Weaning and Extubation
The purpose of mechanical ventilation is to "breathe for the patient" until he or she is sufficiently recovered to breathe on his or her own. This process is usually a gradual one, and is referred to as weaning. During the ventilatory weaning process, the modes of mechanical ventilation are gradually changed to allow the patient to initiate more breaths while the ventilator provides fewer breaths.
Weaning should not be attempted until the patient’s respiratory status is stable and he or she is arousable and able to follow commands. Sedatives/paralytics should be weaned off. If the patient is unstable or unarousable, attempting to wean may cause unnecessary physical stress and may delay recovery. Pulse oximetry and a cardiac monitor should be applied, if not already present. The patient should be suctioned prior to any weaning attempt. Keep in mind that patients may be anxious during this time. They may feel isolated and afraid no one will hear them if they have trouble. Always make sure that your weaning patient has a call light within reach and let him or her see you enter the room frequently.
Weaning is accomplished by decreasing the number of breaths supplied by the ventilator, as well as by changing the way in which those breaths are delivered to the patient. The process also depends on the reason why the patient initially required mechanical ventilation. For example, post-operative cardiac bypass patients are generally weaned within a few hours after surgery. However, a patient with extensive lung disease may require days or weeks to wean. There are also some patients who are never able to completely wean. (This includes patients with spinal cord injuries above the diaphragm). They require a tracheostomy and placement in a long-term ventilator care unit, unless they have family who are able to care for them at home. Some may be able to be off the ventilator during the day, but still need it at night.
One last thought. If you have a stable patient on the ventilator who prematurely extubates himself or herself, the physician may decide to wait to see if the patient tolerates breathing without the ventilator. If the patient can’t tolerate it, he or she should be manually ventilated and reintubated as soon as possible.
Methods of Weaning
There are three primary methods used to wean patients from the ventilator. These include T-piece/CPAP trials, Synchronized Intermittent Mandatory Ventilation (SIMV), and Pressure Support Ventilation (PSV). PSV is often used with SIMV to decrease the work of breathing. PSV augments the patient’s spontaneous inspiration with a positive pressure boost, which decreases the resistance created from breathing through ventilator tubing. The weaning method chosen depends on the patient’s respiratory status and the length of time that he or she has been on the ventilator.
T-piece trials consist of alternating intervals of time on the ventilator with intervals of spontaneous breathing. To facilitate spontaneous breathing, the patient is removed from the ventilator and a T-shaped tube is attached to the endotracheal or tracheostomy tube. One end of this tubing is attached to an oxygen flowmeter and the other end is open; the amount of oxygen used is ordered by the physician. Patients with a T-piece don’t have the ventilator as back-up if they can’t breathe, so they must be monitored closely. If they tire out or their respiratory status becomes unstable, they should be reconnected to the ventilator. The goal of this method of weaning is to gradually increase the amount of time spent off the ventilator. Patients with tracheostomies may be weaned in a similar fashion with a trach collar. This is a mask-like device that delivers humidified oxygen. It fits loosely over the tracheostomy and is held in place by an elastic band around the neck.
Alternatively, CPAP may be used instead of a T-piece. With CPAP, the patient breathes spontaneously, but has the benefit of the ventilator alarms if he or she has difficulty. CPAP maintains constant positive pressure in the airways, which facilitates gas exchange in the alveoli.
SIMV is a ventilator mode that delivers a preset number of breaths to the patient but coordinates them with the patient’s spontaneous breaths. Thus, the ventilator may be set to deliver 12 breaths per minute, but the patient’s respiratory rate may be 16 (12 ventilator breaths plus 4 patient-initiated breaths). The goal of SIMV weaning is to gradually decrease the number of breaths delivered by the ventilator, allowing the patient to take more breaths of his or her own. The ventilator rate is usually decreased by one to three breaths at a time and an arterial blood gas (ABG) is obtained 30 minutes after the change to assess the patient’s respiratory status. The benefits of SIMV weaning are that the patient has the ventilator for back-up if he or she fails to take a breath and the ventilator alarms will sound if he or she is not tolerating weaning. However, the patient should still be closely monitored for signs of respiratory fatigue.
Weaning with pressure support alone consists of placing the patient on the pressure support mode at a level that allows the patient to achieve a spontaneous tidal volume of 6-8 mL/kg. As mentioned above, PSV gives a positive pressure boost that helps the patient overcome the work of breathing. During weaning, the level of PS is decreased by 3-5 cm H2O as long as the patient maintains the desired tidal volume.
(CPAP, SIMV, and PSV were discussed in the section on ventilator modes.)
Weaning criteria are done when a patient seems ready to be extubated. These include a number of simple bedside pulmonary function tests that indicate whether the patient is likely to tolerate breathing without the ventilator or not.
Vital Capacity (VC)
The vital capacity is the maximal amount of air that can be exhaled after a maximal inhalation. The patient’s vital capacity should be at least 10-15 cc/kg.
Negative Inspiratory Force (NIF)
Negative inspiratory force is the ability to take a deep breath and to generate a cough strong enough to clear secretions. The patient’s NIF should be at least –20 cm H20.
Tidal Volume (VT)
Tidal volume is the volume of air inspired and expired during a normal respiratory cycle. The patient’s tidal volume should be at least 5 ml/kg during spontaneous respiration.
Minute Volume (VE)
Minute volume is the total volume of air inhaled and exhaled in one minute. The patient’s minute volume should be less than 10 liters per minute. A greater amount indicates that the patient is working too hard to breathe spontaneously.
