[Ventilation during cardiopulmonary resuscitation (CPR). A literature study and analysis of ventilation strategies]

Abstract

In a recently published German multicenter study, 25% of the patients with witnessed cardiac arrest outside the hospital were resuscitated successfully and discharged from the hospital. Approximately 100,000 people suffer a fatal cardiac arrest in Germany annually, which is approximately tenfold the number of deaths from motor vehicle accidents. Cardiopulmonary resuscitation (CPR) performed by bystanders is an important part of the chain of survival to minimize the time interval without artificial circulation and ventilation in a cardiac arrest victim. This is especially important in areas with long response times of the emergency medical service (EMS). Early examples of ventilation have been described throughout history. References to mouth-to-mouth ventilation (MTMV) are found in the Bible, in a description of the resuscitation of a coal miner in 1744, and in an experiment in 1796 demonstrating that exhaled gas was safe for breathing. In 1954, Elam and colleagues described artificial respiration with the exhaled gas of a rescuer using a mouth-to-mask ventilation method. The modern CPR era started with the combination of MTMV and chest compressions 35 years ago. However, the value of MTMV is currently under discussion because of a widespread fear of transmission of infectious diseases. Healthcare professionals have stated in several studies that they may withhold MTMV when confronted with a cardiac arrest in a stranger. Although an infection with Mycobacterium tuberculosis is more likely than one with HIV via MTMV, the fear of the public is understandable. An expert committee of the American Heart Association stated that MTMV may be omitted in the initial phase of cardiac arrest, and considered recommending chest compressions only if the EMS will arrive rapidly. In paralyzed volunteers, however, ventilation induced by chest compressions was not able to provide sufficient gas exchange, especially when the airway was not protected. Laboratory investigations studying ventilation during CPR showed controversial results; in one animal model of cardiac arrest with muscle paralysis, chest compressions were not sufficient for adequate gas exchange, but active compression-decompression CPR achieved reasonable ventilation. Animal models that prevented gasping during cardiac arrest required ventilation during CPR, whereas gasping animals seemed to be satisfactorily ventilated with chest compressions alone. The question whether spontaneous gasping after cardiac arrest in humans may be sufficient for oxygenation and carbon dioxide elimination is debatable and remains unanswered at this time. When cardiac arrest is monitored, frequent coughing by the patient may maintain artificial ventilation and circulation for 30 s. The strategy to compress the thorax first and then maintain the airway and perform ventilation may only have an advantage for the first 30 s of CPR. Therefore, MTMV remains the therapy of choice to ventilate the victim of cardiac arrest. If a rescuer chooses to not perform MTMV, at least chest compressions should be administered. During ventilation with an unprotected airway, tidal volumes of 0.5 l instead 0.8-1.2 l may have an advantage. This strategy would decrease the inspiratory flow rate and, therefore, peak airway inflation pressure, which is associated with stomach inflation. Animal models indicate that lower esophageal sphincter pressure may decrease rapidly to 5 cm H2O during cardiac arrest, which may further increase the importance of a low peak airway pressure during ventilation with an unprotected airway. Gastric inflation may cause, besides regurgitation, aspiration, and pneumonia, an increased intragastric pressure, which may push up the diaphragm, decrease lung compliance, and induce a vicious circle of hypoventilation and stomach inflation.(ABSTRACT TRUNCATED)