Stability of oxyhemoglobin affinity in patients with obstructive sleep apnea-hypopnea syndrome without daytime hypoxemia.

A decrease in hemoglobin affinity for oxygen is considered an adaptive mechanism against tissue hypoxia. Obstructive sleep apnea-hypopnea syndrome (OSAHS) is characterized by recurrent episodes of apnea and hypopnea resulting in arterial oxygen desaturations during sleep. Maillard et al. (10) observed a right shift of the oxyhemoglobin dissociation curve (ODC) and an increase in 2,3-diphosphoglycerate (2,3-DPG) concentration ([2,3-DPG]) in 15 patients with severe OSAHS, but some had slight daytime arterial hypoxemia while breathing room air. The aim of our study was to measure the ODC and 2,3-DPG concentrations in a group of subjects normoxemic during daytime referred to our sleep laboratory for suspicion of snoring or OSAHS. The patients were recruited during a period of 6 mo. All arterial and venous blood samples were taken early in the morning within 1 h of awakening following a full-night polysomnography. ODC and 2,3-DPG were analyzed in 88 patients: 56 OSAHS (oxygen desaturation index: 27.5 +/- 24.5) and 32 non-OSAHS. We found a significant correlation between the P50 and 2,3-DPG levels in the 88 patients: r = 0.502, P < 0.001. We observed no difference between OSAHS and non-OSAHS for the P50 and for [2,3-DPG]. There was no correlation between the severity of OSAHS and either P50 or [2,3-DPG]. Finally, there was no change in these parameters measured at baseline, after 3 days and after 1 mo of treatment by nasal continuous positive airway pressure in 7 patients with OSAHS. We conclude that patients with OSAHS who are normoxemic during daytime have comparable oxyhemoglobin affinity than nonapneic subjects.

Volumetric capnography: reliability and reproducibility in spontaneously breathing patients.

Volumetric capnography provides a breath-by-breath analysis of ventilation-perfusion imbalances and deadspace volumes. The technique has been best described in intubated and ventilated patients, but promising clinical applications also concern spontaneously breathing patients. The objective of the study was to verify the reliability and reproducibility of a new capnographic program in various types of clinical conditions. In a first step, 56 patients, either healthy or with acute respiratory disorders, were connected to a sidestream gas sampler and flow sensor through a mouthpiece. An acquisition software synchronized expired CO2 and flow data to create volumetric capnographic curves. Mixed expired CO2 partial pressure, corresponding to the exhaled CO2 of the effective tidal volume, was simultaneously collected in a neoprene bag for comparison. In a second step, changes in airway deadspace before and after the adjunction of known spacer volumes were compared in six healthy volunteers. The mean difference between both methods in measuring mixed expired CO2 partial pressure was -0.9 mmHg (SE 0.2 mmHg, P<0.001). The limits of agreement extended from -4.4 to 2.5 mmHg. The interobserver correlation coefficient for reproducibility was 0.98. Airway deadspace volume, after correction for extra volumes, was not statistically different than the basic value (P=0.89). In conclusion, volumetric capnography can be compared with references when used in spontaneously breathing patients. Future developments and clinical applications should clarify its role as a non-invasive method for deadspace and ventilation-perfusion imbalances analysis.

Volumetric capnography as a bedside monitoring of thrombolysis in major pulmonary embolism.

OBJECTIVE: To describe the use of volumetric capnography, a plot of expired CO(2) concentration against expired volume, in monitoring fibrinolytic treatment of major pulmonary embolism. DESIGN AND SETTING: Two case reports in the emergency department of a teaching hospital. PATIENTS: Two conscious and spontaneously breathing patients (69- and 31-year-old women) with major pulmonary embolism requiring thrombolysis. Decision for thrombolysis was based on the association of right ventricular afterload on echocardiography, with respiratory failure and hypotension in the first patient, and dyspnea and hemodynamically stable parameters in the second one. INTERVENTIONS: Successive capnographic measurements were performed before, during, and after thrombolysis. Curves of volumetric capnography were obtained from a sidestream gas monitor with flow sensor and an arterial blood gas analysis for CO(2) partial pressure. MEASUREMENTS AND RESULTS: We calculated late deadspace fraction, previously suggested as the most effective capnographic parameter in the diagnosis of pulmonary embolism. Late deadspace fraction decreased in the two patients, respectively, from 64.4% to 1.1% and from 25.6% to 5.7% after thrombolysis, with a concomitant disappearance of right heart dysfunction signs on echocardiography. CONCLUSIONS: Volumetric capnography can monitor thrombolysis in major pulmonary embolism. Differences between volumetric capnography technology and the more traditional arterial to end-tidal CO(2) gradient are important to take into account for clinical application.