Extracorporeal Blood Flow Rate Research Articles

Effect of Blood Flow Rate on the Accuracy of Central Venous Pressure Measurement during Continuous Renal Replacement Therapy

Background: The objective of this study was to study the influence of extracorporeal blood flow rate (BFR) on the accuracy of central venous pressure (CVP) measurement during continuous renal replacement therapy (CRRT). Methods: Eligible patients were randomly divided into 3 groups based on the location of catheters used for their CRRT and CVP measurement. CVP levels measured at increased extracorporeal BFR (from 0 to 300 mL/min) in the normal and reverse positions of inlet and outlet lines connected to the CV catheter (CVC) in the course of the CRRT session were collected. Results: CVP levels measured at different extracorporeal BFRs did not significantly differ between and among the 3 groups. Inversion of inlet and outlet lines connected to the catheters did not affect the accuracy of CVP measurement. BFR had a negative correlation with inflow/access pressure but a positive correlation with outflow/return pressure. Neither inflow pressure nor outflow pressure was correlated with CVP. Conclusions: Extracorporeal BFR has no influence on the accuracy of CVP measurement during CRRT with the net machine balance adjusted to zero regardless of the location of the catheter and the connection method between catheters and CRRT lines. Thus, CRRT does not need to be discontinued to obtain an accurate CVP measurement.

Effect of extracorporeal blood flow on blood pressure, pulse rate, and cardiac output in hemodialysis patients

Background Intradialytic hypotension (IDH) is a common clinical practice to reduce the extracorporeal blood flow rate (EBFR).Aim The aim of this study is to investigate the effect of changes in EBFR on blood pressure (BP), pulse rate (PR), and cardiac output (COP) in hemodynamically stable patients during hemodialysis (HD).Patients and methods The population of this study consists of 40 patients who were on RD three session weekly. Patients were investigated before and after one conventional HD session. Before the HD session, an echocardiograph was performed to evaluate left ventricular ejection fraction and establish the degree of potential heart failure. Furthermore, arteriovenous fistula recirculation, a confounder of the measurement of EBFR, was excluded at an EBFR of 400 ml/min.Result In this study regarding measure of BP, PR, and COP at EBFR 200, 300, and 400 ml/min, there was a significant increase in systolic BP at an EBFR of 200 ml/min as compared with an EBFR of 300 ml/min and an EBFR of 400 ml/min, but there was no significant change in systolic BP at an EBFR of 300 ml/min as compared with an EBFR 400 ml/min. Regarding diastolic BP, mean arterial pressure, PR, and COP at an EBFR of 200, 300, and 400 ml/min, there was no significant change in mean arterial pressure and COP.Conclusion IDH has been associated with many adverse clinical events including myocardial stunning, cerebral atrophy, and increased mortality. Change of EBFR from 400 ml/min or from 300 ml/min to EBFR 200 ml/min can increase in BP, so it helps in decreased occurrence of complications of IDH, compared with other methods of increasing BP during HD. There is no significant relation between change of EBFR and diastolic BP.

Impact of Extracorporeal Blood Flow on Blood Pressure, Pulse Rate and Cardiac Output in Hemodialysis Patients

Background: If blood pressure (BP) falls during hemodialysis (HD) (intradialytic hypotension (IDH)) a common clinical practice is to reduce the extracorporeal blood flow rate (EBFR). Consequently, the efficacy of the HD (Kt/V) is reduced. Aim of the Work: The aim of the present study is to investigate the impact of changes in extracorporeal blood flow rate (EBFR) on blood pressure (BP), pulse rate (PR) and cardiac output (COP) in hemodynamically stable patients during hemodialysis. Patients and Methods: The population of this study consisted of 40 patients that on renal dialysis (RD) three sessions weekly. Patients were investigated prior to and after one conventional hemodialysis session. Prior to the hemodialysis session, an echocardiograph was performed to evaluate left ventricular ejection fraction (LVEF) and establish the degree of potential heart failure. Result: In the present study regarding measure of BP, PR and COP in EBFR 200 ml/min, 300 ml/min and 400 ml/min, there was significant increase in systolic BP at an EBFR 200 ml/min as compared with EBFR 300 ml/min and EBFR 400 ml/min. but there was no significant change in systolic BP at an EBFR 300 ml/min as compared with an EBFR 400 ml/min. Conclusion: IDH has been associated with many adverse clinical events including myocardial stunning, cerebral atrophy and increased mortality. Change of BFR from 400 ml/min or from 300 ml/min to EBFR 200 ml/min can increase in BP so help in decrease occurrence of complications of IDH beside other methods of increasing BP during hemodialysis.

