CRITERIOS DÉBILES

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CHAPTER FIVE

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12^th and 24^th hour which was at variance to what was observed in the index study. This could be because in both studies by Atashkoii and co workers⁴¹ and Ng et al¹, comparisons were made with a placebo. There were also variations in the doses and volumes of local anaesthetic used compared with this study.

The time to first request for analgesic in the current study of 167.75 ± 75 minutes was slightly lower than the 240 minutes reported by Ng et al¹. The longer duration observed by Ng et al¹ compared to the index study may be attributed to the presence of epinephrine in the bupivacaine used by Ng et al¹. Epinephrine is a vasoconstrictor that is used as an additive to local anaesthetics thus prolonging the duration of action of the local anaesthetic agent. It is said to have intrinsic analgesic properties that may be of clinical benefit.⁴⁹ Atashkhoii and colleagues⁴¹ also recorded a longer time to first analgesic requirement in their combined intraperitoneal and incisional group (5.81 ± 3.04 hours). The use of a higher concentration of bupivacaine (0.375%) in their study compared to 0.25% used in the index study might have contributed to the longer duration of bupivacaine action which they observed.

One of the benefits of multimodal analgesia is the reduction of total opioid consumption and this was evident in this study. There was significant reduction in the total number of doses of pentazocine consumed in the study group (4.05 ± 0.50) as compared to the control group (4.84 ± 0.95). This was similar to what was observed by Ghafouri and coworkers³¹ with a reported significant reduction in meperidine request in their bupivacaine group compared to the placebo group ( 90.53± 13.36mg vs 127.5 ± 23.14). This significant reduction in opioid consumption was also reported by Goldstein and colleagues³⁵ and Gupta et al.⁵⁰ The reduction in opioid requirement has shown a positive analgesic effect of local anaesthetic as a useful component in the multimodal approach to postoperative pain management.

The use of subarachnoid block was preferred over general anaesthesia because

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the surgical operation was amenable to a regional technique. The benefits of subarachnoid anaesthesia include cost effectiveness (the cost of drugs and equipment) compared to general anaesthesia. It has a wider margin of safety as patients are not exposed to a variety of drugs such as intravenous induction agents, inhalational agents and muscle relaxants. There is also minimal danger of aspiration and airway obstruction. It also avoids the problem of difficult intubation. Subarachnoid block is also associated with minimal interference with physiological functions as the patient is conscious and breathing spontaneously.

The complications observed in this study were related to the technique of anaesthesia, the choice of local anaesthetic (bupivacaine) and the study intervention and were found to be moderate. Hypotension was the commonest intraoperative complication recorded. It is a well established adverse effect following subarachnoid block. Subarachnoid block abolishes the basal sympathetic tone which ordinarily maintains vasoconstriction resulting in peripheral vasodilatation, decrease in venous return and ultimate reduction in blood pressure.⁵¹ The rather high rate of 26.9%

recorded in the index study as compared to 8.18% reported by Kolawole and Bolaji52 following lower abdominal and lower limb surgeries may not be unconnected to the modal dermatomal T4 level achieved. Although Kolawole and Bolaji⁵² did not state the maximum block height, higher dermatomal blocks are associated with hypotension. The higher dermatomal level in the index study was desirable to prevent peritoneal irritation following hysterectomy. Up to about T4 level, hypotension results primarily from decreased preload. Preloading, which was conducted in the index study has been shown to minimise the incidence of hypotension following subarachnoid block.^51,53

Carpenter et al ⁵⁴ reported a 33% incidence of hypotension in non-obstetric population. They deduced that variables conferring increased risk for hypotension included a peak block height >T5, spinal puncture at or above L2-3 interspace, age

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>40yr and combination of spinal and general anaesthesia. Age and block height were two variables present in the current study. These might have resulted in an incidence close to what was observed by Carpenter et al.⁵⁴ The hypotension observed in the current study was managed with intravenous fluids. In addition, two patients required ephedrine administration.

The incidence of post spinal shivering in this study was 17.5% compared with 8.18% by Kolawole and Bolaji.⁵² This may also be related to the higher sensory block height observed in the index study with a larger cutaneous anaesthesized area. There are a lot of theories concerning the causes of post spinal shivering. A fall in body temperature by 1-3^oC has been shown to occur during spinal anaesthesia probably due to heat loss from the vasodilated extremities and loss of cutaneous thermosensory input in the anaesthetized area.⁵⁵ Another mechanism proposed to explain this shivering include a decrease in core temperature and misinformation from receptors.⁵⁶ The decrease in core temperature may be due to sympathetic blockade which results in peripheral vasodilatation, increased cutaneous blood flow and subsequent increased heat loss via the skin.⁵⁶ A fall in core temperature may also be due to a cold operating room or the rapid infusion of crystalloid solutions at room temperature.⁵⁷ In this study, the intravenous fluids used were warmed to 38^oC. Shivering may also result from differential inhibition of afferent thermoreceptors fibres within the spinal cord.⁵⁸ The patients that developed shivering were covered with warm drapes (over the upper limbs, away from the surgical site), infusion of warm fluids and administration of 100%

oxygen.

