22 Continuous Peripheral Nerve Blocks
The superiority of peripheral nerve blocks for postoperative analgesia after major shoulder and knee surgery compared to systemic intravenous patient-controlled analgesia (PCA) with opioids has been demonstrated clearly (Borgeat et al 1997, Singelyn et al 1998, Capdevila et al 1999). Continuous epidural analgesia and a continuous femoral nerve block via catheter are considered to be equally effective for postoperative analgesia after extensive knee surgery; because of the lower risk, the peripheral block should be preferred (see below). However, apart from the superiority with regard to the analgesic effect, a significant benefit on the duration of rehabilitation and on the quality of the rehabilitation is also achieved (Capdevila et al 1999).
With the aid of a continuous peripheral nerve block, possible major complications in association with neuraxial blocks can be avoided.
Selective nerve block of the affected lower limb can be reliably achieved with a continuous peripheral block, enabling early mobilization as only one limb is affected. However, it must be borne in mind that motor weakness is present in the affected limb.
In contrast to epidural block, prolonged urinary diversion is not required.
The contraindications with regard to neuraxial techniques are much wider than for peripheral blocks, so that a peripheral nerve catheter for continuous pain management can be placed in cases where a neuraxial procedure is contraindicated or not technically feasible.
Severe postoperative pain
Posttraumatic pain states
Prevention and treatment of amputation stump and phantom pain
22.2.1 Differential Indications
The following are examples of indications for continuous peripheral nerve blocks and suitable catheters for regional pain management.
In arthroscopy of the shoulder, postoperative analgesia by continuous interscalene brachial plexus block is clearly superior to the intra-articular administration of local anesthetics plus suprascapular nerve block. There is no difference between the intra-articular administration of local anesthetics and placebo (Singelyn et al 2004).
Continuous subacromial infusion of local anesthetics for postoperative pain control after reconstructive surgery of the rotator cuff is also clearly less effective than interscalene brachial plexus block (Delaunay et al 2005).
Continuous suprascapular nerve block is well suited for physiotherapy in frozen shoulder syndrome, as long as there has not been any previous surgery. It carries less risk than interscalene brachial plexus block and results in significantly less impairment of the sensory and motor functions in the affected arm.
Interscalene brachial plexus block is the treatment of choice for postoperative pain control after painful shoulder surgery. Continuous subacromial infusion of local anesthetics can be recommended only if there are contraindications to inter-scalene brachial plexus block. Suprascapular nerve block is the procedure of choice in nonsurgical indications (frozen shoulder syndrome).
Elbow, Forearm, and Hand
Continuous axillary block is well suited for postoperative pain control after elbow surgery, one alternative being infraclavicular brachial plexus block.
Postoperative pain after total hip replacement can usually be controlled quite well by intravenous PCA with opioids (Biboulet et al 2004). In high-risk patients, continuous regional analgesia may be indicated, but peripheral regional nerve blocks should be preferred over neuraxial techniques due to the lower risk. Another option would be continuous femoral nerve block via catheter or psoas block (Capdevila et al 2005a). Due to the proximity of the catheter for continuous femoral nerve block to the surgical field and the greater effect of the psoas block, the latter has some advantages over the femoral nerve block. However, any decision for psoas block must be made considering the contraindications to this procedure.
Proximal Femoral Fracture
A femoral nerve block will provide adequate pain control after proximal femoral fracture. If surgery must be delayed, a continuous block technique may be useful until the time of surgery. Because of the close proximity of the catheter to the surgical field, the surgeon should be consulted.
Total Knee Replacement
Apart from major shoulder surgery, total knee replacement is one of the most painful operations. The superiority of regional nerve blocks (continuous epidural analgesia; continuous femoral nerve block via catheter) over PCA with opioids has been demonstrated (Capdevila et al 1999, Singelyn et al 1998). Femoral nerve block without (Barrington et al 2005) as well as in combination with a continuous sciatic nerve block (Al-Zahrani et al 2014) has proven to be as effective as continuous epidural analgesia.
Due to the lesser side effects (PONV) and lower risk, femoral nerve block should be the procedure of choice (Barrington et al 2005).
In female patients undergoing knee replacement surgery under epidural analgesia, the risk of spinal hematoma has been shown to be as great as 1:3,600 (Moen et al 2004). On the other hand, the risk of spinal hematoma under epidural analgesia in obstetrics has been found to be 1:200,000 (Moen et al 2004).
