Discontinuing Ventilatory Support Notes

Discontinuing Ventilatory Support

Learning Objectives (1 of 4)

  • Relationship between Ventilatory Demand and Capacity: Discuss how ventilatory demand relates to a patient’s ability to be weaned off mechanical ventilation and how these factors influence ventilator discontinuance.

  • Factors Associated with Ventilator Dependence: List and explore the various factors that can lead to a patient becoming dependent on ventilatory support.

  • Patient Evaluation for Ventilator Discontinuation: Explain the evaluation process that must be undertaken before attempting to wean a patient from ventilatory support.

Learning Objectives (2 of 4)

  • Weaning Indices: List acceptable values for specific weaning indices that predict readiness for discontinuation of ventilatory support.

  • Optimizing Conditions Prior to Weaning: Describe factors that must be optimized before an attempt at discontinuation or weaning is made.

  • Techniques for Ventilator Weaning: Discuss various techniques used in ventilator weaning, including but not limited to:

    • Daily spontaneous breathing trials (SBT)

    • Synchronized intermittent mandatory ventilation (IMV)

    • Pressure support ventilation (PSV)

    • Newer methods of weaning.

Learning Objectives (3 of 4)

  • Advantages and Disadvantages of Weaning Methods: Contrast the various techniques for weaning from mechanical ventilation by discussing their pros and cons.

  • Assessment Tools for Weaning: Discuss the use of esophageal pressure, diaphragm electrical activity (EAdi), and ultrasound in assessing patient capabilities and predicting weaning success.

  • Weaning the Morbidly Obese Patient: Explore the specific considerations for weaning patients with morbid obesity.

Learning Objectives (4 of 4)

  • New Weaning Guidelines: Discuss updates in weaning guidelines as provided by the ATS/ACCP.

  • Assessment for Extubation: Describe the comprehensive assessment process necessary for determining a patient's readiness for extubation.

  • Reasons for Weaning Failure: List the primary reasons patients may fail a trial of ventilator discontinuance.

  • Challenges in Weaning: Explain why certain patients may not be able to be weaned successfully from ventilatory support.

Introduction (1 of 2)

  • Role of Mechanical Ventilation: Mechanical ventilation is used to support patients until the underlying condition necessitating support is resolved. It sustains life but does not cure.

  • Complications and Hazards: Highlight the potential complications and hazards associated with prolonged mechanical ventilation, emphasizing the urgency of withdrawing support once appropriate.

  • Daily Evaluation: Emphasize the importance of daily evaluations of all patients on mechanical ventilation to assess their ability to wean off the ventilator.

Introduction (2 of 2)

  • Definition of Ventilator Dependence: Define ventilator-dependent patients as those requiring mechanical support for prolonged periods (generally defined as 2 weeks or longer) or those who have shown no improvement after attempts to discontinue.

  • Risks of Delaying Extubation: Discuss the balance between the desire for early extubation and the risks associated with reintubation, including increasing complications like nosocomial pneumonia, myocardial infarction, and mortality.

Methods of Discontinuing Ventilation

  • Primary Methods: Identify the three main methods for discontinuing ventilation:

    • Spontaneous Breathing Trials (SBT): Periodic trials allowing the patient to breathe independently for a set duration.

    • Intermittent Mandatory Ventilation (IMV): A method allowing patient-initiated breaths with mandatory breaths provided by the ventilator.

    • Pressure Support Ventilation (PSV): Support provided during spontaneous breathing to reduce the workload on respiratory muscles.

  • Additional Techniques: Other Weaning techniques include:

    • Volume-support ventilation (VSV)

    • Adaptive support ventilation (ASV)

    • Automatic tube compensation (ATC)

    • Proportional assist ventilation (PAV)

    • Neurally adjusted ventilatory assist (NAVA)

    • Continuous positive airway pressure (CPAP).

Terminology

  • Weaning: A general term that refers to the process of discontinuing ventilatory support, irrespective of time frame or method.

