oa Southern African Journal of Anaesthesia and Analgesia - Comparison of forced expiratory spirometric flow changes following intrathecal bupivacaine and bupivacaine with fentanyl : original research
Background : Higher dermatomal block following spinal anaesthesia impairs inspiratory capacity and decreases forced expiratory flow rates. This decrease in forced expiratory flows can in turn decrease the effectiveness of cough. Intrathecal opioids are important adjuncts to intrathecal local anaesthetics. The objective of our study was to compare the decrease in forced expiratory flows from the baseline values after subarachnoid block with bupivacaine and bupivacaine with fentanyl.
Methods : Institutional ethics committee approval was obtained. Forty ASA I and II adult males, scheduled for elective surgery were included in the study. Informed written consent was obtained from all patients who were randomly allocated into two groups. Group B received intrathecal anaesthesia 15 mgs of bupivacaine with 0.5 ml of normal saline and Group BF received 15 mgs of bupivacaine with 0.5 ml of fentanyl (25 µg) intrathecally. The patients were instructed about the performance of the spirometry on the previous evening of the surgery. Forced vital capacity, forced expiratory volume in one second, peak expiratory flow rate and maximum expiratory pressure (Forced expiratory flows) were measured in supine position before intrathecal block and at 10, 60 and 120 minutes, following the establishment of the block. Highest dermatomal level of sensory blockade was noted.
Results : There was no statistically significant difference in the baseline values of FVC (Group B: 4.188 ± 0.821, Group BF: 4.186 ± 0.575, p - 0.127), FEV1 (Group B: 3.301 ± 0.846, Group BF: 3.276 ± 0.825, p - 0.240), PEFR (Group B: 458.6 ± 43.024, Group BF: 452.6 ± 41.036, p -0.091 ) and PEmax (Group B: 52.64 ± 4.029, Group BF: 53 ± 3.162, p 0 0.119 ) between the two groups. There was highly significant reduction in the values of FVC, PEFR and PEmax when compared to the baseline in both the groups at all three study periods. There was an acute reduction in the values of FVC, FEV1, PEFR and PEmax at 10 minutes. The graphs then achieve a plateau from 10 minutes to 60 minutes. From 60 to 120 minutes there was a gradual upslope in the graph. With regards to FEV1, though at 10 and 60 minutes there were statistically significant reductions when compared to the baseline values in both the groups, at 120 minutes the reductions were not significant. At all three time periods there was no difference in the reductions in FVC, FEV1, PEFR and PEmax values among the two groups. None of the patients in both the groups had PEFR and PEmax values below the critical value.
Conclusion : The addition of 25 µg of fentanyl to intrathecal bupivacaine did not have any adverse effect on forced expiratory flows. There was a decrease in forced expiratory flows in both groups, but the decrease in PEFR and PEmax were never below the critical values. It is unlikely that a combination of intrathecal local anaesthetic and opioids will impair the normal patient's ability to cough effectively.
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