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SCOTI vs. Wee. An assessment of two oesophageal intubation detection devices.

The SCOTI (Sonomatic Confirmation of Tracheal Intubation) is a newly marketed electronic device that relies on recognition of a resonating frequency for detection of tracheal intubation. It was compared with the modified Wee oesophageal intubation detection device, which works on a mechanical principle, in 50 elective surgical patients. All had simultaneous tracheal and oesophageal intubations. The Wee device correctly detected oesophageal and tracheal placement of the tracheal tube in all 50 patients. The SCOTI device incorrectly identified 1 of 50 tracheal intubations and was unable to identify the position of another. It correctly identified all 50 oesophageal intubations. The SCOTI is no better than the simple, cheap and reliable Wee device.

Adult↗

End-tidal carbon dioxide measurement and breathing system filters.

Breathing system filters are recommended for use during general anaesthesia. Manufacturers of gas sampling equipment recommend that gas is sampled from the 'machine side' of these filters, thereby avoiding contamination of the sampling line and waterlogging in the case of heat and moisture exchangers. The aim of this study was to investigate differences between the measured end-tidal carbon dioxide values at either side of the filter. Fifteen adults were studied during mechanical ventilation and 15 during spontaneous ventilation under general anaesthesia. End-tidal carbon dioxide values were significantly lower at the machine side of the filter in both groups (p = 0.00001). The measurement error induced by the inclusion of the breathing system filter was significantly greater in the spontaneously breathing group (p = 0.0004).

Adult↗

Effect of xenon anaesthesia on accuracy of cardiac output measurement using partial CO2 rebreathing.

Cardiac output (CO) determination based on partial CO(2) rebreathing has recently been introduced into clinical practice. The determination of flow is crucial for exact CO readings and the physical properties of xenon, i.e. high density and viscosity, may influence flow readings. This study compared echocardiography-derived CO measurements with the partial rebreathing method during total intravenous (TIVA) vs. xenon-based anaesthesia. Thirty-nine patients ASA physical status III undergoing aortic reconstruction were randomly assigned to receive either xenon (Xe, n = 20) or TIVA (T, n = 19) based general anaesthetic. Paired measurements were taken before xenon administration, after xenon administration, before and after clamping of the abdominal aorta and after declamping and at corresponding time points in the TIVA group. Data were analysed with a Bland-Altmann plot. Bias and precision were acceptable and comparable before xenon administration (T 0.54 +/- 0.92 l.min(-1) vs. Xe 0.11 +/- 1.1 l.min(-1)), but after xenon administration CO was largely overestimated by partial CO(2) rebreathing (T 0.04 +/- 0.91 l.min(-1) vs. Xe -4.0 +/- 2.1 l.min(-1)). In the TIVA group, bias and precision after declamping increased significantly (P < 0.01) compared to all time points except baseline. In its current application, the NICO cardiac output monitor appears to be inappropriate for determination of CO during xenon based anaesthesia.

Aged↗

Awake fibrecapnic intubation: a novel technique for intubation in head and neck cancer patients with a difficult airway.

Awake fibreoptic intubation is the gold standard for difficult airway management but failures are reported in the literature in up to 13% of cases. In case of failure, a tracheotomy is often indicated. We describe a novel technique for intubation in head and neck cancer patients with a difficult airway that we call awake fibrecapnic intubation. The aim of this study was to investigate the feasibility of this technique. We studied prospectively 15 consecutive intubations in head and neck cancer patients before diagnostic or therapeutic surgical procedures. After topical anaesthesia, a fibrescope was introduced into the pharynx. Spontaneous respiration was maintained in all patients. Through the suction channel of the fibrescope a special suction catheter was advanced into the airway for carbon dioxide measurements. When four capnograms were obtained, the fibrescope was railroaded over the catheter and after identification of tracheal rings, a tracheal tube was placed. Tracheal intubation was successful in all patients without bleeding or complications, with a median (range) time to intubation of 3 (2-15) min. Identification of the vocal cords and glottis was difficult in four patients due to extensive anatomical abnormalities or poor visibility; even in these patients, a capnogram was obtained within 4 s.

Aged↗

Phantom capnograph.

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Anesthesia, Closed-Circuit↗

Continuous non-invasive monitoring of energy expenditure, oxygen consumption and alveolar ventilation during controlled ventilation: validation in an oxygen consuming lung model.

