Increasing Maternal Blood Pressure with Ephedrine Increases Uterine Artery Blood Flow Velocity during Uterine Contraction

Background: During labor, ephedrine is widely used to prevent or to treat maternal arterial hypotension and restore uterine perfusion pressure to avoid intrapartum fetal asphyxia. However, the effects of ephedrine on uterine blood flow have not been studied during uterine contractions. The purpose of the study was to assess the effects of ephedrine on uterine artery velocities and resistance index using the Doppler technique during the active phase of labor.

Methods: Ten normotensive, healthy parturients with uncomplicated pregnancies at term received intravenous ephedrine during labor to increase mean arterial pressure up to a maximum of 20% above their baseline pressure. Peak systolic and end-diastolic Doppler flow velocities and resistance indices were measured in the uterine artery before and immediately after administration of bolus intravenous ephedrine and after ephedrine washout. Umbilical and fetal middle cerebral arterial resistance indices and fetal heart rate were also calculated.

Results: After ephedrine administration, mean arterial pressure increased by 17 +/- 4%. End-diastolic flow velocity in the uterine artery at peak amplitude of uterine contraction was restored to 74% of the value observed in the absence of contraction. The systolic velocity was totally restored, and the uterine resistance index was significantly decreased, compared with the values in the absence of contraction. Between uterine contractions, ephedrine induced similar but less marked effects. Fetal hemodynamic parameters were not altered by ephedrine administration.     

Increasing maternal blood pressure with ephedrine increases uterine artery blood flow velocity during uterine contraction

BACKGROUND: During labor, ephedrine is widely used to prevent or to treat maternal arterial hypotension and restore uterine perfusion pressure to avoid intrapartum fetal asphyxia. However, the effects of ephedrine on uterine blood flow have not been studied during uterine contractions. The purpose of the study was to assess the effects of ephedrine on uterine artery velocities and resistance index using the Doppler technique during the active phase of labor. METHODS: Ten normotensive, healthy parturients with uncomplicated pregnancies at term received intravenous ephedrine during labor to increase mean arterial pressure up to a maximum of 20% above their baseline pressure. Peak systolic and end-diastolic Doppler flow velocities and resistance indices were measured in the uterine artery before and immediately after administration of bolus intravenous ephedrine and after ephedrine washout. Umbilical and fetal middle cerebral arterial resistance indices and fetal heart rate were also calculated. RESULTS: After ephedrine administration, mean arterial pressure increased by 17 +/- 4%. End-diastolic flow velocity in the uterine artery at peak amplitude of uterine contraction was restored to 74% of the value observed in the absence of contraction. The systolic velocity was totally restored, and the uterine resistance index was significantly decreased, compared with the values in the absence of contraction. Between uterine contractions, ephedrine induced similar but less marked effects. Fetal hemodynamic parameters were not altered by ephedrine administration. CONCLUSIONS: Bolus administration of intravenous ephedrine reversed the dramatic decrease in diastolic uteroplacental blood flow velocity and the increase in resistance index during uterine contraction, without altering fetal hemodynamic parameters. This suggests that the increase in uterine perfusion pressure during labor could in part restore uterine blood flow to the placenta during uterine contraction.     

Uterine and umbilical blood flow velocity during epidural anaesthesia for Caesarean section

The purpose of this study was to use colour Doppler to determine the effect of epidural anaesthesia on the uterine and umbilical blood flow velocities. After determining the precision of the technique, Doppler insonation of the uterine and umbilical arteries was performed in consenting non-labouring patients requesting epidural anaesthesia for Caesarean section. Patients in Group I were normal and those in Group II were at high risk for uteroplacental blood flow abnormalities. The pulsatility indexes (PI) of both uterine and umbilical arteries were compared at the following times: control, after fluid and after anaesthesia using repeated measure analysis of variance. In Group I (n = 30) the PI increased from 0.72 to 0.82 in the left uterine artery and from 0.71 to 0.85 in the right uterine artery (P < 0.05). In Group II (n = 10) the PI increased from 0.67 to 0.85 in the left uterine artery (NS) and from 0.98 to 1.38 in the right uterine artery (P < 0.05). There was no change in the PI in the umbilical artery. We conclude that the PI of the uterine arteries increases after epidural anaesthesia with lidocaine, epinephrine and fentanyl but there is no change in the umbilical PI. While these changes do not appear to be clinically important in the low-risk population, further studies are required to determine the impact on fetuses at high risk for in utero hypoxaemia.     

