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(Circulation. 1997;96:2102-2112.)
© 1997 American Heart Association, Inc.

Articles

A Reappraisal of Mouth-to-Mouth Ventilation During Bystander-Initiated Cardiopulmonary Resuscitation

A Statement for Healthcare Professionals From the Ventilation Working Group of the Basic Life Support and Pediatric Life Support Subcommittees, American Heart Association

Lance B. Becker, MD, Chair; Robert A. Berg, MD; Paul E. Pepe, MD, MPH; Ahamed H. Idris, MD; Thomas P. Aufderheide, MD; Thomas A. Barnes; EdD, RRT; Samuel J. Stratton, MD; ; Nisha C. Chandra, MD

Key Words: AHA Medical/Scientific Statements • death, sudden • cardiopulmonary resuscitation • ventilation

	Introduction

Top Introduction Historical Rationale for... Does Assisted Ventilation... Are There Adverse Effects... Special Considerations:... Conclusions and Recommendations References

 
Cardiopulmonary resuscitation (CPR) performed by bystanders clearly improves survival and victims of out-of-hospital cardiac arrest and other life-threatening conditions such as drowning and respiratory arrest.^{1 2} However, despite three decades of promulgation, CPR is not performed for the majority of victims who require lifesaving care.^{3 4 5 6} Studies have identified reticence to perform mouth-to-mouth ventilation as a significant barrier to more frequent performance of bystander CPR.^{1 7 8 9 10 11 12 13} In addition to acting as a barrier to initiation of CPR, the mouth-to-mouth ventilation component of CPR may have other adverse effects, such as promoting gastric insufflation^{14 15 16 17} or decreasing the percentage of time allocated to effective chest compression.^{18 19 20}

Because early CPR plays a central role in saving lives, the Ventilation Working Group of the Basic Life Support (BLS) and Pediatric Life Support Subcommittees of the AHA Emergency Cardiovascular Care (ECC) Committee reviewed the scientific evidence on mouth-to-mouth ventilation. The ECC Committee and its subcommittees prepare guidelines and recommendations for providing emergency cardiovascular care and cardiopulmonary resuscitation in the United States and will formally review and publish updated guidelines in the year 2000. Although this report represents a focused analysis and serves as a consensus statement regarding the role of mouth-to-mouth ventilation during CPR, it is not intended to change any current AHA recommendations or guidelines for performance of CPR. The specific purpose of this report is to review the historical rationale for providing mouth-to-mouth ventilation during CPR and to critically analyze, using the available scientific literature, the following questions: (1) Does assisted ventilation during CPR result in improved physiological status or survival? (2) Are there adverse effects that result from inclusion of mouth-to-mouth ventilation in basic CPR techniques? (3) Could mouth-to-mouth ventilation be deferred or delayed in certain cases of bystander CPR? Finally, new recommendations are presented, particularly regarding the ethics of human clinical trials on the performance of CPR techniques without mouth-to-mouth ventilation.

	Historical Rationale for Mouth-to-Mouth Ventilation

Top Introduction Historical Rationale for... Does Assisted Ventilation... Are There Adverse Effects... Special Considerations:... Conclusions and Recommendations References

 
Historical Studies of Ventilation
The importance of ventilation during resuscitation has been accepted for centuries, with the earliest descriptions of assisted ventilation documented in stories of the prophets Elijah and Elisha in the Bible. Examples of mouth-to-mouth ventilation and the suggestion to teach it widely to the public also exist in a description of the resuscitation of a miner overcome by smoke in 1744.²¹ Experiments conducted in 1796 demonstrated that expired air was "safe for breathing."^{22 23} Over the next two centuries various artificial ventilatory techniques were tested during resuscitation, including the use of bellows, rolling the victim over a barrel, or positioning the victim on a trotting horse. Perhaps the most commonly used and effective artificial ventilation techniques were those that were popular both in the United States and Europe in the early 1900s. These included several manual methods of ventilation (eg, Schäfer's prone-pressure method and the Holger-Nielsen method)²⁴ (Fig 1). With many of these techniques the patient was placed in a prone position (perhaps favoring an open airway); pressure was then rhythmically applied to and released from the posterior chest and back while the patient's arms were lifted cyclically. By 1953 at least 105 published articles described methods for artificial resuscitation of adults; 12 articles discussed resuscitation of children.²⁵ During the first half of the 20th century these so-called "manual" techniques were endorsed and taught by the Red Cross and commonly used by lifeguards, the military, and Boy Scouts.

View larger version (54K): [in this window] [in a new window]   Figure 1. Manual techniques of artificial respiration. There was intense interest in artificial ventilation methods during the first half of the 20th century. From Gordon et al.24 Copyright 1950 American Medical Association.

