Therapeutic gases

Question 1

Causes of Hypoxia

Answer 1

1) Hypoxemia = failure of the respiratory system to oxygenate arterial blood (decreased carrying capacity of the blood)
2) Impaired blood flow = inability of cardiac system to adequately deliver blood to the tissues
3) dysoxia = impaired ability for tissue to utilize oxygen

Question 2

describe V/Q mismatch

Answer 2

• Impaired ability of oxygen to diffuse across the alveolar-capillary membrane (increase (A-a)O2)
• CAUSES

–> physiologc/anatomic shunt

–> deadspace

–> aging (decrease elastic recoil of the alveoli)

–> pulmonary fibrosis, edema, or embolism

Question 3

effects of hypoxia

Answer 3

• pulmonary vasoconstriction, pulmonary hypertension

–> protective mechanism

• increase cardiovascular workload (compensation for lack of oxygen)
• harmful effects on myocardial function
• impaired renal function
• cerebral vasodilation, increased cerebral blood flow

Question 4

describe oxygen therapy

Answer 4

• Most common therapy to treat hypoxia/hypoxemia
• GOAL = to maintain adequate tissue oxygenation
• Clinical objectives

–> to correct hypoxema

–> to reflieve symtpoms of hypoxia/hypoxemia

–> to prevent/minimize increased cardiopulmonary workload associated with hypoxia/hypoxemia

Question 5

what are the physiologic effects of breathing 100% inspired oxygen at ATM over time

Answer 5

• 0-12 = normal pulmonary function, tracheobronchitis, substernal chest pain
• 12-24 = decreasing vital capacity
• 24-30 = decrease lung compliance, increases P(A-a)02, decreasing exercise PO2
• 30-72 = decreasing diffusing capacity

**can lead to inflammatory response due to free radicals that are produced**

Question 6

Describe oxygen toxicity

Answer 6

• primarily involves lungs and CNS
• Deteremined by the PO2 and exposure time
• Pathology thought to be caused by oxygen free radicals (oxidation rxns inhibit enzymes function or injure/kill cells)
• Pathological response

–> damage to capillary endothelium

–> thickening of the alveolar-capillary membrane

–> end stage = pulmonary fibrosis and htn

Question 7

Describe oxygen-induced hypoventialtion of COPD patients with chronic hypoxema and hypercapnia

Answer 7

• Central resposne to CO2 is blunted
• leads to primary stimulus to breathe is oxygen deprivation (hypoxemia)
• causing high blood O2 levels suppress peripheral chemoreceptors and depress ventilatory drive

Question 8

describe retinopathy of prematurity (harmful effect of oxygen therapy)

Answer 8

• condition of the eye affecting premature/low-birth weight infants)
• EXCESSIVE blood-oxygen levels produce reitnal vasoconstriction causing encrosis of the blood vessels
• resulting in new vessels forma nd icnrease in number
• leading to hemorrhage of these new vessels causing scarring behind the eyes retina leading to retinal detachment and blindness

Question 9

describe hyperbaric oxygen therapy

Answer 9

• MoA:

–> increase atmosphere pressure –> increase partial pressure

–> decrease air bubble volume

–> increase oxygen content in blood available for tissues

• Indications for use:

–> air embolism, carbon monoxide poisoning, wound therapy

• complications: barotrauma caused by high pressure, CNS and pulmoary complications caused by oxygen toxicitiy

Question 10

describe helium-oxygen therapy (HELIOx)

Answer 10

• low-density gas which lowers the work of breathing (promotes laminar flow in large airways0
• Decrease driving presure to move gas = decrease airway resistance
• CAUTIONS:

–> depresses cough

–> special flow meters required

–> HYPOXEMIA

Question 11

Nitric oxide therapy

Answer 11

• MoA

–> endogenous compound released from endothelial cells to surrounding smooth muscle cells

–> affects calcium channels leading to smooth muscle relaxation

• USES: tx pulmonary htn by dilating pulmonary blood vessles

–> improves V/Q mismatch, oxygenation

–> only FDA-approved for persistent pulmonary htn of the newborn

Question 12

What are NO guidelines

Answer 12

• CAUTIONS:

–> pulmonary toxicity at doses of 50-100ppm (cilia and epithelial damage, imapired surfactant produciton)

–> methemoglobin at high dosese

• NO DELIVERY GUIDELIENS

–> deliver in parts per million

–> adminster via ventilator circuit or closely fitting mask or nasal prongs

–> monitoring, titration and frequent calivration of equipment

Question 13

describe absorption atelectasis (harmful effect of Oxygen therapy)

Answer 13

• Nitrogen, the priamry gas in the alveoli is washed out by oxygen

–> inspired oxygen above 50% depletes botha lveolar and blood nitrogen within minutes

–> removal of nitrogen from the blood lwoers the total pressure of gases in the venous system

–> a large pressure gradient occurs between pulmonary capillary blood and alveoli

–> in obstructed alveoli, oxygen continues its outward movement without repletion causing alveolar collapse

–> this results in increases physiologic shunt (alveoli are perfused but not ventilated)