Surgical Critical Care and Trauma Part 2: Airway Management in Trauma and Critical Care
Airway management gives benefit to the critically ill or injured patient
in three ways. When done well,
management allows provision of gas exchange, protects the lungs from aspiration injury and permits safe and effective treatments.
Humans have an absolute need for oxygen, suffering organ dysfunction,
damage and death if deprived of oxygen for more than a few minutes.
Carbon dioxide removal (technically clearance) is also necessary, but
priority is less than for oxygen provision. Hypercarbia (increased CO2 in the blood) is generally tolerated, perhaps for up to 1 hour. The exception
is for a closed brain injury, where hypercarbia increases cerebral blood volume
through vasodilatation, contributing to a raised intracranial pressure[1].
Oxygenation can be measured by cutaneous pulse oximetry but this may be
difficult in patients with vasoconstriction when cold or shocked. Arterial
blood gas, where available, is an alternative. Ventilation (carbon dioxide
clearance) may be measured by continuous capnography,
sampling CO2 in expiratory gases. Detection of expiratory CO2 provides simultaneous information on the airway
(patency, since CO2 leaves the lungs through the patient`s
airway), the breathing (ventilator
efficiency), and the circulation (the
ability of the cardiovascular system to transport CO2 from the
tissues to the lungs). Capnography provides information rapidly and in real-time.
The CO2 value at the end of expiration is called the end-tidal
value. In healthy patients, the end-tidal CO2 is about 0.5 –
1.0 kilopascal (4-7 mmHg) less than arterial CO2. In ill or injured
patients, especially with severe shock or chest injury, this linkage is lost
and the discrepancy widens. This is due to increased dead-space ventilation of
non-perfused lung tissue.
There are two types of injury – inhalational and iatrogenic. Inhalational injury (aspiration) results from the entry of gastric content,
blood, secretions, or debris into the lungs. This interferes with gas exchange
directly (by physical obstruction) or indirectly (by provoking acute
bronchospasm or delayed inflammation). Gastric content is acidic, highly toxic
and contains particulates which can block the airway. Blood clots and debris
from airway trauma also damage the lungs.
Iatrogenic injury due to misapplied instrumentation such as traumatic
intubation attempts can cause upper airway obstruction from oedema. It can also
result in contamination of the lower airway through aspiration of blood and
debris. The lower airway and lungs may suffer instrumental damage.
Safe and effective airway management allows interventions such as
surgery and mechanical ventilation.
Airway management is required in two broad situations:
1.
When the airway is directly injured.
2.
When treatment of other organ systems is needed.
Sometimes both airway and organs need simultaneous treatment.
Airway management has to be safe, effective and reliable. In trauma and
critical care this can be challenging, requiring high standards of technical
and non-technical competency. Technical skills are related to effective
performance of tasks. Non-technical skills encompass communication, teamwork and
decision-making which contribute to effective judgement. Judgement is increasingly appreciated as a dominant
factor in success or failure, life or death. The National Audit Project 4
analysed all serious airway incidents reported in the UK over a year (2008-9).
These included any unplanned tracheostomy or cricothyroidotomy, death or
unplanned admission to intensive care because of an airway management problem
[2]. The majority of the events
resulted from poor judgement, followed by problems resulting from lack of
education and training. The report highlighted the increased relative risk of
an airway-related death occurring in the Emergency Room and Critical Care
compared to the Operating Room: about 35 and 55 times more, respectively. These
are the most challenging areas in which to provide airway management, because
of four interacting factors: complexity,
risk, uncertainty and dynamism [3].
Complexity arises from
multiple interactions between the patient, his/her problems, and the procedures
and personnel involved in treatment. Added to these are the provision of drugs
and equipment, and transportation.
Risk arises from the severity of
illness or injuries, and possible complications of interventions.
Uncertainty arises from the
unpredictable nature of interacting factors and from the possibility of a
hidden pathology.
Dynamism describes the
rapid, time-sensitive changes in patient physiology and the recognition and
response to these by care providers. As mentioned, the time course of
complications resulting from airway interventions, most importantly hypoxia, is
measured in minutes.
All interventions in medicine and surgery involve an assessment of
expected benefit versus potential for harm. The balance of these is risk. The
common, recognized risks of airway
management include:
1)
Failure to plan and prepare, leading to unexpected
or unmanaged complications.
2)
Failure to achieve airway control, leading to
life-threatening or lethal loss of gas exchange (especially hypoxia) and loss
of airway protection with aspiration lung injury.
3)
Success, but with immediate complications such as
dental damage, airway injury with bleeding, swelling or injury to the larynx,
especially the vocal cords.
4)
Success, followed by delayed complications such as
intubation-related pneumonia, tube blockages or unplanned extubation of the
trachea.
5)
Each of the above can affect future confidence,
with future problems arising from performance anxiety, aversion, or avoidance
of responsibility.
