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Biomedical subjects

I F Hawkins

Publications and source records attributed to I F Hawkins.

At least 19 recordsLinked to original sources
PubMed1998

Carbon dioxide (CO2) digital subtraction angiography: 26-year experience at the University of Florida.

Although the vascular system is presently being imaged by multiple high technology modalities, contrast angiography continues to be the gold standard; however, severe complications rarely occur. During the last 25 years (in over 1400 patients), CO2 has proven to be extremely safe (no allergy or renal failure). However, it is imperative to understand CO2's physical properties and potential dangers. Recently, CO2 is being routinely utilized not only because of safety, but for detection of minute amounts of bleeding, better collateral filling, and for most interventional procedures since unlimited volumes of CO2 can be injected between the catheter and guidewire. Presently, safe, reliable and "user-friendly" delivery systems are now commercially available. CO2 DSA images are now nearly comparable to iodinated contrast, and improvement in DSA images are evolving, including "stacking" software.

Acute Kidney Injury↗
PubMed1998

Angiography with carbon dioxide (CO2).

CO2 possesses many advantages over conventional iodinated contrast agents used for arteriography. It is nonallergic and lacks renal toxicity. Its unique properties permit use of smaller catheters in diagnostic and therapeutic angiographic procedures, allow optimal vascular imaging of various neoplasm, assist in detection of occult gastrointestinal bleeding, and facilitate TIPS procedures. With digital subtraction techniques and stacking programs, CO2 arteriography is as accurate as iodinated contrast studies in most patients and thus is the preferred arterial imaging technique in patients with contrast allergy and renal insufficiency. CO2 is also extremely inexpensive compared with available contrast agents. Understanding of the effects of buoyancy and compressibility is necessary for safe, controlled delivery of CO2 during arteriography, but only rare complications have occurred in our large experience with CO2 angiography. Thus, use of CO2 as an arterial contrast agent significantly expands the safety and utility of arterial imaging in patients with peripheral vascular disease.

Angiography↗
PubMed1998

Sonographic guidance when using the right internal jugular vein for central vein access.

OBJECTIVE: The intent of this study was to substantiate the advantages of the use of sonographic guidance for central venous access via the right internal jugular vein. SUBJECTS AND METHODS: Eighty sequential patients requiring central vein access were examined with a hand-held sonography transducer to determine the size, patency, and location of the right internal jugular vein before puncture. Access to the right internal jugular vein was subsequently performed, under sterile conditions, using sonographic guidance. Periprocedural complications were prospectively recorded. Subsequently, we compared our findings with published reports of complications when visible and palpable anatomic landmarks were used for guidance during cannulation of the internal jugular vein. RESULTS: Among these 80 patients, the anatomy of the right internal jugular vein was typical in only 57 (71%). In another 13 patients (16%), sonography showed a medial position of the right internal jugular vein, anterior to the common carotid artery. In three other patients (4%), the right internal jugular vein was positioned laterally by more than 1 cm. In the remaining seven patients (9%), the vein was thrombosed. Its diameter, measured without use of the Valsalva maneuver, also varied, measuring 0.5-2.0 cm. Cannulation was achieved in all 73 patients with a patent right internal jugular vein. One puncture was required in 68 patients (93%); two punctures in three other patients (4%); and three punctures in the remaining two patients (3%). In no case was the common carotid artery inadvertently punctured. Only one periprocedural complication occurred, and it was unrelated to the use of sonographic guidance. CONCLUSION: Sonographic guidance for central vein access via the right internal jugular vein is safer and more efficient than the traditional landmark approach.

Adolescent↗
PubMed1997

Long-term performance and complications of the Tesio twin catheter system for hemodialysis access.

