Results of an Infection Control Survey in Ultrasound Departments and Recommended Guidelines

Prevention of disease transmission by cross infection is very important in the hospital environment to protect both staff and patients.

At the present time most hospitals have stringent infection control policies which are largely geared toward the wards, critical care units and the operating theatres but there does not appear to be specific guidelines for ultrasound departments. Considering the contact nature of the ultrasound examination and the large number of tests that are performed in most hospitals annually it was felt that this was an area that needed to be addressed. One must be aware not only of protection of patients and staff but also of care in the cleaning of expensive equipment.

We undertook a national survey of the larger general ultrasound departments, vascular and cardiac laboratories to establish current practices and to assess whether these are adequate. We also contacted a number of ultrasound companies and requested cleaning specifications for their equipment.

The full results of the survey, the biological effectiveness of different cleaning techniques and their compatibility with ultrasound transducers will be discussed. Finally, recommendations regarding safe effective cleaning procedures and sensible infection control precautions in ultrasound departments will be made.

Asymptomatic carotid stenosis: a benign lesion?

Recent reports of the risk of asymptomatic carotid stenosis have been compromised by flawed patient selection or the performance of a large number of carotid endarterectomies during follow-up. We report the natural history of a randomly selected group of asymptomatic patients (n = 188; 114 males and 74 females) with documented carotid artery disease who were prospectively followed without intervention for up to 8 years. Risk factors included ischaemic heart disease in 17%, diabetes in 10%, hypertension in 46% and 88% were smokers. The degree of internal carotid stenosis was classified by duplex scanning and a total of 259 vessels had evidence of atherosclerosis. Study end-points included TIA, CVA and death. At mean follow-up of 4 years 3% of the 96 patients with internal carotid artery stenosis of less than 50% had died and 2% suffered a stroke. Six per cent of patients with a stenosis of 50-79% had died and 4% and 2% had suffered a CVA and TIA, respectively. In the 59 patients with greater than 80% stenosis 7% had suffered a TIA and an additional 7% a CVA, while 2% had died. None of the patients suffering a stroke had an antecedent TIA. Though the incidence of ischaemic events is significantly higher in patients with greater than 80% stenosis the incidence of unheralded stroke remains low. We therefore continue to recommend a conservative approach to the management of asymptomatic carotid stenosis.

Duplex ultrasonography and selection of patients for carotid endarterectomy: plaque morphology or luminal narrowing?

Percentage of carotid stenosis and plaque morphology as determined by duplex scanning were correlated with symptoms and CT evidence of infarction in 108 patients. Severity of carotid stenosis less than 49% or greater than 50% narrowing was not associated with an increased risk of ipsilateral symptoms or CT infarction. However, a heterogeneous plaque appearance, suggesting intraplaque hemorrhage, did correlate with ipsilateral cerebral symptoms. Heterogeneous plaque appearance may be a more reliable indication for carotid endarterectomy than a hemodynamically significant stenosis.

Assessment of arterial disease using digital systolic pressure measurement

Digital systolic pressure measurements were made on 140 big toes using a photoplethysmographic technique before and after extrinsic heating of the foot. Most patients with apparent, critically ischemic feet demonstrated vasomotor activity, suggesting that much of the microcirculation of the foot was in fact intact. Significantly, nine of 21 feet which would have fallen into a critically ischemic category were recategorized after heating into a less severe group. These data confirm the value of toe pressure measurements in the assessment of severe ischemia but show that adequate foot vasodilation is essential to allow accurate conclusions to be drawn and to allow meaningful interpretation of results.

Duplex scanning for noninvasive assessment of both carotid luminal diameter and atheromatous plaque morphology

The value of Duplex scanning in 50 consecutive patients with symptomatic carotid stenosis was evaluated. Compared with contrast arteriography, the sensitivity of Duplex scanning, for a greater than 50% internal carotid diameter reduction, was 90% (66/73) with a specificity of 96% (26/27). The overall agreement between Duplex and contrast arteriography as measured by the Kappa value was K = 0.561. One of the 13 arteries felt to be occluded on Duplex scanning was radiologically found to be patent. Excluding the six normal and 13 occluded arteries, 81 carotid plaques were defined as either heterogeneous, suggestive of intraplaque hemorrhage or as homogeneous. Twenty-four of the 32 asymptomatic cerebral hemispheres were associated with ipsilateral homogeneous plaques, while 30 of the 49 symptomatic hemispheres had heterogeneous plaques in the ipsilateral carotid, (p less than 0.001). This study confirms the accuracy of duplex scanning in detecting internal carotid stenosis as well as in identifying plaques which are morphologically heterogeneous and more likely to be associated with ipsilateral cerebral hemispheric symptoms.