- Email: [email protected]
Re-evaluation of cardiopulmonary resuscitation
Resuscitation, 18 (1989) l- 5 Elsevier Scientific Publishers Ireland Ltd.
1
Commentary
RE-EVALUATION
OF CARDIOPULMONARY
RESUSCITATION
EDWARD L. MCNEIL Bedford NY 10506-0507 KJ.S.A.I (Accepted January 26th, 1989)
Key words: First responder CPR - Lay public CPR - Methods of CPR (desirable requirements) - Modified Schafer method
It is unfortunate that, after the prolonged and massive efforts that have gone into teaching cardiopulmonary resuscitation (CPR) to the lay public and first responders, the effectiveness has been jeopardised by the not-unjustified fears that mouth-to-mouth artificial respiration holds dangers of infection of the rescuer by viruses with deadly potential. A concern, less frequently voiced, is the possible infection of a would-be survivor being resuscitated by an alreadyinfected rescuer. Face masks equipped with one-way valves can significantly reduce the chances of contamination. In reality, emergency medical services (EMS) personnel may or may not have a suitably-equipped mask available when faced with a cardiac arrest victim. Very few of the trained public will have a mask to hand when a sudden need arises. Only a minority of those trained to perform CPR have had instruction in the use of a face mask. Ethics could be tortured deciding whether someone, who has voluntarily learnt to perform CPR (or was mandated to do so because of an employment requirement), should risk her or his health and life to give what might be a minimal chance of life to a stranger, however small that risk. The preceding considerations make it timely to look more closely at the methods we are teaching to determine whether some modifications could eliminate dangers to rescuers and also avoid certain risks to a victim (inherent in current methods) without significantly reducing the degree of effectiveness we attribute to currently-accepted methods. Resuscitation performance which immediately utilizes Advanced Life Support (ALS) methods does not present the same urgency for consideration of modifications. Current practice, with the securing of the airway by tracheal intubation eliminates some of the need for mouth-to-mouth ventilations. Early defibrillation, as presently recommended, requires the victim to be supine even if a prone position might be considered for basic CPR. 0300-9572/89/$03.50 0 1989 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
2
Mouth-to-mouth contamination is not the only factor which should prompt more consideration of how CPR methods might be modified. Gastric distention, with regurgitation of stomach contents during resuscitative efforts, continues to be a problem too frequently met and it often ensures a fatal result. It was hoped that two modifications, recommended as part of the revisions of CPR in 1986 (American Heart Association1 would reduce the chances of regurgitation. One recommendation was to reduce the force and rapidity with which a victim’s lungs were inflated by the mouth-to-mouth method. The modification took note of the valvular nature of the esophagus and attempted to lessen the share of the ventilatory effort received by the stomach. It was accepted that the modification might reduce the chance of atelectatic areas of the lungs being re-inflated however, gastric distention causes two major disadvantages; it reduces the downward excursion of the diaphragm putting a lower limit on the capacity of the lungs and, it increases the probability of regurgitation occuring. Another modification was to reintroduce cricoid pressure as a method of preventing regurgitation and for ensuring the lungs receive a lion’s share of any artifical ventilatory effort. The method was first described at a meeting of the Royal Humane Society in London more than one hundred years ago and was brought to attention again by Sellick in 1961 [l]. Sellick described it as a procedure to be used during intubation before anesthesia and its use in CPR was not promulgated at that time. Since cricoid pressure has been recommended, it has been infrequently used for the main reason that it requires three-man CPR. The required number of hands is often lacking at crucial moments. CPR is currently being taught to the lay public concentrating only on one-man CPR. One reason given for this is improved educational effectiveness minimizing loss of skills with time. Before there is any consideration of a method of performing CPR with the victim in a prone position, the desirable requirements of any method of CPR can be listed: (11Can be performed by one rescuer as effectively as by two. (21 Does not require mouth-to-mouth contact. (3) Does not cause gastric distension. (41Relieves gastric distension. (51Avoids the danger of aspiration of vomitus if regurgitation occurs. (6) Avoids the necessity for maneuvers to open the airway. (71Assists ventilation and the circulation with the same maneuver. (8) Can relieve upper airway obstruction by simulating a modified Heimlich maneuver using the same maneuver as is being used for ventilation and circulatory assist. (91Should require less than 30 min to learn. (101The simplicity of the method should promote easy retention of skills. (111If commenced in less than 4 min from the time of cardiac arrest, it should maintain a circulation which has been oxygenated sufficiently to allow ALS methods to have a reasonable chance of success at resuscitation if available within 8 min from the time of arrest. If the current method of performing CPR is evaluated against the requirement listed, it will have to be admitted that it fails to meet the requirements in the first ten out of eleven listed. Before the accepted method of performing CPR was that of giving mouth-tomouth ventilations alternating with chest compressions over the sternum with
3
