Intravascular Doppler technique for monitoring renal venous blood flow in man

BACKGROUND: To measure renal blood flow (RBF) from the renal veins in men using the intravascular Doppler technique (IVD). METHODS: In nine hypertensive male patients (age 46-64 years) undergoing diagnostic renal artery angiography and renal vein catheterization to determine plasma renin activity (PRA), a 3F Doppler catheter was positioned in the renal veins using a 7F guide catheter with a "basket" shaped tip. The radiopaque sectors of the catheter, leaning against the vessel wall, serve to measure the internal diameter of renal veins, and therefore to calculate RBF, by multiplying renal vein cross-sectional area by mean blood flow velocity. The resulting RBF from the left and right renal veins were compared with those obtained by the local thermodilution method (TD). RESULTS: We found good agreement (Bland and Altman's method) between the RBF measurements made with IVD (ranging from 46 mL/min to 1,220 mL/min) and with the TD technique (45-1,030 mL/min) (mean bias, 13+/-20 mL/min, 95% CI -54.77 to 28.77 mL/min). In stenotic kidneys a significant correlation was found between the renal vein PRA and RBF calculated with both methods (IVD: r = 0.96, p = 0.002; TD: r = 0.90, p = 0.01). CONCLUSIONS: The IVD technique applied to the venous side of the renal circulation provides a simple and reliable method for separate measurement of RBF in kidneys with and without renal artery stenosis.     

Poloxamer-188 improves capillary blood flow and tissue viability in a cutaneous burn wound.

After cutaneous burn injury, an area of tissue 1-2 mm thick surrounding the wound is the site of a pronounced inflammatory response where blood flow is reduced. This "zone of stasis" undergoes progressive necrosis within 24-48 h, resulting in an expansion of the burn wound. Poloxamer-188 (P-188) is a surfactant that has been shown to prevent cell death due to electrical injury in vivo and heat shock in vitro. In this study, we investigated the effect of P-188 on blood flow within and around a burn wound and on the expansion of the wound area within 24 h after administration of a full-thickness burn injury. Results show that immediately (0-2 h) after the burn, red blood cell speed decreased to zero in a zone extending up to 1 mm from the center of the burn in both P-188 (200 mg/kg)- and saline (0.9%)-treated animals. Between 1 and 3 mm from the center of the burn, red blood cell speed decreased to 50% of preburn levels in saline controls (n = 5), while no decrease occurred in P-188-treated animals (n = 5). Beyond 3 mm from the center of the burn, red blood speed was equal to the preburn levels in saline controls, while it increased by about 10% in P-188 animals. Twenty-four hours after administration of burn, the "zero red blood cell speed zone," termed as the zone of coagulation, became smaller in P-188-treated animals, with an area of 2.4 +/- 0.5 mm(2) (n = 5) compared to 3.5 +/- 0.5 mm(2) (n = 4) in saline controls (P < 0.01). These results suggest that P-188 prevented the formation of a zone of stasis within 2 h after the burn injury and reduced the area of coagulation observed 24 h after cutaneous burn injury.     

Variations in superficial renal cortical blood flow and tissue oxygenation: an experimental porcine model

Renal cortical microcirculation and its relation to inulin clearance, central haemodynamics and pulmonary gas exchange were studied in eight pigs under continuous intravenous chlormethiazole-pancuronium anaesthesia. The animals were studied during six consecutive 30-min periods. Four of the animals were also studied 19 h after the first period. In the superficial renal cortex, regional blood flow (Qsrc) was measured by laser Doppler flowmetry (LDF) and tissue oxygenation (PtO2) by surface microelectrode technique. Central haemodynamics and pulmonary gas exchange values were distributed within normal ranges. The importance of stable central haemodynamics in order to perform accurate microcirculatory measurements in the renal cortex was documented. A significant relation between Qsrc and pulmonary capillary wedge pressure (PCWP) was found (P less than 0.0001) despite the fact that PCWP was distributed within a range of only 0.7 kPa (all values were well within the normal range for pigs). No other relationships were found between central haemodynamics or pulmonary gas exchange variables and renal microcirculatory parameters. Concerning renal microcirculation and inulin clearance, at least 2-3 h may be required for stabilization after surgery. The average temporal variability between measurements performed every 30 min in each animal was 6 +/- 7% (s.d.) in the LDF values and 21 +/- 21% in the PtO2 values (mean PtO2). No correlations were found between Qsrc or PtO2 and inulin clearance. Since the haemodynamic parameters, pulmonary gas exchange variables and haematocrit were distributed within narrow ranges, we regard the temporal microcirculatory variability obtained here as normal in this experimental situation, and consider the porcine model well suited for further studies concerning renal microcirculation.     

