Effects of positive end expiratory pressure ventilation on respiratory function during general anesthesia in obese patients with obstructive sleep apnea

Objective To investigate the effects of positive end expiratory pressure ventilation on respiratory function during general anesthesia in obese patients with obstructive sleep apnea syndrome (OSAS).Methods Forty ASA Ⅰ or Ⅱ patients aged 26-57 yr undergoing elective uvulo-palato-pharyngoplasty (UPPP) were divided into 2 body weight groups (n =20 each):group A normal body weight patients-BMI＜26 kg/m2 and group B obese patients-BMI＞32 kg/m2.Anesthesia was induced with midazolam,propofol and sufentanil.Tracheal intubation was facilitated with cis-atracurium.Anesthesia was maintained with 1.0％ sevoflurane and continuous infusion of propofol and remifentanil and intermittent iv boluses of cis-atracurium.All patients were mechanically ventilated,first without PEEP for 60 min followed by PEEP 8 cm H2O for 60 min.PET CO2 was maintained at 35-45 mm Hg and Peak airway pressure was maintained at ＜28 cm H2O.Chest wall and lung compliance (CL) and airway resistance (Raw) were monitored and recorded at 5 min (T1),60 min (T2) and 120 min (T3) after tracheal intubation.Arterial blood samples were taken before induction of anesthesia when the patients were awake breathing ambient air (baseline,T0) and at T1-T3.PaO2/FiO2,respiratory index (RI) (PA-aO2/PaO2) and physiologic dead space fraction (VD/VT) were calculated.Results PEEP 8 cm H2O significantly increased PaO2/FiO2,CL and decreased RI at T3 as compared with those at T1 in group B,but there was no significant change in PaO2/FiO2,CL and RI when PEEP 8 cm H2 O was applied at T3 as compared with those at T1 in group A.No adverse reaction occurred in the two groups.Conclusion In obese patients with OSAS,PEEP 8 cm H2O can effectively prevent atelectasis and improve gas exchange and compliance. Key words: Positive-pressure respiration; Respiratory function tests; Obesity; Sleep apnea, obstructive