The value of color Doppler ultrasound in the prenatal diagnosis of hypoplastic umbilical artery

The prenatal diagnosis of hypoplastic umbilical artery has recently been reported, based on the visualization of discordant size between both umbilical arteries in association with discordant umbilical artery flow velocity waveforms. In this report we present two cases of hypoplastic umbilical artery and describe the use of color flow imaging and Doppler ultrasound in the prenatal evaluation of this condition. The principal advantages of these techniques include the confirmation of blood flow within the hypoplastic artery, thus ruling out the possibility of an atrophic non-functional artery, and the demonstration of size discrepancy at the level of the intra-abdominal portion of the umbilical arteries, validating the intra-amniotic cord findings. Color Doppler ultrasound is an important tool for diagnosing and evaluating vascular anomalies affecting the umbilical cord.

Doppler ultrasound screening as part of routine antenatal scanning: prediction of pre-eclampsia and intrauterine growth retardation

OBJECTIVE

To assess the value of incorporating continuous wave Doppler ultrasound of the uterine arteries into the routine scan as a screening test in an unselected population.

DESIGN

A cross sectional study by multiple operators using continuous wave Doppler ultrasound to obtain flow velocity waveforms (FVW) from both uterine arteries of all women attending for routine anomaly scan at 18 to 22 weeks over a period of 12 months. An abnormal FVW in either uterine artery was used to predict intrauterine death, antepartum haemorrhage and three different degrees of severity of pre-eclampsia and growth retardation, singly and in combination.

SETTING

King's College Hospital, London.

SUBJECTS

Two thousand, four hundred and thirty women attending for routine anomaly ultrasound scan.

RESULTS

A total of 2430 women were scanned with a 90% follow up rate. The results demonstrate higher sensitivities than previous studies, but with a high proportion of false positive tests. By including an early diastolic notch in the definition of an abnormal FVW the prediction of pre-eclampsia is markedly improved; the relative risk to a woman with an abnormal waveform of developing moderate or severe pre-eclampsia is increased 24-fold. Although the positive predictive value for babies less than the 5th centile for gestation is only 15%, those at risk of neonatal complications may be identified.

CONCLUSION

This simple test can be performed at a routine visit and a group of women can be identified for further assessment and possible therapeutic intervention.

Improved prediction of preeclampsia by two-stage screening of uterine arteries using the early diastolic notch and color Doppler imaging

OBJECTIVE

To assess the value of the early diastolic notch and color Doppler imaging of the uterine arteries at 24 weeks' gestation in a two-stage Doppler screening test for preeclampsia.

METHODS

Two thousand fifty-eight unselected women had an initial screening study with continuous-wave Doppler at 18-22 weeks' gestation. Color Doppler imaging was used at 24 weeks' gestation to examine both uterine arteries in 273 women with initial abnormal results (high resistance index or diastolic notch).

RESULTS

Three hundred twenty-nine women (16%) had abnormal flow velocity waveforms at the first stage and 104 (5.1%) at the second stage of Doppler screening. The presence of an early diastolic notch in the flow velocity waveform was significantly better than a high resistance index at predicting preeclampsia at both 20 and 24 weeks; the relative risk of developing significant preeclampsia for a woman with a persistent notch at 24 weeks was increased 68-fold. All women delivered before 34 weeks because of severe preeclampsia had abnormal waveforms at both stages of screening.

CONCLUSION

An early diastolic notch in the flow velocity waveform is a better predictor of preeclampsia than are conventional impedance indices. Preeclampsia can be predicted effectively by two-stage Doppler screening.

Antiplatelet and anticoagulant therapy

Antiplatelet therapy is clearly indicated for long-term secondary prevention after transient ischemic attack and ischemic stroke. In stroke-free patients with atrial fibrillation, oral anticoagulants reduce the risk of stroke, and antiplatelet agents may be a lower risk alternative. For the early treatment of the acute phase of ischemic stroke, the role of antiplatelet and anticoagulant therapy is unclear, but is being evaluated in large clinical trials.

Color Doppler imaging of the uterine artery in pregnancy: normal ranges of impedance to blood flow, mean velocity and volume of flow

In a cross-sectional study of 215 healthy women with singleton pregnancies at 18-42 weeks' gestation, color Doppler imaging was used to identify the main uterine arteries for subsequent pulsed Doppler studies. Flow velocity waveforms were obtained and indices of impedance, mean blood velocity and vessel diameter were measured, and the total volume of blood flow to the uterus was calculated. Impedance to flow decreased, I whereas blood velocity and volume flow increased significantly with gestation. Furthermore, impedance to flow was lower and velocity higher in the placental uterine artery, i.e. closest to the main bulk of the placenta, than in the non-placental artery.

