An Introduction to Airway Assessment and Management (Concise Airway Anatomy and Pathophysiology)

Abstract

Abstract
Airway management is a fundamental aspect of anaesthetic practice and of emergency and critical care medicine. Airway problems and obstruction is a preventable cause of deaths worldwide. Without an adequate airway management, all other maneuvers and resuscitation efforts will end with failure. Both elective and emergency airway need a plan and deep knowledge which obtained by good orientation, systemic approach, and close adherence with update protocols and guidelines.

Keywords: Airway, Oxygen, Hypoxia, anesthesia, Intensive care

Full text

DOI: 10.21276/aimdr.2017.3.1.AN1
Book Review ISSN (O):2395-2822; ISSN (P):2395-2814
Annals of International Medical and Dental Research, Vol (3), Issue (1) Page 1
Section: Anaesthesia
An Introduction to Airway Assessment and Management
(Concise Airway Anatomy and Pathophysiology).
Gamal Ejaimi1, Sittelnissa Saeed1
1Assistant Professor of Anaesthesia and intensive care, Department of surgery, Faculty of Medicine, King Khalid University, Abha, Kingdom of
Saudi Arabia, Aseer Central Hospital, Department of Anaesthesia & Critical Care Unit.
Received: November 2016
Accepted: December 2016
Copyright: © the author(s), publisher. Annals of International Medical and Dental Research (AIMDR) is an
Official Publication of “Society for Health Care & Research Development”. It is an open-access article distributed
under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-
commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Airway management is a fundamental aspect of anaesthetic practice and of emergency and critical care medicine . Airway
problems and obstruction is a preventable cause of deaths worldwide. Without an adequate airway management, all other
maneuvers and resuscitation efforts will end with failure. Both elective and emergency airway need a plan and deep
knowledge which obtained by good orientation, systemic approach, and close adherence with update protocols and guide
lines.
Keywords: Airway, Oxygen, Hypoxia, anesthesia, Intensive care.
INTRODUCTION
Airway management is a fundamental aspect of
anaesthetic practice and of emergency and critical
care medicine. However, no doubt medical practice
personal in other medical specialties needs to know
it well.
Airway problems and obstruction is a preventable
cause of deaths worldwide. Without an adequate
airway management, all other maneuvers and
resuscitation efforts will end with failure. Both
elective and emergency airway need a plan and deep
knowledge which obtained by good orientation,
systemic approach, and close adherence with update
protocols and guide lines. Therefore, airway
assessment and management is the most vital
medical conditions.
Goals
1) To obtain an introduction to airway assessment
and management by easy understanding of
human airway anatomy and pathophysiology.
Name & Address of Corresponding Author
Dr. Gamal Ejaimi
Assistant Professor of Anaesthesia and intensive care,
Department of surgery, Faculty of Medicine,
King Khalid University, Abha,
Kingdom of Saudi Arabia,
Aseer Central Hospital,
Department of Anaesthesia & Critical Care Unit.
CONTENTS
1) Concise Airway Anatomy
2) Component of inhaled and exhaled gas
3) Oxygen cascade
4) Oxygen carrying, content, delivery, and
consumption
5) Hypoxia.
6) Cyanosis.
UPPER AIRWAY ANATOMY
Airway anatomy is divided into upper and lower
airway. The upper airway consists of:
• Nose,
• Pharynx,
• Larynx and,
• Trachea.
Nose anatomy
• Pyramidal in shape.
• Consist of cartilage and bone.
• Divided by a midline septum into two nasal
cavities.
• Lateral wall has three concha-shaped bone
called turbinates lying as superior, middle,
and inferior.
• Maintain airway passage, heat and
humidity inspired gas. [1]

Ejaimi & Sittelnissa; Concise Airway Anatomy and Pathophysiology
Annals of International Medical and Dental Research, Vol (3), Issue (1) Page 2
Section: Anaesthesia
Figure 1: Illustration of sagittal section of nose showing lateral wall with turbinate. http://www.amulyabharat.com/nose-
anatomy-external-diagram/
Pharynx anatomy Pharynx compose of exterior and interior parts. The
interior part is divided to Nasopharynx, Oropharynx,
and Laryngopharynx. [1]
Figure 2: Pharynx. http://msk-anatomy.blogspot.com/2012/06/pharynx-anatomy.html

