Notes for Unit 7, Oxygen Therapy

1. = hypoxia-inadequate oxygen delivery to the tissues

&= nbsp; hypoxemia-low oxygen levels in the blood

2. = Four types of hypoxia:

1) hypoxemic- hypoxia cau= sed by low arterial blood oxygen levels

2) anemic or hemoglobin abnormalities- decrease in oxygen carrying capacity due to inadequate or abnormal hemoglobin

3) stagnant or reduced bl= ood flow- inadequate blood flow to the tissues

4) histotoxic or dysoxia- oxygen delivery is adequate but tissues can’t utilize oxygen

3. = Five causes of hypoxemic hypoxia:

&= nbsp; &nbs= p; 1. = low PiO₂

2. = anatomic shunt

3. = hypoventilation

4. = diffusion defect

5. = ventilation/perfusion mismatch

Five causes of hypoxemia:

1. = Ventilation/perfusion mismatch- most common cause; blood flow and ventilation don’t match up, blood is under-oxygenated, e.g. atelectas= is, pneumonia, pulmonary embolism

2. = Hypoventilation- decreased tidal volume +/or breathing rate leading= to decreased alveolar ventilation, e.g. drug overdose, anesthesia, spinal cord injury

3. = Diffusion defect- alveolar capillary membrane distance is increased= or AC membrane is thickened so oxygen doesn’t diffuse into blood as easi= ly, e.g. pulmonary edema

4. = Anatomic shunt- structural defect which allows venous blood to mix = with arterial blood, e.g. congenital heart defect

5. Low PiO_{2-
inadequate oxygen percentage or inadequate partial pressure of oxygen inhal=
ed,
e.g. “mountain sickness”}

4. = Four examples of hemoglobin abnormality (anemic) hypoxia:

1. = anemia- low levels of hemoglobin

2. = carboxyhemoglobin- hemoglobin bound to carbon monoxide instead of oxygen

3. = methemoglobinemia- reduced form of iron atom

4. = hemoglobin doesn’t release oxygen to tissues- alkalosis, hypocarbia

5. = Three examples of reduced blood flow (stagnant) hypoxia:

1. = shock

2. = cardiovascular instability-MI

3. = regional vasoconstriction- hypoxic bowel syndrome=

6. = Example of dysoxia:

1. = cyanide poisoning

7. = Signs and symptoms of acute hypoxemia:

tachycardia (first sign), tachypn= ea, cyanosis, dyspnea, hypertension, mental confusion, dysrhythmias, increased = use of accessory muscles, anxiety, lethargy

8. = Three physiologic reactions of blood vessels to hypoxemia:

1. = vasoconstriction to skin, skeletal muscle and abdominal contents

2. = vasodilation to brain, heart and vital organs

3. = constriction of pulmonary blood vessels leading to increased pulmon= ary vascular resistance

9. = Three pathophysiologic conditions caused by chronic hypoxemia:<= /p>

1. = digital clubbing- spongy, swollen nail beds

2. = secondary polycythemia- hypoxemia stimulates release of erythropoietin which stimulates bone marrow to increase RBC production. Causes increased viscosity of bloo= d.

3. = cor pulmonale- THIS WILL BE ON TEST. Chronic hypoxemia→ pulmonary vasoconstriction→ increased pulmonary vascular resistance→ increased right ventricular workload→ right ventricular hypertrophy&#= 8594; right ventricular failure

10. Three physiologic responses to hypoxia:

1. = stimulate increased breathing rate and depth (respiratory)

2. = increased heart rate and force of contraction (cardiac)<= /span>

3. = decreased renal function (kidneys)

11. Most = common cause of hypoxemia: V/Q mismatch

12. Hazar= ds of oxygen therapy

1. = Retinopathy of prematurity (ROP)- hyperoxmia causes vasoconstriction of retinal blood vessels; additional capillaries develop, impairing light penetration; eventual presence of opaque fibrotic tissue behind lens causes retinal detachment; little problem if PaO_{2
kept below 80 mm Hg in neonate.}

2. = Oxygen-induced hypoventilation-usually observed in patients with chronic CO₂ retention; due to blunting of respiratory drive due = to high PaCO₂; suppresses hypoxic drive; causes increased CO_{2<=
/sub>
retention.}

3. = Absorption atelectasis- due to administration of high oxygen percentages; may wash out nitrogen leaving only oxygen in alveoli; particul= arly in poorly ventilated areas of lungs; more oxygen diffuses into blood than c= an be replaced by breathing; collapse of alveoli because no gas to keep alveoli inflated.

4. = Bronchopulmonary dysplasia (BPD)- result= of high FiO₂, high peak pressures and prolonged inspiratory time on ventilator. Damage to alveola= r and bronchiolar epithelium, poor tissue formation in lung, fibrosis.=

5. = Oxygen toxicity- due to high inhaled oxygen pressures. Mainly a problem when oxygen perce= ntage is greater than 60%. Series of reversible inflammatory changes in lung tissue leading to alveolar congesti= on and fibrosis.

13. Signs= and symptoms of oxygen toxicity

&= nbsp; &nbs= p; tracheobronchitis = &= nbsp; &nbs= p; &= nbsp; refractory hypoxemia

&= nbsp; &nbs= p; bronchopneumonia = &nb= sp; = &nb= sp; infiltrates on chest x-ray

&= nbsp; &nbs= p; cough = ; &n= bsp; = ; &n= bsp; = ; atelectasis

&= nbsp; &nbs= p; substernal pain &= nbsp; &nbs= p; &= nbsp; &nbs= p; decreased compliance

&= nbsp; &nbs= p; nausea and vomiting&nb= sp; = &nb= sp; = hypertension

&= nbsp; &nbs= p; anorexia &n= bsp; = ; &n= bsp; = ; &n= bsp; decreased diffusion

&= nbsp; &nbs= p; paresthesia

14. Probability and severity of oxygen toxicity will increase if oxygen percentage is high (>60%) and am= ount of time on high oxygen percentage is long.

15. ROP-c= aused by increased PaO₂

&= nbsp; Oxygen toxicity- caused by increased PiO₂

&= nbsp; Oxygen-induced hypoventilation- caused by increased PaO₂

&= nbsp; Absorption atelectasis- caused by increased FiO₂(O₂%)

&= nbsp; BPD- caused by increased PiO₂, PIP, and inspiratory time

16. Indic= ations for oxygen therapy:

&= nbsp; 1) treat hypoxemia (PaO₂ < 60 mm Hg, = or O₂ sat < 90%) or treat hypoxia

&= nbsp; 2) treat excessive work of breathing

&= nbsp; 3) treat excessive myocardial work

&= nbsp; 4) treat wounds

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