Respiratory Rate (RR)
The respiratory rate is the number of breaths per minute. The patient’s RR should be less than 25 breaths/minute.
Arterial Blood Gas (ABG)
An ABG should be done before the patient is extubated. The PaO2 should be greater than or equal to 60 mmHg on less than 50% oxygen and with no more than 5 cm H20 PEEP.
Both the nurse and the RT have a role in extubating the patient. The roles differ among institutions and individuals, but both should at least be in the patient’s room at the time of extubation. In general, the RT is responsible for performing the weaning criteria; the nurse should obtain the ABG prior to the weaning criteria being done so the results aren’t altered by the pulmonary function tests. The nurse then usually calls the results of the ABG and the weaning criteria to the physician.
Once the physician’s order to extubate is received, the nurse and RT coordinate a time when they can both be in the patient’s room. The RT is usually responsible for assembling the oxygen delivery system to be used after extubation; this includes a mask and humidification. The nurse should explain the procedure to the patient and prepare suction. The patient should be sitting up at least 45 degrees.
Prior to extubating, the patient should be suctioned both via the ETT and orally. All fasteners holding the ETT should be loosened and a sterile suction catheter should be inserted into the ETT and withdrawn as the tube is removed. (A second sterile suction catheter may be needed if the first is contaminated from oral suctioning.) The ETT should be removed in a steady, quick motion as the patient will likely cough and gag. It’s helpful to have a towel draped across the patient’s chest to set the soiled ETT on and to contain secretions.
The patient should be asked to cough and speak. Quite often, the patient’s first request is for water because of a dry, sore throat. Generally, you can immediately swab the patient’s mouth with an oral swab dipped in water. It may be best to wait for 30-60 minutes before offering ice chips, but this depends on how long the patient was intubated and on the physician’s orders. If the patient is able to tolerate a few ice chips, it’s usually best to not leave a full glass at the bedside. You’ll likely come back to find it empty!
Humidification of inspired air normally takes place in the upper respiratory tract. When this area is bypassed by an artificial airway, humidification must be performed outside the body. The use of supplemental oxygen requires humidification to prevent drying and irritation of the respiratory tract and to facilitate removal of secretions. There are humidification devices available that can be attached to oxygen flow meters.
Patients usually require oxygen delivered through a mask for a few hours after extubation. Encourage the patient to keep the mask on since the humidified oxygen will soothe his or her sore, dry throat.
As nurses, we’re all very familiar with coughing and deep breathing. Every extubated patient should be encouraged to do this as much as possible, along with incentive spirometry exercises. If family is present, include them in any teaching. Best of all, put them to work encouraging the patient to do the exercises. You may have to remind the patient to splint any chest or abdominal incisions in order to limit discomfort while coughing and deep breathing.
Some extubated patients may have Intermittent Positive Pressure Breathing (IPPB) ordered for the first 24 hours after extubation, rather than incentive spirometry. This was mentioned early in this program, but here it is again as a review.
IPPB is used in some institutions to assist patients to take deeper breaths, especially after surgery. The IPPB machine is a pressure-cycled ventilator that delivers compressed gas under positive pressure into the patient’s airway. It’s triggered when the patient inhales, but it allows passive expiration. The specific pressure and volume used are ordered for each patient by the physician. Usually, 10-20 breaths are given every 1-2 hours for 24 hours. Benefits of IPPB include prevention of atelectasis, promotion of full-lung expansion, improved oxygenation, and administration of nebulized medications.
Assessment and Monitoring
The assessment and monitoring criteria are much the same as those discussed above for mechanically ventilated patients. Breath sounds, pulse oximetry, and vital signs should be assessed and recorded immediately upon extubation. Vital signs should be documented frequently for the first few hours after extubation (i.e., every 15 minutes x 1 hour, every 30 minutes x 1 hour, then every hour until stable, although this differs by institution and physician). Most physicians order an ABG to be done 30-60 minutes after extubation. Also, don’t forget to ask the patient how his or her breathing feels, and be sure to leave the call light within reach.
Mr. Hill was kept sedated and paralyzed for 2 days. Today, he is completely weaned off of both drugs and is calm, arousable, and able to follow most commands. The pulmonologist wants to start weaning Mr. Hill so he orders the following: SIMV, rate 10, PS 10, FIO2 40%. Decrease the rate by 2 breaths every 2 hours, and decrease FIO2 as tolerated.
1. How will PS 10 assist Mr. Hill with the SIMV mode?
Pressure support (PS) gives a positive pressure boost with each inhalation. This decreases the work of breathing through the ventilator tubing and circuits.
The physician orders a continuous Versed infusion of 1-10 mg/hr, titrated to effect, and a Nimbex infusion with TOF maintained at 90%.
2. Is Mr. Hill ready to be extubated?
3. What form of oxygen therapy will you administer to Mr. Hill once he’s extubated?
Humidified mask with oxygen at 30%. (The last FIO2 setting he had while intubated.)
4. How will you confirm that Mr. Hill’s respiratory status is stable after he’s extubated?
Monitor pulse oximetry, vital signs, respiratory rate, and breath sounds, and ask Mr. Hill how he feels. Also, remember to check another ABG 30 minutes after extubation (or per physician order).
Thanks to your expert nursing care, Mr. Hill is doing very well. His physician plans to transfer him to the step-down unit in a few days. Both Mr. and Mrs. Hill have said that you’re a wonderful nurse. Today when you arrive for your shift, you find a plate of cookies from Mrs. Hill with a thank you card!