Dr S Parthasarathy MD DA DNB MD Acu Dip Diab Dip Software statistics PhD physiology IDRA FICA The first use of general anaesthesia in Tibet was during the 1904 AngloTibetan War when British military doctors administered chloroform a ID: 908584
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Slide1
Anesthesia at
high
altitude
Dr. S.
Parthasarathy
MD., DA., DNB,
MD (Acu),
Dip
.
Diab
.
Dip
. Software
statistics
PhD
(
physiology
), IDRA , FICA
Slide2The first use of general
anaesthesia
in Tibet was during the 1904 Anglo–Tibetan War, when British military doctors administered chloroform at altitudes of > 4000 m
Greene was the expedition anesthetist
Slide3Lobsang
Tsering, a Tibetan employed as the team’s messenger, fell from his pony and fractured his clavicle on 6th April 1933
Greene administered chloroform Surgery was over but the recovery was very delayed coramine
Slide4So cases may be more !
Transport and conditions are better
More number of people live
More number of tourists Acclimatized and NonAcclimatized
Illness
Emergency and accidents
Slide5Two schools of thought !!
1500 meters !
Slide6Darjeeling 2050
Ooty
- 2250 Amarnath
– 5100mEverest – 8850 m
6650
Golden mount
kailash
Slide7Respiration
Recall the alveolar gas equation:
PAO2=FiO2(PB-PH2O)-PaCO2/RQ
At 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%.
Slide8Hypoxic drive
Hyperventilation
PaCO2 decreaseBut kidneys preserve
acid pH not much change A new comer may show alkalosis !
Slide9That’s the safety !!
Slide10What happens ?
Decreased demands !
240 ml may come down to 210 ml !
at 45000 sq feet , the pp is low that he needs 48 % to achieve sea level conditions
Slide11What does hypoxia do ?
Hyperventilation
May increase by 25-30 %
2,3-DPG levels rise due to hypoxic stress, shifting O2-Hgb dissociation curve back toward the right. This facilitates O2 unloading into tissuesThe normal diffusion capacity for oxygen through the pulmonary membrane is 21 ml / mmHg/ minuteMay increase three times Pulmonary blood flow increase The drive ( pulmonary pressure} increase
Slide12Circulatory changes
Bone marrow stimulated
15 grams
Hb can become 22 gm(Hypoxia and erythropoietin)Muscle myoglobin appears to be increased ataltitude improving oxygen diffusionHypoxia of tissues induced vasodilation can increase cardiac output !
May take three weeks
Slide13Hypothermia
marked irritability of AV Bundle leading to
atrial and ventricular fibrillation
Can it bring down MAC of agents !
Slide14Circulatory system
On exposure to altitudes of 3,500 to 4,000 m, plasma volume is reduced by 3 to 5
mL
/kg. This occurs relatively rapidly after arrival at altitude, and the deficit would appear to persist for at least 3 or 4 months before starting to return toward normal
Slide15Miscellaneous changes !
exercise and hypoxia stimulate rennin release
but
aldosterone release is decreased at high altitudeSodium potassium – no change Capillary density in muscle is unchanged, although the average diameter of muscle fibers appears to be reduced – oxygen to travel less
Slide16The normal pulmonary arterial pressure at sea level is 12mm Hg
high altitude is 28 mm Hg.
Principal etiology is hypoxia
Is it like that
Slide17High Altitude
Illness
High Altitude Illness can take several forms that often overlap
Pathophysiology may be the same ! Acute Mountain Sickness (AMS)High Altitude Pulmonary Oedema (HAPO)High Altitude Cerebral Edema (HACO)
Slide18Acute Mountain Sickness
Anyone can be affected
Exertion
, poor hydration, young age may contribute. Fitness or gender ?? No use
Slide19Acute Mountain Sickness
Symptoms:
Early symptoms (12-24 hours):
Headache - standard analgesics may be useless nausea, anorexia,, sleep disturbances.Can progress to shortness of breath, g, vomiting, hallucinations, and impaired cognitive function,
Can go
upto
frank cyanosis
Slide20Acute Mountain Sickness
Rest
,
hydration, analgesics, oxygen can help.Acetazolamide 250 mg q 8-12 hours may improve symptoms and SaO2 (especially during sleep)Definitive treatment is only descent.
Come down by 500 to 1000m - we are fine !
Slide21Acute Mountain Sickness
Can we prevent !
Ascend slowly, but in army operations possible !
Daily altitude gain of no more than 300m above 3000m.Rest for two nightsHydration and less exercise !
