Weaning from mechanical ventilation.pptx

weaning criteria from mechanical ventilation

1. wEaning from mechanical ventilation By : Dr Nalluru Likhitha Moderator : Dr Rajendra Prasad,Assistant Professor NRIIMS Sanghivalasa

2. Weaning vs extubation Weaning is act of decreasing oxygenation and ventilatory support via the mechanical ventilator and allowing patient to assume greater control of breathing. Extubation is liberation from mechanical ventilation and involves discontinuation of respiratory support and removal of endotracheal tube 2

3. definitions Weaning : process of withdrawing mechanical ventilatory support . Weaning success : effective spontaneous breathing without any mechanical assistance for 24 hrs or more. Weaning failure : when patient is returned to mechanical ventilation after any lenghth of weaning trail. Weaning in progress :intermediate category for patients who are extubated but continue to receive ventilatory support by NIV. 3

4. weaning criteria Weaning criteria are used to evaluate the readiness of a patient for a weaning trail and likelihood of weaning success. Clinical criteria Ventilatory criteria Oxygenation criteria Pulmonary reserve and measurements 4

5. Clinical criteria 5 Resolution of acute phase of disease. Adequate cough Absence of excessive secretions Cardiovascular and hemodynamic stability.

6. Ventilatory criteria Spontaneous breathing trail PaCo2 Vital capacity Spontaneous Vt Spontaneous f f/Vt Minute ventilation Tolerates 20-30min <50mmHg with normal Ph >10ml/kg >5ml/kg <35/min <100breaths/min/L <10L with satisfactory ABG 6

7. ventilatory criteria PaCO2 : weaning should only be attempted if PaCO2 is 35-45mmHg . However acceptable PaCO2 may be slightly higher in COPD depending on patient baseline values prior to ventilation. Vital capacity and SpontaneousTidal volume : 10ml/kg and 5ml/kg respectively. If the patient is on full ventilatory support , it is advisable to allow patient to breathe spontaneously for 3min prior to measurement. For vital capacity measurement active patient effort and coordination is important. 7

8. ventilatory criteria Spontaneous frequency : Should be less than 35/min while Paco2 <50mmHg >35breaths is assosciated with rapid shallow breathing which increases deadspace and highly ineffective for gaseous exchange during spontaneous breathing. The patient should be allowed to breathe sponatenously for 3min to measure spontaneous frequency that allows patient to normalize breathing pattern and thus more reflective of patient response to respirator requirement. 8

9. ventilatory criteria f/Vt or Rapid shallow breathing index : It has been used to evaluate the effectiveness of spontaneous breathing pattern. Calculated by sponatenous breaths /min(f) by average sponatenous Vt in litres . When f/Vt >100breaths/min/L it correlates with weaning failure. Absence of rapid shallow breathing i.e f/Vt <100 is predictor for weaning success. 9

10. ventilatory criteria Procedure to Obtain f/Vt ratio Allow patient at least 3min to stabilise the sponatenous breathing pattern (ventilator frequency should be off if tolerated PSV should not beused ) Measure expired volume and respiratory frequency for one min. Divide Minute volume by frequency to obtain average tidal volume in litre. Divide f by Vt to obtain f/Vt index(breaths/min/L) 10

11. ventilatory criteria Minute ventilation: Should be less than 10L/min for successful weaning outcome. High MV implies the work of spontaneous breathing is more to normalize PaCO2. Excessive MV is due to increased carbon dioxide production secondary to increased metabolic rate , increased alveolar dead space or metabolic acidosis. 11 Increased CO2 production Increased alveolar dead space Burns Elevated body temperature Overfeeding with carbohydrate supplements. Occurs if alveolar ventilation exceeds alveolar perfusion Due to Alveoli overventilated as in hyperinflation of lungs(emphysema) Pulmonary circulation is underperfused (pulmonary embolism,decreased cardiac output)

12. OXYGENATION criteria PaO2 without PEEP PaO2 with PEEP(<8cmH20) SaO2 PaO2/FiO2 Qs/Qt P(A-a)O2 >60mmHg at FiO2 upto 0.4 >100mmHg at FiO2 upto 0.4 >90% at FiO2 upto 0.4 >150mmHg <20% <350Hg at FiO2 of 1.0 12

13. oxygenation criteria PaO2 and SaO2: A PaO2 of 60mmHg corresponds to an SaO2 of about 90%. It is essential to note that in patients with anemia or increased level of dysfunctional hemoglobins , the PaO2 and SpO2 do not reflect true oxygenation status of patient. In those instances the arterial oxygen content (CaO2) and arterial oxygen saturation (SaO2) should be measured. 13

14. oxygenation criteria PaO2/FiO2: The arterial oxygen tension to inspired oxygen concentration is method for estimating the degree of intrapulmonary shunt. P/F ratio >150mmHg suggests acceptable physiological shunt and compatible to successful weaning. 14

15. QS/QT RATIO Physiological shunt to total perfusion ratio is used to estimate how much pulmonary perfusion is wasted. Shunted pulmonary perfusion cannot take part in gas exchange due to mismatch of ventilation.( eg:atelectasis ) Qs/Qt = (CcO2-CaO2)/(CcO2-CvO2) 15 Qs/Qt : shunt fraction in % CcO2:end capillary O2 content CaO2:arterial O2 content CvO2:mixed venous O2 content

16. QS/QT RATIO In clinical setting , a calculated physiological shunt of 10% or less is normal , shunt of 10-20% indicated mild intrapulmonary shunt , shunt of 20-30% shows abnormal shunt . Greater than 25% shunt reflects critical and severe shunt. Since shunt in mechanical ventilation is usually intrapulmonary origin(inadequate ventilation in relation to pulmonary perfusion) weaning failure becomes likely when spontaneous ventilation cannot keepup with pulmonary perfusion. For this reason,significant and severe intrapulmonary shunt (Qs/Qt) should be corrected before any weaning attempt. ABG gives value of shunt fraction indirectly –(venous admixture) 16

17. P(A- a ) O2 The alveolar-arterial oxygen tension gradient (P(A-a)O2) is used to estimate the degree of hypoxemia and degree of intrapulmonary shunt. This gradient is directly related to the degree of hypoxemia or shunt. On room air the P(A-a)O2 should be less than 4mmHg for every 10 years age . On 100% oxygen , every 50mmHg difference in P(A-a)O2 approximates 2% intrapulmonary shunt . 17

18. P(A- a ) O2 In mechanical ventilation , P(A-a)O2 of less than 350mmHg while on 100% oxygen suggests a likehood of weaning success. P(A-a) O2 of 350mmHg while on 100% oxygen approximates 14% shunt and values of greater than 350mmHg may hinder the weaning process. 18

19. Pulmonary reserve and measurements Vital capacity Maximum inspiratory pressure Static compliance Airway resistance Vd /Vt >10ml/kg >-30cmH2O >30ml/cm H20 Stable or improving <60% while intubated. 19

20. vital capacity The vital capacity reflects patient’s pulmonary reserve as it includes inspiratory reserve volume, tidal volume and expiratory reserve volume. Vital capacity measures maximum amount of lung volume that patient can exhale following maximal inspiration. Patient is instructed to breathe in as deeply as possible and exhale all air into spirometer. For successful weaning patient VC to be greater than 10ml/kg. 20

21. maximum inspiratory pressure Maximum inspiratory pressure(negative inspiratory force) is amount of negative pressure that patient can generate in 20 sec while inspiring against an occluded measuring device(negative pressure manometer) If patient is alert ,explain the procedure and encourage the patient to inspire as forcibly as possible. In some mechanically ventilated patients , a waiting period without assisted ventilation may be needed to induce mild hypoxia and hypercapnia for best inspiratory efforts. The MIP is considered a measure of ventilatory muscle strength and weaning will be likely successful if patient can generate MIP of atleast -30cmH2O 21

22. STATIC COMPLIANCE C ST = corrected tidal volume / ( Pplat – PEEP) The lower the compliance the greater the work of breathing will be. The minimal compliance value consistent with successful weaning is 30ml/cmH2O or greater 22

23. airway resistance Can be estimated by dividing the difference between peak inspiratory pressure and the plateau pressure by constant inspiratory flow . Normal range is 0.6-2.4cm H2O/L/sec. Value is higher in ventilatory patients because of assosciated pathological conditions ( eg bronchospasm) and tubing resistance (ET tube,ventilatory circuit) Since retained secretions and bronchospasm contribute to airway resistance , patient airway and lungs to be sunctioned and bronchodilators may be helpful. 23

24. Vd /Vt ratio Dead space to tidal volume ratio. Indicates amount of each breath that is being wasted nor perfused by pulmonary circulation.. Can be calculated as partial pressure of carbon dioxide minus the mean arterial pressure of carbon dioxide in the exhaled air divided by arterial blood carbon dioxide tension. VD/VT = (PaCO2- PeCO2)/PaCO2 Should be less than 60% for successful weaning. 24

25. Combined weaning indices RSBI Simplified weaning index CROP index <100breaths/L/min <9/min >13ml/breath/min 25

26. Simplified weaning index SWI= Fmv (PIP-PEEP)/MIP * Paco2/40 Where Fmv is ventilator frequency PIP is peak inspiratory pressure MIP is maximal inspiratory pressure PaCo2 is arterial co2 tension while on ventilator SWI evaluates patient ventilatory endurance and efficiency of gas exchange SWI <9/min suggests 93% chance of weaning success SWI >11/min suggests 95% chance of weaning failure 26

27. CROP INDEX Compliance rate oxygenation and pressure index. CROP index = Cdyn * MIP * PaO2/PAO2 / f Cdyn is dynamic compliance MIP is maximum inspiratory pressure PaO2 is arterial oxygen tension PAO2 is alveolar oxygen tension F is spontaneous respiratory rate per min. Evaluates patient gas exchange and balance between respiratory demand and respiratory neuromuscular reserve CROP index >13ml/breath/min indicates increased likelihood of weaning. 27

28. Weaning procedure 28 Procedure Steps SPONTANEOUS BREATHING TRAIL (SBT) May use t tube , CPAP,or automatic tube compensation Let patient breathe spontaneously for upto 30min May use low level pressure support ( upto 8cmH2O for adults and 10cmH2O for pediatrics ) to augment spontaneous breathing Assess patient If patient tolerates , consider extubation if blood gases and vital signs are satisfactory

29. Criteria to assess readiness for SBT 29 CRITERIA VALUE Reversal of respiratory failure Adequate oxygenation Hemodynamic stability Respiratory drive evidence of some reversal of underlying cause. PaO2/FiO2 >150 PEEP <5-8cmH20 FiO2<40%-50% pH>7.25 Absence of MI Absnece of hypotension Minimal vasopressrors Able to inititiate respiratory effort

30. procedure Adjust ventilatory settings PS 5cm H20 with PEEP 5cm H20 CPAP 5cm H2O t piece trail 30 30min Perform RSBI RSBI <80 RSBI>100 Proceed with weaning Maintain PS and PEEP for 30-60min If apnea occurs return to previous ventilatory settings If RSBI <80 after 30-60min then extubate Return to previous ventilatory settings

31. T piece trail May use new aerosol setup or existing ventilator circuit. Let patient breathe sponataneously for upto 5mins every 30-180min Retrun patient to mechanical ventilation after 5min Increase duration of spontaneous breathing gradually for upto 2 hrs If patient tolerates trail with good ABG and stable vital signs , extubate patient. 31

32. Sbt trail 32 Clinical criteria and thresholds of SBT failure PaO2<60mmHg on FiO2>50% SaO2<90% on FiO2>50% PaCO2>50mmHg or increase in PaCO2 >8mmHg from baseline Ph<7.32 f/Vt>100breaths/L/min F>35breaths/min or increase in >50% from baseline HR >140 or >20% increase from baseline Systolic BP >180mmHg or >20% increase from baseline Systolic BP<90mmHg Presence of cardiac arrythmias Clinical – agitation,anxiety,diaphoresis,cyanosis and increased work of breathing.

33. Weaning procedure 33 Procedure Steps SIMV Not recommended as a stand alone mode for weaning. Reduce SIMV frequency by 1-3 breaths /min Monitor SpO2 obtain ABG Reduce SIMV frequency further until frequency of 2-4/min is reached. If patient tolerates consider extubation when blood gases and vital signs are satisfactory.

34. Weaning procedure 34 Procedure Steps PSV PSV may be used in conjuction with SBT or SIMV. Start PSV at a level of 5-15cm H2O ( upto 40cm H2O) to augment spontaneous Vt until desired Vt (10-15ml/kg) or spontaneous frequency <25/min is reached. Decrease PS level by 3-6cm H2O intervals until a level close to 5cm H2O is reached. If patient tolerates consider extubation when blood gases and vital signs are satisfactory .

35. Weaning protocol 35 Step Criteria Results 1. Does the patient show Evidence of some reversal of underlying cause Presence of inspiratory effort Hemodynamic stability Adequate oxygenation and acid base status Brief eye contact to voice command If YES to all five questions proceed to step 2. If NO to any one question postpone weaning until next day 2. Perform and measure RSBI with mandatory freq turned off and PS<8,PEEP<5, measurements taken following >3min of spontaneous breathing. If RSBI <100breaths/L/min If YES proceed to step 3 If NO postpone weaning until next day 3. Can patient tolerate sponatenous breathing trail upto 30min without termination criteria If YES proceed to ventilator discontinuation If NO repeat weaning until next day

36. Weaning failure 36 Indicators Examples Blood gases Increasing PaCO2(>50mmHg) Decreasing Ph(<7.30) Decreasing PaO2(60mmHg) Decreasing SpO2(<90%) Decreasing PaO2/FiO2<150mmHg Vital signs Changing blood pressures (20mmHg systolic or 10mmHg diastolic) Increasing heart rate (by 20/min or >110/min) Abnormal ECG(presence of arrythmias) Respiratory parameters Decresing Vt(250ml) Increasing f(>30/min) Increasing f/Vt(>100breaths/min/L) Decreasing MIP(<-20cmH2O) Decreasing static compliance (<30ml/cmH20) Increasing Vd /Vt (>60%)

37. Causes of weaning failure Weaning failure is generally related to A ) increase of airflow resistance B ) decrease of compliance C ) respiratory muscle fatigue 37

38. Increase of airflow resistance ET tubes have an effect of increase in work of breathing. An ET tube of size 8 has cross sectional area of 50mm2 which is slightly smaller than average cross sectional area of adult glottis(60mm2). To minimize the effects of artificial airway on airflow resistance ,ET tubes of size 8 or large used when appropriate to patien’s size. Strategies for decreasing airway resistance can be done by periodic monitoring of ET tube for kinking or obstructions by secretions, check of devices attached such as continuos suction catheter, HME and etCO2 probe. ET tube suctioning and use of bronchodilators has been ued to succerssfully decrease airflow resistance . 38

39. Decrease of compliance Abnormally low lung or thoracic compliance impair patient ability to maintain efficient gas exchange . Low expansion makes lung expansion difficult and contribute to respiratory muscle fatigue and weaning failure . 39

40. Decrease of compliance Clinical conditions that decrease compliance Type of compliance Clinical conditions Decrease static compliance Atelectasis ARDS Tension pneumothorax Obesity Retained secretions in lungs Decrease dynamic compliance Bronchospasm Kinking of ET tube Airway obstruction Retained secretions in airways 40

41. Respiratory muscle fatigue Respiratory work is product of transpulmonary pressure and tidal volume. TPP is increased in conditions og low compliance or high airway resistance leading to respiratory mucle fatigue and weaning failure. Prolonged full ventilatory support and muscle disuse lead to respiratory mucle dysfunction and diaphragmatic atrophy. MV induced oxidative stress is important contributor to MV induced proteolysis and contractile dysfunction. Other factors contributing to muscle weakness include inadequate oxygen delivery .insufficient nutrition or electrolyte imbalance ( hypokalemia,hypophosphatemia,hypocalcemia,hypomagnesemia ) Retraining of atrophied muscles may be accomplished by short T tube trails that imrove respiratory muscle strength. Pressure support ventilation may also be tried as it increases diaphragmatic endurance. 41

42. Terminal weaning It is defined as withdrawl of mechanical ventilation that results in death of a patient. While terminal weaning is considered , four concerns must be evaluated and discussed 1)patient’s informed request 2)Medical futility 3)Reduction of pain and suffering 4)Fear and distress 42

43. Cuff leak test It is used to test postextubation airway patency. The patient is disconnected from mechanical ventilator , cuff is deflated and ET tube is obstructed . A leak around cuff (peritubular leak) suggests airway caliber is adequate and extubation is likely. A leak of less than 110ml (average of three values of six consecutive breaths )indicates high risk of postextubation stridor. Treatment with steroids or racemic epinephrine may be indicated before extubation . 43

44. Sedation holiday Stopping the sedation infusion and allowing patient to awake. Restarted once patient becoming agitated or uncomftable . Should be done on daily basis. This strategy reduces duration of mechanical ventilation and length of ICU stay. 44

45. references Clinical application of Mechanical ventilation by David W Chang 4 edition. Marino’s ICU Book 4 edition. Weaning from mechanical ventilation by Jeremy lermitte . Article weaning from mechanical ventilation bt Chris Nickson ,March 2019. The Washington Manual of Critical Care 3 edition. 45

46. Thank you…..! 46