A longitudinal study of endocrinology and foraging ecology of subadult gray whales prior to death based on baleen analysis

Individual-level assessments of wild animal health, vital rates, and foraging ecology are critical for understanding population-wide impacts of exposure to stressors. Large whales face multiple stressors, including, but not limited to, ocean noise, pollution, and ship strikes. Because baleen is a continuously growing keratinized structure, serial extraction, and quantification of hormones and stable isotopes along the length of baleen provide a historical record of whale physiology and foraging ecology. Furthermore, baleen analysis enables the investigation of dead specimens, even decades later, allowing comparisons between historic and modern populations. Here, we examined baleen of five sub-adult gray whales and observed distinct patterns of oscillations in δ15N values along the length of their baleen plates which enabled estimation of baleen growth rates and differentiation of isotopic niche widths of the whales during wintering and summer foraging. In contrast, no regular patterns were apparent in δ13C values. Prolonged elevation of cortisol in four individuals before death indicates that chronic stress may have impacted their health and survival. Triiodothyronine (T3) increased over months in the whales with unknown causes of death, simultaneous with elevations in cortisol, but both hormones remained stable in the one case of acute death attributed to killer whale predation. This parallel elevation of cortisol and T3 challenges the classic understanding of their interaction and might relate to increased energetic demands during exposure to stressors. Reproductive hormone profiles in subadults did not show cyclical trends, suggesting they had not yet reached sexual maturity. This study highlights the potential of baleen analysis to retrospectively assess gray whales' physiological status, exposure to stressors, reproductive status, and foraging ecology in the months or years leading up to their death, which can be a useful tool for conservation diagnostics to mitigate unusual mortality events.

Climate change-informed dietary modeling in Pacific cod: Experimentally-derived effects of temperature and dietary quality on carbon and nitrogen stable isotope trophic discrimination factors

Stable isotope analysis is a powerful tool for dietary modeling and trophic ecology research. A crucial piece of information for isotopic dietary modeling is the accurate estimation of trophic discrimination factors (TDFs), or the isotopic offset between a consumer's tissue and its diet. In order to parameterize stable isotope dietary models for future climate scenarios, we investigated the effect of water temperature and dietary protein and lipid content on TDFs in juvenile Pacific cod (Gadus macrocephalus). Pacific cod are a commercially and ecologically important species, with stock numbers in the northeast Pacific recently having dropped by more than 70%. We tested four water temperatures (6, 8, 10, and 12°C) and two dietary regimens (low and high lipid content), representing a range of potential ocean temperature and prey quality scenarios, in order to determine carbon and nitrogen TDFs in juvenile Pacific cod. Additionally, we assessed dietary intake and proximate composition of the experimental fish in order to estimate consumption, assimilation, and retention of dietary nutrients. The results of this study suggest that dietary protein catabolism is a primary driver of nitrogen TDF variability in juvenile Pacific cod. Across all temperature treatments from 6 to 12°C, fish reared on the lower quality, lower lipid content diet had higher nitrogen TDFs. The mean TDFs for fish raised on the higher lipid, lower protein diet were +3.40 ‰ for nitrogen (Δ15N) and +0.36 ‰ for lipid-corrected carbon (Δ LC 13C). The mean TDFs for fish raised on the lower lipid, higher protein diet were +4.09 ‰ for nitrogen (Δ15N) and 0.00 ‰ for lipid-corrected carbon (Δ LC 13C). Lipid-corrected carbon isotope data showed that, regardless of temperature, fish consuming the lower lipid diet had essentially no trophic discrimination between diet and bulk tissues. We found no ecologically meaningful differences in TDFs due to water temperature across the 6°experimental range. The results of this experiment demonstrate that dietary quality, and more specifically the use of dietary protein for energetic needs, is a primary driver of trophic discrimination factors. The TDFs determined in this study can be applied to understanding trophic ecology in Pacific cod and closely related species under rapidly changing prey availability and ocean temperature conditions.

Correlating gut microbial membership to brown bear health metrics

The internal mechanisms responsible for modulating physiological condition, particularly those performed by the gut microbiome (GMB), remain under-explored in wildlife. However, as latitudinal and seasonal shifts in resource availability occur, the myriad micro-ecosystem services facilitated by the GMB may be especially important to wildlife health and resilience. Here, we use brown bears (Ursus arctos) as an ecological model to quantify the relationship between wildlife body condition metrics that are commonly used to assess individual and population-level health and GMB community composition and structure. To achieve these aims, we subsampled brown bear fecal samples collected during United States National Park Service research activities at three National Parks and Preserves (Katmai, Lake Clark, and Gates of the Arctic) and extracted microbial DNA for 16S rRNA amplicon sequencing and microbial taxonomic classification. We analyzed GMB communities using alpha diversity indices, subsequently using Spearman’s correlation analysis to examine relationships between alpha diversity and brown bear health metrics. We found no differences in GMB composition among bears with differing body conditions, nor any correlations between alpha diversity and body condition. Our results indicate that GMB composition reflects diverse foraging strategies while allowing brown bears to achieve similar body condition outcomes.

Intrinsic and extrinsic factors influence on an omnivore's gut microbiome

Gut microbiomes (GMBs), complex communities of microorganisms inhabiting the gastrointestinal tracts of their hosts, perform countless micro-ecosystem services such as facilitating energy uptake and modulating immune responses. While scientists increasingly recognize the role GMBs play in host health, the role of GMBs in wildlife ecology and conservation has yet to be realized fully. Here, we use brown bears (Ursus arctos) as an ecological model to (1) characterize GMB community composition associated with location, season, and reproductive condition of a large omnivore; (2) investigate how both extrinsic and intrinsic factors influence GMB community membership and structure; and (3) quantify differences in GMB communities among different locations, seasons, sex, and reproductive conditions. To achieve these aims, we subsampled brown bear fecal samples collected during United States National Park Service research activities at three National Parks and Preserves (Katmai, Lake Clark, and Gates of the Arctic) and extracted microbial DNA for 16S rRNA amplicon sequencing and microbial taxonomic classification. We analyzed GMB communities using alpha and beta diversity indices, subsequently using linear mixed models to examine relationships between alpha diversity and extrinsic and intrinsic factors. Katmai brown bears hosted the greatest alpha diversity, whereas Gates brown bears hosted the least alpha diversity. Our results indicate that location and diet drive GMB variation, with bears hosting less phylogenetic diversity as park distance inland increases. Monitoring brown bear GMBs could enable managers to quickly detect and assess the impact of environmental perturbations on brown bear health. By integrating macro and micro-ecological perspectives we aim to inform local and landscape-level management decisions to promote long-term brown bear conservation and management.

