The use of acetazolamide for the prevention of high-altitude illness

Altitude illnesses

Millions of people visit high-altitude regions annually and more than 80 million live permanently above 2,500 m. Acute high-altitude exposure can trigger high-altitude illnesses (HAIs), including acute mountain sickness (AMS), high-altitude cerebral oedema (HACE) and high-altitude pulmonary oedema (HAPE). Chronic mountain sickness (CMS) can affect high-altitude resident populations worldwide. The prevalence of acute HAIs varies according to acclimatization status, rate of ascent and individual susceptibility. AMS, characterized by headache, nausea, dizziness and fatigue, is usually benign and self-limiting, and has been linked to hypoxia-induced cerebral blood volume increases, inflammation and related trigeminovascular system activation. Disruption of the blood-brain barrier leads to HACE, characterized by altered mental status and ataxia, and increased pulmonary capillary pressure, and related stress failure induces HAPE, characterized by dyspnoea, cough and exercise intolerance. Both conditions are progressive and life-threatening, requiring immediate medical intervention. Treatment includes supplemental oxygen and descent with appropriate pharmacological therapy. Preventive measures include slow ascent, pre-acclimatization and, in some instances, medications. CMS is characterized by excessive erythrocytosis and related clinical symptoms. In severe CMS, temporary or permanent relocation to low altitude is recommended. Future research should focus on more objective diagnostic tools to enable prompt treatment, improved identification of individual susceptibilities and effective acclimatization and prevention options.

Hypoxic preacclimatization combining intermittent hypoxia exposure with physical exercise significantly promotes the tolerance to acute hypoxia

Background: Both hypoxia exposure and physical exercise before ascending have been proved to promote high altitude acclimatization, whether the combination of these two methods can bring about a better effect remains uncertain. Therefore, we designed this study to evaluate the effect of hypoxic preacclimatization combining intermittent hypoxia exposure (IHE) and physical exercise on the tolerance to acute hypoxia and screen the optimal preacclimatization scheme among the lowlanders. Methods: A total of 120 Han Chinese young men were enrolled and randomly assigned into four groups, including the control group and three experimental groups with hypoxic preacclimatization of 5-day rest, 5-day exercise, and 3-day exercise in a hypobaric chamber, respectively. Main physical parameters for hypoxia acclimatization, AMS incidence, physical and mental capacity were measured for each participant in the hypobaric chamber simulated to the altitude of 4500 m in the effect evaluation stage. The effect was compared between different schemes. Results: During the effect evaluation stage, SpO2 of the 5-day rest group and 5-day exercise group was significantly higher than that of the control group (p = 0.001 and p = 0.006, respectively). The participants with 5-day rest had significantly lower HR than the controls (p = 0.018). No significant differences of AMS incidence were found among the four groups, while the proportion of AMS headache symptom (moderate and severe vs. mild) was significantly lower in the 3-day exercise group than that in the control group (p = 0.002). The 5-day exercise group had significantly higher VO2max, than the other three groups (p = 0.033, p < 0.001, and p = 0.023, respectively). The 5-day exercise group also had significantly higher digital symbol and pursuit aiming test scores, while shorter color selection reaction time than the control group (p = 0.005, p = 0.005, and p = 0.004, respectively). Conclusion: Hypoxic preacclimatization combining IHE with physical exercise appears to be efficient in promoting the tolerance to acute hypoxia. Hypoxia duration and physical exercise of moderate intensity are helpful for improvement of SpO2 and HR, relief of AMS headache symptoms, and enhancement of mental and physical operation capacity.

Flying to high-altitude destinations: Is the risk of acute mountain sickness greater?

BACKGROUND

Altitude sojourns increasingly attract individuals of all ages and different health statuses due to the appeal of high-altitude destinations worldwide and easy access to air travel. The risk of acute mountain sickness (AMS) when flying to high-altitude destinations remains underemphasized. Thus, this review aims to evaluate the altitude-dependent AMS incidence depending on the mode of ascending, e.g. by air vs terrestrial travel.

METHODS

A literature search was performed to identify the observational studies assessing AMS incidence after acute ascent of primarily healthy adults to real high altitude. In addition, placebo arms of interventional trials evaluating the prophylactic efficacy of various drugs have been separately analysed to confirm or refute the findings from the observational studies. Linear regression analyses were used to evaluate the altitude-dependent AMS incidence.

RESULTS

Findings of 12 observational studies, in which the AMS incidence in 11 021 individuals ascending to 19 different altitudes (2200-4559 m) was evaluated, revealed an impressive 4.5-fold steeper increase in the AMS incidence for air travel as compared with slower ascent modes, i.e. hiking or combined car and/or air travel and hiking. The higher AMS incidence following transportation by flight vs slower means was also confirmed in placebo-treated participants in 10 studies of drug prophylaxis against AMS.

