Anaesthesia ventilators

anaesthesia ventilators

1. ANAESTHESIA VENTILATORS :CLASSIFICATION, PNEUMATICALLY DRIVEN BELLOWS VENTILATORS, MECHANICALLY DRIVEN PISTON VENTILATORS PRESENTOR- DR SNIGDHA MODERATOR – DR BHAVNA GUPTA

2. DEFINITION A ventilator is an automatic device designed to provide or augment patient ventilation

3. MODERN HISTORY John Hunter developed double bellows for resuscitation in 1775 - one for blowing air in and the other for drawing bad air out. Draeger Medical designed an artificial breathing device“Draeger Pulmoter ” in 1911 that was used by fire and police units

4. NEGATIVE PRESSURE VENTILATORS From mid 1800-1900s, devices were invented that applied negative pressure around body or thoracic cavity. Two successful designs became popular; one is -body of patient was enclosed in an iron box or cylinder and patient’s head protruded out of end 'iron lungs’. Second design was a box or shell that fitted over thoracic area only (chest cuirass).

5. SCANDINAVIAN POLIO EPIDEMIC - 1952 Between July-December of 1952, in Copenhagen, 2722 patients with poliomyelitis were treated in Community Disease Hospital of which 315 patients required ventilatory support. Many principles of IPPV were defined during that time –including use of cuffed tubes, periodic breaths and weaning by reduction of assisted breaths.

6. ERA OF RESPIRATORY INTENSIVE CARE Two types of ventilators and two modes of mechanical ventilation evolved during this period- Ventilator with pressure cycled (PCV).Two ventilators were commonly used for PCV in 1960’s and 1970’s; the Bird Mark 7 and the Bennet PR2. Volume cycled ventilator – VCV. The term ‘weaning’ was used to explain various techniques to test the quality of patient’s spontaneous ventilation before extubation

7. OLD ANAESTHESIA VENTILATORS Offers only volume control ventilation Separate models or different bellows assemblies were required for adult and pediatric patients. Delivered Vt was affected by fresh gas flow and breathing system compliance. User had to manually enable low pressure alarm when the ventilator was turned ON. APL valve should have to be close and turn the bag/ventilator switch when turning on ventilator.

8. OLD ANAESTHESIA VENTILATORS Could not provide as high inspiratory pressures or flows as their ICU counterparts ( eg . If positive end-expiratory pressure (PEEP) were needed The anesthesia provider had to add a PEEP valve to the anesthesia breathing system

9. NEW ANAESTHESIA VENTILATOR An integral PEEP valve is present , and many have several ventilatory modes. High inspiratory pressures and flows can be delivered Ventilator can deliver volumes for a wide range of patients from smallest child to the largest adult. Overcomes effect of fresh gas, breathing system compliance and gas compression on tidal volume. Turning ventilator ON involves fewer steps and automatically enables the low airway pressure alarm

10. CLASSIFICATION POWER : Low powered - generate only modest gas pressures required to deliver Vt with normal and near-normal compliances and resistances. High powered - generate pressures sufficient to overcome the increase in airways resistance and/or reduction in lung compliance that are seen in diseased lungs; Require addition of certain safety features to protect patients with both normal and abnormal lungs from excessive pressures

11. B. CYCLING MECHANISM A ventilator cycle between two phases - inspiratory and expiratory. lnspiratory cycling During inspiratory phase, ventilator delivers- (a)a volume of gas, over (b) a given period of time, producing (c) an increase in airways pressure, also a change in the pattern of (d) flow ( inspiratory waveform) .

12. VOLUME CYCLING ventilator terminate inspiratory cycling -point at which pre-determined volume of gas has left the ventilator and switches its internal mechanism to allow exhalation to occur . TIME CYCLING Incorporated in most new ventilators. Mechanical, pneumatic or electronic timers used to control operation of inspiratory and expiratory valves that govern cycling of ventilator ; it functions independently of delivered tidal volume

13. PRESSURE CYCLING ventilators sense predetermined airway pressure in order to terminate inspiratory phase. FLOW CYCLING Recognition of flow pattern changes has been used to cycle ventilators. rarely employed nowadays.

