Weaning and Discontinuation of Ventilatory Support 215a.

Weaning and Discontinuation of Ventilatory Support

215a

Educational Objectives

• Differentiate between weaning, discontinuation, and

extubation

• List the causes of ventilator dependence

• List the patient parameters evaluated and the values

required prior to initiating weaning

Educational Objectives

• Describe the various techniques of weaning, with

the advantages and disadvantages of each

• Describe the overall factors associated with

successful weaning

• List the steps of extubation

Definitions

• Weaning

– The process of gradually reducing ventilatory support

and its replacement with spontaneous ventilation in

an incremental manner

• Discontinuation

– The permanent removal of the ventilator

Definitions

• Extubation

– Removal of the artificial airway

• Ventilatory Demand

– The level of ventilation required to meet the patient’s

need for elimination of carbon dioxide

Definitions

• Ventilatory capacity

– The level of the patient’s drive (CNS) to breathe

and the ability of the respiratory muscles to

maintain this drive (strength and endurance)

Causes of Ventilator Dependence

• Ventilatory demand in excess of ventilatory

capacity

• Non-respiratory factors

• Psychological factors

• Nutritional needs

Ventilatory Demand in Excess of Ventilatory Capacity

• Factors increasing ventilatory demand

– Increased CNS drive

• Hypoxia• Acidosis

• Pain

• Fear/anxiety

• Stimulation of J receptors



– Increased metabolic rate

• Increased carbon dioxide production

• Fever

• Shivering

• Trauma

• Infection/sepsis



– Decrease in lung compliance

• Atelectasis

• Pneumonia

• Fibrosis

• Pulmonary edema

• ARDS



– Decreased thoracic compliance

• Obesity

• Ascites

• Abdominal distention

• Pregnancy



– Increased airway resistance

• Bronchospasm

• Mucosal edema

• Secretions



– Artificial airways

• Endotracheal tube

• Tracheostomy tube



– Mechanical factors

• Ventilator circuits

• Demand flow systems

• Inappropriate ventilator settings

–Flow

–Sensitivity


• Factors affecting ventilatory capacity

– Decreased PaCO2

– Metabolic alkalosis

– Pain

– Electrolyte imbalance



– Respiratory depressants

• Narcotics

• Sedatives



– Fatigue

• Overall fatigue

• Malnutrition

• Atrophy of respiratory muscles



– Decrease in metabolic rate

– Carbon dioxide retention

– Neurologic or neuromuscular disease

Non-Respiratory Factors

• Cardiovascular factors

– Myocardial ischemia

– Heart failure

– Hemodynamic instability

– Arrhythmias

Non-Respiratory Factors

• Neurological factors

– Decreased central drive

– Decreased peripheral nerve transmission

Psychological Factors

• Confusion/altered mental status

• Fear and anxiety

• Stress

• Depression

• Support from staff and family

Nutritional Needs

• Preferably, patient is not on hyperalimentation

• No excessive carbohydrates

– Increased carbohydrate intake increases respiratory

quotient > 0.8

– Results from increase in carbon dioxide production

Factors Affecting Readiness For Weaning

• Reversal or stabilization of underlying disease

causing initiation of support

• Stable vital signs

– Afebrile

– Pulse, blood pressure within normal limits


• Adequate cardiovascular reserves

– Absence of acute myocardial ischemia

– Minimal requirement for vasopressors to maintain blood

pressure

– No significant arrhythmias


• Adequate blood gas results

– PaO2 ≥ 60 mmHg with FIO2 < 0.5 and PEEP ≤ 5 cmH2O

– pH > 7.25

– PaCO2 at patient’s normal level (may be greater than 45

mmHg for COPD patients)


• Adequate ventilatory status

– Spontaneous respiratory rate < 30 breaths/min

– Spontaneous tidal volume > 5 mL/kg

– Vital capacity > 10 – 15 mL/kg


• Adequate respiratory muscle strength

– Maximum inspiratory force

– MIF < −30 cmH2O


• Adequate ventilatory reserve

– Maximum voluntary ventilation

– MVV > 20 L/min or two times minute

ventilation



– Rapid Shallow Breathing Index (RSBI)• Respiratory rate divided by tidal volume in liters

(f/VT)

• Calculated during one minute of unsupported,

spontaneous breathing

• Pressure support reduces predictive value



– Rapid Shallow Breathing Index (RSBI)

• Most predictive for patients on ventilatory

support less than eight days

• f/VT < 105 predictor of weaning success; < 80

associated with 95% success

Approaches to Weaning

• Spontaneous breathing trials (SBT)

• Synchronized intermittent mandatory ventilation

• Pressure support ventilation

• Extubation

Spontaneous Breathing Trials (SBT)

