Fresh gas flow in coaxial Mapleson A and D circuits during spontaneous breathing

In a lung model simulating spontaneously breathing halothane anaesthesia, the rebreathing characteristics of the coaxial Mapleson A (Lack circuit) and D (Bain circuit) systems were tested. Using decreasing fresh gas flows (VF), the end-tidal carbon dioxide fraction (FACO2) was monitored and the point of rebreathing (R.P.) detected. The effects of changes in minute volume (VE), dead-space to tidal volume ratio (VD/VT) and carbon dioxide elimination (VCO2) were studied. The effect of increased tidal volumes (VT) on FACO2 was investigated for some different fresh gas flows (VF). The VF/VE ratio for R.P. in the Bain circuit was approximately 2 and in the Lack circuit 0.88. In both circuits an increase in VE and a decrease in the VD/VT ratio resulted in higher demands on VF if rebreathing was to be avoided. The latter effect was much more pronounced in the Lack circuit. In neither system did any changes in VCO2 affect the rebreathing characteristics. The conclusion was drawn that the Lack system is a much better choice concerning the fresh gas flows for anaesthesia with spontaneous breathing than the Bain system. It was also concluded that the fresh gas flows recommended by Humphrey for the Lack system (i.e. 51 ml X min-1 X kg b.w.-1) and by the manufacturers for the Bain system (i.e. 100 ml X min-1 X kg b.w.-1) are inadequate and should be increased if a considerable degree of rebreathing is to be avoided.     

Influence of the respiratory flow pattern on rebreathing in Mapleson A and D circuits

In a lung model the rebreathing effects of different respiratory flow patterns (RFP) were studied in the coaxial Mapleson A (Lack) and D (Bain, Coax-II) systems during spontaneous breathing. In the Mapleson A system RFP was not found to have any impact. In the D systems FACO2 was higher with an RFP typical of halothane-anaesthetized patients than with an RFP with an exponentially decreasing expiratory flow and an end-expiratory flow pause (FTEP). The difference in FACO2 was 26% with a VF corresponding to 100 ml X min-1 X kg-1 body weight. The RFP in a non-anaesthetized volunteer was intermediate between these two patterns. Rebreathing decreased in the D systems with prolongation of FTEP and when a decelerating expiratory flow was used.     

Rebreathing, resistance and external work of breathing in three different coaxial Mapleson D systems

Using a lung model, rebreathing characteristics, resistance against gas flow and the external work of breathing were tested in three different coaxial Mapleson D systems: the Medicvent D system, the Bain original system and the Coax-II system. The rebreathing characteristics were found to be similar in all systems in both spontaneous and controlled ventilation. The Bain system was found to have the lowest resistance and work of breathing and the Coax-II system the highest. The differences were small and clinically insignificant. Both the resistance and the work of breathing increased with fresh gas flow. The resistance against expiration was found to be in the range 135-160 Pa at a total gas flow of 31 1.min-1, which is well within the acceptable level. The resulting end-expiratory pressure was never above 100 Pa (1 cmH2O) in any system. We concluded that there was no clinically significant difference among the three systems despite differences in design. The coaxial Mapleson D systems can also be used safely with high fresh gas flows with regard to resistance and end-expiratory pressures.     

Carbon dioxide distribution in Mapleson A and D systems: an experimental study

The distribution of CO2 in the Mapleson A and D rebreathing systems was investigated experimentally during controlled ventilation and with the expiratory valve closed during inspiration. Maximal and minimal levels of CO2-concentration obtained from capnograms along the tubing were used to construct "gas profiles". For both systems, high tidal volumes and low fresh gas flows resulted in a high degree of gas separation with a pool of alveolar gas near the expiratory valve, and longitudinal gas mixing was minimal. In this manner fresh gas loss was prevented and fresh gas utilization optimized. The end of the tubing nearest the patient was found to act as a reservoir for alveolar gas in the Mapleson A system and fresh gas in the Mapleson D system. Fresh gas utilization in the Mapleson D system was somewhat less efficient than in the Mapleson A system due to the fresh gas admixture to exhaled alveolar gas in the patient-near end of the tubing during expiration. The replacement of the usual expiratory valve of the Mapleson A system by a valve which is closed during inspiration makes the A system an alternative to the D system for controlled ventilation.     

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.     

Minimum fresh gas flow requirements of anaesthetic breathing systems during spontaneous ventilation: a graphical approach

A general solution is presented to the problem of finding the minimum fresh gas flow requirements, during spontaneous ventilation, of anaesthetic breathing systems in the Mapleson classification. The solution is applicable to any pattern of breathing, dead space volume and tidal volume. The method is graphical and its use and understanding require no mathematical skills. However, if an analytical form of the respiratory waveform is known, the method is easily extended by use of calculus to obtain a precise analytical solution.     

Rebreathing in the Mapleson A, C and D breathing systems with sinusoidal and exponential flow waveforms

The degree of rebreathing in Mapleson A, C and D breathing systems for sinusoidal and exponential flow waveforms is analysed mathematically. The effects of altering the I:E ratio and of introducing an expiratory pause are investigated. The results for sinusoidal waveforms closely resemble those for a square wave. Exponential flow waveforms produce results similar to triangular flow waveforms. The Mapleson A system is always the most efficient. The Mapleson C system is efficient when the I:E ratio is 1:1, becoming less efficient with longer expiration and very inefficient with an expiratory pause. The Mapleson D system becomes efficient when the expiratory pause is long.     

