48 - Therapeutic Gases Case Study

Question 1

What is hypoxia?

Answer 1

When oxygen delivery to the tissues is inadequate to meet metabolic needs

Question 2

What are the three causes of hypoxia?

Answer 2

1 - Hypoxemia
2 - Impaired blood flow
3 - Dysoxia

Question 3

What is hypoxemia?

Answer 3

A failure of the respiratory system to oxygenate arterial blood

This decreases the carrying capacity of the blood

Can be caused by…

• High altitude (low pressure of oxygen)
• Hypoventilation
• Hb deficiency
• V/Q imbalance
• Anatomic shunt
• Impaired alveolar-capillary diffusion

Question 4

Describe impaired blood flow

Answer 4

This occurs when there is an inability of the cardiac system to adequately deliver blood to the tissues

Local reduction of perfusion can be due to…

• Ischemia
• Clot
• Stenosis
• MI/stroke

Question 5

What is dysoxia?

Answer 5

Impaired ability for tissue to utilize oxygen

The cellular use of oxygen is abnormally decreased - classic example is cyanide poisonin

Question 6

What are the effects of hypoxia on the lungs?

Answer 6

• Pulmonary vasoconstriction

- Pulmonary hypertension (protective mechansim)

Question 7

What are the effects of hypoxia on the heart?

Answer 7

• Increased cardiovascular workload (this is the primary reaction - first thing the body does in a hypoxic state)
• Eventually there will be harmful effects on myocardial function

Question 8

What are the effects of hypoxia on the kidneys?

Answer 8

Impaired renal function

Question 9

What are the effects of hypoxia on the CNS?

Answer 9

• Cerebral vasodilation, increase in cerebral blood flow

- This is another protective mechanism in order to maintain homeostasis and blood flow to the brain

Question 10

What are the systemic effects of hypoxia?

Answer 10

• Anaerobic metabolism
• Lactic acid accumulation
• Metabolic acidosis

Question 11

What is a general trend you see in mild to moderate hypoxia compared to severe hypoxia?

Answer 11

Mild to moderate
- You will see a lot of compensatory mechanisms

Severe
- You will see primarily processes of system failure

Question 12

What is the most common therapy to treat hypoxia or hypoxemia?

Answer 12

• Oxygen therapy

room air is only 21% oxygen

Question 13

What is the goal of oxygen therapy?

Answer 13

• To correct hypoxemia (adults 90, neonates 88)
• To relieve symptoms of hypoxia/hypoxemia
• To prevent/minimize increased cardiopulmonary workload associated with hypoxia/hypoxemia

Question 14

What are the harmful effects of oxygen therapy?

Answer 14

• Oxygen toxicity
• Hypoventilation in chronic CO2 retainers
• Retinopathy in neonates
• Nitrogen washout or nitrogen absorption atelectasis causing the lung to collapse

Question 15

Describe oxygen toxicity

Answer 15

• Primarily involves the lungs and CNS
• Effects are determined by the PO2 and exposure time
• Pathology is thought to be caused by oxygen free radicals

Question 16

What causes oxygen toxicity?

Answer 16

FREE RADICALS

Question 17

Describe the pathological response to free raidical oxygen toxicity

Answer 17

• Damage to capillary endothelium
• Thickening of the alveolar-capillary membrane (interstitial edema)
• Alveolar exudate and consolidation causing physiological shunting
• At end stage, pulmonary fibrosis and hypertension

Question 18

What are the clinical guidelines for oxygen therapy?

Answer 18

• Give minimum dose to obtain desired result
• Order in L/min and/or percent of oxygen (24% or FiO2 0.24)
• Ongoing assessment (use pulse ox and ABG)

Question 19

What is another way to administer oxygen?

Answer 19

Hyperbaric oxygen therapy
- High partial pressure in order to increase oxygen content in blood quickly

Used in air embolism, CO poisoning and wound therapy

Question 20

What is another gas that can be used to treat hypoxia/hypoxemia?

Answer 20

Helium-oxygen therapy (heliox)

Question 21

Describe the clinical use of heliox

Answer 21

• It is a low-density gas which lowers the work of breathing by promoting laminar flow in large airways
• This drives down the amount of pressure it takes to move gas and decreases the airway resistance
• Overall, makes breathing easier

Question 22

What ratio of oxygen/helium is used?

Answer 22

80% He/20% O2

Question 23

What adverse effects can occur with heliox therapy?

Answer 23

• Depresses the ability to cough
• Special flow meters are required
• Hypoxemia can result because you’re using a low level of oxygen

Question 24

What is the last gas therapy we discussed which can be used to treat hypoxia?

Answer 24

Nitric oxide therapy

Question 25

How does nitric oxide therapy work?

Answer 25

• Indigenous compound released from endothelial cells to surrounding smooth muscle cells
• Affects calcium channels leading to smooth muscle relaxation

Question 26

What is the clinical use of nitric oxide therapy?

Answer 26

• Used to treat pulmonary hypertension by dilating the pulmonary blood vessels, improving oxygenation
• Used to treat persistent pulmonary hypertension in the newborn

Question 27

What is the only FDA approved indication of NO therapy?

Answer 27

Persistant pulmonary hypertension of the newborn

Question 28

What are the adverse effects of nitric oxide therapy?

Answer 28

• Pulmonary toxicity at high doses (50-100 ppm)
• Cilia and epithelial damage, impaired surfactant production
• Mehemoglobin at high doses

Question 29

What is the dosing guidelines for nitric oxide therapy?

Answer 29

• Up to 80 ppm/day

- In neonates, standard is 20 ppm/day

Question 30

What is something you need to be aware of when giving nitric oxide therapy?

Answer 30

• Rebound hypertension
• Must ween off slowly
• Requires very close monitoring

Question 31

How do you deliver nitric oxide therapy?

Answer 31

Via a ventilator or a tight fitting mask/nasal canula