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Annals of International Medical and Dental Research, Vol (3), Issue (1) Page 3
Section: Anaesthesia
Larynx
• It makes a conduit between base of the
tongue and trachea.
• The length of larynx is about 44 mm in
adult male and 36 mm in female.
• It composed of; Three unpaired large
cartilages (cricoid, thyroid, epiglottis) and
Three pairs of smaller cartilages
(arytenoids, corniculate, and cuneiform).
• Cricoid cartilage is the only complete
cartilage in the larynx and lie opposite to
C6 Body.
• Have Intrinsic and extrinsic muscles.
• Intrinsic muscles; cricothyroid, posterior
cricoarytenoid, lateral cricoarytenoid,
transverse arytenoid, and thyroarytenoid
muscles.
• All intrinsic muscles of the larynx are
abductor except lateral cricoarytenoid
which is adductor. [1]
Figure 3: Larynx. http://www.gbmc.org/anatomyandphysiology
Upper airway innervation
• Three major neural pathways supply
sensation to airway structures.
• Terminal branches of the ophthalmic and
maxillary divisions of the trigeminal nerve
supply the nasal cavity and turbinates.
• The oropharynx and posterior third of the
tongue are supplied by the
glossopharyngeal nerve.
• Branches of the vagus nerve innervate the
epiglottis and more distal airway structures.
• All intrinsic muscles are supplied by
recurrent laryngeal nerve except
cricothyroidotomy (CT) which innervated
by external laryngeal nerve-branch of
superior laryngeal nerve.
• Injury of external laryngeal nerve during
thyroidectomy or cricothyrotomy result in
hoarseness of the voice and an inability to
produce high-pitched sounds.
• Types of Injuries of recurrent laryngeal
nerve:
• Unilateral = voice changes-hoarseness of
voice.
• Bilateral = aphonia and breathing difficulty.
• Internal laryngeal nerve supply a sensory
innervation to the laryngeal cavity down to
the level of the vocal folds, including
posterior surface of the epiglottis.
• Recurrent laryngeal nerve gives a sensory
innervation to the laryngeal cavity below
the level of the vocal folds. [1]
Trachea:
• Trachea is about 15 cm (6 inches) long and
2 to 3 cm in diameter in adult male.
• Begin from the inferior end of the larynx
(C6 vertebra) to its point of bifurcation
(between T5 and 7 vertebral level).
• Contain a series of 16 to 20 horseshoe-
shaped Cartilaginous rings-having a
posterior part of fibrous tissue.
• Sensory innervation by branches of vagus
nerve including recurrent laryngeal nerve.
[2]

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Figure 4: http://www.nature.com/gimo/contents/pt1/images/gimo2-f5.jpg

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Section: Anaesthesia
COMPOSITION OF INHALED AND EXHALED AIR
Composition Of Inhaled And Exhaled Air[3]
Gas Amount in inhaled air Amount in exhaled air
Oxygen 20.84% 13.6% - 16%
Carbon Dioxide Very small amount (0.04%) 4% - 5.3%
Nitrogen 78.62% 78.04%
Water vapour Small amount (0.5%) Large amount
Argon 0.96% 1%
OXYGEN CASCADE AND OXYGEN
CARRYING CAPACITY, DELIVERY
AND CONSUMPTION
Oxygen cascade:
Oxygen is extracted or transported from atmosphere
to tissue cells mitochondria by cardiorespiratory
system. This process is known as oxygen cascade.
At sea level, the atmospheric pressure is 760mmHg, and
oxygen makes up 21% (20.094% to be exact) of inspired air:
so oxygen exerts a partial pressure of 760 x 0.21 =
159mmHg.This is the starting point of the oxygen cascade, as
one moves down through the body to the cell, oxygen is diluted
down, extracted or otherwise lost, so that at cellular level the
PO2 may only be 3 or 4 mmHg. [4]
Figure 5: The sequential reduction in the partial pressure of oxygen throughout the oxygen cascade, from the air to
mitochondria in muscle cells The Lancet Oncology. Volume 10, No. 6, p598–605, June 2009.
Oxygen carrying capacity:
1) Arterial oxygen content:
• CaO2 is the amount of oxygen bound to
hemoglobin plus the amount of oxygen
dissolved in arterial blood:
• CaO2 (mL O2/dL) = (1.34 x Hb x SaO2) +
(0.0031 x PaO2)
• Normal CaO2 is approximately 20 mL O2/dL.
[5,6]
2) Venous oxygen content:
• CvO2 is the amount of oxygen bound to
hemoglobin plus the amount of oxygen
dissolved in mixed venous blood:
• CvO2 (mL O2/dL) = (1.34 x Hb x SvO2) +
(0.0031 x PvO2)
• Normal CvO2 is approximately 15 mL O2/dL. [6]
Oxygen delivery:
• Oxygen delivery (DO2) is the rate at which
oxygen is transported from the lungs to the
microcirculation.
• DO2 (mL/min) = Q x CaO2
• Normal DO2 is approximately 1000 mL/min.
• Or approximately 500 mL/min/m2 if cardiac
index is substituted for cardiac output. [6]
Oxygen consumption:
• Oxygen consumption (VO2) is the rate at which
oxygen is removed from the blood for use by the
tissues.
• VO2 (mL O2/min) = Q x (CaO2 - CvO2) by
Fick equation

