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Clinical Update

Out-of-hospital cardiac arrest

Out-of-hospital cardiac arrest (OHCA), with its high fatality rate, is a significant public health issue. The aetiology of OHCA is reviewed, and management strategies are discussed, including the "chain of survival", the Utstein method of data collection, and recent developments in advanced cardiac life support emphasising defibrillation.

Alastair D McR Meyer, Peter A Cameron, Karen L Smith and John J McNeil

MJA 2000; 172: 73-76

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Background - Recent advances in management of OHCA - Improving survival rates after OHCA in Australia - References - Authors' details
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Out-of-hospital cardiac arrest (OHCA) is a leading cause of death in First World countries. The estimated incidence in the United States is about 1/1000 population per year (15%-20% of all deaths).1 Current Australian data based on ambulance attendances in metropolitan Melbourne suggest that about 2000 lives are lost from OHCA per year.2

OHCA is often the first presentation of ischaemic heart disease. If victims of OHCA can receive immediate and appropriate treatment, they have a 30%-70% chance of survival.3

There is a paucity of data on survival from OHCA in Australia (Box 1). The Melbourne report of cardiac arrest victims mentioned above, which included all patients with arrhythmia of presumed cardiac cause, suggests that the survival rate may be as low as 3%.2

The management of OHCA is presently the only area of pre-hospital emergency care where there is clear evidence that appropriate intervention leads to improved survival.10 We present a clinical update on the management of OHCA.

Background The usual cause of sudden cardiac death is coronary artery disease, which accounts for up to 90% of all victims;11 most have major pathological changes in two or more coronary arteries.11

An arrhythmia is the most common cause of cardiac arrest, with ventricular fibrillation (VF) being more common12,13 than asystole, pulseless ventricular tachycardia (VT) and other arrhythmias. VF generally has a better prognosis than the other arrhythmias.12,13 Ischaemia, electrolyte imbalance, stress, and neurochemical transmitters (eg, adrenaline, noradrenaline), as well as clotting disorders (eg, massive pulmonary emboli), may trigger arrhythmia.12 VF rarely reverts spontaneously, and the definitive treatment is defibrillation.10

Hypoxic brain injury occurs at four minutes, and death will occur within 12 minutes if no therapy is offered.3,10 It has been predicted that with ideal pre-hospital care, survival rates would be of the order of 70%.3


Recent advances in management of OHCA

The "chain of survival"

Successful resuscitation of victims of OHCA depends on each individual's unique features (eg, prior medical condition, cardiac rhythm associated with the collapse, collapse witnessed or not witnessed), and the system in the community to deal with such problems. The system must provide a "chain of survival". This concept, initially described by Cummins et al in 1991, and adopted by the American Heart Association, focuses attention on four critical links in the resuscitation process of a victim of OHCA:14

  • Early recognition and access to emergency medical services

  • Early cardiopulmonary resuscitation

  • Early defibrillation

  • Early advanced cardiac life support.

Communities with integrated links along this chain have higher survival rates after OHCA than those with deficiencies in these links.15

Analysing emergency medical services (EMS) in different countries has been difficult, but, in 1990, an international Consensus Conference established uniform terms and definitions for out-of-hospital resuscitation.15 The Consensus Conference recommended that a template approach, the Utstein template, be used for reporting data from out-of-hospital resuscitations.16 This allows comparison and benchmarking between EMS in different countries (Box 2).

Early access Recognition of cardiac arrest is often difficult, as it may be confused with fitting or fainting. Cardiac arrest is assumed in an unconscious patient who has no palpable pulse. Spontaneous breathing and pupil size are irrelevant to the diagnosis.

Early access to EMS in Australia needs improvement. Two studies of OHCA found that bystanders do not know who to call and have trouble describing the victim.2,5

Education and training programs have been used to raise community awareness and response to OHCA. The "Phone first" campaign in rural Iowa (USA) decreased access times by over a minute. This simple campaign emphasised the need for citizens witnessing a collapse to call the EMS without delay.17

Early cardiopulmonary resuscitation (CPR)
The available evidence shows that the earlier patients receive CPR, the greater their chance of survival.18-20

For resuscitative efforts to be effective, the patient must be supine, and on a flat, firm surface. Chest compressions are performed in the lower part of the sternum, 4-6 cm in depth and at a rate of 80-100 compressions per minute. During cardiac arrest, properly performed chest compressions can produce systolic blood pressure peaks of 60-80 mmHg. Cardiac output is only 25%-30% of normal.21

Bystander CPR is seldom practised in Australia. Despite there being witnesses to 54% of OHCAs presenting as VF in the Melbourne report, only 22% received bystander CPR and it was often of questionable quality.2 Family members who witness their own relative's OHCA are less likely to perform CPR than a stranger who happens by a victim of OHCA in the street.22,23

