Detoxification with hemabsorption after cardiac arrest does not improve neurologic recovery. Review and outcome study in dogs

We and others hypothesized that noxious substances released after prolonged cardiac arrest from malfunctioning liver, kidneys, or intestine (e.g. bacterial toxins, aromatic amino acids), might hamper recovery of the brain. The highly detoxifying effect of hemabsorption (i.e. hemoperfusion) with microencapsulated activated carbon has been demonstrated in other diseases. We used our dog model of ventricular fibrillation cardiac arrest of 15 min (n = 2 x 4) or 12.5 min (n = 2 x 6), reversed by brief (high flow) cardiopulmonary bypass (CPB). In half of the dogs in each insult group, a charcoal filter (HemoKart) was inserted into the circuit of CPB at low flow, from start of reperfusion to 4 h. Intermittent positive pressure ventilation was to 20 h and intensive care to 96 h after cardiac arrest. Bacterial blood cultures were positive in most of the dogs in both groups 30 min to 20 h after cardiac arrest (but not later) and were uninfluenced by hemabsorption. In the control groups to 4 h after cardiac arrest, serum levels of potentially injurious aromatic amino acids (e.g. phenylalanine, tyrosine) and of branched-chain/aromatic amino acid ratios, remained unchanged. From 12 to 48 h after cardiac arrest, aromatic amino acid levels increased (worsened). The branched-chain/aromatic amino acid ratios changed accordingly in the opposite direction. In the hemabsorption groups to 4 h after cardiac arrest, all amino acid levels were reduced, aromatic amino acids more so than branched-chain amino acids, thus increasing (improving) the ratio, compared with controls (P < 0.01). There was no group difference after discontinuance of hemabsorption at 4 h. Outcome in terms of overall performance categories and neurologic deficit scores from 24 to 96 h and brain histopathologic damage scores 96 h after cardiac arrest, were not significantly different between groups. The lack of a beneficial outcome effect of hemabsorption to 4 h after cardiac arrest does not support the self-intoxication hypothesis. The amino acid levels later after cardiac arrest suggest that more prolonged hemabsorption and more encompassing detoxification treatments, such as plasma phoresis or total body blood washout, might be evaluated.

Cardiovascular function and neurologic outcome after cardiac arrest in dogs. The cardiovascular post-resuscitation syndrome

We studied cardiovascular changes and neurologic outcome at 72 h in 42 healthy dogs after normothermic ventricular fibrillation cardiac arrest (no blood flow) of 7.5, 10, or 12.5 min duration, reversed by standard external cardiopulmonary resuscitation (CPR) (< or = 10 min) and followed by controlled ventilation to 20 h and intensive care to 72 h. We found no difference in resuscitability, mortality, neurologic deficit scores, or overall performance categories between the three insult groups. There was no major pulmonary dysfunction. During controlled normotension post-CPR, all dogs presented a transient reduction in cardiac output. In the 12.5-min cardiac arrest group the decrease in cardiac output persisted beyond 12 h post-CPR (P < 0.01) and was associated with more severe arrhythmias (P < 0.05) and worse morphologic myocardial damage (P < 0.01). Both cardiac and neurologic malfunction at 72 h correlated with arrest time. Only cardiac malfunction correlated with CPR time. Neurologic recovery correlated with mild (inadvertent) pre-arrest hypothermia, diastolic arterial pressure during CPR and absence of cardiovascular impairment at 12 h post-CPR. We conclude that prolonged cardiac arrest in previously healthy dogs is followed by persistent cardiovascular derangements that correlate with impaired neurologic recovery.

