Hypertension with or without hemodilution after cardiac arrest in dogs

Prehospital Post-Resuscitation Vital Sign Phenotypes are Associated with Outcomes Following Out-of-Hospital Cardiac Arrest

OBJECTIVES

The use of machine learning to identify patient 'clusters' using post-return of spontaneous circulation (ROSC) vital signs may facilitate the identification of patient subgroups at high risk of rearrest and mortality. Our objective was to use k-means clustering to identify post-ROSC vital sign clusters and determine whether these clusters were associated with rearrest and mortality.

METHODS

The ESO Data Collaborative 2018-2022 datasets were used for this study. We included adult, non-traumatic OHCA patients with >2 post-ROSC vital sign sets. Patients were excluded if they had an EMS-witnessed OHCA or were encountered during an interfacility transfer. Unsupervised (k-means) clustering was performed using minimum, maximum, and delta (last minus first) systolic blood pressure (BP), heart rate, SpO2, shock index, and pulse pressure. The assessed outcomes were mortality and rearrest. To explore the association between rearrest, mortality, and cluster, multivariable logistic regression modeling was used.

RESULTS

Within our cohort of 12,320 patients, five clusters were identified. Patients in cluster 1 were hypertensive, patients in cluster 2 were normotensive, patients in cluster 3 were hypotensive and tachycardic (n = 2164; 17.6%), patients in cluster 4 were hypoxemic and exhibited increasing systolic BP, and patients in cluster 5 were severely hypoxemic and exhibited a declining systolic BP. The overall proportion of patients who experienced mortality stratified by cluster was 63.4% (c1), 68.1% (c2), 78.8% (c3), 84.8% (c4), and 86.6% (c5). In comparison to the cluster with the lowest mortality (c1), each other cluster was associated with greater odds of mortality and rearrest.

CONCLUSIONS

Unsupervised k-means clustering yielded 5 post-ROSC vital sign clusters that were associated with rearrest and mortality.

Association of prehospital hypotension depth and dose with survival following out-of-hospital cardiac arrest

INTRODUCTION

Hypotension following resuscitation from out-of-hospital cardiac arrest (OHCA) may cause harm by exacerbating secondary brain injury; however, limited research has explored this relationship. Our objective was to examine the association between duration and depth of prehospital post return of spontaneous circulation (ROSC) hypotension and survival.

METHODS

We utilized the 2019 and 2020 ESO Data Collaborative public use research data sets for this study (ESO, Austin, TX). Hypotension dose (mmHg*min.), average prehospital systolic blood pressure (SBP), and lowest recorded prehospital SBP were calculated. The association of these measures with survival to home (STH) and rearrest were explored using multivariable logistic regression. Time to hypotension resolution analyses by hypotension management strategy (push dose vasopressors, vasopressor infusion, or fluid only) were conducted using adjusted Cox proportional hazards models.

RESULTS

17,280 OHCA patients met inclusion criteria, of which 3,345 had associated hospital outcome data. Over one-third (37.8%; 6,526/17,280) of all patients had at least one recorded SBP below 90 mmHg. When modeled continuously, average prehospital SBP (1.19 [1.15, 1.23] per 10 mmHg), lowest prehospital SBP (1.20 [1.17, 1.24] per 10 mmHg), and hypotension dose (0.995 [0.993, 0.996] per mmHg*min.) were independently associated with STH. Differences in hypotension management were not associated with differences in survival or time to hypotension resolution.

CONCLUSION

Severity and duration of hypotension were significantly associated with worse outcomes in this dataset. Defining a threshold for hypotension requiring treatment above the classical SBP threshold of 90 mmHg may be warranted in the setting of prehospital post-resuscitation care.

Cerebral perfusion and metabolism with mean arterial pressure 90 vs. 60 mmHg in a porcine post cardiac arrest model with and without targeted temperature management

AIM

To determine whether targeting a mean arterial pressure of 90 mmHg (MAP90) would yield improved cerebral blood flow and less ischaemia compared to MAP 60 mmHg (MAP60) with and without targeted temperature management at 33 °C (TTM33) in a porcine post-cardiac arrest model.

METHODS

After 10 min of cardiac arrest, 41 swine of either sex were resuscitated until return of spontaneous circulation (ROSC). They were randomised to TTM33 or no-TTM, and MAP60 or MAP90; yielding four groups. Temperatures were managed with intravasal cooling and blood pressure targets with noradrenaline, vasopressin and nitroprusside, as appropriate. After 30 min of stabilisation, animals were observed for two hours. Cerebral perfusion pressure (CPP), cerebral blood flow (CBF), pressure reactivity index (PRx), brain tissue pCO2 (PbtCO2) and tissue intermediary metabolites were measured continuously and compared using mixed models.

RESULTS

Animals randomised to MAP90 had higher CPP (p < 0.001 for both no-TTM and TTM33) and CBF (no-TTM, p < 0.03; TH, p < 0.001) compared to MAP60 during the 150 min observational period post-ROSC. We also observed higher lactate and pyruvate in MAP60 irrespective of temperature, but no significant differences in PbtCO2 and lactate/pyruvate-ratio. We found lower PRx (indicating more intact autoregulation) in MAP90 vs. MAP60 (no-TTM, p = 0.04; TTM33, p = 0.03).

CONCLUSION

In this porcine cardiac arrest model, targeting MAP90 led to better cerebral perfusion and more intact autoregulation, but without clear differences in ischaemic markers, compared to MAP60.

INSTITUTIONAL PROTOCOL NUMBER

FOTS, id 8442.

Acute-stage MRI cerebral oxygen consumption biomarkers predict 24-hour neurological outcome in a rat cardiac arrest model

Brain injury following cardiac arrest (CA) is thought to be caused by a sudden loss of blood flow resulting in disruption in oxygen delivery, neural function and metabolism. However, temporal trajectories of the brain's physiology in the first few hours following CA have not been fully characterized. Furthermore, the extent to which these early measures can predict future neurological outcomes has not been determined. The present study sought to perform dynamic measurements of cerebral blood flow (CBF), oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO₂ ) with MRI in the first 3 hours following the return of spontaneous circulation (ROSC) in a rat CA model. It was found that CBF, OEF and CMRO₂ all revealed a time-dependent increase during the first 3 hours after the ROSC. Furthermore, the temporal trajectories of CBF and CMRO₂ , but not OEF, were different across rats and related to neurologic outcomes at a later time (24 hours after the ROSC) (P < .001). Rats who manifested better outcomes revealed faster increases in CBF and CMRO₂ during the acute stage. When investigating physiological parameters measured at a single time point, CBF (ρ = 0.82, P = .004) and CMRO₂ (ρ = 0.80, P = .006) measured at ~ 3 hours post-ROSC were positively associated with neurologic outcome scores at 24 hours. These findings shed light on brain physiological changes following CA, and suggest that MRI measures of brain perfusion and metabolism may provide a potential biomarker to guide post-CA management.

