Afferent limbThe part of the breathing
system which delivers fresh gas to the patient. If the reservoir is placed in this
limb, as in Mapleson A, B, C and Lack systems, it is an afferent reservoir system.
A, B, and C circuits do not have efferent limbs.
Afferent reservoir systems
eliminate CO2 efficiently but, for controlled ventilation, high gas
flows are needed. B and C are junctional afferent systems, so need high gas
flows for both spontaneous and controlled ventilation.
Aintree Intubation Catheter
An adaption of the Cooks Airway Exchange Catheter, 56cm long, and with a larger
internal diameter of 4.8mm, allowing it to be pre-loaded onto a 4mm fibreoptic
intubating bronchoscope, with the directable distal 3cm left exposed. The external
diameter of 6.5mm allows ET (endotracheal) tubes, with minimum internal diameter of
7mm, to be loaded onto the catheter. The Aintree system allows intubation via an
LMA (or Proseal).
Ambu bag (bag valve mask)Hand-held self-inflating reservoir bag,
to provide ventilation to a patient who is not breathing adequately. Sizes range
from 250 ml to 2 litres, and the bag can deliver about half of it's volume. A
one-way valve prevents re-breathing.
Anaesthetic machinesThe general guidance
for pre-use checking of anaesthetic machines is mandated by the
specific procedures set by the particular manufacturer:
Anti-hypoxia deviceAn interlinking system between the oxygen
and nitrous oxide flow controls, which ensures that the patient does not receive
any nitrous oxide, without also receiving at least 25% oxygen.
ApnoeaSuspension of breathing.
- Residual effects of a narcotic premedication.
- Residual effects of induction, or maintenance agent.
- Hypocapnia - no stimulus for breathing.
- Hypercapnia - usually caused by fault in anaesthetic circuit.
- Severe hypotension.
- Suxamethonium apnoea.
- Pseudo cholinesterase - caused by liver disease.
Armoured Endo-Tracheal tube ET tube,
embedded with metallic helix strip, to prevent kinking and crushing, commonly
used in head and neck surgery, where acute flexion of the neck may
Aspiration(1) Inhalation, (2) Drawing off fluid from a cavity.
A technique to anaesthetise the upper airway, using local anaesthetic, to allow tracheal
intubation without the need for general anaesthesia and muscle relaxants. Nasal or oral
intubation may be performed. The oral route is more stimulating, and may be more difficult.
This technique requires a co-operative patient.
Ayre's T-pieceA Mapleson E valveless
circuit, with corrugated reservoir tubing, typically used for infants. It has minimal dead
space and minimal resistance. Exhaled CO2 flows
through the efferent limb, and is flushed out of the circuit by an adequate gas flow. For safety,
there should be a minimum flow rate of 6 litres/minute, but 10 litres is probably better, as low
flow rates can result in dangerous levels of CO2. Reservoir bag sizes are 500 ml and 1
Reference to a T-piece is usually made to a Mapleson F
Backward Upward Right Pressure (BURP)Pressure exerted on
the thyroid cartilage, to help visualisation of the vocal cords when intubating. The
assistant who performs BURP will move the larynx to the right, whilst the tongue
is displaced to the left by the laryngoscope blade.
Bain circuitFunctionally, a coaxial Mapleson D
circuit, typically used in anaesthetic rooms. Fresh gas flows down the inner
tube, and exhaust gases flow through the outer tube to the exhaust valve. Needs
high FGF to prevent rebreathing of CO2.
If the circuit is attached to a block assembly, connected to the gas outlet of
the anaesthetic machine, and incorporates an expiratory valve, gas scavenging
and intermittent positive pressure ventilation may be facilitated. Bain circuits
are better for assisted than spontaneous ventilation.
Berman Intubating AirwaySimilar to the Guedel pattern Airway,
but with a plastic hinge down the left side, a lateral opening down the right
side, and used as an aid to blind or fibreoptic intubation.
BougieA semi-rigid device, to introduce an endotracheal
tube, when tube placement proves difficult. During laryngoscopy, the Bougie is
carefully advanced into the larynx, and through the vocal cords, until the bent
tip enters a mainstem broncus. Whilst the Anaesthetist maintains the laryngoscope
and Bougie in position, the ODP (or Nurse) threads the tube over the end of the Bougie,
and into the larynx. Once the tube is in place, the Bougie is removed.
Bronchoscopy Basics ||
Awake Intubation ||
Bonfils setup ||
Can't intubate, can't ventilateSee
Emergencies: Can't intubate, can't
Continuous Positive Airway Pressure (CPAP)In
spontaneous ventilation, positive airway pressure is maintained until the end of
expiration. The closing pressure holds open the alveoli so that partial pressure
of arterial oxygen (PO2) is improved, making breathing easier.