CONCLUSIONS

Due to the short time span in going from low to high altitude, reduced acclimatization likely is the main reason for a higher AMS risk when travelling to high-altitude destinations by flight. To avoid frustrating travel experiences and health risks, appropriate and timely medical advice on how to prepare for air travel to high altitude is of vital importance. Effective preparation options include the use of modern pre-acclimatization strategies and pharmacological prophylaxis by acetazolamide or dexamethasone, or even considering alternate itineraries with more gradual ascent.

The changes of electroencephalography in mountaineers on Mount Jade, Taiwan: An observational study

BACKGROUND

The diagnosis of acute mountain sickness, which lacks a reliable and objective diagnostic tool, still depends on the clinical symptoms and signs and remains a major threat and unpredictable disease affecting millions of mountaineers.

OBJECTIVES

To record electroencephalography signals with small, convenient, wireless equipment and to test whether electroencephalography parameters, which are more sensitive and reliable markers, could predict the symptoms of acute mountain sickness.

METHODS

Twenty-five participants were enrolled and separated into two groups to climb Mount Jade in Taiwan. We collected electrocardiography signals and arterial oxygen saturation data at ground, moderate (2,400 m), and high altitude (3,400 m). A spectral analysis of the electrocardiography was performed to assess the study subjects' electroencephalography activity at different frequencies (α, β, θ, δ) and the mean power frequency of electrocardiography. The clinical symptoms and Lake Louise Acute Mountain Sickness scores of the subjects were recorded for comparison.

RESULTS

A significant change in the δ power of electroencephalography was recorded in subjects ascending from the ground to a high altitude of 3,400 m in a 4-day itinerary. In addition, between the two groups of subjects with and without acute mountain sickness (Lake Louise Acute Mountain Sickness scores < 3 and ≥ 3), the δ power of electroencephalography at the fronto-parietal 1 and parietal 3 electrodes at moderate altitude as well as the changes of δ power and mean power frequency of electrocardiography over parietal 4 at high altitude showed a significant difference. At moderate altitude, the increasing δ power of electroencephalography at the parietal 4 electrode was related to the headache symptom of acute mountain sickness before ascending to high altitude.

CONCLUSION

At moderate altitude, the δ power increase of electroencephalography at the P4 electrode could be a predictor of acute mountain sickness symptoms before ascending to high altitude. Thus, electroencephalography had the potential to identify the risk of acute mountain sickness.

Incidence and predictors of severe altitude illness symptoms in Mt. Kilimanjaro hikers: a prospective cohort study

BACKGROUND

Each year several Mt. Kilimanjaro hikers die due to altitude illness (AI) although urgent descent is technically easily possible. The objectives of this study were to determine the incidence and predictors of severe altitude illness (SAI) symptoms and of summit success in Mt. Kilimanjaro hikers, and the measures taken when AI symptoms develop.

METHODS

A prospective observational cohort study in Mt. Kilimanjaro hikers was conducted from December 2019 until March 2020. Participants were asked to complete a questionnaire at the entrance gate and one at the descend gate. A multivariate logistic regression was performed to study the relations between the variables.

RESULTS

A total of 1237 recreational hikers and 266 porters or guides were included. The incidence of severe symptoms was 8.6% in recreational hikers and 1.5% in porters and guides. One percent (1.1%) of hikers was hospitalized due to SAI. A history of SAI, young age, summit failure and lack of clear advice predicted the development of severe symptoms. Uhuru peak was reached by 87.9% of the hikers. Absence of severe symptoms, acetazolamide prophylaxis, climbing higher in daytime, young age and climbing in more days predicted summit success. The majority climbed further despite the presence of mild or severe symptoms. The only measure taken in case of mild symptoms that was associated with a lower incidence of severe symptoms was not climbing further.

CONCLUSION

The incidence of SAI symptoms in Mt. Kilimanjaro hikers was observed to be high. However, how hikers reacted during symptoms was not appropriate. Therefore, travel health counsellors should emphasize even more that hikers do not ascend higher until mild symptoms have resolved and that it is vital to descend immediately when severe symptoms develop. In addition, they can be informed on the measures, which improved summit success.

Risk factors for acute mountain sickness in travellers to Cusco, Peru: coca leaves, obesity and sex

BACKGROUND

Acute mountain sickness (AMS) may occur after rapid ascents to altitudes >2500 m. Cusco (3350 m) in Peru is a popular destination for altitude inexperienced travellers. This study aimed at evaluating the incidence and risk factors for AMS among a cohort of foreign Spanish language students in Cusco.

METHODS

We performed a cohort study among young healthy foreign Spanish language students arriving to Cusco between 2012 and 2016. Consenting students answered an enrollment questionnaire on demographics, travel history and intended AMS preventive behaviour within 48 h of arrival. At 4-5 days after enrollment participants answered a second questionnaire about actual preventive behaviour before symptoms and the development of symptoms compatible with AMS during their first 48 h in Cusco. We used the 2018 Lake Louise Scoring System for AMS diagnosis. Participants with headache and a score ≥ 3 were considered to have AMS.