Outcomes improve with safe, sensible and systematic approaches to all
aspects of patient management. The systematic approach prioritises treatment
responses in the order Airway, Breathing,
Circulation, Disability and Exposure. Airway management is the first
priority. The rare exception is for patients with catastrophic exsanguination, for
whom the “<C> ABC approach“ is necessary [4].
For all trauma patients, airway management is co-incident with
restriction of cervical spine movement, since instability of the cervical
column risks catastrophic spinal cord damage if the head is moved. All trauma
patients with actual or possible neck injury should therefore be managed with neck
immobilisation by rigid cervical collar, with further restriction of head
movement (eg. by use of head blocks
and tape) and initial treatment on a spinal board. These initial interventions
(which aim to immobilise the head in a neutral position), place restrictions on
access to and mobility of the patient`s airway. When tracheal intubation is
planned, the collar, tapes and blocks should be temporarily removed, the head
held in neutral by an assistant, providing “manual in-line stabilization”
(MILS). Airway interventions should be carried out with the head held in this
neutral position, which usually reduces airway patency and increases difficulty
in achieving tracheal intubation. Once intubation is achieved and confirmed,
the immobilisation should be restored until the neck is ‘cleared`, (deemed stable and not a danger to the
patient).
Safe and effective airway management depends on three factors: Personnel, Provision and Planning.
1)
Personnel: wherever possible, management should be provided by skilled, trained
staff with dedicated, trained assistants.
2)
Provision: appropriate equipment should be available at all times. Drugs are
necessary for some types of airway control, notably rapid sequence induction
(RSI) for oro-tracheal intubation.
3)
Planning: this includes the rostering of staff, resourcing of drugs, teaching and
training. Both individual and group planning for the management of expected
(and unexpected) injuries should be an ongoing, fixed part of every care
provider`s job.
The positive interaction of these factors allows the formulation of a
safe “Airway Management Strategy” for your patient [2]. This is a logical,
co-ordinated sequence of plans aimed at providing good gas exchange, protection from injury and permitting further treatment.
Have a series of plans in a sequence of potential approaches to airway
management: use Plan A, Plan B, Plan C then Plan D if needed. These plans vary according to
patient need and practitioner competence, but the priorities (providing gas exchange, protection from aspiration and permitting further treatment) would
apply to all patients. This type of management forms the basis of the Difficult
Airway Society’s (DAS) guidelines on the management of unanticipated difficult
tracheal intubation [5]. The Guidelines apply Plans to three clinical
scenarios: unexpected difficult intubation for elective surgery, unexpected
difficulty during an RSI and failed tracheal intubation with failed facemask
ventilation, the so-called “CICV” situation (“Cannot Intubate Cannot
Ventilate”), more correctly called “CICO” (“Cannot Intubate Cannot Oxygenate”).
The second and third scenarios are relevant to airway management in trauma and
critical care. For example, in a patient with facial injuries who needs a
life-saving laparotomy for traumatic shock, Airway management is: Plan A is RSI
tracheal intubation, Plan B temporary use of a Supraglottic Airway Device (SAD)
e.g. a laryngeal mask airway and Plan C a rescue tracheostomy or
cricothyroidotomy. If the surgical indication was less critical, another
sequence would be that Plan A is RSI tracheal intubation, Plan B abandoning the
anaesthetic and using facemask ventilation (until the patient woke up), Plan C
a SAD if ventilation fails and Plan D a tracheostomy or cricothyroidotomy if
CICO develops.
These guidelines stress the need for a Strategy (planning), early and
prompt recognition of failure, calling for help early and limiting attempts at
tracheal intubation. DAS (The Difficult Airway Society) guidelines currently
advise no more than three attempts at tracheal intubation for an emergency
case. Others advise no more than two attempts for a critical care patient,
since major complication such as cardiac arrest and aspiration risk increases
to about 20% with more than two intubation attempts [6].
Planning an Airway Management Strategy for each patient is aided by asking the following questions. (“the
five As of Airway management”)
1)
Assess immediate risks. The two big risks are anoxia and aspiration.
Anoxia (the desperate form of hypoxia) may be evident from the colour of mucous
membranes, but this sign is lost in severe anaemia or bleeding. Oximetry is
more accurate, but may be lost with vasoconstriction, hypothermia or in hypovolaemic, obstructive or cardiogenic
shock. Hypoxia requires immediate treatment. All trauma patients have an
aspiration risk, where gastric content can enter the lungs. Those with
depressed airway reflexes or facial injuries are especially at risk. Risk of
aspiration can be reduced through a tilting table, access to suction and the
application of cricoid pressure during tracheal intubation.
2)
A, B, C and D? What plans will form your strategy? These determine steps 4 and 5.
3)
Awake or asleep? e.g. tracheostomy under
local anaesthesia (=awake) or oro-tracheal intubation following Rapid Sequence
Induction of anaesthesia (RSI) (=asleep). The choice is informed by considering
the safest option.
