One lung ventilation

1. One Lung Ventilation

2. Ventilation Perfusion Relationship
in Upright Position

3. • Pleural pressure increases by
0.25 cm H2 O every centimeter
down the lung
• The increase in pleural
pressure causes a fourfold
decrease in alveolar volume
from the top of the lung to the
bottom
• When regional alveolar volume
is translated over to a regional
transpulmonary pressure-
alveolar volume curve, small
alveoli are on a steep (large
slope) portion of the curve, and
large alveoli are on a flat (small
slope) portion of the curve.
• Because the regional slope
equals regional compliance,
the dependent small alveoli
normally receive larger tidal
volume

4. • In zone 1, alveolar pressure
(PA) exceeds pulmonary artery
pressure (Ppa), and no flow
occurs because the intra-
alveolar vessels are collapsed
by the compressing alveolar
pressure
• zone 2, Ppa exceeds PA, but
PA exceeds pulmonary venous
pressure (Ppv). Flow is
determined by the Ppa-PA
difference and has been
likened to an upstream river
waterfall over a dam
• In zone 3, Ppv exceeds PA,
and flow is determined by the
Ppa-Ppv difference (Ppa - Ppv),
which is constant down this
portion of the lung
• zone 4, pulmonary interstitial
pressure becomes positive
and exceeds both Ppv and PA.
Consequently, flow in zone 4 is
determined by the Ppa-
interstitial pressure difference
(Ppa - PISF)

5. • Both blood flow and
ventilation increase
linearly with distance
down the normal
upright lung
• Because blood flow
increases from a very
low value and more
rapidly than ventilation
does with distance
down the lung, V̇ /Q ratio
decreases rapidly at
first and then more
slowly

6. • V̇ /Q inequalities have
different effects on arterial
PaCO2 than on arterial
PaO2.
• Blood passing through
underventilated alveoli
tends to retain its CO2 and
does not take up enough
O2
• Blood traversing
overventilated alveoli
gives off an excessive
amount of CO2 but cannot
take up a proportionately
increased amount of O2
• When compared with the
top of the lung, the bottom
of the lung has a low V̇ /Q
ratio and is relatively
hypoxic and hypercapnic

7. Physiology of the Lateral Decubitus
Position

8. Awake, Closed-Chest, Lateral
Decubitus Position (LDP)

9. • Gravity causes a vertical
gradient in the
distribution of pulmonary
blood flow in the LDP
also
• Vertical gradient in the
LDP is less than in the
upright position
• There is less zone 1 and
more zone 2 and 3 blood
flow in the LDP than in
the upright position
• Pulmonary blood flow is
greater in the dependent
lung than in the
nondependent lung

10. • In the lateral
decubitus position
dependent lung lies
on a relatively steep
portion and the
nondependent lung
lies on a relatively
flat portion of the
pressure-volume
curve
• Thus, in the lateral
decubitus position,
the dependent lung
receives most of the
tidal ventilation

11. Role of diaphragm
• In the LDP the dome of the lower part of the
diaphragm is pushed higher into the chest than the
dome of the upper part of the diaphragm; therefore,
the lower portion is more sharply curved than the
upper portion of the diaphragm
• As a result, the lower part of the diaphragm is able to
contract more efficiently during spontaneous
respiration
• Diaphragm overcomes the weight of the abdominal
contents
• In an awake patient in the LDP, the lower lung is
normally better ventilated than the upper lung
• The preferential ventilation to the lower lung is
matched by increased perfusion of this lung, so the
distribution of the V̇ /Q ratios of the two lungs is not
greatly altered

12. Awake, Open-Chest, Lateral
Decubitus Position (LDP)
• Condition associated frequently with
thoracoscopy with intercostal nerve block.
• Two potential complications during
spontaneous respiration
1.Mediastinal shift
2.Paradoxical breathing

13. • The negative pressure
in the intact hemithorax,
compared with less
negative pressure
pressure of open
hemithorax, can cause
the mediastinum to
move vertically
downwards and push
into dependent
hemithorax
• Can create circulatory
changes  shock and
respiratory distress
• Endotracheal intubation
in LDP may be required
Mediastinal shift

