Operative assessment of femorodistal bypass grafts using a new Doppler flowmeter

Prognostic Significance of Intraoperative Graft Flow in Distal Bypass on Long-Term Outcomes in Patients with Chronic Limb-Threatening Ischemia

BACKGROUND

The aim of the study was to determine the prognostic significance of measurement of graft flow on the patency of distal bypass.

METHODS

A retrospective analysis was performed for 208 distal bypasses (208 limbs, 170 patients) with a single segment great saphenous vein conducted in a nonreversed manner from January 2009 to December 2019 in Japan. Patient backgrounds, operative details (including intraoperative mean graft flow), hospital outcomes, and long-term outcomes were evaluated. The primary endpoints were the primary, assisted primary, and secondary patency of the distal bypass graft and the secondary endpoints were limb salvage and wound healing.

RESULTS

The median intraoperative graft flow was 18 [10-30] mL/min. The follow-up rate was 98% in a mean follow-up period of 31 ± 26 months. Primary, assisted primary, and secondary patency in the cohort were 51%, 72%, and 73% at 1 year, and 39%, 59%, and 61% at 3 years, respectively. In multivariate analysis, the independent risk factors for primary patency were low graft flow (P = 0.0022) and female sex (P = 0.0016), and those for secondary patency were also low graft flow (P = 0.0025) and female sex (P < .001). The cut-offs for graft flow predicting primary and secondary patency were both 16 mL/min. The limb salvage rate was 94% at 1 year and 89% at 3 years; and the wound healing rates were 55%, 71% and 84% at 3, 6, and 12 months, respectively. Limb salvage and wound healing were not significantly associated with intraoperative graft flow.

CONCLUSIONS

Intraoperative graft flow was an independent predictor for graft patency in distal bypass, but had no influence on limb salvage and wound healing. The cut-off value for the mean graft flow predicting primary and secondary patency was 16 mL/min.

Input Impedance of Revascularized Skeletal Muscle, Renal, and Mesenteric Vascular Beds

Input impedance describes the relationship between pressure and flow in a vascular system and, hence, characterizes the outflow bed. The purpose of this investigation was to measure input impedance spectra in vascular reconstructions of skeletal muscle, renal, and mesenteric beds.

Input impedance was measured in 107 vascular reconstructions in 96 patients. Reconstructions were performed at the aortofemoral/aortoiliac (AF, n = 20), femoropopliteal (FP, n=18), femorodistal (FD, n=41), infrapopliteal-inframalleolar (IM, n = 6), renal (REN, n = 16), or mesenteric (MES, n= 6) level. Grafts were constructed from autologous vein in all cases except AF bypasses in which bifurcated woven Dacron grafts were employed. Input impedance was measured intraoperatively after reperfusion. For impedance calculation, simultaneously acquired intraluminal pressure (transducer-tipped pressure catheter) and blood flow (electromagnetic probe) waveforms of ten-second duration were digitized at 200 Hz and subjected to Fourier transformation in near real-time.

AF grafts exhibited the highest blood flow (443 ± 72.8 mL/minute) followed by MES (300 ± 30.4), REN (172 ± 43.9), FP (91.6 ± 20.0), FD (59.3 ± 5.09), and IM grafts (22.4 ± 5.44 mL/minute). A similar (inverse) trend was observed with respect to resistance (Rin), ie, MES≈AF<REN<<FP<FD<<IM(15.7 ± 2.2=23.7 ± 6.5<69.2 ± 12.2 < < 120 ± 31.9 < 137 ± 13.0 < < 337 ± 75.8 x 103 dyne•s•cm-5). As expected, AF grafts exhibited the lowest characteristic impedance (Z0 3.5 ± 0.8 x 103 dyne•s•cm-5). However, the Z0 of REN (20.2 ± 3.7 x 103 dyne•s•cm-5) grafts exceeded that of FP and MES grafts (10.5 ± 1.1 and 12.4 ± 4.0 x103 dyne•s•cm-5) and more closely approximated that of FD (22.2 ± 2.2 x 103 dyne•s•cm-5). The highest Z0 was seen in IM grafts (42.1 ± 15.8 x 103 dyne•s•cm-5). Therefore, the highest ratios of Z0/Rin were observed with MES (0.75 ± 0.23) and REN (0.33 ± 0.04) grafts as compared with the other groups (AF 0.23 ± 0.03, FP 0.12 ± 0.13, FD 0.19 ± 0.02, IM 0.16 ± 0.06).

As expected, Rin of vascular reconstructions follows the general trend of MES ≈ AF < REN < < FP < FD < < IM. However, examination of the high-frequency components of the impedance spectra reveals that Z0 follows a different pattern, AF < FP MES < FD ≈ REN < < IM and the ratio of ZO/Rin is highest in REN and MES vascular beds compared with skeletal muscle beds. Thus, although the REN and MES beds are “privileged” (ie, maximally dilatated with low arteriolar tone), the intrinsic properties of the graft and larger blood vessels are no different than those of a femorodistal bypass.

Comparison of the Resistive Properties of Reversed and Nonreversed Saphenous Veins at Arterial Pressure and Flow: Implications for Optimal Graft Configuration

Clinicians continue to debate the hemodynamic advantages of reversed vs nonreversed vein grafts in infrainguinal arterial reconstructions. Vein grafts placed in the reversed configuration do not require valve lysis but have the theoretical drawback of being smaller in caliber at the inflow end than the outflow end. The purpose of this study was to objectively determine the effect of vein valve lysis and flow direction on vein graft hemodynamics by using physiologic levels of pulsatile flow (Q), pressure gradient (AP), outflow resistance (Ro), and longitudinal impedance (ZL).