The Tesio twin catheter system (Medcomp, Harleysville, PA) was developed to overcome the problems with the existing central venous catheters in providing high-efficiency dialysis, such as inadequate blood flows, high recirculation rates, and need for surgical insertion. The relatively large internal lumens and multiple side holes in a spiral pattern allow for high blood flow rates and lower tendency to thrombosis. In this series, 82 catheter pairs were placed in 75 patients and monitored for a period encompassing 231 patient-months. We achieved mean nominal blood pump flow rates of 400 +/- 6 mL/min and an average recirculation of 4.6% +/- 0.5%. In 20 sets of catheters, a nominal blood flow rate of 388 +/- 6 mL/min was measured ultrasonically at 352 +/- 8 mL/min, representing an error of 36 +/- 5 mL/min. Thrombosis of the catheter occurred at a rate of one episode per 21 patient-months, and on all occasions responded to local instillation of urokinase. Despite having two exit sites, the infection rates were comparable to other catheters: exit site infections occurred at a rate of one per 21 patient-months and bacteremic episodes occurred at one per 11.5 patient-months, necessitating catheter removal once per 46 patient-months. Based on these data, we believe that the Tesio twin catheter system is an excellent long- and short-term vascular access for providing high-efficiency dialysis.

Acute Kidney Injury↗
PubMed1997

Examination of renal donors as outpatients using intraarterial digital subtraction angiography and a pigtail catheter.

OBJECTIVE: We performed this study to assess the safety and efficacy of outpatient angiographic renal donor examination using a 3-French pigtail catheter, intraarterial digital subtraction angiography, and a progressively shortened examination time after the procedure. CONCLUSION: For 45 consecutive procedures performed, no complications were reported, and no diagnostic discrepancies were found in patients who proceeded to surgery. Using this method we were also able to eliminate the excretory urogram as well as reduce the total amount of contrast per procedure.

Adolescent↗
PubMed1995

Effects of carbon dioxide arterial infusion on hepatic biochemistry and histology in a rabbit model.

RATIONALE AND OBJECTIVES: The objective of this study was to determine the effect of carbon dioxide (CO2) infusion on hepatic biochemistry and histology in a rabbit model. METHODS: The study population consisted of 24 anesthetized rabbits that received hepatic infusion of either CO2 or saline (control) at doses of 10 mL/kg, comparable with those doses used in human clinical trials. Blood for clinical chemistry analysis was collected at baseline, 1 hour, 24 hours, and 168 hours (7 days) postprocedure. The rabbits were killed at 7 days postprocedure and the liver examined histologically for hepatic damage. RESULTS: There were no significant differences between the CO2 and the control groups in dorsal, ventral, and dorsal/ventral scores. Increases in alanine, an important indicator of hepatocellular membrane injury, in the CO2 group were significantly greater at 1 hour and 24 hours posttreatment (P = 0.037 and 0.013). However, the mean levels at 168 hours (7 days) were not significantly different (P = 0.22). The increases at 1 and 24 hours were small, transient, and considered clinically insignificant. CONCLUSION: No long-term hepatic effects in these animals were suggested by biochemical and histological examinations.

Analysis of Variance↗
PubMed1995

Carbon dioxide digital subtraction angiography: expanding applications and technical evolution.

Although several noninvasive techniques now exist for vascular imaging, including MR imaging, three-dimensional CT, and color-flow and duplex sonography, the gold standard to which these techniques are compared remains catheter angiography. Cut-film and digital subtraction angiography (DSA) using iodinated contrast material are the standard methods by which vascular imaging is performed. However, despite the development of low-osmolar contrast agents, premedication regimens, and careful patient selection, adverse reactions to contrast material, including idiosyncratic reactions and contrast-induced nephropathy, continue to occur in a small number of patients [1-3]. Carbon dioxide (CO2) was developed as an alternative to iodinated contrast material to avoid these problems [4]. Once the behavior of intravascular gas, the methods of safe delivery, and the principles of successful imaging are understood, the use of CO2 as an intravascular contrast agent during DSA allows accurate imaging with little risk. Recent advances in delivery systems, postprocessing capabilities, and its extension to new vascular interventional procedures have greatly expanded the usefulness of CO2 angiography in both diagnostic and interventional vascular radiology.

Angiography, Digital Subtraction↗
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↗