14. Paradoxical respiration
• During inspiration, relative
negative pressure in the
intact hemithorax compared
with Atm pressure in the open
hemithorax causes
movement of air from
nondependent lung to
dependent lung.
• Opposite occurs during
expiration
• Represents wasted
ventilation and can
compromise gas exchange
• Increased by large
thoracotomy or by increased
Paw in the dependent lung
• PPV or adequate sealing of
open chest eliminates
paradoxical breathing

15. LDP, anaesthetized, breathing
spontaneously/paralyzed, chest
closed
• Perfusion: Induction of general
anaesthesia – no significant change in
distribution of blood flow
• Ventilation: In the LDP, more ventilation
is switched from the dependent lung in
an awake subject to the nondependent
lung in an anesthetized patient
• Reasons for this change:

16. 1. Because each lung
occupies a different
initial position on the
pulmonary pressure-
volume curve while
the subject is
awake, a general
anesthesia-induced
reduction in the
FRC of each lung
causes each lung to
move to a lower, but
still different portion
of the pressure-
volume curve

17. • Second, if an anesthetized patient in the LDP is
also paralyzed and mechanically ventilated, the
high, curved diaphragm of the lower lung no
longer confers any advantage in ventilation (as it
does in the awake state) because it is no longer
actively contracting.
• Third, the mediastinum rests on the lower lung
and physically impedes lower lung expansion,
as well as selectively decreases lower lung FRC.
• Fourth, the weight of the abdominal contents
pushing cephalad against the diaphragm is
greatest in the dependent lung, which physically
impedes lower lung expansion the most and
disproportionately decreases lower lung FRC.
• Finally, suboptimal positioning that fails to
provide room for lower lung expansion may
considerably compress the dependent lung.

18. • Anesthetized patient, with or without paralysis, in
the LDP and with a closed chest has a
nondependent lung that is well ventilated but
poorly perfused and a dependent lung that is
well perfused but poorly ventilated, which results
in an increased degree of V̇ /Q mismatching.
• The application of PEEP to both lungs restores
more of the ventilation to the lower lung.
• The lower lung returns to a steeper, more
favorable part of the pressure-volume curve, and
the upper lung resumes its original position on a
flat, unfavorable portion of the curve.

19. Anesthetized, Open-Chest, Lateral
Decubitus Position
• Perfusion: no significant alteration in partitioning of
pulmonary blood flow between the dependent and
nondependent lungs
• Ventilation (with PPV):
1. the upper lung is no longer restricted by a chest wall and
is relatively free to expand and will consequently be
overventilated (and remain underperfused).
2. the dependent lung may continue to be relatively
noncompliant and poorly ventilated and overperfused
3. Surgical retraction and compression of the exposed upper
lung can provide a partial, though nonphysiologic solution
to this problem in that if expansion of the exposed lung is
mechanically or externally restricted, ventilation will be
diverted to the dependent, better-perfused lung

20. Anesthetized, Open-Chest,
Paralyzed LDP
• Perfusion:no significant alteration in
partitioning of pulmonary blood flow
between the dependent and
nondependent lungs; the dependent lung
continues to receive relatively more
perfusion than the nondependent lung
does

21. Anesthetized, Open-Chest,
Paralyzed LDP
• Ventilation:During paralysis and ppv, the passive
and flaccid diaphragm is preferentially displaced
in the nondependent area, where the resistance
to passive diaphragmatic movement by the
abdominal contents is least and vice versa.
• Causes V/Q mismatch because the greatest
amount of ventilation may occur where perfusion
is the least (nondependent lung) and the least
amount of ventilation may occur where perfusion
is the greatest (dependent lung).[

23. Summary of Physiology of the LDP
and Open Chest
• An anesthetized, paralyzed patient in the LDP
with an open chest may have a considerable
V̇ /Q mismatch consisting of greater ventilation
but less perfusion to the nondependent lung
and less ventilation but more perfusion to the
dependent lung
• The blood flow distribution is mainly and simply
determined by gravitational effects
• The relatively good ventilation of the upper lung
is caused in part by the open-chest and
paralyzed conditions

