HYPOXIA

DEFINITION• Oxygen deficiency in the tissues

• Disrupt the intracellular oxidative process and impairs cellular function.

• Brain cells High oxygen demanda) Brain impairment

b) Deterioration of performance

c) Reduced visual function

d) UNCONSCIOUSNESS

KINDS of HYPOXIA1. Hypoxic Hypoxia

a deficiency in alveolar oxygen exchange.Due to :

Reduction in the oxygen partial pressure in inspired air /

Reduction in the effective gas exchange area

Inadequate oxygen supply to the arterial blood

Decrease the amount of oxygen available to the tissues

• Aircrew exposure low barometic pressure

ALTITUDE HYPOXIA

2. Hypemic Hypoxia an oxygen deficiency due to reduction in the oxygen carrying capacity of the blood.

• Normal ventilation and diffusion BUT the rate of delivery of oxygen does not satisfy metabolic requirements (Hb problem).

• Carbon monoxide is significant to air crews because it is present in the exhaust fumes of both conventional and jet engine aircraft, as well as in cigarette smoke.

• Carbon monoxide combines with Haemoglobin about 200 times more readly than does Oxygen and displace oxygen to form carboxyhemoglobin.

• The normal carboxyhemoglobin level is ≤ 1%, but may increase to 6-7% in heavy smoker lower oxygen delivery to the tissue

• Carboxyhemoglobin levels of 15 - 20 %, produces : 1. Headache 2. Nausea3. Muscular weakness 4. Dizzines 5. Confussion

• levels above 25% :1. Electrocardiographic changes 2. Stupor & UNCONSCIOUSNESS

• Release of carbon monoxide from haemoglobin can be accelerated by inhaling oxygen O2 High Pressure (Hyperbaric Oxygen)

3. Stagnant Hypoxia any condition that results in a reduction in total

cardiac output, pooling of the blood, or restriction of blood flow can result in stagnant hypoxia.

• Heart failure, shock, continuous positive pressure breathing, and G forces sustained in flight maneuvers create stagnant hypoxia.

• Local cellular hypoxia can occur as a result of exposure to extreme enviromental temperature, restrictive clothing, or changes in body posture that restrict regional blood flow.

• Hyperventilation also can cause reduced cerebral blood flow and result in cerebral stagnant hypoxia.

• Blood clots or gas bubbles ( as in decompression sickness) can produce pulmonary emboli and create stagnant hypoxia

4. Histotoxic Hypoxia metabolic disorders or poisoning of the

cytochrome oxidase enzyme system can result in inability of the cell to use molecular oxygen

• Only cytochrome A3 molecules can transfer electrons to molecular oxygen in the final step of cellular respiration.

• This process is inhibited by carbon monoxide because it competes with oxygen. Ethyl alcohol, Cyanide, and Hydrogen Sulfide also can produce histotoxic hypoxia.

Treatment of Hypoxia1. Administer Supplemental Oxygen.

Depending severity administer 100% O2 delivered under positive pressure

2. Monitor BreathingAfter hypoxic episode hyperventilation maintaining RR 12-16 breaths/min

3. Monitor Equipment>> causes of hypoxia: lack of oxygen and equipment malfunction conscientious equipment preflight check and frequent in flight monitoring will reduce this hazard

4. Descentincreasing ambient oxygen pressure by descent to lower altitudes particularly below 3048 m.

Recovery from Hypoxic (Altitude) Hypoxia

• Occurs within seconds after reestablishing a normal alveolar partial pressure

• In some instances following sudden administration of oxygen individual develops a temporary increase in the severity of symptoms oxygen paradox subject loss consciousness / develop clonic spasm

• Initially arterial blood pressure ↓ & rate of blood flow ↓ Hypotension due to vasodilation in the pulmonary vascular bed

• Hypocapnia produced by hypoxia and ↓ blood pressure reoxygenation ↓ cerebral blood flow for short period CV effects have passed and PCO2 return to normal stimulate respiratory center to resume ventilation and resolve cerebral hypoxia

PREVENTION of HYPOXIA

by ensuring that the individual has sufficient oxygen to maintain a range of alveolar Po2 between 60 and 100 mm Hg.

Oxygen level is achieved in aircraft by :1. Oxygen system2. Cabin pressurization3. Combination of the two

Cabin Pressurization•In most civilian and military aircraft, maintaining a cabin altitude below 3048 m supplemental oxygen needed if cabin pressurixation system fails

•In most military fighter and trainer aircraft, ordinarily provides a cabin altitude below 7620 m need combined application with supplemental oxygen

Night Requirements•Exposure to reduces oxygen tension at altitudes below 3048 m increases dark adaption time and decreases night vision capability need suplemental oxygen on night flights

Requirement for pressure breathing•Above 12.192 m, 100% oxygen must be breathed with additional pressure •Oxygen regulators are designed to automatically provide positive pressure maintain an alveolar oxygen partial pressure of 87 mmHg, which is equivalent to breathing air at about 1524 m.•Altitude limit for sustained flight is aproximately 13.106 m when using standart pressure breathing equipment that delivers 30 mmHg pressure.

• During pressure breathing inhalation is easy and exhalation is difficult Practice is required.

• Technique for pressure breathing :1. Establish mental dicipline to control the breathing

pattern.2. When inhaling, maintain a conscious tension on the

respiratory muscles. control the expansion of the thorax through muscle tension. as inhalation progresses, steadily decrease muscle tension to allow inflation of the lungs.

3. Pause when the desired lung inflation has occured.4. When ready to exhale, positively increase muscle

tension for a steady, smooth exhalation.5. Pause and breathe at a rate slower than normal.

Requirements for pressure suit•To survive exposure to altitude above 15.240 m protection is provided by counterpressure garment , commonly called pressure suits.•Protection is achieved by applying pressure equally across the body such that sufficiently low physiologic altitude is maintained so that positive pressure breathing is not required

ALTITUDE ACCLIMATIZATION• Chronic exposure to altitude results in altitude

acclimatization, the process by which one becomes more tolerant of an hypoxic environment.

• the means by which acclimatization is achieved includes the following :1. Increased respiration and cardiac output due to the hypoxic stimulation of the carotid and aortic bodies.2. Increased diffusion capacity of the lungs probably achieved by a rise in the pulmonary capillary blood volume and a rise of the pulmonary arterial pressure.

3. Polycytemia directly resulting from hypoxic stimulation of red blood cell production by the bone marrow due to an increased released of erythropoetin by the kidney. This mechanism provides limited benefits within 2 to 3 weeks of exposure.

4. Increased vascularity of tissues resulting from an increased number and size of capillaries.

5. Cellular acclimatization occuring as the capability of the cells to metabolize oxygen increase in spite of the low oxygen tension. Probably due to changes in the cellular oxidative enzyme systems.

6. Decreased affinity of the hemoglobin of oxygen resulting from an increases production of 2,3 diphosphoglyceric acid within the red blood cells.7. The renal mechanism compensates for respiratory alkalosis by retaining ammonium ions and excreting large amounts of bicarbonate.