In the field of respiratory clinical practice, the importance of measuring carbon dioxide (CO2) concentrations cannot be overemphasized. Within the body, assessment of the arterial partial pressure of CO2 (PaCO2) has been the gold standard for many decades. Non-invasive assessments are usually predicated on the measurement of CO2 concentrations in the air, usually using an infrared analyzer, and these data are clearly important regarding climate changes as well as regulations of air quality in buildings to ascertain adequate ventilation. Measurements of CO2 production with oxygen consumption yield important indices such as the respiratory quotient and estimates of energy expenditure, which may be used for further investigation in the various fields of metabolism, obesity, sleep disorders, and lifestyle-related issues. Measures of PaCO2 are nowadays performed using the Severinghaus electrode in arterial blood or in arterialized capillary blood, while the same electrode system has been modified to enable relatively accurate non-invasive monitoring of the transcutaneous partial pressure of CO2 (PtcCO2). PtcCO2 monitoring during sleep can be helpful for evaluating sleep apnea syndrome, particularly in children. End-tidal PCO2 is inferior to PtcCO2 as far as accuracy, but it provides breath-by-breath estimates of respiratory gas exchange, while PtcCO2 reflects temporal trends in alveolar ventilation. The frequency of monitoring end-tidal PCO2 has markedly increased in light of its multiple applications (e.g., verify endotracheal intubation, anesthesia or mechanical ventilation, exercise testing, respiratory patterning during sleep, etc.).

We report the case of a patient with bilateral blephaloptosis associated with a recurrence of diffuse large B-cell lymphoma (DLBCL) in the midbrain. A 70-year-old man experienced acute onset bilateral blephaloptosis; the other ocular movements, except for medial rectus muscle in the right eye, were not impaired. Pupils were isocoric and light reflexes were prompt. Other cranial nerves were intact. Gadolinium-enhanced MRI revealed abnormal enhancement in the midbrain and peri-ventricular regions. FDG-PET revealed an abnormal positive signal in the midbrain, similar to the distribution seen in the MRI scan. Cytology of the cerebrospinal fluid showed large atypical lymphocytes. These findings suggest that the recurrence of DLBCL in the midbrain caused bilateral blephaloptosis. The oculomotor fascicle is localized in the paramedian ventral midbrain. The fascicular fibers are divided topographically into four regions; the lateral, medial, rostral and caudal regions. In three-dimensional arrangement of the oculomotor fascicle, the fibers to the levator palpebrae superioris muscle and medial rectus muscles are located adjacently in caudal regions. Thus, we speculate that recurrence of DLBCL in the midbrain involving the right oculomotor fascicle caused blephaloptosis in the right eye, and then, infiltration of DLBCL to the left oculomotor fascicle subsequently caused blephaloptosis in the left eye. This is a valuable case to be documented in which neurological site of lesions consistent with those are found in radiological study.