Cook Airway Exchange Catheter
A long, flexible, hollow tube, designed to facilitate the exchange of an in situ
endotracheal tube. This technique can be used in the management of patients with
significant tracheal deviation, such as a result of an enlarged thyroid gland.
Additionally, The Cooks Catheter may be used for jet ventilation, or for end-tidal
carbon dioxide measurement.
Cricoid pressure (Sellick's Manoeuvre)
Application of pressure to the anterior arch of the Cricoid cartilage, to
temporarily occlude the lumen of the oesophagus (upper end), preventing aspiration
of stomach contents into the lungs. Typically used during Rapid Sequence Induction,
or during normal intubation when the lower oesophageal sphincter is expected to
be incompetent. A light force is required when the patient is drowsy, and 30-40
Newtons (3-4 kgs) when unconscious.
Note: The airway and breathing are higher priorities than the application
of cricoid pressure.
- Cricotracheal injury
- Active vomiting
- Cervical Spine injury
Note: Obstetric patients are especially susceptible to aspiration during
Dead spaceThe volume of the breathing system from
the patient end to the point at which to and fro movement of expired gas takes place.
Indications for a potentially difficult airway include:
- Less than 3″ (7 cm) between mandible and hyoid bone.
- Less than 5″ (12.5 cm) sternomandibular distance, (head fully extended)
- Less than 35 º neck extension
- Poorly visualized uvula
- Short, thick neck
- Receding mandible
- Protruding teeth
- Emergencies: Difficult Intubation
Double lumen endobronchial tubes
Efferent limbThe part of the breathing system
which carries expired gas from the patient. Efferent reservoir systems (D, E with
Jackson Rees modification of Ayre's T piece) work well with controlled ventilation,
but need high gas flows with spontaneous ventilation.
Failed Rapid Sequence Induction
Camera assisted placement of an ET tube, using a flexible of rigid (Bonfils)
bronchoscope, such as when the patient has limited movement of the jaw, or the
mouth/pharynx are within the operating site.
Fresh gas flowSupply of breathing gas delivered to the patient.
A video laryngoscope which provides a consistently clear, real-time view of the airway
and tube placement.
Anaesthesia UK ||
Small children ||
Humphrey ADE circuitA new circuit which can
be switched between the Mapleson A, D and E systems.
Hypoxic guardAn interlink between oxygen and nitrous oxide
flow controls, which prevents the patient from receiving pure nitrous oxide, and
maintains a ratio of, for example, 1:3 between oxygen and the nitrous oxide. If the
oxygen flow falls below 200 ml/minute, the nitrous oxide flow shuts off.
Inducing a patient into a state of anaesthesia. Once asleep, the patient can be administered
a volaile agent, which might otherwise produce laryngospasm, if the patient were sill
Verification of anaesthesia can be achieved by ensuring an adequate level of
end-tidal carbon dioxide, ET tube condensation (synchronised with respiration), symmetrical
chest movement, auscultation, and oxygen saturation.
- Barbiturates (Thiopentone, Methohexitone)
- Imidazoles (Etomidate)
- Phenols (Propofol)
- Phencyclidines (Ketamine)
Intermittent Positive Pressure Ventilation (IPPV)
Intermittent inflation of the lungs with a positive pressure delivered by a
ventilator, and applied via an endotracheal tube.
- Anaesthetised patients - with muscle paralysis (Atracurium etc)
- Acute respiratory or ventilatory failure.
- To prevent hypoxia.
- Chest injury and lung contusion (bruising).
- Coma with breathing difficulties, such as with drug overdose.
Intubating LMAA laryngeal mask airway, which
allows single-handed blind insertion of an endotracheal tube, without the need to
move the patient's head, or place fingers inside the patient's mouth. Typically used
in emergency or difficult airway situations, or when the patient may have cervical
spinal injury. The LMA section serves as a guide for a reinforced ET tube to be
placed, without having to displace the anatomy.
If the patient suffers from an oesophageal or pharyngeal abnormality, then intubation
via the ILMA is contraindicated, unless used in an airway rescue situation.
IntubationInsertion of an endotracheal tube into the trachea:
23cm (men) and 21cm (women) at incissors. An intubation attempt should not last
longer than 30 seconds, and should be stopped if patient oxygen saturation drops
below 95%. After intubation, patency may be confirmed by:
- End tidal carbon dioxide
- Depth of tube (eg 21/women, 23/men)
- Water vapour within lumen of tube during exhalation
- Equal bilateral chest rise and fall
- Auscultation for equal bilateral breath sounds
- No breathing sounds over the stomach
- No gastric contents in tube
- Tube cuff pressure: 20-25 cm/H2O.
