Correction of metabolic acidosis in experimental CPR: a comparative study of sodium bicarbonate, carbicarb, and dextrose

Sodium Bicarbonate and Calcium Chloride for the Treatment of Hyperkalemia-Induced Cardiac Arrest: A Randomized, Blinded, Placebo-Controlled Animal Study

OBJECTIVES

Current international guidelines recommend administrating calcium chloride and sodium bicarbonate to patients with hyperkalemia-induced cardiac arrest, despite limited evidence. The aim of this study was to evaluate the efficacy of calcium chloride and sodium bicarbonate on return of spontaneous circulation (ROSC) in a pig model of hyperkalemia-induced cardiac arrest.

DESIGN

A randomized, blinded, placebo-controlled experimental pig study. Hyperkalemia was induced by continuous infusion of potassium chloride over 45 minutes followed by a bolus. After a no flow period of 7 minutes, pigs first received 2 minutes of basic cardiopulmonary resuscitation and subsequently advanced life support. The first intervention dose was administered after the fifth rhythm analysis, followed by a defibrillation attempt at the sixth rhythm analysis. A second dose of the intervention was administered after the seventh rhythm analysis if ROSC was not achieved. In case of successful resuscitation, pigs received intensive care for 1 hour before termination of the study.

SETTING

University hospital laboratory.

SUBJECTS

Fifty-four female Landrace/Yorkshire/Duroc pigs (38-42 kg).

INTERVENTIONS

The study used a 2 × 2 factorial design, with calcium chloride (0.1 mmol/kg) and sodium bicarbonate (1 mmol/kg) as the interventions.

MEASUREMENTS AND MAIN RESULTS

Fifty-two pigs were included in the study. Sodium bicarbonate significantly increased the number of animals achieving ROSC (24/26 [92%] vs. 13/26 [50%]; odds ratio [OR], 12.0; 95% CI, 2.3-61.5; p = 0.003) and reduced time to ROSC (hazard ratio [HR] 3.6; 95% CI, 1.8-7.5; p < 0.001). There was no effect of calcium chloride on the number of animals achieving ROSC (19/26 [73%] vs. 18/26 [69%]; OR, 1.2; 95% CI, 0.4-4.0; p = 0.76) or time to ROSC (HR, 1.5; 95% CI, 0.8-2.9; p = 0.23).

CONCLUSIONS

Administration of sodium bicarbonate significantly increased the number of animals achieving ROSC and decreased time to ROSC. There was no effect of calcium chloride on the number of animals achieving ROSC or time to ROSC.

Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care

The goal of therapy for bradycardia or tachycardia is to rapidly identify and treat patients who are hemodynamically unstable or symptomatic due to the arrhythmia. Drugs or, when appropriate, pacing may be used to control unstable or symptomatic bradycardia. Cardioversion or drugs or both may be used to control unstable or symptomatic tachycardia. ACLS providers should closely monitor stable patients pending expert consultation and should be prepared to aggressively treat those with evidence of decompensation.

Comparison of sodium bicarbonate and carbicarb for the treatment of metabolic acidosis in newborn calves

Carbicarb (an equimolar mixture of sodium bicarbonate and sodium carbonate) was compared with sodium bicarbonate alone for the treatment of acidosis in newborn calves: 25 of 49 calves with a blood pH at birth of less than 7-2 and a base deficit of less than -3 mmol/litre were treated intravenously with sodium bicarbonate and 24 were treated with carbicarb. The doses were calculated on the basis of the base deficit in a blood sample taken 10 minutes after birth, and further blood samples were taken immediately after the treatment and 30 and 60 minutes after the treatment for the determination of acid-base status, blood gases and haematological and biochemical variables. Both treatments resulted in a significant increase in blood pH, but there was no difference between them. The mean (sd) blood pH before treatment was 7.09 (0.02) and after treatment it was 7.28 (0.01). There was no increase in the partial pressure of carbon dioxide after treatment with either sodium bicarbonate or carbicarb. Both treatments were associated with an increase in sodium concentration and decreases in the total erythrocyte count, haematocrit and haemoglobin concentration.

