Effect of Various Modes of Mechanical Ventilation in Laparoscopic Cholecystectomies on Optic Nerve Sheath Diameter and Cognitive Functions

Abstract

Aim:

In this study, we aim at investigating the effects of volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) modes on changes in the optic nerve diameter and cognitive functions in laparoscopic cholecystectomy operations.

Materials and Methods:

Sixty patients who underwent laparoscopic cholecystectomy were randomly divided into two groups based on the mode of mechanical ventilation provided: Group P; PCV, Group V; VCV. Optic nerve sheath diameter was measured when the patient was awake (T0), in the 10th minute after induction (T1), in the 10th minute after the initiation of gas insufflation (T2), when maximum gas pressure was reached in the reverse-Trendelenburg position (T3), and pre-extubation (T4). Partial oxygen saturation (PaO₂), PCO₂, end-tidal carbon dioxide (ETCO₂), and peak airway pressure (pPEAK) were also recorded. A Mini-Mental State Examination (MMSE) was conducted on patients preoperatively and in the postoperative third month.

Results:

Between the groups, a statistically significant difference was found in Group P compared with Group V in terms of optic nerve diameter at measurement times T1 (P < .05). In the intragroup comparison, a significant difference was found in the initial values in all measurements except for measurement times T0 and T4 in both Group P and Group V (P < .05). pPEAK values were identified to be statistically significantly lower in Group P than Group V at all measurement times (P < .05). No difference was identified in the MMSE scores in the intergroup and intragroup comparisons.

Conclusion:

Laparoscopic cholecystectomy increases the optic nerve diameter due to the mechanical and systemic effects of the operation, and the PCV mode can be preferred.

Clinical Trial Number: NCT04413903

Introduction

Laparoscopic cholecystectomy operations have become the gold standard method due to shorter hospital stays, minor postoperative pain and complications, and earlier mobilization^1. Pneumoperitoneum is used in these operations to get a better image of the site of the surgery and facilitate the procedure. Therefore, intraperitoneal CO₂ insufflation is usually induced. Reverse-Trendelenburg positioning of the patient to induce pneumoperitoneum is believed to create changes in respiratory, hemodynamic, metabolic, and intracranial pressures (ICP) as it affects vital organs.²

The general anesthesia method is preferred in laparoscopic cholecystectomies to ensure the comfort of the surgeon and the patient.³ Various modes of mechanical ventilation have been experimented to achieve the lung compliance that will ensure sufficient intraoperative oxygenation. Changes in arterial blood gas values and hemodynamic parameters that were caused by these modes of mechanical ventilation might lead to changes in the ICP. Measurement of the effects of laparoscopic surgeries on ICP via optic nerve sheath diameter (ONSD) measurement using noninvasive ocular ultrasound has been shown to yield correct results in detecting ICP in comparison with the results obtained from intraventricular and intraparenchymal devices.⁴ In the studies carried out, 100% sensitivity and specificity have been identified in the prediction that ICP will be >20 mmHg if ONSD is >5.5.^5,6

Postoperative cognitive dysfunction is a decline in memory and higher cerebral functions that might be observed after general anesthesia. Mini-Mental State Examination (MMSE) is usually used to measure postoperative cognitive dysfunction.⁷ In this study, we aim at investigating the effects of modes of volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) on changes in the optic nerve diameter and cognitive functions in laparoscopic cholecystectomy operations.

Materials and Methods

After the approval of the local ethics committee (2017-17/23) of Uludağ University Faculty of Medicine, registration at clinicaltrials.gov (NCT04413903) and written consent of the patients were obtained. Sixty ASA I–II patients aged between 18 and 65 who underwent laparoscopic cholecystectomy with general anesthesia under elective conditions were included in the study. Patients who had a history of eye surgery, an eye disease, an uncontrolled cardiovascular, respiratory, metabolic, and cerebrovascular disease were excluded from the study. Demographic data of the patients (age, gender, weight, height), surgical duration, and perioperative complications were recorded.

