Postoperative Lung Collapse Prevention
Condition: Atelectasis
MeSH terms: Pulmonary Atelectasis
Study type: Interventional

Summary: 
      General anaesthesia is known to promote lung collapse (atelectasis) which will persist in the
      postoperative period. Inflating the lung to a pressure of 40 cmH2O, called a vital capacity
      manoeuvre (VCM), performed a few minutes before extubation followed by the use of 40% of O2
      will prevent postoperative atelectasis formation. This is not the case if VCM is followed by
      application of 100% of O2. However the use of 100% of O2 before tracheal extubation is still
      recommended for safety reason. Application of PEEP associated with pressure controlled
      ventilation before intubation prevents atelectasis formation despite the use of 100% of O2.
      The goal of our study was to show that performing a VCM 15 minutes before arousal followed by
      application of PEEP and pressure support ventilation (PSV) before and after tracheal
      extubation will prevent the recurrence of atelectasis despite the use of 100% of O2.

      Materials and Methods With the ethic committee for research on human beings approval, the
      investigators randomly assigned 16 non-obese patients scheduled for a gynaecological
      laparoscopic surgery in two groups. At the end of the surgery the investigators performed a
      VCM (40cmH2O applied for 12 seconds), then O2 was increased to 100% in both groups. In the
      patients of the study group, a PEEP of 6 cmH2O was applied associated with a PSV of 8 cmH2O.
      This was continued after the extubation for 3 minutes. The O2 was then decreased to 40% and,
      when the expired oxygen saturation was < 50%, PEEP and PSV were removed. For the patients in
      the control group, no positive pressure was applied during spontaneous ventilation (PEEP = 0
      and no PSV). The atelectasis were then measured by computed tomographic scanning.
    

Detailed description: 
      This is a prospective double-blinded study with prior informed written consent obtained from
      all patients.

      Study Population Patients aged 18 to 65 years, American Society of Anesthesiologist (ASA)
      physical status classification I to III, undergoing gynaecological laparoscopic surgery under
      general anaesthesia were included in this prospective, randomised, double-blinded study.

      Exclusion criteria were severe pulmonary disease, body mass index (BMI) more than 30 kg /m2
      or less than 17, pregnancy or any other disease for which hypoxemia could be harmful. If the
      delay between extubation and the computed tomography (CT) scan was over 20 minutes, patients
      were also excluded.

      Study treatments No premedication was given. General anaesthesia was standardized for all
      patients. Standard monitoring was applied. General anaesthesia was induced intravenously with
      fentanyl 1 to 2 μg/kg, propofol 2 to 3 mg/kg, and rocuronium 0.6 mg/kg. The airways were
      secured by endotracheal intubation.

      Desflurane was used for maintenance at 1 minimal alveolar concentration (MAC) in 40% oxygen
      and air. Additional rocuronium was injected in order to maintain a train-of-four ratio (TOF
      ratio) between 0 and 1/4. Supplemental fentanyl was administered in order to maintain blood
      pressure and/or heart rate values within a range of 20% compared to baseline values.

      For ventilation, the investigators used pressure controlled mode with tidal volume guaranteed
      (pressure controlled - guaranteed volume, General Electrics Datex-Ohmeda Aisys®). The
      settings of ventilation were, tidal volume 6-8 ml/kg (ideal body weight), frequency 10 - 20
      per min. (expired CO2 5.3 - 5.8 kPa), PEEP of 6 cmH2O and I:E ratio 1:2.

      Fifteen minutes before the end of the surgery, a VCM (40cmH2O applied for 12 seconds) was
      performed, then O2 was increased to 100% in both groups. Sugamadex (4 mg/kg if TOF <2/4, 2
      mg/kg if TOF >2/4) was administered in order to reverse neuromuscular block. General
      anaesthesia was continued until TOF ratio > 90%.

      Randomization was performed when spontaneous ventilation resumed. In the study group,
      inspiratory support of 8 cmH2O was applied associated with PEEP at 6 cmH2O. After extubation,
      same support was applied by facemask for 3 minutes. O2 was then decreased to 40% and, when
      the expired oxygen fraction was < 50%, PEEP and PSV were switched off.

      In the control group, no positive pressure and no PEEP were applied during spontaneous
      ventilation and 100% of O2 was applied for 3 minutes after extubation with a facemask.

      Patients were then transported to the CT scan breathing 40% of O2 via a facemask. The
      peripheral oxygen saturation was continuously monitored by pulse oximetry. Postoperative pain
      management consisted of the residual effect of intraoperative fentanyl and paracetamol if
      required.

      Measurements Whole lung CT scan with a special low doses protocol was obtained at
      end-expiratory position (at functional residual capacity).

      Measurement was performed for all the lung and the lungs were also divided in 3 zones (upper,
      middle and lower). Each right and left lung surfaces were extracted and a window setting of
      -1000 to +100 Hounsfield Units (HU) was selected to assess the total lung surface. A
      threshold of -1000 to -500 HU was applied to quantify the amount of normally ventilated lung,
      a second threshold of -500 to -100 HU was chosen to establish the surface of poorly
      ventilated lung, and a third threshold of -100 to +100 HU was set to measure the surface of
      atelectatic lung area. The right and left lungs surface were summed and reported to the total
      lung surface(18).

      Study Outcome The primary outcome was diminution of atelectatic and poorly ventilated lung
      volume in the study group compared to the control group.

      Statistical Analysis Values are expressed as mean +/- SD. Baseline results and atelectatic
      surface were compared by a one-way analysis of variance for continuous variables and with X2
      for discrete variables. P < 0.05 was considered significant.
    

Intervention name(s): Positive pressure
Intervention type(s): Procedure
Intervention description(s): Inspiratory support of 8 cmH2O was applied associated with PEEP at 6 cmH2O. After extubation, same support was applied by facemask for 3 minutes
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: prospective double-blinded study Randomization was performed when spontaneous ventilation resumed at the end of the surgery
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Prevention
Keywords: anesthesia, general