Dr Arthur Chun-Wing Lau Associate Consultant Department of Intensive Care

1. Choosing Interfaces for Noninvasive VentilationAnnual Symposium on Emergency and Critical Care Medicine 2012 – NEW IMAGE, NEW DEVELOPMENT6th October 2012 Halloween Masquerade Dr Arthur Chun-Wing Lau Associate Consultant Department of Intensive Care Pamela Youde Nethersole Eastern Hospital, Hong Kong

2. Technical and clinical comparisons of various interfaces • Fitness for different NIV ventilator circuits • Materials • Deadspace, CO2 rebreathing, Exhalation port position • Patient-ventilator synchrony • Noise • Complications • Overall clinical efficacy

3. Interfaces • Nasal – mask, cloth • Oronasal (full face) • Oral mouthpieces • Nasal prong/Nasal pillow/plugs • Hybrid • Total face • Helmet • Custom-fabricated

4. The ideal securing system The ideal interface • Stable (to avoid interface movements or dislocation) • Easy to put on or remove • Non-traumatic • Light and soft • Breathable material • Available in various sizes • Works with various interfaces • Washable, for home care • Disposable, for hospital use • Leak-free • Good stability • Nontraumatic • Light-weight • Long-lasting • Nondeformable • Nonallergic material • Low resistance to airflow • Minimal dead space • Low cost • Easy to manufacture (for the moulded interfaces) • Available in various sizes

5. 1. Fitness for Different NIV Ventilator Circuits • Single limb circuit: continuous flow CPAP, with/without non-rebreathing valve, exhalation port has to be present (e.g. near nasal bridge, plateau exhalation valve, or Whisper Swivel) • Incomplete double limb (e.g. LTV 1000 Pulmonetics) • Double limb circuit: intermittent flow CPAP (ventilator CPAP, bias flow set at 2 L/min), independent limbs for inspiration and expiration, use non-vented mask, no exhalation port should be present Whisper Swivel LTV 1000 Pulmonetics Plateau exhalation valve Non-rebreathing valve Double limb

6. Have to be equipped with a “noninvasive mode” ICU ventilators Dräger Evita 4 Viasys Avea Siemens Servo i Puritan Bennett 840 NIV ventilators SmartAir ST Respironics BiPAP STD Respironics BiPAP Vision

7. Ventilators

8. 2. Materials • Cushion of soft material: polyvinyl chloride, polypropylene, silicon, silicon elastomer, or hydrogel • 4 types of face-seal cushion: transparent noninflatable, transparent inflatable, full hydrogel, full foam • Frame of stiff material: polyvinyl chloride, polycarbonate, or thermoplastic PVC ComfortGel Nasal Cushion Foam and Silicone cushion Silicone forehead pad Transparent inflatable

9. 3. Deadspace, CO2 rebreathing, Exhalation ports • Physiological dead space (= anatomical deadspace + alveolar deadspace; normally around 32% of tidal volume) • Effective apparatus deadspace (due to interface) • Static (when there is no active airflow) = volume inside the apparatus • Dynamic (when there is active airflow) = the effective deadspace when put into actual use • Total static dead space = 1 + 2a • Total dynamic dead space = 1 + 2b

10. Dynamic dead space in face masks used with noninvasive ventilators: a lung model study • Total dynamic dead space was measured with a lung model when using 19 commercially available face masks and a range of ventilators in various ventilation modes • Dead space of the system (mannequin head and trachea) was adjusted to achieve a VD,phys/VT of 32% to mimic the expected physiological deadspace (VD,phys) in patients Saatci E 2004

11. Spontaneous breathing vs NIV VD, app/VT VD,phys/VT set at 0.32 Total dynamic dead space during spontaneous ventilation was increased above physiological dead space from 32% to 42% of tidal volume by using face masks The effective apparatus deadspace consists of mainly the static volume of the apparatus.

12. Where there is airflow, apparatus deadspace becomes dynamic: Bilevel NIV (IPAP/EPAP 16/4) Face masks with expiratory ports over the nasal bridge ? Leak at the nose VD, app/VT VD,phys/VT set at 0.32 Findings: Total dynamic deadspace of bilevel NIV face masks is less c/w spontaneous breathing through various masks. Face masks with expiratory ports over the nasal bridge resulted in beneficial flow characteristics within the face mask and nasal cavity. Ports over the nasal bridge were best followed by those positioned elsewhere within the mask and then those at the junction between the mask and the ventilator circuit (Ferguson GT 1995) Leaks decrease the dynamic dead space and even the physiological deadspace

13. Ventilation modes:Bilevel vs CPAP Both modes give continuous flow during expiration VD, app/VT VD,phys/VT set at 0.32 No important difference in VD/VT between Bilevel and CPAP in term of VD/VT

14. Different ventilator modes: Bilevel vs Pressure support vs Pressure assist (= pt triggered, pressure limited, time cylced) VD, app/VT VD,phys/VT set at 0.32 Findings: EPAP is essential as continuous flow can decrease VD/VT

15. Dynamic apparatus dead space vs static volumes Ref: Saatci E 2004

16. Continuous positive airway pressure delivered with a “helmet”: Effects on carbon dioxide rebreathing • Eight healthy human volunteers • CPAP was delivered with a continuous flow system and a mechanical ventilator. • The helmet predisposes to CO2 rebreathing, but • Adequate continuous high flow (single limb) minimizes CO2 rebreathing • Ventilator (double limb) predisposes CO2 rebreathing Taccone P et al 2004

