Full text of DOI:10.1046/j.1365-2044.2002.288515.x

Anaesthesia, 2002, 57, pages 1134–1145
.....................................................................................................................................................................................................................
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Machine and monitoring failure power outlet on the rear panel of the current to 3 A. In theory, if the power
from electrical overloading
anaesthetic machine (Fig. 1). As soon as load drawn from an individual socket
the kettle was switched on, all the were to exceed its current rating, the
We wish to report a case of electrical equipment connected to the auxiliary outlet circuit breaker would cut off the
failure of a target-controlled infusion power outlets of the anaesthetic power to that socket only, without
(TCI) pump and a Datex-Ohmeda machine failed instantly. This included affecting the function of the remaining
AS ⁄ 3 monitor as a result of accidental the AS ⁄ 3 monitor and the Diprifusor three sockets. However, this incident
overloading of one of the auxiliary infusion pump. As a result, TIVA and demonstrates that if the current rating of
mains socket outlets on the rear instrumental monitoring were inter- the appliance is very high, it is possible
panel of an Aestiva 3000 anaesthetic rupted. We immediately switched to for the ‘master’ circuit breaker to open
machine.
inhalation anaesthesia (isoflurane and in addition to the individual circuit
An ASA 1 patient was undergoing a nitrous oxide) and continued clinical breaker, thereby cutting off power to
rhinoplasty under propofol total intra- monitoring until instrumental monitor- all four sockets. The current drawn by
venous anaesthesia (TIVA) using
Diprifusor Master TCI infusion pump. room. It took several minutes before it the capacity of the auxiliary sockets.
The anaesthetic machine and the AS ⁄ 3 was realised what had happened and the
This incident highlights several safety
monitor had been checked in accord- problem was resolved. Fortunately, the issues.
ance with the Association of Anaesthet- patient was unharmed.
Safety checks. The anaesthetic equip-
The current British and European ment checklist must include inspection
a
ing was brought in from the anaesthetic the kettle was 10 A, much in excess of
ists guidelines [1]. Although the
Diprifusor pump did not have a battery Standard for the anaesthetic workstation of the auxiliary power outlets in the rear
back up, it functioned satisfactorily states that anaesthetic machines can be panel of the machine. The anaesthetist
when plugged into the mains outlet. supplied with up to four auxiliary mains must ensure that only appropriate
At the time of the operation, the pump sockets [2]. These may accept a standard anaesthetic equipment is connected to
was plugged into a four-socket exten- mains plug as with the Datex-Ohmeda the sockets and that the current rating of
sion board placed on the floor. Towards Aestiva 3000. The outlets are intended the equipment does not exceed the
the end of an uneventful operation, the to provide electric supply to anaesthetic limits of the individual circuit breakers.
surgeon asked for a nasal splint to be equipment such as monitors, electrically Connection of appliances such as forced
prepared. The splint (Thackray Instru- operated vaporisers (Tec 6) and infusion air warmers and extension sockets to
ments, Powys, UK) is made of a thermo- pumps. The current load that each of these auxiliary power outlets must never
plastic material, which is moulded to these sockets can handle limits the type be permitted. Extension boards with
fit the nasal contour by immersion in of electrical equipment that can be multiple sockets are particularly danger-
very hot water (approximately 90 ꢀC). connected to these power outlets. The ous, as a wide range of electrical
Hence, one of the theatre staff, without Aestiva has three sockets rated at 1 A appliances used in an operating theatre
the knowledge of the anaesthetist, and a fourth outlet rated at 2 A (Fig. 2). environment can potentially be con-
plugged an electric kettle (rated at Each outlet is provided with a circuit nected to them and thereby to the
2200 Watts) into the four-point exten- breaker, which turns off the power to anaesthetic machine. All members of
sion board on the floor (to which the the socket in the event of an electrical the theatre staff should also be made
Diprifusor pump was connected). It was overload [3]. In addition, there is a aware of the risk of such practice, and
not realised that the extension lead was ‘master’ circuit breaker for all four no one except the anaesthetist should be
actually connected to the auxiliary outlets, which limits the total outlet allowed to plug any device into the
All correspondence should be addressed to Professor M. Harmer, Editor of Anaesthesia, Department of Anaesthetics, University of
Wales College of Medicine, Heath Park, Cardiff CF14 4XN, UK.
Letters (two copies) must be typewritten on one side of the paper only and double spaced with wide margins. In addition, please
include your letter as a Word for Windows or .rtf document on disk or alternatively submit as an e-mail attachment addressed to
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must follow the advice about references and other matters contained in the Notice to Contributors to Anaesthesia printed at the back
of each issue. The degree and diplomas of each author must be given in a covering letter personally signed by all the authors.
Correspondence presented in any other style or format may be the subject of considerable delay and may be returned to the author for
revision. If the letter comments on a published article in Anaesthesia, please send three copies; otherwise two copies of your letter will suffice.
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Correspondence
without
a
battery back up was
unsafe practice. This has since been
addressed.
A. V. Chawla
Queen Victoria Hospital
East Grinstead RH19 3DZ, UK
E-mail: Amit.Chawla@lineone.net
N. I. Newton
Guy’s Hospital,
London SE1 9RT, UK
References
1 AAGBI. Checklist for Anaesthetic
Apparatus 2. London: The Association
of Anaesthetists of Great Britain and
Ireland 1997.
2 BSI. British Standard BSEN 740. British.
London: British Standards Institute,
1999.
3 Datex-Ohmeda. Operations Manual
Aestiva 3000. Helsinki: Datex-
Ohmeda, 1999.
Emergency physicians:
additional providers of
emergency anaesthesia?
