Hypotension during subarachnoid anaesthesia: haemodynamic effects of ephedrine

We have compared the haemodynamic effects of ephedrine alonewith ephedrine and colloid for the treatment of hypotensionproduced by sub arachnoid anaesthesia in 30 patients aged 60–90yr with fractures of the neck of femur. Group one received ephedrineas an initial bolus dose of 0.2 mg kg^–1 followed by aninfusion of 0.5 mg kg^–1 h^–1. Group two receivedephedrine and colloid (polygeline, Haemaccel) 8 ml kg^–1.If necessary, up to three rescue bolus doses of ephedrine (0.1mg kg^–1 and then colloid solution (8 ml kg^–1 weregiven to maintain systolic arterial pressure (SAP) at > 75%of baseline. Arterial pressure was measured by automated oscillotonometry, central venous pressure (CVP) by a manometer andcardiac index (CI), stroke index (SI) and heart rate (HR) bytransthoracic electrical bioimpedance. Systemic vascular resistanceindex (SVRI) was derived. In patients receiving ephedrine only,SVRI, CVP and SI decreased and HR increased (P < 0.0001).Five patients in this group required colloid, the effect ofwhich was to restore CVP, increase CI and SI, and decrease HR(P < 0.02). In patients receiving ephedrine and colloid solution,SVRI decreased and CI, SI and HR increased (P < 0.0001).Ephedrine was not a potent arterial vasoconstrictor and SAPwas maintained mainly by increases in SI and HR.     

CARDIOVASCULAR EFFECTS OF A CHLORMETHIAZOLE INFUSION IN COMBINATION WITH EXTRADURAL ANAESTHESIA

The cardiovascular effects of an infusion of chlormethiazole30–40 ml min^–1 were studied in six patients followingan extradural injection of 2% lignocaine. There were small butstatistically significant decreases in mean arterial pressureand left ventricular ejection time during the infusion. Increasesin the pre-ejection period were noted, but there were no significantchanges in cardiac output, stroke volume or heart rate. Patientacceptance was high. It is concluded that sedation with an infusionof chlormethiazole, during surgery carried out under extraduralanaesthesia, has no clinically adverse cardiovascular effects.     

COMPARISON OF BUPIVACAINE AND BUPIVACAINE WITH FENTANYL IN CONTINUOUS EXTRADURAL ANALGESIA DURING LABOUR

In a randomized, double-blind study of 39 mothers in labour,we have compared a loading dose of 0.5% bupivacaine 6.0 ml andfentanyl 100 µg given extradurally, followed by an infusionof 0.08% bupivacaine 15 ml h^–1 plus fentanyl 37.5 µgh^–1, with a loading dose of 0.5% bupivacaine 6.0 ml andsaline 2.0 ml, followed by an extradural infusion of 0.08% bupivacainealone, per hour. Analgesic levels were more consistent and sustainedin mothers who received fentanyl in addition to bupivacaine,and the duration from the time of the loading dose to the firsttop-up was extended considerably in this group. The only significantside effect was a high incidence of mild pruritus in the fentanylgroup. The addition of fentanyl to the extradural loading doseand subsequent infusion of local anaesthetic is a satisfactoryalternative to giving higher doses of local anaesthetic alone.     

Postoperative extradural analgesia in children: comparison of morphine with fentanyl

We have compared the efficacy and side effects of extraduralmorphine with extradural fentanyl for postoperative pain relief.Thirty children (ages 1–16 yr) were allocated randomlyto receive, after extradural administration of 0.5% bupivacaine0.75 ml kg^–1 and before surgical incision, extreduralmorphine 0.75 µg kg^–1 (group M), with an additionaldose administered 24 h later or extradural fentanyl 2 µgkg^–1 (group F) followed by a continuous extradural infusion(during 48 h). There was no major complication (respiratorydepression). Pain scores were satisfactory in both groups for48 h. Ventilatory frequency was greater in group M 20, 21, 22,23 and 25 h after the beginning of analgesia (P < 0.05).Pruritus, nausea and vomiting were less common with extraduralfentanyl (20% vs 53%, P < 0.05 and 0% vs 33%, P < 0.05)than with morphine. Urinary retention occurred with equal frequency(25%) in the two groups. After a bolus of 2 µg kg^–1,continuous extradural infusion of fentanyl 5 µg kg^–1day^–1 provided analgesia comparable to that from a dailybolus of extradural morphine 0.75 mg kg^–1 and producedfewer side effects.      