14. Expiratory Cycling expiratory volume-cycled ventilator have mechanism- for terminating expiratory phase when reservoir bellows has filled to desired tidal volume required for the next inspiration to identify a selected airways pressure at the end of exhalation that would trigger the next inspiratory phase to switch to the inspiratory phase when desired flow rate at end of exhalation was reached, or of terminating expiratory phase after a predetermined time.

15. VENTILATION MODES IN ANAESTHESIA VENTILATORS Volume control ventilation Pressure-controlled ventilation PCV volume guaranteed Synchronised intermittent mandatory ventilation Pressure-support ventilation

16. VOLUME CONTROL VENTILATION Preset volume is delivered with a constant flow Peak inflation pressure varies with patient’s compliance and airway resistance. Modern anaesthesia ventilators can deliver Vt : 20‑1500 ml. Typical ventilator settings in VCV: • Tidal volume: 6‑10 ml/kg body weight. • Rate: 8‑12 breaths/min. • PEEP: 0‑5 cm H2O to start with and titrated.

17. PRESSURE-CONTROLLED VENTILATION Inspiratory pressure is maintained constant and Vt varies. Inspired volume varies according to changes in compliance and airway resistance. Target pressure is adjusted to produce a reasonable Vt to avoid extremes of atelectasis and volutrauma . PCV mode is useful in neonatal surgeries, in pregnancy , in laproscopic surgery and patients with ARDS.

18. PCV VOLUME GUARANTEED ventilator operates as in PC- mode, but a tidal volume target is also set. It ensure that patient receives uniform Vt regardless of compliance changes caused by packs, retractors, position, surgical exposure or relaxation ventilator delivers preset Vt with low pressure using a decelerating flow. PCV‑VG breaths are characterised by a decelerating flow and a square pressure waveform.

19. INTERMITTENT MANDATORY VENTILATION  used for weaning patients from mechanical ventilation IMV-ventilator delivers mechanical (mandatory, automatic) breaths at a preset rate and permits spontaneous, unassisted breaths of a controllable inspiratory gas mixture between mechanical breaths. spontaneous breaths utilizes either continuous gas flow within circuit or a demand valve that opens to allow gas to flow from a reservoir. Continuous gas flow at a rate greater than peak inspiratory flow involves no additional work of breathing but requires a large volume of fresh gas.

20. SYNCHRONISED INTERMITTENT MANDATORY VENTILATION Synchronizes ventilator-delivered breaths with patient's spontaneous breaths. Time between end of each mandatory breath and beginning of next is subdivided into spontaneous breathing time and trigger time. Reduces incidence of patient-ventilator disharmony and need for sedation or narcosis for patient to tolerate mechanical ventilation.

21. MANDATORY MINUTE VENTILATION Similar to IMV mode except that minimum minute volume is set rather than R/R. Ventilator measures spontaneous minute volume, if found less than preset mandatory minute volume, the difference b/w two is delivered as mandatory breaths by ventilator at preset flow & Vt. Suited for patients with variable respiratory drive

22. PRESSURE SUPPORT designed to augment patient's spontaneous breathing by applying positive pressure to airway in response to patient-initiated breaths. Disadvantage - if patient fails to make any respiratory effort, no pressure-supported breaths will be initiated. A supported breath may be pressure or flow initiated When selected flow or sub-baseline pressure caused by a spontaneous breath is reached, flow from ventilator begins and set pressure is quickly reached and modulates flow to maintain that pressure.

23. Desired tidal volume should be calculated and pressure support level adjusted so that the desired volume is delivered. If exhaled volume is inadequate, inspiratory pressure should be increased or inspiratory rise time decreased (if adjustable). PEEP may cause an increase in tidal volume. As the patient's effort increases, inspiratory pressure can be reduced.

