DISCONTINUATION OF DISCONTINUATION OF VENTILATORY SUPPORTVENTILATORY SUPPORT

Prof. Mehdi Hasan MumtazProf. Mehdi Hasan Mumtaz

DISCONTINUATION OF DISCONTINUATION OF VENTILATORY SUPPORTVENTILATORY SUPPORT

Weaning – Discontinuing mechanical ventilation.

Strict Sense – Weaning refers to a slow decrease in the amount of ventilator support with the patient gradually assuming a greater proportion of overall ventilation.

PATHOPHYSIOLOGICAL DETERMINANTS

A. Adequacy of pulmonary gas exchange.

B. Performance of the respiratory muscle pump.

C. Psychological factors.

ADEQUACY OF PULMONARY GAS EXCHNAGE

Hypoventilation.

Impaired Pulmonary Gas Exchange.

O2 Content of Venous Blood.

RESPIRATORY MUSCLE PERFORMANCE

a. Neuromuscular capacity. Respiratory centre output.– Phrenic nerve dysfunction. Respiratory muscle stregth/endurance.

Hyperinflation. Chest wall motion abnormaliteis. O2 supply. Malnutrition. Respiratory acidosis. Metabolic abnormalities. Endocrinopathy. Drug induced abnormalities. Disease muscle atrophy. Respiratory muscle fatigue.

RESPIRATORY MUSCLE PERFORMANCE

B. Respiratory Muscle Pump Load.

Ventilatory Requirements.

CO2 Production.

Dead Space Ventilation.

Inappropriately Respiratory Drive.

Work of Breathing.

RESPIRATORY N/MUSCULAR CAPACITY

Respiratory Centre Output.

– Respiratory acidosis.

– Indices of drive.

Airway occlusion pressure at0.1sec.

Mean inspirtory flow (Po.1 VT/T1.

– CO2 recruitment threshold.

PHREMIC NERVE FUNCTION

Coronary Bypass Operation.

Hypothermic injury. Inadvertent sectioning. Stretching & compression of nerve. BF To vasavasorum of nerve

RESPIRATORY MUSCLE FUNCTION“Hyperinflation”

Adverse Effects Respiratory muscles operate at

unfavrourable position of their length – tension curve.

Flattening of diaphragm radius. Efficacy due to medial & horizontal

orientation of fibres. Inwardly directed elastic recoil of chest

wall – added elastic load.

ABNORMALITIES IN CHEST WALL MOTION

Asynchrony

Paradox

In Energy Cost.

O2 SUPPLY

CO.

Hypoxaemia. O2 content

Anaemia O2 extraction – Sepsis. LVEJ.

ACUTE RESPIRATORY ACIDOSIS

Contractibility

Endurance Time

METABOLIC ABNORMALITIES

Hypokalaemia.

Hypophosphataemia.

Hypercalcaemia

Hypomagnisaemia.

ENDOCINE DISTURBANCE

Hyperthyroidism.

Hypothyroidism.

Corticosteroid therapy.

RSP MUSCLE PUMP LOAD

Ventilatory Requirements. CO2 production. VD ventilation.– Elevated respiratory drive.

Drive – Hypo ventilation. Drive – Fatigue.

– VD/VT >0.6 significant. Cimpliance. Resistance.

Work of breathing

WORK OF BREATHING

(Determinant of Weaning Outcome) Compliance. Resistance. O2 Cost of Breathing.

Total O2 consumption Total O2 consumptionSpontaneous breathing on mechanical ventilation

Normal <5% of total body O2 consumptionWeaning >50%.

PSYCHOLOGICAL FACTORS

Cmv (dependence).

– Insecurity.

– Anxiety.

– Fear.

– Agony.

– Panic

PREDICTING WEANING OUTCOME

“objective measurements”

“predictive indices” Why? Avoid unnecessary prolongation. Identify fail trial. Prevent premature weaning. Suggest alterations in managements.

PREDICTIVE VARIABLES.

1. Gas Exchange.

PaO2

a. PaO2>60(FIO2<35)= ----------

PAO2

b. P(A-a)O2 < 350.

c. PaO2 / FIO2 > 200.

d. PaO2/PAO2 > .97.

PREDICTIVE VARIABLES.

