Comment on Eva et al. laparoscopic surgery: Ann Med Surg (Lond). 2022 Sep 2;81:104562

Dear Editor, Comment on Eva et al. Laparoscopic surgery: a randomized controlled trial comparing intraoperative hemodynamic parameters and arterial blood gas changes at two different pneumoperitoneal pressure values. Ann Med Surg (Lond). 2022 Sep 2;81:104562. Recently, a randomized controlled trial comparing intraoperative hemodynamic parameters and arterial blood gas changes at two different pneumoperitoneum pressure regimens by Eva and colleagues was published in the Annals of Medicine and Surgery. In this study, the authors demonstrated changes in hemodynamic, respiratory, blood gas, and acid–base parameters in two groups of patients during laparoscopic surgery with a CO2 pneumoperitoneum pressures of 8 and 12 mm Hg. Perioperative measurements were performed before and after anesthesia induction, 30 min after the start of the CO2 pneumoperitoneum, and 5 min after deflation. Since our research studies and clinical work have been closely related to the clinical and experimental aspects of CO2 pneumoperitoneum and its pathophysiology, when we read this article, we found questionable results and shortcomings in this study. From this view, unexpected respiratory rate and pH changes are bizarre and disputable in contrast to their observation concerning pCO2 dynamics during CO2 pneumoperitoneum . The pCO2 dynamics demonstrated increased carbon dioxide concentration during CO2 pneumoperitoneumwith subsequently decreased pCO2 after deflation in both groups. However, the pH value in patients with CO2 pneumoperitoneum pressure of 12 mm Hg increased following the raised carbon dioxide concentration. Further, after deflation, decreased pCO2 was accompanied by increased pH in this group of patients with a CO2 pneumoperitoneum pressure of 12 mm Hg. These observations did not correspond to the physiologic balance between pCO2 and pH . When involved in laparoscopic surgery research, the prior knowledge for surgeons and anesthesiologists should be that pH is the general product of carbon dioxide. Dissolved carbon dioxide (CO2 +H2O) in the human body forms a carbonic acid (H2CO3), which dissociates into two ions: hydrogen (H + ) and bicarbonate (HCO3-). All side effects of CO2 pneumoperitoneum manifested in parameters of blood gases, acid–base balance, and hemodynamic system are triggered mainly by increased pCO2 with decreased pH and subsequent metabolic changes. It is well known that an accumulation of carbon dioxide in the body and its increased partial pressure (pCO2) are accompanied by a linearly decreased pH value. Such an observation was made in our previous experiments in ventilated rabbit models. We demonstrated a constantly increased pCO2 value when the superficial ventilation mode remained unchanged. An increased pCO2 was accompanied by a decreased pH value overall during CO2 pneumoperitoneum. In animals with ventilated lungs without CO2 pneumoperitoneum, main blood gas, and acid–base parameters remained unchanged with slight events of alkalosis. Strangely, the respiratory rate increased enormously after deflation in patients with 12 mm Hg CO2 pneumoperitoneum pressure, although all disturbances of blood gas parameters in patients with 8 mm Hg pressure were in the frame of dynamic changes for these values during laparoscopic surgery and CO2 pneumoperitoneum with lung ventilation management . The authors describe changes in blood gas and acid–base values in the results section needing clarification. In addition, the CO2 pneumoperitoneum time is an essential factor with a crucial impact on blood gas and acid–base values, with subsequent disorders in cardiac and hemodynamic parameters. However, the authors did not describe the CO2 pneumoperitoneum time, types of surgeries, and Trendelenburg positioning during surgery. There is a physiological balance between carbon dioxide content and pH in the human body, which is usually regulated through respiratory system functioning and acid–base buffering systems of homeostasis. Therefore, during laparoscopic surgery with CO2 pneumoperitoneum, the minute volume is traditionally managed by the respiratory rate per minute and by the volume of inspiratory air per stroke (tidal volume) during lung ventilation. aMoscow Institute of Physics and Technology National Research University, Dolgoprudny, Moscow Region, Russia, bNew European Surgical Academy, Berlin, Germany, cRegional TB dispensary of the Health Department of Turkestan Region, dSouth Kazakhstan Multidisciplinary Medical College, eDepartment of General Practitioner, South Kazakhstan Medical Academy, Shymkent, fDepartment of Pharmaceutical Disciplines, Khoja Akhmet Yassawi International Kazakh-Turkish University, Turkistan, Kazakhstan and gDepartment of Specialized Surgical Disciplines, Khoja Akhmet Yassawi International Kazakh-Turkish University, Turkistan, Kazakhstan


Dear Editor,
Comment on Eva et al. Laparoscopic surgery: a randomized controlled trial comparing intraoperative hemodynamic parameters and arterial blood gas changes at two different pneumoperitoneal pressure values. Ann Med Surg (Lond). 2022 Sep 2;81:104562.
Recently, a randomized controlled trial comparing intraoperative hemodynamic parameters and arterial blood gas changes at two different pneumoperitoneum pressure regimens by Eva and colleagues was published in the Annals of Medicine and Surgery [1] .
In this study, the authors demonstrated changes in hemodynamic, respiratory, blood gas, and acid-base parameters in two groups of patients during laparoscopic surgery with a CO 2 pneumoperitoneum pressures of 8 and 12 mm Hg. Perioperative measurements were performed before and after anesthesia induction, 30 min after the start of the CO 2 pneumoperitoneum, and 5 min after deflation [1] .
Since our research studies and clinical work have been closely related to the clinical and experimental aspects of CO 2 pneumoperitoneum and its pathophysiology [2][3][4][5] , when we read this article, we found questionable results and shortcomings in this study.
From this view, unexpected respiratory rate and pH changes are bizarre and disputable in contrast to their observation concerning pCO 2 dynamics during CO 2 pneumoperitoneum [1] . The pCO 2 dynamics demonstrated increased carbon dioxide concentration during CO 2 pneumoperitoneum with subsequently decreased pCO 2 after deflation in both groups. However, the pH value in patients with CO 2 pneumoperitoneum pressure of 12 mm Hg increased following the raised carbon dioxide concentration. Further, after deflation, decreased pCO 2 was accompanied by increased pH in this group of patients with a CO 2 pneumoperitoneum pressure of 12 mm Hg. These observations did not correspond to the physiologic balance between pCO 2 and pH [1] .
When involved in laparoscopic surgery research, the prior knowledge for surgeons and anesthesiologists should be that pH is the general product of carbon dioxide. Dissolved carbon dioxide (CO 2 + H 2 O) in the human body forms a carbonic acid (H 2 CO 3 ), which dissociates into two ions: hydrogen (H + ) and bicarbonate (HCO 3 -). All side effects of CO 2 pneumoperitoneum manifested in parameters of blood gases, acid-base balance, and hemodynamic system are triggered mainly by increased pCO 2 with decreased pH and subsequent metabolic changes [4] .
It is well known that an accumulation of carbon dioxide in the body and its increased partial pressure (pCO 2 ) are accompanied by a linearly decreased pH value. Such an observation was made in our previous experiments in ventilated rabbit models [5] . We demonstrated a constantly increased pCO 2 value when the superficial ventilation mode remained unchanged. An increased pCO 2 was accompanied by a decreased pH value overall during CO 2 pneumoperitoneum. In animals with ventilated lungs without CO 2 pneumoperitoneum, main blood gas, and acid-base parameters remained unchanged with slight events of alkalosis [3,4] .
Strangely, the respiratory rate increased enormously after deflation in patients with 12 mm Hg CO 2 pneumoperitoneum pressure, although all disturbances of blood gas parameters in patients with 8 mm Hg pressure were in the frame of dynamic changes for these values during laparoscopic surgery and CO 2 pneumoperitoneum with lung ventilation management [1] .
The authors describe changes in blood gas and acid-base values in the results section needing clarification [1] . In addition, the CO 2 pneumoperitoneum time is an essential factor with a crucial impact on blood gas and acid-base values, with subsequent disorders in cardiac and hemodynamic parameters. However, the authors did not describe the CO 2 pneumoperitoneum time, types of surgeries, and Trendelenburg positioning during surgery [1] .
There is a physiological balance between carbon dioxide content and pH in the human body, which is usually regulated through respiratory system functioning and acid-base buffering systems of homeostasis. Therefore, during laparoscopic surgery with CO 2 pneumoperitoneum, the minute volume is traditionally managed by the respiratory rate per minute and by the volume of inspiratory air per stroke (tidal volume) during lung ventilation. Subsequently, with the rise in carbon dioxide concentration, the minute volume is increased to keep the pCO 2 value within the frame of the physiologic limits.
In experimental and clinical studies, we found that the intensity of increased carbon dioxide concentration and decreased pH values in the arterial blood were dependent on the CO 2 pneumoperitoneum pressure level and lung ventilation accuracy during CO 2 pneumoperitoneum [2][3][4][5] .
Another shortcoming of this study (Eva et al., 2022) is that sampling blood gas and acid-base parameters were not repeated during CO 2 pneumoperitoneum and deflation. Blood gas and acid-base parameters are very sensitive to any confounding factors; therefore, sampling should be repeated to get the optimal values of these parameters.
Since this study aimed to compare arterial blood gas and hemodynamic changes between two CO 2 pneumoperitoneum pressures, the authors should estimate the CO 2 pneumoperitoneum time. Considering fewer cases in groups, there might be highly distributed blood gases and acid-base values.
In addition, the authors of their randomized controlled trial should have used the correct study design and statistics [1] . This study had 10 patients per group; a suitable study design should be used with nonparametric statistical tests.
We expect an explanation from the authors for such an unexpected observation of pH and respiratory rate distributions when the dynamics of these parameters should be in the frame of limits according to changes in the carbon dioxide partial pressure monitored during surgery.

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