J Med Assoc Thai 2010; 93 (11):1284

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Baby EAR Circuit: A Clinical Determination of Optimal Fresh Gas Flow in Spontaneous Breathing Anesthesia
Theerapongpakdee S Mail, Bunsangjaroen P , Horatanaruang D , Phanpanusit T , Asava-aree C , Uppan K

Background: Baby EAR circuit is a new modified enclosed afferent reservoir anesthetic breathing system invented to use in
pediatric patients. By following His Majesty the King of Thailand’s self-sufficiency philosophy, the circuit is simply made of
low-cost and easy-to-find materials in the operating room.

Objective:
Investigate clinical use of the circuit and to find the optimal fresh gas flow in spontaneous breathing anesthesia.

Material and Method: A prospective descriptive study was conducted in pediatric patients, who weighed 5-20 kg, anesthetized
for surgery and divided into three groups of body weight: groups I (5-<10 kg), groups II (10-<15 kg), groups III (15-20 kg).
The Baby EAR circuit was used for general anesthesia with endotracheal tube and spontaneous breathing. Different fresh gas
flow of 4, 3.5, 3, 2.5, 2, and 1.5 liter per minute (LPM) was used consecutively. The authors recorded end-tidal carbon dioxide
(EtCO2) and mean inspiratory carbon dioxide (ImCO2) while using fresh gas flow at 4, 3.5, 3, 2.5, 2, and 1.5 LPM. EtCO2 of
35-60 mmHg and ImCO2 of < 6 mmHg were considered clinically acceptable.

Results:
Thirty-five patients were enrolled in the present study. Mean value (95% CI) of EtCO2, ImCO2 and fresh gas flow rate
in group I were 42 + 3.2 (39.8, 44.2), 3 + 1.2 (2.2, 3.8) mmHg, and 1.7 + 0.6 (1.2, 2.1) LPM respectively. Mean value (95%
CI) of EtCO2 ImCO2 and fresh gas flow rate in group II were 50 + 5.6 (47.2, 52.8), 3 + 0.9 (2.6, 3.4) mmHg, 2 + 0.4 (1.8,
2.2) LPM respectively. Mean value (95% CI) EtCO2 ImCO2 and fresh gas flow rate in group III were 51 + 7.2 (46.7, 55.3),
2 + 1 (1.4, 2.6) mmHg, and 2 + 0.3 (1.8, 2.2) LPM respectively. No patients had serious complications in the present study.

Conclusion: Baby EAR circuit can be made economically and used safely for general anesthesia with spontaneous breathing
in pediatric patients who weighed 5-20 kg at optimal fresh gas flow rate of > 2.5 LPM.

Keywords: Enclosed afferent reservoir (EAR), Breathing system, Pediatric anesthesia, Fresh gas flow, Spontaneous breathing

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