Jet ventilationJet, or high
frequency ventilation, is a type of mechanical ventilation which employs high
respiratory rates (150+ breaths per minute), and very small tidal volumes. High
frequency ventilation is thought to reduce ventilator-associated lung injury,
especially in the context acute lung injury. This is commonly referred to as lung
protective ventilation. There are different flavors of High frequency ventilation,
and each type has its own advantages and disadvantages. The types of HFV are
characterized by the delivery system and the type of exhalation phase.
Lack circuitFunctionally coaxial Mapleson A afferent
reservoir circuit, similar to the Magill system, but with the expiratory valve at
the machine end. Fresh gas flows up the outer sleeve, expired gas flows down the inner
tube to the exhaust valve.
Laryngeal Mask AirwayAn LMA is a
device which sits over the top of the larynx (supraglottic), for spontaneous or
artificial ventilation. The tip of the LMA sits against the valve at the top of the
oesophagus, thereby providing a partial seal against regurgitation and aspiration
(inhaling fluid or foreign body into the bronchi lungs) of gastic contents. One
advantage over bag/valve/mask insufflation, is the reduced possibility of insufflating
the oesophagus, which might otherwise cause gastric distention. Additionally, an
LMA does not irritate the throat as much as an endotracheal tube.
Endoscopic instrument to aid visualisation of the airway/larynx during intubation. There
are several types of laryngoscope blade available, with the curved Macintosh blade being
used for standard intubation. Sizes range from 0 (neonate) to 4 (large adult).
- Macintosh (curved) - standard use
- McCoy - (curved) hinged tip
- Polio (120°) - obese and large breasted patients
- Magill (straight) - for infants
- Miller (straight) - for infants
The Macintosh blade is positioned in the vallecula, anterior to the epiglottis,
lifting it out of the visual pathway, while the Miller blade is positioned
posterior to the epiglottis, trapping it while exposing the glottis and vocal
Magill circuitThis is the original Mapleson A
system, comprising a three way T shaped tube, which is connected to the fresh gas
outlet (FGF), a reservoir bag (90° to FGF), a corrugated reservoir tube and,
at the other end, an expiratory valve, then the patient connection.
Magill forcepsAn aid to
nasal intubation, and placement of throat packs.
Mallampati classificationA scheme for grading
the visibility of an airway, with respect to endotracheal intubation.
|I||Soft palate, faucial pillars, uvula|
|II||Soft palate, uvula|
|III||Soft palate, base of uvula|
|IV||Soft palate not visible|
Mapleson A circuit (Magill and Lack)An afferent
reservoir circuit, which eliminates CO2
efficiently, but needs high Fresh Gas Flow (FGF) in controlled ventilation. In
spontaneous ventilation, requires FGF matching patient minute volume, to avoid
functional rebreathing. Mapleson A does not have an efferent limb.
Mapleson B circuitA junctional afferent reservoir circuit,
suitable for resuscitation and patient transfers, because the bag and valve are
close to the patient. Requires FGF of 1.5 -
2 times minute volume to avoid functional rebreathing. Does not have an efferent
Mapleson C circuitA
junctional afferent reservoir circuit; best for short term use, such as resuscitation
and patient transfers, because bag and valve are close to the patient. Also found in
Requires FGF of 1.5 - 2 times minute
volume to avoid functional rebreathing. Does not have an efferent limb.
Mapleson D circuitAn efferent reservoir circuit, which needs high
gas flows in spontaneous ventilation, so performs best with controlled ventilation.
Requires FGF of 2 - 4 times minute volume to
avoid functional rebreathing.
Mapleson E circuitThe original Ayre's T-piece; a valveless and bagless
circuit, with low breathing resistance; for spontaneous or assisted ventilation.
Mapleson F circuit Not strictly a Mapleson
classification, but refers to the Jackson-Rees modification of the
Ayres's T-piece system, which connects a two-ended bag to the
expiratory limb of the circuit. Gas escapes via the open end of the bag. A minimal
resistance circuit, which allows intermittent positive pressure ventilation by occluding the
tail of the bag between a finger and thumb, and squeezing the bag. There is also a version with
a closed end bag and an APL valve.
Minute Volume (VT)The total volume
of gas (litres) exhaled from the lungs in one minute; which is the product of respiratory
rate and tidal volume.
Nasal cannula flow rates
|FLow (L/min)||O2 delivered (%)|
With an added 4% for every increase of 1 Litre of flow, to a maximum of 60%.
