Among children admitted to ICUs for emergency treatment of acute asthma, approximately 10% to 30% need intubation and mechanical ventilation for worsening bronchospasm, impaired ventilation, and cardiovascular depression. However, since mechanical ventilation compromises active expiration, the authors state, it should be delayed as long as possible through the use of medical therapy.
One potential method to improve respiratory performance in this situation would be to improve sensitivity to beta agonists. Sensitivity is often impaired in these children by severe acidemia, due to respiratory acidosis and/or associated metabolic acidosis.
The causes of metabolic acidosis in asthma include increased lactic acid production by respiratory muscles due to prolonged and increased work of breathing and tissue hypoxia.
Despite reports that sodium bicarbonate produces clinical improvement, its use in the treatment of life-threatening asthma has not been generally accepted. This lack of acceptance may partly be due to the fear of a potential increase in pCO2 due to increased production and hypoventilation following sodium bicarbonate infusion and removal of the acidemic stimulation of ventilation.
In the Chest article, a team of researchers at a hospital in the Netherlands undertook a retrospective study to assess the effect of sodium bicarbonate administration on pCO2 in children with life-threatening asthma and to evaluate the clinical effect of this treatment.
For their study, the researchers assessed the records of 73 youngsters, with a median age of 6.2 years, who had been admitted to a Rotterdam hospital's pediatric ICU for emergency treatment of life-threatening asthma between January 1999 and November 2003.
Among the patients, 17 remained in respiratory distress following treatment with continuous nebulization, intravenous magnesium sulfate, and intravenous salbutamol. Under hospital protocol, those patients then received sodium bicarbonate as part of combination therapy to treat the acidemia and to thereby improve sensitivity to beta-agonists. The median dose of sodium bicarbonate was 0.9 mmol/kg.
Before, administration of sodium bicarbonate, 13 patients had mixed respiratory and metabolic acidosis, 1 had predominantly respiratory acidosis and 2 had metabolic acidosis alone. In 14, sodium bicarbonate was administered in a last attempt to avoid mechanical intubation. In three patients, sodium bicarbonate was given after intubation and mechanical ventilation because of persistent acidmeia. Eight patients received sodium bicarbonate despite a pH greater than 7.15 resulting from severe respiratory distress and ineffectiveness of beta-agonists. Only one of the 17 patients did not improve (and she required subsequent intubation). There were no fatalities.
The researchers found that, except for that one patient, administration of sodium bicarbonate resulted in relief of respiratory distress and overall clinical improvement in the patients, especially in their level of consciousness.
There was a significant mean decrease in PCO2 after sodium bicarbonate infusion (p=0.007) associated with a significant increase in pH (p<0.005).
The researchers concluded that sodium bicarbonate might be useful as an adjunctive treatment in patients with life-threatening asthma and acidemia in whom mechanical ventilation is considered.
While contending that the fear of an increase in pCO2 is unsubstantiated, they expressed the need for future prospective randomized trials focusing on the use of sodium bicarbonate in therapy for life-threatening asthma.
- Reviewed by Zalman S. Agus, MD Emeritus Professor at the University of Pennsylvania School of Medicine