Increased placental expression of tissue factor is associated with abnormal uterine and umbilical Doppler waveforms in severe preeclampsia with fetal growth restriction

BACKGROUND: This study investigated whether modifications of placental expression of endothelin-1 (ET-1), nitric oxide synthase (NOS) and tissue factor (TF) are associated with abnormal Doppler waveforms. METHODS: Fourteen pre-term severe preeclamptic (PE) women with fetal growth restriction (FGR) and 14 normal preg nant women underwent serial Doppler examination of the uterine and umbilical arteries (UA). Placental ET-1 and T expression was evaluated by in situ hybridization, NOS by NADPH-diaforase staining and in situ hybridization Doppler evaluation was extended to 11 female kidney transplant recipients (Tx), without FGR and/or PE, in wh we previously demonstrated a strong modification of placental ET-1/NOS vasoactive balance. RESULTS: PE women showed a marked reduction of endothelial constitutive NOS (ecNOS) expression in the syncy tiotrophoblast layer of all villi, whereas ET-1 expression was unchanged. All cases showed abnormal uterine artery blood flow velocimetry, 13 out of 14 PE women showed abnormal UA Doppler waveforms. In contrast, all Tx women showed normal UA blood velocimetry, all but one woman displayed a normal uterine artery waveform pattern. The Doppler velocimetry abnormalities were significantly associated with only TF expression, which was markedly increased, exclusively, in the endothelial cells within the basal decidua of PE women. CONCLUSIONS: The modification of ET-1/NOS vasoactive balance, per se, did not lead to Doppler impedance modifica tions in the UA and uterine arteries, observed in pre-term PE women with FGR. Instead, Doppler velocimetry modi fications appeared to correlate with endothelial cell activation, as revealed by increased TF expression.     

Influence of poststenotic collateral pressure on blood flow velocities within high-grade carotid artery stenosis: differences between morphologic and functional measurements

PURPOSE: The driving force for blood flow through a high-grade stenosis in the internal carotid artery can be expressed as the pressure gradient over the stenosis itself, which, however, might be reduced by the back pressure exerted by distal collateral vessels. Theoretically the maximum blood flow velocity as a measure of the functional grade of obstruction may therefore be lower than what is expected from morphologic gradations of the stenosis. This study was designed to test prospectively the influence of intracranial collateral vessels on blood flow velocities within high-grade internal carotid artery stenoses. PATIENTS AND METHODS: Forty-five consecutive patients (age 66 +/- 11) with high-grade internal carotid artery stenoses were investigated before and during carotid endarterectomy. The preoperative investigations included duplex ultrasound scanning of the neck vessels, transcranial Doppler scanning for assessment of collateral flow to the middle cerebral artery and angiography. Carotid endarterectomy was performed with patients under deep general anesthesia without a shunt. Systolic and diastolic internal carotid artery blood pressures were measured before and during intraoperative cross-clamping (ie, stump pressure) of the carotid arteries. RESULTS: Within high-grade internal carotid artery stenoses, maximum systolic and end-diastolic blood flow velocities showed a significant inverse correlation to the corresponding systolic and diastolic stump blood internal carotid artery blood pressures. All patients with spontaneous collateral flow to the ipsilateral anterior part of the circle of Willis were divided into a group with relatively high and another one with low end-diastolic blood flow velocities. The stump pressure was significantly lower in patients with high end-diastolic blood flow velocities in spite of the fact that the mean angiographic grade of stenosis did not differ significantly between the groups. CONCLUSIONS: Flow velocities within a high-grade internal carotid artery stenosis are inversely dependent on the stump pressure, that is the poststenotic collateral perfusion pressure. This should be taken into consideration in case of discrepancies between angiography and ultrasound outcome.     

