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At least 937 records · Page 52Linked to original sources
PubMed2002

Voluntary hyperventilation into a simple mixing chamber relieves high altitude hypoxia.

Involuntary hyperventilation is a critical factor in acclimatization to a high altitude. Unacclimatized subjects do poorly when acutely exposed to high altitude. This may not be due to hypocapnia itself, but rather an associated symptom which inhibits hypoxic respiratory stimulation. In an unacclimatized individual, voluntary hyperventilation may greatly relieve hypoxia and may be an alternative to involuntary hyperventilation. However, subjects voluntarily hyperventilating may overventilate and become disabled from severe hypocapnia. A simple mixing chamber is described which makes voluntary hyperventilation easier, safer, and possibly more effective. A subject breathing into a mixing chamber was able to maintain an SaO2 of 90% at 20,000 ft.

Adult↗
PubMedDate not supplied

Measuring respiratory function to wean patients from non-invasive ventilation in a ward environment.

Non-invasive ventilation (NIV) is increasingly being introduced into various ward environments. NIV is usually used on wards to treat acute exacerbations of chronic obstructive pulmonary disease (COPD). In patients with COPD, carbon dioxide removal will be impaired. In critical care, arterial blood gas sampling remains the 'gold standard' for assessing carbon dioxide levels. Obtaining arterial blood gas samples in a ward environment is problematic, and potentially dangerous. There is currently no reliable substitute for arterial sampling to monitor for hypercapnia in ward areas.

Acid-Base Equilibrium↗
PubMed2004

The valid time of soda lime could be safely prolonged according to the inspired pressure of carbon dioxide.

BACKGROUND: Carbon dioxide (CO2) absorbent, a disposable chemical mixture enclosed in a canister of anesthetic breathing systems functions to remove the carbon dioxide expired from the patients during general anesthesia. The timing of replacing the exhausted CO2 absorbent is usually decided by discoloration of the indicator dye or the valid time of use. However, these methods are subjective. We designed a study to validate our idea of replacing the exhausted CO2 absorbent according to the inspired pressure of carbon dioxide (PiCO2) and comparison of the pressure difference between the arterial carbon dioxide tension (PaCO2) and end-tidal CO2 in the exhausted and fresh CO2 absorbent circuits. METHODS: Fifty-five adult patients undergoing general anesthesia for elective surgeries were enrolled in this study. All the canisters containing fresh soda lime were labeled with the date of filling and valid time of clinical use. The soda lime was replaced only when the PiCO2 reached 6 mmHg. Before and 20 minutes after the replacement, PaCO2 and end-tidal CO2 were obtained and designated as group-Pre and group-Post, respectively. The pressure differences between PaCO2 and end-tidal CO2 in both groups were checked for statistical analysis. RESULTS: The pressure differences in group-Pre and group-Post were 5.8 +/- 3.4 mmHg and 6.1 +/- 3.3 mmHg, respectively, both of which were not statistically significant (P = 0.62). The PaCO2 in group-Pre and group-Post was 43.7 +/- 4.2 mmHg and 40.9 +/- 4.6 mmHg respectively. The end-tidal CO2 in group-Pre and group-Post was 38 +/- 3.5 mmHg and 35 +/- 3.6 mmHg, respectively. There were significant differences in PaCO2 and end-tidal CO2 between the two groups (P < 0.001). By this determination the valid time of soda lime in Omeda, Cato and Kion anesthesia machines was 57.3 +/- 7.2, 35.6 +/- 6.3 and 21.7 +/- 4.2 hours, respectively, all of which were much longer than 8 hours of routine use previously delimited. CONCLUSIONS: Even though the PiCO2 concentration reached 6 mmHg in the rebreathing circuit with exhausted soda lime, the gradient between the PaCO2 and end-tidal CO2 was of no statistical difference compared with that of the fresh soda lime circuit. Thus the pressure difference was not affected by the exhausted CO2 absorbent in spite of a reach of PiCO2 to 6 mmHg. Under CO2 monitoring, the valid time of soda lime could be safely prolonged until the PiCO2 was elevated to 6 mmHg rather than 8 h strictly pursuant to traditional method of discoloration of indicator dye.

Adult↗
PubMed2005

Design parameters of a low flow rate sidestream capnograph.

The use of sidestream capnometers, with a sampling rate of 150-250 cc/min, as a means of measuring a patient's expired CO2 (ETCO2) and respiratory rate, has been a common practice for many years. However, in recent years, there has been a focus on lower flow rate sampling sidestream systems due to the benefits of less loss of tidal volume for patients, such as infants or neonates. When developing a sidestream system, four principle issues must be considered; 1) The signal fidelity of the gas sample must be sufficiently maintained from the sampling site to the measurement site. 2) Condensate from a patient's breath, as well as blood, mucus, or other contaminates often pose problems for sidestream systems and requires mitigation. 3) The mechanics of transporting a gas sample at a constant flow rate through the sampling system, regardless of atmospheric or clinical conditions must be developed. 4) The physics of handling CO2 gas throughout the transport process must be understood in order to ensure accurate readings. These issues lead to a complex web of interrelations that are explored in the development of a low flow rate sidestream capnometer.

Capnography↗
PubMed2005

Design and implementation of an end tidal CO2 simulator for the evaluation of clinical gas analysers.

