Noninvasive intraoperative monitoring: A prospective study comparing Doppler systolic occlusion pressure and segmental plethysmography

Noninvasive lntraoperative Monitoring: A Prospective Comparing Doppler Systolic Occlusion Pressure and Segmental Plethysmography Thomas F. O’Donnell, Jr, MD, Boston, Massachusetts David Cossman, MD, Boston, Massachusetts Allan D. Callow, MD, FACS, Boston, Massachusetts

Technical errors leading to significant arterial occlusion may occur during approximately 14 [I] to 34 per cent [2] of vascular reconstructions, many leading to amputation and some to death of the patient. Any method that would detect problemssuch as thrombosis, embolism, subintimal dissection, stenosis at the anastomosis, or clamp injury &ring the procedure would minimize the rate of reoperation and its attendant risks. Skin color and temperature are too subject to systemic changes in blood volume and vasomotor tone to be used as consistent indicators of intraoperative misadventure [3], whereas palpation of pedal pulses may be impossible, especially in patients with distal occlusive disease [4]. Routine arteriography has been advocated by some surgeons [51, but many find it cumbersome, capable of inducing injury by itself, and misleading at times because it visualizes only in one plane [3]. To provide a more physiologic and quantitative assessment of the success of an arterial procedure, Creech, DeBakey, and Culotta [6] in 1957 recommended monitoring of digital blood flow by venous occlusion plethysmography. Although this approach was the first to employ a functional assessment of graft patency, it had drawbacks: the instrumentation required to measure digital flow was technically demanding and was influenced by systemic changes in cardiac output and vasomotor tone. As the instrumentation for noninvasive assessment of arterial occlusive disease has improved, so have the variety From the Noninvasive Vascular Laboratory and General Surgical Service, Tufts New England Medical Center, Tufts University School of Medicine, Boston, Massachusetts. Data organization and analysis were performed on the PFtDPMT system, a national computer resource sponsored by the ChemicaUSlologlcal Information HandlIngProgram, National Jnstitutes, of Health. Reprint requests should be addressed to Thomas F. O’Donnell, MD. Department of Surgery, Tufts New England Medical Center, 171 Harrison Avenue, Boston, Massachusetts 02111. Presentedat the Fifty-Eighth Annual Meeting of the New England Surgical Society, Portsmouth, New tfampshlre, September 30-October 2, 1977.

of devices recommended for intraoperative monitoring. The mercury strain gauge [2], impedance [ 71, and air plethysmography [I,81 have all been recommended. Despite the large number of devices, there is little quantitative data describing the sequential changes in either segmental plethysmographic amplitude or systolic pressure after commonly performed vascular procedures. At present, most vascular surgeons employ either Doppler systolic occlusion pressures or segmental plethysmography in the general evaluation of the vascular patient. Therefore, we conducted a prospective study with these two commonly used noninvasive hemodynamic methods in order to: (1) document quantitatively what is a “normal” pattern of response after various types of arterial reconstruction; (2) determine whether one method has any unique advantages or disadvantages; and (3) investigate the influence of combined aortoiliac and femoropopliteal segment disease on both the temporal pattern and the magnitude of change after reconstruction. Methods Method of Selection. All patients undergoing vascular surgery by two surgeons (ADC and TFO) for occlusive disease of the aortoiliac and femoropopliteal segments or for abdominal aortic aneurysm were eligible for the study. Only patients with pedal pulses that were auscultated by Doppler ultrasound preoperatively and in whom the ankle cuffs would not impinge on the operative field were admitted to the study groups. Vascular Groups. Preoperatively, all thirty-four patients underwent angiography and noninvasive hemodynamic studies. Segmental plethysmography, or Pulse Volume Recording (PVR), and Doppler systolic occlusion were performed at rest and again after a period of standardized exercise on a treadmill, as described by Darling et al [8]. The patients were separated into four study groups by the type of vascular procedure performed: six abdominal aortic