Nine cryopreserved human greater saphenous veins (length=23 ±1 cm) were perfused via an in vitro circuit utilizing a variable pulsatile perfusion pump, Windkessel, and clamp resistor. Levels of Q and AP were chosen to simulate the known physiologic conditions of infrainguinal bypass grafting while holding Reynolds numbers <2,400. Veins were studied in the reversed configuration prior to valve lysis, after valve lysis by use of a catheter-directed valvulotome with 3 mm cutting head, and in the nonreversed configuration. Ultrasonic transit-time flow and proximal and distal intraluminal pressure were continuously recorded while Ro and pump rate were varied. Waveforms were digitally stored at 200 Hz at pump rates of 60, 100, 140, and 180 beats per minute at a Q of 154 ± 1 and 253 ± 1 mL/min while Pprox was maintained at 100 mmHg. Veins were perfusion fixed at 100 mmHg, sectioned at 2 cm intervals, and analyzed morphometrically. Inner diameter (id) and outer diameter (od) were determined by light microscopy after correction for shrinkage artifact by comparing to outer diameter measured by digital calipers at 2 cm intervals at the time of perfusion. Percent vein taper was calculated as (idmax7idmin)/idmax and wall thickness (t) as (od-id)/2. After Fourier transformation, ZL was calculated as AP/Q at each harmonic and the curves compared by use of Wilcoxon signed-ranks test.

There were one to four valves per vein (idmean=3.6 ±0.3 mm; range 2.3-6.2) with an average taper of -8 + 12% (range: -46-36%) and mean wall thickness of 0.51 ±0.03 mm (range 0.42-0.68 mm). ZL curves were smooth and reproducible over the measured frequency range. Neither valve lysis nor flow direction had an effect on ZL at any level of Q or Ro, even in veins with a taper >25%. Mean wall thickness correlated with ZL (r2=0.43; p=0.05).

In this in vitro system, saphenous vein graft impedance (ZL) was independent of valve lysis, flow direction, and the degree of vein taper but was weakly dependent on wall thickness. In veins of adequate size, hemodynamic considerations should not influence the decision to use the reversed vs nonreversed configuration.

Flow measurement before and after papaverine injection in above-knee prosthetic femoropopliteal bypass

OBJECTIVE

To investigate the value of intraoperative blood flow measurements on early and long-term patency of above-knee prosthetic femoropopliteal bypass.

METHODS

Flow was measured with a transit time flowmeter before (basal flow) and after an intragraft injection of papaverine (papaverine flow) in 87 operations (86 patients) between January 1990 and December 2001. Sixty-one grafts were of polyester, and 26 were of polytetrafluoroethylene. The operations were done under epidural anesthesia. The preoperative angiographic run-off score and clinical risk factors were recorded. Patency rates were analyzed with the product limit method and compared with the log-rank test. Variables found to be near significantly related to patency rates (P < .1) were included in a multivariate analysis performed with the Cox proportional hazard model.

RESULTS

Basal flow measurements were not related to patency. The 2- and 5-year patency rates for grafts with a papaverine flow < or = 500 mL/min were 48% and 18% compared with 66% and 52% for grafts with a papaverine flow > or = 500 mL/min. These differences were statistically significant (P = .012, hazard ratio, 2.6). Two- and 5-year patency rates for smokers vs nonsmokers were 44% and 18% vs 69% and 54%. The patency rates for patients with poor vs good run-off were 42% and 27% vs 66% and 31%. Smoking (P = .008, hazard ratio, 2.75) and poor run-off score (P = .009, hazard ratio, 2.38) were found to be independent risk factors for reduced patency rates. Poor run-off score did not correlate with low values of measured basal or papaverine flow.

CONCLUSIONS

Papaverine flow of < or = 500 mL/min is associated with reduced mid- and long-term patency rates. Additional antithrombotic medication and frequent follow-up for these grafts should be considered. The inferior patency rates of smokers and patients with poor run-off indicate that prosthetic bypass is less suitable for these groups of patients.

Intra-operative Doppler Flow Measurement do not Predict ‘At-risk’ Status of Infrainguinal Bypass Grafts

AIMS

Patients undergoing infrainguinal arterial reconstruction using vein conduits, frequently undergo intra-operative Doppler flow measurements to determine technical adequacy. The aim of this study was to determine the proportion of vein grafts with normal intra-operative haemodynamic parameters that were subsequently discovered to be 'at risk' on post-operative duplex surveillance scanning.

METHODS

We prospectively collected data on 82, primary infrainguinal vein bypass grafts. Post papaverine graft flow and peripheral resistance were measured using the Scimed Opdop intra-operative Doppler machine. All grafts were determined to be technically adequate on the basis of measured peripheral resistance units (mPRU) being < or =1. At 1 week, a post-operative duplex surveillance scan was performed. At risk status was determined and compared to the intra-operative Doppler flow measurement. Statistical analysis was performed using the Mann-Whitney U-test.

RESULTS

The post-operative duplex scan demonstrated that 53 (65%) of the 82 vein bypass grafts were diagnosed as being 'not at risk'; and 29 (35%) were regarded as at risk. When the groups were compared, there was no significant difference in intra-operative haemodynamic parameters between those not at risk and those at risk (P=0.19, Mann-Whitney U-test). The 1 month primary patency rate was 79% with a secondary patency rate of 100%.

CONCLUSION

Despite normal intra-operative Doppler flow measurements, 35% of vein grafts were regarded as being at risk at the 1 week post-operative duplex surveillance scan. No single value may be universally applicable for identifying at risk grafts intraoperatively. Indeed, graft failure appears to be a multifactorial process.

The hemodynamics of vein grafts: measurement and meaning

The long-term patency of infrainguinal vein grafts appears to depend primarily on the size and quality of the venous conduit. Therefore, those quantities which directly relate to the conduit's ability to act as a transporter of blood, namely internal diameter and longitudinal impedance (Z(L)), have predictive value for patency. Autologous grafts of good quality frequently remain patent even with compromised outflow. Therefore, those quantities that are outflow dependent, including deltaP, flow, velocity, shear stress, and resistance, carry less predictive value for long-term performance.

Preoperative angiographic score and intraoperative flow as predictors of the mid-term patency of infrapopliteal bypass grafts

OBJECTIVES

preoperative angiographic characteristics of the outflow tract have emerged as a predictive factor for the outcome of infrapopliteal reconstructions. Direct flow measurement can be routinely performed intraoperatively, but little is known regarding its impact on graft outcome. The present study was undertaken to compare the value of these parameters in predicting the mid-term patency of infrapopliteal bypass grafts.

