1. Introduction to Mechanical Ventilation
11 November 2016 Podcast Supplement
Dr. Tim Nutbeam
Dr. Clare Bosanko
George Beck, RRT, FAARC

2. Overview This module will:
Identify the goals of mechanical ventilation (MV)
List the indications for use of MV
Identify the basic controls for MV
Review the modes of MV
Review the definitions of critical MV terms
*Note: underlined words/phases are key MV terms that are defined at the end of the presentation.

3. Why Mechanically Ventilate?
Multiple studies have demonstrated the efficacy of mechanical ventilation (MV).
Direct correlation between bag-valve mask (BVM) hyperventilation and hypocapnia.
Hypocapnia is directly related to increased mortality in patients with traumatic brain injury (TBI)
One study (Paste, et al. 2004) noted decreased mortality in TBI
Ventilation guided by capnography.
Hypoventilation and hyperventilation of the intubated casualty (Davis, et al. 2006)
Improved outcomes in pts with EtCO2 between 30 to 49 mmHg

4. Goals of MV Ventilation: move gas in and out of the lung
Eliminate carbon dioxide (CO2) during exhalation
Oxygenation: inhalation of O2 to support metabolism
Provide supplemental O2
Maintain arterial blood gases (ABG) within acceptable limits, invasive measurement
Noninvasive:
End-tidal CO2 (EtCO2): indication of ventilation
Pulse oximeter: oxyhemoglobin saturation, SpO2

5. Respiratory System
Lungs are the interchange between the air we breath and the blood that carries O2 to the tissues and returns CO2 to the lungs for elimination

6. Lung Zones 2 Primary lung zones
Conducting: pharynx, trachea, bronchi, etc.
Gas exchange: alveoli
Deadspace: areas of the respiratory system that do not exchange gas and that are rebreathed with each breath
2 parts:
Physiologic: anatomical
System: device components where the volume of the components is rebreathed: endotracheal tube, heat and moisture exchanger (HME), EtCO2 sensor, closed-suction catheter, etc.
System deadspace: can be a constant and is independent of the size of the breath given the equipment used.

7. Gas Exchange
The diffusion of gas, O2 & CO2, across the alveolar capillary membrane
CO2 is moves into the alveoli to be exhaled
O2 diffuses into the blood

8. Indications for MV Acute respiratory failure Trauma Cardiac
PCO2, PO2( /50 mmHg), Acidemia (pH < 7.35)
Trauma
Cardiac
Traumatic brain injury (TBI), increased intracranial pressure (ICP)
Airway resistance / obstruction
Chronic obstructive pulmonary disease (COPD)
Asthma
Neuromuscular pathology
Sedation, analgesia following surgery

9. Mechanics of Breathing
Normal breathing is accomplished through negative pressure
During inspiration negative pressure is created when the diaphragm is contracted forcing it down
Inspiration is active
Exhalation is passive
The body does no work to exhale
This is also during MV

10. Positive Pressure Ventilation (PPV)
The action of mechanical ventilation is opposite of normal respiratory mechanics
With PPV, positive pressure influences inhalation
Gas is forced into the lungs
This affects multiple body systems other than the lungs
Venous return
BP, tissue oxygenation
Cardiac function and workload
Other systems affected as a result

11. Basic Control of Ventilation
Mode: describes the pattern of breath delivery
Respiratory rate (BPM): the number of breaths delivered per minute
I:E ratio: the ratio of the duration of inspiration vs. expiration
Tidal Volume (Vt): the volume delivered to the patient with each breath
Positive end-expiratory pressure (PEEP): the expiratory baseline pressure
Fraction of inspired O2 (FIO2): the ratio of O2 to the total volume of the gas mixture

12. Tidal Volume (Vt)
Amount of a gas either inhaled or exhaled in one breath, expressed in ml
Normally about 400 to ml for spontaneously breathing adult male
For MV 5 to 8 ml/Kg of ideal body weight
Minute volume: the total volume of gas breathed in a minute
BPM x Vt
Inversely proportional to EtCO2

13. Dead Space (VD)
Volume of Vt that remains in the upper airways and does not participate in gas exchange
Normally about 1/3 of Vt
Typical adult VD is ~150 mL
Mechanical deadspace: is the volume of rebreathed gas from the airway, ventilator tubing and other devices in the airway: HME, EtCO2 sensor closed-suction catheter, etc.
Management of mechanical deadspace is critical in pediatric patients!