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aneurysm (AAA) resections; eight femoropopliteal (FP) bypass grafts; eight extraanatomic (EA) bypass grafts; and twelve aortofemoral (AF) bypass grafts. Control Group. Six patients undergoing major abdominal, nonvascular procedures underwent noninvasive hemodynamic studies prior to incision and sequentially throughout surgery. Zntraoperative Studies. The first intraoperative noninvasive hemodynamic (preop OR) measurements were obtained and recorded while the patient was under anesthesia and in a hemodynamically stable condition, as determined by blood pressure, heart rate, and central venous and/or wedge pressure. Five, 30, and 60 minutes after release of the aortic, iliac, or femoral occluding clamp, postreconstruction studies were performed. Repeat hemodynamic studies were obtained on all patients at 24 hours. Both limbs were studied in the AAA group, while in the FP group only the limb undergoing arterial reconstruction was examined. The EA and AF groups were further divided into four subgroups for purposes of comparison: (1) symptomatic; (2) asymptomatic; (3) occluded femoropopliteal segment; and (4) patent femoropopliteal segment. Symptomatic patients had limiting claudication, rest pain, or ischemic gangrene. Asymptomatic patients noted no pain of vascular origin, which was verified by standard hemodynamic criteria [9,10]. Angiographic evidence of femoropopliteal segment occlusion, as well as a significant decrease in both segmental Doppler systolic occlusion pressure and PVR amplitude, indicated anatomically and hemodynamically significant occlusion of the femoropopliteal segment [9]. Based on the results of previous studies [8,11], failure of Doppler systolic pressure or PVR amplitude to improve in the FP group or to equal 50 per cent of the preop OR values in AAA, EA, and AF groups by 60 minutes, dictated arteriography and/or exploration of the graft. Noninvasive Hemodynamic Methods. Since these methods have been previously described in detail by Y ao [IO] and Darling et al [8], they will be only briefly outlined here. A specially constructed sphygmomanometer cuff was placed snugly around the ankle above the malleoli. The bladder of this cuff measured 21.9 X 11.8 cm. The cuffs were taped and placed to assure a snug fit and to guard against accidental displacement during surgery. The position of the cuff was rechecked after the patient was draped and again prior to each determination. The cuff was connected to the monitoring port of the PVR instrument (Life Sciences Inc, 270 Greenwich Ave, Greenwich, CT 06830). To avoid potential contamination of the operative field, monitoring lines measuring 4 feet connected the ankle cuff with the PVR instrument. In the FP patients, the segment of the limb containing the ankle cuff and distal to it was placed in a disposable plastic Lahey bag in which a hole was cut for exit of the monitoring tubes. Monitoring lines then could be conveniently draped with towels to assure a sterile field. Systolic occlusion pressure at the ankle was determined by selecting preoperatively the pedal vessel with the crisper and louder sound. After acquagesic Doppler contact jelly

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had been placed over this vessel, a special disc-like Doppler probe (Parks Electronic Laboratory, 12770 SW, First Beaverton, OR 97005) was taped securely to the limb. The long line from the probe was brought along the course of the PVR monitoring line and connected to the Doppler ultrasound. Segmental plethysmographic (PVR) tracings were obtained by injecting a fixed volume (75 f 10 cc) of atmospheric air into the ankle cuff to a pressure of 65 mm Hg. The PVR was displayed permanently at a standard gain of 1 on a strip recorder, so that the amplitude could be measured in millimeters. Doppler systolic occlusion pressures were obtained by inflating the ankle cuff with a hand bulb and aneroid gauge to a pressure of 20 mm Hg above the systolic pressure. The occluding cuff was slowly deflated with a hand bulb, and the presence on the aneroid gauge where the first Doppler sound was heard was then noted..This was taken as indicative of the systolic pressure at the ankle. Brachial artery pressure was simultaneously obtained by the anesthesiologist, either by auscultation or, in the majority of cases, by direct intraarterial pressure recording at the radial artery. The Doppler systolic ankle/brachial pressure ratio (DSAB) was thereby derived. Statistical Methods. Patient data were entered and stored in the Prophet System Time Sharing Computer. Appropriate paired and unpaired Student t tests were performed.