Effects of different hepatic pathologies on disposition of alfentanil in anaesthetized patients

We have studied the influence of different hepatic pathologies on the disposition of alfentanil in 23 unpremedicated patients (six healthy control subjects, six patients with liver dysfunction of alcoholic aetiology and 11 patients with non-alcohol related liver disease). All patients received a bolus of alfentanil 500 micrograms i.v. as supplement to 67% nitrous oxide and isoflurane in oxygen anaesthesia. Plasma drug concentrations were measured in venous blood samples at intervals up to 24 h by radio-immunoassay and protein binding was determined by equilibrium dialysis. Kinetic estimates were determined using non-compartmental analysis. Patients with non-alcoholic liver disease had lesser plasma clearance (114.8 (range 66.8-213.5) ml min-1) than the alcoholic group (158.8 (100.0-220.7) ml min-1) or controls (187.4 (125.2-269.5) ml min-1). In all three groups, there was considerable intersubject variability, with a bimodal distribution in the non-alcoholic group. This group also had a smaller apparent volume of distribution at steady state. Mean residence time was prolonged in the alcoholic group compared with controls (284.9 (217.8-362.2) min vs 226.8 (201.2-250) min). Protein binding was decreased in the alcoholic group compared with controls (84.9 (SD 4.2)% vs 89.3 (2.1)%); this was attributable to a lesser plasma alpha 1-acid glycoprotein concentration (0.55 (0.18) g litre-1 vs 0.89 (0.21) g litre-1). Free drug clearance was reduced in both liver dysfunction groups compared with controls.

Doppler velocimetry studies of the uterine artery in the early prediction of pre-eclampsia and intra-uterine growth retardation

Pre-eclampsia/proteinuric pregnancy-induced hypertension (PPIH) and intra-uterine growth retardation (IUGR) are associated with incomplete trophoblastic invasion of the uterus in the first half of pregnancy. The uteroplacental circulation can be observed using Doppler ultrasound. We have performed two mid pregnancy screening studies of our antenatal population in the last three years, to assess the use of Doppler velocimetry studies at that time in predicting the subsequent development of PPIH and IUGR. In the first study continuous wave Doppler ultrasound was used to study the uterine circulation. The Resistance Index (RI) was measured once in both uterine arteries in 925 patients between 16 and 24 weeks gestation. There was a significant association between an abnormal RI (greater than 95th centile) and the subsequent development of PPIH, IUGR and severe complications of pregnancy. However, even though the specificity (95%) was high the sensitivity was low (25%). There was no significant association with nonproteinuric hypertension. In an attempt to improve the sensitivity for the second study, colour flow imaging and the use of a diastolic notch as well as an elevated RI were introduced. 2437 patients had continuous-wave Doppler studies of the uterine circulation performed at 20 weeks gestation. 16% had abnormal waveforms, persisting in 5.4% at 24 weeks and 4.6% at 26 weeks when measured with colour/pulsed Doppler. The high sensitivity (76%) of this innovation at 20 weeks is retained at 24 and 26 weeks, while the specificity (from 86% to 97%) and positive predictive value (13% to 44%) improve progressively with gestation.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma concentrations of bupivacaine following combined sciatic and femoral 3 in 1 nerve blocks in open knee surgery

We administered combined femoral 3 in 1 and sciatic nerve blocks to provide postoperative pain relief in 22 consecutive patients undergoing elective knee replacement surgery under spinal anaesthesia. The patients were allocated randomly to two groups. In group A (n = 11) the blocks were performed with 0.5% bupivacaine (with adrenaline) 3 mg/kg body weight and in group B (n = 11) 0.5% plain bupivacaine in the same dose was used. Serial plasma concentrations of bupivacaine were measured for up to 2 h and the duration of postoperative analgesia was measured in both groups. No significant differences were found between the two groups. There were no clinical signs or symptoms of bupivacaine toxicity in each group. This study demonstrated that, after combined sciatic and 3 in 1 femoral block, concentrations of bupivacaine associated with toxicity were not reached, even though the dose of bupivacaine administered exceeded the manufacturer's recommended dose by 50%.