the victim in a supine position, the Schafer method of artifical respiration was commonly taught and it is possible that more than a million people were taught the method and maintained their ability to perform it due to its simplicity. In 1958, when Dr. Peter Safar [2] correctly assumed that mouth-to-mouth ventilation was more effective than ventilating using the Holger-Neilsen or Sylvester methods, it was not considered that the Schafer method, nor the Holger-Neilsen or Sylvester methods, gave any assistance to the circulation. As CPR was being developed, opinion was that the chest compressions were pumping the circulation by intermittently squeezing the heart against the spine. It was only later that Criley and his colleagues [3 - 51demonstrated that the pressure gradients within the thorax during chest compressions had a large effect towards assisting the circulation in both the aortic and pulmonary systems. At the time of being in vogue, the Schafer method was only thought to be a way of giving artificial respiration. It is unlikely that much consideration was given to the thought that the method was perhaps helping the circulation. The victims on whom the method was performed may have been pulseless as well as in respiratory arrest. ALS was not available, as it sometimes is now, that could have successfully resuscitated a victim with a lethal cardiac rhythm who was possibly being maintained by the method of artificial respiration being applied. It is difficult, if not impossible, to judge how better the Schafer method might have been considered if it had been part of a BLWALS interface. Schafer recommended 12 posterior chest compressions per minute. If the rate of compressions would be increased to IO/min, which still would allow recoil of the thorax between compressions and would increase circulatory assistance, it would be valuable to know whether this could give an oxygenated circulation sufficient to allow ALS a chance of success. Should it be shown that the important requirements for ideal CPR can indeed be met by using a modified Schafer method, major benefits would accrue in the fight against the third symptom of coronary heart disease (sudden death), against death by aspiration of vomitus, death by having insufficient hands to perform cricoid pressure, death by fear of AIDS, and death by ribs broken when current CPR is overzealously applied. If Crile [4] and others have shown that CPR can be self-administered by continuous intermittent coughing, a modified Schafer method which would simulate performing 40 modified Heimlich maneuvers per minute should be given a chance of showing if it can be effective. Other reasons for investigating the effectiveness of the modified Schafer method can be found by careful study of Dr. Peter Safar’s paper of 1958 [2]. The two methods of artificial respiration compared with mouth-to-mouth ventilation were the Sylvester method in which the victim was supine, the arms being lifted between anterior chest compressions, and the Holger-Neilsen method in which the patient was prone but the arms were still lifted between posterior chest compressions. The Schafer method, which does not use arm lifting between compressions, was not compared. It is difficult to see how the arm lifting provided any advantages (the spring-
4
back effect of the ribs allowing the thorax to re-expand after compressions) but, it can be seen to cause disadvantages. In the prone position (Holger-Neilsenl arm lifting would cause intermittent flexion and torsion of the neck contributing to airway obstruction. In both positions, prone or supine, arm lifting used up time that reduced the frequency of chest compressions. In the Schafer method, the forehead of the victim would be on the back of one of the forearms of the victim providing a degree of extension and leaving some space for the mandible to fall naturally forward with more chance of opening the airway. Such a position would also limit the torsion of the neck which can also obstruct the airway. Mouth-to-mouth ventilation provides expired air from the rescuer containing approximately 16% oxygen. Approximately 21% oxygen is provided during the inspiratory phase of the Schafer method. When the Holger-Neilsen method was studied by Dr. Safar, it was studied in three circumstances: (11 head extended; (21 natural position; (31 with oropharyngeal airway. The head extended gave the best results (without an artifical airway). Most results were judged on very few breaths (some only 4 or 61. In only one case was a patient studied over 34 breaths (head extended without oropharyngeal airway) and in that case the average tidal volume was 859 ml (range 560 - 9601. Reading the tables documenting the results of the various methods, it can be noted that an average tidal volume was what was judged as the index of efficiency. An example would be one case in which the average tidal volume was 40 ml (range O-5401 in 12 breaths. It can be assumed that some of those breaths must have been with an obstructed airway to give a zero tidal volume. It can also be assumed that some breaths definitely had a tidal volume considerably greater than the deadspace (approx. 150 ml.). The fact that the tidal volumes varied so much from one breath to another in the same patient in the same experiment could be attributed to the intermittent arm-lifting interfering with the head position. Looking back to Gordon’s work in 1951, he did manage to move 1000 ml of air per breath with back pressure (allbeit with endotracheal intubationl but it shows that back pressure can move sufficient air if the airway is patent. It should be remembered that the studies of Dr. Peter Safar in 1958 did not take into account any consideration of pulselessness or the implications of limiting the number of breaths provided because of having to interpose cardiac compressions. Gastric distension was mentioned in the study but its dangers were not mentioned, only that it could be relieved by epigastric pressure. The patients and the volunteers in the study had not had large meals of pizza or spagetti which we frequently have to deal with during the resuscitation of patients who regurgitate the stomach contents. Analysis of the results of Dr. Safar’s experiments should not discourage some re-evaluation of the Schafer method of artificial respiration with a modified rate of posterior compressions which might well be providing CPR. REFERENCES 1
B.A. Sellick, Cricoid pressure to control regurgitation anesthesia, Lance& 2 (1961) 404.
