The respiratory system during resuscitation: a review of the history, risk of infection during assisted ventilation, respiratory mechanics, and ventilation strategies for patients with an unprotected airway
Section snippets
Assisted ventilation: the history
Attempts to provide ventilation for victims of respiratory and cardiac arrest have been described throughout history. Early descriptions are found in the Bible [1], [2], Egyptian mythology [3], and in anecdotal reports in the medical literature of resuscitation of victims of accidents and illness. In A.D. 177, the Greek scientist Galen performed a thoracotomy in swine and ventilated the animal with a self-inflatable bag [4]; in the 16th century, Paracelsus performed a tracheotomy in a pig and
Mouth-to-mouth ventilation and the fear of infectious diseases
In the last decade, the acquired immune deficiency syndrome caused by the human immunodeficiency virus (HIV) became a world-wide health risk, and resulted in a fear of infection during mouth-to-mouth ventilation. For example, 97% of CPR instructors stated in a survey that they would perform mouth-to-mouth ventilation on a 4-year-old drowned child, 54% on a college student, 35% on a haemophiliac, 18% on a stranger in a bus in San Francisco, and only 10% on a person with an overdose of heroin [32]
Respiratory mechanics of the unprotected airway affect stomach inflation
While the discussion about whether healthcare professionals or lay bystanders should or should not perform mouth-to-mouth ventilation has an emotional component, the question of whether satisfactory lung ventilation in an unintubated cardiac arrest patient can be achieved, is clearly a scientific issue. If ventilation strategies can be identified that could be beneficial for the patient, and not harmful for the rescuer, CPR outcome may be improved.
The distribution of ventilation volume between
Bag–valve–mask ventilation, and mouth-to-mouth ventilation in an unprotected airway
In an in vitro model of an unprotected airway, significantly less stomach inflation was found when applying a tidal volume of ∼500 ml with a mechanical ventilator compared with a tidal volume of ∼1000 ml [66]. Controlling inflation time, flow rate, and the flow wave form with a mechanical ventilator may be the best solution to control and to limit peak inflation pressure for a given tidal volume, but these variables may not be controlled easily during manual ventilation. A simple, portable
Cricoid pressure/Sellick manoeuvre to prevent stomach inflation
An option to prevent stomach inflation during ventilation with an unprotected airway is to apply cricoid pressure; this is a simple, effective manoeuvre to prevent stomach inflation [89] that was first described 200 years ago [90]. In a model of human cadavers, an intraoesophageal pressure of 75 cm H2O was required to overcome cricoid pressure; indicating that the Sellick manoeuvre may be able to prevent gastric distension even when ventilating with a high peak inflation pressure [91] (Fig. 4).
Gasping and ventilation induced by chest compressions provide some, but not sufficient gas exchange
In animal models with no muscle paralysis, ventilation induced by gasping and chest compressions was sufficient for adequate carbon dioxide elimination and oxygenation [100], [101]. When gasping during ventricular fibrillation in swine was prevented with a neuromuscular blocking agent, ventilation induced by chest compressions failed to maintain adequate carbon dioxide elimination and oxygenation; and ventilated pigs were more likely to survive than pigs that received chest compressions only
Summary
When an oxygen source is available, it is recommended that tidal volumes are reduced from ∼1000 to ∼500 ml (FiO2≥40%) when ventilating a patient with an unprotected airway. A tidal volume of 500 ml during bag–valve–mask ventilation may be a better trade-off in the basic life support phase of CPR; although mouth-to-mouth ventilation tidal volumes should remain 700–1000 ml. This strategy would provide reasonable ventilation and oxygenation while avoiding massive gastric inflation that may result
Acknowledgements
Supported, in part, by grant 91GIA/721 from the American Heart Association, Florida Affiliate; the Laerdal Foundation for Acute Medicine, Stavanger, Norway; the Austrian Science Foundation grant P14169-MED, Vienna, Austria; the Founders grant of the Society of Critical Care Medicine, Anaheim, California, United States; and the Department of Anesthesiology and Critical Care Medicine, Leopold-Franzens-University, Innsbruck, Austria.
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