Mechanical Ventilation POS Seminar Series December 2010 Dr. J. Wassermann Department of Anesthesia St. Michael’s Hospital University of Toronto

Outline Definition – what is it Indications – when do you use it Ventilator Settings – how do you use it Modes of Ventilation Adverse Effects Summary

Mechanical Ventilation – Definition Use of a mechanical apparatus to provide (or augment) the requirements of a patient’s breathing (i.e. get O2 into and CO2 out of alveoli)

Mechanical Ventilation – Definition Use of positive pressure to physically transport gases into and out of lungs (earlier ventilators used negative pressure) Usually performed via ETT but not always (noninvasive ventilation)

Mechanical Ventilation A supportive measure – not a therapy Must diagnose and treat underlying cause Use ventilator to support patient until underlying disorder improved – and try not to cause harm in the process

Intubation - Indications Airway patency (obstruction) Airway protection (aspiration) Oxygenation (pO2)* Ventilation (pCO2)* Tracheal Toilet (secretions) * don’t necessarily need intubation for these

Mechanical Ventilation – Indications Improve Oxygenation (pO2;  SaO2) Improve Ventilation (pCO2) - or hyperventilate pt Reduce work of breathing (WOB) (i.e. asthma; COPD) ____________________________________________ CHF Hemodynamic Instability

Inadequate Oxygenation Decreased FIO2/PIO2 A/W obstruction Hypoventilation V/Q mismatch* Diffusion Decreased mixed venous O2 RL shunt (i.e. intra-cardiac shunt)

Alveolar Gas Equation PALVO2 = [(PATM – PH2O) × FIO2] – (PCO2 ) RQ NOTE: On 100% O2 , PALVO2 should be ~ 650

Inadequate Oxygenation V/Q mismatch (low V/Q): Pneumonia Aspiration Pulmonary edema Atelectasis/collapse (plug/PTX/HTX/effusions) ARDS Pulmonary contusion Alveolar hemorrhage

Inadequate Ventilation PaCO2  CO2 production Minute Ventilation (VE ) VE = RR x Vt Any condition  inadequate ventilation  increased pCO2 Altered LOC S. cord injuries/NM disorders  weakness

Work of Breathing WOB ~ ventilatory demands (CO2 prod’n) ~ airway resistance (i.e. severe asthma) ~ compliance (lung, c/w, abdo) Increased WOB usually  O2/CO2 problems; May need mech vent purely for WOB (i.e. asthma) c/w = chest wall

Summary thus far Mechanical ventilation indicated in situations with: O2 problems (oxygenation) CO2 problems (ventilation) WOB (often assoc with 1 and/or 2) Don’t always need an ETT

Mechanical Ventilators How do you use them……

Ventilator Settings Mode Rate Volume (VT) Pressure FIO2 PEEP I:E (ratio of insp vs exp time) Insp Flow rate Flow pattern Alarms

Modes of Mechanical Ventilation Controlled Mechanical Ventilation (CMV) Assist Control (AC)/Volume Control (VC) Intermittent Mandatory Ventilation (SIMV) Pressure Control (PCV) Pressure Support Ventilation (PSV)

Modes of Mechanical Ventilation Trigger – what initiates a breath Target – what the vent is trying to achieve Cycle – what causes the breath to end

Continuous Mandatory Ventilation (CMV) Trigger –Ventilator initiates all breaths Patient can not initiate Target – Volume Cycle - Time

Continuous Mandatory Ventilation (CMV) e.g. Settings - Mode: CMV Rate 10; Vt 700cc FIO2 0.5; PEEP 5.0 vent gives 10 bpm @ 700cc each pt gets zero extra breaths (even if tries) very uncomfortable for pt only used if pt paralyzed (i.e. in O.R.)

