.51 ml/100 g/min (mean +/- SD); a 36% reduction in CBF from 76 +/- 21 to 48 +/- 14 ml/100 g/min; and a 61% reduction in CMRG from 8.09 +/- 2.78 to 3.13 +/- 0.77 mg/100 g/min. The oxygen-glucose index was 0.99 +/- 0.10 for the whole brain, 0.87 +/- 0.15 for the active, and 1.27 +/- 0.25 for the basal compartments. These results indicated an active:basal distribution of approximately 50:50 for CMRO2, 40:60 for CBF, and 60:40 for CMRG. The active:basal CMRO2 distribution corroborates earlier data and shows that relative to CMRO2, the active compartment is underperfused with a lower oxygen-glucose index compared with the basal compartment.

Acute cerebral blood flow response to dopamine-induced hypertension after subarachnoid hemorrhage

The effects of dopamine-induced hypertension on local cerebral blood flow (CBF) were investigated in 13 patients suspected of suffering clinical vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The CBF was measured in multiple vascular territories using xenon-enhanced computerized tomography (CT) with and without dopamine-induced hypertension. A territorial local CBF of 25 ml/100 gm/min or less was used to define ischemia and was identified in nine of the 13 patients. Raising mean arterial blood pressure from 90 +/- 11 mm Hg to 111 +/- 13 mm Hg (p < 0.05) via dopamine administration increased territorial local CBF above the ischemic range in more than 90% of the uninfarcted territories identified on CT while decreasing local CBF in one-third of the nonischemic territories. Overall, the change in local CBF after dopamine-induced hypertension was correlated with resting local CBF at normotension and was unrelated to the change in blood pressure. Of the 13 patients initially suspected of suffering clinical vasospasm, only 54% had identifiable reversible ischemia. The authors conclude that dopamine-induced hypertension is associated with an increase in flow in patients with ischemia after SAH. However, flow changes associated with dopamine-induced hypertension may not be entirely dependent on changes in systemic blood pressure. The direct cerebrovascular effects of dopamine may have important, yet unpredictable, effects on CBF under clinical pathological conditions. Because there is a potential risk of dopamine-induced ischemia, treatment may be best guided by local CBF measurements.

The effect of hypothermia on the incidence of delayed traumatic intracerebral hemorrhage

Hypothermia has been shown to cause coagulation abnormalities, primarily related to platelet dysfunction. We reviewed coagulation function and the incidence of delayed traumatic intracerebral hemorrhage in a series of 36 patients with severe head injuries (Glasgow Coma Scale 3-7) enrolled in a prospective, randomized, clinical trial of therapeutic moderate hypothermia. Patients were randomized to a normothermic group (n = 16) or to a group cooled to 32 to 33 degrees C within 6 hours of injury (n = 20). Prothrombin times, partial thromboplastin times, and platelet counts were obtained in the emergency room and then again within 24 hours of randomization. Delayed traumatic intracerebral hemorrhage occurred in 6 of 20 (30%) hypothermic patients and 5 of 16 (31%) normothermic patients. In the hypothermic group, 9 of 17 patients had an increased prothrombin time during hypothermic therapy, as opposed to 11 of 16 in the normothermic group during the corresponding time period. The partial thromboplastin time was prolonged in 2 of 17 hypothermic patients and 2 of 16 normothermic patients. Three patients in the hypothermic group and one in the normothermic group developed thrombocytopenia (a platelet count of less than 100,000). There were no significant differences between the two groups in the incidence of delayed traumatic intracerebral hemorrhage, in measured coagulopathy, or in the mean values of measured coagulation parameters. Although the possibility of a hypothermia-induced coagulopathy has not yet been excluded, the short-term use of hypothermia does not appear to increase the risk for intracranial hemorrhagic complications in head injuries.