24. CLASSIFICATION(according to application) MECHANICAL THUMBS MINUTE VOLUME DIVIDERS BAG SQEEZERS INTERMITTENT BLOWERS

25. MECHANICAL THUMBS

26. MINUTE VOLUME DIVIDERS uses a continuous source pressurised gas fed into a ventilator system -collected by a reservoir-continually pressurised by a spring, a weight or its own elastic recoil. It has one inspiratory valve and another expiratory valve, which are linked together and operated by a “ bistable ” mechanism. Examples of minute volume dividers are East‑Freeman automatic vent, the Flomasta and Manley MP3

27. BAG SQUEEZERS employed in conjunction with a circle or Mapleson D system. Various type of bag (bellow squeezers)- A. rising bellows arrangement B. descending bellows arrangement C. pneumatic piston with mechanical linkage D. pneumatic piston E. cam driven linkage from an electric motor F. screw threaded piston (worm drive) powered by electric motor. Manley servovent ®, Penlon Nuffield 400 series ventilator, Ohmeda 7800, Servo 900 series

28. INTERMITTENT BLOWERS Ventilators are driven by a source of gas or air, at a pressure of 45‑60 psi. The driving gas is normally delivered to patient undiluted, but it may be passed through a venturi device so that air, oxygen or anaesthetic gases may be added to it. Major component is - electronically timed and activated proportional flow valve or a pneumatically timed oscillator that divides driving gas into tidal volumes; size and rate of which can be adjusted. Pneupac and Penlon Nuffield 200 series ventilator

29. CLASSIFICATION OF INTERMITTENT BLOWERS: A. Basic resuscitator B. Sophisticated resuscitator C. Ventilator for intensive care D. Anaesthetic ventilator for Mapleson D system

30. WORKING PRINCIPLE PNEUMATICALLY DRIVEN BELLOWS VENTILATORS bellows are analogous to reservoir bag in breathing circuit Act as interface between breathing system gas and ventilator driving gas. driving gas circuit is located outside bellows and patient gas circuit inside bellows.

31. FUNCTIONING OF BELLOWS-IN–BOX VENTILATOR

32. INSPIRATION

33. INSPIRATORY PAUSE

34. EXHALATION

35. EXPIRATORY PAUSE

36. WORKING PRINCIPLE OF MECHANICALLY DRIVEN PISTON VENTILATORS ventilators use electric motor to compress gas in breathing circuit; Motor’s force compresses gas within piston, raising pressure within it- causing gas to flow into patient’s lungs area of piston is fixed, so volume delivered by piston directly related to linear movement of piston.

37. SPONTANEOUS INHALATION

38. SPONTANEOUS EXHALATION

39. MANUAL

40. MECHANICAL VENTILATION (INSPIRATION)

41. MID EXHALATION

42. EXHALATION ( LATER PART)

43. ADVANTAGE AND DISADVANTAGE OF PNEUMATICALLY DRIVEN BELLOWS VENTILATORS OVER MECHANICALLY DRIVEN PISTON VENTILATORS Advantages of piston ventilators: Greater precision of tidal volume delivery due to rigid piston design, decreased compliance losses Greater precision of pressure control with the use of pressure sensors Electrical control instead of pneumatic control

44. Economical use of wall oxygen (wall oxygen not used to compress a bellows, only used for patient delivery) A perforation in the bellows can allow the driving gas to be delivered to the patient. This can potentially cause barotrauma or unpredictable inspired gas concentrations, including oxygen and volatile anesthetic . No intrinsic PEEP (compared to ascending bellows (2‑3 cm water are mandatory due to the design of ventilator spill valve).) Quiet

45. Disadvantages of piston ventilators Leak in piston diaphragm can lead to hypoventilation Possible entrainment of room air as piston returns to filled position Loss of the familiar visible behaviour of a standing bellows during disconnections. Quiet and less easy to hear regular cycling .