Factors influencing variable outcomes after ventricular fibrillation cardiac arrest of 15 minutes in dogs

Update on cardiopulmonary resuscitation and emergency cardiovascular care guidelines

PURPOSE

The key changes included in the 2005 cardiopulmonary resuscitation (CPR) and emergency cardiac care (ECC) guidelines are reviewed. Advances since publication of the current guidelines are also discussed.

SUMMARY

The 2005 CPR and ECC guidelines include several key changes from the previous version published in 2000. The new guidelines place an increased emphasis on chest compressions and recommend a compression:ventilation (C:V) ratio of 30:2. Current knowledge on defibrillation has also been incorporated by recommending that Emergency Medical Service (EMS) rescuers give two minutes of CPR before defibrillation when the response interval is greater than four to five minutes and EMS responders did not witness the arrest. Another major change is the recommendation for a single shock to be administered followed immediately by CPR with no check of the cardiac rhythm until two minutes of CPR has been performed postdefibrillation. The 2005 guidelines recommend that an automated external defibrillator should be implemented in public locations where there is a relatively high likelihood of witnessed cardiac arrest. In addition, the most recent guidelines highlight the shift from primary-rhythm-based therapies and resuscitation to a focus on neurologic outcomes.

CONCLUSION

Several evidence-based changes were included in the 2005 CPR and ECC guidelines, including a C:V ratio of 30:2 and mitigation of hands-off time, early defibrillation, administration of a single shock versus a three-shock sequence, use of public-access defibrillators, and a shift from primary-rhythm-based therapies to a focus on neurologic outcomes.

Initial cardiac rhythm correlated to emergency department survival

BACKGROUND

This study attempted to correlate the initial cardiac rhythm and survival from prehospital cardiac arrest, as a secondary end-point.

METHODS

Prospective, randomized, double-blinded clinical intervention trial where bicarbonate was administered to 874 prehospital cardiopulmonary arrest patients in prehospital urban, suburban, and rural emergency medical service environments.

RESULTS

This group's manifested an overall survival rate of 13.9% (110 of 793) of prehospital cardiac arrest patients. The most common presenting arrhythmia was ventricular fibrillation (VF) (45.0%), asystole (ASY) (34.4%), and pulseless electrical activity (PEA) (15.7%). Less commonly found were normal sinus rhythm (NSR) (1.8%), other (1.8%), ventricular tachycardia (VT) (0.6%), and atrioventricular block (AVB) (0.5%) as prearrest rhythms. The best survival was noted in those with a presenting rhythm of AVB (57.1%), VT (33.3%), VF (15.7%), NSR (14.3%), PEA (11.2%), and ASY (11.1%) (p = 0.02). However, there was no correlation between the final cardiac rhythm and outcome, other than an obvious end-of-life rhythm.

CONCLUSION

The most common presenting arrhythmia was VF (45%), while survival is greatest in those presenting with AVB (57.1%).

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.

Future directions for resuscitation research. V. Ultra-advanced life support

Standard external cardiopulmonary resuscitation (SECPR) frequently produces very low perfusion pressures, which are inadequate to achieve restoration of spontaneous circulation (ROSC) and intact survival, particularly when the heart is diseased. Ultra-advanced life support (UALS) techniques may allow support of vital organ systems until either the heart recovers or cardiac repair or replacement is performed. Closed-chest emergency cardiopulmonary bypass (CPB) provides control of blood flow, pressure, composition and temperature, but has so far been applied relatively late. This additional low-flow time may preclude conscious survival. An easy, quick method for vessel access and a small preprimed system that could be taken into the field are needed. Open-chest CPR (OCCPR) is physiologically superior to SECPR, but has also been initiated too late in prior studies. Its application in the field has recently proven feasible. Variations of OCCPR, which deserve clinical trials inside and outside hospitals, include 'minimally invasive direct cardiac massage' (MIDCM), using a pocket-size plunger-like device inserted via a small incision and 'direct mechanical ventricular actuation' (DMVA), using a machine that pneumatically drives a cup placed around the heart. Other novel UALS approaches for further research include the use of an aortic balloon catheter to improve coronary and cerebral blood flow during SECPR, aortic flush techniques and a double-balloon aortic catheter that could allow separate perfusion (and cooling) of the heart, brain and viscera for optimal resuscitation of each. Decision-making, initiation of UALS methods and diagnostic evaluations must be rapid to maximize the potential for ROSC and facilitate decision-making regarding long-term circulatory support versus withdrawal of life support for hopeless cases. Research and development of UALS techniques needs to be coordinated with cerebral resuscitation research.

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.

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.

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.