Efficiency of an Enclosed Afferent Reservoir Breathing System During Controlled Ventilation

Abstract

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.

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

“…Day-case patients received no premedication. In all patients, anaesthesia was induced with thiopentone 6-8 mg kg" 1 followed by atracurium 0.5 mg kg" 1 and fentanyl 1-2 ug kg" 1 tained with approximately 66 % nitrous oxide and 0.5-1 % isoflurane in oxygen. Ventilation was controlled using an Ohmeda 7800 ventilator with the I :E ratio set at 1:2.…”

“…Minute volume of ventilation ( VE) was measured using the rotary transducer supplied with the Ohmeda 7800 ventilator and placed between the patient and the breathing system [1]. The accuracies of the flow transducer and the anaesthetic machine flowmeters were checked using a pneumotachograph and a dry gas meter, respectively.…”

“…In an earlier communication, we described a new version of the enclosed afferent reservoir breathing system (EAR) developed by Ohmeda, and its assessment during controlled ventilation in adults [1]. In the present study, the efficiency of the same system has been determined during controlled ventilation in children, and measurements of carbon dioxide production have been used to derive a simple formula for calculating fresh gas flow rates.…”

Fresh Gas Requirements of an Enclosed Afferent Reservoir Breathing System in Anaesthetized, Spontaneously Breathing Adults

“…The enclosed afferent breathing system (EAR), developed by Ohmeda, has been demonstrated to be an efficient breathing system for paediatric use during both controlled [1] and spontaneous ventilation [2], and during controlled ventilation in adults [3]. This study was undertaken to determine the minimum fresh gas flow required to prevent rebreathing when the EAR is used during anaesthesia with spontaneously breathing adults.…”

“…This study was undertaken to determine the minimum fresh gas flow required to prevent rebreathing when the EAR is used during anaesthesia with spontaneously breathing adults. Preliminary work suggests that the efficiency of the EAR is maintained during anaesthesia in relatively young, healthy adults in the supine position [4]. This study aimed to determine the minimum fresh gas requirements for this system when used in elderly patients in the lithotomy position, thus assessing the efficiency of the system under less favourable circumstances found in clinical practice.…”