Respiratory physiology and general stuff

Question 1

What lung parameter is improved with the addition of PEEP in ARDS patients?

Answer 1

functional residual capacity

Question 2

When in the respiratory cycle does PEEP maximize alveolar recruitment?

Answer 2

end expiration

Question 3

What is a consequence of PEEP on cardiac function?

Answer 3

increases pulmonary vascular resistance leading to impeding R vascular stroke volume and therefore L ventricular filling

Question 4

What is thought to initiate the inflammatory cascade in ARDS?

Answer 4

release of IL-1 by neutrophils and TNF by macrophages/monocytes

Question 5

What type of epithelial cells are injured in ARDS?

Answer 5

type 1 and type 2
-d/t degranulation of neutrophils
-leads to exudation of protein-rich fluid, erythrocytes, and plts into distal air spaces

Question 6

What is the treatment for methemoglobinemia?

Answer 6

methylene blue

Question 7

What are the expected PFT trends in a pt w/ COPD?

Answer 7

FEV1 decreases FVC decreases/normal FEV1/FVC decreases
-FVC = forced vital capacity
-if FEV1/FVC is less than normal/expected think obstructive pattern

Question 8

What is West’s lung zone 1?

Answer 8

Pav > Pa > Pv
V/Q > 1
-lung is ventilated but not perfused
-doesn’t occur normally
-see in reduced pulmonary artery pressures, ie. hemorrhage (reduces Pa) or increased alveolar pressures (PPV)

Question 9

What is West’s lung zone 2?

Answer 9

Pa > Pav > Pv
V/Q ~1
-optimal ventilation and perfusion matching
-see intermittent blood flow
-typical for upper portions of lung in an upright person

Question 10

What is West’s lung zone 3?

Answer 10

Pa > Pv > Pav
V/Q < 1
-see at lung bases
-continuous blood flow and highest blood flow
-perfusion > ventilation
-where SG catheters are placed

Question 11

What effect does PPV have on CO?

Answer 11

increases it
-increased intrapleural pressure leads to increased aortic pressures
-increased aortic pressures lead to reduced SVR and LV afterload d/t baroreceptors
-all of that increases CO

Question 12

How do you calculate A-a gradient?

Answer 12

A-a = PAO2 - PaO2
-normal range 5 - 10

Question 13

What is the alveolar gas equation?

Answer 13

PAO2 = (FiO2 x [Patmos - PH20]) - (PaCO2/RQ)
-Patmos = 760mmHg at sea level
-PH2O is water vapor pressure at 37deg = 47mmHg
-RQ = CO2 eliminated / O2 consumed (normal 0.8)

Question 14

How does the A-a gradient change with age?

Answer 14

it increases

Question 15

What is the equation for oxygen delivery?

Answer 15

DO2 = CO x Ca O2 x 10mL/min
-or-
DO2 = CO x (1.34 x Hgb x SaO2) x10
-CO = cardiac output
-CaO2 = oxygen content in arterial blood

Question 16

How do you calculate CaO2 (oxygen content in arterial blood)?

Answer 16

CaO2 = (1.34 x Hgb x SaO2) + (0.003 x PaO2)

Question 17

What is the normal oxygen delivery?

Answer 17

900 - 1100mL/min

Question 18

How do you calculation minute ventilation?

Answer 18

MV = Tv (in L) x RR

Question 19

What West’s zone of the lung is descriptive of what is seen in PPV?

Answer 19

zone 1 and results in ventilation exceeding perfusion
-increases physiologic dead space

Question 20

What is the inspiratory reserve volume (IRV)?

Answer 20

amount of air that can be inhaled with maximal effort in excess of tidal volume

Question 21

What is the residual volume?

Answer 21

The amount of air left in the lungs after the expiratory reserve volume (ERV), or the amount of air in excess of tidal volume that can be exhaled with maximum effort

Question 22

What is the functional residual capacity (FRC)?