Cerebral resuscitation after cardiac arrest: research initiatives and future directions

At present, fewer than 10% of cardiopulmonary resuscitation (CPR) attempts prehospital or in hospitals outside special care units result in survival without brain damage. Minimizing response times and optimizing CPR performance would improve results. A breakthrough, however, can be expected to occur only when cerebral resuscitation research has achieved consistent conscious survival after normothermic cardiac arrest (no flow) times of not only five minutes but up to ten minutes. Most cerebral neurons and cardiac myocytes tolerate normothermic ischemic anoxia of up to 20 minutes. Particularly vulnerable neurons die, in part, because of the complex secondary post-reflow derangements in vital organs (the postresuscitation syndrome) which can be mitigated. Brain-orientation of CPR led to the cardiopulmonary-cerebral resuscitation (CPCR) system of basic, advanced, and prolonged life support. In large animal models with cardiac arrest of 10 to 15 minutes, external CPR, life support of at least three days, and outcome evaluation, the numbers of conscious survivors (although not with normal brain histology) have been increased with more effective reperfusion by open-chest CPR or emergency cardiopulmonary bypass, an early hypertensive bout, early post-arrest calcium entry blocker therapy, or mild cerebral hypothermia (34 C) immediately following cardiac arrest. More than ten drug treatments evaluated have not reproducibly mitigated brain damage in such animal models. Controlled clinical trials of novel CPCR treatments reveal feasibility and side effects but, in the absence of a breakthrough effect, may not discriminate between a treatment's ability to mitigate brain damage in selected cases and the absence of any treatment effect. More intensified, coordinated, multicenter cerebral resuscitation research is justified.

Systematic development of cerebral resuscitation after cardiac arrest. Three promising treatments: cardiopulmonary bypass, hypertensive hemodilution, and mild hypothermia

Since 1970 we have investigated postischemic anoxic encephalopathy and potential treatments for cerebral resuscitation after cardiac arrest by cardiopulmonary-cerebral resuscitation (CPCR). The post-resuscitation syndrome has been studied at the levels of cell, organ, organism and community. Short-term and long-term models in rats, dogs, and monkeys have been developed, and an international multicenter randomized clinical trial mechanism was established. Clinical studies disproved the 5-min limit of reversible cardiac arrest and yielded other valuable data on treatments and prognostication. Thiopental loading or calcium entry blocker therapy (lidoflazine) gave no significant improvement in patients. Free radical scavengers are under investigation in the laboratory. We hypothesize that post-arrest perfusion failure and necrotizing cascades require etiology-specific combination treatments. Standard (control) therapy in a current dog model of cardiac arrest (no flow) of 12.5-20 min, reperfusion with cardiopulmonary bypass, and intensive care for 72-96 h has consistently resulted in survival with brain damage. After ventricular-fibrillation (VF) arrest of 17 min, moderate hypothermia (28-32 degrees C) inconsistently improved cerebral outcome. After VF arrest of 12.5 min, hypertension plus hemodilution normalized the local (multifocal) cerebral hypoperfusion post-arrest and, again, inconsistently improved cerebral outcome. Additional mild hypothermia (34-36 degrees C), however, consistently improved cerebral outcome, whether induced before or during and after arrest.

Simpson's paradox and clinical trials: what you find is not necessarily what you prove

Expensive clinical trials have become the gold standard for evaluating the efficacy of promising new therapeutic agents. Full exploration of the collected data is routine to maximize the yield of the information available. However, potential methodologic flaws in these extensive analyses may not be appreciated by investigators or readers. One such problem with subgroup analyses is discussed, using hypothetical examples and data from a recently completed clinical trial of brain resuscitation as illustrations.

Beneficial effect of mild hypothermia and detrimental effect of deep hypothermia after cardiac arrest in dogs

BACKGROUND AND PURPOSE

Mild cerebral hypothermia (34 degrees C) induced immediately after cardiac arrest improves outcome. Deep postarrest hypothermia (15 degrees C) has not been studied.

METHODS

We used our dog model of normothermic ventricular fibrillation (no blood flow) of 12.5 minutes, reperfusion by brief cardiopulmonary bypass, controlled ventilation to 20 hours, and intensive care to 72 hours. Head surface cooling and bypass cooling were performed from start of reperfusion to 1 hour. Five groups of six dogs each were compared: group I, normothermic controls; group II, deep hypothermia (15 degrees C); group III, moderate hypothermia (30 degrees C); group IV, mild hypothermia (34 degrees C); and group V, mild hypothermia with head surface cooling begun during no flow.

