Principles of Mechanical Ventilation

1. Principles of Mechanical Ventilation RET 2284 Module 7.0 Discontinuation From Mechanical Ventilation

2. Discontinuation From Mechanical Ventilation • Discontinuation (ACCP/SCCM/AARC) • The process of withdrawing mechanical ventilatory support and transferring the work of breathing from the ventilator to the patient whose condition is improving • AKA • Weaning • Gradual reduction • Liberation • Can be accomplished • Abruptly • Gradually

3. Discontinuation From Mechanical Ventilation • Discontinuation Once the need for mechanical ventilation has been resolved, ventilation can be discontinued • About 80% of patients requiring temporary mechanical ventilation do not require a slow withdrawal process and can be disconnected within a few hours or day of initial support • Postoperative – recovery from anesthesia • Uncomplicated drug overdose • Exacerbations of asthma

4. Discontinuation From Mechanical Ventilation • Discontinuation • The ventilator and airway should be discontinued as soon as possible to avoid the risks associated with mechanical ventilation • Ventilator induced lung injury (VILI) • Nosocomial pneumonia • Airway trauma form ET • Unnecessary sedation • Premature discontinuation also is associated with a higher mortality rate

5. Discontinuation From Mechanical Ventilation • Evaluation of Clinical Criteria for Weaning • Criteria for Weaning – Three Key Points • The problem that caused the patient to require ventilation has been resolved • Certain measurable criteria should be assessed to help establish a patient’s readiness for discontinuation of ventilation • A spontaneous breathing trial should be performed to establish readiness for weaning

6. Discontinuation From Mechanical Ventilation • Evaluation of Clinical Criteria for Weaning • Pathology of Ventilator Dependence • Primary pathology that led to ventilatory support must be corrected • In patients who require mechanical ventilation for >24 hours, a formal search should be made for all causes that may be contributing to ventilator dependence

7. Discontinuation From Mechanical Ventilation • Evaluation of Clinical Criteria for Weaning • Weaning Criteria • When a patient’s condition is stable, alert, and cooperative, clinicians commonly evaluate certain ventilatory mechanic and gas exchange values to help assess readiness for weaning

8. Discontinuation From Mechanical Ventilation • Evaluation of Clinical Criteria for Weaning • Measurement of Adequacy of Oxygenation • PaO2 60 mm Hg (FiO2 <0.40) • PEEP 5 – 8 cm H2O • PaO2/FiO2 >200 mm Hg • P(A-a)O2 <350 mm Hg (FiO2 of 100%) • % OS/QT <20% - 30%

9. Discontinuation From Mechanical Ventilation • Evaluation of Clinical Criteria for Weaning • Measurement of Ventilation • PaCO2 <50 mm Hg • VE (spont.) <10 – 15 L/min • VD/VT <0.6 • VT >5 mL/kg • RR (spont.) ≤35 min. or >6 – 10 min. • Resp Pattern Regular

10. Discontinuation From Mechanical Ventilation • Evaluation of Clinical Criteria for Weaning • Respiratory Mechanics • MIP ≤ 20 cm H2O • VC >10 – 15 mL/kg (needed for effective cough) • CS ≥ 30 mL/cm H2O • CD ≥ 22 mL/cm H2O • P0.1 ≤ 6 cm H2O

11. Discontinuation From Mechanical Ventilation • Evaluation of Clinical Criteria for Weaning • Integrated Indices • Respiratory Frequency/Tidal Volume Ratio (f/VT) • Failure to wean may be related to spontaneous breathing that is rapid (high respiratory rate) and shallow (low tidal volume) • Procedure • Disconnect the spontaneous breathing patient from the ventilator and oxygen for 1 minute • VE, respiratory frequency, VT are measured • Calculate f/VT RSBI < 105 associated with successful weaning

12. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of Titrating Ventilator Support • Ventilator support can be reduced as patients become increasingly able to resume part of the work of breathing • Three Common Approaches • Synchronized Intermittent Mandatory Ventilation (SIMV) • PSV – Pressure Support Ventilation (PSV) • Spontaneous Breathing Trial (SBT)

13. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of Titrating Ventilator Support • SIMV – Synchronized Intermittent Mandatory Ventilation • Common practice is to reduce the mandatory rate progressively (1 – 2 breaths/min) at a pace that matches the patients improvement • Pressure support can be added to unload spontaneous breaths through circuit and ET (helps prevent fatigue) • PEEP of 3 – 5 cm H2O is also used to help compensate for changes in FRC Studies done clearly show that weaning took longer with SIMV when compared to PSV and T-piece methods

14. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of titrating Ventilator Support • SIMV – Synchronized Intermittent Mandatory Ventilation Measurements of flow, volume, airway pressure, and esophageal pressure in a patient ventilated with SIMV. The esophageal pressure swings reflect the changes in pleural pressure and are the result of respiratory muscle contraction. These pressure swings are nearly as large during a mandatory breath as during spontaneous breaths. (From Hess DR: Respir Care 47:1007, 2002.)

15. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of Titrating Ventilator Support • PSV – Pressure Support Ventilation • Patient triggered, pressure limited, flow cycled • Patient controls the rate, timing and depth of each breath • Theoretically, PSV allows the clinician to adjust the ventilatory workload for each spontaneous breath to enhance endurance conditioning of the respiratory muscles without causing fatigue

16. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of Titrating Ventilator Support • PSV – Establishing PS level • Set PS level to 5 – 15 cm H2O until a reasonable ventilatory pattern for the patient is accomplished • Or • Reestablish patient’s baseline respiratory rate (15 – 25 breaths/min) • VT (300 – 600 mL/min) Inappropriate PS level will produce tachycardia, hypertension, tachypnea, diaphoresis, excessive use of accessory muscles, paradoxical breathing, respiratory alternans

17. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of Titrating Ventilator Support • PSV – Weaning • Gradually reduce PS level as long as an appropriate spontaneous respiratory rate and VT are maintained and no distress is evident • When PS is reduced to 5 cm H2O it is not high enough to contribute to ventilatory support, but will help overcome the work imposed by the ventilator system and ET

18. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of Titrating Ventilator Support • Spontaneous Breathing Trial (SBT) - Abrupt Method • Patient is removed from full ventilatory support and placed one of the following for a few minutes to assess their ability to perform a more extended spontaneous breathing trial: • T-Piece • Low level of CPAP (e.g., 5 cm H2O) and/or low level of PS (e.g., 5 – 8 cm H2O) – on ventilator • Automatic Tube Compensation (ATC) – on ventilator Considered a screening phase

19. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of Titrating Ventilator Support • Spontaneous Breathing Trial (SBT) - Abrupt Method • During the SBT the patient’s ability to tolerate unsupported ventilation is determined • Respiratory pattern • Adequacy of gas exchange • Hemodynamic stability • Subjective comfort • A patient is considered ready for ventilator discontinuation when they can tolerate an SBT of 30 – 120 minutes

20. Discontinuation From Mechanical Ventilation • Weaning Techniques • Methods of Titrating Ventilator Support • Spontaneous Breathing Trial (SBT) - Gradual Method • Patient is removed from full ventilatory support and placed on T-Tube, ATC, CPAP and/or PS for 5 and minutes and returned to full support for the remainder of the hour • Repeat process with progressively more time on T-Tube, ATC, CPAP and/or PS, working up to 20 – 30 minutes, and less time on full support • Full ventilatory support at night to rest patient • A patient is considered ready for ventilator discontinuation when they can tolerate an SBT of 30 – 120 minutes

21. Discontinuation From Mechanical Ventilation • Weaning Techniques • SBT Clinical Signs and Symptoms Indicating Problems • RR >30 – 35 bpm • Increases in RR >10 bpm from baseline, or RR <8 bpm • Use of accessory muscles • VT  below 250 – 300 mL • Blood Pressure •  20 mm Hg systolic •  30 mm Hg systolic • Systolic values >180 mm Hg • Diastolic values change 10 mm Hg

22. Discontinuation From Mechanical Ventilation • Weaning Techniques • SBT Clinical Signs and Symptoms Indicating Problems • Heart Rate •  >20% from baseline • >140 bpm • PVCs – sudden onset (>4 – 6/hr) • Diaphoresis, pallor, cyanosis • Deterioration of ABG or SpO2 • Agitation, anxiety, drowsiness

23. Discontinuation From Mechanical Ventilation • Weaning Techniques • SBT Clinical Signs and Symptoms Indicating Problems • Patients should not be allowed to experience extreme exhaustion during the SBT • Unnecessary prolongation of a failed SBT can result in muscle fatigue, hemodynamic instability, discomfort and worsening gas exchange

24. Discontinuation From Mechanical Ventilation • Weaning Techniques • SBT • If the patient fails an SBT, the causes of the failure must be determined and corrected when possible • When the reversible causes of SBT failure have been corrected, and if the patient still meets the criteria for discontinuation of ventilation, an SBT should be performed every 24 hours

25. Discontinuation From Mechanical Ventilation • Weaning Techniques • SBT • The clinical focus for the 24 hours after a failed SBT should be on maintaining adequate muscle unloading, optimizing comfort (and thus sedation needs), and preventing complications, rather than on aggressive ventilatory support reduction • When a patient fails an SBT, repeated testing the same day is of no benefit

26. Discontinuation From Mechanical Ventilation • Weaning Techniques • SBT • To date no studies offer any evidence that a gradual support reduction strategy is better than providing full, stable support between once daily SBTs

27. Discontinuation From Mechanical Ventilation • Weaning Techniques • Nonrespiratory Causes That May Complicate Weaning • Cardiac Factors • Acute CHF • Acid-Base Factors • Patients with chronic hypercapnia fail to wean in the presence of relative hyperventilation, respiratory alkalosis and subsequent renal compensation, leading to a decrease in bicarbonate

28. Discontinuation From Mechanical Ventilation • Weaning Techniques • Nonrespiratory Causes That May Complicate Weaning • Metabolic Factors • Electrolyte Imbalances • Hypophosphtemia – muscle weakness • Hypomagnesemia – muscle weakness • Hyopthyroidism – directly impair diaphragmatic function • Pharmacological Agents • Opioids, tranquilizers, hypnotic agents • Depress central ventilatory drive • Must be minimized for weaning to be successful

29. Discontinuation From Mechanical Ventilation • Weaning Techniques • Nonrespiratory Causes That May Complicate Weaning • Nutritional • Inadequate nutrition may blunt response to hypercarbia and hypoxemia • Underfeeding may cause muscle wasting • Overfeeding • Carbohydrates – Causes increased O2 consumption, CO2 production, and VE

30. Discontinuation From Mechanical Ventilation • Weaning Techniques • Nonrespiratory Causes That May Complicate Weaning • Psychological Factors • Psychological ventilator dependence • Anxiety, fear, delirium • Agitation and/or panic during attempt to reduce or D/C ventilatory support • Lack of Motivation • Depression • Effects of drugs • Organic brain dysfunction • Preexisting personality factors