Learn more about Clinical Skills today! Standardize education and management competency among nurses, therapists and other health professionals to ensure knowledge and skills are current and reflect best practices and the latest clinical guidelines.
The respiratory therapist (RT) should evaluate daily a patient’s readiness to wean or the ability to be liberated from mechanical ventilation. The most common readiness to wean factors include, but are not limited to:undefined#ref3">3,4
Standard weaning criteria (SWC) is used to evaluate the patient’s respiratory muscle strength and endurance and to predict the patient’s ability to successfully wean from mechanical ventilation. The most common and effective method is the spontaneous breathing trial (SBT). The SBT is a period that the patient breathes without any ventilatory support or minimal inspiratory pressure support.4,5 The amount of time to remain on an SBT varies but the typical range is 30 to 120 minutes.3,4
During the SBT, the RT observes the patient’s spontaneous breathing parameters such as tidal volume (VT), respiratory frequency (f), minutes volume, and the rapid shallow breathing index (RSBI). Spontaneous tidal volume (VTS) is a measure of ventilation and respiratory muscle endurance. The threshold for VTS is greater than 5 ml/kg.3 The threshold for minute volume is not clear, but most experts recommend that it be in the range of 10 to 12 L/min for successful weaning.4 The RSBI is the ratio of f/VT, and this value is used to gauge respiratory muscle fatigue during the SBT. If the RSBI is less than 105, it predicts successful weaning.1 If the RSBI is greater than or equal to 105, the patient may not be ready to wean from mechanical ventilation.4 These SWC are typically observed during the SBT performed on the mechanical ventilator.
Additionally, there are a variety of SWC that may be helpful to determine readiness to wean in patients who have been on mechanical ventilation for an extended period or have other conditions that make it more difficult to wean from the ventilator.3 These SWC maneuvers may offer more information about respiratory muscle strength and endurance, especially in patients who are older, debilitated, or weak. These criteria may help determine the presence of respiratory muscle fatigue after a weaning period and predict a successful weaning and extubation outcome.
Negative inspiratory force (NIF) may also be called maximum inspiratory force (MIF) or maximal inspiratory pressure (MIP). The measurement of NIF is effort independent, meaning that the patient does not have to cooperate. The threshold used to predict mechanical ventilation weaning success is less than or equal to –20 cm H2O to –30 cm H2O.3 Because this is an effort-independent measurement, the value is reliable with good technique, unless factors such as central respiratory drive impairment, sedation, a cuff leak, or respiratory muscle fatigue are present.
Maximum expiratory pressure (MEP), also referred to as positive expiratory pressure (PEP), may be measured to evaluate the patient’s ventilatory muscle strength. The threshold used to predict successful weaning is greater than 60 cm H2O.4 It provides information about the patient’s ability to cough and clear secretions. It may be used in conjunction with the NIF to predict successful ventilator weaning and extubation.
Vital capacity (VC) is also a measure of respiratory muscle endurance or reserve or both. A fatigued patient is unable to triple or even double the size of a breath. The threshold for VC is greater than or equal to 10 to 15 ml/kg (at least two to three times VTS).3
Beyond SWC, other factors that may affect the patient’s ability to successfully wean from mechanical ventilation include sedation, psychologic status, level of consciousness, and nutrition factors.3 All SWC are best used in combination with overall clinical assessment to determine the appropriateness of mechanical ventilation weaning and extubation.3
The decision to extubate is separate from the patient’s ability to wean from mechanical ventilation.
Additional SWC may be helpful to determine readiness to wean in patients who have been on mechanical ventilation for an extended period or have other conditions that make it more difficult to wean from the ventilator.
Rationale: The respirometer is used to measure VTS and VC. Volume and pressure may be measured while the patient is on the ventilator.
Ensure that no large cuff leak exists because a large leak adversely affects measurements.
If the patient shows signs of intolerance during the procedure, abort the test or perform it for a shorter interval, as tolerated.
A good VC effort requires a maximum inspiration followed by a maximum expiration.
Rationale: A pressure manometer is used to measure NIF.
In most cases, the pressure manometer is attached to the airway via one-way valves (Figure 1). The valves (one is for inspiration and one is for expiration) are capped as necessary to ensure a closed system and a clean measurement device for attachment to the patient's artificial airway.
Do not perform the NIF when the patient’s central respiratory drive is absent because of sedation or neurologic injury.
Rationale: The goal is to obtain the patient’s best effort.
Rationale: PEP is effort dependent (Figure 1).
Rationale: Multiple attempts ensure that the patient’s best effort is recorded.
Abort the test if signs of deterioration occur, including increased respiratory rate, increased heart rate, or decreased oxygen saturation.
Rationale: If the measurements do not meet anticipated levels, the patient may not be ready to wean from mechanical ventilation. If the measurements equal or exceed the goals, weaning trials or extubation may be indicated.
Rationale: Decisions related to weaning trials or extubation are made using the results of these tests in conjunction with current clinical assessments.
MacIntyre, N.R. and others. (2001). Evidence-based guidelines for weaning and discontinuing ventilatory support: A collective task force facilitated by the American College of Chest Physicians; the American Association for Respiratory Care; and the American College of Critical Care Medicine. Chest, 120(6), 375S-395S. doi:10.1378/chest.120.6_suppl.375s
Frazier, S.K. (2017). Chapter 33: Weaning mechanical ventilation. In D.L. Wiegand, (Ed), AACN procedure manual for high acuity, progressive and critical care (7th ed., pp. 277-285). St. Louis: Elsevier.
Cookies are used by this site. To decline or learn more, visit our cookies page.