Case studies on longitudinal mercury content in humpback whale (Megaptera novaeangliae) baleen

Quantification of contaminant concentrations in baleen whales is important for individual and population level health assessments but is difficult due to large migrations and infrequent resighings. The use of baleen allows for a multiyear retrospective analysis of contaminant concentrations without having to collect repeated samples from the same individual. Here we provide case studies of mercury analysis using cold vapor atomic absorption spectroscopy in three individual humpback whales (Megaptera novaeangliae), a 44.5-year-old female and two males aged ≥35 and 66 years, over approximately three years of baleen growth. Mercury concentrations in the female's baleen were consistently 2-3 times higher than in either male. Age did not affect mercury concentrations in baleen; the younger male had comparable levels to the older male. In the female, mercury concentrations in the baleen did not change markedly during pregnancy but mercury did spike during the first half of lactation. Stable isotope profiles suggest that diet likely drove the female's high mercury concentrations. In conclusion, variations in baleen mercury content can be highly individualistic. Future studies should compare sexes as well as different populations and species to determine how the concentrations of mercury and other contaminants vary by life history parameters and geography.

Multi-year progesterone profiles during pregnancy in baleen of humpback whales (Megaptera novaeangliae)

Understanding calving rates of wild whale populations is critically important for management and conservation. Reproduction of humpback whales (Megaptera novaeangliae) is difficult to monitor and, even with long-term sighting studies, basic physiological information such as pregnancy rates and calving intervals remain poorly understood in many populations. We hypothesized that pregnant whales have sustained elevations in baleen progesterone that temporally correlate with gestation. To test this hypothesis, baleen progesterone profiles from two adult female North Pacific humpbacks, both with extensive sighting records and documented pregnancies, were compared to those of a nulliparous female (adult female never seen with a calf) and a juvenile male. Baleen specimens recovered during necropsy were subsampled every 2 cm from the base to the tip of the plate, with each interval representing 30-45 days of growth. Homogenized baleen powder was assayed for progesterone using enzyme immunoassays. The date of growth of each sampling location on the baleen plate was estimated based on stable isotope analysis of annual δ¹⁵N cycles. Progesterone profiles from both pregnant whales showed sustained high progesterone content (>350 ng/g) in areas corresponding to known pregnancies, inferred from calf sightings and post-mortem data. The younger female, estimated to be 13 years old, had higher progesterone during pregnancy than the 44.5 year old, but levels during non-pregnancy were similar. The nulliparous female and the male had low progesterone throughout their baleen plates. Baleen hormone analysis can determine how progesterone concentrations change throughout gestation and has potential for estimating age at first reproduction, pregnancy intervals, failed pregnancies and early calf mortality. Understanding rates of calving and current and historic reproductive patterns in humpbacks is vital to continuing conservation measures in this species.

Exploring Overlap of Feather Molting and Migration in Tundra Swans Using δ2H Analysis

Determining the processes that shape the relative timing of energetically-costly events in the annual cycle of migrating birds is important to our understanding of avian phenology and ecology. We paired satellite tracking and hydrogen stable isotope analysis (δ2H) to examine the relative timing of two such events – migration and feather molting – in tundra swans from four breeding areas in Alaska, USA. Our results show a trend of increasing intra-individual variability in breast feather δ2H values with increasing migration distance, suggesting the overlap of breast feather molting and migration. However, when individual samples were pooled by breeding area, the δ2H values of breast and head feathers showed no trend with migration distance, presumably resulting from high levels of inter-individual variability in δ2H values within each breeding area. We explore potential reasons for this variability, propose potential mechanisms influencing feather δ2H values of tundra swans, and recommend further research into methods for exploring the temporal configuration of events in the annual cycle of migrating birds.

Splitting hairs: dietary niche breadth modelling using stable isotope analysis of a sequentially grown tissue

Stable isotope data from durable, sequentially grown tissues (e.g. hair, claw, and baleen) is commonly used for modelling dietary niche breadth. The use of tissues grown over multiple months to years, however, has the potential to complicate isotopic niche breadth modelling, as time-averaged stable isotope signals from whole tissues may obscure information available from chronologically resolved stable isotope signals in serially sectioned tissues. We determined if whole samples of brown bear guard hair produced different isotopic niche breadth estimates than those produced from subsampled, serially sectioned samples of the same tissue from the same set of individuals. We sampled guard hair from brown bears (Ursus arctos) in four regions of Alaska with disparate biogeographies and dietary resource availability. Whole hair and serially sectioned hair samples were used to produce paired isotopic dietary niche breadth estimates for each region in the SIBER Bayesian model framework in R. Isotopic data from serially sectioned hair consistently produced larger estimates of isotopic dietary niche breadth than isotope data from whole hair samples. Serial sampling captures finer-scale changes in diet and when cumulatively used to estimate isotopic niche breadth, the serially sampled isotope data more fully captures dietary variability and true isotopic niche breadth.

Preoptic area grafts implanted in mammillary bodies of hypogonadal mice: patterns of GnRH neuronal projections

Gonadotropin-releasing hormone (GnRH) axons project to the median eminence, where the peptide is released to stimulate pituitary gonadotrophs. Hypogonadal mice (hpg) do not synthesize GnRH due to a deletion in the gene. When neonatal preoptic area (POA) tissue from normal mice containing GnRH neurons is transplanted into the third ventricle of hpg mice, GnRH axons exit the graft and specifically project to the median eminence, where the release of GnRH in the portal circulation induces the stimulation of the pituitary-gonadal axis. To test the hypothesis that the median eminence region is critical to targeting, we placed POA grafts in the region of the mammillary bodies, which never contains GnRH cell bodies, but is nevertheless close to the median eminence. Control mice received bilateral grafts into the anterior hypothalamus. GnRH axons innervated the median eminence in animals with grafts in the mammillary bodies and posterior hypothalamus. Mice with such grafts for 4-5 months had gonadal development, while those with grafts for shorter periods did not. Anterior hypothalamic grafts merged into the third ventricle and, consistent with previous studies, this resulted in GnRH innervation of the median eminence and gonadal development. However, when grafts were located within dorsal regions such as the thalamus, no median eminence innervation was seen. In these cases, GnRH axons borrowed other bundles of fibers to travel within the host brain. The pattern of innervation from grafts within ventro-caudal regions of the hypothalamus vs. that from dorsal regions supported the hypothesis that the median eminence releases diffusible substances directing GnRH outgrowth.