4)
Above or below the vocal cords? For patients with severe facial injury, airway
control below the vocal cords by temporary cricothyroidotomy or tracheostomy is
a reasonable choice, probably under local anaesthesia.
5)
Afterwards? Once airway control has been achieved, ask “What next for your
patient?” Consider when and where airway devices can be safely removed.
Your Airway Management Strategy may be altered by asking these questions (“SLADE”). These factors are also known as context modifiers [7],:
1)
Skills? What skills do you and your team possess?
2)
Location? Where is your
patient? Management in the ward
may have to be different from the Emergency Room or Operating Theatre because
your resources, drugs, equipment and personnel will most likely be different.
3) Assistance? Teamwork with
good communication and decision-making improves outcome.
4) Destination? Should your
patient be moved to another site for treatment?
5) Equipment? What airway
devices are available to you immediately or from elsewhere in the hospital?
Five approaches can be incorporated into a series of plans (A,B,C,D) as
part of an individualized airway strategy tailored to patient need. These approaches require a variety of skills,
equipment [8], drugs and assistance to achieve successful outcome. Each
requirement should be considered in a proactive way, since the complex, risky,
dynamic and uncertain nature of airway management makes it hard to safely salvage
a situation later.
These principles apply to airway management for adults and children,
bearing in mind that children are different in Physiology, Psychology and Physical status (size and shape).
They also apply to the pregnant patient. Note that the third trimester
brings restricted lung volumes, higher volumes of gastric content and a greater
risk of regurgitation. Importantly, a pregnant patient must be managed with at
least a 15 degree left lateral tilt when lying down to reduce the risk of
supine hypotension resulting from inferior caval compression.
To repeat - airway management is carried out together with measures to
protect from cervical spine injury. If cervical spine precautions are removed
to permit airway intervention such as tracheal intubation above the vocal cords (oral intubation) or below the cords (tracheostomy or cricothyroidotomy), an alternative
form of immobilization, namely MILS should be applied by a staff member
dedicated to the task.
A.
Open type mask, i.e. there is no effective mask seal
with the patient. A lightweight plastic mask with reservoir bag (so-called
`trauma mask`) is usually used. Oxygen should be supplied at at least 10l/min.
Expiration is via the expiratory
ports in the mask.
B.
Closed type mask, used to provide facemask anaesthesia. The mask has an edge (often with an inflated cuff), a body, and a mount. A connector on the mount joins the mask to a breathing
system (or circuit), which is in turn linked to either an anaesthetic machine
or oxygen source. It is important to pull the patient’s face up into the mask
and not press the mask down onto the face.
Breathing systems are usually of the Bag-Valve-Mask variety (systems for
children lack the valve). A seal between the mask edge and the patient’s face
produces most efficient oxygenation, with expiration via the valve. The reservoir bag provides a volume of oxygen for
inspiratory flow. A patient may breathe spontaneously through this device (with
the expiratory valve open) or receive assisted positive pressure breaths by variably closing the expiratory valve. This is
sometimes called manual ventilation.
A common form of bag-valve-mask system has a self-inflating bag and a
fixed expiratory (`fish-lip`) valve. This is derived from the original “Ambu” ™
variety and is usually available in three sizes – for babies (500ml volume
bag), children (1000ml) and adults (2000ml). This is the only system which can
generate positive pressure for ventilating an apnoeic patient without external
oxygen; oxygen comes from inspired air (21%). Other breathing systems have
manually controlled valves.
Effective bag-valve-mask ventilation requires the skill to acquire and
maintain a facemask seal, to judge inspiratory and expiratory rates, and force
of manual ventilation whilst monitoring patient status.
The ability to achieve facemask ventilation varies [9]. Severe facial
injury, use of a cervical collar, blood and secretions are common limitations
in trauma. Pre-existing anatomical factors may complicate matters. A 5 point
(Han) grading system to describe ease of facemask ventilation has been proposed
[10].
Grade 0: facemask ventilation not attempted
Grade1: easy, no other equipment or help needed.
Grade2: moderate difficulty, oral or nasal airways needed.
Grade 3: difficult, oral and/or nasal airways needed with a two-handed
mask-holding technique, with an assistant compressing the bag.
Grade 4: impossible to achieve gas exchange.
With trained staff Han grade 4 only occurs occur in 1 in 20 000 patients.
For a patient with known or suspected unstable neck injury, movement and
manipulation of the obstructed airway is limited to elevation of the mandible.
This is the so-called `jaw thrust`, aimed at lifting the `anterior structures`
of the mouth (tongue and submental tissue) away from the posterior pharyngeal
wall, thus restoring or improving airway patency. Insertion of an oro-pharyngeal
airway (Guedel) may be useful in this situation (Han grade 2), but tolerance
depends on significant depression of airway reflexes, equivalent to a Glasgow
Coma Scale <8. Therefore consider providing a more secure airway, e.g. tracheal intubation. A
nasopharyngeal airway (one or both nostrils) is better tolerated, but avoid if
base of skull fracture is possible.