Assist Control (Volume Control) Trigger – machine and patient Target – volume Settings-Mode: VC Rate 10; Vt 700cc FIO2 0.5; PEEP 5.0 e.g. vent gives 10 bpm @ 700cc each pt initiates 6 bpm – vent provides 700cc

Synchronized Intermittent Mandatory Ventilation (SIMV) Trigger – ventilator and patient Target – ventilator breaths = set volume patient breaths = patient effort Settings-Mode: SIMV Rate 10; Vt 700cc FIO2 0.5; PEEP 5.0 e.g. vent gives 10 bpm @ 700cc each patient takes 6 bpm @ 150 cc each

Pressure Control (PC) Trigger – ventilator and patient Target – Pressure (above PEEP) Settings – Mode: PC Rate 10; Pressure 24 cm H2O FIO2 0.5; PEEP 5 e.g. vent gives 10 bpm to a peak Paw = 29 pt takes 6 bpm targeted to peak Paw =29

Pressure Support Ventilation (PSV) Trigger – patient only Target - pressure Cycle – patient flow decrease Settings – Mode: PSV = 14 cm H2O FIO2 0.4; PEEP 5 e.g. pt takes 18 bpm @ Vt = 500cc machine gives zero breaths

Completely Unassisted Breaths Trigger – patient Cycle – patient effort ceases Settings: CPAP 5; FIO2 0.4 e.g. patient takes 24 bpm @ 250 cc each

Mechanical Ventilator Settings Mode (usually VC or PC to start) Rate Tidal Volume (VC) [or Pressure (PC)] FIO2 PEEP I:E

Choosing a Ventilatory Mode No proven benefit of any mode of another Keys are to: Support pt to allow time for underlying process to improve Avoid/minimize adverse effects of mech ventilation

Adverse Effects of Mechanical Ventilation Pulmonary: Intubation effects Air leaks (pneumothorax/BPF) Ventilator-associated lung injury Ventilator-associated pneumonia Dynamic hyperinflation/Auto-PEEP

Adverse Effects of Mechanical Ventilation Cardiovascular: Increased CVP (↑intrathoracic pressure) Decreased venous return Hypotension Increased RV afterload GI: Stress ulcers/GI bleeding

Adverse Effects of Mechanical Ventilation Neuro/muscular: ↑ ICP Prolonged sedation Myopathies/Neuropathies

Ventilator-Associated Lung Injury (VALI) Volutrauma Barotrauma Atelectotrauma Biotrauma

Ventilator-Associated Lung Injury (VALI) Volutrauma – overdistension of alveoli Barotrauma – high alveolar pressures Atelectotrauma – repetitive opening and closing of alveoli Biotrauma – release of infl mediators into systemic circulation  organ dysfunction

Ventilation of ARDS (baby lung) Moderate PEEP (to keep alveoli open) 10 – 15 cm H20 Small Vt’s (to avoid overdistension) < 6 cc/kg Plateau pressure < 30 cm H2O Permissive hypercapnia & hypoxemia

Summary Mechanical ventilation used to: Improve oxygenation Improve ventilation (CO2 removal) Unload respiratory muscles A support until patients condition improves

Summary Different modes for ventilation differ in how breaths are initiated, ended and assisted differ in independent and dependant variables (i.e. what machine controls and what it doesn’t) no proven advantage of one mode use ventilator strategies to avoid lung injury and other adverse effects

Questions?

Weaning from Mechanical Ventilation Once underlying pathology improves Need to ensure: Adequate respiratory muscle strength WOB not excessive Ventilatory demands Resistance Compliance

Weaning from Mechanical Ventilation Volume overload and myocardial ischemia common causes of failure to wean RR/Vt = good predictor if <80-100 SIMV inferior to SV trials or CPAP/PSV

Noninvasive Ventilation Indications for intubation: Airway patency* Airway protection (aspiration)* Oxygenation Ventilation Tracheal suctioning (toilet)*

Noninvasive Ventilation Avoids intubation and complications Can deliver various modes of ventilation CPAP/CPAP + PSV most common Indications: hypercapneic respiratory failure (COPD exac) cardiogenic p. edema

Noninvasive Ventilation Contraindications: Inability to cooperate (i.e. confusion) Altered LOC Inability to clear secretions Hemodynamic instability

Ventilation Strategies in Specific Situations ARDS Asthma Increased intraabdominal pressure