Mechanical VentilationMechanical Ventilation POS Seminar Series

December 2008

Dr. J. Wassermann

Anesthesia, Critical Care

St. Michael’s Hospital

University of Toronto

OutlineOutlineDefinition – what is itIndications – when do you use itVentilator Settings – how do you use itModes of VentilationAdverse EffectsWeaningSpecific CircumstancesSummary

Mechanical Ventilation – Mechanical Ventilation – DefinitionDefinition

Mechanical Ventilation =

– 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 – Mechanical Ventilation – DefinitionDefinition

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 VentilationMechanical 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 - IndicationsIntubation - Indications

1. Airway patency (obstruction)

2. Airway protection (aspiration)

3. Oxygenation (pO2)*

4. Ventilation (pCO2)*

5. Tracheal Toilet (secretions)

4 P’s: Patency, Protection, Positive Pressure, Pulmonary toilet

Mechanical Ventilation – Mechanical Ventilation – IndicationsIndications

Improve Oxygenation (pO2; SaO2)

Improve Ventilation (pCO2) or hyperventilation

Reduce work of breathing (WOB)(i.e. asthma)____________________________________________

CHF

+ Hemodynamic Instability

Inadequate OxygenationInadequate Oxygenation

– Decreased FIO2/PIO2

– A/W obstruction– Hypoventilation– V/Q mismatch*– Diffusion– Decreased mixed venous O2 (DO2/VO2)– RL shunt

Inadequate Oxygenation - Inadequate Oxygenation - Decreased FIODecreased FIO22/PIO/PIO22

Alveolar Gas Equation:

PO2(alv) = [(Patm – PH2O) 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 OxygenationInadequate OxygenationV/Q mismatch (low V/Q):

– pneumonia– aspiration– pulmonary edema– atelectasis/collapse– ARDS– Pulmonary contusion– Alveolar hemorrhage– PTX/HTX/pleural effusion

Inadequate VentilationInadequate Ventilation

PaCO2 CO2 production Minute Ventilation (VE = RR

x Vt)

Any condition inadequate ventilation

increased pCO2 Altered LOC NM disorders weakness

Work of BreathingWork 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 but:May need mech vent purely for WOB (i.e. asthma)

Summary thus farSummary thus far

Mechanical ventilation indicated in situations with:

1. O2 problems (oxygenation)

2. CO2 problems (ventilation)

3. WOB (often assoc with 1 and/or 2)

Don’t always need an ETT

Mechanical VentilatorsMechanical Ventilators

How do you use them……

Ventilator SettingsVentilator Settings

ModeRateVolume (VT)PressureFIO2

PEEPI:E

Ventilator SettingsVentilator Settings

Flow rateFlow patternAlarms

Modes of Mechanical Modes of Mechanical VentilationVentilation

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

Modes of Mechanical Modes of Mechanical VentilationVentilation

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 Continuous Mandatory Ventilation (CMV)Ventilation (CMV)

Trigger –Machine initiates all breaths

Patient can not initiateTarget – Volumee.g.

vent gives 10 bpm @ 700cc each

pt gets zero extra breaths (even if tries)

Assist Control (Volume Assist Control (Volume Control)Control)

Trigger – machine and patientTarget – volume

e.g. vent gives 10 bpm @ 700cc each

pt initiates 6 bpm – vent provides 700cc

Synchronized Intermittent Synchronized Intermittent Mandatory Ventilation (SIMV)Mandatory Ventilation (SIMV)

Trigger – ventilator and patientTarget – ventilator breaths = volume

patient breaths = patient effortSettings-Mode: SIMV

Rate 10; Vt 700cc

FIO2 0.5; PEEP 5.0e.g. vent gives 10 bpm @ 700cc each

patient takes 6 bpm @ 150 cc each

Pressure Control (PC)Pressure Control (PC)

Trigger – ventilator and patientTarget – 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 Pressure Support Ventilation (PSV)(PSV)

Trigger – patient onlyTarget - pressureCycle – patient flow decrease

Settings – Mode: PSV = 14 cm H2O FIO2 0.4; PEEP 5

e.g. pt takes 18 bpm @ Vt = 500ccmachine gives zero breaths

Completely Unassisted Completely Unassisted BreathsBreaths

Trigger – patientCycle – patient effort ceases

Settings: CPAP 5; FIO2 0.4

e.g. patient takes 24 bpm @ 250 cc each

Mechanical Ventilator SettingsMechanical Ventilator Settings

ModeRateTidal Volume (or Pressure)

• RR x VT = VE

FIO2

PEEP (or CPAP)I:E (time in inspiration vs. expiration)

Ventilator SettingsVentilator Settings

Flow rateFlow patternAlarms

Ventilator SettingsVentilator Settings

e.g.

Volume Control

Rate 12

VT 500 cc

FIO2 0.9

Peep 10

I:E = 1:2

Choosing a Ventilatory ModeChoosing 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 VentilationNoninvasive Ventilation

Indications for intubation:

1. Airway patency*

2. Airway protection (aspiration)*

3. Oxygenation

4. Ventilation

5. Tracheal suctioning (toilet)*

Noninvasive VentilationNoninvasive Ventilation

Avoids intubation and complicationsCan deliver various modes of ventilation

– CPAP/CPAP + PSV most common

Indications:– hypercapneic respiratory failure (COPD exac)– cardiogenic p. edema

Noninvasive VentilationNoninvasive Ventilation

Contraindications:– Inability to cooperate (i.e. confusion)

– Altered LOC (unless 2. pCO2 from COPD)– Inability to clear secretions– Hemodynamic instability

Adverse Effects of Mechanical Adverse Effects of Mechanical VentilationVentilation

Pulmonary:– Intubation effects– Air leaks – Ventilator-induced lung injury– Ventilator-associated pneumonia– Dynamic hyperinflation/Auto-PEEP

Adverse Effects of Mechanical Adverse Effects of Mechanical VentilationVentilation

Cardiovascular:– Hypotension– Increased CVP (↑intrathoracic pressure)– Decreased venous return– Increased RV afterload

GI:– Stress ulcers/GI bleeding

Adverse Effects of Mechanical Adverse Effects of Mechanical VentilationVentilation

CNS:– ↑ ICP– Prolonged sedation– NMB’s (myopathies/neuropathies)

Weaning from Mechanical Weaning from Mechanical VentilationVentilation

Once underlying pathology improves

Need to ensure:– Adequate respiratory muscle strength– WOB not excessive

Ventilatory demands Resistance Compliance

Weaning from Mechanical Weaning from Mechanical VentilationVentilation

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

Ventilation Strategies in Ventilation Strategies in Specific SituationsSpecific Situations

ARDSAsthmaIncreased intraabdominal pressure

SummarySummary

Mechanical ventilation used to:1. Improve oxygenation

2. Improve ventilation (CO2 removal)

3. Unload respiratory muscles

A support until patients condition improves

SummarySummary

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?Questions?