Only the 300μΩ and 500μΩ versions are rated at 5W, and that is only up to 70°C ambient temperature. Construction is a nickel-chromium aluminium resistive element welded to manganese-copper ends. The +20 to +60°C temperature coefficient of the central resistive element is around ±20ppm, but this changes when the end terminations are taken into account. Find the resistors on this Vishay product page, and a useful ‘Temperature Coefficient of Resistance for Current Sensing’ here. The same company recently introduced an isolated precision amplifier for resistive current sensing.