————Weaning from Mechancal Ventilation————-
•CCS•
Weaning is considered when patient medical condition (ie, cardiac, pulmonary) status has stabilized.
Indications for termination of weaning trial
PaO2 falls below 55 mm Hg
Acute hypercapnia
Deterioration of vital signs or clinical status (arrhythmia)
Rapid T-tube weaning method for short-term (<7 days) ventilator patients without COPD. Obtain baseline respiratory rate, pulse, blood pressure and arterial blood gases or oximetry.
Discontinue sedation, have the well-rested patient sit in bed or chair. Provide bronchodilators and suctioning if needed. Attach endotracheal tube to a T-tube with FiO2 >10% greater than previous level.
Set T-tube flow-by rate to exceed peak inspiratory flow. Patients who are tried on T-tube trial should be observed closely for signs of deterioration. After initial 15-minute interval of spontaneous ventilation, resume mechanical ventilation and check oxygen saturation or draw an arterial blood gas sample.
If the 30-minute blood gas is acceptable, a 60-minute interval may be attempted. After each interval, the patient is placed back on the ventilator for an equal amount of time.
If the 60-minute interval blood gas is acceptable and the patient is without dyspnea, and if blood gases are acceptable, extubation may be considered.
Pressure support ventilation weaning method
Pressure support ventilation is initiated at 5-25 cm H2O. Set level to maintain the spontaneous tidal volume at 7-15 mL/kg.
Gradually decrease the level of pressure support ventilation in increments of 3-5 cm H2O according to the ability of the patient to maintain satisfactory minute ventilation.
Extubation can be considered at a pressure support ventilation level of 5 cm H2O provided that the patient can maintain stable respiratory status and blood gasses.
Intermittent mandatory ventilation (IMV) weaning method
Obtain baseline vital signs and draw baseline arterial blood gases or pulse oximetry. Discontinue sedation; consider adding pressure support of 10-15 cm H2O.
Change the ventilator from assist control to IMV mode; or if already
on IMV mode, decrease the rate as follows:
Patients with no underlying lung disease and on ventilator for a brief period (<1 week).
Decrease IMV rate at 30 min intervals by 1-3 breath per min at each step, starting at rate of 8-10 until a rate for zero is reached.
If each step is tolerated and ABG is adequate (pH >7.3-7.35), extubation may be considered.
Alternatively: The patient may be watched on minimal support (ie, pressure support with CPAP) after IMV rate of zero is reached. If no deterioration is noted, extubation may be accomplished.
Patients with COPD or prolonged ventilator support (>1 week)
Begin with IMV at frequency of 8 breath/minute, with tidal volume of 10 mL/kg, with an FiO2 10% greater than previous setting. Check end-tidal CO2.
ABG should be drawn at 30- and 60-minute intervals to check for adequate ventilation and oxygenation. If the patient and/or blood gas deteriorate during weaning trial, then return to previous stable setting.
Decrease IMV rate in increments of 1-2 breath per hour if the patient is clinical status and blood gases remain stable. Check ABG and saturation one-half hour after a new rate is set.
If the patient tolerates an IMV rate of zero, decrease the pressure to support in increments of 2-5 cm H2O per hour until a pressure support of 5 cm H2O is reached.
Observe the patient for an additional 24 hours on minimal support before extubation.
Causes of inability to wean patients from ventilators: Bronchospasm, active pulmonary infection, secretions, small endotracheal tube, weakness of respiratory muscle, low cardiac output.
•HARRISONS•
Although the predictive capacities of multiple clinical and physiologic variables have been explored, the consensus from a weaning task force includes the following recommendations: (1) lung injury is stable/resolving, (2) gas exchange is adequate with low PEEP/FIO2 (<8 cmH2O and FIO <0.5), (3) hemodynamic variables are stable (patient off vasopressors), and (4) patient is capable of initiating spontaneous breaths. This “screen” should be done at least daily. If the patient is deemed capable of beginning weaning, the recommendation of the task force is to perform a spontaneous breathing trial (SBT) because several randomized trials support the value of this approach (Fig. 269-2).
The SBT involves an integrated patient assessment during spontaneous breathing with little or no ventilator support. The SBT is usually implemented with a T-piece using 1–5 cmH2O CPAP or a T-piece with 5–7 cmH2O or PSV from the ventilator to offset the resistance from the endotracheal tube. Once it is determined that the patient can breath spontaneously, a decision must be made about the removal of the artificial airway; this should be done only when it is concluded that the patient has the ability to protect the airway, is able to cough and clear secretions, and is alert enough to follow commands. In addition, other factors must be taken into account, such as the possible difficulty in replacing the tube if that is anticipated.
If upper airway difficulty is suspected, an evaluation using a “cuff leak” test (assessing the presence of air movement around a deflated endotracheal tube cuff) is supported by some internists. Despite the application of all of these methods, ~10–15% of extubated patients require reintubation. Several studies suggest that NIV can be used to avert reintubation; this has been particularly useful in patients with ventilatory failure secondary to COPD exacerbation. In this group, earlier extubation with the use of prophylactic NIV has shown good results. The use of NIV to facilitate weaning in other causes of respiratory failure is not currently indicated.