The art and science of safe intubation

Proper intubation can make the difference between a rocky and a smooth anesthesia

Photo courtesy Phil Zeltzman
Photo courtesy Phil Zeltzman

Patient intubation isn’t exactly a sexy topic. Yet, like anything else we do, there are correct and incorrect ways to perform it. Depending on how it’s handled, an endotracheal tube (ETT) can save a life, lead to complications, or kill a patient. Here are 10 critical points to keep in mind.

1) Materials

Not all tubes are made the same, so it is important to order and use what makes the most sense for your patients. ETTs are made from three main materials: silicone, polyvinyl chloride (PVC), and red rubber.

Despite their higher price, silicone tubes are a great option because they are softer, allowing them to conform more easily to the patient’s anatomy. Being softer, however, is also a disadvantage, as it may make intubation more difficult. Silicone tubes tend to bend during placement and a stylet may be required. Make sure the stylet doesn’t stick out of the tube, as it could lacerate the trachea.

PVC tubes are more rigid, so they are easier to place, but they don’t conform to the trachea as well as their silicone counterparts. However, once the tube is inside the patient, his or her body temperature softens the PVC, allowing it to bend more easily.

Red rubber ETTs have somewhat fallen out of favor given their disadvantages: they can harden over time, they tend to kink, and they do not soften at body temperature and, therefore, do not conform well to the trachea. Further, their color prevents seeing an obstruction by mucus or a blood clot.

2) Parts

The tube itself consists of different parts. There is a bevel at the patient end, which helps insert the tube between the arytenoid folds. The “Murphy eye” is an opening near the beveled end of some tubes, providing an additional pathway for air, should the end of the tube become occluded.

The cuff creates a seal against the trachea, which prevents anesthetic gas from escaping and hopefully avoids aspiration. The pilot balloon gives you an indication of how much the cuff is inflated.

3) Cuffs

It is very important to understand the two different types of cuffs:

  • high-pressure, low-volume; and
  • low-pressure, high-volume.

You can tell the difference between the two because the low-pressure, high-volume cuffs are wrinkly when deflated, giving them a higher surface area when inflated. In contrast, a high-pressure, low-volume cuff sits flush against the tube when deflated. Once inflated, it has a smaller surface area. There are advantages and disadvantages to both.

Low-pressure, high-volume cuffs can have folds between the cuff and the trachea, increasing the risk of aspiration in the event of regurgitation. Lubrication helps create a seal, which should decrease the risk of regurgitation.

High-pressure, low-volume cuffs may provide greater protection against aspiration. However, because there is less surface area, the pressure is greater at the areas of contact. There is increased risk of tracheal irritation, tear, necrosis, or stricture when these tubes are used for long surgical or dental procedures. One option is to periodically deflate the cuff, move the tube, and reinflate the cuff to protect the same area from pressure necrosis.

To be fair, although these risks are smaller with the low-pressure, high-volume cuffs, complications can arise when the cuff is overinflated.

DO YOU KNOW HOW TO LUBE?

The following applies to large, wrinkly, low-pressure, high-volume cuffs:

  • Inflate the cuff to check for leaks
  • Do not deflate it
  • Leaving it inflated is the key step most often missed
  • Roll the cuff in lubricant—preferably sterile (please don’t use the product you use to lube thermometers)
  • Only then should you deflate the cuff
  • Intubate the patient

4) Lubrication

The cuff should be lubricated2 to help facilitate intubation, reduce trauma to tissues, and improve the cuff’s seal (See the info box above).

5) Size

There are tables that help you choose the size of the tube based on the patient’s weight. This can be misleading. Choose the correct tube size based on your patient’s airway size, not their weight.

A 20-lb. beagle with a perfect body condition score (BCS) and an obese 50-lb. beagle have the same tracheal size, despite their weight difference. Brachycephalic patients have a notoriously smaller trachea than expected. Palpate the trachea to determine its size. Since this is a bit subjective, prepare one size above and one size under what you think is appropriate for your patient.