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

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

Umbilical artery Doppler velocimetry in the prediction of intrapartum fetal compromise.

The value of early intrapartum umbilical artery Doppler velocimetry in the prediction of fetal compromise was studied. One hundred patients were recruited into the study and fetal compromise was diagnosed by abnormal first- or second-stage fetal heart rate traces, a 5-minute Apgar score less than 7, or the development of hypoxic ischaemic encephalopathy. Fetal compromise developed in 30 patients. An umbilical artery resistance index (RI) of 0.66 or less did not predict fetal compromise (sensitivity 13%, specificity 89%, positive predictive value 25%, negative predictive value 70%). Since the mean umbilical artery RI was identical in the compromised and the non-compromised groups, we conclude that early intrapartum Doppler velocimetry is of very little clinical value in predicting fetal compromise at term.     

Single bolus compared with a fractionated dose injection technique of bupivacaine for extradural Caesarean section: effect on uteroplacental and fetal haemodynamic state

We studied 26 healthy parturients undergoing elective Caesarean section, allocated randomly to receive extradural block with 0.5% plain bupivacaine in a double-blind manner in either a single bolus or fractionated doses. After a 3-ml test dose, an additional 20 ml of bupivacaine were given over a 5-min period in the single bolus group (n = 13) and over a 25-min period in the fractionated dose group (n = 13). We studied the effects of bupivacaine on blood flow velocities in the maternal placental and non-placental uterine and fetal umbilical arteries before and four times during establishment of extradural block using a pulsed colour Doppler technique. Median sensory block reached T3 in the single-dose group compared with T4 in the fractionated-dose group. Two subjects in each group required i.v. ephedrine to correct transient hypotension (systolic arterial pressure < 90 mm Hg). Blood flow velocity waveform indices of the uterine and umbilical arteries did not differ significantly within or between groups during the study. There was no significant difference in neonatal outcome, as assessed by Apgar scores and umbilical artery pH values. In conclusion, we observed no deterioration in uteroplacental circulation after administration of a single bolus dose of bupivacaine.      

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.     

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.     

Value of transcranial Doppler examination in the diagnosis of cerebral vasospasm after subarachnoid hemorrhage

In 21 patients with subarachnoid hemorrhage secondary to ruptured intracranial aneurysms, we performed serial neurological evaluations, transcranial Doppler examinations, and cerebral blood flow (CBF) determinations. We classified 8 patients as having vasospasm (delayed neurological deterioration, appropriate reduction of CBF) and 13 patients as having no spasm on the basis of this information. Transcranial Doppler flow velocities in the middle cerebral artery and the anterior cerebral artery were significantly elevated for the group with vasospasm on posthemorrhage Days 4 through 12. Elevation of transcranial Doppler velocities preceded clinical signs of cerebral ischemia. The maximal transcranial Doppler flow velocities achieved were compared on the basis of the extent of clot on early computed tomographic (CT) scans. The mean anterior cerebral artery flow velocities were significantly different between CT Grades II and III. The initial transcranial Doppler flow velocities were compared on the basis of the patient's Hunt and Hess grade upon admission. The flow velocities for Grade V patients were significantly lower than those for Grade IV patients. Transcranial Doppler flow velocities were compared with arteriographically observed anterior cerebral artery and middle cerebral artery radii in 12 instances. The correlation was poor, but the data should be interpreted cautiously in view of the small number of arteriograms. We conclude that transcranial Doppler examination has considerable potential in the early diagnosis of delayed ischemic neurological deficit (clinical vasospasm) in patients with subarachnoid hemorrhage.     