New observations on the development of the gonadotropin-releasing hormone system in the mouse

In ongoing efforts to study the ontogeny of gonadotropin-releasing hormone (GnRH) neurons, we serendipitously observed that increasing times of incubation in antibodies enhanced signal detection. Here, we describe significant differences in the early migration pattern, population dynamics, and growth cone morphology from published reports. The first immunoreactive GnRH cells were detected in the mouse at E10.75 (7.6 +/- 2.8 cells; morning after mating = E0.5), prior to the closure of the olfactory placode. Although half of these cells were in the medial wall of the olfactory pit, the other half had already initiated their migration, and approximately one quarter had reached the telencephalic vesicle. Although the migratory pattern of the GnRH cells after E11.00 was identical to that described previously, these earliest migrating cells traveled singly rather than in cords, with some reaching the presumptive preoptic area (posterior to the ganglionic eminence) by E11.75. The number of GnRH cells increased significantly (p < 0.05) to 777 +/- 183 at E11.75 and peaked at 1949.6 +/- 161.6 (p < 0.05) at E12.75. The adult population was approximately 800 cells distributed between the central nervous system (CNS) and the nasal region. Hence, the population of GnRH neurons during early development is much larger than previously appreciated; mechanisms for its decline are discussed. Neuritic extensions on the earliest GnRH neurons are short (30-50 microm) and blunt and may represent the leading edge of the moving cell. By E12.75, GnRH axons in the CNS had a ribboned or beaded morphology and increasingly more complex growth cones were noted from this time until the day of birth. The most complex growth cones were associated with apparent choice points along the axons' trajectory. By E13.75, GnRH axons were seen at the presumptive median eminence in all animals, and it was at this stage that the axons began to branch profusely. Branching, as well as the presence of growth cones, continued post-natally. These results provide further insights into the pathfinding mechanisms of GnRH cells and axons.

Gonadotropin-releasing hormone axons target the median eminence: in vitro evidence for diffusible chemoattractive signals from the mediobasal hypothalamus

The projection of GnRH neurons to the median eminence of the medial basal hypothalamus (MBH) is established early in development and is also seen when preoptic area-derived GnRH cell-containing grafts are placed in the third ventricle of hypogonadal mice. To further study the factors directing GnRH axonal targeting, we cultivated embryonic or postnatal day 1 preoptic area with a coexplant on collagen- and laminin-coated membranes in insert chambers. After 7 days of culture, GnRH-immunoreactive fibers extended significantly farther and in greater number onto the sector of membrane facing a MBH coexplant than in the opposite sector, but not toward coexplants of control tissue. Moreover, such effects were specific, as outgrowth of a general axonal population, immunoreactive for growth-associated protein 43 was not influenced by the presence of the MBH. Preferential GnRH outgrowth toward the MBH was established early and was maintained during 10 days of culture. The importance of substrate-derived guidance was also assessed with confocal microscopy. GnRH axons consistently traveled in the company of growth-associated protein 43-labeled axons, but only erratic associations were seen between GnRH and glial processes extending on the membrane. We suggest that although employing an axonal substrate, GnRH axons follow a diffusible chemoattractive signal(s) secreted by the MBH.

Neuromodulation of transplanted gonadotropin-releasing hormone neurons in male and female hypogonadal mice with preoptic area brain grafts

Implantation of normal preoptic area (POA) tissue into the third ventricle of adult hypogonadal (HPG) mice provides a source of GnRH neurons that innervate the host median eminence and stimulate reproductive development in the sterile mutants. To further evaluate graft-host integration, the effects of N-methyl-D,L-aspartic acid (NMA) and opiate antagonists on LH secretion in HPG mice with POA transplants (HPG/POA) were tested. NMA challenges significantly stimulated LH secretion in 10 of 11 HPG/POA females. Only 5 of 12 HPG/POA males responded to the same treatment. Administration of the opiate antagonists naloxone or naloxone methiodide was ineffective in stimulating LH release in any mice, but opiate antagonist pretreatment significantly potentiated the LH secretory response to NMA in female, but not male, HPG/POA mice. A potential anatomical substrate for this facilitation may be the beta-endorphin-immunoreactive innervation of the POA grafts in all HPG/POA brains examined. beta-Endorphin fibers were also present in the median eminence in the vicinity of GnRH outgrowth from the grafts. However, similar innervation patterns in HPG/POA males that did not respond to opioid antagonism suggests that this is not sufficient. We tested whether the sex difference in HPG/POA responsivity to neuromodulation is related to the steroid milieu in the hosts. 17 beta-Estradiol (E2) treatment facilitated the LH secretory response of male HPG/POA to NMA challenges whether animals were castrated and given an E2 capsule prior to graft implantation or one week before testing two months after graft surgery. Intact or vehicle (sesame oil)-treated, castrated HPG/POA males rarely responded to NMA challenges, yet graft-derived GnRH innervation of the hosts' median eminence was comparable in all treatment groups. GnRH challenge testing indicated that pituitary sensitivity of the HPG/POA males was not significantly altered by E2 treatment, suggesting that estrogen acted centrally. These results indicate that the activity of grafted GnRH neurons may be modulated by endogenous opioids of host origin as well as by the hormonal milieu.

Predictors of acute respiratory failure after bone marrow transplantation in children

OBJECTIVE

To determine factors associated with acute respiratory failure after bone marrow transplantation which can be identified before the onset of lung disease.

DESIGN

Population-based, retrospective study.

SETTING

A referral-based pediatric intensive care unit and bone marrow transplant center.

PATIENTS

Thirty-nine patients with lung disease (abnormal chest radiograph or a need for supplemental oxygen) were identified from a group of 318 pediatric bone marrow transplant patients from 1978 to 1988. Thirty-four of 39 patients with complete data were further classified into patients with mild lung disease (recovery without needing endotracheal intubation, n = 16) and patients with acute respiratory failure (requirement for endotracheal intubation, n = 18).

INTERVENTIONS

Regression analyses were performed to define risk factors for development of respiratory failure (multivariate logistic regression) and for a shortened interval between the identification of lung disease and respiratory failure (Cox proportional hazards analysis).

