Mechanical ventilation is used when a patient is unable to breathe adequately on their own. The purpose of ventilation management is to "breathe for them" until they are sufficiently recovered to initiate respiration. 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 less.
Ventilatory weaning should not be attempted until the patient's respiratory status is stable and they are arousable and able to follow commands. If the patient is unstable or unarousable, attempting to wean may cause unnecessary physical stress and may delay recovery.
The ventilatory weaning process 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 requires 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 three primary methods used to wean patients from the ventilator. These include T-piece, synchronized intermittent mandatory ventilation and pressure support ventilation. A short description of each of these is included here. The method chosen depends on the patient's respiratory status and on how long they have 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 tube or tracheostomy tube. One end of this tubing is attached to an oxygen flowmeter and the other end is open. The amount of oxygen to be
Synchronized intermittent mandatory ventilation (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-initiated breaths plus four patient-initiated breaths.) The goal of SIMV weaning is to gradually decrease the number of breaths delivered by the ventilator, which allows the patient to take more breaths of their 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 they fail to take a breath and the ventilator alarms will sound if they are not tolerating weaning. However, the patient should still be closely monitored for signs of respiratory fatigue.
Pressure support ventilation (PSV) augments the patient's spontaneous inspiration with a positive pressure "boost." This decreases the resistance created from breathing through ventilator tubing and is used with the SIMV mode to decrease the work of breathing.
If the patient tolerates SIMV weaning, the ventilator mode may be changed to constant positive airway pressure (CPAP) as a final trial of spontaneous breathing prior to removing the endotracheal tube. In this mode, patients will breathe on their own but have the benefit of the ventilator alarms if they have difficulty. CPAP maintains constant positive pressure in the airways, which facilitates gas exchange in the alveoli. PSV is often used with the CPAP mode to further decrease the work of breathing. If the patient tolerates CPAP, the endotracheal tube is removed and a face mask with humidified oxygen is applied for a short time. If the patient remains stable, a nasal cannula may be used to deliver oxygen.
If the patient has a tracheostomy, the weaning process is the same as with a endotracheal tube, with the exception that after the ventilator is disconnected, a tracheostomy collar may be used to deliver humidified oxygen instead of a face mask or nasal cannula. This is simply a mask-like device that fits loosely over the tracheostomy and is held in place by an elastic band around the neck.
As discussed earlier, the patient's respiratory status must be stable and they must be arousable and able to follow commands prior to initiating weaning. Patients who require mechanical ventilation are often kept sedated or even paralyzed with drugs to facilitate optimal ventilation. These drugs must be tapered off prior to weaning.
Weaning criteria should be done to determine the patient's readiness to wean. The best indicators include a vital capacity of at least 10-15 cc/kg and a negative inspiratory fraction of greater than -30 cm H2O, however, many other factors are also measured. The patient should be suctioned prior to any weaning attempt, both orally and via the endotracheal tube or tracheostomy. A pulse oximeter and cardiac monitor should be applied if they are not already present. Weaning should be done when there is adequate staffing so the patient can be closely monitored.
The greatest risk of ventilator weaning (especially premature weaning) is respiratory distress. The patient must be closely monitored and the weaning stopped before the respiratory distress becomes too great to control. Patients may also have anxiety or fear about weaning, which can complicate their respiratory distress.
The goal of ventilation management is to wean the patient from mechanical support and to reestablish spontaneous respiration.
Health care team roles
The nurse and respiratory therapist share equal roles in ventilator management. Both are responsible for suctioning and monitoring the patient during weaning periods. Since the nurse is at the bedside the most, they have the primary monitoring role and are often able to predict the best time for a weaning trial. It is the nurse's responsibility to communicate with the respiratory therapist in planning when weaning trials will occur. The respiratory therapist is generally responsible for making the actual ventilator changes. Both the nurse and respiratory therapist
document the ventilator change and their assessment of the patient's respiratory status before, during, and after the weaning period. Both are responsible for teaching and reassuring the patient and family regarding the weaning process.
Patients may be fearful about weaning because it is difficult for them to communicate around the endotracheal tube or tracheostomy. They may be afraid no one will know if they're having difficulty breathing. The nurse should explain all procedures before performing them, reassure the patient that they will be closely monitored, and ensure that the patient's call light is within reach. It is important that the patient actually see the nurse enter the room frequently, as this is the only way they will know they are being monitored.
Alveoli—Saclike structures in the lungs where oxygen and carbon dioxide exchange takes place.
Endotracheal tube—Tube inserted into the trachea via either the oral or nasal cavity for the purpose of providing a secure airway.
Negative inspiratory fraction—The amount of force used to draw air into the lungs during maximal inspiration.
Tracheostomy—Surgically created opening in the trachea for the purpose of providing a secure airway. This is used when the patient requires long term ventilatory assistance.
Ventilator—Device used to provide assisted respiration and positive pressure breathing.
Vital capacity—Maximum volume of air that can be expelled from the lungs after a maximal inspiration.
Thelan, Lynne, et al. Critical Care Nursing: Diagnosis and Management. St. Louis, MO: Mosby, 1998.
Hanneman, H. "Weaning from Short Term Mechanical Ventilation" Critical Care Nurse 19, no. 5 (1999): 86-89.
Abby Wojahn, RN, BSN, CCRN