HAEMODYNAMIC CHANGES DURING ANAESTHESIA INDUCED AND MAINTAINED WITH PROPOFOL

The haemodynamic effects of propofol, given as a single doseof 2 mg kg^–1 immediately followed by a continuous infusionof 6 mg kg^–1 h^–1, were studied in 10 elderly patientspremedicated with lorazepam 1 mg i.v. All patients breathedroom air spontaneously. Unconsciousness was successfully inducedin all patients and persisted during the 60 min of the infusion.Statistically significant decreases in systolic and diastolicarterial pressures were observed 2 min after induction (28%and 19% respectively) and during infusion (30% and 25% respectively)and were related to decreases in systemic vascular resistance(21% following induction and 30% during infusion). Cardiac outputwas not affected at any time nor were stroke volume and heartrate. We conclude that the arterial hypotension associated withthe induction and infusion of propofol is mainly a result ofa decrease in afterload without compensatory increases in heartrate or cardiac output.     

CARDIOVASCULAR SUPPORT DURING COMBINED EXTRADURAL AND GENERAL ANAESTHESIA

We have examined the effect of prophylactic treatment with i.v.fluid 1000 ml, ephedrine 24mg or methoxamine 4 mg on cardiovascularresponses to both extradural and combined extradural and generalisoflurane anaesthesia in 45 adult patients undergoing kneearthroplasty. Heart rate (HR) and systemic arterial pressure(AP) were measured using automated oscillotonometry and cardiacoutput was measured using continuous wave suprasternal Dopplerultrasonography. After lumbar extradural anaesthesia (LEA) therewere no significant differences in arterial pressure betweentreatments, although cardiac index was significantly greaterafter fluid preloading (mean 4.3 (95% confidence interval 3.7–4.9)litre min^–1 m^–2 than after ephedrine (3.1 (2.6–3.6)litre min^–1 m^–2 or methoxamine (2.6 (2.0–3.2)litre min^–1 m^–2 During combined LEA and generalanaesthesia, systolic AP was significantly greater after ephedrine(114 (103–125) mm Hg) than after either preloading (98(88–107) mm Hg) or methoxamine (97 (89–105) mm Hg).The reduction in AP after induction of general anaesthesia wasassociated with a decrease in cardiac index after fluid preloadingand a decrease in vascular resistance after methoxarnine.     

CONTINUOUS EXTRADURAL INFUSION OF 0.0625% OR 0.125% BUPIVACAINE FOR PAIN RELIEF IN PRIMIGRAVID LABOUR

The efficacy of an extradural infusion of 0.0625% or 0.125%bupivacaine was studied in 98 primigravid mothers in activelabour. No special measures were taken to posture the mother(except to avoid aorto-caval compression). The study regimenincluded a control group (no infusion) receiving intermittenttop-ups (0.25%. bupivacaine 8–10 ml), two groups receivingbupivacaine 6.25 mg h^–1 infusion in different concentrations(0.0625% and 0.125%), a fourth group receiving 0.125% bupivacaine12.5 mg h^–1 infusion, and a fifth group receiving 0.125%bupivacaine 18.75 mg h^–1 infusion. The optimum infusionrate was 0.125% bupivacaine 10 ml h^–1 at which 69% ofprimigravid mothers required none or only one "top-up" of 0.25%bupivacaine 8–10 ml during a mean duration of 7.1 h labour.In the group who had no extradural infusion, only 32% of mothersmanaged with one or no top-up. The median interval between top-upswas increased from 145 min in the no infusion group to 245 minin those mothers receiving 0.125% bupivacaine 10 ml h^–1by infusion. Increasing the rate of infusion to 15 ml h^–1did not improve the results. Spread of local anaesthetic tohigher levels was limited (< T5) so that testing sensoryloss at the T5–6 level at 2-hourly intervals should detectaccidental spinal blockade resulting from inadvertent intrathecalinfusion. ^* Present address: Department of Obstetrics and Gynaecology,University of Hong Kong, Hong Kong     

