A generic term covering anything from the lips to the alveoli, although often divided into the upper airway (oral cavity, glottis, trachea) and the lower airway (bronchi down to alveoli). The airway is the top priority in all clinical emergencies, as in the following generic priority sequence:
Singed nose hairs or nasal soot in patients who have suffered
burns elsewhere makes the wise clinician suspicious for airway
burns. Such patients may develop airway edema that could be life-threatening
and that requires intubation to ensure a secure airway. The airway
damage can best be assessed by fiberoptic bronchoscopy (principally
looking for airway edema). Carbon monoxide levels should be measured
in all such patients and 100% oxygen should be given to drive
off the carboxy molecules from the hemoglobin binding sites.
Airway obstruction frequently occurs following the induction of
general anaesthesia. Traditionally this has been attributed to
the tongue falling back against the posterior pharyngeal wall
(and is remedied by placing an appropriately sized oropharyngeal
airway). Recent studies suggest that obstruction by the soft palate
or epiglottis from reduced airway tone may also be responsible.
Hypoventilation may result from airway obstruction, leading to
hypercarbia and then hypoxemia.
Airway obstruction can also occur from airway edema (e.g., following
extensive head and neck surgery or anaphylaxis), from airway infections
(e.g., epiglottitis), from airway tumors( laryngeal papillamotosis),
or from foreign bodies (e.g., aspirated hunk of steak).
Alveolar Ventilation ()
This is the volume of gas per minute that takes part in gas exchange
= (VT - VD)
where VT is the tidal volume, VD is the
respiratory deadspace, and f is the breathing rate (respiratory
frequency). Alveolar ventilation may be reduced with airway obstruction
or low respiratory rates (such as are encountered with excessive
doses of narcotic analgesics such as morphine). Reduced alveolar
ventilation leads to hypercarbia, and possible hypoxemia. Hypoxemia
due to hypoventilation is far less likely when the patient is
Complete cessation of breathing. Obviously apnea must be managed
promptly to avoid hypercarbia and hypoxemia. Ultimately, apnea
leads to cardiac arrest preceeded by bradycardia (usually).
ARDS (Adult Respiratory Distress Syndrome)
ARDS is a sometimes deadly lung problem following trauma, aspiration
pneumonitis and countless other clinical insults, resulting in
small, stiff, hard-to-ventilate lungs. This deadly respiratory
condition is often frequented in the ICU, with ventilators straining
away to push gas into small stiff lungs.
The syndrome histologically is similar to respiratory disease
of the premature newborn (RDS), hence its name, but rather that
resulting from pulmonary immaturity, ARDS is the consequence of
many clinical insults, aspiration pneumonitis, massive trauma,
and septicemia being common examples.
An important part of ARDS therapy is to distend the lung to make
it bigger so that more alveoli are open. This is done using PEEP
(Positive End Expiratory Pressure), a technique where the airway
pressure waveform is maintained positive (e.g., 10 cm H2O)
even during expiration. PEEP therapy impairs venous return to
the heart, making it problematic in hypovolemic patients.Another
problem with ARDS is leaking pulmonary capillaries that may lead
to pulmonary edema. This necessitates careful fluid management
and sometimes requires that PA line monitoring (Swan-Ganz catheter)
ARDS carries with it three management issues:
The high degree of pulmonary shunt present is ARDS necessitates
that two ventilator parameters (FIO2 and PEEP) be adjusted upward
jointly to achieve adequate oxygenation (eg. SaO2 > 0.9 of
PaO2 > 60 mmHg). Fio2 is the fraction of inspired oxygen (eg.
0.5 for 50% oxygen). PEEP is the Positive End Expiratory Pressure
of minimal lung distending pressure (eg. 5 cm H2O). FIO2 and PEEP
are not adjusted independently but rather jointly, even sometimes
by quantitative linking (eg. PEEP = 15 FIO2). Patients that are
hypovolemic may tolerate PEEP less well and require less strong
linkage to FIO2.
Ventilation may be difficult in ARDS patients since high ventilating
pressures are required to achieve normal tidal volumes. The high
ventilating pressures required are suspected to be a cause of
more lung injury, leading some researchers to advocate the use
of "permissive hypercapnia" a ventilating protocol allowing
higher PCO2 levels ad more acidotic pH levels but with much smaller
tidal volumes and airway pressures, and less potential for barotrauma.