14. Inspiratory Time (TI) & I:E Ratio (I:E)TE
Inspiratory time (TI): duration of inspiration (seconds)
Expiratory time (TE): duration of expiration (seconds)
I:E ratio: the ratio of the duration of inspiration vs. expiration
Typical I:E is 1:2.5 to 4
I:E = TI TI+TE

15. Airway Pressure (PAW)
Peak inspiratory pressure (PIP): highest airway pressure over a single ventilatory cycle
Should be kept <40 cmH2O to prevent lung injury
Peak inspiratory pressure (PIP)

16. Positive End-Expiratory Pressure (PEEP)
PEEP: elevation of the baseline end-expiratory pressure
Used to prevent alveolar collapse and improve oxygenation
Typically all pt have a minimum of 5 cm H2O of PEEP
PEEP

17. Fraction of Inspired Oxygen (FIO2)
Given in as a decimal, with being equivalent to 100%
e.g. 50% O2 = FiO2 0.5
Ambient air = FiO2 0.21
Ventilators can use O2 from both high and low pressure sources.
Many times, FiO2 is initially set at 1.0, then decreased.
SpO2 guides the management of the FIO2

18. Other Key Terms Triggering: the action that starts a breath, 2 types:
Time
Patient, pressure or flow
Cycling: the action that ends a breath, 2 types:
Flow

19. Modes of Ventilation
A mode of mechanical ventilation may be defined, in general, as a predetermined pattern of patient-ventilator interaction. It is constructed using 3 basic components: (1) the ventilator breath control variable, (2) the breath sequence, and (3) the targeting scheme.
RESPIRATORY CARE • NOVEMBER 2014 VOL 59 NO 11

20. Assist/Control (AC) Tidal volume is the same for all breaths
Trigger: both time and patient (pt)
Pt triggered breaths are detected as a reduction in the airway pressure as the pt inhales
Cycling: time only
TI is set directly or as a function of the I:E ratio
Flow: constant, square wave
Advantages: provides a minimum rate and low work of breathing (WOB)
Disadvantages: hyperventilation, breath stacking, asynchronyy (bucking)

21. Synchronized Intermittent Mandatory Ventilation (SIMV)
Tidal volume: varies based on the breath trigger
Trigger: both
Time: deliver the preset tidal volume based on the set rate
Patient: pt triggered breaths Vt varies based on pt effort and lung mechanics
Cycling: both
Time: time triggered breaths are time cycled
Patient: pt triggered breaths end when patient effort/mechanics reduces inspiratory flow to a preset limit
Flow: varies based on trigger
Time: constant
Patient: decelerating
Advantages: allows pt some control over their breathing, ventilator waits to deliver timer triggered breaths if the pt is breathing
Disadvantages: may increase work of breathing, use as a weaning mode may cause respiratory muscle fatigue

22. SIMV with Pressure Support (PS)
Similar to SIMV
Pressure Support augments the pt breathing effort by providing increased pressure during the inspiratory period
PS pressure target is set by the user, pressure limited
PS breath is flow cycled
Advantages:
Additional pressure helps pt overcome the work of breathing imposed by the ventilator and tubing
When used at lower rate, SIMV PS allows pt more control over their breathing pattern which ensuring a minimum minute volume (Vt x BPM)
Disadvantage: not appropriate for pt who cannot maintain a consistent breathing pattern

23. Continuous Positive Airway Pressure (CPAP)
Tidal volume and rate are completely controlled by the pt
Trigger: patient
Cycling: flow
Flow: decelerating
Advantages: allows pt complete control over breathing pattern, minimal dissynchrony
Disadvantages: pt breathing through ventilator, circuit and airway can result in increase WOB
Not appropriate for pt who cannot maintain a consistent, effective breathing pattern!
CPAP breathing waveforms

24. CPAP with Pressure Support (PS)
This mode is also known as BiPAP or Bi- Level
Tidal volume and rate are completely controlled by the pt
Patient effort augmented by PS which is set by the user
Trigger: patient
Cycling: flow
Flow: decelerating
Advantages: allows pt complete control over breathing pattern, minimal dissynchrony
PS reduces WOB
Disadvantages: not appropriate for pt who cannot maintain a consistent, effective breathing pattern!
CPAP with PS breathing waveforms

