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Femoral nerve block for pain relief after total knee replacement

Sally Sawyer, RN.

Lupus Support/Research Sister for Rheumatology, Southampton General Hospital, Southampton, Hampshire. This paper was written while the author was Staff Nurse, Pain Service, Royal Bournemouth Hospital

Knee osteoarthritis affects about 15% of older people in the UK (Cooper et al, 1994), and accounts for 9000 total knee arthroplasties a year in England and Wales (Coggan et al, 2000). This figure is likely to increase as the older population grows in the coming years (McGavock, 2002).

 

Knee osteoarthritis affects about 15% of older people in the UK (Cooper et al, 1994), and accounts for 9000 total knee arthroplasties a year in England and Wales (Coggan et al, 2000). This figure is likely to increase as the older population grows in the coming years (McGavock, 2002).

 

 

Major knee surgery is associated with severe postoperative pain (Singelyn et al, 1998; Eledjam et al, 2002). In this age group it can result in increased morbidity due to negative physiological responses such as reduced pulmonary and bowel function, increased catabolism, hypercoagulability, cardiac effort and immunosuppression (Box 1).

 

 

When it is inadequately controlled, severe postoperative pain can impair or prevent functional rehabilitation with detrimental physical, psychological, social and financial consequences (Pinnock et al, 1996). Health professionals should consider these factors when choosing a method of postoperative pain management for older patients undergoing total knee arthroplasty (Box 2).

 

 

Multimodal or balanced analgesia uses a variety of drugs - non-steroidal anti-inflammatory drugs (NSAIDs), paracetamol, local anaesthetics, opioids - with different actions, and sometimes different modes of delivery, to reduce the incidence and severity of side-effects (Kehlet, 1997).

 

 

Peripheral nerve block, in which local anaesthetic is injected into a peripheral nerve, may provide superior pain relief when used as part of a balanced analgesia technique by reducing the dose of each drug required and therefore the likelihood of systemic side-effects (Ping Ng et al, 2001; Allen et al, 1998; Singelyn et al, 2000).

 

 

Femoral nerve blocks and three-in-one blocks, which block the femoral, obdurator and lateral cutaneous nerves, are often used as an adjunct to general anaesthesia and can provide effective analgesia to the operated knee (Figure 1).

 

 

In Royal Bournemouth Hospital, femoral nerve catheters are left in situ with an infusion to provide prolonged postoperative pain relief following total knee arthroplasty.

 

 

The femoral nerve sheath is normally located using a nerve stimulator, and a block achieved by injecting a local anaesthetic into the sheath. If femoral catheterisation is planned, an epidural catheter is used. This is passed into the femoral nerve sheath before injection with local anaesthetic. Three-in-one blockade provides analgesia to both the anterior and posterior aspects of the knee.

 

 

Local analgesia blocks painful impulses by temporarily interrupting nerve conduction to the sensory nerves, which are more sensitive than motor nerves to local analgesia. If the anaesthesia is injected close to a nerve, the painful stimuli caused by surgery to the area is barred (Royal College of Surgeons of England and College of Anaesthetists, 1990). The two local anaesthetic preparations most commonly used for peripheral nerve block are bupivacaine and ropivacaine.

 

 

Advantages of femoral nerve blocks
Femoral nerve blocks can be advantageous to patients when compared with opioids, patient-controlled analgesia (PCA) and epidurals, which are associated with a number of problems. It also has advantages when it comes to issues such as coagulation complications and mobility.

 

 

Opioids
Opioid analgesia is used to treat severe, acute postoperative pain. However, its side-effects may be more severe in older people because of their altered metabolism, distribution and excretion of drugs (Box 3) (Gordon, 1999). While research indicates that age is the best predictor of morphine requirements, clinical experience suggests that often the analgesic prescription reflects a ‘one size fits all’ approach (Macintyre and Jarvis, 1995).

 

 

PCA
The use of PCA devices following total knee arthroplasty can result in better pain relief and less opioid use (Hirst et al, 1996). However, older people often under-use PCA devices, either because they are frightened by the technology and the use of ‘dangerous’ drugs, or they simply assume that pain is part of the postoperative experience (Gordon, 1999; Capdevila et al, 1999).

 

 

Epidurals
There are several limitations in the use of epidurals, even though they can provide superior pain relief. Physical factors such as obesity or osteoporosis may obscure bony landmarks and confuse or prevent epidural placement. Furthermore, maintaining epidural infusions is labour-intensive and inadequate staffing levels can result in suboptimal monitoring and assessment of patients with potentially devastating consequences. Therefore their potential side-effect profile (hypotension, infection risk, risk of catheter migration/rising block) may limit their use at ward level.

