Absolute Basics of Mechanical Ventilation Dr David Howell Consultant in Intensive Care, Respiratory and Acute Medicine

Aims and Objectives Define Positive Pressure Mechanical Ventilation Explain Continuous Mandatory Ventilation (CMV) Explain Synchronised Mandatory Ventilation (SIMV) Explain Pressure Support Ventilation (PSV) Explain Basic Ventilator Settings Not a Talk on Physiology of Mechanical Ventilation

What you Encounter

Positive Pressure Mechanical Ventilator

Lots of Monitors and Knobs to Turn

Some are More Complicated than Others

Wake, Warm & Wean Weaning Screen/standard protocol Long Term Weaning/Individual plan Weaning Non-Invasive Ventilation Oxygen Therapy Mask CPAP Non-invasive support Tracheostomy Intubation Extubation Decannulation Standard Ventilation Advanced Ventilation Invasive support Optimising the Pt for weaning Prone Position Nitric Oxide Suctioning Humidification

NIV is defined as ventilatory support provided via a tight fitting mask or similar interface as opposed to invasive support, which is provided via a laryngeal mask, endotracheal tube or tracheostomy tube. Tight fitting masks deliver can CPAP, BIPAP or NIV via the mechanical ventilator. NIV vs. Invasive Mechanical Ventilation

The work of breathing usually accounts for 5% of oxygen consumption (V0 2 ). In the critically ill patient this may rise to 30%. Invasive mechanical ventilation eliminates the metabolic cost of breathing. Indications for Mechanical Ventilation

Inadequate oxygenation (not corrected by supplemental O 2 by mask). Inadequate ventilation (increased PaCO 2 ). Retention of pulmonary secretions (bronchial toilet). Airway protection (obtunded patient, depressed gag reflex). Indications for Mechanical Ventilation

Intubation

1 Airway: oral Guedel airway to lift tongue off posterior pharynx to facilitate mask ventilation during pre-intubation phase. 2 Liquids: stop feed and aspirate ng tube. 3 Suction: extremely important to avoid pulmonary aspiration. 4 Oxygen: preoxygenate patient and ensure a source of O 2 with a delivery mechanism (ambu-bag and mask) is available. Bare Essentials for Intubation ALSOBLEED

5 Bougie: to facilitate tube insertion in more difficult airway. 6 Laryngoscope: have a long and short blade available. 7 Endotracheal tube: for average adult, cuffed oral endotracheal tube 7.0 for women and 8.0 for men. 8 End tidal CO 2 : to confirm correct position of tube. 9 Drugs: an induction agent, muscle relaxant, sedative are usually required. Bare Essentials for Intubation ALSOBLEED

Principles of Mechanical Ventilation ET tube Ventilator Tubing Major Airways Alveoli PEEP

Positive pressure ventilation involves delivering a mechanically generated ‘breath’ to get O 2 in and CO 2 out. Gas is pumped in during inspiration (Ti) and the patient passively expires during expiration (Te). The sum of Ti and Te is the respiratory cycle or ‘breath’. Principles of Mechanical Ventilation

Flow Pressure Principles of Mechanical Ventilation TiTeTiTe

In the fully ventilated patient, positive pressure breaths are delivered either as preset volume or pressure continuous mandatory breaths (CMV) breaths. The mechanical ventilator triggers the breath and switches from inspiration to expiration when the preset volume, pressure (or time) is achieved/delivered. During CMV the patient takes no spontaneous breaths. CMV is usually used in theatre and in very unwell ICU patients. Principles of Mechanical Ventilation

Volume control Tidal volume is preset Usually 500 mls Airway Pressure is Variable Pressure control Inspiratory Pressure is preset Usually cm H 2 0 Tidal Volume is Variable

Mandatory breaths are delivered during inspiration, to generate a tidal volume (Vt), at a set rate (f), the quotient of which is the minute volume (MV). Minute Volume = Tidal Volume x frequency In volume control ventilation, an inspiratory flow rate is also set. The ratio of the time spent in inspiration:expiration (I:E ratio) is usually 1:2. Principles of Mechanical Ventilation

Flow Pressure TiTeTiTe Principles of Mechanical Ventilation Volume Control BreathPressure Control Breath

