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DISCONTINUATION OF VENTILATORY SUPPORT

DISCONTINUATION OF VENTILATORY SUPPORT. Prof. Mehdi Hasan Mumtaz. DISCONTINUATION OF VENTILATORY SUPPORT. Weaning – Discontinuing mechanical ventilation.

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DISCONTINUATION OF VENTILATORY SUPPORT

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  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 • Adequacy of pulmonary gas exchange. • Performance of the respiratory muscle pump. • 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. • Hyperinflation. • Chest wall motion abnormaliteis. • O2 supply. • Malnutrition. • Respiratory acidosis. • Metabolic abnormalities. • Endocrinopathy. • Drug induced abnormalities. • Disease muscle atrophy. • Respiratory muscle fatigue.

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

  7. 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.

  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. O2 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. • Drive – Hypo ventilation. • 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 breathing on 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. PaO2 a. PaO2>60(FIO2<35)= ---------- PAO2 b. P(A-a)O2 < 350. c. PaO2 / FIO2 > 200. d. PaO2/PAO2 > .97.

  20. PREDICTIVE VARIABLES. 2. Ventilation Pump a. VC>10-15ml/kg. b. Maximum inspiratory Pressure < -30cmH2O. c. MV < 10<. d. MV < twice. • P0.1. • 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” MCA Maximum Compartmental Amplitude -------- = ----------------------------------------------- VT Tidal volume Integrative Indices

  25. INTEGRATIVE INDICES Cdyn X P1 max X (PaO2/PAO2) CROP Index = ------------------------------------------- Respiratory Rate Integrative index = PT1 X (VE40/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-1ASSESSMENT PRIOR TO WEANING No Able to oxygenate with stable, low inspired O2 concentrations? Reventilate patient with weaning mode Yes Patient able to breath spontaneously for 10min? No

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

  35. STEP-3INITIAL ASSESSMENTf/VT < 80 Measure f/VT ratio after 5min of breathing on CPAP circuit f/VT <80 Continue spontaneous breathing with CPAP f/VT >80 but <105 Reassess after 30 min Reassess after 30 min No f/VT <80 Yes Yes Extubate after trial of T-piece breathing-9 f/VT <80

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

  37. 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? No Continue IPPV until conscious level 

  38. Measure Inspiratory Mouth Pressure STEP-6ASSESSMENT OF RESPIRATORY MUSCLE STRENGTH (PI max) PI Max < -20cmH2O PI Max < -20cmH2O

  39. STEP-7LOAD APPLIED TO THE RESPIRATORY MUSCLES Measure Applied Load Cdyn < 50mls/cm H2O No Wean Cautiously Recognising Likely Failure

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