The effects of continuous epidural analgesia on Doppler velocimetry of uterine arteries during different periods of labour analgesia

Background. The transient effects of epidural bupivacaine 0.25–0.5%on the Doppler velocimetry of umbilical and uterine arterieshad been reported, but the effects of continuous lower doseepidural bupivacaine (0.05–0.1%) infusion for labour analgesiahave never been reported. In this study, we evaluated the effectsof continuous epidural bupivacaine 0.075% on the Doppler velocimetryof uterine arteries. Methods. Twenty pregnant women for labour analgesia receivedcontinuous epidural bupivacaine 0.075% infusion. We used a 4-MHzcontinuous-wave Doppler probe (Multigon 500A) with a 200 Hzthump filter to detect uterine blood flow velocity. We recordedthe velocimetry data for uterine relaxation and contractionduring five time periods: pre-epidural insertion, 1, 2, and4 h post-epidural infusion, and after delivery of fetus. Results. Our data showed that the velocimetric indices of uterinevascular resistance were significantly increased 1, 2, and 4h after epidural infusion when compared with the pre-epidurallevel; these returned to the baseline after delivery. Conclusion. Continuous epidural analgesia with bupivacaine 0.075%increases the resistance of uterine artery and therefore possiblyreduces the uterine blood flow.     

The effect of nifedipine on fetal umbilical artery Doppler waveforms in pregnancies complicated by hypertension

The effect of nifedipine 5 mg administered sublingually to pregnant hypertensive patients was examined in a randomised controlled double-blind study. The effect on maternal blood pressure and the fetal umbilical artery Doppler waveform was studied for 30 minutes before and 30 minutes after administration of the drug or placebo. This dose resulted in a significant drop in maternal blood pressure 30 minutes after administration and did not result in a significant change in the Doppler umbilical artery waveform (in fetuses with normal waveforms) when compared with a control group.     

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.     

Multimodal quantitation of the effects of endovascular therapy for vasospasm on cerebral blood flow,transcranial doppler ultrasonographic velocities,and cerebral artery diameters

OBJECTIVE: The goal of this study was to quantify the effects of endovascular therapy on vasospastic cerebral vessels. METHODS: We reviewed the medical records for 387 patients with ruptured intracranial aneurysms who were treated at a single institution (University of California, Los Angeles) between May 1, 1993, and March 31, 2001. Patients who developed cerebral vasospasm and underwent cerebral arteriographic, transcranial Doppler ultrasonographic, and cerebral blood flow (CBF) studies before and after endovascular therapy for cerebral arterial spasm (vasospasm) were included in this study. RESULTS: Forty-five patients fulfilled the aforementioned criteria and were treated with either papaverine infusion, papaverine infusion with angioplasty, or angioplasty alone. After balloon angioplasty (12 patients), CBF increased from 27.8 +/- 2.8 ml/100 g/min to 28.4 +/- 3.0 ml/100 g/min (P = 0.87); the middle cerebral artery blood flow velocity was 1 57.6 +/- 9.4 cm/s and decreased to 76.3 +/- 9.3 cm/s (P < 0.05), with a mean increase in cerebral artery diameters of 24.4%. Papaverine infusion (20 patients) transiently increased the CBF from 27.5 +/- 2.1 ml/100 g/min to 38.7 +/- 2.8 ml/100 g/min (P < 0.05) and decreased the middle cerebral artery blood flow velocity from 109.9 +/- 9.1 cm/s to 82.8 +/- 8.6 cm/s (P < 0.05). There was a mean increase in vessel diameters of 30.1% after papaverine infusion. Combined treatment (13 patients) significantly increased the CBF from 33.3 +/- 3.2 ml/100 g/min to 41.7 +/- 2.8 ml/100 g/min (P< 0.05) and decreased the transcranial Doppler velocities from 148.9 +/- 12.7 cm/s to 111.4 +/- 10.6 cm/s (P < 0.05), with a mean increase in vessel diameters of 42.2%. CONCLUSION: Balloon angioplasty increased proximal vessel diameters, whereas papaverine treatment effectively dilated distal cerebral vessels. In our small series, we observed no correlation between early clinical improvement or clinical outcomes and any of our quantitative or physiological data (CBF, transcranial Doppler velocities, or vessel diameters).     