Local cerebral blood flow measured by xenon-enhanced CT during cryogenic brain edema and intracranial hypertension in monkeys

We developed a closed-skull model of freeze injury-induced brain edema, a model classically thought to produce vasogenic edema, and observed the natural course of changes in edema and blood flow using xenon-enhanced computed tomography (CT) in five rhesus monkeys before and for up to 6 h post insult. Intracranial pressure (ICP) gradually rose throughout the duration of the experiment. CT scans and CBF images permitted direct observation of the evolution of the lesion and revealed early ischemia in the periphery of the injury zone that progressed over time in association with edema. Frequency histogram analysis of local CBF (ICBF) demonstrated subtle but potentially important changes in distribution of ICBF between and within hemispheres at various times post insult. Changes in ICBF distribution were phasic and dissociated from increases in ICP in the latter stages of injury. The Xe/CT CBF method can be used to evaluate the effects of injury and therapy on CBF in this and other models of acute brain injury.

The use of moderate therapeutic hypothermia for patients with severe head injuries: a preliminary report

Animal research suggests that moderate therapeutic hypothermia may improve outcome after a severe head injury, but its efficacy has not been established in humans. The authors randomly assigned 40 consecutively treated patients with a severe closed head injury (Glasgow Coma Scale score 3 to 7) to either a hypothermia or a normothermia group. Using cooling blankets and cold saline gastric lavage, patients in the hypothermia group were cooled to 32 degrees to 33 degrees C (brain temperature) within a mean of 10 hours after injury, maintained at that temperature for 24 hours, and rewarmed to 37 degrees to 38 degrees C over 12 hours. Patients in the normothermia group were maintained at 37 degrees to 38 degrees C during this time. Deep-brain temperatures were monitored directly and used for all temperature determinations. Intracranial pressure (ICP), cerebral blood flow (CBF), and cerebral metabolic rate for oxygen (CMRO2) were measured serially for all patients. Hypothermia significantly reduced ICP (40%) and CBF (26%) during the cooling period, and neither parameter showed a significant rebound increase after patients were rewarmed. Compared to the normothermia group, the mean CMRO2 in the hypothermia group was lower during cooling and higher 5 days after injury. Three months after injury, 12 of the 20 patients in the hypothermia group had moderate, mild, or no disabilities; eight of the 20 patients in the normothermia group had improved to the same degree. Both groups had a similar incidence of systemic complications, including cardiac arrhythmias, coagulopathies, and pulmonary complications. It is concluded that therapeutic moderate hypothermia is safe and has sustained favorable effects on acute derangements of cerebral physiology and metabolism caused by severe closed head injury. The trend toward better outcome with hypothermia may indicate that its beneficial physiological and metabolic effects limit secondary brain injury.

Giardia intestinalis: detection of major genotypes by restriction analysis of gene amplification products

The polymerase chain reaction (PCR) has been used to amplify a 0.52 kb segment of Giardia intestinalis DNA, using primers specific for nucleotide sequences conserved within two genes (tsp11 and tsa417) that encode homologous, cysteine-rich trophozoite surface proteins. Using products amplified from axenic isolates belonging to genetic groups I and II (defined on the basis of allozyme electrophoresis data), restriction endonuclease analysis revealed both tsp11-like and tsa417-like fragments within all samples. The study also identified among the amplification products of group II organisms an additional fragment, containing a novel PstI site, that is not detected in the reaction products of group I isolates. The recovery of three distinct PCR products from each group II isolate was verified by cloning the fragments into the plasmid vector pGEM-7. Fragments containing the new PstI site possess the ClaI site common to both tsp11 and tsa417-like fragments, but they lack the HindIII site which characterizes tsp11-like fragments and also lack the PstI and KpnI sites which characterize tsa417-like fragments. Spot-blot analyses using cloned fragments of all three types as probes showed strong homologous hybridization but weak heterologous hybridization, indicating that each type differs substantially in nucleotide sequence from the others. Because the samples of Giardia DNA used in the PCR were purified from cultures that had been established from single trophozoites, the data indicate that individual trophozoites belonging to genetic group II possess three homologous genes defined by these related fragments. The presence of a PstI site in the amplified segment of the newly-discovered third gene of group II organisms provides a simple diagnostic means of differentiating group I and II isolates.