Lactic Acidosis Update for Critical Care Clinicians

Abstract. Lactic acidosis is a broad-anion gap metabolic acidosis caused by lactic acid overproduction or underutilization. The quantitative dimensions of these two mechanisms commonly differ by 1 order of magnitude. Overproduction of lactic acid, also termed type A lactic acidosis, occurs when the body must regenerate ATP without oxygen (tissue hypoxia). Circulatory, pulmonary, or hemoglobin transfer disorders are commonly responsible. Overproduction of lactate also occurs with cyanide poisoning or certain malignancies. Underutilization involves removal of lactic acid by oxidation or conversion to glucose. Liver disease, inhibition of gluconeogenesis, pyruvate dehydrogenase (thiamine) deficiency, and uncoupling of oxidative phosphorylation are the most common causes. The kidneys also contribute to lactate removal. Concerns have been raised regarding the role of metformin in the production of lactic acidosis, on the basis of individual case reports. The risk appears to be considerably less than with phenformin and involves patients with underlying severe renal and cardiac dysfunction. Drugs used to treat lactic acidosis can aggravate the condition. NaHCO3 increases lactate production. Treatment of type A lactic acidosis is particularly unsatisfactory. NaHCO3 is of little value. Carbicarb is a mixture of Na2CO3 and NaHCO3 that buffers similarly to NaHCO3 but without net generation of CO2. The results from animal studies are promising; however, clinical trials are sparse. Dichloroacetate stimulates pyruvate dehydrogenase and improves laboratory values, but unfortunately not survival rates, among patients with lactic acidosis. Hemofiltration has been advocated for the treatment of lactic acidosis, on the basis of anecdotal experiences. However, kinetic studies of lactate removal do not suggest that removal can counteract lactate production in any meaningful way. The ideal treatment is to stop acid production by treating the underlying disorder.

Tromethamine buffer modifies the depressant effect of permissive hypercapnia on myocardial contractility in patients with acute respiratory distress syndrome

In patients with acute respiratory distress syndrome (ARDS), permissive hypercapnia is a strategy to decrease airway pressures to prevent ventilator-induced lung damage by lowering tidal volumes and tolerating higher arterial carbon dioxide tension. However, in experimental studies hypercapnia impairs myocardial contractility and hemodynamic function. We investigated the effect of short-term permissive hypercapnia on myocardial contractility and hemodynamics in patients with ARDS. We hypothesized that the administration of tromethamine (THAM), a buffer which does not increase carbon dioxide production, would modify these changes. In 12 patients with ARDS, permissive hypercapnia was implemented for 2 h with a target Pa(CO(2))of 80 mm Hg. Patients were randomized to have respiratory acidosis corrected by THAM (pH-corrected group), or not corrected (pH-uncorrected group). Hemodynamic responses were measured, and transesophageal echocardiography (TEE) was used to determine myocardial contractility. Permissive hypercapnia resulted in significant decreases in systemic vascular resistance (SVR) and increases in cardiac output (Q). Myocardial contractility decreased in both groups but significantly less in the pH-corrected group (approximately 10%) than in the pH-uncorrected group (approximately 18%, p < 0.05). Mean arterial pressure decreased and mean pulmonary arterial pressure increased significantly only in the pH-uncorrected group. All values returned to baseline conditions 1 h after permissive hypercapnia was terminated. Our study demonstrates a reversible depression of myocardial contractility and hemodynamic alterations during rapid permissive hypercapnia which were attenuated by buffering with THAM. This may have applicability to the clinical strategy of permissive hypercapnia and allow the benefit of decreased airway pressures to be realized while minimizing the adverse hemodynamic effects of hypercapnic acidosis.

