The experimental development of modern resuscitation

Resuscitation (x972), I, g

The experimental development of modem resuscitation L. H. HAWKINS Department of Biological Sciences, University of Surrey, Guildford, Surrey, U.K.

The paper reviews the experimental work which has led to the techniques ofresuscitation in use today. Methods of artificial ventilation have changed from those involving chest compression to those employing positive pressure inflation of the lungs from expired air or mechanical means. The evidence is examined that positive pressure inflation is deleterious to the circulation, and also the possibility that some methods of artifical ventilation can induce a circulation of blood. The experimental basis of cardiac resuscitation is reviewed. Evidence is given of the effectiveness of external cardiac massage in producing a circulation of blood, and a review is made of the use of electric shock to defibrillate the heart. The role of drugs in cardiac resuscitation is also reviewed. The little-used technique of centripetal arterial blood transfusion is examined as an example of the difficulties facing resuscitation research in applying laboratory findings to the clinical situation.

Introduction Since ancient times man has considered the possibility that death is reversible. The widespread belief in reincarnation and life after death is perhaps no more than the unwillingness to accept the finality of death. Furthermore, from very early times methods have been actively practised to bring back life into the dead. Since life and breathing were considered synonymous, breathing forcibly into the mouth of someone who had apparently died in order to restore life (the mouth-to-mouth or expired air method of artificial ventilation) has been practised since at least Biblical times. Other techniques in use today such as closed chest cardiac compression, electrical stimulation of the heart and mechanical ventilation of the lung, also have histories lasting several centuries (Hawkins, 1970). The important developments in resuscitation in the past 25 years have been threefold. The apparatus and technology required for the application of these previously known techniques have been developed rapidly; secondly, the physiological basis for many of the methods popular in the early part of the century has been reappraised, with the result that many of these methods have been discarded and replaced by more effective ones; thirdly, and perhaps most important, attitudes towards resuscitation have changed. Whereas previously most people considered it improper to interfere with the dead, nowadays it is perfectly respectable-and indeed expected-that even the most drastic attempts should be applied to conserve life. Along with these changing attitudes there has been a greater attempt to educate the public in techniques of emergency resuscitation. The acceptance by the medical 9

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profession of the relatively simple expired air method of artificial ventilation, closed chest cardiac compression, was a prerequisite of public education.

Artiilcial

and

ventilation

The restoration of respiration has always been the major aim of emergency resu&ation. Whatever the cause of the cardio-respiratory crisis, artificial ventilation has to be effectively applied within a few minutes of collapse. For a variety of reasons the ancient method of mouth-to-mouth ventilation was superseded in the nineteenth century by manual chest compression methods, such as those of Dalrymple (1831), Marshall Hall (1856) and Silvester (1858) ; (H aw ki ns, 1870). Fisher (194) lists over 70 different methods. The methods of Schaefer (1904) and Holger Neilsen (1982) introduced in the early part of this century proved the effectiveness of these methods, and they were taught and used in routine First Aid in many countries. However, their effectiveness, especially that of the Schaefer method, began to be questioned almost as soon as they were introduced. Several workers attempted to measure the tidal volume while the various techniques were being performed. Experiments were conducted on animals, on volunteers holding their breath, on cadavers, on sick or injured persons who had stopped breathing, and on persons anaesthetized and rendered apnoeic with curare. The choice of subjects in these experiments was important. The fresh cadaver probably has a chest and lung compliance most closely resembling the deeply asphyxiated patient. Whittenberger et al. (I g5 I) have shown that the pressure-volume relationship of the human thorax is little altered up to 2 h after death compared with measurements taken 12 h before; other authors have considered that cadavers are not reliable experimental material as results from them have been so variable (Karpovitch, Hale & Bailey, 1951). One possible explanation is that the time of onset of rigor mortis is very variable, depending on such factors as the cause of death, the climate and the previous dietary state of the patient. Karpovitch preferred to use subjects who held their breath voluntarily whilst the measurements were carried out but this also probably produces rather variable results. The anaesthetized apnoeic person perhaps represents a more ideal subject for the measurement of tidal volume. Many workers at this time assumed that tidal volume exchange was a good measure of the effectiveness of a method of artificial respiration. Obviously the ability to reverse hypoxaemia and hypercapnia is a much better criterion, but more difficult to examine experimentally in human beings. Measurements such as these could not be made on cadavers, and living subjects would have to be rendered hypoxaemic first. Comroe & Dripps (1946) considered that the prone pressure method (Schaefer) gave least ventilation in the asphyxiated person when it is most needed. They found that the effectiveness of the Schaefer method depended to a large extent on the elastic recoil of the lungs and on the tonicity of the respiratory muscles; since these are minimal in the asphyxiated patient the Schaefer method was of least value when needed most. De Forest & Potthoff (1951) measured the intrathoracic pressures during the Schaefer procedure, and discovered that only a very slight negative pressure develops during the inspiratory phase; they pointed out that the air inflow would be minimal with such a small negative pressure when the respiratory passages were partly obstructed by oedema, mucus, vomitus or water. As early as 1927, Bruns measured the tidal exchange directly on cadavers. He

