6.2. Characteristics of anaesthesia

At the time when the studies for this thesis were started, ambulatory knee surgery was mostly done under 5% lidocaine spinal anaesthesia in Oulu University Hospital. The popularity of spinal anaesthesia in ambulatory surgery has arisen from its ease of administration, rapid onset and high reliability (Standl et al. 1996, Alon et al. 2000). The knowledge of the connection between TNS and lidocaine spinal anaesthesia increased during the time when the anaesthesia studies were done (Hampl et al. 1999, Pollock et al. 1999). The incidence of leg pain and back pain was far higher in the 5% lidocaine spinal anaesthesia group than in the groups with the general anaesthetics used (III), or in the 2% lidocaine spinal anaesthesia group (IV). No connection between TNS and 2% lidocaine spinal anaesthesia could be shown, although some of the 2% lidocaine spinal patients had symptoms that resembled TNS (IV). The number of patients was far too low to show statistical significance. There is still some debate in the literature concerning the origin of TNS. Schneider (1993), Henderson (1998) and Pollock (1999) with their colleagues have found a clear connection between lidocaine spinal anaesthesia and TNS. There are some new studies that have failed to demonstrate such a connection (Wong & Slavenas 1999). The clinical importance of TNS warrants discussion, because neurological deficiences have not been described in any of the studies (Scneider et al. 1993, Hiller & Rosenberg 1997). The pain in TNS reacts well to NSAIDs and opioids, which is against the hypothesis of a neurotoxic origin of TNS (Scneider et al. 1993, Hiller & Rosenberg 1997). Selander renamed TNS as transient lumbar pain, because the symptoms resemble the symptoms of myofascial pain (Hartrick 1997, Selander 1999). The pain mechanism in transient lumbar pain might be the straightening of the lumbar lordosis, which is potentiated by the elevation of the legs after lidocaine spinal anaesthesia (Holmdahl 1998). Lidocaine and mepivacaine cause a larger motor block than bupivacaine, and that might be the reason for the lower incidence of TNS after bupivacaine spinal anaesthesia (Pitkänen et al. 1984, Salmela et al. 1998). In this study, leg and back pain was also described in the general anaesthesia groups (III). This may suggest that TNS does not alone explain the leg pain. One cause for the leg pain may be the effect of the patient"s position (Selander 1999) and the consequences of the usage of a tourniquet. Many ambulatory surgery centres use routinely tourniquets in knee arthroscopies, although there are reports suggesting that the tourniquet increases the risk of complications. Among the 184 consecutive patients scheduled for knee arthroscopy, deep vein thrombosis was detected in 33 (18%) (Demers et al. 1998). The risk of deep vein thrombosis was significantly higher among the patients who had a tourniquet applied for more than 60 minutes (Demers et al. 1998). There are also opposite findings from a group of 120 patients randomized to tourniquet inflation (300 mmHg) or no tourniquet inflation, where the use of a pneumatic tourniquet did not affect the patients’ overall quality of life or functional outcome following routine knee arthroscopy (Kirkley et al. 2000). There are also studies where the skeletal muscle ischaemic metabolic changes were more pronounced with a long tourniquet time in knee ligament reconstruction (Kokki et al. 1998b), and the safe use of a tourniquet should be limited to less than two hours (Kokki et al. 2000b).

