Dentsleeve Technical Note 5 Version 2 - Passage of catheters
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Strategies
for transnasal or oral passage of catheters
Successful introduction and
positioning of catheters is an essential requirement for manometric
recordings. The manometrist needs to evaluate the best approach
for achieving this, especially in patients with motor disorders.
In some settings, intubation can only be achieved through
the use of catheters with design features that are specially
tailored to the situation.
This technical note aims to
inform Dentsleeve
customers about the options for intubation. We are happy to
advise customers on how designs can be best matched to the
technical challenges of a specific situation, in order to
maximise the chances of success.
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Minimisation
of discomfort
of intubation
The advantages of a well-tolerated intubation
are self-evident. Tolerance of an intubation will be maximised
if attention is paid to the following factors:
Use
of the smallest possible diameter catheter
Catheter diameter has a major impact on the tolerance of intubation.
The catheter used for any particular measurement should have
the smallest diameter consistent with reliable achievement of
the measurements required.
It should be noted though, that in some settings, there are
significant limitations from the flexibility of narrow diameter
extrusions.
Dentsleeve has developed a range
of unusually small diameter extrusions: see Section 2 Manometric
extrusions (pages 4-16).
For routine oesophageal manometry we recommend our 4.0 mm diameter
spec #114 extrusion catheters as the best compromise of properties.
Use of catheters made
of flexible materials
Catheters made of very stiff materials resist
flexion around the curvature of the pharynx.
This stiffness results in poor tolerance of the catheter because
it causes excessive mechanical stimulation of the pharynx.
Softer and thinner catheters are associated with greater comfort.
Contrary to what might be expected, the smaller diameter and
softer catheters made by Dentsleeve
still deliver excellent pressure rise rates (see Section 2 Manometric
extrusions - pages 4-16). |
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Minimisation of manometric
catheter movement during recording sessions
Repeated manipulation of a recording catheter causes considerable
discomfort.
Recordings are best tolerated if they use an approach that minimises
the amount of catheter manipulation. The sleeve and multiple
side hole recording approach achieve this aim best.
Avoidance of pharyngeal
water infusion
Pharyngeal manometry is a very convenient way of monitoring
for swallowing.
Interpretation of oesophageal manometric tracings demands that
swallowing be monitored.
Pharyngeal water infusion can however, cause substantial discomfort
and stimulation of swallowing.
A non-perfused, water-filled manometric channel can signal the
occurrence of pharyngeal pressure waves generated by swallowing,
but frequently does this unreliably.
Perfusion of the pharyngeal manometric side hole with air provides
the best technical solution to manometric monitoring for swallowing(1).
This is a standard feature on Dentsleeve
pumps not provided
by others.
An air perfusion rate of between 2 and 4 ml per minute is effective,
and the rate of air infused into the manometric channel is controlled
by a hydraulic resistor in the same way as water perfusion is
controlled.
A specially high value resistor is therefore needed to restrict
air flow to the effective range.
Further explanation of pharyngeal air perfusion manometry is
given in Section 5 - Perfused gas manometry (page 61). |
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Use of the transnasal
intubation route
Transnasal intubation is generally tolerated better than transoral.
This is discussed further immediately below.
Use
of mucosal anaesthesia during intubation
Though local anaesthetic sprays are unpalatable, they improve
the tolerance of intubation, especially through the nose.
Transnasal versus oral intubation
Oral intubation is used in some laboratories, but the disadvantages
of this route substantially outweigh the advantages summarised
below.
Positive for oral intubation
Catheters greater than 5mm diameter are easier to pass,
and better tolerated
Less initial aesthetic "shock"
Positive for transnasal intubation
Less sensory disturbance over time
Less stimulation of swallowing and salivation
Easier and more secure catheter anchorage
More accurate position control
The smaller the diameter of the catheter the greater
are the gains from transnasal intubation. |
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Methods
of introduction of catheters
Catheters can be passed by the following means:
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primarily pushing
on the catheter shaft |
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primarily tugging from the
catheter tip. |
These two generic approaches are sometimes used at different
stages of a single intubation.
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push intubation as far as the stomach
This method relies on the rigidity of the catheter.