PHARMACOKINETICS OF PROPOFOL IN WOMEN UNDERGOING ELECTIVE CAESAREAN SECTION

We have compared the pharmacokinetics of a bolus induction doseof propofol 2 mg kg^–1 in 10 Chinese women undergoing electiveCaesarean section with those in six non-pregnant Chinese womenhaving laparoscopic sterilization. Blood propofol concentrationswere measured using high pressure liquid chromatography withfluorimetric detection. Pharmacokinetic data were analysed bya model independent method based on statistical moment theory.Data from the laparoscopy group also underwent compartmentalanalysis, which produced similar kinetic results. Non-compartmentalanalysis estimated that the women undergoing Caesarean sectionhad a similar elimination half-life (mean 81.27 (SD 18.87) min)and apparent volume of distribution at steady state (2.66 (0.63)litre kg^–1) as non-obstetric patients (99.45 (29.40) minand 3.36 (1.87) litre kg^–1). Clearance was more rapidin the Caesarean section group (39.32 (8.07) ml min^–1kg^–1 vs 29.40 (8.72) ml min^–1 kg^–1) (P <0.05). The increased total body clearance may result from bloodloss and delivery of the fetus and placenta at operation, althoughan increase in extrahepatic clearance is also possible ^*Department of Anaesthesia, North West Regional Health Authority,Manchester     

COMPARISON OF HYPERTONIC SALINE (5%), ISOTONIC SALINE AND RINGER'S LACTATE SOLUTIONS FOR FLUID PRELOADING BEFORE LUMBAR EXTRADURAL ANAESTHESIA

We have compared the haemodynamic effects of fluid preloadingperformed before lumbar extradural anaesthesia with isotonicsaline (NS), 5% hy-pertonic saline (HS) and Ringer's lactate(RL) solutions in 30 ASA I patients undergoing minor orthopaedicsurgery, allocated randomly to the three groups. All patientsreceived an equal amount of sodium (2 mmol kg^–1. Afterfluid preloading, lumber extradural anaesthesia was performed(2 % lignocaine 6 mg kg^–1) and ephedrine was administeredin order to maintain mean arterial pressure (MAP) > 80% ofits control value. Both volume and duration of fluid preloadwere significantly less in group HS (760 (SD 25) ml, 8.8 (SD2.9) min) than in the two other groups (NS: 903 (144) ml, 17.7(3.3) min; RL: 932 (166) ml, 212 (6.0) min) (P < 0.05). Thenumber of blocked segments and the total amount of ephedrineadministered were similar in the three groups. Heart rate increasedsignificantly in all groups immediately after the fluid preloadand remained increased until the end the study (90 min). MAPwas not affected by any fluid preload and its maximal decreaseafter lumbar extradural anaesthesia was similar in all groups.Infusion of 5% HS 2.3 ml kg^–1 was tolerated well and produceda significant (? < 0.05) but moderate hypernatraemia lasting90 min after the end of fluid preloading. We conclude that HSmay be useful when rapid fluid preloading is desired, in situationswhere excess free water administration is not desired. (Br.J. Anaesth. 1992; 69: 461–464) ^*Present address, for correspondence: Département d'Anesthésie–Réanimation,Hopital Saint–Camille, 2 Rue des Péres Camilliens,94366 Bry sur Marne Cedex, France.      

DISPOSITION OF PROPOFOL AT CAESAREAN SECTION AND IN THE POSTPARTUM PERIOD

We have compared the pharmacokinetics of a bolus dose of propofol2 mg kg^–1 in eight patients undergoing Caesarean sectionwith those in eight postpartum patients undergoing sterilizationby mini-laparotomy. The Caesarean section group had a totalbody clearance of (median) 31.5 (range 24.4–53.3) ml min^–1kg^–1, apparent volume of distribution at steady state5.10 (2.46–6.61) litre kg^–1 and mean residence time161 (52.3–251) min; values for the postpartum group were33.8 (21.5–47.2) ml min^–1 kg^–1, 5.17 (3.47–8.09)litre kg^–1 and 163 (92.3–238) min, respectively.The 95% confidence interval for the umbilical venous to maternalvenous ratio of propofol at delivery was 0.62–0.86. Plasmaprotein binding studies showed there was less unbound propofolin maternal plasma (1.28–2.29%) compared with umbilicalplasma (2.08–3.88%) (P<0.01). Neonatal concentrationsof propofol were greater than maternal concentrations at 2 hand were in the range 0.05–0.11 µg ml^–1 at4h.     