Although this retrospective Scandinavian study for the period 1990 to 1999 did not apply the strict guidelines for epidural block under concomitant anticoagulation, one third of the women still fulfilled these criteria. The publication points out that osteoporosis is one etiological factor of epidural hematoma in epidural analgesia which has not been focused on in the past. Particularly older patients undergoing knee replacement surgery fall into this high-risk group. Therefore, a peripheral regional nerve block should be selected for postoperative pain control.
Quality of anesthesia.
No difference for postoperative analgesia was found between continuous femoral nerve block and continuous psoas block (Capdevila et al 2005a), despite the fact that femoral nerve block does not affect the obturator nerve. In a few patients who underwent femoral nerve block for postoperative pain control after total knee replacement, single-shot obturator nerve block (Chapter 13.4) had to be added in the recovery room.
From a risk point of view, continuous femoral nerve block via catheter should be preferred. However, this decision will also be influenced by the type of intraoperative anesthesia.
If the operation is performed under a combined psoas/posterior sciatic nerve block, one option might be to continue the psoas block.
Weakness of the quadriceps femoris.
After lumbar plexus block after total knee replacement has worn off, a certain weakness of the quadriceps femoris muscles with impaired function is often observed. Sometimes this leads to the discussion that regional anesthesia might prolong the postoperative recovery. However, studies have demonstrated that the weakness of the quadriceps femoris muscles can usually be explained by the procedure itself, and not the block.
Even 4 weeks after total knee replacement, patients still display a 62% loss of maximum strength of the quadriceps femoris muscles, with a 17% drop in activation under maximum voluntary innervation. In addition, a 10% rate of muscle atrophy (measured at the maximum cross-sectional area of the quadriceps femoris muscles) was seen compared with the preoperative baseline. The impaired voluntary innervation is regarded as being far more responsible for the loss in muscle power than the atrophy itself. Evidently, pain does not play a central role. No patients in this study received perioperative regional nerve blocks (Mizner et al 2005).
Additional continuous sciatic nerve block.
There is increasing controversy over whether additional continuous sciatic nerve block might offer further postoperative benefits to patients with total knee replacement (Ben-David et al 2004, Geiger et al 2005, Morin et al 2005, Pham Dang et al 2005, Abdallah and Brull 2011, Cappelleri et al 2011, Wegener et al 2011).
About 70 to 85% of the patients will profit from sciatic nerve block in terms of a significant reduction in postoperative pain, this being particularly true for patients with preoperative flexion contracture (Ben-David et al 2004, Geiger et al 2005).
Single-shot administration of a long-acting local anesthetic is not sufficient, as the pain in the area innervated by the sciatic nerve persists for about 36 hours (Pham Dang et al 2005, Wegener et al 2011), and this period cannot be covered by one single-shot block. The combination of a femoral nerve block or a psoas block with a continuous sciatic nerve block offers superior analgesia compared with a continuous femoral nerve block or psoas block alone, but there is disagreement about the effect of an additional sciatic nerve block on the functional result (Ben-David et al 2004, Morin et al 2005, Wegener et al 2011).
It should be noted that intermittent monitoring of the motor function of the dorsal and plantar flexors of the foot is mandatory in order to detect any operative injury to the sciatic nerve at an early stage. This monitoring may be realized by intermittent bolus administration with appropriate neurologic windows or by a low concentration of the local anesthetic (e.g., 0.2% ropivacaine), which makes a differential block with analgesia possible while leaving motor function unaffected.
An increase in nerve damage after total knee replacement due to the introduction of peripheral block techniques for postoperative analgesia has not been found (Jacob et al 2011).
Hebl et al (2005) employed a multimodal concept for postoperative pain control after total hip/knee replacement, with continuous psoas block or femoral nerve block combined with sciatic nerve block being the central element. They were able to demonstrate that the 50% reduction in opioid use in the postoperative period resulted in earlier ambulation, shorter length of stay, significant reduction in PONV, less dysfunctional cognition, and less urinary retention compared with historical controls (Hebl et al 2005).
Tibial Plateau Fracture, Tibial Plateau Osteotomy, Intramedullary Nail
Contrary to the assumption that it is primarily the sciatic nerve that innervates the bone of the tibial plateau, femoral nerve block is a highly efficient procedure for pain control in injuries and surgery at this level. The greatly feared compartment syndrome in connection with a tibial plateau fracture can be detected early, as the function of the sciatic nerve is not impaired. It is important that the surgeon is well aware of this fact. After intramedullary nailing of the lower leg, the substantial pain at the subpatellar point where the nail is inserted into the tibia can be well managed by femoral nerve block.
