1.Dr. Ananya

2. Contents Classification History Introduction Indications Key terms- compliance , ventilatory work Components Control mechanism Variables Triggering Factors to consider in mechanical ventilation Wave-forms 3. Classification According to Robert chatburn Broadly classified into Negative pressure ventilatorsAnd according to themanner in whichPositive pressure ventilators they support ventilation 4. Negative pressure ventilators Exert a negative pressure on the external chest Decreasing the intrathoracic pressure duringinspiration allows air to flow into the lung, fillingits volume Physiologically, this type of assissted ventilation issimilar to spontaneous ventilation It is used mainly in chronic respiratory failureassociated with neuromascular conditions such aspoliomyleitis, muscular dystrophy, a myotrophiclateral sclerosis, and mysthenia gravis. 5. The iron lung, often referredto in the early days as the"Drinker respirator", wasinvented by PhillipDrinker(1894 1972)and Louis Agassiz ShawJunior, professors of industrialhygiene at the Harvard Schoolof Public Health . The machine was powered byan electric motor with airpumps from two vacuumcleaners. The air pumpschanged the pressure inside arectangular, airtight metalbox, pulling air in and out ofthe lungs 6. Biphasic cuirass ventilation Biphasic cuirass ventilation (BCV) is a methodof ventilation which requires the patient to wear anupper body shell or cuirass, so named after the bodyarmour worn by medieval soldiers. The ventilation is biphasic because the cuirass isattached to a pump which actively controls boththe inspiratory and expiratory phases of therespiratory cycle . 7. Disadvantages Complex and Cumbersome Difficult for transporting Difficult to access the patient in emergency claustrophobic 8. Positive pressure ventilators Inflate the lungs by exerting positive pressure onthe airway, similar to a bellows mechanism, forcingthe alveoli to expand during inspiration Expiration occurs passively. modern ventilators are mainly PPV s and are classified based on related features, principles and engineering. 9. History Andreas Vesalius (1555) Vesalius is credited with the first description of positive-pressure ventilation, but it took 400 years to apply hisconcept to patient care. The occasion was the polioepidemic of 1955, when the demand for assisted ventilationoutgrew the supply of negative-pressure tank ventilators(known as iron lungs). In Sweden, all medical schools shut down and medicalstudents worked in 8-hour shifts as human ventilators,manually inflating the lungs of afflicted patients. Invasive ventilation first used at MassachusettsGeneral Hospital in 1955. Thus began the era of positive-pressure mechanicalventilation (and the era of intensive care medicine). 10. INTRODUCTION TO MECHANICALVENTILATION: CONVENTIONAL MECHANICAL VENTILATION Mechanical ventilation is a useful modality for patientswho are unable to sustain the level of ventilationnecessary to maintain the gas exchange functions-oxygenation and carbon dioxide elimination The first positive-pressure ventilators were designed toinflate the lungs until a preset pressure was reached. In contrast, volume-cycled ventilation, which inflatesthe lungs to a predetermined volume, delivers aconstant alveolar volume despite changes in themechanical properties of the lungs. 11. INDICATIONS FOR MECHANICALVENTILATION Respiratory Failure Cardiac Insufficiency Neurologic dysfunction Rule 1. The indication for intubation and mechanicalventilation is thinking of it. Rule 2. Endotracheal tubes are not a disease, andventilators are not an addiction 12. Key terms Ventilatory work- During inspiration , the size of the thoracic cageincreases overcoming the elastic forces of the lungs andthe thorax and resistance of the airways. As the volume ofthe thoracic cage increases, intrapleural pressure becomesmore negative, resulting in lung expansion. Gas flows from the atmosphere into the lungs as a resultof transairway pressure gradient. During expiration, the elastic forces of the lung andthorax cause the chest to decrease in volume andexhalation occurs as a result of greater pressure at thealveolus compared to atm. Press. 