Comparison of sodium bicarbonate, Carbicarb, and THAM during cardiopulmonary resuscitation in dogs

OBJECTIVES

During cardiopulmonary resuscitation (CPR), elimination of CO2 was shown to be limited by low tissue perfusion, especially when very low perfusion pressures were generated. It has therefore been suggested that sodium bicarbonate (NaHCO3), by producing CO2, might aggravate the hypercarbic component of the existing acidosis and thereby worsen CPR outcome. The objectives of this study were to evaluate the effects of CO2 producing and non-CO2 producing buffers in a canine model of prolonged ventricular fibrillation followed by effective CPR.

DESIGN

Prospective, randomized, controlled, blinded trial.

SETTING

Experimental animal research laboratory in a university research center.

SUBJECTS

Thirty-eight adult dogs, weighing 20 to 35 kg.

INTERVENTIONS

Animals were prepared for study with thiopental followed by halothane, diazepam, and pancuronium. Ventricular fibrillation was electrically induced, and after 10 mins, CPR was initiated, including ventilation with an FIO2 of 1.0, manual chest compressions, administration of epinephrine (0.1 mg/kg every 5 mins), and defibrillation. A dose of buffer, equivalent to 1 mmol/kg of NaHCO3, was administered every 10 mins from start of CPR. Animals were randomized to receive either NaHCO3, Carbicarb, THAM, or 0.9% sodium chloride (NaCl). CPR was continued for up to 40 mins or until return of spontaneous circulation.

MEASUREMENTS AND MAIN RESULTS

Buffer-treated animals had a higher resuscitability rate compared with NaCl controls. Spontaneous circulation returned earlier and at a significantly higher rate after NaHCO3 (in seven of nine dogs), and after Carbicarb (six of ten dogs) compared with NaCl controls (two of ten dogs). Spontaneous circulation was achieved twice as fast after NaHCO3 compared with NaCl (14.6 vs. 28 mins, respectively). Hydrogen ion (H+) concentration and base excess, obtained 2 mins after the first buffer dose, were the best predictors of resuscitability. Arterial and mixed venous Pco2 did not increase after NaHCO3 or Carbicarb compared with NaCl.

CONCLUSIONS

Buffer therapy promotes successful resuscitation after prolonged cardiac arrest, regardless of coronary perfusion pressure. NaHCO3, and to a lesser degree, Carbicarb, are beneficial in promoting early return of spontaneous circulation. When epinephrine is used to promote tissue perfusion, there is no evidence for hypercarbic venous acidosis associated with the use of these CO2 generating buffers.

An evidence-based evaluation of the use of sodium bicarbonate during cardiopulmonary resuscitation

The use of bicarbonate is rooted in three decades of clinical experience and observational studies. For many years, bicarbonate passed the tried and true test for clinical therapies; however, administration of sodium bicarbonate during cardiac arrest and hypoxic acidosis has become increasingly controversial. The controversy provides an excellent opportunity to evaluate the impact an evidence-based approach might have on a common clinical practice. Is bicarbonate efficacious in the treatment of the severe acidosis that accompanies cardiac arrest during cardiopulmonary resuscitation (CPR)? Are the deleterious effects of bicarbonate clinically relevant? What is the evidence upon which a rational decision may be based? This review evaluates and ranks the evidence supporting the use of sodium bicarbonate in the therapy of acidosis associated with cardiac arrest during CPR.

Pharmacology of pediatric resuscitation

The resuscitation of children from cardiac arrest and shock remains a challenging goal. The pharmacologic principles underlying current recommendations for intervention in pediatric cardiac arrest have been reviewed. Current research efforts, points of controversy, and accepted practices that may not be most efficacious have been described. Epinephrine remains the most effective resuscitation adjunct. High-dose epinephrine is tolerated better in children than in adults, but its efficacy has not received full analysis. The preponderance of data continues to point toward the ineffectiveness and possible deleterious effects of overzealous sodium bicarbonate use. Calcium chloride is useful in the treatment of ionized hypocalcemia but may harm cells that have experienced asphyxial damage. Atropine is an effective agent for alleviating bradycardia induced by increased vagal tone, but because most bradycardia in children is caused by hypoxia, improved oxygenation is the intervention of choice. Adenosine is an effective and generally well-tolerated agent for the treatment of supraventricular tachycardia. Lidocaine is the drug of choice for ventricular dysrhythmias, and bretylium, still relatively unexplored, is in reserve. Many pediatricians use dopamine for shock in the postresuscitative period, but epinephrine is superior. Most animal research on cardiac arrest is based on models with ventricular fibrillation that probably are not reflective of cardiac arrest situations most often seen in pediatrics.

