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." 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.
Use of manual resuscitators to ventilate a patient is frequently called "bagging" the patientDaniel Limmer and Michael F. O'Keefe. 2005. Emergency Care 10th ed. Edward T. Dickinson, Ed. Pearson, Prentice Hall. Upper Saddle River, New Jersey. Page 140. 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.
History The bag valve mask concept was developed in 1956 by the German engineer Holger Hesse and his partner, Danish anaesthetist Henning Ruben, following their initial work on a suction pump. Hesse's company was later renamed Ambu A/S, which has manufactured and marketed the device since 1956. An Ambu bag is a self-inflating bag resuscitator from Ambu A/S, which still manufactures and markets self-inflating bag resuscitators.
Today there are several manufacturers of self-inflating bag resuscitators. Some, like the original Ambu bag, are durable and intended for reuse after thorough cleaning. Others are inexpensive and intended for single patient use.
Initially produced in one size, BVMs are now available in sizes for use with infants, children or adults.
Standard components Mask
The BVM consists of a flexible air chamber (the "bag", roughly 30 cm 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.
Bag and valve Bag and valve combinations can also be attached to an alternative airway adjunct, instead of to the mask. For example, it can be attached to an endotracheal tube or laryngeal mask airway. Small heat and moisture exchangers, or humidifying/bacterial filters, can be used.
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%.
Bag valve masks come in different sizes to fit infants, children, and adults. The face mask size may be independent of the bag size; for example, a single pediatric-sized bag might be used with different masks for multiple face sizes, or a pediatric mask might be used with an adult bag for patients with small faces.
Most types of the device are disposable and therefore single use, while others are designed to be cleaned and reused.
Method of operation
Manual resuscitators cause the gas inside the inflatable bag portion to be force-fed to the patient via a one-way valve when compressed by the rescuer; the gas is then ideally delivered through a mask and into the patient's trachea, bronchus and into the lungs. In order to be effective, a bag valve mask must deliver between 500 and 600 milliliters of air to a normal male adult patient's lungs, but if supplemental oxygen is provided 400 ml may still be adequate. Squeezing the bag once every 5 to 6 seconds for an adult or once every 3 seconds for an infant or child provides an adequate respiratory rate (10–12 respirations per minute in an adult and 20 per minute in a child or infant).Emergency Care, Pages 142–3
Professional rescuers are taught to ensure that the mask portion of the BVM is properly sealed around the patient's face (that is, to ensure proper "mask seal"); otherwise, pressure needed to force-inflate the lungs is released to the environment.
This is difficult when a single rescuer attempts to maintain a face mask seal with one hand while squeezing the bag with other. Therefore, common protocol uses two rescuers: one rescuer to hold the mask to the patient's face with both hands and focus entirely on maintaining a leak-proof mask seal, while the other rescuer squeezes the bag and focuses on breath (or tidal volume) and timing.Emergency Care, Page 141.
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.
Bag valve masks used in combat Airway obstruction is a leading cause of death in battlefield trauma. Airway management in combat is very different from its civilian equivalent. In combat, maxillofacial trauma is the primary cause of airway obstruction. The injury is frequently complicated by a struggling patient, distorted anatomy, and blood, and these injuries often have significant associated hemorrhage from accompanying vascular injuries.
Military paramedics face extreme challenges, including "darkness, hostile fire, resource limitations, prolonged evacuation times, unique casualty transportation issues, command and tactical decisions affecting health care, hostile environments and provider experience levels". They often have to treat multiple casualties using only the equipment they are carrying on their backs. Therefore, space is of primary importance and compact bag valve masks, such as a Pocket BVM, have been created to save valuable space in the emergency kit.
Complications 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).Wenzel V, Keller C, Idris AH, Dörges V, Lindner KH, Brimbacombe JR. Effects of smaller tidal volumes during basic life support: good ventilation, less risk? Resuscitation 1999: 43:25–29. 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,Dörges V, Sauer C, Ocker H, Wenzel V, Schmucker P. Smaller tidal volumes during cardiopulmonary resuscitation: comparison of adult and paediatric self-inflatable bags with three different ventilator devices. Resuscitation 1999: 43:31–37. 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." 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".Berg MD, Idris AH, Berg RA. Severe ventilatory compromise due to gastric insufflation during pediatric cardiopulmonary resuscitation. Resuscitation 1998: 36:71–73. Another reported complication was a case of stomach rupture caused by stomach over-inflation from a manual resuscitator.Smally AJ, Ross MJ, Huot CP. Gastric rupture following bag-valve-mask ventilation. J Amer Med 2002: 22:27–29. The causative factors and degree of risk of inadvertent stomach inflation have been examined,Wenzel V, Idris AH, Banner MJ, Kubilis PS, Williams JL Jr. Influence of tidal volume on the distribution of gas between the lungs and the stomach in the nonintubated patient receiving positive-pressure ventilation. Critical Care Medicine 1998: 26:364–368. 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