Factors influencing capnography in the bain circuit

The Bain circuit provides continuous fresh gas flow near the airway. The potential mixing of this fresh gas with expired gas may prevent reliable analysis of expired gas. We therefore investigated the interaction of sampling site, fresh gas flow rate, expiratory flow rate, and sampling flow rate on expiratory capnography. Sampling near the fresh gas outlet yielded inaccurate results under several of these conditions. The magnitude of the error was related to the fresh gas and expiratory flow rates. A reliable sampling region near the endotracheal tube was identified.     

Aging is associated with a rapid decline in frequency, alterations in subset composition, and enhanced Th2 response in CD1d-restricted NKT cells from human peripheral blood

NKT cells are important for initiating and regulating immune responses. We investigated the age-related changes in the CD1d-restricted semi-invariant NKT (iNKT) cells in peripheral blood of healthy adults. The iNKT cell frequency was 2.5- to 10.7-fold less in healthy elderly subjects (61 years and over) compared to the healthy young subjects (20-40 years, p<0.001). This age-related decline in iNKT cells was observed both in freshly isolated PBMC and in cultures where iNKT cells were enriched by alpha-GalCer stimulation using either the Valpha24/Vbeta11 TCR antibody pair or the CD1d-tetramer as the iNKT cell marker. The decline in frequency was associated with an alteration in the iNKT cell subset compositions: an increase in the proportion of CD4+ subset and a decrease in the proportion of CD4/CD8 double-negative (DN) subset. The age-related decline in iNKT cells and changes in subset composition were independent from the age-related changes of conventional T cells/T cell subsets. Additionally, there was a Th1 to Th2 shift in the cytokine response profile from iNKT cells with aging. We conclude that aging is associated with a significant decline in iNKT cell frequency in peripheral blood, accompanied with alterations in subset composition and cytokine response profile.     

Intraoperative pulse oximetry: Frequency and distribution of discrepant data

Study Objective: To determine the types of discrepant data during intraoperative pulse oximetry and their frequency and duration.

Design: Prospective study.

Setting: University medical center.

Patients: 46 consecutive ASA physical status I–III patients undergoing general anesthesia for elective surgical operations.

Measurements and Main Results: With an integrated computer algorithm on the pulse oximeter and another computer linked to it, data were screened and the frequency and distribution of the following oximeter signals recorded: absent; low quality or interrupted, as detected by the pulse oximeter algorithm, nonphysiologic, identified by the personal computer as a heart rate change greater than 10 beats per minute within 2 consecutive 2-second samples, with no similar abrupt change reported simultaneously on ECG. The number of episodes per hour of discrepant oximeter data and the duration of the episodes were recorded by phase of anesthesia: induction, maintenance, and emergence. Discrepant data occurred most frequently and lasted longest during emergence (p < 0.05); the majority of episodes of discrepant data during emergence lasted less than 12 seconds. Excluding discrepant data that lasted less than 12 seconds decreased the frequency of discrepant data by 63% and excluding those that lasted less than 30 seconds decreased the frequency of discrepant data by 93%.

Conclusions: Pulse oximeters frequently report discrepant data intraoperatively, most frequently during emergence from anesthesia. An alarm delay triggered by discrepant data and lasting 12 to 30 seconds would keep most discrepant data from becoming false alarms and, thus, may reduce distracting sound pollution in the operating room.     

Duration of carbon dioxide absorption by soda lime at low rates of fresh gas flow

STUDY OBJECTIVE: To determine the impact of a low fresh gas flow rate on the duration of carbon dioxide (CO2) absorption by soda lime. DESIGN: Nonclinical, experimental. SETTING: Experimental laboratory. METHODS: In vitro test with Sodasorb and a semiclosed breathing circle ventilating a test lung with a CO2 inflow of 250 ml per minute. Fresh gas flow rates of 0.25, 0.5, 1, 2, and 4 L/min were studied. MEASUREMENTS AND MAIN RESULTS: CO2 was measured at the breathing circuit test lung interface with a mainstream capnometer. Duration of CO2 absorption was determined as the time for the inspired CO2 tension (PICO2) to increase from 0 mm to 7 mm of mercury. The times of this interval were recorded four times for each fresh gas flow rate and compared by analysis of variance; p less than 0.05 was considered significant. Time to soda lime failure was significantly longer at 2 L/min than at 1 L/min fresh gas flow and at 1 L/min than at 0.25 L/min fresh gas flow. CONCLUSION: Because soda lime color indicators are unreliable, when a semiclosed breathing circle is used at a low rate of fresh gas flow without CO2 monitoring, the CO2 absorbent must be replaced more frequently.     

In vitro comparison of central venous catheters for aspiration of venous air embolism: effect of catheter type, catheter tip position, and cardiac inclination

STUDY OBJECTIVE: To test the relative efficiency of balloon-tipped and plain catheters for aspiration of venous air embolism. DESIGN: The following four single-lumen central venous catheters were studied in a silastic model of the right atrium, tricuspid valve, and vena cavae: (1) the 16-gauge single-orifice catheter; (2) the 14-gauge Bunegin-Albin multiorifice catheter; (3) the 7-Fr pulmonary angiography catheter with balloon distal to orifices; (4) the 7-Fr pulmonary angiography catheter with balloon proximal to orifices. A 10% glycerol-water solution was circulated at 3.7 to 4.0 L/min. Catheter tips were positioned at 1 cm increments from -3 to +3 cm around the superior vena cava-right atrial junction with cardiac inclinations of 65 degrees and 80 degrees. Air (10 ml) was infused over 30 seconds; aspiration from the test catheter began 5 seconds later at 40 ml/min for 75 seconds. The balloon catheters were evaluated with the balloons inflated and deflated. SETTING: Experimental laboratory of a university-affiliated hospital. MEASUREMENTS AND MAIN RESULTS: Amounts of air aspirated were compared by analysis of variance and Tukey's multiple comparison, p less than 0.05, for all combinations. The 16-gauge single-orifice catheter tested best at a 65 degrees cardiac inclination with 86% of the venous air embolism recovered, while the 14-gauge Bunegin-Albin multiorifice catheter tested best at an 80 degrees cardiac inclination with 62% of the venous air embolism recovered. Both catheters functioned most efficiently at or above the superior vena cava-right atrial junction. CONCLUSIONS: This study demonstrated that efficacy of air recovery depends on catheter type, catheter tip position, and cardiac inclination. No benefit was derived from positioning the catheter tip inside the atrium or from using balloon-tipped catheters.