Early defibrillation
Defibrillation is the definitive treatment for VF.24 The chance of success deteriorates with each minute.3 Such is the importance of defibrillation that Wei and Tang have suggested the appropriate sequence to follow in resuscitation from cardiac arrest is D (defibrillation), C (circulation), B (breathing) and A (airway), rather than the more familiar ABC.25

New technology has allowed defibrillators to become more user friendly. Automated external defibrillators (AEDs) can analyse patients' electrical rhythm and can proceed to deliver pre-programmed shocks without further decisions by the rescuer. These machines are simple to operate and are ideal for use by unskilled first responders. This technology is suitable for health clinics and general practitioners' surgeries.26

Members of the public may soon have access to such devices. In the United States, they have been deployed in public buildings, sporting venues and are carried by police. They have also been successfully used by family members of patients known to be at high risk of OHCA.26

New developments in the defibrillating shock may increase the efficacy and safety of defibrillation.26,27 Kerber et al have described a dual-pulse defibrillating shock.27 Different energy waveforms during defibrillation have been described by Bardy et al.28 A damped sinusoidal pattern is most often used for traditional transthoracic defibrillation. These authors have shown that during transthoracic defibrillation, a biphasic shock at 130 J is as effective as a (traditional) monophasic shock at 200 J. The shock also produces less myocardial injury and is potentially safer for bystander use.28

Current-based defibrillation is another promising alternative to traditional energy-based defibrillation. Current-based defibrillation requires the operator to select the electrical dose (amperes) rather than the energy (joules). In this way, delivery of low energy in the face of high transthoracic impedance is avoided. The defibrillator measures the transthoracic impedance, then delivers the exact current requested.26

Early advanced cardiac life support (ACLS)
ACLS has traditionally been described as having three interventions: defibrillation, endotracheal intubation and intravenous medications. Defibrillation now stands alone as the single most vital intervention of resuscitation from OHCA, and must be delivered as early as possible. Consequently, it is now rightly the responsibility of primary responders.

Endotracheal intubation
Endotracheal intubation isolates the airway, keeps it patent, permits tracheal toileting, ensures delivery of a high concentration of oxygen and provides a route for administration of certain drugs. However, no randomised controlled studies have yet been published that demonstrate a significant survival difference with this intervention when compared with basic airway management.18

Intravenous medications
Intravenous medications can be administered by a variety of routes (eg, central vein, peripheral vein). The ideal route for administering drugs to a patient in cardiac arrest is one which delivers the drug to the target organ, is simple and rapid to perform with minimal expertise, and has minimal complications. At present, no single route has all of these features.29 A large antecubital fossa vein is recommended for the initial intravenous access. Intravenous medications are discussed in Box 3.


Improving survival rates after OHCA in Australia
To improve the chance of surviving an OHCA in Australia, data must be collected according to the Utstein template. From this, all aspects of the "chain of survival" can be clearly studied and benchmarked, and developments such as public education programs and public access defibrillators can then be implemented and accurately evaluated (Box 4).

Future modification of ACLS management protocols should only be made on the basis of controlled studies.

