Prophylactic intravenous bolus ephedrine for elective Caesarean section under spinal anaesthesia

BACKGROUND AND OBJECTIVE: To evaluate the efficacy and optimal dose of prophylactic intravenous ephedrine for the prevention of maternal hypotension associated with spinal anaesthesia for Caesarean section. METHODS: After patients had received an intravenous preload of 0.5 L of lactated Ringer's solution, spinal anaesthesia was administered in the sitting position with hyperbaric bupivacaine 2.5 mL 0.5% combined with 25 microg fentanyl. A total of 68 patients were randomized to receive a simultaneous 2 mL bolus intravenously of either 0.9% saline (Group C, n = 20), ephedrine 6 mg (Group E-6, n = 24), or ephedrine 12 mg (Group E-12, n = 22). Further rescue boluses of ephedrine 6 mg were given if systolic arterial pressure fell to below 90 mmHg, greater than 30% below baseline, or if symptoms suggestive of hypotension were reported. RESULTS: There was a significantly higher incidence of hypotension in Group C (60% patients) compared to Group E-12 (27%), but not in Group E-6 (50%). The 95% Confidence Interval for the difference in proportions between Groups C and E-12 was 6-60%, P < 0.05. Fewer rescue boluses of ephedrine were required in Group E-12 compared with Group C (1.8 +/- 1.2 vs. 3.3 +/- 2.1, P < 0.05). There were no significant differences in the incidence of maternal nausea or vomiting, or of neonatal acidaemia between groups. CONCLUSION: A prophylactic bolus of ephedrine 12 mg intravenously given at the time of intrathecal block, plus rescue boluses, leads to a lower incidence of hypotension following spinal anaesthesia for elective Caesarean section compared to intravenous rescue boluses alone.     

Randomised trial of intravenous infusion of ephedrine or mephentermine for management of hypotension during spinal anaesthesia for Caesarean section

This study compared the effects of intravenous infusions of ephedrine and mephentermine for maintenance of maternal arterial pressure and neonatal outcome in pregnant women receiving subarachnoid block for lower segment Caesarean section. Sixty patients who developed hypotension following subarachnoid block for Caesarean section were randomly divided into two groups of 30 each to receive an intravenous infusion of ephedrine or mephentermine. Hypotension was defined as a decrease in systolic blood pressure of > or = 20% from the baseline value or an absolute value of <100 mmHg, whichever was higher. The vasopressor infusion was titrated to maintain systolic blood pressure between 'hypotension' and baseline values. Baseline haemodynamic parameters, haemodynamic changes subsequent to the start of vasopressor infusion, duration of hypotension and amount of vasopressor required were statistically similar for both groups. Neonatal APGAR scores and acid-base profiles were also comparable. To conclude, mephentermine can be used as safely and effectively as ephedrine for the management of hypotension during spinal anaesthesia in patients undergoing elective Caesarean section.     

Comparison of phenylephrine infusion regimens for maintaining maternal blood pressure during spinal anaesthesia for Caesarean section

Background. During spinal anaesthesia for Caesarean section,the optimal phenylephrine regimen and the optimal blood pressure(BP) to which it should be titrated are undetermined. The idealregimen would balance efficacy for maintaining uteroplacentalperfusion pressure against potential for uteroplacental vasoconstriction,both of which may affect fetal acid–base status. We comparedphenylephrine infusion regimens based on three different BPthresholds. Methods. After intrathecal injection, we infused phenylephrine100 µg min^–1 for 2 min. Then, until delivery,we infused phenylephrine whenever systolic BP (SBP), measuredevery 1 min, was below a randomly assigned percentage of baseline:100% (Group 100, n=25), 90% (Group 90, n=25) or 80% (Group 80,n=24). We compared umbilical blood gases, Apgar scores and maternalhaemodynamics and symptoms. Results. Patients in Group 100 had fewer episodes [median 0(range 0–8)] of hypotension (SBP <80% baseline) comparedwith Group 80 [5 (0–18)] and Group 90 [2 (0–7)](P<0.001 in each instance). Total dose of phenylephrine wasgreater in Group 100 [median 1520 µg (interquartile range1250–2130 µg)] compared with Group 90 [1070 (890–1360)µg] and Group 80 [790 (590–950) µg]. Umbilicalarterial pH was greater in Group 100 [mean 7.32 (95% confidenceinterval 7.31–7.34)] than in Group 80 [7.30 (7.28–7.31)](P=0.034). No patient had umbilical arterial pH <7.2. InGroup 100, 1/24 (4%) patients had nausea or vomiting comparedwith 4/25 (16%) in Group 90 and 10/25 (40%) in Group 80 (P=0.006). Conclusions. For optimal management, phenylephrine should betitrated to maintain maternal BP at near-baseline values. Br J Anaesth 2004; 92: 469–74     