I was interested to read the editorial
(Lockey & Black. Anaesthesia 2002; 57:
629–31) having recently returned from
two years working in a ‘Level One’
trauma centre in the USA. The editorial
suggests, on the basis of the American
National Emergency Airway Registry
[1] which collected data from 35 centres
in the US, that the American solution to
the problem of providing emergency
anaesthesia and intubation in the Acci-
dent and Emergency department is a
satisfactory one. In the centre in which I
worked, Physician delivered ‘anaesthe-
sia’ occurred both in the emergency
room and the intensive care unit. My
experience has led me to the following
conclusions, which do not support
Figure 1 Arrangement of electrical components involved in the incident.
anaesthetic machine at any time. In the incident would have been averted if emergency physician delivered anaes-
same vein, the anaesthetic machine the outlet sockets were designed not to thesia.
should always be plugged directly into accept such a plug.
1 When an emergency physician is
a wall or pendant-mounted mains
socket – never into an extension lead.
Inappropriate use of domestic equipment. delivering anaesthesia, he ⁄ she is
Appliances such as electric kettles do removed from their traditional role in
Design safety. The present interna- not meet safety standards for theatre the emergency room. One needs there-
tional standard governing the design of equipment with regard to power con- fore additional emergency department
anaesthetic workstations allows auxiliary sumption and earth leakage currents and medical staff to manage the patient to
mains socket outlets to be mounted on are unsafe in such an environment.
the anaesthetic machine, which accept a Finally, it must be accepted that 2 Patients in the emergency depart-
standard three-pin mains plug. This the use of a Diprifusor infusion pump ment and intensive care are frequently
the same standard.
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Correspondence Anaesthesia, 2002, 57, pages 1134–1145
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depends on the amount of oxygen
consumed by the patient. This is
worked out by the following formula:
Fio2 ð%Þ Â VtI À Feo2 ð%Þ Â VtE
¼ O2 consumed per breath:
where Fi
O
is the fractional inspired
2
concentration of oxygen, Fe
O
is the
2
fractional expired oxygen concentra-
tion, VtI is the inspired tidal volume
and VtE is the expired tidal volume.
Vo2 ¼ O2 consumed per breath
 Respiratory rate:
For a quick calculation, I would
multiply the Fi
the minute ventilation to calculate the
O
) Fe
O difference by
2
2
VO .
2
An important question is whether the
Figure 2 Auxiliary power outlets on the rear panel of the Aestiva 3000.
oxygen consumption calculated by the
above-mentioned formula is limited by
the amount of oxygen flowing into the
circle system?, i.e. the patient cannot
take up more oxygen than that given to
him.
those with the most challenging airways
Measurement of systemic
to manage.
oxygen uptake during low-flow
3 Trauma patients with head injuries
anaesthesia with a standard
and thoracic injuries (including aortic
technique vs. a novel method
injuries) provide special challenges and
Two things I would watch out for:
The FiO – FeO difference. The differ-
will not be well managed with a ‘recipe’-
The recent article (Leonard et al.
type Rapid Sequence Induction.
2 2
Anaesthesia 2002; 57: 654–8) is import-
4 The American system relies on the
ant from the point of view that one
24-h presence of an attending emer-
ence is usually about 5% in an awake
individual. A widening in the difference
may mean that the lungs are extracting
as much oxygen as possible from the
inspired gases (is the oxygen inflow into
the circle limiting oxygen uptake?), or a
high end-tidal carbon dioxide concen-
needs to calculate oxygen uptake (VO )
2
gency physician and in ‘Level One’
trauma centres, an attending anaesthes-
iologist (we attended all trauma calls,
our role frequently being the supervi-
sion of trainee emergency physicians in
airway management).
5 In my experience, failed intubations
and unsatisfactory administration of an-
aesthetic drugs and sedation were more
common in patients who had anaesthesia
delivered by the emergency physician.
In order that we maintain a high
standard of anaesthetic care to our
patients, we should ensure that
adequately trained and experienced
anaesthesia staff are available to attend
the emergency department 24 h a day.
to ensure that adequate oxygen flow is
maintained during low-flow anaesthesia
in a circle system. There is an easier
method of calculating V
O
from the
2
oxygen concentrations in the inspired
and expired gases, which are measured
and displayed by most of the modern
anaesthesia monitors.
In my practice of low-flow anaesthe-
sia, I ensure that the addition of oxygen
into the circle system is slightly over the
tration is reducing the FeO .
2
Response of oxygen consumption to in-
creasing oxygen inflow into the circle. I
perform this to ensure that the inflow of
oxygen into the circle system is not the
limiting factor for the patient’s oxygen
consumption. I increase the fresh gas
flow of oxygen and recalculate oxygen
consumption to ensure that the supply
of oxygen exceeds the use by the
patient.
One of the drawbacks of using low
fresh gas flow in a circle system is the
possibility of delivering a hypoxic mix-
ture. Application of the concept of
oxygen consumption and calculating it
may help to reduce the risk of the
patient becoming hypoxic.
V
O of the patient. The two principles
2
that I follow to attain the lowest
possible flow during low flow anaes-
thesia are:
1 There should be an adequate fresh gas
flow into the circle system to compen-
sate for the VO2 every minute (assuming
D. Farquhar-Thomson
nitrous oxide is not used) and to
overcome trivial leaks. I would accept
the lowest flow that would ensure that
the reservoir bag or the ventilator
bellows remain full in spontaneous and
controlled ventilation, respectively.
