The effect on uteroplacental blood flow of epidural anaesthesia containing adrenaline for caesarean section

The effect on uteroplacental blood flow of an epidural anaesthesia containing adrenaline for caesarean section was investigated in ten healthy women using dynamic placental scintigraphy with indium-113m and a computer-linked gamma camera. The epidural anaesthesia was performed with 18-22 ml bupivacaine 5 mg/ml with adrenaline 2.5 micrograms/ml followed by an i.v. balanced electrolyte infusion of 10 ml/kg b.w. A significant median decrease in the total maternal placental blood flow of 34% was found (P less than 0.01). There was also a significant decrease in maternal mean blood pressure of 3 mmHg (0.4 kPa) (P less than 0.05) and a significant negative correlation between the change in maternal blood pressure and the change in uteroplacental blood flow (r = -0.69, P less than 0.05).     

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.     

UTEROPLACENTAL AND FETAL HAEMODYNAMICS DURING EXTRADURAL ANAESTHESIA FOR CAESAREAN SECTION

We have studied the effects of extradural anaesthesia with bupivacaine(plain) in eight healthy parturients undergoing elective Caesareansection, on blood flow in maternal uterine and placental arcuatearteries and in fetal umbilical, renal and middle cerebral arteries,using a colour Doppler technique. Simultaneously, fetal myocardialfunction was investigated by M-mode echocardiography. Maternaland fetal blood velocity waveform indices did not change significantly.We found no changes in fetal myocardial function with extraduralanaesthesia, except for an increase in the right ventricularinner end-diastolic dimensions. These results suggest that extraduralanaesthesia has no detrimental effects on uteroplacental andfetal circulations in the uncomplicated pregnancy when maternalhypotension is avoided with rapid prehydration.     

Anaesthesia and the sick foetus

The primary cause of foetal illness is placental pathology. The use of diagnostic ultrasound allows for a better understanding of how the foetus may be compromised by inadequate placental function. Anaesthesia affects placental function by changing uteroplacental and umbilical placental perfusion. Regional anaesthesia may have a beneficial effect on these circulations although general anaesthesia may be adapted to produce minimal disturbance of placental circulatory dynamics. The advantages and disadvantages of particular anaesthetic techniques in the delivery of the sick foetus are discussed.     

PLACENTAL BLOOD FLOW DURING CAESAREAN SECTION UNDER LUMBAR EXTRADURAL ANALGESIA

The effect on intervillous blood flow of lumbar extradural analgesiafor Caesarean section was studied in nine healthy women usingxenon-133. Extradural anaesthesia was performed with lignocaine1% 16–20 ml with adrenaline 6µg ml^–1. Impairmentof placental blood flow during the block was observed in sevenpatients, but the mean decrease (13% from the control value)was not statistically significant. The most notable decreasein intervillous blood flow occurred in two patients with simultaneousarterial hypotension.     

Ephedrine and phenylephrine for avoiding maternal hypotension due to spinal anaesthesia for caesarean section. Effects on uteroplacental and fetal haemodynamics

The effects of i.v. vasopressors on Doppler velocimetry of the maternal uterine and placental arcuate arteries and the fetal umbilical, renal and middle cerebral arteries were studied during spinal anaesthesia in 19 healthy parturients undergoing elective caesarean section. Fetal myocardial function was investigated at the same time by M-mode echocardiography. The patients were randomized into two groups, to be given either ephedrine or phenylephrine as a prophylactic infusion supplemented with minor boluses if systolic arterial pressure decreased by more than 10 mmHg from the control value. Both the vasopressors restored maternal arterial pressure effectively. The ephedrine group showed no significant differences in any of the Doppler velocimetry recordings relative to the baseline values, but during the phenylephrine infusion the blood flow velocity waveform indices for the uterine and placental arcuate arteries increased significantly and vascular resistance decreased significantly in the fetal renal arteries. Healthy fetuses seem to tolerate these changes in uteroplacental circulation well, however, since the Apgar scores for the newborns and the acid-base values in the umbilical cord were within the normal range in both groups. The results suggest that some caution is required when selecting the specific vasopressor agent, the dosage and the mode of administration for the treatment of maternal hypotension secondary to spinal anaesthesia for caesarean section.     