This paper presents a new technique to determine the dynamic and frequency response of capnographs using a custom built 'EtCO2 simulator system'. Capnographs are devices that use CO2 from a patients' expired breath to monitor the cardiopulmonary status during anaesthesia and mechanical ventilation. Capnographs at present are routinely calibrated via a static calibration method only. The dynamic response of the capnographs is not accounted for. The frequency and time response are important as they determine if capnographs can be used in high frequency and pediatric ventilation schemes. Experiments performed using the method described in this paper proved that old capnographs usually do not satisfy the manufacturer quoted specifications for time and frequency response. Therefore, a routine check for capnographs is recommended. The method can also be used to verify manufacturer quoted specifications. The EtCO2 simulator system, designed and constructed simulates human respiration cycle. The gas sources used are 5% CO2 and room air that can be switched alternatively. Both supplies are pressure regulated and connected through non-return valves to electric valves. The valves are microprocessor controlled and the on/off time is user defined allowing a wide range of waveforms to be simulated. The output from the simulator is delivered to capnograph. Capnograms are captured by digital video recording. The captured video in 'avi' file format is then converted into individual frames. These frames are converted into digital data through image processing in Matlab. The data obtained is subjected to extensive analysis to determine the frequency and time response of the respective capnograph.

Calibration↗
PubMedDate not supplied

[Methods for automatic correction of the effect of various factors on the results of capnometry].

Factors affecting the results of carbon dioxide (CO2) concentration measurements and methods of their automatic compensation are considered for capnometers of two types: lateral flow (LF) and main flow (MF) capnometers. Advantages of the use of one-channel photometer in LF capnometer with automatic calibration were demonstrated. Compensation for temperature, pressure, and presence of concomitant gases and vapors in inhalation mixture is implemented automatically by introducing correction factors in CO2 concentration value. Calibration curves could be obtained empirically for specific capnometer model integrated into the gas analyzer. Carbon dioxide concentration values measured with LF and MF capnometers should be reduced to standard physical conditions STPD and BTPS conditions, respectively (body temperature and pressure, saturation with water vapors).

Calibration↗
PubMed2005

Cardiodynamic monitoring during laparoscopic cholecystectomy.

With increasing success of laparoscopy, the hemodynamic changes associated pneumoperitoneum (PPM) was described using invasive and non-invasive techniques with variable results. In the present study, we have used non-invasive cardiodynamic monitor to investigate the hemodynamic changes during laparoscopic cholecystectomy. Eleven patients who underwent laparoscopic cholecystectomy under general anesthesia were studied. Cardiodynamic monitor (thoracic bioimpedance) was used to investigate the hemodynamic changes. The following parameters were continuously monitored: Heart Rate (HR), mean arterial blood pressure (MAP), cardiac output (CO) and cardiac index (CI). For statistical purpose, five phases were identified: (A), pre-PPM, (B), 2 min post-PPM, (C), 10 min post-PPM, (D), 30 min post-PPM, and (E), after gas deflation. SPSS package, Version 9 was used for statistical analysis of the data obtained. Student's t-test for paired observations was used for comparisons of the mean values of the data obtained, where P <0.05 was considered significant. There was significant change of the mean value of MAP in phases A and C. Also significant CI changes of the mean values was found between stages A and B (P <0.05). The study showed, transient cardiac depression immediately after PPM with partial recovery after ten min, which was associated with increase in MAP.

Adult↗
PubMedDate not supplied

[Graphical monitoring of the artificial lung ventilation. Part 1. Graphs of gas pressure and flow rate during respiration cycle. Capnogram].

Graphical monitoring of the state of the system patient-apparatus for artificial lung ventilation (MLV) provides instant and illustrative information about the state of the system, which is particularly important under conditions of resuscitation and intensive care. Graphs of time dependence of gas pressure in respiratory pathways, gas flow rate, and changes of lung volume during respiration cycle provide on-line information about ventilation mode and patient state including lungs, respiratory pathways, positive pressure at the end of exhalation, etc. These curves allow MLV efficacy to be monitored and improved. Under certain conditions the capnogram shape provides an opportunity for objective evaluation of ventilation adequacy and patient state. The shapes of the curves in the norm and various pathology are considered. This graphical information is concluded to be important for effective use of modern MLV apparatuses for intensive care and resuscitation.

Capnography↗
PubMed2006

[Anesthetic circle system failure caused by a plastic film--a case report].

A 44-year-old woman, ASA I, with breast cancer was scheduled for mastectomy. The anesthetic induction was performed by inhalation of 5% sevoflurane and 66% nitrous oxide in oxygen. After the loss of eyelash reflex assisted ventilation was initiated. At this point, the capnograph indicated inspired carbon dioxide tension of 18mmHg. Anesthetic machine check was soon carried out again. A visual check of non-return valves detected a plastic film, 18 x 21mm large, caught in the expiratory valve. This plastic film impaired complete occlusion of the orifice for the expiratory gas flow. As a result, the patient was rebreathing carbon dioxide. After removing it, the wave form of the capnograph was normalized and end-tidal carbon dioxide tension decreased immediately from 45mmHg to 33mmHg. As we did not detect any foreign matters at the non-return valves on anesthetic machine check before use, the plastic film might have already existed in the disposable corrugated tube before use. The capnograph is a useful device for detecting anesthetic circle system failure in such a case. It is important that the patients' airway is separated from the anesthetic circle system through the use of a filter to prevent foreign matter from being inhaled.

Adult↗