Dorset County Hospital,
Dorchester DT1 1JY, UK
E-mail: Duncanft@hotmail.com
Reference
1 Anon. National Emergency Airway
R. Shankar
Bedford Hospital,
Bedford MK42 9DJ, UK
Registry. http://www.med.wayne.edu/ 2 An appropriate amount of oxygen
near/near_stu.htm.
should be added to the circle, which
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Cardiac output determination
using compliance
accuracy and averaging these over a
The
pre-operative
anaesthetic
period of about 20 s will eliminate machine check was carried out and
errors from variations in stroke volume. nothing unusual was detected. General
Perhaps greater accuracy of the time anaesthesia was induced for a Caesarean
constant would be available through an section. The ventilator was switched on
optical or perhaps an ultrasonic system and the bellows went up and down
in preference to the older technology of more slowly than determined by the
Last February, I described a method for
deriving cardiac output by dividing the
product of compliance and mean arter-
ial pressure by the time constant of the
arterial system (Campbell. Anaesthesia
2002; 57: 185). A recent letter has been
published in which the theory is accep-
ted but concerns are raised regarding
two practical issues (Linton. Anaesthesia
2002; 57: 715). One concern is that
errors will occur from the variable
increase in systolic pressure in peripheral
arteries so that measurements of the
radial artery systolic pressure will not
equal the aortic systolic pressure. My
response is that these increases have
been recognised for many years and are
associated with the pulse pressure wave
becoming more peaked and narrow as it
passes along the artery. When, however,
the mean arterial pressure in the per-
ipheral vessel is compared with the
mean aortic pressure, they are almost
identical [1]. As it is the mean arterial
pressure that is used for the cardiac
output measurement, there is little error
from this source.
The other concern expressed by
Linton is that reflected waves within
the arterial system produce distortions
that prevent an accurate measurement
of the time constant. A trace was shown
to support this view. To this I would
add that distortions are also commonly
produced from the transducer ⁄ catheter
combination from a variety of artefacts
[2]. As these distortions occur around
the dicrotic notch, accurate readings can
still be obtained from the end part of the
diastolic trace just before the upswing of
the next pulse pressure wave.
liquid-filled pressure transducers.
ventilator settings. More importantly,
For many years, clinicians have the patient was not adequately ventila-
accepted complicated expensive meth- ted as detected by capnography and
ods for measuring cardiac output so that auscultation. A rapid check of the
a new simple method will be viewed anaesthetic machine did not reveal any
with scepticism. If, however, accuracy cause for the malfunction. The patient
equivalent to the standard methods can was hand ventilated for the remainder
be achieved, the exciting potential exists of the procedure.
for cardiac output monitoring to be
available for every major surgical pro- examination of the anaesthetic machine,
cedure.
Postoperatively, a more detailed
a Modulus II Plus manufactured by
Ohmeda (Madison, WI, USA), revealed
that the oxygen pipe that supplies gas to
drive the bellows was mistakenly
connected to the scavenging outlet
underneath the bellows housing. Our
daily anaesthetic machine check did not
detect this problem because when the
drive hose is connected in this fashion
the bellows will still move, although
with a limited range of travel. A reduced
tidal volume is produced, accompanied
by the bellows leaking gas and deflating
at a slow rate. The manifold connec-
tions for both the driving and scaven-
ging pipes are very similar with internal
diameters of 17 mm and 19 mm,
D. I. Campbell
Sydney, Australia
References
1 Kelman GR. The arteries. Applied
Cardiovascular Physiology. Sydney:
Butterworths 1971, 73–4.
2 Hill DW. Unusual pressure waveforms.
Physics Applied to Anaesthesia, 4th edn.
Sydney: Butterworths 1980, 96.
Connector mix-up on an
anaesthetic machine
We would like to report a recent respectively (Fig. 3). The oxygen pipe
ventilator malfunction that occurred as may be attached with ease to the
a result of a design feature making it scavenging connector. There are no
possible to attach the ventilator driving distinguishing features on either con-
gas pipeline to the scavenging outlet.
nector to aid reconnection.
On the trace submitted by Linton,
the time constant is approximately
1.25 s and the mean arterial pressure is
in the region of 70 mmHg. Taking a
reasonable adult arterial compliance of
1.6 ml.mmHg)1 and using these figures
as an example, the cardiac output would
be 5.4 l.min)1 with a systemic vascular
resistance of 1040 dynes.s)1.cm)5, and a
stroke volume of 60 ml at a heart rate of
90 beats.min)1
Multiple readings of the selected part
of each exponential curve will improve Figure 3 Ventilator manifold of Modulus II Plus Anaesthetic Machine.
.
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Correspondence Anaesthesia, 2002, 57, pages 1134–1145
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The distributors of the machine in of Anaesthetists of Great Britain and ous tracheostomy. The procedure
Ireland (Oxygen Care Teo) – have been Ireland states: ‘It is not intended to involved the existing tracheal tube
informed of the problem and have fitted supplant any pre-anaesthetic checking being replaced with a longer 5.0-mm
an alternative manifold with a 30-mm procedures issued by manufacturers, but internal diameter microlaryngeal tube.
scavenging connector that will not should be used in conjunction with Prior to tracheostomy, the cuff was
accept the driving gas pipeline. They them’. deflated and the resulting gas leak
state that newer Datex-Ohmeda The connection installed into the prevented by a pharyngeal throat pack.
machines have this 30-mm connector manifold (0236-0478-700) was changed I consider there are inherent problems
on the manifold. There are approxi- from 19 mm to 30 mm on ECO with this particular technique of airway
mately 14 Modulus II Plus machines 96-3500. Standards were being drafted management that need to be addressed.
in the South of Ireland. The same calling for a 30-mm conical connector (a) The airway pressure may increase
manifold may also be found on other for Anaesthetic Gas Scavenging Systems. following ventilation through a smaller
Ohmeda anaesthetic machines inclu-
ding the Excel 210 and 410. Oxygen
Care Teo have told us that they are
actively seeking out this manifold type
in order to modify it to prevent similar
misconnections. Anaesthetists should be
aware of the possibility of this mix-up
that may escape detection during the
routine anaesthetic machine check.
microlaryngeal tube in patients with
poor lung compliance, and adequate
ventilation may be impossible to
achieve. Mechanical ventilation via a
microlaryngeal tube can lead to hyper-
carbia. The rise in arterial carbon
dioxide may be detrimental in patients
with raised intracranial pressure.
(b) There have been numerous stud-
ies evaluating various airway devices
including the laryngeal mask [1], the
intubating laryngeal mask [2], the air-
way management device [3], the Com-
bitube [4] and a microlaryngeal tube [5]
being used during retrograde transla-
ryngeal tracheostomy. None of these
has achieved widespread acceptance.
