Police say several boxes containing ventilators/Continuous Positive Airway Pressure (CPAP) machines were stolen from the lorry parked in Foxbridge Way, Normanton.
The machines are used by the NHS to treat people with breathing difficulties.
Police said around 175 of the S-Boxes - which measure about 15cms by 7cms - were stolen along with their modems.
Wakefield District Crime Team is appealing for anyone with information about their whereabouts to contact them.
Call Wakefield District Crime Team on 101, quoting crime reference 13220025827.
Information can also be reported anonymously to the independent charity Crimestoppers on 0800 555111 or online.