It is well-known that the Indian Army (IA) routinely operates in some of the most inhospitable terrain on earth ranging from the burning deserts of the Thar to the highest mountain range in the world in the form the Himalayas. It is IA’s deployment in the latter i.e. the high mountains that poses peculiar challenges for soldier acclimatization. While IA has a veritable wealth of experience in operating at such altitudes, rapid acclimatization of troops at such high altitudes continues to be a problem that requires evolutionary approaches. With that in mind, this paper surveys recent trends in the methodology and practice related to rapid acclimatization and the learnings thereof.
Introduction.
In order to stipulate the acclimatization schedule in High Altitude Areas (HAA) for troops, IA defines the following key altitude ranges:
This “three stage” acclimatization schedule extends for a period of up to 14 days. Stage I acclimatization lasts for 06 days for altitudes ranging from 2700m – 3600m, whereas Stage II and III, each span an additional period of 04 days in order to achieve acclimatization.1 During re-entry to HAA, after 10 to 30 days of absence from HAA, 04 days at each stage is needed for acclimatization. After a break of more than 30 days, the full acclimatization schedule delineated above is required to be repeated.1
IA soldiers are deployed at HAA throughout the year amidst inclement weather and snowbound Himalayan ridges. The existing acclimatization schedule of 06-04-04 days for ascent will be tough for troops in a hot war scenario or in an intense operational situation, wherein large numbers of troops will be required to be mobilized within shorter time frames. The effect of hypobaric/ high-altitude hypoxia is ubiquitous. Everyone is equally susceptible to its physical and cognitive performance decrements.
In this context, Acclimatization refers to the normal compensatory responses to acute hypobaric hypoxia and consists of a complex series of physiologic adaptations involving multiple organ systems. Acclimatization begins within minutes of reaching a new altitude and reaches a steady state after several weeks. Acclimatization improves but does not normalize hypoxemia.2
High Altitude and Hypoxia.
Decreased oxygen availability in the ambient air is the only environmental stress unique to HAA. It lowers the oxygen supply to body tissues which cause alt related illnesses. The decline in physical and cognitive performances may also exacerbate pre-existing medical conditions.
There is a curvilinear reduction in the ambient barometric pressure with increasing altitude. The physiologic significance of decreased barometric pressure is related to the concomitant reduction in partial pressure of oxygen (hypobaric hypoxia). Although oxygen makes up approximately 21 per cent of the atmosphere at all altitudes, the progressive decrease in partial pressure of oxygen means there is less actual oxygen (i.e., a lower molecular concentration) compared to sea level available for respiration.3
Acute Mountain Sickness (AMS), High Altitude Pulmonary Oedema (HAPO) and High Altitude Cerebral Oedema (HACO) are known conditions affecting troops serving in HAA.4 Other problems include, pulmonary arterial hypertension of high altitude, chronic mountain sickness, high altitude retinopathy, snow blindness and thrombotic episodes. Management of cases of AMS and HAPO have improved over the years, although the mainstay of treatment of effects of HAA induced illnesses is urgent evacuation to lower altitude and admission for Institutional management.5
Rapid Acclimatization Strategies.
Performing any military mission at HAA requires specialised individual and team preparation. In emergencies/warlike conditions, rapid deployment of military personnel to high altitude frequently occurs without undergoing the adequate degree of altitude acclimatization, resulting in acute mountain sickness (AMS). Various studies have been conducted to test pharmacologically and non-pharmacologically aided rapid acclimatization.
Rapid deployment of unacclimatized soldiers to high altitude/mountain environments may cause debilitating effects on operational capabilities. “Normobaric Hypoxia Chamber” has been developed to provide Intermittent Hypoxic Exposure (IHE) as one of the recent approaches to induce altitude acclimatization. It involves the use of daily intermittent hypoxic exposure in lieu of continuous stay at high altitude. IHE is known as altitude exposure, involves breathing low oxygen air periodically, living in or exercising in reduced air for the purpose of pre-acclimatization/preconditioning to high altitude. It has been found to improve the physical work performance of an individual as well as to reduce the incidence of Acute Mountain Sickness.6
Fig 2. Rapid Induction Strategies at High Altitude
A study was conducted by G. Bhaumik et al. to evaluate the effect of IHE exposure at sea level on incidence of AMS during acute ascent to 3,500 m altitude amongst Indian military personnel.7 IA volunteers were divided into two groups, viz. control and experimental. Experimental group of subjects were exposed to intermittent normobaric hypoxia consisting of 12 % FIO2 (altitude – air equivalent 4,350 m) for 4 hr per day for 04 consecutive days. After giving IHT, the subjects were inducted to 3,500 m altitude (Leh) by air and different physiological parameters like AMS score (LLS), pulse arterial oxygen saturation (SaO2) and ventilatory parameters (V E, VO2, V T/Ti) were recorded daily. IHE-treated group showed a significant reduction in AMS at HA in comparison to control. IHE may be considered as an alternative approach to induce the altitude acclimatization at low altitude-based soldiers before their deployment to high-altitude operations in emergency-like conditions.