Major complications including loss of
airway and hypoxic episodes have been
reported in about 14% of patients
during the process of changing the
existing tracheal tube to a micro laryn-
geal tube during translaryngeal trache-
ostomy [6].
(c) Accurate needle and guidewire
placement in the trachea is an important
step during percutaneous tracheostomy
prior to insertion of single or multiple
dilators. Life-threatening complications
can occur during the needle placement,
dilatation and subsequent placement of
a tracheostomy tube. Fibreoptic bronch-
oscopy is increasingly used and has been
found useful to guide these steps during
tracheostomy [7]. In addition, continu-
ous endoscopic guidance has been
shown to increase the safety of percu-
taneous tracheostomy [8]. This series
reports a case of oesophageal dilatation
and placement of a tracheostomy tube
necessitating thoracotomy for the oeso-
phageal repair. The use of a micro-
laryngeal tube during tracheostomy
P. Mardle
Director, Quality Assurance,
Datex Ohmeda,
Hatfield AL9 5EN, UK
ENT surgeon pipped at the post
by the laryngeal mask airway
We write to describe a novel (mis)use of
the laryngeal mask airway.
´ ´
D. F. O. Croinın
J. Keogh
A fit and well 3-year-old girl required
a general anaesthetic to remove a cherry
seed from her nose. Following induc-
tion with 100 mg propofol, a size 2
classic laryngeal mask airway was inser-
ted upside down and attached to an
Ayre’s T-piece to administer oxygen in
air. The laryngeal mask airway cuff was
inflated to create a seal. Two gentle
puffs of positive pressure expelled the
seed from her nose. There is a small
potential risk of eustachian tube baro-
traumas using this technique. We used a
gentle (sneeze-like) puff of positive
pressure therefore minimising the risk
of eustachian tube insufflation. The
laryngeal mask was then re-inserted
(this time in the correct position) to
allow the child to breathe spontaneously
until she emerged from anaesthesia. No
surgeon required.
Erinville Hospital,
Cork, Ireland
E-mail: keoghj@shb.ie
A reply
Thank you for the opportunity to reply
to Drs Croinin and Keogh’s letter. They
report that is possible to switch hoses on
17-mm and 19-mm manifold connec-
tions. An attempt to switch hoses on a
Mod II Plus was performed. The 17-mm
hose would go onto the 19-mm fitting
with additional force applied. The
19-mm hose (0225-0807-700) that we
supply with our Scavinging assembly
would not stay on the 17-mm fitting.
In the O & M manual, pre-operative
checkout procedures figs 4–9 and 4–10
show the correct connections for the
17-mm and 19-mm hoses. If the
pre-operative check procedures are per-
formed with the 17-mm and 19-mm
switched on, the manifold failures will
be encountered. A failure will be noted
on page 4–16 step 12 where the reading
will be lower than the 3.3–4.3 l speci-
fied, and no up-and-down movement
of the bellows will be visible. On page
4–19 and 4–20 steps 15 and 16 will also
fail. If the Ohmeda pre-operative check
procedures are completed this condition
would be detected.
B. F. van der Griend
D. Gardner-Thorpe
T. M. Cook
Royal United Hospital,
Bath BA1 3NG, UK
Airway management is simpler
with the existing tracheal tube
A recent article (Fisher et al. Anaesthesia
2002; 57: 253–5) describes a new
method of airway management using a does not allow passage of a broncho-
microlaryngeal tube during percutane-
The Checklist for Anaesthetic
Apparatus published by the Association
scope to visualise the key steps of the
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Correspondence
patients. Critical Care Medicine 2002; 30:
815–19.
procedure. The oesophageal tear could
have been avoided by bronchoscopy.
(d) In patients with thick secretions
or blood clot in the airway, it would be
difficult to perform an effective suction
via a microlaryngeal tube during trach-
eostomy.
Despite the growth of multiple per-
cutaneous techniques in recent years,
there has been a decreasing trend
of immediate or early complications of
tracheostomy since the introduction of
the Ciaglia serial dilatational technique.
This may be as a result of more training
and increasing use of bronchoscopy
during the procedure. We believe using
a bronchoscope through the existing
tracheal tube should lead to a safer
percutaneous tracheostomy. The use of
a microlaryngeal tube prevents this
option.
changed over a gum elastic bougie.
The risk of losing the airway during this
part of the procedure was recognised
as a potential problem. The fact that
no difficulties were encountered using
this simple precaution contrasts dra-
matically with the figure of 14%
incidence of complications suggested
by Dr Mallick.
7 Beiderlinden M, Karl Walz M, Sander
A, Groeben H, Peters J. Complications
of bronchoscopically guided percuta-
neous dilational tracheostomy: beyond
the learning curve. Intensive Care Medi-
cine 2002; 28: 59–62.
8 Ravat F, Pommier C, Dorne R. Per-
cutaneous tracheostomy. Annales
Francaises D Anesthesie et de Reanimation
2001; 20: 260–81.
Use of the bronchoscope. It was pointed
out in the original paper that a disad-
vantage of this method was that it did
not allow the utilisation of a broncho-
scope. We agree that the use of a
bronchoscope for confirming the place-
ment of the guide wire and tracheosto-
my tube is desirable. Since the
publication of the paper, we have been
extending our technique so as to permit
the use of a bronchoscope while main-
taining the airway with a microlaryngeal
tube. The oesophageal tear reported in
the series represents a major complica-
tion. This problem may even occur
despite the use of a bronchoscope.
The relevant point here is that the
misplacement of the tracheostomy tube
was readily identified without the loss of
airway control. The situation could be
rectified without loss of the patient’s
oxygenation or ventilation. In the case
reported, the patient was not put at
risk, the tear was explored and repaired
in the neck and did not require a
thoracotomy.
Suctioning via a microlaryngeal tube.
