Weaning and Discontinuation of Ventilatory Support

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

Documents

level of ventilation

various techniques of

permanent removal

educational objectivesdescribe

spontaneous ventilation

drive strength

successful weaninglist

overall factors