Modes of ventilation exams 2014
•
27 likes•1,770 views
Modes of ventilation for students - to understand common modes
Recommended
More Related Content
What's hot
What's hot (20)
Viewers also liked
Viewers also liked (19)
Similar to Modes of ventilation exams 2014
Similar to Modes of ventilation exams 2014 (20)
Recently uploaded
Recently uploaded (20)
Modes of ventilation exams 2014
- 1. Dr. Maninder Dhaliwal Consultant Pediatric Intensivist Medanta – The Medicity Modes Of Ventilation Exams - Summary All the best
- 2. Question 1. • What is a mode of ventilator? • Which mode will you use & why? • Pressure vs Volume ? • Newer mode? • PRVC, VAPS, APRV, BPAP • NAVA • NIV & HFO
- 3. What is a mode? • CMV • Assit Control • SIMV • CPAP • Pressure • Volume
- 6. The word ‘‘control’’ – What it means? • ‘‘Controlled ventilation’’ • ‘‘Assist/Control’’ • ‘‘Dual control’’ • “Control Variable”
- 7. What is a mode? • A “mode” is a predetermined pattern of interaction between the ventilator and the patient. • A well defined mode must describe – control, – phase and – conditional variables & is defined for • Mandatory • Spontaneous • Combined Breaths Respir Care 2013;58(2):348 –366.
- 10. How a Breath is Delivered • CONTROL VARIABLES aka Independent Variable – The primary variable that the ventilator decides how to to achieve inspiration –Pressure : APRV, PCV, NAVA –Volume : Volume control, assist control –Flow: Volume –Time: HFO
- 11. How a Breath is Delivered • Pressure Controller
- 12. How a Breath is Delivered • Volume Controller – The ventilator maintains the volume waveform in a specific pattern, the delivered breath is volume controlled (volume limited, volume targeted)
- 13. How a Breath is Delivered • PHASE VARIABLES – Ventilator-supported breath may be divided into three distinct phases 1. The initiation of inspiration 2. Inspiration itself 3. Expiration – To understand a breath cycle, you must know how the ventilator starts, sustains, and stops inspiration and you must know what occurs between breaths
- 14. How a Breath is Delivered • PHASE VARIABLES – The phase variable is a variable that is measured and used by the ventilator to initiate some phase of the breath cycle • Trigger variable – causes a breath to begin • Limit variable – limits the magnitude of any parameter (pressure, flow, volume) during inspiration • Cycle variable – causes the end of inspiration
- 15. How a Breath is Delivered • Limit Variable – A limit variable is the maximum value a variable (pressure, flow, volume) can attain. This limits the variable during inspiration but does not end the inspiratory phase. • Do not confuse this with cycle variable, which always ends inspiration
- 16. How a Breath is Delivered • Maximum Safety Pressure: Pressure Limiting vs. Pressure Cycling – All ventilators have a maximum pressure limit control, which is used to prevent excessive pressure from reaching a patient’s lungs – reaching the maximum high pressure limit ends the inspiratory phase • AKA – High pressure limit – Upper pressure limit – Pressure limit
- 17. How a Breath is Delivered • Cycle Variable – The variable a ventilator measures to determine the end of inspiration is called the cycling mechanism – once cycling occurs, expiratory gas flow begins • Cycle variables – Pressure – Volume – Flow – time
- 18. How a Breath is Delivered • Pressure Cycled – Ventilator will deliver flow until a present pressure is reached, at which point inspiration ends and expiratory flow begins • The most common application of pressure-cycling is for alarm setting (e.g., high pressure alarm) and IPPB
- 19. How a Breath is Delivered • Flow Cycled – Ventilator will deliver flow until a present level is met, at which point flow stops and expiration begins • The most frequent application of flow cycling is pressure support mode ventilation (to be discussed in a future module)
- 20. How a Breath is Delivered • Time Cycled – Expiratory flow starts because a present time interval has elapsed
- 21. How a Breath is Delivered • Limit Variable This figure illustrates the importance of distinguishing between the terms limit and cycle. A, Inspiration is pressure limited and time cycled. B, Inspiration is flow limited and volume cycled. C, Inspiration is both flow limited and volume limited (because flow and volume reach preset values before inspiratory time ends) and time cycled (after the preset inspiratory hold time). A B C
- 22. How a Breath is Delivered TYPES of Breaths Machine Cycled Mandatory breath T,L,C by ventilator Assisted breath L,C by ventilator Trigger either patient or time Patient Cycled Supported T,C by patient L by ventilator Spontaneous T,L,C by patient
- 23. How a Breath is Delivered • BASELINE VARIABLE – The variable that is controlled during the expiratory phase Note: Most commonly, pressure is controlled during the expiratory phase » PEEP
- 25. [Respir Care 2013;58(2):348 –366.
