Mechanical Ventilation POS Seminar Series December 2008 Dr. J. Wassermann Anesthesia, Critical Care 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 Weaning Specific Circumstances Summary

Mechanical Ventilation – Definition  Mechanical Ventilation = – Use of a mechanical apparatus to provide (or augment) the requirements of a patient’s breathing (i.e. get O 2 into and CO 2 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 &/or rest patient until underlying disorder improved – and hopefully, not cause harm in the process

Intubation - Indications 1. Airway patency (obstruction) 2. Airway protection (aspiration) 3. Oxygenation (pO 2 )* 4. Ventilation (pCO 2 )* 5. Tracheal Toilet (secretions) 4 P’s: Patency, Protection, Positive Pressure, Pulmonary toilet

Mechanical Ventilation – Indications  Improve Oxygenation (  pO 2;  SaO 2 )  Improve Ventilation (  pCO 2 ) or hyperventilation  Reduce work of breathing (WOB) (i.e. asthma) ____________________________________________  CHF  + Hemodynamic Instability

Inadequate Oxygenation – Decreased FIO 2 /PIO 2 – A/W obstruction – Hypoventilation – V/Q mismatch* – Diffusion – Decreased mixed venous O2 (  DO2/  VO2) – R  L shunt

Inadequate Oxygenation - Decreased FIO 2 /PIO 2 Alveolar Gas Equation: PO 2(alv) = [(Patm – P H2O ) x FIO2] – (pCO2/RQ) [(760 – 47) x 0.21] – (40/0.8) ~ 100 mm Hg [(500 – 47) x 0.21] – (40/0.8) ~ 45 mm Hg

Inadequate Oxygenation V/Q mismatch (low V/Q): – pneumonia – aspiration – pulmonary edema – atelectasis/collapse – ARDS – Pulmonary contusion – Alveolar hemorrhage – PTX/HTX/pleural effusion

Inadequate Ventilation  PaCO 2  CO 2 production Minute Ventilation (V E = RR x Vt)  Any condition  inadequate ventilation  increased pCO 2 Altered LOC NM disorders  weakness

Work of Breathing  WOB ~ ventilatory demands (CO 2 prod’n) ~ airway resistance (i.e. severe asthma) ~ compliance (lung, c/w, abdo)  Increased WOB usually  O 2 /CO 2 problems but:  May need mech vent purely for WOB (i.e. asthma)

Summary thus far  Mechanical ventilation indicated in situations with: 1. O 2 problems (oxygenation) 2. CO 2 problems (ventilation) 3. 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 (V T ) Pressure FIO 2 PEEP I:E

Ventilator Settings Flow rate Flow pattern Alarms

Modes of Mechanical Ventilation Spontaneous/Controlled/Dual 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 – who/what starts a breath (pt/vent) Target – what the vent is trying to achieve Cycle – what causes the breath to end

Continuous Mandatory Ventilation (CMV) Trigger –Machine initiates all breaths Patient can not initiate Target – Volume e.g. vent gives cc each pt gets zero extra breaths (even if tries)

Assist Control (Volume Control) Trigger – machine and patient Target – volume e.g. vent gives cc each pt initiates 6 bpm – vent provides 700cc

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

Mechanical Ventilator Settings Mode Rate Tidal Volume (or Pressure) RR x VT = V E FIO 2 PEEP (or CPAP) I:E (time in inspiration vs. expiration)

Ventilator Settings Flow rate Flow pattern Alarms

Ventilator Settings e.g. Volume Control Rate 12 VT 500 cc FIO2 0.9 Peep 10 I:E = 1:2

Choosing a Ventilatory Mode Initially, use mode to rest patient No benefit of any mode wrt better O2/CO2 Use strategy to prevent adverse effects – Avoid overdistention – Avoid repetitive opening and closing – Small Vt – High PEEP

Noninvasive Ventilation Indications for intubation: 1. Airway patency* 2. Airway protection (aspiration)* 3. Oxygenation 4. Ventilation 5. 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 (unless 2.  pCO 2 from COPD) – Inability to clear secretions – Hemodynamic instability

Adverse Effects of Mechanical Ventilation Pulmonary: – Intubation effects – Air leaks – Ventilator-induced lung injury – Ventilator-associated pneumonia – Dynamic hyperinflation/Auto-PEEP

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

Adverse Effects of Mechanical Ventilation CNS: – ↑ ICP – Prolonged sedation – NMB’s (myopathies/neuropathies)

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 < SIMV inferior to SV trials or CPAP/PSV

Ventilation Strategies in Specific Situations ARDS Asthma Increased intraabdominal pressure

Summary Mechanical ventilation used to: 1. Improve oxygenation 2. Improve ventilation (CO2 removal) 3. 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 volutrauma and other adverse effects

Questions?