  • Ventilator Discontinuation: The specific act of disconnecting a patient from mechanical ventilatory support.

  • Discontinuing Ventilation: The overall process of liberating a patient from the ventilator through any method applied.

Discontinuing Ventilatory Support (1 of 2)

  • Categories of Patients:

    • Quick and Routine Removal: The vast majority of ventilated patients fall into this category.

    • Systematic Approach Needed: About 15% to 20% of patients require more systematic methods for discontinuation.

    • Extended Weaning Process: Less than 5% of patients may need days to weeks for gradual weaning.

Discontinuing Ventilatory Support (2 of 2)

  • Unweanable Patients: Defined as less than 1% of patients who cannot be weaned from ventilatory support.

  • Terminal Weaning: Refers to cases where the ventilator is discontinued due to lack of survival chance, accompanied by comfort measures for the patient.

Ventilatory Workload and Demand (1 of 2)

  • Definition of Ventilatory Workload: The workload refers to the amount of work performed by the respiratory muscles to maintain adequate ventilation.

  • Total Ventilatory Workload Determinants:

    • Level of ventilation required

    • Compliance of lungs and thorax

    • Resistance to airflow in the airways

    • Imposed work of breathing (WOBI) arising from mechanical factors of the ventilatory system.

Ventilatory Workload and Demand (2 of 2)

  • Ventilation Level Determinants: The level of ventilation required is influenced by:

    • Metabolic rate of the patient

    • Central nervous system (CNS) drive

    • Ventilatory dead space.

  • Factors Increasing Work of Breathing (WOB): Some mechanical factors contribute to increased work, including:

    • Artificial airways

    • Partial airway obstruction

    • Ventilator circuits

    • Demand flow systems

    • Auto-PEEP

    • Inappropriate ventilator flow settings and sensitivity.

Ventilatory Capacity

  • Definition: Ventilatory capacity is defined by:

    • Central nervous system (CNS) drive

    • Strength of ventilatory muscles

    • Endurance of ventilatory muscles.

  • Muscle Strength Influencers: Strength is impacted by age, sex, muscle bulk, and general health state. Notably,:

    • Malnutrition, starvation, and electrolyte imbalances can cause weakness in ventilatory muscles.

Global Criteria for Discontinuing Ventilatory Support

  • Success Factors: The likelihood of discontinuation success depends on:

    • The relation between ventilatory workload versus capacity

    • Oxygenation levels of the patient

    • Cardiovascular status

    • Psychological factors affecting the patient’s condition.

  • Implications of Workload and Capacity: When ventilatory demands outstrip capacity, success in discontinuation becomes less feasible.

Patient Evaluation

  • Importance of Assessment: A thorough evaluation is essential to ascertain a patient's readiness for mechanical ventilation removal.

  • Duration of Support: The duration of mechanical ventilation is significant; patients with less than 72 hours of support often can be weaned quickly.

The Most Important Criteria

  • Key Questions for Assessment:

    • Is there confirmation of improvement or reversal of the underlying disease?

    • Is the patient's oxygenation status sufficiently adequate?

    • Is the patient hemodynamically stable?

    • Can the patient initiate spontaneous breathing?

Weaning Indices (1 of 3)

  • Clinical Judgment Limitations: Traditional clinical judgment is often ineffective for assessing a patient’s weaning readiness; thus, we rely on specific indices:

    • PaO2/FiO2 Ratio: Measures the efficacy of oxygen exchange.

    • P(A−a)O2: Alveolar-to-arterial oxygen pressure difference.

    • Maximum Inspiratory Pressure (MIP): Strength of the respiratory muscles.

    • Vital Capacity (VC): Total amount of air the lungs can hold.

    • Spontaneous Minute Ventilation (Vesp): Quantity of air volume inhaled or exhaled in one minute.

    • Maximum Voluntary Ventilation (MVV): The maximum amount of air a patient can ventilate in one minute.

Weaning Indices (2 of 3)

  • Newer Indices: Developments have introduced newer assessment metrics:

    • Rapid, Shallow Breathing Index (f/VT): Fast breathing with lower volume suggests poor tolerance.

