Pursuing efficiency in surgical practice.

To examine fluctuations in numbers of patients on surgical wards the dates of admission from January of each of the 5556 patients admitted from 1 January 1985 to 31 December 1987 were examined during computerised audit of a single surgical firm. The numbers of patients under the care of the firm fluctuated widely, often exceeding the 38 beds nominally available. Duration of stay varied from two days or less (3062 admissions) to more than a month (163 admissions). One patient was in hospital for 278 days. The patients admitted for more than a month (2.9% of the total) filled 28% of the beds; not all these patients were elderly. A further increase in throughput of patients undergoing elective operations might be achieved by always admitting patients on the day of operation, and perhaps by discharging patients even sooner than at present. Efficiency would increase but so would overall costs.

Auditing the vascular surgical audit.

The results are presented of vascular surgical audits in Oxford over the 10 years 1975-85. Changes observed include the decreasing use of endarterectomy (other than carotid), the introduction of transluminal angioplasty, and fewer lumbar sympathectomies. The number of major amputations has increased relative to arterial reconstructions. Our audit methods over the 10 years included the use of punch cards, two different computer programs, and a simple weekly audit of cases. The relative merits of these methods are compared. Numbers of procedures performed in Oxford were compared with expected figures calculated from the Hospital In-patient Enquiry, the Lothian audit, and the Vascular Surgical Society survey. In general the calculated and actual numbers are similar. Difficulties in finding comparable operation categories and the totally inadequate classification of nationally collected data highlight the need for improved audit in vascular surgery.

The effect of wall mechanical properties on patency of arterial grafts.

Normal arteries have properties which match the low output impedance of the heart to the high peripheral impedance. These properties can be assessed in terms of compliance (% diameter change per unit pressure change) as well as by other haemodynamic parameters. Experiments were designed using vein, Dacron and expanded polytetrafluoroethylene (PTFE) in a low flow canine femoral artery bypass model. No graft group achieved perfect patency. At twelve weeks 80% of vein grafts, 30% of Dacron grafts, and 15% of PTFE grafts remained patent. The compliance of vein grafts was maintained despite marked thickening of the wall. Patency was correlated at a highly significant level with compliance. The studies demonstrate that the matching of the mechanical properties of grafts to host arteries is important in the design of successful synthetic arterial grafts.

Expanded polytetrafluoroethylene grafts for severe lower limb ischaemia.

Three years' experience with the use of expanded polytetrafluoroethylene grafts for severe lower extremity ischaemia are reported; 44 femoropopliteal bypasses were performed, 35 for limb salvage. The prosthesis was used when no saphenous vein was available (23) or to shorten operation time in infirm patients (21). Of 41 patients with a mean age of 70 years, 19 had significant ischaemic heart disease and 10 were diabetic. The mean follow-up period for patient grafts is now 16 months (4--39 months), and the overall life-table cumulative patency is 59 per cent at 6 months, 52 per cent at 1 year and 40 per cent at 2 years. No correlation was demonstrated between patency and run-off, diabetes or smoking, but above-knee grafts may do better than those below the knee. Twenty grafts have occluded leading to 12 amputations, 3 further reconstructions and 1 death. Nine other deaths have occurred from causes not directly related to the lower limb ischaemia, 4 perioperatively and 5 later. The graft described were used in elderly unfit patients, most of whom would have had amputations before the introduction of polytetrafluoroethylene grafts. The results presented support the continued evaluation of this prosthesis in such selected cases.

In vivo measurement of blood vessel wall thickness.

To understand the mechanical properties of arteries and vascular grafts, it is crucial that the wall thickness in these vessels be known. Unfortunately, all availble methods for measuring this parameter require the removal of the vessel, which precludes the study of such vessels as a function of time. A new radiographic technique for measuring the wall thickness of arteries and vascular grafts in vivo, utilizing contrast materials injected into the vessel lumen and applied to the outer surface of the vessel, is described. Radiographs are obtained with a portable X-ray machine and analyzed using a calibrated microscope. The technique has been successfully applied to the in vivo measurement of wall thickness in canine arteries, veins, and experimental vascular grafts. It is concluded that the method provides better than 95% accuracy in a variety of vessels and that it can be used to study changes in vascular grafts after their implantation into the arterial circulation.

Low compliance and arterial graft occlusion.

Early closure of arterial grafts is not fully understood. Patency loss in saphenous vein at 1 year is 12 to 30%. Synthetic grafts are worse. Stiff grafts may impede pulsatile flow and interfere with energy propagation. In vivo compliance (C, % radial change/mm Hg x 10(2) +/- SEM), derived from pressure and diameter measurements, was assessed in 38 arteries and 60 arterial grafts in a standardized canine femoral artery bypass model. Normal artery (C = 7.40 +/- 0.73) was more compliant than any graft (P < 0.01). At implantation, vein (C = 2.67 +/- 0.18) was more compliant than double velour Dacron (C = 1.86 +/- 0.16) or expanded polytetrafluoroethylene (C = 1.63 +/- 0.14) (P < 0.01). Vein graft patency at 2 weeks was 83%, Dacron 64% (P = 0.13), and PTFE 32% (P < 0.01). Vein compliance did not change with implantation. Vein patency was maintained, but Dacron fell to 29% and PTFE to 14% by 3 months. A definite correlation was shown between patency and compliance. It is suggested that more attention should be devoted to elastic properties in the design of arterial grafts.

Dynamic compliance of arterial grafts.

A cantilever transducer has been developed which allows measurements of diastolic diameter and diameter change in response to pulse pressure in dissected blood vessels during sterile procedures. Preliminary results indicate that it will detect subtle changes in wall elastic properties of arterial grafts at subtle changes in wall elastic properties of arterial grafts at and following implantation, which changes may influence graft function. Compliance, the percentage change in volume per unit pressure, was greater in normal canine femoral artery than in autogenous vein grafts (AVG). Two new graft materials were tested. Mesh-covered modified human umbilical cord vein (DBM) was similar in compliance to AVG but more compliant than double-velour Dacron. Diastolic diameter changes were also recorded. After 2 wk, all three graft materials had increased in diameter: AVG by 8%, DBM by 6%, and Dacron by 5%. After 3 mo, AVG diameter increased by 24%.