Millers_Anesthesia_thoracic Chapter 53
Highlights
- At the time of initial assessment, cancer patients should be
assessed for the “4 Ms” associated with malignancy (Box
53.4): mass effects, metabolic abnormalities, metastases,
and medications. (View Highlight)
- A properly sized, left-sided DLT should
have a bronchial tip 1 to 2 mm smaller than the patient’s left
bronchus diameter to allow for the space occupied by the
deflated bronchial cuff (View Highlight)
- In adults,
depth, measured at the teeth, for a properly positioned DLT,
will be approximately 12 + (patient height/10) cm (View Highlight)
- In a healthy, conscious, spontaneously breathing patient,
the ventilation of the dependent lung will increase
approximately 10% when the patient is turned to the
lateral position (View Highlight)
- Although the ventilation will not
change significantly once the nondependent hemithorax
is open, the FRC of this nondependent lung will tend to
increase approximately 10% (View Highlight)
- When the chest is open, due to disruption of the chest
wall, both lungs tend to collapse to a minimal lung vol-
ume if expiration is prolonged. Thus the end-expiratory
volume of each lung is directly a function of the time
allowed for expiration. The compliance of the entire
respiratory system increases significantly once the non-
dependent hemithorax is open. (View Highlight)
- The
respiratory systems of mammals do not function adequately
with an open hemithorax due to two physiologic problems.
First, paradoxical ventilation (also called “pendelluft”) in
which gas moves into the open-chest lung from the intact
lung during expiration and then reverses flow during inspi-
ration. This leads to hypercapnia and hypoxemia. And
second, due to the swinging motion of the mediastinum
between the hemithoraces during the respiratory cycle,
which interferes with cardiac preload and causes hemody-
namic instability. (View Highlight)
- Because of the fall in FRC and compliance of the
dependent lung in the lateral position, application of
PEEP selectively to this lung only (using a DLT and two
anesthetic circuits), will improve gas exchange.132 This
is different than the effect of nonselectively applying
PEEP to both lungs in the lateral position where PEEP
tends to preferentially distribute to the most compliant
lung regions and will tend to hyperinflate the nonde-
pendent lung without causing any improvement in gas
exchange (View Highlight)
- Atelectasis will develop in an average of 6% of the lung
parenchyma after induction of anesthesia in the supine
position. This atelectasis will be evenly distributed in the
dependent portions of both lungs (View Highlight)
- Turning the patient to
the lateral position, there will be a slight decrease of total
atelectasis to 5% of lung volume but this will now be con-
centrated totally in the dependent lung. (View Highlight)
- Gravity has some effect on distribution of pul-
monary blood flow. In the lateral position, the blood flow
to the dependent lung is generally thought to be increased
by 10% compared to the same lung in the supine posi-
tion (View Highlight)
- Pulmonary arteriovenous
shunt during general anesthesia will usually increase from
approximately 5% in the supine position to 10% to 15% in
the lateral position. (View Highlight)