Mechanical Ventilatory Support Series

Part V:

Weaning & Liberation from Mechanical Ventilation

S a n t i S i l a i r a t a n a , M D

D i v i s i o n o f Pu l m o n a r y M e d i c i n e , D e p a r t m e n t o f M e d i c i n e , Fa c u l t y o f M e d i c i n e Va j i r a H o s p i t a l

N a v a m i n d r a d h i r a j U n i v e r s i t y

Outlines

Rationale of weaning

Weaning failure

Methods of weaning

Predictors of weaning success/failure

Complications of Mechanical Ventilation

Other complicationsET tube complications

malfunction

malposition

self-extubation

nasal/oral necrosis

pneumonia

laryngeal edema

tracheal erosion

sinusitis

Ventilator-related complications

Ventilator induced lung injury

Diaphragm dysfunction

Alveolar hypo/hyperventilation

Atelectasis

Hypotension

Pneumothorax

Diffuse alveolar damage

GI hypomobility

Stress gastropathy

GI hemorrhage

Arrhythmias

Salt-water retention

Malnutrition

Ventilator Days and Survival Chance

Esteban A, Anzueto A, Frutos F, et al.

More ventilation days, more deaths.

Day

Survival chance

Asthma

COPD

ARF

ARDS

Do patients need weaning?

19%

81%

Brochard L, Rauss A, Benito S, et al.

456 patients were enrolled to study weaning methods

347 patients (81%) were successfully extubated within 48 hr

Metabolic Changes during Critical Illness

Critical Illness Recovery

Lung diseases Heart diseases

Neuromuscular disease

Mechanical ventilation MalnutritionElectrolyte

disordersSedation

muscle relaxants

Muscle breakdown, atrophy, weakness

Outlines

Rationale of weaning

Weaning failure

Methods of weaning

Predictors of weaning success/failure

Delayed vs Premature Extubation

Delayed extubation

Premature extubation

Infection Diaphragm dysfunction

Tracheal stenosis

Infection Airway trauma

Respiratory failure

Parameters Used in Prediction of Weaning Success

PaOP: F ratio PaO

A-a DO

Pi

FVC

PaCO

MV

TV MVV

RR

PV

C

C

RSBI CROP index

P

SWI

Predictors Based on Respiratory Physiology

PaO

P: F ratio

P

A-a DO

Pi

FVC

PaCO

MV

TV

MVV

RR

P

V C

C RSBI

CROP index

P

SWI

Oxygenation CombinedLoadStrengthDrive

Indicators of Muscle Performance

Parameter of Oxygenation Weaning Threshold

Pimax <-15 to -30 cm H2O

FVC >10-15 mL/kg

PaCO2 <50 mmHg

Minute Ventilation (MV) <10-15 L/min

Tidal volume (TV) >5 mL/kg

Maximum voluntary ventilation (MVV) >20 L/min

RR <35 breaths/min or >6 breaths/min

f/Vt ratio <105 breaths/min/L

Strength

Stamina

Ashfaq Hasan.

Respiratory Mechanics

Mechanical Indices Weaning Threshold

Dynamic compliance (Cdyn) >22 mL/cm H2O

Static compliance >33 mL/cm/H2O

Work of breathing 0.47 J/L or 33 J/min

Ashfaq Hasan.

Indices of Oxygenation

Parameter of Oxygenation Weaning Threshold

PaO2 (on FiO2 0.5 and PEEP ≤5 cm H2O) >60 mmHg

PaO2/FiO2 ratio (“PF” ratio) >200

PaO2/PAO2 ratio >0.35

Alveolo-arterial oxygen gradient (A-aDO2) <350 mmHg on FiO2 1.0

Shunt fraction (Qs/Qt ratio) 0.2 (<20% shunt)

Ashfaq Hasan.

Composite Indices

Composite Indices Weaning Threshold Failure Threshold

RSBI (f/Vt) ratio <105 breaths/min/mL >105 breaths/min/mL

CROP index >13 mL/breaths/min N/A

P0.1/Pmax ≤0.9 N/A

SWI <9/min >11/min

RSBICROPSWI

Ashfaq Hasan.

