Modes of ventilation and weaning

This ppt comprise of introduction to mechanical ventilation,modes of ventilation, weaning criteria and weaning process.

1. Modes Of Ventilation And W eaning BY : Dr Bhanupriya P.V.V

2. Topics covered… Introduction Modes of ventilation Weaning

3. Introduction Mechanical Ventilation is ventilation of the lungs by artificial means usually by a ventilator. A ventilator delivers gas to the lungs with either negative or positive pressure.

4. purpose To maintain or improve ventilation, & tissue oxygenation. To decrease the work of breathing & improve patient’s comfort

5. TYPES OF VENTILATION Negative pressure ventilation Positive pressure ventilation

6. Negative ventilation Principle – creates a negative pressure on the chest wall The pressure in the airways, alveoli, and pleura are decreased during inspiration Creates a transairway pressure gradient by decreasing the alveolar pressures to a level below the airway opening pressure Two classic devices “IRON LUNG” & “CHEST CUIRASS”

7. Iron lung

8. Negative-pressure ventilators (“iron lungs”) first used in Boston Children’s Hospital in 1928(drinker ventilator) Used extensively during polio outbreaks in 1940s – 1950s

9. The patient’s body i s encased in an iron cylinder and negative pressure was generated Intermittent short-term negative-pressure ventilation is sometimes used in patients with chronic diseases The use of negative-pressure ventilators is restricted in clinical practice, because they limit patient access, positioning and movement and they lack adaptability to large or small body torsos (chests )

10. Positive pressure ventilation Concepts that the military developed during world war II to deliver oxygen and gas volume to fighter pilots operating at high altitude were incorporated into the design of the modern positive-pressure ventilator Intensive use of positive-pressure ventilation gained momentum during the polio epidemic in Scandinavia in 1950’s

11. Positive pressure ventilation is achieved by applying positive pressure at the airway opening Increasing the pressure at airway opening produces a transairway pressure gradient that generates an inspiratory flow This flow results in the delivery of a tidal volume

12. Ventilator mode A ventilator mode can be defined as a set of operating characteristics that control how the ventilator functions Each mode is different in determining how much work of breathing the patient has to do An operating mode can be described by the way a ventilator is triggered into inspiration and cycled into exhalation, what variables are limited during insp , and whether or not the mode allows only mandatory breaths, spont breaths, or both

13. Modes of ventilation

14. Spontaneous M odes Positive End Expiratory Pressure (PEEP ) CPAP PSV BiPAP

15. Positive end expiratory pressure (PEEP) Positive pressure applied at the end of expiration during mandatory \ ventilator breath positive end-expiratory pressure increase the end expiratory or baseline airway pressure to a value greater than atm pr It is applied in conjuction with other ventilator modes Indications intrapulmonary shunting and refractory hypoxemia decreased FRC and lung compliance

16. Physiology PEEP increases alveolar distending pressure increases FRC by alveolar recruitment improves ventilation -improves oxygenation - decreases work of breathing

17. PEEP prevents complete collapse of the alveoli and keep them partially inflated and thus provide protection against the development of shear forces during mechanical inflation BENEFITS Restore FRC/ Alveolar recruitment ↓ shunt fraction ↓WOB ↑PaO 2 with low FiO 2 DETRIMENTAL EFFECTS Barotrauma ↓ VR/ CO ↑ MAP ↓ Renal / portal bld flow

18. AUTO PEEP/ INTRINSIC PEEP -Airflow limitation because of dynamic collapse -No time to expire all the lung volume ( high RR or Vt ) - Lesions that increase expiratory resistance

19. Disadv Barotrauma / volutrauma ↑WOB a) lung overstretching ↓contractility of diaphragm ↑ MAP – CVS side effects May ↑ PVR Minimising Auto PEEP ↓airflow res – secretion management, bronchodilation , large ETT ↓ Insp time ( ↑ insp flow, sq flow waveform, low TV) ↑ exp time (low resp rate ) Apply PEEP to balance AutoPEEP

20. Continuous Positive Airway Pressure (CPAP) Constant positive airway pressure is PEEP applied to the airway of a patient who is breathing spontaneously Same indications as PEEP Pt must have adequate lung function that can sustain E ucapnic ventilation CPAP can be used for intubated and nonintubated patients . In non invasive ventilation- CPAP is given via a tight fitting nasal mask or face mask

21. Bilateral Positive Airway Pressure Ventilation ( BiPAP ) BiPAP is a noninvasive form of mechanical ventilation provided by means of a nasal mask or nasal prongs, or a full-face mask . The system allows the clinician to apply independent positive airway pressures to both inspiration and expiration An inspiratory pressure support level referred to as IPAP An expiratory pressure called EPAP.