Uteroplacental and fetal haemodynamics and cardiac function of the fetus and newborn after crystalloid and colloid preloading for extradural Caesarean section anaesthesia

We have studied the effects of randomized preloading with eithera crystalloid (lactated Ringer's) 15 ml kg^–1 or colloid(hydroxyethyl starch) 7.5 ml kg^–1 solution in 20 parturientsundergoing elective Caesarean section under extradural anaesthesia,on blood flow in maternal placental and non-placental uterineand placental arcuate arteries and in fetal umbilical, renaland middle cerebral arteries, using a pulsed colour Dopplertechnique. Simultaneously, fetal and neonatal myocardial functionwere investigated by pulsed Doppler and M mode echocardiography.We found no changes in maternal or fetal blood velocity waveformindices after crystalloid preloading, but the pulsatility indexof the maternal non-placental uterine artery in creased significantlyafter colloid preloading. Fetal heart rate decreased after preloadingwith crystalloid solution. There were no differences in fetalor neonatal myocardial function between the groups, and theoutcome of the newborn infants were uneventful in all cases.These results suggest that preloading with either a crystalloidor colloid solution may lead to different uterine and fetalhaemodynamics but these solutions had only minimal effects onfetal and neonatal myocardial performance and no effect on theclinical condition of newborns in uncomplicated pregnancies.     

EXTRADURAL BUPIVACAINE AND METHADONE FOR EXTRACORPOREAL SHOCK-WAVE LITHOTRIPSY

Combined extradural bupivacaine and methadone analgesia wasinvestigated in 144 patients who underwent extracorporeal shockwave lithotripsy (ESWL). Patients were assigned randomly toone of three groups: group I—extradural 0.5% bupivacainehydrochloride 0.75 mg kg^–1; group II—extradural0.1% methadone hydrochloride 4 mg after the bupivacaine; groupIII—as group II, plus a continuous extradural infusionof methadone 0.3 mg h^–1 after operation. In all patients,only partial motor deficit occurred. During ESWL, patients whoreceived extradural bupivacaine and methadone had significantlyless pain compared with those who had bupivacaine alone (P <0.025). Extradural anaesthesia and immersion in the warm waterbath were accompanied by only mild fluctuations in arterialpressure. After ESWL, significantly more patients with continuousmethadone infusion were pain free (P < 0.05) and they requiredless systemic analgesics. The anaesthesia during and after theESWL procedure may be carried out safely and effectively bythe administration of small doses of bupivacaine combined withmethadone followed by infusion of the opioid. Presented at the American Society of Anesthesiologists AnnualMeeting, Atlanta Georgia, October 1987. This article is dedicated to the memory of Professor J. T. Davidson,who died during its preparation.     

Effect of intravenous vasopressor on spread of spinal anaesthesia and fetal acid-base equilibrium

Background: We previously found rostral spread of spinal plain levobupivacaineto be less with prophylactic i.v. phenylephrine than with ephedrineduring Caesarean delivery. This study investigated whether rostralspread of spinal hyperbaric bupivacaine is also less with phenylephrinethan with ephedrine. Methods: The study was randomized and double blind. It compared phenylephrine100 µg ml^–1 (phenylephrine group, n = 27), and ephedrine4.5 mg ml^–1 (ephedrine group, n = 27), given by infusionduring spinal anaesthesia for Caesarean delivery. Block heightwas assessed to cold and light touch sensation at 15, 30, 60,and 90-min after the spinal injection of 2.8 ml of hyperbaric0.5% w/v bupivacaine, combined with 0.4 ml diamorphine (1 mgml^–1). Umbilical blood gas values were monitored duringthe study. Results: Block height was similar for both groups at all of the assessmenttimes. Umbilical artery pH was higher with phenylephrine [median7.32 (IQR 7.28–7.34)] than with ephedrine [7.20 (7.10–7.28)](P < 0.0001). There was a strong negative correlation betweenumbilical artery pH and spinal-delivery interval, but only withephedrine: phenylephrine group, r² = 0.09 (P = 0.17), and ephedrinegroup, r² = 0.53 (P < 0.0001). Five-minute Apgar scores werehigher with phenylephrine [10 (9–10)] than ephedrine [9(9–9)] (P = 0.009). Conclusions: In contrast to its effect on spinal plain levobupivacaine, wedid not find rostral spread of spinal hyperbaric bupivacaineto be less with prophylactic phenylephrine than with ephedrine.We observed an unexpectedly high incidence of fetal acidosiswith ephedrine and found evidence that longer spinal-deliveryintervals increase the risk of fetal acidosis developing withephedrine, but not phenylephrine.     

