Experimental study on a causal relationship between sleeping in a face-down position and sudden death in infants

通过动物实验研究用被褥盖住口鼻是否会导致健康婴儿出现致命性低氧血症。[方法]用聚氨酯树脂制作死亡婴儿的口罩，并增加1.5 kg的垂直载荷。一根气管内管被放置在小猪身上，并与口罩的鼻腔相连，小猪通过鼻腔呼吸。连续监测血压（BP）、心率（HR）、动脉血氧饱和度（O_2sat）、呼吸频率（RR）、呼气氧气浓度（exO_2）和呼气二氧化碳浓度（exCO_2），必要时监测动脉血氧浓度（PaO_2）和动脉血二氧化碳浓度（PaCO_2）。床上用品采用软硬日式床（蒲团）和俯卧专用床垫。当口罩面朝下放在柔软的蒲团上时，动物立即开始强制吸气。O_2sat和exO_2在3分钟内迅速下降，PaO_2在3分钟后降至29.8 mmHg。3分钟后将口罩正面朝上放置，呼吸状况和各项检测值迅速恢复正常。将口罩相应放置在硬床垫上，5分钟后PaO_2逐渐降至44.2 mmHg， 25分钟后降至30.1 mmHg， 35分钟后降至31.0 mmHg。O_2sat和exO_2也逐渐减少，50 min后动物死亡。当将口罩放在俯卧专用床垫上时，5分钟后PaO_2降至36 mmHg。O_2sat和exO_2在前3分钟迅速下降，随后与BP、HR和RR一样逐渐下降，25分钟后死亡。[结论]这些发现表明，婴儿俯卧时，尤其是脸朝下时，鼻子和嘴巴都被床上用品覆盖，可能会很快死于低氧血症。

An animal experiment was conducted to investigate whether covering both nose and mouth by bedding may cause lethal hypoxemia in healthy infants.[Methods]A mask of a dead infant was made of polyurethane resin, and a vertical load of 1.5 kg was added. An endotracheal tube was placed in a piglet and linked to the nasal cavity of the mask, through which the piglet breathed. Blood pressure (BP), heart rate (HR), arterial oxygen saturation (O_2sat), respiratory rate (RR), expired air oxygen concentration (exO_2) and expired air carbon dioxide concentration (exCO_2) were monitored continuously, and arterial oxygen concentration (PaO_2) and arterial carbon dioxide concentration (PaCO_2) were monitored as necessary. For bedding, soft and hard Japanese beds (futons) and a mattress dedicated for prone sleeping were used.[Results]1.When the mask was placed in a face-down position on the soft futon, the animal immediately started forced inspiration. O_2sat and exO_2 quickly decreased within three minutes, and PaO_2 decreased to 29.8 mmHg three minutes later. When the mask was placed in a face-up position three minutes later, respiratory condition and all test values quickly returned to normal.2.When the mask was correspondingly placed on the hard futon, PaO_2 gradually decreased to 44.2 mmHg five minutes later, 30.1 mmHg 25 minutes later and 31.0 mmHg 35 minutes later. O_2sat and exO_2 also gradually decreased, and the animal died 50 minutes later.3.When the mask was correspondingly placed on the mattress dedicated for prone sleeping, PaO_2 decreased to 36 mmHg five minutes later. O_2sat and exO_2 quickly decreased for the first three minutes and thereafter decreased as gradually as BP, HR and RR did, and the animal died 25 minutes later.[Conclusion]These findings suggest that infants may quickly die from hypoxemia caused by both nose and mouth being covered by bedding while they sleep in a prone position, especially in a face-down position.