1. Mechanical VentilationPROBLEMS Patiparn Toomtong Department of Anesthesiology Siriraj Hospital Mahidol University

2. Although life-saving, IPPV may be associated with many complications, including: • Consequences of PPV • Aspects of volutrauma • Adverse effects of intubation and tracheostomy

3. Optimal Ventilatory Care Requires • Attention to minimizing adverse hemodynamic effects • Averting volutrauma • Effecting freedom from IPPV as early as possible

4. Common Scenarios • New development of hypotension • Acute respiratory distress (fighting) • Repeated sounding of High pressure alarm • Hypoxaemia • Blood from the endotracheal tube • Problem of diagnosing VAP

5. Barotrauma or Volutrauma • High Paw alone insufficient to cause alveolar rupture • Excessive alveolar volume the likely factor leading to alveolar rupture and air dissection • More frequent in younger age group • May be difficult to detect if small in CXR • “Stretch-induced” Acute lung injury

8. Patient-ventilator Synchrony Flow-targeted breath requires careful adjustment Constant flow of 40-60 lpm not always adequate Monitor: patient response, airway pressure/flow graphics Using decelerating flow pattern may be helpful

9. Patient-ventilator Synchrony • Pressure-targeted breath is better? • Rapid pressurisation of the airway with high initial gas flow • Match Ppl change quicker than flow pattern • Flow is continuously adjusted by the ventilator to maintain a constant airway pressure

10. Patient-ventilator Synchrony • Any problems from pressure breaths? • Max initial flow may not be optimal in all patients depending on drive • Adjustment of the rate of rise may be beneficial • Pressure of what? Proximal airway vs Ppl by muscular effort • So! Carinal or pleural triggering helpful • variable minute ventilation!

11. Weaning from Mechanical Ventilation

12. Definition of Weaning The transition process from total ventilatory support to spontaneous breathing. This period may take many forms ranging from abrupt withdrawal to gradual withdrawal from ventilatory support.

13. Weaning • Discontinuation of IPPV is achieved in most patients without difficulty • up to 20% of patients experience difficulty • requires more gradual process so that they can progressively assume spont. respiration • the cost of care, discontinue IPPV should proceed as soon as possible

14. Reversible reasons for prolonged mechanical ventilation • Inadequate respiratory drive • Inability of the lungs to carry out gas exchange effectively • Psychological dependency • Inspiratory fatigue

15. Weaning • Patients who fail attempts at weaning constitute a unique problem in critical care • It is necessary to understand the mechanisms of ventilatory failure in order to address weaning in this population

16. Why patients are unable to sustain spontaneous breathing • Concept of Load exceeding Capacity to breathe • Load on respiratory system • Capacity of respiratory system

17. Balance Load vs Capacity • Most patients fail the transition from ventilator support to sustain spont. breathing because of failure of the respiratory muscle pump • They typically have a resp muscle load the exceeds the resp neuromuscular capacity

18. Load on RespiratorySystem • Need for increase ventilation increased carbon dioxide production increased dead space ventilation increased respiratory drive • Increased work of breathing

19. Causes of Inspiratory respiratory muscle fatigue • Nutrition and metabolic deficiencies: K, Mg, Ca, Phosphate and thyroid hormone • Corticosteroids • Chronic renal failure • Systemic disceases; protein synthesis, degradation, glycogen stores • Hypoxemia and hypercapnia

20. Capacity of respiratory system • Central drive to breathe • Transmission of CNS signal via Phrenic nerve • Impairment of resp muscles to generate effective pressure gradients • Impairment of normal muscle force generation

21. Evidence based medicine • When to start weaning process? • Decision making, any guideline? How long it will take?

22. When to begin the weaning process? • Numerous trials performed to develop criteria for success weaning, however, not useful to predict when to begin the weaning • Physicians must rely on clinical judgement • Consider when the reason for IPPV is stabilised and the patient is improving and haemodynamically stable • Daily screening may reduce the duration of MV and ICU cost

23. Evidence-based medicine Recommendation 1. Search for all the causes that may contribute to ventilator dependence in all patients with longer than 24 h of MV support, particularly who has fail attempts. Reversing all possible causes should be an integral part of discontinuation process.

24. Daily Screening • Resolution/improvement of patient’s underlying problem • Adequate gas exchange (SaO2 > 90%, PaO2/FiO2 >200) • Respiratory rate < 35/ min • Absence of fever, temperature < 38C • Adequate haemoglobin concentration, > 8-10 g/dl • Stable cardiovascular function: heart rate < 140/min, 180>SBP>90

25. Daily Screening (cont.) • Indices suggesting an adequate capacity of the ventilatory pump: respiratory rate of less than 30/ min, Maximum inspiratory pressure < -20 to -30 cmH2O • Correction of metabolic and electrolyte disorders • Normal state of consciousness

26. Evidence-based medicine Recommendation 2. Patients receiving MV for respiratory failure should undergo a formal assessment of discontinuation potential if the criteria are satisfied. Reversal of cause, adequate oxygenation, haemodynamic stability, capability to initiate respiratory effort. The decision must be individualized.

28. Predictions of the outcome of weaning Variables used to predict weaning success: Gas exchange • PaO2 of > 60 mmHg with FiO2 of < 0.35 • A-a PaO2 gradient of < 350 mmHg • PaO2/FiO2 ratio of > 200

29. Weaningsuccessprediction Ventilation Pump • Vital capacity > 10- 15 ml/kg BW • Maximal negative insp pressure < -30 cmH2O • Minute ventilation < 10 l/min • Maximal voluntary ventilation more than twice resting MV

30. Weaningsuccessprediction • Tidal volume > 325 ml • Tidal volume/BW > 4 ml/kg • Dynamic Compliance > 22 ml/cmH2O • Static compliance > 33 ml/cmH2O • Rapid shallow breathing index < 105 breaths/min/L

32. Clinical observation ofthe Respiratory Muscles • Initially thought to be reliable in predicting subsequent weaning failure • from inductive plethysmographic studies not necessary • a substantial increase in load will effect on the rate, depth, and pattern of breathing • a manifestation of fatigue

33. Both respiratory rate and minute ventilation initially increase, may be followed by a paradoxical inward motion of the anterior abdominal wall during inspiration which indicates the insufficientdiaphragmatic contraction to descend and move the abdominal content downward

34. Cyclic change in breathing patterns with either a chest wall motion or a predominantly abdominal wall motion are another indicator, called respiratory alternans

35. Fatigue Criteria Duration of weaning prior to initial episode of fatigue (days)2.5 (0.25–7.5) Fatigue criteria Hypoxia (PaO2 < 60, SpO2 <90%) 11 (31%) Hypercarbia (PaCO2 > 50 mmHg) 9 (25%) Pulse rate > 120/min 17 (47%) SBP > 180 or < 90 mmHg 2 (6%) Respiratory rate > 30/min 33 (92%) Clinical respiratory distress 27 (75%)

36. Parameters that assess airway patency and protection 1. Maximal expiratory pressure 2. Peak expiratory flow rate 3. Cough strength 4. Secretion volume 5. Suctioning frequency 6. Cuff leak test 7. Neurological function (GCS)

37. Evidence-based medicine Recommendation 3.The removal of the artificial airway from a patient who has successfully been discontinued from ventilatory support should be based on assessment of airway patency and the ability of the patient to protect the airway.

38. Methods of Weaning • Abrupt Discontinuation • T- tube trials • SIMV • Pressure support

39. Spontaneous breathing protocol • Communicate with patient, weaning is about to begin, allow pt to express fear whenever possible • Obtain baseline value and monitoring clinical parameters; vital signs, subj distress, gas exchange, arrhythmia • Ensure a calm atmosphere, avoid sedation • Sit the patient upright in bed or chair • Fit T-tube with adequate flow, observe for 2 hr

40. For How long I will have to monitor the weaning process with SBT in my patient?

41. Evidence-based medicine Recommendation 4. Formal assessments should be done during SBT rather than receiving substantial support. The criteria to assess patient tolerance during SBTs are respiratory pattern, gas exchange, hamodynamics stability and patient comfort. The tolerance of SBTs lasting 30 to 120 minutes should prompt for permanent ventilator discontinuation.

43. SIMV Protocol • Switch to SIMV from assist mode or decrease RR • Begin with RR 8/min decrease SIMV rate by two breaths per hour unless clinical deterioration • if assume to fail, increase SIMV rate to previous level, until stable • if stable at least 1 hour of rate 0/ min extubate • in patient without respiratory disorders, decrease rate with half an hour interval, 2 hr extubate

44. Pressure Support Protocol • Switch to PSV or decrease PS • Begin PSV at 25 cmH2O, decrease PS by 2-4 cmH2O every hour unless clinical deterioration appears, adjust pressure until stable, if stable of PSV = 0 for at least one hour fit with T-tube or CPAP and then observe • In patient without resp problems, decrease pressure at half an hour interval, if able to tolerate PSV = 0 for 2 hours, can be extubated

47. Failed to Wean • Associated with intrinsic lung disease • Associated with prolonged critical illness • Incidence approximately 20% • Increased risk in patient with longer duration of mechanical ventilation • Increased risk of complications, mortality

49. Evidence-based medicine Recommendation 5. Patients receiving MV who fail an SBT should have the cause determined. Once causes are corrected, and if the patient still meets the criteria of DS, subsequent SBTs should be performed every 24 hours.

50. Evidence-based medicine Recommendation 6. Patients receiving MV for respiratory failure who fail an SBT should receive a stable, nonfatiguing, comfortableform of ventilatory support.