Impact of Extracorporeal Blood Flow on Blood Pressure, Pulse Rate and Cardiac Output in Hemodialysis Patients

Background: If blood pressure (BP) falls during hemodialysis (HD) (intradialytic hypotension (IDH)) a common clinical practice is to reduce the extracorporeal blood flow rate (EBFR). Consequently, the efficacy of the HD (Kt/V) is reduced. Aim of the Work: The aim of the present study is to investigate the impact of changes in extracorporeal blood flow rate (EBFR) on blood pressure (BP), pulse rate (PR) and cardiac output (COP) in hemodynamically stable patients during hemodialysis. Patients and Methods: The population of this study consisted of 40 patients that on renal dialysis (RD) three sessions weekly. Patients were investigated prior to and after one conventional hemodialysis session. Prior to the hemodialysis session, an echocardiograph was performed to evaluate left ventricular ejection fraction (LVEF) and establish the degree of potential heart failure. Result: In the present study regarding measure of BP, PR and COP in EBFR 200 ml/min, 300 ml/min and 400 ml/min, there was significant increase in systolic BP at an EBFR 200 ml/min as compared with EBFR 300 ml/min and EBFR 400 ml/min. but there was no significant change in systolic BP at an EBFR 300 ml/min as compared with an EBFR 400 ml/min. Conclusion: IDH has been associated with many adverse clinical events including myocardial stunning, cerebral atrophy and increased mortality. Change of BFR from 400 ml/min or from 300 ml/min to EBFR 200 ml/min can increase in BP so help in decrease occurrence of complications of IDH beside other methods of increasing BP during hemodialysis.

Impact of extracorporeal blood flow rate on blood pressure, pulse rate and cardiac output during haemodialysis.

If blood pressure (BP) falls during haemodialysis (HD) [intradialytic hypotension (IDH)] a common clinical practice is to reduce the extracorporeal blood flow rate (EBFR). Consequently the efficacy of the HD (Kt/V) is reduced. However, only very limited knowledge on the effect of reducing EBFR on BP exists and data are conflicting. The aim of this study was to evaluate the effect and the potential mechanism(s) involved by investigating the impact of changes in EBFR on BP, pulse rate (PR) and cardiac output (CO) in HD patients with arteriovenous-fistulas (AV-fistulas). We performed a randomized, crossover trial in 22 haemodynamically stable HD patients with AV-fistula. After a conventional HD session each patient was examined during EBFR of 200, 300 and 400 mL/min in random order. After 15 min when steady state was achieved CO, BP and PR were measured at each EFBR, respectively. Mean (SD) age was 71 (11) years. Systolic BP was significantly higher at an EBFR of 200 mL/min as compared with 300 mL/min [133 (23) versus 128 (24) mmHg; P < 0.05], but not as compared with 400 mL/min [133 (23) versus 130 (19) mmHg; P = 0.20]. At EBFR of 200, 300 and 400 mL/min diastolic BP, mean arterial pressure, PR and CO remained unchanged. Our study does not show any consistent trend in BP changes by a reduction in EBFR. Reduction in EBFR if BP falls during IDH is thus not supported. However, none of the patients experienced IDH. Further studies are required to evaluate the impact of changes in EBFR on BP during IDH.

Improving the delivery of continuous renal replacement therapy using regional citrate anticoagulation.

Regional citrate anticoagulation during acute renal replacement therapy (RRT) effectively prevents extracorporeal thrombosis and avoids bleeding risk. There have been a number of citrate anticoagulation protocols published; but a simple and predictable scheme with standardized components and procedures, as well as clearly defined citrate pharmacokinetics, is needed for continuous RRT (CRRT) that is now used frequently in the critical care setting. The present study sets forth methodology with standardized blood flow and dialysate composition, and with citrate and calcium infusions that are quantitatively linked to extracorporeal blood flow rate--a predictable and easily replicated CRRT paradigm. CRRT using continuous venovenous hemofiltration with dialysis (CVVHD) was standardized using 150-200 ml/min blood flow, calcium-free dialysate with only moderate sodium (135 mEq/l) and bicarbonate (28 mEq/l) concentrations, and ultrafiltration limited to that needed for overall fluid balance in the intensive care unit. Citrate infusion (ACD-A solution) into the extracorporeal blood and calcium repletion in blood returned to the patient were proportional to blood flow. Anticoagulation was accomplished by keeping extracorporeal ionized calcium below 0.4 mM/l. Filter performance, citrate removal and changes in calcium, sodium and alkali were evaluated longitudinally. CVVHD using this protocol delivered urea clearance exceeding 2 l/h (48 l/d) when filter function was sustained. Filter longevity was markedly improved using citrate when compared with standard heparin anticoagulation, and nursing time spent on initiating and troubleshooting CRRT was approximately halved using this protocol. Sieving coefficients for urea, creatinine and citrate were approximately 0.9 and were sustained through nearly 3 days of filter use. Citrate clearance and removal were quantitatively linked to dialysate and ultrafiltration flow, resulting in 35-50% direct removal of the citrate-calcium chelate and reduced systemic citrate load. Serum tonicity and acid-base status were not problematic. The only notable side effect was modest calcium accumulation that necessitated reduction in calcium repletion rate. CVVHD is well suited to regional citrate anticoagulation. The present protocol is straightforward and predictable, with minor metabolic consequences that can be anticipated and adjusted. These results commend regional citrate anticoagulation to wider application.

