Intraoperative measurement of graft blood flow - a necessity in liver transplantation

Abstract Portal venous and hepatic arterial flow was measured intraop-eratively in the 70 most recent patients undergoing liver transplantation in our institution. Impaired graft flow due to vascular abnormalities was detected in six patients. One patient suffered from arterial steal due to stenosis of the recipient celiac trunk with blood shunting from the hepatic to the splenic artery. Ligation of the recipient hepatic artery restored the arterial graft flow. In two patients we found reduced portal venous flow due to large portosystemic collaterals. The collaterals accountable for the impaired portal flow were identified and ligated, which restored portal venous graft flow. Excessive sensitivity of the portal venous flow to the position of the graft was found in a 6-month-old boy. Portal venous flow varied considerably, depending upon the position of the graft, and intraoperative flow measurement allowed the best position of the graft to be identified. Two patients developed arterial thrombosis in the early postoperative course. Immediate laparatomy with thrombectomy resulted in good, palpable pulsation in the graft artery in both patients. Intraoperative flow measurement demonstrated satisfactory arterial flow in one patient, whereas there was no net flow in the other patient's graft artery. Pulsation in this patient was caused by blood oscillating in and out of the liver. In conclusion, we find that causes of primary graft dysfunction due to technically flawed reperfusion of the graft can be identified and alleviated by intraoperative measurement of the flow in the graft vessels.     

Intraoperative measurement of graft blood flow — a necessity in liver transplantation

Portal venous and hepatic arterial flow was measured intraoperatively in the 70 most recent patients undergoing liver transplantation in our institution. Impaired graft flow due to vascular abnormalities was detected in six patients. One patient suffered from arterial steal due to stenosis of the recipient celiac trunk with blood shunting from the hepatic to the splenic artery. Ligation of the recipient hepatic artery restored the arterial graft flow. In two patients we found reduced portal venous flow due to large portosystemic collaterals. The collaterals accountable for the impaired portal flow were identified and ligated, which restored portal venous graft flow. Excessive sensitivity of the portal venous flow to the position of the graft was found in a 6-month-old boy. Portal venous flow varied considerably, depending upon the position of the graft, and intraoperative flow measurement allowed the best position of the graft to be identified. Two patients developed arterial thrombosis in the early postoperative course. Immediate laparatomy with thrombectomy resulted in good, palpable pulsation in the graft artery in both patients. Intraoperative flow measurement demonstrated satisfactory arterial flow in one patient, whereas there was no net flow in the other patient's graft artery. Pulsation in this patient was caused by blood oscillating in and out of the liver. In conclusion, we find that causes of primary graft dysfunction due to technically flawed reperfusion of the graft can be identified and alleviated by intraoperative measurement of the flow in the graft vessels.     

Direct measurement of hepatic blood flow during living donor liver transplantation in children

Background

The changes in liver blood flow associated with living donor liver transplantation (LDLT) in children have not yet been studied. The aim of the present study was to investigate changes in hepatic hemodynamics before and after pediatric partial liver transplantation.

Methods

In 7 pediatric recipients with congenital cholestasis and native liver Child-Pugh classes B and C, portal vein flow (PVF) and hepatic arterial flow (HAF) were measured using an ultrasonic transit time flow meter before removal of the native liver and after transplantation and compared with donor left PVF and donor left HAF.

Results

The mean portal contribution to total hepatic blood flow was markedly decreased in the recipient native liver compared with that in the donor (69% ± 15% vs 32% ± 15%; P = .0003) and after reperfusion changed to almost the same ratio as that in the donor liver (73% ± 18%; P < .0001).

Conclusion

The extreme imbalance between PVF and HAF that is common in implanted partial liver in adult LDLT recipients was not observed in pediatric LDLT. After transplantation of an appropriately sized liver graft, the portal contribution to total liver blood flow normalized to the value for normal liver.     