Partial amniotic carbon dioxide insufflation (PACI) facilitates fetoscopic interventions in complicated monochorionic twin pregnancies

Background Adequate visualization of the placenta or umbilical cord during fetoscopic procedures in complicated monochorionic twin pregnancies may be difficult because of placental position and spatial constraints, as well as stained amniotic fluid. Partial amniotic carbon dioxide insufflation (PACI) has made it possible to overcome these obstacles in other fetoscopic procedures, but its value has not yet been reported in monochorionic twins. Methods Partial amniotic carbon dioxide insufflation was carried out in five expectant women with complicated monochorionic twin pregnancies between 19 + 6 to 29 + 4 weeks of gestation when adequate fetoscopic visualization of pathological placental surface vessels or the umbilical cord was impossible because of stained or too little amniotic fluid. In four cases, five fetoscopic laser ablations of pathological placental vessels in twin-to-twin transfusion syndrome (TTTS) were performed. In one discordant twin pregnancy with TTTS, PACI was carried out in order to achieve umbilical cord ligation in a recipient with omphalocele and cardiac malformation. Results Partial amniotic carbon dioxide insufflation offered superior visualization and did not result in any acute maternal or fetal complications. After fetoscopic laser coagulation, three women delivered one fetus at 27 + 5, two fetuses at 28 + 6, and two fetuses at 35 + 4 weeks of gestation, respectively. One set of twins with TTTS was lost. Following umbilical cord ligation, the surviving twin was delivered at 37 + 2 weeks of gestation. Conclusions Partial amniotic carbon dioxide insufflation may facilitate fetoscopic procedures in complicated monochorionic twin pregnancies when conventional fetoscopic approaches within amniotic fluid meet difficulties. Further studies are required to allow assessment of benefits, risks, and safety margins of the new approach before it can generally be recommended.     

米非司酮联合吸宫术治疗剖宫产瘢痕部位妊娠的价值

目的探讨米非司酮联合吸宫术在剖宫产瘢痕部位妊娠(CSP)的治疗价值。方法回顾性分析24例CSP患者的临床表现和治疗结局。结果 24例患者均进行口服米非司酮片联合吸宫术,23例成功。1例施行子宫动脉栓塞术后,成功止血;孕囊在4.1cm×1.6cm以下患者出血量显著少于孕囊在4.1cm×1.6cm以上的患者,差异具有统计学意义(P0.05);停经天数60d以内患者出血量显著少于停经天数超过60d的患者,差异具有统计学意义(P0.05)。结论对于妊囊小、孕期短、血HCG值较低的患者可采用米非司酮联合吸宫术及时终止妊娠,可达到良好的治疗效果,为一种经济、简单,效果较好的治疗方式,但是考虑到大出血的可能,术前应做好应急实施子宫动脉栓塞术的准备。     

Effect of short-term physical exercise on foetal heart rate and uterine activity in normal and abnormal pregnancies

The response of a short-term submaximal bicycle ergometer test on foetal heart rate (FHR) and on uterine activity was studied in 61 pregnant women between pregnancy weeks 32 and 40. 28 of the women had uncomplicated pregnancies, 13 were hypertensive, 11 were diabetic, and 9 had intrahepatic cholestasis of pregnancy. After exercise, FHR declined in healthy subjects in pregnancy weeks past 35, whereas no significant change was found in such subjects before week 35 of pregnancy. Analysis of variance revealed a difference of FHR between subjects with umcomplicated and pre-eclamptic pregnancies in relation to time (p = 0.021). Exercise induced uterine contractions in hypertensive subjects. Foetal bradycardia was found in 2 healthy, in 2 pre-eclamptic, and in one cholestatic subject. In healthy pregnant women a non-reactive FHR with concomitant reduced FHR variability was found after exercise (P less than 0.01). The FHR variability of patients with pathologic pregnancies was less affected. These results suggest that, after a relatively strenuous short-term exercise, foetuses of mothers with uneventful pregnancies can be at risk of hypoxia in late pregnancy, but the clinical significance remains uncertain.     