Results

Clinical Data. The six patients in the control group underwent the following procedures: colonic resection (2 patients); gastric resection (2); abdominoperineal resection (1); and placement of an inferior vena caval clip (1). Because of the nature of the surgery all except the last patient received large volume replacements and all were subject to alterations in body temperature, blood pressure, cardiac output, and vasomotor tone. All six patients in the AAA group underwent elective resection. Only one had evidence of mild disease of the femoropopliteal segment. Since an intermittent declamping technic and vigorous crystalloid/colloid preload were used, no patient experienced a significant or prolonged decrease in brachial/radial blood pressure. All FP patients were in the limb salvage category (rest pain or ischemic gangrene). In five of eight patients, a reversed saphenous vein graft was anastomosed below the knee to the distal popliteal or tibia1 vessel, whereas in three patients an expanded polytetrafluoroethylene graft was inserted to the above-knee segment of the popliteal artery. In the eight EA patients, two femorofemoral bypasses were performed for limiting claudication. Five axillofemoral and

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Figure 1. The mean values f SEM for the six controlpatlents demonstrate no signHrcant change in either the PVR (top) of h the Doppkr AfB ratio (bottom). The 24 hour PVR value Increased slgnifkantly over the 60 minute value, perhaps related to a hyperemic response.

femorofemoral bypass grafts were carried out, four for limb salvage and one for limiting claudication. One patient underwent a unilateral axillofemoral graft for an ischemic ulcer. Seven of twelve AF patients presented with limiting claudication, and five presented with rest pain or ischemic gangrene. Noninvasive Intraoperative Studies. Control group (Figure I): Despite volume changes associated

with major intraabdominal surgery, neither the mean DSAB nor the mean PVR was altered significantly during the various procedures. At its maximum, Doppler systolic ankle pressure increased 25 per cent over preop OR values. Since the brachial systolic pressure increased to a greater degree than the ankle pressure, elevated ankle pressures were not reflected in the DSAB. After an insignificant 10 per cent decrease from preop OR values, the DSAB remained remarkably steady at 30 and 60 minutes. Although the mean PVR at 60 minutes (13.2 f 2.2 mm) was lower than the 24 hour value (p <0.05), the 60 minute

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Figure 2. The mean f SEM values for the six aortk aneurysm resections show a slgniflcant decrease in the PVR amplitude at 5 minutes post declampkg whkh persists thmugh 60 mkutes. t@ contrast Doppler A/B ratk (bottom) exhlblts no sign/f/cant change in the postdeclamplng period.

value was well within the control range for PVR amplitude at the ankle (15 f 2 mm). Abdominal aortic aneurysm (AAA) group (Figure 2): Although 5 minutes after declamping both the

DSAB and PVR declined from preop OR values by 17 and 35 per cent, respectively, only the decrease in PVR from 18.1 f 3.2 to 11.8 f 2.8 mm was significant (p <0.05). This trend of lowered PVR persisted at 60 minutes and occurred when the Doppler systolic ankle pressures were comparable to preop OR values (preop OR = 130.9 f 7.9 mm Hg; 5 minutes = 123 f 18 mm Hg; and 30 minutes = 130 f 19.7 mm Hg). Femoropopliteal (FP) group (Figure 3): The DSAB increased twofold at 5 minutes (p <0.05) and remained at this level for 24 hours. In contrast, after an initial increase of more than three fold (p
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Flgure 3. 778emean values for the eight femoropopllteal bypass grafts are associated with a progressive improvement In PVR values to the normal range by 60 minutes post declamplng. The Doppier Aft3 ratio (bottom) increased twotold and rematned at that /eve/ throughout 24 hours.

creased from 48 f 10.6 mm Hg (preop OR) to 105 f 11.9 mm Hg at 5 minutes, and thereafter followed a pattern similar to the DSAB. Extraanatomic

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Preoperatively, only the PVR level was lower in limbs with an occluded femoropopliteal segment (p <0.05). Five, 30, and 60 minutes after declamping, PVR and DSAB values were comparable to preop OR values in both the occluded and patent femoropopliteal limbs. At 24 hours only PVR levels had increased significantly over preop OR levels in the occluded femoropopliteal segment limbs (p <0.05). Although the PVR levels were within the normal range preoperatively in limbs with a patent femoropopliteal segment, they had increased significantly over preop OR values by 24 hours (p = 0.01). When the EA group was divided into symptomatic and asymptomatic patients, more dramatic changes were observed. By 5 minutes the DSAB of symptomatic

