Қолмен жұмыс істейтін өкпе желдеткіші ( қолмен сығылатын қап)

Hand held device to provide positive pressure ventilation

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." 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 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.

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 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.

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. 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. 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.

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.

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)." 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, 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." 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 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 bag valve 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.

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.

Manual resuscitators have no built in tidal volume control — the amount of air used to force inflate the lungs during each breath depends entirely on how much the operator squeezes the bag. In response to the dangers associated with the use of manual resuscitators, specific guidelines from the American Heart Association and European Resuscitation Council were issued that specify recommended maximal tidal volumes (or breath sizes) and ventilation rates safe for patients. While no studies are known that have assessed the frequency of complications or deaths due to uncontrolled manual resuscitator use, numerous peer reviewed studies have found that, despite established safety guidelines, the incidence of provider over inflation with manual resuscitators continues to be "endemic" and unrelated to provider training or skill level. Another clinical study found "the tidal volume delivered by a manual resuscitator shows large variations", concluding that "the manual resuscitator is not a suitable device for accurate ventilation." A separate assessment of another high skilled group with frequent emergency use of manual resuscitators (ambulance paramedics) found that "Despite seemingly adequate training, EMS personnel consistently hyperventilated patients during out of hospital CPR", with the same research group concluding that "Unrecognized and inadvertent hyperventilation may be contributing to the currently dismal survival rates from cardiac arrest." A further examination has recently been made to assess whether a solution to the over ventilation problem may lie with the use of pediatric sized manual resuscitators in adults or use of more advanced flow inflation (or "Mapleson C") versions of manual resuscitators: while "the paediatric self inflating bag delivered the most guideline consistent ventilation", it did not lead to full guideline compliance as "participants hyperventilated patients' lungs in simulated cardiac arrest with all three devices."

"Hyperventilation" can be achieved through delivery of (1) too many breaths per minute; (2) breaths that are too large and exceed the patient's natural lung capacity; or (3) a combination of both. With use of manual resuscitators, neither rate nor inflating volumes can be physically controlled through built in safety adjustments within the device, and as highlighted above, studies show providers frequently exceed designated safety guidelines for both ventilation rate (10 breaths per minute) and volume (5–7 mL/kg body weight) as outlined by the American Heart Association A more recent study published in 2012 expanded knowledge on this topic by evaluating the separate effects of (1) isolated excessive rate with guideline compliant inspiratory volumes; (2) guideline compliant rate with excessive inspiratory volumes; and (3) combined guideline non compliance with both excessive rate and volume. This study found that excessive rate more than triple the current guideline (e. g., 33 breaths per minute) may not interfere with CPR when inspiratory volumes are delivered within guideline compliant levels, suggesting that ability to keep breath sizes within guideline limits may individually mitigate clinical dangers of excessive rate. While this advancement appears to provide a solution to the "rate problem" associated with guideline excessive manual resuscitator use, it may not address the "volume problem", which may continue to make manual resuscitators a patient hazard, as complications can still occur from over inflation even when rate is delivered within guidelines. Currently, 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.

A filter is sometimes placed between the mask and the bag (before or after the valve) to prevent contamination of the bag.

Some devices have PEEP valve connectors, for better positive airway pressure maintenance.

A covered port may be incorporated into the valve assembly to allow inhalatory medicines to be injected into the airflow, which may be particularly effective in treating patients in respiratory arrest from severe asthma.

A separate covered port may be included into the valve assembly to enable a pressure monitoring device to be attached, enabling rescuers to continuously monitor the amount of positive pressure being generated during forced lung inflation.

A pressure relief valve (often known as a "pop up valve") is typically included in pediatric versions and some adult versions, the purpose of which is to prevent accidental over pressurization of the lungs. A bypass clip is usually incorporated into this valve assembly in case medical needs call for inflation at a pressure beyond the normal cutoff of the pop up valve.

Some bags are designed to collapse for storage. A bag not designed to store collapsed may lose elasticity when stored compressed for long periods, reducing its effectiveness. The collapsible design has longitudinal scoring so that the bag collapses on the scoring "pivot point," opposite to the direction of normal bag compression.

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.

Self inflating bags: This type of manual resuscitator is the standard design most often used in both in hospital and out of hospital settings. The material used for the bag portion of a self inflating manual resuscitator has a "memory", meaning after it is manually compressed it will automatically re expand on its own in between breaths (drawing in air for the next breath). These devices can be used alone (thus delivering room air) or can be used in connection with an oxygen source to deliver nearly 100% oxygen. As a result of these features, this type of manual resuscitator is appropriate for in hospital use and in out of hospital settings e. g., ambulances. Flow inflating bags: Also termed "anesthesia bags", these are a specialized form of manual resuscitator with a bag portion that is flaccid and does not re inflate on its own. This necessitates an external flow source of pressurized inflation gas for the bag to inflate; once inflated the provider can manually squeeze the bag or, if the patient is breathing on his/her own, the patient can inhale directly through the bag. These types of manual resuscitators are used extensively during anesthesia induction and recovery, and are often attached to anesthesia consoles so anesthesia gases can be used to ventilate the patient. They are primarily utilized by anesthesiologists administering general anesthesia, but also during some in hospital emergencies which may involve anesthesiologists or respiratory therapists. They are not typically used outside hospital settings. As per a recent Indian study, these flow inflation bags can also be used to provide CPAP in spontaneously breathing children. The study quotes that this mode of CPAP is cost effective in limited resource settings.