Send the kid to a sleep clinic

Serious doubts cast on the accuracy of home oximetry monitors for young patients. Children are not little adults

By Jadzia Jagiellowicz

GPs and pediatricians encouraged by the possibility of home oximetry monitors (HOM) eliminating long lineups for hospital sleep clinics may have to think again. The machines don't measure up to the gold standard of overnight laboratory polysomnography testing done in hospital sleep clinics, according to a University of Calgary study published in the November 2003 issue of Chest. The prospective cohort study found that HOMs often fail to diagnose children with obstructive sleep apnea (OSA) and mistakenly diagnose healthy children.

"There are only four or five sleep clinics specialized in diagnosing and treating children in Canada," says study author Valerie G Kirk, "and waiting lists are long." HOM equipment saves the medical system both time and money, since it can be used at home and doesn't require a technician to observe a sleeping child and score specific events. "It's common for the FP to order abbreviated home monitoring for adult patients," says Dr Kirk. "It's well established in the literature that home oximetry testing works for many adults. There's a lot of pressure to find a less expensive and easier way to get children to testing." As a result to this pressure, she says GPs are now often recommending home oximetry monitors for their pediatric as well as their adult patients.

HOME VERSUS LAB
Dr Kirk and her colleagues investigated 58 children who had been referred to the Paediatric Sleep Service at the Alberta Children's Hospital between the fall of 2000 and winter of 2002. Children spent one night in a sleep laboratory where they received a battery of polysomnography tests. These included tests of respiratory measures such as chest and abdominal wall movement, nasal-oral airflow, end-tidal carbon dioxide and transcutaneous carbon dioxide. A trained sleep technician watched the children sleep and scored sleep architecture and respiratory events. Children were also monitored using a portable oximetry monitor, once during sleep laboratory polysomnography and, within the next week, twice at home. The home oximetry monitor consists of a probe attached to the patient's finger or ear lobe which is linked to a computerized unit that displays the percentage of hemoglobin saturated with oxygen. The unit is designed to automatically score respiratory events.

Laboratory polysomnography diagnosed OSA on the basis of the apnea-hypopnea index (AHI) -- the number of apnea-hypopnea events a child had in each hour of total sleep time. Apnea was defined as a recurring interruption of breathing because of obstruction of the upper airway by relaxed or abnormal pharyngeal tissues, and hypopnea as abnormally shallow breathing due to partial obstruction of the upper airway. Children with scores greater than one on the AHI were diagnosed with OSA.

The HOM automatically calculated a slightly different measure of OSA, called the desaturation index (DI). The DI is based on the percentage of hemoglobin saturated with oxygen. Unlike the battery of measures that comprise laboratory polysomnography, the HOM calculates only one measure, the percentage of hemoglobin saturated with oxygen. The study had some bad news for proponents of the home oximetry equipment. The DI value measured by the HOM agreed poorly with the AHI value measured by laboratory polysomnography in diagnosing moderate OSA, defined as an AHI value of more than five respiratory events per hour. In theory, these measures should have agreed quite closely since they were conceivably measuring the same thing.

The HOM was also poor at picking up OSA and had trouble distinguishing between healthy children and those with the condition. For example, 33% of children who actually had OSA were never diagnosed by the home equipment and in 40% of cases the monitor indicated that healthy children had the condition. The study notes that differences between adults and children with OSA suggest that the monitors may not be as accurate in diagnosing children as they have been proven to be with adults.

ONE HAPPY ENDING
Five-year-old Maxim Esler was one of the lucky ones. His OSA was correctly diagnosed by home oximetry. Maxim was referred to the oto-rhino-laryngology department at Montreal Children's Hospital, after his mother, Natalia Popova, told his pediatrician that night after night she heard loud laboured breathing coming from Maxim's room. Ms Popova was sent home with a portable oximetry machine to monitor Maxim's sleep. After one night of monitoring with the home equipment, hospital staff "thought something was wrong with the machine, his values were so high," Ms Popova says. She repeated the testing a second night. The diagnosis was unequivocal; immediate surgery to remove Maxim's tonsils.

According to Dr Kirk, tonsillectomy or adenoidectomy is the first-line therapy for all moderate cases of OSA. "Surgery is successful in 80-85% of the cases," she says. According to a Montreal Children's Hospital study published in the January issue of Pediatrics, HOM can facilitate logical prioritization of the adenotonsillectomy surgical list and help to predict children who are at highest risk of postoperative complications. Dr Kirk has some parting words of advice for GPs. "The danger is that home oximetry equipment doesn't correlate well with hospital laboratory polysomnography. GPs should maintain a high level of suspicion [of OSA] in a child that is snoring and has large tonsils and adenoids, even if home oximetry has indicated the child is normal."