Bag-Valve-Mask ventilation is the “first and fall-back” method of
providing gas exchange for a patient with apnoea resulting from “disease or
drugs” (injury, illness, poisoning, sedation or anaesthesia). The lungs remain
unprotected from any form of aspiration and gas may be forced into the stomach.
Cricoid pressure (more accurately force), when applied by a trained assistant,
can reduce both of these risks. Cricoid force is designed to occlude the
oesophageal lumen against the sixth cervical vertebral body (in adults, higher
in small children). This is done by pressing with the index finger onto the
patient’s cricoid cartilage while the thumb and middle finger (of the same
hand) prevent the larynx from lateral displacement. The aim is to transfer force
posteriorly through the cartilage without deformation of the larynx.
A force of 30 Newtons is advised (about 3kg equivalent). Effective cricoid
force can achieve two goals, namely to reduce the risk of gastric dilation
during facemask ventilation, especially in children, and reduce the risk of
regurgitation of gastric content during facemask ventilation or tracheal intubation.
Cricoid force is not intended to manage vomiting. Vomiting is an active reflex
process, usually with co-ordinated expulsion of gastric content with glottis
closure. Regurgitation, however, is a passive process and aspiration lung
injury may occur when airway reflexes are lost during disease or drug therapy (anaesthesia
or sedation). In real-life it can be difficult to distiguish vomiting from
regurgitation.
There are recognised problems with use of cricoid force. These are
difficult facemask ventilation or difficulty passing a tracheal tube, resulting
from distortion and compression of the airway. This can happen with misapplied
or appropriate force [11].
Blood, secretions and debris may obstruct the airway, especially with
impaired protective reflexes. Careful use of a suction device can clear fluid.
Rigid (Yankauer- type) suckers or flexible catheters are used. Care should be
taken to avoid further trauma, provoking reflex coughing, retching and vagal
responses (bradycardia, bronchospasm) from deep pharyngeal or laryngeal
stimulation. Inspection of the oral cavity with a light source may reveal solid
debris, which can be removed with forceps, such as the Magill type. Be careful
not to push debris into the airway.
Suction through a tracheal tube using soft catheters may be needed to clear
blood or secretions. Risks include hypoxia from sucking oxygen from the
patient’s lungs, airway trauma and parasympathetic reflexes such as bradycardia
and bronchospasm.
In severe mid face injury (Le Fort 3 type), the maxillae and nasal pyramid
may obstruct the upper airway when supine. A conscious patient will seek to sit
up in an effort to open the airway, but an obtunded or unconscious patient is
in great danger. The mid face should be elevated to open the airway. Suction
and posterior packing of the nasal cavity (with tethered swabs or balloon
catheter) may be used to reduce bleeding.
This is the optimal form of
airway control, proving patency for gas
exchange, protecting the lower airway
and lungs from aspiration (using an inflatable cuff) and permitting effective positive-pressure ventilation.
The most common approach is oral intubation, passing a cuffed tracheal
tube through the oral and pharyngeal cavities, through the glottis (the
aperture between the vocal cords) into the larynx, so that the tube tip lies in
the mid trachea. A cuff is inflated to provide an airway seal. A pressure seal
to 30cm water is the upper safety limit for adults (20cm water for children)
[12]. Sustained higher pressures risk impairment of mucosal blood supply,
injury, bleeding and longer term problems such as subglottic stenosis. Until
recently cuffed tubes were restricted to adult patients, but cuffed paediatric tubes
are now accepted, provided that size selection and cuff inflation (preferably
with a pressure-measuring manometer) is carefully controlled.
Selection of tube size (diameter) and length is very important. The
diameter is traditionally specified as ID (Internal Diameter), measured in mm,
even though it is the external diameter of the tube which determines ease of
insertion. Tubes are available in 0.5mm increments. For average adult males a
tube of 8.5 to 9.0 mm ID is usually acceptable, for females 7.5 to 8.0 mm ID.
The tubes must be sufficiently wide to allow easy passage of suction tubes.
Excessive force must not be applied during tracheal intubation. A smaller size
should always be immediately available. Length of insertion is also important.
If placed too far, the tube will enter a main bronchus and only one lung
ventilated; the other lung will collapse. For adult males insertion length is 20-23
cm, for females 19-22cm. This should be checked and altered if needed (See
Post-procedure checks, below).
Tubes may be cut to desired length which reduce the risks of tube
kinking, aids passage of a suction catheter and reduces the work of breathing
when a patient is self-ventilating. For a patient with facial burns, however,
the tissues can swell markedly and it is wise to leave the tracheal tube uncut.
Tube selection for children depends on the age and size of the child.
