How to avoid ALI after Thoracic Surgery

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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