Eiichi Chihara

Current practice of preoperative fasting: a nationwide survey in Japanese anesthesia-teaching hospitals.

PurposeWe conducted a nationwide survey to investigate the current practice of the preoperative fasting period in Japanese anesthesia-teaching hospitals. Acceptance of the clinical practice guideline published by the American Society of Anesthesiologists (ASA) was also surveyed.MethodsA written type-of questionnaire was mailed to 795 teaching hospitals.ResultsThe response rate of the questionnaires was 57%. Most (>90%) of the respondents had been applying a longer fasting period than the ASA-recommended minimum period specifically in adults; the median duration of fasting was 12–13 h for solids and 6–9 h for liquids. Children or infants were allowed a more liberalized fasting period, frequently being permitted an oral intake of clear fluids up to 3 h before anesthesia. The incidence of pulmonary aspiration was 1/12 500 general anesthesia cases, and application of the ASA guideline appeared not to affect the incidence. Japanese anesthesiologists were still reluctant to depart from their traditional long fasting periods, as most of them could find little benefit in reducing the fasting periods.ConclusionThe long preoperative fasting period is still common practice in Japanese anesthesia-teaching hospitals. A national guideline for a preoperative fasting policy is worth exploring to change the current practice.

Compression of the photoprobe is effective in reducing Hb signals of the frontal skin in near infrared spectrophotometic cerebral tissue oximetry

The cutaneous hemoglobin of the forehead can contribute to near infrared spectrophotometric cerebral tissue oximetry in both light scattering and absorption. Wide distance between the light source and detector was theoretically proved to increase substantial signal from cerebral tissue, however increase in signal to noise ratio was practically undesirable. The tight compression of the probe onto the head expels the subcutaneous blood, which is supposed to improve cerebral signal detection. The spectrophotometric effect of probe compression with a head band was examined by NIRS monitor having temporal resolution of 10 Hz which provided detailed information in tissue hemoglobin signals including pulsatile fluctuations. The measurement for healthy volunteers was done in both supine and sitting positions. The oxygenated Hb and total Hb levels significantly decreased with probe compression in supine position. Compared with pre-compression state, the amplitude of Oxy-Hb pulsation was reduced to 61.0 +/- 10.0 (mean +/- SD)% in sitting position, and 53.3 +/- 68% in supine position (p < 0.01). The postischemic hyperemia was also observed in every measurement. The results indicate that cutaneous blood in the scalp significantly contributes pulsatile Hb signals in cerebral NIRS, and probe compression is a good measure to reduce scalpel effect especially in supine position.

Higher temporal resolution is necessary for continuous-wave near -infrared spectrophotometric monitors in both cerebral and muscular tissue oximetry

Conventional near infrared spectrophotometric monitors have temporal resolution of less than about 1 Hz. However, physiological Hb signals such as pulsation and muscle contraction have higher frequency than 1 Hz. Insufficient sampling rates inevitably lead aliasing of the recorded signals in tissue oximetry for both brain and muscle. Cerebral Hb signals (57 y.o. female artificially ventilated under general anesthesia) and thigh muscle (22 y.o. male with 20 W - 240 W exercise at 1 Hz cycling in semirecumbent ergometer) were measured with NIRS monitor with temporal resolution of 10 Hz (OMRON Co. Ltd., Japan). The detail of physiological fluctuations such as pulsation, ventilation, and muscle pumping was clearly recognized with a 10 Hz sampling. The comparison with recalculated waveforms at slower sampling rate (0.5 Hz, 1 Hz, 2 Hz) revealed that with slower sampling than 1 Hz cerebral respiratory waves were deformed by pulsation, and that magnitudes of muscle pumping could not be properly evaluated in dynamic exercise. In both pulsatile and muscle contractile cycle a phase delay between oxygenated component and deoxygenated one was also detected, which has been overlooked by conventional NIRS monitoring.

Real time monitoring of pulsatile change in hemoglobin concentrations of cerebral tissue by a portable tissue oximeter with a 10-Hz sampling rate

A portable CW tissue oximeter of a 10-Hz sampling rate was developed for examination of pulsatile components of the output signals as a mean of checking the signal reliability during long-term monitoring. Feasible studies were performed on a healthy subject. Changes in Hb and HbO2 signals of cerebral tissue were continuously measured by placing a photoprobe on the forehead during 6-hour sleep. Pulsatile changes in Hb and HbO2 were steadily observed over a whole period of the recording. The phase relation of pulsation in Hb and HbO2 was almost inverse. Not only information for reliable monitoring but also physiological parameters with respect to cerebral circulation and metabolism could be obtained by measuring the pulsatile components.