The transient neurologic syndrome has restricted the use of lidocaine in spinal anaesthesia (Hampl et al. 1995), and compensatory methods have been searched for. Promising results have been obtained when small doses of hypo- or hyperbaric bupivacaine have been used to achieve unilateral spinal anaesthesia (Kuuusniemi et al. 2000, Fanelli et al. 2000, Valanne et al. 2001). The anaesthesia is reliable and the duration allows the most common day-case procedures to be performed. The anaesthetic effect of bupivacaine is longer than the effect of lidocaine. Although lower bupivacaine concentrations have been used (Valanne et al. 2001), home readiness is attained much later compared to the anaesthetics used in the studies 1 and 2. Home readiness has varied from 181 minutes with 4 mg of bupivacaine (Valanne et al. 2001) and 190–200 minutes with 6 mg of bupivacaine (Kuusniemi 2001) to 264 minutes with 8 mg of bupivacaine (Fanelli et al. 2000). Home readiness after 2% lidocaine spinal anaesthesia was shown to be 141 minutes (IV). It seems that the optimal local anaesthetic to substitute lidocaine in terms of short recovery time has not yet been developed. Bupivacaine has been used because of the lower incidence of TNS, but the cost-effectiveness of bupivacaine is not so good as that of general anaesthetics (IV) or the 2% lidocaine spinal anaesthesia (IV) used in the present study. Ben-David and colleagues used mini-dose lidocaine-fentanyl spinal anaesthesia in knee arthroscopies, and they found that home readiness could be achieved within 50 minutes (Ben-David et al. 2001). The short PACU phase is equal to the short PACU phase of the general anaesthetics used in study 1.

There is still a high risk among young patients to develop PDPH after lumbar puncture, although thin special needles are used in ambulatory spinal anaesthesias (Despond et al. 1998). In this thesis, the most common side effect of spinal anaesthesia was PDPH (III). Although the study groups were small, postdural puncture headache was reported. One reason for this might have been the 27 G sharp-pointed needle that was used. It might have been better to use a 27 G pencil-point needle, because there are at least two meta-analyses to show a lower risk of headache when thin pencil-point needles are used for spinal anaesthesia (Halpern & Preston 1994, Flaaten et al. 2000). Flaaten et al. (2000) found the relative risk of developing PDPH to be 0.38 in a pencil-point group compared to sharp-pointed needles. Sharp-pointed needles were routinely used in the unit where the clinical studies for this thesis were done.

Although there are comprehensive reports in the literature concerning the benefits of local anaesthesia in ambulatory knee surgery (Butterworth et al. 1990, Iossifidis 1996, Lorentsen et al. 1997, Ramanathan 1998), the use of local anaesthesia is uncommon. This may be due the impracticability of local anaesthesia when tourniquets are used and the fear of inadequate anaesthesia and patient discomfort (Forssblad & Weidenhielm 1999). One purpose of this thesis was to find an anaesthesia method considered highly satisfactory by patients operated on an ambulatory basis. The finding that patient discomfort was reported in only 0.9% of local anaesthesia arthroscopies in a large patient series (Forssblad & Weidenhielm 1999) favours the the use of local anaesthesia. Recently, the fastest recovery and lowest perioperative costs have been obtained with a combination of local anaesthesia and sedation in ambulatory surgery (Song et al. 2000, Li et al. 2000). However, the value of local anaesthesia is underestimated in ambulatory surgery. The finding that general anaesthesia patients need postoperative opioids in the early recovery phase more often than spinal anaesthesia patients (IV) favours the use of intra-articular local anaesthesia (Allen et al. 1993, Van Ness & Gittins 1995) combined with short-acting general anaesthetics in ambulatory surgery. There are some new findings in the literature which suggest that lower doses of lidocaine should be used in spinal anaesthesia (Wong et al. 2001) and that opiates could be combined with local anaesthetics (Stewart et al. 2001). These studies have reported equal or shorter PACU times with spinal anaesthesia than with novel general anaesthetics.

The laryngeal mask airway was not routinely used in the ambulatory surgery unit of Oulu University Hospital at the time when the clinical studies for this thesis were started. That was the reason for choosing a general anaesthesia method with muscle relaxation and tracheal intubation. Mivacuronium substituted suxamethonium as a short-acting muscle relaxant (Bevan 1995). The use of suxamethonium is not common because of the reported side effects, e.g. muscle pain and stiffness (Smith et al. 1993). The patients were not premedicated, because one aim in ambulatory surgery is a short recovery time and home readiness with minimal possible sedation. Premedication is often substituted by interviewing the patient and by giving adequate information. The patients who wanted to be premedicated were excluded from the study. Alfentanil was given to all patients who participated in the study because of its analgesic and euphorizing effect and short action (Ali-Melkkilä 1999).