RRT: ACCS EXAM QUESTIONS AND
ANSWERS
Respiratory muscle weakness - when inspiratory muscles tire, VT decreases and RR
increases
Normal PaCO2 - ANSWER-40 torr
Normal PetCO2 - ANSWER-34-36 torr
3-5%
Normally 4-6 mmHg lower than PaCO2
Normal ETCO2 percent - ANSWER-3-5 %
Increase PECO2 or PETCO2% - ANSWER-indicates decreased ventilation (ventilatory
failure)
Decrease PECO2 or PETCO2% - ANSWER-indicates increase in ventilation or
decreased perfusion (deadspace disease: pulmonary embolism, hypovolemia)
Low PETCO2 reading immediately following intubation - ANSWER-ET tube is in the
esophagus
Colormetric Detection Device Normal - ANSWER-Purple - Poor
Yellow - Normal
False readings can occur in patients who have been without CPR for a period of time
VD - ANSWER-Deadspace Ventilation
Anatomic Deadspace - ANSWER-amount of inspired tidal volume that does not enter
the alveoli.
Approx. 1 mL per lb of IBW (i.e., 150 lb = 150 mL VD)
Used to approximate alveolar ventilation
Alveolar Deadspace - ANSWER-amount of alveolar ventilation that has no blood
perfusion. Occurs with a Pulmonary Embolism (P.E.)
Physiologic Deadspace - ANSWER-is the sum of anatomic and alveolar deadspace and
is estimated by the Deadspace to Tidal Volume (VD/VT ) Ratio
,VD/VT (%) Ratio - ANSWER-Deadspace to Tidal Volume Ratio
Normal 20 - 40% (up to 60% for ventilated patients)
Acceptable: < 60%
Unacceptable: >60%
Increase in VD/VT ratio indicates a deadspace producing disease (PE, ARDS)
Mechanical Deadspace - ANSWER-amount of circuit tubing between the patient and the
wye adapter in the ventilator circuit.
Approx. 10 mL per inch of flex tubing (i.e., 5" = 50 mL VD)
Can be used to adjust PaCO2 levels
Minute Ventilation (VE) Formula - ANSWER-VE = (VT x F)
Example: A patient is recieving volume ventilation with a tidal volume of 800 mL at a
frequency of 10 breaths per minute.
VE = 800 x 10 = 8000 mL or 8 L
Alveolar Minute Ventilation (VA) Formula - ANSWER-VA = (VT - VD) x f
Example: 68 kg (150 lb) patient is recieving volume ventilation at a tidal volume of 600
mL and a rate of 10.
VA = (600 - 150) x 10 = 4500 mL or 4.5 L
Deadspace to Tidal Volume Ratio (VD/VT) Formula - ANSWER-((PaCO2 - PECO2) /
PaCO2) X 100
Example: Calculate the VD/VT ratio for a patient who has a PaCO2 of 40 torr and a
PECO2 of 30 torr.
((40 - 30)/40) X 100
(10/40) X 100
0.25 or 25%
PECO2 - ANSWER-Average PCO2 of the exhaled air and can be measured by a
capnograph.
Deadspace Ventilation (VD) Formula - ANSWER-VD/VT x VT = VD
Example: A patient with a VD/VT ratio of 25% is receiving mechanical ventilation as a
tidal volume or 800 mL. What is the patients' VD?
VD = 0.25 x 800 mL = 200 mL
,PaO2 - ANSWER-80-100 torr
Alveolar Oxygen Tension (PAO2)
The Alveolar Air Equation - ANSWER-Calculates the partial pressure of oxygen (PO2)
in the alveoli.
Formula: PAO2 = (PB - PH2O) FiO2 - (PaCO2/0.8)
SHORCUT: PAO2 = (FiO2 x 7) - (PaCO2 + 10)
Example: Calculate the PAO2 for a patient receiving 50% oxygen with a PaCO2 of 40
torr at the barometric pressure of 747 torr.
(747 - 47) .50 - (40/0.8) (.50 x 7) - (40 + 10)
(700 x .50) - 50 (350) - (50)
350 - 50 300
300 torr
Alveolar-Arterial Oxygen Gradient (P(A-a)O2 or A-aDO2 or A-a Gradient - ANSWER-
Estimates the difference (gradient) between alveolar and arterial PO2
Best estimated when a patient is breathing 100% O2 for 20 min or more.
Formula: A-aDO2 = PAO2 - PaO2
V/Q Mismatch oxygen therapy - ANSWER-if PaO2 increases with oxygen therapy
Shunt oxygen therapy - ANSWER-if PaO2 does not increase with oxygen therapy
A-a Gradient Normal Values on 100% O2 - ANSWER-25-60 torr - Normal
66-300 torr V/Q Mismatch
>300 torr shunting
Arterial Oxygen Content (CaO2) - ANSWER-Best measurement of oxygen delivered to
the tissues, or best index of oxygen transport.
