Question: How does this procedure fit into the Difficult Airway Algorithm?

Answer: The Aintree becomes a valuable tool following an unexpected airway event when LMA placement successfully reestablishes ventilation following failed mask ventilation and tracheal intubation.

In the instance when mask ventilation and endotracheal tube intubation attempts have unexpectedly failed, placing an LMA or supraglottic airway (SGA) will often reestablish ventilation, allowing for a momentary pause for anesthesia providers to collect their wits and determine the next best step for the patient.

If positive ETCO2 confirms that ventilation has been satisfactorily reestablished with an LMA, the options are as follows:

1. Allow the patient to awaken with the LMA in place

2. Maintain the LMA and proceed with the surgery

3. Fiberoptically convert the LMA to an endotracheal tube

4. Maintain the LMA while a surgical airway is obtained

   
   

The choice of how to proceed will ultimately depend upon the clinical context of each unique scenario. REMOVING the LMA and reattempting efforts at intubation or mask ventilation is risky and is NOT recommended, as doing so has led to severe injury, lost airways and death. In cases when a protected airway is necessary, it is recommended that all providers understand how to place an endotracheal tube fiberoptically through the LMA. Doing so preserves ventilation and oxygenation through the LMA while a secure airway is established and limits excessive instrumentation.

There are numerous methods for fiberoptically converting an LMA to an ETT. The following method is easy to learn, and its versatility makes it compatible with virtually every type of the 40+ FDA approved LMAs on the market (the notable exception is the Teleflex Supreme LMA as this LMA's lumen is simply too small and will not fit an Aintree catheter).

Question: What is the Aintree?

Answer: The Aintree is a device specifically manufactured to facilitate fiberoptic intubations through an LMA or SGA. It is also otherwise known as an "Airway Intubation Catheter" or AIC.

The Cook Aintree catheter is a semi-rigid, 56 cm long intubation catheter designed to fit over an intermediate sized bronchoscope, specifically for the purpose of facilitating intubation. When an Aintree is successfully railroaded over a bronchoscope and into the trachea, a 7-0 ETT can, in turn, be railroaded over the Aintree and into the airway.

Question: What equipment will you need?

1. Aintree catheter

2. Intermediate sized bronchoscope (Olympus 4-0 or Glidescope 3.8mm)

3. A 7-0 ETT

4. Silicone lubricant spray

5. Scope defogging agent

6. Bronch elbow

7. A well seated and functioning LMA (anything but the Supreme LMA will do)

Question: Can you explain more about equipment sizing specific to this procedure?

Note that the outer diameter (OD) of the Aintree is 6.3mm, thus the smallest ETT that can fit over the catheter is the 7-0 ETT (the "7-0" nomenclature refers to ETT internal diameter, which is 7.0mm). A smaller ETT will not be compatible with the Aintree.

The internal lumen of the Aintree (ID 4.7mm) is perfectly compatible with any intermediate sized bronchoscope (i.e. the reusable 4-0 Olympus scope (OD 4mm) & the Verathon Glidescope Slim disposable scope (OD 3.8 mm)).

Question: What vent settings do you prefer with this procedure?

Answer: When ventilating through the LMA for this Aintree intubation technique, we typically opt for PCV with PIP of approximately 15-18 cm H2O and an RR of 14-18. As always, tailor based on clinical needs and context.

Question: What are some equipment factors that can lead to intubation failure with this procedure?

Answer: There are several potential areas for failure with this procedure. Take the following actions and considerations to ensure good results.

1. Ensure appropriate size matching of your equipment

2. Airway narrowing or stenosis inherent or specific to the patient's anatomy can be a limitation of this technique. The smallest ETT compatible with the Aintree is the 7-0 ETT. So, the patient's anatomy must also be able to accommodate, at a minimum, a 7-0 ETT (which depending on the manufacturer has an OD approximately 9.5 mm - this sizing data is always printed clearly on the ETT packaging as well as the ETT itself).

   
   

   

   
   

3. The Verathon Glidescope bronchoscope has inferior textile fidelity, especially with the smaller scopes. Fiberoptic intubations can simply be more frustrating when using this scope. One specific point for failure, however, has occurred despite excellent visualization of the vocal cords. Rarely, even when the procedure is handed over to experienced faculty, there has just been extreme difficulty and eventual failure in advancing the scope through the vocal cords. The cause remains unclear, though it likely has something to do with the flimsy nature of this bronchoscope tip. So for difficult or failed airways, providers may want to request the Olympus tower.

