Respiratory Flashcards
A-a Gradient Equation =
A= [FiO2 x (elevation - barometric pressure) - (PaCO2/Respiratory Quotient)
Definition of A-a Gradient
The difference between the Alveolar and Arterial oxygen concentrations
Normal A-a Gradient value
Less than 15 mm Hg
True or false: The A-a gradient is beneficial as a one-off value.
False: It’s the most useful when used for trending.
Using the P:F ratio, what would an expected arterial PaO2 be on a patient breathing 100% oxygen?
PaO2= ~500 mm Hg
Define the P:F ratio
PaO2:FiO2 ratio is the arterial PaO2 should = ~5x the FiO2
Define the 120 rule
Essentially PaO2 + PaCO2 should be equal to or greater than 120 in an animal with normal pulmonary function. It’s an easier version of the A-a gradient.
Define a V/Q mismatch.
Blood that has traveled through the lungs without becoming properly oxygenated resulting in venous admixture.
What are some causes of a low V/Q?
Pneumonia, PTE, pulmonary edema, asthma
What would cause no
V/Q?
Atalectasis, severe pleural effusion, collapsed alveoli
When can the 120 rule be applied?
It only applies to patients breathing room air at sea level.
What is the function of PEEP (Positive end expiratory pressure) in regards to ventilation?
PEEP maintains positive pressure in the airway during exhalation to prevent the lungs from emptying completely.
How can PEEP be beneficial to a patient requiring ventilation assistance?
PEEP can increase the oxygenating efficiency of diseased lungs by recruiting previously collapsed alveoli.
What would the appropriate PEEP setting be on a ventilator for a patient who has healthy lungs?
0-5 cm of H2O
What would be an appropriate initial PEEP setting for a ventilator patient with lung disease?
5-8 cm of H2O
What is the function of PIP (Positive Inspiratory Pressure) in regards to ventilation?
PIP is the maximum pressure generated during inhalation.
How does your PEEP setting on the ventilator affect your PIP setting?
The PEEP setting will affect the inspiratory pressure as an additional amount of pressure. Essentially, whatever your PEEP setting is, it must be factored in to your PIP setting.
If your PEEP setting is at 5cm of H2O and you want your total PIP to be 20 cm of H2O, what should your PIP setting be?
15cm of H2O
How can your PEEP setting affect venous return?
High PEEP settings maintain elevated intrathoracic pressure during exhalation and can therefore decrease venous return.
If you have a patient with normal healthy lungs on the ventilator and their CO2 is increasingly elevated.
What are 3 indications for mechanical ventilation?
Severe hypoxemia despite oxygen supplementation, severe hypoventilation, excessive respiratory effort with impending fatigue.
True or false: venous blood gas values can be used to diagnose hypoxemia.
False. Only arterial blood gas can be used.
True or false: venous PaCO2 can be used to diagnose hypoventilation in hemodinamically stable patients.
True.
True or false: diseased lungs need higher PEEP and PIP setting, but lower tidal volume settings.
True
Lung compliance is variable, how compliant would you expect a healthy animals lungs to be in regards to tidal volume?
Healthy lungs are significantly more compliant and can handle a higher tidal volume.
If you have a ventilator patient who is consistently hypoxemic, what are some things you can do to trouble shoot?
Increase the FiO2, change the patient to sternal recumbency, increase the PEEP/PIP/Tidal volume if the patient has compliance.
If you have a ventilator patient who is consistently hypercapneic what can you change to trouble shoot?
Assess ET tube, ensure there’s adequate expiratory time, increase the tidal volume and/or respiratory rate.
What is a normal by product of the metabolism of oxygen that can lead to oxygen toxicity if excess accumulation occurs?
Reactive oxygen and nitrogen species AKA RONS.
How do RONS cause oxidative injury?
They damage lipids, nucleic acids and proteins resulting in cellular injury.
What are the 3 predominant systems affected by oxygen toxicity?
Respiratory, Central Nervous, and Cardiovascular.