Special ventilation modes such as inverse ratio ventilation (EI
ratio < I), airway pressure release ventilation, and high frequency
ARDS has associated with it increases in vascular permeability
(leaky capillaries) that mandates special care regarding fluid
management. Hypovolemia can be avoided by monitoring urine output
and cardiac filling pressures (CVP, PCWP).
Patients with ARDS require intubation. High cuff pressures, required
when high ventilating pressures are used, may damage tracheal
mucosa and cause long term injury (eg. Tracheal stenosis from
scarring). After 10 to 14 days of intubation, consideration is
given to a formal tracheostomy. Tracheal suction is also needed
to avoid buildup of secretions. Reintubation of patients with
ARDS may be necessary because of cuff leaks or because of the
buildup of hardened secretions within the lumen of the ETT.
Refers to getting harmful debris [usually gastric in origin] into
the lung's trachea and bronchi with the considerable potential
to cause aspiration pneumonitis, a often deadly inflammatory reaction
leading to ARDS. Aspiration pneumonitis is said to be more likely
when the volume of aspirate exceeds 25 ml and when it has a pH
under 2.5. Techniques to reduce the likelihood of aspiration with
ETT insertion include (1) pharmacological adjuncts such as gastric
motility agents, (2) use of awake intubation (airway reflexes
remain intact), and (3) use of a rapid sequence induction technique
employing preoxygenation, predetermined drug doses and cricoid
Medications used in asthma management include:
In addition, number of anaesthetic agents (eg. halothane, ketamine)
have a salutory effect in asthma.
Inhaled Beta-adrenergic agonists such as albuterol (salbutamol),
terbutaline, fenoterol, pirbuterol or salmeterol remain the mainstay
of treatment; although, their role in the chronic treatment of
asthma is in a flux, with many clinicians preferring the use of
inhaled corticosteroids as first-line therapy and with beta-agonists
reserved for "prn" use.
Intravenously administered theophylline products such as aminophylline
are waning in clinical popularity since they have a very poor
toxic/therapeutic index and do not add significant clinical benefit
in patients already receiving beta-agonists for an acute exacerbation
of asthma. Its main role is not in preventing acute attacks in
the chronic asthmatic, especially at night. In patients with COPD,
improvements in diaphragmatic function and in muco-ciliary clearance
make Theophylline a useful adjunct as well.
Corticosteroids are now taking on a new importance in treating
patients with reactive airways disease ( RAD) as the inflammatory
element in RAD is more appreciated. Inhaled corticosteroids are
now often used as first-line asthma therapy while intravenous
steroids are often used preoperatively in patients in with moderately
severe asthma or in those previously requiring steroid therapy.
However, in contrast to beta-agonists, whose clinical effect is
almost immediate, IV steroids take several hours to work.
The process of inserting an endotracheal tube (ETT) through a
patient's vocal cords into his or her trachea while the patient
is conscious. Patient cooperation is far more easily achieved
by using local anaesthesia or nerve blocks (for example, using
lidocaine in a dose not exceeding 5 mg/kg). Awake intubation has
the advantage that the anesthetist can always "back off"
if intubation becomes difficult, and no bridges have been burned
by giving potent, potentially dangerous drugs to the patient (e.g.
succinylcholine). Awake intubation is often carried out without
drugs in newborns with aspirated meconium (fetal feces) or in
adults who are moribund. Otherwise local airway anesthesia should
"Bail-Out" Algorithm (to awaken patient
after failed intubation)
A strategy used when mask ventilation is becoming difficult following the induction of general anesthesia complicated by unsuccessful intubation. This is a setting where you want the patient to wake up and breath spontaneously.
1. Ensure that the patient is not in laryngospasm and that the
patient's head and jaw are positioned properly. Call for help.
2. Insert an airway of some kind
A - oral airway
B - nasopharyngeal airway
C - LMA (Laryngeal Mask Airway)
WARNING: Airway insertion may lead to laryngospasm in lightly
3. Utilize a two-person technique whereby one person manages the
mask and holds the jaw in position using both hands, while the
other ventilates the patient by hand using the rebreathing bag.