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Flgure 4. The mean values in this group of eight pat/en& are dlvlded Into patent (open circle) and occluded (closed circle) femoropopliteal segments. Only the preop OR PVR values are decreased slgnrricantly In the occluded femoropopliteal segment group. Both patent and occluded femoropopllteat segment groups show no decrease post declamplng, and on/y PVR values increase slgM/cant/y over preop OR measurements at 24 hours.

limbs had increased from a preop OR value of 0.44 f 0.03 to 0.63 f 0.04 (p = 0.01). At 5 minutes and throughout the operative course the DSAB of asymptomatic limbs demonstrated no significant change from preoperative values (0.83 f 0.09). A more dramatic but similar pattern was observed in PVR. In symptomatic limbs, PVR levels increased from a preoperative value of 7.3 f 2.8 to 16.6 f 4.3 mm (p <0.05) at 5 minutes. Thereafter, no significant change in PVR measurements was noted. Doppler systolic ankle pressure differed at only one point from the DSAB-at 5 minutes there was a significant increase from a preop OR value of 60 f 6.5 to 81 f 4.9 mm Hg (p
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Preoperatively, PVR levels alone showed a significant difference between the occluded and the patent femoropopliteal segment limbs (p <0.025). At 5 minutes after aortic declamping, DSAB levels in the occluded femoropopliteal limbs were depressed below preop OR values of 0.64 f 0.05 to 0.35 f 0.06

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and after 30 minutes to 0.39 f 0.09; however, the DSAB at 60 minutes was comparable to the preop OR ratio. In contrast, PVR levels in the limbs with occluded femoropopliteal segments did not decrease below preop OR values through 60 minutes. In limbs with the patent femoropopliteal segments, DSAB values at 5 and 30 minutes post declamping were comparable to preop OR values. At 24 hours, the DSAB had increased significantly over preop OR values (p <0.05). Five minutes after aortic declamping, the PVR amplitude in the patent femoropopliteal limbs had increased from an abnormal value of 10.7 f 1.4 mm to a normal value of 14.8 f 2.1 mm and again at 24 hours to 21.5 f 3.6 mm. Doppler systolic ankle pressure in both the occluded and patent femoropopliteal segment limbs followed trends similar to the DSAB. DSAB and PVR did not change significantly in the symptomatic limbs until 24 hours (0.85 f 0.07 and 16.6 f 2.1 mm, respectively), so that values at 5,30, and 60 minutes were comparable to or slightly greater than preop OR values. Since two asymptomatic limbs had intraoperative occlusions which were corrected after the 30 minute measurement, the 5 and 30 minute values (0.47 f 0.14 and 0.55 f 0.16, respectively) were significantly less than the preop OR value of 0.97 f 0.11. Doppler systolic ankle pressures demonstrate changes identical to those observed with the DSAB. Detection of Operative Accident. In four patients PVR and DSAB levels failed to return to within 50 per cent of preop OR levels by 60 minutes and prompted further evaluation. In one patient from the FP group, arteriography revealed an intimal flap. This was subsequently repaired, and in one month all grafts in the FP patients were patent, as determined by noninvasive criteria. In one patient from the EA group, exploration of the distal anastomosis on the side with the flat PVR and DSAB measurements revealed no defect in the suture line, but passage of a Fogarty catheter removed a distal embolus with marked improvement in the hemodynamic indices. Two patients in the AF group showed abnormalities in hemodynamic indices at 30 minutes. Both showed some pulsatile trace on the PVR, but amplitude was approximately 20 per cent of preop OR values. In one patient stenosis of the outflow track at the distal suture line was corrected and in the other an intimal flap baffling the outflow track was removed. Correction of these two technical errors resulted in restoration of noninvasive hemodynamic levels to preop OR levels within 15 minutes. It is significant that both these problems occurred in the asymptomatic limbs.