References
  1. Becker LB, Smith DW, Rhodes KV. Incidence of cardiac arrest: a neglected factor in evaluating survival rates. Ann Emerg Med 1993; 22: 86-91.
  2. Bernard S. Outcome from prehospital cardiac arrest in Melbourne, Australia. Emerg Med 1998; 10: 25-29.
  3. Larson MP, Eisenberg MS, Cummins RO, et al. Predicting survival from out-of-hospital cardiac arrest. Ann Emerg Med 1993; 22: 1652-1658.
  4. Bett JHN. Experience with a mobile coronary care unit in Brisbane. Ann Emerg Med 1989; 18: 969-974.
  5. Jacobs IG, Oxer HF. A review of pre-hospital defibrillation by ambulance officers in Perth, Western Australia. Med J Aust 1990; 153: 662-664.
  6. Scott IA, Fitzgerald GJ. Early defibrillation in out-of-hospital sudden cardiac death: an Australian experience. Arch Emerg Med 1992; 10: 1-7.
  7. Brennan RJ, Luke C. Failed hospital resuscitation following out-of-hospital cardiac arrest: are further efforts in the emergency department warranted? Emerg Med 1995; 7: 131-138.
  8. Jackson T, Cameron PA. Prehospital defibrillation in Geelong. Emerg Med 1993; 5: 184-187.
  9. Sammel NL, Taylor K, Selig M, O'Rourke M. New South Wales intensive care ambulance system: outcome of patients with ventricular fibrillation. Med J Aust 1981; 2: 546-550.
  10. American Heart Association. Emergency Cardiac Care Committee and Subcommittees. Guidelines for cardiopulmonary resuscitation and emergency care. JAMA 1992; 268: 2171.
  11. Reichenbach DD, Moss NS, Meyer E. Pathology of the heart in sudden cardiac death. Am J Cardiol 1977; 39: 865.
  12. Eisenberg MS, Horwood BT, Cummins RO, et al. Cardiac arrest and resuscitation: a tale of 29 cities. Ann Emerg Med 1990; 19: 179-186.
  13. Eisenberg MS. Prehospital care. In: Skinner D, Swain A, Peyton R, Robertson C, editors. Cambridge textbook of accident and emergency medicine. Cambridge: Cambridge University Press, 1997: 288-298.
  14. Cummins RO, Ornato JP, Theis W, et al. Improving survival from cardiac arrest: the chain of survival concept. Circulation 1991; 83: 1832-1847.
  15. Cummins RO and Graves. Prehospital care II: European and American perspectives. In: Skinner D, Swain A, Peyton R, Robertson C, editors. Cambridge textbook of accident and emergency medicine. Cambridge University Press, 1977: 298-303.
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  18. Maguire JE. Advances in cardiac life support: sorting the science from the dogma. Emerg Med 1997; 9 Suppl: 1-8.
  19. Callahan M, Madsen CD. Relationship of timeliness of paramedic Advanced Life Support interventions to outcome in out-of hospital cardiac arrest treated by first responders with defibrillators. Ann Emerg Med 1996; 27: 638-648.
  20. Weaver WD, Cobb LA, Hallstrom AP, et al. Considerations for improving survival from out-of-hospital cardiac arrest. Ann Emerg Med 1986; 10: 1181-1186.
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  22. De Vreede-Swagamakers JJ, Gorgels AP, Dubois-Arbouw WI, et al. Out of hospital cardiac arrest in the 1990s: a population-based study in the Maastricht area on incidence, characteristics and survival. J Am Coll Cardiol 1997; 30: 1500-1505.
  23. Jackson RE, Swor RA. Who gets bystander cardiopulmonary resuscitation in a witnessed arrest? Acad Emerg Med 1997; 4: 540-544.
  24. Pantridge JF, Geddes JS. A mobile intensive care unit in the management of myocardial infarction. Lancet 1967; 2: 271-273.
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  26. Robertson CE, Nichol NM. Recent advances in defibrillation therapy. Curr Opin Crit Care 1997; 3: 214-217.
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  28. Bardy GH, Marchlinski FE, Sharma AD, et al. Multicentre comparison of truncated biphasic shocks and standard damped sinewave monophasic shocks for transthoracic ventricular defibrillation. Circulation 1996; 94: 2508-2514.
  29. ALS Working Party of the ERC. Guidelines for advanced life support. Resuscitation 1992; 22: 191-195.
  30. Hapnes SA, Robertson CE. CPR-drug delivery routes and systems. Resuscitation 1992; 24: 137-142.
  31. Linder KH, Koster R. Vasopressor drugs during cardiopulmonary resuscitation. Resuscitation 1992; 24: 147-154.
  32. Stiell IG, Herbert PC, Weitzman BN, et al. High grade epinephrine in adult cardiac arrest. N Engl J Med 1992; 327: 1045-1049.
  33. Brown CG, Martin DR, Pepe PE, et al. A comparison of standard dose and high dose epinephrine in cardiac arrest outside hospital. N Engl J Med 1992; 327: 1051-1055.
  34. Callahan M, Madsen CD, Barton CW, et al. A randomised clinical trial of high dose epinephrine and norepinephrine and standard dose epinephrine in prehospital cardiac arrest. JAMA 1992; 268: 2667-2672.
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  37. Linder KH, Dirks B, Strohmenger HU, et al. Randomised comparison of epinephrine and vasopressin in patients with out-of-hospital ventricular fibrillation. Lancet 1997; 349: 535-537.
  38. Stahmer SA, Varon J, Fromm RE. Controversies in cardiopulmonary resuscitation pharmacotherapy. Hosp Physician 1994; 30: 23-30.
  39. Steedman DJ, Robertson CE. Acid-base changes in arterial and central venous blood during cardiopulmonary resuscitation. Arch Emerg Med 1990; 9: 169-176.
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Authors' details
Emergency Department, Royal Melbourne Hospital, Melbourne, VIC.
Alastair D McR Meyer, BSc(Hons), MB BS, FACEM, Research Fellow in Emergency Medicine; and PhD Scholar, Department of Epidemiology and Preventive Medicine, Monash University.
Peter A Cameron, MD, FACEM, Director of Emergency Medicine.

Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, VIC.
Karen L Smith, BSc(Hons), GradDipEpiBiostats, PhD Scholar.
John J McNeil, PhD, FRACP, Professor; and Head of Department.

