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Dec.28.2021
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Mechanical Ventilation: Standard Weaning Criteria (Respiratory Therapy)

OVERVIEW

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

  • Reversal or improvement of the condition that led to the need for mechanical ventilation
  • Oxygen requirement of less than 40% or 50% fraction of inspired oxygen (FIO2)3,4
  • Positive end-expiratory pressure (PEEP) of less than or equal to 8 cm H2O3,4
  • Corrected ventilation and acid-base balance abnormalities
  • Normalized cardiovascular and hemodynamic status
  • Presence of spontaneous respiratory drive
  • Minimal or no sedation

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

EDUCATION

  • Provide developmentally and culturally appropriate education based on the desire for knowledge, readiness to learn, and overall neurologic and psychosocial state.
  • Teach the patient and family about the patient’s respiratory status and any progress toward weaning from mechanical ventilation.
  • Explain the need to measure respiratory muscle strength and endurance.
  • Discuss the expected outcomes and goals of measurements with the patient and family.
  • Discuss the sensations that the patient may experience, such as transient shortness of breath and fatigue and the inability to take a breath during the test maneuver.
  • Explain to the patient the importance of cooperation and maximal effort to achieve valid and reliable measurements.
  • Encourage questions and answer them as they arise.

ASSESSMENT AND PREPARATION

Assessment

  1. Perform hand hygiene before patient contact. Don appropriate personal protective equipment (PPE) based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
  2. Introduce yourself to the patient.
  3. Verify the correct patient using two identifiers.
  4. Verify the weaning or protocol to wean order from the authorized practitioner.
  5. Assess the patient for readiness to wean from mechanical ventilation.
    1. Reversal or improvement of the condition that required mechanical ventilation.
    2. Oxygen requirement of less than 40% or 50% FIO23,4
    3. PEEP of less than or equal to 8 cm H2O3,4
    4. Corrected ventilation and acid-base abnormalities
    5. Normalized cardiovascular and hemodynamic status
    6. Presence of spontaneous respiratory drive
    7. Minimal or no sedation
  6. Assess the patient’s vital signs, breath sounds, and work of breathing.
  7. Assess the patient’s need for a long-term artificial airway.
    The decision to extubate is separate from the patient’s ability to wean from mechanical ventilation.

Preparation

  1. Ensure that respiratory depressants, such as sedation or opioids, are off or minimal.
  2. Suction the airway, as needed.
  3. Position the patient in a high semi-Fowler position, if condition allows.

PROCEDURE

  1. Perform hand hygiene and don gloves. Don additional PPE based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
  2. Verify the correct patient using two identifiers.
  3. Explain the procedure and ensure that the patient agrees to treatment.

Spontaneous Breathing Trial (SBT)

  1. Perform an SBT.
    1. Set the ventilator at zero continuous positive airway pressure (CPAP) and zero pressure support. Pressure support of 5 to 8 cm H2O may be used.4,5
    2. Continuously monitor the patient vital signs and spontaneous breathing parameters, such as f, VTS, minute volume, and RSBI.
      1. If signs of SBT failure are sustained, return the patient to mechanical ventilation support.
        1. Respiratory rate greater than 35 breaths per minute3
        2. Oxygen saturation less than 90%3
        3. Significant change in vital signs, such as heart rate or blood pressure
        4. Agitation, diaphoresis, or severe anxiety
      2. If no signs of intolerance develop, continue the SBT for 30 to 120 minutes.3,4,5
    3. Return the patient to previous mechanical ventilation support and consider extubation.

Additional SWC

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.

