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Biomedical subjects

G I Thomas

Publications and source records attributed to G I Thomas.

At least 19 recordsLinked to original sources
PubMed1992

Relation between middle cerebral artery blood flow velocity and stump pressure during carotid endarterectomy.

BACKGROUND AND PURPOSE: Many patient monitoring techniques have been used for detecting cerebral hypoperfusion during carotid endarterectomy. We compared middle cerebral artery blood flow velocities with carotid artery stump pressures to evaluate the indications for common carotid artery cross-clamp shunting and the probable hemodynamic causes of cerebrovascular complications. METHODS: Blood flow velocities were monitored with transcranial Doppler ultrasound and carotid stump pressures were measured at the time of common carotid artery cross-clamping during 97 carotid endarterectomy procedures. Stump pressures measured with the gauge zero reference at the common carotid artery level were correlated with the percentage change of velocities. RESULTS: Middle cerebral artery blood flow velocities usually decreased upon common carotid artery cross-clamping, depending on collateral availability and the autoregulation response. The best fit of the data was to an exponential function concave to the pressure axis, with velocity as a percentage of the pre-cross-clamp value reaching zero at 15 mm Hg stump pressure (r = 0.85 and p less than 0.001). CONCLUSIONS: There is a less critical margin of error with percentage middle cerebral artery blood flow velocity decreases than with stump pressure measurements. This relation establishes changes in middle cerebral artery blood flow velocities as a reliable parameter for judging the effects of carotid cross-clamping on cerebral blood flow and providing an excellent indicator as to the necessity for shunting.

Blood Flow Velocity↗
PubMed1990

Detection of middle cerebral artery emboli during carotid endarterectomy using transcranial Doppler ultrasonography.

The purpose of our study was to define the signal characteristics and clinical circumstances associated with emboli detected in the middle cerebral artery using 2-MHz pulsed transcranial Doppler ultrasound in patients undergoing carotid endarterectomy. Signals designating emboli were transients displaying harmonic qualities the signatures of which were clearly different from those of mechanical and electronic artifacts. We reviewed the audio/video tape recordings from 91 patients for signals of air bubble emboli occurring upon release of common carotid artery crossclamps; recordings from 35 patients (38%) demonstrated air bubble emboli. Transients with signatures identical to those of air bubble emboli were also discovered when bubbles in the bloodstream were improbable; we defined these transients as representing formed-element emboli. Such signals were found in recordings from 24 patients (26%), and they occurred before (both spontaneously and upon common carotid artery compression), during, and after surgical dissection. Signals indicating formed-element emboli were associated with intraluminal platelet thrombus, with ulcerations in the carotid artery, and with transient ischemic attacks or stroke. Most postoperative formed-element emboli did not cause symptoms but, when persisting for hours, they were associated with strokes and cerebral infarction. This Doppler ultrasound method of detecting emboli will be useful in the study of stroke mechanisms and as a clinical test to guide the medical and surgical treatment of patients at risk of stroke.

Arterial Occlusive Diseases↗
PubMed1990

Blood flow velocity in the middle cerebral artery during carotid cross-clamping: loss of regulatory response to carbon dioxide partial pressure. A transcranial Doppler intraoperative study.

The CO2 reactivity of blood flow velocity in the Middle Cerebral Artery (MCA) was explored by Doppler ultrasound, in nine patients, at the time of common carotid artery cross-clamping during vascular surgery, in order to detect if a regulatory response apply during operative occlusion of common carotid artery. Transcranial Doppler was used to monitor ipsilateral MCA blood velocity during carotid surgery. MCA velocity, arterial blood pressure and pCO2 (arterial or end-tidal) were measured, during carotid cross clamping, before and after an increase in pCO2 was induced by changing respiratory rate and volumes. No relevant changes in MCA flow velocities were detected in patients with stable arterial blood pressure. In those patients showing an increase in blood pressure during the surgical procedure the MCA velocity increased accordingly. It is suggested that the cross-clamping of common carotid artery is a critical condition in which no regulatory response can be elicited: blood flow velocity tends to parallel the perfusion pressure and also CO2 reactivity is lost.

Aged↗
PubMed1986

Carotid endarterectomy after Doppler ultrasonographic examination without angiography.

We prospectively reviewed our experience with 32 carotid endarterectomies in 30 patients performed without angiography in a 7 year period. Although this represents 6.7 percent of our total experience with carotid endarterectomy in this period, carotid endarterectomy without angiography is increasing and comprises 17 percent of the last 2 years' total. We have adhered to strict criteria for patient selection that identifies circumstances for a safe operative experience in seven broad categories. Evidence is also presented to reduce an overriding concern for intracranial aneurysms and siphon stenosis if either one exists unrecognized. We are hopeful that in the future, the latter will be identified by intracranial Doppler studies currently being performed. Our experience in this small series has been favorable, with intraoperatively measured lesions equal to the preoperative noninvasive predictions. We suggest that Doppler ultrasonography in its current form can be effectively used in place of conventional angiography or digital subtraction angiography in selected patients.

