The insufflator in laparoscopy

The description of the insufflator in laparoscopy covers all aspects of this piece of equipment. The technical key steps of the chapter are presented in a step by step way: background, operating principles, prerequisite for laparoscopy, available features, advantages and disadvantages, use and settings, pathophysiological effects, surgical complications, alternatives, criteria for purchase.

Browse the WORLD
Virtual University
English ▼

The   insufflator   in   laparoscopy

Authors
A Garcia, D Mutter, I Jourdan
Abstract
The description of the insufflator in laparoscopy covers all aspects of this piece of equipment.
The technical key steps of the chapter are presented in a step by step way: background, operating principles, prerequisite for laparoscopy, available features, advantages and disadvantages, use and settings, pathophysiological effects, surgical complications, alternatives, criteria for purchase.
Media type
Publication
2005-09
Popular
Favorites
Favorites Media
Audio
en fr cn es


E-publication
WeBSurg.com, Sept 2005;5(09).
URL: http://www.websurg.com/doi-ot02en305.htm

The   insufflator   in   laparoscopy

1. Introduction
The insufflator is a key element in laparoscopic surgery. It helps create an ideal operative space, hence facilitating surgical procedures. The safety of the procedures depends on the quality of the insufflator. The surgeon has to know all about the insufflator’s basic principles. Thus future related applications will be maximized.
2. Background
• Insufflator
An insufflator is necessary to:
- create the pneumoperitoneum;
- maintain it during the procedure;
- control gas pressure within the pneumoperitoneum;
- periodically renew the gas.
• Pneumoperitoneum
A pneumoperitoneum can be exploited to create an operative space for carrying out laparoscopic surgery.
• Background
Laparoscopic surgery has changed the established notion of the operative field.
The first experiments were carried out on animals by George Kelling in 1901 and on humans by Hans Christian Jacobaeus in 1910. Air, oxygen (O2) and nitrous oxide (N2O) were all used before carbon dioxide (CO2) to create the pneumoperitoneum. CO2, which diffuses easily, is highly soluble, and is eliminated through respiration. Its solubility limits the risk of gas embolism. Helium (He), which does not cause the same metabolic problems as CO2, is useful in endocrine surgery, particularly for pheochromocytomas. Xenon (Xe) appears to offer good cardiac stability.
3. Operating principles
• Principles
In order to create a working space between the organs and the abdominal wall, a pneumoperitoneum is established. Gas is injected by an insufflator into the peritoneal cavity, causing distension in the abdominal wall.

An insufflator works as a pressure-controlled closed circuit. The gas is either provided by a bottle with a pressure of 50-200 bars or by a centrally supplied wall unit (3.5-5 bars). The usual intra-abdominal pressure used is 12 mm Hg. Since 1 bar equals 760 mm Hg, it is obvious that for safety reasons one of the insufflator's functions is to serve as a pressure reduction valve to allow safe delivery of gas at a pressure of between 50 and 80 mm Hg. A flow control valve regulates gas delivery and monitors the pressure in the circuit. When the pressure is too low, the valve opens and gas enters the circuit. If the pressure in the circuit is equal to that required, the valve remains closed. This mechanism is relatively straightforward, although minor variations exist among different brands of equipment. Modern insufflators allow different flow rates to be used for insufflation. The lowest rate (1 L/min) is used when creating a pneumoperitoneum with a Veress needle.
• Monitoring
Monitoring of intra-abdominal pressure:
The insufflator is only able to accurately measure intra-abdominal pressure when there is minimal gas flow since at this moment there is pressure equilibrium between the insufflator and the peritoneal cavity. For this reason, the insufflator creates the pneumoperitoneum in a rapid cyclical fashion: insufflation – stop for pressure measurement – insufflation – stop for pressure measurement – etc.

