Oxygen delivery failure resulting from interference with a Bain breathing system

A critical incident is described where the expiratory (scavenging) port of an obsolete version of a Bain-type breathing system valve assembly was inadvertently connected to the common gas outlet of an anaesthetic machine. This resulted in the patient being deprived of a supply of fresh gas. This misconnection was made possible by adding a plastic connector to the valve scavenging port and subsequent wrongful misconnection. The patient fortunately suffered no harm. The case highlights the danger of equipment that has been subjected to unauthorized interference.     

Optimization of a trileaflet valve design

This study investigates the fundamental principles that should govern the basic design of an optimal trileaflet valve. The geometry of the leaflets is described in terms of radius of the base (Rb), radius of the commissures (Rc), height of the valve (H), height of the commissures (Hs), and angle of the open leaflet to vertical (beta). Using computer-aided design software and these design parameters, a computer model of the valve was constructed. Choosing the parameters empirically did not produce an optimal valve. The four criteria for optimal performance were defined as: (1) a certain minimum coaptation height, (2) no folds in the leaflet, (3) minimum valve height, and (4) minimum leaflet flexion. Mathematical relationships were established between the design parameters and the performance parameters. These relationships indicated that the parameters Rc, Hs, and beta could be used to minimize valve height; however, a reduction in valve height must be balanced against the accompanying increase in leaflet flexion. For an optimal valve, the design parameters were Rb = 10 mm, then Rc = 8 to 10 mm, H = 11.5 mm, Hs = 2.4 to 2.6 mm, and beta = 4 degrees to 11 degrees . The optimal valve of any radius can be designed by scaling Rc, H, and Hs with respect to Rb. These design parameters were similar to those of the natural aortic valve. Trileaflet bioprosthetic valves designed on these principles are expected to have enhanced efficiency and longevity.     

High frequency jet ventilation: use of the Bain system for entrainment

The use of a Bain system to convey anaesthetic gases for entrainment during high frequency jet ventilation (HFJV) was evaluated by examining the effect of varying the fresh gas flow (Vf) on the end-tidal carbon dioxide (PECO2) in 46 ASA physical status I and II patients undergoing extracorporeal shock-wave lithotripsy (ESWL). Anaesthesia was induced with methohexitone (1-2 mg.kg-1), fentanyl (1-1.5 micrograms.kg-1) and vecuronium (0.1 mg.kg-1). After endotracheal intubation with a Mallinckrodt Hi-Lo Jet cuffed endotracheal tube, the patient was immersed in a water bath and HFJV at 150 breaths per minute was instituted with an Acutronic AMS 1000 jet ventilator attached to the side channel of the Hi-Lo tube. A Bain system was attached to the proximal end of the endotracheal tube to provide gases for entrainment. Anaesthesia was maintained with an intravenous infusion of methohexitone (5 mg.kg-1.h-1) and 50% nitrous oxide in oxygen for both the jetted and entrained gases. PECO2 was determined at 5-min intervals by a single-breath technique using a calibrated Engstrom Eliza capnograph. Thirty patients were randomly allocated to receive Vf's of 50 (Group 1), 75 (Group 2) and 100 (Group 3) ml.kg-1.min-1, respectively. A further eight patients (Group 4) received a Vf of 100 ml.kg-1.min-1 for 15 min, 75 ml.kg-1.min-1 for the next 15 min and 50 ml.kg-1.min-1 thereafter. In a further group of eight patients (Group 5), Vf was initially 25 ml.kg-1.min-1 for 10 min and was then switched off for the remainder of the procedure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Failure to clear casts and secretions following inhalation injury can be dangerous: report of a case

A 27-year-old man suffered smoke inhalation during a fire. Three days later, he complained of respiratory difficulty and was admitted to our hospital. Bronchoscopy revealed a very large buildup of sputum mixed with soot extending from the left main bronchus to the bifurcation of the upper and lower lobe bronchi and causing both pulmonary atelectasis and pneumonia. The debris was successfully removed the next day with basket forceps via bronchoscopy. The patient's airway pressure dropped significantly, enabling extubation almost immediately. Because of the possibility for respiratory failure caused by viscous secretion, it is important to perform initial bronchoscopy in cases of suspected inhalation injury.     