The Effect of Prophylactic Anticoagulation with Heparin on the Brain Cells of Sprague-Dawley Rats in a Cardiopulmonary-Cerebral Resuscitation Model

After a cardiac arrest (CA) of 5 to 10 min, a marked activation of blood coagulation occurs and microthrombi are found in the cerebral vessels. These microcirculatory disturbances directly affect the outcome on cardiopulmonary resuscitation (CPR). The purpose of this study was to investigate the effects and potential mechanisms of prophylactic anticoagulation on rat brain cells after cerebral CPR. After setting up an asphyxial CA model, we monitored the basic parameters such as the vitals and survival rate of the rats and assessed the respective neurological deficit (ND) and histological damage (HD) scores of their brain tissues. We, furthermore, investigated the influence of heparin on the expressions of TNF-α, IL-1β, CD40, NF-κB, and HIF-1α after asphyxial CA. The results showed that anticoagulation with heparin could obviously improve the outcome and prognosis of brain ischemia, including improvement of neurological function recovery and prevention of morphological and immunohistochemical injury on the brain, while significantly increasing the success rate of CPR. Treatment with heparin significantly inhibited the upregulation of CD40, NF-κB, and HIF-1α induced by asphyxial CA. Thrombolysis treatment may improve the outcome and prognosis of CPR, and future clinical studies need to evaluate the efficacy of early heparin therapy after CA.

Cerebral Blood Flow-Guided Manipulation of Arterial Blood Pressure Attenuates Hippocampal Apoptosis After Asphyxia-Induced Cardiac Arrest in Rats

Background In most post-cardiac arrest patients, the autoregulation mechanism of cerebral blood flow (CBF) is dysregulated. We examined whether recovery of CBF by adjusting mean arterial pressure mitigates post-cardiac arrest neuronal damage. Methods and Results Wistar rats that underwent 8-minute asphyxia-induced cardiac arrest and resuscitation were computer-randomized to norepinephrine or control groups. The CBF was measured at the dorsal hippocampal CA1 region of the left hemisphere. In the norepinephrine group, the mean arterial pressure was adjusted to recover CBF to 80% to 100% of baseline. Twenty-four hours following resuscitation, neurological outcomes were assessed, and brain tissues and blood samples were harvested for neuronal apoptosis and injury assessment. Thirty resuscitated rats were randomized into 2 groups, each containing 12 rats that completed the experiments. Norepinephrine infusion effectively prevented posthyperemia hypoperfusion and recovered CBF to pre-arrest baseline levels; a moderate positive linear correlation between mean arterial pressure and CBF during this period was also observed (P<0.001). There were no significant between-group differences in neurological recovery. In the norepinephrine group compared with the control group, upregulated cleaved caspase-3 protein expression in brain tissue determined by Western blot was reduced (P=0.02) and the densities of apoptotic cells in hippocampal CA1 and CA3 regions determined by terminal deoxynucleotidyl transferase-mediated dUTP biotin nick-end labeling were decreased (P<0.001). No significant differences in serum neuron-specific enolase or S100β levels were detected between the 2 groups. Conclusions CBF recovery demonstrated neuroprotective effects by reducing activation of cerebral apoptosis and number of apoptotic neurons. However, these effects did not significantly improve clinical neurological function, necessitating further investigation.

Association Between Elevated Mean Arterial Blood Pressure and Neurologic Outcome After Resuscitation From Cardiac Arrest: Results From a Multicenter Prospective Cohort Study

OBJECTIVES

Laboratory studies suggest elevated blood pressure after resuscitation from cardiac arrest may be protective; however, clinical data are limited. We sought to test the hypothesis that elevated postresuscitation mean arterial blood pressure is associated with neurologic outcome.

DESIGN

Preplanned analysis of a prospective cohort study.

SETTING

Six academic hospitals in the United States.

PATIENTS

Adult, nontraumatic cardiac arrest patients treated with targeted temperature management after return of spontaneous circulation.

INTERVENTIONS

Mean arterial blood pressure was measured noninvasively after return of spontaneous circulation and every hour during the initial 6 hours after return of spontaneous circulation.

MEASURES AND MAIN RESULTS

We calculated the mean arterial blood pressure and a priori dichotomized subjects into two groups: mean arterial blood pressure 70-90 and greater than 90 mm Hg. The primary outcome was good neurologic function, defined as a modified Rankin Scale less than or equal to 3. The modified Rankin Scale was prospectively determined at hospital discharge. Of the 269 patients included, 159 (59%) had a mean arterial blood pressure greater than 90 mm Hg. Good neurologic function at hospital discharge occurred in 30% of patients in the entire cohort and was significantly higher in patients with a mean arterial blood pressure greater than 90 mm Hg (42%) as compared with mean arterial blood pressure 70-90 mm Hg (15%) (absolute risk difference, 27%; 95% CI, 17-37%). In a multivariable Poisson regression model adjusting for potential confounders, mean arterial blood pressure greater than 90 mm Hg was associated with good neurologic function (adjusted relative risk, 2.46; 95% CI; 2.09-2.88). Over ascending ranges of mean arterial blood pressure, there was a dose-response increase in probability of good neurologic outcome, with mean arterial blood pressure greater than 110 mm Hg having the strongest association (adjusted relative risk, 2.97; 95% CI, 1.86-4.76).

CONCLUSIONS

Elevated blood pressure during the initial 6 hours after resuscitation from cardiac arrest was independently associated with good neurologic function at hospital discharge. Further investigation is warranted to determine if targeting an elevated mean arterial blood pressure would improve neurologic outcome after cardiac arrest.

Therapeutic hypothermia promotes cerebral blood flow recovery and brain homeostasis after resuscitation from cardiac arrest in a rat model

Laboratory and clinical studies have demonstrated that therapeutic hypothermia (TH), when applied as soon as possible after resuscitation from cardiac arrest (CA), results in better neurological outcome. This study tested the hypothesis that TH would promote cerebral blood flow (CBF) restoration and its maintenance after return of spontaneous circulation (ROSC) from CA. Twelve Wistar rats resuscitated from 7-min asphyxial CA were randomized into two groups: hypothermia group (7 H, n = 6), treated with mild TH (33-34℃) immediately after ROSC and normothermia group (7 N, n = 6,37.0 ± 0.5℃). Multiple parameters including mean arterial pressure, CBF, electroencephalogram (EEG) were recorded. The neurological outcomes were evaluated using electrophysiological (information quantity, IQ, of EEG) methods and a comprehensive behavior examination (neurological deficit score, NDS). TH consistently promoted better CBF restoration approaching the baseline levels in the 7 H group as compared with the 7 N group. CBF during the first 5-30 min post ROSC of the two groups was 7 H:90.5% ± 3.4% versus 7 N:76.7% ± 3.5% (P < 0.01). Subjects in the 7 H group showed significantly better IQ scores after ROSC and better NDS scores at 4 and 24 h. Early application of TH facilitates restoration of CBF back to baseline levels after CA, which in turn results in the restoration of brain electrical activity and improved neurological outcome.

Variation in Sedation and Neuromuscular Blockade Regimens on Outcome After Cardiac Arrest

OBJECTIVES

Sedation and neuromuscular blockade protocols in patients undergoing targeted temperature management after cardiac arrest address patient discomfort and manage shivering. These protocols vary widely between centers and may affect outcomes.