- 26. Major VILI – lung protective strategies Barotrauma Volutrauma BiotraumaAtelectotrauma (R/D) High Lung Volume Ventilator-Induced Lung Injury Ventilator-Induced Lung Injury at Low Lung Volumes Biotrauma, Inflammation, and Multiorgan Failure from Ventilator- Induced Lung Injury Low TV PEEP ARDS net ALVEOLI
- 29. How do you normally breath?? Imagine this to be your flow of air in lungs This is your inspiration only………….
- 30. Expiration is passive So graph is mostly similar Volume Ventilation Pressure Ventilation Flow Time Scalar Flow LPM Time Seconds Constant Flow Decelerating Flow
- 31. Understand Volume Mode • Must • Easy • More Informative • P Plat – calculation
- 32. ventilator Diaphragm Ppeak Pres RET tube Rairways Pres Pplat Understanding the pressure-time waveform using a ‘square wave’ flow pattern time pressure The pressure-time waveform is a reflection of the pressures generated within the airways during each phase of the ventilatory cycle. At the beginning of the inspiratory cycle, he ventilator has to generate a pressure Pres to overcome the airway resistance. Note: No volume is delivered at this time. fter this, the pressure rises in a linear fashion o finally reach Ppeak. Again at end inspiration, air flow is zero and the pressure drops by an amount equal to Pres to reach the plateau pressure Pplat. The pressure returns to baseline during passive expiration. Pres
- 34. P peak P plat Inspiratory Pause
- 36. Normal variations – Pressure wave form Paw Pressure VentilationVolume Ventilation 1 2 3 4 5 6 Sec 1 SEC Expiration Flow 1 2 3 4 5 6 VT Liters Constant Flow Decelerating Flow Square Wave Shark Fin
- 38. Pressure Control • Pressure under my control – airway pressure under my control, not transpulmonary – so relative control only as heterogenous lung, false sense of security • Faster tidal volume delivery – high peak flows – early filling of alveoli – but more shear forces • Variable peak inspiratory flows – better adaptation to flow hunger / inspiratory effort of patient – better synchrony in spontaneous mode • Decelerating flow • Favorable gas distribution – like dropping a glass of water on floor & the water trickles into every nook & corner – better in ARDS – Improves oxygenation • Favorable in leak – although volume is lost through leak – the ventilator will continue to pressurize the airway for the duration of Ti – if leak is big – it sometimes mimic constant flow Advantages
- 39. Pressure Control • Many clinicians prefer PCV, because it is easy to control peak airway pressure and keep peak inspiratory pressure below critical limits, thus possibly reducing volutrauma • It have demonstrated an improvement in oxygenation and pulmonary mechanics in ARDS patients who were switched from VCV to PCV while VT, inspiratory time and PEEP were held constant. The finding was thought to reflect an increase in mean airway pressure. Davis K, Branson RD, Campbell RS, et al. Comparison of volume control and pressure control ventilation: is flow waveform the difference? J Trauma
- 40. • The only study - ARDS comparing VCV and PCV within the context of a lung-protecting ventilation strategy showed pressure control to afford safe maintenance of the ventilation parameters and pH levels. • This same study also recorded a decrease in the incidence of multiorgan failure over time. • But no affect on mortality Prospective randomized trial comparing pressure controlled ventilation and volume- controlled ventilation in ARDS. For the Spanish Lung Failure Collaborative Group. Chest. 2000;117:1690---6.
- 41. PC - Disadvantage • The major disadvantage of PCV is that in a patient with unstable or changing lung mechanics, any significant fluctuation in the lung compliance or airway resistance will directly affect the delivered tidal volumes. • Tidal volumes can vary substantially with changes in compliance or resistance, producing undesirable changes in minute ventilation
- 42. PC – Disadvantage: New Proof • The high peak inspiratory flow of PCV may aggravate lung injury because of greater shear forces in PC mode than the lower peak inspiratory flow of VCV Effects of peak inspiratory flow on development of ventilator-induced lung injury in rabbits. Anesthesiology 2004
- 43. • For early management of patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS), in ARDS network centers, volume assist control was the most commonly selected mode of ventilation (56% overall), and volume-targeted ventilation was used in most patients (82%).
- 44. Volume Mode Advantages • Minute ventilation is guaranteed • The set tidal volume is guaranteed • Inspiratory Pause : – to improve Tidal volume distribution – to reduce PaCO2 & to enlarge PaO2, (due to involving a large part of lungs into gaseous exchange) – to refine V/Q ratio (ventilation/perfusion ratio) – Pendelluft effect
- 45. Volume Mode
- 46. Volume mode Hess DR, Dillman C, Kacmarek RM. In vitro evaluation of aerosol bronchodilator delivery during mechanical ventilation: pressure-control vs. volume control ventilation. Intensive Care Med. Jul 2003;29(7):1145- 1150.
