Mechanical Ventilation: The Basics and Beyond

Mechanical Ventilation: The Basics and Beyond

Presented By:Diana Gedamke, BSN, RN, CCRN

Marion College - Fond du LacMasters of Nursing Student

Module 3Ventilator Wave Forms

Two Main Types of Ventilators with Positive Pressure

Volume-cycled ventilation – With a set volume of air delivered per breath; Pressure to deliver breath will vary

Pressure-preset ventilation – With a set volume of pressure to open airways; Volume delivered will vary

Positive Pressure Ventilation

Delivers a preset volume of gas with each machine breath—airway pressures increase in response to the delivered breath

Airway pressures are higher in patients with low compliance or high resistance—high pressures indicate risk of ventilator-induced lung injury

Volume-cycled Ventilation

Spontaneous Breathing vs. Positive Pressure Ventilation

Assist Control (AC) Synchronized Intermittent Mandatory

Ventilation (SIMV)

Volume-cycled Ventilation

Most widely used mode of MV Delivers a minimum number of fixed-

volume breaths Patients can initiate extra assisted

breaths (will get full set volume with each effort)

Assist-control (AC)

Pressure-time TracingsAssist Control Mode

Delivers preset number of fixed-volume breaths

Patient can breathe spontaneously between breaths (rate and depth determined by patient)

Patients often have trouble adapting to intermittent nature of ventilatory assistance

Synchronized Intermittent Mandatory Ventilation (SIMV)

Pressure-time TracingsSIMV Mode

Delivers a predefined target pressure to the airway during inspiration

Resulting tidal volume (VT) and inspiratory flow profile vary with the impedance of the respiratory system and the strength of the patient’s inspiratory efforts

Includes pressure-control (PC) and Pressure support (PS)

Pressure-preset Ventilation

Delivers a preset gas pressure to the airway for a set time and at a guaranteed minimum rate

Patient can breathe in excess of set rate Tidal volume achieved depends on pressure

level, lung mechanics, and patient effort Inspiratory flow rate variable

Pressure-control (PC) Ventilation

Delivers preset airway pressure for each breath

Variable parameters: Inspiratory and expiratory times (respiratory rate), flow rate, and tidal volume (VT)

Pressure Support (PS)

A set number of Mandatory breaths are delivered per minute.

Remainder of patients breath are at his own rate and volume

Spontaneous breaths allowed in SIMV are assisted by PS

Synchronized Intermittent Mandatory Ventilation (SIMV) + Pressure Support (PS)

New modes often introduced Involves nothing more than a modification

of the manner in which positive pressure is delivered to the airway and of the interplay between mechanical assistance and patient’s respiratory effort

Goals: enhance respiratory muscle rest, prevent deconditioning, improve gas exchange, prevent lung damage, improve synchrony, foster lung healing

New Modes of MV

Respiratory rate Tidal volume FiO2 Inspiratory:Expiratory (I:E) ratio Pressure limit Flow rate Sensitivity/trigger Flow waveform

Ventilator Settings

Inspiratory Flow (V) Waveform

Square waveform Decelerating Waveform (constant flow) (decelerating flow)

Square waveform: volume of gas is evenly distributed across inspiratory time. Has highest peak pressure and lowest mean airway pressure. Ideal for those at risk for autopeeping due to short inspiration time

Inspiratory Flow (V) Waveform

Decelerating waveform: Volume of gas flow is high at the beginning of inspiration then tapers off toward the end of the breath. Has lowest peak pressure and highest mean airway pressure. Increased inspiratory time; useful in ARDS.

Inspiratory Flow (V) Waveform

Check for: ◦ Symmetric chest inflation◦ Regular breathing pattern◦ Respiratory rate < 30 bpm◦ Synchrony between patient effort and machine

breath◦ Paradoxical breathing

Patient-Ventilator Synchrony

Inspiratory effort expended by patients with acute respiratory failure is 4 - 6 x normal

Don’t eliminate respiratory effort: causes deconditioning and atrophy

Patient-Ventilator Synchrony

Possible causes:◦ Anxiety or pain◦ Ventilator settings may not be appropriate: check