Combined Continuous Peripheral Nerve Blocks
Combined continuous block of several peripheral nerves in one limb (e.g., femoral and sciatic nerve) is possible, as well as parallel blocks in two limbs (e.g., bilateral continuous axillary block, bilateral distal sciatic nerve block). Bilateral interscalene brachial plexus block is contraindicated! See below for dosages of the local anesthetic.
22.3 Local Anesthetics: Administration, Dosage
Different types of administration can be distinguished:
Intermittent administration of a bolus
Patient-controlled bolus delivery with or without basic continuous infusion
Which of the listed methods will be used depends, among other things, on the local conditions. Numerous variants of local anesthetic administration for postoperative pain therapy through continuous peripheral nerve catheters have been studied (Meyer and Hermann 1998, Singelyn et al 1999, Singelyn and Gouverneur 2000).
The following dosage recommendations can be given for the long-term use of local anesthetics:
Ropivacaine 0.2 to 0.375% (2–3.75 mg/mL), 6 to 12 mL/h
Alternative: bupivacaine 0.125 to 0.375% (1.25–3.75 mg/mL), 5 to 10 mL/h, max. 30 mg/h
When two blocks are to be performed in parallel, 0.33% (3.3 mg/mL) ropivacaine may be delivered continuously for each block at a dose of 6 mL/h, as long as there are no limiting factors on the patient′s side (e.g., decompensated cardiac failure, severely impaired renal clearance). The authors of this atlas look back on substantial experience with this dosing regimen, without having seen any incidents that may be traced back to this dose of the local anesthetic. Under this regimen, intermittent additional bolus administration of 10 mL ropivacaine 0.33% (3.3 mg/mL) up to four times a day is tolerated without any problems.
Ropivacaine should be preferred because of the lower toxicity and reduced motor impairment in the low concentration ranges (Borgeat et al 2001). In the first 24 hours postoperatively, 0.2% (2 mg/mL) ropivacaine at a dosage of 0.25 mg/kg body weight per hour proved ineffective (Salonen et al 2000). Therefore, 0.33 to 0.375% (3.3–3.75 mg/mL) ropivacaine is often used in this situation.
Infusion or syringe pumps.
The use of infusion or syringe pumps has proved useful for techniques of continuous regional anesthesia. Continuous delivery can be provided through perfusor syringes. A disadvantage is that the syringes must be changed frequently at relatively high infusion rates (6–10 mL/h). However, syringe pumps with a freely selectable volume per bolus have been available for some years, and are suitable for greater volumes (60–100 mL).
Devices that enable both continuous and patient-controlled intermittent delivery (PCA) are well tried and tested. A commercially available plastic bag (Polybag) containing 200 mL of ropivacaine can be attached to these pumps. If a higher concentration of ropivacaine is desired, 240 mL of a 0.33% (3.3 mg/mL) solution can be made by adding 40 mL of 1% (10 mg/mL) ropivacaine (Table 22.1). As well as the advantage of less frequent bag changes, which is important for hygiene reasons, these devices provide the patient with greater mobility. The use of large-volume infusion units leads to considerably improved organizational options.
The devices are subject to the medical devices act (MPG). The provisions of this law require among other things, that the user (physician, nurse, etc.) be instructed in its use. The legal requirements have contributed to optimal device safety and faulty operation or programming can be almost completely ruled out.
Elastomer pumps (Fig. 22.1) are also gaining increasing interest; these are filled with a certain volume of local anesthetic (usually 250 mL) and infuse the local anesthetic solution at a fixed delivery rate (e.g., 5 or 10 mL/h). These systems work very reliably with few disruptions and a bolus delivery by the patient is now possible with some of the currently available systems.
22.3.1 Care of Peripheral Pain Catheters in a General Ward
The requirements for care of catheters for peripheral continuous nerve blocks are fundamentally the same as for neuraxial catheters. However, special features differing from neuraxial blockades must be taken into account.
According to the local requirements of current rules, changing the syringes or local anesthetic bags and tubing or filters can theoretically be delegated to nursing personnel, provided they have sufficient knowledge and experience with regard to possible complications, side effects of drugs, and first aid in case of incidents (Van Aken et al 2001).