of stomach contents
during induction of
5 2
P. Safar, L. Escarraga and J. Elam, A comparison of the mouth-to-mouth and mouth-to-airway methods of artificial respiration with chest-pressure arm-lift methods, N. Engl. J. Med., (1958) 258-671. 3 J.M. Criley, J.T. Niemann and J.P. Rosborough, The heart as a conduit in C.P.R., Crit. Care Med., 9(5) (1981) 3’73-374. 4 J.M. Criley, A.H. Blaufuss, G.L. Kissel et al., Cough-induced cardiac compression: self-administered form of C.P.R., J. Am. Med. Assoc., 36 (1976) 1246- 1250. 5 J.T. Neumann, J. Rosborough, M. Hausknecht, D. Brown and J.M. Criley, Cough-CPR: documentation of systemic perfusion in man and in an experimental modei: a “window” to the mechanism of blood flow in external CPR, Crit. Care Med., March 8(3) (1980) 141- 146. 6 A.S. Gordon et al., Air-flow patterns and pulmonary ventilation during manual artificial respiration on apnoeic normal adults, J. Appl. Physiol., 4 (1951) 408- 420.
1
Commentary
RE-EVALUATION
OF CARDIOPULMONARY
RESUSCITATION
EDWARD L. MCNEIL Bedford NY 10506-0507 KJ.S.A.I (Accepted January 26th, 1989)
Key words: First responder CPR - Lay public CPR - Methods of CPR (desirable requirements) - Modified Schafer method
It is unfortunate that, after the prolonged and massive efforts that have gone into teaching cardiopulmonary resuscitation (CPR) to the lay public and first responders, the effectiveness has been jeopardised by the not-unjustified fears that mouth-to-mouth artificial respiration holds dangers of infection of the rescuer by viruses with deadly potential. A concern, less frequently voiced, is the possible infection of a would-be survivor being resuscitated by an alreadyinfected rescuer. Face masks equipped with one-way valves can significantly reduce the chances of contamination. In reality, emergency medical services (EMS) personnel may or may not have a suitably-equipped mask available when faced with a cardiac arrest victim. Very few of the trained public will have a mask to hand when a sudden need arises. Only a minority of those trained to perform CPR have had instruction in the use of a face mask. Ethics could be tortured deciding whether someone, who has voluntarily learnt to perform CPR (or was mandated to do so because of an employment requirement), should risk her or his health and life to give what might be a minimal chance of life to a stranger, however small that risk. The preceding considerations make it timely to look more closely at the methods we are teaching to determine whether some modifications could eliminate dangers to rescuers and also avoid certain risks to a victim (inherent in current methods) without significantly reducing the degree of effectiveness we attribute to currently-accepted methods. Resuscitation performance which immediately utilizes Advanced Life Support (ALS) methods does not present the same urgency for consideration of modifications. Current practice, with the securing of the airway by tracheal intubation eliminates some of the need for mouth-to-mouth ventilations. Early defibrillation, as presently recommended, requires the victim to be supine even if a prone position might be considered for basic CPR. 0300-9572/89/$03.50 0 1989 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
2
Mouth-to-mouth contamination is not the only factor which should prompt more consideration of how CPR methods might be modified. Gastric distention, with regurgitation of stomach contents during resuscitative efforts, continues to be a problem too frequently met and it often ensures a fatal result. It was hoped that two modifications, recommended as part of the revisions of CPR in 1986 (American Heart Association1 would reduce the chances of regurgitation. One recommendation was to reduce the force and rapidity with which a victim’s lungs were inflated by the mouth-to-mouth method. The modification took note of the valvular nature of the esophagus and attempted to lessen the share of the ventilatory effort received by the stomach. It was accepted that the modification might reduce the chance of atelectatic areas of the lungs being re-inflated however, gastric distention causes two major disadvantages; it reduces the downward excursion of the diaphragm putting a lower limit on the capacity of the lungs and, it increases the probability of regurgitation occuring. Another modification was to reintroduce cricoid pressure as a method of preventing regurgitation and for ensuring the lungs receive a lion’s share of any artifical ventilatory effort. The method was first described at a meeting of the Royal Humane Society in London more than one hundred years ago and was brought to attention again by Sellick in 1961 [l]. Sellick