Comparative effects of halothane, enflurane, and isoflurane at equihypotensive doses on cardiac performance and coronary and renal blood flows in chronically instrumented dogs.

In order to compare equihypotensive effects of the three available volatile anesthetics, halothane, enflurane, and isoflurane, dogs were chronically instrumented for measurement of: arterial, left ventricular, and left atrial blood pressures; rate of rise of left ventricular blood pressure; myocardial wall thickening (pulsed Doppler); cardiac output (pulmonary artery electromagnetic flow meter); and coronary and renal blood flows (pulsed Doppler flow meters). All three anesthetics were administered on different days in random order to each dog (n = 10) at doses necessary to decrease mean arterial pressure to 70 and 45 mmHg and two intermediate arterial blood pressures. Changes in cardiac function and regional blood flows were compared to the awake resting state and between anesthetics using analysis of variance and paired t tests. All three anesthetics produced increases in heart rate and decreases in left ventricular dP/dt, myocardial thickening fraction, and stroke volume with the hypotension. The decreases in cardiac performance were similar among the anesthetics except at the high dose (mean arterial pressure = 45 mmHg). During this profound hypotension, cardiac performance was better maintained during isoflurane anesthesia and most depressed by enflurane anesthesia. Coronary and renal blood flows were well preserved with all three anesthetics even at mean arterial pressures of 45 mmHg. Our results suggest that isoflurane may be more beneficial than halothane or enflurane for producing profound intentional hypotension (less than 50 mmHg mean arterial pressure), although extrapolation from animal experiments to the clinical situation should be used with caution.     

EFFECTS OF HALOTHANE AND SODIUM NITROPRUSSIDE ON RENAL FUNCTION AND AUTOREGULATION

The effects of sodium nitroprusside and halothane on renal autoregulationand kidney function were studied in 14 mongrel dogs at meanarterial pressures of 120, 100, 80, 60 and 40mm Hg. In group1, stepwise decreases in mean arterial pressure were achievedby increasing the halothane concentration In group II, meanarterial pressure was decreased by infusing sodium nitroprussideduring halothane anaesthesia. In group I, renal blood flow decreasedsignificantly at mean arterial pressures of 100, 80, 60 and40mmHg. In group II, renal blood flow was well maintained atmean arterial pressures of 100 and 80 mm Hg, but decreased significantlyat 60 and 40 mm Hg; at these low pressures flow was greaterin group II than in group I. There were no significant differencesbetween two groups in inulin clearance, inulin clearance/renalplasma flow, urine output, urine osmolanty and sodium excretionrate. Significantly larger fractions of cardiac output weredistributed to the kidneys in group I. ^*Present address: Department of Anaesthesia, Teikyo UniversitySchool of Medicine, Tokyo, Japan.     

Skeletal Muscle Oxygen Pressure Fields in Artificially Ventilated, Critically 111 Patients

The MDO (Mehrdraht Dortmund Oberfläche) oxygen electrode was used in a study of skeletal muscle oxygen pressure fields. presented as histograms, in critically ill patients artificially ventilated with gas mixtures of different oxygen concentrations. The histograms were compared with forearm blood flow measurements performed with strain gauge plethysmography. Local blood flow and permeability-surface area product (PS) were also studied by the simultaneous clearances of ¹³³xenon and ⁵¹ Cr-EDTA. The histogram distribution type was normal, i.e. approximately Gaussian, at arterial oxygen pressure levels between 10 and 18 kPa. At arterial oxygen pressures outside this range the histogram distribution types were abnormal, i.e. they showed a nonsymmetrical distribution of oxygen pressure values, but their mean was approximately the same as in the normal histogram. However, there were significantly higher tissue oxygen pressure mean values in the patients (3.43 kPa) than in a group of healthy human volunteers (2.25 kPa). Mean forearm blood flow and the clearances of ¹³³ xenon and ⁵¹ Cr-EDTA showed marked variations during the measurements both intraindividually and interindividually. Mean forearm blood now and mean clearances of¹³³ xenon showed opposite trends compared with arterial oxygen pressures. Mean clearances of ⁵¹ Cr-EDTA and mean PS showed only minor variations at the different arterial oxygen pressure levels.     

