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Biomedical subjects

R N Baird

Publications and source records attributed to R N Baird.

At least 19 recordsLinked to original sources
PubMed1995

Clinical and experimental studies of intraoperative autotransfusion using a new filtration device.

The Haemocell S-350 device has recently been introduced for intraoperative autotransfusion. The system uses a novel membrane filter to process shed blood. In the first part of this study a 0.2-micron pore size filter was used in a randomized trial comparing the use of autotransfusion (n = 8) with bank blood controls (n = 9) during aortic reconstruction. This part of the trial was abandoned because of unexpected non-surgical bleeding. Bank blood requirements fell from a median of 3.0 (range 0.0-9.0) units to 1.5 (range 0.0-7.0) units when autotransfusion was used, but these patients had a greater perioperative blood loss (1791 (range 932-3104) versus 1140 (range 440-3840) ml). There was evidence of postoperative heparin excess with an activated partial thromboplastin time ratio of 1.3 (range 0.9-3.0) versus 1.0 (range 1.0-1.2) in controls and an activated clotting time of 206 (range 143-280) versus 137 (range 107-142) s. This was confirmed by raised plasma heparin levels and a prolonged thrombin time normalized by protamine. To improve performance a 0.6-micron pore size filter was studied in ten patients. Filtration efficiency doubled from 19 to 38 per cent. Electron micrographs demonstrated better filter clearance, but 44 per cent of the original concentration of heparin remained in the reinfusate. The S-350 device may be an attractive alternative to centrifugation for intraoperative autotransfusion but, until efficiency is improved, it should only be used for cardiovascular surgery when excess heparin can be reversed with protamine.

Aortic Aneurysm, Abdominal↗
PubMed1995

Postocclusive hyperaemic duplex scan: a new method of aortoiliac assessment.

Aortoiliac duplex scanning, while accurate, is time-consuming and technically demanding. This study aimed to develop a fast, non-invasive screening test for aortoiliac disease. Colour duplex scanning was used to record common femoral Doppler ultrasonographic waveforms following 3 min of arterial occlusion using a thigh cuff in 25 patients with normal aortoiliac segments and 25 patients with significant aortoiliac disease. The latter patients had a prolonged period of postocclusive hyperaemic flow compared with the former. End diastolic velocity, 70 s after cuff release, was a significant discriminant between the two groups (sensitivity of 88 per cent, accuracy of 92 per cent). The postocclusive hyperaemic duplex (PHD) test performed well when used prospectively in a further 50 limbs (sensitivity of 86 per cent, accuracy of 84 per cent). The test was more sensitive than femoral pulse palpation and compared favourably with arteriography. The PHD test provides a simple, noninvasive assessment for aortoiliac disease that can be performed on the initial outpatient clinic visit.

Aged↗
PubMed1995

Colour duplex in assessing the infrainguinal arteries in patients with claudication.

Non-invasive assessment of the lower-limb vasculature may avoid unnecessary arteriography. Colour duplex scanning of the femoral and popliteal arteries was performed in claudicants who were potential candidates for endoluminal therapy. This was compared with the findings of biplanar conventional arteriography and intra-arterial digital subtraction angiography. In 112 lower limbs duplex gave the following results compared with angiography: the sensitivity, specificity, positive predictive value, negative predictive value and accuracy for occlusions (n = 48), stenoses (n = 31), atheromatous vessel (n = 21) and disease-free (n = 12) were all greater or equal to 94%. The lengths of the occlusions were accurately identified by duplex. Clinical examination and spectral analysis at the common femoral artery failed to identify two patients who had an iliac lesion. Colour duplex examination is the investigation of choice in assessing the major infrainguinal arteries in patients with claudication.

Adult↗
PubMed1995

The role of thrombolysis in the management of thromboembolic disorders: a four-year review.

OBJECTIVE: To examine the role of thrombolysis alone, or in conjunction with surgery and angioplasty, in the treatment of thromboembolic disorders. DESIGN: A retrospective review of 70 patients, who received thrombolysis on 73 occasions between 1990 and 1993. PATIENTS AND METHODS: Four groups were defined: (1) thrombolysis alone (40%); (2) thrombolysis followed by angioplasty (23%); (3) thrombolysis followed by surgery (13%) and (4) thrombolysis after failed angioplasty (24%). RESULTS: Twenty-eight patients (40%) received thrombolysis alone of which 13 were successful. In 25 cases (36%) thrombolysis was initially successful in that it permitted further angioplasty or surgical reconstruction. This adjunctive treatment was successful in 16 cases. Overall, when used as a first-line treatment, thrombolysis was successful in 72% of cases. Success in this context includes those in which a further procedure was possible after thrombolysis. These groups included 20 occluded grafts in which thrombolysis played an important part in unblocking 13 (65%) of them. In a separate group of 17 patients (24%) thrombolysis was given after failed angioplasty and was successful on 15 (88%) occasions. Local complications occurred in 17 patients. There were three deaths. There were no intra-cerebral haemorrhages. CONCLUSIONS: Thrombolysis alone can be used successfully. There is a large group in which thrombolysis can help to increase the success rate of interventional radiology.