MEASUREMENTS AND MAIN RESULTS

Ninety-three percent (15/16) of patients with mild lung disease survived. Conversely, only 9% (2/23) of patients with respiratory failure survived. Predictors of respiratory failure included graft vs. host disease (odds ratio 28.3, 95% confidence interval 1.9-421, p = .015), a prelung disease (baseline) circulating creatinine concentration of > 1.5 mg/dL (> 132.6 mumol/L) (odds ratio 28.4, 95% confidence interval 1.4-577, p = .029), and male gender (odds ratio 14.6, 95% confidence interval 1-210, p = .049). Predictors of a shortened time to onset of respiratory failure included baseline serum creatinine value of > 1.5 mg/dL (> 132.6 mumol/L) (hazard ratio 6.2, 95% confidence interval 1.5-26.5, p = .013) and baseline total bilirubin concentration > 1.4 mg/dL (> 23.9 mumol/L) (hazard ratio 4.5, 95% confidence interval 0.98-20.7, p = .053). The median time to onset of respiratory failure was 4 days in patients with baseline creatinine values > or = 1.5 mg/dL (> 132.6 mumol/L) and 5 days in patients with baseline bilirubin concentrations > or = 1.4 mg/dL (> 23.9 mumol/L) vs. > 26 days in patients with creatinine < 1.5 mg/dL (< 132.6 mumol/L) and > 29 days in patients with bilirubin < 1.4 mg/dL (< 23.9 mumol/L) (Kaplan-Meier analysis).

CONCLUSIONS

Renal and liver dysfunction preceded clinical evidence of lung disease in bone marrow transplant patients who developed respiratory failure. Lung disease leading to respiratory failure and adult respiratory distress syndrome appears to develop as one component of the multiple organ failure syndrome in pediatric bone marrow transplant patients.

Variation in approval by insurance companies of coverage for autologous bone marrow transplantation for breast cancer

BACKGROUND

The proper evaluation of new forms of technology depends on the results of clinical trials. However, the treatment of patients in grant-sponsored clinical trials of cancer therapy usually requires that the proposed treatment be approved in advance by an insurance carrier in a process called predetermination.

METHODS

We examined the consistency of predetermination decisions by insurance companies for 533 patients enrolled in grant-supported clinical trials of high-dose chemotherapy and autologous bone marrow transplantation (ABMT) for breast cancer from 1989 through 1992. These decisions about coverage were compared with peer-reviewed decision making according to the study protocol and with clinical outcomes.

RESULTS

Requests for insurance coverage for ABMT were approved in 77 percent of the cases. Of these patients, 23 percent did not undergo bone marrow transplantation for protocol-based or medical reasons. Insurance coverage for ABMT was denied in response to the other requests, primarily because the therapy was considered experimental; of these patients, 51 percent eventually underwent bone marrow transplantation despite the denial of insurance. In some instances, the patient had to hire an attorney to gain coverage. The frequency of approval was not influenced by the pretreatment clinical characteristics of the patients, the design or phase of the study, the year in which the predetermination request was made, or the response to induction therapy. There was substantial inconsistency in the frequency of approval of coverage both among insurers and between decisions made by some individual insurers, even for patients in the same study protocol.

CONCLUSIONS

The predetermination process as applied to patients receiving care in clinical research trials of cancer therapy was arbitrary and capricious. Although most of the patients eventually received financial coverage for entry into clinical trials, the process of predetermination by insurers did not correlate with protocol-based medical decision making, and it was a barrier to obtaining treatment.

Comparison of cerebral blood flow by radionuclide cerebral angiography and by microspheres in cats

BACKGROUND

Radionuclide cerebral angiography is commonly used as an adjunct to the diagnosis of brain death. Despite its acceptance as a diagnostic tool, it is not clear whether the absence of cerebral blood flow by radionuclide cerebral angiography denotes a complete lack of cerebral blood flow.

METHODS

To compare cerebral blood flow estimated by radionuclide cerebral angiography with cerebral blood flow measured by the radiolabeled microsphere technique, we systematically varied cerebral perfusion pressure (mean arterial BP minus intracranial pressure) in anesthetized cats by infusing artificial cerebral spinal fluid into the lateral ventricle to increase intracranial pressure. We measured cerebral blood flow with both techniques as cerebral perfusion pressure was decreased from its baseline of 111 +/- 10 mm Hg to 20, 10, 5, 0, and less than 0 mm Hg, causing a stepwise decrease in cerebral blood flow.

RESULTS

We found a correlation by regression analysis (r2 = .47, p less than .05) between radionuclide cerebral angiography and microsphere measurements of cerebral blood flow, when both blood flow measurements were expressed as a percentage of baseline values. However, if 20% of baseline flow was assigned as a cut-off point for critically low cerebral blood flow (based on human studies), radionuclide cerebral angiography was only 33% sensitive to detect critically reduced cerebral blood flow and had a positive predictive accuracy (of low-flow interpretation) of only 60%. Radionuclide cerebral angiography was unable to demonstrate a complete lack of cerebral blood flow, even in two instances when cerebral blood flow by microspheres was less than 0.1% of baseline.

CONCLUSIONS

We conclude that the ability of radionuclide cerebral angiography to quantify low cerebral blood flow is poor, and that this technique may not identify severely reduced cerebral blood flow.

Brain bioenergetics during cardiopulmonary resuscitation in dogs

Cardiac arrest causes a rapid loss of cerebral adenosine triphosphate [corrected] (ATP) and a decrease in cerebral intracellular pH (pHi). Depending on the efficacy of cardiopulmonary resuscitation (CPR), cerebral blood flow levels (CBF) ranging from near zero to near normal have been reported experimentally. Using 31P magnetic resonance spectroscopy, the authors tested whether experimental CPR with normal levels of cerebral blood flow can rapidly restore cerebral ATP and pHi despite the progressive systemic acidemia associated with CPR. After 6 min of ventricular fibrillation in six dogs anesthetized with fentanyl and pentobarbital, ATP was reduced to undetectable concentrations and pHi decreased from 7.11 +/- 0.02 to 6.28 +/- 0.09 (+/- SE) as measured by 31P magnetic resonance spectroscopy. Application of cyclic chest compression by an inflatable vest placed around the thorax and infusion of epinephrine (40 micrograms/kg bolus plus 8 micrograms/kg/min, intravenously) maintained cerebral perfusion pressure greater than 70 mmHg for 50 min with the dog remaining in the magnet. Prearrest cerebral blood flows were generated. Cerebral pHi recovered to 7.03 +/- 0.03 by 35 min of CPR, whereas arterial pH decreased from 7.41 +/- 0.4 to 7.08 +/- 0.04 and cerebral venous pH decreased from 7.29 +/- 0.03 to 7.01 +/- 0.04. Cerebral ATP levels recovered to 86 +/- 7% (+/- SE) of prearrest concentration by 6 min of CPR. There was no further recovery of ATP, which remained significantly less than control. Therefore, in contrast to hyperemic reperfusion with spontaneous circulation and full ATP recovery, experimental CPR may not be able to restore ATP completely after 6 min of global ischemia despite restoration of CBF and brain pHi to prearrest levels.