Effects of Isoflurane on Vascular Tone and Circulatory Autoregulation in the Feline Small Intestine

The vascular response in autoperfused small intestine was studied in ten cats during basal chloralose anaesthesia and controlled ventilation with either air, nitrous oxide/oxygen (70/30) or 0.7% end-tidal concentration of isoflurane + nitrous oxide/oxygen (70/30). Intestinal blood flow was measured by the optical drop recording technique, and intestinal perfusion pressure was kept constant at either 100, 75 or 50 mmHg (13.30, 9.98 or 6.65 kPa). At perfusion pressures of 100 and 75 mmHg (13.30 and 9.98 kPa), intestinal blood flow was significantly increased and intestinal vascular resistance decreased during isoflurane- + nitrous oxide/oxygen anaesthesia, compared with nitrous oxide/oxygen or air. According to the equation of closed loop gain (Gf), autoregulation was active in the pressure range 100-75 mmHg (13.30-9.98 kPa). In the pressure range 75-50 mmHg (9.98-6.65 kPa), the autoregulatory capacity was attenuated during air or nitrous oxide/oxygen and absent during isoflurane + nitrous oxide/oxygen. The vasodilator responses and the autoregulatory pattern were not changed by post-ganglionic intestinal denervation. The intestinal vasodilator effect of isoflurane was further investigated in the denervated intestine, perfused at systemic arterial pressure by local intra-arterial administration of isoflurane dissolved in a fat emulsion. A dose-dependent vasodilator response was hereby observed.     

The effect of age on cerebral blood flow during hypothermic cardiopulmonary bypass

Cerebral blood flow was measured in 20 patients by xenon 133 clearance methodology during nonpulsatile hypothermic cardiopulmonary bypass to determine the effect of age on regional cerebral blood flow during these conditions. Measurements of cerebral blood flow at varying perfusion pressures were made in patients arbitrarily divided into two age groups at nearly identical nasopharyngeal temperature, hematocrit value, and carbon dioxide tension and with equal cardiopulmonary bypass flows of 1.6 L/min/m2. The range of mean arterial pressure was 30 to 110 mm Hg for group I (less than or equal to 50 years of age) and 20 to 90 mm Hg for group II (greater than or equal to 65 years of age). There was no significant difference (p = 0.32) between the mean arterial pressure in group I (54 +/- 28 mm Hg) and that in group II (43 +/- 21 mm Hg). The range of cerebral blood flow was 14.8 to 29.2 ml/100 gm/min for group I and 13.8 to 37.5 ml/100 gm/min for group II. There was no significant difference (p = 0.37) between the mean cerebral blood flow in group I (21.5 +/- 4.6 ml/100 gm/min) and group II (24.3 +/- 8.1 ml/100 gm/min). There was a poor correlation between mean arterial pressure and cerebral blood flow in both groups: group I, r = 0.16 (p = 0.67); group II, r = 0.5 (p = 0.12). In 12 patients, a second cerebral blood flow measurements was taken to determine the effect of mean arterial pressure on cerebral blood flow in the individual patient. Changes in mean arterial pressure did not correlate with changes in cerebral blood flow (p less than 0.90). We conclude that age does not alter cerebral blood flow and that cerebral blood flow autoregulation is preserved in elderly patients during nonpulsatile hypothermic cardiopulmonary bypass.     

