Hypobarism and Hyperbarism

Question 1

Hypobarism

Answer 1

• A decrease in atmospheric pressure
• Can result in pathology
  
  • Altitude sickness
  • HAPE
  • HACE
  • Decompression Sickness

Question 2

Hyperbarism

Answer 2

A increase in atmospheric pressure

Can result in pathology

Can be used as a therapeutic intervention

Question 3

Henry’s Law

Answer 3

States that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas above the solution and the solubility coefficient of the gas

Question 4

Daltons’s Law of Partial Pressure

Answer 4

The total pressure of a mixture of gases is the sum of the pressure that each gas would exert if it were present alone

Pt= P1 + P2 + P3 + …+Pn

Consider air

• 21% oxygen and 79% nitrogen
• At sea level the total pressure is 760 mmHg
• The partial pressure of oxygen then is 0.21 x 760 mmHg = 160 mmHg
• The partial pressure of nitrogen is 0.79 x 760 mmHg = 600 mmHg
• We calculated PiO2 at 3ATA to be 480 mmHg (with FiO2 0.21). When 1.0 then the PiO2 is 2280 mmHg!

Question 5

Dalton’s Law and HBOT

Answer 5

• If hyperbaric therapy is done with air (21% O2 and 79% N2) both the partial pressure of nitrogen and oxygen are increased in the tissues
• Nitrogen has narcotic effect at increased pressures “Rapture of the Deep”
  
  • 2.5-3 ATA can result in mild euphoria
  • 4-6 ATA can result in significant intoxication which could lead to procedures being performed erroneously
    
    • Confirmation by someone outside the chamber may be required

Question 6

Boyle’s Law

Answer 6

When temperature of a gas is constant, any increase in pressure causes a proportional decrease in the volume of the gas

Thus at a given temperature

P1V1=P2V2

Question 7

Boyle’s Law and HBOT

Answer 7

• Changes in pressure lead to predictable changes in volume
  
  • When the pressure is doubles then the volume is halved
  • Tripling the pressure reduced the volume to 1/3 of original size
• Example- Pneumothorax and “Ascent”
  
  • Consider what will happen to ETT cuff volumes and pressures

Question 8

Altitude Sickness

Answer 8

• Altitude Sickness; Acute Mountain Sickness – AMS
• Generally speaking, not seen below 10,000 feet
  
  • Generally seen in people who do not properly acclimatize when ascending to high altitudes
• Incidence depends upon three things:
  
  • The altitude the individual is ascending to
  • Their rate of ascent – how fast are they climbing
  • The individual’s own susceptibility
• ​The etiology of AMS = Hypoxemia

Question 9

Altitude Sickness Signs and Symptons

Answer 9

Generally start within the first 6 to 12 hours after entering altitude, increase in severity over first 48 hours, and lessen after 72 hours at altitude

Can include:

• Severe fatigue, progressive muscle strength loss, inability to walk
• Headache, dizziness, confusion, insomnia
• SOB, paroxysmal nocturnal dyspnea, periodic breathing
• May progress to pulmonary edema (HAPE) and cerebral edema (HACE)
• Symptoms are worse at night, when the respiratory drive is lessened

Question 10

Altitude Sickness Treatment

Answer 10

• Three options: descend, acclimatize, or descend “artificially”
  
  • With severe AMS the CNS is severely affected
• They need to descend immediately or they will die
• “Artificial” Descent
  
  • Portable & inflatable hyperbaric tent (Gamow Bag)

Question 11

Altitude Sickness

Proper Acclimatization

Answer 11

Generally takes the better part of a week (5 to 6 days ), where the individual ascends at a slow pace to allow for RBC’s due to stimulation of the hormone erythropoietin (due to ¯PaO2 ) and results in increased oxygen carrying capacity

Question 12

Altitude Sickness Prevention

Answer 12

Ascend to altitude slowly

Climb high and sleep low

Don’t go up until symptoms go down

If symptoms get worse – descend

Keep well hydrated

Don’t over exert yourself

Question 13

Altitude Sickness Protective Agents

Answer 13

• Diamox (acetazolomide)
  
  • Carbonic anyhydrase inhibitor; diuretic
  • Can decrease manifestations of mild edema (e.g. headaches)
  • Can induce a relative metabolic acidosis and lead to further respiratory stimulation
• Dexamethasone
  
  • Used prophylactically to prevent HAPE and HACE
  • Must be started 5 days prior to ascent

Question 14

Hyperbarism Indication for Acute Conditions

Answer 14

Decompression Sickness (the “bends”)

Air embolism

CO poisoning

Cyanide poisoning

Thermal injuries

Acute traumatic ischemia

Clostridial gangrene

Necrotizing soft-tissue infection

Ischemic skin graft/flap

Exceptional blood loss

Question 15

Hyperbarism Indication for Chronic Conditions

Answer 15

Nonhealing wounds

Refractory osteomyelitis

Radiation necrosis

Question 16

Hyperbarism Contraindications

Answer 16

High fevers

Hypercapnia (> 60 mmHg)

Obstructive airway disease

Optic neuritis

Seizure disorders

Pneumothorax (*Absolute)

Sinusitis

Upper respiratory tract infections

Viral infections

Question 17

Hyperbarism Primary Physiological Effects

Answer 17

Hyperoxygenation

Reduction in bubble size

Question 18

Hyperbarism Secondary Physiological Effects

Answer 18

Angiogenesis

Vasoconstriction

Increased leukocyte oxidative killing

Bactericidal/bacterial static for anaerobic/ facultative anaerobic bacteria

Question 19

Hyperbarism Effects on the Cardiovascular System

Answer 19

HR: decreased

Cardiac output: decreased (due to decreased HR)

BP: possible minimal increase

SVR: Increased (vasoconstriction 2° increased oxygenation)

This results in increased afterload which could be detrimental to patients with CHF

Treatment for DCS/AE can sometimes be at up to 6 ATA for more severe cases, but, as always, depends on the institution’s protocols.

