Abstract: A medical method comprises the steps of attaching a sensing device to a limb of a patient, automatically operating the sensing device to monitor a circumference of the limb, automatically comparing a measured circumference with a reference value, and automatically generating an alarm signal upon detecting that the measured circumference differs from the reference value by more than a predetermined magnitude. In one application of the method, an intravenous catheter is inserted into a blood vessel in the limb, and a fluid is fed into the blood vessel via the catheter. The limb is covered upon insertion of the catheter and attachment of the sensing device, thereby preventing direct visual observation of the limb during performance of a surgical operation on the patient. The circumference measurements and automatic comparisons are performed periodically.