Perineural catheter technique
Many types of perineural catheter kits exist, and with them come many different methods for accurate perineural catheter placement. We recommend using an out-of-plane approach (where feasible) using a Tuohy needle ideally angled in the direction of the nerves (Fig.1). Once needle tip position has been confirmed sonographically, a non-stimulating catheter is blindly advanced a short distance beyond needle tip. The main advantage of this approach is not only in its effectiveness, but also its simplicity. 1-4
Fig. 1. Out-of-plane needle-probe orientation resulting in a needle orientation relatively longitudinal to nerves/plexus.
Concomitant needle neurostimulation can be useful to confirm appropriate needle tip position. However, low current catheter stimulation of the appropriate innervated muscles (i.e. using a stimulating catheter) is generally not recommended. Doing so certainly confirms intimate catheter-nerve proximity, 5 but the intervention has not been shown to significantly improve indices of catheter function (pain scores, LA consumption) compared to non-stimulating catheters advanced a short distance beyond needle tip. More importantly, catheter stimulation can be technically challenging and adds significant time to the procedure.
Much of the same argument can be made for (not) attempting catheter visualisation with ultrasound. Assuming a blindly advanced catheter is positioned only a short distance beyond the needle tip (3-4 cm for out-of-plane and 1-2 cm for in-plane), further sonographic imaging of the catheter (or catheter injectate) is unlikely to provide any useful additional information that cannot already be assumed. Furthermore, like catheter stimulation, catheter imaging has a false negative rate, 6 so if the operator cannot confidently visualise the catheter tip, the operator is left with a dilemma of potentially removing (to reposition) a catheter that is already satisfactorily placed.
Where possible, the out-of-plane approach is preferred because of the consequent needle orientation more parallel (cf. perpendicular) to the direction of the nerve/plexus and adjacent muscles/fascia. This facilitates catheter advancement through the tissues and subsequent maintenance of nerve-catheter proximity. 7 For deeply situated nerves where the out-of-plane may be too challenging (e.g. infraclavicular brachial plexus, and possibly the distal thigh sciatic nerve), the in-plane approach is often used.
Finally, with the exception of the sciatic nerve, LA is injected through the catheter rather than through the needle. 4 LA injection through the needle prior to catheter advancement is problematic in that catheter function is not declared until the primary block has resolved, which can be 12 hrs or more following catheter placement. If LA is injected through the catheter, catheter function will be declared on emergence, and thus suboptimally placed catheters can be repositioned before recovery room discharge. There are two exceptions to this rule. The distal thigh sciatic nerve and when surgery is to be conducted under the primary block alone (most commonly infraclavicular block for wrist/hand surgery). To maximise surgical anesthesia success, LA is injected through the needle, often with needle repositioning during LA injection depending on the observed LA spread. For sciatic block, to maximise primary block success, we prefer to perform a subfascial LA injection at two separate points prior to catheter advancement.
When the LA through catheter technique is used, either saline or 5% dextrose is (previously) injected via the needle to help confirm appropriate needle tip position, and to "distend" the perineural space before catheter advancement. Dextrose has advantages over saline in that if concomitant neurostimulation is used, motor responses are maintained (or even promoted) with dextrose injection.8
Catheter fixation needs to fulfil the dual requirement of catheter retention, and if ambulatory management is planned, easy catheter removal by patients themselves. 4 Catheter tunnelling via a separate needle tract has been previously advocated to facilitate catheter fixation and theoretically reduce the infection risk. However, the simple method described below is associated with a very low risk of premature catheter dislocation, while also enabling catheter self-removal by patients. Furthermore, catheter infection associated with this technique is exceedingly uncommon. In the author's city of practice, this catheter fixation technique has been used in thousands of patients with excellent success.
Finally, it is a good idea to cut the catheter at its proximal end to a length of 20-30 cm. This will minimise the amount of redundant catheter patients have to deal with; it will make catheter placement less fiddly, and will also minimise catheter flow resistance, which for a given pump pressure flow, may promote multi orifice flow by increasing flow pressure at the catheter tip.
Multiorifice catheters may perform better than single orifice catheters and are generally preferred. 9
1. Infiltrate skin/intended needle tract with lidocaine 1%.
2. The objective of the choice of needle puncture site, regardless of probe-needle alignment is to aim to advance the entire needle shaft under the skin, albeit maintaining a superficial needle tip position. This provides useful catheter tunnelling, which assists with fixation (Fig. 2).
Fig. 2. Illustration of the aim of "tunnelling" a length of needle under the skin.
