A 28-year-old woman from Delhi presents with a 3-day history of severe vomiting following food poisoning. On examination, she is alert but appears dehydrated. Vital signs: BP 100/62 mmHg, HR 110/min, RR 18/min. Laboratory findings: pH 7.52, PaCO₂ 48 mmHg, HCO₃⁻ 38 mEq/L, Na⁺ 138 mEq/L, K⁺ 2.8 mEq/L, Cl⁻ 92 mEq/L. What is the primary acid-base disturbance?