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Noninvasive monitoring of partial pressure of carbon dioxide can be accomplished indirectly with capnography (P ET CO 2) or with transcutaneous carbon dioxide monitoring (P TC CO 2). The use of capnography has been shown to offer an advantage over pulse oximetry alone in the early detection of adverse respiratory events when supplemental oxygen is administered. Furthermore, capnography allows for the monitoring of various respiratory measures, including end-tidal carbon dioxide, respiratory rate, tidal volume, and changes in breathing patterns. Transcutaneous CO 2 also closely approximates arterial CO 2 values, but is not as easy to monitor for prolonged periods. The purpose of this study was to examine the usefulness of capnography and of transcutaneous carbon dioxide monitoring in patients recovering from obesity surgery at high risk of developing postoperative obstructive sleep apnea. In a prospective observational study, 64 bariatric surgery patients at risk of developing obstructive sleep apnea were monitored in the postanesthesia care unit (PACU) with either capnography alone (31 patients) or capnography plus transcutaneous carbon dioxide monitoring (33 additional patients) every 3–5 minutes for the duration of their recovery. Primary endpoints included end-tidal and transcutaneous carbon dioxide, peripheral oxygen saturation, respiratory rate, pain scores, and incidence of adverse respiratory events. Although no adverse pulmonary events were observed, capnography detected several patients who experienced short periods of respiratory apnea while maintaining pulse oximetry readings within normal limits. Transcutaneous values were slow to change and averaged 4.5 ± 5.5 mm Hg (P <.05) higher than corresponding end-tidal measurements. These results indicate the capabilities of both these noninvasive techniques for postoperative monitoring. Capnography acutely monitors changes in respiration, whereas transcutaneous monitoring more accurately reflects arterial CO 2 levels. • Comparison of two patient groups after obesity surgery with opioid sparing anesthesia • Respiratory CO2 and transcutaneous CO2 were analyzed to detect hypoventilation • Transcutaneous values approximate arterial CO2 and are non-invasive • None of these patients showed respiratory depression during recovery [ABSTRACT FROM AUTHOR]

Abstract: We hypothesized that administration of clonidine would decrease the hypocapnic apnoeic threshold (HAT) and widen the CO2 reserve during non-REM sleep. Methods: Ten healthy subjects (4 females) (age 22.3±3.0 years; BMI 25.5±3.4kg/m2) were randomized to receive placebo or 0.1mg/45kg of clonidine on 2 separate nights. Ventilation and upper airway resistance were monitored during wakefulness and sleep. Two separate experiments were performed: Protocol 1 (n =8), CO2 reserve, HAT and HcVR were determined using non-invasive hyperventilation (NIV) to induce hypocapnia for at least 3min; Protocol 2 (n =6), peripheral hypocapnic ventilatory response (HcVR) was determined by NIV using short (3 breaths) hyperventilation. Results: Clonidine decreased the systolic blood pressure by 12±10mmHg but did not affect baseline ventilation or upper airway resistance during wakefulness or sleep. Protocol (1), clonidine was associated with decreased HAT relative to placebo (37.3±3.3mmHg vs. 39.7±3.4mmHg, P <0.05), increased CO2 reserve (−3.8±1.3mmHg vs. −2.8±1.2mmHg, P <0.05), and decreased HcVR (1.6±0.6L/min/mmHg vs. 2.5±1.3L/min/mmHg, P <0.05). Protocol (2), administration of clonidine did not decrease peripheral HcVR compared to placebo (0.5±0.3L/min/mmHg vs. 0.7±0.3L/min/mmHg, P =NS). Conclusion: Clonidine is associated with diminished susceptibility to hypocapnic central apnoea without significant effect on ventilation or upper airway mechanics. Reduced susceptibility to hypocapnic central apnoea is not explained by the peripheral chemoreceptor pathway. This suggests a central rather than a peripheral effect of clonidine on the susceptibility to hypocapnic central apnoea. [Copyright &y& Elsevier]

Abstract: Objective: To compare the PaCO2 with the ETCO2 obtained with the Smart Capnoline™ in the postoperative setting of cardiac surgery during ventilation and after extubation Type of study: Prospective, observational. Patients: Twenty patients after cardiac surgery. Methods: In the intensive care unit, arterial blood gases were measured concomitantly with ETCO2, and difference between PaCO2 and ETCO2 were calculated. Three CO2 sensors were utilized: Filterline H set for intubated patients, Smart Capnoline HO2 (nasal version) and Smart Capnoline O2 (bucconasal version) after extubation. Data were compared with Wilconson test and the intraclass correlation coefficient was calculated. Results: The difference PaCO2 – ETCO2 was significantly larger in extubated patients compared to intubated patients, which is also confirmed for the bucconasal sensor (intubated patients: 6.6±4.3mmHg, nasal sensor: 9.3±3.5mmHg, bucconasal sensor: 15,4±12.9mmHg). Conclusion: In the postoperative setting of cardiac surgery, ETCO2 measurements allow a reliable estimation of PaCO2 in intubated patients in contrast to measurements in extubated patients. The bucconasal CO2 sensor does not show more reliable measurements compared to nasal sensors in the postoperative setting of cardiac surgery. [Copyright &y& Elsevier]