Estimates the amount of oxygen carried by hemoglobin as well as that dissolved in the
plasma.
Formula: CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
SHORTCUT: CaO2 = (Hb/3) x 4
Normal CaO2 - ANSWER-17-20 vol % (mL/dL)
Mixed Venous Oxygen Content (CvO2) - ANSWER-Total amount of oxygen carried in
the mixed venous blood.
Calculated using the same formula as CaO2 except for using mixed venous PO2
(PvO2) and saturation (SvO2).
The blood is drawn from the Pulmonary Artery through a balloon-tipped, flow-directed
(Swan-Ganz) catheter.
Formula: (Hb x 1.34 x SvO2) + (PvO2 x .003)
SHORTCUT: CVO2 = Hb
, CvO2 will decrease when cardiac output decreases
SvO2 will also decrease when cardiac output decreases
Normal CvO2 - ANSWER-12-16 vol% (14 vol%)
Arterial-Venous Oxygen Content Difference (C(a-v)O2) - ANSWER-The CvO2 is
subtracts from the CaO2.
Measures the oxygen consumption of the tissues.
Formula: C(a-v)O2 = CaO2 - CvO2
Used in the Fick equation to calculate cardiac output (L/min) or oxygen consumption
(mL/min)
C(a-v)O2 difference will increase when the CvO2 is decreasing and would indicate a
decreasing cardiac output (Inverse relationship)
Normal C(a-v)O2 - ANSWER-4-5 vol%
P/F Ratio (PaO2/FiO2) - ANSWER-Normal 380 or greater
Mild ARDS <200-300
Moderate ARDS <100-200
Severe ARDS <100 (Diffuse bilateral opacities)
Shunt Equation (QS/QT) - ANSWER-The portion of cardiac output (QT) that is shunted
(QS).
Formula:
((A-aDO20)(.003) / (A-aDO2)(.003) + C(a-v)O2)
SHORTCUT: Take first digit of A-aDO2
Add +1
Multiply by 5
Example:
PAO2 = 400 torr
PaO2 = 100 torr
A-aDO2 = 400-100 = 300 torr
First digit = 3
Add +1 - 3 + 1 = 4
Multiply by 5 - 4 x 5 = 20
Shunt of 20%
Normal Shunt (QS/QT) Value - ANSWER-3-5%
Normal Urine Output - ANSWER-40 mL/hr (approx. 1 Liter/day)
Decreased CVP (<2 mmHg) - ANSWER-Hypovolemia
ANSWERS
Respiratory muscle weakness - when inspiratory muscles tire, VT decreases and RR
increases
Normal PaCO2 - ANSWER-40 torr
Normal PetCO2 - ANSWER-34-36 torr
3-5%
Normally 4-6 mmHg lower than PaCO2
Normal ETCO2 percent - ANSWER-3-5 %
Increase PECO2 or PETCO2% - ANSWER-indicates decreased ventilation (ventilatory
failure)
Decrease PECO2 or PETCO2% - ANSWER-indicates increase in ventilation or
decreased perfusion (deadspace disease: pulmonary embolism, hypovolemia)
Low PETCO2 reading immediately following intubation - ANSWER-ET tube is in the
esophagus
Colormetric Detection Device Normal - ANSWER-Purple - Poor
Yellow - Normal
False readings can occur in patients who have been without CPR for a period of time
VD - ANSWER-Deadspace Ventilation
Anatomic Deadspace - ANSWER-amount of inspired tidal volume that does not enter
the alveoli.
Approx. 1 mL per lb of IBW (i.e., 150 lb = 150 mL VD)
Used to approximate alveolar ventilation
Alveolar Deadspace - ANSWER-amount of alveolar ventilation that has no blood
perfusion. Occurs with a Pulmonary Embolism (P.E.)
Physiologic Deadspace - ANSWER-is the sum of anatomic and alveolar deadspace and
is estimated by the Deadspace to Tidal Volume (VD/VT ) Ratio
,VD/VT (%) Ratio - ANSWER-Deadspace to Tidal Volume Ratio
Normal 20 - 40% (up to 60% for ventilated patients)
Acceptable: < 60%
Unacceptable: >60%
Increase in VD/VT ratio indicates a deadspace producing disease (PE, ARDS)
Mechanical Deadspace - ANSWER-amount of circuit tubing between the patient and the
wye adapter in the ventilator circuit.
Approx. 10 mL per inch of flex tubing (i.e., 5" = 50 mL VD)
Can be used to adjust PaCO2 levels
Minute Ventilation (VE) Formula - ANSWER-VE = (VT x F)
Example: A patient is recieving volume ventilation with a tidal volume of 800 mL at a
frequency of 10 breaths per minute.
VE = 800 x 10 = 8000 mL or 8 L
Alveolar Minute Ventilation (VA) Formula - ANSWER-VA = (VT - VD) x f
Example: 68 kg (150 lb) patient is recieving volume ventilation at a tidal volume of 600
mL and a rate of 10.
