Wollongong CGD, October 31 Mechanical Ventilation

“If you take a dead animal and blow air through its larynx [through a reed], you will fill its bronchi and watch its lungs attain the greatest distention.” Galen

Indications for Ventilation ALI Apnoea and Respiratory Arrest COPD Respiratory Acidosis (elevated PC02) Increased work of breathing Hypoxaemia Hypotension (sepsis, shock, CCF) Neurological Disease (ALS, Muscular Dystrophy)

Types of Ventilation Invasive ventilation (Positive Pressure) Volume Control Pressure Control

Volume Control Ventilation

Pressure Control Ventilation

Complications Barotrauma VALI (Ventilator associated lung injury) Diaphragmatic atrophy Impaired mucociliary function Ventilator associated pneumonia

Ventilator Set-Up. Select mode (CMV / SIMV) Set tidal volume (PS in pressure controlled ventilation) Set IFR Set FIO2 and PEEP (oxygenation) Set RR (ventilation)

Case 1 25 year old female with severe asthma is intubated shortly after arrival to the ED. You have been asked to retrieve the patient. On arrival to the ED you find a very unwell patient. (P 140, BP 70/40, Pulse Ox 80% on 100% oxygen) She is chewing on the tube and is breathing up over the ventilator settings.

Case 1 ABG; pH 7.30, PO2 60, PCO2 70, BE -1. Acute respiratory acidosis with hypoxaemia.

Management?

Case 1 Hypotension - likely due to breath-stacking. Disconnect from ventilator and allow to exhale. Goals are to support fatigued patient and allow adequate time to expire.

Case 1 Set mode to CMV Patients tidal volume should be at a preset 8 mL/kg (based on ideal body weight) Increase IFR to L per minute (allows more prolonged expiratory phase)

Case 1 Oxygenation is usually not a problem. PEEP is for alveolar recruitment, which is not required in this setting. Set PEEP to zero and adjust FIO2 to maintain O2 sats 88-92%.

Case 1 Respiratory Rate - most important setting in asthmatic patient. Set rate low (permissive hypercapnoea) pH and PCO2 up to 90 mmHg.

Case 1 Low breath rate allows adequate exhalation time, preventing autoPEEP and air-trapping. Check the waveform to ensure return to baseline between breaths. If not, then reduce the respiratory rate.

Case 1 Check airway pressures. Peak airway pressure is not useful. Check the PLATEAU Pressure. Press inspiratory hold button to measure. Aim for pressure less than 30 mmHg. If elevated, then reduce tidal volume.

Case 1 Asthmatic patients require deep sedation. Use propofol as it has a bronchodilatory effect. Don't forget to give analgesia as well - use fentanyl infusion.

Case 1 Don't forget to treat the underlying problem (asthma) Steroids, bronchodilators, magnesium

Case 2 65 year old male - MVA 24 hour previously. Admitted to HDU for observation with multiple rib fractures. 18 hour after admission, he becomes severely SOB and requires intubation.

Case 2 ARDSnet showed mortality reduction using a lung protective ventilation strategy.

Case 2 Tidal volume of 6-8 mL/kg Based on lean body weight Start high and reduce rate as needed.

Baby Lungs

Case 2 IFR set lower at L per minute. More comfortable for the patient.

Case 2 Respiratory Rate (ventilation) Start at 18 breaths per minute and titrate to PCO2.

Case 2 - FIO2 / PEEP Oxygenation (SpO %) Increased PEEP does not cause PTx Increased PEEP will cause reduced venous return and hypotension.

Case 2 Benefits of PEEP Reduced atelectasis Reduced shunt Increase in V/Q ratio

Case 2 FIO2 / PEEP; Start at 100% oxygen for the intubation and then reduce down to 40%. Titrate FIO2 and PEEP up to aim for target Sp02.

Case 2 Plateau Pressure should be less than 30 mmHg (lung protective effect) Reduce tidal volume if pressure too high.

Teaching Points 2 main strategies - Obstructive Lung Disease and Acute Lung Injury. COPD / Asthma - oxygenation NOT the issue - it’s fatigue. Permissive hypercapnoea and prolonged expiratory times. ALI - “Baby Lungs” - aim to ventilate only the normal “uninjured alveoli” using lung protective strategy.