A practical method of differential hypothermia to permit use of a low pump oxygenator flow.

By cooling the blood just before returning it to the body, marked reduction in the temperature of the heart, brain, liver, and kidney can be produced easily and with great economy in heat transfer, since the great bulk of the animal or patient, consisting of skin, muscle, and bone, is cooled much more slowly. This results in a marked oxygen saving, due to the direct antimetabolic effect of the cooling. Metabolic acidosis can be avoided and so far no irreversible effects of the cooling have been discoverable. Warming is so greatly facilitated by the heat stored in the nonvital areas that it is not necessary to warm the blood returning from the extracorporeal circuit. The use of safe, low, extracorporeal flows offers a number of possible advantages including great simplicity of cannulation and of the pump oxygenator design and operation.

Use of lower extremity deep veins as arterial substitutes: functional status of the donor leg.

Large veins (superior and inferior vena cava, portal vein) have been replaced successfully with lower extremity deep veins (superficial femoral-popliteal). Femoropopliteal bypass with superficial femoral-popliteal veins has been reported to give excellent long-term results. Nevertheless, this source of autogenous veins has not gained acceptance, in part because of the fear that deep vein removal will result in severe venous outflow restriction in the donor limb. To assess the clinical and functional effect of excising a deep vein, we compared a group of limbs in which the superficial femoral-popliteal vein was resected for use as a femoropopliteal bypass graft (25 legs) with a control group of 22 legs in which a saphenous vein or polytetrafluoroethylene graft was used for femoropopliteal bypass. No significant differences were found in age or sex distribution, time from surgery to the venous test, side of bypass, or the incidence of postoperative extremity swelling, either early or late. A mild but significant calf enlargement was observed in the deep vein group (p less than 0.05), and a pattern consistent with venous outflow obstruction was shown by plethysmography in 21 of 25 extremities (84%) in which a deep vein was used for femoropopliteal bypass but in only 11 of 22 (50%) control extremities (p less than 0.02). It is concluded that a lower extremity deep veins should be considered as a suitable replacement for a large vein or, when superficial vein is not available, as an infrainguinal arterial substitute.

Volume tests for chronic venous insufficiency: an appraisal.

Chronic venous disease is increasingly treated surgically with a variety of experimental procedures. Noninvasive volume tests are commonly used before surgery to select patients and after surgery to assess results. Rapid volume changes are considered to indicate regurgitation. Rigorous statistical validation of tests and the confounding nature of unmeasured arterial inflow are seldom considered. Volume changes were measured in 29 control limbs and 35 limbs with venous disease, with mercury-in-silicone rubber strain gauges, for both exercise and elevation. Normalization for arterial flow permitted calculation of the regurgitation rate. Normal (95% confidence) limits for measured and calculated parameters were determined. Specificity was shown by the percent of normal parameter values for control limbs and sensitivity by the percent of abnormal values for extremities with venous disease. Arterial flow significantly altered volume curves. Normalization increased specificity and sensitivity significantly. Calf exercise tests, even normalized, were too insensitive to be reliable. Elevation tests were significantly more sensitive for determining regurgitation. However, exercise tests were useful and supplied important information about the calf muscle pump. We conclude that, as currently used, many limb volume test procedures are unsuitable but could be improved significantly by normalization to reduce the confounding effect of regional arterial flow and use of an elevation test to measure regurgitation.

Therapeutic implications of phlebographic obstruction in chronic venous stasis.