Aged↗
PubMed1984

The St. Jude experience.

This paper covers our experience with the use of the St. Jude prosthetic heart valve from November 1979 through August 1983 in 91 patients operated on for aortic and mitral valve replacement. Nonfatal complications included hemorrhagic sequela due to anticoagulation, with an annual rate of 1 percent (1.4 percent per 100 patient years), thromboembolism with an annual rate of 0.8 percent (0.87 percent per 100 patient years), sternal infection 1 percent, operative cardiovascular accident 1 percent, and pericardial tamponade 1 percent. Operative mortality was 1 percent, early mortality (within 30 days) was 3 percent, and late mortality was 3 percent, with a total overall mortality of 7 percent. Excluding two patients who died from noncardiac causes, the overall mortality was 5 percent. The mortality rate per year was 2 percent. The survival rate 3.8 years postoperatively was 89 percent for mitral valve replacement patients and 93 percent for aortic valve replacement patients, for an overall 38 year survival rate of 92 percent. All patients were anticoagulated with warfarin. There were no instances of valve failure, replacement, or serious hemolysis. Eighty-three percent were active or working with a New York heart functional class I. In our experience, the complication rate with the St. Jude valve is as low or lower than that for any other mechanical prosthetic cardiac valve available in the world today.

Adult↗
PubMed1983

The middle scalene muscle and its contribution to the thoracic outlet syndrome.

The predisposing anatomic alterations or features of thoracic outlet syndrome have been tallied to better define this difficult and inchoate issue. In the last 34 supraclavicular operations involving 33 patients (for a total operative experience of 128 procedures), we have found the anterior insertion of the middle scalene muscle to be present in 48 percent of our patients. This insertion, forward on the first rib, closes an already small interscalene triangle, so that the posteriorly placed brachial plexus is entrapped or irritated by the anterior edge of this muscle, which may be very sharp and firm. In addition, 10 percent of our patients had a middle scalene band intimately associated with the middle scalene muscle, often-times inseparable, for a 58 percent incidence of middle scalene involvement in the thoracic outlet syndrome. With data such as those presented herein, a more simplified operation than the heretofore popular all-out attack on the first rib may well be in the offering.

Adult↗
PubMed1980

Experiences with autotransfusion during abdominal aortic aneurysm resection.

In a series of 79 elective and ruptured abdominal aortic aneurysm resections, the autotransfuser manufactured by the Bentley Laboratories was used in 50 patients. These 50 patients, in whom the average amount of autotransfused blood was 1,500 cc, required a smaller number of intra- and postoperative transfusions, maintained satisfactory recovery hematocrit levels and had an essentially unchanged platelet count throughout the first 24 hours. There was no evidence of laboratory or clinical coagulopathy. The autotransfusion equipment was set up and operated by the patients' technician, and proved devoid of air embolism or clotting components. Although there are many patients whose aneurysms are easily removed and grafted and who require a small number of whole blood transfusions, there still remain operative traps and pitfalls in many patients that suggest to us that the autotransfuser is a security system, and thus it is routinely set up in all cases.

Aged↗
PubMed1980

Implantation of a larger aortic prosthetic valve in a patient with a small aortic annulus: an operative technique.

A technique for implantation of a larger aortic prosthetic valve in a small aortic annulus is described. The technique consists of passing inverted horizontal mattress sutures in the aortic annulus in the right and left coronary sinuses. In the noncoronary sinus, horizontal mattress sutures are passed from outside through a strip of Teflon felt and then through the aortic wall a few millimeters away from the annulus and finally through the sewing ring of the aortic valve prosthesis. Sutured in this manner, the valve sits below the annulus in the areas of the right and the left coronary sinuses and above the annulus in the noncoronary sinus. This technique is simple, does not add to the aortic cross-clamp time, and permits placement of a prosthesis that is at least 2-4 mm larger than the size of the annulus.

Aortic Valve↗
PubMed1979

Aortic valve replacement and the senior citizen.

The elderly patient, regardless of age, faces an early demise from progressive cardiac decompensation secondary to aortic valve disease. Aortic valve replacement can be carried out at a reasonable operative risk and extend the longevity to very close to that of normal life expectancy. It is our feeling, based on these results, that patients with significant symptoms secondary to aortic valvular disease, regardless of age and without other major organ problems, should be given the choice of aortic valve replacement to enhance the quality and quantity of their lives.

Age Factors↗