Outlines

Rationale of weaning

Weaning failure

Methods of weaning

Predictors of weaning success/failure

Readiness to Wean

The cause of respiratory failure has improved

The patient is oxygenating adequately

The arterial pH is >7.25

The patient is ale to initiate an inspiratory effort

The patient is hemodynamically stable

No myocardial ischemia

Methods of Weaning

Spontaneous breathing with

T-piece

Pressure support

ventilation

SIMV with PSV

SIMV

Rate of Successful Weaning

Weaning technique Relative rate of suscessful weaning (95% CI) P value

Once daily SBT vs SIMV 2.83 (1.36-5.89) <0.006

Once daily SBT vs PSV 2.05 (1.04-4.04) <0.04

Once daily SBT vs intermittent SBTs 1.24 (0.64-2.41) 0.54

SBT

Esteban, A, Frutos, F, Tobin, MJ, et al,

SIMVPSV:

Assessment of Readiness to Wean

Clinical assessment

Objective measurements

Good heart: HR ≤140 bpm

SBP 90-160 mmHg No/minimal vasopressors

Good oxygenation: SaO2 >90% on FiO2 ≤0.4

PEEP ≤8 mmHg

‘3 Cs’ Cough Clean Clear

Good consciousness

Good pulmonary function: RR ≤35 bpm

MIP ≤-20 to -25 cmH2O VT >5 mL/kg

VC >10 mL/kg f/Vt <105 br/min/L

No significant respiratory acidosis

Stable metabolic status

Spontaneous Breathing with T-piece Trial

Weaning with PSV

1 2 3 4 5 6

Record Tidal volume

P peak

Set Level of PS 80-85% of

P peak

Monitor clinical signs periodically

Gradual decrease

PS 2 cmH2O twice per day

PS 6-8 cmH2O PEEP ≤5 cmH2O

T-piece trial or

Extubation

Weaning with SIMV + PSV

1 2 3 4 5 6

Record spontaneous

RR and P peak

Set SIMV rate 75-80% of

spontaneous rate and PS 80-90% of

P peak

Monitor clinical signs periodically

Gradual decrease

RR 1-2 bpm twice per day

RR 0 bpmGradual

decrease PS 2 cmH2O

twice per day

7 8

PS 6-8 cmH2O PEEP ≤5 cmH2O

T-piece trial or

Extubation

Modes of Weaning: Summary

SIMV with PSV

Progressive decrease of SIMV rate

Progressive decrease

of PSVPSV

SB with PSV

SB with T-piece

SB without PSV

Extubation

Outlines

Rationale of weaning

Weaning failure

Methods of weaning

Predictors of weaning success/failure

Weaning Failure

Either

the failure of Spontaneous breathing trial

or

the need for reintubation within 48 h

following extubation

J-M. Boles et al.

Classification of Patients with Weaning Failure

Group/Category Description

Simple weaning Success at the first attempt

Difficult weaning 1-3 attempts of SBT Up to 7 days from the first SBT

Prolonged weaning >3 attempts 7 days of weaning after the first SBT

SBT

J-M. Boles et al.

Causes of Weaning Failure

Weaningfailure

LoadMetabolic

Strength Drive

Cardiac load: Pre-existing cardiac disease Increased workload

Pulmonary load: Increased airway resistance Decreased lung compliance Patient-ventilator dyssynchrony

