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Setting up the Vent

Values in RED are default settings for initial set-up/emergencies. They will need to be reviewed on an ongoing basis with each patient

Mode

SIMV-Volume control (VC)

  • A set tidal volume is delivered

  • Breaths are delivered at a set rate, with the ventilator also supporting additional breaths initiated by the patient

  • Default​

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SIMV – Pressure control (PC)

  • A set pressure is delivered, generating a tidal volume

    • Pressure should be adjusted to achieve appropriate tidal volumes (see below)

  • Breaths are delivered at a set rate, although additional patient initiated breaths are also supported

  • May be better tolerated by patients with variable compliance or ventilatory dysynchrony

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Pressure support

  • All breaths are patient initiated, with the pressure support provided by the ventilator assisting the patient breath

    • Backup ventilatory rate set to prevent total apnoea (typically 10 sec)

  • Requires less sedation

    • Inappropriate if paralysed or deeply sedated due to apnoea or slow respiratory rate

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Oxygenation

Positive End Expiratory Pressure (PEEP)

  • The amount of pressure present at the end of expiration​

  • PEEP should be increased if:

    • Hypoxia (FiO2 >0.5)

    • Obesity (BMI >35 or prominent truncal obesity)

    • Evidence of atelectasis on CXR or auscultation

  • PEEP may be increased to 10-15cmH2O, with up to 20cmH2O in exceptional cases

    • Note that PEEP + Pressure support cannot exceed 35cmH2O to prevent lung damage (barotrauma)

10cmH2O

Fraction of inspired oxygen (FiO2)

  • Set at 100% post intubation

  • Titrate down to maintain oxygen saturation > 88%

    • FiO2 in excess of that required causes atelectasis and direct lung trauma, and should be avoided

    • PaO2 > 60 mmHg is sometimes used as an alternative target, but note:

      • SaO2 must be the primary end-point of oxygen therapy​

      • Increasing FiO2 where saturations are above target, in order to increase PaO2, is almost always unnecessary

Maintain SaO2 > 88%

Ventilation (CO2 Removal)

Tidal volume

  • Tidal volume: 6-8ml/kg of IDEAL BODY WEIGHT

    • This is calculated based on patient HEIGHT

  • Setting tidal volume is dependent on ventilator mode

    • Volume control

      • Directly set by the operator

      • Monitor Peak pressures (PIP) and plateau pressures as this will rise if greater volumes are delivered

  • Pressure control

    • Pressure control determines amount of pressure delivered, and hence tidal volume

    • Monitor delivered volume

  • Pressure support

    • Pressure support determines delivered volume, similar to pressure control

6 - 8 ml/kg IBW

Respiratory rate

  • Typically set at 10-14 initially

    • Faster rates may be used post intubation in patients with hypercarbia and tachypnoea prior to intubation

  • Titrated to maintain arterial CO2 concentrations

    • Up to rate of 30

    • Monitor the I:E ratio - this will change with respiratory rate.

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I:E Ratio (inspiratory to expiratory time ratio)

  • Proportion of each respiratory cycle in inspiration and expiration

    • Determined by respiratory rate, inspiratory flow rate and set tidal volume

  • Normally 1:2

    • Aim to increase in patients with bronchospasm (eg 1:3-4+)

    • Should never be less than 1:1

Commence at 15 breaths/minute

       Author: Dr. Ryan Slack, Peer Reviewer: Dr. Irma Bilgrami Date: 22/03/20

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