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.     

EFFECTS OF EXTRADURAL BUPIVACAINE WITH ADRENALINE FOR CAESAREAN SECTION ON UTEROPLACENTAL AND FETAL CIRCULATION

We have studied the effects of an extradural block using bupivacainewith adrenaline 90–100 µg on blood flow in the maternaluterine and placental arcuate arteries and the fetal umbilical,renal and middle cerebral arteries, using a colour Doppler techniquein eight healthy parturients undergoing elective Caesarean section.Fetal myocardial function was investigated simultaneously byM-mode echocardiography. Maternal heart rate increased and diastolicarterial pressure decreased after extradural administrationof bupivacaine with adrenaline. The latter effect was relievedby increasing the infusion rate in every case and none of thepatients required vaso-pressors. There were no significant differencesin maternal or fetal blood velocity waveforms, and no significantchanges were found in any of the fetal myocardial measurementsrelative to control values. These observations suggest thatextradural anaesthesia using bupivacaine with adrenaline doesnot have an adverse effect on vascular resistance in the uteroplacentalor fetal circulations or on fetal myocardial function in normalpregnancy when bupivacaine-adrenaline is administered fractionallyand maternal hypotension is prevented by rapid crystalloid volumeloading.     

EFFECT OF HIGH THORACIC EXTRADURAL ANAESTHESIA ON VENTILATORY RESPONSE TO HYPERCAPNIA IN NORMAL VOLUNTEERS

We have investigated, in six healthy male volunteers, the effectof high thoracic extradural anaesthesia on the ventilatory patternand hypercapnic ventilatory response. Ventilatory variableswere determined using a respiratory inductive plethysmograph.Duration of inspiration, rib cage excursion and its contributionto tidal volume decreased significantly following extraduralanaesthesia, while mean inspiratory flow rate and minute ventilationincreased. End-tidal PCO₂ and the tidal excursion of the abdomenwere unchanged. Hypercapnic ventilatory response decreased significantlyfollowing extradural anaesthesia, principally because of therib cage component. The slope of the abdominal component didnot change significantly. The results indicate that mechanicalimpairment of rib cage movement can produce decreased ventilatoryresponse to carbon dioxide. The ventilatory impairment and thechanges in breathing pattern induced by the high thoracic extraduralanaesthesia probably reflect blockade of the efferent or afferentpathway (or both) of the intercostal nerve roots.     

EXTRADURAL HAEMATOMA AFTER CONTINUOUS EXTRADURAL ANAESTHESIA

We report a case of extradural haematoma occurring after extraduralanaesthesia in an anticoagulated patient. The diagnosis wasconfirmed by magnetic resonance imaging and the haematoma wasevacuated surgically. A search of the literature revealed onlyfive previous reports of extradural haematoma in associationwith extradural anaesthesia.     

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.     

Effects of amniodistention with carbon dioxide on fetal acid-base status during fetoscopic surgery in a sheep model

BACKGROUND: Because the data from previous experiments on the fetal effects of carbon dioxide (CO2) amniodistention in endoscopic fetal surgery are conflicting, we set out to evaluate the fetal acid-base status during CO2 amniodistention, with or without maternal hyperventilation, using a sheep model for endoscopic surgery. METHODS: We assigned 26 pregnant ewes undergoing amniodistention with CO2 (4-5 mmHg intraamniotic pressure) to one of the following three groups: group I had fetal surgery + no maternal hyperventilation (n = 10); group II had fetal surgery + maternal hyperventilation (n = 10); group III had no fetal surgery + maternal hyperventilation (n = 6). Hyperventilation kept CO2 at 29-31 mmHg; in its absence, pCO2 ranged from 38 to 41. Fetal surgery consisted of fetoscopic tracheal clipping. Maternal blood pressure (mean, 98/69 mmHg) and heart rate (mean, 72 bpm) were kept at values comparable to human pregnancy. Fetal and maternal blood gas measurements were taken every 15 min during 1 h of amniodistention. RESULTS: The ranges for baseline mean fetal pCO2 (mmHg) and pH were 51-55 and 7.24-7.25, respectively, in all study groups. After 1 h of amniodistention, mean +/- SEM values of fetal pCO2 and pH were 88 +/- 3 and 7.06 +/- 0.03 in group I, 69 +/- 4 and 7.13 +/- 0.02 in group II, and 71 +/- 5 and 7.14 +/- 0.04 in group III, respectively. Therefore, maternal hyperventilation attenuated but could not prevent significant fetal hypercarbia and acidosis. Fetal surgical manipulation had no effect on these observations. CONCLUSION: CO2 amniodistention should not be considered for clinical practice until ways of preventing its effects on the fetal acid-base status can be demonstrated.     