Measurement of carotid bifurcation pressure gradients using the Bernoulli principle

Current randomized prospective studies suggest that the degree of carotid stenosis is a critical element in deciding whether surgical or medical treatment is appropriate. Of potential interest is the actual pressure drop caused by the blockage, but no direct non-invasive means of quantifying the hemodynamic consequences of carotid artery stenoses currently exists. The present prospective study examined whether preoperative pulsed-Doppler duplex ultrasonographic velocity (v) measurements could be used to predict pressure gradients (ΔP) caused by carotid artery stenoses, and whether such measurements could be used to predict angiographic per cent diameter reduction. Preoperative Doppler velocity and intraoperative direct pressure measurements were obtained, and per cent diameter angiographic stenosis measured in 76 consecutive patients who underwent 77 elective carotid endarterectomies. Using the Bernoulli principle (ΔP = 4v²), pressure gradients across the stenoses were calculated. The predicted ΔP, as well as absolute velocities and internal carotid/common carotid velocity ratios were compared with the actual ΔP measured intraoperatively and with preoperative angiography and oculopneumoplethysmography (OPG) results. An end-diastolic velocity of ⩾ 1 m/s and an end-diastolic internal carotid artery/common carotid artery velocity ratio of ⩾ 10 predicted a 50% diameter angiographic stenosis with 100% specificity. Although statistical significance was reached, preoperative pressure gradients derived from the Bernoulli equation could not predict actual individual intraoperative pressure gradients with enough accuracy to allow decision making on an individual basis. Velocity measurements were as specific and more sensitive than OPG results. ΔP as predicted by the Bernoulli equation is not sufficiently accurate at the carotid bifurcation to be useful for clinical decision making on an individual basis. However, end-diastolic velocities alone as well as internal carotid artery/ common carotid artery velocity ratios are highly specific in the prediction of clinically significant carotid stenoses. An end-diastolic velocity of ⩾ 1 m/s accurately identifies a 50% or greater diameter stenosis, and thus may in some cases be sufficient for operation.     

Monitoring middle cerebral artery blood velocity during carotid endarterectomy

Transcranial pulsed Doppler ultrasound and spectral analysis were used to monitor blood velocities in the middle cerebral artery of nineteen patients (mean age 61 +/- 9 years) during carotid endarterectomy. A Javid shunt was used in all patients. The intensity weighted mean Doppler frequency for each spectral sweep (at 5 ms intervals) was time-averaged over the cardiac cycle to obtain a mean value for blood velocity in the middle cerebral artery. The range of such values found in the 19 patients was: 12-38 cm s-1 after anaesthesia (baseline); 12-69 cm s-1 during diathermy; 0-30 cm s-1 during carotid clamping; 16-32 cm s-1 during shunting and 18-60 cm s-1 in the recovery room. The average change in middle cerebral artery blood velocity from baseline values showed significant increases during diathermy (P less than 0.005), shunting (P less than 0.05) and in the recovery room (P less than 0.005). Clamping of the internal carotid artery showed a significant decrease in middle cerebral artery blood velocities of all patients (P less than 0.005), three of whom showed no flow in the middle cerebral artery during clamping. Abnormally high amplitude Doppler signals at the commencement of shunting were detected in 17 of the 19 patients. Such Doppler signals are consistent with turbulent blood flow or the introduction of micro-air bubbles by the shunt. Backbleeding in the internal carotid artery before insertion of the shunt was associated with diminished flow in the ipsilateral middle cerebral artery of ten patients, oscillatory forward/reverse flow in three patients and cessation of flow in the remaining six patients.