Cerebral blood flow, cerebral metabolic rate of oxygen and relative CO2-reactivity during craniotomy for supratentorial cerebral tumours in halothane anaesthesia. A dose-response study

Fourteen patients were studied during craniotomy for small supratentorial cerebral tumours. Cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) were measured twice by a modification of the Kety-Schmidt technique using 133Xe intravenously. Anaesthesia was induced with thiopental 4-6 mg kg-1, fentanyl and pancuronium, and maintained with an inspiratory halothane concentration of 0.45% in nitrous oxide 67% at a moderate hypocapnic level. In one group of patients (n = 7) the inspiratory halothane concentration was maintained at 0.45% throughout anaesthesia. About 1 h after induction of anaesthesia CBF and CMRO2 averaged 35 +/- 2 ml 100 g-1 min-1 and 2.7 +/- 0.3 ml O2 100 g-1 min-1 (mean +/- s.c. mean), respectively. During repeat studies 1 h later CBF and CMRO2 did not change. In another group of patients (n = 7) an increase in halothane concentration from 0.45% to 0.90% was associated with a significant decrease in CMRO2 from 2.3 +/- 0.1 to 2.0 +/- 0.1 ml O2 100 g-1 min-1. The CO2-reactivity measured after the second flow measurement was preserved. It is concluded that halothane in this study induces a dose-dependent decrease in cerebral metabolism, an increase in CBF while CO2-reactivity is maintained.     

Effect of spinal versus epidural anaesthesia with 0.5% bupivacaine on lower limb blood flow

Changes in the haemodynamics of the lower extremities, big toe temperature, blood pressure and heart rate were studied in 20 patients undergoing spinal or epidural anaesthesia for transurethral surgery. Calf blood flow was determined by strain gauge plethysmography (SGP) and Doppler ultrasound. Bupivacaine 0.5% was injected at the L3-L4 interspace, the dose being 3-4 ml (mean 3.6) in the spinal and 17-20 ml (mean 18.6) in the epidural group. The number of sensory blocked segments 30 min after anaesthesia was 12.7 +/- 0.7 (mean +/- s.e.mean) and 14.4 +/- 0.7, respectively. Only minor decreases in blood pressure were noted following the blocks. Heart rate remained virtually unchanged. The increase in skin temperature was more pronounced (P less than 0.01) following epidural (mean 8 degrees C) than spinal anaesthesia (mean 4 degrees C). In addition, the arterial blood flow was significantly higher (P less than 0.05) following epidural than spinal block (means 3.5 and 2.2 ml/100 ml/min, respectively). The venous capacity and maximum venous outflow remained practically unchanged in both groups. Obviously, epidural anaesthesia with bupivacaine causes a more intensive sympathetic block than does spinal anaesthesia. As probably no venous pooling occurred, when examined by SGP and Doppler ultrasound, neither of the blocks is likely to contribute to the initiation of deep vein thrombosis.     

Effect of crystalloid and colloid preloading on uteroplacental and maternal haemodynamic state during spinal anaesthesia for caesarean section

We have studied the effects of crystalloid 1 litre (lactated Ringer's) or colloid 0.5 litre (hydroxyethyl starch) preloading in 26 healthy parturients undergoing elective Caesarean section under spinal anaesthesia. Maternal placental uterine artery circulation was measured using a pulsed colour Doppler technique with simultaneous measurement of maternal haemodynamics. A high incidence of maternal hypotension was observed during spinal anaesthesia in the crystalloid group (62%) but the incidence was lower in the colloid group (38%). Central venous pressure was increased significantly in both groups after preload but decreased shortly after induction of spinal anaesthesia to baseline values. The mean pulsatility index (PI) in the uterine arteries did not change during preload or spinal block. A surprising finding was the widespread variation and some high values for the uterine artery PI after spinal anaesthesia. These individual increases in PI were transient and always returned to baseline values within 2 min. These results suggest that preloading with either solution is ineffective in preventing maternal hypotension and that changes in maternal heart rate, systolic arterial pressure and central venous pressure during spinal anaesthesia were not associated with rapid individual increases in uteroplacental vascular resistance. These changes seemed not to have any major effect, however, on the clinical condition of the newborn, as assessed by Apgar scores and umbilical artery pH values.      