The effects of regional anaesthesia for caesarean section on maternal and fetal blood flow velocities measured by doppler ultrasound

We studied the effects of spinal anaesthesia (Group S), epidural anaesthesia (Group E), and combined spinal and epidural anaesthesia (Group SE), on maternal and fetal blood flow in 24 healthy parturients (n = 8/group) with uncomplicated singleton pregnancies using Doppler technique. Prior to the induction of anaesthesia, the patients were prehydrated with balanced electrolyte solution 15 ml kg^-1 over a period of 15 min. After the induction of regional anaesthesia, the systolic blood pressure was maintained within 15% limits of the preoperative values using prophylactic etilefrine infusion in Groups S and SE. The flow velocity waveforms of the maternal femoral artery, the main branch of the uterine artery (placental side), the foetal umbilical and middle cerebral arteries were recorded by Doppler technique before and after prehydration as well as after onset of T7 analgesia and the pulsatility indices (PI) were derived. Rapid intravenous prehydration had no effects on uteroplacental or fetal circulation as indicated by unaltered uterine, umbilical, and fetal middle cerebral artery Pis. After the onset of T7 analgesia, the uterine artery PI was increased in Group S indicating increased uterine vascular resistance while no changes occurred in Groups E and SE. No adverse effects were observed on the neonates as indicated by the Apgar score and the umbilical artery and vein acid–base status in any of the groups.     

孕羊低温体外循环对胎羊血流动力学以及碳水化合物代谢的影响

目的 探讨孕羊低温体外循环(CPB)对胎羊血流动力学以及碳水化合物代谢的影响.方法 孕羊20头,随机分成对照组,开胸不建立体外循环;常温CPB组(35～36℃)、浅低温组CPB(32～34℃)和中低温CPB组(28～31℃),建立常规体外循环,转流降温、复温30 min.分别监测孕羊和胎羊的心率、平均动脉压、胎羊脐动脉和颈内动脉的搏动指数(pulse index,PI),孕羊与胎羊血糖、乳酸含量和HCO-3值的变化.结果 母羊和胎羊平均动脉压差异无统计学意义(P＞0.05).浅低温组和中低温组颈内动脉PI值较对照组和常温组显著增高(P＜0.05),脐动脉PI值组间差异无统计学意义,但随体外循环时间的延长而增高.血糖水平胎羊各组间差异无统计学意义(P＞0.05),但中低温CPB组中胎羊显著低于孕羊(P＜0.05).中低温CPB组胎羊血乳酸随时间延长有上升趋势(P＜0.05),而且显著高于孕羊(P＜0.05),但各CPB组间血乳酸差异无统计学意义.结论 孕羊低温体外循环降温时,胎羊心率明显下降,复温后胎羊心率能回复正常,体外循环对胎羊平均动脉压无明显影响,但低温降低胎羊脑部和脐动脉的血流;低温体外循环导致胎羊血糖水平降低,而血乳酸浓度显著增高.

Abstract：

Objective To evaluate effects of maternal hypothermic cardiopulmonary bypass on fetal homodynamic and carbohydrate metabolism. Methods Twenty pregnant sheep were divided into four groups randomly: control group(n=5),normothermic group (35-36℃)(n=5), mild hypothermic group(32-34℃)(n=5) and moderate hypothermic group (28-31℃)(n=5).Thoracotomy was performed without CPB in the control group. Routine CPB was established with different temperature in other three groups. The temperature of normothermic group was kept normal; the left two groups were cooled down to the set point of temperature and then rewarmed back to normal level. Fetal and maternal temperatures, heart rate,mean blood pressure(BP), pulse index (PI) of fetal umbilical artery (UA) and internal carotid artery (CA) were evaluated at cooling and rewarming stages. Biochemical indicators including blood glucose and lactic acid were also measured at the same time. Results There are no differences in mesn BP of ewas and fetal lambs between the different groups (P＞0.05). CA PI value of mild hypothermic group and moderate hypothermic group were significantly higher than those of control group and normothermic group (P＜0.05). There was no difference of UA PI in the four groups, but PI increased following the prolonged duration of CPB. There was no difference change of blood glucose in the four group of fetus, which was significantly lower than the ewe groups. An upward trend of fetal blood lactic acid with time was observed in three CPB groups. The whole level of fetal blood lactic acid was much higher than that of maternal blood of lactic acid. Conclusion Cooling of maternal bypsss decreases fetal heart rate significantly,and fetal heart rate recovered to base line following rewarming phase. There was no signicant effect of CPB on fetal mean BP. However, CPB impacted on the blood flow of fetal brain and umbilical artey. Hypothermia CPB can increase fetal blood glucose and blood lactic acid dramatically.     

