How to avoid
Acute Lung Injury (ALI) after Thoracic Surgery
-Fortunately,
Acute Lung Injury (ALI) occurs infrequently, with an incidence of 2.5 % of all
lung resections combined, and an incidence of 8% after pneumonectomy. However,
when it occurs, ALI is associated with a risk of mortality or major morbidity
of about 40%.
Causes of ALI:
I. Ventilated
Lung:
1-Hyperoxia:
(Oxygen toxicity, Reactive oxygen species)
2-Hyperperfusion:
(Endothelial damage, Increased pulmonary vascular pressure)
3-Ventilatory
Stress: (Volutrauma, Barotrauma, Atelectrauma)
II. Collapsed
Lung:
1-OLV: (Ischemia/Reperfusion,
Reexpansion, Cytokine release, Altered redox status)
2-Surgery:
(Manipulation trauma, Lymphatic disruption)
III. Systemic:
-Cytokine
release, Reactive oxygen species, Complement activation, Overhydration,
Chemotherapy/Radiotherapy.
Prophylaxis against
ALI:
A) Protective
Lung Ventilation Strategies:
I. Lower Tidal
Volumes (6–8 mL/kg):
-The use of
lower tidal volumes may lead to lung derecruitment, atelectasis, and hypoxemia.
Lung derecruitment may be avoided by the application of external PEEP and frequent
recruitment maneuvers.
II. PEEP (5–10
cm H2O):
-Although PEEP
may prevent alveolar collapse and development of atelectasis, it may cause a
decrease in PaO2 due to diversion of blood flow away from the
dependent, ventilated lung and an increase in the total shunt.
-Thus, PEEP must
be customized to the underlying disease of each patient, and a new application
of PEEP will rarely be the appropriate way to treat hypoxemia that occurs
immediately after the onset of one-lung ventilation.
-Patients with
obstructive pathology may develop intrinsic PEEP. In these patients, the
application of external PEEP may lead to unpredictable levels of total PEEP.
III. Lower FiO2
(50-80%):
-Although the
management of one-lung ventilation has long included the use of 100% oxygen,
evidence of oxygen toxicity has accumulated both experimentally and clinically.
-Clinicians
recommend titrating FiO2 to maintain the O2 saturation
>90%, especially in patients who have undergone adjuvant therapy and are at
risk of developing ALI.
IV. Lower
Ventilatory Pressures:
-Plateau
pressure <25 cm H2O; and peak airway pressure <35 cm H2O,
through the use of pressure-controlled ventilation, may diminish the risk of
barotrauma.
-The flow
pattern results in a more homogenous distribution of the tidal volume and
improved dead space ventilation.
V. Permissive Hypercapnia:
-Periodic ABG
analysis is helpful to ensure adequate ventilation. End-tidal CO2
measurement may not be reliable due to increased dead space and an
unpredictable gradient between the arterial and end-tidal CO2
partial pressure.
VI. At the end
of the procedure:
-The operative
lung is inflated gradually to a peak inspiratory pressure of less than 30 cm H2O
to prevent disruption of the staple line.
-During
reinflation of the operative lung, it may be helpful to clamp the lumen of the
dependent lung, to limit over-distension.
B) IV Fluids:
-Restrict IV
fluids in pulmonary resection to avoid lower lung syndrome (Gravity-dependent
transudation of fluid).
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