High Altitude Illness


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1 : High altitude illness Lt Col Rajesh Deshwal, MD
2 : Ascent to a high altitude subjects the body to a decrease in barometric pressure that results in adecreased partial pressure of oxygen in the inspired gas in the lungs
3 : This change leads in turn to lesspressure driving oxygen diffusion from the alveoli and throughout the oxygen cascade
4 : A normal initial"struggle response" to such an ascent includes increased ventilation, which is the cornerstone ofacclimatization (West, 2000). Hyperventilation may cause respiratory alkalosis and dehydration
5 : Alkalosis may depress the ventilatory drive during sleep, with consequent periodic breathing andhypoxemia
6 : Normal Symptoms at AltitudeHyperventilation/dyspnea on exertion (NO dyspnea at rest)Increased urinationAwaken many times at night (sometimes to urinate)Periodic breathing at night
7 : During EARLY acclimatization, renal suppression of carbonic anhydrase and excretion ofdilute alkaline urine combat alkalosis and tend to bring the pH of the blood to normal
8 : Otherphysiologic changes during normal acclimatization include increased sympathetic tone
9 : Increasederythropoietin levels, leading to increased hemoglobin levels and red blood cell massIncreased tissuecapillary density and mitochondriaHigher levels of 2,3-diphosphoglyceride, enhancing oxygenutilization
10 : Even with normal acclimatization, however, ascent to a high altitude decreases maximalexercise tolerance and increases susceptibility to cold injury due to peripheral vasoconstriction
11 : Finally, if the ascent is made faster than the body can adapt to the stress of hypobaric hypoxemia,altitude-related disease states can result
12 : Edema of AltitudePeripheral edema and facial edema are relatively common It is likely to worsen with ascent, and is more common in women than menIt resolves rapidly with descent
13 : AMS AND HACE
14 : At altitudes over 2400m / 8000 ft, the diagnosis of AMS is based on a headache plus at least one of the following symptoms: GI upset (loss of appetite, nausea, vomiting)Fatigue/weakness Dizziness/light-headedness Insomnia (more than just the usual frequent waking)
15 : Develops 6–12 h after ascent to a high altitude
16 : AMS must be distinguished from exhaustion, dehydration, hypothermia, and alcoholic hangover (Hackett and Roach, 2001)
17 : AMS and HACE are thought to represent opposite ends of a continuum ofaltitude-related neurologic disorders. HACE (but not AMS) is an encephalopathy whose hallmarks areataxia and altered consciousness with diffuse cerebral involvement but generally without focalneurologic deficits
18 : Retinal hemorrhages occur frequently at 5000 m even in individuals without clinical symptoms of AMS or HACE
19 : It is unclear whether retinalhemorrhage and cerebral hemorrhage at high altitude are caused by the same mechanism.However, one report revealed a correlation between HACE and retinopathy (Weidman and Tabin, 1999)
20 : The most important risk factors for the development of altitude illness are the rate of ascent and ahistory of high-altitude illnessExertion is a risk factor, but lack of physical fitness is not
21 : An attractivebut still speculative hypothesis proposes that AMS develops in people who have inadequate cerebrospinal capacity to buffer the brain swelling that occurs at high altitude (Ross, 1985)
22 : Oneprotective factor in AMS is high-altitude exposure during the preceding 2 months (Schneider et al,2002)
23 : Children andadults seem to be equally affected, but people >50 years of age may be less likely to develop AMSthan younger people
24 : Most studies reveal no gender difference in AMS incidence (Hackett and Roach,2001)
25 : Burgess et al (2004) showed that sleep desaturation—a common phenomenon at high altitude—is associated with AMS
26 : Pathophysiology
27 : The exact mechanisms causing these syndromes are unknownEvidence points to a central nervoussystem process
28 : Magnetic resonance imaging (MRI) studies have suggested that vasogenic(interstitial) cerebral edema is a component of the pathophysiology of HACE (Hackett et al, 1998)
29 : Inthe setting of high-altitude illness, the MRI findings are confirmatory of HACE,with increased signal in the white matter and particularly in the splenium of the corpus callosum
30 : Onthe basis of quantitative (as opposed to visual) analysis with lower-resolution imaging (Fischer et al,2004), a 3-tesla MRI study by Schoonman et al (2008) revealed that, in AMS and other conditions,hypoxia is associated with mild vasogenic cerebral edema
31 : This finding is in keeping with case reports of suddenly symptomatic brain tumors and of cranial nerve palsies at high altitude without AMS(Basnyat et al, 2000)Vasogenic edema may become cytotoxic (intracellular) in severe HACE
32 :
33 : Impaired cerebral autoregulation in the presence of hypoxic cerebral vasodilatation and alteredpermeability of the blood-brain barrier due to hypoxia-induced chemical mediators like histamine,arachidonic acid, and vascular endothelial growth factor (VEGF) may all contribute to vasogenicedema (Schilling and Wahl, 1999; Levine et al, 1999)
34 : In 1995, Severinghaus first proposed VEGF as a potent promoter of capillary leakage in the brain at high altitude, and studies in mice (Schoch et al,2002) have borne out this role
35 : Although preliminary studies of VEGF in climbers have yieldedinconsistent results (Maloney et al, 2000; Walter et al, 2001) and have revealed no association with altitude illness.