The effect of ketamine anaesthesia on the acidotic fetal lamb

The following study in pregnant ewes was done to examine the effects of ketamine—oxygen anaesthesia on the fetal lamb made acidotic by partial occlusion of the umbilical cord. Fifteen pregnant ewes were instrumented under general anaesthesia to allow continuous measurement of maternal and fetal mean arterial pressure and pulse rate and for withdrawal of arterial blood samples for blood gas analysis. An occlusion loop was loosely secured around the umbilical cord. Following a recovery period of 48 hours, a tracheostomy was performed on each ewe. After a control period, the umbilical occlusion loop was slowly inflated until fetal pH had decreased to 7.12-7.15. Following inflation the animals were divided into groups A and B. Group A received no anaesthesia. In Group B, the ewes received ketamine 3mg·kg^-1 intravenously and controlled ventilation with F1O₂ of 1.0. After ten minutes ketamine 1 mg·kg_-1 was given. In both groups radioactive microspheres were injected into the fetus at 0, 5, and 15 minutes. Ketamine anaesthesia in the pregnant ewe abolished the fetal hypertension and bradycardia produced by partial cord occlusion. All fetuses survived the 15 minutes of ketamine anaesthesia and there were no significant changes in arterial blood gases or pH. Blood flows determined by the microsphere method to the brain, heart, and kidneys were not significantly altered by ketamine. We conclude that ketamine-oxygen anaesthesia does not cause further deterioration in the acidotic fetal lamb.     

Effect of ropivacaine and bupivacaine on uterine blood flow in pregnant ewes.

The effects of ropivacaine, a new amide local anesthetic, on uterine blood flow and fetal well-being were compared with those of bupivacaine in 10 chronically instrumented pregnant ewes. In random sequence, animals received two intravenous infusions of each drug. The low infusion rate regimens were chosen to result in clinically relevant maternal plasma concentrations of local anesthetics, whereas the more rapid rates of infusions were given to assess the safety of higher maternal drug concentrations. An epinephrine infusion was given to demonstrate the appropriateness of the animal model for the measurement of uterine blood flow. Maternal and fetal heart rates, arterial blood pressure, and the ewe's central venous pressure, intraamniotic pressure, and uterine blood flow were recorded continuously. Arterial blood samples were taken from mother and fetus at frequent intervals to determine acid-base status and local anesthetic concentrations. A total of 39 studies were performed. None of the infusions of either local anesthetic resulted in a significant decrease in uterine blood flow or deterioration in fetal condition. The mean maternal plasma concentrations at the end of infusions were as follows: ropivacaine low dose, 1.60 +/- 0.35 micrograms/mL; bupivacaine low dose, 1.55 +/- 0.15 micrograms/mL; ropivacaine high dose, 2.50 +/- 0.37 micrograms/mL; and bupivacaine high dose, 1.83 +/- 0.19 micrograms/mL. Epinephrine infusion resulted in a 25% decrease in uterine blood flow without adverse fetal effects. We conclude that neither ropivacaine nor bupivacaine, as administered in this study, led to any ill effects on uterine artery blood flow or fetal well-being.     

Comparative maternal, fetal, and neonatal effects of chloroprocaine with and without epinephrine for epidural anesthesia in obstetrics

The effects of epidural chloroprocaine with and without 1:200,000 epinephrine during labor and delivery on uterine activity, progress of labor, fetal heart rate, maternal blood pressure, newborn Apgar scores, neonatal acid-base status, and the Neurologic and Adaptive Capacity Scoring System (NACS) were compared in 28 parturients. Patients in group I (n = 14) received 2% chloroprocaine with 1:200,000 epinephrine and patients in group II (n = 14) received 2% plain chloroprocaine. Addition of epinephrine to chloroprocaine had no significant effects on uterine activity, duration of first or second stages of labor, or fetal heart parameters. Apgar scores, neonatal acid-base status, and the NACS were equally good in the two groups. Duration of analgesia was significantly longer in group I than in group II patients (76 +/- 3.8 vs 42.9 +/- 1 min, P less than 0.001). We conclude that addition of epinephrine to chloroprocaine during epidural anesthesia in the normal parturient has no adverse effects on mother, fetus, neonate, or the progress of labor and that it significantly prolongs the duration of anesthesia.     