Epidural vs general anaesthesia and leg blood flow in patients with occlusive atherosclerotic disease

Total leg blood flow (plethysmography), skin blood flow (laser-Doppler flowmetry), and haemodynamic stability (MAP, HR, RPP) were studied in vascular (ABI less than 1.0; n = 31) and in non-vascular (ABI greater than 1.0; n = 24) surgical patients during epidural or fentanyl-supplemented general anaesthesia. During epidural anaesthesia significant increases in total leg blood flow were observed in vascular (from 1.9 +/- 0.2 to about 3 ml/100 ml tissue/min) as well as in non-vascular (from 2.5 +/- 0.6 to about 7 ml/100 ml tissue/min) patients and leg blood flow remained high in the postanaesthetic period. During general anaesthesia total leg blood did not increase, either in vascular or in non-vascular patients, and in the postanaesthetic period blood flow values even lower than the initial ones were observed. Skin blood flow increased about 4-fold in vascular as well as in non-vascular patients following both types of anaesthesia. In the immediate postanaesthetic period low flow values were again observed but only in the general anaesthesia groups. In vascular patients no critical redistribution of blood flow within the limb was observed irrespective of the type of anaesthesia. Good haemodynamic stability could only be maintained in the epidural group. It is concluded that epidural anaesthesia seems to offer considerable advantages over general anaesthesia for high-risk vascular patients during arterial reconstructions since better haemodynamic stability and higher leg blood flow can be achieved.     

Validation in the sheep of an ultrasound velocity dilution technique for haemodialysis graft flow

BACKGROUND: A simple, rapid, inexpensive method for measuring the flow in a patient's vascular access would permit routine monitoring during haemodialysis, and hence provide information of access graft deterioration sufficiently early to increase the success of minimally invasive remedial procedures. This paper reports the validation of such a method in animals. METHODS: A PTFE graft was implanted in sheep between the carotid artery and the jugular vein. While the sheep was under general anaesthesia and on an haemodialysis circuit, ultrasound velocity in its blood was perturbed by the injection of a 5-10 ml bolus of isotonic NaCl. The pump tubing flow was measured by a transit-time blood flow meter. This flow was combined with the areas of perturbation generated by the injection before and after mixing in the access flow to estimate graft flow. The calculated graft flow was compared to flow measured directly by a transit-time probe on the same carotid artery. RESULTS: Over a 10-fold range, 120-1260 ml/min, graft flow measured by ultrasound velocity dilution agreed well with graft flow measured directly with a scatter of 76 ml/min about the regression line. CONCLUSION: Ultrasound velocity dilution provides a method for measuring flow in the graft accurate enough for clinical evaluation of patients on dialysis.      

Assessment of volume preload on uteroplacental blood flow during epidural anaesthesia for Caesarean section

BACKGROUND AND OBJECTIVE: Epidural and spinal anaesthesia are the preferred mode of anaesthesia for Caesarean section. Volume preloading is recommended to prevent maternal hypotension and a reduction in uteroplacental blood flow, although positive effects of volume preloading on maternal cardiac output and arterial pressure are debatable. Doppler measurements of the umbilical artery beyond deriving pulsatility indices are not routinely performed. METHODS: After Institutional Review Board approval and written informed consent, 14 consecutiVe women with epidural anaesthesia for Caesarean section received either hydroxyethyl starch 500 mL or gelatine 500 mL. Haemodynamic variables monitored were maternal arterial pressure, maximal blood flow velocity and pulsatility indices of the uterine artery derived from Doppler measurements. CONCLUSIONS: Maternal arterial pressure and pulsatility indices in both groups did not change from baseline after intravenous colloid infusion. However, uterine blood flow increased significantly in both groups. The effectiveness of volume preloading may therefore be better described by changes in maximum uterine blood flow velocity than by pulsatility indices or maternal arterial pressure.     