Dialyzer fiber bundle volume and kinetics of solute removal in continuous venovenous hemodialysis.

The relationship between dialyzer fiber bundle volume (FBV), dialyzer life span, and small-solute clearance has yet to be clearly defined in continuous venovenous hemodialysis (CVVHD). This study sought to define this relationship using novel ultrasound dilution technology. We studied 55 sessions in 31 intensive care unit patients on CVVHD therapy. A session was defined as the life span of a single dialyzer. The following variables were assessed every 6 hours throughout each session, starting within 1 hour of initiation of that session: FBV, access recirculation, extracorporeal blood flow rate, effluent (EUN) to blood urea nitrogen (BUN) concentration ratio, effluent creatinine to blood creatinine concentration ratio, and urea nitrogen and creatinine clearances. Data were analyzed using random-effects linear models to estimate trends. Several dialysis-related and solute-removal parameters were analyzed for association with each other. Systemic or dialysis circuit heparin was administered in 28 of 55 sessions. One hundred seventy sets of FBV, 101 sets of urea clearance, and 102 sets of creatinine clearance measurements were performed. There was a declining trend for FBV (0.8 mL/h), heart rate (0.25 beats/min/h), and measured blood flow (0.33 mL/min/h; P < 0.05). Apart from dialysate inflow rate (P = 0.044), there was no significant correlation with EUN-BUN ratio. Session duration was associated with dialysis access site; the femoral access provided longer dialysis sessions than subclavian and internal jugular accesses (P = 0.029). We conclude that small-solute removal remains stable over the course of our CVVHD system life spans despite significant loss of hemodialyzer FBV.

Assessment of access recirculation during haemodialysis.

With dialysis lines in the correct alignment, access recirculation only occurs when the access blood flow rate is exceeded by the extracorporeal blood flow rate. The degree of access recirculation is accurately measured by non-urea-based methods using indicator dilution or differential conductivity methods. The classical urea-based methods have inherent inaccuracies. Access flow rate can be calculated from an accurate measurement of the access recirculation induced by dialysis line reversal. Access flow rate monitoring can detect early access dysfunction; the existence of access recirculation indicates severe access dysfunction.

