4.1 - Oxygenation & Ventilation Flashcards
What is oxygenation?
It refers to the movement of oxygen into the blood and its further transport to the tissues. It is determined by the partial pressure of oxygen present in the alveoli, condition of the alveolar-capillary membrane, and the amount of hemoglobin present and the cardiac output of the patient.
What 5 factors can affect oxygenation?
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Hypoxemia - Occurs when there is insufficent movement of oxygen into the blood
- This is different from hypoxia which is abnormally low oxygen content to a tissue or organ
- Oxygen consumption - It is the rate at which oxygen is removed from the blood
- Oxygen diffusion - The diffusion pressure determines how fast/slow oxygen will diffuse through the alveolar membrane and into the blood & vice-versa
- Hemoglobin - Has an affinity for oxygen allows which allows it to carry more oxygen to tissues than could be dissolved in plasma alone.
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Cardiac output - This will determine how well tissues are perfused with oxygen.
- CO = HR X SV
What is ventilation?
It is the exchange of extrapulmonary and intra alveolar gas mixtures. Ventilation refers to the exchange of oxygen and carbon dioxide at the alveolar-capillary membrane level.
What 3 factors affect ventilation?
- Patency of airway - Does the airway allow for movement of air into the lungs?
- Neuromuscular function - Is there anything impairing the muscular movement of the chest?
- The structural integrity of chest wall - Does it allow for inspiratory and expiratory air flow? Any pneumothorax, etc?
How does a Nasal Cannula affect FIO2 delivery?
- NC is the most common non-invasive oxygen therapy but the exact FIO2 delivered is unknown because it is influenced by peak inspiratory flow demand.
- Each additional liter of flow increases the FIO2 by approximately 4%.
- Flow rates should be limited to 5 L/min or less.
How does a Humidified High Flow Nasal Cannula affect FIO2 delivery (Optiflow)?
- It can deliver heated and humidified oxygen at higher flows and concentrations than a normal NC
- Flow rates up to 50L/min and 100% FIO2
- Optiflow is the most commonly used system.
How does a Venturi mask affect FIO2?
- The precise amount of oxygen delivered is known
- The usual FIO2 amounts ordered are 24%, 28%, 31%, 35%, 40% and 50%.
How does a nonrebreathing mask affect FIO2?
- These masks can achieve oxygen concentrations of 80-90%
- A one-way valve prevents exhaled gases from entering the reservoir bag thus maintaining the FIO2.
What are the 2 types of noninvasive positive pressure ventilation, and for what patient is this type of ventilation indicated for?
- Includes continuous positive airway pressure (CPAP) and bi-level positive airway pressure (BPAP) ventilation.
- These decrease the need for endotracheal intubation and mechanical ventilation in patients with neuromuscular disease, COPD, CHF and postoperative respiratory compromise or insufficiency.
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The use should be limited to patients that are conscious and can cooperate and protect their airway.
- May be poorly tolerated by patients with claustrophobia or aerophagia.
How does CPAP work?
- works by preventing alveolar collapse during expiration.
- Initially 5 cm H2O of pressure should be applied.
- It can be increased by 3-5 cm up to 10-15 cm H2O to relieve hypoxemia.
How does BIPAP work?
- It supports both inspiration and expiration; it decreases the work of breathing (WOB).
- An inspiratory pressure of 5-10 cmH2O and an expiratory pressure of 5 cm are usual starting points.
- Ventilation is determined by the difference between inspiratory and expiratory pressures (i.e. “drive pressure”).
- Inspiratory pressures can be slowly increased to achieve adequate tidal volumes and minute ventilation.
What is exercise tolerance and why is it important?
- It is the ability to perform a normal exercise load.
- This suggests normal oxygenation and ventilation
What is cyanosis and describe its importance in the measurement of oxygenation
- Cyanosis occurs when there is a dusky bluish tint on the skin cue to excessive amounts of unsaturated hemoglobin
- The more central the cyanosis the greater it’s severity. Example: cyanosis evident on the face and chest is more severe than cyanosis limited to the fingertips
How do you measure oxygenation from an ABG?
- To measure oxygenation from an ABG you will want to interpret the PaO2 in light of fraction of inspired oxygen (FIO2).
- As a general rule PaO2 should be 4-5 times the percentage of O2.
- Example: Room air is 21% oxygen, PaO2 is 80-97%
What is a PaO2/FiO2 ratio and what is its importance?
- PaO2/FiO2 ratio describes the degree of impairment in pulmonary gas exchange.
- Normal ratios are 300-500 mmHg
- Low ratios indicate impaired oxygen exchange while ratios less than 200 mmHg indicate severe hypoxemia
How do you conduct an Allen’s test?
The patient’s hand is initially held high with the fist clenched. Bothe the radial and ulnar arteries are then compressed firmly by the two thumbs of the provider. This allows the blood to drain from the hand. The hand is then lowered and the fist is opened. The palm will appear white. The pressure is released from the ulnar artery while the radial artery remains compressed. A pink color should return to the palm, usually within 6 seconds indicating that the ulnar artery is patent and the superficial palmar arch is intact, The time of return of color may vary in patients but 10 seconds or longer is considered abnormal.
How does pulse oximetry work?
- It uses a light emitting diode to transmit light in the trans red and near-infrared wavelengths through tissue
- The device then compares light emitted versus light received to calculate the light absorbed by the oxyhemoglobin
NOTE: The accuracy can be affected by abnormal hemoglobins, movement of the probe causing artifact or if nails are covered with nail polish