RESULTS

We enrolled 142 language students, the median age was 21 years (interquartile range 20-25) and 57% were female. Participants decreased physical activity (38%), increased fluid intake (34%), drank coca leaf tea (34%), took acetazolamide (16%) and acclimatized at a lower altitude (6%) to prevent AMS. Thirty-nine percent had AMS. In the multivariate analysis, obesity [odds ratio (OR) 14.45 (2.33-89.6)] and female sex [OR 4.32 (1.81-10.28)] were associated with increased risk of AMS. Taking acetazolamide [OR 0.13 (0.03-0.56)] was associated with decreased AMS risk. Consumption of coca leaf tea was not associated with decreased risk of AMS.

CONCLUSIONS

In our cohort, AMS affected two out of five travellers. Obesity and female sex were associated with increased risk. Drinking coca leaf tea for prevention did not decrease the risk of AMS. Acetazolamide prophylaxis was associated with decreased risk of AMS.

Salidroside attenuates high altitude hypobaric hypoxia-induced brain injury in mice via inhibiting NF-κB/NLRP3 pathway

Salidroside (Sal), an active ingredient from Rhodiola crenulate, has been reported to exert neuroprotection in cerebral injury from hypobaric hypoxia (HH) at high altitude. However, it remains to be understood whether its protective effects are related to inflammation suppression. In the present work, we aimed to reveal the mechanism of Sal attenuating HH-induced brain injury in mice caused by an animal hypobaric and hypoxic chamber. Our results provided that Sal could attenuate HH-evoked pathological injury and oxidative stress response by decreasing the content of ROS and MDA, and elevating the activities of SOD and GSH-Px. Sal treatment could partly enhance the energy metabolism, evidenced by increasing the activities of Na⁺-K⁺-ATPase, Ca²⁺-Mg²⁺-ATPase, ATP, SDH, HK and PK, while decreasing the release of LDH and LD. Meanwhile, Sal administration reversed the degradation of tight junction proteins ZO-1, Occludin and Claudin-5. Further, the increased levels of TNF-α, IL-1β and IL-6 were confined with Sal administration under the HH condition. Importantly, Sal could downregulate the proteins expression of p-NF-κB-p65, NLRP3, cleaved-Caspase-1 and ASC. Sal also decreased the protein expression of iNOS and COX2 with the increased CD206 and Arg1 expression. Taken together, these data provided that the inhibited NF-κB/NLRP3 pathway by Sal could attenuate HH-induced cerebral oxidative stress injury, inflammatory responses and the blood brain barrier (BBB) damage, attributing to the improved energy metabolism and the microglial phenotype of anti-inflammatory M2. The findings suggested that Sal was expected to be a promising anti-inflammatory agent for high altitude HH-induced brain injury.

Treatment of Focal and Segmental Glomerulosclerosis Secondary to High Altitude Polycythemia with Acetazolamide

Vizcarra-Vizcarra, Cristhian A., Eduardo Chávez-Velázquez, Carmen Asato-Higa, and Abdías Hurtado-Aréstegui. Treatment of focal and segmental glomerulosclerosis secondary to high altitude polycythemia with acetazolamide. High Alt Med Biol 00:000-000, 2022.-Focal segmental glomerulosclerosis (FSGS) is a morphological pattern, caused by glomerular injury and is the leading cause of nephrotic syndrome in adults. We present the case of a 59-year-old female patient, resident of a high-altitude city (3,824 m), who had polycythemia and nephrotic syndrome. A renal biopsy was performed, and the findings were compatible with FSGS. The patient received phlebotomy 500 ml three times, which reduced, partially, the hemoglobin concentration. However, she had refractory proteinuria, despite the use of enalapril and spironolactone. We observed that proteinuria worsened with the increase in hemoglobin levels. So, she was treated with acetazolamide 250 mg bid for 4 months, which reduced proteinuria and hemoglobin. During the coronavirus disease 2019 (COVID-19) pandemic, the patient did not take acetazolamide and again, she had an increase in hemoglobin and proteinuria levels. We conclude that acetazolamide may be an effective treatment in FSGS due to high altitude polycythemia.

Advancing the evidence in altitude and wilderness medicine

The themes of this special issue of the Journal of Travel Medicine are wilderness and adventure travel. We hope that the wilderness medicine and travel medicine communities can work together on these areas of mutual interest.

The Pretravel Consultation: Recent Updates

Estimates suggest that 43%-79% of international travelers may develop travel-related illnesses. Most such illnesses are considered mild and self-limited; however, some are life-threatening. The pretravel consultation is aimed at assessing risks for a range of illnesses, communicating these risks, and then providing individualized recommendations and interventions to minimize or manage such risks. The effective consultation is predicated on a well-prepared clinician and motivated traveler, understanding the traveler's perception of, and tolerance for, risk, and providing education applicable to the actual itinerary. Integral to the clinician's preparation is regular review of up-to-date trip-specific recommendations; country-specific information and recommendations are readily available and can now be efficiently accessed. From the infectious diseases perspective, immunizations, malaria chemoprophylaxis, insect repellent use, and travelers' diarrhea and its self-management are cornerstones of the consultation. This review focuses primarily on updating these 4 topics with recently published information relevant to adult travelers.