This study will test how accurate a blood pressure cuff is during a specific type of chest surgery.

In some lung surgeries, doctors use a method called video-assisted thoracoscopic surgery (VATS), where small tools and a camera are inserted through the chest wall. During these procedures, patients often have only one lung ventilated to give the surgeon more space to work. This setup can affect how well a blood pressure cuff on the arm reflects the true blood pressure inside the body.

This study will compare readings from the arm cuff (non-invasive) with those from a thin tube placed inside an artery (invasive), which is more accurate but also more uncomfortable and carries some risks.

Researchers will use a method called error grid analysis to see how closely the cuff readings match the invasive ones. They want to find out if the cuff is accurate enough to be used safely in these surgeries. If it is, patients might not need an invasive line as often in the future.

People 18 years or older who are already going to have invasive blood pressure monitoring during planned thoracic surgery with one-lung ventilation may be able to join the study. The research team will collect blood pressure measurements about every 20 minutes during surgery, as well as basic information like age, weight, and what medications are given.

This is a prospective observational study designed to evaluate the clinical accuracy and reliability of non-invasive blood pressure (NIBP) monitoring in adult patients undergoing video-assisted thoracoscopic surgery (VATS) with one-lung ventilation (OLV). The accuracy of NIBP will be assessed by comparing it to invasive arterial blood pressure (IABP), which is considered the reference standard. The comparison will be performed using error grid analysis, a method that not only quantifies measurement differences but also categorizes the clinical risk of those discrepancies.

During VATS procedures, one lung is intentionally deflated to improve surgical access, which alters thoracic pressures, ventilation dynamics, and cardiovascular physiology. These changes may affect the accuracy of peripheral blood pressure measurements obtained using an arm cuff. Previous evaluations of NIBP in surgical patients have primarily relied on Bland-Altman analysis, which measures statistical agreement but does not assess the clinical consequences of disagreement between methods.

Error grid analysis overcomes this limitation by mapping paired NIBP and IABP values into predefined clinical risk zones (A-E), based on their potential to affect treatment decisions. Zone A represents measurements with no risk of causing inappropriate treatment, while Zones B through E indicate increasing levels of clinical risk due to measurement error.

In this study, NIBP and IABP measurements will be recorded simultaneously approximately every 20 minutes throughout surgery. The percentage of measurements that fall within each error grid zone will be calculated. If fewer than 90% of the paired measurements fall within Zone A, NIBP will be considered insufficiently reliable for use without concurrent invasive monitoring in this clinical context.

A pilot study of five patients was used to estimate the intracluster correlation coefficient and design effect, which informed the final sample size calculation. Based on these preliminary data, a total sample size of 90 patients is estimated to provide adequate statistical power to evaluate the primary outcome with 95% confidence and a 5% margin of error.

The study will also collect intraoperative data that may influence blood pressure measurement accuracy, such as the use of vasoactive infusions. These data may help identify subgroups in which NIBP is more or less reliable during one-lung ventilation.

The results of this study may help refine intraoperative monitoring strategies and potentially reduce unnecessary use of invasive blood pressure lines in selected thoracic surgical patients, improving both safety and comfort while maintaining clinical reliability.

Inclusion Criteria:

• Age 18 years or older
• Scheduled to undergo video-assisted thoracoscopic surgery with one-lung ventilation
• Will receive invasive arterial blood pressure monitoring as part of routine clinical care

Exclusion Criteria:

• Has peripheral artery disease
• Has congestive heart failure

Participants will be selected from adult patients scheduled for video-assisted thoracoscopic surgery with one-lung ventilation at Koç University Hospital, a tertiary care academic medical center in Istanbul, Turkey.

Anonymized individual participant data (IPD) that underlie the results of the study will be shared. These data will be made publicly available through the Zenodo repository following study completion and publication.

Beginning at the time of the first publication of study results, with no end date.

The anonymized individual participant data (IPD) and supporting documentation will be openly available to the public via the Zenodo data repository. No proposal, request, or data use agreement is required. Researchers may download the dataset directly from Zenodo upon publication. The data are intended for secondary analysis, validation of findings, or meta-research. A citation to the original study publication and dataset DOI is requested when using the data.