CONTINUOUS EXTRADURAL ANALGESIA: COMPARISON OF MIDWIFE TOP-UPS, CONTINUOUS INFUSIONS AND PATIENT CONTROLLED ADMINISTRATION

We have compared three techniques used to provide extraduralanalgesia during the first stage of labour: 0.25% plain bupivacaine10ml demand top-ups delivered by the midwife; continuous infusionof 0.125% plain bupivacaine 10 ml h^–1 and patient-controlledextradural analgesia (PCEA) delivering 3-ml boluses of 0.25%bupivacaine. Each technique produced comparable analgesia achievingequivalent maternal satisfaction, with no difference in modeof delivery and no complications. This regimen for PCEA proveda viable alternative for continuous extradural analgesia andwas popular with the mothers, midwives and anaesthetists. ^*Present address: Department of Anaesthesia, Victoria Infirmary,Langside, Glasgow     

Equivalent dose of ephedrine and phenylephrine in the prevention of post-spinal hypotension in Caesarean section

Background. Comparative studies of ephedrine and phenylephrinein prevention of hypotension after spinal anaesthesia for Caesareansection have lacked a consensus on dose equivalence. The aimof this study was to determine the minimum vasopressor dosefor each of these drugs to calculate the dose ratio for clinicalequivalence in the prevention of hypotension. Methods. Patients with a normal singleton pregnancy beyond 36weeks gestation undergoing elective Caesarean section underspinal anaesthesia were randomized into two groups. The firstpatient in Group A received 50 mg of ephedrine in saline 0.9%w/v, 500 ml, at 999 ml h^–1, the maximum rate possibleon the pump and the first patient in Group B received 500 µgof phenylephrine in saline 0.9% w/v, 500 ml, at the same rate.The initial dose for dilution was an arbitrary choice. The doseof vasopressor in the saline bag for every subsequent patientwas established by the efficacy of the dose in preventing hypotensionin the previous patient according to the technique of up–downsequential allocation. Minimum vasopressor dose for each drugwas determined according to the Dixon–Massey formula. Results. The minimum vasopressor dose in saline 500 ml was 532.9µg (95% CI 506.0–559.8) for phenylephrine and 43.3mg (95% CI 39.2–47.3) for ephedrine. The concentrationneeded for equivalence at an infusion rate of 999 ml h^–1was 1.07 µg ml^–1 for phenylephrine and 86.66 µgml^–1 for ephedrine. Mean (SD) dose used for phenylephrinewas 496.45 (78.3) µg and for ephedrine 39.64 (6.33) mg. Conclusion. This study demonstrates a potency ratio of 81.2(95% CI 73.0–89.7) for equivalence between phenylephrineand ephedrine in prevention of hypotension after spinal anaesthesiafor Caesarean section.     

Randomized controlled study of colloid preload before spinal anaesthesia for caesarean section

We randomized women having elective Caesarean section to receiveeither no preload (control group, n=33) or 4% gelatin solution(Gelofusine) 15 ml kg^–1 (colloid group, n=35)i.v. before spinal anaesthesia. Intravenous metaraminol wastitrated at 0.25–0.75 mg min^–1 to maintainsystolic arterial pressure (SAP) in the target range 90–100%of baseline after the spinal injection. The control group requiredmore vasopressor in the first 10 min [median 1.7 (range 0–2.9)mg vs 1.4 (0–2.8), P=0.02] at a greater maximum infusionrate [0.5 (0–0.75) vs 0.25 (0–0.5) mg min^–1,P=0.0005] and had a lower minimum SAP [90 (51–109) vs101 (75–127) mm Hg, P=0.006] than the colloid group. Nauseawas less frequent in the colloid group (6 vs 24%) but neonataloutcome was similar in the two groups. Colloid preload improvedhaemodynamic stability but did not affect neonatal outcome whenarterial pressure was maintained with an infusion of metaraminolduring spinal anaesthesia for Caesarean section. Br J Anaesth 2001; 87: 772–4     