 

 

Quadriceps muscle spasm is a recognised cause of postoperative pain (Edwards and Wright, 1992). In Royal Bournemouth Hospital an active mobilisation regimen is used, with patients performing flexion exercises in bed on day one, and mobilising on day two. This has implications for the use of epidural analgesia, as bilateral motor block may be apparent. Furthermore hypotension is a recognised side-effect following local anaesthetic (Capdevila et al, 1999), and postural hypotension on mobilising is a common problem, resulting in epidural infusions being discontinued within 48 hours of surgery (Mauer et al, 2002).

 

 

In studies by Singelyn et al (1998) and Capdevila et al (1999) continuous passive movement (CPM) was used to gain knee flexion in the first 48 hours post surgery. While this initially may promote muscle relaxation and reduce the likelihood of postural hypotension, the risks of bed rest and immobility in older people may negate these benefits.

 

 

The likelihood of hypotension and motor block may be minimised with peripheral nerve blocks, as the sympathetic block is limited to a specific area. While femoral nerve blocks require larger volumes of anaesthetic, with the associated potential for plasma toxicity (Eledjam et al, 2002), targeted placement, careful titration and selective use of adjunct analgesia may facilitate patient mobilisation, with the infusion continuing to provide pain relief.

 

 

Coagulation complications
Activation of the neuroendocrine stress response that accompanies major surgery results in hypercoaguability and is responsible for considerable morbidity and mortality, especially in older people.

 

 

Deep vein thrombosis and pulmonary embolism are potentially serious complications following total knee arthroplasty, with an incidence of between 3 and 30% (Kim, 1990). Prophylactic thromboembolic measures are routinely used in clinical practice (Best et al, 1998).

 

 

The use of femoral nerve blocks may be of further benefit by causing unilateral vasodilatation and improved perfusion to the limb, an important consideration where a tourniquet is used to improve the surgical field.

 

 

While prophylactic anticoagulation may be contraindicated in regional analgesia, the consequences of haematoma formation are not as devastating in peripheral nerve block as they may be in epidural/spinal analgesia where the spinal canal is concealed and non-expandable (Horlocker and Wedel, 1998).

 

 

Pain relief and mobility
Initiation of early physical therapy is essential following total knee replacement to enable effective rehabilitation, particularly in older people, as they are at greatest risk of cardiovascular and pulmonary complications. Regaining a degree of autonomy also provides a psychological boost. The literature also suggests that effective peripheral nerve block can improve pain relief and reduce the necessity for opioid drugs (Edkin et al, 1995).

 

 

Singelyn et al (1998) further suggest that local anaesthetic may reduce or prevent pain and impaired muscle function caused by quadriceps muscle spasm by acting both peripherally and centrally to prevent nociceptive activity. In contrast, opioids act centrally once nociception has occurred.

 

 

Single-dose nerve block lasts typically for 24-36 hours. However, mobilisation is routinely started at 48 hours, so nerve-block catheterisation may be beneficial, although literature to support this is inconclusive (Goransen et al, 1997; Hirst et al, 1996; Capdevila et al, 1999).

 

 

In studies by Hirst et al (1996) and Capdevila et al (1999), patients reported pain behind the knee. Weber et al’s (2002) observational study indicated an improvement in pain scoring with the addition of a sciatic block. However, this can be technically difficult and time-consuming to achieve. In clinical practice, non-opioid analgesic drugs are also used, unless contraindicated, as valuable components to a balanced analgesia technique.

 

 

The variations in anaesthetic technique perioperative analgesia, infusion solutions and adjunct analgesia used in the studies discussed make direct comparisons difficult.

 

 

Differences in country of origin, method of data analysis and patient demographics must also be taken into consideration when relating the results to clinical practice. Furthermore, all the studies used a visual analogue scale to measure pain intensity.

 

 

Herr and Mobily (1993) indicated that patients over 65 years old prefer verbal descriptor scales. Therefore choice of appropriate assessment tools is important when introducing a new pain management technique.

 

 

The literature suggests that, although intravenous PCA provides steady analgesia at rest, it may be insufficient for movement. Epidural/spinal analgesia provides superior pain relief; however, the incidence of nausea, urinary retention, bilateral motor block and hypotension may offset this benefit. Nerve block may provide a balance between the two, and facilitate early physical therapy with reduced side-effects.

 

 

Disadvantages of femoral nerve blocks
There is minimal evidence in the literature regarding specific disadvantages associated with femoral nerve block. However, instances of incomplete or ineffective block are cited (Weber et al, 2002). Known complications and contraindications are illustrated in Box 4.

 

 

Introducing nerve block techniques into practice
Controlling postoperative pain following total knee arthroplasty presents considerable challenges. However, changing clinical practice is not always easy, and must be handled carefully with sensitivity and diplomacy.