- 47. Volume Mode • Calculate P Peak & P Plat – Resistance (Difference between P plat - Ppeak – Targeted P Plat in both Asthma & ARDS
- 48. Volume Mode • A major limitation of volume control is the fact that administration of the inspiratory flow in each respiration is fixed in its values, and if the patient is active, he or she may have a variable inspiratory demand, generating ‘‘dyssynchrony due to inadequate inspiratory flow’’ or also a ‘‘double trigger’’ effect in requiring a volume larger than the programmed volume
- 49. • Volume can more easily be directed toward areas of lesser resistance or increased compliance, thereby producing ‘overdistended areas’ – VILI Limited flow may not meet patients desired insp flow rate- flow hunger May cause high Paw ( barotrauma)
- 50. SIMV + PS Mode • How many types of breath present? Controlled mandatory Assisted Synchronized Spontaneous supported
- 52. SIMV • Guaranted minimum vol with assist breath • Respiratory alkalosis less as compared to assist mode as it has a window for spontaneous breaths • Less atrophy of muscles – active participation by patients • All advantages of spontaneous breaths.
- 53. SIMV • Initial mode of choice or is it weaning mode? • Or is it falling out of favour ? • Not preferred by many presently, but still the most popular mode in pediatrics. • With newer modes – this mode will soon become historical
- 54. CPAP vs PEEP CPAP • Is a mode & it usually means without additional inspiratory support • Always in spontaneously inspiration PEEP • Baseline variable • Always in conjunction with positive pressure ventilation as a additional support to some mode – PS, Assist control, SIMV Wrongly called – CPAP + PS, but it is PSV Pressure support is usually above PEEP, so no need to say PS + PEEP Anesth Int Care 1986
- 55. Pressure Support • Reducing the load on respiratory muscles • Improving synchrony between patient and ventilator without excessive sedation • Easing the weaning process
- 56. Equation of motion in pressure support ventilation • Pressure = pressure applied by the ventilator on the airway + pressure generated by respiratory muscles • Pmus is determined by respiratory drive and respiratory muscle strenght Paw + Pmus = Vt/C + VxR + PEP
- 57. Increase in PS level will not affect flow and Vt if there is subsequent decrease in respiratory drive (lower Pmus) or unloading of the respiratory muscles.
- 58. Determinant factors of inspiratory flow in PSV • Pressure support setting • Pmus (inspiratory effort) • Airway resistance • Respiratory system compliance • Vt directly depends on inspiratory flow, but also on auto-PEEP (decreases the driving pressure gradient)
- 59. Auto-cycling • Leaks • Patient movement • Water in the ventilator circuit • Cardiac signals → Signal noise trigerring the vent especially when settings sensitive → Respiratory alkalosis, lung hyperinflation
- 60. Rise time • Time required for the ventilator to reach the PS setting at the onset of inspiration • Should be adjusted to patient comfort, to decrease the work of breathing • Allows to adjust the flow at the onset of the inspiratory phase
- 62. Pressure Support termination (cycling) Goal : cycling to expiration at the end of neural inspiratory time • Flow : Fixed absolute flow or % of peak inspiratory flow ± elapsed inspiratory time
- 64. Drawbacks of a high inspiratory flow at the onset of inspiration • Inspiratory phase may be prematurely terminated if ventilator cycles at a flow that is a fraction of peak inspiratory flow • Flow-related inspiratory terminating reflex → shortening of neural inspiration → shallow inspiratory efforts • Individual patient titration of rise time is necessary in adddition to proper setting of PS to optimize the efficacy of PSV
- 68. Problems faced during PSV • Apneas • Vt variable – alveolar ventilation not guaranteed • If Resistance increases – secretions/compliance • If obstruction increases – asthma • Vt decreases • AutoPEEP : » Increases the effort required to trigger the ventilator » Decreases the delivered Vt » Inspiratory flow decreases slowly → flow cycle criteria not reached at the end of neural inspiration → active exhalation to pressure cycle the breath • If leak +, than flow rate to cycle may never be achieved Also autotriggering – but now managed in new ventilators • Be careful while using in line nebulisers
- 69. Which level of PS ? • Unloading of respiratory muscle : – Should encourage reconditioning and prevention of atrophy – While avoiding fatigue • Objectives : Vt 6 -10 ml / kg, RR < 30-35/mn and no SCM muscle contractions
- 70. Other parameters settings • Triggers set at their higher sensitivity, decreased if auto-cycling • Rise time titration • PEEP according to auto-PEEP and gas exchange • FiO2 according to gas exchange
- 71. Pressure Support Regardless of the goal for pressure support, the simplest method of determining what PS level to use is to use the PS level providing the lowest RR with adequate oxygenation.
- 73. So Many knobs – So Many Modes Student brain running : want to excel ------- want to pass Examiners want it simple – believe me try to keep it simple