4. As a last resort, a surgical airway ( TTJV, cricothyroidotomy)
is sometimes necessary.
Decreased breathing rate, usually under 10 breaths per minute.
This is often due to the administration of narcotic analgesics
such as morphine, meperidine or fentanyl. Other causes may include
increased intracranial pressure (eg from brain tumor). You should
know the differential diagnosis of bradynea.
Can't Intubate Algorithm
This clinical algorithm applies when the the patient cannot be intubated (but can be ventilated adequately with bag/mask/valve resuscitator apparatus)
1. Wake the patient up and proceed with awake intubation
Can't Ventilate Algorithm (patient intubated)
2. Administer 100% O2; Check airway pressure and listen for wheezes and equal air entry bilaterally.
3. Rule out an ETT problem by passing an ETT suction catheter through the ETT after disconnecting from the patient breathing circuit.
REMEMBER TO CALL FOR HELP
Cormack and Lehane Grading of View at Laryngoscopy
Grades III and IV are termed "difficult intubation"
Dead Space (VD)
Volume of gas delivered to the patient in inspiration that does
not participate in gas exchange. VD may be estimated
using the Bohr equation
where VT is the tidal volume, PECO2 is the
mixed expiratory carbon dioxide tension, and PaCO2
is the arterial carbon dioxide tension.
Difficult Intubation (DI)
A situation where the patient is known or expected to be difficult
to intubate using standard laryngoscopes. Such cases are often
managed using a fiberoptic bronchoscope or Bullard laryngoscope
to facilitate ETT placement, often with the patient awake.
Shortness of breath.
Early Morning Sniffing Position
A patient head position that facilitates intubation by lining
up the oral, pharyngeal and laryngeal axes. In the "sniffing
position" the neck is flexed while the atlanto-occipital
joint is extended. Placing a pillow under the shoulders
and head to maintain this position is often helpful.
Endotracheal Tube (ETT)
A "breathing tube", often with a cuff at the distal
end, allowing a sealed leak-free connection between a ventilator
and a patient's trachea. Such an arrangement allows both positive
pressure ventilation and spontaneous breathing. Typically, a size
7.5 (7.5 mm inner diameter) is used for adult women, with a size
8.5 for men. In some centers it is customary to cut the ETT prior
to use (e.g. oral ETTs: women - cut at 23 cm; men - cut at 25
cm). The ETT cuff pressure should be kept below 25 cm H2O
to prevent injury to the tracheal mucosa.
Specialized ETTs are available where ETT kinking is a concern,
for special kinds of surgery (ENT surgery, laser surgery) or where
one-lung ventilation is needed. Uncuffed tubes offer reduced protection
against aspiration and are used in preadolescent children according
to the following approximate guidelines:
ETVC Endotracheal Ventilation Catheter (Tube
A device used to facilitate reintubation following a trial of
extubation. Prior to extubation the ETVC is placed into the ETT
and the ETT withdrawn over it holding the ETVC in place. If reintubation
becomes necessary the ETVC can be used as a guide to direct the
new ETT through the cords. The ETVC can also be used to administer
low flow oxygen deep into the lungs (eg. 2 l/min flow rate) as
well as for capnography or even emergency jet ventilation in a
manner similar to TTJV.
The process of removing an ETT from the patient's trachea. This
should ordinarily only be done with the patient awake and obeying
verbal commands. Even so, catastrophies on extubation can occur,
such as total collapse of the airway in a patient with tracheomalacia.
Sometimes it is wise to extubate over an ETT exchange catheter.
1. Patient should be fully awake
2. Airway tone should be recovered with cough and gag reflexes intact
3. An ETVC should be employed if appropriate (difficult intubation patients)
4. Technical criteria should be satisfied in patients with poor respiratory function.
(a) Patient can maintain adequate oxygenation
(b) VC > 15 ml/kg
(c) NIF > 20 cm H2O
Victims of facial trauma may succumb from airway edema or loss
of airway structural support. Intubation may be difficult in patients
with Lefort I or II fractures (which puts bony fragments in the
nasal airway). Oral intubation may be difficult because of trismus
or even because of bizarre things such as a knife impaled into
the neck. Furthermore, intubation may be complicated by distortions
in the anatomy due to trauma or hematoma formation. Sometimes
fiberoptic intubation works with such patients, but not if the
airway is very bloody (poor view). Sometimes a tracheostomy under
local anaesthesia is needed.