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found that the Schaefer method gave a tidal exchange considerably less than the physiol0gica.l dead space, and this would result in no alveolar ventilation. These findings were confirmed by Gordier ( 19433) and Motley ( 1948). The method received almost universal condemnation between 1927 and 1g#3 as a result of the I 5 or so independent studies of ventilatory effectiveness during its use but, nevertheless, it continued to be practised widely. Most workers in the early 1950s were concerned with modifying the chest compression methods to give maximum ventilation. Whittenberger et al. (1951) found in patients that the prone pressure method did not give as much ventilation as did the back pressure-arm lift and hip lift-back pressure methods. Gordon et al. (1g51b) compared six methods of artifical respiration in 26 normal healthy men anaesthetized and curarized to total apnoea. Their results indicated that the ‘push-pull’ methods, i.e. those involving both active inspiration and expiration, were two to three times more effective than the Schaefer (push only) or the hip lift (pull only) methods. They, too, were concerned with varying the existing methods in order to achieve the optimum ventilatory effectivness. _Y These early studies overlooked the fact that any effective method must produce an adequate tidal exchange in the presence of a natural airway. Gordon and his associates had used endotracheal tubes in order to maintain an open airway in their anaesthetized patients. Safar & McMahon (1958) strongly criticized the work of Gordon since an endotracheal tube is not likely to be available under field conditions. The ideal method of artificial ventilation should aim to provide adequate ventilation without the use of an artificial airway; the most that can be done in normal circumstances is to hyperextend the neck to reduce the obstruction by the tongue caused by the relaxation of the jaw and pharynx in the unconscious person. Safer compared the Holger Neilsen and S&ester methods with and without an endotracheal tube and found that although trained operators could move an adequate volume of air with an endotracheal tube in place, less than the dead space volume of air was moved in 13 out of 16 subjects without a tube. Obviously, under these conditions it would have been impossible to have reversed any hypoxaemia or hypercapnia present. Safar’s results are similar to those of Nims et al. (195 I), who found that only 14a287 ems per respiratory cycle could be moved in apnoeic patients whose lungs or chest walls were stiff. In an earlier study Waters & Bennett (1936) found they could only move similar volumes in subjects whose abdomens and chest walls were heavy from obesity. In fairness to Silvester, it should be pointed out that in his communication describing the method in 1858, he was well aware of the problem of airway obstruction. He advocated raising the shoulders several inches from the ground as well as pulling the tongue forward. Gordon et al (1958) acknowledged that airway obstruction was the major cause of failure to produce adequate ventilation by manual methods. In 1951, Gordon et al. measured the mean arterial oxygen saturation during the Schaefer, Holger Nielsen, hip roll-back pressure and hip lift-back pressure methods. They found that the hip roll-back pressure method gave the most satisfactory arterial oxygen saturation; however, it must be remembered that in this study their subjects were intubated and that it seems likely f+om the later work of Gordon et al. (1958) and from Safar et al. (I 958) that with the natural airway arterial oxygen saturations would not have been so satisfactory.

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Month-to-mouth

methods

In 1954, Elam, Brown h Elder reintroduced the mouth-to-mouth method of resuscitation. Until then experiments were concerned with modifying the chest compression methods to produce maximum effectiveness. The mouth-to-mouth method was seen as a means of overcoming most of the difficulties associated with the manual methods. Safar & McMahon (1958) confirmed the superiority of the mouth-to-mouth method over the manual methods. Elam et al. (1958) measured the alveolar and arterial gas concentrations and arterial pH in apnoeic curarized volunteers ventilated with expired air at twice the normal minute volume. They showed that they were able to increase the arterial oxygen saturation and decrease the arterial carbon dioxide to acceptable levels by using this method. This method, too, had its critics. One such criticism was that positive inflation of the lungs had serious deleterious effects on the circulation. Gordon et al. (1956) showed that any such effects of positive pressure breathing on the circulation can be minimized by avoiding excessive positive pressure during inflation, and by timing the phases so that the inspiratory phase occupies one-third and the expiratory phase two-thirds of the cycle. This lowers the mean airway pressure and allows cardiovascular compensation during a longer expiratory phase. Effect