Effect of stable xenon inhalation on internal carotid artery blood flow in unanesthetized monkeys

Stable xenon (Xe) gas, at inspired concentrations above 30%, reportedly increased cerebral blood flow (CBF) in animals and humans. An unpredictable Xe-induced elevation of CBF could result in erroneous CBF values being measured by Xe-enhanced computed tomography (Xe-CT). In order to detect a potentially rapid and transient effect of Xe on CBF, estimations of supratentorial CBF were obtained by Doppler flow probes chronically and bilaterally implanted on the internal carotid arteries of five adult monkeys. The unanesthetized monkeys with a clear plastic helmet were equilibrated for 15 min on a control gas (33% N2/67% O2) randomly exposed for 5 min to gas mixtures of either 33% Xe/67% O2 or 10% CO2/23% N2/67% O2. The mean control bilateral internal carotid artery blood flow (ICABF) was 23 +/- 10 ml/min (mean +/- SD), mean arterial pressure (MAP) was 101 +/- 13 mm Hg, and PaCO2 was 34 +/- 6 mm Hg. Inhalation of 33% Xe in O2 did not change the ICABF, MAP, or PaCO2. Inhalation of 10% CO2 in O2 increased the ICABF to 39 +/- 15 ml/min (p <0.001), MAP to 112 +/- 16 mm Hg (p <0.05), and PaCO2 to 54 +/- 5 mm Hg (p <0.001). The lack of change in ICABF and PaCO2 with 32% Xe inhalation suggests that a clinically relevant change in CBF is unlikely.

Effect of 80% Xe on Whole Brain Blood Flow and Metabolism in Awake Monkeys

We previously reported that 33% xenon (Xe) did not activate cerebral blood flow (CBF) and metabolism in monkeys as it appears to do in humans. However, monkeys may be less sensitive to Xe than humans are, which would explain the discrepancy in the results, but no one has studied the effects of higher concentrations of Xe on CBF and metabolism in monkeys. Therefore, we studied the effect of 80% Xe on whole-brain CBF, cerebral metabolic rate for oxygen (CMRO2) and glucose (CMRG) in five awake rhesus monkeys. Platinum microelectrodes and catheters inserted into the torcular Herophili were used to measure H2 clearance CBF, and to withdraw cerebral venous blood for O2 and glucose analysis. Cerebral variables were measured after 15 min exposure to 80% N2/20% O2 followed by 80% Xe/20% O2. Eighty percent Xe compared with 80% N2 increased (p <0.01) CBF by 52.7% from 74 +/- 16 to 113 +/- 25 (mean +/- SD) ml 100 g(-1)/min(-1), CBF/CMRO by 154% from 13 to 33, and decreased (p <0.05) CMRO2 by 39.3% from 6.1 +/- 0.9 to 3.7 +/- 0.8 ml 100 g(-1)/min(-1) and CMRG by 52.4% from 8.4 +/- 2.6 to 4.0 +/- 2.0 mg 100 g(-1)/min(-1). Electroencephalogram frequency decreased from a predominantly alpha to dagger rhythm in three of five monkeys. The 40 and 50% reduction in CMRO2 and CMRG, respectively, by 80% Xe suggests an anesthetic effect at this dose in the rhesus monkey but also activates CBF by 50%.

Effect of 33% xenon inhalation on whole-brain blood flow and metabolism in awake and fentanyl-anesthetized monkeys

BACKGROUND AND PURPOSE

Despite the documented diagnostic value of local cerebral blood flow maps by xenon-enhanced computed tomography, reports of cerebral blood flow activation by inhaled 33% Xe raised concerns about the method's safety and accuracy. We evaluated the effect of 33% Xe inhalation on cerebral blood flow and cerebral metabolic rates for oxygen and glucose in four awake and six fentanyl-anesthetized rhesus monkeys.