Effects of lingual gestures on blood flow into the tongue: a pilot study

BACKGROUND: Reduced blood flow has been hypothesized to be a major factor in the formation of postradiation fibrosis. This study examined Doppler ultrasonography as a technique to detect changes in blood flow into the tongue during selected lingual gestures, /t/ and /k/. METHODS: Six normal subjects, three young men (mean age, 26 years) and three older men (mean age, 66 years) were examined in an upright position using Doppler ultrasound imaging of the external carotid artery just below the lingual artery. Measurements were made with a standardized segmentation technique before and after three repetitions of four speech production gestures /t/ and /k/, each with natural and maximal force. RESULTS: Blood flow peak systole increased significantly after the speech gestures (p < .001). Pooled before and after gesture values for older subjects were significantly lower than those for younger subjects (p < or = .05). CONCLUSIONS: Ultrasonography is a clinically useful technique for measuring blood flow during a dynamic gesture and may be useful for measuring effects of tumor treatment and in a lingual exercise program.     

The effect of sevoflurane on cerebral blood flow velocity in children

BACKGROUND: Sevoflurane is a suitable agent for neuroanesthesia in adult patients. In children, cerebrovascular carbon dioxide reactivity is maintained during hypo- and normocapnia under sevoflurane anesthesia. To determine the effects of sevoflurane on middle cerebral artery blood flow velocity (Vmca) in neurologically normal children, Vmca was measured both at different MAC values and at one MAC over a specified time period, using transcranial Doppler sonography. METHODS: Twenty-six healthy children undergoing elective urological surgery were enrolled (16 patients in part I and 10 in part II). In part I of the study anesthesia comprised sevoflurane 0.5, 1.0 and 1.5 MAC in 30% oxygen and a caudal epidural block. Once steady state had been reached at each sevoflurane MAC level, three measurements of Vmca, mean arterial pressure (MAP) and heart rate (HR) were recorded. In part II of the study patients received sevoflurane 1.0 MAC over a 90-min period, with the same variables being recorded at 15-min intervals. RESULTS: Vmca did not vary significantly at 0.5, 1.0 and 1.5 MAC sevoflurane. There was a significant decrease in MAP between 0.5 MAC and 1.0 MAC sevoflurane (P < 0.005) and also between 1.0 MAC and 1.5 MAC (P < 0.01). There was no significant change in Vmca over 90 min at 1.0 MAC sevoflurane. CONCLUSION: Sevoflurane does not significantly affect cerebral blood flow velocity in healthy children at working concentrations.     

Effect of acetazolamide on cerebral artery blood velocity and regional cerebral blood flow in normal subjects

Summary The effect of intravenous acetazolamide L g on cerebral artery blood velocity and regional blood flow (rCBF) was investigated in eight normal subjects. Blood velocity was measured with 2 MHz pulsed Doppler in the proximal segments of the middle, anterior and posterior cerebral artery (MCA, ACA, and PCA) and in the distal extracranial internal carotid artery (ICA). The rCBF in the regions of interest tentatively corresponding to the perfusion territories of these vessels was estimated using¹³³Xe inhalation and a rapidly rotating single photon emission computer tomograph.Both blood velocity and rCBF increased after acetazolamide. There was no significant difference between the percentage ICA blood velocity increase (22 ± 12%) and the percentage rCBF increase in the ICA region of interest (25 ± 9%). In the MCA, ACA, and PCA, however, blood velocity increased more (mean increase 36–42%) than the rCBF in the corresponding regions of interest (mean increase 24–26%). These differences were highly significant suggesting a direct and site specific effect of acetazolamide in narrowing the lumen of the proximal MCA, ACA, and PCA, but not of the extracranial ICA. We also propose that the effect of acetazolamide induces reciprocal changes in the extent of adjacent perfusion territories in individual brain hemispheres.Data compiled from all subjects investigated at two very different perfusion levels (before and after acetazolamide) revealed a significant positive correlation between blood velocity and rCBF.     