The gas flow rate corresponds to the maximum flow rate delivered by the insufflator in a given period of time. However, because the insufflator stops inflation during each cycle to measure the pressure, the actual flow rate per minute is always less than the instantaneous flow rate displayed by the insufflator.
• Other measurements
Other measurements carried out by the insufflator:
The total volume of gas delivered to the patient is measured. In the presence of a major leak, this value will rise steeply indicating that the gas bottle is being emptied rapidly. The pressure in the gas bottle will remain above 50 bars so long as there is liquid CO2 in the bottle. When the CO2 reserve falls below 20%, the contents of the bottle become gaseous and the pressure drops.
4. Prerequisite for laparoscopy
Insufflators make it possible to regulate the pressure and thus maintain a stable pneumoperitoneum. Before 1988, gynecologists were the only surgeons to use laparoscopy regularly. The pneumoperitoneum used then was around 30 mm Hg. Such pressures occasionally resulted in gas embolism. Currently it is recommended to keep the pressure below 15 mm Hg and as low as 6 mm Hg in pediatric surgery. Most insufflators have safety systems that prevent the accidental increase in pneumoperitoneum pressure above 15 mm Hg. Many surgeons set a maximum pressure of 12 mm Hg since; above 12 mm Hg, the cardiac ejection volume is significantly reduced. In addition to rigidifying the abdominal wall allowing highly precise operative movements, a pneumoperitoneum also aids venous capillary hemostasis, since internal venous pressure is lower than the pressure inside the abdominal cavity.

The ideal insufflator:
- uses a gas that is invisible, odorless, inert, soluble in the blood, easily eliminated by respiration and inexpensive;
- permits a high flow rate (>16 l/min actual vs. instantaneous);
- humidifies the gas;
- displays values for flow rate, volume, pressure and gas composition on a monitor and is equipped with a pressure alarm;
- automatically exsufflates in case of excessive pressure.
5. Available features
• Option 1
On-screen readout of circuit pressure:
Certain insufflators are connected between the camera and the video monitor. They superimpose the current pressure in the circuit over the operative image. This allows the laparoscopist to monitor the pressure of the pneumoperitoneum. The disadvantage of this system is that it adds connections between insufflator and monitor and can result in deterioration in the operative image.
• Option 2
Automatic exsufflation:
One of the most serious complications of laparoscopy is gas embolism, which can result from excessive gas pressure within the abdomen. Such accidents can be prevented by automatic limitation of this excessive pressure by gas exsufflation. If excessive pressure develops within the system, then the equipment automatically vents some of the gas reducing the risk of gas embolism. This safety mechanism should be part of all insufflators.

• Option 3
Gas warming:
Laparoscopy can result in significant heat loss by the patient. Heat loss is proportional to the length of the procedure, but is also affected by gas temperature and humidity. Manufacturers have proposed equipment that warms the gas to a temperature of around 41°C. This is monitored where the gas exits from the insufflator or at the termination of the insufflation tubing using temperature sensors. Unfortunately, it has been shown than none of these systems prevent a drop in the patient's core temperature. In fact, the only effective method of preventing heat loss is to insufflate using humidified gas. Ideally insufflators should allow humidification of the insufflation gas under sterile conditions.
• Option 4
Gas replacement:
The composition of the gas in the pneumoperitoneum varies over time. The diffusion capacity of CO2 leads to its progressive elimination due to absorption by the blood and then excretion by respiration. At the same time, the CO2 is replaced by diffusion of the N2O anesthetic gas into the peritoneal cavity. This change in the composition of the gas mixture results in an increased risk of gas embolism as N2O is poorly soluble. There is also the potential risk of explosion due to the large concentration of N2O in the abdomen. Continuous, automatic replacement of CO2 in the pneumoperitoneum prevents these potential complications.
• Option 5
Smoke extraction:
For certain uses, companies have developed systems that allow gas to be aspirated from the operative field and to compensate the aspirated gas, volume for volume, with injected gas. This system is particularly useful in endorectal surgery where the working space is reduced, and where electrocautery would otherwise cause the operative field to rapidly be obscured by smoke. The system aspirates the gas continuously and compensates for this loss by injecting new gas through a second port.
6. Advantages and disadvantages
• Advantages/Drawbacks
Advantages and disadvantages of different gases:
- Air:
The use of air has been proposed, but the main disadvantage is its weak diffusion capacity in the blood, making it more hazardous in the event of gas embolism. Its slow elimination from the abdominal cavity also causes prolonged postoperative pain.

