RESPIRATORY ALKALOSIS DEFINITION A condition due to a primary fall in arterial carbon dioxide partial pressure (typically to 20 to 25 mmHg) where blood pH is elevated and plasma bicarbonate concentration decreased (typically by < 4 mEq/L). It is caused by loss of CO2 due to hyperventilation. Respiratory alkalosis is not life-threatening. TOXIC CAUSES Salicylates (early stage). NON-TOXIC CAUSES Anxiety and hyperventilation Fever Gram-negative septicaemia Hepatic cirrhosis Hepatic coma Hypoxaemia Overventilation of patients with assisted respiration. Primary CNS disorders CLINICAL FEATURES The priniciple clinical feature is hyperventilation. Severe cases may result in tetany with Chvostek's and Trousseau's signs, circumoral paraesthesiae, acroparaesthesiae, and carpopedal cramps due to reduced serum ionized calcium concentration. RELEVANT INVESTIGATIONS Arterial blood gas analysis (pH, bicarbonate) Ionized calcium concentration Serum salicylate concentration TREATMENT The primary treatment of salicylate-induced respiratory alkalosis is treatment of the primary condition (salicylate toxicity). Anxiety-induced respiratory alkalosis is best treated with reassurance. Rebreathing expired carbon dioxide from a paper (not plastic!) bag may be helpful, but might be dangerous in patients with CNS disturbances. Hypoxaemic patients need O2 enrichment of inspired air. Overventilation on mechanical respirators should be corrected or dead space added. CLINICAL COURSE AND MONITORING The acute condition usually subsides quickly with proper management. Patients must be observed for recurrences. Underlying neurological or hepatic disturbances need specialist treatment. LONG-TERM COMPLICATIONS None. AUTHOR(S)/REVIEWERS Author: Dr Janusz Szajewski, Warsaw Poisons Control Centre, Warszawa, Poland. Peer Review: Rio de Janeiro 9/97: J.N. Bernstein, E. Birtanov, H. Hentschel, T.J. Meredith, Y. Ostapenko, P. Pelclova, C.P. Snook, J. Szajewski. London 3/98: T. Della Puppa, T.J. Meredith, L. Murray, A.Nantel.