17. From Castar’s manual • CPAP: use flow generators able to provide a total continuous air and oxygen flow of at least 40 L/min in order to ensure good lavage of the CO2 exhaled • Ventilator: when used with a ventilator, make sure that it is able to deliver a flow, during the inspiratory phase, sufficient to quickly remove the CO2 formed inside the helmet Antonio MatíasEsquinas. NoninvasiveMechanical Ventilation: Theory, Equipment, and Clinical Applications

18. Comparison of patient-ventilator interfaces based on their computerized effective dead space • Numerical simulations with computational fluid dynamics (CFD) software • Effective dead space of the interface gas region is defined as the rebreathed gas volume resulting from the exhaled gas trapped in the interface gas region as well as the volume of fresh air (Vfresh) that is inhaled by the mannequin during each inspiratory cycle Fodil R et al 2011

19. Effective dead space is not related to the internal gas volume included in the interface, suggesting that this internal volume should not be considered as a limiting factor for their efficacy during non-invasive ventilation

20. Physiological effects of different interfaces during noninvasive ventilation for acute respiratory failure 7 hypoxemic and 7 acute respiratory failure patients (Fraticelli AT et al 2009)

22. Non-invasive ventilation in chronic obstructive pulmonary disease patients: helmet vs facial mask Both interfaces improved gas exchange Navalesi P et al 2007

23. Exhalation devices • In mask • In circuit • Whisper-Swivel • Whisper-Swivel II • Plateau expiratory valve Whisper-Swivel II, Respironics Whisper-Swivel Plateau valve

24. Plateau Expiratory Valve Low Airway Pressure High Airway Pressure

25. Exhalation device

26. Amount of CO2 rebreathing. BiPAP ventilator with a single-limb circuit, 3 different exhalation valves Once positive end-expiratory pressure, or expiratory positive airway pressure, was reduced to below 4 to 6 cmH2O, CO2 rebreathing was markedly increased, esp with the Whisper Swivel (Ferguson GT 1995)

27. Position of exhalation port and mask design affect CO2 rebreathing during NIPPV TFM Facial-WS Spontaneous breathing without mask Facial-MEP Schettino GPP et al 2003

28. Effect of the location and type of leak port, the site of O2 injection and the oxygen flow on the measured O2 concentration during NIV delivered via bi-level positive airway pressure in a lung model Schwartz AR et al 2004 Effect on FiO2 O2 flow rate Site of O2 injection

30. 4. Patient-ventilator synchrony Helmet Navalesi Paolo et al 2007

31. Patient ventilator asynchrony with helmet c/w facemask • Significant time delay to activate the ventilatory trigger, the time between the initiation of an inspiratory effort until the preset PEEP level is reached, and the inspiratory pressure time product (i.e. the muscle inspiratory effort) during these two periods Moerer O 2006

32. Triggering and Cycling off • With the helmet: • the initial part of the inspiratory pressure applied was dissipated to pressurize its soft wall (Chiumello D 2003) • Cycling off seems to occur in response to flow changes caused by the mechanical characteristics of the helmet rather than by the patient’s effort and mechanical characteristics (Rocca F 2005) • Leading to patient ventilator asynchrony (Rocca F 2005, Navalesi P 2007)

33. Solutions • Increasing the level of pressure support or PEEP: reduced the delay times and pressure time product (Moerer 2006) • Replace the pneumatic triggering with neural triggering and cycling off using the diaphragm electrical activity (Moerer O 2006) More info at: http://www.maquet.com/

34. Diaphragm electrical activity (Eadi) and ventilatory assist during pneumatically and neurally triggered and cycled-off NIV with helmet Ref: Moerer 2008

35. Breathing comfort by VAS during neurally and pneumatically triggered and cycled off NIV

36. 5. Noise • NIV helmet is associated with significantly greater noise than nasal and facial masks, but is as comfortable as masks, at least in the short term. • Intensity of noise: 105 dB, mostly caused by the turbulent flow through the respiratory circuit • Intensity: Helicopter, Motorised/power mower; 1 m from a disco loudspeaker • Can damage hearing after 1 hour exposure per day Degree of noise caused by the helmet, facial mask, and nasal mask at a PS of 15 cmH2O Cavaliere F 2004

37. 6. Complications • Skin breakdown: Artificial skin patches over the bridge of the nose, Pressure of cushion, headgear, keep mask cushion pressure just 2 cmH2O above airway pressure (Schettino et al 2001) • Nasogastric tube: adapter • Eye irritation • Claustrophobia: nasal and TFM better than facial • Air leaks: less with TFM, more with FM; hydrogel or foam seals, chin strap, lips seal or mouth taping • Nose bridge pain: less with TFM • Oronasal dryness: more with TFM “Nothing worthwhile is ever without complications.” ― Nora Roberts, a bestselling American author of more than one hundred fifty romance novels

38. Pisani L, et al 2012. Minerva Anestesiologica

39. No strong evidence that one type is necessarily or consistently better than the others in terms of clinical efficacy 7. Overall clinical efficacy

40. Conclusion • The interface has to suit both the ventilator circuit and the patient, e.g. single vs double limb • From surveys, ON masks are most commonly used for acute respiratory failure, to be switched to nasal masks when more stable • The static internal volume of an interface bears little relationship to the dynamic deadspace when put into actual use • CO2 rebreathing can be minimized by a smaller mask, continuous high flow CPAP system, use of a non-rebreathing valve, use of CPAP/EPAP > 4 to 6 cmH2O, an expiratory port over the nasal bridge, and when leaks are high (intentional or unintentional) • Use the interface validated for the particular ventilator as much as possible • Helmets have some specific characteristics, but which can be overcome • No strong evidence that one type is necessarily or consistently better than the others in terms of clinical efficacy

41. End Thank you!