Adult↗
PubMed1995

Late reoperation in vascular surgery.

OBJECTIVES: Assessment of late reoperation (after 30 days) following vascular surgery. DESIGN: Analysis of a prospectively collected database of consecutive patients undergoing vascular surgery. SETTING: A single teaching unit's experience between 1986-1993. MATERIALS: Patients undergoing 2501 primary arterial reconstructions. CHIEF OUTCOME MEASURES: Reoperation after 30 days. MAIN RESULTS: One hundred and fifty eight patients (6%) underwent further operations, at more than 1 month after the primary procedure. Primary procedures at highest risk for reoperations were axillobifemoral bypasses and femorodistal bypasses with respective late reoperation rates of 20% and 16%. The majority of patients required late reoperation because of graft occlusion or stenosis. Overall, of the 158 late reoperations performed, 114 were related to the same arterial segment with the same presenting symptoms as the primary operation, and 44 for a different indication. A second or subsequent reoperation was required in 54 patients and the overall operative mortality was 11%. CONCLUSION: Patients undergoing certain vascular procedures, should be informed of the high risk of a subsequent procedure when consent is obtained.

Aged↗
PubMed1995

Treatment of intermittent claudication: the impact on quality of life.

OBJECTIVES: To measure changes in claudicant's quality of life after surgery, angioplasty or unsupervised exercise. To explore the relationship between clinical indicators of limb perfusion and patient's perception of health change. DESIGN: Prospective study. SETTING: University Hospital vascular outpatients. MATERIALS AND METHODS: 202 claudicants referred for Duplex of lower limb arterial disease over a 12 month period. The short form 36 questionnaire was used to determine quality of life. Ankle pressures and walking distances were determined. MAIN RESULTS: The SF-36 was completed by 186 patients (92%) before and after treatment (34 operative patients, 74 angioplasty and 78 treated by exercise alone). Baseline quality of life was worse in surgical patients. Unsupervised exercise produced minimal changes in quality of life. Angioplasty and operation produced similar, significant improvements in physical functioning and pain. Changes in physical function or pain scores were unrelated to changes in ankle pressure. CONCLUSIONS: Unsupervised exercise programs are unlikely to significantly improve patient's quality of life. The benefits of surgery and angioplasty support a relaxation in the indications for investigation and treatment of claudicants. Patients with impaired perceived health should not be denied treatment on the basis of preintervention ankle pressure or walking distance alone.

Analysis of Variance↗
PubMed1995

Preferential use of vein for above-knee femoropopliteal grafts.

OBJECTIVES: Many centres preferentially use polytetrafluoroethylene (PTFE) for above-knee femoropopliteal bypass as surgery is simplified and patency rates are comparable to vein, which is preserved for subsequent revisions or for distal disease progression. In this Unit, vein remains first choice graft material. The aim of this study was to audit our results with respect to above-knee bypass to establish the demand for vein for secondary reconstruction and to document the ultimate fate of the limb. PATIENTS: Between 1983 and 1992, 112 above-knee reconstructions were performed on 109 patients (89 vein and 23 PTFE grafts). PTFE was used where vein was absent or inadequate. Life table analysis of primary graft patency, limb salvage and patient survival up to 36 months follow-up concurs with previously reported series. RESULTS: Twenty-eight vein grafts (31%) and 11 PTFE grafts (48%) occluded during a median follow-up of 64 months (8-116 months). In only four cases was vein required for secondary procedures. The remainder were salvaged by thrombectomy and local procedures for technical problems. Amputation rates following graft occlusion were 12% in the vein group (20% of these being above-knee) as against 26% in the PTFE group (80% above knee). CONCLUSIONS: The demand for vein for secondary procedures is low. Amputation rates when vein grafts do occlude are half those of PTFE and amputation level is significantly influenced by graft type. We advocate preferential use of vein in above-knee femoropopliteal bypass.

Adult↗
PubMed1995

The value of pre-discharge Duplex scanning in infrainguinal graft surveillance.