DESIGN

retrospective clinical study.

PATIENTS

172 infrapopliteal reconstructions using autogenous vein were performed, of which 92 had a crural and 80 a pedal recipient artery.

METHODS

the preoperative angiogram was scored according to the SVS/ISCVS Ad Hoc Committee. At the end of the operation flow was measured with a transit-time flowmeter. Follow-up consisted of pressure measurements and duplex scanning.

RESULTS

the runoff score had no impact on femorocrural graft patency. For pedal grafts there was a tendency for inferior outcome with high runoff score, as the 1-year assisted primary patency for grafts with a completely occluded pedal arch was 11% compared with 52% for grafts with lower scores (p=0.056). Both intraoperative volume graft flow and maximum flow capacity had a highly significant influence on the outcome on crural reconstructions on univariate analysis. For pedal reconstructions only a a severely reduced maximum flow capacity after injection of papaverin was associated with an adverse outcome. Multivariate analysis revealed that maximum flow capacity was an independent significant factor affecting patency of femoroinfrapopliteal grafts (relative risk=0.53 per 30 ml/min increase, p<0.001). The runoff score was also a weak independent predictor of 1-year assisted primary patency in these grafts (relative risk=1.9 for a score >4 in crural and a score >5.5 in pedal grafts, p=0.036).

CONCLUSIONS

a completely occluded pedal arch in preoperative angiography was associated with poor infrapopliteal bypass outcome. Graft flow and maximal flow capacity are good predictors of the 1-year graft patency of femorocrural bypasses.

Effective hemodynamic diameter: an intrinsic property of vein grafts with predictive value for patency

INTRODUCTION

Conduit size and quality are major determinants of the long-term success of infrainguinal autologous vein grafting. However, accurate measurement of the internal diameter of vein grafts is difficult given their variable wall thickness and taper. The purpose of this study was to define the "effective" internal diameter of a vein graft according to its hemodynamic properties and to determine its significance for graft patency.

METHODS

Sixty infrainguinal bypass grafts performed on 57 patients were evaluated intraoperatively. Proximal and distal graft pressure and blood flow (Q(meas)) were measured with fluid-filled catheter transduction and ultrasonic transit-time flowimetry, respectively, after unclamping. Waveforms were recorded digitally at 200 Hz under baseline conditions and after stimulation with 60 mg of papaverine. According to Fourier transformation of the measured pressure gradient (DeltaP), the Womersley solution for fluid flow in a straight rigid tube was used to calculate theoretical flow waveforms (Q(calc)) for a range of graft diameters. The theoretical waveforms were then compared with the measured flow waveforms and the best-fit diameter chosen as the "effective hemodynamic diameter" (EHD). Only grafts in which the correlation coefficient of Q(calc) versus Q(meas) was more than 0.90 were accepted (n = 47) to assure validity of the hemodynamic model. After a mean follow-up of 12.5 months (range, 0.1-43.9 months), patency was determined by the life table method. Hemodynamic and clinical variables were tabulated, and their effect on patency determined the use of univariate and multivariate Cox regression.

RESULTS

Mean EHD was 4.1 +/- 0.1 mm with a range of 2.5 to 5.7 mm. Administration of papaverine caused profound changes in DeltaP (+78% +/- 17%) and Q(meas) (+71% +/- 12%) as expected, but had no effect on EHD (+0.05% +/- 0.1%). Univariate regression identified five variables associated with decreased secondary patency (P <.10): low EHD, conduit source other than the greater saphenous vein, high baseline DeltaP(mean), female sex, and redo operation. Of these, only low EHD was significant after multivariate analysis (P =.03). Patency of small diameter grafts (EHD < 3.6 mm; n = 11) was compared with patency of larger grafts (EHD > 3.6 mm; n = 36) to test a frequently espoused clinical guideline. Grafts with an EHD less than 3.6 mm exhibited significantly lower secondary patency compared with larger grafts (P =.0001). The positive and negative predictive values for an EHD less than 3.6 mm for secondary graft failure for grafts with at least 1 year follow-up were 86% and 88%, respectively.

CONCLUSION

An EHD is a unique parameter that quantifies conduit size and has a significant impact on vein graft patency. An EHD less than 3.6 mm portends graft failure.

Validation of a new and specific intraoperative measurement of vein graft resistance

PURPOSE

Clinical studies have revealed that the most important predictor of successful bypass grafting is the origin and quality of the bypass conduit. Attempts at intraoperative evaluation of the hemodynamic properties of the conduit, including assessment of blood flow (Q), pressure gradients (delta P), and resistance (R), have not been useful. This is because each of these parameters measures the characteristics of the graft plus the outflow bed. To date, no specific measurement of the resistive properties of the conduit only is available. The purpose of this investigation was to evaluate longitudinal impedance (ZL) as a measure of conduit-specific resistance and to evaluate its potential in predicting the outcome of infrainguinal vascular reconstructions.

METHODS

ZL was measured during surgery in 73 infrainguinal autologous vein reconstructions performed in 68 patients in two separate institutions over a 21-month period. Vein graft ultrasonic transit time Q and delta P (from proximal to distal anastomosis) were measured at baseline and after maximal peripheral vasodilatation with an intraarterial injection of papaverine 30 mg. Waveforms were recorded for 10 seconds at 200 Hz using a digital acquisition system. R was calculated as proximal mean pressure divided by mean blood flow (Q). After Fourier transformation, ZL was calculated as delta P/Q at each harmonic and total ZL (integral of ZL) was defined as the integral of moduli from 0 to 4 Hz.

