Presentation on theme: "Anesthesia at the Extremes of Altitude and Environment"— Presentation transcript:
1Anesthesia at the Extremes of Altitude and Environment Major Eric Weissend, M.D.Department of AnesthesiologyWilford Hall Medical CenterLackland AFB, Texas
2Environmental Challenges in the Practice of Anesthesiology Air Force anesthesiology providers are now going far and wide in support of combat and humanitarian operations. The majority of postings are to minimally developed areas where patients and providers are subject to environmental extremes.
3Environmental Challenges in the Practice of Anesthesiology Deployment presents numerous personal and professional challenges. Caring for trauma and surgical disease in the deployed environment can be physically and intellectually challenging. The extremes of heat, cold, and altitude further complicate the care of our patients.
4Environmental Challenges in the Practice of Anesthesiology Military operations in Afghanistan and Iraq serve to illustrate theses types of environments.
5HeatIraq: Daytime temperatures in the summer regularly reaching well over 100 degrees F.
6ColdAfghanistan, Operation Anaconda: Soldiers fought for extended periods in temperatures well below freezing in the mountainous Shah-I-Khot region.
7AltitudeAfghanistan, Operation Anaconda (again): Combat Ops took place between 8,000 and 12,000 feet above sea level.Bagram Air Base located at 5,000 feet above sea level.
8Environmental Challenges in the Practice of Anesthesiology To provide safe and effective anesthesia services to our patients we must understand the effects that extremes of heat, cold, and altitude have on our patients, ourselves, and our equipment.
9How Does Excessive Ambient Heat Effect Anesthetic Practice? Effects on volatile anestheticsHeat injuries
10Inhaled Anesthesia and Heat Temperature effects vaporizer output minimally in normal ranges of temperatures.All vaporizers in use in the EMEDS and MFST systems are temperature compensated.In a consistently climate controlled environment altered output should not be an issue.
12Inhaled Anesthesia and Heat Narkomed M: Currently the Air Force standard anesthesia machine for field anesthesia operations. This machine is equipped with the Draeger Vapor 2000 anesthetic vaporizer.Draeger Vapor 2000 vaporizer is temperature compensated with an operating range of 10 to 40 degrees C ( degrees F)
13Ohmeda Portable Anesthesia Circuit (PAC) with Draw-over Vaporizer
14Inhaled Anesthesia and Heat The Ohmeda Portable Anesthesia Circuit (PAC) Draw-Over Vaporizer System (primarily still in use with MFST).Operating temperature for the PAC vaporizer is 18 to 35 degrees C (65-95 degrees F).
15Inhaled Anesthesia and Heat Use above this ambient temperature range may lead to “potentially hazardous excessive concentrations of anesthetic agent.”
16Inhaled Anesthesia and Heat “Under no circumstances must the temperature of the anesthetic agent reach boiling point, as the output concentration will then become impossible to control.”The boiling points for isoflurane, halothane, and sevoflurane are 48.5, 50.2, and 58.5 degrees C (119, 122.4, 137 degrees F) respectively at 760 mm Hg.
18Inhaled Anesthesia and Heat Is it conceivable that in Iraq, in July, the HV/AC system may fail intraoperatively?
19If using volatile anesthetics at high ambient temperatures Ensure you are operating in a consistent climate controlled environment.AND/ORUse only with end tidal anesthetic gas monitoring (RGM or other) to minimize the risk of volatile anesthetic overdose.
20Inhaled Anesthesia and Heat There currently is no means of monitoring inspiratory or expiratory anesthetic gas in any Air Force deployable anesthetic system.
21Other Anesthetic Options at High Ambient Temperatures Total Intravenous AnesthesiaRegional AnesthesiaNeither method is known to be effected by high ambient temperatures.
22Heat Injuries All heat injuries are manifestations of dehydration Heat illness is the inability of normal regulatory mechanisms to cope with a heat stressMinor injuries include muscle cramps, edema, rash, syncope, and tetanyMajor injuries are heat exhaustion and heat strokeAll heat injuries are manifestations of dehydration
23Heat InjuriesPatients who are injured in and evacuated from areas with high ambient temperatures may suffer heat injuries in addition to their traumatic wounds.Medical personnel suffering heat injuries may have difficulty or even be unable to care for their patients.
24Heat InjuriesAny condition that increases heat gain or decreases heat loss may result in a major heat illness.Hot environments and physical exertion increase the heat load.Strenuous exertion can increase endogeonous heat production ten to twenty-fold.High temperatures and high humidity inhibit heat loss.