Efficacy of Cushing response during development in sheep

Mean aortic pressure (MAP) increases (Cushing response) when intracranial pressure (ICP) approaches MAP. We elevated ICP to levels equivalent to normal baseline MAP with infusion of mock cerebrospinal fluid (CSF) into the lateral cerebral ventricles and contrasted responses in near-term fetal sheep, 1-wk-old lambs, and adult sheep anesthetized with pentobarbital sodium. With CSF infusion 1-wk-old lambs and adults produced sustained increases in MAP of 16 +/- 1 and 22 +/- 2 mmHg, respectively, over a 40-min period. However, cerebral blood flow fell 66 and 57%, and cerebral O2 uptake fell 34 and 37%, respectively. In the near-term fetus, MAP increased by 11 +/- 1 mmHg and cerebral blood fell 49% at 3 min of elevated ICP. However, by 15 min MAP had increased further (+17 +/- 2 mmHg) and cerebral blood flow was nearly restored. In contrast to postnatal sheep, cerebral O2 uptake was maintained throughout in the fetus. The mechanism of increased MAP differed among groups. In adults total peripheral resistance fell significantly, whereas in the fetus and lamb it remained constant. Cardiac output increased in each group, but, because of the fall in peripheral resistance, increased cardiac output was relatively more important to the rise in MAP in adults. In addition, marked vasoconstriction occurred in intestines and skin in the fetus. The Cushing response is well-developed in near-term fetal sheep. After birth it may lose its effectiveness in providing for the basal metabolic demand of the brain.

Intensive management of severe head injury

Intensive management of patients with severe head injury offers the best hope of minimizing death and functional disability in a young, working population. Secondary neurologic insult can be decreased by cardiorespiratory support and ICP control from the outset. Rapid neurologic assessment, airway management, and support of circulation are the basis of emergency management for head injury. Patients with severe head injury require intensive care management for two major reasons: management of ICP and management of organ system dysfunction. Care should not be withheld because of initially grim (and inaccurate) prognostic assessment. Newer techniques for assessing the adequacy of cerebral circulation may allow refinement of management strategies in the future.

Age-related effects of compression rate and duration in cardiopulmonary resuscitation

The effects of various compression rate and duration combinations on chest geometry and cerebral perfusion pressure during cardiopulmonary resuscitation (CPR) were studied in immature swine. Pentobarbital-anesthetized 2- and 8-wk-old piglets received CPR after ventricular fibrillation. At compression rates of 40, 60, 80, 100, 120, and 150/min, duty cycle (compression duration/total cycle time) was increased from 10 to 80% by 10% increments. Mean aortic and sagittal sinus pressures, pulsatile displacement, and deformity of the anterior chest wall were measured. Increasing duty cycle increased cerebral perfusion pressure until chest relaxation time was compromised. Inadequate chest recoil, development of static chest deformation, and limitation of pulsatile chest wall movement occurred in both age groups when relaxation time was very short (150-200 ms in 2-wk-old piglets, 250-300 ms in 8-wk-old piglets). These changes in chest geometry correlated with deterioration of cerebral perfusion pressure only in 8-wk-old piglets. In the younger group, perfusion pressures plateaued but did not deteriorate. These data emphasize the importance of duty cycle in generating cerebral perfusion pressure and indicate that younger animals can tolerate high compression rates except at extremely long duty cycles.

Blood flow during cardiopulmonary resuscitation with simultaneous compression and ventilation in infant pigs

We determined whether the simultaneous chest compression and ventilation (SCV) technique of cardiopulmonary resuscitation (CPR) enhances cerebral (CBF) and myocardial (MBF) blood flows and cerebral O2 uptake in an infant swine model of CPR as it does in most adult animal CPR models. We also tested whether SCV-CPR sustains CBF and MBF for prolonged periods of CPR when these flows ordinarily deteriorate. CPR was performed in two groups (n = 8) of pentobarbital anesthetized piglets (3.5-5.5 kg) with continuous epinephrine infusion (10 micrograms/kg/min). Conventional CPR was performed at 100 compressions/min, 60% duty cycle, 1:5 breath to compression ratio and 25-30 mm Hg peak airway pressure. SCV-CPR was performed at 60 compressions/min, 60% duty cycle and 60 mm Hg peak airway pressure applied during each chest compression. Peak right atrial and aortic pressures in excess of 80 mm Hg were generated during CPR in both groups. At 5 min of conventional and SCV-CPR, MBF was 38 +/- 7 and 46 +/- 7 mL.min-1.100 g-1 (+/- SE), respectively, and CBF was 15 +/- 3 and 13 +/- 2 mL.min1. 100 g-1, respectively. However, as CPR was prolonged to 50 min, the sternum progressively lost its recoil and the chest became more deformed. Lung inflation at high airway pressure with SCV-CPR did not prevent this chest deformation. Aortic pressure gradually declined, whereas right atrial and intracranial pressure remained constant in both groups. Consequently, MBF and CBF fell less than 10 mL.min-1.100 g-1 and cerebral O2 uptake was markedly impaired during prolonged conventional and SCV-CPR.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidural morphine decreases postoperative hypertension by attenuating sympathetic nervous system hyperactivity

Twenty-four adults who were undergoing operations on the abdominal aorta were enrolled in a randomized, double-blind, placebo-controlled study in which epidural morphine sulfate (6 mg) was employed to attenuate the sympathoadrenal response to surgery to evaluate the possible contribution of sympathetic nervous system hyperactivity to postoperative hypertension. Patients who received epidural morphine required less parenteral morphine in the 24 hours following surgery, had lower analogue pain scores, and had markedly lower plasma norepinephrine levels when compared with patients in the control group who received an identical volume of saline in the epidural space. Epidural morphine had no effect on plasma epinephrine or arginine vasopressin levels. Fewer patients in the morphine group (4 of 12 vs 9 of 12 patients in the saline group) required treatment for hypertension (mean arterial blood pressure, greater than or equal to 110 mm Hg) in the 24 hours following surgery. In addition, patients in the morphine group had lower blood pressures in the 24 hours following surgery. These data suggest that sympathetic nervous system activity and not adrenal epinephrine or pituitary secretion of arginine vasopressin is responsible for the development of hypertension following aortic surgery. Furthermore, epidural narcotics appear to provide a means of attenuating this response.

