Hypercapnic acidosis does not modulate the severity of bacterial pneumonia-induced lung injury.
OBJECTIVE
Deliberate induction of hypercapnic acidosis protects against lung injury after ischemia-reperfusion, endotoxin-induced, and ventilation-induced lung injury. The efficacy of hypercapnic acidosis in bacterial lung infection, a common cause of acute respiratory distress syndrome, is not known. Furthermore, its effect may differ depending on the presence or absence of antibiotic therapy. We investigated whether hypercapnic acidosis-induced by adding CO2 to inspired gas-would protect against acute lung injury induced by pulmonary Escherichia coli instillation in an in vivo model in the presence and absence of effective antibiotic therapy.


METHODS
Prospective randomized animal study.


METHODS
University research laboratory.


METHODS
Adult male Wistar-Kyoto rats.


METHODS
The animals were anesthetized and ventilated. In series 1, rats were administered intravenous ceftriaxone (100 mg x kg) and randomized to normocapnia (Normocapnia-ABx; Fico2 0.00, n = 10) or hypercapnia (Hypercapnia-ABx; Fico2 0.05, n = 10) groups. E. coli (8.4 x 10 colony forming units) was instilled intratracheally. Series 2 animals did not receive antibiotics. They were randomized to normocapnia (Normocapnia, n = 10) or hypercapnia (Hypercapnia, n = 10) groups, and intratracheal E. coli was administered. All animals were ventilated for 6 hrs.


RESULTS
In series 1, there were no differences between Hypercapnia-ABx and Normocapnia-ABx groups with regard to: (a-a)o2 gradient (mean +/- sem; 215 +/- 13 vs. 252 +/- 22 mm Hg), Pao2, bronchoalveolar lavage neutrophil count, static lung compliance, or histologic injury. Lung bacterial yield was not different between the groups. In series 2, in the absence of antibiotic therapy, there were no differences between Hypercapnia and Normocapnia groups in: (a-a)o2 gradient (mean +/- sem, 345 +/- 25 vs. 332 +/- 23 mm Hg), systemic Pao2, bronchoalveolar lavage neutrophil count, or static lung compliance. Lung bacterial yield was not altered by hypercapnia in either series 1 or 2.


CONCLUSIONS
We conclude that hypercapnic acidosis did not alter the magnitude of the lung injury induced by intratracheal E. coli instillation in the presence or absence of antibiotics.
O'Croinin
Donall F
DF
Department of Physiology, Conway Institute of Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland.
Hopkins
Natalie O
NO
Moore
Michael M
MM
Boylan
John F
JF
McLoughlin
Paul
P
Laffey
John G
JG
D000142:Acidosis, Respiratory; D000818:Animals; D002443:Ceftriaxone / Q000627:therapeutic use; D004927:Escherichia coli Infections / Q000145:classification / Q000150:complications* / Q000188:drug therapy; D006935:Hypercapnia; D008297:Male; D018410:Pneumonia, Bacterial / Q000145:classification / Q000150:complications* / Q000188:drug therapy; D051381:Rats; D011921:Rats, Inbred WKY; D012128:Respiratory Distress Syndrome / Q000209:etiology* / Q000517:prevention & control; D012720:Severity of Illness Index
D002443:Ceftriaxone