1. DISCONTINUATION OF VENTILATORY SUPPORT Prof. Mehdi Hasan Mumtaz

2. DISCONTINUATION OF VENTILATORY 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.

3. PATHOPHYSIOLOGICAL DETERMINANTS A. Adequacy of pulmonary gas exchange. B. Performance of the respiratory muscle pump. C. Psychological factors.

4. ADEQUACY OF PULMONARY GAS EXCHNAGE  Hypoventilation.  Impaired Pulmonary Gas Exchange.   O2 Content of Venous Blood.

5. RESPIRATORY MUSCLE PERFORMANCE a.  Neuromuscular capacity. –  Respiratory centre output. –Phrenic nerve dysfunction. –  Respiratory muscle stregth/endurance. u Hyperinflation. u Chest wall motion abnormaliteis. u  O2 supply. u Malnutrition. u Respiratory acidosis. u Metabolic abnormalities. u Endocrinopathy. u Drug induced abnormalities. u Disease muscle atrophy. u Respiratory muscle fatigue.

6. RESPIRATORY MUSCLE PERFORMANCE B.  Respiratory Muscle Pump Load. –  Ventilatory Requirements. u  CO2 Production. u  Dead Space Ventilation. u Inappropriately  Respiratory Drive. –  Work of Breathing.

7.  RESPIRATORY N/MUSCULAR CAPACITY   Respiratory Centre Output. –Respiratory acidosis. –Indices of drive. u Airway occlusion pressure at0.1sec. u Mean inspirtory flow (Po.1 V T /T1. –CO2 recruitment threshold.

8. PHREMIC NERVE FUNCTION Coronary Bypass Operation.  Hypothermic injury.  Inadvertent sectioning.  Stretching & compression of nerve.  BF To vasavasorum of nerve

9. 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.

10. ABNORMALITIES IN CHEST WALL MOTION Asynchrony Paradox   In Energy Cost.

11.  O 2 SUPPLY   CO. Hypoxaemia.   O2 content Anaemia   O2 extraction – Sepsis.   LVEJ.

12. ACUTE RESPIRATORY ACIDOSIS  Contractibility  Endurance Time

13. METABOLIC ABNORMALITIES  Hypokalaemia.  Hypophosphataemia.  Hypercalcaemia  Hypomagnisaemia.

14. ENDOCINE DISTURBANCE  Hyperthyroidism.  Hypothyroidism.  Corticosteroid therapy.

15.  RSP MUSCLE PUMP LOAD   Ventilatory Requirements. –  CO2 production. –  VD ventilation. –Elevated respiratory drive. u  Drive – Hypo ventilation. u  Drive – Fatigue. –VD/VT >0.6 significant. –  Cimpliance. –  Resistance.  Work of breathing

16. WORK OF BREATHING (Determinant of Weaning Outcome)   Compliance.   Resistance.  O2 Cost of Breathing. Total O2 consumption  Total O2 consumption Spontaneous breathingon mechanical ventilation Normal <5% of total body O2 consumption Weaning >50%.

17. PSYCHOLOGICAL FACTORS  Cmv (dependence). –Insecurity. –Anxiety. –Fear. –Agony. –Panic

18. PREDICTING WEANING OUTCOME “objective measurements” “predictive indices”  Why?  Avoid unnecessary prolongation.  Identify fail trial.  Prevent premature weaning.  Suggest alterations in managements.

19. PREDICTIVE VARIABLES. 1. Gas Exchange. PaO 2 a. PaO 2 >60(FIO 2 <35)= ---------- PAO 2 b. P(A-a)O 2 < 350. c. PaO2 / FIO2 > 200. d. PaO2 / PAO2 >.97.

20. PREDICTIVE VARIABLES. 2. Ventilation Pump a. VC>10-15ml/kg. b. Maximum inspiratory Pressure < -30cmH 2 O. c. MV < 10<. d. MV < twice. e.P0.1. f. f / VT.

21. PREDICTIVE VARIABLES CROP Index. Integrative Index.

22. AIRWAY OCCLUSION PRESSURE P 0.1

23. RAPID SHALLOW BREATHING (F/VT Ratio= Breaths/min/L)  Attractive features. –Easy to measure. –Independent of effort. –Accurate. –Rounded off value (100)

24. RIB CAGE – ABDOMINAL MOTION “Cohen et al” MCAMaximum Compartmental Amplitude --------=----------------------------------------------- V T Tidal volume Integrative Indices

25. INTEGRATIVE INDICES C dyn X P 1 max X ( PaO2 / PAO2 ) CROP Index = ------------------------------------------- Respiratory Rate Integrative index = P T1 X (V E 40 / VT sb)

26. 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.

27. PHYSICAL EXAMINATION  Auscultation.  Dyspnoea Level.  Mental Status.  Blood Pressure.  Heart Rate.  Rhythm.  Cyanosis.

28. METHODS “discontinuing mechanical ventilation”  Older – Spontaneous breathing trial.  1970s – Intermittent mandatory ventilation.  1980s – Pressure support ventilation.  Continuous positive airway support.

29. METHODS Spontaneous Breathing Trials “T-Piece Trial”  5min trial.  FIO2 – 0.4.   Duration.  Expiratory limb 12” added.  Flow twice x MV.  Monitor – Blood gases.

30. CNS Output Respiratory Drive Pump Capacity Respiratory Muscle Pump Load on the Pump The Fatiguing Process Weaning & Ventilatory Failure

31. FACTORS THAT MAY IMPAIR RSP MUSCLE STRENGTH IN CRITICALLY ILL PATIENTS  Hypophosphataemia.  Hypomagnisaemia.  Hypocalcaemia.  Hypoxia.  Hypercarbia.  Acidosis.  Infection.  Muscle atrophy.  Malnutrition.

32. 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.

33. STEP-1 ASSESSMENT 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 Yes

34. STEP-2 INITIAL ASSESSMENT OF BREATHING Rapid Shallow Breathing Measure f/VT ratio after 5min of breathing on CPAP circuit

35. STEP-3 INITIAL 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 Continue spontaneous breathing with CPAP Reassess after 30 min f/VT <80 Extubate after trial of T-piece breathing-9 Yes No

36. STEP-4 FOLLOWING A WEANING TRIAL Reventilate patient with weaning mode Is the patient awake? Volume cycled SIMV Inspiratory Pressure Support Yes No

37. STEP-5 CONSCIOUS 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

38. STEP-6 ASSESSMENT OF RESPIRATORY MUSCLE STRENGTH (PI max) Measure Inspiratory Mouth Pressure PI Max < -20cmH 2 O

39. STEP-7 LOAD APPLIED TO THE RESPIRATORY MUSCLES Measure Applied Load Wean Cautiously Recognising Likely Failure Cdyn < 50mls/cm H 2 O No