DESIGN

Consecutive patients admitted to 20 centers after resuscitation from cardiac arrest were prospectively entered into the International Cardiac Arrest Registry between 2006 and 2016. Additional data about each center's sedation and shivering management practice were obtained via survey. Sedation and shivering practices were categorized as escalating doses of sedation and minimal or no neuromuscular blockade (sedation and shivering practice 1), sedation with continuous or scheduled neuromuscular blockade (sedation and shivering practice 2), or sedation with as-needed neuromuscular blockade (sedation and shivering practice 3). Good outcome was defined as Cerebral Performance Category score of 1 or 2. A logistic regression hierarchical model was created with two levels (patient-level data with standard confounders at level 1 and hospitals at level 2) and sedation and shivering practices as a fixed effect at the hospital level. The primary outcome was dichotomized Cerebral Performance Category at 6 months.

SETTING

Cardiac arrest receiving centers in Europe and the United states from 2006 to 2016 PATIENTS:: Four-thousand two-hundred sixty-seven cardiac arrest patients 18 years old or older enrolled in the International Cardiac Arrest Registry.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The mean age was 62 ± 15 years, 36% were female, 77% out-of-hospital arrests, and mean ischemic time was 24 (± 18) minutes. Adjusted odds ratio (for age, return of spontaneous circulation, location of arrest, witnessed, initial rhythm, bystander cardiopulmonary resuscitation, defibrillation, medical history, country, and size of hospital) was 1.13 (0.74-1.73; p = 0.56) and 1.45 (1.00-2.13; p = 0.046) for sedation and shivering practice 2 and sedation and shivering practice 3, respectively, referenced to sedation and shivering practice 1.

CONCLUSION

Cardiac arrest patients treated at centers using as-needed neuromuscular blockade had increased odds of good outcomes compared with centers using escalating sedation doses and avoidance of neuromuscular blockade, after adjusting for potential confounders. These findings should be further investigated in prospective studies.

The association of immediate post cardiac arrest diastolic hypertension and survival following pediatric cardiac arrest

AIM

In-hospital cardiac arrest occurs in >5000 children each year in the US and almost half will not survive to discharge. Animal data demonstrate that an immediate post-resuscitation burst of hypertension is associated with improved survival. We aimed to determine if systolic and diastolic invasive arterial blood pressures immediately (0-20 min) after return of spontaneous circulation (ROSC) are associated with survival and neurologic outcomes at hospital discharge.

METHODS

This is a secondary analysis of the Pediatric Intensive Care Quality of CPR (PICqCPR) study of invasively measured blood pressures during intensive care unit CPR. Patients were eligible if they achieved ROSC and had at least one invasively measured blood pressure within the first 20 min following ROSC. Post-ROSC blood pressures were normalized for age, sex and height. "Immediate hypertension" was defined as at least one systolic or diastolic blood pressure >90th percentile. The primary outcome was survival to hospital discharge.

RESULTS

Of 102 children, 70 (68.6%) had at least one episode of immediate post-CPR diastolic hypertension. After controlling for pre-existing hypotension, duration of CPR, calcium administration, and first documented rhythm, patients with immediate post-CPR diastolic hypertension were more likely to survive to hospital discharge (79.3% vs. 54.5%; adjusted OR = 2.93; 95%CI, 1.16-7.69).

CONCLUSIONS

In this post hoc secondary analysis of the PICqCPR study, 68.6% of subjects had diastolic hypertension within 20 min of ROSC. Immediate post-ROSC hypertension was associated with increased odds of survival to discharge, even after adjusting for covariates of interest.

Optimal blood pressure for favorable neurological outcome in adult patients following in-hospital cardiac arrest

BACKGROUND

Adequate cerebral blood flow maintained by optimal blood pressure is important in neurological recovery for patients sustaining transient brain ischemia. Few clinical studies have investigated the relationship between blood pressure and neurological outcomes of patients resuscitated following cardiac arrest.

METHODS

This was a retrospective observational study, from a single medical center, of adult patients between 2006 and 2012 who had in-hospital cardiac arrest and achieved sustained return of spontaneous circulation (ROSC). Multivariable logistic regression analysis was used to identify factors associated with a favorable neurological outcome at hospital discharge. Maximal mean arterial pressure (MAP) during the initial 24h after sustained ROSC was used for analysis.

RESULTS

Of the 319 study patients, 56 (17.6%) achieved a favorable neurologic outcome. The mean MAP was 95 mmHg. MAP above 85 mmHg was found to correlate with a favorable neurological outcome (odds ratio [OR] 4.12, 95% confidence interval [CI] 1.47-14.39, p = 0.01). For patients without arterial hypertension, the optimal MAP was between 85 and 115 mmHg (OR 8.80, 95% CI 3.13-28.55, p < 0.001); for patients with arterial hypertension, the threshold MAP for achieving a favorable neurological outcome was above 88 mmHg (OR 4.04, 95% CI 1.41-13.03, p = 0.01).

CONCLUSIONS

The blood pressure over the first 24h following resuscitation was correlated with neurological outcome. There may be a threshold blood pressure required to affect a favorable neurological outcome. The optimal blood pressure may be dependent on the presence or absence of arterial hypertension.

Effects of levosimendan on hemodynamics, local cerebral blood flow, neuronal injury, and neuroinflammation after asphyctic cardiac arrest in rats

OBJECTIVES

Despite advances in cardiac arrest treatment, high mortality and morbidity rates after successful cardiopulmonary resuscitation are still a major clinical relevant problem. The post cardiac arrest syndrome subsumes myocardial dysfunction, impaired microcirculation, systemic inflammatory response, and neurological impairment. The calcium-sensitizer levosimendan was able to improve myocardial function and initial resuscitation success after experimental cardiac arrest/cardiopulmonary resuscitation. We hypothesized that levosimendan exerts beneficial effects on cerebral blood flow, neuronal injury, neurological outcome, and inflammation 24 hours after experimental cardiac arrest/cardiopulmonary resuscitation.

DESIGN

Laboratory animal study.

SETTING

University animal research laboratory.

SUBJECTS

Sixty-one male Sprague-Dawley rats.

INTERVENTIONS

Animals underwent asphyxial cardiac arrest/cardiopulmonary resuscitation, randomized to groups with levosimendan treatment (bolus 12 µg/kg and infusion for 3 hr [0.3 µg/min/kg]) or vehicle (saline 0.9% bolus and infusion for 3 hr [equivalent fluid volume]). Cardiac index, local cerebral blood flow, and hemodynamic variables were measured for 180 minutes after cardiac arrest/cardiopulmonary resuscitation. Behavioral and neurological evaluations were conducted 24 hours after cardiac arrest/cardiopulmonary resuscitation. Furthermore, neuronal injury, expressed as Fluoro-Jade B-positive cells in the hippocampal formation, cortical and hippocampal inflammatory cytokine gene expression, and blood plasma interleukin-6 values were assessed.

MEASUREMENTS AND MAIN RESULTS

Treatment with levosimendan reduced neuronal injury and improved neurological outcome after 24 hours of reperfusion and resulted in elevated cardiac index and local cerebral blood flow compared with vehicle after cardiac arrest/cardiopulmonary resuscitation. Mean arterial blood pressure was reduced during the early reperfusion period in the levosimendan group. Cortical and hippocampal inflammatory cytokine gene expression and blood plasma interleukin-6 levels were not influenced.