Spinal anaesthesia for Caesarean section: comparison of infusions of phenylephrine and ephedrine

Maternal cardiovascular changes and neonatal acid-base statuswere assessed in 29 healthy women undergoing elective lowersegment Caesarean section under spinal anaesthesia. The patientswere allocated randomly to one of three groups to receive ani.v. infusion of one of the following: ephedrine 1 mg min^–1(group E1: n = 10), ephedrine 2mg min^–1 (group E2: n =9), or phenylephrine 10 µg min^–1 (group P: n = 10).Invasive arterial pressure was monitored continuously and ifhypotension occurred (defined as a 20% decrease from baseline,taken after iv. preload administration), bolus doses of eitherephedrine (6 mg in groups E1 and E2) or phenylephrine (20 µgin group P) were given. Only four patients became hypotensivein group E2, compared with eight patients in group E1 and ninepatients in group P. The total time that the patients remainedhypotensive was greatest in group P (P < 0.005), less ingroup E1 and least in group E2. Neonatal Apgar scores and acid-baseprofiles were similar in all three groups. In this study, aninfusion of phenylephrine 10 µg min^–1 with bolusdoses of 20 µg was shown to be significantly less effectivein maintaining systolic arterial pressure within 20% limitsof baseline compared with an infusion of ephedrine 1 or 2 mgmin^–1 with bolus doses of 6mg     

Randomised double‐blinded comparison of phenylephrine vs ephedrine for maintaining blood pressure during spinal anaesthesia for non‐elective Caesarean section*

In a randomised, double‐blinded study, we compared boluses of phenylephrine 100 μg with ephedrine 10 mg for treating hypotension (systolic blood pressure < 100 mmHg) in 204 patients having non‐elective Caesarean section under spinal anaesthesia. Umbilical arterial (UA) and venous (UV) pH and base excess were similar between groups. In the ephedrine group, UA lactate concentration was higher (median 2.6 [interquartile range 2.3–3.3] vs 2.4 [1.9–3.0] mmol.l^?1, p = 0.002) and UV lactate concentration was higher (2.5 [2.2–3.2] vs 2.3 [1.9–2.8] mmol.l^?1, p = 0.016) and more patients had nausea or vomiting (12.7% vs 3.9%, p = 0.02). Clinical neonatal outcome was similar. Of the protocol‐compliant patients (n = 148), UA Po ₂ and UV Po ₂ were lower in the phenylephrine group although oxygen content was similar. We conclude that phenylephrine and ephedrine are both suitable vasopressors for use in non‐elective Caesarean sections.     