- Oxygen:
Oxygen is contraindicated for creating a pneumoperitoneum because it is explosive. Electrocautery is impossible, and its use has been abandoned.

- Nitrous oxide:
This gas, widely used in anesthesia, has been proposed for carrying out diagnostic laparoscopies. The explosion risk has long been recognized and it is no longer used to maintain the pneumoperitoneum. Even when not used to establish the pneumoperitoneum it slowly diffuses into the abdominal cavity from the circulation and needs to be evacuated (see section 5-gas replacement).

- Helium:
This is a non-inflammable, non-toxic and biologically inert gas. It has the advantage when treating pheochromocytomas of limiting the discharge of catecholamines. Nevertheless, because of its weak diffusion capacity, in the event of gas embolism, it can cause vascular occlusion leading to neurological deficits. Its use is not standard for laparoscopies.

- Other rare gases:
Xenon and Argon have few advantages, other than good hemodynamic stability for xenon, which would allow laparoscopy in patients with severe cardiomyopathy. They are rarely used.
• Hazards
Hazards from pressurized gases and liquids:
As has already been discussed, a significant reduction in the cardiac index is observed with an intra-abdominal pressure higher than 12 mm Hg. However, sudden high increases in pressure can also impair ventilation and cause pulmonary embolism.

Various instruments utilize high pressure gas or liquids during laparoscopic surgery. These include laser coagulation, Argon jet coagulation or tissue glue spraying. They can insufflate several liters of gas per minute into the operative cavity. High-flow-rate irrigation equipment can also increase the overall volume injected into the operative cavity. If high intra-abdominal pressure is left uncorrected, serious injury can be sustained. Systems that control pressure and provide automatic exsufflation increase patient safety.

Things that can increase the pressure:
- laser: 1 to 5 L/min;
- Argon (electrosurgery): 0.5 to 3 L/min;
- tissue glue: 3 to 10 L/min;
- irrigation: 0.5 to 5 L/min.
7. Use and settings
• Safety systems
• Example 1
It is recommended that maximal pressure is always set below 15 mm Hg and usually limited to 12 mm Hg. In pediatric surgery, the pressure should be in the range of 6 mm Hg.

All insufflators on the market allow operative pressure to be pre-adjusted between 0 and 15 mm Hg. Due to the potential dangers of excessive pressure, this pressure cannot be inadvertently exceeded. Two safety systems are found: there is either a security catch that locks the regulator dial or it is necessary to press two preset buttons simultaneously to readjust the pressure setting.
• Other parameters
Modern insufflators allow a choice between two or three insufflation flow rates. The lowest flow rate (1 L/min) is used to create the pneumoperitoneum. This avoids a sudden reduction in venous return and allows the cardiovascular system to adapt.

Before use of any insufflator, a certain number of parameters must be checked and the necessary adjustments carried out, just like a pilot's checklist before takeoff:
- gas gauge:
- sufficient quantity of gas in the bottle;
- presence of a reserve bottle;
- connection to a central gas distribution system (preferable).

This is important, as most insufflators have a gas reserve of several liters, which is sufficient to create the initial pneumoperitoneum. Gas flow failure only occurs later, forcing a halt in the operation while the problem is solved.

- verify the presence of a new filter (disposable only) at the insufflator's outlet;

- ensure correct setting of maximum insufflation pressure (adult: max. 12-15 mm Hg, small child: max. 6 mm Hg usually);

- set to minimum gas flow (1 L/min) for creating the pneumoperitoneum. The flow rate can be increased to its maximum only once the pneumoperitoneum is correctly established.