Question 20

Hyperbarism Effects on Blood Gases

Answer 20

other than the obvious increase PaO2!

Transport of CO2 in the blood occurs as bicarbonate (~75%), carbaminohemoglobin (~20%) and dissolved in the plasma (~5%)

As described by the Haldane Effect, in the presence of oxygen, hemoglobin has less affinity for CO2, thus CO2 is not carried on hemoglobin in a hyperbaric environment

This results in increased levels of CO2 dissolved in the blood

Question 21

HBOT: Principles of Application

Answer 21

• Uses standardized protocols
• E.g. Gas Bubble Disease
  
  • Eg. Decompression sickness (the “bends”) or iatrogenic gas embolism
  • Patient is compressed to 2.8 ATA and then decompressed to 1.9 ATA
  • Periods of 100% O2 breathing are interspersed with short “air breaks”
  • Minimizes oxygen toxicity
  • This treatment schedule proposed for mild DCS

Question 22

Carbon Monoxide Poisoning

Answer 22

Hemglobin binds with CO 200-250 times more readily than with O2

So patient commonly pressurized to 203 ATA times vary depening on the protocol

Question 23

Gas Ambient Pressure and Mean Half Life

Answer 23

Air

• Ambient Pressure
  
  • 1
• Mean Half Life
  
  • > 5 hours

Oxygen

• Ambient Pressure
  • 1
• Mean Half Life
  • 80 min

Oxygen

• Ambient Pressure
  
  • 3
• Mean Half Life
  
  • 23 min

Question 24

Hyperbarism and Barotrauma

Answer 24

• Can occur in any gas containing organ or cavity in the body
• Middle ear (Most common)
• Sinuses
• GI tract
• Teeth
  
  • If infected or restored
• Lungs
  
  • Patients coached during decompression to avoid breath holding

Question 25

Hyperbarism and Oxygen Toxicity

Answer 25

Effects may occur at any point in the treatment Correlated more to the duration of the treatment rather than the number of treatments Can avoid by giving “ait breaks”

Question 26

Hyperbarism and CNS Signs and Symptons

Answer 26

Nausea/vomiting Sweating Visual changes Hallucination Decreased LOC Seizures

Question 27

Hyperbarism and Respiratory Signs and Symptons

Answer 27

Dry cough SOB Chest pain Sub sternal Pulmonary edema

Question 28

The “Bends”

Answer 28

A mild form of decompression sickness Caused by the formation of gas bubbles in the body during rapid ascent (normal ascent allows nitrogen to slowly move out of the body)

Question 29

The “Bends” Signs and Symptons

Answer 29

* Consists of “pain only” manifestations * The pain occurs in the joints * Due to bubble accumulation * Patients avoid or are unable to bend affected joints * Can also include skin mottling and itching

Question 30

Decompression Sickness

Answer 30

Potentially lethal Signs and symptoms will appear gradually First symptom will tend to appear at 20 min and the second at 2 hours

Question 31

Decompression Sickness Signs and Symptons

Answer 31

Pain Mild headache Blurred vision Paresthesia Shortness of breath Cough Vertigo Paralysis Shock

Question 32

DCS and Arterial Gas Embolism

Answer 32

Thus, these bubbles generally become trapped in the pulmonary circulation Arterial gas embolism occurs when there are air bubbles in the arterial system These usually arise due to pulmonary expansion barotrauma! (eg. From a breath hold ascent) Can be lethal depending on location of air embolus

Question 33

Decompression Sickness the Four Cs

Answer 33

Another way to look as the signs and symptoms: The four "C's“: Creeps: sensation of tiny insects moving underneath the skin – bubble formation Cramps: the bends: pain localized in the large joints of the body – severe Chokes: rare: substernal chest pain, SOB, a dry, non-productive cough – caused by pulmonary air emboli Collapse: the end stage, death

Question 34

Nitrogen Narcosis: “Rapture of the Deep”

Answer 34

Pathologydue to the hyperbaric environment (i.e. not during removal from) Only at risk if breathing air (not oxygen) in a hyperbaric environment (\deep sea diving as well!) Due to the high partial pressure of N2 in the tissues (specifically in the brain)

Question 35

Nitrogen Narcosis Clinical Manifestations

Answer 35

Euphoria Impaired judgment Decreased coordination Light-headedness Inattention Hallucinations Coma Death

Question 36

Nitrogen Narcosis Treatment

Answer 36

= Decompression Fully, or at least to a depth where symptoms disappear.