Lparoscopic cholecystectomy was introduced in Canada in early 1990. Its widespread adoption as a therapeutic technique is without precedent in modern surgical history. So popular is this technique that it is now very difficult to undertake prospective clinical trials comparing open and laparoscopic approaches.
General surgeons have continued to develop their expertise in laparoscopic surgery so that it is now commonplace to see procedures such as appendectomy, inguinal hernia repair, gastric surgery, Nissen fundoplication, exploration of common bile duct, large and small bowel surgery performed laparoscopically. Not to be outdone, other surgical specialists are quickly developing expertise in this field. Urologists perform nephrectomies, lymph node excisions, orchidopexies and varicocoele repair by this route. Gynaecologists who, for many years, had experience with simple laparoscopic procedures, have expanded their horizons to include laparoscopic management of infertility, ectopic pregnancy, pelvic pain, bladder neck incompetence and laparoscopic assisted vaginal hysterectomy. Thoracic surgeons have moved from simple thoracoscopies to lung biopsies, wedge resections and pulmonary lobectomies.
What are the implications of these changes for anaesthesia? While each procedure brings its own particular problems, there are some areas which are common to all. The operative technique involves the intra or extra-peritoneal insufflation of carbon dioxide gas through a Verres needle. Electronic variable-flow insufflators terminate flow when a preset pressure is reached, usually between 12 and 18 mmHg. A number of trocars are inserted, the size and location depending on the procedure to be performed. A video laparoscope is inserted through a trocar and the surgical field is visualized by high resolution camera and monitor systems.
Increased PaCO2
During intraperitoneal insufflation of CO2, an increase in PaCO2 has been observed if the minute ventilation is kept constant. During pelvic laparoscopy in the Trendelenburg position, a 20-30% increase in minute ventilation is necessary to maintain normocarbia. Increasing minute ventilation by 12-16% during laparoscopic cholecystectomy maintains the PaCO2 close to the pre-insufflation levels. Patients with preoperative cardiopulmonary disease demonstrate significantly more hypercarbia than normal patients.
During pneumoperitoneum with carbon dioxide, absorption of the gas from the peritoneal cavity and impairment of ventilation by mechanical factors such as abdominal distension and position of the patient, all contribute to the increase in PaCO2. Tan and Lee9 noted that carbon dioxide production increases for the first twenty minutes and then seems to plateau. CO2 is a highly diffusible gas and large amounts are taken up from the abdominal cavity but other factors such as the splanchnic circulation and the concentration gradient between the peritoneal cavity and venous blood can also play a role. Interestingly, during extraperitoneal insufflation, no plateau is seen and increases in PaCO2 and PETCO2 are much more pronounced. Excessive values of PETCO2 can be managed by increasing minute ventilation.
Other factors can contribute to the increase in arterial carbon dioxide.
Ventilation may be impaired by the position of the patient and by abdominal distension
with elevation of the diaphragm. End tidal CO2 should be monitored during laparoscopic
procedures as, generally, it is a reliable indicator of PaCO2.
Subcutaneous Empyhsema, Pneumothorax, Pneumomediastinum and Pneumopericardium
Insufflated carbon dioxide can track along many routes to cause any or all of these problems. Potential channels of communication, between the peritoneal cavity and the pleural and pericardial sacs, may open when intra-peritoneal pressure rises. There may be defects in the diaphragm or tears may be created by the surgeon such as in surgery at the gastro-oesophageal junction. Subcutaneous emphysema can occur almost anywhere depending on the position of the patient.
A high index of suspicion, coupled with careful monitoring, should alert
the anaesthetist to these problems. Development of a tension pneumothorax could be
potentially life-threatening. Most frequent signs include decreased SpO2, increased airway
pressure, increased end-tidal CO2 and a fall in blood pressure. Joris reports that, in
every one of seven patients who developed pneumothoraces, the diagnosis was made by
auscultation.19 This suggests that it would be prudent to place stethoscopes over both
lung fields. Fortunately most pneumothoraces seem to be well tolerated as placement of a
chest tube could compromise the pneumoperitoneum.
CO2 Embolism
This is a rare but potentially lethal complication of laparoscopic
surgery. It generally happens early in the procedure but has been reported to occur later.
The pathophysiology of gas embolism is related to the size of the bubbles and the rate of
entrainment. In laparoscopy, the rapid insufflation of gas under pressure usually leads to
obstruction of venous return and right heart output leading to circulatory collapse.
Management includes cessation of insufflation and release of the pneumoperitoneum.
Resuscitative measures are the same as for air embolism. The high solubility of CO2 in
blood, results in rapid absorption of the gas and usually reversal of the clinical signs.
Pneumoperitoneum for laparoscopic surgery induces hemodynamic changes. The effects of anaesthesia, patient positioning and CO2 must also be considered. There is an increase in mean arterial pressure, systemic and pulmonary vascular resistance. Cardiac index can decrease as much as 50% five minutes after the beginning of insufflation. This is regardless of whether the patient is head-up or head-down, as confirmed by echocardiography.
Increased intra-abdominal pressure results in pooling of blood in the legs. Therefore there is reduced flow in the inferior vena-cava leading to decreased cardiac output. Cardiac and intrathoracic pressures increase with a net fall in right atrial pressure.30 The increase in SVR is related also to release of humoral factors such as vasopressin. After release of the pneumoperitoneum, with the patient still in the head-down position, cardiac output, stroke volume and stroke work indices increase significantly and CVP and SVR decrease.
All these changes seem to be well tolerated in healthy patients. However
since the laparoscopic approach is being increasingly recommended for all patients, for an
ever growing range of procedures, it is important to recognize the problems which may be
encountered in those with cardio- pulmonary disease.
Depending on the surgery to be performed, patients may be placed
head-up, head-down, supine, lateral or in lithotomy position or in any combination of
these. Gravity has profound effects on the respiratory and cardiovascular systems. Head-up
position improves diaphragmatic function and respiratory status15 while decreasing venous
return, leading to a fall in cardiac output and mean arterial blood pressure.30 The
head-down position can result in decreased functional residual capacity, total lung volume
and pulmonary compliance.15 Venous return increases but this seems to have little effect
on cardiac performance, at least in normal patients.35 In patients with coronary artery
disease, these changes are magnified and may lead to increased myocardial oxygen demand.15
For advanced laparoscopic surgery, general anaesthesia is required. During the surgeon's learning curve, the duration of the procedure may far exceed that for open surgery. Once a procedure is well established, there seems to be no significant difference in the time taken as shown by Ortega for appendectomies. This may not be true for procedures such as pulmonary lobectomy where the dissection is slow and tedious.
In planning the anaesthetic, the anaesthetist should keep in mind the pathophysiology of laparoscopic surgery and its possible effects on the patient. Pre-existing cardiopulmonary disease, especially if the planned surgery is expected to take a long time, should suggest that aggressive monitoring be considered. Sudden unexpected complications, such as massive bleeding, can arise at any time and may necessitate conversion to an open procedure. Good muscle relaxation is essential if intra- abdominal and inflation pressures are not to rise above acceptable limits. Choice of anaesthetic agents is left to the individual anaesthetist but many patients, after laparoscopic surgery, are now discharged on the day of surgery. Therfore it is important to choose agents which allow rapid emergence and have a low incidence of nausea and vomiting. Even though decreased pain, compared to open surgery, is cited as one of the major advantages of laparoscopic surgery, these patients still require analgesics.
In summary, advances in laparoscopic surgery present new challenges to
anaesthetists. An understanding of the basic pathophysiology of laparoscopy is required
before dealing with the individual problems of each patient and procedure.
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