Introduction This study highlights the significance of assessing acid-base balance and gas exchange in intensive care patients. The research investigates the applicability of using the "expected (pCO 2 = HCO 3 + 15)" formula, derived from venous blood gas samples, as an alternative to Winter's formula and practical formula. The study emphasizes the importance of identifying the primary acid-base abnormality accurately and efficiently for appropriate clinical intervention in critically ill patients. Methods This study included 400 adult patients admitted to the Anesthesia Clinic in the Third Stage Anesthesia and Reanimation Intensive Care Unit at Hitit University Erol Olçok Training and Research Hospital between April 2020 and July 2023. Blood gas samples were collected simultaneously from both arterial lines and venous catheters. Patients under 18 years, pregnant women, hemodialysis patients, and those with missing data were excluded. The study aimed to calculate the expected partial pressure of carbon dioxide (pCO 2 ) values using Winter's formula and simple formula for both arterial and venous blood gas samples and assess potential correlations between them. Results The results showed a narrow range for arterial pH values (7.12-7.72), a wider distribution for pCO 2 values (17.90-81.30 mmHg), and a moderate dispersion for HCO 3 values (12.80-44.33 mmol/L). Both Winter's and simple formulas were applied to estimate the expected pCO 2 values, showing strong positive correlations between arterial and venous pH, pCO 2 , and HCO 3 values. The scatterplot illustrated a very high level of association (Pearson's correlation coefficient, r = 1) between the expected pCO 2 values derived from both formulas using arterial and venous blood gas samples. Conclusion The clinical study demonstrates that estimating expected pCO 2 values in mixed acid-base disorders can be achieved using a simple and convenient formulation, eliminating the need for arterial blood gas sampling and its associated complications.

The circadian rhythm is the most important of the main rhythms that affect our daily lives and has a significant role in the efficiency of a lot of drugs used in anesthesia. The aim of this study is to prove whether circadian rhythm has an effect on spinal anesthesia and, if any, its effect on post-operative analgesic request by retrospectively studying the patients operated under spinal anesthesia. Methods: We conducted the study on patients operated on inguinal hernia and anorectal surgery under spinal anesthesia in general surgery room. The patients were divided into two groups according to the time when they were taken into surgery: Between 06.00-12.00 (Group 1) and 12.00-18.00 (Group 2). Time to first analgesic request, time to start walking, time to first urination, intraoperative and post-operative side effects, intraoperative hemodynamic data, and patient satisfaction were detected and recorded. Results: The time to first analgesic request in Group 1 was longer than in Group 2, and this difference was statistically significant. The mean heart rate of the groups was found significantly lower in Group 2 than in Group 1 during measurements at the 25 and 30 min when compared with their changes overtime. There were no statistically significant differences between the groups in terms of side effects and the most common side effect was detected to be nausea-vomiting. Conclusion:We found out that the time to first analgesic request after spinal anesthesia was significantly longer in Group 1 than in Group 2.