Near infrared spectroscopy for monitoring flap viability following breast reconstruction

Free flap monitoring is essential to the early detection of compromise thereby increasing the chance of successful salvage surgery. Many alternatives to classical clinical monitoring have been proposed. This study seeks to investigate a relatively new monitoring technology: near infrared spectroscopy (NIRS). Patients were recruited prospectively to the study from a single center. During the research period, 10 patients underwent reconstruction with a free deep inferior epigastric perforator flap (DIEP). Measurements of flap perfusion were taken using NIRS in the preoperative and intraoperative phases and postoperatively for 72 hours. NIRS showed characteristic changes in all cases which returned to theater for pedicle compromise. In these cases, NIRS identified pedicle compromise prior to clinical identification. There were no false-positives. NIRS accurately identified all compromised flaps in our study. In most cases, there was an evidence of changes in oxygen saturation on NIRS prior to clinical observation. Further research, ideally double blind randomized control trials with large sample groups would be required to definitively establish NIRS as an ideal flap monitoring modality.     

Preconditioning: a new technique for improved muscle flap survival.

Musculocutaneous regional and distal flaps have become an important tool available to the head and neck surgeon. Vascularized autogenous muscle transplants allow single-stage reconstruction of complex defects. Ischemic muscle necrosis is a well-recognized complication with serious potential morbidity. It has been shown that myocardial muscle is protected from ischemic damage by brief periods of coronary artery occlusion and reperfusion subsequent to prolonged ischemia. This is called preconditioning. To our knowledge, this technique has never been extrapolated to skeletal muscle. This article presents a discussion of preconditioning and the potential benefits of this new technique as a means to enhance skeletal muscle survival to sustained normothermic global ischemia. Theories behind ischemic muscle injury are presented. A review of the development of preconditioning in myocardial muscle is discussed. Experimental models used to investigate this phenomenon are also presented. In addition, results of our laboratory investigations using the latissimus dorsi porcine model are discussed. Preconditioning is a new, nonpharmacologic means to improve muscle flap survival. This simple technique may have great clinical application in reducing ischemic muscle necrosis in regional and distal muscle transplantation.     

Noninvasive tissue oximetry for flap monitoring: an initial study

The ideal monitoring tool to evaluate free flap success should be noninvasive, continuous, and reliable. A new device, the ViOptix Tissue Oximeter (ODISsey) based on near-infrared spectroscopy was evaluated in 30 patients undergoing autologous tissue perforator free flap breast reconstruction with continuous monitoring of the flap during elevation, transfer, and the postoperative period. The device accurately reflected the ischemic drop in oxygen saturation during flap transfer, and the hyperemic response after flow was reestablished. There were no flap failures, but in two patients, the device indicated a venous thrombosis before it was clinically obvious and allowed for expeditious flap salvage. The noninvasive nature of the device, the ability to replace and move the probe in the postoperative period, and the measurement of end organ oxygenation are all advantages over other currently available techniques.     