After routine monitorization in supine position in the surgery room; fentanyl 1–2 mcq/kg i.v., Propofol 2–3 mg/kg i.v., rocuronium bromide 0.6 mg/kg i.v. were administered to the patient during induction. The patients were randomly divided into two groups based on the mode of mechanical ventilation used: Group P (n = 30) PCV, and Group V (n = 30), VCV. Mechanical ventilation settings were adjusted as 50% O_2, 50% air, 6 mL/kg tidal volume, and positive end-expiratory pressure 5 and the same inhalation agent was used.

During the measurement of the optic nerve diameter, a layer of water-soluble sterile gel was applied on the upper eyelid that was closed. A linear 10–5 MHz ultrasound probe (GE Healthcare Logiqe Series) was carefully held on the upper eyelid over the gel. Part of the optical nerve that enters the orbital globe was monitorized in the 2D mode without exerting much pressure. The diameter of the optic nerve sheath was measured 3 mm behind the optic disk by using an electronic caliper after the right contrast was found between the retrobulbar echogenic fatty tissue and the vertical hypoechogenic band 23. In our study, ONSDs of all patients were measured by the same experienced anesthesiologist. The optic nerve diameter was measured when the patient was awake (T0), in the 10th minute after induction (T1), and in the 10th minute after the initiation of gas insufflation (T2), when the maximum gas pressure was reached in the reverse-Trendelenburg position (T3) and before extubation (T4).

Heart rate, mean arterial pressure (MAP), peak airway pressure (pPEAK), and end-tidal carbon dioxide (ETCO₂) values were also recorded at T0, T1, T2, T3, and T4. Arterial partial oxygen saturation (PaO₂), carbon dioxide pressure (PaCO₂) was measured from arterial blood gas. Intra-abdominal pressure during surgery was standardized as 12 cm H₂O in all measurement times, and reverse-Trendelenburg position was standardized as 30° to 45°. MMSEs and cognitive function tests were conducted preoperatively and in the postoperative third month during the patients' arrival for routine polyclinic follow-up.

Statistical analysis

Data were analyzed by using IBM Statistical Package for the Social Sciences (SPSS) 22.0 statistical package program. In addition to descriptive statistics (frequency, percentage, mean, standard deviation, median, minimum–maximum) that were used in the evaluation of study data, the chi-square (χ²) test was used in the comparison of qualitative data. Whether the data displayed normal distribution was evaluated with the Kolmogorov–Smirnow test. In the study, Mann–Whitney U test was used in intergroup comparisons and the Friedman test was used in multiple time-point comparisons. Spearman's Rho test was used to analyze correlations. Values with a probability (P) that was smaller than α = 0.05 were accepted as significant, meaning that there was a difference between the groups.

Results

Sixty-eight patients participated in our study. Eight patients were excluded for some reasons. One of them is that PaO₂ falls below 60 mmHg, 4 of them fail and the mode of mechanical ventilation changes during operation, 3 of them have PaCO₂ exceeding 50 mmHg. After exclusion, 60 patients were randomly divided into two groups of 30 people (Fig. 1). Demographic features of the patients are outlined in Table 1. A statistically significant difference was not identified between the groups with respect to the demographic features of the patients (P > .05).

FIG. 1.

Flowchart of procedure.

Table 1.

Comparison of the Demographic Values of Patients (Mean ± Standard Deviation, Number)

	Group P (n = 30)	Group V (n = 30)	P
Age, years	46 ± 14.5	47.2 ± 13.4	.706
BMI, kg/m²	28.7 ± 2.8	27.7 ± 2.4	.161
Gender, M/F	7/23	9/21	.563
Duration of operation, minutes	58.60 ± 8.7	56.96 ± 9.5	.94
Duration of anesthesia, minutes	76.50 ± 9.1	73.16 ± 8.65	1.52

BMI, body mass index; F, female; M, male.

A statistically significant difference was identified between the groups in terms of optic nerve diameter measurement values that were lower in Group P at measurement times T1 (P < .05) (Table 2). The measured values at T3 time were lower in Group P than in Group V. However, they were not statistically significant (Table 2). During intragroup comparisons, a statistically significant difference was found between the initial values and values at all measurement times except for T0 and T4 in both Group P and Group V (P < .05) (Table 2).