METHODS

Platinum microelectrodes and catheters in the torcular Herophili were used to measure cerebral blood flow by hydrogen clearance, and oxygen and glucose concentrations. Cerebral variables were measured after 5 and 35 minutes of exposure to room air followed randomly by 67% O2 in 33% N2 or Xe. Five- and 35-minute measurements were combined because the duration of exposure had no effect.

RESULTS

In awake monkeys, 33% Xe compared with 33% N2 reduced (p less than 0.05) cerebral blood flow from 75 +/- 12 to 66 +/- 9 (mean +/- SD) ml.100 g-1.min-1 and oxygen consumption from 6.1 +/- 0.7 to 5.1 +/- 0.6 ml.100 g-1.min-1. In fentanyl-anesthetized monkeys, cerebral variables during 33% N2 versus 33% Xe were cerebral blood flow, 84 +/- 26 versus 79 +/- 23 ml.100 g-1.min-1; oxygen consumption, 5.0 +/- 0.7 versus 4.9 +/- 0.5 ml.100 g-1.min-1; and glucose consumption, 8.4 +/- 1.9 versus 7.9 +/- 2.0 mg.100 g-1.min-1.

CONCLUSIONS

In awake monkeys, 33% Xe reduced rather than activated cerebral blood flow and oxygen consumption by 12% and 16%, respectively; it had no effect in fentanyl-anesthetized monkeys.

CBF measured by Xe-CT: approach to analysis and normal values

Normal reference values and a practical approach to CBF analysis are needed for routine clinical analysis and interpretation of xenon-enhanced computed tomography (CT) CBF studies. We measured CBF in 67 normal individuals with the GE 9800 CT scanner adapted for CBF imaging with stable Xe. CBF values for vascular territories were systematically analyzed using the clustering of contiguous 2-cm circular regions of interest (ROIs) placed within the cortical mantle and basal ganglia. Mixed cortical flows averaged 51 +/- 10ml.100g-1.min-1. High and low flow compartments, sampled by placing 5-mm circular ROIs in regions containing the highest and lowest flow values in each hemisphere, averaged 84 +/- 14 and 20 +/- 5 ml.100 g-1.min-1, respectively. Mixed cortical flow values as well as values within the high flow compartment demonstrated significant decline with age; however, there were no significant age-related changes in the low flow compartment. The clustering of systematically placed cortical and subcortical ROIs has provided a normative data base for Xe-CT CBF and a flexible and uncomplicated method for the analysis of CBF maps generated by Xe-enhanced CT.

Stable xenon does not increase intracranial pressure in primates with freeze-injury-induced intracranial hypertension

Stable xenon (Xe)-enhanced computed tomography is a potentially valuable tool for high resolution, three-dimensional measurement of CBF in patients. However, reports that Xe causes cerebrovascular dilation and increases intracranial pressure (ICP) have tempered enthusiasm for its use. The effects of 5 min of 33% Xe inhalation on ICP (right and left hemispheres) were studied in eight fentanyl-anesthetized Rhesus monkeys after right-sided cortical freeze injury. ICP, CBF, and physiological variables were monitored for up to 6 h postinsult. The preinjury (control) right hemispheric ICP was 8 +/- 5 mm Hg (mean +/- SD) and left hemispheric ICP was 5 +/- 2 mm Hg. Postinjury observations were classified into low (less than 15 mm Hg) and high ICP (greater than or equal to 15 mm Hg) groups. Both right and left ICP values averaged 9 +/- 3 mm Hg in the low ICP group. In the high ICP group, the right ICP was 20 +/- 4 mm Hg and left ICP was 21 +/- 6 mm Hg. ICP was unchanged by Xe inhalation under control conditions as well as in both low and high ICP groups postinjury. Postinjury, the MABP decreased 10-15 mm Hg in the low ICP group and 10-17 mm Hg in the high ICP group 2-3 min after the start of Xe inhalation (p less than 0.05). These results show that 33% Xe inhalation does not increase ICP in fentanyl-anesthetized monkeys but could decrease MABP in stressed states, presumably because of the anesthetic effects of Xe.

