Execution protocol in the US state of Missouri allows for “surgery without anaesthesia” if the typical process of finding a suitable vein to inject the lethal drug doesn’t work, lawyers for a death row inmate say in an appeal aimed at sparing his life.

Brian Dorsey, 52, is scheduled for execution on Tuesday for killing his cousin and her husband at their central Missouri home in 2006. His attorneys are seeking clemency from Gov. Mike Parson and have several appeals pending.

A federal court appeal focuses on how Missouri injects the fatal dose of pentobarbital. The written protocol calls for the insertion of primary and secondary intravenous lines. But it offers no guidance on how far the execution team can go to find a suitable vein, leaving open the possibility of an invasive “cutdown procedure,” Dorsey’s attorneys say.