described it as a procedure to be used during intubation before anesthesia and its use in CPR was not promulgated at that time. Since cricoid pressure has been recommended, it has been infrequently used for the main reason that it requires three-man CPR. The required number of hands is often lacking at crucial moments. CPR is currently being taught to the lay public concentrating only on one-man CPR. One reason given for this is improved educational effectiveness minimizing loss of skills with time. Before there is any consideration of a method of performing CPR with the victim in a prone position, the desirable requirements of any method of CPR can be listed: (11Can be performed by one rescuer as effectively as by two. (21 Does not require mouth-to-mouth contact. (3) Does not cause gastric distension. (41Relieves gastric distension. (51Avoids the danger of aspiration of vomitus if regurgitation occurs. (6) Avoids the necessity for maneuvers to open the airway. (71Assists ventilation and the circulation with the same maneuver. (8) Can relieve upper airway obstruction by simulating a modified Heimlich maneuver using the same maneuver as is being used for ventilation and circulatory assist. (91Should require less than 30 min to learn. (101The simplicity of the method should promote easy retention of skills. (111If commenced in less than 4 min from the time of cardiac arrest, it should maintain a circulation which has been oxygenated sufficiently to allow ALS methods to have a reasonable chance of success at resuscitation if available within 8 min from the time of arrest. If the current method of performing CPR is evaluated against the requirement listed, it will have to be admitted that it fails to meet the requirements in the first ten out of eleven listed. Before the accepted method of performing CPR was that of giving mouth-tomouth ventilations alternating with chest compressions over the sternum with
3
the victim in a supine position, the Schafer method of artifical respiration was commonly taught and it is possible that more than a million people were taught the method and maintained their ability to perform it due to its simplicity. In 1958, when Dr. Peter Safar [2] correctly assumed that mouth-to-mouth ventilation was more effective than ventilating using the Holger-Neilsen or Sylvester methods, it was not considered that the Schafer method, nor the Holger-Neilsen or Sylvester methods, gave any assistance to the circulation. As CPR was being developed, opinion was that the chest compressions were pumping the circulation by intermittently squeezing the heart against the spine. It was only later that Criley and his colleagues [3 - 51demonstrated that the pressure gradients within the thorax during chest compressions had a large effect towards assisting the circulation in both the aortic and pulmonary systems. At the time of being in vogue, the Schafer method was only thought to be a way of giving artificial respiration. It is unlikely that much consideration was given to the thought that the method was perhaps helping the circulation. The victims on whom the method was performed may have been pulseless as well as in respiratory arrest. ALS was not available, as it sometimes is now, that could have successfully resuscitated a victim with a lethal cardiac rhythm who was possibly being maintained by the method of artificial respiration being applied. It is difficult, if not impossible, to judge how better the Schafer method might have been considered if it had been part of a BLWALS interface. Schafer recommended 12 posterior chest compressions per minute. If the rate of compressions would be increased to IO/min, which still would allow recoil of the thorax between compressions and would increase circulatory assistance, it would be valuable to know whether this could give an oxygenated circulation sufficient to allow ALS a chance of success. Should it be shown that the important requirements for ideal CPR can indeed be met by using a modified Schafer method, major benefits would accrue in the fight against the third symptom of coronary heart disease (sudden death), against death by aspiration of vomitus, death by having insufficient hands to perform cricoid pressure, death by fear of AIDS, and death by ribs broken when current CPR is overzealously applied. If Crile [4] and others have shown that CPR can be self-administered by continuous intermittent coughing, a modified Schafer method which would simulate performing 40 modified Heimlich maneuvers per minute should be given a chance of showing if it can be effective. Other reasons for investigating the effectiveness of the modified Schafer method can be found by careful study of Dr. Peter Safar’s paper of 1958 [2]. The two methods of artificial respiration compared with mouth-to-mouth ventilation were the Sylvester method in which the victim was supine, the arms being lifted between anterior chest compressions, and the Holger-Neilsen method in which the patient was prone but the arms were still lifted between posterior chest compressions. The Schafer method, which does not use arm lifting between compressions, was not compared. It is difficult to see how the arm lifting provided any advantages (the spring-
