Focus on: Day caseSpinal anaesthesia: The saviour of day surgery?
Introduction
Spinal anaesthesia is commonly used for inpatients in the United Kingdom (UK), but it remains relatively rare in the day case setting, the reasons for which may be predominantly historical. The rapid development of day surgery in the late 1980s and early 1990s was largely concerned with high volume, comparatively minor procedures on carefully selected and relatively fit patients. There were new hypnotic agents available, including propofol, sevoflurane and desflurane, which were well suited to day case general anaesthesia. The growing popularity of the laryngeal mask airway also helped to ensure that day surgery patients enjoyed rapid recovery with minimal side effects.
Times have changed however, and both the population now presenting for day surgery, and the procedures that can be carried out on a day stay basis, have been transformed. The Department of Health has proposed that 75% of all elective surgery could be carried out on a day case basis.1 If this is to be achieved, anaesthetists must re-examine their selection criteria and consider whether general anaesthesia is always the best choice for their patients. Some procedures now being moved into the day case arena are potentially associated with significant postoperative pain, for example lower limb orthopaedic surgery. Spinal anaesthesia (and other forms of regional techniques) has much to offer in management of early postoperative pain and hence reduction of postoperative morbidity. The British Association of Day Surgery (BADS) has actively promoted the wider use of spinal anaesthesia in day surgery.2
There is a wealth of recent literature on the subject of spinal anaesthesia for ambulatory surgery, the vast majority of which comes from outside of the UK. Studies of interest include the use of bupivacaine, levo-bupivacaine, ropivacaine, and chloroprocaine. This article will therefore include a discussion of local anaesthetic drugs and adjuncts which have not been licensed for intrathecal use in the UK. In fact, only two local anaesthetic agents are specifically indicated for subarachnoid injection in the UK and these are 0.5% hyperbaric bupivacaine and 0.5% ‘plain’ levo-bupivacaine. However, plain bupivacaine is also in use and it is common practice for anaesthetists to use other drugs outside of the licensed indication, including for example intrathecal fentanyl. Lidocaine is also still used occasionally although its popularity has declined because of the association with transient neurological syndrome (TNS). Ropivacaine is available in the UK but at the present time indications on the datasheet do not include intrathecal administration. Chloroprocaine on the other hand is not available in the UK but will be included in the discussion because it has a clinical profile which is very favourable for ambulatory spinal use.
Published studies include both hyperbaric and ‘plain’ solutions, diluted with saline or cerebrospinal fluid, or undiluted, with or without fentanyl. Generally speaking, plain or hypobaric solutions tend to spread unpredictably whereas the spread of the block obtained using hyperbaric solutions can be controlled to some degree using the patient's posture and speed of injection. The addition of fentanyl will make all local anaesthetic preparations more hypobaric3 and hence may affect spread. In general, the dose of local anaesthetic is considered to be the main determinant of the duration of the block4 although the duration may also be prolonged if the spread is restricted for the same dose of local anaesthetic, at least using hyperbaric bupivacaine.5
Following on from this, there are two main methods of modifying conventional spinal anaesthesia for day case patients:
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Reduce the dose of local anaesthetic by careful addition of opioids or clonidine, with the aim of producing a ‘selective spinal anaesthetic’; that is, the sensory nerves are affected to a greater degree than the motor nerves.
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Restrict the spread of local anaesthetic using drug baricity and injection technique so that only selected nerve roots are affected, for example in a unilateral or saddle block.
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The adequacy of anaesthesia for the surgery being performed.
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The time from spinal injection to home readiness.
Section snippets
Bupivacaine
Frustratingly for the day case anaesthetist, individual responses to small doses of intrathecal bupivacaine are highly variable. However, some basic techniques for using ‘low-dose’ bupivacaine have been established.
In 1997, Ben-David and colleagues showed that adding 10 μg of fentanyl to 5 mg bupivacaine (1 ml 0.5% hyperbaric bupivacaine), improved the quality of anaesthesia for knee arthroscopy without delaying discharge.7 Their technique included addition of saline to the bupivacaine so that the
Assessing recovery
Whilst the speed of recovery and ultimately home-readiness is of great importance, the quality of the recovery period is also worth examining. Whilst the incidence and severity of pain and postoperative nausea and vomiting (PONV) may be improved, there are also some troublesome side effects of spinal anaesthesia; acute urinary retention and post dural-puncture headache.
Selection criteria for day surgery
Fitness for general anaesthesia has been used to help select patients for day surgery, and many units continue to reject patients with significant co-morbidities. However, if general anaesthesia can be avoided, some of these patients can also enjoy the benefits of day surgery. This will include patients with significant respiratory disease, including sleep apnoea, gastro-oesophageal reflex, obesity and diabetes. The remarkable cardiovascular stability seen with the low-dose techniques described
Summary
In contrast to the USA and Europe, spinal anaesthesia remains uncommon in UK day surgery practice. Nevertheless, this rapidly developing area of research includes the use of drugs and techniques which are readily available in the UK. Selective spinal anaesthesia and the use of restricted blocks are adaptations of conventional spinal techniques that are especially suitable and their widespread introduction in the UK would make a significant impact on the number of patients who could be treated
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