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Air time for preemie respiration

By Vanessa Hurley

Premature infants have many medical problems, with respiratory distress syndrome (RDS) one of the most common. Nowadays, RDS can be treated with surfactant, a lipoprotein complex that helps air sacs in the lungs stay open, as well as with oxygen therapy. Dartmouth researchers recently studied the effectiveness of one of the newer methods of delivering oxygen-enriched air—heated, humidified high-flow nasal cannula (HHHFNC) therapy.

Flow: Since 1971, continuous positive airway pressure (CPAP) therapy, which delivers a heated, humidified, and pressurized oxygen-air mixture via small nasal tubes, has been used to help the tiniest babies breathe. Now, intensive care nurseries often use HHHFNC for preemies who've graduated from CPAP therapy but still need oxygen. The high-flow therapy is thought to provide many of CPAP's benefits, including CPAP-like pressures. But since the high-flow system is considered easier to use, some places are using it instead of CPAP, even though it's unclear if the high-flow therapy is as effective.

Conflicting evidence about HHHFNC's efficacy led DMS pediatrician and physiologist Robert Darnall,M.D.; former pediatric fellow Zuzanna Kubicka, M.D.; and respiratory therapist Joseph Limauro to conduct an observational study of 27 infants at DHMC from January 2005 to April 2006. The researchers inserted small probes in the infants' mouths to estimate how much pressure HHHFNC generated in the lungs of infants of various weights and sizes. Flow rates ranged from one to five liters a minute. They found that HHHFNC produced clinically significant levels of pressure in only the smallest infants—those who weighed less than 1,500 grams (just over three pounds). In some cases—such as if the baby'smouth remained closed and the nasal cannulas fit too tightly, so air couldn't escape—the pressure buildup was greater than expected. In other cases, there wasn't enough pressure delivered to the lungs.

Babies: In their paper, published in Pediatrics, the researchers cautioned that, while unlikely, it's possible that HHHFNC might create an unsafe level of pressure. Kubicka said they were surprised that some nurseries using the high-flow therapy "didn't really pay attention even to the size" of the nasal cannulas. She worries that the combination of higher flow rates and bigger nasal cannulas "may be dangerous" in the smallest babies.

Clinical trials are needed to further evaluate HHHFNC, says Kubicka, who has finished her Dartmouth fellowship and is now at Children's Hospital of Boston. She suspects that the high-flow therapy may not be an appropriate substitute for traditional CPAP.

Still, says Darnall, when the flow rate is kept closer to one liter per minute, HHHFNC may be better than the therapy that used to be the next step after CPAP—a system that delivered unheated and only partially humidified oxygen.

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