25Photo by Wally Santana/The Associated Press Heat InjuriesPhoto by Wally Santana/The Associated Press
26Heat InjuriesPeripheral vasodilation and sweating are the primary mechanisms of heat lossEvaporation of sweat from the skin is the most important mechanism of heat dissipation.As humidity increases, the efficiency of sweating decreases.
27Heat Injuries Heat Exhaustion Caused by dehydration with inadequate fluid and electrolyte replacement.Usually in nonacclimatized persons who have been working in the heat for several days.
28Heat Injuries Heat Exhaustion SymptomsWeakness, fatigue, frontal headache, impaired judgement, vertigo, nausea and vomiting, muscle crampsOrthostatic dizziness and syncopeSweating persists, often profuseCore temperature less than 40 CNo signs of severe CNS damage
29Heat Injuries Heat Exhaustion Volume depletion is the primary problemTreatmentRest in cool environmentFluid resuscitation
30Heat Injuries Heat Stroke A catastrophic life threatening medical emergencyThe failure of normal homeostatic cooling mechanismsLeads to extremely high temperatures (>40.5C), multisystem tissue damage and organ dysfunction.
31Heat Injuries Heat Stroke SymptomsProfound CNS dysfunction is the HallmarkDelerium and coma are commonAny neurologic manifestation is possibleDry hot skin, though sweating can persistCardiovascularly hyperdynamicHepatic dysfunction with massive rise in transaminasesCoagulopathyRenal damage with acute renal failure in up to 30% of cases.
32Heat Injuries Heat Stroke TreatmentCore Temperature CoolingEvaporative cooling with fans and skin wettingIce-water immersionIce packs, cooling blankets, cool body cavity lavagesSupportive TherapyAirway management (aspiration and seizures are common)Resuscitation and invasive monitoring
33Anesthesia At Altitude As altitude increases atmospheric pressure decreases.Decreased atmospheric pressure has profound effects on inhaled anesthetics and human physiology.Safe and effective anesthesia care requires an understanding of all of these effects.
34Anesthesia At Altitude The composition of the atmosphere is fixed and is independent of altitude. Oxygen is always ~21% of the ambient atmosphere pressure.As atmospheric pressure decreases with elevation however, the partial pressure of oxygen (PO2) declines.
35Anesthesia At Altitude Recall the alveolar gas equation:PAO2=FiO2(PB-PH2O)-PaCO2/RQAt 5000ft elevation, PB is 632 mmHg, PaO2 is 81 mmHg with SaO2 95%.At 10,000ft elevation, PB is 522 mmHg, PAO2 is 59 mmHg, SaO2 84%.
36Sutton JR, et al: J Appl Physiol 64:1309, 1998 Oxygen-Hemoglobin Dissociation Curve. Approximate oxygen saturations are marked for several altitudesSutton JR, et al: J Appl Physiol 64:1309, 1998
37Anesthesia At Altitude “In addition, it is important to maintain a higher concentration of oxygen both during and after administration of the anesthetic to support adequate oxygenation. It is suggested that 30% oxygen be the minimum at 5000 ft and that 40% oxygen be the minimum at 10,000 feet, for both intraoperative anesthetic management and postoperative recovery.”
38Anesthesia At Altitude Recommendations for anesthesia at altitude: “The major risk of anesthesia at high altitude is that anesthetized patients can become hypoxic despite the fact that adequate oxygen concentrations are being administered.”
39Anesthesia At Altitude Nitrous OxideEssentially irrelevant. Unlikely to be available in the deployed environment. Efficacy of N2O is decreased by 50% at 5000 ft and essentially insignificant at 10,000 ft.
40Anesthesia At Altitude Volatile anesthetic agents“The saturated vapor pressure of a volatile anesthetic agent depends only on temperature and is practically independent of total environmental pressure”
41Anesthesia At Altitude Given the relative scarcity of gaseous (or liquid) oxygen in the deployed environment it may be reasonable to conduct as much anesthesia under regional techniques.At altitude, maximizing the use of regional anesthesia not only decreases use of scarce resources, but may improve patient safety postoperatively. Minimizing opioid use decreases the risk of postoperative respiratory depression.
42Anesthesia At Altitude If general anesthesia is required oxygen requirements may be minimized using TIVA techniques.
43Altitude IllnessMilitary personnel deployed rapidly to high altitude regions are all at risk for altitude related illnesses.High altitude begins at 1500m (~5000ft) above sea level.Very high altitude begins at 3500m (~11,500 ft)Extreme altitude begins at 5500m (~18,000 ft)
44Altitude IllnessPhysiologic adjustment to altitude requires time and patience.Sudden exposure to very high and extreme altitude (above 11,500 ft) can be fatal.Unconciousness can occur within minutes and death may follow without supplemental oxygen.