RESULTS

In control group I, five dogs remained comatose (overall performance category [OPC] 4) and one severely disabled (OPC 3). In group II, four dogs achieved OPC 4 and two dogs OPC 3 (NS versus group I). Compared with group I, OPCs were better in group III (p less than 0.05), group IV (p less than 0.05), and group V (p less than 0.05). Neurological deficit scores were also better in groups III, IV, and V than in groups I or II (p less than 0.05). Total brain histological damage scores were better in group III (p = 0.02), group IV (p = 0.06), and group V (p less than 0.05) than in group I. In group II, OPC and neurological deficit scores were the same and histological damage scores numerically worse than in group I and all were worse than in groups III, IV, and V (p less than 0.05). Cardiovascular complications and myocardial morphological damage in groups II and III were worse than in groups I, IV, and V (p less than 0.05).

CONCLUSIONS

Mild or moderate cerebral hypothermia induced immediately after cardiac arrest improves cerebral outcome, more likely when initiated during arrest, whereas deep postarrest hypothermia can worsen cerebral and cardiac outcome.

Multifocal cerebral blood flow by Xe-CT and global cerebral metabolism after prolonged cardiac arrest in dogs. Reperfusion with open-chest CPR or cardiopulmonary bypass

Using the stable xenon-enhanced computed tomography (Xe-CT) method in dogs, we studied local, regional and global cerebral blood flow (LCBF, rCBF and gCBF) in two sham experiments and nine cardiac arrest experiments. Within the same experiments without arrest, gCBF and rCBF values were reproducible and stable. LCBF values varied over time. In group I (n = 4), ventricular fibrillation cardiac arrest (no blood flow) of 10 min was reversed by open-chest cardiopulmonary resuscitation (CPR). In group II (n = 5), ventricular fibrillation cardiac arrest of 12.5 min was reversed by brief closed-chest cardiopulmonary bypass. This was followed by controlled ventilation, normotension, normoxia, normocarbia and normothermia to 4 h (n = 7) or 20 h (n = 2) postarrest. The postarrest CBF patterns were similar in both groups. Open-chest CPR during ventricular fibrillation generated near-baseline gCBF and lower LCBF ranges. During postarrest spontaneous circulation, transient diffuse hyperemia was without low-flow regions, longer in brain stem and basal ganglia than in neocortex. During delayed hypoperfusion at 1-4 h postarrest (n = 9), mean gCBF was 44-60% baseline, rCBF in primarily gray matter regions was 15-49 ml/100 cm3 per min and LCBF voxels with trickle-flow and low-flow values, in percent of CT cut area, were increased over baseline. Global CMRO2 (n = 3 of group II) recovered to near baseline values between 1 and 4 h postarrest, while gCBF and O2 delivery were about 50% baseline (mismatching of O2 uptake and O2 delivery).

Dynamic heterogeneity of cerebral hypoperfusion after prolonged cardiac arrest in dogs measured by the stable xenon/CT technique: a preliminary study

After prolonged cardiac arrest and reperfusion, global cerebral blood flow (gCBF) is decreased to about 50% normal for many hours. Measurement of gCBF does not reveal regional variation of flow or permit testing of hypotheses involving multifocal no-flow or low-flow areas. We employed the noninvasive stable Xenon-enhanced Computerized Tomography (Xe/CT) local CBF (LCBF) method for use in dogs before and after ventricular fibrillation (VF) cardiac arrest of 10 min. This was followed by external cardiopulmonary resuscitation (CPR) and control of cardiovascular pulmonary variables to 7 h postarrest. In a sham (no arrest) experiment, the three CT levels studied showed normal regional heterogeneity of LCBF values, all between 10 and 75 ml/100 cm3 per min for white matter and 20 and 130 ml/100 cm3 per min for gray matter. In four preliminary CPR experiments, the expected global hyperemia at 15 min after arrest, was followed by hypoperfusion with gCBF reduced to about 50% control and increased heterogeneity of LCBF. Trickle flow areas (LCBF less than 10 ml/100 cm3 per min) not present prearrest, were interspersed among regions of low, normal, or even high flow. Regions of 125-500 mm3 with trickle flow or higher flows, in different areas at different times, involving deep and superficial structures migrated and persisted to 6 h, with gCBF remaining low. These preliminary results suggest: no initial no-reflow foci (less than 10 ml/100 cm3 per min) larger than 125 mm3 persisting through the initial global hyperemic phase; delayed multifocal hypoperfusion more severe than suggested by gCBF measurements; and trickle flow areas caused by dynamic factors.