on the circulation

The effect of artifical ventilation upon the circulation is one that had escaped the attention of many workers. Two possibilities exist. A poorly designed method might well impair the circulation to such an extent that any effective alveolar ventilation would be minimized by a poor pulmonary circulation. A second possibility is that a well-designed rhythmic inflation and deflation of the lungs might produce an artificial circulation under some circumstances. The first experimental work of the circulatory effects of artificial respiration was that of Hemingway & Neil (I g& . They showed in dogs that the Eve rocking method benefited circulation because of the changes in intrathoracic pressure produced by tilting the body. Eve (1947) claimed that an artificial circulation could be maintained by rocking but this has never been substantiated (Whittenberger, 1955). Johnson & Kirby (rwg) found that some blood flow was produced by inflation and deflation of the lungs but that the amount was not easily measurable. Gordon (1951~) measured the circulatory effects of four manual methods and of the Eve rocking method on 20 adults with drug-induced apnoea. Cardiac outputs measured by the Fick principle were elevated during all of the manual methods; the conclusion from this is that whatever interference with venous return might have resulted from the pressure phases of the method, it was not enough to prevent a considerable rise in the cardiac output. Lauson et al. (1946) showed that while normal expiratory pressure decreases venous return to the right atrium only, manual compression of the chest reduces venous return to both atria. This observation would have suggested that the interference to venous return might be serious, but in practice any effect seems to be compensated for in the inspiratory phase. However, as might be expected, the most important effects on circulation are produced not by the negative pressure methods, i.e. the chest compression methods, but those employing positive pressure such as the expired air method. Pollock (1942) and Thompson et al. (1946, 1947) have shown that rhythmic mechanical inflation and deflation of the lungs can induce circulation of blood, and this

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might well be considered an added bonus of the expired air method, although they found that positive inspiration with negative pressure expiration (rather than passive expiration) was most efficient. However, the possibility exists that the pressure exerted on the lung during expired air inflation might be considerable, and that this could prove harmful. Gordon et al. (1958) measured the airway pressures using different techniques of art&&l respiration; this work showed that during mouth-to-mouth respiration an inspiratory pressure of up to 15 mm mercury could be exerted. During the expiratory phase of the mouth-to-mouth method the airway pressure was zero. During all of the manual methods of artificial ventilation the inspiratory pressure was negative and the expiratory pressure positive. This represents a very real physiological difference between the effect of mouth-to-mouth, i.e. positive pressure ventilation, and the manual chest compression, i.e. negative pressure methods. This relatively high positive pressure during inspiration could have serious effects on the circulation. Several physiological reasons for a decrease in cardiac output under these circumstances have been postulated. The first of these is a vagal inhibitory effect. This vagal influence originating in afferent vagal receptors in the lung or aortic arch is postulated as acting directly on the myocardium. However, several authors have shown that vagal section and denervation of the aortic arch do not significantly alter the fall in systemic arterial blood pressure during inflation (Sarnoff et al. 194.8; Sharpey-Schaefer & Bain, 1932). The second possible effect is that the expanding lungs may hinder filling of the right ventricle by compression of the heart and venae cavae. This effect is generally held to be the most important, and has been called cardiac tamponade (Humphreys et al. 1939; Taylor & Gerbode, 1951). The circulatory effects of pulmonary inflation can be seen not only as a fall in cardiac output and hence the decline in systemic arterial blood pressure, but also as a rise in external jugular venous pressure. The effect of cardiac tamponade was demonstrated by measurements of external jugular venous pressure. When the lungs were inflated by positive pressure the external jugular pressure rose. If compression of the venae cavae and heart were prevented by right pneumonectomy then no rise in external jugular pressure was recorded. Taylor & Gerbode (195 I) were able to show that venous pressure response to pulmonary inflation did not indicate the systemic arterial pressure response accurately. Their conclusion was that the obstructive effect of high pulmonary pressure on the pulmonary capillary bed and cardiac tamponade were the two most important factors in producing circulatory depression. Circulatory depression is very likely to be a factor in artificial respiration since Taylor & Gerbode and others have found it to occur with pressures as low as 15 mm mercury. Kelman 8z Prys-Roberts (1967) showed that the mean intrathoracic pressure was raised during intermittent positive pressure ventilation. By using a dyedilution technique to measure cardiac output on curarized healthy adults undergoing minor surgery they found that in the range -0.8 cm water to +3*8 cm water ( -0.6 mm to + 2 mm mercury) intrathoracic pressure had no significant effect. Cardiac output in this case was most affected by the arterial PCOr. Although the pressures investigated in this study fall far below those found during all the manual methods of artificial respiration, it is interesting to note that the major factor affecting cardiac output was the arterial PC02 in this low pressure range. It is very likely to have a major effect up to the pressures shown to produce circulatory depression, and might therefore explain the anomaly in one study (Gordon et al.