CONCLUSIONS

Levosimendan increased cerebral blood flow after experimental cardiac arrest/cardiopulmonary resuscitation. This effect coincided with reduced neuronal injury and improved neurologic outcome. Findings seem to be independent of inflammatory effects because no effects by levosimendan on cerebral or systemic inflammation could be detected. In summary, levosimendan is a promising agent to improve neurological outcome after cardiac arrest/cardiopulmonary resuscitation.

The role of Levosimendan in cardiopulmonary resuscitation

Although initial resuscitation from cardiac arrest (CA) has increased over the past years, long term survival rates remain dismal. Epinephrine is the vasopressor of choice in the treatment of CA. However, its efficacy has been questioned, as it has no apparent benefits for long-term survival or favorable neurologic outcome. Levosimendan is an inodilator with cardioprotective and neuroprotective effects. Several studies suggest that it is associated with increased rates of return of spontaneous circulation as well as improved post-resuscitation myocardial function and neurological outcome. The purpose of this article is to review the properties of Levosimendan during cardiopulmonary resuscitation (CPR) and also to summarize existing evidence regarding the use of Levosimendan in the treatment of CA.

[Post-resuscitation syndrome. Role of inflammation after cardiac arrest]

Cardiac arrest with subsequent cardiopulmonary resuscitation causes an ischemic reperfusion syndrome of the whole body resulting in localized damage of particularly sensitive organs, such as the brain and heart, together with systemic sequelae. The main factor is a generalized activation of inflammatory reactions resulting in symptoms similar in many aspects to those of sepsis. Systemic inflammation strengthens organ damage due to disorders in the macrocirculation and microcirculation due to metabolic imbalance as well as the effects of direct leukocyte transmitted tissue destruction. The current article gives an overview on the role of inflammation following cardiac arrest and presents in detail the underlying mechanisms, the clinical symptoms and possible therapeutic approaches.

RECOVER evidence and knowledge gap analysis on veterinary CPR. Part 7: Clinical guidelines

OBJECTIVE

To present a series of evidence-based, consensus guidelines for veterinary CPR in dogs and cats.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence and quality, and development of consensus on conclusions for application of the concepts to clinical practice. Questions in five domains were examined: Preparedness and Prevention, Basic Life Support, Advanced Life Support, Monitoring, and Post-Cardiac Arrest Care. Standardized worksheet templates were used for each question, and the results reviewed by the domain members, by the RECOVER committee, and opened for comments by veterinary professionals for 4 weeks. Clinical guidelines were devised from these findings and again reviewed and commented on by the different entities within RECOVER as well as by veterinary professionals.

SETTING

Academia, referral practice and general practice.

RESULTS

A total of 74 worksheets were prepared to evaluate questions across the five domains. A series of 101 individual clinical guidelines were generated. In addition, a CPR algorithm, resuscitation drug-dosing scheme, and postcardiac arrest care algorithm were developed.

CONCLUSIONS

Although many knowledge gaps were identified, specific clinical guidelines for small animal veterinary CPR were generated from this evidence-based process. Future work is needed to objectively evaluate the effects of these new clinical guidelines on CPR outcome, and to address the knowledge gaps identified through this process.

The association between early hemodynamic variables and outcome in normothermic comatose patients following cardiac arrest

BACKGROUND

Currently, few data exist on the association between post-cardiac arrest hemodynamic function and outcome. In this explorative, retrospective analysis, the association between hemodynamic variables during the first 24 h after intensive care unit admission and functional outcome at day 28 was evaluated in 153 normothermic comatose patients following a cardiac arrest.

METHODS

Medical records of a multidisciplinary intensive care unit were reviewed for comatose patients (Glasgow Coma Scale < or = 9) admitted to the intensive care unit after successful resuscitation from an in- or an out-of-hospital cardiac arrest. The hourly variable time integral of hemodynamic variables during the first 24 h after admission was calculated. At day 28, outcome was assessed as favorable or adverse based on a Cerebral Performance Category of 1-2 and 3-5, respectively. Bi- and multivariate regression models adjusted for relevant confounding variables were used to evaluate the association between hemodynamic variables and functional outcome.

RESULTS

One hundred and fifty-three normothermic comatose patients were admitted after a cardiac arrest, of whom 64 (42%) experienced a favorable outcome. Neither in the adjusted bivariate models (r(2), 0.61-0.78) nor in the adjusted multivariate model (r(2), 0.62-0.73) was the hourly variable time integral of any hemodynamic variable during the first 24 h after intensive care unit admission associated with functional patient outcome at day 28 in all patients as well as in patients after an in- or an out-of-hospital cardiac arrest.

CONCLUSION

Commonly measured hemodynamic variables during the first 24 h following intensive care unit admission due to a cardiac arrest do not appear to be associated with the functional outcome at day 28.

Ventilation and cardiopulmonary resuscitation

Ventilation is essential for oxygenation of the alveoli and arterial blood. Comatose humans have upper airway soft tissue obstruction unless the head is tilted backwards and sometimes, in addition, the jaw thrust forward. In 1960, measurements on comatose humans with or without cardiac arrest, with or without a tracheal tube, showed essentially no ventilation by sternal compressions alone. This led to combining step A (airway control), step B (mouth-to-mouth ventilation), and step C (sternal (cardiac) compressions) into basic life support. In animal models, sternal compressions alone can produce some ventilation with or without a tracheal tube, because the straight upper airways of animals do not obstruct in coma. In witnessed sudden cardiac death, the C-A-B sequence makes physiological sense, but other causes of sudden coma need the A-B-C sequence. Lay persons should continue to be taught cardiopulmonary resuscitation steps A-B-C.

Differences in cerebral reperfusion and oxidative injury after cardiac arrest in pigs

BACKGROUND

An investigation of the free radical scavenger sodium 2-sulfophenyl-N-tert-butyl nitrone (S-PBN) and the weak vasodilatator Tris buffer mixture (TBM) on cerebral cortical blood flow (CCBF) and the jugular bulb concentration of two eicosanoids, indicators of oxidative stress and inflammation, was undertaken in 30 anaesthetized piglets during cardiopulmonary resuscitation (CPR) and after restoration of spontaneous circulation (ROSC).

METHODS

Thirty animals were subjected to 8 min of untreated circulatory arrest followed by 8 min of closed-chest CPR. During CPR, the animals were randomized to receive 60 mg/kg S-PBN, 1 mmol/kg TBM or 2 ml/kg normal saline (n = 10 in each group). Systemic haemodynamic variables, CCBF and jugular bulb plasma concentrations of 8-iso-PGF2alpha and 15-keto-dihydro-PGF2alpha were measured.

RESULTS

The CCBF during reperfusion after ROSC was greater in the TBM group than in the S-PBN group, the regression coefficient between CCBF and mean arterial blood pressure being lower in the S-PBN group than in the TBM group. The jugular bulb plasma concentration of 8-iso-PGF2alpha during the first 30 min after ROSC was greater in the TBM group than in the S-PBN group. Administration of TBM after vasopressin did not attenuate the pressor effect of vasopressin.