36 : Indirect evidence for a role for this cytokine in AMS and HACE comes from the observation that dexamethasone, when used in the prevention and treatment of AMS and HACE, blocks hypoxic upregulation of VEGF (Klekamp et al, 1997)
37 : Increased sympathetic activity triggered by hypoxia may also contribute to blood-brain barrier leakage(Reeves, 1993)
38 : Moreover, enhanced optic-nerve sheath diameter with increasing severity of AMS hasbeen noted and suggests an important role for increased intracranial pressures in the pathophysiology of AMS (Sutherland et al, 2008)
39 : Finally, the effect of hypoxia on reactive oxidant species and the roleof these species in clinical AMS are unclear
40 : The pathophysiology of the most common and prominent symptom of AMS—headache—remainsunclear because the brain itself is an insensate organ; only the meninges contain trigeminal sensorynerve fibers
41 : In 1999, Sanchez del Rio and Moskowitz proposed that the cause of high-altitude headache is multifactorial and that various chemicals and mechanical factors activate a final common pathway, the trigeminovascular system
42 : In the genesis of high-altitude headache, the response tononsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids provides indirect evidence for involvement of the arachidonic acid pathway and inflammation (Ferrazzini et al, 1987; Broome et al,1994; Burtscher et al, 1998)
43 : Although the International Headache Society acknowledges that highaltitude may be a trigger for migraine (Baumgartner et al, 2007), It is unclear whether high-altitudeheadache and migraine share the same pathophysiology
44 : Prevention and Treatment
45 : Gradual ascent, with adequate time for acclimatization, is the best method for the prevention ofaltitude illness
46 : Above 3000 m, a graded ascent of 300 m from the previous day’s sleeping altitude isgenerally recommended, and taking every third day of gain in sleeping altitude as an extra day foracclimatization is helpful
47 : Spending one night at an intermediate altitude before proceeding toa higher altitude may enhance acclimatization and attenuate the risk of AMS
48 : Management of Altitude IllnessAcute mountain sickness (AMS),mildDiscontinuation of ascentTreatment with acetazolamide (250 mg q12h)
49 : AMS, moderateImmediate descent for worsening symptomsUse of low-flow oxygen if availableTreatment with acetazolamide (250 mg q12h) and/ordexamethasone (4 mg q6h)Hyperbaric therapy
50 : High-altitude cerebral edema(HACE)Immediate descent or evacuationAdministration of oxygen (2–4 L/min)Treatment with dexamethasone (8 mg PO/IM/IV; then 4 mg q6h)Hyperbaric therapy if descent is not possible
51 : Pharmacologic prophylaxis at the time of travel to high altitudes is warranted for people with a historyof AMS or when a graded ascent and acclimatization are not possible—e.g., when rapid ascent isnecessary for rescue purposes or when flight into a high-altitude location is required
52 : Acetazolamide(125–250 mg twice a day), administered for 1 day before ascent and continued for 2 or 3 days, iseffective (Hackett and Roach, 2001)
53 : Higher doses generally are not required (Basnyat et al, 2003)
54 : Paresthesia and a tingling sensation are common side effects of acetazolamideDexamethasone (8mg/d in divided doses) is also effective (Hackett et al, 1988)
55 : A randomized, double-blind, placebo controlled trial by Gertsch et al (2004) clearly showed that ginko biloba is not effective in the prevention of AMS To date, no trials of NSAIDs in the prevention of AMS have been reported
56 : For the treatment of mild AMS, rest alone with analgesic use may be adequate (Basnyat and Murdoch, 2003)
57 : Descent and the use of acetazolamide and (if available) oxygen are sufficient to treat most cases of moderate AMSEven a minor descent (400–500 m) may be adequate for symptom reliefFor moderate AMS or early HACE, dexamethasone (8 mg orally or parenterally) is highly effective
58 : ForHACE, immediate descent is mandatory. When descent is not possible because of poor weatherconditions or darkness, a simulation of descent in a portable hyperbaric chamber is effective and, likedexamethasone administration, “buys time.”