In a landmark study in the 1950s, Safar and colleagues²⁶ demonstrated that the tongue and soft palate commonly obstructed the upper airway in unconscious persons. They further demonstrated that the manual ventilation techniques developed in the 1900s were relatively ineffective in the presence of such obstruction. The chin-lift and jaw-thrust techniques for opening the airway of the supine patient were developed to remove obstructions and maintain airway patency.^{27 28} Safar and colleagues^{29 30} then demonstrated a practical advantage of expired breath ventilation over previous manual methods with the patient lying supine. Specifically they compared tidal volumes generated during mouth-to-mouth (or mouth-to-airway) ventilation with those generated using the older manual techniques in paralyzed and anesthetized adults with normal circulation. Although the Holger-Nielsen method (one of the most effective manual techniques) generated >340 mL/min tidal volume in five of six patients, it was still less effective than mouth-to-mouth ventilation (Fig 1). On the basis of these and similar confirmatory studies, mouth-to-mouth ventilation became the therapy of choice for out-of-hospital respiratory arrest by the 1960s.^{31 32}

While these studies on ventilatory techniques were being conducted, other laboratories sought a practical method of providing circulatory support during cardiac arrest. Because external chest compression could provide partial circulatory support, the mouth-to-mouth ventilation technique was added to chest compression to create modern CPR. The "ABC" sequence of resuscitation—Airway patency, Breathing (with mouth-to-mouth ventilation), and Circulation (chest compression)—emerged as a practical and empirical means of CPR (Fig 2).^{33 34} Because most adult cardiac arrest victims become apneic or generate abnormally diminished respiratory efforts, it has long been assumed that mouth-to-mouth ventilation should be an integral component of CPR. On the basis of the physiological principle of rapidly restoring "normal" breathing and circulation and the subsequent success of CPR in the clinical setting, a sequence of mouth-to-mouth ventilation at a rate of 10 to 12 breaths per minute for adults, with each breath followed by five chest compressions (two rescuers), was recommended by consensus and adopted by the AHA.^{1 35}

View larger version (43K): [in this window] [in a new window]   Figure 2. The ABCs of resuscitation. Modern CPR was a combination of ventilatory support with circulatory support. From the Cardiopulmonary Resuscitation Committee.34 Copyright 1966 American Medical Association.

Effectiveness of Traditional Techniques of Cardiopulmonary Resuscitation
Over the past 25 years many studies have reinforced the empirical practice of the ABC sequence for CPR by confirming the effectiveness of bystander-initiated CPR.^{2 4 5 36 37 38 39} The outcome of most cases of adult cardiac arrest depends primarily on the time interval from cardiac arrest until defibrillation.^{5 40 41 42 43 44} Therefore, rapid provision of defibrillation is considered the most important determinant of successful outcome.^{1 40 41 43 44} However, traditional CPR extends the time available for successful defibrillation and resuscitation.^{43 44} Specifically investigations of "adult" type cardiac arrest in laboratory animals indicate that (1) maintenance of adequate coronary perfusion pressure and resultant myocardial blood flow during chest compression are critical for optimal survival and (2) the window for successful bridging until defibrillation is 10 to 18 minutes.^{45 46 47 48 49 50 51 52 53} Clinical studies similarly indicate that success of CPR improves when (1) the cardiac arrest is witnessed, (2) immediate bystander CPR is provided, (3) adequate coronary perfusion pressures are obtained during CPR, (4) the initial rhythm is ventricular fibrillation, and (5) early defibrillation is provided.^{5 36 40 41 42 43 44 54 55 56 57 58 59 60 61} Data from both animals and humans concur: time is of the essence. Traditional bystander-initiated CPR can improve survival when it is started within 4 to 6 minutes from the time of collapse and followed with advanced cardiac life support within 10 to 12 minutes of collapse.^{43 44} Nevertheless, although these studies have reinforced the value of the ABC technique, few studies have focused on the relative efficacy of mouth-to-mouth ventilation or chest compression alone.

	Does Assisted Ventilation Improve Outcome of Cardiopulmonary Resuscitation?

