The Diagnosis of Acute Mountain Sickness in Preverbal Children FREE

THE EXPOSURE of young children to high altitudes has become commonplace with the boom in outdoor recreation, improvements in infant-transporting equipment, and frequent relocation of families to high-altitude communities. Adults who visit the mountains commonly experience acute mountain sickness (AMS). However, very little is known regarding the occurrence of AMS in infants and young children. Primary care providers at ski resorts frequently see preverbal children who are unexplainably fussy without an obvious source of their discomfort. In the setting of recent altitude gain, the diagnosis of AMS is often made in these children, but the clinician may be hampered by the lack of clear diagnostic criteria. The diagnosis frequently results in alterations of holiday travel plans for the families involved. A few case reports of AMS in young children exist, yet no controlled investigations of AMS in preverbal children have been published.^{1 - 4}

In adults, AMS is diagnosed using the Lake Louise Scoring System (LLSS) in the context of recent altitude gain. This requires the presence of a headache and 1 of the following: fatigue, dizziness, gastrointestinal tract disturbance, or sleep disturbance.⁵ The lack of data regarding AMS in preverbal children is, in part, due to a lack of established criteria for making the diagnosis in this age group, and the inability of infants to communicate verbally the usual complaints associated with AMS in adults.

The purpose of this investigation was to develop the criteria for making the diagnosis of AMS in children younger than 3 years and to confirm the occurrence of AMS in this age group.

Subjects were recruited from the Denver, Colo, metropolitan area (altitude, 1610 m). Children aged 3 through 36 months with permanent residence at or below 1645 m were included. Children who were excluded were no longer napping during the day or had a history of motion sickness, current otitis media, any acute medical illness, or any significant underlying medical problem, including but not limited to cardiac shunting defects, pulmonary hypertension, or a seizure disorder.

This investigation was approved by the Colorado Multiple Institutional Review Board, University of Colorado Health Sciences Center, Denver. One or both parents of all subjects signed an informed consent prior to participation in the protocol.

Modification of the LLSS allowed parents to assess and score their own children's behavior. The headache score was replaced with a previously established infant fussiness score (FS).^{6 - 7} Fussiness was defined as a state of irritability without a readily identifiable cause, such as hunger, wet diaper, teething, or pain from an injury. Fussy behavior may include crying, restlessness, or muscular tension. Fussiness was scored on a scale of 1 to 6 and separated into amount (duration) and intensity components. The FS was the sum of both fussiness components (Figure 1). The remainder of the LLSS questions were modified to create the pediatric symptom score (PSS). The modified gastrointestinal score assessed the child's appetite and presence of vomiting; the fatigue or weakness questions were replaced with an assessment of the amount of playful activity demonstrated by the child; and the sleep disturbance score was changed to apply to sleep during the afternoon napping period. No equivalent for the dizziness score was created since we could not assess this in children. The PSS was the sum of each of the components (Table 1).

Prior to the beginning of the study, an investigator (M.Y. or N.W.) met with the parents to discuss the study protocol and train the parents in the application of the FS and PSS.

The study took place on 2 consecutive weekends during the summer season. Each child served as his/her own control. The study was designed to control for the effects of travel, a change in surroundings, and a change in altitude. Observation began at 11 AM and continued until 5 PM on each of 4 days. Days 1 and 2 were baseline measurements at home to assess normal variations; day 3 reflected travel without altitude change from Denver to Ft Collins, Colo (1615 m); and 1 week later, day 4 involved travel from Denver to Keystone, Colo, and a gondola ascent to the summit lodge (3488 m). On days 3 and 4, both sites had indoor facilities with adjacent napping areas and a yard available for outside activities. A luncheon was provided for all participants while activity for the subjects and their families was unrestricted. Children had access to similar toys, games, and other activities at each site. Experienced preschool teachers helped entertain and supervise the children. On days 3 and 4, families recorded their travel time to each site; on arrival at each study site there was 1 hour of free playtime followed by lunch between noon and 1:00 PM, with 2 hours for napping and playing thereafter.

Parents recorded the FS at 11 AM, 1, 3, and 5 PM, and the PSS at 3 PM each day. At approximately 3:00 PM on days 3 and 4, pulse oximetry (SpO₂) and pulse were recorded using a pulse oximeter monitor (Ohmeda 4700, Ohmeda Corporation, Louisville, Colo), respiratory rate was estimated by chest wall observation for 15 seconds, and all adult family members and study personnel completed the LLSS. At 3:00 PM on days 3 and 4, the families left the study sites and the measurements at 5 PM were made at home.