Careful attention must be paid to the pressure measured in the abdominal cavity during creation of the pneumoperitoneum. Normally, the pressure is zero or even slightly negative at the outset. It progressively increases, along with an increase in abdominal size. Liver percussion sounds should disappear quickly, followed by generalized abdominal distention. If intra-abdominal pressure is high to begin with, insufflation must be stopped in order to determine the source of the problem (closed valve, insufflation into the abdominal wall, etc.). If the pressure increases rapidly without increase in abdominal size, the source of the problem must be sought (trocar tap turned off, insufflation into tissues, patient insufficiently relaxed, etc.). The quantity of gas insufflated can also be monitored but this parameter is of no use for monitoring the pneumoperitoneum as gas may leak or be intentionally discharged during the procedure.


8. Pathophysiological effects
• Cardiovascular system
The pneumoperitoneum decreases venous return (preload) and cardiac output; it increases the pulse rate, average arterial pressure, systemic vascular resistance (afterload) and pulmonary resistance. These hemodynamic and cardiovascular changes are produced by the increase in intra-abdominal pressure and stimulation of the vasoactive neurohormonal system (vasopressin and the renin-aldosterone-angiotensin system). These changes are independent of the type of gas used and are well tolerated in patients in good health so long as the intra-abdominal pressure does not exceed 15 mm Hg. These hemodynamic changes are more pronounced if the patient is in the head-up position, which induces venous stasis in the lower extremities and increases the risk in deep vein thrombosis.

Hemodynamic changes are the greatest during induction of the pneumoperitoneum. Insufflation must be as slow as possible in order for the cardiovascular system to adapt progressively. The patient is placed in Trendelenburg or reverse Trendelenburg once intra-abdominal pressure is stable. Adequate preoperative volume loading helps compensate for these disturbances.

A hyperdynamic period is observed when the pneumoperitoneum is exsufflated.
• Pulmonary system
Pulmonary system and gas exchange:
The use of CO2 for the pneumoperitoneum causes hypercapnia and respiratory acidosis due to CO2 absorption into the systemic circulation from the peritoneal cavity (there is no increase in PaCO2 if another gas is used). The increase in intra-abdominal pressure caused by the pneumoperitoneum results in an increase in intrathoracic pressure, a decrease in thoracopulmonary compliance and an increase in airways resistance (restrictive syndrome). The lung bases are compressed due to anesthetic-induced diaphragmatic relaxation and the increase in intra-abdominal pressure. This reduces lung volume and pulmonary compliance, increases the physiological dead space and creates a ventilation-perfusion mismatch. The Trendelenburg position aggravates these effects.

Gas exchange during laparoscopy can be improved with the choice of anesthetic technique and the use of positive end-expiratory pressure (PEEP). During CO2 insufflation, PaCO2 will increase 8-10 mm Hg, with a corresponding reduction in pH, before reaching a plateau at about 15-20 minutes after establishing the pneumoperitoneum. A patient in good health usually compensates for the pulmonary changes caused by the CO2 in the pneumoperitoneum.
• Organ perfusion
Intra-abdominal organ perfusion:
• Renal perfusion
The pneumoperitoneum reduces renal perfusion and glomerular filtration rate, which is reflected by a reduction in urine output. Increased intra-abdominal pressure causes direct pressure on the renal parenchyma, as well as on renal arteries and veins. Renal function decreases proportionally to the increase in intra-abdominal pressure. The pneumoperitoneum also activates the renin-angiotensin system, which causes renal vasoconstriction. An intra-abdominal pressure of <15 mm Hg is of no consequence in patients with normal renal function.

• Portal perfusion
Circulation in the hepatoportal system diminishes progressively with an increase in intra-abdominal pressure. Hepatic enzyme levels may elevate with prolonged laparoscopy or excessive intra-abdominal pressure.