Descending aortic blood flow and cardiac output: a clinical and experimental study of continuous oesophageal echo-Doppler flowmetry

BACKGROUND: Several studies have demonstrated that perioperative optimisation of oxygen delivery and haemodynamics can reduce mortality and morbidity for high-risk surgical patients. To optimise cardiac output, reliable, continuous and "less invasive" methods for measuring cardiac output are urgently needed. METHODS: Eight landrace pigs were studied during experimental repeated cardiac tamponade and 14 patients during liver transplantation. Aortic blood flow was measured by using transoesophageal echo-Doppler technique. A total of 91 paired measurements of aortic blood flow and cardiac output with different techniques were performed in the pigs and 124 paired measurements in the patients. RESULTS: Transoesophageal echo-Doppler did provide continuous real-time monitoring of the rapid and dramatic haemodynamic changes occurring during cardiac tamponade and during liver transplantation, while only intermittent information was obtained from the bolus thermodilution technique. Changes in haemodynamics were more difficult to detect with the "continual" cardiac output thermodilution technique. Changes in aortic blood flow closely followed changes in cardiac output determined by the bolus thermodilution technique both in pigs (r= 0.89) and in patients (r=0.80). In patients, aortic blood flow constituted about 70% of cardiac output determined by the bolus thermodilution technique. CONCLUSIONS: A combined echo-Doppler technique can be valuable for continuous monitoring of haemodynamic changes in the perioperative setting, and changes in aortic blood flow agree well with corresponding changes in cardiac output intermittently obtained by thermodilution cardiac output measurements. With the combined echo-Doppler technique a proper position of the Doppler beam is greatly facilitated by the M-mode echo visualisation of the aortic wall and aortic cross-sectional area is continuously measured.     

Early effects of experimental arterial subarachnoid haemorrhage on the cerebral circulation part I: Experimental subarachnoid haemorrhage in cat and its pathophysiological effects methods of regional cerebral blood flow measurement and evaluation of microcirculation

Summary Studies of pathophysiological changes, regional cerebral blood flow (rCBF) and cerebral microcirculation were performed in cats subjected to arterial subarachnoid haemorrhage (SAH). An original method for SAH imitating aneurysm rupture was developed. The bleeding was induced by puncturing of the internal carotid artery approached tranpresphenoidally and followed by immediate closure of the skull opening. It was found, that arterial subarachnoid bleeding elevates intracranial pressure and results in a transitory fall in cerebral perfusion pressure which is not prevented by elevation of arterial blood pressure (Cushing reflex). A depression in brain electrical activity and respiration rate were present in the course of subarachnoid haemorrhage.     

A review of the effects of external pressure on skin blood flow

The human foot is a complex mechanical structure consisting of bones, ligaments and joints. They act together to provide a robust system capable of absorbing and dissipating the intermitted pressure that is subjected to its plantar surface during walking to prevent soft tissue breakdown. Current studies suggest that plantar foot pressure may lead to soft tissue breakdown (e.g. neuropathic ulceration) and hence research has so far concentrated on investigating the mechanical effects of plantar foot pressure on the foot’s integrity. This has been possible through the widely available pressure and force platforms as well as in-shoe pressure systems. However, to understand how plantar foot pressure causes soft tissue breakdown it is vital to investigate both the physiological–mechanical interactions between the skin and plantar foot pressure. This review suggests that with the current advances in technology, the physiological response of skin blood flow to mechanical plantar foot pressure should be investigated and correlated further, both during static and dynamic loading, by developing a new system capable of either measuring both variables simultaneously or by synchronising two systems in real time.     

The lower limit of tissue blood flow for safe colonic anastomosis: An experimental study using laser doppler velocimetry

In order to determine the absolute minimum tissue blood flow (TBF) for safe colonic anastomosis, the wound healing process of anastomotic sites with varying degrees of TBF, measured by laser Doppler velocimetry (LDV), was examined in dogs. Firstly, to clarify how well the LDV value reflects TBF, the correlation between the LDV value and TBF measured by the hydrogen gas clearance method was examined. There was a good correlation between the two methods, with an r value of 0.91. Secondly, after transection and anastomosis of the colon had been performed with varying degrees of devascularization, the anastomotic wound healing process was examined. The LDV values at the anastomotic sites of all dogs in which anastomotic dehiscence had occurred were less than 0.8. In the 2-cm and 4-cm devascularization groups, the mean LDV values were 1.23±0.34 and 0.88±0.20, respectively. There were significant differences between the latter two groups concerning postoperative course, histological features, and hydroxyproline concentration ratio. Thus, as far as TBF is concerned, if the LDV value at the anastomotic site is at least 1.0, corresponding to about 30% of the TBF of the intact colonic wall, the anastomosis is considered to be safe, without risk of dehiscence.     