4. Very rarely the Aintree has travelled through the oropharynx and into the glottic opening at such an acute angle that, once the scope is removed, the Aintree catheter itself is forced into a bent or kinked position within the oropharynx. In these cases, the ETT cannot be railroaded and gets "hung up" at a shallow depth somewhere within the oropharynx and at the point of kinking. If this is suspected (as evidenced by inability to railroad the ETT beyond a shallow depth of 10-11 cm), manually feel along the Aintree catheter for this point of "kinking" and "unkink" it with your fingers.

Question: The Aintree package comes with two adaptors. Should I try those out?

Answer: There are two adaptors, one 15mm circuit adaptor and one jet ventilator adaptor. Neither adaptor is appropriate for elective use and ventilation/oxygenation through the Aintree should typically be reserved for emergencies, when unforeseen delays or difficulties are encountered with railroading the ETT into the trachea.

Simple "blow by" oxygenation using low flow oxygen through the 15mm circuit adaptor presents a lower risk of barotrauma than jet ventilation. Not handled with care, jet ventilation through these devices can quite easily deliver large tidal volumes, leading to breath stacking, barotrauma, and pneumothorax (see below).

Question: Can't I just save some steps and ventilate through the Aintree Catheter?

Answer: Sure, but that would never be my first option, and I'll explain why.

Given the option of 1) ventilating through the Aintree catheter or 2) railroading a 7-0 ETT over the Aintree and ventilating through the ETT, I would always choose the ETT because,

1. The ETT is cuffed and protects against aspiration and improves ventilation ability.

2. The ETT's internal lumen is much larger than the Aintree's internal lumen and provides a dedicated "pathway" for exhalation. There is no such pathway for exhalation when ventilating through the Aintree which means that any volume delivered to the lungs must travel through an unreliable path of egress AROUND and external to the Aintree. In the presence of any upper or lower airway obstruction the resistance to egress may be high, leading to a higher risk for breath stacking and barotrauma. (And it goes without saying that if railroading of an ETT over an Aintree failed, there is a high probability that significant airway obstruction is present)

Question: I successfully placed the Aintree in the trachea but was unable to railroad the 7-0 ETT over it and into the airway. Should I opt to ventilate the patient through the Aintree now?

Answer: That depends. If the patient is hypoxic, oxygenating through the Aintree can be lifesaving, but certain precautions should be taken to prevent iatrogenic injury.

So long as the Aintree is confirmed to be in the trachea (you can always quickly check again with the bronch), you can temporarily opt to ventilate the patient through the Aintree.

Keep in mind, this is a short-term solution to a larger problem. In this scenario, when a 7-0 ETT cannot be passed over the Aintree, there is very likely some point of obstruction in the airway, meaning that resistance to exhalation will be higher and thus meaning that risk of breath stacking and barotrauma are, in turn, also higher.

Question: If I must jet ventilate through the Aintree, what are some safety measures to guard against barotrauma and a potential tension pneumothorax?

1. Avoid main-stemming - Jet ventilation to only one lung will obviously increase the risk of breath stacking to that lung. The average distance between carina and incisors in an adult female is approximately 23cm +/- 1cm (26cm +/- 1cm in males). Ensure that your catheter remains in the trachea by ensuring a maximum depth of no more than this depth, preferably slightly less.

2. Alleviate upper airway obstruction - Elevate the head of the bed, place an oral and nasal airway, and hold jaw thrust

3. Use low inspiratory pressures - Twist the jet ventilator knob to set a maximum delivered pressure of 15-20 PSI

   
   

   

   
   

4. Use short inspiratory times - Using inspiratory pressures of 15-20 PSI, you can expect to easily deliver a normal tidal volume to normal lungs (approximately 400mL) with an inspiratory time of 1/2 second. We only carry manual jet ventilators, so you'll have to estimate inspiratory time.

5. Prolong expiratory time - You are relying on passive recoil of the lungs through a high resistance conduit (around and external to the Aintree) for exhalation. Aim for a respiratory rate of 6-10 bpm to stretch the expiratory time.

In summary, when jet ventilating through the Aintree, take these precautions to decrease risk.

1. Depth of < 23 cm (<26cm in males)

2. Alleviate any upper airway obstructions

3. Keep tidal volumes minimal with 15-20 PSI x 1/2 sec

4. RR 6-10 bpm

5. High risk for barotrauma. Sudden decompensation should prompt urgent evaluation and treatment for tension pneumothorax.

6. MOST IMPORTANTLY, this is a TEMPORARY solution. CALL FOR MORE HELP and begin making expedient preparations for placement of a surgical airway.