Chest
Volume 124, Issue 4, October 2003, Pages 1312-1317
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Clinical Investigations
Asthma
Effects of Short-term 28% and 100% Oxygen on Paco2 and Peak Expiratory Flow Rate in Acute Asthma: A Randomized Trial

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Study objective

We conducted the first randomized controlled study to assess the effects of short-term 28% and 100% oxygen on Paco2 and peak expiratory flow rate (PEFR) in patients with acute severe asthma.

Patients and interventions

Seventy-four patients (mean age, 37.9 ± 9.7 years [± SD]; PEFR, 41.0 ± 12.1% of predicted) from two emergency departments were randomized to receive 28% or 100% oxygen during 20 min.

Results

The administration of 100% oxygen significantly increases Paco2 (p = 0.03) and decreases PEFR (p = 0.001) as compared with administration of 28% oxygen. Paco2 before and during oxygen administration correlated significantly (p = 0.001) in both groups. Patients breathing 28% oxygen experienced a Paco2 fall; on the contrary, patients who received 100% oxygen showed an increase in Paco2, particularly those with Paco2 before oxygen treatment > 40 mm Hg.

Conclusions

This study confirmed previous observations that oxygen dose should be variable and based on achieving and maintaining target arterial oxygen saturation measured by pulse oximetry ≥ 92% rather than on prescribing predetermined concentrations or flow rates of inspired oxygen.

Section snippets

Subjects

We recruited all adult patients with acute asthma who were seen in two emergency departments of Uruguay (Hospital Central de las Fuerzas Armadas in Montevideo, and Hospital de Paysandú, in Paysandú) over a 6-month period (March to August 2002). The inclusion/exclusion criteria for patients were as follows: (1) diagnosis criteria of asthma of the American Thoracic Society16; (2) age from 18 to 50 years; (3) peak expiratory flow rate (PEFR) < 60% of predicted value; and (4) patients were excluded

Results

A total of 79 consecutive adults with an acute exacerbation of asthma were recruited for entry into this study. Two patients were excluded because they were unable to maintain a Spo2 ≥ 90%. Seventy-seven adults were randomly assigned to treatment: 38 patients to the 28% group and 39 patients to the 100% group. Three patients (two patients in the 28% group, and one patient in the 100% group) refused the use of the facemask. Finally, 74 patients (36 patients in the 28% group, and 38 patients in

Discussion

To our knowledge, this is the first randomized controlled trial that provided data on the effect of two oxygen concentrations on Paco2 and PEFR in adult patients with acute severe asthma. The results showed that 100% of inspired oxygen resulted in a significant increase in Paco2. Forty-two percent of the 100% oxygen group patients had increases in Paco2 averaging 5.0 mm Hg (range, 2.4 to 14.3 mm Hg). As shown in Figure 1, Figure 2, Paco2 during oxygen administration highly correlated with the Pa

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