Under normal circumstances, a relatively small amount of push
is needed for oesophageal intubation, since motor mechanisms
aid passage of the catheter across the sphincters and along
the oesophageal body.
It is easier to pass small diameter catheters (2.5 to 1.8
mm) by pushing in children and infants compared to adults,
since the smaller diameter oesophageal and nasal lumina help
prevent buckling and turning back of the catheter when it
is pushed.
The force of "push" intubation can be greatly increased
and directed more effectively by passing a catheter over a
previously positioned guidewire - see below - "principles
of push intubation by passage of catheters over a guidewire",
and Dentsleeve Technical Note
6 - Guidewire assisted passage of catheters.
The force of "push" intubation that can be applied
with a particular type of catheter can also be increased by
stiffening it - see below - "stiffening of manometric
catheters". |
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Gravity
tug intubation
With this intubation approach, forward movement of the catheter
depends on the development of forces at the catheter tip itself.
The modest gravitational tug of a weighted tip is sufficient
to pull a soft, medium to small diameter (3.5 to 1.8 mm) catheter
through the nasal cavity, pharynx, oesophagus and stomach.
The effect of gravitational tug can be maximised by:
Posturing of the patient to maximise the effect of
gravity
When the weight is being passed through the nose, the head
is held back, and then when it is traversing the pharynx,
oesophagus and upper two-thirds of the stomach, the patient
sits or stands.
Passage of the weighted tip into the distal antrum under the
influence of gravity is assisted by positioning the patient
in the right lateral position.
Controlled introduction of the catheter at the nostril
Sufficient length needs to be available for the weighted tip
to move freely, so that the catheter needs to be introduced
in a stepwise manner at the nostril. |
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Freeing
of the tip weight from entrapment
The relatively modest tug of a weighted tip may lead to its
failure to advance by merely being caught up in a mucosal
fold.
This can be minimised by the use of vibration and by maximisation
of the gravitational tug - see immediately below.
Augmentation of gravitational tug of the tip weight
This can be done by having the patient make rapid body movements
against gravity during intubation.
Most importantly, passage of the tip weight into the proximal
antrum can be greatly assisted by having the subject jump
on the spot.
Once the tip has reached this position, its further passage
can be aided by gentle shaking of the abdomen with the patient
in the right lateral position.
Other methods of applying tug to catheter tips
Tug can also be applied to the tip of an catheter by inflation
of a small (10 to 15 mm) diameter tip balloon (see pages 49-50).
Balloon-aided intubation has only been evaluated for the small
intestine, and in this setting is a very valuable aid to the
achievement of deep small intestinal or colonic intubation
via the nose or mouth.(2,3)
Balloon and gravity tug intubation depends substantially
on normal sphincter relaxation and existence of some propulsive
motor activity in non-sphincteric regions.
The greatest levels of tip tug are achieved by towing an catheter
tip with an endoscope - see below - "tug intubation by
endoscopic towing". |
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| Push
intubation by passage of catheters over a guidewire
GENERAL PRINCIPLES
Catheters can be pushed into place over a guidewire that has
been placed endoscopically or fluoroscopically.
Endoscopic placement of a guidewire has the disadvantage of
requiring the re-routing of the wire through the nose if the
studies are to benefit from the transnasal route.
The success of push intubation over a guidewire depends mainly
on the use of a slip tube and specially chosen and designed
Dentsleeve catheters.
The use of a slip tube is explained in Dentsleeve
Technical Note 6.
The guidewire needs to be sufficiently stiff to guide the
catheter during its passage. Excessive bowing of the guidewire
can readily lead to backwards displacement of the guidewire
tip.
For adults, transpyloric intubation requires a stiff guidewire,
at least 1mm in diameter.
We have insufficient experience of this mode of intubation
to make any comment on the smallest suitable guidewire for
use in this way in children.
When guidewires are used for this application they
must be placed and manipulated by adequately qualified people
who are alert to the potential for perforation.
Catheters need to be designed specifically for passage over
a guidewire, with an opening for the guidewire channel at
the end of the catheter.
The largest possible diameter guidewire channel should be
used by careful selection of the extrusion type for the catheter,
to make passage on a guidewire, and its removal as easy as
possible (see below).