ABG and alert individual responsible for ventilator orders

◦ Auto-PEEP◦ Pneumothorax

Patient-Ventilator Asynchrony

Ventilator Alarms and Common Causes

High Pressure Low Pressure Low Exhaled Volume

Kink in tubingPatient biting ETT

Ventilator disconnected from ETT

Pressures exceeding high pressure limit

Secretions Cuff leak Cuff leak

Coughing Extubation Ventilator disconnected

Bronchospasm

Foreign body

PEEP – positive-end-expiratory pressure applied during mechanical ventilation

CPAP - continuous positive airway pressure applied during spontaneous breathing

Definitions

Improves oxygenation - increases functional residual capacity (FRC) above closing volume to prevent alveolar collapse◦ permits reduction in FIO2

Reduces work of breathing Increases intrathoracic pressure -

decreases venous return to right heart - decreases CO

Titrate to least amt. necessary to achieve O2 sat > 90% or PO2 > 60 mm Hg with FiO2 < 0.6

PEEP

Auto-PEEP/intrinsic PEEP (PEEPi)/inadvertent PEEP/occult PEEP - positive end expiratory alveolar pressure occurring in the absence of set PEEP. Occurs when expiratory time is inadequate.

Auto-PEEP

Assessing Flow Waveform for Presence of Auto-PEEP

Resistance and Compliance

Peak Airway Pressure (Ppk)◦ An increase in Ppk indicates either an increase

in airway resistance or a decrease in compliance (or both).

Plateau Pressure (Ppl) - end-inspiratory alveolar pressure

Definitions

Airway Pressure Analysis

High volumes and pressures can injure the lung, causing increased permeability pulmonary edema in the uninjured lung and enhanced edema in the injured lung

Alveolar overdistention + repeated collapse and re-opening of alveoli

Ventilator-Induced Lung Injury

resistance to expired flow results in air trapping/hyperinflation hyperinflation may result in

cardiopulmonary compromise Goal: meet minimal requirements for gas

exchange while minimizing hyperinflation Allow increased time for expiratory flow

Mechanical Ventilation in Obstructive Lung Disease

Decrease inspiratory time◦ Increase flow rate◦ Square waveform

Decrease minute ventilation (VE)◦ RR x TV

Increasing Time for Exhalation

Monitor plateau pressure: in general, Pplat < 30 cm H20 to decrease risk of hyperinflation and alveolar overdistension

Permissive hypercapnia

Monitoring Patients with Obstructive Lung Disease Requiring Mechanical Ventilation

Watch for overventilation post intubation High Ppk common May require sedation to establish

synchronous breathing with ventilator Avoid paralytics Ventilate as stated above (Increase

exhalation time by decreasing RR and TV, increasing inspiratory flow rate, and using square waveform)

May want to use SIMV

Respiratory Failure Due to Asthma

Ppk typically not as elevated as in asthma; when it is, think other pathologic processes

Many patients with COPD have chronic hypercapnia; ventilatory support titrated to normalize pH and not PCO2

Small levels of set PEEP may decrease WOB

May try NIPPV

Respiratory Failure Due to COPD

Cooperative patient Functionally intact upper airway Minimal amount of secretions Done by full face or nasal mask Watch for gastric distension; may

increase risk of aspiration May use standard ventilators Monitor patients closely for

decompensation and need for intubation

Noninvasive Positive Pressure Ventilation (NIPPV)

Non-recruitable

Recruitable

Normal

ARDS: A Three Lung Unit Model

Refractory hypoxemia Avoid ventilator induced lung injury

◦ pressure-limited approach keep Pplat < 30 cm H20 small tidal volumes (6 ml/kg)

◦ permissive hypercapnia Avoid O2 toxicity; apply moderate levels

of PEEP

Respiratory Failure Due to ARDS

May need to increase inspiratory time Inverse ratio ventilation (IRV)

◦ I:E > 1:1◦ May require sedation/paralysis◦ Use as second-line strategy if PEEP fails to

improve oxygenation

ARDS

Present with acute or subacute respiratory failure, usually with hypercapnia

progressive neurologic dysfunction (amyotrophic lateral sclerosis, muscular dystrophies, Guillain-Barre, CNS dysfunction due to head injury or drug ingestion)◦ usually ventilated without difficulty unless RF is

complicated by secondary conditions (atelectasis or pneumonia)

◦ lung compliance and gas exchange remain relatively normal

Mechanical Ventilation in Patients with Neuromuscular Weakness