48 - Therapeutic Gases Case Study Flashcards
What is hypoxia?
When oxygen delivery to the tissues is inadequate to meet metabolic needs
What are the three causes of hypoxia?
1 - Hypoxemia
2 - Impaired blood flow
3 - Dysoxia
What is hypoxemia?
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
Describe impaired blood flow
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
What is dysoxia?
Impaired ability for tissue to utilize oxygen
The cellular use of oxygen is abnormally decreased - classic example is cyanide poisonin
What are the effects of hypoxia on the lungs?
- Pulmonary vasoconstriction
- Pulmonary hypertension (protective mechansim)
What are the effects of hypoxia on the heart?
- 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
What are the effects of hypoxia on the kidneys?
Impaired renal function
What are the effects of hypoxia on the CNS?
- Cerebral vasodilation, increase in cerebral blood flow
- This is another protective mechanism in order to maintain homeostasis and blood flow to the brain
What are the systemic effects of hypoxia?
- Anaerobic metabolism
- Lactic acid accumulation
- Metabolic acidosis
What is a general trend you see in mild to moderate hypoxia compared to severe hypoxia?
Mild to moderate
- You will see a lot of compensatory mechanisms
Severe
- You will see primarily processes of system failure
What is the most common therapy to treat hypoxia or hypoxemia?
- Oxygen therapy
room air is only 21% oxygen
What is the goal of oxygen therapy?
- To correct hypoxemia (adults 90, neonates 88)
- To relieve symptoms of hypoxia/hypoxemia
- To prevent/minimize increased cardiopulmonary workload associated with hypoxia/hypoxemia
What are the harmful effects of oxygen therapy?
- Oxygen toxicity
- Hypoventilation in chronic CO2 retainers
- Retinopathy in neonates
- Nitrogen washout or nitrogen absorption atelectasis causing the lung to collapse
Describe oxygen toxicity
- 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
What causes oxygen toxicity?
FREE RADICALS
Describe the pathological response to free raidical oxygen toxicity
- 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
What are the clinical guidelines for oxygen therapy?
- 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)
What is another way to administer oxygen?
Hyperbaric oxygen therapy
- High partial pressure in order to increase oxygen content in blood quickly
Used in air embolism, CO poisoning and wound therapy
What is another gas that can be used to treat hypoxia/hypoxemia?
Helium-oxygen therapy (heliox)
Describe the clinical use of heliox
- 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
What ratio of oxygen/helium is used?
80% He/20% O2
What adverse effects can occur with heliox therapy?
- Depresses the ability to cough
- Special flow meters are required
- Hypoxemia can result because you’re using a low level of oxygen
What is the last gas therapy we discussed which can be used to treat hypoxia?
Nitric oxide therapy
How does nitric oxide therapy work?
- Indigenous compound released from endothelial cells to surrounding smooth muscle cells
- Affects calcium channels leading to smooth muscle relaxation
What is the clinical use of nitric oxide therapy?
- Used to treat pulmonary hypertension by dilating the pulmonary blood vessels, improving oxygenation
- Used to treat persistent pulmonary hypertension in the newborn
What is the only FDA approved indication of NO therapy?
Persistant pulmonary hypertension of the newborn
What are the adverse effects of nitric oxide therapy?
- Pulmonary toxicity at high doses (50-100 ppm)
- Cilia and epithelial damage, impaired surfactant production
- Mehemoglobin at high doses
What is the dosing guidelines for nitric oxide therapy?
- Up to 80 ppm/day
- In neonates, standard is 20 ppm/day
What is something you need to be aware of when giving nitric oxide therapy?
- Rebound hypertension
- Must ween off slowly
- Requires very close monitoring
How do you deliver nitric oxide therapy?
Via a ventilator or a tight fitting mask/nasal canula