CONCLUSION

Administration of S-PBN during CPR results in less cerebral oxidative stress, possibly by promoting normal distribution of cerebral blood flow.

Pediatric cardiopulmonary-cerebral resuscitation: an overview and future directions

The evolving understanding of pathophysiologic events during and after pediatric cardiac arrest has not yet resulted in significantly improved outcome. Exciting breakthroughs in basic and applied science laboratories are, however, on the immediate horizon for study in specific subpopulations of cardiac arrest victims. Strategically focusing therapies to specific phases of cardiac arrest and resuscitation and evolving pathophysiologic events offers great promise that critical care interventions will lead the way to more successful cardiopulmonary and cerebral resuscitation in children.

Survival without brain damage after clinical death of 60-120 mins in dogs using suspended animation by profound hypothermia

OBJECTIVES

This study explored the limits of good outcome of brain and organism achievable after cardiac arrest (no blood flow) of 60-120 mins, with preservation (suspended animation) induced immediately after the start of exsanguination cardiac arrest.

DESIGN

Prospective experimental comparison of three arrest times, without randomization.

SETTING

University research laboratory.

SUBJECTS

Twenty-seven custom-bred hunting dogs (17-25 kg).

INTERVENTIONS

Dogs were exsanguinated over 5 mins to cardiac arrest no-flow of 60 mins, 90 mins, or 120 mins. At 2 mins of cardiac arrest, the dogs received, via a balloon-tipped catheter, an aortic flush of isotonic saline at 2 degrees C (at a rate of 1 L/min), until tympanic temperature reached 20 degrees C (for 60 mins of cardiac arrest), 15 degrees C (for 60 mins of cardiac arrest), or 10 degrees C (for 60, 90, or 120 mins of cardiac arrest). Resuscitation was by closed-chest cardiopulmonary bypass, postcardiac arrest mild hypothermia (tympanic temperature 34 degrees C) to 12 hrs, controlled ventilation to 20 hrs, and intensive care to 72 hrs.

MEASUREMENTS AND MAIN RESULTS

We assessed overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), regional and total brain histologic damage scores at 72 hrs (total HDS >0-40, mild; 40-100, moderate; >100, severe damage), and morphologic damage of extracerebral organs. For 60 mins of cardiac arrest (n = 14), tympanic temperature 20 degrees C (n = 6) was achieved after flush of 3 mins and resulted in two dogs with OPC 1 and four dogs with OPC 2: median NDS, 13% (range 0-27%); and median total HDS, 28 (range, 4-36). Tympanic temperature of 15 degrees C (n = 5) was achieved after flush of 7 mins and resulted in all five dogs with OPC 1, NDS 0% (0-3%), and HDS 8 (0-48). Tympanic temperature 10 degrees C (n = 3) was achieved after flush of 11 mins and resulted in all three dogs with OPC 1, NDS 0%, and HDS 16 (2-18). For 90 mins of cardiac arrest (n = 6), tympanic temperature 10 degrees C was achieved after flush of 15 mins and resulted in all six dogs with OPC 1, NDS 0%, and HDS 8 (0-37). For 120 mins of cardiac arrest (n = 7), three dogs had to be excluded. In the four dogs within protocol, tympanic temperature 10 degrees C was achieved after flush of 15 mins. This resulted in one dog with OPC 1, NDS 0%, and total HDS 14; one with OPC 1, NDS 6%, and total HDS 20; one with OPC 2, NDS 13%, and total HDS 10; and one with OPC 3, NDS 39%, and total HDS 22.

CONCLUSIONS

In a systematic series of studies in dogs, the rapid induction of profound cerebral hypothermia (tympanic temperature 10 degrees C) by aortic flush of cold saline immediately after the start of exsanguination cardiac arrest-which rarely can be resuscitated effectively with current methods-can achieve survival without functional or histologic brain damage, after cardiac arrest no-flow of 60 or 90 mins and possibly 120 mins. The use of additional preservation strategies should be pursued in the 120-min arrest model.

Neurological outcome after experimental cardiopulmonary resuscitation: a result of delayed and potentially treatable neuronal injury?

BACKGROUND

In experimental cardiopulmonary resuscitation (CPR) aortic balloon occlusion, vasopressin, and hypertonic saline dextran administration improve cerebral blood flow. Free radical scavenger alpha-phenyl-N-tert-butyl-nitrone (PBN) and cyclosporine-A (CsA) alleviate neuronal damage after global ischemia. Combining these treatments, we investigated neurological outcome after experimental cardiac arrest.

METHODS

: Thirty anesthetized piglets, randomly allocated into three groups, were subjected to 8 min of ventricular fibrillation followed by 5 min of closed-chest CPR. The combined treatment (CT) group received all the above-mentioned modalities; group B was treated with balloon occlusion and epinephrine; and group C had sham balloon occlusion with epinephrine. Indicators of oxidative stress (8-iso-PGF(2 alpha)), inflammation (15-keto-dihydro-PGF(2 alpha)), energy crisis (hypoxanthine and xanthine), and anoxia/hypoxia (lactate) were monitored in jugular bulb venous blood. Neurological outcome was evaluated 24 h after CPR.

RESULTS

: Restoration of spontaneous circulation (ROSC) was more rapidly achieved and neurological outcome was significantly better in the CT group, although there was no difference in coronary perfusion pressure between groups. The jugular venous PCO2 and cerebral oxygen extraction ratio were lower in the CT group at 5-15 min after ROSC. Jugular venous 8-iso-PGF(2 alpha) and hypoxanthine after ROSC were correlated to 24 h neurological outcome

CONCLUSIONS

: A combination of cerebral blood flow promoting measures and administration of alpha-phenyl-N-tert-butyl-nitrone and cyclosporine-A improved 24 h neurological outcome after 8 min of experimental normothermic cardiac arrest, indicating an ongoing neuronal injury in the reperfusion phase.

Cerebral resuscitation potentials for cardiac arrest

Permanent brain damage after cardiac arrest and resuscitation is determined by many factors, predominantly arrest (no-flow) time, cardiopulmonary resuscitation (low-flow) time, and temperature. Research since around 1970 into cardiopulmonary-cerebral resuscitation has attempted to mitigate the postischemic-anoxic encephalopathy. These efforts' results have recently shown outcome benefits as documented in clinically relevant outcome models in dogs and in clinical trials. Pharmacologic strategies have so far yielded relatively disappointing results. In a recent exploration of 14 drugs in dogs, only the antioxidant tempol administered at the start of prolonged cardiac arrest improved functional outcome in dogs. Cerebral blood flow promotion by hypertensive reperfusion and hemodilution has resulted in improved outcome in dogs, and brief hypertension after restoration of spontaneous circulation is associated with improved outcome in patients. Postarrest hypercoagulability of blood seems to yield to therapeutic thrombolysis, which is associated with improved cerebral outcome in animals and patients. In a clinically relevant dog outcome model, mild postarrest cerebral hypothermia (34 degrees C), initiated with reperfusion and continued for 12 hrs, combined with cerebral blood-flow promotion increased from 5 to >10 mins the previously longest normothermic no-flow time that could be reversed to complete cerebral recovery. Mild hypothermia by surface cooling after prolonged cardiac arrest in patients has been found effective in recent clinical studies in Australia and Europe. Preliminary data on the recent randomized study in Europe have been reported. For presently unresuscitable cardiac arrests, research since the 1980s in dog outcome models of prolonged exsanguination cardiac arrest has culminated in brain and organism preservation during cardiac arrest (no-flow) durations of up to 90 mins, perhaps 120 mins, at a tympanic temperature of 10 degrees C and complete recovery of function and normal histology. This "suspended animation for delayed resuscitation" strategy includes use of an aortic flush of cold saline (or preservation solution) within the first 5 mins of no flow. This strategy should also be explored for the larger number of patients with unresuscitable out-of-hospital cardiac arrests. Suspended animation for prolonged preservation of viability could buy time for transport and repair during hypothermic no flow followed by resuscitation, or it could serve as a bridge to prolonged cardiopulmonary bypass.