22. IPAP- improves hypoxemia and hypercapnia EPAP- improves oxygenation by increasing FRC and enhancing alveolar recruitment Indications - BiPAP appears to be of value in preventing intubation of the end-stage COPD patient - in supporting patients with chronic ventilator failure -restrictive chest wall diseases -neuromuscular diseases - Nocturnal hypoventilation

23. In a spont breathing patient the IPAP and EPAP may set at 8cm H2O and 4cm H2O respectively In spont/timed mode- BPM is set 2-5 breaths below the pt’s spont rate In timed mode- BPM is set slightly higher than the pt’s spont rate A BIPAP device can be used as a CPAP device by setting IPAP and EPAP at the same level IPAP may be increased in increments of 2cm H2O to enhance the pressure boost to improve alveolar vent, normalize PaCO2, and reduce the work of breathing EPAP may be increased in increments of 2cm H2O to increase FRC and oxygenation in pts with intrapul shunting

24. Pressure support ventilation ( psv ) The patient breathes spontaneously while the ventilator applies a pre-determined amount of positive pressure to the airways upon inspiration Helps to overcome airway resistance, reduces the work of breathing and augments the tidal volume Pressure supported breaths - pt triggered, pressure limited, flow cycled - tidal vol varies with the pt’s insp flow demand - insp lasts only for long as the pt actively inspires - insp is terminated when the the pts insp flow demand decreases to a preset minimal value Breath – SPONTANEOUS Trigger – PATIENT Limit - PRESSURE Cycle – FLOW ( 5-25% OF PIFR)

25. Indications - is commonly applied along with SIMV mode when the pt takes spont breaths to increase tidal volume to decrease resp rate to decrease work of breathing B- To facilitate weaning The level of pressure support is titrated until Tidal volume = 10 to 15ml/kg or Spont resp rate < 25/min

26. VOLUME MODES Controlled Mandatory Ventilation (CMV) Assist Control (AC) Intermittent Mandatory Ventilation (IMV) Synchronized Intermittent Mandatory Ventilation ( SIMV) Mandatory Minute Ventilation (MMV)

27. Controlled mandatory ventilation(cmv) The ventilator delivers the preset tidal volume Every breath is time triggered Inspiration is terminated by the delivery of a preset tidal volume (volume cycled) Patient cannot change the ventilator respiratory rate or breath spontaneously It is used only when the patient is properly medicated with a combination of sedatives, neuromuscular blockers Breath - MANDATORY Trigger – TIME Limit - VOLUME Cycle – VOL / TIME

28. Indications “fighting” or “bucking” Tetanus or any other seizure activities that interrupt the delivery of mechanical ventilation. Complete rest Pt with chest injury in which spontaneous inspiratory efforts produce paradoxical chest movement.

29. Disadvantages Apnoea & hypoxia- in case of accidental disconnection or the ventilator should fail to operate. If not paralysed completely- Any spont resp effort would be like attempting to inspire through a completely obstructed airway Psychologically devastating- for the pt to realize that he or she has no control over his or her breathing.

