Mechanical ventilation for SARS The basics

Mechanical ventilation for SARSThe basics

Charles GomersallDept of Anaesthesia & Intensive CareThe Chinese University of Hong Kong

Prince of Wales Hospital

Version 1.0April 2003

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Disclaimer

• Although considerable care has been taken in the preparation of this tutorial, the author, the Prince of Wales Hospital and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from its use.

The problem

• Heterogenous involvement of lung– Normal compliance compliance– Overall: compliance

Inflates and deflates

normally

Inflates and deflates

normally

Hyperinflates

Hyperinflates

Hyperinflates

Tidal opening and collapse

Tidal opening and collapse

Collapsed

The problem

• Hyperinflated risk of volutrauma• Recurrent opening and collapse

risk of shear injury• Some alveoli persistently collapsed

shunting

The problem

• Heterogenous involvement of lung– Normal compliance compliance

• High risk of “barotrauma”

Barotrauma & volutrauma• Unrestricted lungs

– Pulmonary oedema at PAW of 45 cmH2O

• Restricted lungs– No pulmonary oedema at same

pressures

The problem

• Heterogenous involvement of lung– Normal compliance compliance

• High risk of barotrauma• Large shunt

– High oxygen requirement• Risk of oxygen toxicity

Principles

• Minimize FIO2

– SpO2 88-94%

Principles

• Minimize FIO2

• Low tidal volume and low inspiratory pressure– Start with 8ml/kg PBW and work down

to 4-6 ml/kg

Principles

• Minimize FIO2

• Low tidal volume and low inspiratory pressure– Start with 8ml/kg PBW and work down

to 4-6 ml/kg– Increase respiratory rate to maintain

minute ventilation• Check for intrinsic PEEP

Principles

• Minimize FIO2

• Low tidal volume and low inspiratory pressure– Start with 8ml/kg PBW and work down to 4-

6 ml/kg– Increase respiratory rate to maintain minute

ventilation• Check for intrinsic PEEP

– Allow PaCO2 to rise– Keep pH>7.3 if possible

Principles

• Minimize FIO2

• Low tidal volume and low inspiratory pressure– Start with 8ml/kg PBW and work down to 4-6

ml/kg– Increase respiratory rate to maintain minute

ventilation• Check for intrinsic PEEP

– Allow PaCO2 to rise– Keep pH>7.3 if possible– Sedation ± paralysis

Practice

• Start with FIO2=1.0• Choose the mode that you and the

other staff in your ICU are most familiar with

Volume controlPRVCPressure control

Before selecting a mode of ventilation download and printthe relevant algorithm for ventilating SARS patients

Download

http://www.aic.cuhk.edu/web8/mech%20vent%20SARS.htm

Volume control

• Measure patient’s height and calculate PBW

• Set PEEP 6-12 cmH2O, I:E=1:2• Start with VT=8 ml/kg PBW• At 1-2 hour intervals decrease VT by 1

ml/kg to a minimum of 4 ml/kg– Maintain 4-6 ml/kg

• Every 4h and after each change measure Pplat, PEEPi, and pH

Click here to continue

Volume control

• PEEPi

– Aim for <2 cmH2O– ie PEEPtotal – PEEPe <2


Volume control

• Pplat

– Aim for 25-30 cmH2O• <25: VT up to 6 ml/kg• 25-30: VT up to 7-8 ml/kg and

respiratory rate if PEEPi increased due to rapid respiratory rate

• >30: VT to minimum of 4 ml/kg


Volume control

• Aim for pH>7.3– 7.15-7.3:

set respiratory rate until– Rate=35 bpm or– pH=7.3 or

– PaCO2<3.25

• If RR=35 and pH<7.3 NaHCO3 may be given.