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Respiratory Physiology During Cardiopulmonary Resuscitation
Pulmonary function involves both oxygenation (diffusion of O₂ into the bloodstream) and ventilation (movement of a volume of gas in and out of the lungs, resulting in removal of CO₂). Although the roles of ventilation and oxygenation are intertwined during breathing, each has important, separate considerations in patient management. Inadequate oxygenation of the blood (ie, hypoxemia) can occur during CPR, due to hypoventilation (high arteriolar PCO₂), pulmonary alveolar shunting, and ventilation-perfusion mismatch. These physiological abnormalities may be the result of lung deflation, frank atelectasis, pulmonary edema, airway obstruction, or pulmonary aspiration of gastric contents before or during CPR. Supplemental oxygen administration and recruitment of lung volume through reinflation are the mainstays of therapy for hypoxemia in these circumstances. Endotracheal intubation is often necessary for reinflation, particularly in view of diminished lung compliance after several minutes of apnea and chest compression.^{62 63 64 65}

Traditionally the ventilatory goals of CPR training techniques have stressed empirically that minute ventilation be more or less normal.³⁴ However, current techniques for mouth-to-mouth ventilation were developed in paralyzed anesthetized subjects with normal circulation, conditions not typically present during CPR scenarios. Both oxygenation and ventilation requirements may be altered during circulatory arrest because cardiac output and pulmonary blood flow generated even during CPR that is well performed are far lower than blood flow during spontaneous circulation. With low blood flow, end-organ tissues become ischemic, extract a higher percentage of O₂, and accumulate higher levels of CO₂ ("tissue acidosis"),^{66 67} but arterial blood gases may not reflect these tissue conditions.⁶⁸ As a result, the goals of oxygenation and ventilation during CPR have not been established, and interpretation of arterial blood gases is not clear.^{68 69} Therefore, it is difficult to evaluate current oxygenation/ventilation techniques. Collectively there is little evidence that oxygenation and ventilation need to be "normalized" during fibrillatory cardiac arrest because the primary disorder is due to low blood flow, not respiratory insufficiency.

Sources of Ventilation During Cardiopulmonary Resuscitation
Although active mouth-to-mouth ventilation has been stressed in traditional CPR training, it is also important to consider that many other sources of gas movement can contribute to oxygenation and ventilation in patients receiving CPR. Indeed, there are several potentially important sources of ventilation during cardiac arrest with attempted resuscitation including compression-induced ventilation and gasping respiration. Compression-induced ventilation commonly results when gas is expelled from the lungs and is "passively inhaled" following elastic recoil of the chest wall during the relaxation phase.^{70 71 72 73 74 75 76} In multiple animal studies, compression-induced ventilation alone has proved quite substantial when measured.^{71 74 75 76 77} However, measured minute ventilation and arterial oxy-genation decrease after 4 to 10 minutes of CPR with or without assisted ventilation, possibly because of progressive chest compression–induced atelectasis and thoracic deformity.^{71 78} Thus, with longer periods of cardiac arrest, ventilation may become more important. This is supported by animal studies in which chest compression periods were more prolonged, demonstrating that chest compression with assisted ventilation and adequate lung inflation result in better oxygenation compared with chest compression without assisted ventilation.^{71 74} In addition to compression-induced ventilation, spontaneous respiration, usually in the form of agonal or gasping breathing, commonly occurs during cardiac arrest in both animals and humans, further contributing to total ventilation.^{75 76 78 79} Several recent investigations in animals have specifically established that spontaneous gasping occurs early during CPR and is associated with a better outcome.^{74 75 76 78 79} Spontaneous gasping may simply reflect improved oxygen delivery to the medulla during CPR, or it may reflect a shorter cardiac arrest interval. However, the mechanics of gasping may also improve the effectiveness of CPR because of (1) improved venous return during the negative-pressure inspiratory efforts, (2) augmentation of cardiac output due to increased intrathoracic pressure during the expiratory phase of gasping, and (3) improved pulmonary gas exchange due to both increased airflow and the more physiological "pulling open" of those dependent lung zones subject to deflation. In one study of swine, spontaneous gasping contributed approximately half of the measured minute ventilation during chest-compression-only CPR, compared with <10% during chest compression plus mechanical ventilation.⁷⁴

Therefore, in human and animal studies some component of compression-induced ventilation and gasping respiration—which by themselves may be important sources of gas exchange—is present unless specifically prevented. In turn, studies reporting CPR performed "without ventilation" may not be strictly accurate; the authors more likely mean "without mouth-to-mouth ventilation" or "without assisted ventilation." Although not necessarily measured or reported, the contributions of compression-induced ventilation and gasping respiration may still be substantial in the absence of mouth-to-mouth ventilation. In contrast to the original studies of mouth-to-mouth ventilation in which anesthetic and paralytic agents were administered to subjects with normal circulation, these components of ventilation during CPR may be sufficient for a short time to produce survival when coupled with effective chest compression.