The purpose of this work was to evaluate the functional characteristics of the venous system of patients with chronic obstruction of their deep veins proved by phlebography. Sixty-eight extremities in 34 normal volunteers and 21 extremities in 17 patients with chronic venous stasis and phlebographically demonstrated obstruction of their deep veins (popliteal-superficial femoral in 33.3%, common femoral in 23.8%, iliac in 33.3% and inferior vena cava in 9.5%) were evaluated using mercury in silastic strain gauges on the feet to measure venous volume changes on elevation and exercise. Regurgitant flow, corrected for arterial foot blood flow, was calculated. In the control group, the apparent regurgitation range was 0 to 2.3 ml %/min (mean +/- 2 SD). Sixty-two percent of extremities with obstructed deep veins had significant functional regurgitation. Regurgitation was detected by phlebography in only 14.3% of cases. From these results we conclude that obstruction of the deep venous system by phlebography may or may not signify functional obstruction and, in itself, therefore, does not indicate that bypass surgery is an appropriate method of treatment. Selection for surgical correction requires quantitative determination of insufficiency since higher grades of regurgitation probably contraindicate venous bypass.

Clinical trials of a new polytetrafluoroethylene-silicone graft.

A self-sealing polytetrafluoroethelene (PTFE)-silicone graft designed to be used early after implantation was placed in 30 end-stage renal disease patients. Thirty-five conventional PTFE grafts were used in the control group. All patients were followed for 1 year. In the PTFE-silicone graft group, median time for first use was 1 day after implantation. Conventional PTFE grafts were first used 2 to 4 weeks after implantation. Early punctures of the PTFE-silicone grafts (first 10 sessions), although more difficult to perform than late punctures, were not more difficult than punctures of conventional PTFE grafts. Late punctures in PTFE-silicone grafts were easier than conventional PTFE graft punctures. Bleeding after needle removal was significantly decreased after early and late punctures of PTFE-silicone grafts compared with conventional PTFE grafts (p less than 0.001). The PTFE-silicone graft can be used immediately after implantation, sparing patients additional access procedures for short-term dialysis. This results in less morbidity, decreased bleeding complications, shorter hospital stay, and a significant reduction in expenses.

Clinical trial of a self-sealing PTFE-silicone dialysis graft.

A double wall PTFE graft with a silicone rubber middle layer (PTFE-sil) shown in a canine model to be self-sealing after needle puncture, was tried in 30 dialysis patients. Thirty-five patients with PTFE grafts were controls. All patients were followed for 1 year. In the PTFE-sil group, mean time to first dialysis was 1.3 days after implantation; during first 10 treatments, 17% of punctures did not bleed, 61% bled minimally, and 4% required 10 or more minutes of compression. No bleeding complications were encountered at any time. Complications of PTFE-sil vs. PTFE were as follows: thrombosis 36.6% vs. 28.5%; infection 13.3% vs. 11.4%; seroma 3% vs. 0%; steal 3% vs. 0%; pseudoaneurysm 0% vs. 17.1%; one year primary patency 63% vs. 66%; secondary patency 75% vs. 67%. In conclusion, the PTFE-sil graft, can be used immediately after implantation, sparing patient additional access procedures for acute dialysis. This results in less morbidity, decrease in bleeding complications, considerable shortening of hospital stay and significant reduction in expenses.

Arterial flow in venous volume studies.

The rate of venous refilling after exercise is commonly used in noninvasive exercise tests to assess chronic venous regurgitation. Volume refilling is the sum of venous regurgitation and arterial blood flow. Our hypothesis is that volume data do not accurately measure regurgitation unless blood flow is known. Foot volume data after exercise and elevation were obtained, using the mercury-in-silastic strain gauge, for 68 control and 131 extremities with venous disease. Measured values for the time of half-volume refilling were compared to values corrected for arterial flow. The arterial flow accounted for virtually half the volume change, but showed wide and unpredictable variations. Corrected times of half-volume refilling had significantly narrower variations and regurgitation was better estimated (p less than 0.001). For regurgitation to be comparable between patients or over time in venous volume tests, arterial flow must be determined.

Radiological evaluation of the chronic venous stasis syndrome.