Hypertension with hemodilution prevents multifocal cerebral hypoperfusion after cardiac arrest in dogs

BACKGROUND

Improved neurological outcome with postarrest hypertensive hemodilution in an earlier study could be the result of more homogeneous cerebral perfusion and improved O2 delivery. We explored global, regional, and local cerebral blood flow by stable xenon-enhanced computed tomography and global cerebral metabolism in our dog cardiac arrest model.

METHODS

Ventricular fibrillation cardiac arrest of 12.5 minutes was reversed by brief cardiopulmonary bypass, followed by life support to 4 hours postarrest. We compared control group I (n = 5; mean arterial blood pressure, 100 mm Hg; hematocrit, greater than or equal to 35%) with immediately postarrest reflow-promoted group II (n = 5; mean arterial blood pressure, 140-110 mm Hg; hypervolemic hemodilution with plasma substitute to hematocrit, 20-25%).

RESULTS

After initial hyperemia in both groups, during the "delayed hypoperfusion phase" at 1-4 hours postarrest, global cerebral blood flow was 51-60% of baseline in group I versus 85-100% of baseline in group II (p less than 0.01). Percentages of brain tissue voxels with no flow, trickle flow, or low flow were lower (p less than 0.01) and mean regional cerebral blood flow values were higher in group II (p less than 0.01). Global cerebral oxygen uptake recovered to near baseline values at 3-4 hours postarrest in both groups. Postarrest arterial O2 content, however, in hemodiluted group II was 40-50% of that in group I. Thus, the O2 uptake/delivery ratio was increased (worsened) in both groups at 2-4 hours postarrest.

CONCLUSIONS

After prolonged cardiac arrest, immediately induced moderate hypertensive hemodilution to hematocrit 20-25% can normalize cerebral blood flow patterns (improve homogeneity of cerebral perfusion), but does not improve cerebral O2 delivery, since the flow benefit is offset by decreased arterial O2 content. Individualized titration of hematocrit or hemodilution with acellular O2 carrying blood substitute (stroma-free hemoglobin or fluorocarbon solution) would be required to improve O2 uptake/delivery ratio.

National medical response to mass disasters in the United States. Are we prepared?

Preparing for a resuscitation response to mass disasters, such as major earthquakes or industrial disasters, requires revisions of present local, regional, and national disaster plans. These should include the following: (1) life-supporting first aid and basic rescue capability of the lay public; (2) advanced trauma life support and advanced (heavy) rescue capability brought quickly to the scene from local and surrounding (regional) emergency medical services systems; and (3) trauma hospitals sending medical resuscitation teams to, and receiving casualties from, the disaster scene for resuscitative surgery and definitive care. Local and regional everyday emergency medical services systems would respond first. The armed forces should help, at least for transport and security. We propose that the National Disaster Medical System replace its civil defense model with an emergency medical services model, designed to mobilize rapid support for local emergency medical services systems from regional, state, and national resources. Coordination should be by one federal agency, such as the Federal Emergency Management Agency, which, however, needs to focus more on resuscitation through physician input.

External cardiopulmonary resuscitation preserves brain viability after prolonged cardiac arrest in dogs

Standard external cardiopulmonary resuscitation (CPR) steps A-B-C produce a low blood flow that may or may not preserve brain viability during prolonged cardiac arrest. A dog model was used with ventricular fibrillation (VF) of 20 minutes, reperfusion with brief cardiopulmonary bypass, controlled ventilation to 20 hours, and intensive care to 96 hours. A retrospective comparison was made of the results of one series, now called "group I" (n = 10)--which received CPR basic life support interposed from VF 10 to 15 minutes, and CPR advanced life support with epinephrine (without defibrillation) from VF 15 to 20 minutes--to the results of another series, now "control group II" (n = 10)--which received VF no flow (no CPR) for 20 minutes. All 20 dogs within protocol were resuscitated. All 10 of group I and 7 of 10 of group II survived to 96 hours. Pupillary light reflex returned after the start of cardiopulmonary bypass at 7.7 +/- 3.7 minutes in CPR group I, versus 16.3 +/- 7.4 minutes in control group II (P = .032). At 96 hours postarrest, final overall performance categories (1, normal; 5, brain death) were better in group I. Six of 10 dogs achieved normality (overall performance category 1) in group I, as compared with none of 10 in group II (P = .004). Final neurologic deficit score (0%, best; 100% worst) was lower (better) in group I (15% +/- 20%) than in group II (51% +/- 6%; P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Profound hypothermia (less than 10 degrees C) compared with deep hypothermia (15 degrees C) improves neurologic outcome in dogs after two hours' circulatory arrest induced to enable resuscitative surgery