Tip weights are incompatible with the design of most catheters
intended for passage over a guidewire, but tip balloons are
technically feasible in such catheters. |
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Push
intubation of
stiffened catheters
The rigidity, and so the push that can be transmitted to the
tip of the catheter can be greatly increased by incorporation
of a stiffener along the length of the catheter.
Catheters can be stiffened permanently by installation of
a length of nickel-titanium wire within one manometric channel.
Alternatively, a closed channel can be used to insert a removable
guidewire for situations when stiffening is required. If the
guidewire is to be removed during measurement, a slip tube
will usually be necessary for all but oesophageal catheters
- see Dentsleeve Technical
Note 6.
Stiffening of catheters is especially useful in some measurement
settings in which small diameter (2.5 to 1.8mm) catheters
are usedsee commentary on intubation of individual sphincters
below.
When catheters are stiffened, they must be used in the knowledge
that they can apply substantial force to the tip of the catheter
thereby increasing the risk of perforation.
Difficult intubations with stiffened catheters should always
be approached with great caution, and whenever possible, be
done with concurrent fluoroscopy. |
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| Tug
intubation by
endoscopic towing
Endoscopes can be used to tug catheters into the duodenum.
The tip of the catheter is equipped with a loop of strong
black silk which can be grasped by endoscopic grasping forceps.
The loop should be long enough to allow the forceps holding
the loop, to be withdrawn into the endoscope, without the
tip of the catheter being pulled up against the lens of the
endoscope.
It is recommended that the catheter be passed firstly into
the stomach via the nose.
The endoscope is then passed through the mouth into the stomach,
and the suture loop at the tip of the catheter is located
and grasped with the forceps.
The endoscope and the catheter are then directed into the
duodenum after the grasping forceps have been withdrawn safely
into the endoscope channel.
The catheter is driven as far as possible into the duodenum
with the endoscope.
The endoscope is then withdrawn, but friction between the
catheter and the endoscope is a major limitation of this method.
This friction tends to lead to withdrawal of the catheter
with the endoscope unless special precautions are taken to
minimise this friction, and to break the adhesion between
the endoscope and the catheter with each withdrawal.
The catheter can be made more resistant to unwanted withdrawal
through friction with the endoscope by being stiffened with
a guidewire positioned within a sealed channel of the catheter.
This guidewire needs to be relatively stout.
Other measures are usually also necessary to minimise or overcome
the friction between the endoscope and the catheter. |
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Upper
oesophageal and oesophageal body intubation
This usually poses no difficulty, apart from patients who
have a cricopharyngeal bar or a Zencker's diverticulum.
In these patients, the upper oesophageal sphincter opens poorly
and is very sensitive.
In patients with Zencker's diverticulum, there is the added
hazard of the tip of the catheter passing into the diverticulum
and then rupturing it.
The hazards and mechanical resistance of passage of a catheter
across the upper oesophageal sphincter in patients with cricopharyngeal
bars and Zencker's diverticulum can be minimised by passage
of the catheter over a guidewire that has been carefully placed
previously with the aid of fluoroscopic control.(4)
Catheters need to be specifically designed for passage
in this manner, and should only be passed under fluoroscopic
control. |
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Lower
oesophageal sphincter (LOS)
When the LOS relaxes normally, it is rare to encounter any
difficulty with passage of even a very flexible and soft catheter
across the LOS.
In a non-dilated, but poorly relaxing oesophagus, catheter
passage depends significantly on development of an effective
push force across the lower oesophageal sphincter. This can
be achieved by:
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use of an inherently stiff
catheter
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stiffening of an catheter with a fixed
or removable stiffener
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passage over a guidewire placed fluoroscopically
or endoscopically |
The LOS relaxes poorly not
only in patients with achalasia or a tight fundoplication,
but also during anaesthesia in normal humans and animals.
In these settings, successful passage of catheters may require
that they be stiffened.
Oesophageal dilatation or deformity can make LOS intubation
difficult, because the catheter tip may not engage effectively
with the lumen at the upper end of the sphincter.
In addition oesophageal dilatation can make it difficult to
transfer push effectively to the catheter tip, because of
bowing or even turning back of the catheter within the oesophageal
lumen.
