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1 The comparative study of optimal fresh gas flow used in Lack-Plus and Lack s circuit on spontaneously breathing anesthetized adults Sucher S, Theerapongpakdee S, SathitkarnmaneeT, MD Department of Anesthesiology, Faculty of Medicine, Khon Kaen University Lack s circuit is a modified co-axial Mapleson A breathing system Lack circuit. Anaesthesia UK Available from: Commonly used in spontaneously breathing Not depend on carbon dioxide absorption Rely on adequate supply of FGF to prevent rebreathing หล กการพ ฒนาตามแนวพระราชดาร เข าใจ เข าถ ง พ ฒนา เป นบ นได ข นส ความสาเร จ Advantages Compact, lightweight, portable Convenient access to the exhaust valve Easy scavenging Low expiratory resistance Lack-Plus circuit is a modified Lack s circuit with. intraluminal one-way valve 2. active gas scavenging system Minimise FGF, save anaesthetic gas and eliminate OR environment pollution Objective To compare the Lack-Plus and Lack s circuit on the minimal FGF requirement with no and clinically acceptable rebreathing in spontaneously breathing anesthetized adults

2 Prospective, randomized crossover study This study was approved by The Khon Kaen University Ethics Committee in Human Research (HE5729) All patients gave informed consent before recruitment Age -60 yr Inclusion criteria ASA physical status I-II BMI 0 kg/m² No fever (BT < 7. C) Elective peripheral surgery under GA in supine position Patient refusal Exclusion criteria Severe respiratory or cardiovascular disease Patients with contraindication for succinylcholine Pilot study on 0 patients SD = 0. LPM at ImCO 2 > 0 mmhg Minimal expected difference between the two mean = 0.6 LPM Significance criterion of 0.05 Total number of samples required was Drop out 0% n = 6 (/group) Lack-Plus circuit Lack circuit 2 patients group (LP-L) 2 patients group 2 (L-LP) 2 patients Lack-Plus circuit (LP) Lack circuit (L) Lack s circuit (L) Lack-Plus circuit (LP) 2

3 Diazepam mg/kg Paracetamol 0-5 mg/kg orally hr before transfering to OR Start with FGF L/min Premedicated fentanyl -2 mcg/kg IV Induction propofol mg/kg IV Intubation succinylcholine -.5 mg/kg IV Reduced FGF 0.5 L/min every 5 minutes Record ETCO 2, ImCO 2, RR, MAP and SpO 2 until ImCO 2 > 0 Continued until FGF was 2.5 L/min (or ImCO 2 not exceeding 6 mmhg) Maintenance spontaneously breathing with 50% N 2 O/O 2 /Desflurane -6%, fentanyl titration to control optimal RR 0-6/min Switch anesthetic circuit and repeat procedure Statistical analysis Statistical analysis SPSS for Windows 7.0 Continuous demographic data are presented as means ± SD The categorical as the number of patients The primary and secondary outcome were presented as a mean ± SD and 95% confidence interval (CI) Compared using a Paired T-test Results 2 patients who fullfilled criteria were enrolled Demographic data Table : Patient demographic data LP-L (N = 2) L-LP (N = 2) Age (year).5±.9 6.5± Gender Male Female 0.02 BMI (kg/m²) 2.6±. 22.± ASA physical status I II Operation Orthopedics ENT Plastic

4 Primary outcome Secondary outcome Table 2 : FGF, ETCO 2, RR, MAP, SpO 2 at the point of rebreathing (ImCO 2 > 0 mmhg) Table : ImCO 2, ETCO 2, RR, MAP, SpO 2 at the FGF 2.5 L/min L LP Mean differences FGF (L/min).± ± %CI (- 0.0) <0.00 ETCO 2 (mmhg).±. 6.9± RR (tpm).9±.6.5± MAP (mmhg) 72.9±. 7.± SpO 2 (%) 99.2±. 99.2± L LP Mean differences 95%CI ImCO 2 (mmhg).2±2.6.5± (-.76) <0.00 ETCO 2 (mmhg) 6.5±. 7.0± RR (tpm).±..2± (-0.0) 0.06 MAP (mmhg) 76.2±.9 72.± SpO 2 (%) 99.±. 99.± Among non-absorber circuits which are commonly used during GA for spontaneous respiration in adult are Lack s, Magill s and Bain circuits () Lack s circuit has the lowest ImCO 2 and ETCO 2 by using a FGF of 70 ml/kg/min () FGF requirement in Lack s, Magill s and Bain circuits that just cause rebreathing were 5,7 and 5 ml/kg/min, respectively () Lack s circuit is superior in performance to Magill s and Bain circuits for spontaneous respiration in adults () economical use of FGF convenient access to the exhaust valve easy scavenging facilities () D. Humphrey., JRSM, 92; 75: () D. Humphrey., JRSM, 92; 75: Primary outcome, the minimal FGF at point of rebreathing of Lack-Plus in our study was statistically significant less than Lack s circuit (2.7 ± 0. and. ± 0.5 L/min: P<0.00) No difference from Martin L. et al. which shown the minimal adequate FGF to prevent rebreathing of Magill s circuit was.-.6 L/min (),(2) Secondary outcome at the point of FGF was 2.5 L/min, ImCO 2 of the Lack-Plus was statistically significant less than in the Lack s circuit (.5 ± 2.0 and.2 ± 2.6 mmhg respectively: P<0.00) Demonstrates that the intraluminal one-way valve can prevent rebreathing effectively () Martin L Kain, et al., Section of anesthesia. 967; 60: (2) Martin L. Kain, John F. Nunn., Anesthesiology. 96; 29(5):

5 Conclusion Lack-Plus circuit can be used safely, effectively, and requires less amount of FGF than Lack s circuit in spontaneously breathing anesthetized adults with BMI 0 kg/m² Thank you! The optimal FGF requirement for Lack-Plus circuit to prevent rebreathing is 2.7±0. L/min 5