RESULTS

All hemodynamic variables were significantly affected by papaverine vasodilatation (delta P, 3.9 +/- 0.5 vs 6.3 +/- 0.8 mm Hg; Q, 78.2 +/- 7.0 vs 126 +/- 11 ml/min; R, 134 +/- 17 vs 72.7 +/- 6.2 x 10(3) dyne.sec.cm-5; p < 0.0001), except integral of ZL, which remained constant (31.1 +/- 2.8 vs 30.8 +/- 2.8 x 10(3) dyne.cm-5; p = NS). After follow-up of 1 week to 17 months (median, 5 months), the 1-year primary, primary-assisted, and secondary patency rates were 72% +/- 7%, 77% +/- 6%, and 81% +/- 6%, respectively. Using Cox analysis, primary patency was significantly associated with decreased integral of ZL (p = 0.0001), but not with baseline or papaverine-stimulated delta P, Q, delta P/Q, or R integral of ZL > 47 x 10(3) dyne.cm-5 predicted primary failure with 90% positive and negative predictive value.

CONCLUSIONS

Intraoperative measurement of integral of ZL in infrainguinal vein grafts is independent of outflow conditions (that is, does not change with papaverine), and hence describes the resistive properties of the conduit only. In addition, these preliminary data suggest that integral of ZL is predictive of short-term primary patency. integral of ZL is the first available hemodynamic measurement that is conduit-specific and may therefore be a better predictor of graft patency than currently available methods.

Measurement of vascular input impedance in infrainguinal vein grafts

The purpose of this investigation was to measure vascular input impedance in infrainguinal vein grafts and assess the importance of clinical and hemodynamic parameters in predicting graft patency. Fifty-seven patients undergoing infrainguinal vein bypass grafting for limb salvage (n = 40) or claudication (n = 17) were prospectively studied. At the time of revascularization, simultaneously acquired intraluminal pressure and blood flow waveforms were digitized at 200 Hz and subjected to Fourier transformation in near real-time. Input impedance was calculated at baseline (immediately after unclamping) and after stimulation with either papaverine or completion arteriography. Resistance (Rin) was calculated as mean pressure divided by mean blood flow (Q). Characteristic impedance (Z0) was calculated as the mean of harmonics 3-10. Intraoperative data acquisition required approximately 5 min, utilized the completion angiography cannula already in place, and was uncomplicated in all patients. Stimulation with either papaverine or arteriography resulted in increased Q (72 +/- 7 to 146 +/- 11 ml/min, p < 0.001), decreased Rin (126 +/- 13 to 52 +/- 4 x 10(3) dyne.s.cm-5, p < 0.001), and slightly decreased Z0 (18 +/- 2 to 15 +/- 1, p = 0.002). After a mean follow-up of 20 months, the 2-year primary patency, secondary patency, limb salvage, and survival rates were 61 +/- 8%, 74 +/- 7%, 76 +/- 6%, and 86 +/- 6%, respectively. Primary patency was not associated with any of the clinical variables studied including age, sex, smoking history, history of previous vascular surgery, hypertension, coronary artery disease, diabetes mellitus, creatinine, indication for revascularization (claudication versus limb salvage), anesthesia (general versus regional), or level of distal anastomosis (popliteal versus infrapopliteal). Furthermore, there was no association between primary patency and baseline Q, baseline Rin, or stimulated Z0. However, using univariate analysis, patency was positively associated with decreased stimulated Rin (p = 0.002), elevated stimulated Q (p = 0.006), and decreased baseline Z0 (p = 0.02). Multiple regression analysis identified stimulated Rin as the only independent predictor of primary patency (p = 0.002). Stimulated Rin > or = 50 x 10(3) dyne.s.cm-5 was 71% sensitive and 65% specific for graft failure. It is concluded that 1) vascular input impedance can be simply and reliably measured in the operating room, and 2) elevated stimulated Rin is an independent predictor of primary patency.

Angioscopy for quality control of saphenous vein during bypass grafting

OBJECTIVES

Although autogenous vein is the conduit of choice for infrainguinal bypass grafting, some 20-30% of vein grafts fail during the first year postoperatively. Many of these failed veins are now known to have pre-existing pathological changes. Angioscopy enables intraoperative endoluminal visualisation of veins and can reveal anomalies, some previously unsuspected, despite preoperative Duplex ultrasound mapping and normal external appearances. The aim of this study was to compare angioscopic findings with contemporary histological appearances and with subsequent graft outcome and ultimately, to identify those endoluminal features which might be predictive for failure.

METHODS

Angioscopic vein inspection was carried out using Olympus 1.4 and 2.2mm angioscopes in patients undergoing femoropopliteal/distal bypass. Severe disease in the veins of five patients led to preferential use of polytetrafluoroethylene (PTFE) for above-knee bypasses. The remaining 38 videotaped sequences were reviewed by two surgeons and scored using a scale of 0 to 3, based on frequency and distribution of angioscopically detected lesions. These included haemorrhagic mural plaques, flimsy intraluminal strands, webs/bands and mobile/adherent thrombus. Vein harvested at operation was assessed by a pathologist according to the level of pre-existing abnormality.

RESULTS

There were significant associations between angioscopy/histology scores and graft survival (chi 2 = 22.00; df:3; p < 0.001; chi 2 = 22.43; df:3; p < 0.001 respectively). There was a significant correlation between angioscopy and histology scores (R8 = 0.725; p < 0.001).

CONCLUSIONS

Angioscopy allows immediate identification of the at risk, poor quality vein graft at the time of surgery, without the delays inherent with histological preparation and assessment. Recognition of abnormalities at angioscopy may ultimately improve graft outcome by prospectively eliminating use of poor vein.

The additional value of intraoperative angiography in infragenicular reconstruction

OBJECTIVE

To evaluate the ability of preoperative intraarterial digital subtraction angiography (IADSA) to predict the feasibility of infragenicular reconstruction and site of the distal anastomosis.

DESIGN

Prospective study.

SETTING

University Hospital

MATERIALS

45 patients with 50 ischaemic limbs, considered potential candidates for infragenicular reconstruction.

CHIEF OUTCOME MEASURES

Pre-reconstruction intraoperative angiography (IOA) was used as the gold standard. Analysis of angiograms was performed blindly and independently by a single observer. In patients who ultimately underwent primary amputation, exploration and attempted angiography of the crural and ankle vessels was performed to verify the IADSA findings.