Usually, Dentsleeve oesophageal
catheters designed for passage over a guidewire do not require
a slip tube.
The strategies for intubation outlined above should be considered
on a case-by-case basis, always in the light of a careful
assessment of the risks of intubation associated with each
approach. |
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| Gastric
and pyloric intubation
Passage of a catheter into the distal antrum can be achieved
relatively easily with push or tug methods, regardless of
the presence or absence of a motor abnormality.
In individuals with normal gastric motility, transpyloric
passage of an catheter is also usually easily achieved with
tug from a weighted tip as outlined in the section that deals
with tug intubation above.
Tip weight tug intubation has a substantial failure rate in
individuals with gastroparesis.
Blind push intubation is a relatively poor option for traversing
the pylorus for the following reasons:
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the catheter tip cannot be steered
effectively to engage in the pylorus
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push is transferred fairly poorly to
the catheter tip. |
When a radiologist expert in fluoroscopically controlled pyloric
intubation is available, this is a very efficient option, provided
an appropriately stiffened catheter is used.
Push intubation is impossible with standard catheters that have
pyloric sleeves incorporated into them, since these catheters
have a specially designed maximally flexible segment just distal
to the sleeve. |
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The flexibility of this segment
allows the catheter to traverse the acute curvature of the proximal
duodenum without applying leverage forces to the sleeve when
it is correctly positioned in the pylorus, but makes it impossible
for push to be transmitted to the tip of an unstiffened catheter.
Consistently successful passage of catheters into the distal
duodenum of patients with significant gastroparesis requires
close attention to detail and special tailoring of catheter
design to the method of intubation used. Options to be considered
are:
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push intubation with a specially stiffened
catheter with subsequent withdrawal of the stiffener if
a pyloric sleeve is to be used - a slip tube is required.
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push intubation over a previously positioned
guidewire - a slip tube is required.
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endoscopic tug intubation. |
The options listed are dealt with in more detail in sections
of this commentary above.
Dentsleeve Technical Note 6
deals with slip tubes and their use. |
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Small
intestinal and colonic intubation
Push intubation of any type is relatively ineffective beyond
the ligament of Treitz.
Tug intubation with tip weights is also a relatively ineffective
approach beyond the ligament of Treitz.
The best option is the use of a tip balloon to provide tug
on the end of the catheter by stimulation of propulsive motor
patterns(2,3).
It is unclear whether it is best to wait for the balloon to
pass into the duodenum before it is inflated, but this is
the usual practice and so is recommended.
Colonic manometric catheters may also be tugged retrogradely
by colonoscopy. There is no reported experience with push
intubation over a guidewire, using a slip tube.
References
1. Omari et al. Gut (1997) 40:370-375
2. Fone et al. Gastroenterology (1990);98:568-575
3. Kerlin et al. Aust NZ J Med (1983);13:591-593
4. Cook et al. Gastroenterology (1992);103:1229-1335
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Warning
Intubation of the upper
gastrointestinal tract can sometimes pose a very significant
challenge. The various strategies outlined above all
carry significant risks if they are used inadvisedly,
or in an unskilled manner. The clinician responsible
for the intubation must assume total responsibility
for the safety of the use of the methods outlined above. |
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Potential
Application and Technical Challenges
This Technical Note provides more detailed guidance on methods
of "push" intubation. For general information, please
see our Technical Note 5 Version 2 - Passage of catheters.
Users of catheters sometimes wish to stiffen catheters with
removable guidewires, or to pass catheters over guidewires that
have already been placed radiologically or endoscopically.
Once a catheter has been correctly positioned, there may be
a need to remove the guidewire.
Passage over a guidewire or removal of a guidewire is frequently
difficult or impossible for catheters for use in the distal
stomach, duodenum or small intestine because friction between
the catheter material and the guidewire is too high. This is
a major limitation even when a channel is large enough to easily
accommodate the diameter of a guidewire.
Excessive friction results when the catheter is curved around
bends in the gut, even though it will be possible to insert
and remove a guidewire from a manometric catheter channel when
it is held straight prior to insertion.
Slip coatings on guidewires are not usually sufficiently effective
to overcome these frictional problems.