Deaths from uncontrollable hemorrhage might be prevented by arresting the circulation under protective hypothermia to allow resuscitative surgery to repair these injuries in a bloodless field. We have shown previously that in hemorrhagic shock, circulatory arrest of 60 minutes under deep hypothermia (tympanic membrane temperature, Ttm = 15 degrees C) was the maximum duration of arrest that allowed normal brain recovery. We hypothesize that profound cerebral hypothermia (Ttm less than 10 degrees C) could extend the duration of safe circulatory arrest. In pilot experiments, we found that the cardiopulmonary system did not tolerate arrest at a core (esophageal) temperature (Tes) of less than 10 degrees C. Twenty-two dogs underwent 30-minute hemorrhagic shock (mean arterial pressure 40 mm Hg), rapid cooling by cardiopulmonary bypass (CPB), blood washout to a hematocrit of less than 10%, and circulatory arrest of 2 hours. In deep hypothermia group 1 (n = 10), Ttm was maintained at 15 degrees C during arrest. In profound hypothermia group 2 (n = 12), during cooling with CPB, the head was immersed in ice water, which decreased Ttm to 4 degrees-7 degrees C. The Tes was 10 degrees C in all dogs during arrest. Reperfusion and rewarming were by CPB for 2 hours. Controlled ventilation was to 24 hours, intensive care to 72 hours. In the 20 dogs that followed protocol, best neurologic deficit scores (0% = normal, 100% = brain death) at 24-72 hours were 23% +/- 19% in group 1 and 12% +/- 8% in group 2 (p = 0.15). Overall performance categories and histologic damage scores were significantly better in group 2 (p = 0.04 and p less than 0.001, respectively). We conclude that profound cerebral hypothermia with CPB plus ice water immersion of the head can extend the brain's tolerance of therapeutic circulatory arrest beyond that achieved with deep hypothermia.

Monkey model of severe volume-controlled hemorrhagic shock with resuscitation to outcome

Seventeen cynomolgus monkeys under N2O analgesia and sedation were subjected to severe volume-controlled hemorrhagic shock (shed blood volume of 21 or 27 ml/kg). In 12 monkeys, resuscitation was started after increasing periods of hemorrhagic shock from 30 min to 5 h. In five additional monkeys, volume-controlled hemorrhage was modified at hemorrhagic shock 30 min to control MAP at 30 mmHg: resuscitation was started at hemorrhagic shock of 2 h. A clinically relevant resuscitation protocol consisted of a field phase from 0 to 6 h (lactated Ringer's solution, spontaneous breathing), and a hospital intensive care phase from 6 h to 48 h (blood, lactated Ringer's solution to mean arterial pressure (MAP) greater than or equal to 70 mmHg, controlled ventilation, advanced life support). Fifteen of the 17 monkeys survived. After outcome evaluation at 4 or 7 days, the eight monkeys with "moderate insult" had only transient functional impairment. Of the nine with "severe insult," three showed signs of moderate transient non-oliguric renal failure. Eight of the 12 monkeys studied morphologically showed scattered liver cell damage. None of the monkeys developed pulmonary dysfunction or functional or morphologic evidence of cerebral damage. This study establishes a new hemorrhagic shock-resuscitation model simulating field-to-hospital life support. Severe hemorrhagic shock with MAP 30-40 mmHg for 90-120 min (without trauma or sepsis) can lead to complete functional recovery after transient malfunction of liver and kidneys.