Table 2.

Optic Nerve Sheath Diameter Measurement Values

	Group P (n = 30)	Group V (n = 30)	P^a
T0	39.12 ± 3.6	40.17 ± 3.7	.351
T1	40.54 ± 3.7	42.89 ± 2.7	.005
T2	43.83 ± 4.6	45.9 ± 4.4	.104
T3	44.25 ± 4.4	45.89 ± 2.9	.057
T4	41.16 ± 4.1	42.06 ± 4.8	.658
P ^b	<.05	<.05

Value in bold is significantly significant.

Intergroup comparison (Mann–Whitney U test).

Intragroup comparison (Friedman).

T0, preoperative; T1, 10th minute after induction; T2, initiation of gas insufflation in the supine position; T3, when maximum gas pressure is reached in reverse Trendelenburg position; T4, pre-extubation in the supine position.

When intergroup ETCO₂ values at measurement times are compared, they were identified to be statistically significantly higher in Group P at measurement time T1 (P < .05) (Table 3). A statistically significant difference was not found when PaCO₂ values were evaluated between the groups (P > .05) (Table 3).

Table 3.

End-Tidal Carbon Dioxide and Partial Arterial Carbon Dioxide Values

	Group P (n = 30)	Group V (n = 30)	P^a
ETCO₂
T1	32.8 ± 2.4	30.8 ± 2.1	.001
T2	34.3 ± 2.5	33.1 ± 2.4	.070
T3	35.3 ± 2.5	34.9 ± 2.8	.715
T4	33.6 ± 1.8	33.3 ± 2.2	.517
pCO₂
T1	31.3 ± 2.3	31.6 ± 2.5	.647
T2	34.6 ± 2.1	33.6 ± 2.2	.339
T3	37.4 ± 3.03	36.8 ± 4.3	.547
T4	34.5 ± 3.12	33.8 ± 3.3	.998

Value in bold is significantly significant.

Intergroup comparison (Mann–Whitney U test).

ETCO₂, end-tidal carbon dioxide; T1, 10th minute after induction; T2, 10th minute after initiation of gas insufflation in the supine position; T3, when maximum gas pressure is reached in reverse-Trendelenburg position; T4, pre-extubation in the supine position.

The pPEAK values were observed to be statistically lower in Group P than in Group V at all measurement times (P < .05) (Table 4).

Table 4.

Average Airway Pressure (pPEAK) Measurement Values

pPEAK	T1	T2	T3	T4
Group P (n = 30)	16.5 ± 3.5	18.7 ± 3.8	19.2 ± 3.9	18.4 ± 3.4
Group V (n = 30)	19.6 ± 4.2	22.1 ± 3.8	22.3 ± 4.7	21.5 ± 3.6
P ^a	.001	.030	.048	.035

Mann–Whitney U test.

pPEAK, average airway pressure; T0, preoperative; T1, 10th minute after induction; T2, initiation of gas insufflation in the supine position; T3, when maximum gas pressure is reached in reverse-Trendelenburg position; T4, pre-extubation in the supine position.

A statistically significant difference was not identified between preoperative MMSE scores and MMSE scores during follow-up in the third month (Table 5).

Table 5.

Mini-Mental State Examination and Optic Nerve Percentage Change

MMSE	Group P (n = 30)	Group V (n = 30)	P^a
Before the operation	26.5 ± 3.1	26.8 ± 2.2	.904
Third month	26.9 ± 2.9	26.8 ± 2.6	.652
P	.564	.433
Percentage change
MMSE	2.9 ± 15.9	0.518 ± 14.3	.433
Optic nerve T0–T3	11.6 ± 10.4	15.3 ± 10.5	.206
Pearson correlation	−0.115	0.131
P ^b	.546	.491

Mann–Whitney U test.

Spearman's correlation.

MMSE, Mini-Mental State Examination; T0, preoperative; T3, when maximum gas pressure is reached in the reverse-Trendelenburg position.