Increase in the use of rebreathing gas flow systems and in the utilization of low fresh gas flows in Finnish anaesthetic practice from 1995 to 2002

BACKGROUND: The use of rebreathing systems together with low fresh gas flows saves anaesthetic gases, reduces the costs of anaesthesia, causes less environmental and ergonomic adverse effects, i.e. less air contamination in the operating room, and has favourable physiological effects. We assessed whether the use of non-rebreathing vs. rebreathing gas flow systems and high vs. lower fresh gas flows has changed during recent years. METHODS: The use of rebreathing and non-rebreathing systems and the utilization of fresh gas flows were evaluated by sending a questionnaire to the heads of anaesthesia departments at all public health care hospitals in Finland in 1996 and 2003. The data was gathered from the previous years 1995 and 2002, respectively. RESULTS: The use of rebreathing systems increased from 62% to 83% of all instances of general anaesthesia (P < 0.001). In rebreathing gas flow systems, there was a significant shift from high fresh gas flows (3 l min(-1) and more) towards lower fresh gas flows (between 1 to 2 l min(-1) and even below 1 l min(-1)) (P < 0.001). CONCLUSIONS: The benefits of low fresh gas flows have now been achieved in most instances of rebreathing system anaesthesia, which was not the case in 1995.     

Biological response to woven carbon fibre pads in the knee. A clinical and experimental study

We assessed the use of woven carbon fibre pads to resurface osteochondral defects in animals and in patients. The pads became filled with structurally strong and compliant fibrous tissue and did not provoke a synovial reaction, though pigmentation was induced in some animals. Of the patients, 77% had a satisfactory response to resurfacing, with no synovitis. Our initial experiments indicate that carbon pads may provide a satisfactory treatment for localised articular defects.     

A dye study in fresh cadavers to outline retrograde flaps of the lower limbs and to examine clinical implications

The reconstruction of distal lower limb defects to meet functional and cosmetic requirements is challenging. The aim of this study was to ascertain the safe hemodynamic territory of various retrograde flaps that are frequently used. We carried out a dye study on both lower limbs of ten fresh cadavers using methylene blue to assess the safe limit of retrograde flaps of different types (i.e., fasciocutaneous flap, adipofascial flap, and fasciocutaneous flap with adipofascial extension) based on the two lower perforators of the posterior tibial artery. The dye penetrated the vascular network up to 20 cm in the fasciocutaneous flaps from a point 8 cm proximal to the tip of the medial malleolus. The extent of the dye was 40 and 20% less in adipofascial flaps and fasciocutaneous flaps with adipofascial extension, respectively, compared to fasciocutaneous flaps. In live subjects, the safe territory is expected to be about 2 cm more in each flap, based on our clinical observations. These findings are of significance since such flaps can be safely selected for various defects depending on their location, their dimensions, and the availability of suitable local tissues.     

The challenge of sustainability in healthcare systems: Frequency and cost of inappropriate patterns of breast cancer care (the E.Pic.A study)

ObjectivesIn a context of decreasing economic health resources and a rise in health needs, it is urgent to face this sustainability crisis through the analysis of healthcare expenditures. Wastages, deriving from inappropriate interventions, erode resources which could be reallocated to high-value activities. To identify these areas of wastages, we developed a method for combining and analyzing data from multiple sources. Here we report the preliminary results of a retrospective cohort study evaluating the performance of breast cancer (BC) care at IRST, an Italian cancer institute.Materials and methodsFour data sources gathered in a real-world setting (a clinical database, two administrative databases and a cancer registry) were linked. Essential Key Performance Indexes (KPIs) in the pattern of BC diagnosis (KPI 1 and 2) and treatment (KPI 3 and 4) based on current guidelines were developed by a board of professionals. The costs of inappropriate examinations were associated with the diagnostic KPIs.ResultsWe found that 2798 patients treated at IRST from January 2010 to June 2016 received a total of 2516 inappropriate examinations accounting for € 573,510.80. Linkage from multiple routine healthcare data sources is feasible: it allows the measurement of important KPIs specifically designed for BC care, and the identification of areas of low-value use of the resources.ConclusionIf systematically applied, this method could help provide a complete picture of inappropriateness and waste, redirect these resources to higher-value interventions for patients, and fill the gap between proper use of the resources and the best clinical results.     

Major differences between the testis and epididymis in the induction of granulomas in response to extravasated germ cells. I. A light microscopical study in mice

A spermatic granuloma is a chronic inflammatory lesion which surrounds extravasated spermatozoa. Clinically, the lesion develops in the interstitial spaces of the epididymis and vas deferens, and only exceptionally in the testis itself. In the present study, murine testes and epididymides were injured using a needle and the histological appearances of these organs was then compared. Traumatic injury induced extravasation of germ cells in both testes and epididymides. A few days later, spermatic granulomas consistently formed in the epididymides, however, such lesions were not induced in the testes. To examine the possibility that epididymal spermatozoa have inherently greater ability to form spermatic granulomas than do testicular germ cells, isolated epididymal spermatozoa or testicular germ cells were locally injected into the testes and epididymides of recipient mice. Spermatic granulomas readily formed in the epididymides after local injection of either epididymal spermatozoa or testicular germ cells. In contrast, such lesions did not form in the testes even when epididymal spermatozoa were injected. Therefore, this study suggests that the microenvironment of the testicular interstitium, rather than the extravasated components from the ruptured seminiferous tubules, is the main factor determining the limited formation of spermatic granulomas in the testis.