MAIN RESULTS

There was 87% accuracy (kappa = 0.66) between IADSA and IOA in differentiating between a normal, stenosed and occluded tibial artery and there was 86% accuracy (kappa = 0.67) in determining the adequacy of run-off into the pedal arch. IADSA had a positive predictive value of 100% to determine the feasibility of reconstruction but a negative predictive value of only 73%. After excluding those patients tha IADSA deemed non-reconstructable, IADSA had a positive predictive value of 97% to determine the correct artery and 92% to determine the correct segment of artery for distal anastomosis.

CONCLUSIONS

IADSA could not determine when reconstruction was not possible, but in those deemed reconstructable by IADSA, the surgeon can confidently expose the appropriate artery at the appropriate level knowing the pedal run-off status in 86% of patients. IADSA should not be used to exclude reconstruction (i.e. pre-reconstruction IOA is still required in these patients) but for the remainder, IADSA can be used to plan surgical strategy without recourse to IOA.

The effect of postocclusion reactive hyperaemia, papaverine and nifedipine on duplex derived haemodynamic parameters of infrainguinal bypass grafts

OBJECTIVES

The aim of the present study was to analyse the effects of various vasodilating stimuli on postoperative infrainguinal graft haemodynamics.

DESIGN

Duplex derived haemodynamic parameters of infrainguinal bypass grafts were measured at rest and after postocclusion reactive hyperaemia, intraarterial papaverine (40 mgm) injection and peroral nifedipine (10 mg) administration.

SETTING

Department of Surgery, University Hospital.

MATERIALS

Twenty-nine patients with infrainguinal bypass grafts were studied by Duplex scanner after a median of 25 months postoperatively.

CHIEF OUTCOME MEASURES

Peak systolic velocity (PSV), mean velocity (MV) and volume flow (VF) were measured at rest and after various stimuli.

MAIN RESULTS

VF at rest increased from 125 +/- 16 ml/min (mean +/- S.E.M.) to 271 +/- 26 ml/min after papaverine administration and to 205 +/- 19 ml/min during reactive hyperaemia (p < 0.001). PSV, MV and VF increased significantly during postocclusion reactive hyperaemia and papaverine injection. After nifedipine administration VF increased to 154 +/- 21 ml/min after 30 min (p < 0.001) and there was a significant increase in MV (p < 0.05).

CONCLUSIONS

Duplex derived flow measurement of infrainguinal bypass grafts can evaluate graft and limb haemodynamics in the postoperative period. Pharmacological manipulations, such as vasodilation, can influence the physiological runoff with subsequent increase in volume flow through the graft.

The effect of epidural anaesthesia on peripheral resistance and graft flow following femorodistal reconstruction

OBJECTIVE

To determine the extent to which epidural anaesthesia influences peripheral resistance and graft blood flow following femorocrural reconstruction.

DESIGN

Prospective, controlled study measuring blood flow, arterial pressure and peripheral resistance in femorocrural bypass grafts for 20 min following onset of epidural anaesthesia with 15ml of 0.25% bupivacaine.

PATIENTS

Twenty patients undergoing femorocrural reconstruction for critical lower-limb ischaemia with in situ long saphenous vein, under general anaesthesia. Ten patients had epidural cannulae inserted preoperatively and injected with bupivacaine after completion of the graft.

RESULTS

Peripheral resistance fell in all 10 patients receiving epidural anaesthesia from a mean (range) of 1.07 PRU (0.32-2.2) to 0.49 PRU (0.19-0.72), compared to control values of 0.95 PRU (0.39-2.0) to 0.91 PRU (0.41-1.51; P < 0.01, Wilcoxon). There was a tendency for blood pressure to fall in the study patients (not significant) but graft blood flow still increased from 98 ml min-1 (41-221) to 160 ml min-1 (101-250), compared to flow in the control patients of 101 ml min-1 (45-176) at baseline to 104 ml min-1 (56-168; p < 0.01) at 20 min.

CONCLUSIONS

Epidural anaesthesia significantly decreases peripheral resistance and increases graft blood flow in femorocrural grafts and would appear, therefore, to be of benefit for patients undergoing femorodistal reconstruction.

Extracranial carotid artery flow measurement during carotid endarterectomy using a Doppler ultrasonographic flowmeter

A study was performed to evaluate immediate changes in carotid artery blood flow after carotid endarterectomy using a Doppler ultrasonographic flowmeter. Forty-seven consecutive patients aged 49-78 (median 64) years with symptomatic internal carotid artery (ICA) stenosis underwent carotid endarterectomy. Volume flow, resistance and pulsatility index were measured in the common carotid artery (CCA) and ICA both before and after operation. ICA flow increased by 54 per cent (P < 0.01) and resistance decreased by 58 per cent (P = 0.01). CCA flow rose by 17 per cent (P = 0.1) and resistance fell by 21 per cent (P = 0.02). The pulsatility index did not change significantly. The Doppler ultrasonographic flowmeter offers a simple, non-invasive and convenient means of improving understanding of the immediate haemodynamic effects of carotid endarterectomy. It is useful in everyday practice to confirm the adequacy of endarterectomy, particularly in the absence of other methods of quality control. Duplex ultrasonography might still be necessary after surgery if the flowmeter does not demonstrate an increase in flow compared with the preoperative value.

Infusion methods for determination of peripheral resistance: influence of infused medium and back pressure

It has been suggested that peripheral vascular resistance (PR), measured intraoperatively, can predict the outcome of infrainguinal reconstructions. There is, however, a great deal of variability in design and predictive value with this method, and it is prone to technical difficulties and possible errors. The present study evaluated the influence of the choice of infusion medium and the back pressure on PR as measured by the infusion technique. In a porcine model of experimentally induced stenosis, standard PR (calculated by the pressure difference across the stenosis and the Doppler volume flow) was compared with PR based on infusions of blood or saline solution. With blood as the infusion medium there was a significant correlation between the PR and the standard values (r = 0.795, p = 0.0005), whereas there was no correlation when saline solution was infused (r = 0.067, p = 0.345). Subtracting the back pressure resulted in a slight improvement in the correlations between standard PR and PR measured after infusion of blood but not saline solution. In summary, blood should be used as an infusion medium in methods of PR determination, but the influence of back pressure remains uncertain.

