Using Anesthesia Bags
by
Tom Trimble, RN CEN
 

Anesthesia Bag Attributes:

What has no moving mechanical parts and can be:

1. used to administer oxygen,
2. monitor tidal volume,
3. assist respirations,
4. sense compliance,
5. give constant positive airway pressure,
6. control respirations,
7. is quiet,
8. runs only on compressed gas,
9. and (as with any other medical device) only needs a skilled and vigilant operator?

Nomenclature:

        The answer is what is commonly known as an "anesthesia bag". The soft rubber bags used as part of a gas flow system to monitor and control the patient's breathing.   Nomenclature varies: Ayre's Bag, the A-Bag, Norman Elbow, Jackson-Rees Circuit, Mapleson-F Circuit, etc., depending on its functional design or placement in anesthesia apparatus and local custom.

        The simplicity of design is elegantly coupled with its versatility of application. Its utility is such that it is the prime choice of many emergency professionals in dealing with respiratory emergencies. Let's explore the ways it can help you give better care.

Compressed Gas-Dependent; self-refilling O2BVM essential "spare":

        The one absolute drawback, it must be said, is its absolute reliance on a continuous source of compressed gas: the bag is not inherently self-refilling, and cannot therefore be used to ventilate the patient if the gas supply fails. This is why, in transport, one should always have a conventional (self-refilling O2 Bag-Valve-Mask) resuscitation bag available that can be operated with "room air" should it be necessary.

Construction & operating principle:

        The essence of construction is an elbow connecting via a 15mm/22mm port to a mask or endotracheal device the gas inflow in a minimal dead space manner to the large-bore low-resistance exhaust and reservoir. If the minute volume of gas flow is two to three times the minute tidal volume delivered, an essentially non-rebreathing condition occurs. Manipulating the exhaust and /or compressing the bag diverts flow into the lungs in a manually-cycled (therefore, time-cycled) manner. One must then provide an outflow leak to permit exhalation.

         Most commonly, the soft bag is made from latex: this would be contraindicated in a latex-allergic or latex-sensitive patient. Anaphylaxis is possible. Non-latex bags are available and should be used when indicated. Be aware of what you are using and of this possibility.

Advantages:

        Are there other practical advantages to the A-Bag compared with the conventional self-refilling resuscitation bag? Yes! The supple bag is far less fatiguing to the hands with prolonged use. When used with an endotracheal device, its extension tubing from the elbow permits straighter and freer posture easing the strain on one's back. The flexibility of this connection minimizes the risk of accidental extubation which also makes gurney transport safer and more comfortable. [With all conventional BVMs except the Laerdal, the fixed valve does not permit this and interposing flex-tubing would increase the dead-space, and self-refilling bags inherently limit the tidal volume {as bag size is fixed, smaller than the larger A-Bag} and operator ability to squeeze an adequate volume from the bag.]

       The A-bag will deliver the highest achievable FIO2 to the patient with adequate flow rate when no leaks are present.

Gentle Ventilation:

       Slow and gentle ventilations without excessively high peak airway pressures are easily delivered with the A-Bag, as compared to the Bag-Valve-Mask resuscitation bag. BVM valves are closed  (open to expiration side) unless there is a positive pressure from squeezing the bag or by too-rapid gas flow spilling through the valve into the airway, or by a negative pressure generated by the patient to breathe through the valve (different valves respond differently as to work of breathing imposed). Most operators tend to briskly squeeze the stiffer self-refilling bag due to the poorer "feel" which generates shorter inspiratory times with higher peak airflows. Excessive flow and pressure tends be insufflated via the esophagus into the stomach, if using the mask, inhibiting diaphragm movement and predisposing to vomiting. If using an airway tube, there is greater likelihood of barotrauma, or dropping the blood pressure by reducing cardiac preload, as positive pressure ventilation is a reversal of normal intrathoracic pressure changes.

       The A-Bag with its constant flow characteristic and no valve can provide gentle positive pressure breaths by manually occluding the tail, allowing the fresh gas flow to enter the patient inflating the lungs with gentle enhancement by squeezing the bag by hand or against the bed to provide a sufficiently large breath and appropriate inspiratory time. Releasing the tail releases pressure, eliminates work of breathing, and the constant fresh gas flow exhausts the exhalation and provides the first increment of the next breath volume in non-rebreathing fashion (if flow is 2-3 times minute volume). This is gentle to the patient and non-tiring to the operator. It is always important to match the gas flow to need so that the bag does not become over-distended: this can cause barotrauma to the patient in a closed system.

        This technique can be somewhat mimicked with a Bag-Valve-Mask resuscitation bag that has an open tubing reservoir by thumb-valving the aerosol tubing's open end to achieve the same effect, but this should only be done by a skilled operator as the fast gas flows needed may overflow the inspiratory valve forcing the patient to breathe against the additional resistance of the flow; "sticking" the valve like this is not good for the patient! In addition, the stiffer bag of a BVM will not give visual cuing of the patient's ventilatory pattern and status. Again, gas flow should be carefully monitored.

