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Biomedical subjects

I F Hawkins

Publications and source records attributed to I F Hawkins.

At least 37 records · Page 2Linked to original sources
PubMed1995

Current status of carbon dioxide angiography.

The current status of carbon dioxide as an angiographic contrast agent is reviewed in this article. The physical characteristics of intravascular carbon dioxide, pertinent physiology, and principles of imaging are discussed. In addition, the advantages and limitations of carbon dioxide are compared with those of iodinated contrast. Examples of diagnostic and therapeutic procedures in both the arterial and venous systems show the utility of carbon dioxide angiography.

Angiography↗
PubMed1994

CO2 digital angiography: a safer contrast agent for renal vascular imaging?

Although the new nonionic contrast agents are safer than ionic agents, renal insufficiency and even death still occur occasionally. Therefore, we have explored the use of carbon dioxide (CO2) as an alternative angiographic contrast agent used in combination with digital subtraction angiography. Clinical observations have been made in over 800 patients. The images obtained are of equivalent diagnostic quality compared with those using conventional iodinated contrast agents. Recent advances in imaging, including "stacking," provide images comparable with iodinated contrast. Very small vessels, equivalent to third-order branches of the renal artery, can be imaged satisfactorily with CO2. Occasional studies with CO2 yield information not apparent with iodinated contrast agents, including excellent visualization of arteriovenous shunts, collateral circulations, malignant tumors, and minute amounts of arterial bleeding. Many of the advantages and disadvantages of CO2 derive from its special physical and chemical properties. The advantages include no allergic potentiation and no renal metabolism of CO2, because CO2 is cleared by the lungs and does not recirculate. Other advantages include delivery by very small catheters because of the low viscosity of CO2, minimal discomfort on injection, and very low cost. However, the low-density and compressibility of CO2 poses some special problems. Imaging requires digital subtraction angiography with electronic enhancement and injections require an experienced investigator and, ideally, a dedicated CO2 injector. The dedicated CO2 injector provides calculated, controlled dosing and rates for injection, while excluding the possibility of air contamination. The buoyancy of CO2 inhibits good filling of dependent vessels. Accordingly, CO2 does not normally produce good nephrographic images, although proximal renal arteries are normally shown clearly. Experimental studies in dogs, whose renal arteries have been injected repeatedly with very large doses of CO2, demonstrate only transient changes in renal blood flow and no endothelial cell damage. However, these studies also showed clearly that renal ischemia can occur due to a "vapor lock" phenomenon if the kidney is positioned vertically above the injection site, and recurrent injections are given without time for absorption of the arterially delivered CO2 boluses. Uncontrolled studies in over 800 patients have confirmed that CO2 likely has a very low renal toxicity. At the University of Florida, CO2 is the radiologic contrast agent of choice in patients with renal insufficiency, especially those with diabetes mellitus, and in those with pre-existing allergy to iodinated contrast agents. Further controlled clinical studies are required to define the true clinical utility and safety of CO2 compared with conventional radiologic contrast agents.

Angiography, Digital Subtraction↗
PubMed1994

Captopril renography and the hypertensive renal transplantation patient: a predictive test of therapeutic outcome.

PURPOSE: To detect predictive accuracy of captopril renography in transplant recipients with hypertension. MATERIALS AND METHODS: This prospective study was performed to evaluate findings on 18 renal scans acquired after administration of captopril (captopril renograms) in 14 transplantation patients with new-onset or poorly controlled hypertension. Captopril renography was not used to affect case management but to predict response to angioplasty. RESULTS: Arteriograms were abnormal in 12 of 18 studies. In the six cases in which angiograms were normal, captopril renograms also were normal. In the 12 cases in which angiograms were abnormal, captopril renograms were normal in five and abnormal in seven. In the five cases in which renograms were normal, hypertension did not improve, although angioplasty was technically successful. In the seven with abnormal renograms, four patients underwent angioplasty with excellent results. These patients had a significant (P < .05) decrease in diastolic blood pressure (-15 mm Hg) and in creatinine concentration (-0.4 mg/dL) compared with patients with normal renograms and abnormal angiograms. CONCLUSION: In this small population, captopril renography appeared to be predictive of physiologically meaningful renal artery stenosis.

Adolescent↗
PubMed1993

Follow-up evaluation after renal artery bypass surgery with use of carbon dioxide arteriography and color-flow duplex scanning.

