Initiation of hemofiltration in a patient in septic shock can cause hemodynamic compromise potentially leading to cardiac arrest. We propose that the standard '4Hs and 4Ts' approach to the differential diagnosis of a cardiac arrest should be supplemented in critically ill patients with anaphylaxis and human and technical errors involving drug administration (the 5(th) H and T). To illustrate the point, we report a case where norepinephrine infused through a central venous catheter (CVC) was being removed by the central venovenous hemofiltration (CVVH) catheter causing the hemodynamic instability. CVVH has this potential of interfering with the systemic availability of drugs infused via a closely located CVC.