59 : Like nifedipine, phosphodiesterase inhibitors have no role in the treatment of AMS or HACE
60 :
61 : HAPE
62 : Unlike HACE (a neurologic disorder), HAPE is primarily a pulmonary problem and therefore is notnecessarily preceded by AMS (Basnyat and Murdoch, 2003)
63 : HAPE develops within 2–4 days afterarrival at high altitude; it rarely occurs after more than 4 or 5 days at the same altitude, probably because of remodeling and adaptation that renders the pulmonary vasculature less susceptible to the effects of hypoxia (West and Mathieu-Costello, 1999)
64 : A rapid rate of ascent, a history ofHAPE, respiratory tract infections, and cold environmental temperatures are risk factors
65 : Men are more susceptible than women
66 : People with abnormalities of the cardiopulmonary circulation leading topulmonary hypertension—e.g., patent foramen ovale (PFO), mitral stenosis, primary pulmonaryhypertension, and unilateral absence of the pulmonary artery—are at increased risk of HAPE, even atmoderate altitudes
67 : Echocardiography is recommended when HAPE develops at relatively low altitudes (<3000 m) and whenever cardiopulmonary abnormalitiespredisposing to HAPE are suspected
68 : The initial manifestation of HAPE may be a reduction in exercise tolerance greater than that expectedat the given altitude. Although a dry, persistent cough may presage HAPE and may be followed by theproduction of blood-tinged sputum, cough in the mountains is almost universal and the mechanism ispoorly understood (Mason and Barry, 2007)
69 : Symptoms - At least two of the following: Dyspnea at rest  Cough  Weakness or decreased exercise performance Chest tightness or congestion
70 : Signs - At least two of the following: Crackles or wheezing in at least one lung field Central cyanosisTachypneaTachycardia
71 : Tachypnea and tachycardia, even at rest, are importantmarkers as illness progressesCrackles may be heard on auscultation but are not diagnostic
72 : HAPEmay be accompanied by signs of HACE
73 : Patchy or localized opacities or streaky interstitialedema may be noted on chest radiography
74 :
75 :
76 :
77 : In the past, HAPE was mistaken for pneumonia due to thecold or for heart failure due to hypoxia and exertion Kerley B lines or a bat-wing appearance are notseen on the radiograph
78 : Electrocardiography may reveal right ventricular strain or even hypertrophy.
79 : Hypoxemia and respiratory alkalosis are consistently present unless the patient is takingacetazolamide, in which case metabolic acidosis may superveneAssessment of arterial blood gases isnot necessary in the evaluation of HAPE; an oxygen saturation reading with a pulse oximeter isgenerally adequate
80 : A subclinical form of HAPE probably exists, but hard evidence correlating it with the development of clinically relevant HAPE is lacking (Cremona et al, 2002)
81 : Pathophysiology
82 : HAPE is a noncardiogenic pulmonary edema characterized by patchy pulmonary vasoconstriction thatleads to overperfusion in some areas (Hackett and Roach, 2001)
83 : This abnormality leads in turn toincreased pulmonary capillary pressure (>18 mmHg) and capillary “stress” failure (Maggiorini et al, 2001)
84 : The exact mechanism for the vasoconstriction is unknownEndothelial dysfunction due tohypoxia may play a role by impairing the release of nitric oxide, an endothelium-derived vasodilator (Duplain et al, 2000)
85 : At high altitude, HAPE-prone persons have reduced levels of exhaled nitric oxide (Busch et al, 2001)
86 : The effectiveness of phosphodiesterase-5 inhibitors in alleviating altitude-inducedpulmonary hypertension, decreased exercise tolerance, and hypoxemia supports the role of nitricoxide in the pathogenesis of HAPE (Ghofrani et al, 2004; Richalet et al, 2005)
87 : Maggiorini andcolleagues (2006) demonstrated that prophylactic use of tadalafil, a phosphodiesterase-5 inhibitor,decreases the risk of HAPE by 65%
88 : The endothelium synthesizes endothelin-1, apotent vasoconstrictor whose concentrations are higher than average in HAPE-prone mountaineers(Yanagisawa et al, 1988; Sartori et al, 1999)
89 : Bosentan, an endothelin receptor antagonist, has been shown to attenuate hypoxia-induced pulmonary hypertension (Modesti et al, 2006), but further field studies with this drug are necessary
90 : Exercise and cold lead to increased pulmonary intravascular pressure and may predispose to HAPE
91 : Inaddition, hypoxia-triggered increases in sympathetic drive may lead to pulmonary venoconstriction and extravasation into the alveoli from the pulmonary capillariesConsistent with this concept, alphaadrenergic blockade by phentolamine improves hemodynamics and oxygenation in HAPE more than do other vasodilators (Hackett et al, 1992)
92 : In the study of tadalafil Maggiorini and colleagues (2006) also investigated dexamethasone in the prevention of HAPE Surprisingly, dexamethasone reduced the incidence of HAPE by 78%—a greater decrease than with tadalafil
93 : Besides possibly increasing the availability of endothelial nitric oxide, dexamethasone may have altered the excessive sympathetic activity associated with HAPE: the heart rate of subjects in the dexamethasone arm of the study was significantly loweredFinally, people susceptible to HAPE alsodemonstrate enhanced sympathetic activity during short-term hypoxic breathing at low altitudes(Duplain, 1999).
