Preliminary Evaluation of the Enclosed Magill Breathing System

et al. 1991

We describe an enclosed afferent reservoir (EAR) breathing system developed by Ohmeda and designed to operate efficiently in spontaneous and controlled ventilation. The efficiency of the system was evaluated by calculating the fractional utilization of fresh gas in 10 ASA I-III patients during anaesthesia with controlled ventilation. Maximum efficiency occurred when the minute ventilation to fresh gas flow ratio was greater than 1.5. Under these conditions, fractional utilization was relatively constant with a value of 0.73 (95% confidence interval 0.69-0.78). The minimum fresh gas flow for use during controlled ventilation was determined in another eight ASA I-III patients when the minute volume to fresh gas ratio was greater than 1.5. In view of an increased arterial to end-tidal carbon dioxide partial pressure difference in patients in the first part of the study (1.03 kPa), normocapnia was defined as an end-tidal carbon dioxide partial pressure of 4.3 kPa. Normocapnia was achieved with a mean fresh gas flow of 66 ml kg(-1) min(-1), while 70 ml kg(-1) min(-1) produced mild hypocapnia.

Section: Discussionsupporting

confidence: 86%

Efficiency of an Enclosed Afferent Reservoir Breathing System During Controlled Ventilation

Droppert

Meakin

et al. 1991

“…1). A defective valve in the EAR system tested by Bruce and Soni [9] may have resulted in their finding somewhat smaller (although significant) differences in end-tidal carbon dioxide partial pressures between patients during ventilation of the lungs with the EAR and the Bain system [10].…”

Section: Discussionmentioning

confidence: 98%

Fresh Gas Requirements of an Enclosed Afferent Reservoir Breathing System During Controlled Ventilation in Children

Meakin

Jennings

et al. 1992

An enclosed afferent reservoir breathing system (EAR) designed by Ohmeda was evaluated during anaesthesia with controlled ventilation in 104 healthy children. Carbon dioxide production and arterial carbon dioxide tension were measured in 12 children in order to determine the proportion of fresh gas (VF) involved in gas exchange. When the ratio of minute volume ventilation to fresh gas flow (VE:VF) exceeded 1.5, fractional utilization of fresh gas with the EAR was 0.92. This value and values of carbon dioxide production obtained from 43 children were used to derive a simple formula relating fresh gas flow requirements to body weight. The formula, VF = 0.6 x weight 0.5, was assessed in 49 children weighing 10-70 kg. The mean end-tidal partial pressure of carbon dioxide in these patients was 4.5 kPa (range 3.8-5.2 kPa). We conclude that the EAR has an efficiency of 92% in the use of fresh gas during controlled ventilation in healthy children, provided the VE:VF ratio is greater than 1.5. Under these conditions, normocapnia to mild hypocapnia was produced accurately using the formula VF = 0.6 x weight 0.5.

Physical Characteristics of an Enclosed Afferent Reservoir Breathing System

Jennings

Michell²,

et al. 1992

We have assessed the characteristics of the Ohmeda Enclosed Afferent Reservoir Breathing System (EAR) using simulated spontaneous ventilation and controlled ventilation. The additional work of breathing through the system was measured and shown to be comparable to that of a modified Mapleson D breathing system (Bain) for fresh gas flows producing similar end-tidal carbon dioxide concentrations. It was shown under conditions of simulated controlled ventilation that end-tidal gas concentration was relatively insensitive to variations in inspired to expired ratio (I: E), tidal volume (VT) and deadspace (VD). Measurement of the volume of carbon dioxide rebreathed using simulated spontaneous ventilation led to the prediction that rebreathing of carbon dioxide would begin to occur in the EAR when fresh gas flow to total ventilation ratio (VF: VE) was approximately 0.87. However, comparison of the results of model lung tests and clinical data suggests that great caution should be taken in extrapolating such results into clinical advice.