Reprints will not be available from the authors.
Correspondence: Dr A D McR Meyer, Research Fellow in Emergency Medicine, Emergency Department, Royal Melbourne Hospital, Grattan Street, Parkville, VIC 3050.

©MJA 2000
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→  Karen L Smith, John J McNeil, on behalf of the Emergency Medical Response Steering Committee. Cardiac arrests treated by ambulance paramedics and fire fighters Med J Aust 2002; 177 (6): 305-309. [Medicine and the Community] <http://www.mja.com.au/public/issues/177_06_160902/smi10834_fm.html>

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1: Survival from out-of-hospital cardiac arrest - Australian studies

 

StudyPatients/presenting rhythmSurvival (%) to discharge
Bett (1989)4 Ventricular fibrillation110 (9%)
Jacobs and Oxer (1990) 5Ventricular fibrillation231 (22%)*
Scott and Fitzgerald (1992) 6All patients with OHCA103 (17%)
Brennan and Luke (1995)7All patients with presumed cardiac arrest, arriving at hospital274 (5%)
Bernard (1998) 2All OHCA victims, presumed cardiac cause, all rhythms 361 (3%)
Jackson and Cameron (1993) 8Ventricular fibrillation/pulseless ventricular tachycardia79 (18%)
Sammel et al (1981) 9Ventricular fibrillation/pulseless ventricular tachycardia434 (21%)
*28 days after discharge. OHCA=Out-of-hospital cardiac arrest.
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2: The Utstein Consensus Conference

Two meetings in 1990 with representatives from the American Heart Association, the European Resuscitation Council, the Heart and Stroke Foundation of Canada, and the Australian Resuscitation Council:

  • Established uniform terms and definitions for out-of-hospital resuscitation;
  • Established a reporting template for resuscitation studies to ensure comparability;
  • Defined time points and time intervals relating to cardiac resuscitation;
  • Defined clinical items and outcomes that the emergency medical service should gather; and
  • Developed guidelines for describing resuscitation systems.
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3: Intravenous medications in early advanced cardiac life support

  • Adrenaline
    Catecholamines, such as adrenaline and noradrenaline, are vasopressors and have long been used as adjuncts to improve the success rate in CPR. These catecholamines increase aortic diastolic pressure by producing arteriolar vasoconstriction and improve blood delivery to the central circulation. If exogenous catecholamines are administered, improved myocardial and cerebral perfusion occurs. The optimal dose range for humans in both the prehospital and hospital stage remains unclear. 30 Three large North American multicentre trials have failed to show any benefit from the administration of high-dose adrenaline or noradrenaline in the prehospital or inhospital setting. 31-33 The recommended dose is 1mg intravenously repeated at 2-3-minute intervals. 34 There is evidence, however, that the use of adrenaline may make absolutely no difference to the outcome of VF cardiac arrest. 35,36

  • Vasopressin
    There are encouraging results with the use of vasopressin in OHCA. 37 In cardiac arrest of long duration, vasopressin seems to have greater efficacy in restoring spontaneous cardiovascular function compared with adrenaline alone. 37 More evidence is required before this drug can be recommended.

  • Antiarrhythmics
    There are many agents which have antiarrhythmic properties in patients with a cardiac output. However, the overwhelming evidence is that antiarrhythmic drug therapy has very little, if any, role to play in the treatment of OHCA. 38


    Acidaemia
    When cardiac arrest occurs, anaerobic metabolism occurs in tissues and this results in the production of large amounts of lactic and other organic acids. Good quality CPR and adequate alveolar ventilation limits the development of acidaemia. 39 Significant falls in arterial pH do not occur for the first 20 minutes after cardiac arrest. Correction of the acidosis through measures other than ventilation and restoration of circulation has not been shown to improve outcome. 38

  • Calcium
    Calcium ions play a role in myocardial contractility. A deficiency of calcium is associated with cardiac arrest. However, there is no benefit for the use of calcium in patients with asystole or VF. 40 There may be some use for this agent in specific situations of pulseless electrical activity secondary to hyperkalaemia, calcium channel blocker overdose, or hypocalcaemia.40
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    4: Strategies to improve survival from out-of-hospital cardiac arrest in Australia

    • Improved education of the public and healthcare providers in recognising cardiac arrest and accessing emergency medical services (EMS)
    • Improved training of laypersons in cardiopulmonary resuscitation
    • Increased deployment of automatic external defibrillators
    • Public access defibrillation
    • Improved ambulance response times
    • Improved data collection by the EMS throughout Australia
    • Improved communication between units researching pre-hospital resuscitation
    • An evidence-based approach to allocating resources for pre-hospital early advanced cardiac life support protocols
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