Cerebral blood flow during experimental epidural bleeding in swine

Summary Regional cerebral blood flow (rCBF) was studied during an aggressive epidural bleed, using a ventilated swine model. rCBF, regional organ blood flow and cardiac output were measured using the radioactive microsphere technique. Blood flows were measured prior to the start of bleeding (Stage 1), when intracranial pressures had reached a plateau and supratentorial perfusion pressure was reduced by about 50% (Stage 2), and at isoelectric EEG (Stage 3).Supratentorial rCBF did not change significantly between stages 1 and 2 while rCVR decreased, implying autoregulatory activity. Cerebral ischaemia developed between stages 2 and 3 when rCBF values fell to levels between 20 and 50% of control values. Infratentorial rCBF changes were similar but less marked, so that adequate brain stem perfusion was maintained below the upper mesencephalon.The left temporal and left parietal cortex and upper mesencephalon suffered a greater reduction in rCBF than other regions, due to proximity to the haematoma and tentorial herniation.The supratentorial pefusion pressure at stage 2 was 60 mm Hg associated with a haematoma volume of 6% of the intracranial volume (ICV). The infratentorial perfusion pressure never fell below 60 mm Hg.The Cushing response was absent when the EEG became isoelectric. This is tentatively ascribed to the absence of hypoxia, because mechanical ventilation was used. Instead systemic arterial hypotension accompanied bleeding in this ventilated model. This hypotension was due to falling cardiac output and peripheral vasodilation.     

Regional blood flow and tissue oxygen pressures of the collateral-dependent myocardium during isoflurane anesthesia in dogs

The authors investigated the effects of isoflurane on blood flow and tissue oxygen pressures of a collateral-dependent myocardium. Seventeen dogs divided into two groups were studied 3-4 weeks after implantation of ameroid coronary artery constrictors to completely occlude the proximal part of the left anterior descending artery. Experiments were performed during anesthesia with an opiate that was infused intravenously throughout the experiments. In Group 1 (n = 9), measurements were obtained during control and during isoflurane- (1.6-2.2 vol%) induced hypotension (mean arterial pressure, 60 mmHg). In Group 2 (n = 8), the identical protocol was applied, but norepinephrine was infused to maintain normotension. Dipyridamole effects were studied in five animals of Group 2 after a second control period at least 1 h after discontinuation of isoflurane. Isoflurane-induced hypotension caused reductions of blood flow and surface tissue oxygen pressures in the collateral flow-dependent area. Vasodilation in the normal left ventricular areas was demonstrated by an unchanged blood flow despite a reduced oxygen consumption and by a significantly increased coronary sinus hemoglobin oxygen saturation. When arterial pressure was maintained at its control level by norepinephrine, tissue oxygen pressures remained constant and collateral as well as normal area flow increased significantly during isoflurane. Coronary vascular resistance was lower during administration of isoflurane and norepinephrine compared with that during isoflurane induced hypotension, suggesting a significant contribution of tissue oxygen demand in regulation of coronary vascular resistance. At comparable levels of arterial pressure and left ventricular oxygen consumption, normal zone blood flow was significantly higher during dipyridamole than during isoflurane and norepinephrine. Thus, isoflurane-induced hypotension decreased blood flow and tissue oxygen pressures of collateral flow-dependent myocardial areas. However, neither isoflurane nor dipyridamole caused such alterations when arterial pressure was normal.     

The effects of ketamine and innovar on the renal cortical and medullary blood flow of the dog.

To study the effects of Ketamine and Innovar on renal function, the renal cortical and medullary blood flows of dog were measured using a thermo-electrical flowmeter, along with the urine output, blood pressure and pulse rate. Ketamine decreased the renal cortical blood flow and the urine output. Innovar increased the renal cortical blood flow, but did not alter the medullary blood flow appreciably, and decreased the urine output. Neither of these variations in renal blood flows ran parallel with variations in the arterial pressure nor did variations in the urine output run parallel with those in the blood flows. All anaesthetic agents are inhibitory to kidney, but Innovar may be preferred to other anaesthetics in view of the finding that the renal blood flows are well maintained even under anaesthesia with this agent.     

The effects of graded experimental trauma on cerebral blood flow and responsiveness to CO2.