Sodium bicarbonate in cardiac arrest: a reappraisal

The routine use of sodium bicarbonate in patients with cardiac arrest has been discouraged, with the benefit of outcome evaluation. Current recommendations include an elaborate stratification of circumstances in which bicarbonate is to be used. The physiological and clinical aspects of bicarbonate administration during cardiopulmonary resuscitation in animal and human studies were reviewed. The onset of significant acidemia or alkalemia is associated with adverse system specific effects. The administration of bicarbonate may mitigate the adverse physiological effects of acidemia, improve response to exogenously administered vasopressor agents, or simply increase venous return due to an osmolar effect, resulting in increased coronary perfusion pressure. Likewise, bicarbonate may have adverse effects in each of these areas. The preponderance of evidence suggests that bicarbonate is not detrimental and may be helpful to outcome from cardiac arrest. An objective reappraisal of the empirical use of bicarbonate or other buffer agents in the appropriate "therapeutic window" for cardiac patients may be warranted.

Does hypoxia or hypercarbia independently affect resuscitation from cardiac arrest?

STUDY OBJECTIVE

In a previous cardiopulmonary resuscitation (CPR) study in swine, ventilation was associated with improved rate of return of spontaneous circulation (ROSC) compared with nonventilated animals, which had greater hypoxia and hypercarbic acidosis. We used the same model to determine the independent effect of hypoxia and hypercarbic acidosis on ROSC after cardiac arrest.

DESIGN

Laboratory model of cardiac arrest.

SETTING

University teaching hospital laboratory.

PARTICIPANTS

Domestic swine (23 to 61 kg).

INTERVENTIONS

Twenty-four swine were randomly assigned to three groups receiving ventilation during CPR with 85% O2/15% N2 (control), 95% O2/5% CO2 (hypercarbia), or 10% O2/90% N2 (hypoxia). All animals had ventricular fibrillation for 6 min without CPR, then CPR with one of the ventilation gases for 10 min, then defibrillation. Animals without ROSC received epinephrine, 85% O2, CPR for another 3 min, and defibrillation.

MEASUREMENTS AND RESULTS

During the tenth minute of CPR, the hypercarbic group had more mean (SD) arterial hypercarbia than the control group (PCO2, 47 +/- 6, compared with 34 +/- 6; p < 0.01), and greater mixed venous hypercarbia (PCO2, 72 +/- 14, compared with 59 +/- 8; p < 0.05), while mean arterial and mixed venous PO2 was not significantly different. The hypoxic group had significantly less mean arterial (43 +/- 9 compared with 228 +/- 103 mm Hg) and mixed venous (22 +/- 5 compared with 35 +/- 7 mm Hg) PO2 when compared with the control group (p < 0.01), while mean arterial and mixed venous PCO2 were not significantly different. Thus, the model succeeded in producing isolated hypercarbia without hypoxia in the hypercarbic group and isolated hypoxia without hypercarbia in the hypoxic group. The rate of ROSC was 6/8 (75%) for the control group, 1/8 (13%) for the hypercarbic group, and 1/8 (13%) for the hypoxic group (p < 0.02).

CONCLUSIONS

Both hypoxia and hypercarbia independently had an adverse effect on resuscitation from cardiac arrest. In this model with a prolonged interval of untreated cardiac arrest, adequate ventilation was important for resuscitation.

Ventilatory effects of active compression-decompression in dogs

STUDY OBJECTIVE

To determine the ventilatory effect of active compression-decompression CPR and to compare it with two other techniques, standard manual cardiac massage and mechanical cardiac massage.