Development and application of a simplified liquid ventilator

Perfluorocarbon liquid ventilation has been shown to have advantages over conventional gas ventilation in premature newborn and lung-injured animals. To simplify the process of liquid ventilation, we adapted an extra-corporeal life-support circuit as a time-cycled, volume-limited liquid ventilator. Laboratory study that involved sequential application of gas and liquid ventilation in normal cats and in lung-injured sheep. A research laboratory at a university medical center. Eight normal cats weighing 2.7 to 3.8 kg (mean 3.1 +/- 0.5), and four lung-injured young sheep weighing 10.4 to 22.5 kg (mean 15.9 +/- 5.0). Normal cats were supported with traditional gas ventilation for 1 hr (respiratory rate 20 breaths/min, peak inspiratory pressure 12 cm H2O, positive end-expiratory pressure 4 cm H2O, and FIO2 1.0). The lungs were then filled with perfluorocarbon (30 mL/kg) and tidal volume liquid ventilation was instituted, utilizing a newly developed liquid ventilation device. Liquid ventilatory settings were 4 secs for inspiration time, 8 secs for expiration time, 5 breaths/min for respiratory rate, and 15 to 20 mL/kg for tidal volume. Liquid ventilation utilizing this device was also applied to sheep after induction of severe lung injury by right atrial injection of 0.07 mL/kg of oleic acid, followed by saline pulmonary lavage. Extracorporeal life support was instituted to provide a stable model of lung injury. For the first 30 mins of extracorporeal support, all animals were ventilated with gas. Animals were then ventilated with 15 mL/kg of perfluorocarbon over the ensuing 2.5 hrs. In normal cats, mean PaO2 values after 1 hr of liquid or gas ventilation were 275 +/- 90 (SD) torr (36.7 +/- 10.4 kPa) in the liquid-ventilated animals and 332 +/- 78 torr (44.3 +/- 10.4 kPa) in the gas-ventilated animals (NS). Mean PaCO2 values were 40.5 +/- 5.7 torr (5.39 +/- 0.31 kPa) in the liquid-ventilated animals and 37.6 +/- 2.3 torr (5.01 +/- 0.31 kPa) in the gas-ventilated animals (NS). Mean arterial pH values were 7.35 +/- 0.07 in the liquid-ventilated animals and 7.34 +/- 0.04 in the gas-ventilated animals (NS). No significant changes in heart rate, mean arterial pressure, lung compliance, or right atrial venous oxygen saturation were observed during liquid ventilation when compared with gas ventilation. In the lung-injured sheep, an increase in physiologic shunt from 15 +/- 7% to 66 +/- 9% was observed with induction of lung injury during gas ventilation. Liquid ventilation resulted in a significant reduction in physiologic shunt to 31 +/- 10% (p < .001). In addition, the extracorporeal blood flow rate required to maintain the PaO2 in the 50 to 80 torr (6.7 to 10.7 kPa) range was substantially and significantly (p < .001) lower during liquid ventilation than during gas ventilation (liquid ventilation 15 +/- 5 vs. gas ventilation 87 +/- 15 mL/min/kg). Liquid ventilation can be performed successfully utilizing this simple adaptation of an extracorporeal life-support circuit. This modification to an existing extracorporeal circuit may allow other centers to apply this new investigational method of ventilation in the laboratory or clinical setting.

Blood Flow Rate and Access Recirculation in Hemodialysis

We studied the effect of extracorporeal blood flow rate (BFR) on access recirculation (recirc) in 19 hemodialysis patients. BUN was determined in simultaneous peripheral (P), arterial (A), and venous (V) blood obtained at BFRs of 200, 400, and 600 ml/min. Percent recirc was calculated for each BFR using the formula (P-A)/(P-V) x 100. Venous drip-chamber (VP) and pre-blood-pump (AP) pressures were measured at each BFR. Fistulograms were performed in 10 patients, and stenoses were identified in 5, all at the proximal (arterial) end of the access. Recirc increased with increasing BFR from 200 to 400 ml/min but increased little from 400 to 600 ml/min. At all BFRs recirc in the stenotic patients was higher than that of non-stenotic or unstudied patients. Urea clearance, corrected for recirc, rose with blood flow both in stenotic and non-stenotic patients. There were no differences in AP or in VP between stenotic and non-stenotic patients. At BFR greater than or equal to 400 ml/min, a recirc threshold of 15% identified stenoses with sensitivity 100% and specificity 71%. We conclude (1) recirc increases with increasing BFR but not enough to outweight the concomitant increase in urea clearance; (2) significant access stenosis and recirc may be present even with low VP; (3) recirc was associated with arterial side stenoses; (4) at BFR greater than or equal to 400 ml/min, access stenosis is associated with recirc greater than 15%.

Traitement inotrope postopératoire dans la chirurgie cardiaque du nouveau-né et du nourrisson

