Thoracic Chapter Flashcards
Ch 25-Anesthesia for thoracic surgery
What is the dependent lung? What does it have more of?
It’s always the lung that is down (the down lung). It has more blood flow
In the awake state (spontaneously breathing), what does the dependent lung receive more of?
The dependent lung also receives more ventilation because: (1) contraction of the dependent hemidiaphragm is more efficient compared with the nondependent [upper] hemidiaphragm and (2) the dependent lung is on a more favorable part of the compliance curve
T/F Ventilation and perfusion are NOT matched in lateral decubitus spontaneous vent
FALSE. They are matched during lat decubitus spontaneous vent
With induction of anesthesia, which lung is better ventilated?
The decrease in functional residual capacity (FRC) with induction of general anesthesia moves the upper lung to a more favorable part of the compliance curve, but moves the lower lung to a less favorableposition (Figure 25-2). As a result, the upper lung is ventilated more than the dependent lower lung; ventilation/perfusion mismatching occurs because the dependent lung continues to have greater perfusion.
How does the bean bag mess stuff up?
Using a rigid “bean bag” to maintain the patient in the lateral decubitus position further restricts movement of the dependent hemithorax.
W/out one lung ventilation, what does PPV do to the non-dependent lung?
It makes it more compliant, allowing for more ventilation of the non-dependent (upper) lung
Explain what negative pleural pressure does to the lung
The lungs are normally kept expanded by a negative pleural pressure—the net result of the tendency of the lung to collapse and the chest wall to expand. When one side of the chest is opened, the negative pleural pressure is lost, and the elastic recoil of the lung on that side tends to collapse it.
Explain paradoxical respiration in a spontaneously breathing patient
Spontaneous ventilation in a patient with an open pneumothorax also results in to-and-fro gas flow between the dependent and nondependent lung (paradoxical respiration [pendeluft]). During inspiration, the pneumothorax increases, and gas flows from the upper lung across the carina to the dependent lung. During expiration, the gas flow reverses and moves from the dependent to the upper lung
Patient develops a large right to left intrapulmonary shunt when what?
When the patient has collapse of the operative lung
On one lung ventilation, the mixing of unoxygenated blood from collapsed lung with oxygenated blood from still ventilated lung does what to A-a O2 gradient? It often results in what?
During one-lung ventilation, the mixing of unoxygenated blood from the collapsed upper lung with oxygenated blood from the still-ventilated dependent lung widens the alveolar-to-arterial (A-a) O2 gradient and often results in hypoxemia.
HPV does what to the non-ventilated lung as far as blood flow?
Fortunately, blood flow to the nonventilated lung is decreased by hypoxic pulmonary vasoconstriction (HPV) and possibly surgical compression of the upper lung.
When HPV is inhibited, what increases?
Pulmonary admixture, and worsening of the right to left shunt
What factors are known to inhibit HPV? Name 6.
Factors known to inhibit HPV (increasing venous admixture), and thus worsen the right-to-left shunting, include (1) very high or very low pulmonary artery pressures; (2) hypocapnia; (3) high or very low mixed venous Po2; (4) vasodilators such as nitroglycerin, nitroprusside, phosophodiesterase inhibitors (milrinone and inamrinone), β-adrenergic agonists, calcium channel blockers; (5) pulmonary infection; and (6) inhalation anesthetics.
Why are factors that decrease blood flow to dependent lung bad?
Factors that decrease blood flow to the ventilated lung can be equally detrimental; they counteract the effect of HPV by indirectly increasing blood flow to the collapsed lung, meaning more perfusion without ventilation, bigger right to left shunt
What are the factors that decrease flow to the dependent (non-ventilated) lung?
Such factors include (1) high mean airway pressures in the ventilated lung due to high positive end-expiratory pressure (PEEP), hyperventilation, or high peak inspiratory pressures; (2) a low Fio2, which produces hypoxic pulmonary vasoconstriction in the ventilated lung; (3) vasoconstrictors that may have a greater effect on normoxic vessels than hypoxic ones; and (4) intrinsic PEEP that develops due to inadequate expiratory times.
