Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China*Corresponding author
Submitted for presentation in part as a free paper at the 2001 Annual Meeting of the American Society of Anesthesiologists, New Orleans, USA, October 2001.
Accepted for publication: July 17, 2001
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Abstract |
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Br J Anaesth 2001; 87: 7724
Keywords: anaesthetic techniques, subarachnoid; anaesthesia, obstetric; complications, hypotension; colloids, gelatin
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Introduction |
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Methods and results |
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We allocated patients randomly using sequentially numbered, coded envelopes, to receive no preload (control group) or 4% succinylated gelatin solution 15 ml kg1 (Gelofusine; B. Braun Medical, St Gallen, Switzerland) i.v. over 15 min (colloid group). This volume is at the upper end of the range of volumes investigated previously.3 Preloading was supervised by a research nurse. To maintain blinding, the anaesthetists and other investigators remained outside the operating theatre during the preloading period. Patients were not blinded.
Immediately after the preloading period, spinal anaesthesia was induced with the patients in the lateral position, using 0.5% bupivacaine 2.0 ml plus fentanyl 15 µg. Patients were then turned supine with left lateral tilt and lactated Ringers solution was infused at 2 ml min1, controlled with an infusion pump. Arterial pressure was measured at 1-min intervals beginning 1 min after the spinal injection. An i.v. infusion of metaraminol 0.5 mg ml1 was started after the SAP had decreased to <90% of baseline. A bolus of metaraminol 0.5 mg was given and the infusion was titrated at 0.250.75 mg min1 with a syringe pump to maintain SAP in the target range 90100% of baseline, using a protocol we have described previously.2 4 We recorded the rate of metaraminol infusion each minute and the cumulative consumption of metaraminol 5 and 10 min after spinal injection and at the time of uterine incision.
Ten minutes after spinal injection, the block level was checked and preparation for surgery was started. Oxygen 5 litre min1 was given by face mask until delivery. Times of skin incision, uterine incision and delivery were recorded with a stopwatch. Nausea and vomiting not associated with hypotension were treated with metoclopramide 10 mg i.v. After delivery, oxytocin 10 IU was given i.v. and the study was terminated. Apgar scores were assessed at 1 and 5 min by the attending paediatrician and arterial and venous blood samples were taken from a double-clamped segment of umbilical cord for immediate blood gas analysis.
Prospective power analysis based on data from previous studies in our department showed that 33 patients per group would give 80% power with =0.05 to detect a 20% difference between groups in the total amount of metaraminol required. To allow for potential dropouts, we recruited 35 patients per group. Data are presented as median (range) and were analysed using MannWhitney and Fishers exact tests. Serial haemodynamic measurements up to the time of the earliest uterine incision were analysed by repeated measures analysis of variance.5 P<0.05 was considered significant.
Two patients in the control group were excluded because of protocol violations. Except for one patient in the colloid group, all patients received metaraminol. Patient characteristics, block height and surgical times were similar between groups.
Haemodynamic changes and metaraminol infusion rates are shown in Fig. 1. There was a significant change in SAP over time (P<0.0001); this did not differ between groups (P=0.26), although the pattern of change was different between groups (significant group x time interaction, P=0.03). The minimum recorded SAP was lower in the control group than in the colloid group [90 (51109) vs 101 (75127) mmHg, 95% confidence interval (CI) of the difference 316 mmHg, P=0.006]. Twenty-one patients (64%) in the control group had a decrease in SAP of greater than 20% compared with 11 patients (31%) in the colloid group (P=0.01). Heart rate was lower in the control group than in the colloid group (P=0.01), with no significant group x time interaction (P=0.8). Serial changes in metaraminol consumption were similar in the two groups; however, compared with the colloid group, the control group had a greater cumulative metaraminol consumption at 5 min [1.1 (01.9) mg vs 0.8 (01.8) mg; 95% CI of the difference 00.4 mg, P=0.01] and 10 min [1.7 (02.9) vs 1.4 (02.8) mg; 95% CI of the difference 01.7 mg, P=0.02] and required a greater maximum infusion rate [0.5 (0.250.75) vs 0.25 (00.5) mg min1; 95% CI of the difference 00.25 mg min1, P=0.0005]. The total dose of metaraminol at uterine incision was similar between groups [3.1 (04.8) vs 3.5 (0.96.3) mg; 95% CI of the difference 0.1 to 1.1 mg, P=0.08].
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Comment |
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However, preload with colloids has potential disadvantages, including cost and the risks of haemodilution, fluid overload and anaphylactoid reactions.6 Therefore, in healthy patients, some clinicians may prefer to rely on vasopressors alone and not to use colloids routinely. This approach appears safe because we found neonatal outcome in the control group was as good as in the colloid group. However, the increased early vasopressor requirement in non-preloaded patients should be noted.
Our findings are similar to those of a previous study in which we investigated preload with 20 ml kg1 of crystalloid using a similar method.2 In both of these studies, we chose to maintain arterial pressure with an infusion of metaraminol. Although ephedrine has been recommended more commonly as a vasopressor in obstetrics, we have shown previously that an infusion of metaraminol results in less fetal acidosis than an infusion of ephedrine.4
Some patients in our study had isolated and transient low arterial pressures recorded. This was not associated with adverse neonatal outcomes and might have been avoided by starting the vasopressor infusion earlier rather than waiting for the initial decrease in arterial pressure, as specified in our protocol.
In summary, we found that when maternal arterial pressure was maintained with an infusion of metaraminol, colloid preload improved haemodynamic stability and reduced maternal nausea and vomiting but had no effect on neonatal outcome.
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Acknowledgements |
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References |
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2 NganKee WD, Khaw KS, Lee BB, Wong MMS, Ng FF. Metaraminol infusion for maintenance of arterial pressure during spinal anesthesia for Cesarean delivery: the effect of crystalloid preload. Anesth Analg 2001; 93: 7038
3 Ueyama H, He YL, Tanigami H, Mashimo T, Yoshiya I. Effects of crystalloid and colloid preload on blood volume in the parturient undergoing spinal anesthesia for elective cesarean section. Anesthesiology 1999; 91: 15716[ISI][Medline]
4 Ngan Kee WD, Lau TK, Khaw KS, Lee BB. Comparison of metaraminol and ephedrine infusions for maintaining arterial pressure during spinal anesthesia for elective cesarean section. Anesthesiology 2001; 95: 30713[ISI][Medline]
5 Ludbrook J. Repeated measurements and multiple comparisons in cardiovascular research. Cardiovasc Res 1994; 28: 30311[ISI][Medline]
6 Weeks S. Reflections on hypotension during Cesarean section under spinal anesthesia: do we need to use colloid? Can J Anaesth 2000; 47: 60710