Mechanical Ventilation
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Transcript of Mechanical Ventilation
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Wollongong CGD, October 31
Mechanical Ventilation
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“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
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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)
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Types of Ventilation
• Invasive ventilation (Positive Pressure)
• Volume Control
• Pressure Control
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Volume Control Ventilation
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Pressure Control Ventilation
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Complications
• Barotrauma
• VALI (Ventilator associated lung injury)
• Diaphragmatic atrophy
• Impaired mucociliary function
• Ventilator associated pneumonia
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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)
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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.
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Case 1
ABG; pH 7.30, PO2 60, PCO2 70, BE -1.
Acute respiratory acidosis with hypoxaemia.
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Management?
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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.
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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 80-100 L per minute (allows more prolonged expiratory phase)
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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%.
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Case 1
• Respiratory Rate - most important setting in asthmatic patient.
• Set rate low (permissive hypercapnoea)
• pH 7.0 - 7.1 and PCO2 up to 90 mmHg.
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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.
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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.
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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.
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Case 1
• Don't forget to treat the underlying problem (asthma)
• Steroids, bronchodilators, magnesium
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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.
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Case 2
ARDSnet showed mortality reduction using a lung protective ventilation
strategy.
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Case 2
• Tidal volume of 6-8 mL/kg
• Based on lean body weight
• Start high and reduce rate as needed.
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Baby Lungs
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Case 2
• IFR set lower at 60-80 L per minute.
• More comfortable for the patient.
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Case 2
• Respiratory Rate (ventilation)
• Start at 18 breaths per minute and titrate to PCO2.
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Case 2 - FIO2 / PEEP
• Oxygenation (SpO2 88-92%)
• Increased PEEP does not cause PTx
• Increased PEEP will cause reduced venous return and hypotension.
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Case 2
• Benefits of PEEP
• Reduced atelectasis
• Reduced shunt
• Increase in V/Q ratio
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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.
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Case 2
• Plateau Pressure should be less than 30 mmHg (lung protective effect)
• Reduce tidal volume if pressure too high.
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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.