Chronic venous stasis is an extremely complex clinical syndrome of pain and changes in the skin that can involve the superficial, deep, and perforating veins. This syndrome is commonly referred to as "the postphlebitic syndrome," implying that thrombophlebitis is its sole etiology. To test this hypothesis, we performed ascending venography on 51 limbs of patients with the chronic venous stasis syndrome and demonstrated that 32 had no radiological evidence of recent or old thrombophlebitis. Instead, they had normal-appearing veins, suggesting primary incompetence of the deep and/or perforating venous valves rather than thrombophlebitis as the etiology. Since various operations have recently been proposed to correct or bypass malfunctioning valves, precise demonstration of pathological change is required to choose the appropriate procedure and to evaluate results. Descending venograms were combined with the ascending studies in 42 limbs for this purpose. In addition to outlining the abnormalities responsible for chronic venous stasis syndrome in individual cases, interesting conclusions regarding the syndrome itself were reached.

Assessing pulmonary function in acute respiratory insufficiency: a clinical charting sheet.

A sheet to chart the clinical respiratory variables relevant to acute respiratory insufficiency (ARI) therapy is presented. The chart permits plotting shunt fraction (Qsp/Qt) and efficiency (E or 1--Qsp/Qt) vs. load (L). L is the volume of oxygen (combined and dissolved) that would be exchanged in the lung per minute, if venous blood became fully equilibrated with alveolar gas. L relates cardiac output (Qt), hemoglobin concentration, alveolar oxygen tension, venous oxygen saturation and tension, and the oxygen-hemoglobin combining and oxygen solubility constants. Oxygen consumption (VO2) isopleths are added to the sheet (VO2 = L X E). Qt, VO2, and hence L are indexed per m2 (body surface area), and the approximate normal VO2 range is indicated. Using this sheet hopefully simplifies the correlation of complex pulmonary oxygen exchange data and enhances information recognition and analysis. It provides special help in determining the optimal PEEP in difficult ARI cases. To illustrate its use, a case is detailed.

Foot blood flow measurements improve venous plethysmographic studies.

The time for foot volume restoration after exercise is widely used as a measure of venous regurgitation. Since this is also a function of arterial inflow rate, we have tested the hypothesis that uncorrected for arterial inflow, these tests may be misleading. Change in venous foot volume after elevation and on exercise was measured in 44 subjects. Arterial inflow was also determined. In a few patients arterial flow was varied by cooling or by exercise. The times of half-volume restoration were measured. Calculated were: the rate of total blood flow into the foot; the rate of venous regurgitation; and "venous sufficiency indices" for elevation and for exercise with and without correction for arterial inflow rate. These indices combine volume and time data in a single numeric value. Volume change on elevation was uninfluenced by the rate of arterial inflow. Volume change on exercise and the halftime of volume restoration varied significantly with the rate of arterial inflow as did the "venous sufficiency indices." These variances were significantly reduced by correcting for arterial inflow rate. We conclude that for foot volume studies to measure regurgitation and for data obtained at different times to be comparable, corrections must be made for the rate of arterial inflow to the foot.

A self-sealing dialysis prosthesis. Coaxial double PTFE-silicone graft.

The performance of a new dialysis prosthesis designed to self-seal after puncture was tested ex vivo and in vivo. It consists of two coaxial polytetrafluoroethylene tubes (PTFE), the space between them filled with silicone rubber sealant (PTFE-sil). Ex vivo: Three PTFE-sil, three double PTFE (without silicone), and three single PTFE grafts were placed sequentially between scribner shunts in the hind limb of four dogs. Bleeding on puncturing with an 18-gauge needle was measured for 30 seconds. PTFE-sil bled less than the controls (g): PTFE-sil; 16 +/- 18; double PTFE: 32 +/- 10; single PTFE: 52 +/- 19 (p less than 0.001). In vivo: Six PTFE-sil and five single PTFE grafts were interposed between the carotid artery and jugular vein of dogs and were punctured with a 16-gauge needle on days 1, 3, and 7. Bleeding was measured through an incision over the puncture site at 5 minutes. In 11 punctures of PTFE-sil, there was no bleeding; three bled less than 20 g. In 13 control punctures, none bled less than 70 g. Patency: Grafts were studied for patency in arteriovenous (AV) fistulas in 34 dogs. Each dog received a PTFE-sil graft in one groin and a single PTFE control graft in the other. At 4 months, patency rates were: PTFE-sil, 84%; single PTFE, 87% (NS). Four months after implantation, hemostasis after puncture in PTFE-sil grafts required 70 +/- 49 seconds versus 207 +/- 48 seconds for PTFE grafts (p less than 0.005). In conclusion, PTFE-sil grafts are self-sealing, can be used immediately after implantation, and need minimal compression after needle removal.

