Under normal breathing, the lungs inflate under a slight vacuum when the chest wall muscles and diaphragm expand; this "pulls" the lungs open, causing air to enter the lungs to inflate under a gentle vacuum. However, when using a manual resuscitator, as with other methods of positive-pressure ventilation, the lungs are force-inflated with pressurized air or oxygen. This inherently leads to risk of various complications, many of which depend on whether the manual resuscitator is being used with a face mask or ET tube. Complications are related to over-inflating or over-pressurizing the patient, which can cause: (1) air to inflate the stomach (called gastric insufflation); (2) lung injury from over-stretching (called volutrauma); or (3) lung injury from over-pressurization (called barotrauma). Stomach inflation / lung aspiration When a face mask is used in conjunction with a manual resuscitator, the intent is for the force-delivered air or oxygen to inflate the lungs. However air entering the patient also has access to the stomach via the esophagus, which can inflate if the resuscitator is squeezed too hard (causing air flow that is too rapid for the lungs to absorb alone) or too much (causing excess air to divert to the stomach)." Gastric inflation can lead to vomiting and subsequent aspiration of stomach contents into the lungs, which has been cited as a major hazard of<unk><unk> -mask ventilation, with one study suggesting this effect is difficult to avoid even for the most skilled and experienced users, stating "When using a self-inflatable<unk> , even experienced anesthesiologists in our study may have performed ventilation with too short inspiratory times or too large tidal volumes, which resulted in stomach inflation in some cases." The study goes on to state that "Stomach inflation is a complex problem that may cause regurgitation, gastric acid aspiration, and, possibly, death." When stomach inflation leads to vomiting of highly acidic stomach acids, delivery of subsequent breaths can force these caustic acids down into the lungs where they cause life-threatening or fatal lung injuries including Mendelson's syndrome, aspiration pneumonia, acute respiratory distress syndrome and "pulmonary injuries similar to that seen in victims of chlorine gas exposure". Apart from the risks of gastric inflation causing vomiting and regurgitation, at least two reports have been found indicating that gastric insufflation remains clinically problematic even when vomiting does not occur. In one case of failed resuscitation (leading to death), gastric insufflation in a 3-month-old boy put sufficient pressure against the lungs that "precluded effective ventilation". Another reported complication was a case of stomach rupture caused by stomach over-inflation from a manual resuscitator. The causative factors and degree of risk of inadvertent stomach inflation have been examined, with one published study revealing that during prolonged resuscitation up to 75% of air delivered to the patient may inadvertently be delivered to the stomach instead of the lungs. Lung injury and air embolism When an endotracheal tube (ET) is placed, one of the key advantages is that a direct air-tight passageway is provided from the output of the manual resuscitator to the lungs, thus eliminating the possibilities of inadvertent stomach inflation or lung injuries from gastric acid aspiration. However this places the lungs at increased risk from separate lung injury patterns caused by accidental forced over-inflation (called volutrauma or barotrauma). Sponge-like lung tissue is delicate, and over-stretching can lead to adult respiratory distress syndrome – a condition that requires prolonged mechanical ventilator support in the ICU and is associated with poor survival (e.g., 50%), and significantly increased care costs of up to $30,000 per day. Lung volutrauma, which can be caused by "careful" delivery of large, slow breaths, can also lead to a "popped" or collapsed lung (called a pneumothorax), with at least one published report describing "a patient in whom a sudden tension pneumothorax developed during ventilation with a<unk><unk>  device." Additionally, there is at least one report of manual resuscitator use where the lungs were accidentally over-inflated to the point where "the heart contained a large volume of air," and the "aorta and pulmonary arteries were filled with air" – a condition called an air embolism which "is almost uniformly fatal". However, the case was of a 95-year-old woman, as the authors point out that this type of complication has previously only been reported in premature infants.
Bag valve mask
Hutchinson's mask
Schimmelbusch mask
Pocket mask
Binasal occlusion
Venturi mask
Simple face mask
Surgical mask