By
Prof. M. Ezzat Moemen (M.D)
Dr. Omayma Abdel Azem Hassan (MSC)
Nasr City Health Insurance Hospital, Cairo
And
Prof. Fathy Sayed Nasr (MD)

1. Prof. Salwa A. Shaalan (MD)

Faculty of Medicine for Girls

Al- Azhar University, Cairo

From Thesis submitted (1999), by Dr. Omayma Abdel Azem Hassan (MSC), for the partial fulfillment of the requirements for the MD degree in anaesthesia.

ABSTRACT

The present study has been conducted at Nasr City Health Insurance Hospital (600 beds), after the approval of the Council of Faculty of Medicine for Girls, Al-Azhar University and the authorities of the General Organization of Health Insurance.

The study has been designed to investigate the intraoperative ventilatory changes during laparoscopic versus open cholecystectomy as previous literature for this period is poor.  However, literature is rich concerning the post operative changes in spirometric pulmonary functions.

The study has been carried out on 25 patients of either sex, ASA I and II.  Their age ranged between 30 and 50 years, and their body weight between 60 and 75 kg.  They were included in two groups after their consent for anaesthesia and the type of surgical intervention:
Group I: included 10 patients scheduled for open cholecystectomy.
Group II: included 15 patients scheduled for laparoscopic cholecystectomy.

All operations were carried out on morning lists by either one or the other of two top surgeons or both of them.  Anaesthestic management was carried out by the worker (Dr. Omayma A. Hassan) guided by one of the supervisors (Prof. M. Ezzat Moemen) and helped by the same surgical assistants and nursing staff.  Pieces of equipment for anaesthetic management and monitoring were fixed for all patients with continuous calibration and maintenance.

Each patient was premedicated by i.m. midazolam (0.15 mg/kg), 30 min. before operation A 16 gauge cannula was fixed at a peripheral vein and 500 mls volume of Ringer solution was delivered for prehydrtion followed by intraoperative 10ml/kg rate.

Anaesthesia was delivered through Narkomed anaesthetic machine.  After preoxygenation, induction was done by fentanyl (1 μg/kg) and a sleep dose of 2.5% thiopentone.  Suxamethonium (1 mg/kg) facilitated tracheal intubation.  Anaesthesia was maintained by halothane (0.5%), 50% N2O in oxygen and atracurium (0.5 mg/kg) for muscle relaxation with repeated doses as needed.  Ventilation was initially adjusted to keep PeTCO2 around 30-35 mmHg and a controlled RR of 10-12/min. ECG, SpO2, PeTCO2 and inspired-expired gases were constantly measured by Datex monitor (Helsinki, Finland). Cannulatins of raidal artery and internal juglar vein were done after induction and before the end of anaesthesia for measurement of blood gases by ABL3 blood gas analyzer (Radiometer, Copenhagen, Denmark).

Open cholecystectomy for the control group of patients was surgically done by the conventional procedure.  Laparoscopic cholecystectomy for the study group was done by using Storz electronic laparoflator.  Insufflation of CO2 to a pressure around 13-15 mmHg intraperitoneally followed by 10-15º reverse Trendlenburg lift facilitated laparoscopic surgery.  Ventilatory and haemodynamic stability were assured intraoperatively by optimizing the settings of the ventilator and proper fluid therapy.  At the end of surgery, anaesthetics were discontinued and muscle relaxation was reversed by clinical titration using proper doses of neostigmine and atropine and extubation was done.

Patients were kept pain free in the semistting position with oxygen mask and proper monitoring in the recovery area till being allowed to be transferred to the ward.

The following measurements were done for gas exchange just before insufflation and just after deflation of CO2 in the laparoscopic group and at the start and end of anaesthesia in the open cholecystectomy control group.

1. P(A-a)O2 = Alveolar-arterial oxygen tension gradient.
2. P(a-ET)CO2 = Arterial – end tidal CO2 tension gradient.
3. PaO2/FiO2 = Oxygenation index.
4. P(A-a)O2/PaO2) = Respiration index.
5. P (a/A)O2 – Arterial-alveolar oxygen tension ratio.
6. Blood gases: Arterial and mixed venous blood.

1. 
   Qs/Qt = Measured shunt =
2. Qs/Qt = calculated shunt
3. Qs/Qt = [(1-SaO2) / (1-SvO2)]
4. Qs/Qt = 

Date were statistically analyzed using students “t” paired test for intragroup comparison and unpaired test for intergroup comparison.  Correlations between measured shunt and each of the other oxygenation parameters including calculated shunts were done using Pearson regression equation.

Results showed intragroup significant changes for Pa/AO2, PaCO2 and serum HCO3 in open group and significant intragroup changes for SvO2, PH and serum HCO3 in laparoscopic group.  An intergroup significant change was noted for P(a/A)O2.  However, all these statistically significant changes were clinically non significant.

Correlations between measured shunt and other oxygenation parameters showed negative relationships except for correlation with Cc’O2 which is logic, being the important item in the shunt equation.

No complications related to the anaesthetic or the surgical technique were reported in any patient of the two groups.

The following could be concluded:

1. Ventilatory gas exchange during open or laparscopic choelcystectomy is affected by common factors of decreasing hypoxic pulmonary vasoconstriction and the development of regional atelectatic areas in the lung.  The effect of carbon dioxide peritoneal insufflation for laparoscopic cholecystectomy can be nullified by the reverse Trendlenburg patient positioning and optimizing the ventilator settings.  In addition, optimizing halothane concentrations and proper fluid therapy can maintain haemodynamic stability with the net result of normalizing intraoperative gas exchange.

1. Monitoring gas exchange during laparoscopic cholecystectomy my be achieved by any of the oxygenation parameters used in the present study, namely, P(A-a)O2, P(a-ET)CO2, PaO2/FiO2, P(a/A)O2, P(A-a)O2/PaO2, or Qs/Qt.  However, these parameters are non-sensitive tools of measuring gas exchange.

1. The measured shunt should be considered as the “Gold Standard” for measuring gas exchange during laparoscopic cholecystectomy because the study did not prove any positive correlation between the measured shunt and any of the other oxygenation parameters or either of two calculated shunt equations.

1. The intraoperative non deleterious ventilatory and haemodynamic changes during laparoscopic cholecystectomy (proved in the present study), add positively to the beneficial changes of spirometric post-operative achievements allowing the technique to be preferred for cholecystectomy provided that it should be carried out by a surgeon with adequate experience in using the surgical laparoscope and an anaesthetist with sufficient knowledge of ventilatory mechanics.

The present study recommends the following:

1. A central venous line should be fixed for each patient undergoing laparoscopic cholecystectomy, for two reasons.  Firstly, this line may be used for management of gas embolism in its rare occurrence.  Secondly, mixed venous blood samples will facilitate measuring the shunt fraction if clinically needed by the anesthetist at any situation peri-operatively.

1. The present study showing benign changes in ventilatory gas exchange parameters with haemodynamic stability during laparoscopic cholecystectomy in ASA I and II patients, would encourage other authors to study the same parameters for gas exchange in ASA III and IV patients undergoing laparoscopic cholecystectomy.