There is variability, so checking for correct sizing is crucial. Again,
alternative sizes must be immediately ready for use.
One set of formulae for selection is [13]: (ID in mm)
Neonate to 3 months: 3.0 length
10 cm
3-9 months: 3.5 length 11 cm
9-21 months: 4.0 length 12 cm
>21 months: (age in years)
/4 +4 length = (age
in years) /2 +12 cm
Formulae for tube selection correctly calculate appropriate sizes in
only 30% cases. Ultrasound assessment at the level of the cricoid cartilage
will double success [13].
A variety of tube types are available. For adults, the commonest are the
precurved cuffed tubes. Tubes reinforced with spiral wire are less prone to
kinking and often used in neurosurgery and head and neck cases, but may be more
difficult to suction through. Double lumen tubes are used in thoracic surgery
to selectively isolate and collapse one lung. In trauma these can be used with
massive bleeding in one lung to prevent the non-injured lung from drowning.
Tracheal intubation requires visualization of the laryngeal inlet with a laryngoscope. Traditional
laryngoscopes are either straight or curved-bladed and permit visualization of
the laryngeal inlet by elevating the epiglottis. For curved blades (Macintosh
type) this is achieved indirectly.
The tip of the laryngoscope blade is inserted into the valleculla followed by
antero-inferior traction on the laryngoscope handle sufficient to tension the
hyo-epiglottic ligament, raising the epiglottis, exposing the glottis to direct
view, a “line of sight”. For straight blades (Miller or Magill type), this is
achieved directly. The blade is
positioned posterior to the epiglottis followed by antero-inferior handle
traction and the epiglottis is lifted directly. The straight blade technique is
harder to learn and results in a greater level of airway stimulation, but with
training, is the superior in terms of success. The curved blade method is
easier to learn because there is a definite target in placing the blade tip in
the vallecula, and nowhere else. For this reason the curved blade method is by
far the most popular approach for adult patients.
Both blade methods allow tracheal intubation by achieving two goals:
1.
A “line of sight” is gained between the intubator and
the larynx. The patient’s oral, pharyngeal and laryngeal planes are more
closely aligned, but this is hindered in the trauma situation because of
consideration of neck injury.
2.
An “airway space” or “working space” is achieved by
correct technique, with antero-posterior separation of tissues to allow tube
passage through the upper airway and the larnyx. At least 25 successful attempts at intubation “in context”
(in the setting of trauma with MILS applied) is necessary for competence.
Failure is always a possibility, hence the importance of back-up Plans B, C and
D.
All laryngoscopes suffer a major drawback in trauma or critical care: the
view is lost with any airway soiling by blood, debris, vomit or secretions.
Unless these can be cleared by suction or removal, the device will not aid
intubation and another plan is needed quickly.
Curved blade laryngoscopy is more likely to fail in one of four
situations:
1.
A base of tongue
or vallecula lesion prevents successful location of the blade.
2.
Prominent upper
anterior dentition impede blade placement to allow the “line of sight”.
3.
Use of a curved
blade requires displacement of the tongue into the mandibular space. If, for
anatomical reasons, this volume is small (e.g.
a short, receding jaw) the tongue cannot be accommodated (it contains blood and
cannot be compressed) and is displaced posteriorly This impedes blade
progression into the vallecula and prevents acquisition the “line of sight”.
4.
If a patient’s
epiglottis is big, long or floppy (e.g.
a baby) it may not be successfully elevated.
For each of these reasons, a straight blade technique using a “paraglossal
approach” [14] may be more successful.
The Cormack and Lehane grading scale for the laryngeal view is widely
accepted, but only applies to curved blade laryngoscopes:
Grade 1: all the glottis is seen.
Grade 2: the posterior portion of the glottis is seen, the posterior commissure.
Grade 3: only the epiglottis is seen.
Grade 4: only the tongue is seen.
Grade 3 is considered to be “difficult”. Grade 4 is usually considered
to be “impossible”. Application of MILS, and performing the intubation attempt
in the neutral position (as opposed to extending the head on the atlanto-axial
complex and flexing the lower neck, which is done during elective anaesthesia)
usually increases the view by one grade.
Other laryngoscopes are available. A variety of Rigid Indirect
laryngoscopes have been introduced [15]. They share a common feature, in that
they do not need to form a straight “line of sight” to view the glottis and are
marketed for patients with “difficult airways”. They allow the intubator to
“see around the corner” by using a variety of technologies: rigid fibreoptic bundle (Bullard™,
Upsher™, Wu™ laryngoscopes), digital camera (“videolaryngoscopes” such as the
McGrath 5™, AP Advance™, C Mac™, AWS™ etc) or optical prisms and lenses (Airtraq™).