Correlation of EEG spectral entropy with regional cerebral blood flow during sevoflurane and propofol anaesthesia

ENTROPY index monitoring, based on spectral entropy of the electroencephalogram, is a promising new method to measure the depth of anaesthesia. We examined the association between spectral entropy and regional cerebral blood flow in healthy subjects anaesthetised with 2%, 3% and 4% end-expiratory concentrations of sevoflurane and 7.6, 12.5 and 19.0 microg.ml(-1) plasma drug concentrations of propofol. Spectral entropy from the frequency band 0.8-32 Hz was calculated and cerebral blood flow assessed using positron emission tomography and [(15)O]-labelled water at baseline and at each anaesthesia level. Both drugs induced significant reductions in spectral entropy and cortical and global cerebral blood flow. Midfrontal-central spectral entropy was associated with individual frontal and whole brain blood flow values across all conditions, suggesting that this novel measure of anaesthetic depth can depict global changes in neuronal activity induced by the drugs. The cortical areas of the most significant associations were remarkably similar for both drugs.     

Metabolic regulation of cardiac output during inhalation anaesthesia in dogs

BACKGROUND: The metabolic regulation of tissue blood flow manifests itself in a linear relation between blood flow and oxygen consumption, the latter being the independent variable. It is unknown, however, if this fundamental physiological principle operates also during inhalation anaesthesia known to be associated with decreases in both cardiac output (Q) and oxygen consumption (VO2). METHODS: Seven dogs (23-32 kg) with chronically implanted flow probes around the pulmonary artery were repeatedly anaesthetized with halothane, enflurane, isoflurane, sevoflurane, and desflurane at increasing minimum alveolar concentrations (1-3 MAC). Cardiac output (ultrasound transit-time flowmeter) and VO2 (indirect calorimetry) were measured continuously. We also imposed selective changes in Q, and thus of O2 supply, to see if and to what extent this would alter VO2 during anaesthesia (1.5 MAC). RESULTS: In awake dogs under basal metabolic conditions, VO2 was 4.6 +/- 0.1 ml.kg-1.min-1 and Q 105 +/- 3 ml.kg-1.min-1 (mean +/- SEM). During inhalation anaesthesia, VO2 and Q decreased by approximately 30% and 60%, respectively. The concentration-effect relations of both variables did not differ between anaesthetics, yielding a uniform Q/VO2 relation, which was nearly linear in the range (0-2 MAC) with an average slope of 39 +/- 1 (range 30-55). Above 2 MAC, Q decreased more for a given change in VO2, and O2 extraction increased by 50%, indicating compromised oxygen delivery (DO2). Imposed changes in Q, both in awake and anaesthetized dogs, yielded Q/VO2 relations which were notably steeper (slopes 114 to 187) than those observed during inhalation anaesthesia. More important, imposed increases in Q and thus DO2 during anaesthesia (1.5 MAC) to rates comparable to that in the awake state produced a much less than proportional increase in VO2 without restoring it to baseline. CONCLUSIONS: Inhalation anaesthesia is characterized by a uniform Q/VO2 relation with an almost linear course at an anaesthetic concentration up to 2 MAC, regardless of the anaesthetic. Metabolic regulation of blood flow apparently operates also during inhalation anaesthesia up to 2 MAC so that the decrease in VO2 determines Q. This implies that cardiac output alone provides little information on the function of the circulation during inhalation anaesthesia unless related to metabolic demands, i.e. to VO2.     

