Pulmonary Flashcards
What is physiologic dead space?
Anatomic (nasal, oropharynx, terminal & respiratory bronchioles) and alveolar; ~2 ml/kg (150 ml)
shunt fraction equation? Normal percentage?
Qs/Qt = (CcO2 - CaO2)/(CcO2 - CvO2); CcO2 is pulmonary capillary O2 content, CvO2 is mixed venous O2 content; 4-5%
Dead space equation, amount
Vd/Vt = (PaCO2 - PETCO2)/PaCO2; ~300 ml
Alveolar gas equation
PAO2 = FiO2(Patm - PH2O) - PaCO2/0.8
Right shift oxyhemoglobin dissociation curve (4)
High CO2, high H+, high temp, high 2,3 DPG (anemia, cirrhosis, increased altitude)
Left shift oxyhemoglobin dissociation curve (7)
Low CO2, low H+, low temperature, low 2,3 DPG, fetal hemoglobin, methemoglobin, carboxyhemoglobin
What is FRC?
ERV + RV
When does FRC decrease? (6)
Pregnancy, ascites, neonates, GA, obesity, supine position
When does FRC increase?
PEEP and emphysema
What happens when closing capacity is greater than FRC?
Shunting
What is closing capacity?
CC = CV + RV; volume at which small airways in the lung close
When does CC increase?
Age, chronic bronchitis, LV failure, surgery, smoking, obesity
When is closing capacity lowest?
During teenage years
Arterial O2 content equation
CaO2 = (1.34 x HgB x sat) + (0.003 x PaO2)
What is the P50?
Partial pressure of oxygen at which hemoglobin is 50% saturated
P50 adults? Infants?
27 mm Hg and 19 mm Hg
Partial pressure and O2 sat of mixed venous?
40 mm Hg and 75%
Partial pressure at 90% sat?
60 mm Hg
What happens with a right shift in the Oxy-Hb curve?
Increased unloading of oxygen to tissues
What happens with a left shift in the Oxy-Hb curve?
Decreased unloading of oxygen to tissues
What is the Bohr effect?
Oxy-Hb dissociation curve shifts with changes in CO2
What is the Haldane effect?
The more deoxygenated blood is the more CO2 (in the form of carbamino compounds) it can carry without altering the PaCO2
Where should mixed venous O2 sat be measured?
Pulmonary artery
What is normal PvO2 and sat?
35-45 mm Hg and 65-75% sat
What factors determine PvO2?
Cardiac output, O2 consumption, amount of hemoglobin, loading of hemoglobin
What do carotid and aortic bodies respond to and what are their effects?
Respond to PaO2 levels lower than 60 (not low O2 content/sat) carotid bodies impact ventilation and aortic bodies impact circulation
Where are chemosensitive areas in brainstorm located? What nerves are nearby?
Medulla, close to IX glossopharyngeal and X vagus
Describe CO2 response curve and its parameters
Ventilatory response is linear between CO2 20-80, CO2 becomes ventilatory depressant >100
What does left shift of CO2 curve indicate and what causes it?
Indicates increased sensitivity to CO2; arterial hypoxemia, metabolic acidemia, central causes (increased ICP, anxiety, fear, cirrhosis)
What does right shift of CO2 curve indicate and what causes it?
Indicates decreased sensitivity to CO2; aminophylline, salicylates, catecholamines, narcotics, physiologic (metabolic alkalemia, denervation of peripheral chemoreceptors, normal sleep, drugs)
What causes a down and right CO2 curve shift?
High dose narcotics, volatile anesthetics (with higher doses curve flattens with little CO2 response)
Zone 1
PA > Ppa > Ppv
Zone 2
Ppa > PA > Ppv
Zone 3
Ppa > Ppv > PA
FiO2 - PaO2 relationship
Every 10% increase in FiO2 equals 50 torr PaO2 increase
What is hypoxic pulmonary vasoconstriction? Causes?
Regional pulmonary vasoconstriction in response to regional lung hypoxia (PAO2); mixed venous <30 indirectly induces HPV
Benefits of HPV
Decreases shunting by decreasing blood flow by 50%
What decreases HPV response? (10)
Increased pulmonary vascular pressure, increased cardiac output, hypocapnea, acidosis, alkalosis, hypothermia, CCB, nitroprusside, isoproterenol, high frequency ventilation
What inhibits HPV?
Inhaled anesthetics, nitrous
Define dead space
Ventilation with no perfusion; V/Q ratio is infinity
Define shunt
Perfusion with no ventilation; V/Q ratio is 0
Altitude
Inspired O2 diminishes as altitude increases and barometric pressure decreases
A-a gradient
About 1/4 patients age
RA normal A-a gradient?
5-10 mm Hg
100% A-a gradient?
20-30 mm Hg
What causes shunt?
Thesbian veins, bronchial veins, R-L intracardiac shunt, pneumothorax, bronchospasm, pneumonia
How does shunt affect PaO2 and PaCO2?
Linear decline in PaO2 with shunting. PaCO2 does not increase until shunt fraction exceeds 50% (because of increased solubility of CO2)
Why does A-a gradient increase under GA?
Decreases in cardiac output, FRC, lung and chest wall compliance. Airway resistance is increased.
When FRC greatest after surgery? How long does decrease last?
Greatest 3-5 days post (most severe with upper abdominal) and lasts 10-14 days
How much O2/min is removed from alveoli? CO2 produced?
250 ml/min O2 removed; 200 ml/min CO2 produced
What is the treatment for pulmonary edema?
100% O2, PEEP, nitroglycerin to reduce preload, inotrope to increase cardiac contractility, LASIK, fluid restriction, PA catheter
What causes pulmonary edema? (4)
- Increased capillary pressure - mitral stenosis, heart failure, fluid retention, negative pressure pulmonary edema 2. Increased capillary leak - aspiration, ARDS, burn, neurogenic 3. Decreased oncotic pressure - low albumin from burn/poor nutrition 4. Lymphatic obstruction - tumor
What symptoms are associated with cardiogenic pulmonary edema?
Bibasilar rales, patchy infiltrates, and pink, frothy sputum, high PCWP
What causes non-cardiogenic pulmonary edema? Symptoms?
Massive blood transfusion, smoke inhalation, sepsis, DIC; bibasilar rales
Pulmonary vascular resistance equation
PVR =
What causes pulmonary HTN? (3)
Increased blood flow - L-R cardiac shunt; increased pulm resistance - hypoxia, hypercarbia, acidosis, lung disease, pulm vascular bed destruction, embolism; increased backward pressure - mitral stenosis/regurg
How does smoking cause hypoxia?
It increases closing capacity relative to FRC
What happens after 24-48 hours after smoking cessation? One week? Months?
Decrease carboxyhemoglobin levels to normal (2.5%), corrects left shift of oxy-hemoglobin curve. Decreased pulm secretions. Normal mucociliary clearance.
Post-op complications associated with smoking?
Atelectasis, pneumonia, hypoxia
How many weeks are needed of smoking cessation to decrease chance of postoperative pulm complications?
6-8 weeks
What is nitric oxide?
Endothelial derived relaxin factor that vasodilates smooth muscle
How is NO deactivated?
Binding to hemoglobin