Evaluation of pre-emptive intramuscular phenylephrine and ephedrine for reduction of spinal anaesthesia-induced hypotension during Caesarean section

Pre-emptive intramuscular (i.m.) vasopressors were evaluatedin 108 patients undergoing elective Caesarean section underspinal anaesthesia, assigned to four groups in a randomized,double-blind, placebo-controlled study. Group 1 received pre-emptivephenylephrine 4 mg i.m., group 2 received phenylephrine 2 mgi.m., group 3 received ephedrine 45 mg i.m., while controlsreceived an i.m. injection of saline, all given immediatelyafter induction of spinal anaesthesia. Hypotension was definedas a 25% decrease in mean arterial pressure (MAP). Rescue intravenous(i.v.) boluses of ephedrine were given if the patient was hypotensiveor reported nausea, vomiting or dizziness. The incidence ofhypotension was 33% in the phenylephrine 4 mg group comparedwith 70% in the control and phenylephrine 2 mg groups (P=0.03),and 48% in the ephedrine 45 mg group. The phenylephrine 4 mgand ephedrine 45 mg groups had a significantly lower percentagereduction in MAP (–21 (SD 14)% and –22 (14)%) comparedwith controls (–32 (18)%, P=0.04). They also had a lowertotal dose of rescue i.v. ephedrine (15.7 (15.7) mg and 15.8(15.6) mg) compared with controls (28.8 (20.6) mg, P=0.02).We conclude that pre-emptive i.m. phenylephrine 4 mg and ephedrine45 mg reduce the severity of hypotension and the total doseof rescue i.v. ephedrine during spinal anaesthesia for Caesareansection. Br J Anaesth 2001; 86: 372–6     

Prospective evaluation of systolic arterial pressure control with a phenylephrine infusion regimen during spinal anaesthesia for caesarean section

BackgroundHypotension and nausea occur frequently during spinal anaesthesia for caesarean section. The aim of this evaluation was to assess systolic arterial pressure control with our routine prophylactic intravenous phenylephrine infusion regimen. We audited a local standard for an incidence of hypotension of ?25% during the first 15 min of anaesthesia.MethodsOne hundred healthy women undergoing elective caesarean section were assessed. Following intravenous preload with 10 mL/kg Hartmann’s solution, 0.5% hyperbaric bupivacaine 2.8 mL combined with diamorphine 400 μg was given intrathecally in the sitting position. Intravenous phenylephrine was then started at 67 μg/min (the maximum rate). Systolic arterial pressure was recorded every 2 min. The infusion was titrated, according to local guidelines, to maintain systolic arterial pressure close to baseline.ResultsThe median dose of phenylephrine given by infusion was 1000 [interquartile range 670–1000] μg, with 51 patients not requiring any change to the infusion rate. Eleven patients (11%, 95% CI 6–19) developed hypotension, defined as a systolic arterial pressure <80% of baseline. A further four patients were given a bolus of phenylephrine for suspected hypotension. The incidence of hypotension or suspected hypotension was therefore 15% (95% CI 9–24). Thirteen patients (13%, 95% CI 7–21) developed nausea. No patient vomited.ConclusionsOur routine phenylephrine infusion regimen was effective at minimizing hypotension and nausea during relatively high-dose spinal anaesthesia. This was achieved with a low intervention rate, in conjunction with a 2-min rather than a 1-min non-invasive blood pressure cycle time and a relatively low volume of intravenous fluid.     

Sequential compression device with thigh-high sleeves supports mean arterial pressure during Caesarean section under spinal anaesthesia

Background. This study investigated the use of a SequentialCompression Device (SCD) with thigh-high sleeves and a presetpressure of 50 mm Hg that recruits blood from the lower limbsintermittently, as a method to prevent spinal hypotension duringelective Caesarean section. Possible association of arterialpressure changes with maternal, fetal, haemodynamic, and anaestheticfactors were studied. Methods. Fifty healthy parturients undergoing elective Caesareansection under spinal anaesthesia were randomly assigned to eitherSCD (n=25) or control (n=25) groups. A standardized protocolfor pre-hydration and anaesthetic technique was followed. Hypotensionwas defined as a decrease in any mean arterial pressure (MAP)measurement by more than 20% of the baseline MAP. Systolic (SAP),MAP and diastolic (DAP) arterial pressure, pulse pressure (PP),and heart rate (HR) were noted at baseline and every minuteafter the spinal block until delivery. Results. A greater than 20% decrease in MAP occurred in 52%of patients in the SCD group vs 92% in the control group (P=0.004,odds ratio 0.094, 95% CI 0.018–0.488). There were no significantdifferences in SAP, DAP, HR, and PP between the groups. Conclusion. SCD use in conjunction with vasopressor significantlyreduced the incidence of a 20% reduction of MAP. Br J Anaesth 2003; 91: 695–8     

