Respiratory physiology and general stuff Flashcards
What lung parameter is improved with the addition of PEEP in ARDS patients?
functional residual capacity
When in the respiratory cycle does PEEP maximize alveolar recruitment?
end expiration
What is a consequence of PEEP on cardiac function?
increases pulmonary vascular resistance leading to impeding R vascular stroke volume and therefore L ventricular filling
What is thought to initiate the inflammatory cascade in ARDS?
release of IL-1 by neutrophils and TNF by macrophages/monocytes
What type of epithelial cells are injured in ARDS?
type 1 and type 2
-d/t degranulation of neutrophils
-leads to exudation of protein-rich fluid, erythrocytes, and plts into distal air spaces
What is the treatment for methemoglobinemia?
methylene blue
What are the expected PFT trends in a pt w/ COPD?
FEV1 decreases FVC decreases/normal FEV1/FVC decreases
-FVC = forced vital capacity
-if FEV1/FVC is less than normal/expected think obstructive pattern
What is West’s lung zone 1?
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)
What is West’s lung zone 2?
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
What is West’s lung zone 3?
Pa > Pv > Pav
V/Q < 1
-see at lung bases
-continuous blood flow and highest blood flow
-perfusion > ventilation
-where SG catheters are placed
What effect does PPV have on CO?
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
How do you calculate A-a gradient?
A-a = PAO2 - PaO2
-normal range 5 - 10
What is the alveolar gas equation?
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)
How does the A-a gradient change with age?
it increases
What is the equation for oxygen delivery?
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
How do you calculate CaO2 (oxygen content in arterial blood)?
CaO2 = (1.34 x Hgb x SaO2) + (0.003 x PaO2)
What is the normal oxygen delivery?
900 - 1100mL/min
How do you calculation minute ventilation?
MV = Tv (in L) x RR
What West’s zone of the lung is descriptive of what is seen in PPV?
zone 1 and results in ventilation exceeding perfusion
-increases physiologic dead space
What is the inspiratory reserve volume (IRV)?
amount of air that can be inhaled with maximal effort in excess of tidal volume
What is the residual volume?
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
What is the functional residual capacity (FRC)?
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
What mechanical ventilation setting(s) can be changed to change the FRC?
-PEEP increases FRC
-any increase in mean airway pressure
How do you calculate lung compliance?
compliance = (tidal vol mL) / [plateau pressure (cmH2O) - PEEP(cmH2O)]
-or-
compliance = (exhaled tidal vol mL) / [end inspiratory pressure (cmH2O) - PEEP(cmH2O)]
What is compliance?
change in lung volume over the change in transpulmonary lung pressure
-lower compliance requires more pressure to produce the same level of lung expansion
How is plateau pressure measured?
With an inspiratory pause at the end of inspiration
What is the normal range for lung compliance?
50-80mL/cmH2O
-stiff or non-compliant lungs are typically 10-20mL/cmH2O
What does a V/Q ratio < 1 indicate?
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%
What does a V/Q ratio > 1 indicate?
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
What two processes cause hypercarbia?
-increased CO2 production
-carbohydrate overfeeding
-vent dependent pts
-hypoventilation
-intoxication
-neuromuscular diseases
In COPD what leads to the areas of low V/Q seen?
-bronchospasm
-inflammation
-airway obstruction d/t excessive mucus
In pts w/ COPD does NIPPV help improve the areas of high V/Q or the areas of low V/Q to improve oxygenation?
areas of low V/Q
What are the normal values of mixed venous oxygen saturations (SvO2)?
68-77%
What circumstances can a patient have a normal appearing SvO2 but hypoxia is actually present?
-high oxygen delivery (DO2) and high oxygen consumption (VO2)
-low DO2 and low VO2
What would be the expected FEV1, FVC, and FEV1/FVC for COPD?
-FEV1 decreased
-FVC decreased/normal
-FEV1/FVC ratio decreased
What FEV1/FVC ratio is suspicious for an obstructive pattern?
less than the lower limit of normal
How does hypovolemia change pressures within the lung (West zones)?
-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)
What would you see on a flow-volume loop in a patient with an extrathoracic obstruction?
flattening of the inspiratory component (the curve under the line)
-unilateral vocal cord paralysis
-intratracheal lipoma or other mobile tumors
What would you see on a flow-volume loop in a patient with an intrathoracic obstruction?
flattening of the expiratory component
-bronchogenic cysts
-intrathoracic tracheomalacia
What would you see on a flow-volume loop in a patient with a fixed airway obstruction?
flattening of both components of the loop
-tracheal stenosis
What would you see on a flow-volume loop in a patient with a lower airway obstruction?
scooped out appearance of expiratory loop from premature airway closure
-COPD
What is the single biggest parameter that determines the oxygen content of blood?
Hgb
[CaO2 = (1.34xHgbxSaO2) + (0.003xPaO2)]
