PLACE OF RADIONUCLIDE IMAGING IN THE INTE NSIVE-CARE UNIT

The real place of isotopic imaging in intensive care patients remains still unclear. This review aimed to consider the indications of isotop ic imaging for improved diagnosis and therapy and to specify its place among the other techniques of exploration. Pulmonary perfusion and ve ntilation scintigraphies are valuable for the diagnosis of pulmonary e mbolism (PE). A << high probability >> scintigraphy of the lungs ascer tains the diagnosis of PE and allows to start a specific treatment wit hout requiring a pulmonary angiography. This is not the case in the pr esence of a history of previous PE or if the arguments for a PE are on ly weak. A normal lung scintigraphy eliminates the diagnosis of a clin ically significant PE all the more as an exploration of good quality o f the lower limb veins remains negative. In the opposite a << non diag nostic >> scintigraphy justifies a pulmonary angiography in intensive care patients. The diagnosis of myocardial contusion is made uneasy as the clinical symptoms, the ECG, the cardiac enzymes and the chest X-r ay are only of limited value. Isotopic explorations of the heart could provide additional valuable data or be an alternative for 2 D echocar diography. The comparison of CPK-MB concentrations with a myocardial s cintigraphy using thallium 201 is given as being very reliable, with p ositive and negative predictive values higher than 80 %. An exploratio n restricted to the cardiac ejection fractions is only of limited valu e. In the future, an improvement will perhaps be obtained with tracers such as MIBI labelled with technetium 99m, which allow the simultaneo us assessment of myocardial perfusion and the ventricular ejection fra ctions as well. The localisation of centres of infection, especially w hen intra-abdominal, remains difficult in intensive care patients. Iso topic imaging, especially the scintigraphies with labelled polynuclear s, could allow in combination with conventional imaging techniques (co mputed tomography and 2 D echocardiography) to prevent from errors in diagnosis. An array of arguments is essential for ascertaining the pre sence of an abscess. Scintigraphies with leucocytes labelled with indi um [1] or technetium 99m are qualified as having a sensitivity and a s pecificity greater than 90 %. The conventional techniques of measureme nt of the cerebral blood flow (CBF) using xenon 133 require a special equipment or are invasive. Other cerebral tracers, such as cyclic amin es (HMPAO) labelled with technetium 99m and administrable by i.v. rout e, allow the use of a standard tomo-gamma camera, and could be of help in various pathological conditions. In association with cerebral comp uted tomography, the assessment of CBF with an isotopic technique woul d allow to differentiate an irreversible ischaemia from a functional h ypoperfusion complicating a vasospasm. A cerebral scintigraphy using H MPAO labelled with technetium allows the diagnosis of cerebral death. In case of acute renal failure, the isotopic renal explorations (scint igraphies using DTPA and MAG labelled with technetium 99m) take part i n the assessment strategy. These techniques are neither invasive nor t oxic. They allow a simultaneous evaluation of the renal perfusion, the glomerular filtration, the tubular secretion and the urinary tract as well. The perfusion phase assesses the renal blood flow. The analysis of the captation phase allows the distinction between unilateral or b ilateral and segmentary or global renal failure. The elimination phase can show an obstacle in the upper or lower urinary tract. Isotopic im aging allows sometimes to restrict in intensive care patients the indi cations for conventional radiology. It also allows a better monitoring and an improved treatment of these patients.