PURPOSE: Postoperative evaluation of renal artery bypass grafts historically has been obtained by contrast renal arteriography before discharge from the hospital. Recent reports have advocated replacing arteriography with abdominal duplex scanning for evaluating and monitoring the integrity of renal artery bypasses. We propose a combination of these two techniques, which provides minimal risk to the patient and renal parenchymal function. PURPOSE: Between July 1, 1990, and Dec. 31, 1991, 17 patients (8 men, 9 women) underwent 24 renal artery bypasses for poorly controlled hypertension or deteriorating renal function. In the immediate postoperative period each patient underwent carbon dioxide (CO2) renal arteriography to detect any technical defects and to define bypass graft anatomy. Subsequently, color-flow duplex scanning of the renal artery bypass grafts were done at 3-month intervals with the postoperative CO2 arteriogram for baseline comparison. CO2 arteriography clearly defined proximal/distal anastomotic anatomy, bypass conduit integrity, and bypass conduit runoff. RESULTS: Procedural morbidity was zero because no hematomas developed and serum creatinine remained stable. Duplex scanning for a mean follow-up of 8.3 months revealed antegrade flow in 23 bypasses with peak systolic velocity of 60 to 100 cm/sec. One bypass graft had a peak systolic velocity greater than 150 cm/sec suggestive of a proximal anastomotic stenosis; however, the patient died before a repeat, verifying CO2 arteriogram could be obtained. Recurrent hypertension developed in one patient with velocities less than 100/cm/sec, and repeat CO2 arteriography revealed no evidence of graft or anastomotic stenosis. CONCLUSION: CO2 arteriography and duplex scanning provide an accurate means of initially evaluating and subsequently monitoring renal artery bypass grafts, with minimal risk of renal or patient morbidity.

Adult↗
PubMed1993

Carbon dioxide gas as an arterial contrast agent.

OBJECTIVE: To investigate the clinical utility of CO2 gas as an arterial contrast agent, the experience with CO2 arteriography at the University of Florida was reviewed. SUMMARY BACKGROUND DATA: Preliminary studies have demonstrated the feasibility of CO2 arteriography and shown that arterial injection of CO2 gas appears non-toxic (which could limit the risks of contrast induced renal injury and allergic reaction). However, numerous technical problems make CO2 arteriography a demanding technique and recent studies have suggested that distal lower extremity vessels are difficult to image using CO2 arteriography, especially when significant arterial occlusive disease is present. METHODS: One hundred twenty-eight CO2 arteriograms done in 115 patients were reviewed. CO2 arteriograms were graded as excellent, good, poor, or inadequate by two blinded observers and results of CO2 studies compared to results of standard contrast studies (done in 98 patients for image comparison). In addition, a therapeutic plan based on the CO2 arteriograms was compared with the therapy each patient received. RESULTS: One hundred-seventeen (91%) of the CO2 arteriograms were of good or excellent quality and agreement between CO2 studies and standard contrast studies was seen in 93 of 98 cases (95%). Accurate therapeutic plans based on CO2 studies were possible in 92% of cases with inadequate visualization of infrapopliteal arteries being the major limitation (7 cases). No allergic reactions occurred and only one patient potentially had contrast-induced nephrotoxicity. CONCLUSIONS: CO2 arteriography provides accurate, clinically useful arterial imaging with minimal risk. Thus, this new technology significantly increases the utility of arteriography in patients with peripheral vascular disease.

Adult↗
PubMed1992

Angiography of the lower extremity in atherosclerotic vascular disease. Current techniques.

With the vast array of technology available, detailed diagnostic information is now routinely obtained in patients with peripheral vascular disorders. In addition, percutaneous intervention and advanced surgical techniques now safely permit the patient to return to an active life, and in advanced vascular disease, the extremity can be salvaged when previously the only option was amputation. We feel strongly that the maximum amount of information about the arterial system should be obtained throughout the patient's management. In addition, these complex procedures require considerable experience and judgment, and our practice of ongoing communication with the vascular surgery staff during both the diagnostic and the therapeutic phases of the patient's treatment has been extremely beneficial.

Angiography↗
PubMed1991

Carbon dioxide as an angioscopic medium. Comparison to various methods of saline delivery.

