A 28-year-old male from Bangalore with a known diagnosis of Leigh syndrome (mitochondrial encephalomyopathy due to cytochrome c oxidase deficiency) presents with acute onset lethargy, ataxia, and seizures during a febrile illness. Serum lactate is 9 mmol/L (normal < 2), and arterial pH is 7.28 with HCO3− of 16 mEq/L. Brain MRI shows bilateral putaminal necrosis. What is the most appropriate immediate next step in management?