OBJECTIVES: Protocols and criteria for Duplex-based graft surveillance programmes (GS) vary widely as to the optimum regimens for maximising detection of "at risk" grafts. Few centres recommend starting GS before discharge. The aim of this study was to audit our experience with respect to early scanning. SETTING: Vascular Studies Unit, Bristol Royal Infirmary. METHOD: The records of 123 patients entering GS from January 1992 were reviewed. Patients were scanned at 1 week, 6 weeks and 3, 6, 9 and 12 months post-bypass. Haemodynamic criteria used were a peak mean velocity (PMV) less than 45 cm/s and a focal velocity disturbance with a V2/V1 ratio of 1.5 or more. RESULTS: Forty-six abnormalities (37% detection rate) were identified on scans within one week. In all cases, on-table completion studies with either arteriography and/or flow measurements had failed to identify the anomalies subsequently detected by Duplex. At 1 week, six grafts had occluded, 27 had a focal PMV increase (mean V2/V1 ratio: 2.6; range 1.5-4.3), four had low flow velocities, four had arteriovenous fistulae, one contained mobile thrombus, two had retained cusps and two had hamstring entrapment. Of 40 patent, but compromised grafts, 18 warranted immediate investigation. Of the 27 patients with velocity disturbances on Duplex, 25 were simply observed but, eight have since required intervention for definitive stenoses at these sites which, in retrospect, were evident within the first postoperative week. CONCLUSIONS: Pre-discharge scanning is a useful modality for detecting technical problems. Intrinsic graft abnormalities, possibly the sites of future definitive stenoses, have been visualised even at 1 week and once identified, can be more closely scrutinised thereafter. Pre-discharge colour Duplex is recommended as standard practice for quality control after infrainguinal bypass.

Arterial Occlusive Diseases↗
PubMed1995

Quantitative endoluminal measurements during angioscopy: an innovative technique.

AIM: To evaluate angioscopy in this Unit with respect to its application in lower limb vascular reconstructions. By providing magnified, colour images of the luminal surfaces of vein grafts, anastomoses and native arteries, angioscopy allows direct visualisation of imperfections and is sensitive in diagnosing technical problems. However, assessment is qualitative and magnification of the image can distort the operator's impression of true size. Angioscopy would be more versatile if it were possible to quantify the observed images. METHOD: A new technique has been developed to measure intra-luminal diameter from the angioscopic images. A linear displacement transducer is attached to the angioscope and accurately monitors its axial shift. Signals from the transducer are received by a personal computer equipped with a video frame grabber and analogue digital converter, together with appropriate software. The computer generates calculated dimensions based on geometrical principles, once each angioscope has been appropriately calibrated at the outset. RESULTS: Laboratory studies examining tubes of known dimensions have confirmed the reproducibility and accuracy of the technique. Simultaneous angioscopic and Duplex ultrasound measurements of the internal diameters of segments of vein suspended in a water bath were then carried out. Using the Duplex results as the 'gold standard', there was a strong correlation between the measurements obtained with the two techniques (Rs = 0.92). CONCLUSIONS: In the clinical context, this system has the capability to generate accurate endoluminal measurements during angioscopy. This has application for quality control in the selection of veins and inspection of run-off vessels during bypass grafting and in completion studies, following both operative and percutaneous procedures.

Analog-Digital Conversion↗
PubMed1995

Non-invasive aortoiliac assessment.

OBJECTIVES: To assess the accuracy of Duplex ultrasound in the assessment of aortoiliac disease. DESIGN: Prospective, semi-blind study. SETTING: Vascular laboratory and radiology departments, University Hospital. MATERIALS AND METHODS: Ninety-two patients underwent assessment of the aortoiliac segment by femoral pulse palpation, Duplex ultrasound and biplanar arteriography. Of these 184 aortoiliac segments, 68 were also assessed by intraarterial pressure measurements and 80 by magnetic resonance angiography (MRA). MAIN RESULTS: Femoral pulses were abnormal in all 32 occluded aortoiliac segments. Of 152 patent segments, femoral pulse palpation was misleading in 50 (33%). MRA detected all occlusions and had a sensitivity of 71% and specificity of 68% for stenoses, compared to arteriography. Colour flow Duplex misdiagnosed four occlusions as stenoses. Duplex had a sensitivity of 91% and specificity of 93% for stenoses when compared to arteriography. Two stenoses, detected by Duplex and confirmed by pressure gradients, were missed by arteriography. CONCLUSIONS: Pressure measurements remain the gold standard for aortoiliac examination, arteriography providing only morphological information. The limitations of femoral pulse palpation should be appreciated. Although MRA was faster, Duplex examination proved slightly more sensitive to stenoses. At present, colour Duplex provides the best non-invasive assessment of aortoiliac disease and could prevent unnecessary arteriograms.