• Splanchnic perfusion
Increased intra-abdominal pressure mechanically compresses mesenteric vessels and capillaries, reducing splanchnic microcirculation and disrupting oxygen diffusion to the intra-abdominal organs. Patients in good health compensate for this decreased perfusion.
• Immune system
Stress response and the immune system:
The influence of the pneumoperitoneum on the immune system and the response to stress is not clearly understood. Most studies are experimental and measure indirect parameters (cytokines, products of cellular degradation), rather than intrinsic activity of the immune cells (concentration, activity).

Results from studies looking at the influence of parameters such as pressure and type of gas are contradictory. It appears that, compared with CO2, helium depresses cellular immunity less, limits bacterial translocation and reduces the stress response. However, these results do not appear to be confirmed in clinical practice.

When laparoscopy was introduced, cases of metastases at the trocar scar site were reported. This complication can be avoided if certain precautions are taken, which include minimal tumor handling, trocar fixation to avoid disconnection, incision irrigation with an iodine solution and protection of the abdominal wall during extraction of the specimen. At present time, the number of metastases to the wall after laparoscopy is no greater than that observed after laparotomy.
9. Surgical complications I
• Injuries/pneumoperitoneum
• Generalities
Injuries during induction of the pneumoperitoneum:
Twenty to forty percent of complications that occur during a laparoscopy occur during creation of the pneumoperitoneum. Although rare (<1% of all laparoscopic procedures), these complications are often serious.

Two techniques have been described for creating the pneumoperitoneum: the closed technique using a Veress needle (1936) and Hasson's open technique (1971). The open technique is preferable due to reduced morbidity associated with its use. Nonetheless, the same type of complications can occur with both techniques.
• Vascular injuries
Vascular injuries are rarer (0.04-0.05%) than visceral lesions, but potentially more dangerous (mortality: 8-17%).
Epigastric vessels, followed by those of the greater omentum, are the most often affected. However, any vessel can be injured during insertion of the Veress needle or a trocar. Major vessel damage (aorta, vena cava, portal or iliac vessels, etc.), while exceptional, is fatal in almost one case in two (44% in reported literature).



• Visceral injuries
The small intestine is most often affected, followed by the colon and the liver. The morbidity is usually associated with a failure to recognize that an injury has occurred. If left untreated for the first 24 hours major septic complications develop (frequency: 0.06-0.14%; mortality: up to 20% if the lesion is unrecognized).
• Gas embolism
• Mechanisms
This is a very rare complication (<0.6%), but is potentially lethal. Pulmonary embolism is the most frequent; cases of coronary and cerebral artery emboli have also been described.

There are three mechanisms of gas embolism:
a) The most frequent occurs during creation of the pneumoperitoneum and is due to direct puncture of a vessel with the Veress needle or the first trocar. It is important to use a safe technique when inserting trocars and to use low flow during insufflation (<1 L/min) when creating the pneumoperitoneum.
b) Intraoperative injury of a vessel within a parenchymal organ (the liver, for example) can result in a large flow of gas directly into the circulation.
c) Rarely, gas embolism can be caused by excessive intra-abdominal pressure (>20 mm Hg) when using a gas like helium that is only slightly soluble.

Since CO2 is highly soluble and easily eliminated, the risk of gas embolism is very slight. In fact, the equivalent of 2 mL/kg/min of CO2 must be injected into an animal's vein before potentially fatal cardiac problems are observed. If the pneumoperitoneum is not renewed regularly, its composition changes and contains an increasing amount of N2O from the anesthetic. This N2O, which also carries a risk of explosion, is less soluble than CO2 and can therefore lead to a gas embolism. Helium, which is only very slightly soluble, is less well tolerated if gas embolism occurs and only 0.1 mL/kg/min is necessary to cause cardiac complications.
• Management
To avoid the risk of gas embolism, one must:
- use a safe technique when placing trocars;
- avoid excessive intra-abdominal pressure;
- use a highly soluble gas.

Trans-esophageal Doppler echography is the most sensitive means to detect gas embolism, but it is not routinely used in laparoscopic surgery. Gas embolism is usually suspected based on a decrease in end-tidal CO2, which results from a reduction in cardiac output and an increase in dead space. A simultaneous drop in PaO2 increases suspicion of pulmonary embolism. ECG changes are also observed if the embolism is large.