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ICJ~I~), that an unexpected rise in cardiac output was found during artificial respiration by four chest compression methods and the Eve rocking method, despite the theoretical fall which might occur from interference with venous return. The arterial PC02 was not measured in Cordon’s study. Another interesting consideration is that some methods of infant resuscitation, in particular, appear to produce both ventilation and augment the circulation. In the method of Rainer & Bullough (rg57), for instance, the legs of the child are raised and then the knees are flexed and pushed to the chest. These authors suggest that blood flows from the limbs to the abdominal viscera during the leg-raised phase; it is then squeezed out of the abdomen into the chest by the subsequent abdominal compression phase. Pressure of the knees on the chest causes positive expiration and also passage of blood from the chest to the periphery. The possibility of adapting

CUTOFFl.5cm, TO. BE INSERTED -INlQcBILD (NOT INFANT)

TO BE INSERTED -INTOADULT

Fig. I. Three d&rent types of airway. (a) The Brook airway, an oral airway with a lip-seal and nonreturn valve (redrawn by kind pern&sion of the British Oxygen Co. Ltd.). (b) The War oropw1 airway. A simple device that can be home-made, overcomes the aesthetic objections and promdea a patent airway. (c) The ‘mouth-to-lung’ airway proposed by Don-Michael (reproduced 9 kind mission of the Editor of the L.uncct). A more complicated device, which would have to be ms & trained personnel. It seals the oesophagus and prevents gastric distension.

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this in the form of abdominal compression to augment the circulation in adults does not appear to have received serious consideration. Crile (1914) described the successful induction of blood circulation by rhythmic compression of the chest and abdomen. The result of the work of these and many other authors has been that the manual chest compression methods have been superseded by the mouth-to-mouth expired air method. It is very simple to teach, and more effective in increasing ventilation and causing adequate arterial oxygen saturation. Circulatory depression is minimized by making the expiratory phase twice as long as the inspiratory phase. It remains, therefore, today to be the method of choice for emergency artificial respiration. Improved

airways

Many suggestions have been made to improve the expired air method, and in particular to make it less unpleasant, as the application of the operator’s lips to those of the patient probably inhibits the initiation of the mouth-to-mouth method. One

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difficulty with this method is that air can be easily blown into the stomach, especially if the position of the head and neck is not correct. This may then cause vomiting and inhalation of vomitus. Sellick (1961) first proposed that posterior displacement of the cricoid cartilage by pressure with the ring finger could be used during induction of anaesthesia to prevent regurgitation of stomach contents. Brown (I 968) has suggested this technique to prevent stomach inflation during expired air resuscitation and DonMichael et al. (1968) have devised an airway which overcomes the aesthetic problem and gastric distension. Other types of airway have been introduced which do more to overcome (Fig. I) the problem of ‘kissing a moribund stranger’ than to ensure an open air passage. One such airway was devised by Safar,and is constructed from two metal Connell oropharyngeal airways welded together to form an S-shaped instrument; by using a small airway at one end and a larger one at the other, the instrument provides two sizes, one suitable for a child and the other for an adult. The operator inserts the airway into the mouth of the patient and expands the patient’s lungs by forcibly blowing into it (Safar & McMahon, I 958). Another type of airway in common use is the Brook Airway (Brook et al. 1962). This device has an oral airway, a mouth guard which forms a lip-seal, and a non-return valve. These innovations to the basic technique of expired air resuscitation may well improve the efhciency and acceptability of the method, but it must be borne in mind that the inclusion of any apparatus in a technique for resuscitation has certain disadvantages. First, the technique can no longer be considered suitable for lay use since some degree of additional skill and expertise is necessary to apply the apparatus. Secondly, emergencies happen most frequently in the absence of such refinements, and therefore techniques requiring no equipment whatever are the most useful for the first-aider or lay person. Other advances in artificial ventilation have been the reintroduction of bellows and bags. Such devices, used since Paracelsus in the early sixteenth century, present a means of inflating the lungs with fresh air and even, in the right circumstances, with oxygen rather than expired air. Their use is normally confined to hospitals, but they are also widely available in ambulances, beach first-aid units, ships, mines, factories etc. In the United Kingdom the Ambu resuscitator (British Oxygen Co. Ltd.) is one example of this type of apparatus. The rubber bags are filled with foam rubber so that when they are squeezed air is forced out by a non-return valve to the casualty and, when pressure on the bag is released, they re-expand automatically to refill with room air (Plate I). Oxygen can be added by a side connection. Carden h Bernstein (1970) have evaluated nine of the most commonly used bags and for most purposes recommend the Ambu. Kreiselman (1928) reintroduced a concertina type bellows device, principally for inflating the lungs of asphyxiated babies. Later developments of this type of apparatus have been, for example, in this country, the Oxford Inflating Bellows (Longworth Scientific Instrument Co. Ltd.). This works in a similar way to the Ambu bag except that it requires a negative phase to be brought about manually; that is, it does not automatically reinflate (Plates I and 2). Since it is extremely easy for an adult to over-inflate the lungs of a small child or a neonate, a special type of mechanical ventilator for neonates has been devised (Samson, 1968). This is known as the Blease Samson Neonatal Resuscitator. It incorporates a system of pressure regulating holes to ensure that pressures in excess of 60 cm water cannot be generated, and that any pressure cannot be maintained for long periods.

