Dr David Birt,
Royal Hospital for Sick Children, Glasgow

Mr BG Thomas,
Resuscitation Training Officer

Dr Iain Wilson,
Royal Devon and Exeter Hospital (Wonford), Exeter EX2 5DW

Introduction		Avanced Life Support
Background Physiology and Pathophysiology		Specialised Life Support
Causes of Cardiac Arrest		Ventricular Fibrillation or Pulseless Ventricular Tachycardia
Prevention of Cardiac Arrest		Post Arrest Mangement
Resuscitation		Further Reading
Basic Life Support

Introduction

In recent years, organisations such as the European Resuscitation Council, the American Heart Association and the International Liaison Committee on Resuscitation have produced guidelines in an attempt to improve the quality of cardiopulmonary resuscitation (CPR). They are based on international consensus views and the most recent of them, relating to Advanced Life Support, were published in 1998. The techniques of CPR, based on such guidelines, have now become a standard part of health professional training in many parts of the world.

The aim of this article is to provide an overview of resuscitation based on these guidelines and will be confined to the management of cardiac arrest including some comment on the more specialised areas of electrocution, drowning and arrests related to anaesthesia. 

Background Physiology And Pathophysiology

The maintenance of normal tissue metabolism relies principally on an adequate delivery of oxygen, in a functioning circulation. Failure of delivery rapidly results in the following changes:

Hypoxia After a brief period of cardiac arrest, PaO2 falls dramatically as oxygen continues to be consumed. In addition, progressive accumulation of carbon dioxide shifts the oxygen-haemoglobin dissociation curve to the right. This initially improves oxygen transfer to the tissues but without further delivery tissue hypoxia ensues. In the brain, the PaO2 falls from 13kPa to 2.5 kPa within 15 seconds and consciousness is lost. After a minute, the PaO2 will have fallen to zero.

Acidosis The brain and heart have a relatively high rate of oxygen consumption (4mls/min and 23mls/min respectively) and O2 delivery to them will fall below critical levels during cardiac arrest. In the case of ventricular fibrillation, myocardial metabolism continues at an approximately normal rate, exhausting oxygen and high energy phosphate supplies. Acidosis then arises as the result of increased anaerobic metabolism and the accumulation of carbon dioxide in the tissues.

The degree of acidosis developing in the brain, even with basic life support, will threaten tissue survival within 5 - 6 minutes. Also, in the heart, even with the restoration of a perfusing rhythm, acidosis depresses contractility and there is a higher risk of further arrhythmias.

Cardiovascular collapse prompts a massive stress response. Catecholamines are released in large amounts, together with adrenal corticosteroids, anti-diuretic hormone and other hormonal responses. The possible detrimental effects of these changes include hyperglycaemia, hypokalaemia, increased lactate levels and a tendency towards further arrhythmias. 

Causes Of Cardiac Arrest

There are many causes of cardiac arrest. In the developed world most are related to ischaemic heart disease. Table 1 lists other common causes.

Table 1. Causes of Cardiac Arrest
Cardiac disease	Respiratory causes
Ischaemic heart disease	Hypoxia (usually causes asystole)
Acute circulatory obstruction	Hypercapnia
Fixed output states	Metabolic changes
Cardiomyopathies	Potassium disturbances
Myocarditis	Acute hypercalcaemia
Trauma and tamponade	Circulating catecholamines
Direct myocardial stimulation	Hypothermia
Circulatory causes	Drug effects
Hypovolaemia	Direct pharmacological actions
Tension pneumothorax	Secondary effects
Air or pulmonary embolism	Miscellaneous causes
Vagal reflex mechanisms	Electrocution
	Drowning

Prevention Of Cardiac Arrest

Patients who develop a cardiac arrest may have been severely ill for some hours prior to the event. Warning signs such as: hypotension, tachycardia, chest pain, dyspnoea, fever, restlessness or confusion indicate that a patient is seriously ill. Hypoxaemia, hypovolaemia and sepsis may progress to cardiac arrest unless rapidly diagnosed and corrected. CPR for patients who are septic or hypovolaemic usually fails. 