The role of xenon CT measurements of cerebral blood flow in the clinical determination of brain death

The demonstration of absent blood flow to the brain is often used as a confirmatory test of brain death. Traditionally, cerebral angiography and dynamic radionuclide brain scanning have been used for this purpose. Recently, xenon CT cerebral blood flow techniques have been developed and applied to a wide variety of clinical problems, including the confirmation of brain death. We report our experience with xenon CT studies performed over a 7-year period (1983-1989) in 30 patients with brain injuries. These patients met clinical criteria for brain death within 24 hr of the study. Twenty patients had average global flow values of less than 5 ml/100 ml/min. Seven patients demonstrated mixed flow patterns, whereby large areas of brain showed flow values of less than 5 ml/100 ml/min and residual pockets of flow greater than 5 ml/100/ml/min. Globally symmetric normal to hyperemic flows were seen in three patients. Our study suggests that the demonstration of average global flows of less than 5/ml/100 ml/min is confirmatory of brain death. Demonstration of persistent flow to the entire brain or regions of the brain is not diagnostic of brain death but also does not exclude such an outcome in patients with severe brain injuries. Xenon-derived flow information may be clinically useful in determining the patient's prognosis and in counseling the patient's family.

Intracranial pressure response to stable xenon inhalation in patients with head injury

Cerebral blood flow measured by xenon-enhanced computed tomography may provide useful information in victims of severe head injury. To assess the effect of stable xenon inhalation on intracranial pressure, intracranial pressure was measured in 17 mechanically ventilated patients with severe head injury undergoing cerebral blood flow studies with xenon-enhanced computed tomography. Under hypocapnic conditions, mean intracranial pressure increased by less than 1 mm Hg (p less than 0.05) late in the inhalation period only in patients whose baseline intracranial pressure was less than 20 mm Hg. It was concluded that under hypocapnic conditions, the magnitude of this increase in intracranial pressure does not prohibit the safe evaluation of cerebral blood flow in victims of head injury using xenon-enhanced computed tomography.

Approach to management of the heartbeating 'brain dead' organ donor

In recent years, transplantation has assumed an important role in the treatment of patients with end-stage diseases of most major organ systems. However, the greatest limitation in organ transplantation today is organ supply. Among factors that can affect the organ supply favorably, donor management has received the least attention. This review addresses management of the multi-organ donor within the intensive care unit. With an increased awareness of donor management issues and the application of a rational physiological approach, the supply of functional organs for transplantation can be increased.

Local "inverse steal" induced by hyperventilation in head injury

Hyperventilation is used routinely to reduce intracranial pressure in victims of severe head injury. In the clinical setting, the effects of hyperventilation on regional cerebral blood flow usually are not known. We describe a case in which hyperventilation resulted in local, paradoxic increases in cerebral blood flow (i.e., "inverse steal") associated with a reduction in intracranial pressure. Although the reduced intracranial pressure was thought to be beneficial, serial computed tomographic scans suggested that the inverse steal response could have promoted cerebral edema, resulting in secondary brain injury.

Xenon-enhanced computed tomography in brain death

The absence of cerebral blood flow is a valuable adjunct confirming clinical criteria of brain death. However, current methods to confirm absent cerebral blood flow have problems that limit their clinical use. We reviewed cerebral blood flow data obtained with xenon-enhanced computed tomography in nine patients who were being evaluated for brain death. In eight patients who met clinical criteria for brain death, mean cerebral blood flow was 1.6 +/- 2.0 mL X 100 g X min. This value was within the range of error inherent in the method, and therefore represented absent flow. In a patient with persistent respiratory efforts, flow values compatible with absent flow were obtained in the supratentorial compartment, while mean flows as high as 24 mL X 100 g X min were measured in selected regions of interest in the infratentorial compartment, correlating with the clinical evidence of residual function of the brain stem. Xenon-enhanced computed tomography may be a useful test to confirm the absence of cerebral blood flow in patients being evaluated for brain death.