Silicone rubber especially has a high "grippiness"
to guidewire stiffeners, but this limitation can be overcome
by simple strategies outlined below. |
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Do Not Use Lubricants!
It is of paramount importance that silicone rubber catheters
do not contact silicon oil or grease. This is absorbed by silicone
rubber, causing it to swell and weaken, making the catheter
unserviceable and potentially dangerous.
Other lubricants may attack the catheter materials and are fairly
ineffective, and so are best avoided.
Passage
Over a Guidewire For Oesophageal Manometry
This is usually only needed in patients who have moderate to
severe oesophageal dilatation or a diverticulum.
Because of the straightness of the oesophagus, and the relative
shortness of the catheter, intubation is usually possible over
a previously placed guidewire without a slip tube. The catheter
used must have a large channel that opens at the tip.
Passage Over a Guidewire For Manometry In Regions Other
Than the Oesophagus
Users of Dentsleeve silicone
rubber catheters must use a slip tube insert for this procedure.
A slip tube is a thin-walled Teflon tube just small enough to
fit snugly within a manometric catheter channel large enough
for a guidewire. The slip tube is inserted into the catheter
before each intubation and retained within the guidewire channel
of the catheter throughout the measurement. It is removed from
the catheter after extubation, and before the catheter is cleaned
and autoclaved.
The natural low friction of the slip tube allows the guidewire
to move freely within it, despite quite tight curvature of the
catheter, whether it is being pushed into place over a guidewire
or if the guidewire is being withdrawn from a positioned catheter.
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Choice
of Catheter Extrusion Suitable for Use With a Slip Tube
A catheter with a large channel of at least 1.5mm diameter
should be selected. Our 12+1 E56 and our 20+2+1 E55 are best
suited, as they allow for the largest guidewire diameters.
The slip tube supplied is tailored to the specific extrusion.
Catheters to be used for passage over a guidewire with a slip
tube must be made for this purpose, and have three main features:
| 1) |
The large channel opens
at the catheter tip
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The diameter of the large channel
is stepped down at the tip to retain the slip tube within
the catheter, yet allow free movement of the guidewire
into the channel through the catheter tip
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The single lumen tube connected to
the guidewire channel at the junction between the multi-lumen
extrusion and the single lumen connector tubes is made
only 20cm long.
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Naturally, a large channel assigned for use with a slip tube
is not available for another purpose, except for use as an
infusion/aspiration channel at its tip, if the guidewire is
removed.
Infection Control
Slip tubes will be supplied for specific catheters to a length
equal to the total length of the guidewire channel.
Dentsleeve has not validated
any disinfection process for the slip tubes. These are therefore
offered as single use items. |
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Slip
Tube Installation
For greatest ease of use, the following sequence of steps is
recommended:
| 1) |
Insert a guidewire into
the slip tube
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Inject 1-2mL of isopropyl
alcohol into the catheter guidewire channel. Do not flush.
This briefly makes the silicone rubber slippery.
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Pass the guidewire-stiffened
slip tube down the catheter guidewire channel, with the
catheter held straight on a bench. Pass the slip tube
until it reaches the reduced diameter portion of the guidewire
channel at the catheter tip. Pass the final centimetre
or so of slip tube by milking the connector tube, so that
the slip tube is fully within the guidewire channel.
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| 4) |
Remove the guidewire.
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Flush the guidewire channel
gently with 20mL of water, then 20mL of air to remove
all traces of isopropyl alcohol.
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The catheter is now ready for passage over the guidewire.
Slip Tube Removal
This must be done directly after extubation. Lay the catheter
out straight on a bench. Milk the slip tube out of the connector
tube fitting by stretching and pinching the connector tube.
Once the slip tube protrudes from the connector tube fitting,
gently withdraw it from the catheter. This is easier if an assistant
holds the tip of the catheter. |
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WARNINGS
Intubation with processes described
above requires specialised training and judgement about
the specific procedure being performed and individual
patient characteristics. Choice of guidewire will influence
the safety and efficacy of the procedure. Dentsleeve
cannot be held responsible for any injury resulting
from the use of slip tubes and guidewires. |
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Dentsleeve International Ltd |
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Technical Notes |