Experimental Studies of Assisted Ventilation
With the recognition that ventilatory requirements during cardiac arrest are unclear and acknowledging that compression-induced ventilation and gasping respiration may be important sources of gas movement, the requirement for and timing of mouth-to-mouth ventilation can be questioned. A canine study on the effects of mechanically assisted breathing (as an approximation of human mouth-to-mouth ventilation) was performed in 1983 by Meursing et al.⁸⁰ In this study CPR was delayed for 5 minutes following sudden circulatory arrest, and no significant fall in arterial PO₂ or rise in PCO₂ was observed. Chest compression was then initiated, but assisted ventilation was withheld for 2 minutes. No significant fall in arterial PO₂ or rise in PCO₂ was demonstrated over the next 30 seconds. This study, reported only in an abstract, was a key consideration in CPR guidelines developed in the Netherlands and reflects a lack of conviction regarding the importance of immediate ventilation. Instead of using the ABC sequence, the Netherlands approach to sudden witnessed arrests is "CAB" (Circulation, Airway, Breathing). Rescue breathing is delayed (several seconds and, infrequently, several minutes) to enable prompt provision of chest compression. Survival outcomes with CAB appear to be similar to, if not better than, those reported with ABC CPR.⁸¹

Many laboratory studies support this concept. Berg and colleagues⁸² demonstrated that fibrillatory cardiac arrest in swine provided with chest compression alone for 9.5 minutes maintained an arterial pH of 7.33 and arterial PCO₂ of 48 mm Hg. In a nonintubated canine cardiac arrest model, Chandra et al⁷⁰ demonstrated that arterial oxygen saturation could be maintained above 90% with a measured minute ventilation of 5 L/min being generated during the fourth minute of chest compression alone without any assisted ventilation.

The need for assisted ventilation during CPR for fibrillatory arrest has been evaluated in four swine studies with long-term survival. Each reported nearly identical 24-hour survival and neurological outcome with chest compression alone versus chest compression plus assisted ventilation.^{74 75 76 82} Fibrillatory cardiac arrest intervals varied from 30 seconds to 5 minutes, and CPR was provided for 8 to 12 minutes. In a more recent study swine underwent a 5-minute fibrillatory cardiac arrest interval, followed by 8 minutes of (1) chest compression alone, (2) chest compression plus assisted ventilation, or (3) no CPR at all. Assisted ventilation (at 15 mL/kg tidal volume) was provided with 17% oxygen and 4% carbon dioxide to better simulate the exhaled gas delivered during human mouth-to-mouth ventilation. The results showed that without CPR there were no survivors. Both the chest-compression-alone group and the chest-compression-plus-assisted-ventilation group had significantly better survival than the no-CPR group. However, whether or not assisted ventilation was performed made no detectable difference on either return of spontaneous circulation or 24-hour survival rates (Fig 3).⁷⁶

View larger version (15K): [in this window] [in a new window]   Figure 3. Survival with chest compression with and without assisted ventilation. Five minutes after ventricular fibrillation, swine were treated for 8 additional minutes with simulated mouth-to-mouth exhaled gas ventilation (17% O2 and 4% CO2) plus chest compression (CC & vent), chest compression alone (CC alone), or no CPR. No differences could be detected between groups with or without ventilation if chest compression was provided. Both CPR groups tended toward improved survival compared with no CPR. Open bar indicates return of spontaneous circulation; solid bar, 24-hour survival. Data from Berg et al.76

Idris and colleagues⁸³ have demonstrated that with prolonged arrest intervals beyond 6 minutes, supplemental oxygenation and assisted ventilation should still be considered critical determinants of CPR success. In one study, swine underwent 6 minutes of untreated ventricular fibrillation, followed by 10 minutes of chest compression plus assisted ventilation (12 mL/kg) with 85% oxygen versus chest compression without assisted ventilation. The nonventilated animals were paralyzed to prevent gasping and its effect on total ventilation. Return of spontaneous circulation was achieved in 9 of 12 (75%) ventilated animals versus only 1 of 12 (8%, P<.002) nonventilated animals. However, with arrest intervals of less than 6 minutes, these differences were not apparent. The investigators further demonstrated that assisted ventilation with either hypoxic or hypercarbic gas admixtures during CPR resulted in lower resuscitation rates compared with assisted ventilation with 85% oxygen.⁸⁴

In summary the published experimental data on animals collectively suggest that assisted ventilation may not be critical in the early minutes after onset of sudden fibrillatory cardiac arrest if adequate chest compression is provided. However, after relatively longer intervals of untreated fibrillatory cardiac arrest, some form of ventilatory support is likely to become critical for successful resuscitation outcomes. Whether mouth-to-mouth ventilation as the form of ventilatory support is helpful during even prolonged fibrillatory cardiac arrest remains unclear.

Clinical Studies of Mouth-to-Mouth Ventilation
Are the results obtained from animal studies applicable to CPR in human beings? Upper airway anatomy of animals differs from that of human beings; thus, upper airway obstruction during cardiac arrest may differ among species. Many animal species demonstrate frequent and prolonged gasping. Laboratory animals also do not have coronary artery disease. Unlike animal studies, the adequacy of oxygenation and ventilation during chest-compression-only CPR (ie, without mouth-to-mouth ventilation) has not yet been demonstrated in human beings receiving CPR.