We defined the Children's Lake Louise Score (CLLS) to be the sum of the FS and PSS. Scores in excess of the 95th percentile of all the values collected for the FS and PSS on days 1 through 3 were considered abnormal and established the diagnosis of AMS. Data were analyzed using the Student t test and Kruskal-Wallis rank tests, with results reported as the mean ± SD.

Twenty-five children were enrolled; 2 were excluded after day 3 due to an acute illness. Twenty-three children (14 boys), whose mean age was 20.7 ± 9.0 months, and 45 adults (26 women), whose mean age was 35.0 ± 9.5 years, completed the study and were included in data analysis. The ambient indoor temperature on day 3 was 23°C in Ft Collins and 22°C on day 4 in Keystone. Travel time on day 3 was 77 ± 15 minutes, and 95 ± 22 minutes on day 4 (P<.01).

The mean FS for each time period and day and the PSS and CLLS for each day were calculated. No significant differences were seen between or within the control days (days 1-3) in the FS, PSS, and CLLS values. On days 1 through 3, the 95th percentile of all the scores was exceeded when the FS value was 4 or higher, the PSS value was 3 or higher, and therefore the CLLS was 7 or higher (Figure 2 and Figure 3). These values of FS and PSS were used to establish the criteria for the diagnosis of AMS.

On day 4, 5 subjects (21.7%) had AMS (FS, ≥4; PSS, ≥3; and CLLS, ≥7) (Table 2). Disturbance of sleep was the most prominent factor responsible for the increased PSS, followed by decreased playfulness then decreased appetite. One child was reported to have excessive sleepiness rather than inability to sleep. Fussiness scores did not differ from control values immediately after ascent. A linear increase in the FS was noted during the next 2 observations. Two hours after descent the FS of all subjects returned to control values (Figure 4).

Values for SpO₂, pulse, and respiratory rate were significantly different for the entire group at both study sites (Table 3); however, no differences existed between the subjects with or without AMS regarding SpO₂, pulse, and respiratory rate.

Of the 45 adults who participated, 9 (20%) had AMS, determined by the LLSS criteria, 4 hours after ascent. No familial tendency toward susceptibility to AMS was evident.

This study, which used a newly developed clinical assessment instrument, suggests that fussiness plus changes in appetite, playfulness, and sleep can be used to define the presence of AMS in preverbal children. Each component of the CLSS was developed in an effort to reproduce the LLSS as closely as possible. The FS serves as the headache equivalent because it expresses the general discomfort experienced by all individuals with a headache. The previous use of the FS in the assessment of infant colic provides some validity to its use in preverbal children.^{6 - 7} Occasional unexplained fussiness is common among young children; in the study cohort 1 child had an FS of 4 and another a score of 6 during the baseline observations at home (days 1 and 2). In all cases, when the FS of subjects increased after ascent, there was a return to control values 2 hours after descent, indicating that this scale is sensitive to the effect of altitude exposure. During the 3 control days prior to ascent, the PSS also exhibited alterations from normal, yet no child manifested a score greater than 2.

The incidence of AMS in adults and older children is directly related to the rate of ascent, final altitude gained, and time spent at the higher altitude.⁸ The children in this study developed AMS at a rate similar to the accompanying adults under circumstances of rapid ascent and a 4-hour exposure to 3488 m. Previous studies at moderate altitudes (1890-2910 m) have revealed that approximately 25% of children (aged 9-14 years) and adults develop AMS within 1 or 2 days after exposure to higher altitude.^{8 - 9} Sixty-five percent of the adult subjects who experienced AMS at moderate altitudes developed their symptoms in less than 12 hours.⁸ Adult volunteers subjected to rapid ascent (2 hours) via automobile on Mount Evans, Colo (4348 m), had a 46% rate of AMS development when assessed after 8 hours of exposure to the higher altitude.¹⁰ The incidence of AMS in our subjects may have been higher if the altitude of residence had been lower, the time of exposure to higher altitude had been longer, or the final altitude gained had been higher.

Several other limitations exist in this investigation. The small number of subjects in the study cohort may inadequately represent a larger population. The small sample size also precludes any definitive conclusions regarding familial predisposition to AMS. Although genetic susceptibility to AMS has been suggested,¹¹ no familial predisposition is evident in the present study.

