All orthopaedic procedures are not necessarily considered an emergency, and in patients that have sustained traumatic orthopaedic injuries, surgery, and therefore anaesthesia, is likely to be postponed until the patient is considered stable, and concurrent injuries, pulmonary contusions, hypovolaemic shock, have been corrected. It should be remembered that some fractures can result in significant blood loss, particularly pelvic or femoral fractures, and so hypovolaemia and anaemia are always a concern in these patients, either on presentation, or a few days post-trauma; therefore, assessment of the patient's haemodynamic status should be assessed and corrected prior to anaesthesia, along with treatment of anaemia if required.
As well as initial stabilization, any fractured limbs or wounds should be appropriately dressed, and wounds debrided if open fractures are present. Placement of supportive dressings in patients with fractures will result in some pain relief due to reducing movement and dislocation of bone fragments, along with preventing further trauma of the limb.
Once the patient is deemed suitably stable for anaesthesia, then a plan can be created. The premedication combination will be determined by the individual patient’s status, but commonly will be a combination of a sedative (acepromazine or an alpha-2 agonist at low doses) and a pure opioid (methadone) are appropriate choices. An appropriate opioid is used to provide analgesia, muscle relaxation and sedation, whilst its combination with a sedative will allow a reduction in the dose of both induction and inhalation agents. For induction of anaesthesia, most of the commonly used short-acting induction agents are appropriate (e.g., propofol or alfaxalone). Anaesthesia is then maintained using either isoflurane or sevoflurane administered, remembering both these agents result in a dose-dependent decrease in cardiac output and therefore blood pressure, so careful monitoring is required.
Analgesia
Effective analgesia is essential in all patients, but in patients that have sustained traumatic injuries pain can have severe effects on multiple organ systems. Inappropriately treated pain makes trauma patients more prone to systemic inflammatory response syndrome (SIRS), immunosuppression, sepsis, and long-lasting maladaptive pain.
Pain has negative effects on wound healing, with greater post-surgical pain being associated with delayed wound healing and also increasing serum cortisol levels which again will impair wound healing.
Overall, a multimodal approach to analgesia in trauma patients should be used. By utilizing analgesic agents that act on different points on the pain pathway, along with agents that work synergistically, we can reduce the dosages and therefore side effects associated with individual drugs. Opioids are an excellent choice for orthopaedic patients as they are effective, titratable, and reversible whilst having minimal cardiovascular side effects. Another group of agents worth considering are local anaesthetics, which can be used as part of a regional block.
Placement of Local Anaesthetic Blocks
The use of local anaesthetic blocks as part of a multimodal approach to analgesia, is potentially the most effective form of analgesia for many small animal surgeries, but also, for the majority of veterinary clinics, the most underused. For the majority of the blocks that will be discussed all that is needed is a syringe, a needle, local anaesthetic and a knowledge of the relevant anatomy. Technically these blocks do not require any specialist equipment, but nerve location equipment is recommended to guide perineural injections of local anaesthetics.
Local anaesthetic blocks can be used to enhance analgesia whilst the animal is under general anaesthesia, this means that less volatile agent will be required to maintain anaesthesia, and is likely to result in a ‘smoother’ anaesthetic. Local anaesthesia can also be used in sedated or occasionally conscious patients in order to allow minor surgical procedures or manipulations to be performed. Local anaesthetics are the only class of analgesics that are true analgesics, in that they completely block pain sensations, all the other drugs that are considered to be 'analgesics’. Local anaesthetic drugs block pain because they stop the nerves conducting the pain signals and so work on the transmission part of the pain pathway.
When performing any of the local blocks, aspiration to check for blood, following needle insertion, but prior to local anaesthetic injection, should always be performed, as local anaesthetics (with the exception of lidocaine in certain circumstances) should never be given intravascularly. Intravenous administration or overdose of local anaesthetics can cause cardiotoxic (peripheral vasodilation, hypotension, decreased myocardial contractility and arrhythmias) or neurotoxic (sedation, disorientation, ataxia, convulsions) side effects.