These devices generally give a good view of the larynx, provided the patient
can open their mouth sufficiently, but passage of a tracheal tube may be problematic
because they do not align airway axes and create limited “airway space”. There
is currently little evidence to determine which device is superior for
difficult patients [16]. These
devices may not be available in many African clinical contexts, and they are
used in only a minority of airway management cases in other settings.
The flexible fibre optic bronchoscope is a versatile device which can be
used for tracheal intubation, upper and lower airway inspection and lung
toilet. It is however, expensive, delicate, requires intense decontamination
and a high degree of skill to be used well. Even when available, it is not
routinely used in the trauma setting.
The upper airway, especially the larynx, has a dense nerve supply
serving speech, breathing, swallowing, coughing and gagging. Vocal cord closure
is termed laryngospasm.
Penetration of the larynx with a tracheal tube requires profound
suppression of reflexes. These include the motor reflexes mentioned above and
also autonomic responses, both sympathetic (provoking tachycardia, arrhythmia
and hypertension) and parasympathetic (provoking bradycardia and bronchospasm).
Upper and lower airway secretions increase.
For patients requiring tracheal intubation, the most effective approach
is to provide an anaesthetic as part of a rapid sequence induction (RSI). There
are usually three parts to the anaesthetic: unconsciousness, immobility and reflex suppression. A hypnotic agent provides unconsciousness, a
neuromuscular blocking agent (sometimes called a muscle relaxant or paralyzing
drug) provides muscular immobility or relaxation and thirdly a reflex
suppressing drug, e.g. an opioid, may be given. An anticholinergic agents (e.g atropine) may be given to reduce
secretions or risk of bradycardia.
An obtunded patient successfully intubated without recourse to drugs is
usually desperately ill or injured, and the prospects for survival are low.
Giving an RSI anaesthetic is a complex, co-ordinated procedure, best
achieved by a trained team, optimally of four people:
1)
The airway intubator.
2)
A person to provide cricoid force.
3)
A person to stabilize the patients`s head,
providing MILS. (when neck injury is known or suspected)
4)
A person to supply the required equipment directly
to the intubator.
The RSI usually proceeds as follows:
1)
The team understands the situation.
2)
The team has a planned airway management strategy.
3)
Drugs and equipment are readily available, monitors
applied and vascular access achieved.
4)
Drug doses are calculated and equipment sizes
estimated.
5)
The cervical collar is removed and MILS applied.
6)
Oxygen is administered using a facemask via a
bag-valve-mask system for 3 minutes.
7)
An induction agent is given (e.g. sodium pentothal, ketamine).
8)
Following loss of consciousness, cricoid force is
applied. (30 Newton force, equivalent to a weight of about 3 kg)
9)
A neuromuscular blocking agent (e.g suxamethonium) is given. Intravenous
opioid or lidocaine may be used to obtund autonomic responses (e.g. in head injury). Intravenous anticholinergics
(e.g. atropine) may also be given.
10)
Clearance of airway secretions may be needed.
11)
Oral intubation is achieved. If the view of the
glottis is restricted, a tracheal introducer (“bougie”) may be inserted and
used to guide the placement.
12)
Two or three attempts are advised. If these fail,
resume mask-ventilation immediately.
13)
The tracheal cuff is inflated, the seal confirmed,
the breathing system is connected to the tube and positive pressure ventilation
is started.
14)
Post procedure checks confirm successful placement.
15)
Cricoid force is removed.
16)
Post procedure management is started.
There are four post procedure
checks:
1.
Most importantly, the tube must be in the trachea. If not, hypoxia will start
immediately. Confirmation is achieved clinically,
with capnography (where available) or
by compression of the bulb of an oesophageal detector device. The device is
attached to the tracheal tube and the bulb compressed. If the tube is placed in
the trachea, the bulb will quickly re-inflate. If the tube is in the oesophagus,
the bulb will remain deflated.
Clinical confirmation uses the human senses: Look, Listen, Feel. Ideally, look to see the tube passing through the
cords and then look for chest expansion resulting from positive-pressure
ventilation. Listen (using a
stethoscope) on both sides of the chest for breath sounds and listen over the epigastrium to exclude noise resulting from
unintended esophageal placement. Feel (with
your hand) for chest expansion during ventilation.
Capnography provides the best way to confirm
tracheal intubation, with detection of expired CO2 (after four
expiratory cycles). Unrecognised oesophageal intubation is catastrophic. Remember: “When in doubt, take it out!”
2.
Confirm that the cuff seal has been achieved by
listening to exclude an audible leak during positive-pressure ventilation.
3.
Confirm that both lungs are effectively ventilated.
A tracheal tube inserted too far into the airway will penetrate a main bronchus
(usually the right in adults), resulting in one-sided chest expansion and
one-sided auscultation with subsequent risk of hypoxia and hypercarbia. The
tube should be withdrawn.
4.
Chest radiography should be performed to provide
information about tube position, bony integrity and lung shadows. This is best
done during the post-procedure management phase.
Post-Procedure Management includes:
1.