Depressed central drive: Metabolic alkalosis Sedative-hypnotic medications

Electrolyte abnormalities: Hypokalemia

Hypophosphatemia Hypomagnesemia

Ventilator induced diaphragm dysfunction Steroid-induced myopathy CINMA

Malnutrition/Overweight

Anemia

Sleep deprivation

Adrenal Insuffiency

Inadequate Central Drive

Excess sedation

Metabolic alkalosis: Nasogastric suctioning

CNS diseases: Stroke

Encephalitis Encephalopathy

Sleep disordered breathing: central sleep apnea

Obesity hypoventilation syndrome

Cardiogenic Weaning Failure

Oxygen consumption by muscle

Oxygen delivery by the heart=

Oxygen delivery

Stroke volume x HR (O+ (0.0031 x PaO

Weaning-induced Pulmonary Edema

Physiologic parameter Positive Pressure Ventilation Spontaneous breathing

Preload Decrease Increase

Afterload Decrease Increase

Cardiac oxygen consumption Decrease Increase

Cardiac output Increase Decrease

Pulmonary Causes of Weaning Failure

Increased resistive load: Bronchoconstriction

airway edema secretions

Increased elastic load: Dynamic hyperinflation

Alveolar filling Atelectasis

Pleural disease Chest wall disease

Abdominal distension

Pulmonary vascular disease Pulmonary hypertension

Pulmonary embolism

Critical Illness Polyneuropathy & Myopathy

Microvascular alterations

Vasodilatation

Increased permeability

Endoneural edema

Hypoxemia

Extravasation

Cytokine production

Metabolic alterations

Hyperglycemia

Hormone imbalance

Hypoalbuminemia

Amino acid deficiency

Proteolysis

Bioenergetic failure

Antioxidant depletion

Increased ROS

Mitochondrial dysfunction

Apoptosis

Electrical alterations

Channelopathy

Cell depolarization

Cell inexcitability

Altered Cahomeostasis

Changes in excitation-contraction coupling

Sleep Deprivation

Ventilatory response to hypercapnia

Ventilatory response to hypoxia

Increased collapsibility of upper airway

Negative nitrogen balance

Decreased respiratory muscle endurance

Increased oxygen consumption

Increased carbon dioxide production

Signs and Symptoms of Weaning Failure

Subjective indices

Agitation and anxiety Depressed mental status Diaphoresis Cyanosis Accessory muscle use Facial signs of distress Dyspnea

Objective measurements

PaO2 ≤50-60 mmHg on FiO2 ≥0.5 SaO2 <90% PaCO2 >50 mmHg PaCO2 increase >8 mmHg pH <7.32 or decrease ≥0.07 f/Vt >105 br/min/L RR >35 bpm or increase ≥20% SBP ≥180 mmHg or increase ≥20% SBP <90 mmHg Cardiac arrhythmia

RR ▲ >10/min HR ▲ >20 /min

SBP ▲ >30 mmHg

Management of Weaning Failure

Early detection

Record V/S Physical Exam

Obtain an ABG if possible

Put back previous settings

Identify causes

Cause-specific Management

Respiratory load

Nerve impulse from brain

Cardiac load

Metabolic

Daily Interruption of Sedation Correction of metabolic alkalosis

Bronchodilators Diuretics Nutrition

Diuretics Inotropics Antiarrhythmic drugs Nitrate/PCI

Correct hypokalemia, hypomagnesemia, hypophosphatemia Correction of anaemia, blood transfusion

Sleep deprivation Adjust environment Short-acting sedative/hypnotic drugs

Management of Weaning Failure

Rest24 hours

Correct the cause(s)

Retry weaning

Retry with gradual

modes

Tracheostomy Long-term ventilation

Postextubation Laryngeal Edema: Risk

Normal vocal cords

Vocal cord edema

Age >60 years

Female

Duration of intubation ≥3 days

Severe disease (APACHE II, SAPS II score)

Large tube size

High cuff pressure

History of self-extubation/reintubation

Underlying DM, CKD, Liver disease

Postextubation Laryngeal Edema: Detection

Suction and clearing airway

Switch ventilator to VCV mode Set tidal volume to be inspired (Vti)

Deflate ET tube cuff

Record tidal volume of expiration (Vte) 5-10 breaths to calculate mean values

Vti - Vte >110 mL

associated with adequate patency of the airway

(Specificity 99%)

Postextubation Laryngeal Edema: Management

All intubated patients

At risk: • Female • Longer duration of intubation • High APACHE II, SAPS II score • Large tube size • High cuff pressure • History of self-extubation • Negative cuff leak test

Not at risk

Consider: • Methylprednisolone 20 mg q 4 h 3-4

doses; at least 12 hr prior to extubation attempt

• Place airway exchanger catheter

Extubation with close observation

Consider discharge

Consider: • Prednisolone 0.5 mg/kg • Epinephrine 1 mg in NSS 5 mL NB • Helium 40% + O2 60% inhalation

PES • Re-intubation • Continue

steroids

No improvement in 1 hr

No symptom in 1 hr

Thank You