Early reoperation rates after arterial surgery

Between 1 January 1985 and 31 December 1991, 2426 patients underwent arterial surgery. Three hundred and seventy one reoperations were performed on 258 patients within 30 days of the initial procedure. One hundred and ninety three (52%) of the operations were attempted revascularisations, 95 (26%) were amputations and 58 (16%) were to control bleeding. One hundred and sixty nine (66%) of first operations were successful, but 76 patients required a further 113 reoperations. The mortality of reoperation was 16%, while the mortality of patients not requiring reoperation was 9% (p < 0.01). The mean hospital stay in days was higher in patients requiring reoperation (p < 0.05). Where appropriate, patients should be informed of the significant incidence of reoperation and reoperative mortality after vascular surgery. The increased hospital stay in reoperated patients has financial implications.

The effects of intraoperative vasodilators and angiographic contrast medium on the endothelium and smooth muscle cells of vein grafts

Cellular injury is a major cause of intimal hyperplasia in vein grafts. The effects of exposure of vein samples to iopamidol, papaverine and iloprost were studied in vitro in an organ chamber to determine whether these agents cause endothelial and/or smooth muscle cell injury. Smooth muscle cell function was assessed by eliciting a dose response curve to noradrenaline. Endothelial cell function was assessed by measuring the degree of endothelial-dependent relaxation of sub-maximally contracted vein samples. Iopamidol and iloprost did not have any deleterious effect on endothelial or smooth muscle cell function. Papaverine did not affect endothelial-dependent relaxation but did produce a significant decrease in smooth muscle contraction. The use of these intraoperative agents during femorodistal bypass does not appear to cause functional injury to the endothelial or smooth muscle cells.

Prediction of early graft occlusion in femoropopliteal and femorodistal reconstruction by measurement of volume flow with a transit time flowmeter and calculation of peripheral resistance

A transit time flowmeter (Transonic TC101DTM, Transonic Inc., U.S.A.) was used for flow measurements and calculation of peripheral resistance in 48 primary femoropopliteal and femorodistal reconstructions. The results were correlated with primary graft occlusions during the first 90 postoperative days. There were 25 men and 23 women with a median age of 75 years (67-83). Eight were diabetic. Indications for surgery were rest pain (n = 23), ischaemic ulcer (n = 16), gangrene (n = 8) and popliteal aneurysm (n = 1). Measurements were made before reconstruction on the artery at the site of the distal anastomosis. After reconstruction flow measurements were made on the graft near the proximal and distal anastomoses together with a proximal graft pressure measurement. The peripheral resistance was calculated. Eleven grafts occluded and six patients died, four with patient grafts. Patients with graft occlusions had a significantly lower flow before (4 vs. 20 ml/min) and after (60 vs. 110 ml/min) reconstruction and a higher peripheral resistance, (1238 vs. 625 mPRU) than patients with patent grafts. The most significant differences were found in the femorodistal bypass grafts. The transit time flowmeter was easy to use. The flow before and after reconstruction as well as the peripheral resistance could be used for the prediction of graft function within 90 days of surgery.

Intraoperative measurement of vascular graft resistance as a predictor of early outcome

The quality of distal run-off is one of the most important factors influencing the early outcome of femorodistal vein grafting. During femoropopliteal and infrapopliteal bypass, assessment of graft resistance and flow were made using a combination of Doppler flowmeter recordings and measurements of arterial pressure. In a series of 100 reconstructions there were 12 early failures. The mean (95 per cent confidence interval (c.i.)) maximal flow measurement in the group of grafts that failed when anastomosed to the popliteal artery or tibioperoneal trunk was 125 (74-176) ml/min compared with 256 (223-289) ml/min in successful grafts (P = 0.006). The corresponding figures for grafts inserted into a single crural vessel were 99 (72-126) and 165 (137-193) ml/min (P < 0.02). In the group that failed the mean (95 per cent c.i.) resistance after papaverine injection was 1.02 (0.82-1.22) peripheral resistance units (p.r.u.) compared with 0.47 (0.44-0.51) p.r.u. in the successful group (P < 0.001). Using a combination of resistance > 0.9 p.r.u. and capacity loss ratio after papaverine injection < 10 per cent to identify grafts that subsequently failed, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 92, 97, 85, 99 and 97 per cent respectively. These results confirm that haemodynamic measurements can be used at operation to identify a group of patients in whom bypass is likely to fail.

Selection of patients with critical limb ischaemia for femorodistal vein bypass

The merits of an aggressive policy of distal reconstruction have been questioned by some observers. To determine the factors affecting graft patency and mortality, we analysed 78 consecutive infragenicular femorodistal vein grafts performed in 72 patients with critical limb ischaemia. The primary, primary assisted and secondary graft patency rates at 36 months were 29, 57 and 64%, respectively. The limb salvage and patient survival rates at 36 months were 67 and 74%, respectively. Univariate analysis (log-rank test) was performed to identify factors affecting graft patency, limb salvage and mortality at 1 month (perioperative) and 1 year. Independent variables of age, sex, diabetes, presentation, level of anastomosis and vein technique (reversed or in situ) did not affect graft patency. The ankle systolic pressure did not predict graft patency but was an independent variable affecting mortality (p = 0.047), as did diabetes (p = 0.019). These results show that excellent limb salvage can be successfully achieved in severely ischaemic patients by adopting an aggressive approach to femorodistal bypass, and that age, gender and poor medical condition are not contraindications to femorodistal bypass. The difference between the primary and primary assisted patency rates in this series is dramatic and reflects the impact of a vein graft surveillance programme in preventing graft occlusion.