24. • The relatively poor ventilation of the dependent
lung is caused in part by the loss of dependent
lung volume with general anesthesia and by
compression of the dependent lung by the
mediastinum, abdominal contents, and effects of
suboptimal positioning
• In addition, poor mucociliary clearance and
absorption atelectasis with an increased FIO2
may cause further volume loss in the dependent
lung.
• Consequently, two-lung ventilation under these
circumstances may result in an increased
alveolar-arterial oxygen tension difference (PAO2
-PaO2 ) and less than optimal oxygenation

25. Summary of Physiology of the LDP
and Open Chest

26. Physiologic Solution
• Selective application of PEEP to the dependent
lung (through a DLT)
• Selective PEEP to the lower lung should
increase the ventilation to this lung by moving it
up to a steeper, more favorable portion of the
lung pressure-volume curve
• PEEP increases the dependent lung PVR
diverting some blood to nondependent lung – as
a result gas exchange is better in zero PEEP
ventilated non-dependent lung

27. Physiology of One-Lung Ventilation
Blood Flow Distribution during One-Lung
Ventilation
• blood flow to the nondependent,
nonventilated lung
• blood flow to the dependent ventilated
lung

28. Blood Flow To The Nondependent,
Nonventilated Lung
• During Two Lung Ventilation in LDP 40%
and 60% of CO goes to nondependent
and dependent lung respectively
• Normally the venous admixture in lateral
position is 10% of CO, equally divided into
5% in each lung
• So, average percentage of CO
participating in gas exchange is 35% in
non-dependent lung and 55% in
dependent lung

29. Blood Flow To The Nondependent,
Nonventilated Lung
• After initiation of one-lung ventilation the
nondependent lung is nonventilated
• passive mechanical and active vasoconstrictor
mechanisms are usually operant during one-lung
ventilation to minimize blood flow to the
nondependent, nonventilated lung
• prevents PaO2 from decreasing as much as
might be expected on the basis of the
distribution of blood flow during two-lung
ventilation

30. The passive mechanical
mechanisms
1. Gravity,
• causes a vertical gradient in the distribution of
pulmonary blood flow in the LDP,
• constant with respect to both time and magnitude
2. surgical interference with blood flow, variable with
respect to both time and magnitude
3. the extent of preexisting disease in the
nondependent lung,
• if nondependent lung is severely diseased, there
may be a fixed reduction in blood flow to this lung
preoperatively, and collapse of such a diseased lung
may not cause much of an increase in shunt
• but collapse of such a normal lung may be
associated with higher blood flow and shunt to the
nonventilated nondependent lung

31. Active Vasoconstrictor Mechanism
• The normal response of the pulmonary
vasculature to atelectasis is an increase in PVR
(in just the atelectatic lung)
• This increase, thought to be due almost entirely to
HPV
• Diverts blood flow from the atelectatic lung toward
the remaining normoxic or hyperoxic ventilated
lung
• The diversion of blood flow minimizes the amount
of shunt flow that occurs through the hypoxic lung
• HPV is an autoregulatory mechanism that
protects PaO2 by decreasing the amount of shunt
flow that can occur through hypoxic lung

32. Expected Effect Of HPV On Arterial Oxygen
Tension (Pao2 ) As The Amount Of Lung That Is
Made Hypoxic Increases
• When very little of the lung is hypoxic (near
0%), it does not matter, in terms of PaO2 ,
whether the small amount of lung has HPV
operating because in either case the shunt
will be small
• When most of the lung is hypoxic (near
100%), there is no significant normoxic
region to which the hypoxic region can
divert flow

33. Expected Effect Of HPV On Arterial Oxygen
Tension (Pao2 ) As The Amount Of Lung That Is
Made Hypoxic Increases
• When the % of lung
that is hypoxic is
intermediate (between
30% and 70%) (the
one-lung ventilation-
anesthesia condition)
there is a large
difference between
the PaO2 expected
with a normal amount
of HPV (which is a
50% reduction in blood
flow for a single lung)
and that with no HPV