The effects of graded mechanical cerebral trauma on cerebrovascular reactivity to CO2 was studied in 26 cats. A fluid-wave percussion model was employed which delivered an epidural trauma of fixed duration and variable amplitude. The animals were maintained at arterial normoxia, with constant monitoring of intracranial and systemic arterial pressures, electroencephalograms, and end-tidal CO2. Following trauma, cerebral blood flow was measured using the H2 ion clearance technique at PaCO2 levels ranging sequentially from 20 to 60 mm Hg. Cerebrovascular reactivity for control animals (uninjured) was 2.7%. In the group with mild trauma (0.76 to 1.90 atm) reactivity was impaired (1.7%), and it was abolished in the severely injured group (2.90 to 4.60 atm). Mild injuries did not alter resting blood flows, while severe trauma resulted in a significant decrease in cerebrovascular resistance. Intracranial and systemic arterial pressures were altered proportionately to the level of cerebral injury. The authors propose that trauma to the brain-stem vasoregulatory centers accounts for these findings.     

Pathophysiology of pulmonary edema following experimental brain death in the chacma baboon

Systemic and pulmonary hemodynamics have been studied during the induction of brain death in the chacma baboon. In 11 animals brain death was induced by acute intracranial hypertension. Continuous recording of blood flow through both the pulmonary artery and the aorta was obtained by electromagnetic flow meters placed around these vessels. Mean arterial, central venous, pulmonary arterial, and left atrial pressures were recorded continuously. Systemic and pulmonary vascular resistances were calculated. During the agonal period marked sympathetic activity occurred, with significant increases in circulating catecholamines and systemic vascular resistance. The great increase in systemic resistance resulted in acute left ventricular failure. Mean left atrial or pulmonary capillary wedge pressure rose above the mean pulmonary arterial pressure in 9 animals. As the systemic vascular resistance rose, a significant difference between pulmonary artery and aortic blood flows occurred, leading to blood pooling within the lungs. A mean of 72% of the total blood volume of the animal accumulated within these organs. The increase of left atrial pressure to levels higher than pulmonary artery pressure indicated a state of pulmonary capillary blood flow arrest. This, associated with the blood pooling within the lungs, almost certainly resulted in disruption of the anatomic integrity of the pulmonary capillaries (blast injury); 4 animals developed pulmonary edema, with alveolar septal interstitial hemorrhage.     

Skeletal Muscle Oxygen Pressure Fields in Healthy Human Volunteers: A Study of the Normal State and the Effects of Different Arterial Oxygen Pressures

The MDO (Mehrdraht Dortmund Oberfläche) oxygen electrode was used for studies of tissue oxygen pressure fields (presented as histograms) in healthy human volunteers breathing room air and gas mixtures with different oxygen concentrations. Forearm blood flow measurements were performed with strain gauge plethysmography, and local blood flow and permeability-surface area product (PS) were studied by the clearances of ¹³³xenon and ⁵¹Cr-EDTA. At ordinary arterial oxygen pressure levels the histograms were normal, i.e. their distribution type was approximately Gaussian. Higher arterial oxygen pressures caused changes in tissue oxygenation. However, at arterial oxygen pressure levels above 31 kPa two types of abnormal histogram distribution types were distinguished: scattered multi-population histograms (type a) and a type with predominantly low values (type b). Mean forearm blood flow showed only minor variations, whereas the clearances of ¹³³xenonand and ⁵¹Cr-EDTA were higher with higher PaO₂. A parallel increase was also seen in PS.     

A comparative clinical study on the effects of cardiopulmonary bypass with different flows and pressures on skeletal muscle cell metabolism in patients undergoing coronary bypass grafting

