Maternal cardiovascular consequences of positioning after spinal anaesthesia for Caesarean section: left 15 degree table tilt vs. left lateral

Sixty healthy women undergoing elective Caesarean section were randomly allocated to either a measured 15 degrees left table tilt position (n = 31) or full left lateral position (n = 29) for a 15-min period after spinal blockade. Arm and leg blood pressure, ephedrine requirements, symptoms, fetal heart rate, cord gases and Apgar scores were recorded. Mean ephedrine requirements and incidence of hypotension were similar in the two groups. Arm systolic arterial pressure over time was similar in both groups, but leg systolic arterial pressure over time was significantly lower in the tilt group (p < 0.001); the mean leg systolic arterial pressure was lower for all 15 sequential recordings in the tilt group, reaching statistical significance (p < 0.05) at 4, 5, 6 and 8 min. Differences in maternal nausea, vomiting and bradycardia and fetal outcome were not statistically significant. Following spinal anaesthesia, even a true 15 degrees left table tilt position is associated with aortic compression.     

The effect of 10 degrees head-up tilt in the right lateral position on the systemic blood pressure after subarachnoid block for Caesarean section

Forty women presenting for elective Caesarean section under spinal anaesthesia were randomly assigned to have anaesthesia induced in the right lateral position either in the horizontal position or with 10 degrees head-up tilt. Hyperbaric bupivacaine 2 ml 0.5% with 0.1 mg of morphine was injected intrathecally before the parturients were placed in the supine position with 15 degrees left lateral tilt. Blood pressure and heart rate were monitored every minute and the sensory level (loss of sharp sensation to pinprick) was monitored every 3 min until clamping of the umbilical cord. Ephedrine 6 mg was given every minute that the systolic blood pressure decreased below 90 mmHg. The mean systolic blood pressure during the first 5 min after induction of spinal anaesthesia was lower in the control group compared to the tilted group (99 mmHg vs. 109 mmHg; p = 0.043). The upper limit of block was higher in the control group compared to the tilted group (p = 0.002). The use of 10 degrees head-up tilt resulted in a reduced incidence of hypotension initially and less extensive sensory block.     

Hypotension following combined spinal-epidural anaesthesia for Caesarean section. Left lateral position vs. tilted supine position

Eighty-seven pregnant mothers undergoing elective Caesarean section were randomly allocated either to the full left lateral position (n = 45) or to the supine position with 12 degrees left lateral tilt (n = 42) after a combined spinal-epidural (CSE) in the sitting position and an initial 2 min in the full right lateral position. Fewer mothers were hypotensive while in the study position [29 (64%) in lateral group vs. 38 (90%) in the tilted supine group; p = 0.03]. Mothers in the lateral group tended to become hypotensive after turning them back to the tilted supine position immediately before surgery; hence the number of mothers who were hypotensive from the insertion of the CSE until delivery were similar [36 (80%) vs. 38 (90%)]. Mothers in the lateral group needed a lower dose of ephedrine to treat their hypotension while in their study position (median (interquartile range [range]) 6 (0-12 [0-36]) mg vs. 12 (6-18 [0-36]) mg, respectively; p = 0.04) but ephedrine requirements were similar overall (12 (6-12 [0-36]) mg vs. 12 (6-18 [0-36]) mg), respectively. The full left lateral position reduces the incidence of early hypotension compared with the tilted supine position with tilt, and makes it easier to treat.     

Spinal anaesthesia for Caesarean section: effect of Sprotte needle orientation

We induced spinal anaesthesia in 100 women presenting for elective Caesarean section with the mother in the right lateral position. Patients were allocated randomly to have the side eye of the 24-gauge Sprotte spinal needle pointing in one of four directions: group A, cephalad; group B, right lateral; group C, left lateral; group D, caudad. Isobaric bupivacaine 0.5% (2.5 ml) was injected over 30 s before the mother was placed supine with a 15 degree left lateral tilt. Onset time and height of the subsequent analgesic and anaesthetic blocks were assessed by a blinded observer. Onset of sensory block to T4 was significantly faster in group A (P = 0.001). There were no differences in final block height, incidence of hypotension, nausea and vomiting or ephedrine requirements.      