94 : Because many patients with HAPE have fever, peripheral leukocytosis, and an increased erythrocytesedimentation rate, inflammation has been considered an etiologic factor in HAPE
95 : However, Swensonand colleagues (2002) provided evidence that inflammation in HAPE is an epiphenomenon rather thanthe primary problem
96 : Although inflammation may not be the main trigger for HAPE, inflammatoryprocesses like viral respiratory tract infections do predispose to HAPE, even in people constitutionallyresistant to its development (Durmowicz et al, 1997)
97 : Another proposed mechanism for HAPE is impaired transepithelial clearance of sodium and water fromthe alveoliAdrenergic agonists upregulate the clearance of alveolar fluid in animal models
98 : In adouble-blind, randomized, placebo-controlled study of HAPE-susceptible mountaineers, prophylacticinhalation of the -adrenergic agonist salmeterol reduced the incidence of HAPE by 50% (Sartori et al,2002)
99 : GeneticsAlthough gene polymorphism may influence susceptibility to HAPE, the data on this point are unclear.
100 : Although angiotensin-convertingenzyme gene polymorphism appears to confer a performance advantage at high altitude, an association with susceptibility to HAPE is lacking (Dehnert et al, 2002).
101 : Endothelial nitric oxide synthase gene polymorphism has been associated with susceptibility to HAPEin Japan (Droma et al, 2002) but not in Europe (Weiss et al, 2003).
102 : Prevention and Treatment
103 : Allowing sufficient time for acclimatization by ascending gradually is the best way to prevent HAPE
104 : High-altitude pulmonary edema(HAPE)Immediate descent or evacuationMinimization of exertion while patient is kept warmAdministration of oxygen (4–6 L/min) to bring O2 saturation to>90%Adjunctive therapy with nifedipinee (30 mg extended release q12h)Hyperbaric therapy if descent is not possible
105 : Sustained-release nifedipine (30 mg), given once or twice daily, prevents HAPE in people who must ascend rapidly or who have a history of HAPE (Bartsch et al,1991)
106 :
107 : Acetazolamide has been shown to blunt hypoxic pulmonary vasoconstriction (Teppema et al, 2007)and this observation warrants further study in HAPE prevention; however, one recent field study failedto show a decrease in pulmonary vasoconstriction in partially acclimatized individuals givenacetazolamide (Basnyat et al, in press)
108 : Descent and the use of supplementary oxygen (aimed at bringing oxygen saturationto >90%) are the most effective therapeutic interventions
109 : Exertion should be kept to a minimum,and the patient should be kept warm. Hyperbaric therapy in a portable altitude chamber may be usedif descent is not possible and oxygen is not available
110 : Oral sustained-release nifedipine (30 mg once or twice daily) can be used as adjunctive therapy (Oelz et al, 1991)
111 : Inhaled agonists, which are safeand convenient to carry, are useful in the prevention of HAPE and, by extension, may be effective inits treatment, although no trials have yet been carried out
112 : Inhaled nitric oxide (Anand et al, 1998)and expiratory positive airway pressure (Larson, 1985) may also be useful therapeutic measures but may not be available in high-altitude settings
113 : No studies have investigated phosphodiesterase inhibitors in the treatment of HAPE, but reports have described their use in clinical practice (Fagenholz et al, 2007). The mainstays of treatment remain descent and (if available) oxygen.
114 : REASCENTIn AMS, if symptoms abate (with or without acetazolamide), the patient may reascend gradually and with caution to a higher altitude.
115 : Unlike that in acute respiratory distress syndrome (another noncardiogenic pulmonary edema), the architecture of the lung in HAPE is usually well preserved, withrapid reversibility of abnormalities .
116 : This fact has allowed some people with HAPE to reascend slowly after a few days of descent and rest (Litch and Bishop, 2001) In HACE, reascent after a few days is not advisable.
117 : Thank You

 

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Added On : 5 Years ago.
Acute Mountain Illness, High Altitude Pulmonary Edema, High Altitude Cerebral Edema- Slides
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