During this series, no procedure needed
to be abandoned due to difficulty with
maintaining an airway. On a number of
occasions following re-intubation, the
microlaryngeal tube needed to be
cleared of secretions using a suction
catheter of the appropriate size. It is
feasible that torrential haemorrhage
could occur during tracheostomy with
the formation of large clots. It would be
anticipated that the percutaneous pro-
cedure would need to be abandoned in
such an instance.
A reply
Thank you for allowing us to take the
opportunity of replying to Dr Mallick’s
letter. Dealing with the points raised
sequentially.
Control of ventilation. We agree that
the control of ventilation during trach-
eostomy is important. Provided that the
ventilator is adjusted to the ‘constant
volume’ mode and that the inspired
tidal volume is adjusted so that the
exhaled tidal volume and minute ven-
tilation remain close to or greater than
that recorded prior to commencing the
tracheostomy, then the arterial carbon
dioxide tension can be maintained at an
optimal value. Under these conditions,
the peak airway pressure will rise due to
the resistance of the smaller tracheal
tube; however, there is no or little
change in the plateau pressure. Correct
packing of the pharynx will reduce any
gas leak to a minimum.
If an ordinary tracheal tube is used
with a bronchoscope, then depending
on the relative sizes of the relative size
of the tracheal tube and the broncho-
scope, the effective diameter of the
tracheal airway may well be reduced to
a value not dissimilar to that of a micro-
laryngeal tube.
A. Mallick
Leeds General Infirmary,
Leeds, UK
References
1 Dosemeci L, Yilmaz M, Gurpinar F,
Ramazanoglu A. The use of the laryn-
geal mask airway as an alternative to the
endotracheal tube during percutaneous
dilatational tracheostomy. Intensive Care
Medicine 2002; 28: 63–7.
2 Verghese C, Rangasami J, Kapila A,
Parke T. Airway control during per-
cutaneous dilatational tracheostomy:
pilot study with the intubating laryngeal
mask airway. British Journal of Anaes-
thesia 1998; 81: 608–9.
3 Johnson R, Bailie R. Airway manage-
ment device (AMD) for airway control
in percutaneous dilatational tracheos-
tomy. Anaesthesia 2000; 55: 596–7.
4 Mallick A, Quinn A, Bodenham A,
Vucevic M. Use of the Combitube for
airway maintenance during percutane-
ous dilatational tracheostomy. Anaes-
thesia 1998; 53: 249–55.
Following insertion of the tracheos-
tomy tube, ventilation can still be
maintained via the micro laryngeal tube.
This allows for the correct placement of
the tracheostomy tube to be confirmed
before the original airway is lost. This is
not always possible when the original
tracheal is used and pulled back as the
tracheostomy tube is inserted into the
trachea.
5 Fantoni A, Ripamonti D. A non-de-
rivative, non-surgical tracheostomy: the
translaryngeal method. Intensive Care
Medicine 1997; 23: 386–92.
D. Read
D. Duane
The Princess Royal Hospital, Haywards
Heath RH16 4EX, UK
6 Cantais E, Kaiser E, Le-Goff Y,
Palmier B. Percutaneous tracheostomy:
prospective comparison of the transla-
ryngeal technique versus the forceps-
dilational technique in 100 critically ill
Changing the existing tracheal tube for a
microlaryngeal tube. In the series repor-
ted, the tracheal tube was always
L. Fisher
Derriford Hospital,
Plymouth, UK
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Correspondence Anaesthesia, 2002, 57, pages 1134–1145
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Stylet for reinforced laryngeal
mask airway
trauma and occupying the oral space. the RLMA. It allows tight fixation by
The inner devices (metal stylet, small inflating the cuff and smooth removal
tracheal tube [3], combined metal stylet by deflating it after insertion of the
With more widespread use of the and tracheal tube [4]) also have some RLMA. To produce this stylet for a size
reinforced laryngeal mask airway problems. It is difficult to remove them 4 RLMA, we used a cuffed tracheal
(RLMA), many devices have been after the insertion of the RLMA when tube (ID 4.5 mm, Lo-ContourTM
,
created to facilitate its insertion, since the stylet is tightly fitted to the Mallinckrodt, Ireland), Nelaton’s cath-
it has a longer and more flexible tube RLMA. If it is too loose, however, it eter (No.6, Mizuho, Japan) and a PVC-
(Fig. 4A) than the classic laryngeal can rotate along its axis. We would covered stylet for children (Portex, UK)
mask airway. These are classified into like to describe an improved combi- (Fig. 5A). First, the children’s stylet is
two categories: outer and inner devices. nation metal stylet and tracheal tube passed into the Nelaton’s catheter.
The outer devices (standard Magill (Fig. 5B).
Then, the Nelaton’s catheter is passed
forceps [1], Bosworth introducer [2])
Our idea was to use the cuff of the into the tracheal tube (Fig. 5B).
have potential disadvantages of causing tracheal tube to fix the stylet against Adequate lubrication of the stylet and
Figure 4
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Correspondence
Figure 5
tracheal tube allows smooth insertion RLMA. Since we have no adequate
of the stylet into the RLMA. The stylet for adults to give rigidity to the
length of the tracheal tube just fits tracheal tube, the Nelaton’s catheter
the size 4 RLMA, so the distal end enlarges the stylet. We have found
does not protrude through the grill of this stylet with a cuffed tracheal tube
the mask (Fig. 5C). To fix the stylet is convenient for insertion of the
against the RLMA, the cuff of the tra- RMLA.
References
1 Welsh BE. Use of a modified Magill’s
forceps to place a flexible laryngeal
mask. Anaesthesia 1995; 50: 1002.
2 Bosworth A, Jago HR. The Bosworth
introducer for use with the flexible
reinforced laryngeal mask airway.