不同穿刺体位在腰-硬联合麻醉剖宫产术中的比较

目的比较不同穿刺体位在腰-硬联合麻醉(CSEA)剖宫产术中的效果。方法拟行剖宫产术的足月妊娠产妇90例,随机分为两组,每组45例。选择L3~4椎间隙作为穿刺点。R组右侧穿刺腰麻后保持穿刺体位2 min后左倾30°仰卧至手术开始,L组左侧穿刺腰麻后仰卧位,并调整手术床左倾30°直至手术开始。腰麻药物均为1.0%罗哌卡因1.5 ml+10%葡萄糖0.5 ml。观察腰麻药物注入后15 min内产妇感觉阻滞效应及不良反应情况,记录新生儿Apgar评分,检测脐动脉血p H值。结果 R组产妇最终阻滞平面明显低于L组,达到最终阻滞平面所需时间明显短于L组(P0.05)。R组麻黄碱用量为0(0~6)mg,明显低于L组的6(0~12)mg(P0.05)。R组脐动脉血p H值明显高于L组(P0.05)。两组新生儿Apgar评分差异无统计学意义。结论剖宫产术采用右侧卧位穿刺注药后保持穿刺体位2 min后30°仰卧,其麻醉效果优于左侧卧位穿刺后30°仰卧体位。     

Prevention of spinal hypotension associated with cesarean section by aortocaval compression--left 15 degree table tilt vs. uterine displacement by hand

Women undergoing elective cesarean delivery were randomly assigned to receive a spinal anesthesia in either the semi-lateral (group SL) position or the supine position with uterine displacement (group UD). After spinal injection, group SL patients were turned to a 15 degrees left lateral supine position, and group UD patients had uterine displacement by hand. Ephedrine 4 mg i.v. was administered in case of nausea/vomiting and/or hypotension, defined as a systolic blood pressure below 100 mmHg. Arm systolic arterial pressure and leg systolic arterial pressure were similar in both groups, but the lowest leg systolic arterial pressure until delivery was significantly lower in the UD group (P < 0.05). Mean ephedrine requirement was significantly less in the SL group (P < 0.05). Apgar scores did not differ, but umbilical artery pH values were significantly higher in patients of the group SL (P < 0.01).     

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.     

体位对择期剖宫产产妇循环和新生儿的影响

目的观察体位对产妇血流动力学及新生儿Apgar评分的影响。方法硬膜外麻醉下行择期剖宮产的产妇80例均分为四组,分别采用平卧位(S组)、左侧倾斜30°位(L组)、左侧倾斜15°同时头低15°位(LT组)、仰卧同时头低15°位(ST组)。记录各组麻醉前、麻醉后5、10、15 min、胎儿娩出即刻患者的MAP、HR、SpO2及新生儿1-、5-min的Apgar评分。结果麻醉后10 min,S、LT、ST三组MAP与麻醉前比较明显降低(P<0.05),也明显低于L组(P<0.05);新生儿出生后1-、5-min的Apgar评分组间差异无统计学意义。结论左侧倾斜30°位可有效降低剖宮产术中低血压的发生率。     

RIGHT VERSUS LEFT LATERAL TILT FOR CAESAREAN SECTION

In 60 mothers with normal placental function, the relative meritsof right and left lateral tilt during Caesarean section wereassessed. Maternal-foetal biochemical values and relationshipswere generally more satisfactory with the left lateral position.The incidence of hypotension (revealed aorto-caval occlusion)before and after induction of anaesthesia, was significantlygreater (P<0.001) with the "right side down" posture.     

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.     

Extradural anaesthesia for caesarean section in a patient with moyamoya disease

We report a case of moyamoya disease in a patient presenting for Caesarean section at 37 weeks' gestation. Extradural anaesthesia was administered using 0.5% bupivacaine and pethidine 25 mg. A stable haemodynamic state was produced using left lateral uterine displacement, i.v. crystalloids and an i.v. infusion of ephedrine. The patient suffered no neurological deficit and there was no significant intraoperative decrease in cerebral oxygenation measured by near infrared spectroscopy.      