Effects of U74006F on multifocal cerebral blood flow and metabolism after cardiac arrest in dogs

Lipid peroxidation reactions during reperfusion after cardiac arrest may contribute to postischemic cerebral hypoperfusion, which in turn can contribute to permanent neurological dysfunction. We designed this study to determine whether the aminosteroid U74006F, a putative inhibitor of lipid peroxidation, mitigates cerebral multifocal hypoperfusion after cardiac arrest. We used our established dog model of ventricular fibrillation cardiac arrest (no blood flow) of 12.5 minutes, reperfusion by cardiopulmonary bypass of less than or equal to 5 minutes, and control of extracerebral variables during 4 hours postarrest. Cerebral blood flow was monitored by the stable xenon computed tomography method. Changes in cerebral oxygen consumption were obtained from mean blood flow values of coronal slices and the cerebral arteriovenous (sagittal sinus) oxygen content difference. A treatment group (n = 5) received U74006F starting with reperfusion (1.5 mg/kg i.a. plus 1.5 mg/kg i.v.) and three additional (graded) doses over 4 hours (total dose 4.5, 7.5, or 14.5 mg/kg). The U74006F-treated group showed the same postarrest transient hyperemia and protracted hypoperfusion in terms of global (computed tomography slice), regional, and local (multifocal) cerebral blood flow values and the same global cerebral oxygen consumption pattern as a concurrent control group (n = 5). At 1-4 hours postarrest, in both groups there was mismatching of global cerebral oxygen consumption, which reached baseline values, in relation to global cerebral blood flow and oxygen delivery, which remained at 50% of baseline. We conclude that treatment with U74006F after prolonged cardiac arrest causes no deleterious side effects and does not seem to alter multifocal postarrest cerebral blood flow and oxygen consumption.

Improved survival of hemorrhagic shock with oxygen and hypothermia in rats

A previously established model in awake rats of hemorrhagic shock (HS) with 25% spontaneous survival rate (without resuscitation) was used to evaluate the effects of 4 novel life-supporting first aid (LSFA) measures on survival time and rate. After shed blood volume (SBV) of 3.25 ml/100 g, withdrawn over 20 min, hemodynamic and respiratory responses were recorded to 3 h and survival to 24 h. The 5 groups of 20 rats each (total n = 100) were as follows: group I, controls without treatment; II, oxygen 100% inhalation; III, external cooling to rectal temperature 30 degrees C; IV, Ringer's solution 5 ml/100 g rectally; and V, acoustic and surface stimuli for arousal. Survival rates were: control group I, 35% at 3 h and 15% at 24 h; oxygen group II, 75% (P less than 0.05 compared with group I) at 3 h and 60% (P less than 0.05 compared with group I) at 24 h; hypothermia group III, 65% at 3 h and 45% (P less than 0.05 compared with group I) at 24 h; rectal fluid group IV, 50% at 3 h and 40% at 24 h; stimulated group V, 15% at 3 h and 15% at 24 h. Compared with group I, median survival times during HS 0-3 h were longer in groups II and III; and self-resuscitation attempts were longer in groups II, III and IV. We conclude that in untreated severe hemorrhagic shock, chances of survival to delayed arrival of advanced life support with i.v. fluid resuscitation might be increased with O2 inhalation and/or moderate external cooling.

