1. During CPR blood flow to the lungs is substantially reduced so an adequate ventilation-perfusion ratio can be maintained with tidal volumes and respiratory rates lower than normal(8).

2. Not only is hyperventilation (too many breaths or too large volumes) unnecessary but it is harmful because it increases intra-thoracic pressure thus decreasing venous return to the heart and diminishing cardiac output; survival is consequently reduced(9).

3. When the airway is unprotected a tidal volume of 1 L produces significantly more gastric distention than a tidal volume of 500 ml(10).

4. Low minute ventilation (lower than normal tidal volume and respiratory rate) can maintain effective oxygenation and ventilation during CPR(11-14). During CPR a tidal volume of approximately 500 - 600 ml should be adequate.

5. Interruptions in chest compressions (for example to give rescue breaths) have a detrimental effect on survival(15). Giving rescue breaths over a shorter time will help to reduce the duration of essential interruptions.

A major change in the new guidelines is the emphasis on minimizing the interruptions of chest compressions. The new recommendation is to give 30 compression and 2 rescue breaths rather than the 15 and 2 in the guidelines of 2000(1). The reason behind this recommendation is that coronary blood flow decreases substantially when chest compressions are stopped and several compressions are then necessary before the coronary flow recovers its previous level(3,4).

There is insufficient evidence to support a specific hand position for chest compression during CPR in adults. The new guidelines recommend placing the heel of the hand in the center of the chest with the other hand on top(6).

The previous guideline of finding the middle of the lower half of the sternum by placing one finger on the lower end of the sternum and sliding the other hand down to it has been omitted.

Another major change from the previous guidelines is related to defibrillation. The new guidelines emphasize the importance of early defibrillation as the ability to deliver early defibrillation is one of the most important factors in determining survival from cardiac arrest. However these guidelines recommend, for out-of-hospital but not in-hospital VF or VT, to give a period of CPR for two minutes before defibrillation despite the evidence supporting this being weak and coming only from animal studies(16,17,18).

The recent guidelines recommend giving only one shock wave of 150-360 J of bi-phasic or 360 J of mono-phasic defibrillators, followed immediately by CPR for two minutes without the need to check for the rhythm or pulse after delivering the shock wave. The reason is to prevent interruptions of CPR during defibrillation as this is associated with post-resuscitation myocardial dysfunction and reduced survival as well as reducing the chances of converting VF to another rhythm. Furthermore the first shock efficacy of biphasic wave forms exceeds 90% and failure to convert VF successfully is more likely to suggest the need for a period of CPR rather than a further shock.

Even if the defibrillation attempt is successful in restoring a perfusing rhythm, it is very rare for the pulse to be palpable immediately after defibrillation. Moreover, even if a perfusing rhythm has been restored, giving chest compressions does not increase the chances of VF recurring(15,16,19,20,21).

Here is a summary of the latest ERC Guidelines for Adult Resuscitation (12-03-2005) released by ERC:

• The decision to start CPR is made if the victim is unresponsive and is not breathing normally.

• Rescuers should be taught to place the hands on the center of the chest instead of wasting time by using the “rib margin” method.

• Each rescue breath is given over 1 second rather than 2 seconds.

• The ratio of compression to ventilations is 30:2 for adult victims of cardiac arrest.

• For an adult victim the first two rescue breaths are omitted, with 30 compressions being given immediately after cardiac arrest is established.

• Public access defibrillation (PAD) programs are recom mended for locations where the expected use of an AED for witnessed cardiac arrest exceeds once in two years.

• A single defibrillatory shock (at least 150 J biphasic or 360 J monophasic) is delivered, followed immediately by 2 minutes of uninterrupted CPR without a check for termination of VF or a check for signs of life or a pulse.
 

C) Main changes in adult advanced life support (Figure 2).
 

Figure 2:  Adult Basic Life Support Cardiac Arrest Algorithm

• In an out-of-hospital cardiac arrest attended but not witnessed by health care professionals equipped with manual defibrillators, give CPR for 2 minutes (i.e. about 5 cycles at 30:2) before defibrillation.

• Don’t delay defibrillation if an out-of-hospital arrest is witnessed by a health care professional.

• Don’t delay defibrillation for in-hospital cardiac arrest.

• Treat VF/pulseless VT with a single shock, followed by immediate resumption of CPR (30 compressions to 2 ventilations). Do not reassess the rhythm or feel for a pulse. After 2 minutes of CPR check the rhythm and give another shock (if indicated).

• The recommended initial energy for biphasic defibrillators is 150-200 J. Give second and subsequent shocks at 150-360 J.

• The recommended energy when using a monophasic defibrillator is 360 J for both the initial and subsequent shocks.

• If there is doubt about whether the rhythm is asystole or fine VF, do not attempt defibrillation, instead continue chest compressions and ventilation.

• VF/VT: Give adrenaline 1 mg IV if VF/VT persists after a second shock. Repeat the adrenaline every 3-5 min thereafter if VF/VT persists.

• PEA/Asystole: Give adrenaline 1mg IV as soon as intravenous access is obtained, and repeat every 3-5 min thereafter until return of spontaneous circulation (ROSC) is achieved.

• If VF/VT persists after three shocks, give amiodarone 300 mg by bolus injection. A further dose of 150 mg may be given for recurrent or refractory VF/VT, followed by an infusion of 900 mg over 24 hours.

• If amiodarone is not available lidocaine 1mg/kg can be used as an alternative but do not give lidocaine if amiodarone has been given already. Do not exceed a total of 3 mg/kg of lidocaine during the first hour.

• Consider thrombolytic therapy when cardiac arrest is thought to be due to proven or suspected pulmonary embolus. Thrombolysis may be considered in adult cardiac arrest on a case-by-case basis following initial failure of standard resuscitation in patients in whom an acute thrombotic etiology for the arrest is suspected. Ongoing CPR is not a contra-indication to thrombolysis.