Aorta, Abdominal↗
PubMed1994

Pulse-generated run-off versus dependent Doppler ultrasonography for assessment of calf vessel patency.

Pulse-generated run-off (PGR) is an established technique in the assessment of calf vessel patency. Dependent Doppler ultrasonography is proposed as a fast and simple alternative. Twenty-six limbs with severe ischaemia were evaluated by PGR, dependent Doppler examination and intra-arterial digital subtraction angiography (DSA). PGR was performed and scored as previously described. Dependent Doppler ultrasonography was performed after 5 min of foot dependency and scored as for PGR. Angiograms were scored by an independent radiologist, who awarded 2 for a vessel widely patent to the ankle, 1 for a diseased vessel crossing the ankle and 0 if no vessel was visualized. Of 78 calf vessels evaluated, 59 (76 per cent) appeared patent on PGR and dependent Doppler examination but only 33 (42 per cent) appeared patent to the ankle with intra-arterial DSA. There was very good agreement between PGR and dependent Doppler for detection of patent calf vessels (kappa = 0.93). Doppler signals were biphasic in six calf vessels on dependency and in 22 vessels with PGR. PGR and dependent Doppler ultrasonography detected 26 vessels communicating with the pedal arch compared with seven detected angiographically. There was good agreement between PGR and dependent Doppler examination for diagnosis of the most suitable vessel for distal anastomosis (kappa = 0.80). The wide availability and simplicity of dependent Doppler ultrasonography mean that no patient with a critically ischaemic limb should be denied reconstructive surgery on the basis of angiographic findings alone.

Angiography, Digital Subtraction↗
PubMed1994

A multicenter study of popliteal aneurysms. Joint Vascular Research Group.

PURPOSE: The purpose of this study was to determine current practice in the treatment of all categories of popliteal aneurysms (PA) in light of the efficacy of intraarterial thrombolysis in PA presenting as acute ischemia. METHODS: Prospective data collected from 19 vascular surgeons from 200 PA in 137 patients during a 4-year period from 1989. RESULTS: The most common presentation (125 PA) was leg ischemia, with the most severe symptom being claudication in 58, acute limb-threatening ischemia in 56, and digital atheroembolism in 11 limbs. The nonischemic group (75 PA) included 43 symptom-free cases and 32 cases with local symptoms arising from the popliteal fossa. Of 62 patients requiring emergency treatment, bypasses were done in 56, 10 of whom had early occlusion. Thrombolysis was used alone or in combination with bypass on 23 occasions, with 16 successful outcomes. Of 138 PA presenting electively, 80 underwent bypass, with one early occlusion, and 58 were observed. In the observed group, 18 later underwent bypass during a median follow-up of 22 months. The indications for late bypass were expansion of a small (< 2 cm) asymptomatic PA and the development of distal ischemia. There were 18 deaths in the observed group because of medical unfitness; limb ischemia did not develop during follow-up. CONCLUSIONS: Intraarterial thrombolysis is of value in restoring the distal run off before bypass in PA presenting as acute limb-threatening ischemia. However, the results do not justify an expectant policy for asymptomatic aneurysms.

Adult↗
PubMed1994

Criteria for identification of the "at-risk" infrainguinal bypass graft.

The criteria for identifying the "at-risk" femorodistal bypass are controversial. Eighty-eight patients were entered into a surveillance programme using ankle-brachial pressure indices (ABPI), colour Duplex and intraarterial digital subtraction angiography (IADSA). Changes in ABPI of more than 0.1 identified 12/22 (51%) grafts thought to be "at-risk". In the 88 grafts, a PMV (peak mean velocity) < 45 cm per second had a sensitivity and specificity of 55 and 85% compared to 91 and 95% if a PMV < 45 cm per second and a V2/V1 ratio of greater than 2 was used to identify the 22 grafts "at-risk". In total 341 examinations were performed, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy for impedance analysis was 70, 90, 48, 97 and 91% respectively, compared to 93, 97, 77, 99 and 97% for colour Duplex in identifying the "at-risk" grafts. Between 6 weeks and 12 months the mean PMV was seen to drop by 29% and the mean impedance score by 19%. The most sensitive mode of non-invasive graft surveillance is colour Duplex providing the assessment involves both a measurement of the velocity ratio and the absolute velocity. However, impedance analysis is a better screening test than ABPI and PMV.

Angiography, Digital Subtraction↗