Dying pattern in volume-controlled hemorrhagic shock in awake rats

We previously determined that in awake, unmonitored Sprague-Dawley rats, bleeding of 2.5 ml/100 g over 20 min resulted in hemorrhagic shock (HS) with about a 75% survival rate over 24 h, and bleeding of 3.0 ml/100 g in about 25% survival to 24 h. In the present study, we monitored systolic and mean arterial pressure (MAP), central venous pressure (CVP), breathing movements, electroencephalogram (EEG), and arterial blood gases to 3 h in order to study dying patterns. After cannulation under light anesthesia and awakening for 2 h, the rats were bled over 20 min. Ten rats in each of four groups were studied. Shed blood volume (SBV) in group I was 2.0 ml/100 g; in group II, 2.5 ml; in group III, 3.0 ml; and in group IV, 3.5 ml. Three hour survival rates were 100% for group I, 80% for group II (survival time 149 +/- 65 [106-180] min), 40% for group III (survival time 116 +/- 72 [93-180] min), and 0% for group IV (survival time 32 +/- 38 [5-69] min). MAP decreased at end of bleeding, increased transiently to moderately hypotensive levels (attempted self-resuscitation), and then either recovered to normotension or declined to cardiac arrest (death), which was defined as simultaneous apnea, systolic arterial pressure less than or equal to 30 mmHg without pulsations, and isoelectric EEG. EEG depression began with hypotension to MAP less than or equal to 50 mmHg. During HS, PaO2 increased, and PaCO2, pHa, and Hct all decreased. The results suggest that this model with SBV of 3.25 ml/100 g would give a low, but not zero 3 h survival, and therefore would be suitable for the study of responses to field resuscitation potentials.

A comparison of cardiopulmonary resuscitation with cardiopulmonary bypass after prolonged cardiac arrest in dogs. Reperfusion pressures and neurologic recovery

Resuscitability and outcome after prolonged cardiac arrest were compared in dogs with standard external cardiopulmonary resuscitation (CPR) vs. closed-chest emergency cardiopulmonary bypass (CPB). Ventricular fibrillation (VF) was with no blood flow from VF 0 min to VF 10 min. Subsequent CPR basic life support (BLS) was from 10 min to VF 15 min. Then, group I (n = 13) received CPR advanced life support (ALS) from VF 15 min until restoration of spontaneous circulation to occur not later than VF 40 min. Group II (n = 14) received CPR-ALS from VF 15 min to VF 20 min without defibrillation, and then total CPB to defibrillation attempts started at VF 20 min, followed by assisted CPB to 2 h. Total ischemia time (no-flow time plus CPR time of MAP less than 50 mmHg) was unexpectedly shorter in group I (14.3 +/- 2.5 min) than in group II (18.6 +/- 2.3 min) (P less than 0.01). During CPR-BLS, coronary perfusion pressures were 25 +/- 9 mmHg in group I and 18 +/- 8 mmHg in group II (NS). Epinephrine during CPR-ALS, before countershock, raised coronary perfusion pressure to 40 +/- 10 mmHg in group I and 27 +/- 10 mmHg in group II (NS). In group II, coronary perfusion pressure increased during total CPB to 58 +/- 16 mmHg (P less than 0.01 vs. group I). Spontaneous normotension was restored in 11/13 dogs of group I and all 14 dogs of group II (NS). Ten dogs in each group followed protocol and survived to 96 h. Five of ten in group I and six of ten in group II were neurologically normal (NS). We conclude that: (1) Reperfusion with CPB yields higher coronary perfusion pressures than reperfusion with CPR-ALS; and (2) even after no blood flow for 10 min, optimized CPR can result in cardiovascular resuscitability and neurologic recovery, similar to those achieved by CPB.

A simple survival model of volume-controlled hemorrhagic shock in awake rats

A simple rat model was developed for the study of spontaneous survival after volume-controlled hemorrhage. The objective was to determine in awake, unrestrained rats the shed blood volume (SBV) in ml/100 g body weight that without fluid resuscitation, would result in either a high or a low percentage of survivors within 24 h. About 24 h after cannulation under light anesthesia, the awake rats were insulted with arterial blood withdrawal at a constant rate over 20 min, while mean arterial pressure (MAP) was monitored (N = 78). Then, the arterial catheter was removed, and the rats were observed for 24 h or until death. With increasing SBV, survival rate decreased, SBV of 2.50 ml/100 g (group I) resulted in 74% survivors at 2 h and 24 h; SBV of 2.75 ml/100 g (group II), in 67% survivors at 2 h and 46% at 24 h; SBV of 3.00 ml/100 g (group III), in 35% survivors at 2 h and 20% at 24 h; and SBV of 3.50 ml/100 g (group IV), in no survivors to 2 h. MAP declined similarly over 20 min blood withdrawal in the four insult groups, without difference between ultimate survivors vs. nonsurvivors. All rats survived to the end of 20 min hemorrhage (i.e. hemorrhagic shock [HS] time = 0 min). Deaths at HS time 0-2 h occurred after SBV of 2.50 ml/100 g, at HS time 56 +/- 35 min; after SBV of 2.75 ml/100 g, at HS 81 +/- 26 min; after SBV of 3.00 ml/100 g, at HS 37 +/- 33 min; and after SBV of 3.50 ml/100 g, at HS 11 +/- 2 min. Weight may have affected MAP response and survival. We conclude that a volume-controlled HS model in rats without anesthesia or restraint is feasible. SBV of 2.50 ml/100 g should be suitable for testing additional insults. SBV of 3.00 ml/100 g should be suitable for testing resuscitative therapies. The model should be modified to allow monitoring of key variables after hemorrhage.