If gas embolism is suspected, insufflation is stopped immediately and the pneumoperitoneum is exsufflated. The patient is placed in Trendelenburg with left lateral tilt to limit gas flow from the right ventricle into the pulmonary circulation. Administration of N2O is stopped, and the patient is ventilated with 100% O2 to correct hypoxia. The patient is hyperventilated to counteract the increase in dead space and to increase pulmonary excretion of CO2. If these simple measures are not sufficient, a central venous catheter must be inserted into the pulmonary artery to aspirate the gas. Usually, the high solubility of CO2 allows rapid reversion of the symptoms of gas embolism without treatment. The elimination of CO2 via the lungs is facilitated by the sharp concentration gradient that exists across the alveoli since the ventilation gas is almost free of CO2.
• Diffusion
• Subcutaneous emphysema
During laparoscopy, CO2 under pressure can diffuse, dissect extraperitoneal tissue, and cause subcutaneous emphysema. This effect may be accidental or inevitable (extraperitoneal surgery). The consequence of this complication is an increase in CO2 absorption leading to an increase in PaCO2 absorption, which is sometimes uncontrollable. This increase in PaCO2 is proportional to the severity of the emphysema.

Any increase in PaCO2 after the first 20 minutes of pneumoperitoneum must cause the surgeon to suspect the development of subcutaneous emphysema. Usually an increase in minute ventilation stabilizes the situation. If this is not the case, insufflation must be momentarily interrupted so that the CO2 can be eliminated.



• Pneumothorax
Intra-abdominal pressure can open vestigial embryonic peritoneopleural channels and provoke a 'spontaneous' pneumothorax. In practice, this almost always occurs during surgery near the diaphragm, classically during lower esophageal dissection (fundoplication, for example).

This results in an increased airways pressure and PaCO2, and a decreased PaO2 and arterial oxygen saturation. From a hemodynamic standpoint, the pneumothorax increases pulmonary resistance and diminishes cardiac output, which is partially compensated for by a rising tachycardia.

Treatment consists in using PEEP (5 cm H2O). This is usually sufficient to re-inflate the lung and flush out the CO2 from the pleural cavity, avoiding thoracic drainage and correcting the hemodynamic disturbances. The following additional measures are also useful: stop N2O administration, increase the fraction of inspired O2 and decrease intra-abdominal pressure. If a radiograph at the end of the procedure demonstrates a persistent pneumothorax, it is usually asymptomatic. Thoracentesis is unnecessary, as the CO2 will be resorbed within 30 minutes, and the pneumothorax will disappear.

It is important to differentiate a CO2 pneumothorax from that resulting from the rupture of emphysematous alveoli caused by positive-pressure ventilation used during laparoscopy. In this case, PEEP will aggravate the situation by reducing cardiac output even further. Air in a pneumothorax will not be eliminated spontaneously like CO2 and thoracic drainage is necessary.
• Pneumomediastinum
The principle is identical to that of the pneumothorax. Gas can diffuse via the retroperitoneum or during esophageal dissection near the diaphragm. The problem here is the possible development of subcutaneous emphysema in the face and neck, particularly in the head-up position. This disappears spontaneously when the pneumoperitoneum is stopped and does not require treatment.
• Pneumopericardium
This rare complication is due to the recannalization of vestigial embryonic peritoneopericardial channels or to a puncture of the pericardial envelope. There are hemodynamic consequences if intra-abdominal pressure is excessive. Generally no symptoms occur at pressure <15 mm Hg.
• Excessive pressure
• Hyperpressure 1
Excessive intra-abdominal pressure:
Any increase in intra-abdominal pressure leads to circulatory, cardiac and respiratory changes. Excessive pressure aggravates these changes and increases the risk of gas diffusion out of the abdominal cavity (gas embolism, subcutaneous emphysema, etc.). Tolerance varies between individuals and depends upon the physical condition of the patient. A pressure of <12 mm Hg with an adult in good health is considered safe (<7 mm Hg in children). These changes are partially compensated for by adequate preoperative volume loading. It is recommended to use the lowest intra-abdominal pressure that will result in an adequate exposure of the operative field.
• Hyperpressure 2
Excessive pressure occurs most frequently when a patient is no longer sufficiently paralyzed and anesthesia is not deep enough. Forceful contraction of the abdominal wall musculature can cause significant intra-abdominal pressure exceeding 20 mm Hg. The rapid introduction into the abdominal cavity of liquid (irrigation, lavage) or of another gas (Argon coagulation) can also cause excessive pressure rises. In rare instances, the insufflator can malfunction, and this is often very difficult to detect.

