Why is carbon dioxide (CO2) the gas used for insufflation?

Why is carbon dioxide (CO₂) the gas used for insufflation?

Many gases have been utilized to create the pneumo-peritoneum to facilitate the exposure necessary for surgical laparoscopy. These gases include helium, argon, nitrous oxide (N₂O), and CO₂. Each gas has problems associated with its use. Nitrous oxide supports combustion. Helium and argon are insoluble and are more likely to be associated with adverse events following embolic phenomena. CO₂ pro-vides the safest profile. It is safe during electrocautery and laser surgery and can easily be eliminated through the lungs. Additionally, CO₂ is rapidly absorbed into the blood-stream. Its absorption is greater during extraperitoneal insufflation (laparoscopic inguinal hernia repair) com-pared with intraperitoneal insufflation. Extraperitoneal insufflation occurs when gas accumulates accidentally in the subcutaneous tissues or in the potential space between the fascia and the peritoneum, as is the goal for inguinal hernia repair. This absorption proves beneficial if moderate hypercapnia is maintained because the resulting cardiovas-cular stimulation helps to offset some of the hemodynamic burden imposed by the pneumoperitoneum. However, intraoperative hypercapnia is not completely benign. In patients with poor reserve (i.e., ischemic heart disease), whose arterial CO₂ (PaCO₂) levels approach 55–65 mmHg, there is a significant increase in systolic blood pressure, heart rate, and cardiac output. Hypercarbia causes sympa-thetic nervous system stimulation as manifest by a 2- to 3-fold increase in plasma catecholamine concentrations. When the PaCO₂ is >65 mmHg, cardiodepressive effects predominate with possible cardiovascular collapse or fatal dysrhythmias. Hypercapnia also causes pulmonary vaso-constriction that may worsen right ventricular ischemia or pulmonary hypertension. Patients with increased intra-cranial pressure may also be adversely affected by increases in PaCO₂.

End-tidal CO₂ (ETCO₂) provides an estimation of PaCO₂ levels. In relatively healthy individuals, the PaCO₂–ETCO₂ gradient approximates 3–5 mmHg, and is not affected dur-ing short laparoscopic procedures. However, in patients with severe cardiopulmonary disease or in prolonged operations, the PaCO₂–ETCO₂ gradient increases in an unpredictable manner and the usual PaCO₂–ETCO₂ relationship may be lost.

Not all increases in PaCO₂ result from increased absorp-tion. Absorption is responsible for the increases in PaCO₂ that occur initially, until a plateau level is reached 15–30 minutes after the onset of gas insufflation. Any sig-nificant increases thereafter require a search for the cause. The differential diagnosis of hypercarbia is:

·  Absorption of CO₂

·  Hypoventilation

·  Increased dead space

·  CO₂ embolism

·  Pneumothorax, pneumomediastinum, pneumoperi-cardium

·  Subcutaneous emphysema

·  Exhausted CO₂ absorber

·  Unidirectional valve dysfunction

·           Malignant hyperthermia