Corrective cardiac surgery in infants and neonates induces acute circulatory and anatomical changes which, together with the myocardial ischaemia of cardiopulmonary bypass, impair cardiac function. Although this cardiac dysfunction usually disappears without any after-effects, inotropic treatment is mandatory for a short time. There, however, is no easy way to monitor cardiac output in these small patients. Neither is there much universally recognized objective data available to help choose between these drugs available or between different protocols. Physiologically, infants are not small adults. In the neonatal period, the heart works virtually at its maximum, with little reserve : the stroke volume has a limited capacity to increase because of poor compliance, and the heart rate is high. Cardiac output is therefore rate dependent. To improve therapeutic adjustment, an attempt is made to rationalize the use of inotropic drugs in the postoperative period. Cardiac dysfunction can frequently be recognized already in theatre. It is of paramount importance to exclude faulty surgical repair by measuring the pressures and oxygen saturation in all the cardiac chambers and vessels. The severity of haemodynamic impairment will then have to be defined. As well as the usual clinical criteria (blood pressure, diuresis), the trend in the capnographic curve during a reduction of extracorporeal blood flow rate and acid-base measurements are most helpful. If no further immediate surgery is found to be necessary, the most serious cases are treated by cardiopulmonary support (right to left, or cardiac left to left, or exceptionally biventricular), usually for 1 to 3 h. During this period, a low atrial pressure (< 5 mmHg) must be maintained and all inotropic support stopped. Improvement is frequently rapid and long-term support is very uncommon. Moderate cases of cardiac dysfunction are treated with catecholamines. Dobutamine is administered at a dose of 5 g · kg −1 · min −1 which, if necessary, can be increased by 5 g · kg −1 · min −1 increments. When this is not successful, isoprenaline or an association of two drugs are often effective. In the intensive care unit, echography and Doppler ultrasound are used routinely to assess the anatomical and circulatory results of the surgical repair and to monitor cardiac fibre contractility and stress. These last two factors are useful guidelines for therapeutic adjustment. Nevertheless, the only way to choose the optimal dose of the best drug is to measure cardiac output ; an accurate technique fit for routine use has yet to be discovered.

The assessment of arteriovenous fistulae created for haemodialysis from pressure and thermal dilution measurements.

A technique is described for the assessment of arteriovenous fistulae created for haemodialysis. This involves the measurement of intrafistula pressures and 'useful fistula flow' (UFF). The latter we define as the maximum blood flow available for twin needle haemodialysis without recirculation and without unacceptable pressures in the arterial ('A') and venous ('V') lines. The test circuit resembles that used for conventional haemodialysis except there is 'A' and 'V' line pressure and temperature monitoring and no dialyser. Intrafistula pressures are first measured at the time of insertion of the fistula needles. 'A' and 'V' line pressures are then recorded as the extracorporeal blood flow rate is increased in increments from zero to 500 ml/min. A check for recirculation is made at each flow rate. A bolus of cold saline injected into the 'V' line causes a momentary decrease in 'A' line temperature when recirculation is present; when there is no recirculation, 'A' line temperature remains constant. The blood flow rate at which recirculation is first detected will be above the useful fistula flow by definition. This technique allows identification of those patients who obtain high blood flows at the expense of recirculation and thus dialyse inefficiently. Combined pressure and thermal dilution measurements yield valuable information in the investigation of failing or problem fistulae.

Blood recirculation during hemodialysis with a coaxial counterflow single needle blood access catheter.

1. The average and the range of blood recirculation during hemodialysis employing a coaxial counterflow single needle blood access catheter are markedly reduced compared to those observed in the same patients using a standard "Y" type needle and external flow direction control device. 2. In a large group of patients, the average measured recirculation of blood of 3.8% at a blood flow rate of 200 ml/min is sufficiently small as to have little or no effect on the efficiency of dialysis. 3. Recirculation increases with increasing extracorporeal blood flow rate but remains sufficiently low to not significantly affect increased dialysis efficiency obtained at higher blood flow rates. 4. The coaxial counterflow single needle catheter permits single fistula puncture, eliminates the need for a flow direction control device, and is associated with negligible blood recirculation. It offers a most attractive alternative to both double needle and present single needle blood access techniques for hemodialysis.

Extracorporeal oxygenation in puppies and in newborn and fetal lambs

1. Extracorporeal blood oxygenation was achieved by the membrane oxygenator described by Peirce and Galletti in 6 puppies, 1 to 4 months old, 7 near and at term fetal lambs, and 4 4-hour- to 4-day-old newborn lambs. The mean weight of the animals was 3,310 grams. Mean duration of extracorporeal assistance was 3 hours and 18 minutes. Mean extracorporeal blood flow rate was 104 ml. per minute per kilogram. Partial heart-lung bypass was achieved by right atrial venous drainage and carotid arterial infusion.2. None of the fetal animals breathed during the perfusion period; breathing in the newborn animals ceased at the beginning of the perfusion. The puppies were asphyxiated for different periods during extracorporeal circulation.3. Fourteen animals (out of 17) gained less than 4 per cent of their initial body weight.4. Satisfactory artificial oxygenation could be achieved but CO2 release was poor with the 0.5 mil thick cast Teflon membranes used. No problems of metabolic acidosis or electrolytic imbalance were encountered.5. Over-all survival rate was low (517) but higher (36) in puppies than in fetal or newborn lambs (211). The role of species, age, patency of shunts, anesthesia of the ewe, fetal anoxia before perfusion, coagulation defects, and endotoxic shock is discussed.