Responses to Alternative Techniques

Retroperitoneal Insufflation

Pathophysiology of laparoscopy has been investigated vis-a-vis intraperitoneal insufflation of gas. Although many of the phenomena pertaining to gas insufflation into the peritoneal cavity likely apply to retroperitoneal insufflation as well, some important differences need to be highlighted. Some clinical studies have suggested that extraperi-toneal insufflation (51,93,94) increases CO2 absorption; however, experimental studies failed to prove this finding (95-97). Using cuffed-balloon ports that minimized gas leakage into the subcutaneous tissue as opposed to the conventional ports used in prior clinical studies, Ng et al. (98) found no difference in CO2 absorption during extraperitoneal versus transperitoneal laparoscopy, suggesting that subcutaneous emphysema may have confounded the earlier clinical studies.

When compared to intraperitoneal insufflation, extraperitoneal insufflation appears to have less untoward physiologic sequelae.

In two different experimental studies in the porcine model, extraperitoneal insufflation altered venous pressures and cardiac output similar to intraperitoneal insufflation, but of a lesser magnitude (96,97). Giebler et al. found no change in cardiac output up to retroperitoneal insufflation pressures of 20 mmHg (99). In a comparative clinical study, the same investigators subsequently determined that retroperitoneal insufflation actually augmented venous return slightly, whereas intraperitoneal insufflation reduced venous return (100). The smaller volume of gas required to fill the retroperitoneal space compared to the intraperitoneal space may possibly account for some of these differences.

Alternative Insufflants/Gasless Laparoscopy

The rapid absorption of CO2 is well tolerated physiologically as long as the hyper-capnia can be maintained at moderate levels (PaCO2 = 45 mmHg). In fact, cardiovascular stimulation by moderate hypercapnia alleviates some of the hemodynamic burden of pneumoperitoneum (35,36,45-47). However, because excessive hypercap-nia is cardiodepressive and can produce dysrhythmias (see below), there has been interest in investigating alternative gases for laparoscopic insufflation. Following the first published reports of the physiologic hazards of CO2 pneumoperitoneum (101), nitrous oxide (N2O) was employed as an alternative gas insufflant (102). N2O is similar to CO2 in its rapid absorption (Table 2) and has fewer physiologic effects at the blood concentration achieved with intraperitoneal insufflation. N2O, however, can support combustion in the abdominal cavity.

N2O is a suitable alternative for intra-abdominal insufflation only if a heat source (electrocautery or laser) is not used. N2O insufflation is excellent for diagnostic laparoscopy under local anesthesia because it is less irritating than CO2 to the peritoneal membrane (103-105).

Helium and argon, monoatomic noble gases not supporting combustion, are other alternative gases (47,106). These gases are not associated with insufflant-related cardiopulmonary problems (106,107), and are absorbed slowly (Table 2). Because argon may have some adverse hemodynamic effects, helium appears more attractive (105). Helium insufflation has been successfully employed in several clinical laparoscopic series (46,108-110). For example, laparoscopic nephrectomy being performed in a patient with severe pulmonary disease who developed extreme hypercapnia was completed after switching the insufflant gas to helium (111). The slow absorption of helium is a liability, however, because the clinical effects of a venous gas embolism may be exacerbated (see below). Because the risk of venous gas embolism is higher during the initial insufflation, starting the procedure with CO2 insufflation and then switching to helium

When compared to intraperitoneal insufflation, extraperitoneal insufflation appears to have less untoward physiologic sequelae.

N2O is a suitable alternative for intraabdominal insufflation only if a heat source (electrocautery or laser) is not used. N2O insufflation is excellent for diagnostic laparoscopy under local anesthesia because it is less irritating to the peritoneal membrane than CO2.

TABLE2 ■ Insufflant Characteristics

Solubilitya

Diffusibilitya

Tissue permeancea

Nitrogen

1.0

1.0

1.0

Helium

0.7

2.7

1.3

Oxygen

1.9

0.9

1.8

Argon

2.2

0.9

2.0

Nitrous oxide

33.0

0.9

28.0

Carbon dioxide

47.0

0.9

39.0

aValue relative to nitrogen. Source: From Ref. 49.

A reasonable precaution against hemodynamic compromise is to operate at the minimal intra-abdominal pressure that provides adequate exposure.

Gasless laparoscopy is another alternative to CO2 pneumoperitoneum in patients with significant cardiac or pulmonary disease, which would place them at risk of physiologic complications during CO2 pneumoperitoneum.

Most venous gas embolisms occur during and within a few minutes of initial gas insufflation, but delayed cases have been reported.

Whenever hemodynamic compromise due to excessive intra-abdominal pressure is suspected, immediate desufflation will quickly improve the situation, and the surgeon may be able to complete the procedure using a lower intra-abdominal pressure.

Tension pneumoperitoneum is the precipitous reduction of venous return, cardiac output, and blood pressure due to increased intra-abdominal pressure from gas insufflation.

Most physiologic complications may be prevented by knowledgeable control of intra-abdominal pressure and fluid status, and careful intraoperative patient monitoring. However, complications can occur even in prepared hands.

to address the occurrence of dangerous hypercapnia is probably the best approach (111,112). The gas regulator used for helium is different than that for CO2; thus, even if helium tanks are available to the surgeon, these gases cannot be used until the appropriate gas-specific regulator has been fitted to the laparoscopic insufflator. Due to flow characteristics different from CO2, helium alters the behavior of the insufflator and leaks more easily around laparoscopic ports.

Finally, laparoscopy can be performed with an abdominal wall-lifting device creating a working space without insufflation of gas. There are many technical concerns with this approach, including more difficult surgical exposure for some procedures and no pneumoperitoneum-induced tamponade of bleeding by increased intra-abdominal pressure from gas insufflation. From the physiological standpoint, however, the use of an abdominal wall-lifting device rather than pneumoperitoneum obviates all of the aforementioned physiological considerations (65,113,114).

Gasless laparoscopy is another alternative to CO2 pneumoperitoneum in patients with significant cardiac or pulmonary disease, which would place them at risk of physiologic complications during CO2 pneumoperitoneum.

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