Physiology of Resuscitation

Brain hypoperfusion post-resuscitation

Post-resuscitation brain hypoperfusion is an all too common problem following successful CPR in dogs and cats. The deterioration of neurologic status may occur, regardless of the clinician's ability to restore and maintain heart rate and rhythm, mucous membrane color, capillary refill time, and arterial blood pressure. New insight has been gained into the mechanisms responsible for post-resuscitation brain hypoperfusion, which has improved current treatment regimens and the development of new therapeutic modalities. Proper use of fluids (isotonic or hypertonic saline, oncotic solutions), diuretics, corticosteroids, and sedatives, combined with appropriate CPR techniques, can improve outcome. New drugs and therapeutic techniques offer exciting potential for the future limitation of this problem.

Ultrastructural and ionic studies in global ischemic dog brain

A time course of tissue ionic changes, and their relation to ultrastructural findings during reperfusion following a 15-min global ischemic brain insult was studied in a dog model. Parietal cortex was analyzed for Ca, Na, K, Mg and Fe in controls and after 10 min, 2, 4, and 8 h of reperfusion. After 8 h of reperfusion, the mean values (mumol/g tissue wet wt.) for Ca (control = 1.43, 8 h = 2.76) and Na (control 60.4, 8 h = 107.4) doubled and K (control = 90.4, 8 h = 48.5) decreased to half that of the control. Ultrastructural studies and subcellular localization of calcium in parietal cortex of in situ-fixed brains after 8 h showed cortical neurons with clumping of nuclear chromatin, dilatation of endoplasmic reticulum and disruption of plasma membranes. Large amounts of electron-dense precipitates of calcium were present within dilated astrocytic processes, synaptic vesicles, cytoplasm of edematous dendrites and mitochondria. Cortical neurons from postischemic dogs without reperfusion showed only slight chromatin clumping and edema of astrocytic processes, but no calcium accumulation. The large ionic shifts noted between 4 and 8 h of reperfusion, indicate a progressive inability of the cells to maintain normal transmembrane gradients of these ions and may reflect a membrane destructive process, as demonstrated ultrastructurally at 8 h. Enhanced calcium entry into the neuron during reperfusion appears to be a part of the cytotoxic mechanism leading to neuronal necrosis.

Should calcium be used in cardiac arrest?

Calcium salts have been recommended for and used in the treatment of various forms of cardiac arrest for many years. Although calcium plays a major role in excitation-contraction coupling, it can have a deleterious effect in some processes of cellular injury. Clinical trials suggest that calcium salts are not effective in ventricular fibrillation and asystole, but that some patients with electromechanical dissociation may have a favorable hemodynamic response. Because of the potential risks of calcium salts, their use should be limited to specific subsets of patients with cardiac arrest.

Controversies in resuscitation

Many controversies, only a few of which have been discussed here, are now raging in the field of resuscitation. Much is expected to change in the next five to ten years. The American Heart Association is now considering changes for its new advanced cardiac life support course, which should be ready this year. The course will not include some of the possible changes mentioned in this article, because too few studies have been done. Physicians and other rescuers should abide by the guidelines of the American Heart Association as a standard of practice because its recommendations are the result of the best possible consensus. Over the next several years, many exciting changes in resuscitation will occur and may lead to improved survival rates and quality.

Prolonged cardiac arrest and resuscitation in dogs: brain mitochondrial function with different artificial perfusion methods

Clinical techniques for artificial perfusion have not previously been examined directly for their effects on brain high-energy metabolism. Our study involved 24 large mongrel dogs that were anesthetized, instrumented for central venous intravenous access, and subjected to craniotomy to expose the dura and underlying parietal cortex. The animals were divided into the following six experimental groups of four animals each: nonischemic controls; 15-minute cardiac arrest without resuscitation; 45-minute cardiac arrest without resuscitation; 15-minute cardiac arrest plus 30 minutes resuscitation with conventional cardiopulmonary resuscitation (CPR); 15-minute cardiac arrest plus 30 minutes resuscitation with interposed abdominal compression (IAC) CPR; and 15-minute cardiac arrest plus 30 minutes resuscitation with internal cardiac massage. Cardiac arrest was induced by central venous injection of KCl 0.6 mEq/kg, and it was confirmed by continuous ECG monitoring. The three active resuscitation models included administration of NaHCO3 and epinephrine, but no attempt was made to restart the heart by defibrillation during resuscitation. At the indicated time in each group, a 4- to 5-g sample of brain was removed through the craniotomy, immediately cooled to 0 C and processed for isolation of mitochondria. The mitochondria were studied for their content of superoxide dismutase and for quantitative oxygen consumption with glutamate/malate substrate during resting and ADP-stimulated respiration. Our results show a significant drop in brain mitochondrial superoxide dismutase activity during the first 15 minutes of cardiac arrest. There is minimal injury to brain mitochondrial oxygen consumption during both 15 and 45 minutes of complete ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Post resuscitation iron delocalization and malondialdehyde production in the brain following prolonged cardiac arrest

Assays for brain tissue malondialdehyde (MDA) and low molecular weight chelated (LMWC) iron were used to examine samples of the cerebral cortex obtained from dogs 2 h after resuscitation from a 15-min cardiac arrest. The effect of post-resuscitation treatment with lidoflazine and/or desferrioxamine was similarly examined. Non-ischemic brain samples had LMWC iron levels (in nmol/100 mg tissue) of 12.32 + 2.60 and MDA levels (in nmol/100 mg tissue) of 8.46 + 1.35. Animals subjected to cardiac arrest and resuscitation and standard intensive care (SIC) had LMWC iron levels of 37.04 + 4.58 (p less than .01 against non-ischemic controls) and MDA levels of 12.24 + 1.9 (p less than .05 against non-ischemic controls). All treatment interventions significantly reduced the LMWC iron (p less than .05), but only treatment with desferrioxamine alone significantly reduced MDA (p less than .05), although a trend toward reduction of the MDA was also evident in animals treated with both desferrioxamine and lidoflazine. LMWC iron levels are increased in the post-ischemic brain, and this increase may be related to lipid peroxidation in the brain following resuscitation from cardiac arrest. These changes are probably pathologic and are amenable to pharmacologic intervention.

Use of calcium blockers in electromechanical dissociation

Calcium antagonists have been shown to protect the myocardium against the deleterious effects of ischemia and reperfusion in both focal and global models. The mechanism of this protection is probably related to their ability to decrease the rapid and massive cytosolic and mitochondrial calcium overloading that occurs with reperfusion of severely ischemic myocardium. This calcium overloading uncouples oxidative phosphorylation, preventing repletion of ischemia-depleted ATP stores. The mode of action of calcium antagonists in protecting heart muscle is complex, and may ultimately depend on their ability to preserve sufficient energy to maintain intracellular ionic homeostasis. The cellular events that occur with prolonged cardiac ischemia have been well documented in animal studies, and are reflected in the clinical picture of electromechanical dissociation (EMD). ATP production is decreased during ischemia and quickly results in depleted energy stores. The electrical and mechanical activities of the heart are energy-consuming processes that gradually come to a halt in the presence of prolonged ischemia. In excised totally ischemic hearts, electrical activity persists for a time after contractions have ceased, resulting in the clinical picture of EMD. Eventually electrical activity stops as well, causing asystole. Calcium antagonists administered during resuscitation from EMD, as well as other terminal arrhythmias, may protect the myocardium from reperfusion injury and preserve the ATP stores necessary for normal cardiac function.