The limitations of angiography, when it is used as the sole method of vascular assessment, are increasingly apparent as vascular intervention becomes more sophisticated. Angioscopy could be an adjunctive diagnostic modality by differentiating among thrombus, dissection, and atheroma, and by monitoring the response to therapy. However, angioscopy requires a blood-free field for adequate visibility, and this may be difficult to obtain. The feasibility of carbon dioxide (CO2) and various saline delivery methods for clarifying the viewing field for percutaneous angioscopy was investigated. Angioscopy of femoral and iliac arteries on nine dogs was performed. Saline was infused by hand injection, pressure bag infusion, or mechanical power injection, and CO2 gas was injected using a special gas injector. The clarity of the viewing field was graded for each medium and method. Excellent quality antegrade femoral angioscopy was obtained with CO2. The superiority of CO2 injection in comparison with power-injected saline approached statistical significance (P = .06). Power-injected CO2 and power saline were superior to hand-injected or pressure bag-injected saline for maintaining sufficient visibility. Retrograde iliac angioscopy was possible without inflow occlusion, but required high flow rates (only possible with power-injected saline or CO2). CO2 injected under controlled circumstances holds promise as a medium to improve angioscopic visibility.

Angiography↗
PubMed1990

Dynamic CT of hepatic masses using intraarterial enhancement: advantages and pitfalls.

Forty-two patients were evaluated by dynamic incremental computed tomography (CT) following transcatheter infusion of contrast material into the celiac and hepatic arteries. Most of these patients had liver metastases from colorectal carcinoma, but the series also included two cases of hepatic hemangiomas, one case of granulomas due to atypical mycobacterium, and two cases of retroperitoneal tumors involving the liver. Several distinct patterns of liver opacification were recognized, reflecting differential perfusion of hepatic lobes during selective intraarterial contrast enhancement. The spectrum of observed findings, as well as the advantage or limitations of this technique, are described.

Colorectal Neoplasms↗
PubMed1990

Guide-wire reinforcement and lengthening with coaxial locking guide wires: the crimping technique.

The authors developed a technique to increase the size of a guide wire and permit single-step placement of catheters and large sheath systems over previously inserted small-caliber guide wires. The technique involves compression of metal cannula against a smaller in-dwelling wire or inner cannula. It has been used successfully during laser-assisted balloon angioplasty and percutaneous nephrolithotomy.

Angiography↗
PubMed1990

A solution to the problem of high-flow jets from miniature angiographic catheters.

In this study we evaluated methods for reducing high-flow jets from 5-French catheters that occur when injection pressures approach catheter tolerance (1000 psi [6.9 MPa]). This "jet effect" has been responsible for subintimal extravasation of contrast material in patients. We designed a physical model that accurately measures flow rates through the end hole and each side hole of 5-French high-flow catheters under simulated physiologic arterial pressure. When a standard catheter commonly used for injection of contrast material was studied, flow of contrast material was 34% through the end hole and 31% through the distal side-hole pair at high injection pressures (1000 psi). We examined the effect of altering the size and configuration of catheter side holes and end hole in an effort to create an improved flow profile, and thus a safer angiographic catheter. End-hole flow rate was reduced by 73% to 9% of total flow by tapering the 5-French catheter to 0.018 in. (0.046 cm) and by using smaller 0.015-in. (0.038-cm) side holes for even flow distribution. The high-flow jets present with standard high-flow 5-French catheters do not occur when flow-restrictive end holes and side holes are used. A uniform flow profile can be obtained without sacrificing delivery of contrast material through small catheters.

Angiography↗
PubMed1989

Effect of CO2 and blood media on laser probe temperature.

Blood may limit laser ablation of arterial plaque by decreasing thermal energy transfer from metal-capped probes to arterial occlusions. Since a gas is a good insulator of heat, CO2 may be a better medium for laser recanalization. To study this possibility, a metal-capped fiber was positioned in a segment of blood-filled polyethylene tubing and activated with an argon laser. Probe temperatures were measured in blood and as the blood was displaced by flowing CO2 gas. Probe temperatures were higher at all powers studied in CO2 gas than in blood. Maximum probe temperatures averaged 518 +/- 24 degrees C after CO2 infusion versus 320 +/- 7 degrees C in blood, (P less than 0.0001). Blood aggregate formation was noted on the probe surface in blood but not in CO2 medium. Thus CO2 gas may be a preferable medium for laser recanalization, since higher probe temperatures are achieved, and the probe surface remains free of insulating blood coagulate.