Braxton-Hicks contractions can alter uteroplacental perfusion

Color flow imaging was used to study the effect of spontaneous low-amplitude uterine contractions (Braxton-Hicks) on flow velocity waveforms obtained from the main uterine artery in 13 women between 26 and 34 weeks' gestation. Eight women had abnormal waveforms, as defined by the presence of an early diastolic notch, and five women had normal waveforms. In the former group, three women with chronic hypertension were started on the calcium antagonist nifedipine during this study. Contractions, which were monitored by external tocography, occurred more frequently in the group with abnormal waveforms and were temporally associated with an increase in impedance to blood flow. This effect occurred to the same degree in both normal and abnormal groups, but in the abnormal group the already impaired blood flow to the intervillous space was further diminished, resulting in absence of forward flow in diastole. Such acute reductions of flow in response to frequent, impalpable uterine contractions may cause a prolonged and silent insult to uteroplacental perfusion, which could hasten fetal compromise. This effect appeared to be abolished in patients on nifedipine, suggesting a possible therapeutic role for this drug in uteroplacental insufficiency.

Middle cerebral artery flow velocity waveforms in fetal hypoxaemia

In 81 small-for-gestational age fetuses (SGA) colour flow imaging was used to identify the fetal middle cerebral artery for subsequent pulsed Doppler studies. Impedence to flow (pulsatility index; PI) was significantly lower, and mean blood velocity was significantly higher, than the respective reference ranges with gestation. Fetal blood sampling by cordocentesis was performed in all SGA fetuses and a significant quadratic relation was found between fetal hypoxaemia and the degree of reduction in the PI of FVWs from the fetal middle cerebral artery. Thus, maximum reduction in PI is reached when the fetal PO2 is 2-4 SD below the normal mean for gestation. When the oxygen deficit is greater there is a tendency for the PI to rise, and this presumably reflects the development of brain oedema.

Disposition of alfentanil in patients receiving a renal transplant

The disposition of alfentanil has been investigated in 10 anaesthetized patients with chronic renal failure undergoing kidney transplantation and compared with eight age matched anaesthetized patients with normal renal function. Plasma samples were collected to 660 min following intravenous administration of alfentanil 3-5 mg (50 micrograms kg-1). Drug concentrations were measured by RIA; and alfentanil binding to plasma proteins by equilibrium dialysis against 0.1 M phosphate buffer, pH 7.4. Alfentanil binding to plasma proteins was 87.6% (s.d. 2.0) in the patients with chronic renal failure, and 89.7% (1.2) in patients with normal renal function (P = 0.025). There was no correlation between alfentanil binding and plasma albumin, total plasma proteins, plasma urea or plasma creatinine concentrations. In both groups, the drug concentration-time profile decayed in a curvilinear manner; in the chronic renal failure patients, restoration of function did not influence the decay profile. Elimination half life, mean residence time and apparent volume of distribution at steady state were not different in the two groups of patients (mean values: 142.4 and 120.2 min; 128.5 and 136.0 min; and 40.5 and 27.6 L, respectively in chronic renal failure patients and patients with normal renal function). Total drug clearance and Vd area were significantly increased in the chronic renal failure patients: 341.9 vs 211.8 mL min-1; and 69.3 and 35.5 L. There were no differences in intrinsic clearance or apparent volume of distribution at steady state for unbound drug between the two patient groups.

Alfentanil for caesarean section complicated by severe aortic stenosis. A case report

Alfentanil 35 micrograms kg-1, was used successfully in a patient with severe aortic stenosis, in order to minimize the haemodynamic responses to intubation and surgery during Caesarean section. The baby was delivered apnoeic, unresponsive and with poor muscle tone, but responded rapidly to naloxone. Plasma alfentanil concentrations and percentage binding to plasma proteins were measured in both maternal and neonatal blood. Free drug concentrations were similar in both mother and neonate, but maternal plasma proteins had a higher affinity for alfentanil. Only 67.26% of neonatal plasma alfentanil was bound to plasma protein. This value did not differ significantly from those estimated from the blood of a further 12 healthy neonates.