Nasopharyngeal AirwayThe nasopharyngeal airway is less likely to
induce gagging than an oropharyngeal airway, and can be used in a conscious
patient when the airway is at risk of compromise. It can be life-saving in a
patient with a clenched jaw, trismus, or maxillofacial injuries.
NebulizerA device which converts a liquid to a fine mist, which
is then inhaled. Typically used to treat respiratory disorders.
Non-rebreather maskProvides a patient
with an oxygen concentration of 90-100%, whilst exhausting expired carbon dioxide.
Non-rebreathing circuitCircuits where the elimination of carbon
dioxide is accomplished by removing all expired gases from the circuit, and
venting them to the atmosphere. This is normally achieved by allowing the fresh
gas flow from the anaesthetic machine to direct the expired gases out of the
circuit, via a valve or other arrangement.
In general, non-rebreathing systems provide good control of inspired gas
concentrations, since fresh gas delivered from the anaesthetic machine is
inspired in each breath. They are, however, less economical in use than
rebreathing systems, because the minute volume of ventilation (or more) must be
supplied to the patient to prevent rebreathing, and they contribute more to
atmospheric pollution with anaesthetic agents. They are also less forgiving of
operator error, since an inadequate fresh gas supply will result in rebreathing.
See Mapleson A, D, E
Oropharyngeal airwayIn an unconscious patient, the
muscles in the jaw relax, allowing the tongue to obstruct the airway. An oropharyngeal
(or Guedel pattern) airway is a device which maintains a patent (open) airway, by
preventing the tongue from covering the epiglottis, which could prevent the patient
from breathing. The correct size is chosen by measuring from the corner of the
patient's mouth to the tip of the earlobe. The oropharyngeal airway is then inserted
into the patient's mouth upside down. Once contact is made with the back of the throat,
the oropharyngeal airway is rotated 180 degrees. These airways are often used in
conjunction with head tilt and jaw thrust techniques.
Oxygen toxicityA condition resulting from the harmful effects
of breathing molecular oxygen at elevated partial pressures (hyperoxia). Severe
cases can result in cell damage and death, with effects most often seen in the
central nervous system, lungs and eyes. Oxygen toxicity is a concern for those
on high concentrations of oxygen - particularly premature babies - and those
undergoing hyperbaric oxygen therapy.
- Burning sensation with deep breathing
- Other breathing problems
- Vision changes
Pin index systemMechanical system of ensuring correct fitting
of gas cylinders to their respective housings, according to ISO standard 407 for
Small medical gas cylinders. The positions of the holes on the cylinder
valve correspond with the pins fitted to the yoke attachment, such as on an
Positive End Expiratory PressureAt the end of
expiration, PEEP exerts pressure to oppose passive emptying of the lungs, and to
keep airway pressure above atmospheric. The presence of PEEP opens up collapsed
or unstable alveoli, and increases functional residual capacity. The closing pressure
holds open the alveoli so that partial pressure of arterial oxygen (PO2) is
improved, making breathing easier.
A laryngeal mask airway, with a reinfoced airway tube, bite block, and a drain tube
which opens at the upper oesophageal sphincter, allowing drainage of gastric secretions,
and access to the alimentary tract.
The total amount of air/gas exchanged between the lungs and the ambient air.
RAE tubePreformed endotracheal tube, cuffed and
uncuffed types, named after their creators - Ring, Adair, Edwin. South and
North facing RAE tubes are available, designed to facilitate Ear, Nose, & Throat surgery.
Rapid Sequence Induction (crash induction)
Rapid induction for patients at risk of gastric aspiration, such as non-fasted
and obstetric patients. Details
Schrader valvePush-fit connector for low
pressure gas supplies. A "tug" test confirms connection.
See-saw breathingBreathing pattern, seen in airway
obstruction, where the chest and abdomen move in opposite directions.
Specialist laryngoscopes and endoscopes
Transmit images, so bending possible.
- Retractor type eg, Macintosh and McCoy.
- Rigid fibeoptic.
- Flexible fibreoptic.
StyletUsed for pre-forming a tracheal tube to a required
shape, prior to insertion.
Tidal volume (VT)Total air moved with each normal
breath. Typically 6-8 ml/kg in adults.
a deep breath and, keeping the mouth closed and nostrils pinched, attempt
exhalation. The result is a rise in stroke volume.
VentilationThe process of inhalation and exhalation - taking in oxygen,
and expelling carbon dioxide by exhalation. During anaesthesia, the paralyzed patient
will need assistance to ventilate, by hand or machine.
Venturi (air-entrainment) maskA
medical device to deliver inspired air mixed with a known oxygen concentration to
patients on controlled oxygen therapy.