Assessing extubation criteria, and then deciding when to extubate a patient safely can sometimes be a difficult decision. In anesthesia, we often obsess about safety during induction and maintenance. In fact, the numbers of closed claims cases [1,2] for death due to induction of anesthesia have decreased significantly. Cases of brain damage have also decreased. Unfortunately, the same can’t be said of extubation. About 12% of close claims were linked to extubation. Never take extubation for granted.

Extubation Criteria

We all know the common extubation criteria:

• recovery of airway reflexes and response to command;
• inspiratory capacity of at least 15 ml/kg;
• no hypoxia, hypercarbia, or major acid/base imbalance;
• no cardiopulmonary instability;
• signs of intact muscle power;
• absence of retraction during spontaneous respiration;
• absence of a distended stomach.

In other words, you want your patient:

• to be stable,
• capable of breathing without help, and
• capable of protecting the airway.

Nevertheless, sometimes the decision is not so easy. Here I describe a case of a patient who met some but not all of the extubation criteria. The reason turned out to be due to a rare complication: plugging of the endotracheal tube. However, getting to that solution required working through the extubation algorithm. 

Case

I once cared for an otherwise healthy 40-year-old woman who had undergone a cholecystectomy for cholecystitis. Surgery and the anesthetic were very uneventful.

However, during wakeup, her oxygen saturation dropped to the low 90s and she developed diffuse very loud rhonchi. Pulse and blood pressure were stable. She was breathing spontaneously. But her tidal volumes were shallow at 160-200 ml. This occurred even though she appeared to have a fairly vigorous inspiratory force. She was awake and obeying all commands.

My first thought was residual muscle relaxation. Muscle strength must recover before extubation criteria are met. But, assessing “intact muscle power” can sometimes be difficult. The patient’s oropharyngeal musculature must be coordinated enough to hold the airway open once the tube is removed. However, with the tube in place, these muscles aren’t needed to carry out this function. So what signs do you evaluate to meet extubation criteria?

Assessing Reversal Of Muscle Relaxation

Neuromuscular blocking agents adhere to acetylcholine receptors and restrict the action of acetylcholine. This blocks neuromuscular transmission and the muscle becomes paralyzed. The anesthesiologist often uses a nerve stimulator after a general anesthetic. A train of 4 is a medical test to evaluate the level of remaining paralysis. This assesses whether the paralytic muscle relaxants given for surgery have worn off enough. The goal is to make sure the patient can breathe on their own. This device uses externally applied electrodes to stimulate the nerves and evaluate the resulting muscle twitch response. Anesthesia providers look at several different tests:

• Train of four testing: How many full strength twitches are visible? These twitches occur during a rapid-fire series of 4 electrical impulses. Less than 4 twitches, or 4 twitches of varying strengths show blockade still exists.
• Whether or not there is a sustained muscle contraction (sustained tetanus), with no fall off in strength of contraction.

Train-of-Four Is An Imperfect Extubation Criteria

The nerve stimulator may not be sensitive enough to measure full reversal of the paralysis. A complete train-of-four response returns when 75% of the receptors are still blocked. This means that if you see a complete train-of-four, the number of receptors still blocked is between zero and 75%. Obviously a major difference. Sustained tentanus (no fall fade of contraction with continuous stimulous) returns when blockade drops below 50%. Again, you would not detect fade if 49% of the receptors are still blocked.

The test is not sensitive enough to definitively detect persistent blockade. So, even with an intact train-of-four the patient might not have adequate strength to cough or deep breathe. They may also struggle to keep an open airway.

Alternatively, anesthesiologists often rely on the patient’s ability to lift their head off the bed for a full 5 seconds. The patient can’t sustain a head lift for 5 seconds unless fewer than 25% of the receptors are blocked. This test is a simple and reliable method for testing strength. It also tells you whether the patient can follow commands. Still, be aware that abdominal pain interferes with the patient’s ability to cooperate. Splinting of abdominal muscles from pain can hinder head lift. Always have the equipment readily available to ventilate or reintubate the patient before any extubation.

My patient, nevertheless, appeared to have excellent strength and met reversal extubation criteria. She followed all commands including maintaining a sustained head lift for a full 10 seconds. She also seemed to have a forceful inspiratory capacity. Why were her tidal volumes and saturation running low?

Case Resolution

I couldn’t hear wheezing. There were rhonchi. If this was bronchospasm, perhaps I simply couldn’t hear the wheezing because she was too tight. I gave her an albuterol treatment. No change in physical exam or her saturation, which was still 93 on 100% FiO2.

At this point I started to concentrate on the quality of the rhonchi. Although I heard coarse sounds over all the lung fields, they didn’t quite sound like the typical diffuse rhonchi. Diffuse rhonchi sound somewhat different in the various areas because not all the airways are affected in the same way. These rhonchi were loudest over the trachea, and elsewhere they sounded like a distant version of the tracheal sounds. This made me wonder if the problem was mucous plugging of the endotracheal tube. I tried suctioning the endotracheal tube. Although the suction catheter came back clean, I couldn’t pass the suction catheter all the way down the tube.

I have had other patients who experienced significant endotracheal tube obstruction from mucous plugging. (follow this link for a discussion of two such cases). If it were a plugged endotracheal tube, removing the tube was the right next step. Even if this were bronchospasm, removal of the endotracheal tube and its stimulation can sometimes break the bronchospasm. I decided to extubate the patient as a trial to see if this improved ventilation.

Considering a Trial of Extubation

Extubating a patient when the patient has not met extubation criteria is a calculated risk. My criteria for doing so in this case included:

• Patient had been easy to intubate and ventilate
• Her vital signs were stable
• Her saturation was 93% and her end tidal CO2 was 49. Not perfect but certainly adequate
• She had equal, bilateral breath sounds
• I didn’t hear wheezing or rales, just coarse breath sounds that appeared to be located over the tracheal area
• She had intact muscle strength and good inspiratory effort
• She was awake and following commands
• I was a skilled intubator with confidence that if she did fail a trial of extubation that I could safely reintubate her, and I was ready to do so

I removed the endotracheal tube and found that the distal end was full of very sticky secretions. She immediately was able to take deep breaths and her saturation shot up to 100%.

In this case, mucous plugging of the endotracheal tube was indeed causing my patient’s problem. Extubating a patient before they meet extubation criteria is a significant risk. But sometimes it’s the right thing to do.

You can find a more complete discussion of extubation criteria and planning for difficult extubation here:

• Extubation: Plan For The End At The Beginning

For 3 review articles on minimizing risk and avoiding common complications in adults and children see:

• Boredom Interrupted: 10 Causes of Airway Complications And How to Avoid Them
• Always Prepare for Failure: 10 Rules for Approaching Difficult Intubation
• 10 Common Pediatric Airway Problems—and Their Solutions

Note: This article was revised from the original, published under the name “To Extubate or Not to Extubte, That Is The Question” on 2016/01/07

References

1. Cheney FW, Posner KL, Caplan RA. Adverse respiratory events infrequently leading to malpractice suits. A closed claims analysis. Anesthesiology. 1991;75(6):932-939.
2. Peterson GN, Domino KB, Caplan RA, et al. Management of the difficult airway: a closed claims analysis. Anesthesiology. 2005;103(1):33-39

May The Force Be With You

Christine E. Whitten MD, author:

Anyone Can Intubate: A Step-by-Step Guide, 5th Edition
Pediatric Airway Management: A Step-by-Step Guide
Basic Airway Management: A Step-by-Step Guide