30. Assist control (ac) In this mode patient can increase the ventilator resp rate in addition to the preset mechanical resp rate. Each control breath provides a preset, ventilator delivered tidal volume Each assist breath also results in a preset, ventilator delivered tidal volume This mode does not allow the patient to take spont resp Breath – MANDATORY ASSISTED Trigger – PATIENT TIME Limit - VOLUME Cycle – VOLUME / TIME

31. Control breath- time triggered Assist breath- patient triggered Inspiration is terminated by the delivery of a preset tidal volume (volume cycled ) Indications - pt who have stable resp drive with spont inspiratory efforts of atleast 10-12/ min

32. Advantages work of breathing – very small This mode allows the patient to control the resp rate and therefore the minute volume required to normalize the patient’s PaCO2 Complications Alveolar hyperventilation- resp centre damage-high drive Hypocapnia Resp alkalosis

33. Intermittent mandatory ventilation ( imv ) IMV is a mode in which the ventilator delivers mandatory breaths and allows the patient to breath spontaneously at any tidal volume the patient is capable of in between the mandatory breaths Partial ventilator support Complication- breath stacking if spont breath and mandatory breath delivered at same time  barotrauma Barotrauma can be minimized by setting appropriate high pressure limits Replaced by SIMV mode Breath – MANDATORY SPONTANEOUS Trigger – PATIENT time Limit - VOLUME Cycle - VOLUME

34. Synchronized Intermittent mandatory ventilation ( simv ) This mode also allows the patient to breath spontaneously at any tidal volume the patient is capable of in between the mandatory breaths The mandatory breaths are synchronized with the patient’s spontaneous breathing efforts so as to avoid breath stacking Mandatory breath- time triggered or patient triggered Spontaneous breaths- resp rate and tidal vol are totally dependent on the pt’s breathing effort Synchronization window- 0.5 sec Breath – SPONTANEOUS ASSISTED MANDATORY Trigger – PATIENT TIME Limit - VOLUME Cycle – VOLUME/ TIME

35. Indications - to provide partial ventilator support.. ie ., a desire to have the patient actively involved in providing part of the minute ventilation - weaning Advantages maintains resp ms strength/ avoids ms atrophy Reduces ventilation- perfusion mismatch Decreases mean airway pressure Facilitates weaning Complications- ms fatigue if the patient is weaned too rapidly

36. MANDATORY minute ventilation (mmv) Also called minimun minute ventilation This mode provides a predetermined minute ventilation when the pt’s spontaneous breathing efforts become inadequate It is an additional function of the SIMV mode It is intended to prevent hypercapnia by automatically insuring that the pt receives a minimum preset minute ventilation

37. Esp useful in the final stages of weaning with SIMV During weaning, if the pt becomes apneic, then without MMV the reduced minute ventilation would cause hypercania and and resp acidosis However, om MMV-equipped ventilators , a decrease in the pt’s spont minute volume would trigger an automatic increase in the ventilators mandatory resp rate Important to monitor alveolar minute vol  in distressed pt.. Increased resp rate.. Minute vol will be normal but high rate low tidal vol increases dead space… so decreased alveolar minute volume .. So high resp rate alarm should be set at approximately 10/min greater than the patient’s baseline spont resp rate Exception: Hamilton Veolar ventilator: every breath is pressure supported.. No mandatory breaths

38. PRESSURE MODES Pressure control ventilation (PCV) Pressure support ventilation (PSV) Continuous Positive Airway Pressure (CPAP ) Bilateral Positive Airway Pressure Ventilation (BiPAP)

39. Pressure control ventilation (PCV) Invasive ventilation Full ventilator support… gives only mandatory breaths Pt should be properly medicated with a combination of sedatives, neuromuscular blockers Time triggered, pressure limited, time cycled Pressure controlled breaths.. Once inspiration begins, a pressure plateau is created and maintained for a preset inspiratory time Breath – MANDATORY Trigger – TIME Limit - PRESSURE Cycle – TIME/ FLOW

40. It is usually indicated for pts with severe ARDS who require high peak inspiratory pressures in volume mode in this mode the peak inspiratory pressures can be reduced while still maintaining adequate oxygenation and ventilation Reduces risk of barotrauma

41. OTHER newer modes Inverse Ratio Ventilation (IRV) Airway Pressure Release Ventilation (APRV) Proportional Assist Ventilation (PAV ) Neurally Adjusted Ventillatory Assist (NAVA) D ual modes- Volume assured pressure support (VAPS) Volume support (VS) Pressure regulated volume controlled (PRVC)

42. Proportional assist ventilation ( pav ) it is a mode of assisted ventilation where pressure is applied by the ventilator in proportion to the patient generated flow and volume Flow assist or Volume assist Occurs during assisted breaths only The adv of PAV is its ability to track changes of ventilator effort and promotes pt - ventilator synchrony Improves ventilation and decreased work of breathing PAV with CPAP – reduction of inspiratory muscle work- improves exercise tolerance