The long Bain breathing system: an investigation into the implications of remote ventilation

A long version of the Bain breathing system is commonly used when remote anaesthesia is required, such as during magnetic resonance imaging or radiotherapy. We compared the static compliance and distal pressures over a range of flows in a 1.6 and 9.6 m Bain system. We examined the effect on ventilation of increasing the length of the Bain system in lung models for 10, 20 and 70 kg patients. We found that static compliance was increased in the long Bain system. We found that with matched peak inspiratory ventilator pressures there was a reduction in peak inspiratory pressures at the patient end with the longer system (p < 0.001). A reduction in tidal volume was found with the 9.6 m Bain (p < 0.001), and positive end-expiratory pressure was increased (p = 0.01). Although the effect on tidal volume was proportionally small in the 70 kg simulation (660 and 617 ml in 1.6 and 9.6 m systems, respectively) it increases in significance in children, with a 23% reduction in tidal volume in the 10 kg mock lung (95 and 73 ml in 1.6 and 9.6 m systems, respectively). Anaesthetists should be aware of the reduction in tidal volume and increased positive end-expiratory pressure. During remote anaesthesia with a long Bain system, the ventilator should be adjusted to compensate.     

Inspiratory valve malfunction in a circle system: pitfalls in capnography

Capnography is a useful technique in monitoring the integrity of anaesthetic equipment such as the malfunctioning of unidirectional valves in circle system. However, the lack of a precise mechanism in existing capnographs to identify the start of inspiration and the beginning of expiration in the capnograms, makes the analysis of the carbon dioxide waveforms during inspiration difficult and thus results in inaccurate assessment of rebreathing. We report a case where, during the malfunction of the inspiratory unidirectional valve in the circle system, the capnograph failed to detect the presence of substantial rebreathing. Critical analysis of the capnogram recorded during the malfunction revealed that there was substantial rebreathing which was underestimated by the capnograph as it reports only the lowest CO2 concentration rebreathed during inspiration in such abnormal situations.     

Calculation of end–tidal carbon dioxide fractions in the Bain system

The validity of the Stenqvist-Sonander formula for calculating the end-expiratory fraction of carbon dioxide (FACO2) in the coaxial Mapleson D (Bain) systems was evaluated using a lung model for simulated spontaneous breathing with an optional respiratory wave form. Two different respiratory flow patterns were used, one representing relaxed breathing in a volunteer and one resembling the respiration found in halothane anaesthesia. Each pattern was used with five different fresh gas flows and three different respiratory rates. The formula was found to be quite accurate when the flow pattern of an awake volunteer was simulated, but it underestimated the observed FETCO2 value by about 10% in halothane breathing. It is concluded that the formula can be recommended for use in theoretical and educational situations but that it is too complicated for application in clinical practice.     

Scutting: a dangerous pastime?

Scutting is a pastime which has taken place in Dublin for many years. To scutt is to gain a ride on the back of a moving vehicle holding onto it by any means possible. Injuries sustained while scutting have never previously been reported.

A total of 38 children presented at the Accident and Emergency Department of The Children's Hospital, Temple Street during the period January 1985 to July 1987 with injuries sustained while scutting. The injuries were analysed with regard to type, pattern, severity and outcome; nine children died from their injuries and 34.2 per cent of the children were admitted to hospital with an average stay of 5 days. All of those admitted alive made a full recovery.

Comparison is made with other more everyday sensible pastimes and with road traffic accidents involving children. Scutting is shown to be the most dangerous pastime and is responsible for more deaths than any other type of road traffic accident involving children. Suggestions are made to stop this pastime taking place.