13. This ventilatory work is proportional to the pressure required for inspiration times the tidal volume. LOAD- The pressure required to deliver the tidal volume is referredto as the load that the muscles or ventilator must workagainst. loadelastic ( volume & inv. Prop t0 compliance)resistance ( Raw & inspiratory flow) 14. Equation of motion for respiratorysystem Muscle pressure + ventilator pressure = (volume / compliance)+ (resistance x flow) Flow- its the unit of volume by unit of time. Resistance- it is the force that must be overcome to movethe gas through the conducting airways. It is described by the poiseulles law. 15. Lung compliance Lung compliance: Is the change in volume per unit change in pressureCOMPLIANCE = Volume / Pressure 16. Types Static compliance- is measured when there is no air flow. Reflects the elastic properties of the lung and the chestwall Dynamic compliance is measured when air flow ispresent Reflects the airway resistance (non elastic resistance) andelastic properties of lung and chest wall Static compliance=Corrected tidal volumePlateau pressure-PEEP Dynamic compliance corrected tidal volumePeak inspiratory pressure-PEEP 17. What is a mechanical ventilator? A machine or a device that fully or partially substitute for the ventilatory work accomplished by the patients muscles. Components INPUT POWER DRIVE MECHANISM CONTROL CIRCUITOUTPUT WAVEFORMSALARMS 18. INPUT POWER It can be Pneumatically powered(uses compressed gases) Electrically powered(uses 120 Volts AC/12Volts DC)Here the electric motor drives pistons and compressorsto generate gas flows . Microprocessor controlled- combined.Also called as 3rd generation ventilators. 19. Source of Gas Supply Air - Central compressed air, compressor, turbine flowgenerator, etc Oxygen Central oxygen source, O2 concentrator, O2cylinder Gas mixing unit O2 blender 20. DRIVE MECHANISM Its the system used by the ventilator to transmit orconvert the input power to useful ventilatory work. This determines the characteristic flow and pressurepatterns produced by the ventilator. It includespistons bellows reducing valves pneumatic circuits 21. Piston mechanismBellows mechanismPneumatic mechanism 22. Pneumatic circuits- uses pressurized gas as powersource. these are microprocessor controlled with solenoidvalves. use programmed algorithms in microprocessor toopen and close solenoid valves to mimic any flow orpressure wave pattern. 23. Control circuit Its the system that governs the ventilator drivemechanism or output control valve. Classified as- Open circuits- desired output is selected and venti.achieves it without any further input from clinician. Closed circuits- desired output is selected and venti.Measures a specific parameter (flow/vol/press)continuously and input is constantly adjusted tomatch desired output.a.k.a SERVO controlled. 24. Control parameters Pressure Volume Flow Time 25. Ventilators deliver gas to the lungs using positivepressure at a certain rate. The amount of gasdelivered can be limited by time, pressure orvolume. The duration can be cycled by time,pressure or flow.If volume is set, pressure varies..if pressure is set,volume varies.. .according to the compliance... 26. Mechanical- employs levers or pulleys to control drivemechanism. Pneumatic Fluidic- applies gas flows and pressure to controldirection of other gas flows and to perform logicfunctions based on the COANDA effect. Electronic- uses resistors and diodes and integratedcircuits to provide control over the drive mechanism. 27. Pressure controller Ventilator controls the trans-respiratory systempressure . This trans-respiratory system gradient determines thedepth or volume of respiration. Based on this a ventilator can be positive or negativepressure ventilator. 28. Volume controller Volume cycled ventilation delivers a: set volume; with a variable Pressure - determined by resistance, compliance and inspiratory effort 29. Flow controller Allows pressure to vary with changes in patient scompliance and resistance while controlling flow. This flow is measured by vortex sensors or venturipnemotachometers.Time controllermeasures and controls inspiratory and expiratory time.These ventilators are used in newborns and infants Inspiratory time is a combination of the inspiratory flowperiod and time taken for inspiratory pause. The followingdiagram depicts how the addition of an inspiratory pauseextends total inspiratory time. 30. Normal inspiratory time of a spontaneously breathing healthy adult is approximately 0.8- 1.2 seconds, with an inspiratory expiratory (I: E) ratio of 1:1.5 to 1:2 2.Its advantageous to extend the inspiratory time in order to: improve oxygenation - through the addition of an inspiratory pause; or toincrease tidal volume - in pressure controlled ventilationAdverse effects of excessively long inspiratory times are haemodynamic compromise,patient ventilator dysynchrony, and the development of autoPEEP. 