An 8 month female baby presented with 1 day h/o lethargy. She had vomited several times. Her drug addict mother said she appeared "intoxicated".O/E: baby was obtunded but she was easily arousable and muscle tone was normal. RR = 60/min. Pupils are normal. BP was 112/62.Ix: Na+= 135 K+ = 4.2 ,Glucose 5.9 mmol/l , Cl- = 116 ,Urinalysis: pH = 5.0; negative for glucose & ketones, positive for calcium oxalate crystals. ABG: pH = 7.19, pCO2 = 20, PO2 = 100 , HCO3 = 6.2 ?