Current concepts in brain resuscitation

The area of cerebral resuscitation has become an exciting area of research in critical care medicine. It is a complicated field, however, which has seen attempts to protect the brain using a single therapy such as barbiturates ultimately disappoint investigators in the field. It is likely that much more work needs to be done in understanding the intracellular metabolic and biochemical effects of ischemia before therapies can be designed that are likely to be effective. This work might ultimately require knowledge of how ischemia or hypoxia interrupt cellular RNA and DNA machinery before these effective therapies can be developed. Before we are discouraged by the difficulty of the task, however, it is useful to review how much progress has been made in understanding the pathophysiology of ischemic brain injury in the past decade, so that we may be challenged to continue our efforts in this exciting area of critical care medicine.

Organ blood flow and somatosensory-evoked potentials during and after cardiopulmonary resuscitation with epinephrine or phenylephrine

Pure alpha-adrenergic agonists, such as phenylephrine, and mixed alpha- and beta-adrenergic agonists, such as epinephrine, raise perfusion pressure for heart and brain during cardiopulmonary resuscitation (CPR). However, with the high doses used during CPR, these drugs may directly affect vascular smooth muscle and metabolism in brain and heart. We determined whether at equivalent perfusion pressure, continuous infusion of phenylephrine (20 micrograms/kg/min) or epinephrine (4 micrograms/kg/min) leads to equal organ blood flow, cerebral O2 uptake, and cerebral electrophysiologic function. During 20 minutes of CPR initiated immediately upon ventricular fibrillation in anesthetized dogs, left ventricular blood flow was similar with epinephrine (45 +/- 9 ml/min/100 g) or phenylephrine (47 +/- 8 ml/min/100 g) infusion. The ratio of subendocardial to subepicardial blood flow fell equivalently during CPR with either epinephrine (1.23 +/- 0.06 to 0.70 +/- 0.05) or phenylephrine (1.32 +/- 0.07 to 0.77 +/- 0.05) administration. At similar levels of cerebral perfusion pressure (44 +/- 3 mm Hg), similar levels of cerebral blood flow were measured in both groups (27 +/- 3 ml/min/100 g). Cerebral O2 uptake was maintained at prearrest levels in both groups. Somatosensory-evoked potential amplitude was modestly reduced during CPR, but it promptly recovered after defibrillation. During CPR and at 2 hours after resuscitation, there were no differences between drug groups in the level of regional cerebral or coronary blood flow, cerebral O2 uptake, or evoked potentials. Therefore, with minimal delay in the onset of CPR and with equipotent pressor doses of phenylephrine and epinephrine, we found no evidence that one agent provides superior coronary or cerebral blood flow or that epinephrine by virtue of its beta-adrenergic properties adversely stimulates cerebral metabolism at a critical time that would impair brain electrophysiologic function. Moreover, epinephrine did not preferentially impair subendocardial blood flow as might be expected if it enhanced the strength of fibrillatory contractions.

Noninvasive determination of hemoglobin saturation in dogs by derivative near-infrared spectroscopy

An in vivo method utilizing derivative near-infrared spectroscopy was developed to noninvasively determine cerebral venous hemoglobin O2 saturation (SVO2). The method was tested on eight pentobarbital-anesthetized dogs ventilated with differing inspired O2 mixtures to force changes in SVO2 over a wide range. Spectral data obtained by transilluminating the tissues surrounding the superior sagittal sinus (SS) were transformed into first derivative units for correlation with SVO2 data measured from the SS. Linear regression analysis was applied to data obtained from five dogs and used to build a three-wavelength algorithm for predicting brain SVO2. In three dogs, SVO2 was varied to test this equation ability to predict SVO2. The standard deviation of differences between measured SVO2 and SVO2 predicted from 31 separate spectra was 3.2%. These predicted values, when regressed against the sampled SVO2, yielded an r value of 0.97. The results demonstrate that during hypoxic hypoxia (HH) it is possible to noninvasively quantify SVO2 with the use of infrared spectroscopy.

Cerebral blood flow and evoked potentials during Cushing response in sheep

We determined how alterations in systemic hemodynamics, characteristic of the Cushing response, are related to changes in cerebral blood flow (CBF), cerebral metabolic rate of O2 (CMRO2), and brain electrical conductive function, as assessed by somatosensory-evoked potentials (SEP) and brain stem auditory-evoked responses (BAER). In three groups of eight pentobarbital-anesthetized sheep, intracranial pressure was gradually elevated to within 50, 25, or 0 mmHg of base-line mean arterial pressure and then held constant for 40 min by intraventricular infusion of mock cerebrospinal fluid. Microsphere-determined CBF fell when cerebral perfusion pressure was less than 50 mmHg. CMRO2 fell when CBF fell greater than 30-40%. Mean aortic pressure and cardiac output increased when CBF fell greater than 40%, i.e., at approximately the level at which CMRO2 fell. Furthermore, the magnitude of the increase in arterial pressure and cardiac output correlated with the reduction of CMRO2. SEP latency did not increase unless CBF fell greater than 55-65%, corresponding to a 20-30% reduction of CMRO2. Increased latency of BAER wave V was associated with a fall in midbrain blood flow of greater than 65-70%. Thus increase in SEP and BAER latencies required reductions of flow greater than those required to elicit a systemic response. This demonstrates that there is a range of intracranial pressure over which the increase in arterial pressure preserves sufficient CBF to sustain minimal electrical conductive function. The best predictor of the onset and magnitude of the Cushing response in adult sheep is the decrease in CMRO2.

The physiology of cardiopulmonary resuscitation

As the pathophysiology of CPR is understood, ways to alter cerebral blood flow and neurologic outcome following CPR are likely to develop. This review highlights those areas likely to be of clinical importance in the near future.

Effect of PEEP and jugular venous compression on canine cerebral blood flow and oxygen consumption in the head elevated position

Cerebral blood flow (CBF) (radiolabelled microspheres) and oxygen consumption (CMRO2) were studied in nine dogs during 30 min of either neck vein compression or application of positive end-expiratory pressure (PEEP) ventilation. With the animal in the prone position, elevation of the head from horizontal to 30 cm above the heart markedly decreased cisterna magna (PCSF) and dorsal sagittal sinus pressure (PCV). With the head elevated, compression of neck veins using neck tourniquet (pressure 40 mmHg) increased PCSF and PCV from 3.6 +/- 2.2 to 6.8 +/- 4.8 and -2.5 +/- 2.7 to 2.3 +/- 2.3 mmHg (mean +/- SE, P less than 0.05), respectively, while total or regional CBF and CMRO2 remained unchanged. Application of PEEP (15 cm H2O) increased right atrial pressure (-4.7 +/- 1.7 to -0.1 +/- 3.4 mmHg, P less than 0.05), but did not affect PCSF or PCV (3.4 +/- 3.3 to 3.3 +/- 3.7 and -3.5 +/- 2.6 to -4.1 +/- 2.4 mmHg, respectively, P greater than 0.05). Total or regional CBF and CMRO2 were also unaffected. These data demonstrate that, although neither maneuver affects CBF or CMRO2, neck vein compression elevates PCV above atmospheric pressure, but PEEP does not. In patients at risk for cerebral venous embolism, intermittent neck vein compression should be used as a prophylactic measure to prevent air embolism.