A statistically significant difference was not found between the groups when ratios of percentage change between the initial and T3 measurements of optic nerve diameter were compared (P < .05). A correlation was not observed between third month follow-up values and ratios of percentage change (P = .626). A correlation was not identified between the initial and follow-up MMSE scores and percentage change scores at T0–T3 in both groups (Table 5).

Discussion

In our study, we evaluated the effect of modes of mechanical ventilation on intraocular pressure in patients who underwent cholecystectomy by means of laparoscopy by way of measuring ONSD by ultrasonography. In our study carried out with 60 patients, ONSD was lower in Group P at T1 measurement time and the difference was statistically significant between the groups. In the intragroup comparison, initial values in both groups were found to be significantly different in all measurement times except for T0 and T4. The pPEAK values were identified to be statistically significantly lower in Group P than Group V at all measurement times. A difference was not identified between the groups in the preoperative scores of MMSE and scores at the postoperative third month.

Volume control ventilation is the conventional ventilation method in laparoscopic surgeries, whereas PCV is an alternative mode of ventilation that is asserted to regulate gas exchange in patients who suffer from acute respiratory distress syndrome in intensive care units.⁸ We have not encountered studies that investigate the effect of these modes of mechanical ventilation on ONSD but we think that they can have an effect on ONSD due to their mechanical and systemic effects. Schirmer-Mikalsen et al. investigated the effects of modes of mechanical ventilation on ICP by way of comparing PCV and pressure-regulated volume control modes in patients who had traumatic brain injury by measuring PaCO₂ and ICP and found the average values of ICP and PaCO₂ to be similar.⁹ Sen et al. evaluated the effects of PCV and VCV modes on respiratory mechanics and oxygenization during laparoscopic cholecystectomy.¹⁰ In their study, they reported pPEAK, compliance and oxygenization to be higher in the PCV group, and shunt and dead space to be lower. In a similar study, Tyagi et al. did not find a significant difference between preoperative PaO₂ and ETCO₂ values whereas pPEAK values of the PCV group were identified to be lower than those of the VCV group.¹¹ Similarly, Ogurlu et al. evaluated 60 patients who underwent laparoscopic gynecological surgery in the Trendelenburg position.¹² The pPEAK values were lower and compliance values were significantly higher in the PCV group at all measurement times. Based on these results, they stated that decreased pPEAK resulted from the pattern of decreasing flow rate in the PCV mode and the resultant earlier breakdown of flow resistance.

Distinctly, Mihalj et al. concluded that PCV and VCV were equally effective in ensuring adequate ventilation, oxygenization, and hemodynamic stability in the observed patients.¹³ Consistent with these studies, no differences were present in PaO₂ and PaCO₂ levels at all measurement times in our study whereas pPEAK values were significantly lower in the PCV group. The ONSD values at the 10th minute after induction were found to be significantly lower in the PCV mode than in the VCV mode. The reason for significantly higher ONSD in the VCV group compared to PCV in the first 10 minutes (T1) was high pPEAK values in VCV mode to reach the target tidal volume. We think that higher pPEAK values in the VCV group than in the PCV group in our study were important in increased ICP.

Duration of the pneumoperitoneum and patient position, as well as ventilation, can affect cardiopulmonary and metabolic changes in laparoscopic surgeries. Respiratory acidosis that results in increased intraabdominal pressure secondary to pneumoperitoneum, decreased venous return, hypercapnia, and absorption of CO₂ along the peritoneal surface leads to systemic physiological outcomes.¹⁴ Increased intraabdominal and intrathoracic pressure during insufflation disturb the venous drainage of the lumbar on absorption of the cerebrospinal liquid, thus increasing the vascular component in the sacral gap.² This might lead to increased ONSD by increasing ICP. There is a growing body of evidence that shows a positive correlation between intraabdominal pressure and ICP. Rauh et al. emphasized that intraabdominal pressure of 15 mmHg and higher led to respiratory changes in laparoscopic cholecystectomies and that the degree of pneumoperitoneum followed by high intraabdominal pressure was much more influential on changes that occur during the operation than patient position.¹⁵