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     

EXTRADURAL ANALGESIA DURING LABOUR USING ALFENTANIL

Sixteen primiparous patients requesting pain relief during labourreceived a continuous infusion of alfentanil 30 µg kg^–1h^–1 via an extradural catheter. Supplementary (extradural)bolus doses {30 µg kg^–1) were administered whendeemed necessary. Excellent pain relief was rapidly obtainedearly in labour in all patients. However, analgesia was inadequatein the latter part of stage I and during the second stage infive of the 16 patients—notwithstanding several additionaldoses of alfentanil, and bupi-vacaine had to be administered.No serious maternal side-effects, except nausea, were en-countered.Although all neonatal Apgar scores were between 7 and 10, theAmiel-Tison test clearly indicated the existence of neonatalhypotonia. The continuous extradural administration of alfentanilproved to be unsatisfactory for pain relief in labour.     

HAEMODYNAMIC AND HEART RATE REFLEX RESPONSES TO PROPOFOL IN THE RABBIT: Comparison with Althesin

Propofol was administered to eight rabbits by constant i.v.infusion at 0.2, 0.4 and 0.6 mg kg^–1 min^–1 to producelight sedation. The lowest does was compared with an infusionof Althesin 0.1 mg kg^–1 min^–1. The rabbits had beenpreviously implanted with aortic and vena caval perivascularballoon cuffs to examine the baroreceptor-heart rate reflexand an aortic thermistor catheter for cardiac output (CO) measurements.A silastic catheter was placed in the pericardial sac so thatthe cardiac nerves could be blocked with local anaesthetic.Mean arterial pressure (MAP) was well maintained with all anaestheticinfusions. At the lower doses of propofol, CO increased by 20%(P < 0.01) with a corresponding decrease in total peripheralresistance (TPR). However, CO and TPR were not changed significantlyby Althesin. Bothanaesthetics induced a similar tachycardia.Cardiac nerve blockade did not abolish the different CO andTPR responses observed for the two agents. A dose-related reductionin the range and gain of the baroreceptor-heart rate reflexwas observed with propofol (P < 0.05). The pattern of alterationof the reflex curve, however, differed between the two anaestheticsand the vagal efferent component was more resistant to blockadewith propofol. The relative preservation of baroreceptor reflexresponses, and the reduction in TPR by a reduction of restingconstrictor tone, suggest propofol may have significant clinicaladvantages when used as a sedative infusion.     

Hypotension during subarachnoid anaesthesia: haemodynamic analysis of three treatments

We have compared three methods of preventing hypotension duringsubarachnoid anaesthesia. We attempted to maintain systolicarterial pressure (SAP) greater than 75% of baseline by useof i.v. fluids (preloading with normal saline 16 ml kg^–1and, if necessary, three subsequent boluses of 2.5 ml kg^–1),an infusion of metaraminol titrated as necessary between 0 and5 mg h^–1 and an infusion of ephedrine titrated as necessarybetween 0 and 120 mg h^–1. SAP and mean arterial pressure(MAP) were measured by automated oscillotonometry, central venouspressure (CVP) by a manometer and cardiac index (CI), strokeindex (SI) and heart rate (HR) by transthoracic electrical bioimpedance.Systemic vascular resistance index (SVRI) was derived. Fluidsalone failed to maintain SAP in five of 10 patients. AlthoughCI and CVP were maintained, SVRI decreased (25 (SD 15)%; P =0.02). Metaraminol maintained SAP in all 12 patients. The maincardiovascular change was decreased HR (15 (8)%; P = 0.0001).Ephedrine failed to maintain SAP in two of 12 patients and wasaccompanied by several cardiovascular changes: HR (21 (12)%;P = 0.001) increased and SI(16 (10)%; P = 0.0001), CVP (3.8(1.5) cm H₂O; P = 0.0001) and SVRI (24 (6)%; P = 0.0001) decreased.Treatment failures resulted from failures to maintain SVRI inthe fluid group and CVP and SVRI in the ephedrine group. (Br.J. Anaesth. 1994; 72: 151–155)