(b) rte I. (a) Ambu resuscitator. An example of a self-filling portable respirator (British Oxygen Co. Ltd.). Oxford inflating bellows. An example of a non-self-filling respirator (Longworth Scientific Instrument Ltd.).

2. Minepac resuscitator (British Oxygen Co. Ltd.). A time-cycled volume limiting device employing pneumatic switches and supplied by a light-weight oxygen cylinder. A pre-set tidal volume is delivered at inflation pressures of up to 60 cm water. A safety valve prevents over pressurization.

Plate

Lamp External

Cardiac

Compressor

Purhingateering

handle

Footboard

3 prong

ground

reiexe

adapter

Charging

umbilicus

so

Maintenance

switch

Max mobile intensive care and emergency resuscitation unit (Smith-Kline Instrument CO. Ltd.). It provides on one trolley facilities for ventilation, cardiac compression, defibrillation, pacemaking and electrocardiographic monitoring.

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Cardiac remudtation Research in cardiac resuscitation has been in four main areas: (i) the effectiveness of cardiac massage in maintaining a circulation; (ii) problems associated with reversal of cardiac asystole and ventricular fibrillation by electric current discharge; (iii) the aetiology of cardiac arrest; (iv) the use of drugs. The first comprehensive account of cardiac resuscitation was given in 1904. D’Halhrin was the first person to measure blood pressure during direct cardiac massage and thus to put this technique on a physiological basis. The pioneering work on the effect of chloroform and ether on the heart, and the treatment of cardiac arrest by direct massage, was done by the Swiss physiologist Moritz Schiff (1882). The first cardiac massage in patients had been done by Langenbuch in 1887. This early attempt was unsuccessful in restarting the hearts, as were several other attempts made in the following 14 years, such as those of Niehans of Berne (1889) and the French surgeon Tuffier (1898). Prus ( rgoo) conducted extensive research into cardiac massage and in the same year Maag had some success with a patient who lived for I I h after restoration of cardiac contraction. The first truly successful use of cardiac massage took place in 1go I: and was reported by Igglesrud in 1904. In rgon Starling & Lane published the first report of a successful treatment of cardiac arrest occurring in a patient undergoing appendectomy. Many reports of successful cardiac massage followed these pioneering efforts, but many surgeons would not recognize its value and some were even hostile to attempts to restart the heart once it had stopped. Consequently, direct cardiac massage was carried out only infrequently over the next half century, although, with the increasing use of chloroform and ether as an anaesthetic, cardiac arrest on the operating table had become an increasing problem. The need to open the chest in order to massage the heart had meant that direct cardiac massage could only practically be used on the operating table. The emergency use of cardiac massage outside hospitals had remained almost non-existent until Kouwenhoven et al. popularized the technique of closed chest cardiac massage in 1960. This meant that for the first time a circulation could be re-established without opening the chest. However, this was not a new technique. Boehm had first described the use of closed chest cardiac compression in 1878 in cats, but it was first used clinically by John Hill, a British dentist, in 1868. Maas in Gottingen described the technique in 1892 and an American surgeon, George Crile, described a successful case of external cardiac compression in 1904. Apart from an unsuccessful attempt in Boston by Cheevers in 1905, no other reports were published until those of Kouwenhoven in 1960. Since the work of Kouwenhoven, several reports have been published comparing the effectiveness of cardiac massage by the direct and closed chest methods. It has been maintained that closed chest cardiac massage cannot be effective because on compression of the thorax the intraventricular and intra-aortic pressures will increase to the same degree, so no forward flow will result (Weale, I g6 I). However, the aorta is continuous with vessels outside the thorax, which would be at a lower pressure than the compressed chest, and flow will occur in this direction. Some doubt has been cast on the efficiency of external massage as compared with direct massage. Weale & Rothwell-Jackson (1962) compared venous and arterial pressures during internal and external massage of the dog heart in which ventricular fibrillation had been induced. They found that direct compression of the heart gave 2