  1. Attach a portable respirometer to the airway via the adapter and the series of one-way valves. If the patient is receiving positive-pressure ventilation (PPV), place the patient back on the ventilator (or manually ventilate with a self-inflating manual resuscitation bag) to rest for a few minutes between all measurements.
    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.
  2. Measure VTS.
    1. Instruct the patient to breathe normally.
    2. Count the frequency and record the minute ventilation.
    3. Divide minute ventilation by f to obtain the average VTS.
      If the patient shows signs of intolerance during the procedure, abort the test or perform it for a shorter interval, as tolerated.
  3. Measure VC. The VC may be tested more than once to obtain the best effort.
    A good VC effort requires a maximum inspiration followed by a maximum expiration.
    1. Verify that the respirometer is at the starting point.
    2. Instruct the patient to inhale as deeply as possible.
    3. Instruct the patient to exhale as much as possible.
  4. Measure NIF.
    1. Close or cap the inspiratory one-way valve, ensuring a closed system for measurement of inspiratory effort but allowing exhalation.
    2. Attach the pressure manometer to the airway with the adapter and one-way valves. Some ventilators allow the measurement to be accomplished with the patient on the ventilator.
      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)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.
    3. Instruct the patient to inhale as deeply as possible.
    4. Observe the manometer needle during inspiration.
      1. This test can be done for 20 seconds,2 with multiple attempts by the patient.
      2. This test may be done even if the patient is not able to actively participate.
    5. After the patient has been attached to the closed system manometer for a few seconds, instruct the patient to initiate a series of breaths and generate a negative pressure.
      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.
    6. Watch the manometer during the inspiration and stop the procedure after the NIF measurements peak within the maximum time allowed or if the patient does not tolerate the procedure (e.g., experiences agitation, bradycardia, significant oxygen desaturation).
  5. Measure PEP.
    1. Cap the expiratory valve, ensuring the patient can breathe in but must exhale against a closed system.
    2. Attach the pressure manometer to the airway via the adapter and one-way valves.
    3. Instruct the patient to take a deep breath and exhale forcefully.
      Rationale: PEP is effort dependent (Figure 1)Figure 1.
    4. Instruct the patient to exhale forcefully several times (not to exceed 20 seconds).2 Record the greatest positive number.
      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.
  6. Encourage and coach the patient throughout all measurements to achieve best effort and reduce anxiety.

Completing the Procedure

  1. Discard supplies, remove PPE, and perform hand hygiene.
  2. Document the procedure in the patient’s record.

MONITORING AND CARE

  1. Compare the SWC measurements to the desired patient goals.
    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.
  2. Discuss the results with the team.
    Rationale: Decisions related to weaning trials or extubation are made using the results of these tests in conjunction with current clinical assessments.
  3. Observe the patient for signs or symptoms of pain. If pain is suspected, report it to the authorized practitioner.

EXPECTED OUTCOMES

  • SBT completed for 30 to 120 minutes3,4
  • RSBI less than 1053,4
  • Additional SWC measurements, such as VTS, VS, and NIF

UNEXPECTED OUTCOMES

  • Invalid and unreliable measurements
  • Decline in respiratory, physical, emotional, or hemodynamic status
  • Stoppage of the procedure

DOCUMENTATION

  • Education
  • Best measurements obtained
  • Patient's tolerance of the tests
  • Unexpected outcomes and related interventions
  • Respiratory interventions

OLDER ADULT CONSIDERATIONS

  • In adults older than 65 years and those patients on the ventilator for 7 days or longer, the RSBI is less reliable to predict successful mechanical ventilation weaning.4

REFERENCES

  1. Baptistella, A.R. and others. (2018). Predictive factors of weaning from mechanical ventilation and extubation outcome: A systemic review. Journal of Critical Care, 48, 56-62. (Level I)
  2. Cortes, E., Parrado, K., Arango. F. (2017). Negative inspiratory pressure as a predictor of weaning mechanical ventilation. Journal of Anesthesia & Intensive Care Medicine, 3(1):555602.doi:10.19080/JAICM.2017.03.555602 (Level VII)
  3. Kacmarek, R.M. (2021). Chapter 53: Discontinuing ventilatory support. In R.M. Kacmarek, J.K. Stoller, A.J. Heuer (Eds.), Egan’s fundamentals of respiratory care (12th ed., pp. 1184-1211). St. Louis: Elsevier.
  4. Proud, K. and others. (2020). Chapter 16: Ventilation discontinuance. In D.C. Shelledy, J.I. Peters (Eds.), Mechanical ventilation (3rd ed., pp. 637-666). Burlington, MA: Jones & Bartlett Learning.
  5. Quellette, D.R. and others. (2017). Liberation from mechanical ventilation in critically ill adults: An official American College of Chest Physicians/American Thoracic Society clinical practice guideline: Inspiratory pressure augmentation during spontaneous breathing trials, protocols minimizing sedation, and noninvasive ventilation immediately after extubation. Chest, 151(1), 166-180. doi:10.1016/j.chest.2016.10.036 (Level I)

ADDITIONAL READINGS

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.

Elsevier Skills Levels of Evidence

  • Level I - Systematic review of all relevant randomized controlled trials
  • Level II - At least one well-designed randomized controlled trial
  • Level III - Well-designed controlled trials without randomization
  • Level IV - Well-designed case-controlled or cohort studies
  • Level V - Descriptive or qualitative studies
  • Level VI - Single descriptive or qualitative study
  • Level VII - Authority opinion or expert committee reports
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