HBG2 and delirium: Significant reactions that were secondary to elevated levels of methemoglobinemia did not occur during the use of HDDCT, as they have been noted to occur at methemoglobin levels that are greater than 30% with life threatening reactions reported at levels of 50% or greater (arrhythmias; altered mental status, delirium, seizures, coma; profound acidosis) [91].