title: Prolonged inspiratory time produces better gas exchange in patients undergoing laparoscopic surgery: A randomised trial.
abstract: BACKGROUND
  Laparoscopic surgery performed with a patient in the Trendelenburg position is known to have adverse effects on pulmonary gas exchange and respiratory mechanics. We supposed that prolonged inspiratory time can improve gas exchange at lower airway pressure.
  
  
  METHODS
  One hundred patients undergoing gynaecologic laparoscopic surgery were randomly assigned to one of four groups: conventional inspiratory-to-expiratory (I : E) ratio (Group 1 : 2), I : E ratio of 1 : 1 (Group 1 : 1), 2 : 1 (Group 2 : 1), or 1 : 2 with external positive end-expiratory pressure (PEEP) of 5 cmH2 O (Group 1 : 2 PEEP). Tidal volume was set to 6 ml/kg, and I : E ratio was adjusted at the onset of pneumoperitoneum. Arterial blood gas analysis with measurements of partial pressure of arterial oxygen/fraction of inspired oxygen (PaO2 /FiO2 ), and physiologic dead space-to-tidal volume ratio (VD /VT ) was performed 15 min after anaesthetic induction (T1), and 30 (T2) and 60 min (T3) after onset of CO2 insufflation.
  
  
  RESULTS
  PaO2 /FiO2 at T3 in Groups 1 : 1, 2 : 1, and 1 : 2 PEEP were higher than Group 1 : 2. The partial pressure of arterial carbon dioxide at T3 in Group 2 : 1 was lower than the other groups. The VD /VT at T2 and T3 were lower in Groups 1 : 1 and 2 : 1 than Groups 1 : 2 and 1 : 2 PEEP. Peak or plateau airway pressure was higher in Group 1 : 2 PEEP than the other groups.
  
  
  CONCLUSIONS
  A prolonged inspiratory time demonstrated a beneficial effect on oxygenation. Furthermore, it showed better CO2 elimination without elevating the peak or plateau airway pressure compared with applying external PEEP. In terms of gas exchange and respiratory mechanics, a prolonged inspiratory time appears to be superior to applying external PEEP in patients undergoing laparoscopic surgery in the Trendelenburg position.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: W H
authors.initials: WH
authors.lastname: Kim
authors.forename: T S
authors.initials: TS
authors.lastname: Hahm
authors.forename: J A
authors.initials: JA
authors.lastname: Kim
authors.forename: W S
authors.initials: WS
authors.lastname: Sim
authors.forename: D H
authors.initials: DH
authors.lastname: Choi
authors.forename: E K
authors.initials: EK
authors.lastname: Lee
authors.forename: S M
authors.initials: SM
authors.lastname: Lee
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000097:blood; D005260:Female; D006801:Humans; D010535:Laparoscopy; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012121:Respiration, Artificial / Q000379:methods*; D015656:Respiratory Mechanics / Q000502:physiology*; D016037:Single-Blind Method; D013990:Tidal Volume / Q000502:physiology; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen