Initiation of mechanical ventilation and weaning

MODES OF VENTILATION

1. INITIATION OF MECHANICAL VENTILATION AND WEANING MODERATOR: DR. AHSAN SIDDIQUI BY: DR. PRIYAL GUPTA DR. ABHISHEK PRAKASH DR. SHIV SHANKAR YADAV

2. Mechanical Ventilation is ventilation of the lungs by artificial means usually by a ventilator. PURPOSES To improve gas exchange To relieve respiratory distress To improve pulmonary mechanics To permit lung and airway healing To avoid complications by protecting lung and airway

3. INDICATIONS M echanical ventilation is indicated when the paient cannot maintain spontaneous ventilation to provide adequate oxygenation or carbon dioxide removal INDICATION EXAMPLES 1. Acute ventilatory failure Apnoea or bradypnoea Acute lung injury (ALI), ARDS pH<7.3, PaCO2>50mmHg 2. Severe hypoxemia PaO2<40mmHg, SaO2<75% P/F ratio≤300mmHg for ALI, ≤200mmHg for ARDS 3. Impending ventilatory failure Progressive acidosis and hypoventilation to pH<7.3, PaCO2>50mmHg Spontaneous frequency>30/min 4. Prophylactic ventilatory support Post anaesthesia recovery Muscle fatigue Neuromuscular disease

4. ACUTE VENTILATORY FAILURE Sudden increase in PaCO2 to greater than 50mmHg with an accompanying respiratory acidosis (pH<7.30). In the COPD patient, mechanical ventilation is indicated by an acute increase in PaCO2 above the patient’s normal baseline PaCO2 accompanied by a decompensating respiratory acidosis . Other helpful signs: apnoea, severe cyanosis If hypoxemic patient is able to maintain adequate ventilation as documented by the PaCO2, then patient may be supported with supplemental O2 or CPAP. SEVERE HYPOXEMIA Hypoxemia can be assessed by measuring the PaO2 or the alveolar-arterial oxygen pressure gradient [P(A-a)O2]. Severe hypoxemia is present when PaO2<60mmHg on 50% or more of oxygen or <40mmHg at any FiO2

5. ASSESSMENT OF IMPENDING VENTILATORY FAILURE PARAMETER LIMIT Tidal volume <3 to 5mL/kg Respiratory rate and pattern >30 /min Laboured or irregular respiratory pattern Minute ventilation >10L/min Vital capacity <15mL/kg Max. inspiratory pressure <-20cm H2O PaCO2 trend Increasing to over 50mmHg Vital signs Increase in heart rate, blood pressure

6. INDICATIONS FOR PROPHYLACTIC VENTILATORY SUPPORT INDICATION EXAMPLES Reduce risk of pulmonary complications Prolonged shock Head injury Smoke inhalation Reduce hypoxia of major body organs Hypoxic brain Hypoxia of heart muscles Reduce cardiopulmonary stress Prolonged shock Coronary artery bypass surgery Other thoracic or abdominal surgeries

7. CONTRAINDICATIONS ABSOLUTE: Untreated tension pneumothorax : mechanical ventilation at any positive pressure level must not be done without a functional chest tube to relieve the pleural pressure RELATIVE: Patient’s informed request Medical futility Reduction or termination of patient pain and suffering

8. TYPES OF MECHANICAL VENTILATION

9. NEGATIVE PRESSURE VENTILATION : creates a transairway pressure gradient by decreasing the alveolar pressures to a level below the airway opening pressure (i.e. below atmoshperic pressure) Classic devices: iron lung, chest cuirass POSITIVE PRESSURE VENTILATION D eliver gas to the patient under positive-pressure, during the inspiratory phase and classified according to how the inspiratory phase ends. The factor which terminates the inspiratory cycle reflects the machine type . Types: pressure-cycled ventilator volume cycled ventilator time-cycled ventilator flow-cycled ventilator

10. Volume-cycled ventilator : The ventilator delivers a preset tidal volume (VT), and inspiration stops when the preset tidal volume is achieved . Pressure-cycled ventilator : The ventilator delivers a preset pressure; once this pressure is achieved, expiration occurs . Time-cycled ventilator : In which inspiration is terminated when a preset inspiratory time has elapsed. Time cycled machines are not used in adult critical care settings. They are used in pediatric intensive care areas.

11. MODES OF MECHANICAL VENTILATION A ventilator mode can be defined as a set of operating characteristics that control how the ventilator functions. An operating mode can be described by the way a ventilator is triggered into inspiration and exhalation and whether it allows mandatory breaths or spontaneous breaths or both.

12. CONTROLLED MANDATORY VENTILATION (CMV) Also known as continuous mandatory ventilation or control mode. The ventilator delivers a preset tidal volume at a time-triggered respiratory rate . The patient cannot change the ventilator respiratory rate or breathe spontaneously. Should only be used when the patient is properly medicated with a combination of sedatives, respiratory depressants and neuromuscular blockers. Indicated when the patient ‘fights’ the ventilator in the initial stages. Primary hazard is the potential for apnoea and hypoxia if the patient becomes accidently disconnected or if the ventilator fails to operate.

13. ASSIST CONTROL VENTILATION (ACV) The mandatory mechanical breaths may be either: -patient triggered by the patient’s spontaneous inspiratory efforts ( assist ) -time triggered by a preset respiratory rate ( control ) Typically used for patients who have a stable respiratory drive (spontaneous efforts of at least 10 to 12 BPM). Patient’s work of breathing requirement is very small when the triggering sensitivity(pressure or flow) is set appropriately. This mode allows the patient to control the respiratory rate and therefore the minute volume required to normalize the patient’s PaCO2 Potential hazard associated is alveolar hyperventilation (respiratory alkalosis).

14. INTERMITTENT MANDATORY VENTILATION (IMV) The ventilator delivers control breaths and allows the patient to breathe spontaneously at any tidal volume the pt is capable of in between mandatory breaths. Primary complication is the random chance for ‘ breath stacking ’ causing increased lung volume and airway pressure. This occurs when pt takes a spontaneous breath and the ventilator delivers a time-triggered mandatory breath at the same time. No new adult ventilators offer IMV mode but are designed to provide synchronised IMV.

15. SYNCHRONIZED INTERMITTENT MANDATORY VENTILATION (SIMV) The ventilator delivers either assisted breaths to a patient at the beginning of a spontaneous breath or a time triggered mandatory breath. Synchronization window : the time interval just prior to time triggering in which the ventilator is responsive to the patient’s spontaneous inspiratory effort. It is approximately 0.5sec, though may differ with different manufacturer. In between mandatory breaths, SIMV permits the pt to breathe spontaneously to any tidal volume the pt desires. Mandatory breaths are volume cycled and the patient controls spontaneous rate and volume.

16. The primary indication is to provide partial ventilatory support so that the pt provides a part of the minute ventilation. Advantages: Maintains respiratory muscle strength/avoids muscle atrophy Reduces ventilation to perfusion mismatch Decreases mean airway pressure Facilatates weaning Main disadvantage is the desire to wean the patient too rapidly, leading first to high work of spontaneous breathing and ultimately to muscle fatigue and weaning failure.

17. PRESSURE CONTROL VENTILATION (PCV) The pressure controlled breaths are time trigggered by a preset respiratory rate. Once inspiration begins, a pressure plateau is created and maintained for a preset inspiratory time. Pressure controlled breaths are therefore time triggered, pressure limited and time cycled. It is usually indicated for patients with severe ARDS who have extremely high peak inspiratory pressures during mechanical ventilation in a volume-cycled mode. Using this mode would reduce the peak inspiratory pressure while still maintaining adequate oxygenation(PaO2) and ventilation(PaCO2) therefore reducing the risk of barotrauma in such patients.

18. PRESSURE SUPPORT VENTILATION (PSV) PSV is used to lower the work of spontaneous breathing and augment a patient’s spontaneous tidal volume. These breaths are spontaneous because: They are patient triggered Tidal volume varies with the patient’s inspiratory flow demand Inspiration lasts only for as long as the patient actively inspires Inspiration is terminated when the patient’s inspiratory flow rate falls to 25% of the peak level. Low levels of PSV (5-10cm H2O): used during weaning to overcome the resistance to flow in artificial airways and ventilator tubing. High levels of PSV(15-30 cm H2O): to augment tidal volume as a form of noninvasive ventilation. Pressure supported breaths are technically flow-cycled by a minimum spontaneous inspiratory flow threshold.

19. SPONTANEOUS MODE Not an actual mode since the rate and tidal volume during spontaneous breathing are determined by the patient. Role is to provide: Inspiratory flow to the patient in a timely manner Flow adequate to fulfil a patient’s inspiratory demand Provide adjunctive modes such as PEEP to compliment a patient’s effort. Apnoea ventilation : a safety feature which in the event of apnoea or an extremely slow respiratory rate, invokes backup ventilation to give a predetermined tidal volume, FiO2 etc.

20. INVERSE RATIO VENTILATION (IRV) This mode reverses the I:E ratio so that inspiratory time is equal to, or longer than, expiratory time (1:1 to 4:1). IRV improves oxygenation by: Reduction of intrapulmonary shunting Improvement of V/Q matching Decrease of deadspace ventilation These can also be achieved by use of conventional modes with PEEP. 2 notable changes in IRV: Increase of mean airway pressure Presence of auto-PEEP Adverse effects: increase of mean alveolar pressure and volume, incidence of barotrauma Used in conjunction with pressure control (PC-IRV)

21. PRESSURE REGULATED VOLUME CONTROL VENTILATION (PRVC) Also known as adaptive pressure ventilation . Used primarily to achieve volume support while keeping the peak inspiratory pressure at lowest possible level. Alters the peak flow and inspiratory time in response to changing airway compliance characteristics. Automode : provides time-triggered, PRVC breaths when prolonged apnoea is detected.

22. POSITIVE END-EXPIRATORY PRESSURE (PEEP) PEEP increases the end-expiratory or baseline airway pressure to a value greater than atmospheric pressure(0cmH2O). Applied in adjunction with other ventilator modes. 2 major indications: 1. Intrapulmonary shunt and refractory hypoxemia 2. Decreased FRC and lung compliance PEEP reinflates the collapsed alveoli and maintains alveolar inflation during exhalation. Once ‘ recruitment ’ of the alveoli has occurred, PEEP lowers the alveolar distending pressure and facilitates gas diffusion and oxygenation. Complications: . 1. Decreased venous return and cardiac output 2. Barotrauma 3. increased intracranial pressure

23. AIRWAY PRESSURE RELEASE VENTILATION (APRV) APRV employs prolonged periods of spontaneous breathing at high end-expiratory pressures , which are interrupted by brief periods of pressure release to atmospheric pressure . It is a variant of CPAP. The CPAP in APRV improves arterial oxygenation by opening collapsed alveoli (alveolar recruitment) and preventing further alveolar collapse. The pressure release is designed to facilitate CO2 removal.

24. Ventilator settings: High airway pressure - this should be equal to end-inspiratory alveolar pressure (plateau pressure) but should not exceed 30cm H2O Low airway pressure - set to zero (atmospheric pressure) to maximize the driving pressure for rapid pressure release Timimg - time spent at high airway pressure is usually 85-95% of the total cycle time Disadvantage: contraindicated in severe asthma and COPD, cardiac output is often decreased due to high mean airway pressures.

25. HIGH FREQUENCY OSCILLATORY VENTILATION (HFOV) HFOV uses high-frequency, low volume oscillations to create a high mean airway pressure. Improves gas exchange in the lungs by opening collapsed alveoli (alveolar recruitment) and preventing further alveolar collapse. It is used in paediatric cases. The small tidal volumes (typically 1-2mL) limit the risk of alveolar overdistension and volutrauma . Ventilator setting: specialized ventilator required frequency and amplitude of oscillations (4-7Hz) mean airway pressure bias inspiratory flow rate inspiratory time Cardiac output is often decreased during HFOV and requires augmentation of intravascular volume.

26. ADAPTIVE SUPPORT VENTILATION (ASV) Also known as intelligent ventilation . The ventilator measures the dynamic compliance and expiratory time constant to adjust the mechanical tidal volume and frequency for a target minute ventilation. The therapist inputs the patient’s body weight and the percent minute volume. Predetermined setting of 100mL/min/kg for adults and 200mL/min/kg for children is used. The percent minute volume from 20% to 200% of the predetermined adult or child setting can be selected. Test breaths are used by the ventilator to measure to measure the system compliance, airway resistance and any intrinsic PEEP. With increasing triggering efforts, the number of mandatory breaths decreases and the pressure support level increases until tidal volume=alveolar volume+2.2mL/kg of deadspace volume.

27. CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP) CPAP is spontaneous breathing at a positive end-expiratory pressure . Requires only a source of oxygen and a face mask with an expiratory valve that maintains a PEEP. Usually set at 5-10cm H2O. Patient must have adequate lung functions that can sustain eucapnic ventilation documented by PaCO2. In neonates, nasal CPAP is the method of choice. It is a limited form of ventilatory support as it does not augment the tidal volume and thus limits its use in acute respiratory failure.

28. BILEVEL POSITIVE AIRWAY PRESSURE ( BiPAP ) BiPAP is CPAP that alternates between two pressure levels . It is actually a variant of APRV. High pressure level is inspiratory positive airway pressure (IPAP) and low pressure level is expiratory positive airway pressure (EPAP). More time is spent at the low pressure level. Requires a specialized ventilator. Indications: COPD patients, chronic ventilatory failure, restrictive chest wall disease, neuromuscular disease etc. Initial settings of IPAP as 5cm H2O and EPAP as 10cm H2O with inspiratory time of 3sec. Further adjustments in pressure are determined by the resultant changes in gas exchange (P/F ratio, PaCO2) and signs of respiratory distress.

29. VENTILATOR SETTING

30. PARAMETERS Mode of ventilation Respiratory rate Tidal volume PEEP level Fraction of inspired O2 conc.(FiO2) I:E ratio Peak flow/ flow rate Minute volume

31. MODE Full ventilatory support vs partial ventilatory support. Pressure vs volume control or dual control mode (volume targeted, pressure limited and time cycled) RESPIRATORY RATE If the patient has no spontaneous respirations, the RR is set to achieve the estimated minute volume (4×BSA in males and 3.5×BSA in females) but not more than 35 breaths/min. If the pt is triggering each ventilator breath, rate is set at just below the pt’s spontaneous RR. The arterial PCO2 is checked after 30 minutes and RR is adjusted to achieve the desired PCO2. Patients who are breathing rapidly and have an acute respiratory alkalosis or evidence of occult PEEP, consider switching over to SIMV.

32. TIDAL VOLUME Initial volume of 8mL/kg using predicted body weight. Reduce tidal volume to 6mL/kg over the next 2 hours if possible. Monitor the peak alveolar pressure and keep it <30cm H2O to limit risk of volutrauma . In voulme control mode the peak alveolar pressure is the end-inspiratory occlusion pressure, also called the plateau pressure. In the pressure control mode, the peak alveolar pressure is the end-inspiratory airway pressure

33. PROTOCOL FOR LUNG PROTECTIVE VENTILATION IN ARDS I. Tidal volume goal : Vt =6mL/kg (predicted body weight-PBW) 1. Calculate patient’s PBW males: PBW=50+[2.3*(height in inches-60)] females: PBW=45.5+[2.3*(height in inches-60)] 2. Use volume controlled ventilation and initial Vt set at 8mL/kg 3. RR set to match baseline minute ventilation but not>35/min 4. PEEP at 5cm H2O 5. Reduce Vt by 1mL/kg every 1-2hrs until Vt =6mL/kg 6. Adjust PEEP and FiO2 to maintain SpO2 of 88-95% II. Plateau pressure goal : Ppl <=30cm H2O If Ppl >30cm H2O and Vt at 6mL/kg, decrease Vt in 1mL/kg increments until Ppl falls to <=30cmH2O or Vt reaches a min. of 4mL/kg. III . pH goal : pH=7.30-7.45 1. if pH=7.15-7.30, increase RR until pH>7.30, PaCO2<25mmHg or RR=35bpm 2. if pH<7.15, increase RR to 35bpm. If pH remains<7.15, increase in Vt in 1mL/kg increments until pH>7.15 ( Ppl target maybe exceeded) 3. if pH>7.45, decrease RR, if possible

34. INSPIRATORY FLOW RATE Select an inspiratory flow rate of 60L/min if pt is breathing quietly or has no spontaneous respiration. Use higher inspiratory flow rates ( eg . 80L/min) for patients with respiratory distress or a high minute ventilation (> 10mL/min). I:E RATIO The I:E ratio should be >=1:2 If the I:E ratio is <1:2, options for increasing I:E ratio include a. increasing inspiratory flow rate b. decreasing the tidal volume c. decreasing the respiratory rate Inverse I:E ratio is used to correct refractory hypoxemia in ARDS patients with very low compliance

35. PEEP Set the initial PEEP to 5cm H2O to prevent the collapse of diatal airspaces at end-expiration. Further increases may be required in: 1. a toxic level of inhaled oxygen (>60%) is required to maintain adequate oxygenation (saO2>=90%) 2. hypoxemia is refractory to oxygen therapy OCCULT PEEP Check the flow rate at the end of expiration to detect presence of auto PEEP. If present, prolong the expiratory time by increasing I:E ratio If this is not possible or not successful, measure the level of occult PEEP with end-inspiratory occlusion method and add extrinsic PEEP at a level just below the occult PEEP.

36. FiO2 For patients with severe hypoxemia or abnormal cardiopulmonary functions (post resuscitation, smoke inhalation, ARDS) initial FiO2 maybe set at 100%. FiO2 is evaluated by means of arterial blood gas analyses after stablization of the patient. Should be adjusted accordingly to maintain a PaO2 between 80 and 100mm Hg. After patient stablization , the FiO2 is best kept below 50% to avoid oxygen-induced lung injuries. For patients with mild hypoxemia and normal cardiopulmonary functions, the initial FiO2 may be set at 40% and changed accordingly by subsequent ABG analyses.

37. TRIGGER SENSITIVITY The sensitivity function controls the amount of patient effort needed to initiate an inspiration Increasing the sensitivity (requiring less negative force) decreases the amount of work the patient must do to initiate a ventilator breath. Decreasing the sensitivity increases the amount of negative pressure that the patient needs to initiate inspiration and increases the work of breathing . The most common setting for pressure sensitivity are -1 to -2 cm H2O

38. FLOW PATTERN Principal flow patterns are: S quare/constant flow pattern- used initially when setting up a ventilator, initial peak flow overcomes airway resistance and the peak flow throughout the inspiratory phase enhances gas distribution in lungs. Accelerating/ ascending flow pattern - increasing flow throughout respiratory cycle, it may improve ventilation distribution in partial airway obstruction. Decelerating/ descending flow pattern- high initial inspiratory pressure and decrease in flow improves gas exchange and distribution of tidal volume. Sine wave flow pattern- more physiologic, similar to normal spontaneous breathing.

39. VENTILATOR ALARM SETTINGS Basic ventilator alarms: Low exhaled volume alarm : 100mL lower than expired Vt , used to detect system leak or circuit disconnection. Low inspiratory pressure alarm : 10-15cm H2O below the observed PIP. High inspiratory pressure alarm : 10-15cm H2O above the PIP, can be triggered due to water in circuit, kinking or biting of ET tube, airway secretions, bronchospasm, tension pneumothorax, decreased lung compliance, coughing, increased airway resistance. Apnoea alarm : 15-20 sec time delay High respiratory rate alarm : 10-15bpm over the observed RR, sign of respiratory distress. High and low FiO2 alarms : 5-10% over and below the analysed FiO2.

40. HAZARDS AND COMPLICATIONS

41. Related to positive pressure ventilation: barotrauma (pneumothorax, mediastinal air leak, subcutaneous air leak) hypotension, decrease in cardiac output oxygen toxicity bronchopleural fistula upper GI hemorrhage Related to patient condition: infection (due to reduced immunity) physical and physiological trauma multiple organ failure (may be pre-existing)

42. Related to equipment (ventilator and artificial airway): ventilator and alarm malfunction circuit disconnection accidental extubation endobronchial intubation ET tube blockage tissue damage atelectasis Related to medical professionals: nosocomial pneumonia inappropriate ventilator settings misadventures (lapses of understanding and communication)

43. WEANING FROM MECHANICAL VENTILATION

44. Weaning is the process of withdrawing mechanical ventilatory support and transferring the work of breathing from the ventilator to the patient. Weaning success: effective spontaneous breathing without any mechanical assistance for 48hrs or more. Weaning failure: when pt is returned to mechanical ventilation after any length of weaning trial.

45. EVALUATING A PATIENT FOR WEANING A daily routine follow up should be done in every patient receiving mechanical ventilation and exploring the following condition Resolution/improvement of the underlying disease Stop sedation Core temperature below 38 ºC Stable haemodynamics Adequate haemoglobin ( Hb > 8 g/ dL ) Adequate mentation ( arousable , GCS > 13) No major metabolic and/or electrolyte disturbances

46. WEANING CRITERIA CLINICAL CRITERIA Adequate cough Absence of excessive tracheobronchial secretions Resolution of the disease acute phase for which the patient was intubated Cardiovascular and hemodynamic stability OBJECTIVE CRITERIA Ventilatory criteria Oxygenation criteria Pulmonary reserve Pulmonary measurements

47. VENTILATORY CRITERIA Spontaneous breathing trial tolerates 20 to 30 mins PaCO 2 < 50 mmHg with normal pH Vital Capacity > 10 ml/kg Spontaneous V T > 5 ml/kg Spontaneous RR < 35/min f/ Vt <105 breaths/min/L Minute ventilation < 10 l/min with satisfactory ABG

48. OXYGENATION CRITERIA PaO 2 without PEEP > 60 mmHg at FiO 2 < 0.4 PaO2 with PEEP >100mmHg at FiO2 upto 0.4 (<8cm H2O) SaO 2 > 90% at FiO 2 < 0.4 PaO 2 /FiO 2 ≥ 150 mmHg Qs/ Qt <20% (physiologic shunt to total perfusion) P(A-a)O 2 < 350 mmHg at FiO2 of 1.0 (corresponds to 14% shunt)

49. PULMONARY RESERVE Vital capacity >10mL/kg Max. Insp. Pressure (MIP) > -30 cmH 2 O in 20 sec Pulmonary reserve can be assessed by measuring the vital capacity (VC) and maximum inspiratory pressure (MIP) which require active patient co-operation. For successful weaning patient should have a vital capacity of greater than10mL/kg.

50. PULMONARY MEASUREMENTS Static compliance > 30 ml/cm H 2 O Airway resistance stable or improving V d / V t ( deadspace to tidal volume) < 60% while intubated Not dependent on patient’s co-operation or effort. Used to indicate the amount of pulmonary workload that is needed to support spontaneous ventilation.

51. Weaning is more likely to succeed if a patient meets most of the criteria. If a patient can meet only one or two of the weaning criteria, the success rate is likely to be low. Though not fool proof, all patients who fit most of the criteria can undergo a formal spontaneous breathing trial (SBT).

52. COMBINED WEANING INDICES Since respiratory failure is multifactorial, individual parameters are unreliable predictors of weaning outcome Indices integrating several physiological variables may be more effective predictors of weaning outcome RSBI (Rapid shallow breathing index) CROP Index SWI Index

53. RAPID SHALLOW BREATHING INDEX (RSBI) Respiratory frequency to tidal volume (f/ Vt ) ratio . Rapid (high RR) and shallow (low Vt ) breathing pattern induces inefficient, deadspace ventilation. >105 suggests potential weaning failure. Patient is taken off the ventilator and allowed to breath spontaneously for 3 min or until a stable breathing pattern is established. More accurate predictor of weaning success than any other parameter studied Disadvantage : excessive false + ve

54. COMPLIANCE RATE OXYGENATION AND PRESSURE (CROP) INDEX Evaluates pulmonary gas exchange and balance b/w respiratory demands and respiratory neuromuscular reserve CROP Index= ( C d × MIP × P a O 2 /P A O 2 )/f Where: C d = dynamic compliance MIP= maximum inspiratory pressure PaO 2 = Arterial oxygen tension PAO 2 = Alveolar oxygen tension f = spontaneous respiratory rate per minute Should be > 13 ml/breath/min for successful weaning Widespread application limited by complicated calculation & no. of variables involved

55. SIMPLIFIED WEANING INDEX (SWI) Evaluates efficiency of gas exchange and ventilatory endurance SWI = ( f mv (PIP – PEEP)/MIP) × PaCO 2 /40 PIP = peak inspiratory pressure PEEP = Peak end expiratory pressure MIP = Maximal inspiratory pressure fmv = ventilatory frequency PaCO 2 = Arterial CO 2 tension while on ventilator When SWI< 9/min, it is highly predictive (93%) of weaning success. SWI> 11/min there is a 95% probability of weaning failure.

56. WEANING PROCEDURE Rapid ventilator discontinuation Spontaneous breathing trials Pressure support ventilation (PSV) SIMV Other Modes used for weaning

57. RAPID VENTILATOR DISCONTINUATION Considered in patients with no underlying cardiovascular, pulmonary, neurologic, or neuromuscular disorders and patients receiving ventilatory support for short periods e.g. post-op patients. SBTs are superior to both SIMV and PS in both duration of weaning and the likelihood of success after weaning . Patient on ventilator for < 72 hrs SBT for 20 to 30 min . EXTUBATE if no other limiting factor Good spont RR, MV, MIP, f/ Vt

58. SPONTANEOUS BREATHING TRIAL SBT can be in the form of T – tube trial or PSV of 5-10 cm H 2 O or CPAP 5-7 cmH 2 O T-Tube trial : allows spontaneous breathing interspersed with periods of full ventilatory support ADVANTAGES Tests pt’s spontaneous breathing ability Allows periods of work and rest Weans faster than SIMV DISADVANTAGES Abrupt transition difficult for some pts No alarms, unless attached to ventilator Requires careful observation .

59. SIGNS OF INTOLERANCE OF SBT Agitation, anxiety, diaphoresis or change in mental status RR > 30 to 35/min SpO2 < 90% > 20% ↑ or ↓ in HR or HR > 120 to 140/min SBP > 180 or < 90 mmhg . Such patients are returned to full ventilatory support for 24 hrs. to allow the respiratory muscles to recover.

60. T-TUBE ADAPTER A T-piece (or trach -collar) trial involves the patient breathing through a T-piece (essentially the endotracheal tube ( ett ) plus a flow of oxygen-air and no ventilatory assistance) for a set period of time. The work of breathing is higher than through a normal airway (although this simulates laryngeal edema /airway narrowing). If tolerated, the chances of successful extubation are high. If not reattachment to a ventilator is simple. Gas flow to inspiratory limb should be at least twice that of the patient’s spontaneous minute ventilation in order to meet the patient’s peak inspiratory flow rate. An extension piece of about 12 inches should be added to the expiratory limb to prevent entrainment of room air

61. WEANING PROTOCOL FOR SBT WITH A T-TUBE Prepare for T-Tube trial 3 min. screening trial Measure TV,RR Measure MIP thrice s electing the best . Formal SBT for 20 to 30 min MIP < -20 cm H20 TV spon . > 5 ml/kg RR spon . < 35/min. no signs of intolerance If signs of intolerance are present Put the patient back on previous ventilator settings Repeat next trial after 24 hrs extubate Optimize the patient’s medical condition suction, adequate humidification, bronchodilator therapy, good nutrition, optimal position, psychological counseling, adequate staff, equipment, no sedatives

62. SBT WITH CPAP CPAP circuit overcomes some of the work of breathing through the tracheal tube and prevents airway collapse. CPAP may improve lung mechanics and reduce the effort required by mechanically ventilated patients with air flow obstruction and may enhance breath triggering in patients with significant auto-PEEP.

63. WEANING WITH SIMV Breaths are either spontaneous or mandatory Mandatory breaths are synchronized with patient’s own efforts ADVANTAGES Gradual transition Easy to use Minimum MV guaranteed Alarm system may be used Should be used in comb. with PSV/CPAP DISADVANTAGES Prolongs weaning May worsen fatigue

64. PROTOCOL OF SIMV WEANING Start with SIMV rate at 80% of full support f is then decreased by 2 – 4 breaths twice daily If the patient tolerates an SIMV rate of 2-4 breaths for > 2 hrs Consider extubation Monitor patient’s appearance, respiratory rate, SpO 2 , BP, obtain ABG sample If deterioration → ↑ SIMV rate Allow pt’s resp msls to rest at night by ↑ ing SIMV rate

65. WEANING WITH PSV Pressure support is given with each spontaneous breath to ensure an adequate TV. Trachea can be extubated directly from PS as PS overcomes the tube resistance 7cmH 2 O of pressure support is required to overcome the resistance through a size 7.5mm (internal diameter) endotracheal tube 3cmH 2 O PS is required through a tracheostomy If a smaller tube is in place, pressure support of 10 cmH 2 O is required . ADVANTAGES Gradual transition Prevents fatigue Increased pt comfort Weans faster than SIMV alone Pt can control cycle length, rate and inspiratory flow. Overcomes resistive WOB d/t ET tube and circuit . DISADVANTAGES ↑ ed MAP versus T-Tube TV not guaranteed

66. PROTOCOL OF PSV WEANING PSV is adjusted to deliver TV 10-12 ml/kg, ( PSV max ) PSV level is decreased by 2-4 cm H 2 O twice daily to maintain TV If patient tolerates PSV level of 5-8 cm H 2 O for greater than 2 hrs Consider extubation Monitor patient’s appearance, respiratory rate, SpO 2 , BP, obtain ABG sample

67. ROLE OF TRACHEOSTOMY IN WEANING Early tracheostomy ( in 2 days of admission ) reduces mortality, risk of pneumonia, accidental extubation , ICU length of stay. Reduces dead space Less airway resistance ↓ ed WOB Better suctioning Improved pt comfort Facilitates weaning

68. WEANING : SELECTING AN APPROACH!!! Many studies have compared the different methods of weaning. Common conclusions are: No clear superiority exists between T-tube weaning and pressure support based weaning SIMV is the least efficient technique of weaning

69. OTHER MODES USED FOR WEANING Non invasive ventilation (NIV) Biphasic positive airway pressure ( BiPAP ) Automatic tube compensation (ATC) Volume support (VS) Volume assured pressure support (VAPS) Mandatory minute ventilation (MMV) Servo controlled ventilation ( Automatic Ventilatory Support)

70. WEANING PROTOCOLS Weaning protocols provide structured guidance regarding weaning of patients on mechanical ventilation. Protocols are usually presented as written guides or algorithms, and ventilator settings are manually adjusted by healthcare professionals. 3 components A list of objective criteria (often referred to as “readiness to wean” criteria) Structured guidelines for reducing ventilatory support e.g. abrupt/gradual using different weaning modes A list of criteria for deciding if the patient is ready for extubation

71. WEANING FAILURE Weaning failure is defined as either the failure of SBT or the need for reintubation within 48 h following extubation .

72. INDICATORS OF WEANING FAILURE Inadequate gas exchange Arterial oxygenation saturation (SaO 2 ) <85% - 90% PaO 2 <50 – 60 mmHg pH < 7.32 Increase in PaCO 2 >10 mmHg Unstable ventilatory /respiratory pattern Respiratory rate >30 – 35 breaths/minute Respiratory rate change over 50% Hemodynamic instability Heart rate change greater than 20% Systolic blood pressure >180 mmHg or <90 mmHg Blood pressure change greater than 20% Vasopressors required

73. Change in mental status Coma Agitation Anxiety Somnolence Signs of increased work of breathing Nasal flaring Paradoxical breathing movements Use of accessory respiratory muscles

74. FACTORS WHICH MAY INCREASE VENTILATORY WORKLOAD Increased ventilatory demand Increased CNS drive : hypoxia, acidosis, pain, fear, anxiety and stimulation of J receptors ( pulmonary edema) Increased metabolic rate : increased CO 2 production, fever, shivering, agitation, trauma, infection, and sepsis Increased dead space :COPD, pulmonary embolus Decreased compliance Decreased lung compliance : atelectasis , pneumonia, fibrosis, pulmonary edema, and ARDS Decreased thoracic compliance : obesity, ascites , abdominal distension, pregnancy

75. Increased resistance Increased airway resistance : bronchospasm, mucosal edema, and secretions Artificial airways : endotracheal, tracheostomy tube Other mechanical factors : ventilator circuits, demand flow systems, and inappropriate ventilator flow and/or sensitivity settings Cardiac load Increased cardiac workload leading to myocardial dysfunction; dynamic hyperinflation; increased metabolic demand; unresolved sepsis Neuromuscular Depressed central drive: metabolic alkalosis; sedative/hypnotic medications Peripheral dysfunction: primary causes of neuromuscular weakness; critical illness neuromuscular abnormalities (CINMA )

76. Metabolic Metabolic disturbances - hypokalemia , hypomagnesemia , hypophosphatemia , hypothyroidism, hypoadrenalism Role of corticosteroids Hyperglycaemia Nutrition Overweight Malnutrition Ventilator-induced diaphragm dysfunction Neuropsychological Delirium Anxiety, depression

77. QUESTIONS

78. 1. PEEP is indicated in patients who have a decreased: Tidal volume, chronic hypercapnia FRC, refractory hypoxemia Vital capacity, acute hypercapnia Tidal volume, refractory hypoxemia

79. Ans : b PEEP increases the FRC and is useful to treat refractory hypoxemia (low PaO2 not responding to high FiO2). Initial PEEP is set at 5cm H2O Subsequent changes of PEEP should be based on the patient’s blood gas results, FiO2 requirement, tolerance of PEEP and cardiovascular responses. REF: clinical application of mechanical ventilation, David W. Chang, 4 rd edition, Page no. 225

80. 2 . The primary purpose of prophylactic mechanical ventilation include all of the following except: To minimize risk of pulmonary complications To reduce prolonged hypoxia of major body organs To reduce the work of cardiopulmonary system To monitor arterial blood gases and vital signs

81. A ns : d Prophylactic ventilatory support is provided in clinical settings in which risk of pulmonary complications, ventilatory failure or oxygenation failure is high. This will reduce the work of breathing and oxygen consumption and preserve cardiopulmonary system and promote patient recovery. REF: clinical application of mechanical ventilation, David W. Chang, 3 rd edition, Page no. 218

82. 3. The application of CPAP or PEEP leads to all except: Increased FRC Reduction in preload in patients with acute cardiogenic pulmonary oedema Increased intracranial pressure Increased cardiac output

83. Ans : d PEEP increases alveolar distending pressure and increases FRC by alveolar recruitment. Since PEEP increases both peak inspiratory pressures and mean airway pressures, it has the potential to decrease venous return and cardiac output. Due to impedance of venous return from the head, PEEP may increase the ICP in patients with normal lung compliance. REF : clinical application of mechanical ventilation, David W. Chang, 4 rd edition, Page no. 89

84. 4. A 45 yr male in ICU with acute pancreatitis, is having severe ARDS and refractory hypoxia. PEEP and FiO2 have been increased over the day. Now, SpO2 is 85% on FiO2 0.65 with PEEP at 15cm H2O and plateau pressure of 29cm H2O. I:E is 1:1 and pt is sedated and paralysed. Most effective next step ? Commencing inhaled NO Adjusting PEEP to 20cm H2O Placing the pt in prone position Inverting the I:E ratio.

