Blood carbon dioxide tension changes during hysteroscopy.

During hysteroscopy the uterus may be distended with carbon dioxide (CO 2 ), nitrous oxide (N 2 O), or Hyskon (a high molecular weight dextran). An initial study in 27 patients (group 1) using arterialized venous blood samples demonstrated rises in carbon dioxide tension (PCO 2 ) when N 2 O was insufflated by using a laparoscopy insufflating device—a constant-pressure, variable-volume gas source. Cardiovascular collapse occurred in one patient in this group, most probably as a result of macropulmonary emboli of N 2 O. The rise in PCO 2 is accounted for by an increase in physiologic dead space. In another 24 patients (group 2) the gaseous media were introduced by using a constant-volume, variable-pressure gas source; this resulted in minimal changes in arterial PCO 2 . The choice of whether a gaseous or liquid distending medium is used for hysteroscopy is governed by the state of the endometrium. If a gaseous medium is indicated, then CO 2 is preferable to N 2 O and should be introduced with a constant-volume, variable-pressure gas source.