Nevertheless, the available human data to date are consistent with findings in animals.^{38 75 85 86} For example, Weil et al⁸⁶ demonstrated that during the first few minutes of CPR in humans, arterial pH, PaCO₂, and bicarbonate change little from prearrest values. In addition, agonal respiration or gasping has also been documented in 40% of 445 out-of-hospital cardiac arrest victims and 55% of those victims with witnessed arrests.⁸⁵ Furthermore, as in animal studies, agonal respiration or gasping was associated with improved survival. Survival was 27% when gasping was present, compared with 9% when it was not. It is uncertain if the gasping was a marker for better central nervous system perfusion or shorter arrest intervals or if the agonal breaths themselves contributed to improved outcome.

Notably, recent investigations in humans with the active compression-decompression CPR device (plunger type) demonstrated that excellent minute ventilation (>6 L/min) was maintained in four cardiac arrest victims without assisted ventilation or intubation of the airway.⁸⁷ New investigations are still necessary to determine whether standard chest compression consistently results in adequate gas exchange for successful resuscitation of human victims of cardiac arrest.

Although physiological studies are informative, long-term survival in the clinical setting is the major therapeutic end point of CPR. The Belgian Cerebral Resuscitation Group^{38 39} prospectively evaluated 3053 out-of-hospital arrests. Physicians on the ambulances evaluated the quality of bystander CPR for compression and ventilation. Long-term survival of those treated with good-quality chest compression alone and those treated with good-quality chest compression plus mouth-to-mouth ventilation was comparable (15% and 16%, respectively) (Fig 4). Survival when either of these techniques was used was significantly superior to survival without any CPR (6%, P<.001). The data confirm that bystander CPR can be lifesaving but also suggest that mouth-to-mouth ventilation may not be necessary for survival of cardiac arrest, at least during the immediate moments after arrest. The authors of the study cautioned that conclusions drawn from these observations should be limited to adult patients with witnessed fibrillatory cardiac arrest.

View larger version (16K): [in this window] [in a new window]   Figure 4. Survival rates in comparison of good quality chest-compression-only CPR. The quality of bystander CPR was assessed by physician observers on ambulances. Comparisons of long-term survival rates are demonstrated after good quality chest-compression-only bystander CPR (CC alone), good quality chest-compression-plus-mouth-to-mouth-ventilation bystander CPR (CC&MMV), good quality mouth-to-mouth-ventilation-only CPR (MMV alone), and no bystander CPR. Outcome after chest-compression-only bystander CPR or chest-compression-plus-mouth-to-mouth-ventilation bystander CPR did not differ. Survival with either of these techniques was superior to survival with no bystander CPR (P<.001). Data derived from two studies of the Belgian Cerebral Resuscitation Study Group.38 39

Lengthier periods of arrest may require earlier ventilatory support. The observation that some ventilatory interventions are helpful after prolonged fibrillatory cardiac arrest may indicate an oxygenation or lung inflation requirement as much as a need for ventilation (CO₂ elimination). It seems probable that progressive lung deflation and airway closure occurs during chest compression without gasping or mouth-to-mouth ventilation. Such lung deflation will lead to increased pulmonary shunting and progressive hypoxemia. Reversal of lung deflation with an occasional lung inflation may be the critical pulmonary intervention to prevent hypoxia. If so, it may still be unnecessary to "normalize" respiratory rates in fibrillatory cardiac arrest until spontaneous circulation returns. Future studies should therefore attempt to delineate the critical timing, tidal volumes, and rates for optimal resuscitation.

	Are There Adverse Effects of Mouth-to-Mouth Ventilation?

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Respiratory Effects
When no endotracheal tube is in place, assisted ventilation maneuvers often are associated with gastric insufflation and pulmonary aspiration of gastric contents, which in turn may cause adult respiratory distress syndrome, pneumonitis, and possible death.⁶³ Some studies suggest a 10% to 35% incidence of pulmonary aspiration of gastric contents associated with CPR. During mouth-to-mouth ventilation, positive pressure in the oropharynx forces air into the lungs. Gas, however, flows down the path of least resistance, which may be either the trachea and lungs or the esophagus and stomach. Gastric insufflation is more apt to occur when (1) pulmonary compliance decreases (eg, with CPR, pulmonary edema, atelectasis, obesity, and the supine position), (2) airway resistance increases (eg, obstructive pulmonary disease), or (3) lower esophageal sphincter tone decreases.^{14 15 88 89}

