Ventilation

Michelle JardinePICU Cons

Oxygenation IndexOI= MAP×FiO2÷PaO2OI>40 predictive of mortality ≥ 80%Consider ECMO OI> 25, mandatory when OI>40.Higher mental developmental score and lower incidence of mortality at one year when ECMO instituted early

Ventilation /Perfusion mismatchPerfect lung- ventilation and perfusion equally matchedNormal lungs- upper zones over-ventilated lower zones over-perfused and under-ventilatedDiseased lungs marked mismatch between ventilation and perfusionShunt deoxygenated venous blood passes unventilated alveoli to enter the systemic arterial system with unchanged PO2.

Diffusion of oxygen into the bloodNormal lung- diffusion of oxygen into blood rapidLung can compensate- poor gas diffusion rare cause of hypoxia except in diseases like alveolar fibrosisHypoxic pulmonary vasoconstriction- blood vessels of lung vasoconstrict and reduce blood flow to areas that are under-ventilated- reduces effects of shunt.

Failure to OxygenateObstruction of gas exchange between alveoli and capillaries.Interstitial process- pulmonary oedemaDiffusion defect- alveolar fibrosisVentilation/ perfusion mismatchShuntAlveolar dead spaceRight to left intra-pulmonary shunting

Cardiopulmonary InteractionsBlood pressure↓ as Ventilation ↑Intra-thoracic pressure transmitted to vena cavaeAlters effective pre-load

Acute Lung InjuryNon- cardiogenic pulmonary oedemaPaO2/FiO2 < 300Bilateral infiltrates on CXREnd result broad range injuries either local or remotePneumonia, Aspiration, Radiation, Sepsis, Burns, Trauma, Poisoning etc

ARDSARDS= severe form lung injury (PaO2/FiO2 <200)Systemic inflammation, increased capillary permeability, protein-rich fluid in alveoli, deficiency of surfactant, hyaline membrane formation, lung collapseInflammatory phase (0-7days)Proliferative phase (7-21 days)Fibroitic phase (day 10 +)

Mechanisms ARDSOxygen toxicityOver distension of alveoli (volutrauma and barotrauma)Repetitive opening and closing causing shear stress- triggering further inflammation(atelectrauma)

Pressure Volume loopsVolume

inspiration

Expiration Upper inflection point

Lower inflection pointPressure

Volume ventilation Pressure Ventilation

Volume Volume

Expiration

Pressure Pressure

Inspiration Expiration Inspiration

Conventional ventilation modesControl- Every breath fully supported by ventilator. Patient unable to breathe except at controlled rate.IMV-Vent synchronises IMV breath with patient’s effort. Breaths above set rate not supported.Pressure support- Vent supplies pressure support, but no set rate.

Modes on BabyPAC ventilatorCMV controlled mechanical ventilationCMV + active PEEP (provides CPAP in-between ventilations)IMV ventilator attempts to synchronise with patients respiratory effortCPAP continuous PEEP

Which mode should I use?CMV

Controls & FeaturesMonitor Module Incorporating patient pressure manometer and illuminated visual alarms / indicators

Separate controls for inspiratory and expiratory times Allows easy selection of optimum ventilationInspiratory Time = 0.25 seconds to 2 secondsExpiratory Time = 0.25 seconds to 4 seconds (on IMV, E Time = 2.5 seconds to 40 seconds)

Four Operating Modes:• CMV +PEEP• CMV +ACTIVE

PEEP• IMV + CPAP • CPAP

Inspiratory Pressure Control12-70 cmH2OWith click action warning at & above 40 cmH2O

PEEP/CPAP ControlWith click action warning at & above 10 cmH2O.0-20 cmH2O on CMV + PEEP only.3 - 20 cmH2O on CPAP & CMV + Active PEEP

Unique variable concentration gas mixing system Oxygen concentrations between 21% and 100% can be selected. With O2 supply Only = 45 - 100%With Air supply Only = 21%With O2 & Air Supply = 21% - 75%