Effects of halothane on myocardial high-energy phosphate metabolism and intracellular pH utilizing 31P NMR spectroscopy

Utilizing 31phosphorus nuclear magnetic resonance (NMR) spectroscopy, the authors tested the two hypotheses that the negative inotropic action of halothane is the result of: 1) myocardial intracellular acidosis, and 2) a decrease in myocardial high-energy phosphates. In isolated, paced, Langendorff-perfused rabbit hearts, halothane (1.5 vol %) dissolved in the coronary perfusate produced a 48 +/- 2% decrease (P less than 0.01) in left ventricular developed pressure. In contrast, halothane administration had no significant effect on myocardial intracellular pH (7.18 +/- 0.04 at control vs 7.21 +/- 0.02 during halothane). Halothane exposure decreased (P less than 0.01) the forward rate constant of the creatine kinase reaction by 32 +/- 6%, as measured using saturation transfer NMR, suggesting a decline in the rate of high-energy phosphate metabolism. This was further indicated by a concomitant decrease (P less than 0.05) in myocardial oxygen consumption (20 +/- 5%). During the halothane-induced reduction in left ventricular developed pressure, only small decreases in the myocardial steady state concentrations of phosphocreatine (7 +/- 1%; P less than 0.01) and beta ATP (12 +/- 4%; P less than 0.05), and an increase in Pi (18 +/- 6%; P less than 0.05) were observed. However, similar changes in steady-state high-energy phosphate metabolites were also measured in time-control hearts not exposed to halothane. These results indicate that the negative inotropic action of halothane is not mediated by myocardial intracellular acidosis. Moreover, these findings do not support the concept that the negative inotropic action of halothane is the result of a reduction in myocardial high-energy phosphates.

Evaluation of sepsis in a critically ill surgical population

We report a new clinical rating system which assesses septic patients' ongoing disease course and its severity. Our system incorporates the Therapeutic Intervention Scoring System (TISS) and Acute Physiology and Chronic Health Evaluation to measure discrete organ system abnormalities, plus a multiple system organ failure scale to quantify the number of abnormal organ systems. The resulting score, which reflects the severity of multiple organ dysfunction and grades responsiveness to therapy, was validated against the actual disease course. Retrospective and prospective profiles of individual surgical ICU patients demonstrated that this tracking method was a more effective indicator of severity of sepsis and more sensitive to the day-to-day changes in clinical status than either the TISS or APACHE II components alone. We also demonstrate that a graphic illustration of daily system scores yields clinically useful information relevant to the patients' septic course.

O2 radicals mediate reperfusion lung injury in ischemic O2-ventilated canine pulmonary lobe

This study was undertaken to determine whether lung injury after a period of ischemia reperfusion is caused by O2 ventilation during ischemia and whether this injury is mediated by reactive O2 metabolites. Isolated canine left lower pulmonary lobes were subjected to room temperature ischemia for 6 h while being ventilated with either 100% O2, room air, or 100% N2. After the ischemic period, all lobes were perfused with autologous blood and ventilated with 100% O2 for an additional 4 h. In lobes ventilated with 100% O2 during the ischemic period, massive weight gain (228%) occurred 4 h after reperfusion. A marked increase in pulmonary shunt was noted. Lobes ventilated with room air behaved similarly. In contrast, lobes ventilated with 100% N2 gained significantly less weight (54%) and did not manifest any increase in pulmonary shunt. When lobes ventilated with 100% O2 or room air were pretreated with superoxide dismutase (SOD), the injury was significantly reduced. Pressure-volume deflation study of lobes, after ischemia only, demonstrated that ventilation with 100% O2 and with 100% N2 both equally decreased pulmonary compliance. We conclude that lung ischemia-reperfusion injury is related to O2 ventilation during ischemia and that injury can be prevented by administration of SOD or ventilation with 100% N2. This suggests that the injury is related to O2 metabolites produced during O2 ventilation in the absence of the circulation.

Age-related changes in chest geometry during cardiopulmonary resuscitation

We studied alterations of chest geometry during conventional cardiopulmonary resuscitation in anesthetized immature swine. Pulsatile force was applied to the sternum in increments to determine the effects of increasing compression on chest geometry and intrathoracic vascular pressures. In 2-wk- and 1-mo-old piglets, permanent changes in chest shape developed due to incomplete recoil of the chest along the anteroposterior axis, and large intrathoracic vascular pressures were generated. In 3-mo-old animals, permanent chest deformity did not develop, and large intrathoracic vascular pressures were not produced. We propose a theoretical model of the chest as an elliptic cylinder. Pulsatile displacement along the minor axis of an ellipse produces a greater decrease in cross-sectional area than displacement of a circular cross section. As thoracic cross section became less circular due to deformity, greater changes in thoracic volume, and hence pressure, were produced. With extreme deformity at high force, pulsatile displacement became limited, diminishing pressure generation. We conclude that changes in chest geometry are important in producing intrathoracic intravascular pressure during conventional cardiopulmonary resuscitation in piglets.

Comparison of thermal clearance measurement of regional cerebral blood flow with radiolabelled microspheres

A thermal clearance technique for measuring cerebral blood flow is described and compared with the radiolabelled microsphere technique. The thermal technique involves measurement of the rewarming curve generated after bolus infusion of 4-5 ml of ice-cold saline into the common carotid artery with a subdural thermistor placed on the parietal cortex. Evaluation of the biexponential decay curves obtained with this technique demonstrated a close correlation with total hemispheric, parietal, and parietal gray blood flow determined by simultaneous microsphere measurement. Despite significant correlations (p less than 0.001), scatter in the data produced a broad 95% confidence interval, thus making interpretation of blood flow with the thermal clearance technique impossible. Furthermore, instrumentation with the thermal probe, which required opening of the dura, blunted the cerebral blood flow response to hypercapnia. We conclude that the major limitations of the thermal clearance technique include: nonhomogeneous clearance function, significant variability, and depression of CO2 reactivity. These limitations must be addressed before this technique can be used reliably in the laboratory.

