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

Principles of Mechanical Ventilation

RET 2284 Module 7.0Discontinuation From Mechanical Ventilation

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


DiscontinuationOnce 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


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


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


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


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


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%


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


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


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


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)



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


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.)



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



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



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



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



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



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


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



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



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



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



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



To date no studies offer any evidence that a gradual support reduction strategy is better than providing full, stable support between once daily SBTs


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



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



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



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

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