Anaesthesia 1997; 52: 281–2.
cheal tube is inflated with approxi-
mately 0.5 ml of air. This arrangement
allows the tube of the RLMA to be
rigid enough (Fig. 4B) to insert it easily
without trauma. After insertion of the
RLMA, the cuff of the tracheal tube
is deflated, allowing smooth removal
of the stylet without displacing the
O. Shimoda
3 Asai T, Stacey M, Barclay K. Stylet for
reinforced laryngeal mask airway.
Anaesthesia 1993; 46: 636.
A. Yoshitake
Kumamoto University School of
Medicine, Kumamoto 860–8556,
Japan
4 Maino P, Pilkington M, Popat M.
Combined introducer for reinforced
laryngeal mask airway. Anaesthesia
1998; 53: 91.
E-mail: shimoda@kaiju.medic.
kumamoto-u.ac.jp
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Correspondence Anaesthesia, 2002, 57, pages 1134–1145
.....................................................................................................................................................................................................................
Joint disagreement
events in smokers and non-smokers
undergoing general anaesthesia. Acta
Anaesthesiologica Scandinavica 1997;
41: 348–55.
volatile anaesthetic, initially sevoflurane
in oxygen. The saturation fell signifi-
cantly when nitrous oxide was added
and so maintenance was continued with
100% oxygen and sevoflurane was
changed to a high percentage of isoflu-
rane. Ventilation was assisted manually
and with the application of continuous
We read with great interest the case
report entitled ‘Cannabis abuse and
laryngospasm’
(White.
Anaesthesia
2002; 57: 622–3). However, we disag-
ree with the author’s conclusion that
there exists ‘an association between
cannabis smoking and peri-operative
laryngospasm’.
Cannabis smoking and
anaesthesia
I read with interest the account of positive airway pressure via the circle
severe laryngospasm following extuba- system. The position of the nasotracheal
tion of a patient who was a known tube was checked visually and with
cannabis smoker (White. Anaesthesia auscultation of the chest. There were no
2002; 57: 622–3). Over 2 years ago, I signs of bronchospasm.
The report documents a case of
laryngospasm during general anaesthesia
in a patient with a ‘five a day cannabis-
containing cigarette habit’. The author
mentions that prior to extubation,
direct laryngoscopy under deep anaes-
thesia proved the laryngopharynx to be
clear of debris. We assume, though are
not told, that extubation then occurred
under deep anaesthesia. We do not
accept that cannabis was the most likely
cause of laryngospasm. Laryngospasm
could have been caused by an inad-
equate depth of anaesthesia (be that
either insufficiently deep or insuffi-
ciently light), or by the tobacco smoke
contained within the ‘joint’ [1]. Com-
mon things occur commonly, or in this
case common things lead to common
complications. To infer from one case
report that the laryngospasm was due
to the cannabis content of a tobacco-
containing cigarette is a large assumption
and not statistically sound. A cause–effect
relationship cannot be established in a
situation where an equally likely trigger
exists as a confounding variable, namely
cigarette smoke.
encountered unexpected problems dur-
To achieve a satisfactory level of
ing the induction and maintenance of anaesthesia, three boluses of propofol
anaesthesia in a patient who had know- 50 mg were required, and two addi-
ingly withheld the fact that he was a tional increments of midazolam 1 mg.
cannabis smoker. The 34-year-old man Ketorolac 10 mg was also given and
was 5 foot 6 inches tall, weighed 94 kg local anaesthetic infiltrated by the sur-
and was scheduled for surgical removal geon. The surgery was performed as
of wisdom teeth as a day case. The quickly as possible. Despite the high
Assessment Clinic blood pressure was concentration of volatile and intraven-
115 ⁄ 80 mmHg.
ous anaesthetic, the blood pressure and
He had no complaints other than pulse rate remained high at the pre-
heartburn with occasional reflux. He induction levels. The end- tidal carbon
rarely drank alcohol but admitted to dioxide varied between 5 and 7 kPa.
smoking 10–20 cigarettes a day. He Also, during induction he seemed to
denied any problems with his chest and have a short fit or convulsion. I thought
had had an anaesthetic one year previ- that this might have been caused by the
ously, which he said had been unevent- propofol, but this reaction was also seen
ful. He had beta-Thalassaemia Trait during emergence from anaesthesia.
with a haemoglobin of 14 g.dl)1. The There were no respiratory problems or
patient was asked not to smoke on the laryngeal spasm following extubation.
day of surgery and given ranitidine He recovered rapidly and the oxygen
150 mg to take on the evening and saturation
morning before the operation.
Pre-operatively, he was assessed as face mask. No further analgesia was
being ‘fit and well’ and had drunk only required. This was a memorable ‘stor-
water 3 h before. In the anaesthetic my’ anaesthetic.
room, he seemed to be very nervous
with a pulse rate of 95 min)1 and blood tively he said: ‘How was it?’ (as if he was
pressure of 150 ⁄ 80 mmHg. Midazolam expecting there to have been a problem).
2 mg, metoclopramide 10 mg and dex-
amethasone 8 mg were given intraven- cult to anaesthetise.’
was
100%
breathing
5 l.min)1 of oxygen via a Hudson
To demonstrate an association
between cannabis use and postextuba-
tion laryngospasm, one should com-
pare the frequency of laryngospasm in
groups of patients controlled for tobacco
smoking, i.e. compare tobacco smokers
with those who smoke tobacco and
cannabis or compare non-smokers with
those who smoke cannabis joints con-
taining no tobacco.
When I saw the patient postopera-
I said; ‘Actually you were very diffi-
ously. Otrivine nose drops were
administered. After pre-oxygenation, thing it might incriminate me.’
He replied: ‘Well if I tell you some-
anaesthesia was induced with fentanyl
100 lg, propofol 200 mg and the lungs confidence.’
ventilated with oxygen and sevoflurane He replied: ‘I smoked cannabis last
via facemask and circle system. night.’ He denied taking any other
I said: ‘You may tell me anything in
H. A. Brownlow
a
P. D. Sutherland
Succinyl choline 100 mg was given to drugs. I advised him to refrain from
facilitate intubation with a cuffed naso- smoking cannabis for as long as possible
tracheal tube size 6.5 mm. A pharyngeal before an anaesthetic and also empha-
throat pack was inserted. Spontaneous sised the importance of giving doctors a
respiration returned quickly but he was full drug history. He was discharged
very difficult to ‘settle’, even with a from the Day Unit 3 h after the end of
very high inspired concentration of surgery.
