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ARTICLE:
Paresh B. Pandit, Sherry E. Courtney, Kee H. Pyon, Judy G. Saslow, and Robert H. Habib
Work of Breathing During Constant- and Variable-Flow Nasal Continuous Positive Airway Pressure in Preterm Neonates
Pediatrics 2001; 108: 682-685 [Abstract] [Full text] [PDF]
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[Read eLetters] CPAP and work of breathing
Kenneth Harkavy   (18 October 2001)

CPAP and work of breathing 18 October 2001
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Kenneth Harkavy,
Neonatologist
Columbia Hospital for Women

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Re: CPAP and work of breathing

klhark46{at}aol.com Kenneth Harkavy

Read with interest the two articles on variable flow CPAP in September 2001 and February 2001. I am concerned about the missing patients, the correction for weight in change in volume, the correction for tidal volume for WOB, and the elaborate statistics for what appears to be paired tests each in the same patient.

Each article refers to 35 patients recruited, but one reported on 32, the other on 24. No data are provided on the missing patients, nor on the reasons that they were deleted from anaylsis. This raises questions about the generalizability of the results.

While the correction of volume changes for body weight permit comparison to individual patients, would like reassurance that failure to correct doesn't change the statistics.

Since variable flow CPAP is associated with larger tidal volumes, correction of WOB by dividing by Vt will result in a apparently lower WOB for these babies, even if the total WOB is actually the same. What has improved is the efficiency of breathing if the larger Vt are useful, but the caloric consumption will be the same. It appears from the figures that 6-8 cm constant flow CPAP might be clinically comparble to 4-6 cm of variable flow CPAP.Can you compare the WOB for the two styles of CPAP at similar clinical settings to show that variable flow CPAP has less WOB for similar ventilation.

Thank you.