A Comparison of the Face Mask and Oral Mask Ventilation After Nasal Surgery

American Society of Anesthesiologists (ASA) physical class I or II, adult patients aging 19-45 yr, scheduled for nasal surgery will be recruited.

Patient characteristics will be recorded; age, gender ASA physical status, height, weight. Simple randomization will be accomplished with a computer-generated sequence of numbers and sealed envelopes will be used to allocate patients into 2 treatment sequences, Sequence O: oral mask ventilation followed by face mask ventilation and Sequence FM: face mask ventilation followed by oral mask ventilation.

Patients will be premedicated with midazolam. Ringer's lactate infusion at 15 mL•kg-1•h-1 will be initiated. Standard monitors will be established including neuromuscular monitorization and the Bispectral index monitor (BIS).

The patients head will be placed in the neutral position on a positioning pad Anesthesia will be induced with propofol 2 ml kg and fentanyl 50 mcg. Anesthesia will be maintained with oxygen in nitrous oxide and sevoflurane. The patient was ventilated trough an face mask. The appropriate size mask with the best fit will be selected and the mask size will be noted. Gas flow will be 4 L min. During the induction period the mask ventilation grade of the patients will be determined (Grade 0: ventilation by mask not attempted, Grade 1: ventilated by mask, Grade 2: ventilated by mask with oral airway or other adjuvant, Grade 3: difficult mask ventilation (inadequate, unstable, or requiring two practitioners), Grade 4: unable to mask ventilate (Han's grading scale)) and patients with Grade ≥ 2 will be excluded from the study. Muscle relaxation and intubation will be facilitated with rocuronium 0.6 mg kg-1. At the end of surgery trachea will be extubated when TOF 0.9 is obtained and the patient is spontaneous breathing, meanwhile inhalation anesthesia will be continued (BIS 50-70). After extubation, spontaneous ventilation will be assisted with mask ventilation. Mask ventilation will be applied according to sequence allocation and the mask ventilation grades with each mask technique will be determined with the same grading system. Spontaneous ventilation will be assisted with mask ventilation.

The face mask will be applied with the one handed EC-clamp technique. The mask will be placed over the bridge of the nose and mouth and a chin-lift, head tilt maneuver will be used. The oral mask; size 1 or 2 child's mask will be placed only over the mouth and the one handed EC-clamp technique with the chin-lift, head tilt maneuver will be used again. The masks will be changed after three consecutive measurements for each mask technique and the crossover time will be short.

The respiratory parameters will be measured with the monitor contained in the Drager Primus anesthesia machine. The observer providing mask ventilation is experienced in mask ventilation and will be blinded to the monitor display. All patients will be ventilated by the same observer. Data will be recorded by independent residents. The mask ventilation classification will be recorded. mean airway pressure (Pmean), maximum airway pressure (Ppeak) , tidal volume (TV), expired tidal volume (TVe) minute volume leak (MVleak) and minute volume (MV) will be recorded during spontaneous ventilation. Volatile anesthesia will be ceased after observing that the patients are calm and not coughing and the respiratory measures will be evaluated thereafter. The APL (airway pressure release) valve will be closed during the evaluation of mask ventilation. Sufficient chest movement, mask leak, gastric insufflations will be assessed. Indicators for difficult mask ventilation are defined as; TV< 4 ml kg, inadequate chest movements, the need for an oropharyngeal airway, two handed mask ventilation, need to increase the gas flow, gastric insufflations, need to ventilate with two operators.

It was planned to enroll 30 patients in this study. After performing a pilot study we calculated that 10 patients in each group was sufficient to detect a difference between groups concerning tidal volume with 0.95 power and 0.05 alfa error. We decided to enroll 24 patients in the study due to possible drop outs.