The main objectives of the study is 1) to determine whether Plasmalyte® promote the development of metabolic acidosis in comparison with an acetate-free balanced solutions: Ringer lactate (chloride concentration of 111 mmol/L) and 2) to determine Acetate & gluconate clearance during fluid resuscitation of severely burn patients Plasmalyte® (chloride concentration of 98 mmol/L) . Severely burn patients will be randomized to receive Plasmalyte® or Ringer Lactate for initial fluid resuscitation during the first 5 days following admission.