Laser Doppler flowmetry for bone blood flow measurement: correlation with microsphere estimates and evaluation of the effect of intracapsular pressure on femoral head blood flow

Laser Doppler flowmetry (LDF) was used to measure bone blood flow in the rabbit femoral head and femoral condyles. To correlate the LDF output signal blood cell flux to in vivo blood flow, simultaneous measurements using LDF and 85Sr-labeled microspheres were made in an adult rabbit model. There was no correlation between the two methods for blood flow in the femoral condyles and the correlation between the two methods for blood flow in the femoral head does not achieve statistical significance. An LDF signal of 0.4 V was approximately equal to a microsphere measured flow rate of 0.4 ml blood/g bone/min. The strength of the correlation in the latter case may have been affected by (a) large arteriovenous shunts, (b) inadequate mixing of the microspheres with a left ventricular injection, and (c) insufficient numbers of microspheres present in the bone samples with which to satisfy the mathematical requirements of the microsphere method. When LDF was used to evaluate the effect of elevated intracapsular pressure on femoral head blood flow in skeletally mature rabbits, femoral head subchondral bone blood flow declined with increasing intracapsular pressure from a baseline value of 0.343 +/- 0.036 to a value of 0.127 +/- 0.27 at 120 cm of water pressure. The decline in femoral head blood flow was statistically significant at pressures of 40 cm of water or higher (p less than 0.001), and evaluation of sections of the proximal femora made from preterminal disulphine blue injections confirmed these findings. Intracapsular tamponade has an adverse effect on femoral head blood flow beginning well below central venous pressure and should be considered in the pathophysiology of posttraumatic and nontraumatic necrosis of the femoral head. Laser Doppler flowmetry was easy to use and appears to be a reproducible technique for evaluating femoral head blood flow, offering distinct advantages over the microsphere technique for measuring bone blood flow. Further studies of the in vivo calibration of the LDF method for bone blood flow are necessary for the method to have potential for clinical application.     

Renal physiology: blood flow,glomerular filtration and plasma clearance

The homeostatic and excretory functions of the kidney are dependent on its perfusion, totalling 20–25% of cardiac output, and the process of glomerular ultrafiltration. Renal blood flow (RBF) is directly proportional to the trans-renal gradient which is autoregulated across a mean arterial pressure of 50–150 mmHg in a normotensive person. Selective molecular filtration in the glomerulus is achieved by the glomerular filtration barrier and is related to the size, shape and electrical charge of molecules. The process of ultrafiltration is determined by the balance between hydrostatic and colloid osmotic pressures in the glomerular capillary and Bowmans's space, and is affected by renal plasma flow, altered surface area and changes in afferent and efferent renal arteriole vascular resistance. The phenomenon of renal plasma flow autoregulation minimizes changes in the volume of ultrafiltration through myogenic and tubuloglomerular feedback mechanisms. Glomerular filtration rate can be measured using exogenous inulin, or estimated (eGFR) from creatinine clearance, several equations can be used to calculate eGFR but their limitations in estimating the true excretory function of the kidney need to be taken into consideration.     

Renal physiology: blood flow,glomerular filtration and plasma clearance

The kidney depends on its blood flow (20–25% cardiac output) and glomerular ultrafiltration (20% renal plasma flow) to perform it's homoeostatic and excretory functions. More than 90% of blood flow serves the cortex. Selectivity of molecular filtration in the glomerulus is related to molecular size, shape and electrostatic charge of molecules, and structure of the glomerular filtration barrier with its negatively charged glycoproteins. Ultrafiltration is determined by the balance between hydrostatic and colloid osmotic pressures (Starling forces) in the glomerular capillary and Bowman's space. It is influenced by changes in renal plasma flow, altered surface area and changes in vascular resistance afforded by afferent and efferent arterioles (mediated by sympathetic nerve activity, vasoconstrictors and vasodilators). Autoregulation of renal plasma flow minimizes changes in volume of ultrafiltration (hence, filtered load) through myogenic and tubuloglomerular feedback mechanisms. Renal clearance measurements have practical application in terms of assessing renal plasma flow and glomerular filtration rate (creatinine, inulin) along with some other measurements but all have their limitations.     

