Factors Affecting Performance of Air Tonometry Using the TONOCAP^®

Abstract

Saline tonometry has been replaced by automated air tonometry (TONOCAP ® ). As with saline tonometry there are some pitfalls to consider. We investigated the influence of different filling handicaps to the tonometry catheter sampling balloon on measurement of regional PCO 2 (PrCO 2 ). In an in vitro set-up, PrCO 2 was measured using the TONOCAP ® at intervals of 10 minutes from a 8F tonometry catheter sampling balloon placed in a container with constant PCO 2 (PcCO 2 ). Catheter alarms displayed by the TONOCAP® device were noted. The following experiments were performed: A) control measurement without modifications; B) adding deadspace of 7 ml into the sampling line; C) placing the sampling balloon in a 3 ml syringe; D) cross-clamping of the sampling balloon. Each experiment was performed four times using two catheters on two TONOCAP ® devices. Differences between PcCO 2 and PrCO 2 were calculated as Pc-rCO 2. Results are presented as mean±SD and were compared using ANOVA with Scheffe's correction. Pc-rCO 2 in the control set-up (A) amounted to 0.16±0.22%. Increasing catheter deadspace (B) resulted in a higher Pc-rCO 2 of 3.2±0.57% (P<0.0001). Restriction of balloon expansion (C) caused an Pc-rCO 2 gap of 1.17±0.36% (P<0.0001). With filling restriction (D) the Pc-rCO 2 gap increased to 3.87±0.29% (P<0.0001). The catheter alarms provided were not able to indicate all catheter problems and initial alarms disappeared although the problems continued. We conclude that impaired catheter deadspace to balloon volume relation can negatively influence accuracy of PrCO 2 measurement by the TONOCAP ®.

Visceral and Renal Tissue Oxygenation During Supraceliac Aortic Crossclamping and Left Heart Bypass with Selective Organ Perfusion

“…Analysis of the gastrointestinal mucosal blood flow by tonometrically measuring the intraluminal pCO2 are known to have many confounding factors. 17,18 Whether this difference must be interpreted as a preservation of intestinal mucosal blood flow during SOP, or indeed as diminished mucosal blood flow is not clear from this study. It needs to be proven whether the reduced regional visceral tissue oxygenation found during LHB and SOP, in comparison with the physiological state, can prevent systemic release of gut-derived chemical mediators, compared with no visceral perfusion at all.…”

Sublingual capnometry: a non-invasive measure of microcirculatory dysfunction and tissue hypoxia

“…While air tonometry has simplified the measurement process (over saline tonometry) and eliminated the possible errors associated with the use of non-buffered saline this technology has a number of limitations (Graf et al 2000, Barry et al 1998, Tzelepis et al 1996, Taylor et al 1997, Dullenkopf et al 2002. Gastric tonometry is logistically and practically difficult and this may be the main factor which has prevented the widespread use of this technology.…”

Regional carbon dioxide monitoring to assess the adequacy of tissue perfusion

“…While air tonometry has simplified the measurement process (over saline tonometry) and eliminated the possible errors associated with the use of non-buffered saline this technology has a number of limitations [44][45][46]85,86]. Gastric tonometry is logistically and practically difficult and this may be the main factor that has prevented the widespread use of this technology.…”