This study compares the effects of cardiopulmonary bypass with different flows and pressures on intracellular energy metabolism, acid-base equilibrium, and muscle water compartments in two groups of patients undergoing coronary artery bypass grafting. Eighteen patients (16 men and two women aged 54 +/- 7 years, New York Heart Association class I-II) undergoing low flow (flow rate 1.5 L/min/m2 at 26 degrees C), low pressure (mean arterial pressure 40 to 60 mm Hg) cardiopulmonary bypass, as well as 10 age-matched and sex-matched patients undergoing normal flow (flow rate 2.2 L/min/m2 at 26 degrees C), normal pressure (mean arterial pressure 60 to 80 mm Hg) bypass were studied. Intracellular acid-base equilibrium (intracellular pH and intracellular bicarbonate), cell energetics (adenosine triphosphate, diphosphate, and monophosphate, phosphocreatine, and lactate), and muscle water compartments were evaluated in specimens of the quadriceps femoris muscle obtained by needle biopsy before and at the end of cardiopulmonary bypass. In both the low flow-low pressure and normal flow-normal pressure groups, adenosine triphosphate levels were unchanged at the end of bypass, whereas phosphocreatine concentration was decreased; muscle total water and extracellular water increased without variations of intracellular water; muscle and plasma lactate increased as intracellular bicarbonate decreased; intracellular pH values remained unchanged. The present study suggests the following: (1) Cardiopulmonary bypass is associated with the overall preservation of intracellular compartment metabolism in skeletal muscle (about 40% of body cell mass) of patients undergoing coronary bypass grafting, even though low phosphocreatine values and increased plasma and muscle lactate values found at the end of bypass could be an expression of cell functional reserve exhaustion; (2) the effects of cardiopulmonary bypass on cell metabolism are comparable, regardless of the flows and pressures used.     

Changes in splanchnic circulation during an alveolar recruitment maneuver in healthy porcine lungs

Recruitment maneuvers (RM) are advocated as a complement to mechanical ventilation during anesthesia and in acute lung injury. However, they produce high intrathoracic pressures and volumes that may compromise hemodynamics. Our aim was to analyze the effect of a RM on hemodynamics in 10 anesthetized pigs. We assessed carotid, pulmonary, femoral, and hepatic arterial pressures, hepatic and portal venous pressures, total splanchnic (celiac trunk + superior mesenteric artery), hepatic, splenic, renal, and carotid arterial flows, and portal venous flow. We recorded hemodynamics, respiratory mechanics and blood gases before and at 8 min after RM (sustained inflation to 40 cm H(2)O of airway pressure lasting 20 s). Hemodynamics were also measured during RM, and at 1, 3, and 5 min after RM. All flows (P = 0.030) and arterial pressures (P < or = 0.048) decreased during RM, whereas venous pressures increased (P = 0.030). Flows and pressures returned to 75%-109% of baseline immediately after RM. Total splanchnic, renal and portal flows remained decreased at 8 min after RM (P < or = 0.042). Oxygenation did not change, and respiratory mechanics improved after the RM. RM produced a marked, though transitory, impairment of blood flow in all studied vessels. Despite prompt partial recovery, total splanchnic circulation remained reduced at 8 min after RM. This residual decrease may present a risk in conditions with markedly compromised circulatory reserves. IMPLICATIONS: Recruitment maneuvers (RM) produce high intrathoracic pressures and volumes that may compromise hemodynamics. We found a marked transient impairment of hemodynamics during a RM in 10 anesthetized pigs. At 8 min after RM, blood flow remained reduced in the celiac trunk, superior mesenteric, and renal arteries, as well as in the portal vein. This residual decrease may present a risk in conditions with markedly compromised circulatory reserves.     

The effects of nicardipine on dynamic cerebral autoregulation in patients anesthetized with propofol and fentanyl

We investigated the effects of nicardipine on dynamic cerebral pressure autoregulation in 13 normal adult patients undergoing gynecologic or orthopedic surgery. Anesthesia was induced and maintained with propofol and fentanyl. Hypotension to a mean arterial pressure of 60-65 mm Hg was induced and maintained with a continuous infusion of nicardipine. Time-averaged mean blood flow velocity in the right middle cerebral artery was measured continuously by using transcranial Doppler ultrasonography. The cerebral autoregulatory responses were activated by releasing thigh cuffs. The actual blood flow velocity in the right middle cerebral artery response to acute change in mean arterial pressure was fitted to 1 of 10 computer-generated curves to determine the dynamic rate of cerebral autoregulation (dRoR), and the best fitting curve was used. The autoregulation test was repeated until two values of dRoR were obtained at baseline and during induced hypotension. Nicardipine significantly reduced dRoR values of 13.1% +/- 3.6%/s at baseline to 8.3% +/- 2.6%/s during hypotension (P: < 0.01). During deliberate hypotension induced by nicardipine, the cerebral dynamic autoregulatory response is impaired in normal adult patients. IMPLICATIONS: During deliberate hypotension induced by nicardipine, the cerebral dynamic autoregulatory response is impaired in normal adult patients.     