Extended rat-ear flap model: a new rodent model for studying the effects of vessel supercharging on flap viability

A new extended rat-ear flap model, with both an axial and a random component, is described. The flap is based on an axial supply by the posterior auricular artery and the posterior facial vein. The random portion, consisting of the rat dorsum, is capable of being supercharged at two separate sites-in the scapular and pelvic regions. There are several advantages to this composite flap. It is a combined axial and random flap. When used as a free flap, the viability of the axial portion serves as an indicator for anastomotic patency. The random portion allows for the investigation of the effects of pharmaceutical manipulation or surgical intervention, e.g., flap supercharging. The results indicate that the axial supply alone can cover approximately 50 percent of the extended rat-ear flap. Moreover, adding supercharging perforators to the random portion significantly increases the area of flap survival. Of interest, an axial vascular supply, coupled with more distal dorsal perforators (pelvic) than proximal (scapular) perforators, may increase survival for the so-called "watershed" area in the middle of the random portion of the flap. Additionally, this study also investigated the relative importance of arterial supply vs. venous drainage, using the extended rat-ear flap model. The flap was either supercharged with both the perforators of the scapular and pelvic arteries, or both scapular and pelvic veins. The results of the study suggests that augmenting venous drainage provides statistically significant improvement (87 percent vs. 51.6 percent) in increasing flap survival, when compared to augmenting the arterial supply. Arterial supercharging provided no improvement in flap survival, when compared to no supercharging (axial vessels + arterial supercharging, 51.6 percent vs. axial vessels alone, 49.9 percent). The results also suggest that providing adequate venous outflow is more important than providing additional arterial blood, and that impaired venous outflow may contribute to some cases of flap failure. However, it should be kept in mind that the best flap survival occurs with both arterial and and venous supercharging.     

Microdialysis – a new technique for free flap surveillance: methodological description

Early detection of impaired circulation in free flaps is vital for their survival. In the present investigation metabolic changes, known to occur in various tissues during ischemia, were studied using microdialysis. Five patients provided with free flaps, were included in the study. Microdialysis catheters were placed in the flap and in normal control tissue. Laser Doppler flowmetry was used postoperatively to verify circulatory changes. During flap transfer, and the ischemia that was induced by the operation, the glucose concentration in the interstitial flap tissue decreased substantially, whereas the lactate and glycerol concentrations both increased. When vascular anastomoses had been completed these three parameters tended to return to preoperative levels. This metabolic pattern was not seen in the control tissue, thus suggesting that it may be typical for local ischemia. In two of the patients the pattern reappeared in connection with postoperative venous thrombosis, and disappeared when the thromboses were surgically removed. This observation lends further support to the notion that transcient ischemia induces a specific metabolic pattern which can be detected by microdialysis. Consequently, microdialysis appears to be a useful tool in the surveillance of microsurgical free flaps. Received: 31 December 1997 / Accepted: 20 May 1998     

End-tidal CO2 and tissue pH in the monitoring of acid-base changes: a composite technique for continuous, minimally invasive monitoring

The infrared CO2 analyzer continuously monitors the CO2 tension in exhaled air at end-tidal expiration. In experimental animals, we found a consistent relationship between PaCO2 and end-tidal CO2 (ET.CO2) in the normal steady state, and in acid-base disturbances (respiratory acidosis and alkalosis, and hypoperfusion acidosis). Paired data analyses of PaCO2 (X) and ET.CO2 (Y) yielded correlation coefficients of r = 0.98 (Y = 0.96X + 4.43) during progressive hypercarbia (PaCO2: 32----110 torr), and r = 0.93 (Y = 0.89X + 0.93) during hyperventilation hypocapnia (PaCO2: 41----14 torr). The relationship between PaCO2 and ET.CO2 was seen during hypovolemic shock if pulmonary perfusion was maintained uniform in all areas of lung. The ability of the ET.CO2 sensor to predict instantaneously the PaCO2 makes it attractive enough to be used in conjunction with the subcutaneous tissue pH(pHe) sensor in the management of acid-base disturbances. After hypercarbia (FiCO2 0.15 X 40 min; PaCO2/ET.CO2: 100/101 torr), when the dogs were returned to room air, abruptly both the ET.CO2 and pHe sensors were sensitive to the changes in Fi.CO2. But the response of the ET.CO2 was swifter. The advent of transcutaneous gas monitors has shown that intermittent blood gas analyses, however frequent, are inadequate for the monitoring of the rapidly altering blood gas status in the acutely ill. The ability of the pHe sensor to identify whole-body acidosis and alkalosis combined with the speed and ease of the ET.CO2 monitor in pinpointing hypercarbic and hypocarbic states makes this two-parameter system suitable for the continuous, noninvasive monitoring of the critically ill.     

