Eucapnic Hyperventilation Technique

Updated: Dec 16, 2015
  • Author: Rakesh Vadde, MBBS; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Technique

Positioning

The test is conventionally done with the patient sitting. The mouthpiece of the spirometry is placed in the patient’s mouth and sealed by the lips.

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Anesthesia

Generally anesthesia is not needed for this procedure

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Technique

The patient should be clinically stable, and the technician should be trained to manage unwanted response such as bronchospasm. The test is done in a standard pulmonary function laboratory and is generally safe procedure.

Initially, baseline spirometry is performed twice to obtain two values for FEV1 that are reproducible. The better of the two values is taken as baseline FEV1, which has to be greater than 75% of predicted normal for sex, age, and height. For subjects with lower lung function or those known to have moderate to severe asthma, the progressive protocol for eucapnic hyperventilation is recommended. [12]

The patient wears nose clips and orally inhales a mixture of dry hypercapnic air (5% CO2 and 21% O2 balanced with N2). The eucapnic hyperventilation test allows significant hyperventilation at a rate of approximately 30 times per minute. The rate to be achieved can be calculated assessing 30 x FEV1 or 0.85 x maximum voluntary ventilation (MVV), [13] whichever is greater. [8] Further studies regarding the optimal minimum threshold minute ventilation for eucapnic hyperventilation testing in nonathletes need to be established. [14]

Using a large, nondiffusing gas bag and a 2-way nonrebreathing valve, the patient is instructed to actively hyperventilate through the mouthpiece inhaling the balanced gas mixture. The patient is encouraged to maintain this hyperventilation for 6 minutes. The FEV1 is measured immediately after the end of test and then at 5, 10, 15, and 20 minutes.

Although this particular protocol for eucapnic hyperventilation is recommended, the inspired air temperature, ventilation rate, and duration of the test can be changed to simulate the conditions under which the athlete is provoked.

The test result is positive if the FEV1 values measured within 20 minutes after the test falls more than 10% from the baseline. [8]

The percentage fall in FEV1 is calculated as follows:

100 × FEV1 (baseline) - lowest value for FEV1 (posttest)/FEV1 (baseline)

Bronchial responsiveness to a provoking stimulus is often referred to and interpreted as mild, moderate, or severe.

The response is mild if the fall in FEV1 is between 10-19.9% when the ventilation is 60% MVV or more and moderate when the fall is between 20-29.9%. The response is severe when the fall in FEV1 is 30% or more at any level of ventilation or if a fall greater than 10% occurs at a ventilation rate less than 30% MVV.

A short acting beta-agonist is given to the patients who develop bronchospasm and spirometry is repeated after 15 minutes. Patient should be observed until clinically stable. This test still remains subjective, and FEV1 most of the time is effort related.

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