Limb Blocks
Local blocks are an excellent choice for orthopaedic patients as most aspects of limbs can be desensitized using a number of different regional blocks.
Intra-articular Analgesia
This is a simple local anaesthetic block which can be done pre- or post any surgery involving a joint, including arthroscopy. As with all local anaesthetic blocks, it must be done in a strictly aseptic manner to avoid introducing infection into the joint. This technique should be carried out as a ‘one-off’ rather than as a continuous infusion. As with all analgesia, pre-emptive administration is best, and so ideally the drug should be injected before surgery (often this can be performed once a joint tap has been performed, using the same needle left in place). Alternatively, it can be injected at the end of surgery just before the joint is closed. Bupivacaine is used as the local anaesthetic of choice, but in animals with chronic joint disease morphine can also be added to the local anaesthetic. In such cases of chronic joint inflammation, synovial opioid receptors are upregulated, and morphine should improve the quality and the duration of the analgesia.
Brachial Plexus Block
Blocking the nerves of the brachial plexus will provide excellent analgesia for procedures below the elbow. The traditional brachial plexus (axillary) block, injecting approximately 10–15 ml of local anaesthetic (for a 25-kg dog) into the axillary space at the level of the point of the shoulder blocks the lower forelimb, but not the shoulder or the proximal humerus.
1. The patient should be positioned in lateral recumbency with the leg to be blocked placed uppermost, being held in a natural position (perpendicular to the longitudinal axis of the body).
2. The proposed puncture site should be clipped and aseptically prepped.
3. Insert a spinal needle into the axillary region, medial to and at the level of the shoulder joint, directed toward the costochondral junction and parallel to the vertebral column.
4. The needle’s distal end should lie just caudal to the spine of the scapula.
5. As with any local block, aspirate the syringe to avoid intravascular administration, and then inject two-thirds of the dose. Inject the remaining one-third as you slowly withdraw the needle.
6. Increasing the volume of local anesthetic used by diluting it with sterile saline solution up to 50% can improve the degree of blockade by increasing the volume injected.
Pneumothorax is a potential complication of both of these brachial plexus blocks and aspiration to check for air should be performed before each injection. Bilateral blocks should be avoided due to potential blockade of the phrenic nerve.
Pelvic Limb Blocks
The sciatic nerve block may be combined with either a femoral nerve or lumbar plexus block to provide analgesia for pelvic limb surgery. Electroneurolocation is recommended for these techniques to improve accuracy, ensure safety and reduce the dose of local anaesthetic required. It is also unlikely satisfactory local anaesthesia will be gained without electroneurolocation. The sciatic nerve is blocked at its proximal location caudal to the greater trochanter of the femur. The puncture site is located at the junction of the cranial and middle thirds between a line drawn between the greater trochanter of the femur and the ischial tuberosity. The depth of needle insertion varies depending on the size of patient and may be up to 6 cm to 8 cm. The femoral nerve is blocked at its location on the medial aspect of the pelvic limb in the femoral triangle. The femoral artery is palpated within the femoral triangle, held in place with light digital pressure and the femoral nerve is located and blocked cranial to the artery, usually in a superficial location. An alternative to the femoral nerve block is the lumbar plexus block, which allows for the femoral nerve to be blocked more proximally and avoids the risk of missing the saphenous nerve high within the inguinal region. The saphenous nerve supplies the cutaneous innervation to the stifle and therefore, if missed, a patient may respond to skin incision. The lumbar plexus block is performed with the patient positioned in lateral recumbency with the side to be blocked uppermost. The dorsal process of L7 is palpated and from this the dorsal process of L5 identified. The needle is inserted lateral to L5 (approximately 2 cm to 3 cm) until the transverse process is contacted. The needle is then walked off bone caudally and a loss of resistance may be felt as it passes through the intervertebral ligament. Local anaesthetic is then injected after aspiration.