Wound local anesthetic infusions

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CHAPTER 13 Wound local anesthetic infusions

Jack Barrett

Placing local anesthetic in or close to the surgical wound has become a popular method of providing intra- and postoperative analgesia. The technique is applied by a single injection or by continuous infusion using an indwelling catheter. Wound infusions can be an important component of the multi-modal approach to postoperative pain relief. They have been shown to have a significant opioid-sparing effect. For more minor surgical incisions, such as those used for arthroscopic surgery, local anesthetic infusions alone may provide adequate analgesia.

Local anesthetic infusions are more practical now with the development of portable infusion devices. Catheters with multiple holes or permeable membranes disperse local anesthetic over a wider area. These techniques have the advantage of simplicity of performance and, to date, are considered to be safe. The equipment needed, of course, adds to the cost of the procedure but these costs may be offset by a shorter stay in hospital and increased patient satisfaction.

Crile, a surgeon from Cleveland, USA, was the first to describe, in 1913, the benefit of local anesthesia application to the surgical wound in providing analgesia and decreasing morbidity and mortality. Capelle, in 1935, described the use of an infusion apparatus to deliver local anesthesia to the wound.1 In 1950, Blades and Ford used a fine catheter to deliver local anesthetic to thoracotomy wounds.

Over the past 20 years, numerous papers have reported the use of local anesthesia in wounds of major abdominal incisions, gynecological and obstetric procedures, orthopedic operations, plastics procedures and mastectomy, among others. These studies have confirmed a decrease in pain scores at rest and during activity. They have, in addition, been associated with a decreased incidence of side-effects.2

Rationale for using local anesthetic infusion

Postoperative pain arises from the interaction of three factors:

1 Impulses generated from injured nerve fibers innervating the site of surgery.
2 Inflammatory mediators, such as prostaglandins and cytokines are at increased concentrations at the surgical site and sensitize nerve fibers.
3 Sensitization of pain-transmitting pathways in the spinal cord that elevates their responsiveness to non-painful stimuli such as pressure or touch. Prolonged peripheral sensitization as a result of surgery can result in central sensitization. This is thought to be a significant cause of chronic postoperative pain.3

Local anesthetics can be used peri-operatively to affect all three of the above.4 In addition, because these systems are relatively simple to use they can and have been used in the home setting postoperatively.5

Mechanisms of action

Local anesthetics are known to block impulse transmission in all peripheral nerves by virtue of their ability to block sodium channels and thus inhibit conduction in the nerve axon. Infiltration of local anesthetic around the site of surgery can suppress the generation and propagation of injury-induced discharge from ectopic foci in injured nerves. Continuous infusion of slow release formulations of local anesthetic may extend such inhibition for days after surgery.

In addition, it is now apparent that systemic concentrations of local anesthetic i.e. lignocaine 2–4 µg per mL for only a few hours peri-operatively can have an analgesic effect postoperatively for a number of days. The mechanism for this is unknown at present.

Local anesthetics have an anti-inflammatory action also, through their effects on cells of the immune system, as well as on other cells, e.g. microorganisms, thrombocytes and erythrocytes.

Potential problems

Initial fears regarding the potential risks of infection and effects on wound healing would appear to be unfounded, as studies have not shown any adverse effects on wound healing or increased rates of infection.

Local anesthetics are known to have myotoxic properties, but in concentrations used for infusion these have not been observed to date.

It would appear that local anesthetic infusions have very few side-effects and as a result their risk–benefit ratio is positive.2

Positioning

To date most catheters are placed in position by the operating surgeon under aseptic conditions. Aseptic placing of the catheter is obviously essential and great care regarding asepsis must be taken when recharging the infusion system.

The fact that surgeons place catheters has the added advantage of making them more aware of postoperative pain and empowering them to assist its palliation. Postoperative pain has up to recently not been seen as a complication in surgical terms. The incidence of post-surgical chronic pain is higher than many surgeons appear to realize.6

Catheters can be placed in the wound itself or at some distance from the incision. Because of fear of infection, it is advocated by some that it is better to place the catheter outside the wound. The optimal positioning will depend on the direction of the nerve supply to the area. It may require the use of two catheters if there is a nerve supply from both sides, as in the chest for example.

In the abdomen, catheters should be placed in the muscle plane in which the nerve supply runs. These will be dealt with in more detail in the individual sites below.

Orthopedic procedures

Shoulder surgery

Arthroscopic surgery

Wound catheter techniques decrease opioid requirements without significant side-effects.

Subacromial catheter placement is recommended (Fig. 13.1) but intra-articular catheters have also been used. A flow rate of 2–5 mL/hr is adequate.

image

Figure 13.1 Subacromial placement of catheter.

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