All of the children's behavioral measurements were recorded by the parents, who were not blinded to ascent. The reproducibility of these scores was not tested. In some cases, both parents were present, yet only 1 parent completed the scale; thus, interrater agreement was not calculable. The ability of an adult with AMS to accurately score his/her own child is a further source of potential error. It would not be possible for a clinician to evaluate a child without an extended period of observation or parental history, because the FS and PSS require intimate knowledge of a child over an extended period. The threshold values for AMS were developed retrospectively after data analysis. This diagnostic tool needs further prospective evaluation and confirmation.

The stressful effects of travel on children have not been studied in a controlled fashion. Theis and associates⁹ attempted to control for the effects of travel in older children by studying similar subjects after travel to sea level and high-altitude settings. The current study controlled for travel by observing the same subjects on 2 different days in low- and high-altitude settings. Travel time to the 2 different sites was statistically different, yet the additional 18 minutes required to drive to the Keystone site was unlikely to have been clinically disruptive. Travel without altitude gain did not cause a change in the CLLS scores from baseline measurements.

Previous reports of presumed AMS in children have noted appetite and sleep disturbances, change in stool pattern, and general fussiness in infants shortly after arrival at the higher altitude.^{4 ,12} It is a challenge for clinicians to differentiate unexplained fussiness and behavioral changes secondary to benign normal variation from a more serious underlying medical problem.^{13 - 14} Conditions such as infectious diseases (bacteremia, otitis media, or a viral syndrome), trauma (corneal abrasion, subdural hematoma, or nonaccidental trauma), and gastrointestinal tract complaints (gastroesophageal reflux or intussusception) may present as fussiness without any obvious signs or symptoms that suggest another specific medical problem.^{14 - 15} Although AMS in infants is generally regarded as self-limiting,⁴ adults who proceed to higher altitudes despite symptoms of AMS can develop life-threatening conditions of high-altitude pulmonary edema or high-altitude cerebral edema.¹⁶ We believe that continued ascent for children with AMS may have the same consequences, and is therefore contraindicated.

The development of diagnostic criteria for AMS in the preverbal child will increase awareness of this entity and help clinicians and parents evaluate a fussy child with appetite, activity, and sleep alterations. Prompt recognition of AMS in infants may limit their distress and may help to prevent dehydration resulting from food refusal or vomiting. When faced with the acute development of this symptom complex and recent exposure to high altitude, the diagnosis of AMS should be considered.

We define AMS in preverbal children as a CLSS of 7 or higher, including an FS of 4 or higher and PSS of 3 or higher in the setting of recent altitude gain. The incidence of AMS in these young children (21.7%) was similar to that among accompanying adults (20%).

The presence of both fussiness and alterations of appetite, activity, and sleep patterns, in the setting of recent exposure to high altitude, warrants inclusion of AMS in the differential diagnoses of the clinician. Parents play a key role in recognition and proper intervention, including arranging primary medical care and/or descent. Thus, parents who plan to travel to high altitudes with their preverbal children should be educated regarding the potential for and the characteristics of AMS.

Accepted for publication January 30, 1998.

Funding was provided by the Colorado Emergency Medicine Research Center, Denver, and the Colorado Altitude Research Institute, Keystone.

Presented in part at the Society of Academic Emergency Medicine Annual Meeting, Denver, Colo, May 5, 1996, and the 10th Biennial International Symposium on Hypoxia and Mountain Medicine, Lake Louise, Alberta, February 18, 1997.

We thank David Ferguson, MD, for providing the Ft Collins facility; the Keystone Ski Resort for their cooperation and support; the Friends' School (Boulder, Colo) for the loan of toys and supplies; the Ohmeda Corporation for the loan of the oximeter and assistance in data collection; Courtney Kane and Jennifer Frank for their assistance with child care; and Matt Frank, Amaryllis Soler, Eve Ely, Nory Waldman, DDS, Sara Waldman, Adrianna D'Amico, and Alexandra Volturo for their help with data collection and logistic support.

Editor's Note: Only 2 weeks ago, I flew in a small plane alongside the top of Mount Everest (8848 m). Incredible sight, but based on this study and a dozen other reasons, I'd not advise taking children of any age to that altitude.—Catherine D. DeAngelis, MD

Corresponding author: Michael Yaron, MD, Division of Emergency Medicine, University of Colorado Health Sciences Center, Box B-215, 4200 E Ninth Ave, Denver, CO 80262.