Noninvasive evaluation of chronic venous insufficiency. Use of foot mercury strain-gauge plethysmography.

Twenty-seven patients (40 extremities) with chronic venous insufficiency and 30 controls (60 extremities) were studied using noninvasive measurements of foot volume (foot mercury strain-gauge plethysmography [FMSGP]). Tests were performed with exercise (sitting) and with elevation (Trendelenburg), with and without tourniquets, to evaluate muscle pump efficiency and valvular competence. Empiric venous sufficiency indexes were calculated for exercise and for Trendelenburg's test. Test results were compared with invasive ambulatory venous pressure (AVP) data (13) and with ascending and retrograde venography (25). Distinctive plethysmographic patterns revealed the insufficiency was saphenous (four), calf perforators (14), saphenous plus perforators (seven), and deep venous (15), including occlusion (four). Correlation with AVP and venography was good but FMSGP was more discriminating, providing precise anatomical information, better reproducibility, and distinguishing poor muscle pump function from regurgitation. Patients accept FMSGP well. Repeated postoperative data are readily obtained for evaluation of surgical procedures.

Pathophysiologic evaluation of chronic venous stasis with ambulatory venous pressure studies.

Seven normal controls and 51 lower extremities with venous insufficiency in 45 patients were studied with ambulatory venous pressure. Measurements were done at rest and during 15 seconds of exercise without a tourniquet and with 1 or 2 tourniquets at different levels of the extremity. The decrease in pressure during exercise and the time to return to standing levels were used to calculate a venous sufficiency index. Six pathologic categories were identified in patients with chronic venous stasis. Incompetence of perforators was present in 17 cases. A combination of long saphenous vein and perforator incompetence was detected in 10 cases. Thirteen cases had a pattern of regurgitant deep vein incompetence. Two cases had incompetence of the saphenous system. A deep vein obstruction pattern was present in 3 other patients. Ascending and retrograde phlebography was done in 30 of these cases. There was an 83.3% correlation between the venous pressure and phlebographic tests. Contrast studies were found to be complementary and added extra-anatomical information. Based on these special studies, a rational approach to the treatment of venous insufficiency has evolved. The early results are encouraging.

A rational approach to surgery of the chronic venous statis syndrome.

Ambulatory venous pressure (AVP) and ascending and retro-grade phlebography have been used to elucidate the precise pathogenetic factors in cases of venous stasis. On the bases of this information, procedures aimed at the correction of the particular pathophysiological alterations were carried out. Fifty-two lower extremities in 49 patients suffering from chronic venous statis were studied. The AVP was performed by having the patient walk in place for 15 seconds without tourniquet and with one or two tourniquets at different levels of the extremity. The per cent drop of pressure in a foot vein during exercise and the time to return to standing pressure were used to determine a venous sufficiency index. Four distinct factors or groupings could be distinguished: incompetent perforators (31), deep vein incompetence (14), incompetence of the saphenous vein (3), and obstruction of deep veins (4). Six types of surgical procedures were done: ligation of perforators (25), superficial femoral valvuloplasty (3), segmental venous transposition (1), ligation of the superficial femoral vein (1), cross femoral venous bypass (1) and high ligation and stripping of the long saphenous vein (3). Three patients had skin sloughing after perforator ligation, and one patient developed a hematoma requiring evacuation following segmental venous transfer. Post-operative AVP evaluation in 11 patients after perforator ligation, two patients following superficial femoral valvuloplasty, one patient after segmental venous transfer, and one patient after cross femoral venous bypass showed significant improvement. Early follow-up results are very satisfactory.