PTFE bypass grafting to isolated popliteal segments in critical limb ischaemia

Although the quality of the distal run-off has been considered as an important factor affecting the success of bypass grafting, reasonable results have nevertheless been reported for bypass grafts to a popliteal artery with no direct communication with the tibial or peroneal vessels (isolated popliteal segment, IPS). The use of autogenous vein has produced the best results in this situation with most authors finding polytetrafluoroethylene (PTFE) less satisfactory. Improved results have nevertheless been shown for femoropopliteal and femorotibial PTFE grafts by the incorporation of vein patches into the anastomoses. In this paper, the influence of this technique on the patency of PTFE grafts to IPS is evaluated. Thirty-three PTFE grafts to an IPS and 67 to the below knee (BK) popliteal artery with one or more run-off vessels were studied. All IPS grafts were carried out for limb salvage and in the BK popliteal group, 46 (69%) were for limb salvage and 21 (31%) were for severe claudication. Groups were matched in terms of age, smoking history and prevalence of diabetes mellitus. Cumulative patency rates of 84% at 1 year and 76% at 3 years were achieved in the IPS group compared to 90 and 81% for the BK popliteal group with one or more run-off vessels. Using the Taylor patch technique, comparable 3 year patency rates can be expected for PTFE grafts to IPSs and to BK popliteal arteries with patient tibial or peroneal run-off.

Intra-arterial papaverine and leg vascular resistance during in situ bypass surgery with high or low epidural anaesthesia

In situ saphenous vein arterial bypass flow was studied in 16 patients with respect to level of epidural anaesthesia. Arterial pressure and electromagnetic flow were used to evaluate arterial tone by intra-arterial (i.a.) papaverine. Eight patients had a low epidural block (< or = Th. 10) and eight patients were operated during high epidural anaesthesia (> Th. 10). Flow increased and arterial pressure decreased after i.a. papaverine in all patients. When compared with patients operated during high epidural anaesthesia, flow increase and decrease in vascular resistance took place in patients operated during low epidural anaesthesia (P < 0.02). Increase in arterial flow after i.a. papaverine was not significantly different in patients operated in low epidural and general anaesthesia (n = 8). In eight patients with insulin-dependent diabetes mellitus who had low epidural anaesthesia, the increase in flow after i.a. papaverine was not significantly different to that noted during high epidural anaesthesia. The results indicate that the level of analgesia influences graft flow after i.a. papaverine, probably reflecting differences in the effect of epidural anaesthesia on sympathetic tone to the leg.

Praxilene (naftidrofuryl oxalate) as an alternative for the augmentation of femoro-distal bypass blood flow

In 30 patients undergoing femoro-distal bypass the effect of papaverine and praxilene on blood flow in the graft was measured. The mean resting flow was 129 ml min-1 (range: 91-167) and after papaverine was 202 ml min-1 (142-262) and after praxilene was 205 ml min-1 (143-267). Praxilene has a similar effect to papaverine in the augmentation of blood flow, and further investigation is needed to see if long-term praxilene administration might improve graft survival.

Iloprost reduces peripheral resistance during femoro-distal reconstruction

A randomised placebo-controlled trial was conducted to investigate the effect of iloprost, a stable prostacyclin mimetic, on peripheral resistance during femoro-distal bypass. Patients undergoing femoro-distal long saphenous vein bypass for critical ischaemia received 3000 ng of iloprost or placebo infused into the graft via an unligated side branch over 2 min. Graft blood flow and peripheral resistance were measured for 20 min, using an operative Doppler flowmeter (OpDop 130, SciMed, U.K.) and a pressure transducer to record graft pressure. Postoperatively, graft blood flow was assessed by daily duplex ultrasound for 7 days. Iloprost produced an immediate drop in peripheral resistance in all cases (n = 18) by a mean (range) of 40% (4-80%) compared with controls (n = 15) in whom there was a 5.3% (-8 to +36%) increase in resistance (p less than 0.01, Wilcoxon test). Decreased peripheral resistance in iloprost-treated patients persisted to 20 min. The largest decreases in peripheral resistance occurred in patients with the highest initial resistances (r = 0.56, p less than 0.02). Graft flow during the same period increased by 52% (-7 to 294%) compared with controls in whom there was a 6% (-17 to 26%) increase in flow, (p less than 0.01). Flow remained elevated by 53% over baseline values at 1 week post-infusion in the iloprost-treated group but this did not achieve statistical significance compared to controls in whom flow also increased by 13%. Iloprost produces an immediate decrease in peripheral resistance associated with a prolonged increase in graft blood flow. This may reduce graft failure in the early postoperative period.

PTFE, collars, and patches

The results of PTFE grafts to crural vessels have been sufficiently poor for some surgeons to consider primary amputation for critical ischemia in the absence of suitable lengths of autologous vein from arm or leg. However, the results of two anastomotic techniques using a short segment of interposed vein, are encouraging. We have attained 1-year patency rates of 74% (n = 72) using PTFE with the Taylor patch technique (personal communication) and 47% (n = 27) using PTFE with Miller collar anastomoses to distal crural vessels. To investigate the hemodynamic benefit of these techniques, they have been tested (using a pulsatile flow model incorporating standard pressure, viscosity, graft and vessel length, and anastomotic angle) against a standard end-to-side PTFE anastomosis to cadaver internal mammary artery. There was no significant difference in flow between the anastomotic methods. Downstream resistance was dictated by the diameter of the recipient vessel providing a vein interposition technique was used (r greater than .80), but this relationship was lost if a direct PTFE-arterial anastomosis was performed (r = .06), suggesting additional anastomotic resistance in the latter. This constitutes experimental evidence to suggest that direct PTFE-arterial anastomosis risks hemodynamically important technical errors, which are avoidable by the use of either the Miller collar or Taylor patch.

Duplex scanning for the intraoperative assessment of infrainguinal arterial reconstruction: a useful tool?

