Effect of Preoperative Prewarming on Serum Lactate Levels in Patients Undergoing Elective Nephrectomy

Nephrectomy is a major surgical procedure, performed via open or laparoscopic approaches, that is associated with a substantial physiological stress response. Reduced tissue perfusion and increased anaerobic metabolism during major surgery can raise serum lactate levels, and maintaining perioperative metabolic stability is an important goal in these patients.

Prewarming refers to active warming of a patient's body surface before induction of anesthesia, with the aim of reducing intraoperative core-temperature drop and its downstream effects on tissue perfusion and oxygenation. Clinical practice regarding the use and duration of prewarming varies among anesthesiologists, and there is no fixed institutional protocol dictating whether, or for how long, it should be applied.

This is a prospective, single-center, observational study conducted over a one-year period. Consecutive adult patients undergoing elective nephrectomy who meet the eligibility criteria will be enrolled and followed as part of routine clinical care (see Eligibility Criteria for full details). Whether a given patient receives prewarming, and for how long (typically 10-15 minutes when used), is determined solely by the anesthesia team providing care in the operating room; the study does not intervene in this clinical decision or modify usual care in any way. Outcomes will be compared between patients who receive prewarming and those who do not.

For each patient, a range of preoperative and postoperative physiological and laboratory parameters is recorded as part of routine perioperative monitoring (see Outcome Measures for the specific parameters and their timing). In addition, length of stay in the intensive care unit, need for blood transfusion, and the occurrence and type of postoperative complications are documented. All data are obtained from existing anesthesia records, nursing charts, laboratory results, intensive care information systems, and patient files, and are transcribed onto a predefined case report form; the study does not add any invasive procedures, blood draws, or deviations from routine clinical protocol.

Continuous variables will be compared between the prewarming and control groups using the independent-samples t-test or Mann-Whitney U test, as appropriate, and categorical variables will be compared using the chi-square test or Fisher's exact test. Regression analysis will be used to examine associations between prewarming and outcomes. A p-value <0.05 will be considered statistically significant. A power analysis (G*Power v3.1.9.2), assuming a medium effect size (Cohen's d=0.5) for the primary between-group lactate comparison, indicated that at least 64 participants per group (128 total) would be needed to achieve 80% power at α=0.05.

Inclusion criteria

• Scheduled for elective nephrectomy
• Adults aged 18-90 years
• ASA (American Society of Anesthesiologists) physical status classification I-III
• Signed informed consent form

Exclusion criteria

• Emergency nephrectomy
• Concurrent additional major surgical procedure planned in the same session
• Age under 18 or over 90 years
• ASA physical status classification IV or higher
• Incomplete preoperative records (missing pre- or postoperative measurement of at least one primary outcome variable)