Ascent rate and the Lake Louise scoring system: An analysis of one year of emergency ward entries for high-altitude sickness at the Mustang district hospital, Nepal

Abstract

More travellers are making swift ascents to higher altitudes without sufficient acclimatization or pharmaceutical prophylaxis as road connectivity develops in the Himalayan region of Nepal. Our study connects ascent rate with prevalence and severity of acute mountain sickness (AMS) among patients admitted to the emergency ward of the Mustang district hospital in Nepal. A register-based, cross-sectional study was conducted between June 2018 and June 2019 to explore associations of Lake Louise scores with ascent profile, sociodemographic characteristics, and comorbidities using chi-square test, t-test, and Bayesian logistic regression. Of 105 patients, incidence of AMS was 74%, of which 61%, 36%, and 3% were mild, moderate, and severe cases, respectively. In the Bayesian-ordered logistic model of AMS severity, ascent rate (odds ratio 3.13) and smoking (odds ratio 0.16) were significant at a 99% credible interval. Based on the model-derived counterfactual, the risk of developing moderate or severe AMS for a middle-aged, non-smoking male traveling from Pokhara to Muktinath (2978m altitude gain) in a single day is twice that of making the ascent in three days. Ascent rate was strongly associated with the likelihood of developing severe AMS among travellers with AMS symptoms visiting Mustang Hospital's Emergency Ward.

Fig 1. Various travelling routes used by AMS patients visiting the emergency ward of Mustang district hospital.

Each line represents a unique travelling route. Important locations in routes are plotted against their respective elevations in the y-axis. The cumulative land-travel time on x-axis is the sum of the average land-travel time from Kathmandu, whether by bus, jeep, or on foot, depending on the road’s characteristics. All-weather roads are those that have public bus routes. On seasonal roads, off-road four-wheelers provide transit most months of the year except during snowfall and heavy rain. On trails, walking is the only mode of travel. Among major routes within Mustang, all except for Damodar Kunda (4890 m) are passable with a motorized vehicle at least seasonally. Except for the route from Manang through Thorong La, all other routes pass the Mustang district hospital during both ascent and descent. Trekkers travelling in Thorong La route pass hospital only during the descent.

Fig 2. The counterfactual probability plot for AMS severity with ascent rate, age, and smoking status derived from model 4 of Table 2.

The baseline is represented by a male with no comorbidities, with a permanent address at an altitude of 542m (median in the dataset), reaching the peak altitude of 3800m (altitude of Muktinath temple) without drinking alcohol during the ascent. Bold lines are posterior means. Shaded areas are posterior 95% credible intervals, and thin lines are sampled fitted lines from the posterior. For a middle-aged (31–60 years), non-smoker male travelling from Pokhara to Muktinath in a single day, the odds of developing moderate or severe AMS increase twofold (2.069) compared to those of a three-day journey.