Duplex scan, arteriography, and graft flow rates were used intraoperatively to assess 56 infrainguinal arterial reconstructions for technical error. Intraoperative duplex scan identified a technical defect or low graft flow velocity in 22 of 56 (39%) grafts. Eleven of the defects were judged to be clinically significant and were corrected. Four of these defects were missed by the completion arteriogram. One technical defect identified by completion arteriography was missed by duplex scan. Fifty percent (5/10) of grafts with an abnormal intraoperative duplex scan which were not corrected occluded within 30 days. Graft flow rates measured by the electromagnetic flowmeter were neither predictive of technical defect nor early graft outcome. Although the sensitivity of arteriography and duplex scan (88% sensitivity for both) were both high for predicting early graft occlusion, the combination of duplex scan and completion arteriography was significantly more accurate (p less than .0001) in predicting early graft outcome than either study alone. Duplex scan identified significant graft defects which were not detected by completion arteriography or graft flow rate measurement. The duplex scan also provided hemodynamic information which was predictive of early graft outcome. The duplex scan can be an important adjunct to completion arteriography for the intraoperative assessment of infrainguinal arterial reconstruction.

Failed femorocrural reconstruction does not prejudice amputation level

From January 1985 to December 1989, 500 consecutive patients presented to a single vascular unit with limb-threatening acute or critical ischaemia. Vascular reconstruction was attempted unless the patient had insufficient viable tissue to permit weight bearing or complete absence of run-off vessels in the calf. Fifty patients underwent a primary amputation and 450 patients underwent vascular reconstruction, of whom 265 had a femorocrural bypass. Sixty secondary amputations were performed following femorocrural bypass failure. The below-knee amputation to above-knee amputation ratio (BKA:AKA) was 2.0 in the primary amputation group and 1.1 in the secondary amputation group. Direct comparison between the two groups is not valid as they are clinically different. The combined BKA:AKA ratio was 1.4. This compares favourably with the BKA:AKA ratio of recent published series and figures from the National Amputation and Limb Fitting Services. It suggests that an unselective policy of vascular reconstruction for critical ischaemia does not lead to a higher proportion of above-knee amputations.

Iloprost improves femoro-distal graft flow after a single bolus injection

A double-blind, randomised, placebo-controlled trial was conducted to study the effect of the stable prostacyclin analogue iloprost on femoro-distal graft blood flow. After completing femoro-distal reconstruction, 3000 ng of iloprost or placebo was injected into the graft over 2 min. Graft blood flow, measured by electromagnetic flowmetry, increased by a mean (range) of 94% (12 to 192%) in patients receiving iloprost (n = 15) compared to 6% (-34 to 53%) in controls (n = 16; p less than 0.0001, t-test). Increased graft flow, measured by duplex ultrasound, was maintained in the iloprost group over a 7 day period postoperatively (F = 5.2, p = 0.03; analysis of variance) and remained higher at 7 days (p = 0.007, t-test). Iloprost produces an immediate, sustained increase in graft blood flow after femoro-distal reconstruction and may therefore be of benefit in reducing the incidence of early graft failure.

The "isolated" popliteal segment: a comparative evaluation of its vascular resistance

During femoro-popliteal and femoro-distal bypass, measurement of vascular resistance (VR) at the site of graft outflow may be used to quantify "run off". Intra-operative measurements were made in 51 lower limbs to compare VR in different categories of outflow; the "isolated" popliteal segment (IPS group, n = 11), the popliteal artery in continuity with patent vessels to the pedal arch (PIC group, n = 26) and the single calf vessel (SCV group, n = 14). VR was measured both before and after intra-arterial papaverine. The values in the 37 popliteal arteries were correlated with two different methods of arteriographic scoring. Vascular resistance in the IPS group (median 1149 mPRU, P = 0.003) but not significantly different from VR in the SCV group (median 1014 mPRU, range 743-1541 mPRU). VR in the SCV group was significantly greater than that in the PIC group (P = 0.006). After papaverine administration, the same relationships were observed between the IPS, PIC and SCV groups. Both before and after papaverine, VR in the popliteal artery correlated significantly with both arteriographic scores. In terms of VR, the isolated popliteal segment provides an outflow comparable to that of a single calf artery but less favourable than a popliteal artery wtih patent run off.

Outflow resistance and early occlusion of infrainguinal bypass grafts

Distal outflow vascular resistance (VR) has been measured intra-operatively during 67 infrainguinal bypass procedures to establish whether it might have a role as a predictive test for early graft thrombosis. The graft outflow was popliteal artery above the knee (48), popliteal artery distal to the knee (6) or a single calf vessel (13). VR was measured before anastomosis of the graft, calculated from the relationship between pressure and flow in the outflow artery during infusion of the patient's own blood at a constant rate. VR was measured before and after vasodilation with papaverine. Primary graft patency at 30 days was documented. In the 10 limbs in which graft thrombosis occurred, VR was 1167 +/- 367 mPRU, significantly higher than VR in 57 limbs with a patent graft, 850 +/- 310 mPRU (P = 0.02, Mann-Whitney U test). After papaverine, VR was 823 +/- 368 mPRU in the limbs with a thrombosed graft, significantly higher than that of limbs with a patent graft, 463 +/- 211 mPRU (P = 0.001). VR appeared to show most promise as a predictor of early thrombosis in the group of femoro-tibial and femoro-peroneal grafts. In this group, the value of 800 mPRU after papaverine was 92% efficient and was 80% sensitive, 100% specific and had a predictive value of 100% for early thrombosis. Distal outflow VR is an important factor in early graft thrombosis and might have a practical application as a predictor of early thrombosis of femoro-distal bypass grafts.

Measurement of arterial blood flow by Doppler ultrasound

A review is given of quantitative techniques and clinical applications of arterial Doppler ultrasound. The currently available Doppler equipment of stand-alone continuous wave and pulsed wave units, duplex systems and colour flow systems is briefly described. Doppler ultrasound can be divided into procedures concerned with waveform analysis, volume flow measurement and more recently colour flow imaging. Arterial Doppler waveform analysis is considered for a number of areas including carotid, lower limb, renal and renal transplant, obstetrics, adult cerebral, neonatal cerebral, and tumour studies. Using a duplex scanner volume flow in arteries can be measured from estimates of vessel cross sectional area, mean Doppler frequency and beam-vessel angle. The errors associated with each of these measurements is discussed, and reports of experimentally determined in vivo accuracy of volume flow measurements made using this technique are considered. Other volume flow measurement techniques including the promising attenuation compensation method are also explored.