One Lung Ventilation (OLV) Effects on Troponin T and I Levels in Thoracic Surgical Procedures

Technical Summary: Effects of One-Lung Ventilation on Troponin Levels in Thoracic Surgery

Problem Statement
One-lung ventilation (OLV) is the standard anesthetic technique for thoracic surgery, facilitating surgical access by collapsing the operative lung. However, OLV induces significant physiological changes, including ventilation-perfusion mismatches and potential hypoxemia, which may compromise cardiovascular function. Postoperative myocardial infarction (PMI) is a critical complication in major surgeries, with elevated cardiac biomarkers serving as sensitive indicators of myocardial injury. While the risks of PMI are well-documented in general major surgery, the specific relationship between OLV-induced physiological stress and postoperative elevations in Troponin T and Troponin I levels in thoracic procedures requires further elucidation. This study addresses the gap in understanding how OLV parameters and perioperative hemodynamics influence myocardial injury markers in this specific surgical context.

Methodology
This research employed a prospective, single-group cohort design conducted at Prof. Dr. Margono Soekarjo Hospital. The study utilized consecutive sampling to recruit 39 patients undergoing thoracic surgery who met specific inclusion criteria.

• Intervention: All participants underwent OLV with standardized ventilation settings: a 50% air to 50% oxygen ratio, a tidal volume of 5–6 mL/kg body weight, and a respiratory rate of 12 breaths/min.
• Data Collection: Preoperative and postoperative levels of Troponin T and Troponin I were measured. Additionally, perioperative parameters were recorded, including hemodynamic status (systolic/diastolic blood pressure, mean arterial pressure, pulse rate), surgical duration, OLV duration, intraoperative bleeding volume, postoperative hemoglobin, and arterial blood gas values (PaO₂ and PaCO₂).
• Statistical Analysis: The study utilized the Wilcoxon test to compare preoperative and postoperative biomarker levels. Bivariate analysis (Pearson/Spearman correlation) was performed to identify factors associated with troponin levels, followed by multivariate analysis to determine independent predictors.

Key Results
The study observed a statistically significant increase in cardiac biomarkers following thoracic surgery with OLV:

• Troponin Levels: Postoperative Troponin T levels rose significantly from a mean of 6.32 ± 1.19 ng/L preoperatively to 8.19 ± 2.43 ng/L postoperatively (p < 0.001). Similarly, Troponin I levels increased from 49.84 ± 16.30 ng/L to 57.02 ± 17.33 ng/L (p < 0.001).
• Bivariate Correlations: Several factors showed significant correlations with elevated troponin levels, including Mean Arterial Pressure (MAP) during surgery, diastolic blood pressure, duration of OLV, postoperative hemoglobin, intraoperative bleeding, and postoperative PaO₂ and PaCO₂.
• Multivariate Findings: In the multivariate analysis, postoperative PaO₂ emerged as the most influential independent factor affecting postoperative troponin levels for both markers (Troponin T: B = 0.530, p = 0.002; Troponin I: B = 0.544, p = 0.013). Other factors, such as OLV duration and intraoperative bleeding, lost significance when adjusted for other variables.

Significance and Claims
The paper concludes that patients undergoing thoracic surgery with OLV exhibit a significant postoperative elevation in Troponin T and I levels, indicating subclinical or clinical myocardial injury. The study identifies postoperative PaO₂ as a critical determinant of these elevations.

The authors suggest that the mechanism likely involves an imbalance between myocardial oxygen supply and demand. During OLV, intrapulmonary shunts and ventilation-perfusion mismatches can lead to systemic hypoxemia. Conversely, the study notes that hyperoxia (excessively high PaO₂) may also induce oxidative stress and coronary vasoconstriction, potentially damaging myocardial tissue. Therefore, the authors posit that optimal regulation of PaO₂ is essential to mitigate myocardial injury in this setting.

Limitations
The authors acknowledge several limitations to their findings:

1. Temporal Scope: Troponin levels were measured only at a single preoperative and postoperative time point, preventing the assessment of the trajectory of biomarker changes during the intraoperative period or long-term effects.
2. Assay Specifics: The use of research reagents for troponin measurement provided comparative data but lacked established normal reference ranges for the specific assay used.
3. Scope of Parameters: The study relied solely on troponin levels as the dependent variable. The authors note that future research should incorporate additional cardiac parameters, such as ECG and echocardiography, to provide a more comprehensive assessment of cardiac function.
4. Causality: As an observational cohort study, the findings demonstrate association rather than definitive causation regarding specific OLV mechanisms and myocardial injury.

Conclusion
The study establishes a direct relationship between the OLV technique and increased postoperative troponin levels in thoracic surgery patients. It highlights postoperative PaO₂ as a key modifiable factor influencing myocardial injury, suggesting that careful management of oxygenation is vital for cardiovascular safety in these procedures.