Pulmonary complications have been a leading cause of significant morbidity and mortality after anesthesia and surgery. Pulmonary complications include atelectasis, pneumonia, empyema, pulmonary embolism, and acute respiratory failure (1). Many of these complications have declined with the use of antibiotic prophylaxis, improvements in analgesia, implementation of protective ventilation strategies, and postoperative chest physiotherapy. However, mechanical ventilation is necessary for some types of anesthesia and surgery, and it increases the risk for certain pulmonary complications. Appropriate ventilation strategies during anesthesia are important to improving patient outcomes.
Among pulmonary complications, acute lung injury (ALI) remains high, with an incidence reported as 2%–7% in large cohort studies. The mortality associated with lung injury is reported to be as high as 50% (2). The causes of ALI are often multifactorial, with surgical trauma, ventilator-induced injury, and fluid overload identified as contributing factors.
Mechanical ventilation is consistently recognized as an important risk factor for perioperative ALI. Lung overinflation, hypoxia with oxidative stress, and reperfusion injuries from mechanical ventilation increase the release of proinflammatory mediators contributing to alveolar injury (3) Protective ventilation strategies reduce the risk of complications after anesthesia and surgery. The use of lower tidal volumes, recruitment maneuvers, and the application of peak-end expiratory pressure (PEEP) have been widely recognized as core elements in protective lung ventilation. Licker et al. evaluated the impact of a protective lung strategy protocol using a combination of tidal volumes <8 mL/kg predicted body weight, inspiratory plateau pressures <35 cmH2O, PEEP 4–10 cmH2O, and the use of recruitment maneuvers on clinical outcomes. This study revealed a lower incidence of ALI in the protective ventilation group than in the conventional ventilation group (0.9% vs. 3.7%, P < 0.01) (4).
Additionally, driving pressure is a surrogate for dynamic lung strain and can be defined as the difference between the plateau pressure of the airways at end-inspiration and PEEP. Blank et al. demonstrated that for every unit increase in driving pressure (∼1 cmH2O), there was a 3.4% increase in the risk of major morbidity. The incidence of postoperative pulmonary complications was reported to be 5.5% in driving pressure-guided ventilation compared to 12.2% in patients with conventional protective ventilation during thoracic surgery. These research findings should lead to changes in the current recommendations for protective lung ventilation and encourage the use of driving pressure-guided ventilation strategies during anesthesia (1).
Furthermore, special attention should be given to ventilator settings for specific patient populations. For instance, cancer patients with prior exposure to bleomycin have a risk of lung injury during mechanical ventilation (1). A higher FiO2 is often required to prevent hypoxemia during ventilation, and anesthesiologists may need to tolerate a lower oxygen saturation with a lower FiO2 in patients on bleomycin. Patients with restrictive lung disease may require the addition of PEEP to reduce atelectasis and pulmonary shunting during ventilation. In contrast, chronic obstructive pulmonary disease (COPD) may develop auto-PEEP during surgery, increasing the risk of hyperinflation and increased shunt. Permissive hypercapnia (elevated blood carbon dioxide levels) is generally well-tolerated, and anesthesiologists should refrain from adjusting ventilator settings to reduce blood carbon dioxide concentration. In fact, Wei et al. demonstrated that therapeutic hypercapnia during mechanical ventilation not only improves respiratory function but also mitigates local and systemic inflammation in patients undergoing thoracic surgery. However, hypercapnia may not be safe in specific patient populations. Elevated blood carbon dioxide levels can cause tachycardia and increased systolic blood pressure, which could be detrimental to patients with a significant cardiac history. Therefore, lung-protective strategies for mechanical ventilation during anesthesia should be carefully performed to minimize complications in patients with significant comorbidities (1).
References
1. Hagberg CA, Nates JL, Riedel BP, Vijaya N.R. Gottumukkala, Buggy D. Perioperative Care of the Cancer Patient E-Book. Elsevier Health Sciences; 2022.
2. Tandon S, Batchelor A, Bullock R, et al. Peri-operative risk factors for acute lung injury after elective oesophagectomy. Br J Anaesth. 2001;86(5):633-638. doi:10.1093/bja/86.5.633
3. Kilpatrick B, Slinger P. Lung protective strategies in anaesthesia. Br J Anaesth. 2010;105 Suppl 1:i108-i116. doi:10.1093/bja/aeq299
4. Licker M, Diaper J, Villiger Y, et al. Impact of intraoperative lung-protective interventions in patients undergoing lung cancer surgery. Crit Care. 2009;13(2):R41. doi:10.1186/cc7762