Answer 22

amount of air remaining in the lungs after normal tidal volume
-the 2nd of the two volumes that can be manipulated w/ mechanical ventilation
-residual volume + ERV

Question 23

What mechanical ventilation setting(s) can be changed to change the FRC?

Answer 23

-PEEP increases FRC
-any increase in mean airway pressure

Question 24

How do you calculate lung compliance?

Answer 24

compliance = (tidal vol mL) / [plateau pressure (cmH2O) - PEEP(cmH2O)]
-or-
compliance = (exhaled tidal vol mL) / [end inspiratory pressure (cmH2O) - PEEP(cmH2O)]

Question 25

What is compliance?

Answer 25

change in lung volume over the change in transpulmonary lung pressure -lower compliance requires more pressure to produce the same level of lung expansion

Question 26

How is plateau pressure measured?

Answer 26

With an inspiratory pause at the end of inspiration

Question 27

What is the normal range for lung compliance?

Answer 27

50-80mL/cmH2O -stiff or non-compliant lungs are typically 10-20mL/cmH2O

Question 28

What does a V/Q ratio < 1 indicate?

Answer 28

blood flow is excessive compared to ventilation -intrapulmonary shunting -most commonly secondary to inhaled gas not reaching alveoli d/t: -PNA, pulmonary contusions, ARDS -has poor response to supplement O2 -P/F below 200 correlates to a shunt of >20%

Question 29

What does a V/Q ratio > 1 indicate?

Answer 29

ventilation is greater than blood flow -there are areas of where alveolar gas does not participate in ventilatory exchange -known as dead space ventilation -physiologic in the large airways (trachea) -pathologic when alveolar capillary interface is destroyed -COPD, excessive PEEP, large PE

Question 30

What two processes cause hypercarbia?

Answer 30

-increased CO2 production -carbohydrate overfeeding -vent dependent pts -hypoventilation -intoxication -neuromuscular diseases

Question 31

In COPD what leads to the areas of low V/Q seen?

Answer 31

-bronchospasm -inflammation -airway obstruction d/t excessive mucus

Question 32

In pts w/ COPD does NIPPV help improve the areas of high V/Q or the areas of low V/Q to improve oxygenation?

Answer 32

areas of low V/Q

Question 33

What are the normal values of mixed venous oxygen saturations (SvO2)?

Answer 33

68-77%

Question 34

What circumstances can a patient have a normal appearing SvO2 but hypoxia is actually present?

Answer 34

-high oxygen delivery (DO2) and high oxygen consumption (VO2) -low DO2 and low VO2

Question 35

What would be the expected FEV1, FVC, and FEV1/FVC for COPD?

Answer 35

-FEV1 decreased -FVC decreased/normal -FEV1/FVC ratio decreased

Question 36

What FEV1/FVC ratio is suspicious for an obstructive pattern?

Answer 36

less than the lower limit of normal

Question 37

How does hypovolemia change pressures within the lung (West zones)?

Answer 37

-decreasing circulating volume increases dead space -converts zone 3 areas (Pa > Pv > Pav) into zone 1 (Pav > Pa > Pv) and zone 2 (Pa > Pav > Pv)

Question 38

What would you see on a flow-volume loop in a patient with an extrathoracic obstruction?

Answer 38

flattening of the inspiratory component (the curve under the line) -unilateral vocal cord paralysis -intratracheal lipoma or other mobile tumors

Question 39

What would you see on a flow-volume loop in a patient with an intrathoracic obstruction?

Answer 39

flattening of the expiratory component -bronchogenic cysts -intrathoracic tracheomalacia

Question 40

What would you see on a flow-volume loop in a patient with a fixed airway obstruction?

Answer 40

flattening of both components of the loop -tracheal stenosis

Question 41

What would you see on a flow-volume loop in a patient with a lower airway obstruction?

Answer 41

scooped out appearance of expiratory loop from premature airway closure -COPD

Question 42

What is the single biggest parameter that determines the oxygen content of blood?

Answer 42

Hgb [CaO2 = (1.34xHgbxSaO2) + (0.003xPaO2)]