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

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.

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

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

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

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.

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

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

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

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

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

Tidal Volume (Vt) Amount of a gas either inhaled or exhaled in one breath, expressed in ml Normally about 400 to 500 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

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!

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

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)

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

Fraction of Inspired Oxygen (FIO2) Given in as a decimal, with 1.0 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

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

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

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)

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

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

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

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

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

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.

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.

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.