43. Airway Pressure Release Ventilation (APRV) APRV is similar to CPAP in that the patient is allowed to breathe spontaneously without restriction During spont exhalation, the PEEP is dropped to a lower level and this action simulates an effective exhalation maneuver Pressure release time- 1-2sec

44. The ventilator must have a high flow CPAP circuit that has been modified with the addition of a release valve The airway pressure increases during insp to CPAP pressure and is maintained for the duration of insp APRV breaths are pressure lmited With APRV, pt’s tidal volume will vary directly with changes in lung compliance and inversely with airway resistance Provides effective partial vent support with lower peak airway pressure than the PSV and SIMV modes in ARDS pts

45. Inverse ratio ventilation ( irv ) I:E ratio – the ratio of inspiration time to expiration time In conventional mech ventilation- I:E ratio ranges from about 1:1.5 to 1:3 This resembles normal I:E ratio during spont breathing, and it is considered physiologically beneficial to normal cardiopulmonary function Increasing inspiratory time promotes oxygenation The inverse ratio in use is between 2:1 to 4:1 and often it is used in conjunction with pressure control ventilation

46. The increase in mean airway pressure and presence of auto-PEEP during IRV helps to reduce shunting and improves oxygenation in ARDS pts USES: Reduction of intrapulmonary shunting Improvement of V/Q matching Decrease of dead space ventilation Adverse effects - barotrauma - pulmonary edema –because of transvascular fluid flow induced by increase alveolar pressure

47. weaning Weaning is the gradual reduction in the level of ventilatory support . A systemic approach to wean a patient off mechanical ventilation by using a set of clinical measurements as a guide Weaning success : effective spontaneous breathing without any mechanical assisstance for 24 hrs or more. Weaning failure : when pt is returned to mechanical ventilation after any length of weaning trial. Signs of weaning failure : abnormal blood gases, diaphoresis, tachycardia, tachypnea, arrhythmias , hypotension.

48. WEANING CRITERIA Used to evaluate the readiness of a patient for weaning trial. Common weaning criteria : Ventilatory criteria Oxygenation criteria Pulmonary reserve Pulmonary measurements Other factors

49. VENTILATORY CRITERIA PaCO2: < 50 mmhg with pH >/= 7.35 VC: > 10 to 15 ml/kg Spontaneous VT: > 5 to 8 ml/kg Spontaneous RR: < 30/min Minute ventilation: < 10 lts

50. OXYGENATION CRITERIA PaO2 without PEEP > 60 mmhg @FiO2 upto 0.4 PaO2 with PEEP > 100 mmhg @ FiO2 upto 0.4 SaO2 > 90% @ FiO2 upto 0.4 Qs/ Qt < 20% P(A-a)O2 < 350 mmhg PaO2/FiO2 > 200 mmhg

51. PULMONARY RESERVE AND MEASUREMENTS Pulmonary reserve: Max. voluntary ventilation – 2×min. vent@FiO2 upto 0.4 Max. Insp. Pressure < -20 to -30 cmH2O in 20 sec. Pulmonary measurements : Static compliance > 30 ml/cm H2O Vd / Vt < 60%

52. COMBINED WEANING INDICES Simplified weaning index : evaluates efficiency of gas exchange. = ( f * (PIP – PEEP)/MIP) × PaCO2/40 should be < 9/min 93% success CROP index : evaluates pulmonary gas exchange and balance b/w respiratory demands and respiratory neuromuscular reserve. = ( Cd × MIP × PaO2/PAO2)/f. Should be > 13 ml/breath/min. RSBI: should be < 100 cycles/min/ lt = f/Vt. Most accurate test to predict weaning success.

53. others Metabolic factors Inadequate nutrition – protein catabolism Overfeeding - ↑ CO2 production Phosphate, ? Magnesium deficiency - ↓ respi pump functn Impaired O2 delivery - ↓ respi pump functn . Renal function : Patient should have adeq renal output (> 1000 ml/day) Monitor electolytes to ensure adequate respi msl functn Cardiovascular function Ensures sufficient O2 delivery to tissues Cardiac rate, rhythm, BP, CO should be optimal with minimal pressure support CNS assessment Assess for LOC, anxiety, dyspnea, motivation CNS should be intact for protection of airway.