• Method

– Prepare the patient psychologically

– Set FIO2 either at the ventilator setting or 10% above

setting

– Patient placed on T piece or left on ventilator with no

backup rate and CPAP set at zero


• Method

– Start with five minutes off the ventilator (or less, if

not tolerated by patient); may increase initial time

up to 120 minutes if tolerated well


• Method

– Response is monitored; trial discontinued if changes

observed

• f > 35 breaths/min

• SPO2 < 90%

• Heart rate > 140 beats/min or increase by 20%


• Method

– Response is monitored; trial discontinued if changes

observed

• BP ≥ 20% change; systolic >180 mmHg and

diastolic > 90 mmHg

• Diaphoresis

• Increased anxiety


• Method

– If first trial unsuccessful and patient has auto-PEEP

secondary to airway obstruction, may add 5 cmH2O

– If patient has nasal ET tube or small ET tube,

5 to 7 cmH2O pressure support may be added

– If patient fails SBT, patient replaced on ventilatory

Support to rest for one to four hours


• Method

– Increase duration of spontaneous breathing trials

– Some patients may tolerate the procedure so well

that they do not have to resume ventilator use at all


• When weaning is difficult, process can last weeks or

months

• Generally, ventilatory support is resumed overnight

Synchronized Intermittent Mandatory Ventilation

• Method

– Initially, respiratory rate and tidal volume set to

provide full ventilatory support

– Initiation of weaning by SIMV

• May wait until patient’s condition has improved

considerably

• May begin as soon as patient’s condition allows


• Method

– Rate decreased in increments of two with assessment

of patient following each adjustment

– May be reduced more rapidly as patient condition

improves

– Once rate is equal to 4 breaths/min and can be

tolerated at least two to four hours, the patient may

be extubated


• Decreases respiratory muscle atrophy and

discoordination

• Minimizes chance of barotrauma through rapid

reduction of mean airway pressure

Pressure Support Ventilation

• Mode of ventilatory support that assists the

patient’s spontaneous inspiratory effort with

a level of positive airway pressure


• Mode works best for short-term weaning (< 72

hours); if used for long-term weaning, increase

support to near maximum at night to allow patient

to rest


• Technique

– Begin with pressure support level at which

respiratory rate and tidal volume are close to

full support

– Gradually reduce support as tolerated by patient


• Technique

– Continue to reduce support until a minimum level of

between 5 and 10 cmH2O can be tolerated

– When patient can maintain this level for a minimum

of two and four hours, the patient is considered

weaned

Extubation

• Decision to wean and decision to extubate are

separate decisions

Extubation

• Guidelines for extubation

– No immediate need for mechanical ventilation

– Achievement of adequate oxygenation and

ventilation during spontaneous breathing

Extubation


– Minimal risk of upper airway obstruction

• Minimal upper airway edema; perform cuff

leak test

–Suction upper airway above cuff

–Deflate cuff

Extubation



• Minimal upper airway edema; perform cuff leak

test

–Briefly occlude endotracheal tube

– If patient is unable to breathe around the

occluded endotracheal tube with the cuff

deflated, laryngeal edema may be present

Extubation



• No evidence of mass obstructing airway

– Minimal risk of aspiration

– Adequate protection of airway

– Adequate clearance of pulmonary secretions

Failure to Wean

• Approximately 25% of patients removed from

ventilatory support experience enough respiratory

distress to require reinstitution of support

Causes of Weaning Failure

• Oxygenation problems

– Decreased ventilation/perfusion ratio

• Asthma

• Emphysema

• Chronic bronchitis

• Bronchospasm



– Increase in shunt

• Atelectasis

• Pneumonia

• ARDS

• Pulmonary edema



– Low oxygen content of mixed venous blood


• Ventilation problems

– Central hypoventilation

• Neurological injury

• Drugs

– Impaired neuromuscular function



– Increased dead space

• Embolism

• ARDS

• Emphysema



– Increased carbon dioxide production

• Increased carbon dioxide production from

increased muscle activity

• Carbohydrate overfeeding

• Fever


• Cardiovascular problems

– Left ventricular failure

– Hemodynamic instability

Terminal Weaning

• Discontinuation of ventilatory support in the

presence of catastrophic or irreversible illness

Terminal Weaning

• Decision to terminally wean made by family in

conjunction with physician and according to

established ethical and legal guidelines

– Patient’s prior known desire to not continue life

support

– Predictions of a low chance of survival

Terminal Weaning

• Decision to terminally wean made by family in

conjunction with physician and according to

established ethical and legal guidelines

– Likelihood of significant future cognitive impairment

– Inability to maintain blood pressure without

continuous need for medication

Terminal Weaning

• Patient is discontinued from ventilator after all

procedures to ensure as much comfort as possible

for the patient have been performed

Weaning and Discontinuation of Ventilatory Support 215a.

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