Vigilance to these situations is essential and when suspected, surgery must be interrupted momentarily and a trocar opened to evacuate the pneumoperitoneum. Using an insufflator that is capable of automatic exsufflation is an added safety measure.
• Other complications
• Bacterial contamination
Bacterial contamination of the patient:
The use of non-sterile gas during laparoscopy involves the risk of potential contamination of the patient. A disposable filter interposed between the insufflator output and the patient-side sterile gas tubing will prevent this type of contamination.
• Cellular dissemination
Cellular dissemination into the environment:
There is a theoretical risk of dissemination of infected or cancerous cells from the patient into the environment with the possible contamination of personnel or equipment. Although filters connected to trocar valves would be a means of prevention, the ability of this cellular aerosol to seed and grow has not been demonstrated.
10. Surgical complications II
Pain:
Laparoscopic surgery does not completely eliminate postoperative pain, but it is of a different character to that associated with open surgery. Parietal pain, which is predominant with open surgery, is reduced, improving mobilization and respiration. The patient is more aware of deep visceral pain which, in open surgery, is masked by the parietal discomfort.
Another result of laparoscopy is scapular pain. This is due to constant diaphragmatic tension caused by the pneumoperitoneum and perhaps to irritation of the diaphragm by CO2 (acidity). It can be reduced by complete evacuation of CO2 at the end of the procedure, by lavage with warm saline and possibly by subdiaphragmatic instillation of a local anesthetic (bupivacaine, for example). The usefulness of heated and humidified gas during the procedure remains controversial.

Nausea/vomiting:
Nausea and vomiting after laparoscopy do not appear to be any different than after open surgery. Their origin is multifactorial, and the frequency depends mainly on the type of anesthesia, the surgery and the postoperative administration of opiates.

Respiratory function
As with open surgery, laparoscopy also leads to a degree of respiratory compromise due to diaphragmatic dysfunction. The resulting alveolar collapse may produce hypoxia and increases the work of respiration. The administration of opiates to control postoperative pain can cause further respiratory depression. In laparoscopy, postoperative pain is less severe and of shorter duration and thus respiratory compromise is minimized. For these reasons, laparoscopy remains the surgical technique of choice in patients at high risk for postoperative respiratory complications (obesity, chronic obstructive pulmonary disease).

Special case: pregnancy
Today, pregnancy is no longer an absolute contraindication for laparoscopy. However, its indication remains limited in general to emergency situations such as acute cholecystitis and acute appendicitis. Given the increased risk of abortion during the first trimester and the volume of the uterus during the third trimester, the second trimester is the period with the least risk.