54. Weaning methods Spontaneous breathing trial SIMV with pressure support. PSV Rapid v entilator discontinuation (off the ventilator)

55. Rapid ventilator discontinuation pt.on vent for < 72 hrs., has good spont RR, MV, MIP, f/ Vt EXTUBATE if no other limiting factor

56. T-Tube trial: allows spont. breathing several times per day interspersed with periods of ventilatory support. Initial SBT’s may last only 5 to 30 min. Resume mechanical ventilation at night or if distress occurs. ADVANTAGES -Tests pt’s spon breathing ability -Allows periods of work and rest -Weans faster than SIMV DISADVANTAGES -Abrupt transition difficult for some pts -No alarms, unless attached to vent so requires careful observation Spontaneous Breathing Trial

57. Weaning protocol for a SBT with a T-Tube Pt is put on T-piece for 5min every 30- 180 min Return pt to mechanical ventilation The duration of T-tube is gradually increased as tolerated by the patient for upto 2hrs If pt tolerates – he can be extubated if ABG, vital signs are normal

58. 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 pts are returned to full ventilatory support for 24 hrs. to allow the ventilatory msls . to recover.

59. Weaning with SIMV Involves gradual reduction in machine rate based on ABG and clinical assessment. Rate is decrease by 2 breaths/min…followed by pt assessment and ABG after 30min Rate decreased upto 0… if pt tolerates.. extubate ADVANTAGES -Gradual transition -Easy to use -Minimum MV guaranteed -Alarm system may be used -Should be used in comb. with PSV/CPAP DISADVANTAGES - Pt. – ventilator asynchrony - Prolonges weaning and may worsen fatigue

60. Pressure Support Ventilation (PSV) Patient determines RR, V E , inspiratory time – a purely spontaneous mode Parameters Triggered by pt’s own breath Limited by pressure Affects inspiration only Uses used along with SIMV mode Does not augment T V but overcomes resistance created by ventilator tubing Helps reduce the airway resistance imposed on the pt by the ET tube and ventilator circuit Augments inflation volumes.

61. Begin with PSV(5 – 15cm H2O) Adjust pressure( upto 40cmH2O) to achieve a TV of 8 to 10 ml/kg or spont rate of <25BPM Reduce PSV 3 to 6 cm H2O intervals until a level of close to 0 is achieved Consider extubation when pt. tolerates weaning with no apparent distress and with normal ABG and vital signs

62. ADVANTAGES Gradual transition Prevents fatigue Increased pt comfort Weans faster than SIMV alone Every breath is supported Pt can control cycle length, rate and inspiratory flow. Overcomes resistive WOB due to ET tube and circuit DISADVANTAGES DISADVANTAGES DISADVANTAGES Large changes in MV can occur ↑ ed MAP versus T-Tube TV not guaranteed

63. CPAP ventilation without artificial airway : -Nasal , face mask Advantages Avoid intubation / c/c Preserve natural airway defences Comfort Speech/ swallowing + Less sedation needed Intermittent use Disadvantages Cooperation Mask discomfort Air leaks Facial ulcers, eye irritation, dry nose Aerophagia Limited P support e.g. BiPAP , CPAP

64. Extubation failure Defined as need for reinstitution of vent support within 24 – 72 hrs of ETT removal. Occurs in 2 – 25 % of pts. Predisposing factors - advanced age -duration of mech. Vent. - anemia -use of cont. IV sedation Find & manage the cause

65. Terminal weaning Defined as withdrawal of mechanical ventilation that results in death of the pt. pt’s informed consent TERMINAL WEANING is justified -if medical interventions futile or hopeless - to stop pain and suffering Carries many ethical and legal implications.

66. Thank u

67. References David W Chang, Clinical application of mechanical ventilation 2 nd ed. Paul L Marino, The ICU Book, 3 rd ed . Susan P. Pilbeam , Mechanical ventilation, 4 th ed.