Southampton General Hospital,
Southampton SO 16 6YD, UK
Reference
1 Schwik B, Bothner U, Schraag S,
Georgieff M. Peri-operative respiratory
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Correspondence
I had no previous experience of Critical Care (TRICC) trial. In the re-reading will confirm that our con-
knowingly anaesthetising patients who TRICC trial [1], a restrictive transfu- clusion was actually that the real and
were habitual cannabis smokers. On sion strategy (haemoglobin target of potential harm of a blood transfusion
discussing this with my colleagues, it 7.0–9.0 g.dl)1 and transfusion trigger should be balanced against the evidence
was felt that perhaps the patient had also of 7.0 g.dl)1) was found to be at least as indicating that a haemoglobin (Hb)
been taking ‘class A’ drugs. However, it effective, and possibly superior to, a concentration down to 8 g.dl)1 or
could be said that all the responses seen liberal transfusion strategy (haemoglo- lower is safe in the critically ill.
were due to the effects of cannabis.
bin target of 10.0–12.0 g.dl)1 and
If they care to delve into some of the
As a result of slow elimination, transfusion trigger of 10.0 g.dl)1). 55 references, they will find plenty of
cannabinoids may be present in the However, the average haemoglobin in evidence on the limits of acute anaemia
tissues of users for weeks and may the restrictive group was 8.5 g.dl)1. On but little or none that a Hb level of
interact with a number of anaesthetic the basis of this evidence, it is not 8 g.dl)1 or even lower causes serious
agents. Cannabis smoking is associated possible to comment on the safety of a harm. Our editorial acknowledges the
with an impairment of lung function, haemoglobin of 8 g.dl)1 or less.
similar to that associated with tobacco The authors also dismiss case reports the best critical care evidence currently
smoking [1]. Cannabinoids have com- in which anaemic patients with chronic available.
limitations in Hebert’s paper, but it is
plex actions on seizure activity and obstructive pulmonary disease (COPD)
We did state that the subgroup
exert both anticonvulsant and procon- requiring ventilation were successfully analysis of the TRICC trial did not
vulsant effects. They may also cause a weaned after their haemoglobin was confirm the five case reports of suc-
variety of psychological effects such as increased to at least 12 g.dl)1 [2]. In cessful weaning of COPD patients
anxiety, and physical signs including support of their argument, the authors after transfusion. This does not imply
tachycardia [1]. It was fortuitous that I quote one of the subgroup analysis of a dismissal of the case reports. How-
had given dexamethasone (to reduce the TRICC trial [3]. This subgroup ever, objective evidence in the form of
any swelling caused by the surgery). analysis looked at all patients requiring a larger controlled study of the benefits
Dexamethasone is also recommended mechanical ventilation and consisted of of transfusion in facilitating weaning of
as prophylaxis for cannabis smokers a heterogeneous group of critically ill COPD patients has not been forth-
undergoing general anaesthesia [2].
patients and not a subgroup of patients coming even though 4 years have
with COPD. elapsed since Schonofer et al. published
We are not advocating liberal trans- their article. We do not know, or
fusion policies but feel that more evi- suggest, an optimal haemoglobin con-
dence is required before conclusions can centration for the critically ill. Our
be made about the optimal haemoglo- article focused on the balance between
I. E. Symons
Barnet General Hospital,
Barnet EN5 3DJ, UK
References
bin level in critically ill patients.
the advantages of a higher Hb and the
risks of an allogenic blood transfusion.
1 Kumar RN, Chambers WA, Pertwee
RG. Pharmacological therapeutic uses
of cannabis and cannabinoids. Anaes-
thesia 2001; 56: 1059–68.
P. Jefferson
D. R. Ball
D. Goldhill
Dumfries and Galloway Royal
Infirmary, Dumfries DG1 4AP, UK
H. Boralessa
The Royal London Hospital,
London E1 1BB, UK
2 Mallat A, Roberson J, Brock-Utne JG.
Pre-operative marijuana inhalation an –
an airway concern. Canadian Journal of
Anaesthesia 1996; 43: 691–3.
References
1 Hebert PC, Wells G, Blajchman MA,
et al. A multicentre, randomized, con-
trolled trial of transfusion requirements
in critical care. New England Journal of
Medicine 1999; 340: 409–17.
Not so free flowing
Devices to prevent backflow of blood
or solutions in intravenous lines have
been readily available for some time. In
our hospital we have available such a
one-way valve device, namely, the
R-Lockꢂ (Article-No. MF1543),
Blood transfusion in the
critically ill
2 Schonhofer B, Bohrer H, Kohler D.
Blood transfusion facilitating difficult
weaning from a ventilator. Anaesthesia
1998; 53: 181–4.
In their recent editorial, Goldhill and
colleagues (Goldhill et al. Anaesthesia
2002; 57: 527–9) conclude that a
haemoglobin concentration down to
8 g.dl)1 or lower is safe in the critically
ill. Where is the evidence for this?
Certainly, prospective randomised con-
trolled studies in this area are limited.
The authors quote three papers by
3 Hebert PC, Blajchman MA, Cook DJ, manufactured by Impromediform Gmbh
et al. Do blood transfusions improve
outcomes related to mechanical venti-
lation? Chest 2001; 119: 1850–7.
(Fig. 6). We decided to ascertain to
what extent flow rates were affected by
using this device when administering
intravenous fluids.
We attached a standard blood giving
set (Baxter Ref RMC2071B), to a
Hebert and colleagues, which all repor- A reply
ted results and subgroup analysis from We are pleased that Drs Jefferson and 500-ml bag of 0.9% saline. This was
the same Transfusion Requirements in Ball read our editorial. However, a suspended from a height of exactly 1 m.
