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Nrnp 6566 week 11 final exam study guide

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Final Exam-Study Guide
Week 6 and 7
1.
Interpret arterial blood gases (ABG). Differentiate alkalosis/
acidosis and respiratory / metabolic
2.
Identify a ventilation perfusion mismatch and how to treat it
If there is a mismatch between the alveolar ventilation and the
alveolar blood flow, this will be seen in the V/Q ratio. If the V/Q ratio
reduces due to inadequate ventilation, gas exchange within the
affected alveoli will be impaired. As a result, the capillary partial
pressure of oxygen (pO2) falls and the partial pressure of carbon
dioxide (pCO2) rises.
To manage this, hypoxic vasoconstriction causes blood to be
diverted to better ventilated parts of the lung. However, in most
physiological states the hemoglobin in these well-ventilated
alveolar capillaries will already be saturated. This means that red
cells will be unable to bind additional oxygen to increase the pO2.
As a result, the pO2 level of the blood

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remains low, which acts as a stimulus to cause hyperventilation,
resulting in either normal or low CO2 levels.
A mismatch in ventilation and perfusion can arise due to either
reduced ventilation of part of the lung or reduced perfusion.
Ventilation/perfusion mismatch Mechanical ventilation can
alter two opposing forms of ventilation/perfusion mismatch (V/Q
mismatch), dead space (areas that are overventilated relative to
perfusion; V>Q) and shunt (areas that are underventilated relative
to perfusion; V<Q). By increasing ventilation (V), the institution of
positive pressure ventilation will worsen dead space but improve
shunt.
Increased dead space Dead space reflects the surface area
within the lung that is not involved in gas exchange. It is the sum of
the anatomic plus alveolar dead space. Alveolar dead space (also
known as physiologic dead space) consists of alveoli that are not
involved in gas exchange due to insufficient perfusion (ie,
overventilated relative to perfusion). Positive pressure ventilation
tends to increase alveolar dead space by increasing ventilation in
alveoli that do not have a corresponding increase in perfusion,
thereby worsening V/Q mismatch and hypercapnia.
Reduced shunt An intraparenchymal shunt exists where there
is blood flow through pulmonary parenchyma that is not involved in
gas exchange because of insufficient alveolar ventilation. Patients
with respiratory failure frequently have increased intraparenchymal
shunting due to areas of focal atelectasis that continue to be
perfused (ie, regions that are underventilated relative to perfusion).
Treating atelectasis with positive pressure ventilation can reduce
intraparenchymal shunting by improving alveolar ventilation,
thereby improving V/Q matching and oxygenation.
This is particularly true if PEEP is added. (See "Positive end-
expiratory pressure (PEEP)" and "Measures of oxygenation and
mechanisms of hypoxemia", section on 'V/Q mismatch'.)
3.
Be able to calculate an Aa gradient. Be able to interpret an Aa gradient.
The alveolar to arterial (A-a) oxygen gradient is a common
measure of oxygenation ("A" denotes alveolar and "a" denotes
arterial oxygenation). It is the difference between the amount of the
oxygen in the alveoli (ie, the alveolar oxygen tension [PAO
2
]) and
the amount of oxygen dissolved in the plasma (PaO
2
):
A-a oxygen gradient = PAO
2
- PaO
2
PaO
2
is measured by arterial blood gas, while PAO
2
is calculated
using the alveolar gas equation:
PAO
2
= (FiO
2
x [Patm - PH
2
O]) - (PaCO
2
÷ R)

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Final Exam-Study Guide Week 6 and 7 1. Interpret arterial blood gases (ABG). Differentiate alkalosis/ acidosis and respiratory / metabolic 2. Identify a ventilation – perfusion mismatch and how to treat it If there is a mismatch between the alveolar ventilation and the alveolar blood flow, this will be seen in the V/Q ratio. If the V/Q ratio reduces due to inadequate ventilation, gas exchange within the affected alveoli will be impaired. As a result, the capillary partial pressure of oxygen (pO2) falls and the partial pressure of carbon dioxide (pCO2) rises. To manage this, hypoxic vasoconstriction causes blood to be diverted to better ventilated parts of the lung. However, in most physiological states the hemoglobin in these well-ventilated alveolar capillaries will already be saturated. This means that red cells will be unable to bind additional oxygen to increase the pO2. As a result, the pO2 level of the blood remains low, which acts as a stimulus to cause hyperventilation, resulting in either normal or low CO2 levels. A mismatch in ventilation and perfusion can arise due to either reduced ventilation of part of the lung or reduced perfusion. Ventilation/perfusion mismatch — Mechanical ventilation can alter two opposing forms of ventilation/perfusion mismatch (V/Q mismatch), dead space (areas that are overventilated relative to perfusion; V>Q) and shunt (areas that are underventilated relative to perfusion; V ...
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