DESIGN

Prospective, randomized laboratory investigation.

PARTICIPANTS

Mongrel dogs.

INTERVENTIONS

Nine adult mongrel dogs were anesthetized, intubated, and mechanically ventilated. They were instrumented to measure arterial pressure, esophageal pressure, airway pressure, end-tidal carbon dioxide concentration, and minute ventilation.

RESULTS

After induction of ventricular fibrillation, three sequences of cardiac massage were performed randomly during mechanical ventilation, standard cardiac massage, mechanical cardiac massage, and active compression-decompression technique. The animals then were disconnected from the ventilator, and the three sequences were performed again. Active compression-decompression created negative minimum esophageal pressures and significantly decreased the minimum airway pressure as compared with the other techniques. Whatever the ventilatory condition, minute ventilation was increased dramatically during active compression-decompression.

CONCLUSION

In this model of cardiac arrest, an important increase in minute ventilation was observed during active compression-decompression. This effect was significantly greater than the increases observed with other techniques of cardiac massage and was related to the negative pressure generated by active decompression.

Lack of uniform definitions and reporting in laboratory models of cardiac arrest: a review of the literature and a proposal for guidelines

BACKGROUND

Researchers are interested in improved uniformity of definitions and standards of reporting data for human CPR studies, and international guidelines (Utstein style) have been developed. However, no guidelines exist for animal CPR investigations.

OBJECTIVE

To assess published animal CPR studies for adequacy of reporting and uniformity of methods and definitions regarding such important factors as the interval from the onset of ventricular fibrillation to the start of CPR (the nonintervention interval), ventilation, chest compression, coronary perfusion pressure, and return of spontaneous circulation.

DESIGN

A blinded review of the methodology described in 42 articles concerned with animal CPR research published during the last ten years. An article had to report cardiac arrest and CPR as part of the protocol and return of spontaneous circulation as one of the outcome variables in order to be included in this study. We excluded abstracts, nonresuscitation models, and human CPR studies.

MEASUREMENTS AND MAIN RESULTS

There was wide variation in the experimental methods reported in the studies. The nonintervention interval ranged from 0 to 15 minutes. The majority of studies initiated CPR within three minutes after the onset of ventricular fibrillation. Twenty-two percent of studies reported tidal volume, and 18% reported minute ventilation. Of the 14 studies that used blood pressure or coronary perfusion pressure as a target for titration of chest compression force, 12 used different target blood pressure values. We found 29 different definitions of return of spontaneous circulation. The duration of return of spontaneous circulation ranged from 30 seconds to 60 minutes; however, 52% of studies did not report a duration.

CONCLUSION

Important differences exist in animal CPR research methodology among laboratories. Failure to define or report minute ventilation, coronary perfusion pressure, and return of spontaneous circulation made it difficult to compare studies. In order to make valid comparisons of studies, blood flow and ventilation should be measured and controlled when they are not experimental variables. Uniform definitions and guidelines for reporting should be developed for laboratory CPR research.