VA = (600 - 150) x 10 = 4500 mL or 4.5 L
Deadspace to Tidal Volume Ratio (VD/VT) Formula - ANSWER-((PaCO2 - PECO2) /
PaCO2) X 100
Example: Calculate the VD/VT ratio for a patient who has a PaCO2 of 40 torr and a
PECO2 of 30 torr.
((40 - 30)/40) X 100
(10/40) X 100
0.25 or 25%
PECO2 - ANSWER-Average PCO2 of the exhaled air and can be measured by a
capnograph.
Deadspace Ventilation (VD) Formula - ANSWER-VD/VT x VT = VD
Example: A patient with a VD/VT ratio of 25% is receiving mechanical ventilation as a
tidal volume or 800 mL. What is the patients' VD?
VD = 0.25 x 800 mL = 200 mL
,PaO2 - ANSWER-80-100 torr
Alveolar Oxygen Tension (PAO2)
The Alveolar Air Equation - ANSWER-Calculates the partial pressure of oxygen (PO2)
in the alveoli.
Formula: PAO2 = (PB - PH2O) FiO2 - (PaCO2/0.8)
SHORCUT: PAO2 = (FiO2 x 7) - (PaCO2 + 10)
Example: Calculate the PAO2 for a patient receiving 50% oxygen with a PaCO2 of 40
torr at the barometric pressure of 747 torr.
(747 - 47) .50 - (40/0.8) (.50 x 7) - (40 + 10)
(700 x .50) - 50 (350) - (50)
350 - 50 300
300 torr
Alveolar-Arterial Oxygen Gradient (P(A-a)O2 or A-aDO2 or A-a Gradient - ANSWER-
Estimates the difference (gradient) between alveolar and arterial PO2
Best estimated when a patient is breathing 100% O2 for 20 min or more.
Formula: A-aDO2 = PAO2 - PaO2
V/Q Mismatch oxygen therapy - ANSWER-if PaO2 increases with oxygen therapy
Shunt oxygen therapy - ANSWER-if PaO2 does not increase with oxygen therapy
A-a Gradient Normal Values on 100% O2 - ANSWER-25-60 torr - Normal
66-300 torr V/Q Mismatch
>300 torr shunting
Arterial Oxygen Content (CaO2) - ANSWER-Best measurement of oxygen delivered to
the tissues, or best index of oxygen transport.
Estimates the amount of oxygen carried by hemoglobin as well as that dissolved in the
plasma.
Formula: CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
SHORTCUT: CaO2 = (Hb/3) x 4
Normal CaO2 - ANSWER-17-20 vol % (mL/dL)
Mixed Venous Oxygen Content (CvO2) - ANSWER-Total amount of oxygen carried in
the mixed venous blood.
Calculated using the same formula as CaO2 except for using mixed venous PO2
(PvO2) and saturation (SvO2).
The blood is drawn from the Pulmonary Artery through a balloon-tipped, flow-directed
(Swan-Ganz) catheter.
Formula: (Hb x 1.34 x SvO2) + (PvO2 x .003)
SHORTCUT: CVO2 = Hb
, CvO2 will decrease when cardiac output decreases
SvO2 will also decrease when cardiac output decreases
Normal CvO2 - ANSWER-12-16 vol% (14 vol%)
Arterial-Venous Oxygen Content Difference (C(a-v)O2) - ANSWER-The CvO2 is
subtracts from the CaO2.
Measures the oxygen consumption of the tissues.
Formula: C(a-v)O2 = CaO2 - CvO2
Used in the Fick equation to calculate cardiac output (L/min) or oxygen consumption
(mL/min)
C(a-v)O2 difference will increase when the CvO2 is decreasing and would indicate a
decreasing cardiac output (Inverse relationship)
Normal C(a-v)O2 - ANSWER-4-5 vol%
P/F Ratio (PaO2/FiO2) - ANSWER-Normal 380 or greater
Mild ARDS <200-300
Moderate ARDS <100-200
Severe ARDS <100 (Diffuse bilateral opacities)
Shunt Equation (QS/QT) - ANSWER-The portion of cardiac output (QT) that is shunted
(QS).
Formula:
((A-aDO20)(.003) / (A-aDO2)(.003) + C(a-v)O2)
SHORTCUT: Take first digit of A-aDO2
Add +1
Multiply by 5
Example:
PAO2 = 400 torr
PaO2 = 100 torr
A-aDO2 = 400-100 = 300 torr
First digit = 3
Add +1 - 3 + 1 = 4
Multiply by 5 - 4 x 5 = 20
Shunt of 20%
Normal Shunt (QS/QT) Value - ANSWER-3-5%
Normal Urine Output - ANSWER-40 mL/hr (approx. 1 Liter/day)
Decreased CVP (<2 mmHg) - ANSWER-Hypovolemia