There was no reported incidence of local anaesthetic toxicity in the present study. This observation was similar to the results from systematic reviews by Moiniche et al³⁰ and Kahokehr et al.³⁹ The doses of bupivacaine used in the index study were 50mg and125mg and though the dose in the study group was large, this however did

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not exceed the maximum safe dose for individual patients. The range of plasma concentrations between 0.92 – 1.14g/ml after intraperitoneal instillation of plain bupivacaine, 100 -150mg has been reported to be well below the toxic concentration of 3g/ml^59,60 and the maximum amount of 125mg administered in the index study was within this limit. Similar serum concentrations below the toxic level have been associated with paraesthesia, perioral numbness and tingling sensation in some volunteers following intravenous administration of bupivacaine.⁶¹ The need for caution is always advised during administration to prevent inadvertent intravascular administration and this is unlikely during intraperitoneal instillation.

Postoperative vomiting was the commonest postoperative complication. The aetiology of postoperative nausea and vomiting is usually multifactorial, involving anaesthetic and analgesic agents, the type of procedure and patient factors with females undergoing abdominal and/or gynaecological procedures found to be at a higher risk.⁶² The incidence of 30.8% in the index study is similar to an observation by LeGouez et al that a 40% risk of postoperative nausea and vomiting obtains in patients undergoing gynaecologic surgery.⁶³ Postoperative vomiting was higher in the incisional group (66.6%) and this group recorded a higher pentazocine consumption, with vomiting being a common side effect of opioid use. In the study by Callensen et al,⁶⁴ three patients reported this complication with one in the ropivacaine group and two in the placebo group. Vomiting was also observed within the 24 hour postoperative period as was seen in this study. The patients were administered 10mg metoclorpramide intravenously as a statum dose with relief of symptoms.

Post dural puncture headache (PDPH) is another common complication following subarachnoid block and an 8.75% incidence was reported in the index study..

The mechanism of PDPH is believed to be caused by continuing loss of CSF through the hole made in the dura by the spinal needle consequently causing traction on the

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meninges.⁶⁵ The onset is usually 12 - 24 hours following dural puncture. It is postural, worse on standing, relieved on lying down and usually occipital. Many factors are known to affect the incidence and severity of PDPH including age, sex and race of patients, technique of SAB, number of dural attempts, position of needle bevel at dura puncture, needle size and needle tip design.^65,66 The size and configuration of the spinal needle is the most important and significant factor in the occurrence of PDPH. ⁶⁶ A meta-analysis by Halpern and Presto⁶⁷ revealed that non- cutting needles produced a lower incidence of PDPH than cutting needles. Turnbull and Shepherd ⁶⁶ in a review reported the incidence of 0 - 14.5% with a 25G Whitacre needle. In that review, the upper limit was observed in parturients who have a higher incidence of PDPH.⁶⁶ The incidence of 8.75% in the index study falls within this range as the index study was in non- obstetric population. The incidence of PDPH is also common in the young and females.⁶⁶ The spinal needles used in the current study were size 25G Whitacre specification.

Evidence in the literature does not support a causal relationship between incisional and intraperitoneal local anaesthetics and delayed wound healing or infection.

Local anaesthetics have been observed to inhibit the local inflammatory response to injury.⁶⁸ They reduce the release of inflammatory mediators from neutrophils, reduce neutrophils adhesion to endothelium and oedema formation.⁶⁸ The observation in the index study is similar to the systematic review by Kahokehr and colleagues³⁹ and also by Gupta et al⁵⁰ with no report of delay in wound healing or breakdown. This verifies the finding that local anaesthetics reduce harmful wound activity which normally results in impaired healing and excessive scar formation.⁶⁹ Hannibal and co workers⁷ compared bupivacaine incisional infiltration with placebo and reported two cases of wound infection, one in each group. In that study, the cause of wound infection was not stated but it could be speculated that since it occurred in both groups, it was probably

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unrelated to the intervention and could have been due to other factors for example surgical technique or patient related factors.

It was also observed that patients used better descriptors in rating their satisfaction with pain management in the combined intraperitoneal and incisional group in contrast to those in the control group. These ratings were similar to comments by patients studied by Cindea and co workers.³⁸ The adequacy of pain relief was rated higher in their bupivacaine group. Thus multimodal analgesic technique enables pain to be managed at different sites of the pain pathway, thus providing better outcome.

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