Mechanical ventilation for SARS The basics Charles Gomersall Dept of Anaesthesia & Intensive Care The Chinese University of Hong Kong Prince of Wales Hospital Version 1.0 April 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

Hyperinflates

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 P AW of 45 cmH 2 O 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 F I O 2 –SpO %

Principles Minimize F I O 2 Low tidal volume and low inspiratory pressure –Start with 8ml/kg PBW and work down to 4-6 ml/kg

Principles Minimize F I O 2 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 F I O 2 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 PaCO 2 to rise –Keep pH>7.3 if possible

Principles Minimize F I O 2 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 PaCO 2 to rise –Keep pH>7.3 if possible –Sedation ± paralysis

Practice Start with F I O 2 =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 print the relevant algorithm for ventilating SARS patients Download

Volume control Measure patient’s height and calculate PBW Set PEEP 6-12 cmH 2 O, I:E=1:2 Start with V T =8 ml/kg PBW At 1-2 hour intervals decrease V T by 1 ml/kg to a minimum of 4 ml/kg –Maintain 4-6 ml/kg Every 4h and after each change measure P plat, PEEP i, and pH Click here to continue

Volume control PEEP i –Aim for <2 cmH 2 O –ie PEEP total – PEEP e <2 Click here to continue

Volume control P plat –Aim for cmH 2 O <25:  V T up to 6 ml/kg 25-30:  V T up to 7-8 ml/kg and  respiratory rate if PEEP i increased due to rapid respiratory rate >30:  V T to minimum of 4 ml/kg Click here to continue

Volume control Aim for pH>7.3 – :  set respiratory rate until –Rate=35 bpm or –pH=7.3 or –PaCO 2 <3.25 If RR=35 and pH<7.3 NaHCO 3 may be given. Click here to continue

Volume control –<7.15:  set RR to 35 If RR=35 and pH 7.15 (P plat target may be exceeded) Click here to continue

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 cmH 2 O, I:E =1:2 Start with pressure control level that results in V T =8 ml/kg PBW At 1-2 hour intervals  pressure to  V T 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, PEEP i, and pH Click here to continue

Pressure control PEEP i –Aim for <2 cmH 2 O –ie PEEP total – PEEP e <2 Click here to continue

Pressure control P AW and V T –Aim for cmH 2 O and V T 4-6 ml/kg <25 and V T <6 ml/kg:  pressure to  V T up to 6 ml/kg 25-30:  pressure to  V T up to 7-8 ml/kg and  respiratory rate if PEEP i increased due to rapid respiratory rate >30 or V T >6 ml/kg:  pressure (do not allow V T to fall below 4 ml/kg) Click here to continue

Pressure control Aim for pH>7.3 – :  set respiratory rate until –Rate=35 bpm or –pH=7.3 or –PaCO 2 <3.25 If RR=35 and pH<7.3 NaHCO 3 may be given. Click here to continue

Pressure control –<7.15:  set RR to 35 If RR=35 and pH 7.15 (P AW target may be exceeded) Click here to continue

Pressure 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 regulated volume control Measure patient’s height and calculate PBW Set PEEP 6-12 cmH 2 O Set upper pressure alarm limit=35 Start with V T =8 ml/kg PBW At 1-2 hour intervals decrease V T by 1 ml/kg to a minimum of 4 ml/kg –Maintain 4-6 ml/kg Every 4h and after each change measure P AW, PEEP i, and pH Click here to continue

Pressure regulated volume control PEEP i –Aim for <2 cmH 2 O –ie PEEP total – PEEP e <2 Click here to continue

Pressure regulated volume control Recurrent “Limited pressure breath” or high airway pressure alarm –  V T to minimum of 4 ml/kg Click here to continue

Pressure regulated volume control P AW –Aim for cmH 2 O <25:  V T up to 6 ml/kg 25-30:  V T up to 7-8 ml/kg and  respiratory rate if PEEP i increased due to rapid respiratory rate Click here to continue

Pressure regulated volume control Aim for pH>7.3 – :  set respiratory rate until –Rate=35 bpm or –pH=7.3 or –PaCO 2 <3.25 If RR=35 and pH<7.3 NaHCO 3 may be given. Click here to continue

Pressure regulated volume control –<7.15:  set RR to 35 If RR=35 and pH 7.15 (Upper pressure limit may be increased and P AW target may be exceeded) Click here to continue

Pressure regulated 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

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 F I O 2 –Low tidal volumes and inspiratory pressures titrated against pH –Consider prone ventilation