34. Blood Flow To The Dependent
Ventilated Lung.
Dependent ventilated lung has an
increased amount of blood flow because of
• passive gravitational effects
• active nondependent lung vasoconstrictor
effects
However, the dependent lung may also
have a hypoxic compartment (area of low
V̇ /Q and atelectasis) that was present
preoperatively or that developed
intraoperatively

35. Reasons For Development Of Hypoxic
Compartment
• First, in the LDP the ventilated dependent
lung usually has a reduced lung volume
resulting from the factors of
a) induction of general anesthesia and
b) circumferential compression by the
mediastinum from above,
c) by the abdominal contents pressing against
the diaphragm from the caudad side, and
d) by suboptimal positioning effects (rolls, packs,
chest supports) pushing in from the dependent
side and axilla

36. Reasons For Development Of Hypoxic
Compartment
• Second, absorption atelectasis occur in
regions of the dependent lung that have low
V̇ /Q ratios when they are exposed to a high
FiO2
• Third, difficulty in removal of secretions may
be cause of poorly ventilated and atelectatic
areas in the dependent lung
• Finally, maintaining the LDP for prolonged
periods may cause fluid to transude into the
dependent lung and cause a further decrease
in lung volume and an increase in airway
closure in the dependent lung

38. Alveolar Ventilation During OLV
• Comparison of Arterial Oxygenation
and Carbon Dioxide Elimination during
Two-Lung versus One-Lung Ventilation

39. Other Causes Of Hypoxemia
During One-lung Ventilation
• Gross hypoventilation of the dependent lung can be a major
cause of hypoxemia
• Mechanical failure of the oxygen supply system or the
anesthesia machine
• Malfunction of the airway lumen of the dependent lung
(blockage by secretions) and malposition of the DLT
• Resorption of residual oxygen from the nonventilated lung
• decreased cardiac output,
• increased oxygen consumption
1. excessive stimulation of the sympathetic nervous system,
2. hyperthermia,
3. shivering
• TRALI

40. Management of One-Lung
Ventilation
• Conventional Management of One-Lung
Ventilation
• Differential Lung Management of One-
Lung Ventilation
• Combined Conventional and Differential
Lung Management of One-Lung Ventilation

41. Conventional Management of One-
Lung Ventilation
• considers the usual management of OLV in terms
of the most appropriate FIO2 , VT, and RR
Maintain two-lung ventilation as long as possible.
Use FIO2 of 1.0
Begin one-lung ventilation with a tidal volume of 8-
10 mL/kg
Dependent lung PEEP - No or just a very low level
Adjust the respiratory rate so that PaCO2 = 40 mm
Hg
Use continuous monitoring of oxygenation and
ventilation

42. Inspired Oxygen Concentration
• Benefits of ventilating the dependent lung with
100% oxygen far exceed the risks of absorption
atelectasis and oxygen toxicity exist,
• A high FIO2 in the single ventilated lung may
critically increase PaO2 from arrhythmogenic
and life-threatening levels to safer levels
• high FIO2 in the dependent lung causes
vasodilation, thereby increasing the dependent
lung's capability of accepting redistributed blood
flow

43. Tidal Volume
• The dependent lung should be ventilated with VT
of approximately 8 to 10 mL/kg
• much smaller tidal volume might promote
atelectasis of the dependent lung
• much greater tidal volume might excessively
increase airway pressure and vascular
resistance in the dependent lung
• If a VT of 8 to 10 mL/kg causes excessive Paw, it
should be lowered (after mechanical causes [i.e.,
tube malfunction] have been ruled out) and the
respiratory rate increased

44. Dependent Lung PEEP
• No or just a very low level of dependent
lung PEEP (<5 cm H2 O) should be used
initially because more PEEP may increase
dependent lung PVR
• the presence of intrinsic PEEP during one-
lung ventilation may make the total PEEP
excessive

45. Respiratory Rate
• The respiratory rate should be set so that PaCO2
remains at 40mm Hg
• Because a dependent lung VT of 10 mL/kg
represents a 20% decrease from the usual two-lung
VT, the respiratory rate usually has to be increased
by 20% to 30% to maintain CO2 hemostasis
• Unchanged MV during OLV (versus TLV) can
continue to eliminate a normal amount of CO2
because of its high diffusibility
• Hypocapnia should be prevented because may
excessively increase dependent lung PVR and may
also directly inhibit HPV in the nondependent lung

