Changes in respiratory mechanics during extraperitoneal insufflation in inguinal hernia surgery.

INTRODUCTION

Most laparoscopic surgeries involve intraperitoneal insufflation gas in the abdominal cavity, while the extraperitoneal approach is commonly used for various laparoscopic procedures such as inguinal hernia repair, prostatectomy and varicocelectomy.[1]

The adverse respiratory and cardiovascular changes seen during intraperitoneal insufflation have been extensively studied.[2345] There are several reports on the haemodynamic effects of extraperitoneal insufflation, but there is sparse data to evaluate the effect of extraperitoneal insufflation on changes in respiratory mechanics.[16]

METHODS

After institutional ethics committee approval and written informed consent from the patients, 100 male patients, belonging to the American Society of Anesthesiologists Physical Status I and II in the age group of 18–75 years (body mass index <30 kg/m2) undergoing TEP were included in this prospective cohort study.

After arrival in the operation theatre, intravenous access was obtained. Monitoring included noninvasive blood pressure, electrocardiogram, oxygen saturation, end-tidal CO2 (EtCO2) and neuromuscular monitoring.

Anaesthesia was induced with midazolam 1 mg, fentanyl 2 μg/kg and propofol 2 mg/kg intravenously. Vecuronium bromide 0.1 mg/kg intravenously was used for muscle relaxation followed by endotracheal intubation. Anaesthesia was maintained with 1-2% sevoflurane in 50% O2 and N2O gas mixture. Intraoperative analgesia was provided with incremental doses of intravenous fentanyl 1 μg/kg and muscle relaxation maintained with intermittent boluses of vecuronium bromide 0.02 mg/kg intravenously.

Ventilation was performed using the Penlon AV 900 ventilator with a rebreathing circuit incorporating a CO2 absorber. A continuous fresh gas flow of 1.6 L/min (0.8 L O2 and 0.8 L N2O), an inspiratory to expiratory ratio of 1:2 and zero end-expiratory pressure was applied. The tidal volume was set at 8 ml/kg and respiratory rate adjusted to maintain EtCO2 between 35 to 45 mmHg throughout the duration of surgery.

We designed this prospective, observational cohort with the primary objective of studying the dynamic effects of extraperitoneal CO2 insufflation in patients undergoing elective laparoscopic extraperitoneal inguinal hernia repair (total extraperitoneal [TEP]) with respect to changes in respiratory mechanics, namely, dynamic respiratory compliance (Cdyn) and also airway resistance (R), work of breathing (WOB), peak inspiratory pressure (PIP) and minute ventilation (MV). The secondary objective was to evaluate the changes in haemodynamics i.e., heart rate (HR) and mean arterial blood pressure (MAP).

The respiratory mechanics were monitored using a side stream spirometry device (respiratory mechanics module, GE medical system, Milwaukee USA) which displayed the readings of Cdyn, WOB, R, PIP and MV.

The insufflation pressure of CO2 was limited to 12 mmHg and maintained throughout the surgery with the patient in neutral position.

The recordings (Cdyn, WOB, R, PIP, MV, HR, SBP, DBP and MAP) were made 5 min after tracheal intubation, every 10 min after insufflation, at the time of deflation, 5 min after deflation and 5 min after tracheal extubation. At the end of surgery, the neuromuscular block was reversed with intravenous neostigmine methylsulphate 50 μg/kg and glycopyrrolate 10 μg/kg.

The statistical analysis was performed using the SPSS program for Windows, version 17.1 (SPSS, Chicago, Illinois, USA).

RESULTS

A total of 100 patients were included in the study. Eighteen patients were excluded post-recruitment from the analysis as they developed significant intraperitoneal CO2 insufflation during surgery. The average age (53.3 ± 15.49 years), weight (70.87 ± 10.32 kg). Amount of CO2 insufflation (50.71 ± 23.67 L) were noted. We noted three patients with subcutaneous emphysema of chest wall, not extending to the neck, after surgery. The respiratory parameters observed during the study are shown in Table 1, and the haemodynamic values are provided in Table 2.

Table 1

Respiratory parameters

Table 2

Haemodynamic parameters

DISCUSSION

The results from our study demonstrate that after extraperitoneal insufflation, the dynamic lung compliance decreased by about 37% from baseline after 10 min of CO2 insufflation (P < 0.01). After 5 min of deflation, the compliance did not return to the baseline value (P < 0.01). The decreased lung compliance and increased PIP reflect reduced diaphragmatic excursion and premature closure of small airways resulting in reduced functional residual capacity.

A preliminary study conducted on nine patients by Bordes et al. reported a significant decrease in end expiratory lung volume from 2115 ± 635 ml to 1716 ± 444 ml and thoracopulmonary compliance from 49.5 ± 6.3 to 40.1 ± 5 ml/cmH2O at 5 min after extraperitoneal insufflation, which is similar to our observations. They also observed that end-expiratory lung volume increased during application of 10 cmH2O PEEP which also homogenised ventilation distribution.[7]

These findings led us to assume that extraperitoneal insufflation effects are similar to those of pneumoperitoneum where there was also increase in the abdominal cavity pressure accompanied with cranial movement of the diaphragm. CT-scan study performed during extraperitoneal insufflation may help in corroborating this mechanism, as previously reported by Andersson during intraperitoneal insufflation in patients undergoing laparoscopic cholecystectomy.[8]

The cephalad displacement of the diaphragm and decreased pulmonary compliance may impair respiratory muscle efficiency and increase the work of breathing, as has been observed in our study.

After CO2 insufflation, the MV required to maintain EtCO2 between 35-45 mmHg was achieved by increasing the respiratory rate. These findings emphasise that there is a significant absorption of CO2 after extraperitoneal insufflation.

We noted a significant increase in HR and MAP till 20 min after insufflation which settled thereafter. This can be explained by the increased sympathetic output as well as initial increase in preload and cardiac output following CO2 insufflation. Our results indicate a significant rise in MAP in contrast to a study by Wright et al. where no changes were reported in the mean arterial pressure.[1]

The limitation of our study is that we have observed the effects of extraperitoneal insufflation in neutral position. However, as head down position and insufflation pressure of more than 12 mmHg for TEP may be practiced by a majority of surgeons, these changes may get exaggerated and have further deleterious effects on respiratory mechanics and haemodynamic parameters.

CONCLUSION

Extraperitoneal insufflation causes significant impairment in respiratory mechanics and haemodynamics. As the TEP approach has gained ascendance, our results call for further research in ways to minimise its consequences in patients with reduced cardiopulmonary reserve.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.