45Physiologic Response to Altitude Lower PB leads to lower PAO2, decreased SAO2 and PaO2 and elevated Alveolar-arterial oxygen gradients.Hypoxic Ventilatory Response to low PaO2 leads to hyperventilation.Hyperventilation leads to decreased PaCO2.
46Physiologic Response to Altitude As hyperventilation is the primary means of adaptation to ascent, the ability to tolerate hypoxic environments depends largely on sufficient pulmonary reserve.
47Physiologic Response to Altitude 2,3-DPG levels rise due to hypoxic stress, shifting O2-Hgb dissociation curve back toward the right. This facilitates O2 unloading into tissues.ErythropoiesisIncreased cardiac output secondary to Hypoxia
48Altitude IllnessHigh Altitude Illness can take several forms that often overlap and share common pathophysiology.Acute Mountain Sickness (AMS)High Altitude Pulmonary Edema (HAPE)High Altitude Cerebral Edema (HACE)
49Acute Mountain Sickness All visitors to higher altitudes are susceptible to AMS.Overexertion, poor hydration, and young age may contribute. Physical fitness and gender don’t seem to effect incidence.
50Acute Mountain Sickness Symptoms:Early symptoms (12-24 hours): headache refractory to standard analgesics, nausea, anorexia, lassitude, sleep disturbances.Can progress to shortness of breath, intense snoring, vomiting, hallucinations, and impaired cognitive function,Advanced symptoms: severe dyspnea, cyanosis, decreased SaO2, ataxia.
51Acute Mountain Sickness Definitive treatment is descent.Often descent of 500 to 1000m leads to complete resolution of symptoms.Rest, hydration, analgesics, oxygen all can help.Acetazolamide 250 mg q 8-12 hours improves symptoms and SaO2 (especially during sleep)
52Acute Mountain Sickness PreventionAscend slowly, not always possible in military opsDaily altitude gain of no more than 300m above 3000m.After ascending 1000m spend two consecutive nights.Rest on arrival at altitude, avoiding overexertion, adequate hydrationAcetazolemide 250mg q8 hours beginning at least 24 hours before ascent and continued for 2 to 3 days after reaching highest altitude.
53High Altitude Pulmonary Edema (HAPE) A malignant form of AMS with similar early symptoms. Life threatening.May occur in any healthy individual after rapid ascent above 2500 m (8200 ft)Dyspnea, tachypnea, chest pain, rales, tachycardia,dry cough, followed by the production of pink frothy sputumRespiratory failure and death can quickly ensue.
54High Altitude Pulmonary Edema (HAPE) CXR shows patchy infiltrates, which spare lung bases and costophrenic angles.Elevated pulmonary artery pressure secondary to hypoxia.ECG shows right heart strainLV function is normal
55High Altitude Pulmonary Edema (HAPE) TreatmentRapid descent to lower altitudeSupplemental O2Morphine ?PEEPIf descent is not possible, consider Gamow bag
56High Altitude Cerebral Edema (HACE) Another severe form of AMS, also be life threatening.Thought to be due to increased cerebral blood flow and alterations in blood-brain barrier permeability (due to severe hypoxemia)Early symptoms similar to AMS.
57High Altitude Cerebral Edema (HACE) Early symptomsHeadacheAnorexiaNauseaEmesisPhotophobiaFatigueIrritabilityDecreased socializationLate symptomsAtaxia (appendicular to truncal)IrrationalityHallucinationsVisual disturbancesFocal neurological deficitsAbnormal reflexes
58High Altitude Cerebral Edema (HACE) Patients may have concurrent HAPE symptomsDeath may be imminent when symptoms of HACE become severe
59High Altitude Cerebral Edema (HACE) Lumbar puncture may show markedly elevated CSF pressure.CT suggestive of brain edema
60High Altitude Cerebral Edema (HACE) TreatmentImmediate, rapid descentDexamethasone 10 mg IV or IM, then 6 mg q 6 hrs.Supplemental O2, may be helpful if pulmonary symptoms are presentDiuretics may reduce brain edema, but may worsen an already dehydrated state
65Cold Injuries Frostbite Peripheral vasoconstriction limits radiant heat loss in cold ambient temperaturesOccurs when tissue temperature decreases to less than 0 degrees CIce crystal formation leads to cellular architectural damageMicrovascular stasis and thrombosisExtent of injury is determined by duration and extent of cold contact with the skin
66Cold Injuries Frostbite Distal extremities, nose, ear, and penis are most at riskNumbness is most common presenting symptom
67Cold Injuries Frostbite TreatmentRapid rewarming by immersion bath in degree C water. Reheating with static heat is much more injurious to tissue.If patient requires surgical care and anesthesia allow for passive rewarming to minimize risks of worsening injury.
