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ferences of 5.0 mmHg，with an estimated standard devi⁃ tients requiring a vasopressor to maintain hemodynamic
ation of differences of 9.9 mmHg，at a significance level stability or experiencing a hemodynamic fluctuation ex⁃
α of 0.05 using a paired t⁃test. Given the possibility of ceeding 20% were excluded. Data collected before the
loss to follow ⁃ up，we increased the sample size by use of a vasopressor or hemodynamic instability could
10%，resulting in a required sample size of 50. still be used for analysis. Close communication was
1.2.2 determination of PTCCO2 and PETCO2 maintained with surgeons during the surgery. Patients
After entering the operating room，a 16⁃G intrave⁃ were excluded if the peritoneum had been ruptured，
nous（Ⅳ）catheter was inserted into the median cubi⁃ but the data collected before peritoneal rupture was re⁃
tal vein for fluid and drug administration，while a 20⁃G tained. Patient’s temperature was continuously moni⁃
arterial catheter was cannulated in the non ⁃ operated tored and maintained above 36 ℃，while the room tem⁃
radial artery for continuous blood pressure（BP）monitor⁃ perature was set at 23-25 ℃. The retroperitoneal CO 2
ing and ABG sampling. The arterial catheter was pressure was maintained at 12 -15 mmHg during the
flushed with 500 mL of heparinized saline using a pres⁃ surgery. PaCO2，PETCO2，and PTCCO2 of each patient
sure bag. Standard monitoring including electrocardio⁃ were measured at four time points：before CO2 insuffla⁃
gram（ECG），saturation of pulse oxygen（SpO2），and arte⁃ tion，30，60 and 90 min after CO2 insufflation.
rial BP was performed for all patients before anesthesia， If PETCO2 exceeded 50 mmHg during the surgery，

with these values recorded as baseline values. Anesthe⁃ adjustments could be made such as increasing respira⁃
sia induction comprised propofol（1.5-2.5 mg/kg），fen⁃ tory rate，adjusting tidal volume，increasing the flow of
tanyl（2-4 μg/kg），and rocuronium（0.6 mg/kg）. Fol⁃ fresh oxygen，reducing pneumoperitoneum pressure
lowing intubation，patients were ventilated with volume within the surgeon’s acceptable range，or pausing the
control ventilation（VCV）using 60% oxygen（2 L/min）. operation or closing the pneumoperitoneum if neces⁃
The PETCO2values were maintained ideally between 35- sary to enhance CO 2excretionand lower PETCO2 levels.
45 mmHg by adjusting tidal volume，respiratory rate， 1.3 Statistical analysis
and aspiration ratio（inspiratory∶expiratory，I∶E），with Statistical analyses were performed using Graph⁃
an upper limit of 50 mmHg allowed. PETCO2 was mea⁃ Pad 8.0 software（GraphPad Prism，La Jolla，California，
sured by side stream spirometry（Mindray，BeneView USA）. Quantitative data were presented as means ±
T6，Shenzhen，China），while PTCCO2 was measured standard deviation（x ± s）or median with interquartile
with the TCM ⁃ 4 monitor（Radiometer，Copenhagen， range［M（P25，P75）］depending on the type of distribu⁃
Denmark）. Before placement，calibration was per⁃ tion. A difference of ≤5 mmHg between PaCO 2 and PET⁃
formed by a trained author（LIU Shijiang）according CO2，or between PaCO 2 and PTCCO2，was considered
to the manufacturer’s recommendation. The electrode within the clinical acceptable range. Categorical vari⁃
was then placed onto the patient’s chest wall of the ables，presented as frequencies（proportions）［n（%）］，
non⁃operated side，which was cleaned with alcohol to were analyzed using the chi⁃square test or Fisher’s exact
facilitate the adhesion of the disk to the skin，with the test as appropriate. Pearson correlation coefficient was
electrode working temperature set at 44 ℃. PaCO2 was employed to assess the correlation between P ETCO2 and
determined using a blood gas/electrolyte analyzer PaCO2，as well as the correlation between PTCCO2 and
（GEM premier 3000，Instrumentation Laboratory Co. PaCO2. Additionally，linear regression analysis was uti⁃
MA 01730 ⁃ 2443，USA）. Before ABG sampling，pa⁃ lized to model and quantify these relationships. Bland⁃
tients’hemodynamic was relatively stable for at least Altman analysis was used to compare the agreement be⁃
tween PaCO2 and PETCO2，or between PaCO2 and PTCCO2.
5 min to ensure a stable P aCO2. PTCCO2 and PETCO2
were recorded simultaneously with ABG sampling. P < 0.05 is considered statistically significant.
Anesthesia was maintained with propofol，sevoflu⁃
2 Results
rane，and remifentanil to limit the BP and heart rate
（HR）fluctuations within 20% of baseline values. Pa⁃ Ninety ⁃ seven patients were initially assessed for