2. Ventilation Pumpa. VC>10-15ml/kg.

b. Maximum inspiratory Pressure < -30cmH2O.

c. MV < 10<.

d. MV < twice.

e. P0.1.

f. f/VT.

PREDICTIVE VARIABLES

CROP Index.

Integrative Index.

AIRWAY OCCLUSION PRESSURE

P 0.1

RAPID SHALLOW BREATHING

(F/VT Ratio= Breaths/min/L)

Attractive features.– Easy to measure.– Independent of effort.– Accurate.– Rounded off value (100)

RIB CAGE – ABDOMINAL MOTION

“Cohen et al”

MCA Maximum Compartmental Amplitude -------- = -----------------------------------------------

VT Tidal volume

Integrative Indices

INTEGRATIVE INDICES

Cdyn X P1 max X (PaO2/PAO2)

CROP Index = -------------------------------------------

Respiratory Rate

Integrative index = PT1 X (VE 40/VT sb)

PHYSICAL EXAMINATION

Careful physical examination. Elevated RR. Bed side VT. Clinical impression – Work of breathing.

– Nasal flaring.– Accessory muscle use.– Suprasternal recession.– Intercostal recession.– Paradoxical movement.

PHYSICAL EXAMINATION

Auscultation.

Dyspnoea Level.

Mental Status.

Blood Pressure.

Heart Rate.

Rhythm.

Cyanosis.

METHODS

“discontinuing mechanical ventilation”

Older – Spontaneous breathing trial.

1970s – Intermittent mandatory ventilation.

1980s – Pressure support ventilation.

Continuous positive airway support.

METHODS

Spontaneous Breathing Trials

“T-Piece Trial” 5min trial. FIO2 – 0.4. Duration. Expiratory limb 12” added. Flow twice x MV. Monitor – Blood gases.

CNS Output

Respiratory Drive

Pump

Capacity

Respiratory

Muscle Pump

Load on the

Pump

The Fatiguing

Process

Weaning & Ventilatory Failure

FACTORS THAT MAY IMPAIR RSP MUSCLE STRENGTH IN CRITICALLY ILL PATIENTS

Hypophosphataemia. Hypomagnisaemia. Hypocalcaemia. Hypoxia. Hypercarbia. Acidosis. Infection. Muscle atrophy. Malnutrition.

FACTORS ing THE LOAD ON RESPIRATORY MUSCLES IN PATIENTS

IN ICU

Bronchoconstriction. Left Ventricular Failure. Hyperinflation. Intrinsic +ve End Expiratory Pressure. Artificial Airways. Ventilator Circuits.

STEP-1ASSESSMENT PRIOR TO WEANING

Able to oxygenate with stable, low

inspired O2 concentrations?

Patient able to breath

spontaneously for 10min?

Reventilate patient with weaning mode

No

No

Yes

STEP-2INITIAL ASSESSMENT OF BREATHING

Rapid Shallow Breathing

Measure f/VT ratio

after 5min of breathing

on CPAP circuit

STEP-3INITIAL ASSESSMENT

f/VT < 80 Measure f/VT ratio

after 5min of breathing on CPAP circuit

f/VT >80 but <105

Reassess after 30 min

f/VT <80

f/VT <80

Continue spontaneous breathing with CPAP

Reassess after 30 min

f/VT <80

Extubate after trial of T-piece breathing-9

Yes

Yes

No

STEP-4FOLLOWING A WEANING TRIAL

Reventilate patient with weaning mode

Is the patient awake?

Volume cycled SIMV

Inspiratory Pressure Support

Yes

No

STEP-5CONSCIOUS LEVEL

Patient awake & orientated?

Is Patient triggering ventilator?

Is Patient overventilated?

Check PaCO2/ABG’s

Adjust IPPV to Normocapnia

Is Patient triggering ventilator?

Continue IPPV until conscious level No

STEP-6ASSESSMENT OF RESPIRATORY

MUSCLE STRENGTH (PI max)

Measure Inspiratory

Mouth Pressure

PI Max < -20cmH2O

PI Max < -20cmH2O

STEP-7LOAD APPLIED TO THE

RESPIRATORY MUSCLES

Measure Applied Load

Wean Cautiously Recognising Likely Failure

Cdyn < 50mls/cm H2ONo