A patient with asthma has a personal best peak expiratory flow of 450 L/min. Today the best of three readings is 300 L/min. Based on a standard asthma action plan, which zone is the patient in?
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Answer: A
- Percent of personal best = today's reading ÷ personal best × 100.
- 300 ÷ 450 = 0.667.
- 0.667 × 100 ≈ 67%.
- Zones: green 80–100%, yellow 50–79%, red below 50%. 67% is in the yellow zone.
Yellow zone, at about 67% of personal best: Correct. 300 ÷ 450 × 100 ≈ 67%, which falls in the yellow (caution) zone of 50% to 79%.
Green zone, at about 150% of personal best: This divides the personal best by today's reading instead of the reverse.
Red zone, at about 33% of personal best: This uses the drop (150 L/min) rather than the reading itself; 150 ÷ 450 = 33%.
Green zone, at about 80% of personal best: The green zone is 80% to 100% of personal best; 300 is only about 67% of 450.
Red zone, at about 67% of personal best: The percentage is right, but the red zone is below 50% of personal best.
Peak flow is judged against the patient's own personal best: green 80–100%, yellow 50–79%, red below 50%.