Although laparoscopic surgical interventions are gaining popularity, the induction of pneumoperitoneum has been seen to lead to alterations in respiratory mechanics.1 Previous studies on this issue have revealed the positive effects of administration of 10 cmH2O positive end-expiratory pressure (PEEP) on elastance and resistance in the respiratory system during laparoscopic surgery.2–4 On the downside, pneumoperitoneum induction has been known to increase the intraocular pressure (IOP) and the administration of PEEP in patients receiving mechanical ventilation in the ICU has been demonstrated to cause a rise in IOP not only in the short term but also following extended use.5 This study aimed to investigate the effects of 10 cmH2O PEEP administration on IOP in patients who underwent 15 mmHg pneumoperitoneum. The secondary objective was intragroup differences between groups zero end-expiratory pressure (ZEEP) and PEEP and the effect of head-up position on IOP.
Fatih University Medical Faculty Ethical Committee approved this study in 3 May 2012 (no: B302FTU00000/0837, Chairperson Professor S. Dane). From May 2012 to June 2014, the study included 40 patients between the ages of 18 and 60 years, with American Society of Anesthesiologists physical status (ASA) class I or II, who were scheduled to undergo laparoscopic cholecystectomy. Written informed consent was obtained from all the patients. The criteria for exclusion were the presence of acute or chronic eye disease, corneal thickness abnormal enough to affect IOP, use of drugs known to influence IOP, present hypertension, pulmonary disease and obesity. After routine monitoring, anaesthesia was induced with 3 mg kg−1 propofol, 1 μg kg−1 fentanyl and 0.6 mg kg−1 rocuronium. Subsequent to intubation, 6% desflurane within 40% oxygen and 60% NO2 was used for anaesthesia maintenance. The patients were randomised into two groups with the sealed envelope method. All patients received volume-controlled mechanical ventilation with a tidal volume of 8 ml kg−1 (optimal body weight). The ZEEP group (n = 20) received no PEEP, whereas the PEEP group (n = 20) received 10 cmH2O PEEP. The respiratory rate was adjusted to provide an end-tidal CO2 level between 35 and 40 mmHg. All the patients underwent pneumoperitoneum with 15 mmHg CO2 insufflation and were placed in the head-up (15°) tilt supine position. IOP levels were measured at preinduction, after induction, 5 min after the initiation of mechanical ventilation (after PEEP administration in PEEP group), pneumoperitoneum inflation, head-up position, deflation of pneumoperitoneum and extubation.
IOP measurements were performed with Tono-Pen AVIA Applanation Tonometer (Reichert, Munich, Germany). Hand-held tonometer displays digital numeric values after contact with the cornea. The device displays the average of 10 independent readings along with a statistical confidence indicator and ensuring accurate, repeatable and reliable tonometry results. The instrument was calibrated before use and a protective cover was used to avoid contamination. The measurement was executed so as to avoid inflicting any injury on locally anaesthetised eyes.
Sample size was determined by a power analysis (α = 0.05, β = 0.2, mean difference = 4.0, SD = 3.3 in our pilot study), which revealed that at least 14 patients should be included in each group. Statistical analysis was performed with Statistical Package for the Social Sciences program, version 20 (SPSS Inc., Chicago, Illinois, USA). Intergroup comparisons of normally distributed variables were performed using Student's t test and variables without normal distribution were evaluated using the Mann–Whitney U test. For intergroup comparison of categorical data, χ2 test was utilised and paired samples t test was used for intragroup comparisons. Results are shown as mean ± SD; P less than 0.05 was considered as statistically significant.
Demographical and operative characteristics and basal IOP levels were similar between the groups (P > 0.05; Table 1). During intraoperative follow-up, no significant difference was observed with respect to heart rate, mean arterial pressure, saturation and end-tidal CO2 levels (P > 0.05). Ppeak and Pmean levels and dynamic compliance measurements were observed to be higher in the PEEP group (P < 0.05; Table 2). When Ppeak, Pmean and dynamic compliance (Cdynamic) levels were compared between postintubation and intraoperative follow-up, increases were observed in both groups (P < 0.05). There were no differences of IOP increase between the two groups (P > 0.05). In case of intragroup analysis, IOP levels measured after induction and 5 min after mechanical ventilation were seen to be lower than basal levels in both groups (P < 0.05; Fig. 1). When compared with basal levels, IOP levels after deflation of pneumoperitoneum were similar in the PEEP group (P = 0.290) but were significantly lowered in the ZEEP group (P = 0.032). IOP measurements after induction and mechanical ventilation revealed a significant increase in the PEEP group but no significant difference for the ZEEP group (P = 0.001 and 0.172, respectively). IOP measurements after mechanical ventilation and pneumoperitoneum showed a significant rise in both groups (P = 0.002 and 0.047; Fig. 1). There was a statistically significant difference between IOP levels in the head-up position after the induction period and mechanical ventilation period in the PEEP group. In the ZEEP group, there was a significant difference between IOP levels in only the head-up position after the induction period (P < 0.005; Fig. 1).
In this study, we investigated the effect of 10 cmH2O PEEP on IOP during laparoscopic cholecystectomy. Although Ppeak, Pmean and Cdynamic levels were seen to be increased in the PEEP group when compared with the ZEEP group, IOP measurements revealed no significant difference between the groups. Both groups, when compared with basal levels, showed a decrease in IOP with induction. In the PEEP group, a significant increase was observed when intragroup analyses of the measurements were done after induction and after initiation of mechanical ventilation were compared. The comparisons of IOP levels after mechanical ventilation and pneumoperitoneum displayed an increase in both groups but IOP levels during pneumoperitoneum did not surpass basal levels in either group.
In a review by Pinkney et al.,6 the authors compared patient positioning with IOP changes in laparoscopic surgery and reported that an increase in pressure and the head-down position were prominently correlated and that special caution needed to be observed against perioperative sight loss as a catastrophic complication of surgery. Studies on this issue suggested that the administration of intraoperative PEEP for pneumoperitoneum induced alterations in the respiratory mechanics.2–4 Pneumoperitoneum cause sympathetic activation, catecholamine and vasopressin release and induced increases in arterial pressure, systemic and pulmonary vascular resistances and mean arterial pressure. Additionally, pneumoperitoneum and PEEP administration induce a rise in intrathoracic pressure and reduce drainage of the jugular veins. As a result, an increase in IOP may be observed.7,8 In a study hypothesising that potential haemodynamic changes during PEEP administration may impair cerebral perfusion, it was concluded that cerebral oxygen saturation and haemodynamic stability were both conserved upon the administration of 10 cmH2O PEEP.9 Nonetheless, risks of pneumoperitoneum, such as an increase in IOP and subsequent postoperative sight loss, should be kept in mind, especially in morbidly obese patients. Our observation was that the use of pneumoperitoneum and 10 cmH2O PEEP in laparoscopic cholecystectomy in head-up position led to an increase in IOP when compared with postinduction levels, but the rise was not above basal levels. This condition may be the result of the short operation period and also the head-up position may mask the probable effect of the PEEP and pneumoperitoneum. As a result, we believe that 10 cmH2O can be used to improve respiratory mechanics in laparoscopic surgery in the head-up position without concern over the rise in the IOP.
Acknowledgements related to this article
Assistance with the study: none.
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Conflicts of interest: none.
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