Attach a 10 mL dextrose 5% filled syringe directly to the needle hub. Having the syringe connected to needle enables the operator to simultaneously manipulate needle, inject dextrose and sonographically monitor tissue displacement or needle tip and injectate spread (Fig. 3).
Fig. 3. Syringe attachment directly to needle hub.
3. All peripheral catheter techniques require fascial penetration (always associated with a "pop" when using an 18G Tuohy needle – this requires a short, sharp deliberate needle movement once the needle tip is against the fascia).
4. Consider eliciting a brief motor response at 0.8mA (rarely helpful for femoral; use 1.5mA for sciatic) to confirm the target neural structure.
5. Inject dextrose 5% aiming to observe appropriate injectate spread.
6. Drop the probe, stabilise this needle position by transferring the hand previously holding the probe to hold the needle hub. Disconnect syringe and advance the catheter with the catheter-advancing piece sited within the needle hub. Advance catheter at least 5 cm beyond needle tip (Fig. 4).
Fig. 4. Catheter advancement. Note the back of the left hand stabilised against the patient - ensuring needle stability.
7. Withdraw the needle over the catheter. For catheters in challenging parts of the body (e.g. neck), stabilise the catheter by pressing catheter against the skin with finger at skin entry point (Fig. 5).
Fig. 5. Catheter stabilisation (immediately after needle withdrawal) prior to definitive fixation.
8. Withdraw catheter to 1-4 cm beyond needle tip (3-4 cm for out-of-plane; 1-2 cm for in-plane). Be very careful during the last cm of catheter withdrawal as the catheter can have a tendency to spontaneously dislocate at this point.
9. Carefully apply medical cyanoacrylate e.g. Dermabond® (Ethicon) to the skin entry site (aids fixation and minimises LA leakage) (Fig. 6).
Fig. 6. Cyanoacrylate application (minimises leakage and assists fixation).
10. Apply tincture of benzoin to a 2 cm radius of skin around catheter puncture site (improves Lockit-skin adhesion) (Fig. 7). An alternative to tincture of benzoin is "Skin-Prep"®(Smith&Nephew) - see Appendix.
Fig. 7. Tincture of benzoin application (assists "lockit"-skin adhesion).
11. Apply Lockit catheter fixation device (Fig. 8).
Fig. 8. "Lockit" catheter-skin fixation device.
12. Protect catheter from surgical drapes/tourniquet using small gauze and paper tape.
13. Dress catheter after surgery (see below).
Catheter fixation (See Figs. 9-12, Video 1)
1. Apply tincture of benzoin to an area of skin 2 cm around the Lockit device then air-dry to make the skin "tacky" (Fig. 9). Alternatively, use "Skin-Prep" (Smith&Nephew) - see Appendix.
Fig. 9. Friar's balsam.
2. Cover the Lockit with a small non-occlusive dressing (e.g. Tegaderm®) (Fig. 10).
Fig. 10. Tegaderm.
3. Cover the small tegaderm with a round piece of non-woven fabric (e.g. hypafix® or mefix®) with a small circle cut in its centre. NB. Stretching the skin while applying hypafix will assist fixation (Fig. 11).
Fig. 11. Hypafix (or Mefix).
4. Apply second piece of hypafix (or Tegaderm®) to 10 cm length of catheter and skin (Fig. 12).
Fig. 12. IV Cannula Tegaderm.
N.B: Occassionally, problematic bleeding occurs at the catheter entry site immediately after needle removal. This is not only unsightly, but can make subsequent catheter fixation difficult. An effective solution is to apply additional cyanoacrylate (Video 2).
Local anesthetic regimen
Unfortunately, previous clinical trials evaluating different local anesthetic dose regimens have been limited by the use of different catheter placement techniques (ultrasound vs. neurostimulation), and different catheter orifice configurations (multi-hole vs. end-hole). The flow pressures from different pumps have also varied, which may have influenced single vs. multi orifice flow. Therefore it is difficult to generalise the results from these studies to today's techniques. A local anesthetic dose regimen we commonly use involves the use of the On-Q PainBuster elastomeric pump. This pump delivers 2 ml/hr with "On-Demand" patient controlled boluses of up to 5 ml every hour. Bolus flow is delivered at 150 ml/hr. This pump is appropriate for all peripheral catheter indications, however, for continuous lumbar plexus block, we prefer a higher background infusion e.g. 5 ml/hr (e.g. On-Q C-bloc).
Video 1. General technique for perineural catheter fixation using the "Lockit" device, Tegaderm and Hypafix (or Mefix). The technique fulfills the dual requirements of satisfactory catheter fixation and patient self removal.
Video 2. Management of perineural catheter site bleeding using cyanoacrylate.
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