68Cold Injuries Hypothermia Mild: Core body temperature CExcitation stage, to retain and generate heat (shivering, increased heart rate, cardiac output, and blood pressure)Moderate: degrees CSlowing stage, to decrease oxygen utilization and CO2 production (shivering ceases, HR. CO, BP all decrease)Severe: Below 30 degrees CECG changes and dysrhythmias (Osborn J waves T-wave inversions, PR, QRS, and QT prolongation, sinus bradycardia to atrial fibrillation with slow ventricular response to ventricular fibrillation to asystole)
69Cold Injuries Hypothermia Osborn J wave/ From Marx: Rosen's Emergency Medicine
70Cold Injuries Hypothermia Other ManifestationsPulmonaryTachypnea, bronchorrhea, diminished cough and gag reflex (increased aspiration risk)CNSConfusion, lethargy, incoordination, decreased consciousness, comaLeftward shift of Oxyhemoglobin dissociation curveImpairs release of O2 to tissues
71Cold Injuries Hypothermia Other manifestationsRenalDecreased renal concentrating abilities leads to “cold diuresis” and severe dehydrationHemeHemoconcentration, disseminated intravascular coagulation (decreased enzymatic function at lower core body temperatures)GIPancreatitis, decreased hepatic function (impaired drug metabolism)
72Cold Injuries Hypothermia TreatmentHandle GentlyOxygen (warmed, humidified)IV fluids (warmed)Monitor: core temperature, oxygen saturation, cardiac rhythmDysrhythmias may be refractory to treatment until patient is rewarmed
73Cold Injuries Hypothermia TreatmentRewarmingPassive: allow patients to rewarm passively and slowlyActive: rewarm with external (water immersion, radiant heat, forced warm air heating blankets) and core techniques (heated IV fluids, body cavity lavage, cardiopulmonary bypass pumpResuscitation with Lactated Ringers should be avoided as the cold liver inefficiently metabolizes lactateNeither passive nor active rewarming has been shown to be superior, however…
74Cold Injuries Hypothermia Indications for rapid rewarmingCardiovascular instabilityModerate or severe hypothermia (<32.2 C)Inadequate rate or failure to rewarmEndocrine insufficiencyTraumatic or toxilogic peripheral vasodilationSecondary hypothermia impairing thermoregulation.
75Cold Injuries Hypothermia As anesthesiology providers we are most likely to become involved with hypothermia caring for patients suffering from traumatic injury in addition to hypothermia.Surgical requirements will likely force active treatment of hypothermia while undergoing surgical stabilization.
76Cold InjuriesNo known effect of cold ambient temperature to the delivery of any form of anesthesia.
77ReferencesBuckenmaier CC, Lee EH, Shields CH, Sampson JB, Chiles JH: Regional anesthesia in austere environments. Reg Anesth and Pain Med 28: ,2003.DeHart RL, Davis JR: Fundamental of Aerospace Medicine, 3rd ed. Pg Philadelphia, PA, 2002, Lippincott, Williams and Wilkins.Draeger Vapor 2000 Anesthetic Vaporizer: operating instructions. Telford, PA, September 2000, Draeger Medical, inc.Ehrenwerth J, Eisenkraft JB: Anesthesia Equipment: Principles and Practice. Pg St. Louis, MO, 1993, MosbyJames MFM, Manson EDM, Dennett JE: Nitrous Oxide analgesia and altitude, Anaesthesia 37:285-88, 1982.James MFM, White JF: Anesthetic considerations at moderate altitude. Anesth Analg 63: , 1984.Kuo DC, Jerrard DA: Environmental insults: smoke inhalation, submersion, diving, and high altitude. Emerg Med Clin N Am 21:475-97, 2003.
78ReferencesMarx: Rosen’s Emergency Medicine: Concepts and Clinical Practices, 5th ed., Mosby 2002: pg ,Miller: Anesthesia, 5th ed. Pg , , Philadelphia, PA, 2000, Churchill Livingstone.Ohmeda Portable Anesthesia Circuit (PAC): operation and maintenance manual. Madison, WI, January 1997, Ohmeda Inc.Powell JN, Gingrich TF: Some aspects of nitrous oxide anesthesia at an altitude of one mile, Anesth Analg 48:680-85, 1969.Safar P, Tenicela R: High altitude physiology in relation to anesthesia and inhalation therapy, Anesthesiology 25:515-31, 1964.Sessler DI: Complications and treatment of mild hypothermia. Anesthesiology 95:531-43, 2001.Wexler RK: Evaluation and treatment of heat related illnesses. Am Fam Physician 65: , 2002.Woodward G: Altitude Illness. Clin Ped Emerg Med 2: