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USMLE Step 1

USMLE Step 2

Physiologic Dead Space (VD)

Tidal Volume (VT)

Which of the following most closely describes the volume of air displaced between normal inspiration and expiration in the absence of extra effort?

Partial pressure of arterial CO2 (PaCO2)

Which of the following variables in the equation for physiologic dead space (VD) can be measured using arterial blood gas (ABG)?

Partial pressure of CO2 in expired air (PECO2)

Which of the following variables in the equation for physiologic dead space (VD) can be obtained using capnometry?

VD = TV x (PaCO2-PECO2) / PaCO2

Which of the following equations is used to calculate physiologic dead space (VD)?

A-a Gradient

Partial pressure of alveolar oxygen (PAO2)

Which value is included in the formula for the A-a gradient?

Partial Pressure of Arterial O2 (PaO2)

Normal 10 to 15 mmHg

Which of the following number ranges or values are best associated with a normal A-a gradient?

Hypoxemia with an Abnormal A-a Gradient

Shunting, dead space, and diffusion problems can all contribute to what?

Diffusion problem

An abnormal A-a gradient can be due to what?

Shunting (Low V/Q)

Dead space (high V/Q)

Alveolar Gas Equation

Partial Pressure of Alveolar Oxygen (PAO2)

Which value does the alveolar gas equation attempt to obtain?

Partial Pressure of Oxygen in the Inspired Air (PIO2)

Which of the following values typically equals 150 mmHg?

PIO2 Normally Approximated = 150 mmHg

Which of the following is most accurate regarding PIO2?

Arterial Partial Pressure of CO2 (PaCO2)

A patient can be classified as hyperventilated or hypoventilated primarily based on which value?

Respiratory Quotient (R)

What is another name for the value of CO2 produced divided by O2 consumed?

R Normally Approximated = 0.8

Which of the following is most accurate regarding the respiratory quotient?

PAO2 = PIO2 - (PaCO2/R)

Which of the following best describes the Alveolar Gas Equation?

Equation

Winter's Formula

Evaluates Respiratory Compensation

Which of the following is the most appropriate utility of Winter's formula?

Used in Metabolic Acidosis

In which of the following conditions is Winter's formula most useful?

(HCO3 x 1.5 ) + 8 plus-minus 2 = PCO2

Which of the following is Winter's formula?

Steps

Bicarbonate (HCO3) x 1.5

In Winter's formula, bicarbonate should be multiplied by which of the following?

In Winter's formula, which of the following is the most likely next step after multiplying bicarbonate (HCO3) x 1.5?

± 2

Complete the following equation for Winter's formula: (HCO3 x 1.5 ) + 8 ________________________ =  PCO2.

= Expected Value for PCO2

Winter's formula is used to solve for which of the following?

Light's Criteria

Determines Transudative vs. Exudative Source of Pleural Effusion

Which of the following conditions is Light's criteria best used to determine?

Exudate if (At Least One of the Following):

Effusion/Serum Protein Ratio > 0.5

Which of the following conditions would best describe an exudative effusion according to Light's criteria if met?

Effusion/Serum LDH Ratio > 0.6

Effusion LDH > Two-thirds Upper Serum LDH Range

Respiratory Calculations

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