In an analysis carried out to evaluate the effect of pneumoperitoneum and head position during laparoscopic surgery on ICP using the sonographic measurements of ONSD, the pneumoperitoneum was demonstrated to lead to an increase in ICP.¹⁶ In our study, ONSD was identified to increase in Group V after induction and at the onset of gas insufflation. Intraabdominal pressure was maintained at 12–15 mmHg throughout the laparoscopic surgery. A statistically significant difference was not identified between the groups during the comparison of intergroup ETCO₂ values at measurement times. There was a significant difference in ETCO₂ values in VCV mode at 10th minute after induction (T1). But this was not correlated with at the same time PaCO₂ values. Effective tidal volume was maintained quickly and CO₂ eliminated therefore ETCO₂ was lowered in VCV mode. We thought that low ONSD values that were measured in Group P at T1 was observed to be independent from ETCO₂.

Considering the studies investigating the effect of patient position on ONSD, 57 female patients who underwent laparoscopic surgery were grouped according to their intraoperative positions (Trendelenburg position, reverse-Trendelenburg position) and it was found that ONSD increased mildly on application of pneumoperitoneum but no differences were present between the positions.¹⁷ In addition to this, a significant difference was not observed in the PaCO₂, ETCO₂, and MAP values. In trendelenburg position increase on ONSD is significant. The ONSD did not restore its initial values in the groups; on the contrary, an increase was identified compared with the initial values.

Contrary to this, Verdonck et al. stated that an ICP increase was low in the Trendelenburg position and that ONSD did not change.¹⁸ Kim et al. observed a 12.5% increase in ONSD during the pneumoperitoneum in the Trendelenburg position and, therefore, stated that an increase in ICP that corresponded to such change in ONSD could be predicted.¹⁹ This finding suggested that intraabdominal pressure increase, rather than patient position, had a strong effect on increased ONSD. In our study, the patients were in the reverse-Trendelenburg position and ONSD was observed to be higher than the basal values in both groups when maximum gas pressure was reached in the reverse-Trendelenburg position on introduction of gas insufflation and the measurements did not restore their initial value after the position. We consider this to be due to the effect created by physical changes during laparoscopic cholecystectomy operations.

Postoperative cognitive dysfunctions can be short term or long term.²⁰ Various other suspected factors such as glucocortoid levels, pre-existing cognitive impairments, neuroinflammation, age, brain hypoperfusion, hypoxia, and genetic factors, as well as anesthetic agents, are believed to cause such dysfunction. Tests that evaluate postoperative cognitive dysfunctions and that have been developed for clinical neuropsychology have been used in geriatric age groups.²¹

Most studies carried out relating to laparoscopic surgeries or other surgeries have compared the effects of anesthetic agents that are used intraoperatively on cognitive functions.²² Studies related to cognitive dysfunction that is caused by the type of surgery have not been encountered. In our study, the patient population belonged to the middle age group. Although optical nerve diameter varied in the groups, a significant difference in terms of MMSE scores was not observed in the intragroup and intergroup comparisons. This was considered to be due to the fact that ONSD values that were measured did not increase enough to cause a cognitive dysfunction and due to the average age of the patients.

Limitations

Our study had limitations. First of all, our study was not a blind study to the core, as the anesthesiologist was aware of the mode of ventilation used. Therefore, it seems that the investigation of the ONSD and cognitive functions according to the ventilator mode during laparoscopic cholecystectomy surgeries is not much clinically significant. Moreover, respiratory parameters of the modes of mechanical ventilation were not investigated in detail. The short operation time in laparoscopic cholecystectomies has limited the measurement of optic nerve diameter changes. The Mini-Mental State Exam had to be conducted in the postoperative 24th hour. More research is recommended to investigate the effects of modes of ventilation on ICP.

Conclusion

In our study, we have observed that laparoscopic cholecystectomy surgery increases ONSD due to its mechanical effects and we think that the PCV mode can act as an alternative to volume-controlled mode of ventilation in preventing the side effects of the pneumoperitoneum. Although it caused increased ONSD, this surgical procedure was not observed to lead to postoperative cognitive dysfunctions. Further research is required to investigate these dissimilarities.

Footnotes

Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

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