    • Airway Occlusion Pressure (P0.1): Measures the effort needed to trigger a breath.

    • Measures of Work of Breathing: Assess the overall workload required to breathe.

Weaning Indices (3 of 3)

  • Measurements for Predictive Success:

    • Spontaneous Rate: Between 6 to 30 breaths/min

    • Spontaneous Tidal Volume (VT): Greater than 5 ml/kg

    • f/VT (RSBI): Must be less than 105 for predictability of tolerance.

    • Minute Ventilation: Under 10 L/min is desirable.

    • MIP Levels: Should be less than -20 to -30 mm Hg.

    • P0.1 Levels: Below 6 cm H2O.

    • P0.1/MIP Ratio: Should be less than 0.3.

    • CROP Score: Should be greater than 13 for a good outcome prediction.

Oxygenation

  • Critical Status for Weaning: Inadequate oxygenation is often linked to failures in weaning protocols.

  • Required Oxygenation Levels:

    • PaO2: Must be greater than 60 mm Hg (or >55 mm Hg in COPD with CO2 retention) with FiO2 <0.40 to 0.50.

    • PEEP Levels: Should be 5 to 8 cm H2O or lower.

    • PaO2/FiO2 Ratio: Required to be 150 to 200 mm Hg or more.

Acid-Base Balance

  • Impact of Metabolic Status: Patients with metabolic acidosis may exhibit an increased ventilatory drive, complicating the weaning process.

  • Metabloic Alkalosis and Ventilation: Those experiencing metabolic alkalosis or previous hyperventilation may have a diminished drive, complicating weaning.

Metabolic Factors

  • Effect on Long-term Support Patients: Metabolic factors can considerably impact the capacity to wean off ventilation, especially in patients needing prolonged support.

  • Carbohydrate Impact: Overfeeding on carbohydrates can lead to increased CO2 production, potentially leading to acute hypercapnic respiratory failure.

Renal Function and Electrolytes

  • Monitoring Requirements: Ensure adequate urine output and watch for inappropriate weight gain or edema.

  • Fluid Management: Avoidance of fluid overload is critical to prevent congestive heart failure and pulmonary edema.

Cardiovascular Function

  • Evaluation Necessity: Patients should be assessed for arrhythmias, hypotension, and severe hypertension prior to considering discontinuation of ventilatory support.

  • Associated Challenges: Conditions such as left ventricular dysfunction, myocardial ischemia, and cardiovascular instability decrease the likelihood of successful discontinuation.

Physiologic Factors and CNS Assessment

  • CNS Status Evaluation: The patient should ideally be awake, alert, capable of following instructions, and free of seizures.

  • Impairs on Control of Ventilation: Factors such as brainstem strokes, sedation, muscle relaxants, and narcotics can hinder the neuromuscular control necessary for ventilation.

  • Psychological Wellbeing: Address fears, anxiety, pain, and stress; maintain constant communication with healthcare staff, patients and their families.

Integrated Indices

  • Composite Measures Enhancing Prediction: Integrating multiple metrics of respiratory ability increases accuracy in predicting successful weaning.

  • CROP Score: Utilizes measures of ventilatory load, respiratory muscle strength, and gas exchange.

  • Adverse Factor/Ventilator Score: Combines ratings of 15 adverse factors affecting weaning.

  • Weaning Index: Merges strength, endurance, and efficiency of gas exchange measures.

  • Burns Weaning Assessment Program: Comprised of a 26-item assessment, combining 12 general factors with 14 respiratory-focused factors for a holistic assessment.

Evaluation of the Airway

  • Distinction between Ventilator Discontinuation and Extubation: Care must be taken in separating the decision to withdraw ventilatory support from the decision to extubate.

  • Patient Considerations: Some patients who can be detached from the ventilator shouldn’t be extubated; tracheotomies can be useful for enhancing comfort, improved suctioning, reduced airway resistance, and facilitating speech and eating abilities.