Invasive Mechanical Ventilation

Has the advantage of allowing the patient to take a spontaneous breath at any point during a mandated breath and so improves synchrony and facilitates transitioning to spont breathing.

P low (PEEP).  Start at 5cmH20 unless Fi02 determines higher PEEP required.

P high. Set to achieve Tv of 6-8mls/kg.  Typically 10-15cmH20 higher than P low.

T high and T low.  Initially fix to achieve I:E of 1:2 at rate of 15 /min (14-24/min is the usual range).

A dual mode of ventilation that automatically adjusts the inspiratory pressure to the lowest level required to achieve a pre-determined Tv, and so minimises the risk of barotrauma.

Initial settings

• Tv 6-8 mls/kg
• Peak insp pressure 35 cmH20, Plateau pressure < 30cmH20
• PEEP 5-8 cmH20 (but increased in accordance with Fi02)
• RR 15/min
• T insp is normally around 1 sec, to achieve I:E of 1:2

PRVC is not recommended when there is obstructive lung pathology due to fluctuating Tv or if patient ventilatory drive is particularly high.

Taken from ARDSnet

High PEEP strategy should be considered in patients with moderate to severe ARDS in whom compliance is evidently improved by the application of PEEP.

PEEP tables provide guidelines only and ventilator settings should be tailored based on an individuals response

Care must be taken to avoid Pplat exceeding 30cmH20, by adjusting Tv targets.

1. Rapid hypoxaemia
   • Exclude pneumothorax, bronchospasm, pulmonary oedema, PE, endobronchial intubation, mucus plugging
2. Gradual hypoxaemia
   • Increase Fi02
   • Increase mean airway pressure, by either increasing PEEP or inspiratory time (move to I:E of 1:1 or reversed
3. Gradual hypercapnia
   • Increase RR
   • Eliminate dead space: Increase inspiratory time, Increase PEEP
   • Check for leaks
   • Assess for dyssynchrony
   • Take care not to increase Tv or P peak or plateau beyond safe levels; it is often preferable to tolerate hypercarbia
4. Ventilator dyssynchrony
   • Ineffective triggering (commonest): reduce trigger sensitivity
   • Inadequate flow ("fish out of water"): increase flow rate or frequency.  Change from PRVC to BiLEVEL
   • Premature cycling: increase trigger sensitivity
   • Breath-stacking: monitor closely for if obstructive pathology.  Ensure exp flow has ceased prior to next breath.  Reduce T insp to 0.8 sec and increase I:E to 1:4-6.

STEP 1- Staff & Equipment

• Ensure adequate numbers of staff available (5, inc. airway Dr)
  • Introduce themselves and state their role.
  • Airway Doctor positioned at the head end of the patient and is responsible for co-ordinating the procedure. At least two other people either side of the patient, depending on the size of the patient. Additional staff should be allocated to the management of chest drains/ ECMO cannulas if in situ.

• Consider:
  • Investigations/ procedures/ transfers that may be difficult post proning.
  • Airway trolley checked and available. Note intubation grade and current ETT details.
  • Adequate sedation
  • NBM prior to proning. Document NGT length & skin integrity.

• Securely tie the ETT, with tapes and pad between ties and skin. Suction oropharynx and airway prior to procedure & ensure closed circuit suctioning is available. If tracheostomy, then change inner tube.
• Pre-oxygenate with 100% O₂.
• Check ventilator settings- note Vt and pInsp. Perform pre-proning ABG and document results.
• Ensure all lines/ drains are sutured and secured (above waist to head, below waist to feet).
• Prepare vasopressor/ inotropes in case of CVS instability & discontinue non-essential infusions and monitoring. ECG electrodes removed.
• Stop feed and aspirate tube.
• Clean, lubricate and protect eyes.

STEP 2 - Positioning

• Patient should be laid flat with the bed in a neutral position, on a clean sheet with a slide sheet beneath.
• The arm closest to the ventilator is tucked underneath the buttock with the palm facing anteriorly (See diagram).

STEP 3 – Wrapping the patient

• Pillows placed over the chest, iliac crest, and knees- strategically, according to the patient’s body habitus to reduce the pressure placed upon the abdomen.
• A clean bed sheet should be placed on top of the patient leaving only the head and neck exposed The edges from the top and bottom bed sheets are rolled tightly together thereby encasing the patient between the two and keeping the pillows in the correct position on top of the patient.

STEP 4- The ‘Roll’

• Keeping the bed sheets pulled taught and the edges rolled tight, the patient should be moved horizontally to lie on the edge of the bed – the opposite side to the ventilator.
• On the call of the Airway Doctor, at the head end, whilst maintaining a tight grip on the rolled-up sheets the patient is rotated 90°, to lie on their side (now facing towards the ventilator).
• Staff on either side should then adjust their hand positions on the rolled-up sheets, so that they now have hold of the opposite edge when compared to the horizontal move.
  • This should be done one hand at a time, led by one person.
• On the call of the person at the head end, the rolled-up sheet is pulled up from beneath the patient whilst the patient is carefully turned into the prone position. As the patient is moved from lateral to prone, the Airway Doctor is to turn the head to face the ventilator.
  • Ensure the ETT is not kinked and that a CO₂ trace is still present on the capnograph. Note the length of the ETT at the lips and review ventilator settings.
  • Reattach the ECG electrodes and ensure all monitoring is re-established.

STEP 5- Repositioning & ‘Swimming’

• Ensure the patient is in the centre of the bed. Then, remove the slide sheet. An absorbent pad should be placed under the patient’s head for secretions.
• Position the arms in the ‘swimmers’ position’. Raise one arm on the same side to which the head is facing whilst placing the other arm by the patient’s side.
  • The shoulder should be abducted to 80° and the elbow flexed 90° on the raised arm.
  • The position of both the head and arms should be alternated every two to four hours.
• The patient should be nursed at 30° in the ‘reverse Trendelenburg’ position.
• Finishing points:
  • Ensure optimal positioning of pillows tailored to the patient’s body habitus.
  • Pressure areas should be meticulously checked.
    • No direct pressure on the eyes.
    • Ears not bent over.
    • ETT not pressed against the corner of the mouth / lips.
    • Nasogastric tube not pressed against nostril.
    • Penis hanging between the legs with the catheter secured.
    • Lines / tubing not pressed against the skin.

PRONE POSITIONING CHECKLIST

In the event of multiple casualties and / or constraints of the austere environment it will be necessary to monitor oxygen supplies

Gas consumption can be estimated from:

(minute ventilation + bias flow) x (Fi02 -0.2/0.8) + cycling requirement)

As a guide for the EVE-TR2 ventilator

- It does not consume oxygen to operate given it has an internal air turbine

- Oxygen flow can be calculated as: 02 Flow (L/min) = (MV + Bias Flow) x (FI02 -21/80)

Bias flow is typically 3L/min

At a minute vol of 8L/min and Fi02 of 60% this equates to 5.4L/min

-  Oxygen flows will be much higher if the ventilator is used for NIV, up to 50 - 60L/min delivering Fi02 100%