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Department of Anesthesia and Intensive Care (Ghai, Panda, Makkar) Department of Radio Diagnosis and Imaging; Post Graduate Institute of Medical Education & Research; Chandigarh, India; fatakshay{at}yahoo.com (Saxena)
To the Editor:
Sedation and analgesia in children has been recently reviewed from the perspective of the anesthesiologist (1). However, it is important that anesthesiologists understand the needs of radiologists to obtain the best possible scan. We routinely do computed tomographic (CT) scans under sedation or general anesthesia administered by an anesthesiologist. Awareness of the following aspects of CT scanning can help anesthesiologists provide the best possible care for the patient.
A typical CT scan involves registration of patient data on the operator console by a CT technician followed by positioning of the patient. This is followed by a localizing image called a topogram. Radiologists plan their study according to the topogram. Any cranio-caudal movement by the patient after acquisition of the topogram would lead to incorrect imaging. The best time to sedate the patient is after registration of patient data and before the topogram is acquired.
The next step depends on the site: head or body. Head scans involve taking serial tomograms. Body scans require acquisition of spiral data. Patient movement during acquisition of tomograms/spiral data degrades image quality and may necessitate a repeat scan. Because the contrast dose should not exceed 3 mL/kg (2), repeat scanning may not be feasible on the same day, necessitating another patient visit. Repeat scans also increase the radiation dose, which is not benign (3). Fortunately, acquisition of data is over in less than 1 min, after which patient movement does not hamper the quality of the study.
The size of the IV cannula should be guided by the type of contrast enhancement required. If contrast is not needed, a thin bore cannula (e.g., 24 G) can be used. Also, if the expected pathology is inside the blood-brain barrier, the CT scan is done 10 min after contrast administration, and again a 24-G cannula can be used (4). However, if body imaging is required, IV contrast has to be injected as a rapid bolus with a pressure injector (5,6). In this case, the largest possible cannula should be used. The IV cannula should be placed in the arm (7), as placement in the leg or foot causes pooling of contrast in the lower limb. Also, it may lead to opacification of the inferior venacava in abdominal CT angiographic studies.
REFERENCES
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