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a higher mean arterial pressure and a lower mean venous pressure than external compression. The results of these experiments cannot necessarily be applied to man since the shape of the chest and position of the heart are entirely different from that of the dog. Other authors have attempted to investigate problems of closed chest cardiac massage by using the dog. Redding & Cozine (1g61) found great variation in carotid blood flow rates and arterial pressures from dog to dog although their mean values for external and direct massage were insignificantly different. Milstein (1963) measured the venous and arterial pressures during external cardiac massage in man and was able to show a systolic rise of about 3o-35 mm mercury in arterial pressure with negligible rise in venous pressure. Other authors have had more satisfactory results. Nixon (1961) measured the arterial pulse in closed chest massage in man, and recorded bra&al artery pulses of about 120120 mm mercury. Kouwenhoven et al. (1960) also reported that satisfactory arterial pressures are obtained by closed chest cardiac compression. These results tend to disprove the observations of Weale & Rothwell-Jackson, and demonstrate the difficulty of applying the results of animal experiments to human beings. Optimum rate of cardiac compression The optimum rate and form of compression of the heart has also received some attention. Bost (rg23), in analysing the 75 cases of attempted direct cardiac massage recorded before 1923, stated that it was ‘pretty well agreed that gentle compression of the heart should be carried out at about half the normal rate to allow the heart to fill well’. Lee & Downs (1g24), adding a further 24 cases to those of Bost, recommended a rate of 20 times per min. Barber & Madden (1844) recommended rates of 40 to 50 per min. Ruzicka & Nicholson (1947) agreed that a rate of 40 times per min was optimum but Crafoord (1947) considered that the same rhythm as the normal heart beat should be used. The first experimental work to determine the optimum rate of performing cardiac compression was carried out by Johnson & Kirby (I 949). They found that the rate of blood flow in the carotid artery and thoracic aorta of dogs was increased as the rate of cardiac compression was increased from 30 to IOO times per min. The rate of blood flow was only about half of that produced by a spontaneous heart beat in the open chest. From their experiments it would be concluded that the optimum rate is the fastest found feasible to maintain. The problem of allowing the heart to refill that influenced the earlier workers does not seem to exist. A very fast rate of direct manual compression cannot be maintained for long periods because the operator’s hand becomes fatigued. Milstein (1861) thinks a good compromise between efficiency and fatigue is a rate of 50 to 60 times per min. Kouwenhoven et al (1960) have shown that arterial systolic pressures of 80-100 mm mercury can only be achieved by very forceful rapid compression at a rate of about 80 per min. It is of interest that Maas, who was one of the first to perform external cardiac compression in man in 1891, advocated compression at the rate of r 20 per min. Modern technology has produced machines that will take over the work of both external cardiac massage and lung ventilation. As well as being able to maintain resuscitation for a long time, they allow optimum timing of cardiac compression and lung inflation to obviate some of the difficulties associated with interference of

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circulation by positive pressure in&&on. One such apparatus is the Max trolley (Plate 2). The maintenance of a circulation by cardiac compression is an emergency measure which must be followed up eventually by specific treatment to reverse the underlying cause of the cardiac arrest. Scherf ik Bornemann (1960) have shown that mechanical stimulation of the heart in asystole can re-establish a normal beat. Scherf credits Schott (1820) with first describing the procedure. Many other authors have also shown that this simple procedure of ‘thumping the precordium’ is effective. DonMichael & Stanford (I 963) document the successll reversal of asystole by thumping the chest.

IaracardiacinjectionsanddefibriUPtion If the heart is in asystole and mechanical shock is insufficient to restart it, the treatment consists of injecting I o/ocalcium chloride or I in I o 000 adrenaline solution into the chambers of the heart. If the circulation is being maintained manually the injection can be given intravenously. Calcium chloride causes an increase in the tone and contractility of the myocardium and was first used for this purpose in resuscitation by Kay & Blalock (1951). Alternatively, the heart can be stimulated to contract by application of a small current to the chest wall through an external pacemaker. A normal beat can be restored to the fibrillating heart also by the application of an electric shock. The passage of short duration electric current through the ventricles renders all the fibrillating muscle fibres refractory simultaneously. All muscle contraction then ceases and after a pause a co-ordinated beat is resumed. This observation was first made in 1899 by Prevcst & Battelli but was not re-investigated until 1932 (Kouwenhoven et al.). Their apparatus employed a 60 cycle a.c. current of 1-5-2 A at 12o-130 V applied directly to the heart surface. Hooker et al. (1933) and Wiggers (1g40) confirmed the effectiveness of alternating current in defibrillating an exposed heart. Wiggers advised serial defibrillation with weak repeated shocks because sometimes a single shock renders only part of the muscle refractory. Ferris et al. (rg36), working with dogs, first demonstrated defibrillation of a heart by an electric current through the intact chest wall. Beck et al. (1947) were the first to report a successful defibrillation of a human heart by electric shock, but in 1~2 Adams & Hand had reported the use of procaine in successfully defibrillating a human heart. Although it was known to be possible to defibrillate the heart from such an early date, experiments to determine the optimum voltages, currents and times do not seem to have been carried out until the 1950s. The defibrillating current has been shown to be optimum between I ‘5 and 3.8 A (Mackay, Mooslin & Leeds, 195 I). Beattie et al. (1953) showed the electrical resistance of the heart to be about IOO ohms. By application of Ohm’s Law, voltages of between 150 and 380 seem most suitable for defibrillation if the electrodes are on the surface of the heart. If the electrodes are placed on the chest wall, the resistance encountered is not only much greater but will also be more variable ffom patient to patient. A prediction of the voltage required is therefore difficult. Zoll et al. (I 956) used an alternating current in the range 18o-720 V but found that 300-4~ V was the most usual requirement. A current of 5 A was delivered for o-1-o-2 s. The use of direct current from a capacitor discharge has received scant attention