Moderate hypothermia after cardiac arrest of 17 minutes in dogs. Effect on cerebral and cardiac outcome

Moderate hypothermia (30 degrees C) induced before circulatory arrest is known to improve neurologic outcome. We explored, for the first time in a reproducible dog outcome model, moderate hypothermia induced during reperfusion after cardiac arrest (resuscitation). In three groups of six dogs each (N = 18), normothermic ventricular fibrillation cardiac arrest (no blood flow) of 17 minutes was reversed by cardiopulmonary bypass--normothermic in control group I (37.5 degrees C) and hypothermic to 3 hours in groups II (32 degrees C) and III (28 degrees C). Defibrillation was achieved in less than or equal to 5 minutes and partial bypass was continued to 4 hours, controlled ventilation to 20 hours, and intensive care to 96 hours. All 18 dogs survived. Electroencephalographic activity returned significantly earlier in groups II and III. Mean +/- SD best neurologic deficit between 48 and 96 hours was 44 +/- 8% in group I, 38 +/- 12% in group II, and 35 +/- 7% in group III (differences not significant). Best overall performance category 2 (good outcome) between 48 and 96 hours was achieved in none of the six dogs in group I and in four of the 12 dogs in the combined hypothermic groups II and III (difference not significant). Mean +/- SD brain total histologic damage score was 130 +/- 22 in group I, 93 +/- 28 in group II (p = 0.05), and 80 +/- 26 in group III (p = 0.03). Gross myocardial damage was greater in groups II and III than in group I--numerically higher overall and significantly higher in group III for the right ventricle alone (p = 0.02). Moderate hypothermia after prolonged cardiac arrest may or may not improve cerebral outcome slightly and can worsen myocardial damage.

Hyperthermia-induced cardiac arrest in dogs and monkeys

The pattern of dying from immersion hyperthermia was documented in 8 dogs, 9 rhesus monkeys and 12 pigtail monkeys. Under light general anesthesia and spontaneous breathing, the animals were immersed into water of 45 degrees C, which was subsequently adjusted to control brain (parietal epidural) temperature at 42 +/- 0.5 degrees C. Transient initial hypertension, tachycardia, tachypnea and hypocarbia were followed by progressive hypotension with decreasing central venous pressure and pulmonary artery occlusion pressures (measured in three dogs only), bradycardia and bradypnea. Cardiac arrest occurred in the dogs after immersion of 288 +/- 66 min and more rapidly (P less than 0.02) in the rhesus monkeys (at 137 +/- 75 min) and pigtail monkeys (at 178 +/- 26 min). EEG silence occurred in the monkeys at MAP 40 mmHg and in the dogs at MAP 25 mmHg. Cardiac arrest occurred in form of sudden ventricular fibrillation (2/5 dogs, 2/9 rhesus monkeys, 3/12 pigtail monkeys), or later in electromechanical dissociation leading to electric asystole (3/5 dogs, 7/9 rhesus monkeys, 9/12 pigtail monkeys). The mean blood glucose levels decreased to less than 30 mg/dl (P less than 0.002), whereas hematocrit, serum osmolality, lactate and potassium levels increased. Necropsies revealed macroscopic petechial hemorrhages in all extracerebral organs, but not in the brain. There was no gross evidence of cerebral edema. Death seemed to be the result of primary cardiovascular failure leading to secondary (ischemic) cerebral failure (EEG silence) and apnea, which coincided with pulselessness.