Laparoscopy is preferable to open surgery because the reduced postoperative discomfort allows minimal use of opiates and causes little deterioration in maternal respiratory function. However, the increase in intra-abdominal pressure during the procedure reduces maternal respiratory compliance and uterine perfusion. Thus, it is essential to use the lowest possible pressure during surgery. A pressure of <10 mm Hg is desirable. The patient must also be placed in a position that avoids compression of the inferior vena cava by the uterus, which aggravates reduction in venous return. Using CO2 can cause fetal acidosis with the risk of abortion if maternal hyperventilation is insufficient. It is important to monitor end-tidal CO2 and blood gases closely to ensure adequate elimination of CO2 and avoid fetal acidosis.
11. Alternatives
• Mechanical exposure
• Objective
Numerous physiological changes are linked to increasing the intra-abdominal pressure notably affecting the cardiovascular and respiratory systems. Even if the consequences of these changes are limited in most patients, it is occasionally important to avoid even small changes. Creating an operative space with mechanical means makes it possible to work with a pressure equivalent to that of the operating room.
• Retractors
Abdominal wall lifting devices:
A number of systems for lifting the abdominal wall are on the market. More than 10 different systems with intra-abdominal retraction or placement of subcutaneous fixation systems have been invented since 1997. The mechanical portion of the retractor is placed in the abdominal cavity through a 10 mm to 20 mm incision and connected to a system of articulations attached to the operating table. The advantage of these systems is the prevention of complications secondary to excessive intra-abdominal pressure. They also avoid the risk of gas embolism during procedures such as hepatectomy where central venous injury may occur. However, they do have the disadvantage of providing a more limited operative field compared with a conventional pneumoperitoneum. Postoperative pain is the same with both techniques, but operating time is significantly longer. Complete exploration of the operative cavity is not possible with these kinds of retraction devices.

Since the pneumoperitoneum has been implicated in the seeding of cancerous cells to trocar ports, abdominal wall retractors could be of use in preventing such a complication: an experimental study comparing the effects of laparotomy, laparoscopy with insufflation and parietal retraction has demonstrated a lower incidence of seeding with retractor use. This experimental finding has never been confirmed by clinical observation. Indeed the poor exposure obtained with retractors may well lead to inappropriate tumor handling leading to increased risk of intraoperative tumor spread. In our own experience, no significant advantage is offered by such devices.
• Tightness balloon
Tightness of a large port incision may be obtained thanks to specific balloon trocars.
• Exposure balloons
The operative space can be created with the help of dissection balloons, but in most cases, the field is then maintained by a standard insufflator. Balloons have also been used to maintain the operative space; however, there is no obvious advantage to using this technique, which often complicates the procedure.
• Disadvantages
Overcrowding:
Systems for mechanical exposure always involve at least one arm attached to the operating table, impeding easy manipulation of operating instruments.

Space between organs:
Insufflation has the effect of retracting tissues around the operative field as it pushes up the diaphragm and abdominal wall, and displaces the viscera. This facilitates the mobilization and insertion of instruments.

Evacuation of smoke:
The gas injected into the abdomen can facilitate smoke evacuation. With mechanical exposure systems, when smoke accumulates in the abdomen there is no way to evacuate it except by repeated aspiration. The pneumoperitoneum allows constant evacuation of the gas. As a valve on one of the trocars is always left open, the smoke-contaminated gas escapes constantly from the abdominal cavity and is replaced by continuous insufflation of fresh gas. The operative field thus remains perfectly clear.
12. Criteria for purchase
The criteria to take into consideration when purchasing an insufflator are:

• Imperative
- high flow rate >16 L/min minimum;
- automatic exsufflation;
- gas filtered with a disposable filter.

• Optional (to improve work quality)
- insufflator data displayed on the screen;
- system integrated with the management of all other data in the operating room;
- humidification of the gas.

• Unnecessary
- heated gas.
13. Conclusions
Although several systems have been proposed to create and maintain the operative space, the pneumoperitoneum remains the standard method. CO2 has been used for many years, and no other gas has proven to be superior, despite isolated publications of studies claiming advantages for nitrous oxide or helium.

The main technological innovations have arisen through better knowledge of the physiology of the pneumoperitoneum, the consequences of excessive pressure and the possibilities offered by electronics in terms of control of pressure and gas quality in the operative field. Future improvements might include real-time analysis of gas composition using gas chromatography allowing automated extraction of smoke or nitrous oxide. Finally, integration of insufflators into remote- or voice-controlled systems would give the surgeon easier real-time control of insufflator function.