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L

Comments

The present study demonstrates that two common and technically simple forms of noninvasive intraoperative monitoring, Doppler systolic ankle ultrasound and PVR, provide consistent physiologic data on the immediate success of peripheral vascular surgery. There are, however, important differences in the time and magnitude of the postreconstructive hemodynamic responses which depend on several factors: (1) the type of vascular procedure performed; (2) the relative changes in blood volume and vasomotor tone; (3) the character of the hyperemic response; (4) the status of the arterial tree proximal to the monitoring device; and (5) the physiologic mechanisms upon which the particular type of hemodynamic method is based. The relatively wide range of patients and procedures in our study permits an analysis of how each one of these factors interrelates with and influences intraoperative hemody-

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namic changes, so that a quantitative guide can be given for intraoperative monitoring of each procedure. Although large volume shifts and alterations in vasomotor tone occurred with major intraabdominal surgery in our control group, maintenance of adequate perfusion by monitoring with arterial pressure, central venous pressure (or wedge pressure), and hourly urine output were associated with very little change in PVR or DSAB. Although placement of the monitoring cuff at the ankle level avoids many vagaries of cutaneous flow inherent in digital plethysmography [S], inadequate volume replacement or profound hypothermia with marked vasoconstriction are systemic factors which do modify PVR amplitude and systolic pressure. Correction of these abnormalities should be the initial focus when there are flat hemodynamic’ indices in the early postdeclamping period, before an operative error is assumed. After the release of a proximal arterial occlusion, a period of incre,ased blood flow usually occurs [12]. Since blood flow has an important relationship to segmental plethysmographic amplitude and systolic pressure, recognition of how this response may vary with the type of operation, the degree of preoperative ischemia, and the amount of residual disease distal to the arterial reconstruction is important in evaluating hemodynamic changes post reconstruction. The effect of the type of operation on the hyperemic response can be seen in a comparison between the aortic (AAA and AF) and peripheral (FP and EA) procedures. FP patients or EA patients with symptomatic limbs and patent femoropopliteal segments demonstrated prompt increases in DSAB and PVR, which were more marked in the FP group. In contrast, in the postdeclamping period, the AAA group showed a 15 per cent decrease in the DSAB and a more significant 35 per cent decrease in PVR. Since in these patients Doppler systolic ankle pressure remained stable during the postdeclamping period, the decreased DSAB was related to a disproportionate elevation in brachial pressure, probably due to reflex vasoconstriction [13]. On the other hand, the diminished PVR in the AAA patients underlines some of the important differences between Doppler pressure and PVR amplitude measurements. Vasoconstriction, especially at the cutaneous level, leads to opposite changes-Doppler systolic ankle pressure may be increased while PVR amplitude is lowered [13]. Therefore, in AAA patients, PVR amplitude may be somewhat delayed in returning to preoperative levels, but it should be at least greater than 10 mm in the patient without concomitant occlusive disease. Since in AAA patients Doppler systolic ankle

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pressure appears less subject to declamping phenomena, it provides a method of corroborating a successful arterial procedure. Since the degree of preoperative ischemia and residual disease distal to the arterial reconstruction influence hemodynamics, the hyperemic response in the AF patients is more complex. Many of the changes are opposite to those observed in the AAA patients. In the limbs with patent femoropopliteal segments, both DSAB and PVR values are comparable to preop OR values. In contrast to peripheral reconstructions (FP and EA groups), several investigators [12,15] have demonstrated that maximal arterial flow is delayed in aortofemoral reconstructions, so that initial segmental plethysmographic values may be no different than preoperative values [I,S]. The paradoxic occurrence of vasospasm in previously ischemic limbs [13], the gradual me.chanical dilatation of the recipient vascular bed [15], and the greater fluxes in extracellular fluid space volume all alter the hyperemic response after aortofemoral bypass and have been related to a delay in the improvement of noninvasive hemodynamic indices. Occlusive disease of the femoropopliteal segment further modifies the hyperemic response in AF patients. DSAB levels are depressed to less than preop OR levels through 60 minutes, at a time when PVR values are not statistically different than preop OR values. Griffin et al [I] noted that when femoropopliteal occlusive disease is present, PVR amplitudes at the calf average only 70 per cent of preoperative values at 20 minutes, whereas Darling et al [8] stated that the PVR amplitude should return to at least 50 per cent of its preoperative level. Since the hemodynamic significance of the femoropopliteal occlusion and actual plethysmographic data were not provided in these previous studies, a comparison of their patient populations to ours is difficult. It is apparent, however, that hemodynamically significant femoropopliteal disease delays improvement in PVR amplitude and is associated with actual decreases in the DSAB from preop OR values. Whether the difference between the results from Doppler and PVR monitoring in the AF patients are related to pressure/volume flow alterations has not been settled by our study. Practical Considerations. Like other surgeons who employ noninvasive hemodynamic monitoring intraoperatively, we routinely obtain data 5 minutes after declamping, at which time the systemic hemodynamics should have stabilized. Since preoperatively the limbs have been categorized by angiography and vascular laboratory studies into occluded

