Brendan Docherty, MSc, RN, PGCE.
Clinical Manager - Cardiology and Critical Care
Early advanced life support provided by a hospital cardiac arrest team or ambulance crew is an important element of the ‘chain of survival’ for patients in cardiorespiratory arrest (Chellel, 2000).
In 2000 the first international resuscitation guidelines were produced to ensure that the underlying scientific principles of life-saving techniques are similar across the globe (Winser, 2001). The Resuscitation Council UK guidelines are based on these international principles (RCUK, 2000a) and all health-care personnel should follow these guidelines when diagnosing and treating patients experiencing cardiorespiratory arrest, whatever their location.
The cardiac arrest treatment algorithm divides cardiopulmonary resuscitation into the treatment of shockable rhythms - ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT) (Figure 1); and the treatment of non-shockable rhythms - asystole and pulseless electrical activity (PEA) (Figure 2).
In cases of sudden cardiorespiratory arrest where the collapse has been witnessed or monitored, a precordial thump should be delivered (RCUK and ERC, 2000). Although this is not highly effective, it will in some cases revert a shockable rhythm into a rhythm with a cardiac output (RCUK and ERC, 2000).
In order to determine the cardiac arrest rhythm, a monitor/defibrillator is attached to the patient. This is done either using the three-lead technique or via two large multifunction electrode pads - the latter is thought to have a small but significantly more positive effect on outcomes due to the time saved (Hand, 2002; Perkins et al, 2001). Use of defibrillator paddles to take a ‘quick look’ at the victim’s rhythm is not advocated because it is unreliable (RCUK, 2000b) and if there is any delay in the arrival of the monitor/defibrillator, basic life support (BLS) should be commenced (Docherty and Hall, 2002).
Once a rhythm is seen on the monitor trace BLS should be stopped and the victim assessed for signs of a circulation for 10 seconds using the carotid pulse; all rhythms are electrical impulses and may therefore not reflect the actual mechanical output of the heart (Tortora and Grabowski, 2001).
After oxygen, Epinephrine (adrenaline) is the main first-line cardiac arrest drug and is used every two to three minutes. Alpha effects include increasing myocardial contractility, therefore lowering the electrical threshold and making it easier to revert a shockable rhythm back to a perfusing rhythm; and peripheral vasoconstriction, ensuring that blood resources are pooled centrally to optimise BLS. Beta effects include bronchodilation to aid oxygenation and central dilation of the coronary and cerebral arteries to aid perfusion (BMA/RPSGB, 2002).
- VF (Figure 3) is a chaotic pattern of electrical activity in the ventricles of the heart where impulses arise from many different foci, producing no effective muscular contraction and therefore no cardiac output (Docherty and Roe, 2001). It appears on an electrocardiogram (ECG) as irregular and abnormal deflections of varying height and width and the baseline is irregular without any identifiable QRS complexes (Hand, 2002).
- VT (Figure 4) is usually a regular pattern of electrical activity in the ventricles of the heart where impulses usually arise from a ventricular focus in the right or left ventricle. This rhythm may or may not result in effective muscular contraction of the ventricles. It appears on an ECG as a regular or slightly irregular ventricular rate of between 100 and 220 beats per minutes, QRS complexes are wide and bizarre and no P-wave activity is visible (Hand, 2002; Docherty and Roe, 2001). When pulseless, VT is treated as VF.
Shockable rhythms are treated with defibrillation. Defibrillation is the passage of an electrical current across a critical mass of myocardium to depolarise myocardial cells simultaneously and allow natural pacemaking tissue to resume control (RCUK and ERC, 2000). Defibrillator shocks should be delivered as soon as possible as the survival rate falls by approximately 7-10% for each minute that passes after collapse (RCUK and ERC, 2000).
Up to three consecutive defibrillatory shocks are delivered as this grouping of shocks acts to reduce the transthoracic impedance offered by the structures of the chest, increasing the effectiveness of shocks. Applying 10kg force when pressing the defibrillator paddles down firmly on the patient’s chest will further reduce impedance (Jevon, 2002; RCUK and ERC, 2000).
If the victim is in a non-shockable rhythm then Figure 2 is followed.
- Asystole (Figure 5) is a total absence of electrical activity in the heart resulting in no mechanical activity and no cardiac output. It appears on an ECG trace as an isoelectric line with some slight wandering baseline movement - rarely is it a perfectly straight line (Docherty and Roe, 2001).
- PEA (Figure 6) is the absence of a pulse with an ECG tracing in which you would normally expect to see a pulse (RCUK and ERC, 2000; Docherty and Roe, 2001).
BLS is performed on both sides of the algorithm to deliver oxygen to the victim and circulate that oxygen to the brain and heart (RCUK, 2000a). While carrying out BLS, the victim’s airway should be secured, ideally through endotracheal intubation, and 100% oxygen delivered, intravenous access obtained (if possible sending blood for analysis) and drugs delivered.
If these resuscitation techniques are initially unsuccessful the eight common potentially reversible causes of cardiorespiratory arrest (Figure 2) should be investigated and either eliminated or treated before the resuscitation attempt is abandoned.
ANATOMY AND PHYSIOLOGY
- Blood contains haemoglobin, which is responsible for carrying oxygen to the tissues - saturated haemoglobin is called oxyhaemoglobin. One red blood cell contains approximately 280 million haemoglobin molecules
- In normal function, we consume only one-quarter of circulating oxygen from haemoglobin, hence we expire 16% oxygen in respiration processes
- The heart has 1% autorhythmic tissue (for example in the sino-atrial node) and has the ability to repeatedly generate contracting impulses called the cardiac cycle
- The autonomic nervous system regulates cardiac and respiratory function through sympathetic (fight or flight response) and para-sympathetic (restorative) neural networks
(Tortora and Grabowski, 2001).
- In a recent audit of resuscitation outcomes, of those patients who arrested with a shockable rhythm 42% were discharged alive. At follow-up at six months, 82% of this group were still alive. For those with non-shockable rhythms only 6% were discharged from hospital care
- The factors that contribute to a more successful resuscitation attempt include a cardiac arrest which is a shockable rhythm, return of the spontaneous circulation within three minutes of the arrest and in those aged 70 years or under
- Using electrocardiogram leads to monitor cardiac arrests reduces the incidence of artefact and spurious asystole. The use of hands-free adhesive electrodes may also improve outcomes by a further 5% (RCUK, 2000c; RCUK, 2000d)
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