Intraoperative evaluation of coronary bypass grafts by measuring myocardial blood flow using the electrolytic hydrogen clearance method

The regional myocardial blood flow (MBF) was measured in 33 patients who underwent coronary bypass graft surgery in order to evaluate the efficiency of coronary bypass grafts in restoring MBF. MBF was measured by the electrolytic hydrogen clearance method during the coronary bypass surgery. The mean prebypass MBF was 161±19, 162±12, 80±12, 43±14, 104±18 ml/min/100 g in segments supplied by the left anterior descending coronary artery (LAD) showing ≦50 per cent, 75 per cent, 90 per cent, 99 per cent, and 100 per cent stenosis with collaterals, respectively. After bypass grafting of the LAD, the mean MBF increased from 70±13 and 126±12 ml/min/100 g to 133±14 and 163±9 ml/min/100 g in the segments with and without infarction, respectively. The mean postbypass MBF was 149±10 and 152±14 ml/min/100 g in the segments supplied by the LAD bypassed with saphenous vein grafts and mammary artery grafts, respectively. Postbypass MBF was dependent upon the magnitude of myocardial infarction. Measurement of MBF by the electrolytic hydrogen clearance method made it possible to quantitatively evaluate myocardial perfusion at the time of operation. It also provided direct information about the effectiveness of myocardial revascularization.     

Effects of hypoxia and isoflurane on liver blood flow: the role of adenosine

We investigated the role of endogenous adenosine in mediatingthe effects of hypoxia and isoflurane on portal tributary bloodflow (PTBF) and hepatic arterial blood flow (HABF) in rats.Liver blood flows were determined using radiolabelled microspheres.Hypoxia resulting from the exposure of rats to an atmospherecontaining 15% oxygen for 30 min decreased PTBF (23%) (P<0.05)and cardiac index (15%) (P<0.05), and increased HABF (78%)(P<0.05). Isoflurane (1.4 vol%) increased HABF in both normoxicand hypoxic conditions but did not affect PTBF. The adenosinereceptor antagonist 8-phenyltheophylline attenuated the hypoxia-inducedincrease in HABF but did not affect that resulting from theadministration of isoflurane. In conclusion, in contrast tothe increase in HABF induced by hypoxia, that induced by isofluraneappears to be independent of endogenous adenosine. Br J Anaesth 2000; 86: 425–7     

Recovery of portal blood flow after percutaneous transhepatic biliary drainage in patients with obstructive jaundice

Using an ultrasonic Doppler system, we prospectively studied the changes in portal venous flow (PVF) following percutaneous transhepatic biliary drainage (PTBD) and evaluated the correlation between PVF and liver function in 10 patients with obstructive jaundice. The patients were divided into two groups according to their rate of decrease in serum bilirubin (“b”). Group A comprised 5 patients with a “b” of less than −0.1, while group B consisted of 5 patients who did not meet this criterion. The mean PVF increased following PTBD (P<0.01). The increase in PVF was due to an increase in the maximum velocity of the portal vein (Vmax). The rate of increase in the Vmax in group A was significantly higher than that in group B on both the 7th and 14th postdrainage days (P<0.05). The rate of increase in the Vmax correlated significantly with the rate of decrease in the serum bilirubin concentration (P<0.01). Based on the above findings, we conclude that measuring the Vmax by Doppler ultrasonography is useful in evaluating the liver function in patients with obstructive jaundice.     