Increased myocardial infarct size by thiopental after coronary occlusion in the dog

The effect of a single dose (10 mg/kg) of intravenous thiopental (TP), during acute myocardial infarction, on infarct size was studied in conscious dogs randomized 10 minutes after left circumflex coronary artery occlusion to either the TP group (n = 10) or a control group given 0.9% saline solution (n = 10). During the first hour following therapy, myocardial blood flow (microspheres), arterial pressure, left atrial pressure, and arterial blood gases were similar in the two groups, but the heart rate (140 +/- 3 vs 110 +/- 3 bpm; p less than 0.001) and rate-pressure product (15,090 vs 12,210 bpm X mm Hg; p less than 0.025) were greater in the TP group. Infarct size (planimetry) and occluded bed size (postmortem coronary arteriography) measured 2 days later revealed that: the slope of the relation between infarct and occluded bed mass, as a percentage of the left ventricle (% LV) was greater with TP than with saline solution (1.10 vs 0.61; p less than 0.001); excluding hearts (four TP and three saline solution) with small occluded beds (less than 22% LV), infarcts were also larger with TP (n = 6) than with saline solution (n = 7), both as a percentage of the left ventricle (26.4 vs 12.2%; p less than 0.02) or occluded bed (61.5 vs 28.9%; p less than 0.005); and transmural and endocardial extents of the infarcts on topographic maps were greater with TP than with saline solution. In 12 other conscious dogs, increasing the heart rate between 10 and 70 minutes after left circumflex coronary artery occlusion to the average rate of the TP group (140 bpm) by atrial pacing resulted in infarcts larger than those in control dogs but similar to those in the TP group. Thus, TP therapy after left circumflex occlusion increased infarct size in dogs. This effect appeared to be due mainly to the increased heart rate, probably via increased myocardial oxygen demands.

A comparison of nitroglycerin and nitroprusside for inducing hypotension in children: a double-blind study

Intravenous nitroglycerin (NTG) and sodium nitroprusside (SNP) were compared as hypotensive agents in anesthetized children and adolescents. The drugs were studied in a prospective, randomized, double-blind fashion in 14 patients anesthetized with nitrous oxide: oxygen, morphine, and thiopental. NTG in doses as high as 40 micrograms X kg-1 X min-1 was ineffective at decreasing mean arterial pressure (MAP) below 55 mmHg or causing a decrease in MAP greater than one-third of baseline values. SNP was uniformly successful at inducing hypotension in all patients, including those patients in whom NTG failed. The dose of SNP required to induce hypotension was 6-8 micrograms X kg-1 X min-1. Both NTG and SNP decreased systemic vascular resistance, although SNP did so to a much greater degree than NTG (64% vs. 29%; P less than 0.01). Only SNP increased cardiac index significantly (2.27 +/- 0.35 to 4.44 +/- 1.36; P less than 0.003). Both drugs reflexly increased heart rate, necessitating the use of intravenous propranolol (range from 1 to 3 mg) in all patients. Both drugs produced small decreases in arterial oxygen tension and increases in the average alveolar-arterial oxygen tension gradient (SNP, 44 +/- 13 vs. NTG, 41 +/- 6). SNP use was associated with a slight metabolic acidosis (pH = 7.38 +/- 0.01; base excess [BE] = -6 +/- 1). Neither drug produced any other untoward reaction. SNP appears to be the agent of choice for the reliable and sustained induction of deliberate hypotension in children and adolescents.

Organ blood flow during high-frequency ventilation at low and high airway pressure in dogs

Using the radiolabeled microsphere technique, the authors studied hemodynamic variables and regional blood flow to multiple peripheral organs during conventional positive-pressure ventilation (CV) and high-frequency ventilation (HFV) at low and high mean airway pressure (Paw). Twenty supine anesthetized, paralyzed dogs were ventilated using CV (14-16 breaths/min) and HFV (rate = 10 Hz) in random order. In the first group (low Paw, n = 10), Paw was maintained at 3 cmH2O during CV and HFV. In the second group (high Paw, n = 10), Paw was increased to 13 cmH2O during CV and HFV. Pulmonary capillary wedge pressure and right atrial pressure remained constant during low and high Paw trials. No differences in heart rate, systemic arterial pressure, intracranial pressure, or cardiac output were noted during CV and HFV within the low and high Paw groups. In addition, blood flow to multiple peripheral organs during CV and HFV remained constant within each Paw group, except for a small decrease in cerebellar blood flow during HFV at high Paw trials showed a significant decrease in hepatic arterial and outer kidney cortical flow at high Paw. Total cerebral blood flow was decreased at high Paw, as were regional flows to diencephalon, midbrain, pons, medulla, and cerebellum. However, these differences were not attributable to differences in cerebral perfusion pressure or intracranial pressure, and cerebral oxygen delivery was not different between high Paw and low Paw groups. It is concluded that under conditions of similar Paw in anesthetized dogs, HFV does not significantly alter hemodynamic patterns or regional circulation relative to CV.

Current concepts in brain resuscitation

In spite of the tremendous amount of effort and money put forth to reduce morbidity and mortality associated with global cerebral ischemia, the outlook for patients suffering an ischemic insult remains dismal. The lack of a sufficient substrate supply during the period of ischemia as well as the production of toxic metabolites in response to ischemia have been incriminated as key factors causing brain damage. As discussed in this article, modes of therapy have included efforts to minimize the duration of ischemia (eg, effective cardiopulmonary resuscitation, hemodilution, heparinization, calcium antagonists) and decrease the production of toxic metabolites (eg, barbiturates, calcium antagonists). Although the barbiturates have also been proposed to decrease the metabolic needs during ischemia, they have no therapeutic value for global cerebral ischemia. The initial evaluation of the calcium antagonists has been more promising.

Lack of validity of diagnosis-related group payment systems in an intensive care population

Case mix based on diagnosis-related groups (DRGs) was studied over 3 years for duration of stay and mean charges for a pediatric intensive care unit (PICU) and a general ward (WARD) population. Case mix variation for 2403 PICU and 14,552 WARD patients was analyzed, and a subset of 856 PICU and 2222 WARD patients examined for variations in duration of stay and mean charges in nine DRGs. Whereas case mix by DRG was consistent over time for both groups, the PICU case mix differed consistently from WARD case mix (P less than 0.001). After adjustment for inflation and for differences in case mix, average stay for the PICU was 10.7 days, versus 6.1 for the WARD (P less than 0.025), with a mean charge of $7172 per PICU and $2946 per WARD patient (P less than 0.01). Furthermore, the case mix-adjusted differences in duration of stay and mean charge between the PICU and WARD populations increased over time. Pediatricians will need to address DRG-based reimbursement systems that place intensive care units, and their institutions, at a significant financial disadvantage.