Angioplasty, Balloon↗
PubMed1989

Absolute ethanol renal angioinfarction for control of hypertension.

Six patients (11 renal units) underwent ethanol renal angioinfarction for medically uncontrollable hypertension. The mean preablation blood pressure was 175/112 mm Hg despite antihypertensive medications. Five of the patients demonstrated elevated renal vein renin levels prior to angioinfarction. Hypertension was improved in all 6 patients, during a mean follow-up period of fifty-one months. Systemic hypertension was completely eliminated in 4 patients. Two patients continue to require antihypertensive medication to control their hypertension. There were no major complications directly related to intra-arterial injection of ethanol. Transcatheter renal ablation employing intra-arterial injection of absolute ethanol for control of severe hypertension appears to be a safe and efficacious procedure. It should be considered an alternative to nephrectomy in selected high-risk patients.

Adult↗
PubMed1989

A phase II study of the efficacy of diamminedichloroplatinum (cisplatin) for the control of locally recurrent and intransit malignant melanoma of the extremities using tourniquet outflow-occlusion techniques.

A phase II trial was conducted with 15 patients (mean age of 65.7 years) with locally recurrent or intransit melanoma of the extremities. After total outflow occlusion with pneumatic tourniquet, the cell-cycle nonspecific anti-neoplastic agent cis-diamminedicholoroplatinum (CDDP) was infused intra-arterially in a mean dose of 26.7 mg/m2 per infusion (2.6 infusions per patient). The aim of this study was to determine the efficacy of CDDP infusion for control of intransit and recurrent melanoma of the extremities. Three to four weeks postinfusion, all visible residual disease was resected. Partial remissions were observed in ten patients (67%); five patients achieved stable disease status. No patient had complete regression of disease. At an average follow-up interval of 18.3 months (range 4-44 months), the mean local/regional disease-free survival was 14.8 months. Eighty per cent of patients (twelve of 15) had local/regional control of disease at an average follow-up of 14.8 months after CDDP infusion and surgical resection. Of five melanoma-related deaths, three patients had had no local/regional recurrence at the time of their demise. Three compartment syndromes resulted as a complication of the infusional therapy and occurred within 1-3 days of the treatment. In vitro growth of melanoma from lymph nodes draining the infused area was seen in all subjects studied. Outgrowth from tumor within the tourniquet infusion area was observed in two patients, both of whom experienced recurrences clinically at 24-months' postinfusion. Pharmacokinetic data of total CDDP concentrations from tissue and blood (n = 4) were available from pretreatment to 1 hour post-therapy. Biopsy data from patients pre- and post-treatment suggest substantial tumor uptake of CDDP as compared to local or distal normal skin, with minimal CDDP loss to the systemic circulation. Pharmacologic and clinical data of this phase II trial suggest that intraarterial infusion with tourniquet outflow-occlusion augments tumor tissue levels of CDDP within the infused extremity and enhances local control of high-risk and intransit disease.

Adult↗
PubMed1989

Miniaturization of catheter systems for angiography.

Miniature techniques offer many advantages for performance of routine angiography, as well as invasive vascular procedures. On the basis of the authors' experience with over 16,000 diagnostic and interventional procedures, this report describes the equipment and methods used for miniangiography. Development of sturdy, high-flow 3-5-F catheters and 0.014-0.018-inch guide wires, combined with the use of small needle puncture techniques, has improved the safety of angiography and intervention such that outpatient procedures are now routine. Miniature catheter systems are now preferable to larger catheter systems in most instances.

Angiography↗
PubMed1989

New high-flow "cloud" catheter for safer delivery of contrast material.

The authors describe a new angiographic catheter, which delivers equal flow rates through the side holes and reduced flow through the end hole compared with conventional catheters. Computer analysis of catheter-flow models revealed that placement of larger side holes proximally and smaller side holes distally produces more uniform flow rates out of the holes. This decreases the risk of potentially hazardous delivery of high-pressure jets of contrast material from the end hole. The flow pattern is so uniform that it resembles a cloud of contrast material on injection. This catheter design is particularly applicable for 3-5-F catheters, which require high-pressure injections. Clinical testing in 50 cases revealed no extravasations or unintentional selective injections with use of this catheter.

Angiography↗