Hypercapnic respiratory failure in obesity-hypoventilation syndrome: CO₂ response and acetazolamide treatment effects.
OBJECTIVE
In obesity-hypoventilation-syndrome patients mechanically ventilated for hypercapnic respiratory failure we investigated the relationship between CO₂ response, body mass index, and plasma bicarbonate concentration, and the effect of acetazolamide on bicarbonate concentration and CO₂ response.


METHODS
CO₂ response tests and arterial blood gas analysis were performed in 25 patients ready for a spontaneous breathing test, and repeated in a subgroup of 8 patients after acetazolamide treatment. CO₂ response test was measured as (1) hypercapnic drive response (the ratio of the change in airway occlusion pressure 0.1 s after the start of inspiratory flow to the change in P(aCO₂)), and (2) hypercapnic ventilatory response (the ratio of the change in minute volume to the change in P(aCO₂)).


RESULTS
We did not find a significant relationship between CO₂ response and body mass index. Patients with higher bicarbonate concentration had a more blunted CO₂ response. Grouping the patients according to the first, second, and third tertiles of the bicarbonate concentration, the hypercapnic drive response was 0.32 ± 0.17 cm H₂O/mm Hg, 0.22 ± 0.15 cm H₂O/mm Hg, and 0.10 ± 0.06 cm H₂O/mm Hg, respectively (P = .01), and hypercapnic ventilatory response was 0.46 ± 0.23 L/min/mm Hg, 0.48 ± 0.36 L/min/mm Hg, and 0.22 ± 0.16 L/min/mm Hg, respectively (P = .04). After acetazolamide treatment, bicarbonate concentration was reduced by 8.4 ± 3.0 mmol/L (P = .01), and CO₂ response was shifted to the left, with an increase in hypercapnic drive response, by 0.14 ± 0.16 cm H₂O/mm Hg (P = .02), and hypercapnic ventilatory response, by 0.11 ± 0.22 L/min/mm Hg (P = .33).


CONCLUSIONS
Patients with obesity-hypoventilation syndrome and higher bicarbonate concentrations had a more blunted CO₂ response. Body mass index was not related to CO₂ response. Acetazolamide decreased bicarbonate concentration and increased CO₂ response.
Raurich
Joan-Maria
JM
Intensive Care Unit, Hospital Universitari Son Dureta, Andrea Doria 55, 07014, Palma de Mallorca, Illes Balears, Spain. joan.raurich@ssib.es
Rialp
Gemma
G
Ibáñez
Jordi
J
Llompart-Pou
Juan Antonio
JA
Ayestarán
Ignacio
I
D000086:Acetazolamide; D000368:Aged; D000471:Alkalosis / Q000503:physiopathology; D001639:Bicarbonates / Q000097:blood / Q000378:metabolism*; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood / Q000378:metabolism*; D002257:Carbonic Anhydrase Inhibitors; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010845:Obesity Hypoventilation Syndrome / Q000503:physiopathology* / Q000628:therapy; D012121:Respiration, Artificial; D012125:Respiratory Center / Q000502:physiology*; D015300:Ventilator Weaning / Q000379:methods
D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D002245:Carbon Dioxide; D000086:Acetazolamide