Blunt and penetrating head trauma victims from motor vehicle accidents
often require intubation to allow therapeutic hyperventilation
to reduce cerebral edema. A PaCO2 level
between 28 and 32 mmHg is often sought. In addition, these patients
may need intubation simply to protect the airway against aspiration,
as the patient's gag reflex may be obtunded from the head injury.
Ventilation inadequate to the body's metabolic needs, so that
Laryngeal Mask Airway (LMA)
A relatively new method of airway management that has become extremely
popular in Europe (and to a lesser degree in North America). The
LMA is a device that is seated over the glottis with the epiglottis
often sitting in its bowl. Advantages of the LMA over the ETT
include: ease of insertion, less stimulating to the airway and
reusability. The main disadvantage of LMA is that it does not
protect against aspiration or laryngospasm.
An instrument to provide illumination to the glottis so as to
facilitate passing an ETT through the patient's vocal cords. Of
course, laryngoscopes are also used to examine for any pathology
(edema, bleeding, polyps, fibrosis). The most popular laryngoscope,
the Macintosh design, is curved so that the end fits into the
vallecula, lifting the epiglottis out of the way to expose the
vocal cords. Special laryngoscopes also exist, such as the straight
blade (Miller) design (passed posterior to the epiglottis, avoiding
the vallecula, and the Bullard laryngoscope, often very helpful
when mouth opening is quite limited.
The art and science of viewing the larynx. First achieved indirectly
using mirrors in the middle 1800s, direct laryngoscopy followed
in the late 1800s / early 1900s to allow tracheal intubation.
When laryngoscopy is performed for diagnostic or therapeutic purposes
under general anaesthesia (eg. by propofol infusion) one's goals
are to provide for relaxation of the jaw muscles and vocal cords
during the procedure, with subsequent recovery of the laryngeal
reflexes without incurring the wrath of laryngospasm. More commonly,
however, laryngoscopy is carried out to allow intubation.
Management of Laryngospasm
Laryngospasm, the reflex closing of the glottis by the glottic
musculature, is a protective mechanism provided by evolution that
sometimes makes airway management difficult. Laryngospasm may
occur from airway irritation such as might occur following excessive
instrumentation of the airway or with secretions and blood irritating
the vocal cords at light planes of anesthesia. Full laryngospasm
may make ventilation impossible, at least until the muscles relax
from the resulting severe hypoxia. While applying sustained positive
pressure or deepening the anaesthetic with IV lidocaine or propofol,
are sometimes effective in breaking laryngospasm, I prefer to
use small doses of succinylcholine (as little as 10 mg will often
do) to break laryngospasm when necessary. Always inspect inside
the mask and mouth if laryngospasm occurs - sometimes laryngospasm
is the first sign that the patient has aspirated some gastric
Obese patients are at increased risk of obstructive sleep apnea.
Very obese patients may be difficult to intubate and even more
difficult to ventilate after induction of anaesthesia, since anesthesia
often leads to decreased muscle tone in the upper airway. This,
in conjunction with redundant folds of oropharyngeal tissue, often
leads to the tongue, soft palate and/or epiglottis obstructing
the airway. Obese patients are also more prone to hypoxemia because
of their small FRC and heavy chest wall.
Positive Pressure Ventilation (PPV)
The process of forcing gases down a patient's trachea using either
a manual control technique or using an automatic ventilator. PPV
can be done using a manual resuscitator or the rebreathing bag
on the anaesthesia machine. But for long cases it makes more sense
to use an automatic ventilator.
Since the commercialization of pulse oximetry two decades ago,
thousands of lives have been saved by early detection of patient
hypoxemia. Using the technologies of infrared spectroscopy and
microprocessor-based signal processing, the pulse oximeter provides
an indication of tissue oxygenation on an ongoing basis with a
simple little finger probe not much bigger than a clothespin.