UTEROPLACENTAL AND FETAL CIRCULATION DURING EXTRADURAL BUPIVACAINE-ADRENALINE AND BUPIVACAINE FOR CAESAREAN SECTION IN HYPERTENSIVE PREGNANCIES WITH CHRONIC FETAL ASPHYXIA

We have studied the effects of an extradural block during Caesareansection using either bupivacaine plain or with adrenaline 85–100µg on blood velocity waveforms of maternal uterine andplacental arcuate arteries and fetal umbilical, renal and middlecerebral arteries, in 20 hypertensive parturients with chronicfetal asphyxia. Fetal myocardial function was investigated atthe same time by M-mode echocardiography. Extradural anaesthesiaresulted in a significant decrease in maternal mean systolicand diastolic arterial pressures in both groups, but this wasmore marked after plain bupivacaine. There were no significantdifferences in any of the Doppler recordings relative to baselinevalues after plain bupivacaine, but after bupivacaine with adrenalinethere were significantly increased blood flow velocity indicesfor the maternal uterine and placental arcuate arteries andsignificantly decreased indices in the fetal renal and middlecerebral arteries. Neonatal outcome as evaluated by Apgar scoresand acid-base values in the umbilical cord were similar in thetwo groups. The results suggest that adrenaline added to thesolution of bupivacaine increased vascular resistance in theuteroplacental circulation, indicating impaired blood flow.     

ANAESTHESIA FOR CAESAREAN SECTION IN A PATIENT WITH EHLERS-DANLOS SYNDROME TYPE IV

We report the successful use of combined spinal and extraduralanaesthesia for elective Caesarean section in a primigravidpatient with Ehlers-Danlos type IV (EDS IV). EDS IV is a raredisorder with a high pregnancy-related mortality. Previous reportshave not addressed the question of anaesthesia for delivery.It is not possible to be didactic about anaesthetic techniquefor such patients. The relative risks of general and regionalanaesthesia must be discussed fully, and the risks weighed againstthe wishes of the woman and her partner. (Br. J. Anaesth. 1992;69:517–519)     

EXTRADURAL ANAESTHESIA FOR CAESAREAN SECTION IN ACHONDROPLASIA

We describe the successful management of a 26-yr-old achondroplasticdwarf undergoing elective Caesarean section under extraduralanaesthesia. The patient had marked thoraco-lumbar kyphoscoliosisand clinical features which suggested that tracheal intubationwould prove difficult. Block sufficient for surgery requiredonly 5 ml of 0.5% bupivacaine and, apart from an initial unilateralblock and mild intraoperative hypotension, her perioperativecourse was uneventful. ^* Present address: Department of Anaesthesia, Green Lane Hospital,Green Lane, Auckland, New Zealand.     

MATERNAL AND FETAL HAEMODYNAMIC EFFECTS OF SPINAL AND EXTRADURAL ANAESTHESIA FOR ELECTIVE CAESAREAN SECTION

Serial haemodynamic investigations were performed in 32 womenwho were allocated randomly to receive either spinal or extraduralanaesthesia for elective Caesarean section. Cardiac output wasmeasured by Doppler and cross-sectional echo-cardiography atthe aortic valve. Doppler flow velocity waveforms were recordedalso from the umbilical artery. Preloading with Ringer lactatesolution 1 litre increased cardiac output in both groups. Afterinjection of bupivacaine, cardiac output remained increasedin the extradural group, but decreased in the spinal group.This was associated with an increase in umbilical artery pulsatilityindex in the spinal group. Umbilical artery pH was less in thespinal group (7.22 vs 7.27). although no neonate was depressedat birth. The maximum percentage change in cardiac output andumbilical artery pulsatility index correlated with umbilicalartery pH (r = 0.54, r = 0.72, respectively). There was no significantcorrelation with change in arterial pressure.     

The effects of ephedrine and etilefrine on uterine and fetal blood flow and on fetal myocardial function during spinal anaesthesia for caesarean section

The effects of two vasopressors, ephedrine and etilefrine, on blood flow in maternal uterine, fetal umbilical, middle cerebral and renal arteries and on fetal myocardial function were studied by colour Doppler and M-mode echocardiography techniques during spinal anaesthesia for caesarean section. There were 7 healthy pregnant women in each treatment group. The vascular resistance of maternal uterine arteries increased significantly after both of the vasopressors while the vascular resistance of the umbilical artery remained unchanged. Ephedrine decreased the blood velocity waveform indices in the fetal middle cerebral and renal arteries, increased fetal right ventricular contractility and decreased left ventricular inner end-diastolic dimension. Fetal heart rate was unchanged. Etilefrine caused no detectable changes in fetal haemodynamics or in fetal myocardial function. These findings demonstrate that vasopressors administered for the treatment of minor maternal arterial pressure fall produce vasoconstriction in the uterine circulation during spinal anaesthesia, yet healthy fetuses seem to tolerate these haemodynamic alterations well. On the other hand, ephedrine caused changes in fetal myocardial function and in the vascular resistance of fetal middle cerebral and renal arteries, which demonstrates the potential modifying effect of vasoactive drug given to the mother on fetal haemodynamics.     