Secure the tube at the correct depth. The choices
include: a tie (avoided in head injury as it can obstruct venous drainage),
tape, or (when secretions or bleeding is problematic) fixation to a secure
tooth with dental wire.
2.
Insertion of a bite-block (rolled-up gauze) between
the molar teeth to prevent biting onto the tube.
3.
Reapplication of cervical spine immobilizing
devices.
4.
Gastric drainage via an oesophageal tube. For head injury, the wisest route is oro-gastric
tube placement.
5.
Action of drugs given for RSI wear off and
therefore effective sedative therapy such as a propofol or benzodiazepine
infusion is needed to facilitate further management. Further neuromuscular
blockade may be needed.
Failed tracheal intubation:
The priorities are provision of
oxygenation and protection from
aspiration. Options include: resort to facemask ventilation (Approach 1), temporary
supraglottic airway (Approach 4) or a “Front of Neck” approach (a form of
subglottic management, either cricothyroidotomy or tracheostomy –
Approach 5). Alternatively, where safety dictates, ventilation may be supported
(Approach1) until the patient recovers and wakes up.
Supraglottic Airway Devices
(SADs) are midway between facemask ventilation and tracheal intubation in terms
of anatomical location, invasiveness and security. All are inserted blindly.
They are very commonly used in
elective anaesthesia and difficult airway management, either expected or
unexpected [17].
A SAD is designed to form a periglottic seal. This allows for positive
pressure ventilation, at pressures less than 20 cm water for early devices.
The original device is the laryngeal mask airway (LMA), now called the
`Classic LMA`, and many types are now available, both reusable and disposable.
Most SADs are of the `first generation` type, providing airway patency with a
low pressure seal. They do not provide protection from regurgitation and
aspiration of gastric content, but may provide protection from aspiration of naso
-or oro-pharyngeal bleeding (the so-called `umbrella effect`).
“Second generation” SADs have one or more
additional features designed to increase efficacy and safety, such as increased
pharyngeal seal pressure, a gastric drain tube (to achieve functional
separation of the aero-digestive tract) and an integral bite block. The
archetypal second generation device is the ProSeal ™ [18].
SADs are best for elective anaesthesia where risk
of regurgitation is low. They also have a place in the management of a failed tracheal intubation where hypoxia
is developing. They are usually placed easily (cricoid force should be removed
to allow the tip of the device to position properly) and can rescue and
temporize a dangerous situation, permitting other responses, (such as
tracheostomy) to be used. The best second generation device to use is the ProSeal™,
if available.
These devices can also be used as an intubating
conduit, guiding one of a variety of intubation aids, such as the Aintree
Intubating Catheter ™ or tracheal introducer.
In a failed tracheal intubation during an RSI,
laryngeal masks can be life-saving, but they are temporary airway devices. They
are recommended in guidelines for use in unexpected difficulty and failed
tracheal intubation with life-threatening hypoxia [5].
This is the fifth and final approach to airway management, the so-called
`Front-of-Neck-Access` or “Emergency Percutaneous Airway” [5,19] which includes
either cricothyroidotomy (a temporary approach) or tracheostomy (a definitive
airway).
These may be the first choice for airway control, for example in complex
maxillofacial injury or as part of a rescue plan when other approaches have
failed. Either may be achieved with local or general anaesthesia, and both are
more easily performed when a cervical collar is removed and MILS done.
Cricothyroidotomy is done using narrow or wide bore devices.
A: Narrow bore (<2mm
internal diameter) include catheter-over-needle devices, most simply an intravenous
cannula, or with a dedicated cannula such as the Ravussin™ catheter, attached
to an aspirating syringe during placement. There are five major considerations:
1.
Accurate placement via the cricothyroid membrane into the airway lumen is vital. Paratracheal
or oesophageal placement of either needle or cannula must be avoided. Careful
syringe aspiration during the needle procedure and following placement coupled
with confirmation with capnography will avoid this complication.
2.
Cannulae (especially intravenous types) are prone
to kinking.
3.
The resistance to oxygen flow via the cannula is sufficiently high that a dedicated high pressure
jet ventilation device (eg. the
Manujet™ system) is needed. Anaesthetic breathing systems cannot generate
sufficient pressure to inflate a patient’s lungs. High pressure jet ventilation
devices are not likely to be available in many African settings, in which case
a wide bore device is indicated.
4.
Expiration must be achieved through the patient`s
upper airway.
5.
There is no protection from aspiration.
Narrow bore cricothyroid cannulae used with jet ventilation is more
useful in controlled elective situations.
B: Wide bore devices (>4.0mm internal diameter) usually have greater utility in the
setting of the trauma airway. Various devices are available which rely on a dilational
step with wire guidance (Melker ™) or without (QuickTrach ™). Some of these
tubes have an inflatable cuff, offering better protection form aspiration and
aiding ventilation.