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to date, but what evidence exists indicates that in some ways it is preferable to alternating current. Gurvich & Yumev (x847) in the Soviet Union have found a capacitor discharge highly effective in defibrillating the heart, whereas Kouwenhoven & Milnor (1954) report inconsistent results. Later work by Lown et al. (1962) has demonstrated that direct current seems to be at least as effective in reversing ventricular fibrillation, and has the advantage that far less arrhythmia occur after the use of direct current than with alternating current. In Lown’s experiments on dogs, atrial fibrillation followed 174 of the 200 reversions (87%) with a.c. whereas only five cases out of 550 reversions (0.9%) were noted with d.c. By using a direct current, slightly higher voltages are used, but only with pulse widths of the order of 0*004 s. Use of drugs The use of drugs in cardiac resuscitation has been mentioned in passing. D’Halluin (I 904) made use of Ringer’s demonstration of the antagonizing effect between potassium and calcium ions by advocating the injection of potassium chloride to treat ventricular fibrillation. Potassium chloride reduced the myocardial tone, after which Locke’s solution or calcium chloride was used to stimulate a coherent myocardial contraction. Many drugs have been used to assist in the restoration of the heart beat and to maintain a failing heart. Probably one of the most important and widely employed is sodium bicarbonate, used to restore the acid-base balance after circulatory collapse (Brooks & Feldman, 1962). An organic buffer, 2-amino-2-hydroxymethylpropane1,8-diol (tris or tham), has been introduced for the same purpose by Nahas (1959). The use of this substance has received considerable attention. One advantage is that buffering can be accomplished without the administration of sodium; another is that, unlike sodium bicarbonate, tris acts as an intracellular as well as an extracellular buffer. It is claimed that tris facilitates electric defibrillation of the heart (Lee et al. x962) and also that it improves the response to adrenaline (epinephrine) and noradrenaline (Levarterenol or norepinephrine) ; Darby et al. (I 960). However, there seems little evidence that tris has any special advantages over sodium bicarbonate and the important effects, such as increased success of cardiac resuscitation by drugs or shock, are only those found also after administration of bicarbonate (Bleith & Schwartz, cited 1969). Kirimli et al. (1964) have shown that the energy required to defibrillate the hearts of dogs under light pentobarbitone anaesthesia is reduced if bicarbonate is first given (from 28 W s at pH 7.28 to 21 w s after bicarbonate at pH 7.58-7’61). The last-named authors also demonstrated a greater success of defibrillation (in dogs) if they administered a combined infusion of adrenaline and sodium bicarbonate rather than bicarbonate alone. Many other authors have also concluded that the correction of the acidosis resulting from circulatory arrest is an essential prerequisite for successful cardiac resuscitation. The multitude of drugs now available to the clinical resuscitator has arisen mainly as a result of clinical impressions rather than from conclusion of well-designed drug trials. The large group of pressor drugs now available are derivatives of adrenaline and are used to increase systemic arterial blood pressure by peripheral vasoconstriction (the so-called alpha-active drugs) or to increase rate of heart-beat and cardiac output with peripheral vasodilatation (the beta-active drugs). Adrenaline itself has mixed alpha and beta activity. The ideal drug for use in cardiovascular