25. Volume vs. Pressure Targeting
Breath target: the breath parameter the user wants to control during inspiration
Once selected this parameter becomes the independent variable while the other becomes dependent
Example: when tidal volume (Vt) is the target, the ventilator will deliver the set Vt for every breath
The peak airway pressure (PAW) will vary based on the tidal and the pulmonary mechanics

26. Key Terms Arterial blood gases (ABG)
A test that measures the acidity (pH) and the levels of oxygen and carbon dioxide in the blood from an artery. This test is used to check how well the pt lungs are able to move oxygen into the blood and remove carbon dioxide from the blood.
Assist/Control (AC)
A commonly used mode of mechanical ventilation in medical intensive care units. A key concept in the AC mode is that the tidal volume (VT) or pressure target of each delivered breath is the same, regardless of whether it was triggered by the patient or the ventilator.
Bilevel positive airway pressure (BiPAP)
Also referred to as BPAP, is very similar in function and design to CPAP however, the patient’s inspiratory efforts are supported by a preset pressure, pressure support.
breath stacking
A series of breaths that occur in a short sequence whereby the lung is not able to empty before the next inspiration starts. If breath stacking continues AutoPEEP can result.
Breath target
The breath parameter, volume or pressure, the user wants to control during inspiration.
Capnography
The noninvasive measurement of the partial pressure ofCO2 in exhaled breath expressed as the CO2 concentration over time. The relationship of CO2 concentration to time is graphically represented by the CO2 waveform.
closed-suction catheter
An endotracheal suctions system that allows for suctioning without disconnecting the patient from the ventilator circuit. Its use is associated with reduced infection rates and cost.
Continuous Positive Airway Pressure (CPAP)
A mode of ventilation that uses mild air pressure to keep the airways open to a spontaneously breathing pt. It can be used with both intubated and nonintubated pt.

27. Key Terms Cycling The action that ends a breath, either time or flow.
Deadspace
Areas of the respiratory system that do not exchange gas and that are rebreathed with each breath.
Dyssynchrony
Failure of synchronous interaction between a patient's natural breathing effort and the timing of a ventilator.
endotracheal tube
A plastic tube with a cuff that is secured in the pt’s trachea to enable positive pressure ventilation.
EtCO2
The level of carbon dioxide released at the end of an exhaled breath.
Fraction of inspired O2 (FIO2)
The ratio of O2 to the total volume of the gas mixture.
Heat and moisture exchanger (HME)
Devices that are used with mechanically ventilated patients intended to help prevent complications due to drying of the respiratory mucosa by capture the heat and moisture of the exhaled gas and returning it to the inspired gas.
Hyperventilation
Hyperventilation occurs when the rate and quantity of alveolar ventilation of carbon dioxide exceeds the body's production of CO2 resulting in a dramatic decrease the exhaled CO2.
hypocapnia
A state of reduced carbon dioxide in the blood most often as a result of hyperventilation.
I:E ratio
Ratio of the duration of inspiration vs. expiration.
Mechanical deadspace
The volume of rebreathed gas from the airway, ventilator tubing and other devices in the airway: HME, EtCO2 sensor closed-suction catheter, etc.
Minute volume
The total volume of gas breathed in a minute. The product of BPM x Vt.

28. Key Terms Mode Describes the pattern of breath delivery. Oxygenation
Inhalation of O2 to support metabolism.
Oxyhemoglobin saturation (SpO2)
The fraction of oxygen-saturated hemoglobin relative to total hemoglobin.
Peak inspiratory pressure (PIP)
The highest airway pressure over a single ventilatory cycle.
Positive end-expiratory pressure (PEEP)
Elevation of the baseline end-expiratory pressure.
Positive Pressure Ventilation (PPV)
Delivery of air and/or O2 using positive pressure to facilitate the movement gas into and out of the lungs.
Pressure support
Augments the pt breathing effort by providing increased pressure during the inspiratory period.
Pulse oximeter
A noninvasive method for monitoring a pt’s O2 saturation.
Respiratory rate (BPM)
The number of breaths delivered to a pt per minute.
Synchronized Intermittent Mandatory Ventilation (SIMV)
A mode of breathing where ventilator-assisted breaths are different than spontaneous breaths.
System deadspace
See Mechanical deadspace
Tidal Volume (Vt)
The volume delivered to the patient with each breath.
Triggering
The action that starts a breath, 2 types: time and patient
Ventilation
The movement of air between the environment and the lungs via inhalation and exhalation.
Work of breathing (WOB)
The work required to inspire air into the lungs.