Invasive CO ₂ monitoring with arterial line compared to end tidal CO ₂ during peroral endoscopic myotomy

Background and study aims  Peroral endoscopic myotomy (POEM) has become a recognized treatment for achalasia. The technique requires CO ₂ insufflation. It is estimated that the partial pressure of CO ₂ (PaCO ₂ ) is 2 to 5 mm Hg higher than the end tidal CO ₂ (etCO ₂ ), and etCO ₂ is used as a surrogate for PaCO ₂ because PaCO ₂ requires an arterial line. However, no study has compared invasive and noninvasive CO ₂ monitoring during POEM. Patients and methods  Seventy-one patients who underwent POEM were included in a prospective comparative study. PaCO ₂ plus etCO ₂ was measured in 32 patients (invasive group) and etCO ₂ only in 39 matched patients (noninvasive group). Pearson correlation coefficient (PCC) and Spearman's Rho were used to calculate the correlation between PaCO ₂ and ETCO ₂ . Results  PaCO ₂ and ETCO ₂ were strongly correlated: PCC R value: 0.8787 P  ≤ 0.00001, Spearman's Rho R value: 0.8775, P  ≤ 0.00001. Within the invasive group, the average difference between PaCO ₂ and ETCO ₂ was 3.39 mm Hg (median 3, standard deviation 3.5), within the 2- to 5-mm Hg range. The average procedure time (scope in to scope out) was increased 17.7 minutes ( P  = 0.044) and anesthesia duration was 46.3 minutes. Adverse events (AEs) included three hematomas and one nerve injury in the invasive group and one pneumothorax in the noninvasive group. There were no differences in AE rates between the groups (13 % vs 3 % P  = 0.24). Conclusions  Universal PaCO ₂ monitoring contributes to increased procedure and anesthesia times without any decrease in AEs in patients undergoing POEM. CO ₂ monitoring with an arterial line should only be performed in patients with major cardiovascular comorbidities; in all other patients, ETCO ₂ is an appropriate tool.