Intraoperative assessment of blood flow and tissue viability in small-bowel ischemia by laser Doppler flowmetry

Laser Doppler flowmetry (LDF) was used for intraoperative assessment of blood flow and tissue viability in 23 patients with small-bowel ischemia, and the signal levels in ischemic bowel were compared with previously obtained reference values from normal ileum and jejunum. The average LD signal was 6.8 +/- 2.9 V in nonischemic bowel, 0.3 +/- 0.2 V in segments with macroscopically irreversible ischaemia and 2.1 +/- 1.2 V in segments with clinically uncertain viability. In 12 cases with strangulated bowel it was possible, following LDF, to avoid resecting nine of ten bowel segments with clinically uncertain viability. In four of the six patients with mesenteric vascular occlusion, LDF indicated that clinical judgement had underestimated the extent of severe ischemia. Among the five cases of iatrogenic ischemia there was one failure, with postoperative irreversible ischemia and anastomotic leakage. LDF is concluded to be a useful method for intraoperative assessment of intestinal blood flow in patients with small-bowel ischemia and it provides substantial information on tissue viability affecting surgical strategy.     

A new technique for measuring blood flow in polytetrafluorethylene grafts for hemodialysis.

A method has been described for the measurement of blood flow in non branching grafts using the isotope dilution principle. The technique is simple, reproducible and consistent and can be performed in less than ten minutes.     

Techniques of postoperative blood flow monitoring after free tissue transfer: An overview

Ever since free tissue transfer has been established in microsurgery, success rates have greatly improved over the years, partly due to improved technical performance of microvascular anastomoses with better optical and instrumental aids. However, flap failure still occurs in 5–10%, mainly due to blood vessel thrombosis within the first 24 postoperative hours. Salvation rates of failing free tissue transfers can be optimized by in-time diagnosis of irreversibly compromised tissue blood flow and immediate operative reexploration. Therefore, there is a special demand for adequate and reliable postoperative monitoring techniques. This article gives an overview of all monitoring techniques, which have been performed both in the experimental and clinical setting thus far. © 1994 Wiley-Liss, Inc.     

A new thermal diffusion flow probe for continuous monitoring of cerebral blood flow in small animals

The Peltier stack, which allows quantitative measurement of cerebral blood flow (CBF) by means of thermal diffusion, has a probe too large for use in small animals. However, it is difficult to measure CBF by a thermal diffusion method involving the use of a constantan heating wire, because of heat conduction between the two gold plates. The authors developed a new thermal diffusion flow probe, using a constantan wire as a heat source rather than the Peltier stack. With the new probe, separation of the gold plates and attachment of a pair of long thermocouples minimize heat conduction between the two plates. Moreover, the probe itself is considerably smaller than that of the Peltier stack. The new probe was inserted to the subdural space of rabbits and the voltage (V; mV) was measured with an amplifier by the circuit of constant current method. CBF (F; ml/100 g/min) was measured simultaneously by the hydrogen clearance method in the adjacent cortex. A regression equation of F = 29, 111 (1/V-1/226) was obtained between 35 pairs of F and V (r = 0.92, p less than 0.001), which verified that CBF can be accurately measured with the new probe.     

Intracompartmental pressure, PO2, PCO2 and blood flow in the human skeletal muscle

Measurement of PO2, PCO2, and blood flow in skeletal muscle could be a supplement to examination in clinical practice. Mass spectrometry was utilized to measure these parameters in the resting anterior tibial muscle of healthy adults. The partial pressures of oxygen and carbon dioxide were 21 +/- 3.6 and 46 +/- 2.5 Torr, respectively. The intracompartmental pressure was 8 +/- 1.1 Torr. The oxygen tension in muscle varied only slightly when arterial partial pressure was increased. The blood flow (tissue perfusion coefficient) estimated by washout of an inert gas was 5.4 +/- 0.8 ml/100 g/min. The results are in accordance with those from animal studies of skeletal muscle. The study demonstrates the feasibility of measuring PO2, PCO2, and blood flow in skeletal muscle by mass spectrometry.