Intraoperative hemodynamic measurements of the vertebral artery and common carotid artery

The hemodynamics in the vertebrobasilar artery (VBA) system were investigated in patients with vertebrobasilar insufficiency (VBI). Vertebral artery (VA) stump pressure and blood flows in the VA and common carotid artery (CCA) were intraoperatively measured in 45 patients who underwent surgical correction of the first segment of the VA (V1) for angiographic tortuosity, kinking, and/or stenosis manifesting as symptomatic VBI. The effects of changes in the systemic arterial blood pressure (SABP) induced by trimethaphan, phenylephrine, and cervical epidural anesthesia were also investigated. The VA stump pressure was 79.3 +/- 13.6 (mean +/- SD) mmHg and the ratio of the VA stump pressure to the SABP was 0.87 +/- 0.08. The baseline values were SABP 90.5 +/- 10.1 mmHg, VA blood flow 53.4 +/- 33.0 ml/min, and CCA blood flow 204.3 +/- 50.3 ml/min. During changes in the SABP, autoregulation of the blood flow in the VA appeared tighter than in the CCA. During cervical epidural anesthesia, blood flows in both the VA and CCA were significantly reduced in response to SABP reduction. This study demonstrated that the VBA system maintains excellent autoregulation with good collateral flows and cervical sympathetic nerve function. However, this autoregulatory capacity may be overwhelmed by unexpected occlusion of the VA due to postural changes associated with tortuosity, kinking, and/or stenosis of the V1 segment.     

Evidence of an autoregulatory mechanism of regional bone blood flow at hypotension

Background

Blood flow in various organs is determined by an autoregulatory mechanism that guarantees constant organ perfusion over a wide range of arterial blood pressure changes. This physiological principle has been proven for the kidney, brain and intestinal tract, but so far not for bone. This study was carried out to determine whether there is an autoregulatory mechanism of bone or not.

Methods

The fluorescent microsphere reference sample method was used to determine blood flow within the bone and kidneys. Eight anesthetized female New Zealand rabbits received left ventricular injections of fluorescent microspheres over a wide range of arterial pressure levels prior to removal of kidney, femur and tibia. Blood flow values were calculated by measurement of fluorescence intensity in kidney and bone and correlated to fluorescence intensity in the peripheral blood (reference sample).

Results

Despite a reduction of mean arterial pressure from 100 to 80 mmHg bone blood flow remained constant. Further reduction of mean arterial pressure results in a linear decrease in bone blood flow.

Conclusion

The correlation between arterial pressure and organ perfusion in the bone is similar to blood flow within the kidney, indicating the presence of an autoregulated blood flow mechanism within the bone tissue.     

The Effect of Halothane on the Distribution of Cardiac Output and Organ Blood Flows in the Hemorrhagic, Hypotensive Dog

Halothane was given to dogs which had been bled to an arterial mean blood pressure of 60 mmHg, and the circulatory effects were studied with the aid of the radioactive microsphere technique. The cardiac output and coronary blood flow were well maintained, whereas the arterial mean blood pressure was slightly, and the stroke volume markedly increased, indicating an improved heart function. The blood flows to the brain, lungs, liver and kidneys were well preserved throughout the anesthesia. The effect of retransfusing the withdrawn blood was also studied, and it resulted in an increased cardiac output, arterial mean blood pressure and increased blood flows to the heart, lungs, spleen, bowel and liver.     

