PARADAS TECNICAS

compared with a pinprick or a scratch. A cold stimulus may produce an assessment of a sympathetic blockade conducted by the smaller myelinated B-fibres that generally assess approximately two segments higher than A-delta or C-fibres.³²

The second reason may be the mean age of the patients in this study. In geriatric patients bupivacaine produces a slightly greater block height compared with that produced in younger patients. In one study,⁵⁹ patients in their twenties receiving a given volume of isobaric bupivacaine 0.5% demonstrated a T9 level compared with a T6 level for patients in their eighties. In this present study, the peak sensory block was T6 and T4 for the bupivacaine alone Group and bupivacaine/fentanyl Group respectively. The higher level of spinal block observed in the elderly could be due to some physiological changes associated with the elderly. With advancing age, the nerves become more sensitive to local anaesthetics, and CSF volume decreases with an associated increase in specific gravity.⁵⁹

Large doses of bupivacaine cause intense motor block and this could be potentiated by the addition of fentanyl as adjunct to the bupivacaine spinal anaesthesia.This present study showed a significant prolongation of motor block in the bupivacaine-fentanyl combination compared to the bupivacaine alone. This finding is similar to the report of Kuusniemi et al,¹³ which demonstrated that the addition of fentanyl 25µg to 0.5% bupivacaine 10mg for spinal anaesthesia resulted in effective anaesthesia with prolonged and intense motor block. However, this finding is different from the report of other workers that demonstrated a shorter duration of motor block. 9, 13, 57

It has been shown that the combination of intrathecal local anaesthetics with opioids provides anaesthesia.¹³ Opioids work in the intrathecal space by activating opioid receptors in the dorsal grey mater of the spinal cord, which modulates the function of afferent fibres.³² In this study,

the analgesic effect of intrathecal opioid-local anaesthetic could not be reliably assessed due to the administration of diclofenac suppository at the induction of spinal anaesthesia. The main goal of anaesthesia is to ensure that the patient never feels pain. However, 80% of the patients in the bupivacaine-fentanyl Group requested for postoperative analgesia with in the 24 hours of the study, whereas all (100%) of the patients in the bupivacaine alone Group received postoperative analgesia.

Although the haemodynamic status of the patients in the two groups in the present study was similar, the bupivacaine-fentanyl Group had a more stable haemodynamic profile. The literature on the effect of the addition of fentanyl to intrathecal bupivacaine is conflicting.

While some reports claim that the addition of fentanyl to intrathecal bupivacaine, does not affect haemodynamics,^56,57 others report the contrary.^{14, 60} Walsh et al¹⁴ reported that fentanyl did not alter the haemodynamic response in the patients given intrathecal hyperbaric bupivacaine 10 mg plus fentanyl 25 μg, but affected only the spread of the block.

The cardiovascular effects of subarachnoid block are proportional to the height of block and result from denervation of the sympathetic outflow tracts. One of the commonest adverse effects observed in this study was bradycardia. This was found in both groups with relatively similar incidence. Bradycardia following intrathecal local anaesthetic administration results from the blockade of sympathetic cardiac accelerator fibers and decreased venous return to the heart.⁶¹ In this study, bradycardia occurred in both groups with significant intergroup variation at some intervals; this finding agrees with the report of Singh et.al.³² All the patients who had bradycardia were promptly treated with intravenous atropine, with satisfactory outcome.

Following an intrathecal bupivacaine injection, the cephalad spread produces neuronal transmission blockade that results in decrease in sympathetic tone of blood vessels.⁶¹ The decrease in the vasomotor tone leads to the dilatation of the arterioles and pooling of blood in the capacitance vessels, resulting in hypotension.^{61, 62} The incidence of hypotension was higher in the bupivacaine alone Group (14.28%) that recorded the lowest SBP of 77mmHg, DBP of 51mmHg and MAP of 55mmHg compared to the bupivacaine-fentanyl Group (7.69%) that had the lowest SBP of 86mmHg, DBP of 55mmHg and MAP of 60mmHg. Hypotension was managed with intravenous crystalloid. However, two patients in the bupivacaine alone Group also received intravenous ephedrine injection.

Regional anaesthesia is frequently associated with shivering.⁴⁶ Shivering may be a normal thermoregulatory mechanism in response to core hypothermia due to redistribution of heat from core to periphery.⁴⁶ However, non-thermoregulatory shivering also occurs in normothermic patients. Although the incidence of shivering was low (3.84%) in the bupivacaine-fentanyl Group, the bupivacaine alone Group had a higher rate (17.85%) in this study. Chow et al⁶³ in their study also demonstrated a low incidence of shivering in a group that received bupivacaine and fentanyl (12.2%), compared to the group that received only bupivacaine (65.8%). Kang et al⁶⁴ also had a low incidence in their study with patients that received bupivacaine with fentanyl (0%)compared to the group that received only bupivacaine (33.3%).

The mechanism of shivering under spinal anaesthesia is not fully understood. However, shivering following spinal anaesthesia can occur as a result of a fall in body temperature of about 1-3 ºC, which is probably due to the loss of thermo-sensory inputs, and heat loss from vasodilated anaesthesized areas.⁴⁶ In this study efforts were made to control some possible contributing factors such as operating room temperature which was maintained at 24 °C,

warming of the intravenous crystalloid solutions and irrigation fluid during the TURP.