Alterations of mesenteric blood flow after cardiopulmonary bypass: a Doppler sonographic study

OBJECTIVE: Mesenteric ischemia after cardiopulmonary bypass is a serious complication associated with high mortality. It was the aim of this study to investigate mesenteric blood flow with the help of Doppler sonography in asymptomatic patients before and after cardiopulmonary bypass and cardiac surgery. DESIGN: Observational study of consecutive patients. SETTING: Nonuniversity cardiac center. PARTICIPANTS: Twenty-five patients undergoing elective coronary revascularization with normal left ventricular function and stable postoperative circulations with no need for catecholamines. MEASUREMENTS AND MAIN RESULTS: Preoperative and postoperative color and CW-Doppler sonography of the superior mesenteric artery. Diameter of the superior mesenteric artery and the Doppler flow profile were analyzed. Preoperative and postoperative hemodynamic data were measured by using a pulmonary artery thermodilution catheter. Mesenteric systolic flow velocity was 135 +/- 11 cm/s preoperatively and 193 +/- 13 cm/s postoperatively (p < 0.05). The corresponding preoperative and postoperative values of diastolic flow velocity were 14 +/- 4 and 4 +/- 2 cm/s (p < 0.05) and the values of mean flow velocity were 24 +/- 3 and 17 +/- 2 cm/s (p < 0.05), respectively. The preoperative Pourcelot resistive index was 0.87 +/- 0.05, and the preoperative Gosling pulsatility index was 4.6 +/- 0.5. Both indices increased postoperatively to values of 0.98 +/- 0.04 and 9.5 +/- 0.7, respectively (p < 0.05). Preoperative and postoperative hemodynamic data did not differ significantly. CONCLUSION: The postoperative changes in the flow velocities and the increases of the resistive and pulsatility index are indications of rigidity of the mesenteric vascular bed and decreased mesenteric perfusion after cardiopulmonary bypass.     

Evaluation of the effect of age on functioning hepatocyte mass and liver blood flow using liver scintigraphy in preoperative estimations for surgical patients: comparison with CT volumetry

BACKGROUND: The effect of age on functioning hepatocyte mass and liver blood flow was examined using (99m)Tc-galactosyl-human serum albumin (GSA) liver scintigraphy in patients with liver tumors awaiting surgery. MATERIALS AND METHODS: Seventy-two patients with liver tumors, but normal liver parenchyma, were included in this study; patients with compromised hepatic blood flow as a result of vascular invasion or thrombus were excluded. The liver volume, calculated liver volume, and liver blood flow index (K value) were preoperatively determined by liver scintigraphy using GSA. These three parameters and liver volume measured by computed tomography volumetry (CT-LV) and the standard liver volume (ST-LV), calculated from the patient's body surface area, were examined for correlations with the patient's age. The K value was compared with the indocyanine green dye retention rate, and both sets of results were examined for correlation with the patient's age. RESULTS: Both the CT-LV and the ST-LV decreased with age, resulting in an unchanged CT-LV/ST-LV ratio with aging. The liver volume and calculated liver volume measured by scintigraphy both decreased with age, even when body size was taken into account. Therefore, in elderly patients, the liver was not morphologically smaller, but the hepatocyte mass in the liver decreased. Furthermore, liver blood flow per unit of functional liver volume determined from the blood flow index did not change with age. CONCLUSIONS: These results, suggesting a discrepancy between liver volume estimated by CT and actual functioning hepatocyte volume in the elderly, may have a critical impact on preoperative liver functional reserve evaluation prior to hepatic resection in elderly patients.     

术中胃浆膜下血流测定在胃-食管吻合部位选择中的临床意义

目的测定食管切除术中胃浆膜下血流量在胃游离前后的变化,评价胃底浆膜下血流量对于选择胃-食管吻合部位的临床意义。方法将294例行食管部分切除 胃代食管吻合术的食管癌患者随机分为常规组和改进组。常规组于胃底最高点吻合,改进组先用激光多普勒血流仪测定胃游离前后胃底不同部位浆膜下血流量变化情况,然后选择血流量最丰富部位吻合,比较两组术后吻合口漏发生率。结果胃游离前后胃底浆膜下血流量有统计学差异,游离后浆膜下血流量均比游离前明显下降(P<0.05)。胃底不同部位血流量下降程度差异有统计学意义(P<0.05),胃后壁下降最少(46.1%),胃小弯侧下降最多(73.2%)。术后吻合口漏发生率改进组(0.60%)明显低于常规组(3.97%),差异有统计学意义(P<0.05)。结论术中采用激光多普勒血流测定仪测定胃底浆膜下血流量具有非侵入性、方便、准确的优点,有助于选择血流最丰富部位进行胃-食管吻合,从而减少术后吻合口漏发生率。