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and patent femoropopliteal segments, the particular hemodynamic pattern that should develop is known. If the ankle hemodynamic indices are not equal to preoperative values in AAA or AF patients or if they have not improved in FP patients or in asymptomatic EA patients, attention initially should be directed toward establishing that no technical problems are present, such as poorly applied ankle cuffs. If systemic hemodynamics are not stable, the surgeon can obtain any necessary hemostasis in the retroperitoneal area while volume deficits are being corrected. By 20 minutes after declamping, if PVR or DSAB levels have not increased to preoperative levels, the graft is systematically checked from proximal to distal anastomoses for any obvious technical errors. If this inspection is negative, intraoperative arteriography is obtained in FP patients, and a small graftotomy is performed for intraluminal visualization of the distal anastomosis in AF, AAA, and EA patients. Fogarty catheters are passed retrograde and prograde when no technical problem is noted at the anastomoses.

5.

6. 7.

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10. 11. 12.

13. 14.

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Summary

Seventy-two limbs in forty patients underwent Doppler systolic ankle pressure and Pulse Volume Recording (PVR) amplitude measurements intraoperatively. Control patients and patients undergoing abdominal aortic aneurysm (AAA) resections showed no significant decrease in Doppler systolic anklemrachial pressure ratio (DSAB). PVR measurements were slightly decreased after declamping in the AAA patients. Femoropopliteal bypass was associated with a prompt increase in PVR and DSAB levels. In contrast, postreconstruction values in the extraanatomic (EA) and aortofemoral (AF) bypass groups were dependent upon the patency of the femoropopliteal segment. Intraoperative monitoring provides a quantitative assessment of the immediate success of arterial surgery. Acknowledgnents: We wish to thank Madison Thompson, PA, for technical assistance and John Ruggiero, BS, for statistical assistance. References 1. Griffin LH, Wray CM, Vaughan BL, Monet2 WM: Detection of vascular occlusion during operation by segmental plethysmography and skin thermometry. Ann Surg 173: 389, 1971. 2. Dickson AH, Strandness DE, Bell JW: The detection and sequelae of operative accidents complicating reconstructive arterial surgery. Am J Surg 109: 143, 1965. 3. O’Donnell TF, Raines JK, Darling RC: lntraoperative monitoring using the pulse volume recorder. Surg GynecolObstet145: 252, 7977. 4. Radke HM. Bell JW, Strandness DE, Jesseph JE: Monitoring of

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digit volume changes in angioplastic surgery: use of strain gauge plethysmography. Ann Surg 154: 818, 1961. Renwick S, Royle JP, Martin P: Operative angiography after femoral-popliteal arterial reconstruction; its influence on failure rate. Br J Surg 55: 134, 1968. Creech 0, DeBakey MD, Culotta R: Digital blood flow following reconstruction surgery. Arch Surg 74: 5, 1957. Couch WP, Van De Water JM, Dmochowski JR: Non Invasive measurement of peripheral arterial flow. Arch Sup 102: 435, 1971. Darling RC, Raines JK, Brener BJ, Austen WG: Quantitative segmental pulse volume recorder: a clinical tool. Surgery 72: 873, 1972. Raines JK, Darling RC, Buth J, Brewster DC, Austen WG: Vascuiar laboratory criteria for the v of peripheral vascular disease of the lower extremltles. Surgery 79: 21, 1976. Yao JST: New techniques in objective arterial evaluation. Arch Surg 106: 600, 1973. Strandness DE, Bell JW: Ankle pressure responses after reconstructive arterial surgery. Surgery 59: 514, 1966. Renwick S, Gabe IT, Shillingford JP, Martln P: Blood flow after reconstructive arterial surgery measured by implanted electromagnetic flow probe. Surgmy64: 544, 1968. Strandness DE, Sumner DS: Hemo@namics for Surgeons. New York, Grune & Stratton, 1975. Strandness DE: Waveform analysis In the diagnosis of arteriosclerosis obliterans. Peripheral Arterial Disease, A Physiologic Approach. Boston, Little Brown, 1969. Mannick JA, Jackson BT, Coffman JD: Hemodynamics of arterial surgery in atherosclerotic limbs. II. Comparison of intraoperative arterial pressure and flow with prs and postoperative exercise blood flow. Surgery60: 578, 1966.

