Perioperative Pulmonary Atelectasis: Part II. Clinical Implications

Abstract

The development of pulmonary atelectasis is common in the surgical patient. Pulmonary atelectasis can cause various degrees of gas exchange and respiratory mechanics impairment during and after surgery. In its most serious presentations, lung collapse could contribute to postoperative respiratory insufficiency, pneumonia, and worse overall clinical outcomes. A specific risk assessment is critical to allow clinicians to optimally choose the anesthetic technique, prepare appropriate monitoring, adapt the perioperative plan, and ensure the patient's safety. Bedside diagnosis and management have benefited from recent imaging advancements such as lung ultrasound and electrical impedance tomography, and monitoring such as esophageal manometry. Therapeutic management includes a broad range of interventions aimed at promoting lung recruitment. During general anesthesia, these strategies have consistently demonstrated their effectiveness in improving intraoperative oxygenation and respiratory compliance. Yet these same intraoperative strategies may fail to affect additional postoperative pulmonary outcomes. Specific attention to the postoperative period may be key for such outcome impact of lung expansion. Interventions such as noninvasive positive pressure ventilatory support may be beneficial in specific patients at high risk for pulmonary atelectasis (e.g., obese) or those with clinical presentations consistent with lung collapse (e.g., postoperative hypoxemia after abdominal and cardiothoracic surgeries). Preoperative interventions may open new opportunities to minimize perioperative lung collapse and prevent pulmonary complications. Knowledge of pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should provide the basis for current practice and help to stratify and match the intensity of selected interventions to clinical conditions.

Figure 1:

Lung Computed Tomography: bilateral opacities of the dependent retrocardiac lung regions (red lines) revealing the typical aspect of severe perioperative pulmonary atelectasis in an obese patient requiring re-intubation for postoperative respiratory failure 2 days after coronary artery bypass graft surgery.

Figure 2:

Sagittal cross-section magnetic resonance images showing the effect of general anesthesia and paralysis in the supine position: dorsal cephalad shift of the diaphragm dome and atelectasis of the dorso-caudal lung.

Figure 3:

Detection of pulmonary atelectasis by ultrasound. (A) Pulmonary atelectasis revealed using lung ultrasound by a pulmonary consolidation surrounded by a pleural effusion (white arrow). (B) Color doppler imaging showing the persisting pulmonary blood flow within consolidated lung (yellow arrow) due to incomplete hypoxic pulmonary vasoconstriction, which may result in a shunt effect.

Figure 4:

Pre and postoperative regional distribution of the tidal impedance variation, assessed with lung electrical impedance tomography, in a patient presenting postoperative respiratory failure 2 days after coronary artery bypass graft surgery. Note that pulmonary atelectasis observed on computed tomography is associated with a reduced impedance variation signal in the dorsal hemithorax.

Figure 5:

Principles of esophageal manometry and the use of transpulmonary pressure. (A) position of the esophageal pressure balloon at the lower third of the esophagus, and relationship amongst the different pressures measured in the respiratory system. Transpulmonary pressure (P_L) is an approximate of the elastic recoil pressure of the lung or P_el(L). (B) Selection of PEEP consistent with a positive P_L during the expiration period is expected to maintain alveoli recruited throughout the breathing cycle. (C) By contrast, negative P_L allows for the collapse of lung units. P_alv=alveolar pressure; P_ao=pressure at airway opening; P_es=esophageal pressure; P_pl=pleural pressure.

Figure 6:

Algorithm for intraoperative management of pulmonary atelectasis. A standard ventilatory strategy targeting surgical patients is implemented after anesthesia induction (PEEP 2–5 cmH₂O, no recruitment maneuvers, V_T 6–10 ml/kg of predicted body weight). In patients presenting intraoperative respiratory compromise consistent with pulmonary atelectasis, fixed higher PEEP is set following a recruitment maneuver. Attention is given to basic maneuvers to eliminate additional causes, e.g., secretions and bronchoconstriction, and maintain safety (transient increase in FIO₂). If the respiratory dysfunction persists despite empiric alveolar expansion, an individualized strategy can be considered in high-risk conditions for atelectasis: PEEP titration targeting optimization of usually available (e.g., compliance, driving pressure) or advanced respiratory measurements (transpulmonary pressure, ultrasound, electrical impedance tomography). If individualization of lung recruitment fails to improve lung function or in patients without specific risk for intraoperative atelectasis, a specific diagnostic approach should be implemented without delay using lung imaging or bronchoscopy. * hypoxemia may be defined by SpO₂ drop by more than 5% or FIO₂ increase by more than 30% to maintain oxygenation with PEEP=5cmH₂O (presuming other causes such as airway, ventilator, or hemodynamic issues have been excluded); ** significant respiratory mechanics change may be defined by a C_RS drop by more than 20%, or a driving pressure ≥15cmH₂O with PEEP=5cmH₂O and V_T=6ml/kg PBW; ‡ attend to hemodynamic stability during recruitment maneuvers; § BMI ⩾ 35 kg/m², pneumoperitoneum, Trendelenburg position, upper abdominal surgery with diaphragmatic surgical retractors, diaphragmatic injury, intraoperative lung injury or pulmonary edema. C_RS=compliance of the respiratory system; EIT= electrical impedance tomography.