31. Phase variablesA. Trigger . What causes the breath to begin? B CB. Limit What regulates gas flow during the breath? AC. Cycle . What causes the breath to end? 32. Phases of ventilator supported breathinspirationchange from inspiration to expirationexpirationchange from expiration to inspirationTypes of ventilator breaths- Mandatory breath Assisted breath Spontaneous breath 33. Trigger variable Its the variable that determines start of inspiration Triggering refers to the mechanism through which theventilator senses inspiratory effort and delivers gas flow ora machine breath in concert with the patients inspiratoryeffort. Can use pressure or volume or time or flow as a trigger. In modern ventilators the demand valve is triggered byeither a fall in pressure (pressure triggered) or a change inflow (flow triggered). With pressure triggered a preset pressure sensitivity has tobe achieved before the ventilator delivers fresh gas into theinspiratory circuit. With flow triggered a preset flowsensitivity is employed as the trigger mechanism. 34. Time triggering 35. Pressure Triggering Breath is delivered when ventilator senses patients spontaneousinspiratory effort. sensitivity refers to the amount of negative pressure the patientmust generate to receive a breath/gas flow. If the sensitivity is set at 1 cm then the patient must generate 1cm H2O of negative pressure for the machine to sense thepatients effort and deliver a breath. Acceptable range - -1 to -5 cm H2O below patient s baselinepressure If the sensitivity is too high the patients work of breathing willbe unnecessarily increased. It is not a reasonable course ofaction to increase the sensitivity to reduce the patientsrespiratory rate as it only increases their work of breathing. 36. Flow Triggering The flow triggered system has two preset variables fortriggering, the base flow and flow sensitivity. The base flow consists of fresh gas that flowscontinuously through the circuit. The patients earliestdemand for flow is satisfied by the base flow.The flow sensitivity is computed as the differencebetween the base flow and the exhaled flow Here delivered flow= base flow- returned flowHence the flow sensitivity is the magnitude of theflow diverted from the exhalation circuit into thepatients lungs. As the subject inhales and the set flowsensitivity is reached the flow pressure controlalgorithm is activated, the proportional valve opens,and fresh gas is delivered. 37. Flow triggerAdvantages --The time taken for the onset of inspiratory effort to the onset ofinspiratory flow is considerably less. -decreases the work involved in initiating a breath. 38. Limit variable 39. Cycle variable Defined as the length of one complete breathing cycle. Inspiration ends when a specific cycle variable isreached. This variable is used as a feedback signal to endinspiratory flow delivery which then allows exhalationto start. Most new ventilators measure flow and use it as afeedback signal. So volume becomes a function of flow and time Volume= flow x inspiratory time 40. Baseline variable The variable controlled during expiration phase. Mostly its pressure 41. Basic definitions Airway Pressures Peak Inspiratory Pressure (PIP) Plateau pressures Positive End Expiratory Pressure (PEEP) Continuous Positive Airway Pressure (CPAP) Inspiratory Time or I:E ratio Tidal Volume: amount of gas delivered with eachbreath 42. Pressures Mechanical ventilation delivers flow and volume to thepatients as a result of the development of a positivepressure gradient between the ventilator circuit andthe patients gas exchange units as illustrated in thediagram above. There are four pressures to be aware ofin regards to mechanical ventilation. These are the:PeakPlateauMean; andEnd expiratory pressures. 43. Peak Inspiratory Pressure (PIP)- The peak pressure is the maximum pressure obtainableduring active gas delivery. This pressure a function ofthe compliance of the lung and thorax and the airwayresistance including the contribution made by thetracheal tube and the ventilator circuit. Maintained at