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Dr David Lamond 2015
¡ Principles of Ventilation / Ventilator terminology§ 2 strategies
1. Injury – Every patient except #22. Obstruction – asthma / COPD
¡ Modes¡ Autoflow¡ NIV
Baseline variable¡ Positive End Expiratory Pressure (PEEP) –expiration passive
¡ PEEP of 3-‐5 cmH2O thought to be physiological when ETT insitu
¡ So even in Head injury should have at least 5 cmH2O
¡ Decreases shunt, improves V/Q match, decreases atelectasis /trauma
¡ Fraction of Inspired Oxygen Concentration (FiO2)§ Air mix = FiO2 60% or 0.6§ Oxylog3000 has oxygen blender = FiO2 0.4-‐1.0 (calculated not measured ie no oxygen sensor)
§ Always start at FiO2 = 1§ Correct after 1st gas, aim for FiO2 0.5 or less
¡ Start at 100% and PEEP 5 then titrate on ABG¡ Goal = PaO2 55-‐80mmHg or SaO2 88-‐95%
FiO2 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.7
PEEP 5 5 8 8 10 10 10 10 12
FiO2 0.7 0.8 0.9 0.9 0.9 1.0
PEEP 14 14 14 16 18 18-‐24
¡ Respiratory Rate (RR)§ Near physiological as
possible 10-‐20 breaths/min§ Usually set 18 breaths/min
– remember dead space§ Adjust on CO2§ Slow rates in COAD to
permit long expiration§ High rates in noncompliant
lungs with low VT(remember compensatory resp alkalosis)
¡ Tidal Volume (VT)§ Set to avoid excessive stretch 6-‐8 mls/kg
§ In ARDS 6mls/kg§ Use plateau pressure (Pplat) to measure –ideal should be < 30 cmH2O
§ Should not be altered to fix ventilation unless Pplat . 30cmH2O
¡ Plateau Pressure (Pplat)§ Most reflective of peak alveolar pressure
§ Should be less than 30 cmH2O
§ Occurs as expiratory valve remains closed for duration of Tinsp
§ Use Inspiratory Hold button
¡ Minute Ventilation (VE)§ The total amount of volume
moving in and out of the lung in one minute
§ VE = RR x VT (L/min)§ Ideal VE = 60ml/kg/min when
not intubated – needs to be doubled to 120ml/kg/min for deadspace
§ Need 240 ml/kg/min to change CO2 from 40 to 30
¡ Flow Rate§ Is the speed at which VT is delivered = patient comfort§ Normal setting 60-‐80 L/min§ Flow rate is chief determinate of Tinsp and thus I:E ratio
§ High flow > 60 L/min good for COAD (shorter Tinsp) but may increase Peak inspiratory Pressure (PiP)
§ Low flow rates (20 to 50 L/min) = increase inspiratory time with improved distribution gases
§ Most transport ventilators internal microchip controls flow based on VT, Pressure, I:E ratio and RR
¡ Rise time (Ramp)§ The amount of time it takes for set pressure to be reached from beginning inspiration
§ Adjusts the peak inspiratory flow rate
¡ Inspiratory: Expiratory Ratio (I:E ratio)§ Normal 1:2§ Shorter insp times
increase dead space ventilation
§ Longer insp times improve oxygenation but increase haemodynamic instability
§ Dependant on flow rate, inspiratory time and frequency
§ Adjunct to volume controlled ventilation
§ Delivers the set Tv at the lowest possible inspiratory pressure
§ Reduces peak airway pressure
§ Limits the inspiratory pressure control to 5 below P max
§ Breath is delivered with minimal flow to deliver the set volume within the set inspiratory time
§ Resulting end inspiratory pressure is used for inspiratory pressure for next breath
§ Then uses a decelerating inspiratory flow profile§ Once expiration begins it compares inspiratory volume to set tidal volume and adjust next inspiratory pressure
§ Adjusts +/-‐ 3 cmH2O per breath§ “VT low, pressure limit” if pressure required > 5 cm H2O below Pmax
¡ Goal = As much expiratory time as possible¡ TV = 8ml/kg¡ Flow Rate = 80-‐100 lpm so I:E of 1:4-‐5¡ PEEP = 0¡ FiO2 = usually 40%¡ RR = start at 10¡ Permissive Hypercapnia – Keep pH > 7.1
¡ Auto / Intrinsic PEEP§ (pulmonary gas trapping,
endogenous PEEP, occult PEEP, dynamic hyperinflation)
§ Result of insufficient expiratory time ie high RR, inverse I:E ratio
§ Continues until elastic recoil overcomes pressure
§ Measured doing expiratory hold
¡ Peak Inspiratory Pressure§ Peak pressure delivered during inspiration
§ Should not exceed 40 cmH2O – NB: plateau pressure does the damage
§ Ventilator CPR mode >60cmH2O the delivers inconstant volume at pressure
¡ Synchronised Intermittent Mandatory Ventilation / Assisted Spontaneous Breathing (ASB)
¡ Fixed mandatory minute volume (MV) set with VTand RR
¡ Patient can breathe spontaneously between the mandatory ventilation
¡ Supports inadequate spontaneous breathing or weaning
¡ The following are set on the screen: § Tinsp§ PEEP§ Trigger
¡ Successful patient triggering is indicated by an asterisk
¡ Prevents increase in frequency by prolonging next breathing time
¡ Minimum ventilation = VT x RR
¡ Trigger window = enables synchrony
¡ Pressure Control Ventilation (PCV)§ Upper Airway Pressure Level
is set and remains constant.§ Respiratory Rate is set.§ Tidal volumes will vary
according to lung compliance.
§ Ventilator will deliver set pressure level whether patient triggers a breath or mandatory breath is being delivered
§ Minute volume alarm and ETCO2 critical
¡ Assisted Spontaneous Breathing
¡ Detects flow then provides additional pressure over PEEP for breath
¡ ASB terminated if flow zero during phase 1, after 4 secs or flow < 25% in phase 2
¡ Continuous (Constant) Positive Airway Pressure (CPAP)§ Is a strictly patient dependant mode; patient must be breathing spontaneously.
§ CPAP is a constant set pressure that does not change during inspiration or expiration.
§ Weaning mode.