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.