Supply Gas Failure IndicatorAir

Supply Gas Failure IndicatorOxygen

Independent, adjustable, pneumatic, high pressure alarm 12-80 cmH2O

baby

PA

C B

100

Alarm moduleba

byP

AC

B10

0 High Pressure IndicatorFlashes red, with audible alarm, at set alarm pressure and with continuous positive pressure

Normal Cycle IndicatorFlashes green each time inflation pressure rises through 10 x100Pa

Low Pressure (disconnect) IndicatorFlashes yellow, with audible medium priority alarm, if pressure does not rise through 10 x100Pa (10cmH2O) within 7.5 seconds

Silence/Mute ButtonSilences audible alarm for 60 seconds

Silenced/Muted IndicatorFlashes orange to indicate alarm silenced or muted

Single Gas Operation IndicatorFlashes green whenever the ventilator is operating on a single gas supply (oxygen or air only)

Low Battery IndicatorProvides both visual low voltage indication as early warning and battery failure alarm (visual and audible)

Patient Inflation Pressure MonitorIndicates from -10 to +100 x100Pa (-10 to +100cmH2O)

Modes on Evita 4BIPAP (Like pressure control but synchronised; can also add ASB above PEEP) SIMV (Like volume control but synchronised; can also add ASB above PEEP)ASB (CPAP or pressure support ventilation)APRV (Pressure ventilation with inverse I:E ratio

Which mode should I use?SIMV large patients, post-op

cuffed tubes, stable patients

BIPAP small patients, high pressures,uncuffed tubes, unstable patients

How would I ventilate a baby?Start with 50% Oxygen when unwellUnless cardiac!Inspiratory time 0.5 secondsPressures 16/5 if not lung problemPressures higher 25/7 if primary lung problemRate of 35

How would I ventilate a child?Start with 50% oxygen when unwellInspiratory time 0.7 secondsPressures 18/5 if not lung problemPressures 30/10 if primary lung problemRate of 25

How would I ventilate a teenager?Start with 50% oxygen if unwellVolume ventilate use tidal volume of 500mls (may need 750mls if big patient)Watch how much pressure generatedRate of 20

Lung protection ventilation strategiesRecruitment- Ventilating just below upper inflection point with HFOVPermissive hypercarbia- Aim pH ≥ 7.25 ignore CO2, limit VT, lower mortalityProne- minimises alveolar collapse in dependant lung regions- changes regional lung perfusion and recruitment of dorsal lung

Lung protection ventilation strategiesLower tidal volume and high PEEPLarge swings in tidal volume= volutrauma + barotraumaPEEP improves oxygenation- moves fluid from alveolar to interstitial space, recruits small airways and collapsed alveoliKeep PEEP above the lower inflection point

How would I ventilate?AsthmaPulmonary Oedema/ HaemorrhageBronchiolitisPulmonary hypertensionHead Injury

When should I use sedation?As soon as intubatedProviding blood pressure is adequateStart with IV sedation

Opioids- MorphineOnly agent used in neonates Combined with midazolam in infants and childrenReceptors mu- thalamus and spinal cordKappa- hypothalamusDelta deep cortex and amygdalaMorphine acts at mu and Kappa receptors

Opioids- MorphineElimination half life 9 hours preterm, 7 hours neonate and 5 hours in the older infant.Bolus 20mcg/kg (can be repeated)Make 1mg/kg up to 50mls (1ml=20mcg/kg)Start infusion 20mcg/kg/hr

Benzodiazapines- MidazolamMost common drug used for sedationSite of action- limbic and reticular activating systemFacilitate GABA opening of chloride channels (decreases neuronal excitability)

Benzodiazapines- MidazolamMidazolam half life of 1-4 hoursCan get withdrawal after modest useBolus 100mcg/kg (can be repeated)Make up 50mg in 50mlsRun @ 0.1ml/kg/hr= 100mcg/kg/hr

Oral SedationFrequently used route in childrenReduces IV sedation usedChloral hydrate (metabolised in liver, renal excretion, half life 8-66hrs)Chloral hydrate 50mg/kg qdsVallergan/ Trimeprazine 1mg/kg qds