In a study conducted by G. Sikri et al. in Western Himalayas, it was observed that Indian Army soldiers take 11 days (6 days of acclimatization and 5 days of travel) on a sea-level to high altitude road (SH road) to reach a high altitude location (HAL) situated at an altitude of 11,500 feet from sea-level location (SLL) at an altitude of 1150 feet while following acclimatization schedule (AS). AS has an extra safety margin over the conventional ‘mountaineering thumb rule’ of not exceeding 500 m sleeping altitude above 3000 m altitude. The study carried out this randomised field trial to study the feasibility of moving large number of troops rapidly from SLL to HAL on SH road in western Himalayas in 04 days under pharmaco-prophylaxis. Based on the pharmaco-prophylaxis, at SLL 508 healthy lowland soldiers were divided into two groups: ‘A’ (n = 256) with Acetazolamide + Dexamethasone and ‘B’ (n = 252) with Acetazolamide + Placebo. They travelled rapidly by road to HAL in 04 days and prevalence of acute mountain sickness (AMS), high altitude pulmonary oedema (HAPO) and high altitude cerebral oedema (HACO) during the ascent was measured. Prevalence of AMS was found to be 1.56% and 1.59% in group ‘A’ and group ‘B’ respectively during the ascent with no cases of HAPE and HACE.8
The study by G. Sikri et al concluded that, at least on SH road, troops can be inducted rapidly to HAL from SLL in 4 days under pharmaco-prophylaxis with Acetazolamide with minimal occurrence of acute high-altitude illnesses.8
Use of Dexamethasone in support of High Altitude ground Operations has been implemented by U.S.Army. Common dexamethasone dosages to prevent AMS for adults ascending to altitude are either 2mg every 6 hours or 4mg every 12 hours. However, for the ground operator who is rapidly deployed to altitudes exceeding 11,000 feet, a very high dose of 4mg may be considered every 6 hours, but duration of use should not exceed 10 days. A dosage range of 8mg to 16mg was more efficacious prophylactic treatment for AMS than placebo and is especially worthwhile when ascent rate is high. This prophylaxis can however, affect sleep quality in some individuals as a negative effect. Caution must be exercised because dexamethasone can give false sense of security, causing one to ascend to higher altitude to which the body has not acclimatized.9
A study of survival strategies for improving acclimatization of lowlanders at high-altitude conducted by Poornima Sharma et al in 2023, opined that Human Acclimatization and therapeutic approaches are the core components for conquering the physiological variations at high altitude (≥2500 m) exposure. The declined atmospheric pressure and reduced partial pressure of oxygen at high altitudes tend to decrease the temperature by several folds. Hypobaric hypoxia is a major threat to humanity at high altitudes, and its potential effects include altitude mountain sickness. On severity, it may lead to the development of conditions like high-altitude cerebral oedema (HACO) or high-altitude pulmonary oedema (HAPO) and cause unexpected physiological changes in the healthy population of travellers, athletes, soldiers, and low landers while sojourning at high altitude. Previous investigations have been done on long-drawn-out acclimatization strategies such as the staging method to prevent the damage caused by high-altitude hypobaric hypoxia. Inherent Limitations of this strategy hamper the daily lifestyle and time consuming for people. It is not suitable for the rapid mobilization of people at high altitudes. There is a need to recalibrate acclimatization strategies for improving health protection and adapting to the environmental variations at high altitudes. This narrative review details the geographical changes and physiological changes at high altitudes and presents a framework of acclimatization, pre-acclimatization, and pharmacological aspects of high-altitude survival to enhance the government efficacy and capacity for the strategic planning of acclimatization, use of therapeutics, and safe de-induction from high altitude for minimizing the life loss. The application of pre-acclimatization techniques can be a boon for people serving at high altitudes, and it can be a short bridge for the rapid translocation of people at high altitudes by minimizing the acclimatization time.10
In a study conducted by Xian-Sheng Liu et al titled, A hypothesis study on a four-period prevention model for high altitude disease, it has been opined that under certain special conditions, the army cannot perform staging acclimatization according to guide. To supplement, people can exercise appropriately in the plain or at an alt of 2000-2500m. Research has shown that short-time hypoxia with physical activity can significantly reduce the incidence of AMS at a simulated alt of 4200m. At the same time, it can also reduce the severity of AMS and improve soldiers’ work abilities. Research in China on the use of drugs that increase the body’s hypoxic endurance for HAD prevention include Chinese herbal medicine, such as the Codonopsis pilosula, Rhodiola rosea, milkvetch root- Poria cocos compound, Dracocephalum heterophyl-lum, Dracocephalum tanguticum Maxim, Astragalus, Cordyceps sinensis, Acanthopanax and Rosa acicularis.11
With respect to Western medical practice, Acetazolamide and dexa-methasone are commonly used drugs. Nifedipine is the first drug to prevent high alt pulmonary oedema (HAPO). For most people, these drugs can improve the efficiency of gas exchange and movement, ease the acute symptoms of HAD, improve sleep and maintain oxygen saturation. If combined with aspirin, these drugs can also improve oxygen content in tissue, reduce prostaglandin synthesis and be effective in the treatment of plateau headache. In addition, Ginko biloba extract (EGb761) and theophylline are efficient in preventing AMS and promoting acclimatization to the plateau altitude.11
Fig 3. Recruits do cycling exercises with auxiliary devices to help simulate low-pressure and low-oxygen conditions at a training base under the PLA Xizang Military Command.
Fig 4. PLA Recruits run with auxiliary devices to help simulate low-pressure and low-oxygen conditions at a training base
CONCLUSION
Studies should be taken up to validate pharmacologically aided rapid acclimatization in Stages II and III High Altitude Areas for combatants of IA. Cognitive impairments if any also need to be ascertained through follow up of soldiers after induction to remote and isolated posts. The findings of such studies will help in framing newer policies for HAA ascent for troops during operational move and reduce burden of non-operational casualties.
DISCLAIMER
The paper is the author’s individual scholastic articulation and does not necessarily reflect the views of Delhi Defence Review. The author certifies that the article is original in content, unpublished and it has not been submitted for publication/ web upload elsewhere and that the facts and figures quoted are duly referenced, as needed and are believed to be correct.
References.
Major Indrayudh Banerjee is serving in the Armed Forces Medical Services
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