Mechanically ventilated patients usually receive positive end-expiratory pressure (PEEP), to overcome the loss of physiological PEEP provided by the larynx and vocal cords. PEEP is delivered throughout the respiratory cycle and is synonymous to CPAP, but in the intubated patient. Standard PEEP setting is 5 cm H 2 0. Sedation is often required to prevent ventilator-patient asynchrony. Principles of Mechanical Ventilation

Basic Settings on the Ventilator Tidal Volume Pressure controlled breath (15-20 cm H 2 0) Volume controlled breath (500 mls) Rate (frequency) (10-12 breaths/minute) Positive end expiratory pressure (PEEP) (5 cm H 2 0) FiO 2 (0.21-1) Peak airway pressure (PAP)

Principles of Mechanical Ventilation Why is the peak airway pressure (PAP) important? Ventilator Induced Lung Injury (VILI). Mechanical ventilation is injurious to the lung. Aim PAP< 35 cm H 2 0.

Flow Pressure TiTeTiTe Principles of Mechanical Ventilation Volume BreathPressure Breath 35 cm H 2 0

Pneumothorax

Principles of Mechanical Ventilation Don’t forget that the peak airway pressure will also include the PEEP that is added

Once stabilised on CMV, the level of ventilatory support may be reduced (weaning). This can be done by providing a mixture of synchronised intermittent mandatory breaths (SIMV) and spontaneously triggered pressure supported breaths (PSV). Principles of Mechanical Ventilation

Ventilator assisted breaths are synchronized with the patient’s breathing to prevent the possibility of a mechanical breath on top of a spontaneous breath. However, the patient’s attempt at a breath would not be enough to generate an adequate tidal volume on its own, hence the term ‘pressure support’. Principles of Mechanical Ventilation

Pressure support is only delivered during inspiration and the patient’s attempt at breathing triggers the breath rather than the ventilator. A standard level of pressure support delivered in inspiration is 20 cm H 2 0 Principles of Mechanical Ventilation

SIMV and Pressure Support Ventilation VentilatorPatient

As patients improve, mandatory breaths are withdrawn and receive pressure-supported breaths alone. Finally, as tidal volumes improve, the level of pressure support is reduced and then withdrawn so patients breathe spontaneously with PEEP alone. Extubation can now be contemplated. Spontaneous modes of breathing should always be encouraged as respiratory muscle function is maintained Principles of Mechanical Ventilation

Pressure Support Ventilation Patient

To succeed, the initiating cause of respiratory failure, sepsis, fluid and electrolyte imbalance and nutritional status should all be treated or optimised. Failure to wean is associated with: Ongoing high V0 2. Muscle fatigue. Inadequate drive. Inadequate cardiac reserve. Successful Weaning and Extubation

Weaning screens exist to help select patients for extubation. In the unsupported patient, if f/Vt is >100, extubation is likely to be unsuccessful. There is some evidence to support extubation to NIV, particularly in patients with COPD. Successful Weaning and Extubation

Continuous Mandatory Ventilation (CMV) Pressure control Volume control No spontaneous breathing Ventilator triggers breath Synchronised intermittent mandatory ventilation (SIMV)/Pressure Support Ventilation (PSV) Pressure control (SIMV) Volume control (SIMV) Some spontaneous breathing is allowed (PSV) Mixture of ventilator and patient triggered breaths Basic Ventilatory Modes: Summary

Pressure Support Ventilation (PSV) Spontaneous breathing with inspiratory support All patient triggered breaths PEEP/CPAP (5 cm H 2 0) Entirely spontaneous breathing Consider extubation Basic Ventilatory Modes: Summary

Mode O 2 Respiratory Rate Inspiratory Action Inspiratory Time Expiratory Action Standard Ventilator Settings MORITE

ModeCMV, Volume Control O (50% 0 2 ) Respiratory Rate12/minute Inspiratory ActionSet Vt at 500 mls Inspiratory TimeSet I:E ratio 1:2 Expiratory ActionSet PEEP at 5 cm H 2 0 Be AwarePAP ≤35 cm H 2 O Standard Ventilator Settings MORITE

Patient Requiring Basic Invasive Mechanical Ventilation Spontaneously Ventilating Patient Failing Conventional Therapy Escalation BIPAP OptimiseConsider Patient PositionHumidification CMV (VCV or PCV) PSVPEEP/CPAP NIV on ICU BIPAP on Ward IMV (VCV or PCV) De-escalation CPAP on Ward