A bag valve mask (BVM), sometimes known by the proprietary name Ambu bag or generically as a manual resuscitator or "self-inflating bag", is a hand-held device commonly used to provide positive pressure ventilation to patients who are not breathing or not breathing adequately. The device is a required part of resuscitation kits for trained professionals in out-of-hospital settings (such as ambulance crews) and is also frequently used in hospitals as part of standard equipment found on a crash cart, in emergency rooms or other critical care settings. Underscoring the frequency and prominence of BVM use in the United States, the American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Care recommend that "all healthcare providers should be familiar with the use of the bag-mask device."[1] Manual resuscitators are also used within the hospital for temporary ventilation of patients dependent on mechanical ventilators when the mechanical ventilator needs to be examined for possible malfunction or when ventilator-dependent patients are transported within the hospital. Two principal types of manual resuscitators exist; one version is self-filling with air, although additional oxygen (O2) can be added but is not necessary for the device to function. The other principal type of manual resuscitator (flow-inflation) is heavily used in non-emergency applications in the operating room to ventilate patients during anesthesia induction and recovery.[citation needed]
Ambi-hi-lo chamber manual
Use of manual resuscitators to ventilate a patient is frequently called "bagging" the patient[2] and is regularly necessary in medical emergencies when the patient's breathing is insufficient (respiratory failure) or has ceased completely (respiratory arrest). Use of the manual resuscitator force-feeds air or oxygen into the lungs in order to inflate them under pressure, thus constituting a means to manually provide positive-pressure ventilation. It is used by professional rescuers in preference to mouth-to-mouth ventilation, either directly or through an adjunct such as a pocket mask.
The BVM consists of a flexible air chamber (the "bag", roughly a foot in length), attached to a face mask via a shutter valve. When the face mask is properly applied and the "bag" is squeezed, the device forces air through into the patient's lungs; when the bag is released, it self-inflates from its other end, drawing in either ambient air or a low pressure oxygen flow supplied by a regulated cylinder, while also allowing the patient's lungs to deflate to the ambient environment (not the bag) past the one way valve.[citation needed]
A bag valve mask can be used without being attached to an oxygen tank to provide "room air" (21% oxygen) to the patient. However, manual resuscitator devices also can be connected to a separate bag reservoir, which can be filled with pure oxygen from a compressed oxygen source, thus increasing the amount of oxygen delivered to the patient to nearly 100%.[4]
An endotracheal tube (ET) can be inserted by an advanced practitioner and can substitute for the mask portion of the manual resuscitator. This provides more secure air passage between the resuscitator and the patient, since the ET tube is sealed with an inflatable cuff within the trachea (or windpipe), so any regurgitation is less likely to enter the lungs, and so that forced inflation pressure can only go into the lungs and not inadvertently go to the stomach (see "complications", below). The ET tube also maintains an open and secure airway at all times, even during CPR compressions; as opposed to when a manual resuscitator is used with a mask when a face mask seal can be difficult to maintain during compressions.[citation needed]
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).
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)."[11] Gastric inflation can lead to vomiting and subsequent aspiration of stomach contents into the lungs, which has been cited as a major hazard of bag-valve-mask ventilation,[12] with one study suggesting this effect is difficult to avoid even for the most skilled and experienced users, stating "When using a self-inflatable bag, 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."[11] 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".[11] 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".[13] Another reported complication was a case of stomach rupture caused by stomach over-inflation from a manual resuscitator.[14] The causative factors and degree of risk of inadvertent stomach inflation have been examined,[12][15] 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.[15]
Two factors appear to make the public particularly at risk from complications from manual resuscitators: (1) their prevalence of use (leading to high probability of exposure), and (2) apparent inability for providers to protect patients from uncontrolled, inadvertent, forced over-inflation.
Manual resuscitators are commonly used for temporary ventilation support, especially flow-inflation versions that are used during anesthesia induction/recovery during routine surgery. Accordingly, most citizens are likely to be "bagged" at least once during their lifetime as they undergo procedures involving general anesthesia. Additionally, a significant number of newborns are ventilated with infant-sized manual resuscitators to help stimulate normal breathing, making manual resuscitators among the first therapeutic medical devices encountered upon birth. As previously stated, manual resuscitators are the first-line device recommended for emergency artificial ventilation of critical care patients, and are thus used not only throughout hospitals but also in out-of-hospital care venues by firefighters, paramedics and outpatient clinic personnel.
Currently,[when?] the only devices that can deliver pre-set, physician-prescribed inflation volumes reliably within safety guidelines are mechanical ventilators that require an electrical power source or a source of compressed oxygen, a higher level of training to operate, and typically cost hundreds to thousands of dollars more than a disposable manual resuscitator.
In a hospital, long-term mechanical ventilation is provided by using a more complex, automated ventilator. However, a frequent use of a manual resuscitator is to temporarily provide manual ventilation whenever troubleshooting of the mechanical ventilator is needed, if the ventilator circuit needs to be changed, or if there is a loss of electrical power or source of compressed air or oxygen.A rudimentary type of mechanical ventilator device that has the advantage of not needing electricity is a flow-restricted, oxygen-powered ventilation device (FROPVD). These are similar to manual resuscitators in that oxygen is pushed through a mask to force-inflate the patient's lungs, but unlike a manual resuscitator where the pressure used to force-inflate the patient's lungs comes from a person manually squeezing a bag, with the FROPVD the pressure needed to force-inflate the lungs comes directly from a pressurized oxygen cylinder. These devices will stop functioning when the compressed oxygen tank becomes depleted.[citation needed]
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