Support for the development of this report was provided by B Braun
“Spinal anaesthesia is simple, safe, reliable and cheaper than general anaesthesia”, according to Dierk Vagts, (Head of Department of Anaesthesiology and Intensive Care Medicine, Marienhaus Hospital, Neustadt/Weinstrasse, Germany).
The technique (which involves injecting a local anaesthetic directly into the cerebrospinal fluid) was first introduced at the end of the nineteenth century by Beer. “It is very reliable and if it does not work it is because it has been wrongly placed and nothing to do with the drug or the patient”, said Professor Vagts.
Four drugs have been widely used for the technique – mepivacaine, lidocaine, bupivacaine and ropivacaine – but all have durations of action that last for four or five hours and so general anaesthetics have been preferred for short procedures.
Spinal anaesthesia
The spinal anaesthetic is administered by inserting a spinal needle into the intervertebral space between the third and fourth lumbar vertebrae (L3/L4). This position is used because it is below the level where the spinal cord ends and provides a convenient point for injecting drug into the intrathecal space, explained Professor Vagts. It should not be inserted any higher than this level so as to avoid accidentally piercing the spinal cord.
Local anaesthetic is injected (infiltrated) into the surrounding skin first and then a fine needle (24G or 26G) is used for the intrathecal injection. In the past, 18G needles were used but this was associated with headaches for patients so now the finer needles are used, said Professor Vagts.
When the needle is in place, cerebrospinal fluid is aspirated to check that it is correctly positioned. The drug can then be administered. This provides an anaesthetised area from about the level of T4 (breast level) downwards (to the feet).
It is suitable for operations such as gynaecological, urological, vascular and orthopaedic procedures and also for trauma surgery.
Spinal anaesthesia results in complete muscle relaxation, a high level of comfort with no pain and minimal side effects. At the end of the operation with a general anaesthetic, it is necessary to wait some time for the patient to recover.
In contrast, if a spinal anaesthetic is used, recovery is very rapid and patients can leave the operating theatre sooner. This rapid turnover is associated with lower costs, said Professor Vagts. However, to achieve this, a drug with fast onset, high efficacy and fast offset of action with rapid regression of motor blockade is required.
In addition, the drug needs to be metabolised in a consistent, predictable way – a feature that is critical for day surgery. Bupivacaine, for example, is metabolised over a period of six to eight hours but can be up to 14 hours, making it unsuitable for day surgery, explained Professor Vagts.
The ideal local anaesthetic would also be non-toxic and not cause post-operative urinary retention (POUR).
Day surgery units are organised to deal with short surgical procedures and have limited recovery facilities. Long-acting drugs such as bupivacaine and ropivacaine are not ideal in these circumstances. Moreover, with lidocaine, transient neurological symptoms (TNS) have been reported in up to 30% of patients. The new formulations of prilocaine and chloroprocaine offer major advantages in this respect.
Prilocaine is an amide-type local anaesthetic that is rapidly metabolised by esterases. The active metabolite (orthotoluidine) is not cardiotoxic. Although it can cause methaemoglobinaemia, the amounts are so small as to be clinically insignificant, said Professor Vagts.
Prilocaine has intermediate lipid solubility and low/intermediate plasma binding – features that ensure fast onset and offset of action. The offset of sensory blockade is two hours earlier with prilocaine compared to bupivacaine. Operations lasting up to 120 minutes are possible with prilocaine anaesthesia, although, in practice, the mean duration ‘of operations is about 35 minutes.
“Patients want to walk home after their operations so the duration of motor blockade is critical”, said Professor Vagts. After 120–150 minutes the motor blockade (estimated by Bromage score) with prilocaine had completely resolved compared with 210 minutes with bupivacaine, according to one study.1 In addition, the ‘time to voiding’(of urine) and ‘time to discharge’ from the post-operative recovery room were both significantly longer with bupivacaine.
TNS – described as ‘transient but distressing post-operative back pain that involves the buttocks and/or legs’ – occur in up to 30% of patients receiving lidocaine for spinal anaesthesia, according to early analyses.
A Cochrane review showed that prilocaine was clearly better in this respect.2 The incidence of TNS with prilocaine, chloroprocaine, bupivacaine and ropivacaine is about 1–2% but is much higher with lidocaine and mepivacaine. The relative risk of TNS with lidocaine is about five-times greater than with other local anaesthetics, noted Professor Vagts. One recent review of prilocaine usage showed no TNS in a series of 5000 cases, he added.3
Furthermore, a recent study comparing hyperbaric prilocaine with plain prilocaine identified no cases of TNS.4 Persistent neurological deficits such as cauda equina syndrome (CES) are reported to occur in 5% of patients receiving spinal lidocaine but hitherto there have been no reports of CES with prilocaine. In addition, there have been no reports of urinary retention with spinal prilocaine. “It looks as if prilocaine is very safe for spinal anaesthesia”, said Professor Vagts.
He concluded that the good safety profile combined with rapid recovery and early discharge home, made spinal anaesthesia using hyperbaric prilocaine an attractive option for day surgery.
Chloroprocaine
Turing to chloroprocaine, Professor Vagts said that this also was not a new drug but early formulations had contained preservatives that made the injection toxic. Chloroprocaine has very low lipid solubility and so has a fast onset and offset of action.
