Assessing extubation criteria, and then deciding when to extubate a patient safely can sometimes be a difficult decision.
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, able to breathe without help, and able to protect the airway.
However, sometimes the decision is not so easy. Here I describe a case of a patient who met some but not all of the criteria for extubation. 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.
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 despite the fact that she appeared to have a fairly forceful inspiratory force. She was awake and following all commands.
My first thought was residual muscle relaxation. “Intact muscle power” can sometimes be hard to assess because 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 perform this function. So what signs do you evaluate?
Assessing Reversal Of Muscle Relaxation
After a general anesthetic the anesthesiologist often uses a nerve stimulator to determine whether the paralytic muscle relaxants given for surgery have worn off enough to let the patient breath on their own. This device uses externally applied electrodes to stimulate the nerves and evaluate the resulting muscle twitch response. Anesthesiologists look at several different tests:
- how many full strength twitches can be seen during a rapid fire series of 4 electrical impulses (train of four testing)
- whether or not there is a sustained muscle contraction (sustained tetanus), with no fall off in strength of contraction,
However, the nerve stimulator may not be sensitive enough to measure full reversal of the paralysis. A complete train four response returns when 75% of the receptors are still blocked. If you see a complete train of four you simply can’t tell if 75% of the receptors are blocked or none of them are. Sustained tentanus returns when blockade drops below 50%.
In both of these cases, the patient may not have adequate strength to cough or maintain their airway because the test is not picking up the presence of persistent blockade. Anesthesiologists often rely on the patient’s ability to lift their head off the bed for a full 5 seconds. A head lift can be sustained for 5 seconds or more only if less than 25% of the receptors are still blocked. This test is a simple and reliable method for testing strength. It also tells you whether the patient can follow commands. However, be aware that abdominal pain and splinting of abdominal muscles from pain may interfere with the patient’s ability to cooperate. You should always have the equipment readily available to ventilate or reintubate the patient prior to any extubation.
My patient, however, appeared to have excellent strength. 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?
I couldn’t hear wheezing but there were rhonchi —perhaps this was bronchospasm and I simply could not 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 could hear 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 impacted 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 and 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.
Extubating a patient when you are not certain that the patient is breathing well 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. Removal of an endotracheal tube when you are not sure of the reason why a patient is not meeting extubation criteria is a risk not to be taken lightly. But sometimes it’s the right thing to do.
May The Force Be With You
Christine Whitten MD
Author: Anyone Can Intubate: a Step by Step Guide, 5th Edition
Pediatric Airway Management: A Step by Step Guide
Please click on the covers to see inside the books at amazon.com