Volume control

– <7.15: set RR to 35

• If RR=35 and pH<7.15 and NaHCO3 has been considered, VT may be in 1 ml/kg steps until pH>7.15 (Pplat target may be exceeded)


Volume control

– >7.45 set respiratory rate until patient RR>set

RR (do not decrease set RR below 6 bpm)

Click here to return to the modes menu

Pressure control

• Measure patient’s height and calculate PBW

• Set PEEP 6-12 cmH2O, I:E =1:2• Start with pressure control level that

results in VT=8 ml/kg PBW • At 1-2 hour intervals pressure to VT by

1 ml/kg to a minimum of 4 ml/kg– Maintain 4-6 ml/kg

• Every 4h and after each change measure airway pressure, PEEPi, and pH


Pressure control

• PEEPi



Pressure control

• PAW and VT

– Aim for 25-30 cmH2O and VT 4-6 ml/kg• <25 and VT <6 ml/kg: pressure to VT

up to 6 ml/kg• 25-30: pressure to VT up to 7-8 ml/kg

and respiratory rate if PEEPi increased due to rapid respiratory rate

• >30 or VT >6 ml/kg: pressure (do not allow VT to fall below 4 ml/kg)


Pressure control

• Aim for pH>7.3– 7.15-7.3:

set respiratory rate until– Rate=35 bpm or– pH=7.3 or

– PaCO2<3.25



Pressure control

– <7.15: set RR to 35

• If RR=35 and pH<7.15 and NaHCO3 has been considered, pressure may be to VT in 1 ml/kg steps until pH>7.15 (PAW

target may be exceeded)


Pressure control




Pressure regulated volume control• Measure patient’s height and calculate

PBW• Set PEEP 6-12 cmH2O• Set upper pressure alarm limit=35• Start with VT=8 ml/kg PBW• At 1-2 hour intervals decrease VT by 1

ml/kg to a minimum of 4 ml/kg– Maintain 4-6 ml/kg

• Every 4h and after each change measure PAW, PEEPi, and pH


Pressure regulated volume control• PEEPi



Pressure regulated volume control• Recurrent “Limited pressure

breath” or high airway pressure alarm VT to minimum of 4 ml/kg


Pressure regulated volume control• PAW

– Aim for 25-30 cmH2O• <25: VT up to 6 ml/kg• 25-30: VT up to 7-8 ml/kg and

respiratory rate if PEEPi increased due to rapid respiratory rate


Pressure regulated volume control• Aim for pH>7.3

– 7.15-7.3: set respiratory rate until

– Rate=35 bpm or– pH=7.3 or

– PaCO2<3.25



Pressure regulated volume control

– <7.15: set RR to 35

• If RR=35 and pH<7.15 and NaHCO3 has been considered, VT may be in 1 ml/kg steps until pH>7.15 (Upper pressure limit may be increased and PAW target may be exceeded)


Pressure regulated volume control




Prone ventilation

Mediastinum

Consolidated lung

ventilation, perfusion

ventilation, perfusion

Prone ventilation

• In prone position:– ventilation now

preferentially goes to dorsal region

– recruitment of alveoli

– alveoli in ventral regions remain open because of PEEP

Prone ventilation

• Improved VQ matching– ventilation to

dorsal region improved

– perfusion continues to go preferentially to dorsal region

Prone ventilation

• On return to supine position:– alveoli in dorsal

regions may remain open because of PEEP resulting in a persistent response

Complications

• Accidental extubation• Others:

– pressure effects on skin and eyes– disconnection of intravenous lines– haemodynamic instability

Practical aspects

• Consider for patients requiring more than 50% oxygen

• Turn prone and leave prone until for a minimum of a few hours

• Pillows under chest, abdomen and pelvis. Head support

Practical aspects

• If a responder turn back to supine once a day– Nursing care– Examination– Change lines– Persistence of response

• If not a responder try removing pillow from under abdomen

Practical aspects

• Do not disconnect from ventilator• Care with ETT and lines• Check pressure points including

eyes• Heavy sedation ± paralysis

Key points

• Minimize further lung damage– Minimize FIO2

– Low tidal volumes and inspiratory pressures titrated against pH

– Consider prone ventilation

Mechanical ventilation for SARS The basics

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