A wide bore
cricothyroidotomy device or a standard endotracheal tube may be placed using a
`surgical` approach. One method is the 4 step approach [20]:
1)
Identification of the membrane.
2)
Horizontal scalpel stab incision through the skin
and cricothyroid membrane.
3)
Insertion of a tracheal hook (superior or
inferiorly) to control access.
4)
Insertion of a tracheal tube, preferably cuffed.
Care must be taken to avoid endobronchial placement.
A wide bore device permits both inspiratory and expiratory flow through
the artificial airway. It protects from aspiration when a cuffed airway is
inserted and successful ventilation can be achieved with standard breathing
systems without recourse to a jet ventilator.
Tracheostomy is an alternative but is somewhat more technically
demanding since tracheal access is deeper in the neck than the cricothyroid
approach. The isthmus of the thyroid may have to be divided with considerations
of haemostasis. Open and percutaneous (Seldinger) techniques are available. In
trauma or critical care tracheostomy should only be performed by an experienced
operator.
Once inserted, verification of correct placement of either wide bore
cricothyroidotomy or tracheostomy is done in the same way as for oral insertion
of a tracheal tube.
Airway management allows provision of gas exchange, protects the lungs from aspiration
injury and permits safe and effective
treatments.
Airway control (with due regard for cervical spine integrity) using one
or more of five approaches is the first priority for safe and effective
management. This is the first step in the systematic, sequential care of the
critically ill or injured patient.
1 Protheroe RT, Gwinutt CL. Early hospital care of severe traumatic
brain injury. Anaesthesia 2011;66:1035-47.
2 Royal College of Anaesthetists. 4th National Audit Project
of the Royal College of Anaesthetists and the Difficult Airway Society. Report
and findings. March 2011. http://www.rcoa.ac.uk/docs/NAP4_es.pdf (accessed 11/11/2011)
3 Gaba DM, Maxwell M, DeAnda A. Breaking the chain of accident
evolution. Anesthesiology 1987;66:670-6.
4 Hodgetts TJ, Mahoney PF, Russell MQ, Byers M. ABC to <C>ABC:
redefining the military trauma paradigm. Emerg Med J 2006;23:745-6.
5 Henderson JJ, Popat MT, Latto IP, Pearce AC. Difficult Airway Society
guidelines for the management of the unanticipated difficult intubation.
Anaesthesia 2004;59:675-94.
6 Mort T. Emergency tracheal intubation: complications associated with
repeated laryngoscopic attempts. Anesth Analg 2004;99:607-13.
7 Hung O, Murphy M. Context-sensitive airway management. Anesth Analg
2010;110:982-3.
8 Ross AK, Ball DR. Equipment for airway management. Anaesthesia and
Intensive Care Medicine 2009;10:471-5
9 Ramachandran SK, Kheterpal S. Difficult mask ventilation: does it
matter? Anaesthesia 2011;66(Suppl 2),40-4.
10 Han R, Tremper KK, Kheterpal S, O’Reilly M. Grading scale for mask
ventilation. Anesthesiology 2004;101:267.
11 Palmer HMG, Ball DR. The effect of cricoids pressure on the cricoids
cartilage and the vocal cords: an endoscopic study in anaesthetized patients.
Anaesthesia 2000;55:263-8.
12 Seegobin RD, Van Hasselt GL. Endotracheal cuff pressure and tracheal
blood flow: endoscopic study of effects of four large volume cuffs. BMJ
1984;288:965-8.
13 Bae J-Y, Byon H-J, Han S-S, et al. Usefulness of ultrasound for
selecting a correctly sized uncuffed tracheal tube for paediatric patients.
Anaesthesia 2011;66:994-8.
14 Henderson JJ. The use of paraglossal straight blade laryngoscopy in
difficult tracheal intubation. Anaesthesia 1997;52:552-60.
15 Behringer EC, Kristensen MS. Evidence for benefit vs novelty in new
intubation equipment. Anaesthesia
2011;66(Suppl 2),57-64.
16 Mihai R, Blair E, Kay H, Cook T. A quantitative review and
meta-analysis of performance of non-standard laryngoscopes and rigid fibreoptic
stylets. Anaesthesia 2008;63:745-60.
17 Timmermann A. Supraglottic airways in difficult airway management:
successes, failures, use and misuse. Anaesthesia 2011;66(Suppl 2),45-56.
18 Cook TM, Lee G, Nolan J. The ProSeal™ laryngeal mask airway: a review
of the literature. Can J Anaesth 2005;52:739-60.
19 Hamaekers AE, Henderson JJ. Equipment and strategies for emergency
tracheal access in the adult patient. Anaesthesia 2011;66(Suppl 2),65-80.
20 Brofeldt BT, Panacek EA, Richards JR. An easy cricothyroidotomy
approach- the rapid four-step technique. Acad Emerg Med 1996;3:1060-3.