Communication

The decision to perform PNB for ambulatory surgery patients will impact directly on a number of people in your healthcare facility. Good communication prior to commencing a PNB service is vital to ensure all members of the healthcare team are supportive of the concept.

Many surgeons are unfamiliar with PNB for anesthesia or analgesia and may feel initially uncomfortable operating on patients who are awake. They may also have experienced poor regional anesthesia practice with failed or partial blocks and apparent delays to the operating schedule. Patients may be less inclined to accept a PNB if their surgeon is unconvinced of the benefits. In our experience, a well run PNB service will result in the surgeon recommending PNB to their patients.

Nursing staff need to be familiarized with the techniques and their expected outcomes, as well as the type of assistance required. Nurses in the recovery or post-anesthesia care unit (PACU) must be aware that many patients undergoing PNB for anesthesia can bypass the PACU (79% vs 25% for general anesthesia (GA) patients), going directly to the ward. Ward nurses have to be made aware that patients can usually be discharged faster compared to patients post GA.

Consent

Patients should give their informed consent for a procedure. The relative benefits and risks of the block should be discussed with each patient so they can make their own risk/benefit analysis. Benefits include improved pain relief compared to opioids, less PONV, quicker recovery and earlier discharge from hospital compared with GA. Risks include those of local anesthetic (LA) toxicity and neural damage, which has a 1 : 10 000 chance of nerve injury persisting beyond 3 months. Minor, short-lived and expected side-effects such as paresthesia and numbness should be explained to the patient. A written record of this discussion and the patient’s agreement or not to have PNB should be recorded.

Working environment

Compared with GA, the performance of PNB takes longer to achieve anesthesia, as the time to onset includes both the time to perform the block and for the LA to act. However, a number of studies^3,4 have shown that less time is spent in the operating theatre (20 mins), the PACU (40 mins) and the hospital (40–100 mins), resulting in an overall time gain with PNB compared to GA (Fig. 8.1). There is a 20 minute increase in the amount of time the anesthesiologist spends with the patient.

Figure 8.1 Differences in time between GA and PNB in an ambulatory setting for upper limb surgery; SDCU: Surgical Day Care Unit.

From Armstrong KP, Cherry RA. Can J Anaesth 2004;51(1):41–4.

An effective schedule is required to ensure these time benefits are realized. Some suggestions are to have a second anesthesia provider (nurse anesthetist or another anesthesiologist) available who can monitor one patient while another is having a PNB placed, starting either earlier to place the PNB or commencing the operating schedule with a GA case.

The use of a dedicated block room has been advocated but this may not be cost effective unless it serves a number of operating theatres and has a regular patient load.⁴ A more practical solution is to perform the blocks in the PACU, hence utilizing the nursing staff and facilities already available.⁵

Performance of techniques

Proper preparation is vital for the safe provision of regional anesthesia and this is discussed in greater detail in another chapter of this book. Briefly, the following equipment and drugs are required (Box 8.3) and we would recommend that a dedicated regional anesthesia trolley be organized. Importantly, Intralipid must be stored as part of the emergency drugs.

Although the successful use of Intralipid for LA toxicity in humans has only been documented in case reports, the results have been so dramatic that its use is recommended. Intralipid has been effective in LA toxicity resulting from the long-acting amides bupivacaine, ropivacaine and levobupivacaine. While successful use has been described for the short-acting LA, mepivacaine, to date the only use for lidocaine has been in a pediatric patient who received both lidocaine and ropivacaine for psoas compartment block.⁶

The individual nerve block techniques are described in detail in their respective chapters. The type of block to choose for a particular surgical procedure is discussed in the relevant upper or lower limb section.

Modern peripheral nerve blockade is performed using either a nerve-stimulation technique (NST) or ultrasound guidance (USG) to locate the relevant nerves. USG for PNB is generally accepted to result in a faster onset (about 5 minutes), higher success rates (3–10% greater when compared to multi-stimulation techniques) and possibly lower LA volumes compared to NST.^7,8 However, whether these differences will result in benefit in the average ambulatory setting is debatable. The advantage of USG may be offset by its significantly increased capital cost.