Randomized trial of bolus phenylephrine or ephedrine for maintenance of arterial pressure during spinal anaesthesia for Caesarean section

Thirty-eight healthy women undergoing elective Caesarean section under spinal anaesthesia at term were allocated randomly to receive boluses of either phenylephrine 100 micrograms or ephedrine 5 mg for maintenance of maternal arterial pressure. The indication for administration of vasopressor was a reduction in systolic pressure to < or = 90% of baseline values. Maternal arterial pressure (BP) and heart rate (HR) were measured every minute by automated oscillometry. Cardiac output (CO) was measured by cross-sectional and Doppler echocardiography before and after preloading with 1500 ml Ringer lactate solution and then every 2 min after administration of bupivacaine. Umbilical artery pulsatility index (PI) was measured using Doppler before and after spinal anaesthesia. The median (range) number of boluses of phenylephrine and ephedrine was similar; 6 (1-10) vs 4 (1- 8) respectively. Maternal systolic BP and CO changes were similar in both groups, but the mean [95% CI] maximum percentage change in maternal HR was larger in the phenylephrine group (-28.5 [-24.2, - 32.9]%) than in the ephedrine group (-14.4 [-10.6, -18.2]%). As a consequence atropine was required in 11/19 women in the phenylephrine group compared with 2/19 in the ephedrine group (P < 0.01). Mean umbilical artery pH [95% CI] was higher in the phenylephrine group (7.29 [7.28-7.30]) than in the ephedrine group (7.27 [7.25-7.28]). The results of the present study support the use of phenylephrine for maintenance of maternal arterial pressure during spinal anaesthesia for elective Caesarean section.      

Rachianesthésie pour césarienne : la vitesse d'injection a-t-elle une influence sur l'incidence de l'hypotension ?

OBJECTIVE: To study effect of injection rate on spinal blockade and haemodynamic of spinal bupivacaine for Caesarean section. STUDY DESIGN: Prospective and randomized. PATIENTS AND METHODS: Sixty ASA I-II patients scheduled for elective Caesarean section were randomized to receive either fast (20 seconds, group R, n=30) or slow (60 seconds, group L, n=30) spinal injection of 10 mg of hyperbaric bupivacaine 0.5% associated with 25 microg of fentanyl and 100 microg of morphine. Sensory and motor blockade and haemodynamic parameters were recorded. RESULTS: Profiles of sensory and motor block were similar in both groups. Variations of arterial blood pressure and total dose of ephedrine were not different between R and L groups. However, the number of patient with systolic blood pressure lower than 100 mmHg were significantly lower in L group than in R group (p=0.04). Incidences of adverse effects were similar in both groups. CONCLUSION: Result of the present study suggests that a slow rate of injection would induce lower incidence of hypotension induced by spinal bupivacaine for Caesarean section.     

Effect of delayed supine positioning after induction of spinal anaesthesia for caesarean section

BACKGROUND: The study tested the hypothesis that the incidence of hypotension during spinal anaesthesia for caesarean section is less in parturients who remain in the sitting position for 3 min compared with parturients who are placed in the modified supine position immediately after induction of spinal anesthesia. METHODS: Spinal anaesthesia was induced with the woman in the sitting position using 2.8 ml hyperbaric bupivacaine 0.5% at the L(3-4) or L(2-3) interspace. Ninety-eight patients scheduled for elective caesarean section under spinal anaesthesia were randomised to assume the supine position on an operating table tilted 10 degrees to the left (modified supine position) immediately after spinal injection (group 0, n=52) or to remain in the sitting position for 3 min before they also assumed the modified supine position (group 3, n=46). Isotonic saline 2-300 ml was given intravenously over 15 min before spinal injection followed by 15 ml/kg over 15-20 min after induction of spinal anaesthesia. If the systolic blood pressure decreased to less than 70% of baseline or to less than 100 mmHg or if there was any complaint of nausea, ephedrine was given in 5 mg boluses intravenously every 2 min. RESULTS: The blood pressure decreased significantly in both groups following spinal injection (P<0.001). Blood pressure variations over time differed significantly between the two groups (P<0.05). However, the incidence of maternal hypotension before delivery was similar in the two groups. The difference was caused by the time to the blood pressure nadir being significantly shorter in group 0 compared with group 3 (9.1+/-4.5 min vs. 11.7+/-3.7 min, P<0.01). Similar numbers of patients received rescue with ephedrine before delivery: 35 (67%) in group 0 vs. 26 (57%) in group 3 (NS). The mean total dose of ephedrine before delivery was 10.9 mg in group 0 vs. 9.2 mg in group 3 (NS). There were no differences in neonatal outcome between the two groups. CONCLUSION: At elective caesarean section, a 3-min delay before supine positioning does not influence the incidence of maternal hypotension after induction of spinal anaesthesia in the sitting position with 2.8 ml of bupivacaine 0.5% with 8% dextrose.     