4
back effect of the ribs allowing the thorax to re-expand after compressions) but, it can be seen to cause disadvantages. In the prone position (Holger-Neilsenl arm lifting would cause intermittent flexion and torsion of the neck contributing to airway obstruction. In both positions, prone or supine, arm lifting used up time that reduced the frequency of chest compressions. In the Schafer method, the forehead of the victim would be on the back of one of the forearms of the victim providing a degree of extension and leaving some space for the mandible to fall naturally forward with more chance of opening the airway. Such a position would also limit the torsion of the neck which can also obstruct the airway. Mouth-to-mouth ventilation provides expired air from the rescuer containing approximately 16% oxygen. Approximately 21% oxygen is provided during the inspiratory phase of the Schafer method. When the Holger-Neilsen method was studied by Dr. Safar, it was studied in three circumstances: (11 head extended; (21 natural position; (31 with oropharyngeal airway. The head extended gave the best results (without an artifical airway). Most results were judged on very few breaths (some only 4 or 61. In only one case was a patient studied over 34 breaths (head extended without oropharyngeal airway) and in that case the average tidal volume was 859 ml (range 560 - 9601. Reading the tables documenting the results of the various methods, it can be noted that an average tidal volume was what was judged as the index of efficiency. An example would be one case in which the average tidal volume was 40 ml (range O-5401 in 12 breaths. It can be assumed that some of those breaths must have been with an obstructed airway to give a zero tidal volume. It can also be assumed that some breaths definitely had a tidal volume considerably greater than the deadspace (approx. 150 ml.). The fact that the tidal volumes varied so much from one breath to another in the same patient in the same experiment could be attributed to the intermittent arm-lifting interfering with the head position. Looking back to Gordon’s work in 1951, he did manage to move 1000 ml of air per breath with back pressure (allbeit with endotracheal intubationl but it shows that back pressure can move sufficient air if the airway is patent. It should be remembered that the studies of Dr. Peter Safar in 1958 did not take into account any consideration of pulselessness or the implications of limiting the number of breaths provided because of having to interpose cardiac compressions. Gastric distension was mentioned in the study but its dangers were not mentioned, only that it could be relieved by epigastric pressure. The patients and the volunteers in the study had not had large meals of pizza or spagetti which we frequently have to deal with during the resuscitation of patients who regurgitate the stomach contents. Analysis of the results of Dr. Safar’s experiments should not discourage some re-evaluation of the Schafer method of artificial respiration with a modified rate of posterior compressions which might well be providing CPR. REFERENCES 1
B.A. Sellick, Cricoid pressure to control regurgitation anesthesia, Lance& 2 (1961) 404.
of stomach contents
during induction of
5 2
P. Safar, L. Escarraga and J. Elam, A comparison of the mouth-to-mouth and mouth-to-airway methods of artificial respiration with chest-pressure arm-lift methods, N. Engl. J. Med., (1958) 258-671. 3 J.M. Criley, J.T. Niemann and J.P. Rosborough, The heart as a conduit in C.P.R., Crit. Care Med., 9(5) (1981) 3’73-374. 4 J.M. Criley, A.H. Blaufuss, G.L. Kissel et al., Cough-induced cardiac compression: self-administered form of C.P.R., J. Am. Med. Assoc., 36 (1976) 1246- 1250. 5 J.T. Neumann, J. Rosborough, M. Hausknecht, D. Brown and J.M. Criley, Cough-CPR: documentation of systemic perfusion in man and in an experimental modei: a “window” to the mechanism of blood flow in external CPR, Crit. Care Med., March 8(3) (1980) 141- 146. 6 A.S. Gordon et al., Air-flow patterns and pulmonary ventilation during manual artificial respiration on apnoeic normal adults, J. Appl. Physiol., 4 (1951) 408- 420.