Basics of Mechanical Ventilation

136 Pages·2018·6.21 MB·English

by  Hooman Poor

Hooman Poor
Basics of Mechanical
Ventilation
123
Basics of Mechanical
Ventilation
Hooman Poor
Basics of Mechanical
Ventilation
Hooman Poor
Mount Sinai – National Jewish Health Respiratory Institute
Icahn School of Medicine
New York, NY
USA
ISBN 978-3-319-89980-0 ISBN 978-3-319-89981-7 (eBook)
https://doi.org/10.1007/978-3-319-89981-7
Library of Congress Control Number: 2018944605
© Springer International Publishing AG, part of Springer Nature 2018
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Preface
Mechanical ventilators can be mysterious and intimidating.
When using the ventilator, one is taking on the responsibility
of breathing for another human being. Mechanical ventila-
tion is one of the most complex and integral aspects of critical
care medicine.
As a pulmonary and critical care physician, I have taught
mechanical ventilation to many medical students, residents,
and fellows. During these teaching sessions, I have encoun-
tered many shared misconceptions about how ventilators
work. Much of this misunderstanding stems from the fact that
the current nomenclature used in mechanical ventilation is
inconsistent and confusing. My hope is that this book clarifies
the fundamental concepts of mechanical ventilation.
The ventilator does not function in isolation—it works in
concert with the patient’s respiratory system. One cannot
simply set the ventilator and walk away. Instead, it is impor-
tant to monitor and adjust the ventilator settings based upon
the complex interactions between the ventilator and the
patient. Proper ventilator management is not merely a set of
prescriptive steps; ventilator settings must be individually and
continuously tailored to each patient and unique situation.
Therefore, an in-depth understanding of how a ventilator
operates is essential to achieving increased patient comfort
and optimal patient outcomes.
Learning how to manage patients on ventilators can be
daunting. While there are many excellent, comprehensive
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viii Preface
textbooks on mechanical ventilation, these tomes can be
overwhelming to even the most dedicated students. The avail-
able “shorter” books are insufficient as they often glance over
crucial basic principles. As is the case with learning medicine
in general, it is more effective to understand the foundational
concepts than to simply memorize algorithms. This book
delves into those foundational concepts, and does so clearly
and succinctly.
This book is written for anyone who cares for patients
requiring mechanical ventilation—physicians, nurses, respira-
tory therapists—and is intended for providers at all levels of
training. It provides the nuts and bolts of how to properly
manage the ventilator and serves as a practical resource in
the intensive care unit in order to better care for critically ill
patients.
New York, NY, USA Hooman Poor
Contents
1 Respiratory Mechanics ........................ 1
Lung Volume ................................ 1
Transpulmonary Pressure ...................... 2
Spontaneous Breathing........................ 3
Modeling the Respiratory System ............... 7
Suggested Readings........................... 10
2 Phase Variables .............................. 11
Anatomy of a Breath.......................... 11
Trigger...................................... 12
Target....................................... 18
Cycle ....................................... 25
Baseline..................................... 26
Suggested Readings........................... 27
3 Basic Modes of Ventilation..................... 29
Volume-Controlled Ventilation ................. 29
Pressure-Controlled Ventilation................. 30
Pressure Support Ventilation ................... 33
Volume-Controlled Ventilation Vs.
Pressure- Controlled Ventilation................. 35
Pressure-Controlled Ventilation Vs. Pressure
Support Ventilation ........................... 37
Suggested Readings........................... 38
4 Monitoring Respiratory Mechanics.............. 39
Two-Component Model ....................... 39
Airway Pressures ............................. 42
ix
x Contents
Diagnostic Algorithm ......................... 44
Suggested Readings........................... 48
5 Acute Respiratory Distress Syndrome ........... 49
Volutrauma.................................. 50
Barotrauma.................................. 51
Atelectrauma ................................ 52
Permissive Hypercapnia ....................... 55
Suggested Readings........................... 60
6 Obstructive Lung Diseases..................... 61
Breath Stacking and Auto-PEEP................ 61
Ventilator Management Strategies .............. 68
Suggested Readings........................... 73
7 Patient-Ventilator Dyssynchrony................ 75
Trigger-Related Dyssynchrony.................. 75
Target-Related Dyssynchrony .................. 88
Cycle-Related Dyssynchrony................... 89
Suggested Readings........................... 93
8 Indications for Mechanical Ventilation........... 95
Increased Work of Breathing................... 95
Increased Demand............................ 98
Neuromuscular Weakness...................... 100
Alveolar Hypoventilation...................... 100
Hypoxemia .................................. 101
Airway Protection ............................ 102
Suggested Readings........................... 103
9 Weaning from the Ventilator ................... 105
Assessing Readiness to Wean................... 105
Spontaneous Breathing Trial ................... 106
Cuff Leak Test ............................... 112
Suggested Readings........................... 114
10 Hemodynamic Effects of Mechanical Ventilation.. 115
Cardiopulmonary System ...................... 115
Intrathoracic Pressure . . . . . . . . . . . . . . . . . . . . . . . . . 117
Preload ..................................... 118
Afterload.................................... 119
Specific Hemodynamic Conditions . . . . . . . . . . . . . . 123
Suggested Readings........................... 127
Index .......................................... 129
Chapter 1
Respiratory Mechanics
Understanding mechanical ventilation must start with a
review of the physiology and mechanics of normal spontane-
ous breathing. Spontaneous breathing is defined as move-
ment of air into and out of the lungs as a result of work done
by an individual’s respiratory muscles. Positive pressure
ventilation, on the other hand, is defined as movement of air
into the lungs by the application of positive pressure to the
airway through an endotracheal tube, tracheostomy tube, or
noninvasive mask.
Lung Volume
The lungs sit inside a chest cavity surrounded by the chest
wall. The potential space between the lungs and the chest wall
is known as the pleural space. The lungs, composed of elastic
tissue, have a tendency to recoil inward, and the chest wall has
a tendency to spring outward. If the lungs were removed from
the chest cavity and were no longer being influenced by the
chest wall or the pleural space, they would collapse like a
deflated balloon. Similarly, removing the lungs from the chest
cavity would cause the chest wall, no longer being influenced
by the lungs or the pleural space, to spring outward. The equi-
librium achieved between the lungs’ inward recoil and the
© Springer International Publishing AG, 1
part of Springer Nature 2018
H. Poor, Basics of Mechanical Ventilation,
https://doi.org/10.1007/978-3-319-89981-7_1