Uteroplacental haemodynamics during spinal anaesthesia for caesarean section with two types of uterine displacement

The effects of two types of uterine displacement, on uterine and umbilical artery blood flow waveforms were investigated in 22 healthy parturients undergoing elective caesarean section. Displacement was accomplished with either a wedge under the right hip or a mechanical displacer plus 5 degrees left lateral tilt of the operating table. The first 14 patients were assigned randomly into one of the two displacement methods and the left (underlying) uterine and umbilical artery blood flow waveforms were recorded. In a further 8 patients the displacer was used and flow velocity waveforms for both the right and left uterine arteries and the umbilical artery were recorded. Arterial resistance was expressed in terms of the pulsatility index (PI). There were no significant changes in Doppler velocimetry recordings after preloading in either group, but blood flow velocity waveform indices for the underlying left uterine artery increased significantly (P < 0.001) following spinal anaesthesia when the mechanical device was used. This finding indicates increased vascular resistance in the left uterine artery and is probably due to mechanical compression. A wedge as a method for displacing the gravid uterus seems preferable since its use had no effect on the blood flow indices. The unaltered umbilical artery index values in the groups suggest a great tolerance of minor changes in maternal uterine circulation on the part of the fetus.     

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.     

Phenylephrine added to prophylactic ephedrine infusion during spinal anesthesia for elective cesarean section

BACKGROUND: Because ephedrine infusion (2 mg/min) does not adequately prevent spinal hypotension during cesarean delivery, the authors investigated whether adding phenylephrine would improve its efficacy. METHODS: Thirty-nine parturients with American Society of Anesthesiologists physical status I-II who were scheduled for cesarean delivery received a crystalloid preload of 15 ml/kg. Spinal anesthesia was performed using 11 mg hyperbaric bupivacaine, 2.5 microg sufentanil, and 0.1 mg morphine. Maternal heart rate and systolic blood pressure were measured at frequent intervals. A vasopressor infusion was started immediately after spinal injection of either 2 mg/min ephedrine plus 10 microg/min phenylephrine or 2 mg/min ephedrine alone. Treatments were assigned randomly in a double-blind fashion. The infusion rate was adjusted according to systolic blood pressure using a predefined algorithm. Hypotension, defined as systolic blood pressure less than 100 mmHg and less than 80% of baseline, was treated with 6 mg ephedrine bolus doses. RESULTS: Hypotension occurred less frequently in the ephedrine-phenylephrine group than in the ephedrine-alone group: 37% versus 75% (P = 0.02). Ephedrine (36+/-16 mg, mean +/- SD) plus 178+/-81 microg phenylephrine was infused in former group, whereas 54+/-18 mg ephedrine was infused in the latter. Median supplemental ephedrine requirements and nausea scores (0-3) were less in the ephedrine-phenylephrine group (0 vs. 12 mg, P = 0.02; and 0 vs. 1.5, P = 0.01, respectively). Umbilical artery pH values were significantly higher in the ephedrine-phenylephrine group than in the group that received ephedrine alone (7.24 vs. 7.19). Apgar scores were similarly good in both groups. CONCLUSION: Phenylephrine added to an infusion of ephedrine halved the incidence of hypotension and increased umbilical cord pH.     

Low-dose combined spinal-epidural anaesthesia vs. conventional epidural anaesthesia for Caesarean section in pre-eclampsia: a retrospective analysis