Low-dose Carbicarb improves cerebral outcome after asphyxial cardiac arrest in rats

STUDY OBJECTIVE

Controversy surrounds the use of buffers during cardiac arrest to correct acidosis. The objective of this study was to determine whether attenuation or neutralization of cerebral acidosis by Carbicarb alters hippocampal glutamate levels, neuronal cell death, and neurologic deficits after reperfusion from asphyxial cardiac arrest in rats.

METHODS

Rats were prospectively randomized to either a control (n=45), low-dose Carbicarb (LDC; 3 mL/kg, n=45), or high-dose Carbicarb (HDC; 6 mL/kg, n=45) group in a blinded fashion during resuscitation after 8 minutes of asphyxial cardiac arrest. Microdialysis was used to assess brain pH and glutamate. A neurologic deficit score and neuronal cell death in the hippocampus were determined at day 7.

RESULTS

Resuscitation was greatest in LDC rats (42/45) and least in HDC rats (28/45) versus that in control rats (34/45). Brain pH was higher in the LDC and HDC rats 10 minutes after resuscitation and remained higher than that of control rats for 120 minutes after resuscitation. Glutamate levels at 10 to 120 minutes after reperfusion were lowest in the LDC rats. LDC rats had the lowest neurologic deficit score (1+/-2) versus that of control rats (13+/-8) and HDC rats (19+/-6). Hippocampal neuronal cell death was lowest in LDC rats (30+/-20) versus that in control rats (86+/-47) and HDC rats (233+/-85).

CONCLUSION

LDC administered during resuscitation from asphyxial cardiac arrest attenuated acidosis, improved resuscitation, and reduced neurologic deficits and the number of dead hippocampal neurons. Neutralization of cerebral acidosis with HDC increased the number of dead hippocampal neurons and neurologic deficits after resuscitation from cardiac arrest in rats.

Managing the post-resuscitation patient in the field

The principal goal after successful resuscitation of a cardiac arrest patient is to maintain the patient's pulse and avoid a pulseless state. Of equal importance in the post-resuscitation patient are efforts to prevent myocardial dysfunction and increase the likelihood of a good neurologic outcome. To optimize cardiac and hemodynamic resuscitation, paramedics should obtain good background information, which could provide clues to factors contributing to the cardiac arrest, such as the use of certain drugs or being overdue for dialysis, and could aid in customizing therapy for rhythm disturbances and hemodynamic aberrations. Treatment of rhythm disturbances depends on the type of arrhythmia identified, the history of present illness, and the resuscitation efforts provided. Common post-resuscitation dysrhythmias are wide-complex tachycardia, narrow-complex tachycardia, and bradycardia. Optimizing neurologic resuscitation is difficult, but evidence suggests that hypertensive reperfusion, hemodilution, and mild hypothermia may be of benefit in improving neurologic outcome after resuscitation. Unfortunately, to date, no proven therapies are available to improve neurologic outcome after resuscitation from cardiac arrest.

Antioxidant Tempol enhances hypothermic cerebral preservation during prolonged cardiac arrest in dogs

The authors are systematically exploring pharmacologic preservation for temporarily unresuscitable exsanguination cardiac arrest in dogs. They hypothesized that the antioxidant Tempol improves cerebral outcome when added to aortic saline flush at the start of cardiac arrest. In study A, no drug (n = 8), Tempol 150 mg/kg (n = 4), or Tempol 300 mg/kg (n = 4) was added to 25 mL/kg saline flush at 24 degrees C (achieving mild cerebral hypothermia) at the start of 20-minute cardiac arrest. In study B, no drug (n = 8) or Tempol 300 mg/kg (n = 7) was added to 50 mL/kg saline flush at 2 degrees C (achieving moderate cerebral hypothermia) at the start of 40-minute cardiac arrest. Cardiac arrest was reversed with cardiopulmonary bypass. Mild hypothermia lasted for 12 hours, controlled ventilation was sustained to 24 hours, and intensive care was provided for up to 72 hours. In study A, overall performance category 1 or 2 (good outcome) was achieved in all eight dogs treated with Tempol compared with three of eight dogs in the control group ( P = 0.03). In study B, good outcome was achieved in all seven dogs treated with Tempol versus only two of 8 dogs in the control group ( P = 0.007). In both studies, neurologic deficit scores were significantly better in the Tempol group, but not total histologic damage scores. At 72 hours, electron paramagnetic resonance spectroscopy of Tempol revealed direct evidence for its presence in the brain. Single- and double-strand DNA damage, nitrotyrosine immunostaining, total antioxidant reserve, and ascorbate acid levels were similar between groups, and thiol levels were decreased after Tempol in study B. The authors conclude that when added to aortic saline flush at the start of prolonged cardiac arrest, the antioxidant Tempol can enhance mild or moderate hypothermic cerebral preservation in terms of improved functional outcome. The mechanisms involved in this beneficial effect need further clarification.

Fructose-1,6-bisphosphate and MK-801 by aortic arch flush for cerebral preservation during exsanguination cardiac arrest of 20 min in dogs. An exploratory study

