The calculated distance (air line) between Salavan and Nakhon Phanom is approximately 160 miles respectively 257 kilometers.
By car or train, the actual journey to Nakhon Phanom is certainly longer, as only the direct route (as the crow flies) between Salavan and Nakhon Phanom has been calculated here.
Air line (approximately)
257 kilometers
139 nautical miles