 

 

Nerve block was introduced at Royal Bournemouth Hospital as a result of several factors highlighted by ward staff, anaesthetists and the acute pain service, including:

 

 

- Older and higher-risk category patients were undergoing total knee arthroplasty

 

 

- Audit results indicated instances of suboptimal pain relief and side-effects relating to intravenous PCA and epidural use

 

 

- Ward staff and physiotherapists were concerned about inadequate pain relief on initial mobilisation at 48 hours

 

 

- A newly appointed anaesthetist made a request to use this technique.

 

 

Embracing the change
Turrill (1986) proposed that for successful change to occur, there must be a clarity of overall purpose and a widely shared vision of a better future. It therefore requires a belief in the necessity for change, open channels of communication and trust (Ellis and Hartley, 1995).

 

 

Staff must feel fully informed about any change and its likely implications (Hargie et al, 1994). As the ward staff had already raised concerns over the pain management of some patients, it was not anticipated that introducing peripheral nerve block would be problematic.

 

 

To initiate effective change, staff must be fully aware of the plans, and involved at all stages and receive any training they require.

 

 

To address these issues, a meeting between the anaesthetist and the acute pain service was arranged to discuss the concept of using peripheral nerve block following total knee arthroplasty.

 

 

The technique would be audited over a specified period to enable feedback from patients and staff. Benne et al (1976) suggest that people will change more readily, and the change will be longer lasting, if they are involved in analysing the problem, and planning and implementing the necessary changes. Therefore, the acute pain service sister approached the clinical leaders of the orthopaedic wards to discuss the rationale and feasibility of using peripheral nerve block at ward level.

 

 

It was agreed that clear nursing guidelines must be available, and that there was to be no variation in prescription initially, to minimise risk.

 

 

Orthopaedic ward staff already cared for patients using potentially high-risk pain-relief methods (epidural, PCA, intrathecal opioids). This required a high degree of co-operation and communication between all disciplines, supported by clear guidelines and protocols to ensure a clear understanding of potential problems. However, the clinical leaders highlighted the need for ward staff to receive adequate training in peripheral nerve block techniques.

 

 

Training issues
Several training sessions were organised by the acute pain service for all ward staff. It included:

 

 

- The rationale for using peripheral nerve block, and its limitations

 

 

- The assessments required

 

 

- The side-effects of this method

 

 

- The importance of adjunct analgesia such as paracetamol and NSAIDs.

 

 

These sessions also provided a forum to address concerns and questions.

 

 

No change is complete without evaluating the outcomes, and being prepared to alter direction or admit mistakes (Gillies, 1994).

 

 

Furthermore, evidence-based practice integrates individual clinical expertise with best available evidence, and should also incorporate identification and compassionate use of individual patients’ predicaments, rights and preferences in making clinical decisions about their care (Sackett et al, 1996).

 

 

Reviewing the change
Informal interviews with patients and a review of pain-assessment charts indicated that the technique was acceptable and effective in most cases. Feedback from the ward staff indicated that:

 

 

- The strength of bupivacaine initially used caused a dense motor block, preventing compliance with physiotherapy; furthermore surgeons were concerned about complications such as compartment syndrome being overlooked, and nurses were worried about the increased risk to pressure areas

 

 

- There was no additional impact on nursing care, compared to pain relief methods already in use

 

 

- In contrast to reports that pain relief is prolonged after the block wears off, there did not appear to be a significant difference in pain relief with femoral nerve block (unless an infusion was used), compared to PCA or intrathecal opioids, but anecdotally the incidence of nausea, and drowsiness was reduced

 

 

- There was still uncertainty about titration of infusion rates, and mobilisation of patients with the infusion in situ; the infusions were often discontinued after the initial syringe was complete.

 

 

- Several patients experienced quite severe pain behind the knee - this is now managed with oral opioids (Oramorph) and adjunct analgesia.

 

 

Ownership issues
‘Ownership’ of the change is important in order to maintain momentum, and these observations were discussed with the anaesthetists, physiotherapists and ward staff to enable them to decide whether the outcomes of this technique are acceptable.

 

 

Many of the concerns have been resolved, and femoral nerve block +/- infusion is sometimes used as an alternative method of pain relief for patients undergoing total knee arthroplasty. There is a need continually to review the use of peripheral nerve block to ensure it meets user demand, so a formal audit of outcomes (analgesia use; pain scores; side-effects in the first 24 hours) is in progress.

 

 

Conclusion
This paper has discussed the advantages and disadvantages of peripheral nerve block and the practicalities of introducing it into clinical practice.

 

 

The literature suggests it is a safe option for postoperative pain management. New and improved techniques will improve success rates, postoperative recovery and patient safety, resulting in both individual and health-care system benefits.

 

 

The problems encountered when introducing the technique have been alluded to.

 

 

However, feedback from patients and staff in this hospital has encouraged us to continue using it, and since its introduction, several more anaesthetists have shown an interest.

 

 

The results of the audit will be known shortly and will guide future developments with this pain relief system.

 

 

 

 

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