Hypoxia and hyperventilation

Question 1

What are the 4 types of hypoxia and give examples?

Answer 1

1. Hypoxic - lack of O2 diffusing into blood eg. Increasing altitude, hypovebtilation, medical conditions that decrease SA aid lungs - emphysema
2. Hypaemic - reduction of OCC of blood eg, haemorrhage, thallassemia, abn Hb
   3 . Stagnant: poor Q to tissues eg. Heart failure, Embolus, arteriolar constriction, trauma
3. Histiotoxic - tissue poisoning Sutlej to cells not able to utilise available O2 ie CO poisoning, cyanide, alcohol

Question 2

What are the stages of hypoxia?

Answer 2

1. Indifferent: MSL - 10kft
Sl decrease in night vision
2. Compensatory 10kft- 15kft
Chemoreceptor response > increase PR, HR, CO 
3. Disturbance stage 15-20kft
Compensatory mechanisms are no longer effective
LOC by 30-45 min
4. Critical st >20kft
Rapid hypoxia . LOC by 3-5 min

Question 3

What are the different PAO2 @ different altitudes in the atmosphere?

Answer 3

• MSL 760 mmHg PAO2 103
• 10kft 523mmHg PAO2 55
• 18kft 380mmHg PAO2 40
• 25kft 282mmHg PAO2 30
• 40kft 187mmHg PO2 10
• 45kft 111 MmHg PAO2 0

Need to add in supplemental O2 from 10kft in unpressurised cabin, will allow PAO2 to stay at 103 until 40kft

Question 4

What are the sx of hypoxia?

Answer 4

Cognitive - slowing down of reaction time, self absorbed, failing to notice events, short term memory loss

Physical - feeling flushed, increased HR and work of breathing, tingling, visual changes

Emotional -l

Question 5

What are the factors affecting hypoxia?

Answer 5

1. Altitude - increased altitude decreased PAO2&raquo_space; increased hypoxic sx
2. Rate of decompression
3. Duration of exposure
4. Individual tolerance
5. Physical fitness and tolerance
6. Psychological fix
7. Medication and drugs

Question 6

What are the actions to take in an event of hypoxia?

Answer 6

If O2 system available:

1. O2 regulator on
2. Oxygen diluted level on 100% O2
3. O2 pressure level on emergency
4. Check connections then pressure breath. PRICE check
5. Descend < 10kft
6. Declare emergency, PAN

If O2 system not available:

1. Check CO detector
2. Descend < 10kft
3. Concentrate on breathing, don’t hyperventilate - ACBC: breathe in 5s-hold for 5s- breath out 5sec
4. PAN
5. Land ASAP

Question 7

What are the differing TUC at different altitudes?

Answer 7

• @ 18kft: 30min
• @ 25kft: 5 min
• @ 30kft: 2 min
• @ 35kft: 60 sec
• @ 40kft: 15-20 sec
• @ 43kft: 9-12 sec

Question 8

Definition of hyperventilation?

Answer 8

Condition where pulmonary ventilation is greater than that required to eliminate CO2 produced in tissue

Question 9

Causes of hyperventilation in aviation?y

Answer 9

1. Occurs when PAO2 < 55mmHg ie at 10kft altitude
   2 emotional stress
2. If > 12kft then always consider Hypobaric hypoxia
   4.

Question 10

What is the physiological mechanism underlying trapped gas disorder?

Answer 10

1. Boyle’s law - at a constant temperature, pressure is inversely proportional to volume
2. Increase in altitude decreases pressure which increases volume and pocket of air within the body&raquo_space; trapped air disorder

Question 11

Which organs can be affected by trapped gas disorder? Which area is most commonly affected

Answer 11

Ears, sinus, teeth, GI tract, lungs, after surgery/trauma

GI is most commonly affected

Question 12

What are the initial actions for Barotrauma?

Answer 12

1. Slow or halt descent. Ascend if possible
2. Valsalva, descent more slowly
3. Vasoconstrictor spray (use as last resort)
4. Handover control if pain is distracting/declare PAN if incapacitating
5. Seek AVMO review

Question 13

What are the clinical mx of Trapped gas disorders?

Answer 13

As per PM220:

TMUFF
analgesia
Decongestants
Antibiotics if indicated
Imaging
Referral if recurrent

Question 14

What are some of the aeromedical retrieval issues that need to be considered?

Answer 14

1. Transport of patient at altitude - caution if trapped gas in critical body parts (skull brain eyes joints)
2. Equipment and timing of use ie. IV lines, drips, ventilators, infusions