Low-flow anesthesia in children: theory and clinical practice

There has been increased interest recently in low-flow anesthesia to minimize wastage of expensive volatile anesthetics and reduce atmospheric pollution. With the help of modern anesthetic apparatus and the availability of comprehensive gas monitoring, low-flow anesthesia can be performed safely in children. However, pediatric anesthesiologists have been more reluctant to adopt low-flow techniques. In this review article, the safety and efficacy of low-flow anesthesia will be discussed to help the anesthesiologists who want to employ this technique in children.

The effect of low fresh gas flow rate on sevoflurane consumption / 대한마취과학회지

BACKGROUND: In an era of medical cost containment, cost-effectiveness has become a major focus in healthcare. The effect of a new policy on the use of low fresh gas flow during maintenance of general anesthesia with volatile anesthetics was evaluated. METHODS: The numbers and duration of general anesthesia cases using sevoflurane 5 weeks prior to and 15 weeks after policy implementation were retrieved from the electronic medical records database. The number of sevoflurane bottles consumed was also assessed. The anesthesia hours per bottle of sevoflurane were compared before and after policy implementation. RESULTS: The number of anesthesia hours performed per bottle of sevoflurane increased by 38.3%. The effect varied over time and tended to fade with time. CONCLUSIONS: The implementation of a low fresh gas flow rate policy effectively reduces the amount of sevoflurane consumed for the same duration of anesthesia.

Comparison between High Flow and Low Flow Anesthesia for Positive Pressure Ventilation in Pediatrics Using the Laryngeal Mask Airway / 대한마취과학회지

BACKGROUND: Low flow anesthesia provides many advantages, including reduced cost, conservation of body heat and airway humidity. This study was performed to compare low flow anesthesia with high flow anesthesia and to investigate whether the advantages of low flow anesthesia during positive pressure ventilation can be combined with the laryngeal mask airway in paralyzed pediatric patients. METHODS: Thirty-one pediatric patients of ASA physical status 1 or 2 were studied and divided into two groups according to the fresh gas flow (FGF) in the breathing system; low flow group (FGF approximation 1 L/min, n = 17) or high flow group (FGF approximation 4 L/min, n = 14). Each respiratory parameter was measured when a steady state was reached at 20 min after induction. RESULTS: There were no significant differences of respiratory data between the two groups except that the inspired oxygen concentration was lower in the low flow group than in the high flow group. Hemodynamic changes with the laryngeal mask airway insertion were not statistically significant. CONCLUSIONS: A laryngeal mask airway is an effective airway device for low flow anesthesia as well as for high flow anesthesia in paralyzed pediatric patients.

Clinical Evaluation of Low-Flow Enflurane Anesthesia in Infants / 대한마취과학회지

BACKGROUND: The purpose of this study was to evaluate the safety and efficacy of low-flow anesthesia with a semi-closed circle anesthesia system in infants. METHODS: Twenty, ASA physical status 1 or 2, infants were randomly assigned into two groups: high-flow anesthesia (HFA) or low-flow anesthesia (LFA). An identical semi-closed Dr ger circle anesthesia system (Cato) was used to all patients. Initial fresh gas flow (FGF) was N2O 1.5 L/min and O2 1.5 L/min in both groups. This FGF of 3 L/min was maintained in the HFA group. After 10 min of HFA, the FGF was reduced to 500 ml/min (N2O 250 ml/min and O2 250 ml/min) in the LFA group. RESULTS: Hypoxic or hypercarbic gas concentrations were not observed in all patients. Enflurane consumption during LFA was about 1/3 of that during HFA (6.8 +/- 1.3 ml vs. 19.5 +/- 5.8 ml). The mean highest esophageal temperature was similar in both groups. The mean highest inspiratory gas and soda lime temperatures were significantly higher in the LFA group than in the HFA group. CONCLUSIONS: Low-flow anesthesia in a circle system with a fresh gas flow of N2O 250 ml/min and O2 250 ml/min could be performed safely and economically for infants.

Low Flow Anesthesia with Continuous Infusion of Liquid Enflurane into Breathing Circuit / 대한마취과학회지

BACKGROUND: Lowe and Ernst's square root of time model employs direct injection of liquid agent into breathing circuit for low flow anesthesia. Intermittent injections of the agent by Lowe's method change rapidly arterial partial pressure of the agent and fail to maintain hemodynamic stability to surgical stimuli. We designed to investigate the possibility and safety of low flow anesthesia with continuous infusion of liquid enflurane into breathing circuit. METHODS: Twenty patients, ASA physical status I or II, undergoing gastrectomy under inhalational general anesthesia were randomly divided into two groups. Anesthesia was maintained with a fresh gas flow of O2 500 ml/min and continuous infusion of liquid enflurane. An identical semiclosed Dr ger circle anesthesia system was used to all patients. Liquid enflurane calculated by the Lowe's method (group I) or simplified by patient's weight (group II) was continuously infused directly into inspiratory limb of breathing circuit using syringe pump. Inspiratory and expiratory concentrations of enflurane, enflurane consumptions, hemodynamic parameters, carboxyheomoglobin were checked intraoperatively. Hepatic and renal functions were evaluted postoperatively. RESULTS: Liquid enfurane was initially infused at a rate in ml/hr of 16.1 0.8 weight in kg in group I and 1.0 weight in kg in group II. After 5 minutes the infusion rate was reduced to 20% of this value and then well adjusted to maintain blood pressure within 20% of the reference preoperative value. Enflurane consumptions and recovery time were similar between the two groups. There were no clinical significant changes in arterial blood gas, carboxyheomoglobin, and hepatic and renal functions. CONCLUSIONS: These data show that low flow anesthesia with continuous infusion of liquid enflurane into breathing circuit is safe and effective, and that the infusion method simplified by patient's weight may easily be applied to clinical practice for low flow anesthesia.