6) Length

The ETT’s diameter is not the only important factor to determine—its length also needs to be chosen wisely. If the tube is too short, you won’t maintain the airway as well. If it is too long, you risk placing the tube in one of the main stem bronchi. This is called endobronchial intubation (as opposed to endotracheal intubation) and it can cause cyanosis or hypoxia. Measure the length of the ETT from the patient’s nose to the middle of the neck. In other words, the tube should end midway between the larynx and the thoracic inlet. In some cases, you can cut the tube (on the breathing circuit end) to decrease the mechanical dead space, which can significantly impact smaller patients.1

7) Position

The patient’s position is instrumental for atraumatic and proper placement of the ETT. Ideally, he or she should be in sternal recumbency, the head and the neck positioned in a straight line to visualize the airway. Periodically check the tube placement and pilot balloon throughout the anesthetic procedure. To keep it simple, do this every time you take a reading of your patient’s vitals, which should be every five to 10 minutes.

8) Leak

After you’ve intubated your patient, connect the tube to the anesthesia system. Manual ventilation (i.e. squeezing the bag) should be performed to know how much air to inject in the cuff to prevent leaks. Smaller tubes typically require less than 3 ml of air, while larger tubes may need 6 to 10 ml. The goal is to inflate the cuff so there is no sound of leakage (hissing) and no anesthetic gas smell. When ventilating, never go above 20 cm H2O pressure.

The next step is to secure the ETT to prevent shifting throughout the procedure. If the patient needs to be moved, the tube should always be disconnected from the breathing circuit and then reconnected to prevent damage to the trachea (including a tracheal tear).3 Most will then tie the patient to the table to maintain the proper position. I strongly recommend connecting the patient to the anesthesia monitor before that. Positioning and securing the patient can wait—knowing your patient is still alive cannot. If that’s not enough, you should also cover your patient around that time to prevent hypothermia.

9) Extubation

During recovery, ETTs should remain in place until patients show they are capable of maintaining their airway on their own (i.e. they are “awake” enough). The “three swallows” rule is a complete myth. How many times a patient swallows is irrelevant. What matters is whether they will be safe and conscious enough to breathe without an ETT. Once removed, the tube should be inspected for any abnormalities, such as punctures, blood, or mucus. Anything found should be documented in the patient’s recovery notes.

10) Cleaning

Rather than letting secretions dry, place the ETT in water if you don’t have time to clean it right away. The outside and the inside of the tube should be washed gently with soapy water. A pipe cleaner or a nylon brush may help clean it on the inside. Strive to remove blood, mucus, or debris that covers or may have obstructed the tube. Some nurses blow through endotracheal tubes, especially the smaller ones, to be 100 percent sure there is no obstruction.

Inflate low-pressure, high-volume cuffs during cleaning to help remove secretions between their folds. Some people then disinfect their tubes with various products, such a chlorhexidine. Be sure to rinse it very well if you use chlorhexidine, as it may irritate the next patient’s mucosa. Next, air-dry it on a dedicated rack.

Some sterilize their ETTs before reusing them. Depending on the type of material, some tubes can be autoclaved, whereas others have to be gas-sterilized with ethylene oxide. Some practices use a brand new, sterile tube for each patient, which saves time and effort to clean used ETTs.

Intubation is a great time to perform an oral exam to detect masses that would be difficult to notice during a general exam. Proper intubation is an art as much as a science. It can make the difference between a rocky and a smooth anesthesia.

EVER HEARD OF ETTS WITHOUT A CUFF?

Some ETTs don’t have a cuff and are used in very small patients and many exotics. Cuffs should never be inflated when used on avian patients, as they have complete tracheal rings that can be ruptured by inflation. Instead, use a Cole tube, which is somewhat cone-shaped and is well suited for bird intubation.

A supraglottic airway device maintains the airway, but does not physically go in it. It can be used in patients who are difficult to intubate, such as rabbits. They also exist for dogs and cats. The disadvantage is that its “blind” placement can occlude the airway. Close patient monitoring is critical to notice any abnormality.

Phil Zeltzman, DVM, DACVS, CVJ, Fear Free Certified, is a board-certified veterinary surgeon and author whose traveling surgery practice takes him all over Eastern Pennsylvania and Western New Jersey. You can visit his website at DrPhilZeltzman.com. He also is cofounder of Veterinary Financial Summit, an online community and conference dedicated to personal and practice finance (vetfinancialsummit.com). AJ Debiasse, a technician in Blairstown, N.J., contributed to this article.

References

1 See vasg.org/dead_space.htm

2 Better lubrication: bit.ly/2PIHrRj

3 Tracheal rupture: SL Mitchell et al. “Tracheal rupture associated with intubation in cats: 20 cases (1996-1998).” JAVMA 2000, Vol 216, N 10, p. 1592-5.

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