Re-evaluation ofim ephedrine as prophylaxis against hypotension associated with spinal anaesthesia for Caesarean section

Purpose

To assess the safety and efficacy of 37.5 mg ephedrineim in preventing hypotension associated with spinal anaesthesia for Caesarean section.

Methods

In a double-blind randomised controlled study, 40 patients (20 in each group) were given either 37.5 mg ephedrine or placeboim. The following parameters were recorded: (i) blood pressure; (ii) heart rate; (iii) ephedrineiv supplementation; (iv) umbilical venous blood gases and neonatal Apgar scores.

Results

The incidence of hypertension in the study group was 30% compared with 20% for the control group (P:NS). There was no difference in mean highest blood pressure or mean highest heart rate between the groups. The incidence of hypotension was lower but not significantly lower in the study group (50%) than in the control group (80%) (P:NS). However, the incidence of delayed hypotension was only 10% in the study group patients compared with 50% in the control group patients (P < 0.05).

Conclusion

Giving 37.5 mg ephedrineim prior to spinal anaesthesia was not associated with reactive hypertension or tachycardia. Intramuscular ephedrine provided more sustained cardiovascular support than intravenous ephedrine.     

Maternal and neonatal effects of bolus administration of ephedrine and phenylephrine during spinal anaesthesia for caesarean delivery: a randomised study

BackgroundMaternal haemodynamic changes and neonatal well-being following bolus administration of ephedrine and phenylephrine were compared in 60 term parturients undergoing elective caesarean delivery under spinal anaesthesia.MethodsIn a randomised double-blind study, women received boluses of either ephedrine 6 mg (group E; n=30) or phenylephrine 100 μg (group P; n=30) whenever maternal systolic pressure was ?80% of baseline.ResultsChanges in systolic pressure were comparable in the two groups. There were no differences in the incidence of bradycardia (group E: 0% vs. group P: 16.7%; P>0.05), nausea (group E: 13% vs. group: P 0; P>0.05) and vomiting (group E: 3.3% vs. group P: 0; P>0.05). Umbilical artery (UA) pH (group E: 7.29 ± 0.04 vs. group P: 7.32 ± 0.04; P=0.01) and venous pH (group E: 7.34 ± 0.04 vs. group P: 7.38 ± 0.05; P=0.002) were significantly greater in group P than in group E. UA base excess was significantly less in group E (-2.83 ± 0.94 mEq/L) than in group P (-1.61 ± 1.04 mEq/L; P<0.001). Apgar scores at 1, 5 and 10min and neurobehavioural scores at 2-4 h, 24 h and 48 h were similar in the two groups (P>0.05).ConclusionsPhenylephrine 100 μg and ephedrine 6 mg had similar efficacy in the treatment of maternal hypotension during spinal anaesthesia for elective caesarean delivery. Neonates in group P had significantly higher umbilical arterial pH and base excess values than those in group E, which is consistent with other studies.     

Respiratory effects of spinal anaesthesia for Caesarean section

We report the changes observed in a number of pulmonary function tests performed on 36 patients undergoing Caesarean section under spinal anaesthesia. The tests comprised peak expiratory flow, forced expiratory volume in one second, forced vital capacity, forced expiratory volume in one second to forced vital capacity ratio and the maximal mid-expiratory flow. Significant changes occurred that are consistent with a restrictive ventilatory defect. These changes persisted for four hours after the induction of spinal anaesthesia. Administration of 35% oxygen by facemask failed to change significantly fetal umbilical vein pH or partial pressure of oxygen.