BACKGROUND AND OBJECTIVE: Epidural anaesthesia is the preferred technique of anaesthesia for Caesarean section in pre-eclampsia. Spinal anaesthesia is considered by some as a safe and effective alternative, which is especially useful in emergency situations. Combined spinal-epidural anaesthesia, using low doses of local anaesthetics with opioids, is effective and reduces the incidence of hypotension in normal pregnancy. We performed a retrospective chart analysis to evaluate the effects of combined spinal-epidural anaesthesia on maternal haemodynamics and fetal outcome compared to conventional epidural anaesthesia. METHODS: A retrospective anaesthesia chart analysis of all pre-eclamptic patients who underwent Caesarean section over a 4 yr period was performed. Patient characteristic, obstetric, haemodynamic, fetal and neonatal data were gathered and analysed according to the anaesthetic technique used. RESULTS: Seventy-seven pre-eclamptic parturients undergoing Caesarean section were identified (26 women were severely pre-eclamptic and 51 demonstrated mild pre-eclampsia). Epidural anaesthesia was performed in 62 patients and combined spinal-epidural anaesthesia was performed in 15. No differences in patient characteristic and obstetric data were noted. Highest mean arterial pressure prior to anaesthesia was comparable between the groups (epidural: 106 +/- 12 vs. combined spinal-epidural anaesthesia: 109 +/- 18 mmHg) as well as the lowest recorded mean arterial pressure following anaesthesia (epidural: 93 +/- 13 vs. combined spinal-epidural anaesthesia: 98 +/- 17 mmHg). In the combined spinal-epidural anaesthesia group more ephedrine was used compared to the epidural group (14.6 +/- 4.4 vs. 3.6 +/- 4.6 mg, P < 0.05). However, more lactated Ringer's was used in the epidural group. Umbilical artery pH was lower in the epidural group (7.26 +/- 0.01 vs. 7.29 +/- 0.02, P < 0.05). Similar results were noted in 26 severely pre-eclamptic patients. Seven women underwent combined spinal-epidural anaesthesia and 19 underwent epidural anaesthesia in the severely pre-eclamptic group. Also more ephedrine was used in the combined spinal-epidural anaesthesia group. A tendency towards a lower umbilical artery pH was observed in the epidural group but this difference did not reach statistical significance. CONCLUSIONS: Combined spinal-epidural anaesthesia appears to be safe as anaesthetic technique for pre-eclampsia and severe pre-eclampsia. However, it is important to consider the retrospective design of the study and the large number of epidural anaesthetics performed.     

Phenylephrine Added to Prophylactic Ephedrine Infusion during Spinal Anesthesia for Elective Cesarean Section

Background: Because ephedrine infusion (2 mg/min) does not adequately prevent spinal hypotension during cesarean delivery, the authors investigated whether adding phenylephrine would improve its efficacy.

Methods: Thirty-nine parturients with American Society of Anesthesiologists physical status I-II who were scheduled for cesarean delivery received a crystalloid preload of 15 ml/kg. Spinal anesthesia was performed using 11 mg hyperbaric bupivacaine, 2.5 [mu]g sufentanil, and 0.1 mg morphine. Maternal heart rate and systolic blood pressure were measured at frequent intervals. A vasopressor infusion was started immediately after spinal injection of either 2 mg/min ephedrine plus 10 [mu]g/min phenylephrine or 2 mg/min ephedrine alone. Treatments were assigned randomly in a double-blind fashion. The infusion rate was adjusted according to systolic blood pressure using a predefined algorithm. Hypotension, defined as systolic blood pressure less than 100 mmHg and less than 80% of baseline, was treated with 6 mg ephedrine bolus doses.

Results: Hypotension occurred less frequently in the ephedrine-phenylephrine group than in the ephedrine-alone group: 37%versus 75% (P = 0.02). Ephedrine (36 +/-16 mg, mean +/- SD) plus 178 +/-81 [mu]g phenylephrine was infused in former group, whereas 54 +/-18 mg ephedrine was infused in the latter. Median supplemental ephedrine requirements and nausea scores (0-3) were less in the ephedrine-phenylephrine group (0 vs. 12 mg, P = 0.02; and 0 vs. 1.5, P = 0.01, respectively). Umbilical artery p H values were significantly higher in the ephedrine-phenylephrine group than in the group that received ephedrine alone (7.24 vs. 7.19). Apgar scores were similarly good in both groups.     

Effect of lateral versus supine wedged position on development of spinal blockade and hypotension

Aortocaval compression may not be completely prevented by the supine wedged or tilted positions. It is commonly believed, however, that the unmodified full lateral position after induction of spinal anaesthesia might allow excessive spread of the block. We therefore compared baseline arterial pressures in the supine wedged, sitting, tilted and full lateral positions in 40 women who were about to undergo elective caesarean section. They were then given spinal anaesthesia in the left lateral position and randomised to be turned to the right lateral or the supine wedged position, after which speed of onset and spread of blockade to cold sensation were measured every 2 min for 10 min and mean arterial pressure and ephedrine requirement were recorded every minute for 20 min. Baseline mean arterial pressure was 9 mmHg (95% CI 3 to 14) lower in the left lateral (measured in the upper arm) than in the sitting position; those in the supine wedged and tilted positions were intermediate. Following spinal anaesthesia, hypotension (defined as a reading 相似文献