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Annals of International Medical and Dental Research, Vol (3), Issue (1) Page 6
Section: Anaesthesia
• Normal VO2 in a normal person at rest is
approximately 250 mL O2/min. [6]
Oxygen extraction:
• Oxygen extraction is the slope of the relationship
between oxygen delivery (DO2) and oxygen
consumption (VO2).
• O2 Extraction Ratio = (CaO2 - CvO2)/CaO2
• Normal O2 extraction ratios range from 0.25 to
0.3. [6]
HYPOXEMIA AND HYPOXIA
• Hypoxemia is low oxygen tension in the blood-
NR=80-100 mmHg.
• Hypoxia is low oxygenation at tissue level.
Type of hypoxia
• Hypoxemic hypoxia.
• Stagnant hypoxia or circulatory hypoxia.
• Anemic hypoxia.
• Histotoxic hypoxia.
• Oxygen affinity hypoxia. [7]
Hypoxemic hypoxia:
• PAO2 = Fio2 × (BP − PH2O) − PCO2 / R.
• PAO2 = 0.21 × (760 − 47) – 40 / 0.8=100
mmHg.
Where:
• PAO2 is the alveolar oxygen tension,
• Fio2 is the fraction of inspired oxygen.
• BP is the barometric pressure (760 mmHg
at sea level).
• PH2O is the pressure of water vapor in the
inspired air (47 mmHg),
• PCO2 is the arterial carbon dioxide tension,
and
• R is the respiratory quotient (assumed to be
0.8 in most patients).
• (the A-a gradient), the difference between
alveolar and arterial oxygen tension
(normal < 20).
Hypoxemic hypoxia Causes:
• Low PaO2; (decreased Fio2, low barometric
pressure, or causes of elevated Pco2). Any
cause of hypoventilation will cause
hypoxemia if Pco2 rises high enough.
• V/Q mismatch; in the lungs causing a
widened A-a gradient. V/Q mismatch
responds to oxygen therapy. Pneumonia,
heart failure, and atelectasis are common
causes of V/Q mismatch.
• Increased pulmonary shunt: Increased
pulmonary shunt (Qs/Qt), resulting in
perfusion without gas exchange which does
not respond to oxygen therapy. Adult
respiratory distress syndrome (ARDS) is an
example of severe Qs/Qt. [7]
Stagnant hypoxia:
• Stagnant hypoxia also known as circulatory
hypoxia. [7]
Causes:
• Decrease in cardiac output., Extremely low
cardiac out-put (e.g., cardiogenic shock).
• Non-pulmonary shunt, like liver cirrhosis when
large amounts of blood flow bypass the
lungs entirely preventing gas exchange.
Anemic hypoxia:
• In anemic hypoxia, the reduction of tissue
oxygenation is a consequence of low
hemoglobin or hemoglobin with abnormal
oxygen carrying capacity. [7]
Histotoxic hypoxia:
• In histotoxic hypoxia, oxygen is available
but tissues will not able to utilize it due to
binding with another agent like cyanide
poisoning, where cyanide interferes with
aerobic cellular metabolism and bind to
tissue instead of oxygen. [7]
Figure 6: The oxygen dissociation curve from
Anaesthesia UK.
http://www.frca.co.uk/article.aspx?articleid=100345
CYANOSIS
Cyanosis is a physical sign causing bluish
discoloration of the skin and mucous membranes.
Cyanosis is caused by a lack of oxygen in the blood
which may be due to many different causes. During
airway management, it is mainly due to lack of
oxygen because of airway obstruction or failure to
secure patent airway. It is one of alerting signs,
beside paradoxical breathing movements, cyanosis
and intercostal retractions, which indicate respiratory
insufficiency and impending arrest. Again, Cyanosis
is alerting signs during airway management which

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Annals of International Medical and Dental Research, Vol (3), Issue (1) Page 7
Section: Anaesthesia
occur during difficult or failure intubation or
inadequate mask ventilation. [8]
REFERENCES
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Anatomy. The pharynx and larynx. Dartmouth Medical
School. Available on;
http://www.dartmouth.edu/~humananatomy/
2. O'Rahilly, Müller, Carpenter & Swenson. Basic Human
Anatomy. The esophagus, trachea and main bronchi.
Dartmouth Medical School. Available on;
http://www.dartmouth.edu/~humananatomy/
3. P.S.Dhami, G.Chopra, H.N. Shrivastava (2015). A Textbook
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4. Lee W Jones, Neil D Eves, Mark Haykowsky, Stephen J
Freedland, and John R Mackey. Exercise intolerance in cancer
and the role of exercise therapy to reverse dysfunction. Lancet
oncology: June 2009; Volume 10, No. 6: p598–605.
5. Lawrence Martin. The Four Most Important Equations In
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http://www.globalrph.com/martin_4_most2.htm
6. Steven E. Lucking, Frank A. Maffei, Robert F. Tamburro,
Neal J. Thomas. Pediatric Critical Care Study Guide. Oxygen
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Springer: 19-38.
7. Jonathan A. Myers, Keith W. Millikan, Theodore J.
Saclarides. Common surgical diseases. Hypoxemia and
hypoxia. Springer: Second Edition; 392 – 394.
8. Management of respiratory arrest. ACLS. On
https://acls.com/free-resources/respiratory-arrest-airway-
management/managing-respiratory-arrest.
How to cite this article: Ejaimi G, Sittelnissa A. Saeed. An
Introduction to Airway Assessment and Management
(Concise Airway Anatomy and Pathophysiology). Ann. Int.
Med. Den. Res. 2017; 3(1):AN01-AN07.
Source of Support: Nil, Conflict of Interest: None declared