46. Differential Lung Management of
One-Lung Ventilation
• Intermittent Inflation of the Nondependent
Operative Lung
• Selective Dependent Lung PEEP
• Selective Nondependent Lung CPAP
• Differential Lung PEEP/CPAP

47. Intermittent Inflation of the
Nondependent Operative Lung
• Intermittent inflation of the collapsed lung
with oxygen during one-lung ventilation
may be expected to increase PaO2
• In one study the beneficial effect of each
inflation persisted, even if at a gradually
decreasing level, upto 19 minutes

48. Selective Dependent Lung PEEP
• The effect of dependent lung PEEP on arterial oxygenation
1. Positive effect of increasing dependent lung FRC and V̇ /Q
ratio and
2. Negative effect of increasing dependent lung PVR and
shunting blood flow to the nonventilated lung
• Various one-lung ventilation-PEEP studies have had patients
who have had an increase, no change, or a decrease in
oxygenation
• In patients with a very diseased dependent lung (low lung
volume and low V̇ / Q ratio), the positive effects of selective
dependent lung PEEP (increased lung volume and
increased V̇ /Q ratio) might outweigh the negative effects
(shunting of blood flow to the nonventilated, nondependent
lung), whereas in patients with a normal dependent lung, the
negative effects would outweigh the benefits
• Therapeutic margin of using PEEP to increase PaO2 during
one-lung ventilation is quite narrow

49. Selective Nondependent Lung
CPAP
• The application of CPAP (without tidal ventilation) to only the
nonventilated lung significantly increases oxygenation with no
significant hemodynamic effect
• In all clinical studies the application of 5 to 10 cm H2 O CPAP
has not interfered with the performance of surgery and may, in
fact, facilitate intralobar dissection
• blood flow to the nonventilated nondependent lung decreased
by application of this CPAP
• Because low levels of nonventilated lung CPAP are as
efficacious as high levels and have less surgical interference
and hemodynamic implications, it is logical to use low levels
of nonventilated CPAP first
• oxygen insufflation at zero airway pressure did not
significantly improve PaO2 and shunting

50. Differential Lung PEEP/CPAP
• The ideal way to improve oxygenation during one-lung
ventilation is the application of differential lung
PEEP/CPAP
• the ventilated (dependent) lung is given PEEP in the
usual conventional manner in an effort to improve
ventilated lung volume and V̇ /Q relationships
• Simultaneously, the nonventilated (nondependent) lung
receives CPAP in an attempt to improve oxygenation
of the blood perfusing this lung
• Therefore, with differential lung PEEP/CPAP the blood
flow has at least some chance to participate in gas
exchange with alveoli that are expanded with oxygen

51. Combined Conventional and
Differential Lung Management of
One-Lung Ventilation

52. Indications for separation of the two
lungs and/or one-lung ventilation
• Absolute
1. Isolation of one lung from the other to avoid spillage or
contamination
 Infection
 Massive hemorrhage.
2. Control of the distribution of ventilation
 Bronchopleural fistula
 Bronchopleural cutaneous fistula
 Surgical opening of a major conducting airway
 Giant unilateral lung cyst or bulla
 Tracheobronchial tree disruption
 Life-threatening hypoxemia from unilateral lung disease
3. Unilateral bronchopulmonary lavage
 Pulmonary alveolar proteinosis

53. • Relative
1. Surgical exposure — high priority
 Thoracic aortic aneurysm
 Pneumonectomy
 Upper lobectomy
 Mediastinal exposure
 Thoracoscopy
2. Surgical exposure — medium (lower) priority
 Middle and lower lobectomies and subsegmental
resections
 Esophageal resection
 Procedures on the thoracic spine
3. Post-cardiopulmonary bypass status after removal of totally
occluding chronic unilateral pulmonary emboli
4. Severe hypoxemia from unilateral lung disease