EXPERIMENTAL

DEVELOPMENT

OF RESUSCITATION

2I

collapse should combine the properties of improving coronary artery flow and enhancing myocardial contractility; it should raise the blood pressure and cardiac output, but the myocardial oxygen consumption in relation to work load (cardiac efficiency) should not be increased. Waldhausen et al. (1965) have measured these requirements with a variety of catecholamines and generally conclude that Metaraminol (aramine) most closely fits these specifications. As well as the catecholamines, other useful drugs are xylocaine (Lidocaine), which acts as an anti-ax-rhythmic by raising the fibrillation threshold, and procainamide (Pronestyl) has also been used as an anti-arrhythmic, which depresses the excitability of the heart. Milstein & Brock (I 954) recommend the use of procainamide hydrochloride to abolish ventricular fibrillation. Procainamide seems to have certain advantages over procaine, which was first used as a defibrillator by Adams & Hand (1942). Procainamide is very similar in activity to quinidine and some authors consider quinidine to be superior. Another anti-ax-rhythmic drug that has found considerable use is propanolol hydrochloride (Inderal), which is a beta-receptor blocking agent and seems to produce its effect by depressing pacemaker activity and increasing the refractory period of the myocardium. Chtripetal

arterial blood transfusion

The technique of intra-arterial blood transfusion seems worthy of consideration mainly because it has attracted much experimental consideration, which in many countries has never gained acceptance. It is today probably only used to any large extent in the Soviet Union. The blood pressure in the coronary arteries must not fall below about 5o-6o mm mercury for very long if recovery is to be successful (Smirenskaya & Maksimishin, I g5 I). Intra-arterial blood transfusion would appear to act at least in part by helping to maintain this perfusion of the coronary circulation. Some authors consider that the important effect of intra-arterial transfusion is the reversal of hepatic hypoxia (Danziger, 1955 ; Frank et d. Ig46), whereas others consider that correction of renal hypoxia is important. Another mechanism, especially in haemorrhagic shock, is that ii-ma-arterial transfusion replaces the blood volume more quickly and therefore more effectively than does intravenous transfusion (Smythe et al. 1954; Case et al. I 953). The maintenance of a cerebral circulation is held to be an important effect by some, although Negovskii (1960) points out that maintaining cerebral activity is quite useless unless the activity of the heart is also restored fairly soon afterwards. Probably a combination of these mechanisms is operative, but whatever the mode of action there is no doubt that the injection of blood or other perfusion fluid into an artery towards the heart is an important technique in states of shock and also in cardiac arrest. Drugs can be added to the transfusion and also the blood can be oxygenated so that hypoxic tissues can be quickly re-oxygenated and perfused at a reasonable pressure (Cowie, 1955). Resuscitation suffers perhaps more than most other branches of clinical practice in that because of the life or death nature of the emergency there is no time to try novel ideas or poorly proven techniques. It would be unethical to withhold known life-saving treatment, however ineffective it might be, in order to substitute an experimental technique. On the other hand if novel ideas are only tried when all else fails, as is often the case at the moment, then a true picture of the value of these

22

L. H. HAWKINS

never be established. It is this understandable reluctance to introduce into clinical practice laboratory produced techniques that will undoubtedly delay advances in human resuscitation in the future. can

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Res. 8, I 242. De Fore+ R. E. & Potthoff, C. J. (1951) Back pressure-arm lift method for administering artificial respiration recommended.3.A.M.A. x47,1455. D’Halluin, M. (1904) Resurrection& Gxur. Paris: Vigot Freres. Don-Michael, T. A. & Stanford, R. L. (x963) P recordial percussion in cardiac asystole. Lmcet.(i), 688. Don-Michael, T. A., Lambert, E. H. & Mebran, A. (I@?) ‘Mouth-to-lung airway’ for cardiac resuscitation. Lwcet. (ii), 1329. Elam, J. O., Brown, E. S. & Elder, J. D. Jr. (1954) Artificial respiration by mouth-to-mask method: study of respiratory gas exchange of paralysed patients ventilated by operator’s expired air. J%e

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& Blalock, A. (1931) The use of calcium chloride in the treatment of cardiac arrest in patients. Surgery Gyncc. Obstat. s 97. Kehnan, G. R. & Prys-Roberts, C. (1867) The influence of art&&l ventilation on cardiac output. 3. Physiol., (Land.). xgn, 87 P. Kirimli, B., Hanis, L. C. Jr. & Safar, P. (1964) Sodium bicarbonate and epinephrine in cardiac resuscitation. Anorsthssiol0~. as105. Kouwenhoven, W. B., Hooker, D. R. & Langworthy, 0. R. (1932) The current flow through the heart unda conditions of electric shock. Am. 3. PhyssX. loo, 344. Kouwenhoven, W. B. & Mihror, W. R. (1954) Treatment of ventricular fibrillation using a capacitor d&charge. 3. a# Physiol, 7, 253. Kouwenhoven, W. B., Jude, J. R. & Knickerbocker, G. G. (1g6o) Closed chest cardiac massage. Kay, J- 2

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