Discussion C. Darling (Boston, MA): All patients undergoing arterial reconstruction of the aorta or distal vessels should undergo operative monitoring by Doppler pressures. I agree with the authors that with an open distal system these pressures should return to the preoperative value before the patient leaves the operating room. Certain patients facing amputation will paradoxically improve clinically after aortoprofunda bypass, although their ankle pressures may not improve for hours, days, or even weeks postoperatively. Second, the indications for arterial reconstruction in the United States are rapidly changing, es are the requirements for those who are doing these operations. The number of peripheral arterial procedures remains approximately 100,000 per year. The great majority, at least in the lower extremity, are now reconstructions to distal diseased vessels. Thus, to be effective, the monitoring device must be placed distally, and this will require a sterile PVR or Doppler probe. In summary, let us consider the wise words of Dr. George Dunlop on the cost-benefit ratio regarding the national health dollar. Most knowledgeable vascular surgeons admit that expensive reoperations may be required because of technical problems occurring at the initial operation. Angiography can be very misleading and expensive. Simple inexpensive noninvasive monitoring devices, ae described herein, are educationally important, economically sound, and in the best interests of our patients.

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John Mannick (Boston, MA): I agree with the authors and Dr. Darling that noninvasive monitoring can certainly provide reassurance to the vascular surgeon at the time of operation that a physiologically acceptable result has been produced. However, I caution against the abandonment of on-the-table angiography, which although a nuisance to the surgeon, remains the best way of determining the technical adequacy of an arterial reconstruction, particularly below the level of the knee joint. In approximately 3 or 4 per cent of our patients undergoing femorotibial reconstructions, angiography has revealed minor technical problems, particularly at the level of the distal anastomosis, which we consider worth correcting to prevent future graft failure. These little technical deficiencies ordinarily will not produce a pressure gradient across the reconstruction or prevent flow through the reconstruction, and so would not be detected by noninvasive technics. Therefore, the noninvasive methods should be a supplement to rather than a substitute for on-the-table angiography, particularly in the complex reconstructions that we seem to have been doing with increasing frequency in recent years.

Thomas F. O’Donnell (closing): Dr. Darling wondered how we monitored distal arterial reconstructions, and Dr. Mannick rightly pointed out the important role of intraoperative arteriography in complicated distal tibia1 or

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isolated popliteal artery reconstruction. Following is a case illustrating both of these points. A twenty-two year old man sustained a gunshot wound to the popliteal area. A cuff was placed across the transmetatarsal area for monitoring distal arterial reconstructions, while remaining out of the operative field. After preoperative arteriography and arterial exploration with repair of a lacerated anterior tibia1 artery, the patient showed a flat Pulse Volume Recording at the metatarsal level. While waiting 10 to 15 minutes for a repeat study, we tidied up the wound. Since repeat studies revealed a persistently flat tracing, arteriography was performed, and no obstruction was noted, although intense vasospasm was evident. This case illustrates that noninvasive intraoperative assessment is a screening device to alert the surgeon to potential difficulties and that it is based on physiologic rather than anatomic principles. I would, therefore, fully agree with Dr. Mannick that in complicated femoropopliteal bypass grafts to the distal tibial vessels or tci isolated popliteal segments, corroboration of the hemodynamic (noninvasive) studies with arteriography is important. Whether subtle angiographic changes in the vein graft at the anastomosis without immediate hemodynamic effects will have long-term hemodynamic consequences, as implied by Dr. DeWeese, is an unsettled question now. At present we recommend routine intraoperative monitoring in all vascular cases and restriction of arteriography to positive studies or to distal reconstruction.

The American Journal d Surgery