Verapamil: placental transfer and effects on maternal and fetal hemodynamics and atrioventricular conduction in the pregnant ewe

Verapamil may have application in the field of obstetrics for treatment of maternal and fetal tachyarrhythmias. This study was performed to assess the maternal and fetal hemodynamic effects of this drug, as well as to determine its placental transfer and effects on maternal and fetal atrioventricular conduction in the pregnant ewe. Verapamil, 0.2 mg/kg, administered intravenously over 3 min, resulted in a transient decrease in maternal mean and diastolic blood pressures. There was, however, no significant change in fetal systolic, diastolic, and mean blood pressures. Maternal and fetal heart rates also were unchanged throughout the experiment. Atrioventricular conduction, assessed by measurement of PR intervals, was prolonged in both the ewe (41%) and the fetus (78%). Placental transfer of verapamil was limited, as shown by the umbilical vein to uterine artery drug concentration ratios of 0.35-0.45 throughout most of the experiment. Fetal hepatic extraction of the drug appeared to be substantial, since the drug concentration in the fetal carotid artery was less than that of the umbilical vein at 1, 3, and 5 min after drug injection.     

Placental passage and uterine effects of fentanyl

Using the chronic maternal-fetal sheep preparation, 27 pregnant ewes were studied to determine the effects of intravenous fentanyl on maternal and fetal physiology, with particular reference to its placental passage, and its effects on uterine blood flow and uterine tone. Three doses of fentanyl were studied--50, 75, and 100 micrograms. Maternal and fetal arterial blood was collected for determination of fentanyl levels. All blood levels, both maternal and fetal, were normalized to the 50-micrograms dose. The maternal normalized blood levels were found to fit a biexponential equation describing a two-compartment open model. The half-life of the maternal elimination phase was 42 +/- 7.0 min with an overall elimination constant (K) of 0.21 min-1. Maternal plasma fentanyl levels decreased very rapidly in the first 10 min after injection, at which time only 9% of the peak value remained. Fentanyl was detectable in fetal blood as early as 1 min and levels peaked at 5 min. Once equilibrium was established between maternal and fetal blood, the maternal levels remained 2.5 times those of the fetal level from 5 min to 60 min after drug injection. Both maternal and fetal drug levels declined in an approximately parallel fashion. No significant deleterious changes were seen in any maternal or fetal cardiovascular or acid-base parameters, and uterine blood flow and uterine tone were also unaffected (P greater than 0.05).     

The placental transfer and fetal effects of levobupivacaine, racemic bupivacaine, and ropivacaine.

BACKGROUND: The purposes of this study were to assess the effects of levobupivacaine on uterine blood flow and fetal well-being and to compare its placental transfer with that of bupivacaine and ropivacaine. METHODS: After a control period, pregnant ewes that were fitted with instruments for long-term monitoring were randomized to receive a two-step intravenous infusion of levobupivacaine, bupivacaine, or ropivacaine, in a blinded manner, for 1 h. Maternal and fetal hemodynamics were monitored during the study. Arterial blood samples were drawn at 30 and 60 min of infusion from the mother and fetus to determine the acid-base status (60 min only) and serum drug concentrations. The fetal brain, heart, liver, lungs, adrenal glands, and kidneys were obtained to measure tissue drug levels. RESULTS: Maternal blood pressure, central venous and intraamniotic pressures, acid-base status and uterine blood flow were unaffected by any drug infusion. In contrast to the other two local anesthetics, the infusion of bupivacaine was associated with a small but significant decrease in the ewe's heart rate. At the end of the study, the heart rate in the bupivacaine-treated animals was significantly less than in the animals treated with the other two drugs. All fetuses were in good condition at the start of study, and none of the local anesthetics affected fetal well-being. No significant differences were found among the three drugs in the maternal serum, fetal serum, fetal tissue concentrations, and tissue:serum concentration ratios. CONCLUSIONS: Levobupivacaine was similar to bupivacaine and ropivacaine in causing no important hemodynamic changes in the pregnant ewe and fetus. There were no significant differences in the fetal serum and tissue levels of the drugs.