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Anaesthesia for fracture repair

Anaesthesia for orthopaedic procedures should blunt the stress response to surgery, and provide muscle relaxation and profound perioperative analgesia. Surgical trauma is an injury, and the body reacts locally (inflammation) and systemically (endocrine and metabolic activation). Central neuraxial blockade (epidural anaesthesia, spinal anaesthesia) modulates both endocrine and metabolic responses: a single dose inhibiting the stress response for only few hours, a 24 hours epidural analgesia for few days postoperatively. The influence of peripheral blocks on stress response to surgery appears to be negligible, however they provide effective long lasting analgesia.

Good knowledge of the technique and the use of dedicated material decrease the incidence of side effects and complications during regional anaesthesia: Tuohy needles and Loss-Of-Resistance technique for epidurals, nerve locator and dedicated needles for peripheral blocks, and care in selecting the drug and the dose to be administered should be used. Regional techniques can also lead to early mobilization, early oral intake and early discharge from the practice. In some patients the administration of analgesics through a long term epidural catheter can provide better analgesia during functional recovery and/or physiotherapy.

Local anaesthetics bupivacaine, ropivacaine and levobupivacaine can be safely used for epidural and spinal anaesthesia. Lidocaine should be better avoided because of its neurotoxicity. Duration of the block depends from the drug and the dose used. Morphine can be used to provide long lasting analgesia distant to the site of injection, due to its unique ability to spread cranially in the CSF. However, this may potentially lead to respiratory depression, therefore the dose should be carefully titrated according to patient’s need. Although fentanyl does not cause delayed respiratory depression, it is shorter lasting and does not provide distant analgesia. Central neuraxial alpha-2 agonists provide analgesia and do not cause respiratory depression, however they may cause bradycardia, and hyper- or hypo- tension. Only local anesthetics and alpha-2 agonists (as an adjunct to LA) have been shown to be effective for peripheral blockade.

Although general anaesthesia may limit the perception of the injury, it is now well established that this may not be associated with blunting of the stress response. Although high plasma levels of opioids may transiently alter stress response to surgery, they are associated to side effects and complication including bradycardia, respiratory depression, etc. During balanced anaesthesia inhalational agents are used to provide unconsciousness, while opioids, alpha-2 agonists, ketamine and NSAIDs to provide analgesia. NeuroMuscular Blocking Agents (NMBAs) can be used to provide muscle relaxation during general anaesthesia, however positive pressure ventilation is required and close monitoring of recovery of neuromuscular function is mandatory to avoid ventilatory depression at emergence from anaesthesia. NMBAs provide less effective muscle relaxation compared to regional techniques.

 

Spinal anaesthesia (second part)

Advantages of spinal anaesthesia include rapid onset, reliability, low plasma levels of the drugs used, and the use of lower doses compared to epidural anaesthesia. Systemic absorption in the subarachnoid space is minimal, compared to the epidural space. Disadvantages include short duration of action, impossibility of titration to clinical effect, and the inability to provide extensive surgical blockade without side effects. Indications for spinal anaesthesia are surgical procedures involving rectum, prostate, sacral area, hind limbs and caudal abdomen, including obstetric procedures. As a general principle, the greater the extent of anaesthesia required (i.e. exploratory laparotomy), the lesser is regional anaesthesia indicated, however spinal anaesthesia may still be a valuable part of a balanced technique in operations above the level of the umbilicus.

Hypotension and bradycardia are well known side-effects of spinal anaesthesia: they may be prevented with careful dose titration, and they are treated with fluids, alpha-adrenergic drugs (e.g. phenylephrine and metaraminol), or mixed alpha and beta adrenergic agonists (e.g. ephedrine and epinephrine) administration. Severe complications are rare: sporadically reported cardiac arrest always follows severe untreated hypotension, and it is usually responsive to CPR (Casati A and Vinciguerra F, Curr Opin Anaesthesiol 2002). Selection of local anaesthetic  is usually based on the expected duration of surgery in order to ensure excellent surgical anaesthesia with quick functional recovery (Casati A and Vinciguerra F, Curr Opin Anaesthesiol 2002). However recent concerns about lidocaine toxicity have increased the interest in other spinal local anaesthetics, and the use of small doses of long-acting agents (Kuusniemi KS et al, Reg Anesth Pain Med 2001) and analgesic additives such as lipophilic opioids (Ben-David B et al, Anesth Analg 1997; Vaghadia et al, Can J Anesth 2001) or alpha-2 agonists has been investigated.