In our exsanguination cardiac arrest (CA) outcome model in dogs we are systematically exploring suspended animation (SA), i.e. preservation of brain and heart immediately after the onset of CA to enable transport and resuscitative surgery during CA, followed by delayed resuscitation. We have shown in dogs that inducing moderate cerebral hypothermia with an aortic arch flush of 500 ml normal saline solution at 4 degrees C, at start of CA 20 min no-flow, leads to normal functional outcome. We hypothesized that, using the same model, but with the saline flush at 24 degrees C inducing minimal cerebral hypothermia (which would be more readily available in the field), adding either fructose-1,6-bisphosphate (FBP, a more efficient energy substrate) or MK-801 (an N-methyl-D-aspartate (NMDA) receptor blocker) would also achieve normal functional outcome. Dogs (range 19-30 kg) were exsanguinated over 5 min to CA of 20 min no-flow, and resuscitated by closed-chest cardiopulmonary bypass (CPB). They received assisted circulation to 2 h, mild systemic hypothermia (34 degrees C) post-CA to 12 h, controlled ventilation to 20 h, and intensive care to 72 h. At CA 2 min, the dogs received an aortic arch flush of 500 ml saline at 24 degrees C by a balloon-tipped catheter, inserted through the femoral artery (control group, n=6). In the FBP group (n=5), FBP (total 1440 or 4090 mg/kg) was given by flush and with reperfusion. In the MK-801 group (n=5), MK-801 (2, 4, or 8 mg/kg) was given by flush and with reperfusion. Outcome was assessed in terms of overall performance categories (OPC 1, normal; 2, moderate disability; 3, severe disability; 4, coma; 5, brain death or death), neurologic deficit scores (NDS 0-10%, normal; 100%, brain death), and brain histologic damage scores (HDS, total HDS 0, no damage; >100, extensive damage; 1064, maximal damage). In the control group, one dog achieved OPC 2, one OPC 3, and four OPC 4; in the FBP group, two dogs achieved OPC 3, and three OPC 4; in the MK-801 group, two dogs achieved OPC 3, and three OPC 4 (P=1.0). Median NDS were 62% (range 8-67) in the control group; 55% (range 34-66) in the FBP group; and 50% (range 26-59) in the MK-801 group (P=0.2). Median total HDS were 130 (range 56-140) in the control group; 96 (range 64-104) in the FBP group; and 80 (range 34-122) in the MK-801 group (P=0.2). There was no difference in regional HDS between groups. We conclude that neither FBP nor MK-801 by aortic arch flush at the start of CA, plus an additional i.v. infusion of the same drug during reperfusion, can provide cerebral preservation during CA 20 min no-flow. Other drugs and drug-combinations should be tested with this model in search for a breakthrough effect.

Brain energetics of cardiopulmonary cerebral resuscitation

Recovery of normal brain energetic conditions during and after resuscitation from cardiac arrest is critical for survival and good neurologic outcome. This review emphasizes the glucose-driven metabolic processes during and after ischemia and on the post-resuscitation development of secondary energy derangements. It also explores some potential therapeutic interventions designed to attenuate these energy derangements. The article summarizes some bench research and is not intended to provide treatment strategies for clinical application.

The effect of mild hypothermia and induced hypertension on long term survival rate and neurological outcome after asphyxial cardiac arrest in rats

STUDY OBJECTIVE

we studied the long-term effect of a combined treatment with resuscitative mild hypothermia and induced hypertension on survival rate and neurological outcome after asphyxial cardiac arrest (CA) in rats.

METHODS

36 male Wistar rats, were randomised into three groups: Group I (n=10): anaesthetised with halothane and N(2)O/O(2) (70/30%) had vessel cannulation but no asphyxial CA; mechanical ventilation was continued to 1 h. Group II (n=13): under the same anaesthetic conditions and vessel cannulation, was subjected to asphyxial CA of 8 min, reversed by brief external heart massage and followed by mechanical ventilation to 1 h post restoration of spontaneous circulation (ROSC). Group III (n=13): received the same insult and resuscitation as described in group II, but in contrast to the previous group, a combination treatment of hypothermia (34 degrees C) and induced hypertension was started immediately after ROSC and maintained for 60 min ROSC. Survival rate and neurological deficit (ND) scores were determined before arrest, at 2 and 24 h, and each 24-h up to 4 weeks after ROSC.

RESULTS

Baseline variables were the same in the three groups. Comparison of the asphyxial CA groups (groups II and III), showed an increased, although not statistically significant, survival rate at 72 h after ROSC in group III, and it became highly significant at 4 weeks after ROSC. The ND scores were the same in both asphyxial CA groups (groups II and III).

CONCLUSIONS

Resuscitative mild hypothermia and induced hypertension after asphyxial CA in rats is associated with a better survival rate. This beneficial effect persisted for 4 weeks after ROSC.

Improved cerebral blood supply and oxygenation by aortic balloon occlusion combined with intra-aortic vasopressin administration during experimental cardiopulmonary resuscitation

BACKGROUND

Intravenous administration of vasopressin during cardiopulmonary resuscitation (CPR) has been shown to improve myocardial and cerebral blood flow. Aortic balloon occlusion during CPR may also augment myocardial and cerebral blood flow and can be used as a central route for the administration of resuscitative drugs. We hypothesized that, as compared with intravenously administered vasopressin, the administration of this drug above the site of an aortic balloon occlusion would result in a greater increase in cerebral perfusion and oxygenation during CPR and after restoration of spontaneous circulation (ROSC).

METHODS

Twenty piglets were subjected to 5 min of ventricular fibrillation followed by 8 min of closed-chest CPR and were treated with 0.4 U kg(-1) boluses of vasopressin intravenously (the IV-vasopressin group with sham aortic balloon) or above the site for an aortic balloon occlusion (the balloon-vasopressin group). The aortic balloon catheter was inflated in the latter group 1 min after commencement of CPR and was deflated within 1 min after ROSC. Systemic blood pressures, cerebral cortical blood flow, cerebral tissue pH and PCO2 were monitored continuously and the cerebral oxygen extraction ratio was calculated.

RESULTS

During CPR, arterial blood pressure and cerebral perfusion pressure were greater in the balloon-vasopressin group, as compared with the IV-vasopressin group. These pressures did not differ between the groups after ROSC. Cerebral cortical blood flow was not significantly greater in the balloon-vasopressin group during CPR, whereas significantly higher cortical blood flow levels were recorded after ROSC. Cerebral tissue pH decreased in the IV-vasopressin group during the post-resuscitation hypoperfusion period. In contrast, decreasing pressures during the hypoperfusion period did not result in increasing tissue acidosis in the balloon-vasopressin group.

CONCLUSIONS

During CPR, intra-aortic vasopressin combined with aortic balloon occlusion resulted in significantly greater perfusion pressures but not in greater cerebral cortical blood flow. After ROSC, however, a greater increase in cortical blood flow was recorded in the balloon-vasopressin group, even though the aortic balloon was deflated and perfusion pressures did not differ between the groups. This suggests that vasopressin predominantly gives vasoconstrictive effects on cerebral cortical vessels during CPR, but results in cerebral cortical vasodilatation after ROSC.

Cardiopulmonary and cerebral resuscitation

The future of cardiopulmonary resuscitation lies in new technologies for monitoring and generating vital organ perfusion during cardiac arrest and the post-resuscitation phase and in pharmacologic agents that will enhance ROSC and reverse ischemia-reperfusion injury. ROSC is the first step toward survival, so interventions that improve ROSC deserve further investigation. Long-term survival with good neurologic recovery is the critical endpoint. Interventions recommended for clinical practice must therefore demonstrate improved long-term survival. The resources required to provide many of the interventions discussed in this article, principally invasive perfusion technologies, cannot be justified unless there is clear benefit. The allocation of such resources to provide intensive resuscitation and post-resuscitation support will need to be addressed from medical and societal viewpoints.