However, the incidence of shivering observed in this study during the intraoperative period after injecting the study solutions were low and well tolerated; none of the patients required treatment. Postoperatively all the patients were adequately covered with blankets to prevent the occurrence of shivering; that may result from heat loss.

Fentanyl is a highly ionized, lipophilic μ-receptor agonist. When it is administered intrathecally, the unionized component is rapidly transferred into the spinal cord. The reduction of shivering in the bupivacaine-fentanyl Group in this study may be attributable to the effect of fentanyl on the thermo-regulator which could further affect afferent thermal inputs at the spinal cord.⁶⁵ Mato et al⁶⁶ demonstrated that low dose ketamineis a pharmacological method that can be used to manage post spinal shivering. Another useful pharmacological agent in the management of post spinal shivering is meperidine.⁶⁷

Another adverse effects observed was pruritus, which occurred in one of the patients who received intrathecal bupivacaine-fentanyl. Pruritus is a well-known adverse effect of neuraxial narcotics. The exact mechanism is yet to be determined. The relationship of fentanyl with activation of supraspinal and dorsal horn mu receptors has been suggested.⁶⁸ An incidence as high as 95% has been reported following intrathecal injection of fentanyl 25μg for spinal analgesia during labour.⁶⁹ Antihistamines have been used in an attempt to reduce the incidence of intrathecal opiate-induced pruritus with varying degrees of success.⁶⁹ This effect was observed in 3.84% of the bupivacaine-fentanyl Group only. It was mild and well tolerated, requiring no treatment.

Spinal opioid carries the risk of respiratory depression especially in the elderly. Mild respiratory depression evidenced by SaO2 ranging between 82 and 84% in room air, but with

no depression of the respiratory rate was observed in the bupivacaine-fentanyl group (3.84%) in this study. Fernandez-Galinski et al⁷⁰ observed that intrathecal fentanyl 25µg induced arterial oxygen desaturation. The arterial oxygen desaturation (SpO2 82 - 84%) in room air observed following the administration of the intrathecal opioid, with no depression of respiratory rate was managed with oxygen administration, via a facemask throughout the intraoperative period.

Transurethral resection of prostate syndrome is a known major complication of transurethral resection of the prostate. It is associated with intravascular absorption of large volumes of irrigation fluid through the exposed venous sinuses around the surgical capsule, leading to some clinico-physiological changes.⁶ The risk is increased by surgery time of more than 60 minutes, prostate gland size of more than 45 g and irrigation fluid bag height of more than 60 cm.⁶ TURP syndrome has an incidence of about 2.5 - 20%, with perioperative mortality rate of about 0.5 – 5%;^{18, 20} however, there was no case of TURP syndrome in the present study. The mean duration of surgery and irrigation fluid volume was comparable in both groups. TURP syndrome presents with restlessness, mental confusion, malaise, stupor, coma, nausea, vomiting, dizziness, headache, transient visual changes, heart rate changes (bradycardia or tachycardia), cardiac arrhythmias, hypertension, hypotension, and pulmonary oedema.⁷ Early detection of TURP syndrome is important in preventing significant effects.^{6, 7} Measures used to prevent TURP syndrome includes good preoperative preparation of the patient, adequate hydration, good coagulation profile and electrolyte balance. Other measures includes limiting the surgery time to ≤ 60 minutes, keeping the irrigation fluid height to ≤ 60 cm from the surgical field, limiting the urinary bladder distention by the irrigation fluid and careful resection of the prostate.^{6, 18} When TURP syndrome is diagnosed, the procedure should be terminated and intravenous furosemide 1mg/kg and normal saline be administered.¹⁸ Other supportive measures include ventilation support as needed and reassurance of the patient.

Results of investigations to confirm the diagnosis.^{6, 18}

Hyponatraemia is associated with the TURP syndrome.⁶ It is well known that sodium (serum sodium level of 135 – 145 mmol/L) is essential for proper function of excitatory cells, particularly those of the heart and brain.⁷¹ Several factors have been associated with low plasma sodium levels in TURP syndrome patients. Such factors includedilution of serum sodium through excessive absorption of irrigation solution, loss of sodium into the stream of the irrigation fluid from the prostatic resection site, loss of sodium into pockets of irrigation solution accumulated in the periprostatic and retroperitoneal spaces and larger amounts of glycine stimulate the release of atrial natriuretic peptide in excess of that expected by the volume load, which further promote natriuresis.⁷¹ Preoperative hyponatraemia evidenced by electrolyte assay result is an absolute contraindication to TURP, however surgeons can be advised of the option of general anaesthesia.⁷¹

The treatment of hyponatraemia is always indicated in a symptomatic patient.^{6, 71} Although there is a growing concensus, the answer to how that treatment is most safely accomplished remains unsettled. Over cautious and slow treatment with normal saline and diuretic (furosemide) for symptomatic acute hyponatremia (≤0.7 mmol/l/hr),⁷¹ has been shown to be associated with high mortality and morbidity than rapid correction (≥1.0 mmol/l/hr).⁷¹