Respiratory: Gaseous Exchange: Hyper- and Hypo-Baric Pressures

Question 1

Alveolar gas equation

Answer 1

Question 2

Acclimatization

Answer 2

Days to weeks for humans

Hyperventilation and hypocapnia

-> respiratory alkalosis -> renal bicarb excretion -> increase RR

increase Hb conc

increase 2,3-DPG

Question 3

Pressure units conversion

Answer 3

Question 4

Mild acute mountain sickness

symptoms

Answer 4

• occurs abouve 6,000 feet
• Symptoms of mild AMS include dyspnoea, headache, nausea, fatigue and sleep disturbance associated with Cheyne-Stokes respiration.
• related to the speed of ascent

Question 5

Severe acute mountain sickness

1. symptoms
2. treatment

Answer 5

• High altitude pulmonary oedema (HAPO)
  
  • associated with exercise.
  • 1 % of climbers
  • high mortality if untreated
  • caused by excessive pulmonary vasoconstriction
  • Symptoms:
  • persistent cough, bringing up a white, watery or frothy fluid
• High altitude cerebral oedema (HACO)
  • symptoms: hallucinations and coma

Question 6

Chronic mountain sickness symptoms

Answer 6

Symptoms of chronic mountain sickness

The following symptoms occur in populations who live at altitude:

• Poor hypoxic response to ventilation
• CO2 retention
• Polycythaemia
• Cyanosis
• Clubbing

Question 7

Even 10m underwater the pressure increases by?

Answer 7

1 atmosphere

100kPa

Question 8

Symptoms of rapid decompression

Answer 8

Symptoms of rapid decompression

• Barotrauma in any air filled space, such as the lungs or ear
• Arterial air embolus
• Potentially permanent neurological damage
• Bubbles forming in vessel poor tissues (cartilage) with avascular necrosis

These symptoms may also occur on ascent after diving.

Question 9

Hyperbaric oxygen treatment

Answer 9

• administration of 100 % oxygen at a pressure of 2-3 atm
• 1-2 h via a tight fitting facemask, repeated daily for up to 30 days
• oxygen content of arterial blood only increases marginally with hyperbaric oxygen (from about 19 to 25 ml/dl)
• At 3 atm venous O2 content increases substantially
• Tissue oxygen content approximates with venous content
• Indications:
  
  • anaerobic infections
  • CO poisoning

Question 10

Management of decompression sickness

Answer 10

• Avoid: slow decompression
• Treatment: emergency recompression in a hyperbaric chamber and the administration of oxygen

Question 11

Hypobaric pressures: possible consequences for the anaesthetist?

Answer 11

Patients with hypoxia at sea level will be more vulnerable to desaturation and may require additional oxygen

Pressurization and depressurization in aeroplanes occurs suddenly during take off and landing. This may cause air filled spaces within a patient, such as bullae and pneumothorax, to expand suddenly

Valves in breathing systems may stick

The boiling point of all the volatiles will fall, but in practice unaltered vapourizers have been used safely at altitude for many years. The commonest issue being inappropriately light anaesthesia because of inadequate vapourization of volatiles due to low temperature, which accompanies the altitude

Question 12

What do you think are the possible consequences for the anaesthetist when patients have been exposed to increased pressure?

Answer 12

Divers breathing air at more than 30 m may become anaesthetized by nitrogen

Sudden decompression may produce severe barotrauma and gas embolism, which may be macroscopic or microscopic

The treatment of carbon monoxide poisoning and burns may involve hyperbaric oxygen