Lower esophageal sphincter tone usually prevents regurgitation of gastric contents and provides resistance to gastric air flow during positive pressure ventilation. The normal esophageal sphincter opening pressure is about 20 to 25 cm H₂O.^{90 91} However, this energy-dependent muscular tone decreases rather quickly after circulatory arrest. In a swine model of CPR, mean esophageal sphincter opening pressure decreased from 20.6 cm H₂O before cardiac arrest to 5.6 cm H₂O after 5 minutes of cardiac arrest.⁹² In anesthetized patients with adequate circulation, gastric insufflation commonly occurs with bag-valve mask ventilation unless cricoid pressure is provided.⁹³ During cardiac arrest and CPR, pulmonary compliance decreases, increased inspiratory pressures may be needed to inflate the lung, and lower esophageal sphincter tone may decrease, all factors that increase gastric insufflation. Regurgitation was noted to occur primarily after the stomach was insufflated with air.¹⁶ Not surprisingly, in one series gastric insufflation and pulmonary aspiration were documented in nearly half of cardiac arrest victims after CPR with mouth-to-mouth ventilation.¹⁷

Another consideration is whether there are important differences between exhaled gas and ambient air. While room air has 21% O₂ and 0.03% CO₂, exhaled gas was observed to contain a mean O₂ concentration of 16.6% to 17.8% and a mean CO₂ concentration of 3.5% to 4.1% during one- and two-rescuer CPR.¹⁹ Thus, as provided during mouth-to-mouth ventilation, expired gas is slightly hypoxic and contains considerably more CO₂ than ambient air ventilation achieved with gasping and compression-induced ventilation alone.⁹⁴

Although expired gas rescue breathing is safe and may be life-saving for patients with respiratory arrests, the hypercarbia may have adverse cardiovascular effects when compared with ambient air ventilation during circulatory arrest. In one study of isolated hypercarbia, animals ventilated (12 mL/kg) with 95% O₂ and 5% CO₂ did as poorly as animals receiving no assisted ventilation at all during CPR.⁸⁴ Another investigation showed that swine ventilated with room air during 6 minutes of CPR had a rate of successful resuscitation (83%) twice that of animals ventilated with simulated exhaled gas ventilation when both groups received similar tidal volumes (38%, P<.01).⁹⁵ Consistent with animal studies are cellular studies that demonstrate modest increases in concentration of CO₂ can inhibit the rate and force of cardiac contraction, suggesting that elevated CO₂ has a direct cardiodepressive effect.^{96 97}

Circulatory Effects
Obviously a single rescuer performing CPR on an adult or child cannot provide chest compression and mouth-to-mouth ventilation simultaneously. Thus, it follows that with more time spent attempting ventilation, less time will likely be allocated to chest compression and vice versa. As noted, successful resuscitation has been highly correlated with the timing and degree of restored myocardial blood flow and coronary perfusion pressure, which are in turn dependent on the effective provision of chest compression of a sufficient rate and depth.^{98 99 100 101} Therefore, time spent attempting ventilation may take away valuable coronary perfusion. In support of this concept are recent studies that suggest that when rescuers attempt ventilation using current AHA recommendations, the compression rate and depth become inadequate.¹⁰² Current AHA guidelines for adult CPR recommend a chest compression rate of 80 to 100 per minute and a respiratory rate of approximately 12 breaths per minute, with compression/ventilation ratios of 15:2 with one rescuer and 5:1 with two rescuers. However, achieving these recommended guidelines in the real world has been demonstrated as problematic for both one- and two-rescuer adult CPR with mouth-to-mouth ventilation.^{18 19 20 101 102 103} One study of in-hospital two-rescuer CPR found that only 2 of 12 rescuers gave 80 compressions or more per minute,¹⁰³ whereas another investigation of simulated two-rescuer CPR on a manikin found that compression rates averaged 75 per minute and that the depth of compression was inadequate in 14% to 22%.¹⁰¹ These inadequacies of chest compression observed in two-rescuer CPR appear to be even worse in studies of one-rescuer CPR.^{18 19 20} In a study of healthcare professionals performing one-rescuer CPR on a manikin, only 15% achieved a rate of 80 compressions per minute despite continuous coaching.¹⁹ Further investigation confirmed that even immediately after successful completion of a basic CPR course, compression rates were particularly inadequate; on average, only 56 compressions per minute were provided by the 129 medical students studied.²⁰

These data suggest that the competition between time for ventilation and time for compression during one-rescuer CPR is a "zero-sum" game; time spent on ventilation takes precious time away from chest compression and support of myocardial blood flow. It is surprising that this aspect of CPR as practiced in the real world (ie, cycle time spent on ventilation versus cycle time spent on compression) has not been studied. It is worrisome that multiple studies have demonstrated survival rates to be consistently correlated with coronary perfusion pressure whereas no studies of fibrillatory arrest have shown improved rates of survival with early ventilation. Future studies need to take these real-world factors into account and not assume that performance of CPR is in complete adherence with AHA guidelines (which appears to be infrequently achieved).

Does Mouth-to-Mouth Ventilation Inhibit Performance of Bystander Cardiopulmonary Resuscitation?
Despite widespread acknowledgment of its value and efficacy, CPR is not performed by bystanders in the majority of cases for which it is indicated. Furthermore, several recent studies have documented a lower overall frequency of bystander CPR performance compared with earlier investigations.³ Although this latter finding may have several possible explanations (including the failure of the medical community and public health officials to effectively teach the public the skills of CPR), the perceived risk of disease transmission during CPR, even by healthcare workers, has become increasingly suspect as a major factor.

The actual risks of disease transmission during mouth-to-mouth ventilation are quite small. There are isolated reports of possible transmission of Helibacter pylori,¹⁰⁴ Mycobacterium tuberculosis,¹⁰⁵ meningococcus,¹⁰⁶ herpes simplex,^{107 108 109} shigella,¹¹⁰ streptococcus,¹¹¹ and salmonella.¹¹² No reports on transmission of HIV can be found. Nevertheless, despite the remote chances of its occurring, fears regarding disease transmission are common in the current era of universal precautions. Indeed, not only laypersons but physicians, nurses, and even BLS instructors are extremely reluctant to perform mouth-to-mouth ventilation.^{7 8 9 12 113} The most commonly stated reason for not performing mouth-to-mouth ventilation is fear of contracting AIDS.¹³ In one survey, only 15% of 975 respondents reported a willingness to perform chest compression with mouth-to-mouth ventilation on a stranger, whereas 68% would "definitely" perform chest compression alone if it was offered as an effective alternative CPR technique.¹²

Fear of disease transmission may not be the only reason that mouth-to-mouth ventilation inhibits bystanders from initiating CPR. When mouth-to-mouth ventilation is combined with chest compression, the CPR technique becomes a complex psychomotor task that can be difficult to teach, learn, remember, and perform.^{82 114} Educational principles suggest that a simpler technique, such as chest compression without mouth-to-mouth ventilation, would be far easier to teach the public. If it were known that the use of chest compression alone was nearly as efficacious as when combined with mouth-to-mouth ventilation, potential rescuers might start chest-compression CPR faster and more frequently because it is easier to perform in an actual emergency. In addition, the greater ease of learning, retaining, and performing such a simple procedure could lead to more widespread performance of bystander CPR, thereby improving survival rates for victims of cardiac arrest.

	Special Considerations: Implications for Future Guidelines

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It is important to emphasize that this report makes no changes in current AHA CPR guidelines and to consider why no changes are warranted. To summarize, during fibrillatory cardiac arrest, mouth-to-mouth ventilation may provide a modest therapeutic advantage over chest compression alone, and it may have some deleterious effects. Both experimental and very limited clinical studies to date suggest that mouth-to-mouth ventilation may be deferred for several minutes in the patient with sudden fibrillatory arrest. No studies on mouth-to-mouth ventilation are yet available for asphyxial cardiac arrest. On the basis of this review, in the most applicable clinical scenario for delaying mouth-to-mouth ventilation, an adult (older than 40 years) suddenly collapses from ventricular fibrillation. The collapse is witnessed by a bystander who can immediately initiate chest compression. However, this is a limited subpopulation of cardiopulmonary arrests and is not applicable to many resuscitations, such as those conducted for children, victims of submersion, respiratory failure, and many other arrest types. In addition, the available data from laboratory animals also suggest that after several minutes of fibrillatory arrest some form of ventilation is helpful, presumably to reinflate collapsing gas exchange units and prevent profound hypoxia. Therefore, it is important for future studies to delineate the specific circumstances and time limits under which mouth-to-mouth ventilation might be deferred. Without these data, rational guidelines cannot be provided. Although the current data are insufficient to warrant a change in CPR guidelines and training, they are compelling enough to recommend additional experimental and human trials to better delineate what the exact role of mouth-to-mouth ventilation should be during CPR.

It is also important to note that the current discussion and available research focus only on the contribution of mouth-to-mouth ventilation in the setting of sudden adult fibrillatory cardiac arrest. The potential application of mouth-to-mouth ventilation may be much broader than merely responding to fibrillatory arrest. Intuitively, mouth-to-mouth ventilation seems clearly indicated in cases of cardiopulmonary arrest associated with airway obstruction, water submersion, or preceding respiratory symptoms. Likewise, in children and young adults, respiratory compromise, not cardiac arrest, is the more common threat to life; thus, respiratory management should not be deferred. Submersion and respiratory problems are the typical precipitating causes of nontraumatic cardiac arrest in pediatric patients and young adults.^{6 115 116} In addition, a child's pulse may be difficult to locate and measure.^{117 118 119 120} These children may only be hypotensive (or even normotensive), and ventilatory support from mouth-to-mouth ventilation seems the highest priority under these circumstances.

Although the above recommendation on usefulness of mouth-to-mouth ventilation during asphyxial arrest for children with respiratory failure is logical, not even this is supported by data comparing the effectiveness of mouth-to-mouth ventilation with chest compression alone. A large amount of research is needed before the role and timing of mouth-to-mouth ventilation can be better clarified. As in adults, the relative importance of mouth-to-mouth ventilation and prompt defibrillation may be quite different among the many subgroups of cardiac arrest victims.¹²¹ Unfortunately, as with adults, in the majority of pediatric out-of-hospital arrest patients, basic bystander CPR is not attempted. The working group continues to recommend prompt ventilatory support in the form of mouth-to-mouth ventilation for apneic, pulseless, unresponsive children.

	Conclusions and Recommendations

Top Introduction Historical Rationale for... Does Assisted Ventilation... Are There Adverse Effects... Special Considerations:... Conclusions and Recommendations References

 
Traditional bystander CPR with chest compression and mouth-to-mouth ventilation has been documented to save lives. Nevertheless, CPR is not being performed in the majority of cases for which it is needed. As a result, an alarming number of premature deaths occur each year in the United States alone due to failure to provide basic CPR.¹ Requiring that mouth-to-mouth ventilation be an essential component of one-rescuer CPR has added to the complexity of teaching, learning, remembering, and performing this procedure. Provision of mouth-to-mouth ventilation has important potential disadvantages, including gastric insufflation and less cycle time spent on effective chest compression. Above all, aesthetic and infectious disease concerns by the public and healthcare providers appear to be major barriers to provision of basic CPR.

Although it seems possible that mouth-to-mouth ventilation is not needed during the first minutes of sudden witnessed circulatory arrest with suspected ventricular fibrillation, it is likely that mouth-to-mouth ventilation should be the initial intervention for arrest of suspected respiratory etiology. If a delay in mouth-to-mouth ventilation is being considered, the overall net impact on the public for saving lives from all causes of arrest, not merely sudden fibrillatory circulatory arrest, must also be taken into account. Updated guidelines on CPR are published at regular intervals. It is the hope of the working group that additional data will be available for consideration at the international conferences on CPR planned for the year 2000.

The working group recommends that

• Current guidelines for performing mouth-to-mouth ventilation during CPR should not be changed at this time. Indeed, it should be noted that the current AHA guidelines state that if a person is unwilling to perform mouth-to-mouth ventilation, he or she should rapidly attempt resuscitation, omitting mouth-to-mouth ventilation.¹ Clearly provision of chest compression without mouth-to-mouth ventilation is far better than not attempting resuscitation at all.³⁸
• Additional research initiatives are required to expressly delineate the role of mouth-to-mouth ventilation in the management of sudden death. Such studies on ventilation should evaluate the timing, rate, and depth as well as conditions under which respiratory assistance should be used. In addition to determining optimal CPR in the laboratory, more research on real-world obstacles to learning, remembering, and actually performing CPR should be evaluated and incorporated into future recommendations.
• Clinical trials involving human subjects who receive chest compression with or without mouth-to-mouth ventilation are ethical and necessary to determine how to save the most lives with basic CPR. Institutional review boards and national agencies interested in public safety should be aware of the limitations of current data to adequately justify current practice guidelines. Well-designed studies that answer important questions on CPR should be encouraged.
• Organizations and agencies interested in public safety and reduction of premature death should allocate resources for research on these high-yield issues that will determine future CPR guidelines. Unlike many areas of medicine, the design and methods to find definitive answers to these questions are readily available and merely await financial support for completion.

	Footnotes

 
"A Reappraisal of Mouth-to-Mouth Ventilation During Bystander-Initiated Cardiopulmonary Resuscitation" was approved by the American Heart Association Science Advisory and Coordinating Committee in July 1997.

This article also appears in Annals of Emergency Medicine (November 1997), Journal of Respiratory Care (September 1997), and Resuscitation.

A single reprint is available after September 30, 1997 by calling 800-242-8721 (US only) or writing the American Heart Association, Public Information, 7272 Greenville Avenue, Dallas, TX 75231-4596. Ask for reprint No. 71-0118. To purchase additional reprints: up to 999 copies, call 800-611-6083 (US only) or fax 413-665-2671; 1000 or more copies, call 214-706-1466, fax 214-691-6342, or

© 1997 American Heart Association, Inc.

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