Influence of aortic blood flow velocity on changes of middle cerebral artery blood flow velocity during isoflurane and sevoflurane anaesthesia

BACKGROUND AND OBJECTIVE: We studied the influence of systemic (aortic) blood flow velocity on changes of cerebral blood flow velocity under isoflurane or sevoflurane anaesthesia. METHODS: Forty patients (age: isoflurane 24-62 years; sevoflurane 24-61 years; ASA I-III) requiring general anaesthesia undergoing routine spinal surgery were randomly assigned to either group. Cerebral blood flow velocity was measured in the middle cerebral artery by transcranial Doppler sonography (depth: 50-60 mm). Systemic blood flow velocity was determined by transthoracic Doppler sonography at the aortic valve. Heart rate, arterial pressure, arterial oxygen saturation and body temperature were monitored. After standardized anaesthesia induction (propofol, remifentanil, vecuronium) sevoflurane or isoflurane were used as single agent anaesthetics. Cerebral blood flow velocity and systemic blood flow velocity were measured in the awake patient (baseline) and repeated 5 min after reaching a steady state of inspiratory and end-expiratory concentrations of 0.75, 1.00, and 1.25 mean alveolar concentrations of either anaesthetic. To calculate the influence of systemic blood flow velocity on cerebral blood flow velocity, we defined the cerebral-systemic blood flow velocity index (CSvI). CSvI of 100% indicates a 1:1 relationship of changes of cerebral blood flow velocity and systemic blood flow velocity. RESULTS: Isoflurane and sevoflurane reduced both cerebral blood flow velocity and systemic blood flow velocity. The CSvI decreased significantly at all three concentrations vs. 100% (isoflurane/sevoflurane: 0.75 MAC: 85 +/- 25%/81 +/- 23%, 1.0 MAC: 79 +/- 19%/74 +/- 16%, 1.25 MAC: 71 +/- 16%/79 +/- 21%; [mean +/- SD] P = 0.0001). CONCLUSIONS: The reduction of the CSvI vs. 100% indicates a direct reduction of cerebral blood flow velocity caused by isoflurane/sevoflurane, independently of systemic blood flow velocity.     

A comparison of propofol and sevoflurane anaesthesia: effects on aortic blood flow velocity and middle cerebral artery blood flow velocity

We compared systemic (aortic) blood flow and cerebral blood flow velocity in 30 patients randomly allocated to receive either propofol or sevoflurane anaesthesia. Cerebral blood flow velocity (CBFv) was measured in the middle cerebral artery using transcranial Doppler. Systemic blood flow velocity (SBFv) was measured in the aorta using transthoracic Doppler sonography at the level of the aortic valve. Bispectral index (BIS) was used to measure the depth of anaesthesia. Measurements were made in the awake patient and repeated during propofol or sevoflurane anaesthesia, with BIS measurements of 40-50. The effects of SBFv on CBFv were estimated by calculating the cerebral/systemic blood flow velocity-index (CsvI). A CsvI value of 100 indicating a 1 : 1 relationship between CBFv and SBFv. The results demonstrated that propofol anaesthesia produced a significantly greater reduction in CsvI than did sevoflurane anaesthesia [propofol: 60 (19); sevoflurane: 83 (16), p = 0.009, t-test]. This suggests a direct reduction in CBFv independent of SBFv during propofol anaesthesia. The greater reduction of CBFv occurring during propofol anaesthesia may be due to lower cerebral metabolic demand compared with sevoflurane anaesthesia at comparable depths of anaesthesia.     

Spinal anaesthesia for obstetrics

For a long time, epidural anaesthesia has been considered the method of choice for Caesarean delivery. The increased incidence of hypotension by the rapid onset of sympathetic blockade under spinal anaesthesia has been associated with a decline in uteroplacental blood flow and significant fetal acidosis, which may compromise neonatal well-being. Nevertheless, a decrease in fetal pH has not been shown to reduce neonatal Apgar or neurobehavioural assessment scores. Maternal blood pressure can be preserved with little side effects with low doses of vasopressors. On the other hand, spinal anaesthesia conveys significant advantages over epidural anaesthesia such as the simplicity of its use and the speed of onset, which allows neuraxial anaesthesia in urgent Caesarean sections and thus reduces the necessity for general anaesthesia. The small doses of local anaesthetics required to perform spinal anaesthesia reduce the risks of systemic toxicity to zero. Spinal anaesthesia is now considered the method of choice for urgent Caesarean section. The use of intrathecal opioids has profoundly changed the quality of spinal anaesthesia, with improved analgesia, a reduction in local anaesthetic requirements and shorter duration of motor blockade. Preliminary studies indicate that spinal anaesthesia may be safely performed in patients with severe pre-eclampsia, in whom spinal anaesthesia was previously considered contraindicated.     