BACKGROUND: We have developed a combined indirect calorimetric and breath-by-breath capnographic device (GEM) for respiratory monitoring: oxygen consumption (VO2), carbon dioxide excretion (VCO2), respiratory quotient (RQ), energy expenditure (EE), alveolar ventilation (VA) and dead space/total ventilation (VD/VT). METHODS: The device was tested in a lung model in which VO2 was achieved by combustion of hydrogen. VCO2 was achieved by delivering CO2 into the single alveolus combustion chamber. VO2, VCO2, compliance, and anatomical dead space could be varied independently. RESULTS: Measured VO2 was 101 +/- 3% (SD) of set value at a F1O2 < 0.6 and 101 +/- 7% at a F1O2 > 0.6 during 15 hours of testing. The corresponding VCO2 values were 99 +/- 2% and 102 +/- 7%. The GEM could with good accuracy measure accumulated energy expenditure (EE) during simulated unstable patient conditions up to a F1O2 of 0.8. At F1O2 above 0.8 VCO2 and VO2 could be estimated using a default RQ value of 0.85. On-line estimated VA and VD/VT values could be obtained at any F1O2 up to 1.0. In a test sequence with stable VO2 and VCO2 the GEM adequately followed changes in VA, induced by changes in anatomical dead space, breathing frequency and compliance. CONCLUSION: The overall performance of the device is satisfactory and well comparable with any equipment tested. It allows near-continuous non-invasive monitoring of EE, VO2, VCO2, VA, VD/VT in ventilated, critically ill patients, providing a rationale for ventilator settings and nutritional support.

Capnography↗

The detection of carbon dioxide embolism during laparoscopy in pigs: a comparison of transesophageal Doppler and end-tidal carbon dioxide monitoring.

BACKGROUND: The aim of the study was to compare the value of transesophageal Doppler and end-tidal carbon dioxide monitoring to detect venous carbon dioxide embolism in pigs during laparoscopic cholecystectomy. METHOD: Ten pigs were anesthetized under constant ventilation, and instrumented for laparoscopic cholecystectomy. CO2 pneumoperitoneum was performed at 15 mmHg and then, successive increased intravenous gas boluses of 0.1 to 4 ml/kg injected through the femoral vein using a 55-mm long catheter. The responses indicative of embolism were defined as: 1) a change in Doppler tone placed facing the junction of the right atrium and inferior vena cava; 2) a change in end-tidal CO2 > or = 0.4 kPa. RESULTS: Doppler was more sensitive in detecting 0.1, 0.2 and 0.4 ml/mg of CO2 embolism than end-tidal CO2 (P < 0.05). Over 0.4 ml/mg no differences in sensitivity were found but the Doppler signal modifications occurred earlier than the changes in end-tidal CO2. Moreover, these changes always consisted of a reduction of the value. CONCLUSION: During laparoscopic cholecystectomy in pigs, transesophageal Doppler was a highly sensitive monitor which provided an earlier detection of CO2 embolism and at lower doses than end-tidal CO2 monitoring.

Animals↗

Air contamination of a closed anesthesia circuit.

Closed-circuit anesthesia (CCA) has certain advantages such as decreased cost, decreased anesthetic gas pollution, improved inhalational gas humidity and temperature in comparison to conventional inhalational anesthesia using a high fresh gas flow, i.e. more than 2 L x min(-1), with a semi-closed breathing circuit. The main disadvantage of CCA is the possibility of hypoxic anesthetic gas delivery. This potentially lethal situation is caused by an insufficient oxygen flow rate for the body metabolism or by the accumulation of inactive gas, usually nitrogen, within the breathing circuit in spite of a sufficient oxygen concentration in the fresh gas supply to the breathing circuit. In the latter case, the accumulation of inactive gas may also lead an increased risk of awareness because of its dilution effect on the concentrations of inhalational anesthetics. We herein present a case of air contamination of the breathing circuit through a sampling line of an anesthetic gas monitor. The air caused a decrease in the oxygen concentration during closed circuit anesthesia.

Air↗

Endoscopic intratracheal carbon dioxide measurements during pediatric flexible bronchoscopy.

BACKGROUND: CO2 monitoring is recommended for thoracic telescopic procedures and for spontaneous breathing general anesthesia in children. During flexible bronchoscopy (FB) in children, the various currently available methods of CO2 measurements are limited. The CO2 falls and increases have been reported in FB but it is unknown whether airway lesions predispose to CO2 change. The aim of this study was to describe and validate endoscopic intratracheal CO2 measurements in children undergoing FB under spontaneously breathing GA. METHODS: Endtidal CO2 (P(E)CO2) measurements at the start (Start-CO2) and end (End-CO2) of FB on 100 consecutive children were performed using a newly designed endoscopic intratracheal method. To validate the method blood gas sampling was simultaneously performed in 28 children and results analyzed using the Bland and Altman method, intraclass correlation and 95% range for repeatability. RESULTS: End-CO2 and CO2-change (End-CO2 minus Start-CO2) were significantly different in children with airway lesions (CO2 change: no lesion = 3 mmHg, extrathoracic airway lesion = 4.5, intrathoracic airway lesion = 8, P = 0.038). There was no significant difference in Start-CO2 values among the groups. CO2-change in those aged < or =12 months was similar to those >12 months. Intratracheal CO2 measurements were comparable with arterial blood values in the Bland and Altman plots. The intraclass correlation was 0.69 and 95% range for repeatability was 3.7-4.17 mmHg. CONCLUSIONS: Midtracheal P(E)CO2 provides a useful estimate of P(a)CO2 for monitoring the respiratory status of children undergoing FB. The presence of airway lesions rather than age is associated with significant increased PCO2 rise.

Adolescent↗