Haemodynamic and organ blood flow responses to sevoflurane during spontaneous ventilation in the rat: a dose-response study

To determine the systemic haemodynamic and organ blood flow responses to the administration of sevoflurane during spontaneous ventilation, heart rate, cardiac index, mean arterial pressure, arterial blood gases, and blood flows to the brain, spinal cord, heart, kidneys and splanchnic organs were measured awake (control values) and after 30 min of anaesthesia with 0.5, 1.0, 1.2 or 1.5 MAC sevoflurane in rats. Cardiac output and organ blood flows were measured using radiolabelled microspheres. The MAC (mean +/- SEM) of sevoflurane was found to be 2.30 +/- 0.05%. At each concentration, haemodynamic variables were similar to awake values with the exception of a 12% reduction in mean arterial pressure at 1.5 MAC (P less than 0.01). Arterial PCO2 increased in a dose-related fashion. Cerebral and spinal cord blood flows increased at 1.2 and 1.5 MAC whereas coronary and renal blood flows did not change significantly. Portal tributary blood flow and preportal vascular resistance were unaffected. Hepatic arterial flow increased by 63% at 1.5 MAC (P less than 0.05) but total liver blood flow remained unchanged compared with awake values. In conclusion, the administration of sevoflurane during spontaneous ventilation produces a high degree of cardiovascular stability and maintains blood flow to major organs in the rat.     

Significance of retrograde diastolic uterine artery blood flow during regional anesthesia in instrumented pregnant sheep

Background: We studied the interactions between uterine and placental hemodynamics during maternal hypotension in chronically instrumented fetal sheep. In addition, we investigated maternal hemodynamic characteristics, fetoplacental hemodynamics and fetal acid–base status when a retrograde diastolic uterine artery blood flow pattern is present during maternal hypotension. Methods: Invasive maternal and fetal hemodynamic parameters, uterine (Q_UtA) and placental (Q_UA) volume blood flows and acid–base values were examined in 24 chronically instrumented sheep at baseline and during epidural‐induced maternal hypotension at 117–132 (term 145) days of gestation. Uterine artery blood flow velocity waveforms were obtained by Doppler ultrasonography. Results: Maternal hypotension decreased Q_UtA without affecting Q_UA. During hypotension, eight out of 24 sheep demonstrated a retrograde diastolic blood flow velocity waveform pattern in the uterine artery. Maternal systolic, diastolic and mean arterial blood pressures were significantly lower in the retrograde group than in the antegrade group. No statistically significant differences in Q_UtA, Q_UA and fetal blood gas values were detected between the two groups during hypotension. Conclusions: An acute decrease in uterine artery volume blood flow during maternal hypotension is not compensated by increased placental volume blood flow. A retrograde diastolic blood flow pattern in the uterine artery is related to lower maternal arterial pressures, especially during diastole. A uterine artery retrograde diastolic blood flow pattern does not have any additional detrimental short‐term effects on fetal acid–base status.     

Effects of celiac plexus block on splanchnic circulation--II: Changes in the systemic hemodynamics and the blood flow of the liver and kidney in dogs

Effects of celiac plexus block (CPB) on systemic and splanchnic circulation, especially of liver and kidney, were investigated in twenty nine mongrel dogs. CPB was performed by an anterior approach through a catheter placed in a paraaortic compartment using 7 mg.kg-1 of 2% mepivacaine. Tissue blood flow measurement was performed by a hydrogen clearance method in eleven dogs, and vascular blood flow was measured in eighteen dogs by an electromagnetic flow meter. Swan-Ganz catheter was inserted to measure mean arterial pressure (ABP), heart rate (HR), central venous pressure (CVP), mean pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP) and cardiac output (CO). Then stroke volume (SV), systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR) were calculated. Following CPB, ABP, HR, CVP and C.O. were significantly decreased at 7 to 9%. PAP decreased at 5%. PCWP, SV, SVR and PVR were unchanged. The hepatic arterial blood flow increased significantly, and portal venous blood flow decreased after CPB transiently, and then recovered to control value or to a higher level at 60min after CPB. The tissue blood flow of the liver tended to increase, but the change was not significant. In the kidney, both arterial and tissue blood flows increased significantly after CPB. The results suggest that following CPB, hepatic and renal tissue blood flows increased because of the increments of their arterial blood flows, unless a profound systemic hemodynamic depression occurred.