Sedation has potential advantages and disadvantages. Disadvantages are mainly related to excessive sedation or loss of the airway. Advantages of sedation include a reduction in patient anxiety, increased comfort during prolonged (>1 hour) surgery and improved patient cooperation during block performance. The choice of sedation is one for each anesthesiologist, but in our experience in the ambulatory setting intravenous midazolam often negates the benefits of a PNB technique, and either low doses of fentanyl, alfentanil or propofol result in patient comfort and controlled sedation. For longer surgery, a low dose target-controlled infusion of propofol (1–2 µg/mL) is an alternative. However, continuous monitoring of respiratory effort and oxygen saturation is necessary.

Choice of local anesthetic

The main determinant of the type of LA to use is the duration of surgery. In reality, the duration of the shorter acting LAs such as the ester prilocaine (3–4 mg/kg), or amides lidocaine (4.5 mg/kg) and mepivacaine (5–6 mg/kg) is sufficient for most ambulatory surgery. The addition of epinephrine (1 : 200 000) prolongs the duration of action of lidocaine from 1–1.5 hours to 3.5–4 hours, which is equivalent to mepivacaine. Adding epinephrine also increases the permitted dose of lidocaine to 7 mg/kg.

Other adjuncts can be added – tramadol prolongs mepivacaine and clonidine increases block duration for both lidocaine and mepivacaine. Unfortunately, the doses of clonidine (2 µg/kg) required often result in sedation, which may be undesirable in a day surgery setting and delay discharge.

Long-acting LAs such as levobupivacaine and ropivacaine are generally not used because of the prolonged motor blockade. The use of a continuous technique allows lower doses to be used, providing a motor sparing effect, and is useful for more major ambulatory surgery such as shoulder arthroplasty.⁹ There are no studies in the ambulatory setting comparing the duration of analgesia of long- versus short-acting LAs, but it is reasonable to assume that the benefits seen with long-acting LAs for in patients would be similar. Performing selective analgesic blocks with a long-acting LA while using a short-acting LA for the main block and anesthesia, is an effective technique (for example, for a Dupuytren’s contracture, performing an axillary block with mepivacaine and an ulnar block at the elbow with levobupivacaine).

Multi-modal analgesia

The duration of analgesia provided by PNB is usually longer than the duration of anesthesia, but, depending on the choice of LA or if a single shot technique is performed, this may be limited to 6–8 hours post-block. Importantly, patients’ perception of pain post block resolution is often much higher than would otherwise be anticipated. This is most likely as a result of the loss of profound analgesia following block resolution.

Therefore a multi-modal approach to analgesia is required. The use of acetaminophen and non-steroidal anti-inflammatories (NSAIDs), both prior to and regularly post block resolution, is effective in clinical practice. Oral opioids may be required, depending on the type and extent of surgery.

Postoperative care

The postoperative management of patients who receive a PNB in an ambulatory setting is particularly important, as they will be discharged relatively earlier from the healthcare facility.

Although there has been some debate regarding the feasibility and safety of discharging a patient home with an insensate limb, general consensus is that patients can be discharged if some basic principles are followed.

Firstly, the anesthesiologist has to be prepared to accept the clinical situation. Even with short-acting LAs, 50% of patients will have residual block present when they are otherwise fit for discharge home.¹⁰ The discharge criteria normally used for patients undergoing GA, such as the modified Aldrete score, are inappropriate because they require the patient to move all four limbs.¹¹ A scoring system not requiring limb movement, such as the Postanesthesia discharge scoring system (PADSS), may have to be incorporated into your practice¹² (Table 8.1).

Table 8.1 Post-anesthesia discharge scoring system (PADSS) for determining home readiness

Maximum score = 10.

Patients scoring ≥ 9 are fit for discharge.

Modified after Chung F, Chan VW, Ong D. J Clin Anesth 1995;7(6):500–6.