Constant Positive Airway Pressure can be maintained with the anesthesia bag in difficult airway situations to pneumatically open and splint the soft tissues apart. Therefore, it is especially useful when a situation of "Difficult Mask Ventilation" occurs, as it helps maintain an open airway. This is an advantage over the conventional Bag-Valve-Mask resuscitation bag, which has a brief positive pressure phase and a zero pressure phase, unless used with a "PEEP" valve for Positive End-Expiratory Pressure. The A-Bag is simpler in this respect. It can also be used therapeutically to recruit collapsed alveoli in atelectasis or pulmonary edema by maintaining pressure support and PEEP.
 

NOTE: Simplicity, flexibility, light weight [constant fresh gas flow ~ 2-3 X > minute volume ensures non-rebreathing without imposing additional work due to valves]

NOTE: Flex connection adds deadspace between valve & patient

Easy gas flow:

        Similarly, the absence of mechanical valve leaves or springs and discs in the elbow facilitate better dispersion and delivery of bronchodilator aerosols "mainlined" to the patient. The wide-bore tubing and components mean easier flow with less resistance especially at high flow rates. In addition, the constant inward flow at the elbow when the exhaust is occluded and the bag squeezed makes for easier inflation of the lungs (conventional BVMs are notably deficient in actual delivered volume by less than highly skilled users.) while also pushing exhaled gasses rapidly before it and out the bag's exhaust.
 

Use in Nasal Intubation:

        A uniquely useful attribute of the A-Bag helps oxygenate and prepare the patient for Awake Nasal Intubation. Not uncommonly, as the nasal passage is prepared with topical anesthetic and vasoconstriction, the patient's oxygen saturation will fall through haphazard and indifferent oxygen delivery. Pre-connecting the A-Bag to the endotracheal tube permits constant delivery of oxygen to the pharynx, observation of exhaled mist in the clear plastic of the ETT, and upon successful pass of the ETT between the vocal cords during inspiration the bag will rise and fall with each respiratory cycle.

Open-tail or Closed-tail?

        When the bag is used to hand-ventilate a patient with a mask, it may be used in either "closed-tail" or "open-tail" mode. Open-tail is easiest to master as a novice (the mask is kept clamped to the face, and exhaust is provided through the tail. Inflation occurs when the tail is pinched and the bag squeezed).  Closed-tail operation mandates that the operator manually provide for exhaust by lifting the mask slightly from the face (inflow will help divert exhalation out the mask, reclamping the mask then permits refill of the bag which is then compressed to fill the lungs). When the elbow is fixed to an endotracheal or tracheostomy tube (a "closed" system), exhaust must be provided for by an open-tail.

Titrate gas flow vigilantly:

        Controlling gas-flow is the essential principle of use. Balancing inflow, controlling leaks, having sufficient gas-flow to inflate the patient and exhaust the exhalations briskly without rebreathing, and still have an adequate reserve of fresh gas in the bag so that the patient's inhalation is pure, and adequate out-flow without resistance that could be transmitted to the patient's lungs which could cause barotrauma. All these are important responsibilities.

         It is  especially important to immediately adjust the fresh gas flow when changing from mask ventilation to an endotracheal tube or supraglottic airway device (LMA, CombiTube, etc.) as the dead air space will have been thereby lessened and excessive flow will lead to barotrauma.

Emergency Relief of Pressure and Bag-Distention:

         Should the bag too-rapidly fill or become over-distended, immediately break open the circuit! If using a mask, lift the mask from the face to exhaust the gas flow, and adjust the gas flow. If connected to a airway tube, separate the connectors instantly, and adjust the gas flow before reconnecting.

         Analyze! Either . . .

• The spontaneously breathing patient has just altered his respiratory pattern, or stopped breathing.
• The airway has become occluded (laxity in holding Triple Airway Maneuver throughout the respiratory cycle, vomiting, kinking of tube or tube against wall, etc.)
• Fresh gas flow was too high
• You weren't paying attention to ventilations, especially with the non-breathing patient. Focus on the patient and his breathing.
• The tail's valve is stuck or there is another obstruction to exhaust

Monitor pressure at airway port:

        With a port near the elbow, one may connect a manometer to monitor airway pressures. Thus, one may accurately determine peak airway pressure, compliance, and patient effort.. If the manometer is placed near the patient's shoulder, one may watch the patient's head, neck, chest, and the gauge simultaneously, thus observing patient effort, reading the manometer, noting the "feel" of the bag, and listening to the patient and the system for maximal feedback as to effectiveness obtained

Gain supervised experience:

        Try using an anesthesia bag, with a mentor available, in different circumstances. As skill grows, you will find it an excellent tool for difficult and changing situations.

"Using Anesthesia Bags"
[http://ENW.org/A-Bags.htm]
is a webarticle presented by:
Emergency Nursing World ! [http://ENW.org]
©Tom Trimble, RN [Tom@ENW.org

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