Acute tolerance to fentanyl during anesthesia in dogs

The effect of fentanyl on increases in heart rate and mean arterial pressure elicited by electric stimulation of a branch of the radial nerve was studied in anesthetized, paralyzed, and artificially ventilated dogs. In one group, a bolus of 100 micrograms/kg of fentanyl depressed the evoked changes in heart rate and arterial pressure by 82 and 75%, respectively, by 5 min, and recovery occurred within 90 min. A second group was given increasing bolus doses of fentanyl from 1.5 to 100 micrograms/kg every 20 min for 200 min. The doses and intervals were chosen to give a logarithmic increase in plasma concentration of fentanyl to include a final bolus dose of 100 micrograms/kg and were predicted by a two-compartment pharmacokinetic model derived from data of the first group. In the second group, the bolus dose of 100 micrograms/kg after 5 min had no significant effect on evoked cardiovascular responses. Over the following 2 h, the evoked changes in heart rate and arterial pressure increased above those preceding the 100 micrograms/kg dose. An additional bolus dose of 100 micrograms/kg given 2 h after the first did not depress the evoked reflexes below the control values. It was concluded that tolerance to the effects of fentanyl can occur within 3 h and that for evoked responses to arterial pressure, rebound withdrawal effects can be seen within an additional 90 min.

Chemical modification and ligand binding studies with Escherichia coli glutamate synthase

The structure and function of Escherichia coli glutamate synthase were studied by ligand binding and chemical modification experiments. Binding of NADP+ was to a single dinucleotide site per alpha beta protomer with a Kd of approximately 5 microM. Phenylglyoxal modified an essential arginyl residue required for binding of NADP+. E. coli glutamate synthase thus employs a single dinucleotide binding site which functions in the NADPH to flavin electron transfer for glutamine-dependent glutamate synthase and for direct reduction of 2-iminoglutarate by NADPH in the NH3-dependent reaction. Binding of 2-oxoglutarate was complex. "Half of the sites" binding of 2-oxoglutarate (Kd less than 0.25 microM) was obtained in the absence of glutamine. Binding to half of the sites was pH independent. In the presence of glutamine, the 2-oxoglutarate binding ratio was approximately 1 equiv per protomer (Kd = 2-3 microM) at pH 7.5. This binding was pH dependent and varied between 0.43 equiv per protomer at pH 6.7 and 2.3 equiv per protomer at pH 9.0. Correlation of half of the sites binding with negative cooperativity for 2-oxoglutarate saturation indicates the utilization of low-Kd 2-oxoglutarate sites for NH3-dependent glutamate synthase. Binding of glutamine promotes a conformational change that exposes additional 2-oxoglutarate sites having a Kd of 2-3 microM which are utilized in the glutamine-dependent reaction. Chemical modification with pyridoxal 5'-phosphate caused inactivation of glutamine-dependent but not NH3-dependent glutamate synthase. Inactivation was ascribed to modification of one to two lysyl residues per protomer by Schiff base formation. The essential lysyl residue has a role in the binding of glutamine.

Comparative pharmacokinetics of fentanyl and alfentanil

The pharmacokinetics of fentanyl and alfentanil were compared by the simultaneous i.v. administration of both drugs, measurement of plasma concentrations and compartmental analysis. In addition, plasma protein binding, erythrocyte:plasma partition, and heptane:water partition were compared. Alfentanil was found to have a very much smaller apparent volume of distribution, smaller total clearance, and shorter terminal half-time in plasma. Alfentanil was also found to have a greater plasma protein binding, but in contrast to fentanyl, no binding to erythrocytes. It is concluded that alfentanil is less cumulative than fentanyl, has restricted hepatic clearance, and will exhibit non-linear kinetics at very high doses. An appendix describes the model-fitting procedure in detail.

The uptake of fentanyl by erythrocytes

Fentanyl passed rapidly into and out of erythrocytes to equilibrate with plasma concentration, and a red cell/plasma partition coefficient of 1.01 +/- 0.0083 s.e.m. was found in 15 normal subjects. Most of the binding of fentanyl by red cells was by haemoglobin. 10% was bound by the cell membrane. Partition was unaffected by haematocrit, pH, or the concentration of fentanyl up to 0.5 mg ml-1 of blood. Dilution of plasma proteins, and replacement of plasma by buffer showed that uptake of fentanyl by red cells is a linear function of the concentration of free drug in plasma. A partition coefficient for red cells/buffer of 4.91 +/- 0.032 s.e.m. was found. This relation was confirmed where binding to plasma proteins was altered in uraemia or hyperlipoproteinaemia, or by competitive displacement of fentanyl by aspirin and phenylbutazone thereby changing the size of the free fraction of fentanyl in plasma. Quinidine, however, inhibited the binding of fentanyl to plasma proteins and red cells equally, to maintain a partition coefficient of unity.

