Mouth-to-mouth resuscitation is believed to be a quick, effective method for providing oxygen to a victim. The International Guidelines of 2000 have recommended reducing the risk of gastric inflation during mouth-to-mouth ventilation by delivering slow breaths at the lowest tidal volume that would still raise the chest visibly with each ventilation. For mouth-to-mouth ventilation in most adults, the tidal volume would be approximately 10 ml/kg (ca. 700-1000 ml). It should be delivered over 2 s. Can however, an appropriate amount be blown in even if there is no special instruction when an untrained citizen suddenly encounters an accident? We investigated the mean tidal volume during mouth-to-mouth resuscitation by untrained citizens, and it was ca. 800 ml, which corresponds to the recommended value of the current guidelines. In the mouth-to-mouth resuscitation, the composition of the expired air that the rescuer administers to the victim was PO
2 and PCO
2 of 115±1 mmHg and 32±1 mmHg when the tidal volume was 500 ml. When the tidal volume was 1 l, PO
2 and PCO
2 were 120±1 mmHg and 29±1 mmHg, respectively (N=10). Moreover, when the ventilation experiment was done to the animal (beagle), the following results were shown (N=7). The amount of ventilation was ca. 20 ml/kg, and 12 breaths per minute. In addition, arterial PaO
2, PaCO
2, and pH were measured. Consequently, after mouth-to-mouth ventilation, PaO
2 decreased to 71±1 mmHg (normal value = 95-100 mmHg), PaCO
2 increased to 54±2 mmHg (normal value = 40 mmHg), and the pH became 7.27±0.02. To improve the respiratory state after mouth-to-mouth ventilation, we developed a new Portable Ventilation System (PVS) to the improve ventilation efficiency and to alleviate the risk of infectious disease. By using PVS, the composition of inflow air of the mouth-to-mouth ventilation by rescuers was PO
2 139±2 mmHg and PCO2 15±1 mmHg (N=10), when the tidal volume was 500 ml and PO
2 and PCO
2 were 131±2 mmHg and 19±1 mmHg, respectively when the tidal volume was 1 l (N=10). This ventilation experiment was performed on animals (beagle). After artificial ventilation with gas made by PVS, changes of arterial PaO
2, PaCO
2 and pH were improved to 84±2 mmHg, 46±1 mmHg, and 7.37±0.01, respectively (N=7). Consequently, results showed that the ventilation efficiency of the new PVS was higher than that for mouth-to-mouth ventilation.
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