In veterinary spinal anaesthesia there is no  easy way to calculate the dose to be administered, and the reduction of the intended epidural dose does not consider the different distribution of intrathecally injected isobaric local anaesthetics compared to the epidural route. The dose should be chosen according to the crown-rump length, the body area to be blocked, the expected duration of surgery, and the expected surgical stimulation. As a result, a skilled surgeon limiting the surgical field and stimulation, along with careful positioning of the patient on the operating table, will allow to reduce the dose of local anaesthetic used, also reducing side effects and improving recovery (i.e. ability to walk and return of normal urination). This approach may be even more effective in patients requiring general anaesthesia or sedation to perform regional anaesthesia, as most of our patients are.

 

The surgical patient (second part)

Surgeons in theatreA few considerations regarding the control of surgical stress and peri-operative pain (i.e. pain during and after surgery) may be of some interest, even though their diffusion in the veterinary world still seems to be limited. Surgical trauma is an injury that may range from complications following minor elective surgery to a massive insult following major procedures complicated by sepsis. Inflammation constitutes the local response, and endocrine metabolic activation, leading to hypermetabolism with substrate mobilisation, constitutes the general response. The general response is highly dependent on the severity of injury, with procedures involving the thorax and the abdominal cavity eliciting a response that may last up to several days. The stress response has usually been considered an homeostatic defence mechanism extremely important for tissue healing and adaptation to the noxious insult, without considering the potentially harmful effects of surgically induced endocrine response, hypermetabolism, and the resulting increased demands on physiologic reserve. Nowadays, however, the biochemical changes after injury need not to be considered as an homeostatic response important for survival and recovery, since physiologic disturbances may be prevented or treated, and substrates, blood, and other fluids are readily available. During the last few decades the astonishing increase in knowledge within surgery and anaesthesia has allowed even major procedure to be performed in patient with severe complicating disease, previously contraindicating surgery. This explains the growing interest in mechanisms involved in surgical stress response and in techniques which may limit it.

Many studies have investigated methods to blunt the stress response to surgery. Though general anaesthesia may limit the perception of the injury, this has been proved not to be necessarily followed by a limitation of stimuli directed to hypothalamus, which means stress response may remain unaltered. Most injectable and inhalational anaesthetics have poor or no effect on endocrine changes induced by surgical trauma if administered at clinical doses, and this is true both for the intra-operative and (above all) for the post-operative period. Also high dose opioid anaesthesia, usually administered for cardiac surgery, has only a transient inhibitory effect on the stress response that is related to high plasma and tissue concentrations, and it has no prolonged postoperative effects on metabolism. Scientific evidence suggest that opioids, which are widely used to control peri-operative pain, do not produce a significant reduction in stress response to surgery, unless high doses are used. Since metabolites of the arachidonic cascade are involved in several steps of the response to injury, pre-operative administration of NSAIDs (non-steroid anti-inflammatory drugs) may only result in a slight modification of stress response and immunosuppression. However clinical implications of this modification are unknown. The peripheral application of local anaesthetics in the wound may reduce both pain and endocrine response, but not other systemic reactions (leukocytosis, temperature, etc.). Conversely, as far as epidural administration of local anaesthetics is concerned, many studies in human beings have proved its effectiveness, at T4 level, in effectively reducing endocrine response during surgery of the pelvis and lower limbs. Analgesia is more effective if upper dermatomes are blocked and the duration of sensitive blockade is prolonged. An epidural anaesthetic block lasting less than 4 hours has a transient inhibitory effect, with a 24 hours epidural analgesia demonstrated an inhibitory effect lasting for not less than 4 days. When surgery is performed above the umbilicus or in the thorax, epidural administration of local anaesthetics can only partly reduce the stress response. It has been assumed that in this case, stress response is activated by vagal, sympathetic and frenic afferent fibres, which are not blocked by epidural anaesthesia. The epidural administration of opioids produces effective analgesia, but the mitigation of stress response is less intense and less prolonged, compared to epidural local anaesthetics. However, at the same doses, the epidural administration is comparatively more effective than the intravenous administration, therefore requiring smaller doses. Duration of effect in the post-operative period does not exceed 8 hours, or slightly longer. Moreover, analgesia and reduction of stress response are not necessarily correlated. Peripheral nerve blocks have proved to produce no effects on stress response during abdominal or thoracic surgery, despite a good degree of analgesia. It is possible that peripheral blocks are more suitable as surgical stress inhibitors as far as lower or caudal parts of the body are involved, though this aspect has not been deeply investigated so far. The association of general anaesthesia with nerve blockade has no additional inhibiting or stimulating effect on neuroendocrine response, and the results are perfectly comparable with what can be obtained with epidural anaesthesia by itself.

In the light of these considerations, it seems evident that regional techniques are particularly appropriate even in a traumatized patient, though the presence of multiple lesions and respiratory or cardiovascular instability will require a  general anaesthetic to prevent aspiration, to assist ventilation, and to provide cardiovascular stability.

 

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