Plasma protein binding of fentanyl: the effect of hyperlipoproteinaemia and chronic renal failure

Hyperlipoproteinaemic patients with raised pre beta-, or pre beta- and beta-lipoprotein fractions showed a significant (P less than 0.001) increase in binding of fentanyl to whole plasma, compared with normal subjects. The presence of chylomicra had no significant effect on binding. In patients with chronic renal failure, a correlation of probability P less than 0.07 was found between percent binding and concentrations of pre beta-lipoprotein (P = 0.001), serum albumin (P = 0.0101), total protein minus albumin (P = 0.0576) and beta-lipoprotein (P = 0.0625). There was no significant correlation of binding with elevation of alpha- or gamma-globulins, with urea or creatinine concentrations, or with age or sex (P greater than 0.223). The magnitude of changes in the free fraction found in these patients should not produce a clinical effect as the total distribution volume of fentanyl exceeds 200 litres.

Plasma protein binding of fentanyl

Whole plasma of 15 normal volunteers bound 79·16% ± 0·16 s.e. (n = 45) of fentanyl, at a concentration of 0·6 ng ml−1. Measurement was by equilibrium dialysis at 37°C, pH 7·4. The largest contribution to binding appears to be due to serum albumin, since 45·52% ± 0·40 s.e. (n = 3) of fentanyl was bound to a solution of purified albumin at a concentration of 46 g litre−1 in buffer. Physiological concentrations of isolated very low density, low density and high density lipoprotein fractions in buffer bound 18·39% ± 0·65 s.e.; 39·14% ± 0·42 and 21·18% ± 0·51 (n = 15) respectively. A significant correlation was found between percent binding and serum albumin concentration (r = 0·745, P = 0·0022) and oestrogen and progestagen therapy (r = 0·766, P = 0·0014). There was no significant correlation with fasting serum cholesterol, triglyceride, age, sex or the concentration of total protein minus albumin. Binding to fibrinogen and α1-acid glycoprotein did not occur. Binding increased with increasing pH, temperature and ionic strength of the buffer. The results were compatible with hydrophobic bond formation between fentanyl and proteins. Fentanyl concentration did not affect the percent bound to whole plasma or the protein fractions over a range of 0·6 ng-10 mg ml−1. Dilution of plasma with buffer gave a linear relation of percent bound or free to log plasma dilution. The binding of fentanyl to pooled plasma of the normal subjects was not affected by a wide variety of anionic, cationic and uncharged drugs when these were tested at a concentration of 20 μg ml−1. At higher concentrations, aspirin, phenylbutazone and quinidine caused inhibition of fentanyl binding. A linear relation was found between percent bound and concentration of the inhibitory ligand. For aspirin, r = 0·873, P <0·01; for phenylbutazone, r = 0·81, P <0·05; and for quinidine, r = 0·982, P <0·01. Aspirin and phenylbutazone inhibited binding of fentanyl to albumin, while quinidine caused inhibition of binding to lipoproteins of all three densities, but not to albumin. Changes in the concentrations of the common ions of plasma (except H+), of free fatty acids and of creatinine did not affect fentanyl binding to whole plasma. 8 M urea reduced binding by 25% of the normal value.

Modification by monoamine oxidase inhibitors of the analgesic, hypothermic and toxic actions of morphine and pethidine in mice

A single injection of phenelzine 100 mg kg-1 given 18 h before, decreased the analgesia and hypothermia induced by morphine, but potentiated the analgesic and hypothermic effects of pethidine, when the analgesics were administered either intraperitoneally, or intracerebroventricularly. The modification of pethidine analgesia and hypothermia, but not morphine analgesia, was antagonized by methysergide (10 mg lg-1, s.c.). The LD50 of pethidine, but not that of morphine, was 30-40% lower in mice treated with phenelzine tranylcypromine or iproniazid 6 h before the test. The increased lethality of a single dose of pethidine induced by phenelzine was also prevented by methysergide. Pretreatment of mice with 100 mg kg-1 phenelzine was followed by a significant rise in both brain tryptophan and 5-hydroxytryptamine (5-HT) concentrations which lasted for 24 h. Therefore, the changes in pethidine effects could have been due to raised brain tryptophan and 5-HT concentrations.