85. Ans : c Switching from supine to prone position can improve pulmonary gas exchange by diverting blood away from poorly aerated lung regions in the posterior thorax and increasing blood flow in aerated lung regions in anterior thorax. A recent study combining lung protective ventilation with prone positioning showed lower than expected mortality rate in patients with severe ARDS. Inhaled NO is a selective pulmonary vasodilator that can improve arterial oxygenation in ARDS but this is temporary and no effective survival benefit with associated side effects of NO . REF: The ICU book, Paul Marino, 4 th edition, page 459-460

86. 5. Out of the following the only parameter that suggests successful weaning is: Spontaneous frequency (f)= 40/min Spontaneous Vt = 7mL/kg Minute ventilation= 16L PaCO2= 55mmHg REF : clinical application of mechanical ventilation, David W. Chang, 4 rd edition, Page no. 520

87. 6. In assist-control ventilation (ACV ): Breaths triggered by the ventilator result in the full preset tidal volume being delivered,while breaths triggered by the patient are unsupported by the ventilator All breaths result in the full preset tidal volume being delivered, regardless of whether they are initiated by the ventilator or by the patient All breaths must be initiated by the patient The patient is incapable of triggering breaths

88. Ans : b The essence of ACV is that all breaths receive the full preset tidal volume regardless of whether the breaths are initiated by the ventilator or by the patient. With ACV if the ventilator is set at Vt = 500 mL, the frequency is set at 10 breaths/min, and the patient exhibits no respiratory effort, the ventilator will deliver 500 mL breaths 10 times per minute . If that same patient makes 8 respiratory efforts in addition to the 10 mandatory breaths, the ventilator will deliver 500 mL breaths 18 times per minute. REF: clinical application of mechanical ventilation, David W. Chang, 4 rd edition, Page no. 94-96

89. 7. In pressure-support ventilation (PSV), inspiration ends (and expiration begins) when: A preset tidal volume has been achieved A preset airway pressure has been achieved Flow decreases to a preset level A preset amount of time has passed

90. Ans : c In PSV, inspiration is triggered by a patient’s respiratory effort. A continuous airway pressure is maintained by gas flow that decreases throughout inspiration. When flow decreases to a preset fraction of the peak flow (usually 25% of peak flow), gas flow into the inspiratory limb ends and expiration begins. Choice A describes volume- preset ventilation, often called “volume control .” Choice B is incorrect because in PSV, a preset airway pressure is maintained throughout inspiration. Choice D is incorrect because in PSV, decrease in flow(not a preset time) determines the length of inspiration . REF: clinical application of mechanical ventilation, David W. Chang, 4 rd edition, Page no. 102

91. 8. A patient is at greatest risk for requiring endotracheal intubation and mechanical ventilation if the SpO2 is 91% while breathing Room air 4 L/min of oxygen via nasal cannula 15 L/min of oxygen via a non-rebreathing mask with reservoir bag Noninvasive positive-pressure ventilation with an FIO2 of 35%

92. Ans : c The non-rebreathing mask with reservoir bag can deliver an FIO2 of nearly 100% when oxygen flow is 15 L/min or greater. An SpO2 of 91% on an FIO2 of 100% should alert the clinician to the likely need for endotracheal intubation and mechanical ventilation. Choice D is incorrect assuming that other variables are safe and stable (PaCO2, mental status, ability to protect airway). Many chronic obstructive pulmonary disease patients in the ICU benefit from short-term support from noninvasive positive-pressure ventilation and do quite well with SpO2 readings in the low 90s REF: clinical application of mechanical ventilation, David W. Chang, 4 rd edition, Page no. 218

93. 9. According to the weaning protocol for mechanical ventilation, the time limit for a spontaneous breathing trial should be upto ------ unless terminated earlier: 5min 30min 120mins 4hours REF: clinical application of mechanical ventilation, David W. Chang, 4 rd edition, Page no. 520

94. 10. A mechanically ventilated, 70-kg patient has an arterial blood gas of pH = 7.06, PCO2 = 83 mmHg , and PO2 = 140 mm Hg on volume control ventilation (tidal volume = 450 mL, respiratory rate = 8, FIO2 = 50%, and positive end-expiratory pressure [PEEP] = 8 cm H2O). The most appropriate next step in the management is: Increase PEEP Increase FIO2 Increase the respiratory rate Administer sodium bicarbonate

95. Ans : c This is a case of nearly pure respiratory acidosis. The pH is very low as a result of a significantly elevated PCO2. The management of a respiratory acidosis consists of increasing the minute ventilation by increasing either respiratory rate (choice C) or tidal volume (not given as an answer choice). Choices A and B are incorrect because neither would result in an increased minute ventilation. Choice D is incorrect because giving bicarbonate will temporarily increase the pH, but will not address the underlying problem of inadequate elimination of CO2 .

96. THANK YOU