What is the next best step in managing a 65-year-old gentleman with acute colonic pseudo-obstruction (Ogilvie's syndrome), characterized by a dilated proximal colon with a maximum sacral diameter of 12 centimeters, hypokalemia (low potassium), and hypomagnesemia (low magnesium), who has not responded to conservative management?

I recommend a trial of intravenous neostigmine for this patient. The clinical presentation strongly suggests acute colonic pseudo-obstruction (Ogilvie's syndrome), characterized by massive colonic dilation without mechanical obstruction. The patient has multiple risk factors including recent hip surgery, Parkinson's disease, electrolyte abnormalities (hypokalemia and hypomagnesemia), and prior narcotic use. With a cecal diameter of 12 cm and worsening distension despite 40 hours of conservative management, there is significant risk of perforation. Neostigmine, a parasympathomimetic agent that increases acetylcholine levels and stimulates colonic motility, is appropriate at this stage. The typical dose is 2 mg administered intravenously over 3-5 minutes with continuous cardiac monitoring due to potential bradycardia. The patient should be monitored for rapid clinical response, which typically occurs within 30 minutes. If unsuccessful, colonoscopic decompression would be the next step, with surgery reserved for cases with perforation or failed decompression. While addressing the electrolyte abnormalities is important, the worsening clinical picture despite initial conservative measures necessitates more aggressive intervention at this point.