Thiopental combination treatments for cerebral resuscitation after prolonged cardiac arrest in dogs. Exploratory outcome study

We postulate that mitigating the multifactorial pathogenesis of postischemic encephalopathy requires multifaceted treatments. In preparation for expensive definitive studies, we are reporting here the results of small exploratory series, compared with historic controls with the same model. We hypothesized that the brain damage mitigating effect of mild hypothermia after cardiac arrest can be enhanced with thiopental loading, and even more so with the further addition of phenytoin and methylprednisolone. Twenty-four dogs (four groups of six dogs each) received VF 12.5 min no-flow, reversed with brief cardiopulmonary bypass (CPB), controlled ventilation to 20 h, and intensive care to 96 h. Group 1 with normothermia throughout and randomized group 2 with mild hypothermia (from reperfusion to 2 h) were controls. Then, group 3 received in addition, thiopental 90 mg/kg i.v. over the first 6 h. Then, group 4 received, in addition to group 2 treatment, thiopental 30 mg/kg i.v. over the first 90 min (because the larger dose had produced cardiopulmonary complications), plus phenytoin 15 mg/kg i.v. at 15 min after reperfusion, and methylprednisolone 130 mg/kg i.v. over 20 h. All dogs survived. Best overall performance categories (OPC) achieved (OPC 1 = normal, OPC 5 = brain death) were better in group 2 than group 1 (< 0.05) and numerically better in groups 3 or 4 than in groups 1 or 2. Good cerebral outcome (OPC 1 or 2) was achieved by all six dogs only in group 4 (P < 0.05 group 4 vs. 2). Best NDS were 44 +/- 3% in group 1; 20 +/- 14% in group 2 (P = 0.002); 21 +/- 15% in group 3 (NS vs. group 2); and 7 +/- 8% in group 4 (P = 0.08 vs. group 2). Total brain histologic damage scores (HDS) at 96 h were 156 +/- 38 in group 1; 81 +/- 12 in group 2 (P < 0.001 vs. group 1); 53 +/- 25 in group 3 (P = 0.02 vs. group 2); and 48 +/- 5 in group 4 (P = 0.02 vs. group 2). We conclude that after prolonged cardiac arrest, the already established brain damage mitigating effect of mild immediate postarrest hypothermia might be enhanced by thiopental, and perhaps then further enhanced by adding phenytoin and methylprednisolone.

On the future of reanimatology

This article is adapted from a presentation given at the 1999 SAEM annual meeting by Dr. Peter Safar. Dr. Safar has been involved in resuscitation research for 44 years, and is a distinguished professor and past initiating chairman of the Department of Anesthesiology and Critical Care Medicine at the University of Pittsburgh. He is the founder and director of the Safar Center for Resuscitation Research at the University of Pittsburgh, and has been the research mentor of many critical care and emergency medicine research fellows. Here he presents a brief history of past accomplishments, recent findings, and future potentials for resuscitation research. Additional advances in resuscitation, from acute terminal states and clinical death, will build upon the lessons learned from the history of reanimatology, including optimal delivery by emergency medical services of already documented cardiopulmonary cerebral resuscitation, basic-advanced-prolonged life support, and future scientific breakthroughs. Current controversies, such as how to best educate the public in life-supporting first aid, how to restore normotensive spontaneous circulation after cardiac arrest, how to rapidly induce mild hypothermia for cerebral protection, and how to minimize secondary insult after cerebral ischemia, are discussed, and must be resolved if advances are to be made. Dr. Safar also summarizes future technologies already under preliminary investigation, such as ultra-advanced life support for reversing prolonged cardiac arrest, extending the "golden hour" of shock tolerance, and suspended animation for delayed resuscitation.

Hypothermic aortic arch flush for preservation during exsanguination cardiac arrest of 15 minutes in dogs

BACKGROUND

Trauma victims rarely survive cardiac arrest from exsanguination. Survivors may suffer neurologic damage. Our hypothesis was that a hypothermic aortic arch flush of 500 mL of isotonic saline solution at 4 degrees C, compared with 24 degrees C (room temperature), administered at the start of prolonged exsanguination cardiac arrest (CA) would improve functional neurologic outcome in dogs.

METHODS

Seventeen male hunting dogs were prepared under light N2O-halothane anesthesia. The animals were randomized into two groups: group I (n = 9) received 4 degrees C isotonic saline flush and group II (n = 6) received 24 degrees C flush. Two additional dogs received no flush. While spontaneously breathing, the dogs underwent normothermic (tympanic membrane temperature [Ttm] = 37.5 degrees C) exsanguination over 5 minutes to cardiac arrest, assured by electric induction of ventricular fibrillation. After 2 minutes of arrest, the flush was administered over 1 minute into the aortic arch by means of a 13 French balloon-tipped catheter inserted by means of the femoral artery. After 15 minutes of CA, resuscitation was with closed-chest cardiopulmonary bypass, return of shed blood, and defibrillation. For the first 12 hours after CA, core temperature was maintained at 34 degrees C. Mechanical ventilation was continued to 20 hours and intensive care to 72 hours, when final evaluation and perfusion-fixation killing for brain histologic damage scoring were performed.

RESULTS

Three dogs in group I were excluded because of extracerebral complications. All 14 dogs that followed protocol survived. During CA, the Ttm decreased to 33.6 +/- 1.2 degrees C in group I and 35.9 +/- 0.4 degrees C in group II (p = 0.002). At 72 hours, in group I, all dogs achieved an overall performance category (OPC) of 1 (normal). In group II, 1 dog was OPC 2 (moderate disability), 3 dogs were OPC 3 (severe disability), and 2 dogs were OPC 4 (coma). Both dogs without flush were OPC 4. Neurologic deficit scores (NDS 0% = normal, 100% = brain death) were 1 +/- 1% in group I and 41 +/- 12% in group II (p < 0.05). The two dogs without flush achieved an NDS of 47% and 59%. Total brain histologic damage scores were 35 +/- 28 in group I and 82 +/- 17 in group II (p < 0.01); and 124 and 200 in the nonflushed dogs.

CONCLUSION

At the start of 15 minutes of exsanguination cardiac arrest in dogs, hypothermic aortic arch flush allows resuscitation to survival with normal neurologic function and histologically almost clean brains.

Mild protective and resuscitative hypothermia for asphyxial cardiac arrest in rats

It has been shown in dogs that mild hypothermia (34 degrees C) during or immediately after ventricular fibrillation cardiac arrest can improve cerebral outcome. The effect of mild hypothermia on outcome after 8 minutes of asphyxiation (5 minutes' cardiac arrest) was studied for the first time in rats. Restoration of spontaneous circulation was with external cardiopulmonary resuscitation and observation to 72 hours. Three groups of 10 rats each were studied. At 72 hours postarrest, compared with the normothermic control group 1, final overall performance categories (OPC) and neurological deficit scores (NDS) were numerically better in the resuscitative (post-arrest) hypothermia group 2 and significantly better in the protective (pre-intra-arrest) hypothermia group 3 (P < .05). Total brain histopathological damage scores (HDS) were 17 +/- 5 in group 1, 14 +/- 6 in group 2 (NS), and 6 +/- 2 in group 3 (P < .001 versus group 1). HDS correlated with OPC (r = .6, P < .05) and NDS (r = .7, P < .05). Mild hypothermia improved cerebral outcome after asphyxial cardiac arrest in rats, more when induced before than after arrest. The model's insult is within the therapeutic window, which makes it also suitable for screening other cerebral resuscitation potentials.