Acetazolamide
250mg
8 hourly prophylaxis and treatment !! .CA inhibitors – unknown benefits
Slide22High Altitude Pulmonary
Oedema
(HAPO)
A Life threatening form of AMS with similar early symptoms. May occur in any healthy individual after rapid ascent above 2500 m (8200 ft)Dyspnea, chest pain,crepitations , tachycardia, dry
cough,
pink
frothy sputum
Respiratory failure and death can
ensue.
Protein rich exudates in hyaline membranes
Form of ARDS !
Slide23High Altitude Pulmonary
Oedema
(HAPO)
CXR - patchy infiltrates, Bases may not be affected ! Elevated pulmonary artery pressure secondary to hypoxia.ECG shows right heart strainBut with normal LV function
Slide24High Altitude Pulmonary
Oedema
(HAPO)
Treatment
Slide25High Altitude Cerebral
Oedema
(HACO)
One more danger ! Increased BBB permeability and increased cerebral vascular blood flow ! Hypoxia is the cause !
Slide26High Altitude Cerebral
Oedema
(HACO)
Early symptomsHeadacheAnorexiaNausea, EmesisPhotophobiaFatigueIrritability
Late symptoms
Ataxia
Hallucinations
Visual
disturbances
( retinal dots can also be there ! )
Focal neurological deficitsAbnormal reflexes
Cerebral edema in CT
Slide27HACO and HAPO may co exist !
Dexa
and oxygen may help but diuretics may worsen dehydration !
Slide28The Gamow Bag
Slide29The Gamow Bag
Portable
, lightweight,
fabric hyperbaric chamber.Can generate 103 mm Hg of pressure above ambient pressure.Artificial descent of 4000 to 9000 ft at moderate altitudes.
Slide30ANAESTHESIA AT HIGH ALTITUDE
General Principles
Prone for perioperative hypoxemia
Non acclimatized person more important Hb may not be high !
Volume Resuscitation
Bleeding :
high venous pressure, increased blood volume, venous dilatation increased capillary density
Slide31Infection
pollution
Fire
? Kerosene lamp operations !
Slide32Vaporizer !!
VO= (
CGxSVP) / (
Pb-SVP) Where VO=vapor output (ml), CG= carrier gas flow(mL.min), SVP=saturated vapor pressure (mm Hg) at room temp, and Pb- barometric pressure
Slide33Vaporizer !
At a higher altitude where the barometric pressure is ½ that at sea level, the amount of
isoflurane
vapor output increases due to the lower barometric pressure. Therefore, the settings that delivered 2% isoflurane now deliver 4% isoflurane.
Slide34What we need is partial pressure !!
partial pressure of
isoflurane delivered would be approximately the same at both altitudes since 2% isoflurane at 760mm Hg (15.2 mm Hg) is the same as 4% isoflurane at 380mm Hg (15.2 mm Hg).
Slide35Shafer says !
our vaporizer, set for 1.1%,
We need 1.5 %
is actually producing 1.7%,Some overcompensation
Slide36But !!
Desflurane
vaporizer is electrically heated to 39 degrees centigrade, which creates a vapor pressure of 2 atmospheres inside the vaporizer, regardless of ambient pressure.
The number on the dial reflects the percentage that will be delivered. So at any altitude, when you dial 5%, it will give us 5%
Slide37Slide38Flow meters
At a simulated altitude of 10,000 ft (3048 m), both nitrous oxide and O
2
flow meters under-read the actual flow rate. May be upto 20 % O2 analyser !!
Actual
Reading
Slide39TIVA
Slide40Venturi
-type gas-mixing devices tend to deliver higher concentrations of O
2
at altitude than they do at sea levelat an altitude of 10,000 ft (3048 m), mask designed to deliver 35% O2 at sea level actually delivered 41% O2
41 %
May be with less total flow
Slide41GA - considerations
Titrated premedication
Good
preoxygenation Increased FiO2 Sedatives and opioids – titrated Nitrous may dilute oxygen – may be avoided70% may actually be 50% nitrous ! agents same percentage
Muscle relaxation OK - ? Hypothermia !
Postoperative oxygen
Slide42Miscellaneous
Wait till acclimatization
Temperature of OT and the patientPostoperative oxygen for
atleast one hour Pain killers – less narcotics Watch for respiratory depression in the post op
Slide43Nepal in 1940s
Slide44Regional OK
But spinal headache is more common
Bladder bowel distension is more !
Local anesthetic duration may be shortened Cause ?
Slide45Summary
Definition
Changes AMS, HAPO , HACO
Anesthesia – RA GA – narcotics FiO2, agents , Temperature , TIVA
Himalayan task
Slide46Thank you all