This trial studied the effects of pneumoperitoneum on the CSA measurements of IJV and SCV. According to the results of the study, pneumoperitoneum applied with a pressure of 12 mmHg caused significant increases in CSA of IJV and SCV at both expiration and inspiration. After desufflation of intraabdominal gas IJV and SCV CSAs decreased significantly. Measurements at desufflation period showed greater IJV CSA than basal measurements and this probably resulted from an elevated intrathoracic pressure due to mechanical ventilation.
The effect of manuvers increasing intraabdominal pressure has been previously studied. Hepatic compression [4] and increased valsalva maneuver [5] have been similarly reported to increase CSA. The hemodynamic effects of pneumoperitoneum, on the other hand, are somewhat more complicated. Increased intraabdominal pressure can be considered to have a biphasic effect on venous return [11]. It is hypothesized that an increase of venous return occurs as a result of the compression of abdominal capacitance veins initially, followed by decrease in it as a result of increased resistance against venous return in the abdomen and extremities. However, some studies have suggested that when right atrial pressure is normal to high, that is when the patient is not hypovolemic, pneumoperitoneum increases venous return; it may be reasonable to argue that such studies have conveyed a more accurate information [12]. We felt no necessity to discuss the hemodynamic effects of severe hypovolemia and cardiovascular disorders as none of our patients had these morbidities.
Pneumoperitoneum affects cardiovascular system by two ways, namely by direct pressure effect and hypercarbia. However, alterations induced by hypercarbia are less pronounced compared to those induced by the mechanical effects of increased intraabdominal pressure [12]. We prevented hypercarbia by adjusting end-tidal CO2 controlled respiratory rate. Hemodynamic changes secondary to increased intraabdominal pressure by gas insufflation vary by several factors including intravascular volume, the magnitude of intraabdominal pressure, and patient position. In this study, we tried to standardize these variables by making measurements in supine position, administering i.v. fluids during the fasting period, performing a standard intraabdominal pressure application, and adjusting respiratory rate by EtCO2 control.
Since no different pneumoperitoneum pressures were used in our study, their effect could not be assessed. However, prior studies have shown that different pressures have variable hemodynamic effects [13]. Dexter et al. randomized subjects undergoing laparoscopic cholecystectomy into two groups with pneumoperitoneum pressures of 7 mmHg and 15 mmHg. They found heart rate and mean arterial pressure increase in both groups, but stroke volume and cardiac output were significantly reduced in the 15 mmHg group (10 and 26 %, respectively) [14]. McLaughlin et al. reported a 30 % reduction in cardiac output and stroke volume and a 60 % increase in mean arterial pressure after the application of a 15-mmHg pneumoperitoneum compared to the pre-insufflation period [15]. Another study showed that pressures below 15 mmHg increased venous return by squeezing venous bed while pressures of 15 mmHg or above caused a reduction in venous return and blood pressure as a result of inferior vena cava compression [16].
Moreover, the effect of intubation and mechanical ventilation on intrathoracic pressure should not be overlooked. That is, combined effect of increased intraabdominal and intrathoracic pressures may have contributed to CSA increase. This may explain the lack of a biphasic central vein CSA change despite pneumoperitoneum’s biphasic effect on venous return.
Central catheters are not routinely used for monitorization of patients with a low ASA category in laparoscopic cholecystectomy operations. However, they may be necessary in case of severe cardiovascular insufficiency or respiratory complications. Although USG is now widely utilized for central catheterization, the latter is performed blindly by using reference points at many centers. A knowledge of diameter change in central veins will reduce the rate of complications in laparoscopic surgeries. According to the results of our study, central venous intervention can be more easily performed after laparoscopic insufflation in such patients. Future studies may investigate if CSA increments will be more exaggerated when maneuvers producing CSA increments, such as PEEP or Trendelenburg position, are applied in conjunction with laparoscopy, or whether different CSA increments will be obtained when different intraabdominal pressure limits are used.
This study had some limitations. First of all, as the patients were undergoing cholecystectomy operation, they were placed in head up and left lateral tilt position after CO2 insufflation and trocar’s placement at the first stage of laparoscopy procedure. Therefore, the study was so designed that the measurements could only be made at the first stage of laparoscopy and 5 min after placing patients again in supine position following the end of the procedure. A study that would be conducted on patients continuously remaining in neutral position may allow performing more frequent measurements that would facilitate the observation of possible changes in every stages of laparoscopy procedure. As a result, after we observed the effect of intraabdominal pressure increase on vein CSAs, we decided to investigate the correlation of CSA changes with pressure alterations in abdominal compartment syndrome in a future study.