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Correspondence Anaesthesia, 2002, 57, pages 1134–1145
.....................................................................................................................................................................................................................
Figure 6
To the end of the giving set we initially might have helped them to define the epidural needle shafts and catheters and
attached a 16G Vygon Biovalveꢂ can- effect better. They measured the brea- of the origins of the technique of
nula. We then measured the volume of thing at 5-min intervals after injection estimating the length of catheter inser-
0.9% saline that passed through this of alfentanil 10 lg.kg)1. In our anaes- ted into the epidural space.
system over a 2-min period. Subse- thetised patients, the mean time to peak
We have encountered four 16G
quently, we placed a R-Lockꢂ device effect (i.e. to the longest expiratory Portex Tuohy needles with 2-cm gra-
between the cannula and the giving set time) after 2–5 lg.kg)1 was 82 s, and dations dividing the 8-cm shaft in four,
and repeated the same measurement.
With no R-Lockꢂ device attached, a By 5 min, the effect would have five 1-cm divisions (Fig. 7). The needle
flow rate of 163.5 ml.min)1 was recor- diminished.
tip, shaft length and catheter were
ded. However, when the R-Lockꢂ This could explain why Conti et al. normal. Each of the needles was used
the mean half-life of effect was 146 s. instead of the usual 3-cm blank tip and
device was attached, a flow rate of only saw a reduced minute ventilation, but successfully for epidural catheter inser-
56 ml.min)1 was achieved. This equates could not find significant changes in tion. Identification of the epidural
to a reduction in flow rate of 66%. either tidal volume or respiratory rate; space, estimation of its depth, and
Neither we, nor many of our colleagues any change in minute ventilation can subsequent estimation of length of
realised how significantly this particular occur only if one or other or both of catheter insertion were not difficult in
device impairs flow through an other- these variables change. By referring any of the four cases. There were no
wise satisfactory fluid giving set. As our back to our work, and noting that the instances of dural puncture.
study has shown, the R-Lock effect- ventilatory rate in their patients was less
The manufacturer has been unable to
ively converts a grey (16G) cannula to a than baseline at 5 min, even if not explain the manner by which the
pink (20G) one with regard to its flow statistically significant, they could have chemical etching process went awry.
characteristics.
presumed that alfentanil affects ventila- To our knowledge, this style of marking
We feel that these devices should tory rate.
therefore be used with caution, especi-
is not standard for any other country.
Different needle lengths and styles of
marking exist currently (e.g. the
B ⁄ Braun range of epidural needles is
marked to the tip in 1-cm gradations)
but none employs markings other than
1 cm.
Cheng in 1958 was the first to report
an epidural needle with depth markings,
which he manufactured from a con-
ventional 16G spinal needle [1]. The
shaft was 8 cm long and graduated in
centimetres and millimetres, allowing
measurement of the depth from skin to
epidural space. He claimed to be able to
estimate the length of catheter insertion
within the epidural space, although it is
N. W. Goodman
ally in cases where there is potential
need for significant fluid replacement.
Southmead Hospital,
Bristol BS10 5NB, UK
A. Kitsberg
E-mail: Nev.W.Goodman@bris.ac.uk
S. Agarwal
Chase Farm Hospital,
Enfield EN2 8JL, UK
Reference
1 Goodman NW, Vanner RG, Wade JA.
Effects of incremental doses of alfentanil
and propofol on the breathing of
anaesthetized patients. British Journal of
Anaesthesia 1989; 63: 548–53.
Referring to earlier work would
have refined conclusions
The authors (Conti et al. Anaesthesia
2002; 57: 540–3) omitted to cite our Two-stripe Tuohy, when too
study on the effect of small doses of deep?
alfentanil on breathing [1] because
(personal communication) our patients The appearance in our unit of unusually unclear from his description whether
were anaesthetised but theirs were marked Tuohy needles has prompted a the catheter he employed had markings.
awake. This is true, but our findings review of the history of the markings on Lee, in 1960, described a Tuohy needle
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Anaesthesia, 2002, 57, pages 1134–1145
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Correspondence
References
1 Cheng PA. Blunt-tip needle for Epi-
dural Anesthesia. Anesthesiology 1958;
19: 556–9.
2 Lee JA. Specially marked needle to
facilitate extradural block. Anaesthesia
1960; 15: 186.
3 Lee JA. A new catheter for continuous
extradural analgesia. Anaesthesia 1962;
17: 248.
4 Doughty A. A precise method of
cannulating the lumbar epidural space.
Anaesthesia 1974; 29: 63–5.
5 Laishley RS. An aid to the unmarked
Tuohy needle. Anaesthesia 1984; 39:
1253–4.
6 Jawalekar SR. A procedure for meas-
uring the length of the catheter in the
Figure 7
epidural space. Anesthesiology 1982; 57:
67–8.
with depth markings (4 cm blank tip
When encountering an unmarked or
7 Pradines B, Doubovetzky B, Jaulin L,
Bergis A, Guignard JD. [Lumbar epi-
dural catheterization: estimation of the
length of the inserted catheter]. Annales
Francaises D Anesthesie et de Reanimation
1989; 8: 287–9.
and four 1-cm markings), and asserted a unusually marked epidural needle, one
reduced incidence of dural puncture as may have difficulty estimating the depth
its principal advantage [2]. In 1962, Lee of needle and catheter insertion, and may
described a catheter with a blind end, have an increased risk of dural puncture.
single side hole and graduations that Several methods have been described to
made possible accurate measurement overcome these problems [5–7].
the depth of catheter insertion [3],
S. H. Scott
although it was not until 1974 that
V. Herodes
Doughty formally described a method of
John Radcliffe Hospital,
precise estimation of depth of catheter
Oxford OX3 9 DU, UK
insertion within the epidural space [4].
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