Sodium bicarbonate versus Carbicarb in canine myocardial hypercarbic acidosis

The objective of this study was to compare the in vivo effects of sodium bicarbonate (NaHCO3) and Carbicarb infusion on regional contractile performance and acid-base status in the setting of hypercarbic acidosis. Animals (N = 9) were anesthetized and paralyzed using sodium pentothal, halothane, and pancuronium bromide, and mechanically ventilated with an air-O2 mixture so that arterial PO2 was > or = 300 mm Hg. Following beta-adrenergic blockade, alveolar ventilation was gradually reduced over a 50-minute period to increase arterial PCO2 to 60 to 80 mm Hg. Each of the following solutions was then infused in consecutive order directly into the left anterior descending artery coronary artery for 15 minutes: (1) 8.4% NaHCO3 at 2 mL/min; (2) 5% sodium chloride at 2 mL/min, equivalent to NaHCO3 in osmolality; (3) 6.3% Carbicarb at 0.5 mL/min, equivalent to NaHCO3 in buffer capacity; and (4) 6.3% Carbicarb at 2 mL/min, equivalent to NaHCO3 in volume. Regional stroke work analog (ultrasonic dimension transducers), interstitial myocardial pH (Khuri electrode), coronary blood flow (doppler flow probe), and hemodynamic/metabolic variables (heart rate, blood pressure, arterial and coronary venous blood gases) were measured at 1, 5, 10, and 15 minutes during each infusion and 10 minutes after the infusion was discontinued, ie, at 25 minutes. Animals were allowed to recover for 45 minutes between interventions. Values at each time point were compared with baseline for statistical significance. Small reductions in interstitial myocardial pH (P < .05) and stroke work (P > .05) were observed within 1 minute of NaHCO3 administration. Both parameters increased significantly from baseline levels thereafter, ie, interstitial myocardial pH at 5 minutes and stroke work at 15 minutes. Infusion of Carbicarb invariably was associated with an increase (P < .05) in interstitial myocardial pH. Stroke work increased (P < .05) during low-dose Carbicarb administration, but infusion of the higher dose was accompanied by a biphasic response, ie, an increase (P < .05) from 0 to 5 minutes, followed by a gradual decrease that achieved statistical significance 10 minutes after termination of the infusion. End-diastolic length was inversely proportional to changes in stroke work, and coronary blood flow varied directly with changes in coronary venous Pco2. Myocardial O2 consumption decreased (P < .05) during Carbicarb infusion, but changes during NaHCO3 did not reach statistical significance. Our findings lend support to the hypothesis that intramyocardial pH determines myocardial function independent of CO2 production by buffer therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Atropine administration in experimental electromechanical dissociation

Atropine can have a place during cardiopulmonary resuscitation (CPR) in the management of asystole, where parasympathetic influence might be excessive. However, the beneficial effects of atropine in electromechanical dissociation (EMD) have not been clearly demonstrated. The authors studied the effects of atropine in combination with epinephrine on an experimental model of EMD in the closed-chested dog. In 15 pentobarbital-anesthetized, mechanically ventilated dogs (mean weight 20 kg), EMD was induced by ventricular fibrillation followed by an external countershock, and was observed for 2 minutes before CPR was started. After 5 minutes of chest compression using a CPR thumper, either atropine 0.5 mg or D5W was administered, and the same injection was repeated every 5 minutes until recovery. Epinephrine 1 mg was administered in alternans. Each dog was submitted to two successive episodes of CPR, using either atropine or D5W, in a randomized order. Of a total of 28 CPRs, five were successful with chest compression alone. In the treatment groups, 10 of 11 were successful with atropine, but only eight of 12 with D5W (P < .01). The duration of CPR was also significantly shorter when atropine was used (9 minutes 56 seconds +/- 14 seconds versus 12 minutes 08 seconds +/- 43 seconds, P < .001). During the recovery period, atropine-treated animals had higher arterial pressure, heart rate, cardiac output and stroke volume. On this experimental model, the administration of high doses of atropine together with epinephrine enhances the recovery from EMD and results in a better cardiac function during recovery.

Controversies in cardiopulmonary resuscitation: pediatric considerations

This article addresses some therapeutic controversies concerning medications that may be needed during advanced pediatric life support (APLS) and the routes of administration that may be selected. The controversies that are discussed include the appropriateness and selection of various routes for drug administration during APLS; the determination of whether epinephrine hydrochloride is the adrenergic agent of choice for APLS and its appropriate dose; treatment of acidosis associated with a cardiopulmonary arrest; recommendations for atropine sulfate doses; and the role, if any, of calcium in APLS. Background information differentiating pediatric from adult cardiopulmonary arrest is presented to enable the reader to have a better understanding of the specific needs of children during this life-threatening emergency. The article also presents an overview of various drugs used for APLS and a table of their typically recommended doses and routes of administration.