Although pulse oximeters suffer form many pitfalls (eg. poor signals
when patients are cold or vasoconstricted) they are an essential
component to patient monitoring. No elective case should be started
without a pulse oximeter. Pulse oximeters indicate the arterial
blood saturation ie, the degree to which arterial blood hemoglobin
binding sites are occupied with oxygen molecules. Patients are
hypoxemic when arterial saturation falls under 90%.
A measure of the distensibility of the lung and chest wall, expressed
as volume change per unit pressure change (ml/cm H2O)
In its most basic form, PaCO2 too high or
PaO2 too low.
Resuscitation from cardiac arrest and other deadly situations
often requires intubation both to supply high concentrations of
oxygen and ventilate off carbon dioxide, as well as to protect
the airway from being soiled by gastric contents.
Retrograde intubation involves passing a guidewire out the mouth
via a puncture through the cricothyroid membrane. The guidewire
is then strengthened by loading a sheath over it and passing an
ETT into the trachea using the sheath as a guide. It offers special
potential as a means of awake intubation in locations where fiberoptic
intubation is unavailable (eg. third world countries).
Spontaneous Ventilation (SV)
Breathing using diaphragmatic +/- intercostal muscles. The diaphragm
is innervated by C3 C4 C5 , so
high cervical injuries are sometimes incompatible with SV and
these patients may need diaphragmatic pacemakers for survival.
SV can be disturbed in many ways: obstructive sleep apnea, airway
infections (eg. epiglottitis), trauma to the airway etc. In such
cases the use of positive pressure ventilation (PPV) may sometimes
Syracuse-Patil Face Mask
An anesthesia face mask with a side port for the introducion of
a fiberoptic bronchoscope.
Increased breathing rate. As lungs become stiff the patient finds
it easier to take in smaller breaths and make up the difference
with an increase in respiratory rate. Other causes may apply too,
such as breathing in cardon dioxide in a bad rebreathing system,
or sepsis syndrome. You should know the differential diagnosis
Tidal Volume (VT)
Volume of gas delivered to the lungs during inspiration.
Transtracheal Jet Ventilation (TTJV - Needle
In desperate circumstances injection of oxygen under high pressure
directly into the trachea can be life-saving. This is done by
inserting a #14 gauge IV catheter through the cricothyroid membrane
and applying intermittent bursts of high-pressure oxygen through
this catheter. A special nonkinkable needle for TTJV is available
The original description of this technique, known as transtracheal
jet ventilation (TTJV) suggested a 50 PSI pressure head, but clinical
experience at this pressure shows that barotrauma (eg. pneumothoraces)
are common at this pressure. A more reasonable amount might by
10 PSI; no one knows what the "best" choice is yet.
Because of these concerns, many experts advocate the use of an
emergency cricothyroidotomy kit. [Complications of TTJV include
pneumothorax, pneumomediastinum, pneumopericardium, subcutaneous
emphysema, esophageal perforation and infection.
Ventilators are used in operating rooms and intensive care units (ICU) for respiratory support of patients who cannot breathe on their own. ICU ventilators are more complicated and more flexible than OR ventilators. There are 5 main ventilator parameters.
Main Ventilator Parameters
1. Tidal Volume (eg. 700 ml) [Volume of gas injected into trachea
with each breath]
2. Respiratory Rate (eg. 12 breaths/minute)
3. FIO2 (Fraction of Inspired Oxygen) (eg. 0.6 or 60%
4. PEEP (Positive End Expiratory Pressure) (eg. 5 cm H2O)
5. I:E ratio (eg. 1:3)
Time for inspiration in relation to time for expiration
|ABG||Arterial Blood Gases|
|CVP||Central Venous Pressure|
|DLT||Double Lumen ETT|
|ICU||Intensive Care Unit|
|ILM||Intubating Laryngeal Mask|
|LMA||Laryngeal Mask Airway|
|PaCO2||Arterial carbon dioxide level|
|PaO2||Arterial oxygen level|
|PEEP||Positive End Expiratory Pressure|
|PPV||Positive Pressure Ventilation|
|SaO2||Arterial oxygen saturation|
|TTJV||TransTracheal Jet Ventilation|