Resuscitation

The primary aim of resuscitation is to restore a beating heart and a functioning circulation. This article considers basic and advanced life support. 

Basic Life Support

Basic Life Support (BLS) establishes a clear airway followed by assisted ventilation and support of the circulation, all without the aid of specialised equipment. The recommended sequence for BLS is shown in figure1. When approaching a patient who appears to have suffered a cardiac arrest the rescuer should check that there are no hazards to himself before proceeding to treat the patient. Although this rarely arises in hospital, patients may suffer a cardiac arrest due to electric shocks or toxic substances. In these situations the rescuer may be in considerable danger, and must ensure that any hazard is taken account of and eliminated as a risk. Checking responsiveness is best done by speaking loudly to the casualty, and trying to rouse them by shaking a shoulder. If there is no response send for help as the patient is being treated. Opening the airway This can normally be done by simply extending the head and performing a chin lift. In some patients a jaw thrust will be required along with the insertion of an oropharyngeal airway. False teeth that are loose or other debris within the airway should be removed. Assisted ventilation should be provided if the patient is not breathing. It may be provided using expired air ventilation (mouth to mouth, mouth to nose, using a Laerdel pocket mask) or by using a self inflating bags, usually with supplemental oxygen. Oxygen should be added to self inflating bag, using a reservoir on the inlet side of the bag. Adequacy of ventilation is judged by each breath producing adequate movement of the chest on inspiration. In general tidal volumes of 400 - 500mls are optimal.

Chest compressions (previously known as cardiac massage) are used whenever a central pulse (carotid) is absent. The technique creates positive pressure within the chest and forces blood out of the chest during the compression phase. Due to the valves within the venous system and the heart, most of the blood flows forward through the arteries. When the chest recoils to its normal position blood returns to the chest from the venous side of the circulation. A small amount of flow is produced by direct compression of the heart between the sternum and the spine. During chest compressions approximately 25% of the normal cardiac output is produced.

Current guidelines advise that 5 chest compressions are carried out for each ventilation when two rescuers are available. In the event of only one rescuer, 15 compressions should be followed by 2 ventilations. The overall rate of chest compressions should be 100/minute.

When starting chest compressions: Get the patient on a firm surface Feel the xiphisternum, and measure 2 finger breadths up on the sternum (figure 2). Without moving your fingers, place the heel of the second hand on the sternum. Put both hands together as shown in figure 3 and depress the sternum 4-5cm in an adult. Keep your elbows (figure 4) straight, and ensure that all the pressure is directed through the sternum and not through the ribs. To perform chest compressions adequately, it is necessary to be above the patient. Stand on a platform if necessary. During a cardiac arrest change the person performing chest compressions regularly, as it is tiring when performed properly. The rescuer performing chest compressions should count out loud "1,2,3,4,5", and the rescuer ventilating the patient should count the number of cycles completed. Early BLS has been shown to improve outcome, particularly when access to advanced airway management and defibrillation is likely to be delayed. Although the barely adequate level of oxygen delivery achieved during BLS may be regarded as a holding measure, it is of great importance and will occasionally reverse the primary cause of the cardiac arrest and restore some circulation preventing the rhythm degenerating into asystole.  Advanced Life Support Advanced Life Support refers to the use of specialised techniques, in an attempt to rapidly restore an effective rhythm to the heart. The most important components of the advanced life support techniques are direct current defibrillation and efficient BLS. The general principles involved with resuscitation from a cardiac arrest are shown in Table 2, and each technique involved with ALS is described below. Table 2: General Management Principles for Cardiac Arrest Establish the safety of the victim and potential rescuer. Confirm the diagnosis of an arrest Send for help Establish Basic Life Support Aim for early and frequent defibrillation if indicated, with regular doses of adrenaline and CPR. If there is doubt about the rhythm, or no ECG monitor is available, treat adults as being in VF. Except for defibrillation, chest compressions should not be interrupted for more than 10 seconds to allow invasive procedures or advanced airway management. Administer drugs intravenously whenever possible. Use a 20-50ml 0.9% saline flush with the peripheral route. Consider and treat any underlying causes Consider antiarrhythmic drugs and sodium bicarbonate as described below.

(Continued ...)

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