Cerebral blood flow, cerebral metabolic rate of oxygen and relative CO2 reactivity during neurolept anaesthesia in patients subjected to craniotomy for supratentorial cerebral tumours

In 10 patients subjected to craniotomy for supratentorial cerebral tumours in neurolept anaesthesia, cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) were measured twice peroperatively by a modification of the Kety & Schmidt technique, using 133Xe. The relative CO2 reactivity was assessed indirectly as the % change of the arteriovenous oxygen difference (AVDO2) per mm change in PaCO2. The patients were premedicated with diazepam 10-15 mg perorally. For induction, thiopentone 4-6 mg/kg, droperidol 0.2 mg/kg and fentanyl 5 micrograms/kg were used, and for maintenance N2O 67% and fentanyl 4 micrograms/kg/h. During the first flow measurement the median and range of CBF was 30 ml/100 g/min (range 17-45), of AVDO2 8.0 vol % (range 4.1-9.5), and of CMRO2 2.28 ml O2/100 g/min (range 1.57-2.84). During the second CBF study, AVDO2 increased to 9.3 vol % (range 3.4-11) (P less than 0.05), and CMRO2 increased to 2.51 ml O2/100 g/min (range 1.88-3.00) P less than 0.05, while CBF was unchanged. The CO2 reactivity was present in all studies, median 1.8%/mmHg (range 0.5-15.1). The correlation coefficients between jugular venous oxygen tension/saturation, respectively, and CBF were high at tensions/saturations exceeding 4.0 kPa and 55%, indicating that hyperperfusion is easily unveiled by venous samples from the jugular vein during this anaesthesia.     

The effect of plasma volume expansion on uteroplacental blood flow in hypertensive pregnancies

The effect of plasma volume expansion on uteroplacental blood flow was investigated in 20 hypertensive women in the 3rd trimester of pregnancy by measuring the radioactivity in the region of the placenta with a gamma camera after an intravenous injection of indium-113. Despite a significant increase in plasma volume there was no change in maternal blood pressure or in uteroplacental blood flow. This suggests an autoregulation of both blood pressure and uteroplacental blood flow.     

Effects of epidural anaesthesia on microcirculatory blood flow in free flaps in patients under general anaesthesia

It has been suggested that epidural anaesthesia may increase blood flow in free flaps on the lower extremity. The objective of the present study was to test this hypothesis in 21 patients undergoing reconstructive surgery of the lower extremity with free muscle (n = 8), fasciocutaneous (n = 6) or musculocutaneous (n = 7) flaps. Microcirculatory blood flow was measured continuously with a multichannel laser Doppler flowmetry, both in muscle and skin of the free flap as well as in the intact skin and muscle on the same extremity. After completion of surgery, general anaesthesia was continued and the epidural block was induced by an injection of 2% lignocaine-hydrochloride into a pre-operatively inserted and tested epidural catheter. The epidural block caused no change in microcirculatory flow in the intact skin and muscle, however, it resulted in a marked decrease in microcirculatory blood flow in all the free flaps studied (20-30%; P < 0.05). The epidural block also caused a significant decrease in mean arterial blood pressure, from 85 (+/- 2.8) mmHg to 68 (+/- 2.8) mmHg (P < 0.01). It was concluded that epidural anaesthesia may decrease microcirculatory blood flow in free flaps on the lower extremity by diverting flow away from the flap to normal intact tissues (a steal phenomenon).