The motor blockade has resolved by 90 minutes after a 30mg spinal dose of chloroprocaine. The duration of the sensory block is such that procedures of up to 75 minutes can be undertaken, but in practice the mean duration of such procedures is 27 minutes. This makes the drug suitable for short operations such as gynaecological procedures.
Urinary retention
The risk factors for POUR are well known so individual risk can be assessed in advance (see Box).
The risk of POUR increases with the duration of blockade of the detrusor vesicae muscle which receives its innervation from S2–S4. Prilocaine and chloroprocaine have the advantage that they only block the nerve supply to this muscle for 60–90 minutes, noted Professor Vagts.
Economic evaluation of spinal anaesthesia
The cost of using a drug includes not only the acquisition cost of the drug but also the cost of disposables (needles, syringes, etc), the cost of treating side effects such as vomiting and the cost of personnel (nurses’ and doctors’) time.
The cost of 5ml vials of 0.5% bupivacaine (hyperbaric and isobaric) ranges from about €1 to €6 across Europe, whereas the cost of prilocaine 2% ranges from €5 to €10 per vial.
For the purpose of analysis it was assumed that an operation lasts 60–90 minutes and uses the same equipment, regardless of whether bupivacaine or prilocaine is used for spinal anaesthesia. Undesirable side effects including bradycardia, post-operative nausea and vomiting, headache and lower back pain are somewhat more common with prilocaine but can be neglected in terms of costs, said Professor Vagts.
The key cost driver is the cost of personnel, especially nurses, in the recovery room. Protocol requires a nurse to stay with a patient during the recovery process and so the longer this takes, the greater the cost. The cost of a nurse in the recovery room is £40 per hour in the UK and €25 per hour in Germany, said Professor Vagts.
In the UK, if the patient remains in the recovery room for less than 85 minutes, it is still cheaper to use bupivacaine – although patients rarely, if ever, recover in such a short period in practice, noted Professor Vagts. For stays longer than 85 minutes, prilocaine becomes the cheaper option.
Similarly in Germany, a stay in the recovery room for longer than 80 minutes favours the use of prilocaine. Analyses using the prilocaine figures show that prilocaine 2% is cost-effective for stays in recovery of less than 155 minutes in the UK and 120 minutes in Germany.5
It is usually possible to discharge a patient from the recovery room in 90 minutes after prilocaine, Professor Vagts noted.
Similar analyses have been performed for chloroprocaine, although this drug is not available in all countries. In six of seven studies analysing the use of chloroprocaine, the time to discharge from recovery was less than 117 minutes and so, even at a cost of €10, it was cheaper to use one ampoule of chloroprocaine for procedures of about 30 minutes duration, he said.
Comparing spinal anaesthesia with general anaesthesia for ambulatory surgery, even if propofol and remifantil are used for general anaesthesia, spinal chloroprocaine allows faster discharge from theatre and faster recovery.
As soon as the motor block has worn off, the patient is ready for discharge and it is not necessary to wait for voiding of urine, said Professor Vagts. Older protocols that require this step were written before the introduction of short-acting spinal anaesthetics, he explained.
Theatre throughput
Another way of looking at these data is to work out how many patients could be processed in a theatre suite using either bupivacaine or prilocaine for spinal anaesthesia. If it is assumed that there are two operating theatres and eight places in the recovery room, then a work flow analysis shows that in an eight-hour period, 24 patients could be processed using prilocaine compared with 14 using bupivacaine. Even if the procedure itself only takes 30 minutes, the patient has to remain in recovery until the motor block has resolved.
“There is a huge economic benefit because nearly twice the number of patients can be processed in one day”, he said.
Professor Vagts concluded that hyperbaric prilocaine and chloroprocaine can improve the process of day surgery and its efficiency, provided that patients require less than 120 minutes in the recovery area.
Economic benefits of short-acting spinal anaesthetics was a satellite symposium supported by B Braun Melsungen AG at the 23rd Congress of the European Association of Hospital Pharmacists held in Gothenburg, Sweden, 21–23 March 2018.
Author
Christine Clark PhD FRPharmS
References
1 Rätsch G et al. Spinal anaesthesia in day-case surgery. Optimisation of procedures. [Article in German] Anaesthesist 2007;56:322–7.
2 Zaric D, Pace NL.Transient neurologic symptoms (TNS) following spinal anaesthesia with lidocaine versus other local anaesthetics. Cochrane Database Sys Rev 2009;15;(2):CD003006.
3 König W, Ruzicic D. Absence of transient radicular irritation after 5000 spinal anaesthetics with prilocaine. Anaesthesia 1997;52:182–3.
4 Camponovo C et al. A prospective, double-blinded, randomized, clinical trial comparing the efficacy of 40 mg and 60 mg hyperbaric 2% prilocaine versus 60 mg plain 2% prilocaine for intrathecal anesthesia in ambulatory surgery. Anesth Analg 2010;111:568–72.
5 Vagts DA, Bley CH, Mutz CW. Use of 2% hyperbaric prilocaine for spinal anesthesia : sensitivity analysis in outpatient surgery. [Article in German] Anaesthesist 2013;62:271–7.
