This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
A patient undergoing caesarean section following prolonged labour under subarachnoid block developed carpopedal spasm. Lignocain was used as anesthetic agent. The most likely diagnosis is: 
Select and explain. 
A. Amniotic fluid embolism, B. Lignocaine toxicity, C. Hypocalcemia, D. Hypokalemia
C: Hypocalcemia
Answer: C: Hypocalcemia 
Explanation: Pain due to prolonged labour may lead to hyperventilation and resultant respiratory alkalosis. This will cause a decrease in the level of free ionized calcium in the ECF, resulting in hypocalcemia and precipitating carpopedal spasm. Ref: Primer on The Metabolic Bone Diseases and Disorders of Mineral Metabolism Edited By Clifford J. Rosen, 7th Edition, Page 354 ; Nutrition Therapy and Pathophysiology By Marcia Nahikian Nelms, 2007, Page 196 ; Essentials of Medical Pharmacology By KD Tripathi, 5th Edition, Page 479