The landing is just as important as the take off: a closer look at assessing a patient for extubation

Intro:

Before reading further, refer to this article, where Dr. Ramaswamy discussed vitals and quick physical examination techniques to do when assessing a patient for extubation. Understanding that article will help form a framework for what we’re going to discuss below.

The process: 

While extubating can be viewed as an art, a study by Stroetz and Hubmayr found that clinical “gestalt” by intensivists cannot accurately predict if a patient is going to tolerate a spontaneous breathing trial (SBT), let alone tolerate an extubation. It was this fact alone that justified the need for objective weaning predictors that can be applied when determining if a patient is ready for extubation. 

It may sound like common sense, but assessing a patient for ventilator weaning and extubation should be done as soon as the patient’s reason for intubation in the first place is being addressed. Whether it is pneumonia, stroke, altered mental status, or airway obstruction, attention should be shifted toward weaning the ventilator when the patient starts improving. The earlier this is addressed, the smoother the ventilator weaning process will go. Failure to recognize this causes delay in ventilator withdrawal, which can lead to higher costs, longer length of stays (LOS), excessive medications used for sedation, and increased infection risks. On the other hand,  premature ventilator withdrawal can lead to airway loss, poor gas exchange, aspiration, and inspiratory muscle fatigue. A good rule of thumb is that if the patient can tolerate an Fio2 of 40% and a PEEP of 8 cm H2O, he or she may be ready for an SBT, permitted the cause of respiratory failure has been addressed and there is no significant respiratory acidosis. 

Ideally, patients should undergo SBT daily. A proper SBT should be 30 minutes but no longer than 120 minutes, as patients can become fatigued and will be less likely to tolerate an extubation after already working for 2 hours on an SBT. Evidence has shown that most complications that will happen during an SBT occur within the first 30 minutes of the trial. Stay tuned for the types of spontaneous breathing trials in an upcoming post. 

A patient tolerating SBT well is only the beginning of the weaning process. Below are some other things to think about: 

History: 

— Was the patient a difficult intubation? What made the intubation difficult and if the extubation fails, do you have the tools necessary to re-intubate? 

Physical exam: 

— Is there an upper airway obstruction the ETT is bypassing which would allow the patient to pass the SBT but become distressed when the ETT is removed. ? 

— Can the patient clear secretions? Check how robust a patient’s cough and gag are with the suctioning on the endotracheal tube. 

— Is there a risk of post extubation stridor? These are patients with a long standing duration of mechanical ventilation (something we’re seeing more and more with covid), female sex, trauma, and repeated or traumatic intubation. If this is the case, assess for a cuff leak. How to perform a cuff leak test and manage the patient in the setting of absence of one will be discussed another time. 

— Can the patient protect his or her airway when extubated? This not only includes the cough/gag reflex mentioned above, but includes the mental status and physical strength as well. Is the patient extremely agitated or calm? Is the patient able to move extremities, namely the head? Can the patient protrude the tongue? A review of the literature suggests that a Glasgow coma score above 8 is compatible with successful extubation. 

Vitals: 

— Is the patient hemodynamically stable? If a patient is on high amounts or multiple vasopressors, extubating may increase the metabolic demands, and worsen the oxygen delivery and/or consumption. 

— Is the patient becoming tachycardic or hypertensive during the breathing trials? Is there a significant amount of pain, withdrawal of medication, or fevers that need to be addressed first? 

On the ventilator: 

— Can the patient initiate breaths and is the minute ventilation adequate? Minute ventilation of <10L/minute has been shown to be a good predictor of extubation success. 

— Another parameter is the rapid shallow breathing index (RSBI), which is the ratio of the frequency of breaths to the tidal volume. In the original study by Yang and Tobin, this test was performed by having the patient breathe room air without any ventilatory assistance for one minute. An appropriate RSBI is <105, but this is falling out of favor as this test is often done on people with mechanical ventilator assistance and not in the way the original study described. 

— The negative inspiratory force (NIF or Pimax)  is commonly used to test the strength of a diaphragm. This is a good test to do for neurological patients (ie: ALS). To do this maneuver, the proximal end of the endotracheal tube is occluded for 20 seconds with a one way valve that allows the patient to exhale but not inhale. This forces the patient to increase the inspiratory effort, and if the patient is able to do this, the diaphragm strength is intact. Several studies have shown that a Pimax less than -20 or -30 has a high sensitivity (but low specificity) of predicting success of extubation. Because of the low specificity, this parameter is not used in an isolated manner, but can be a tool in aiding the clinician in making further decisions 

Using the Ultrasound: 

— An important cause of failure to wean in patients with heart failure is the so called ‘weaning-induced cardiac dysfunction (to be discussed in a later post). A study was done looking at diastolic function (E/Ea) as a determining factor in mechanical ventilator failure. Impaired diastolic dysfunction (E/Ea >1.5) was strongly associated with weaning failure. They also found that systolic dysfunction was not associated with weaning failure.

— A quick lung examination assessing for b lines, or pulmonary edema can also be done. If a patient has several b lines, consistent with pulmonary edema (or fluid), addressing this may be beneficial. 

— As the ventilator can be used to assess for diaphragm strength, an ultrasound can be utilized to examine how well it is moving. Using a curvilinear probe, the ultrasound is placed in the mid axillary line at the 5-6th rib space or until the diaphragm can be visualized (a bright white line). The magnitude of diaphragmatic excursion as well as its thickening fraction can be used to assess for diaphragmatic weakness.

Outro: 

Despite intensivists doing all the above mentioned examinations and maneuvers, 15% of patients fail extubation in the intensive care unit within the first 24 hours. This may sound like it’s a bad thing, but intensivists should have a failure rate at around this number. This means that patients are not being intubated longer than they should be, which can cause more complications. It is important to discuss with families and patients that there is a chance the extubation may fail, and always get an answer as to whether the patient will want to be re-intubated in the case of a failure BEFORE extubating!