Post operative pulmonary complications can cause huge burden on the cost of the treatment especially after major abdominal surgeries, which includes pneumonia, pulmonary oedema, pulmonary thromboembolism, atelectasis, and acute exacerbation of COPD. Many of the predisposing factors are either related to the patient condition or surgical procedure, hence anaesthesiologist have very little role in modifying the same favorably. Of the five risk factors identified as predisposing factors for post operative pneumonia, none were modifiable. Of all strategies to minimize postoperative pulmonary complication, a combination of low tidal volume ventilation, application of optimal PEEP and institution of recruitment manoeuvre has been advocated. However, there is no agreement regarding the optimal peep during IPPV, therefore it is required to be determined before initiation of mechanical ventilation in every instance. 6 This is cumbersome and time consuming, which may make it less practical for routine implementation. Hence, the current study is undertaken to determine most common optimal peep among surgical patient undergoing elective laparoscopy.
PROCEDURE This cross-sectional observational study will be conducted after obtaining approval from the Institutional Ethics Committee. A pre-anaesthetic evaluation with a detailed medical history, systemic examination and airway examination will be done and reviewed on the previous day and on the day of surgery. Informed and written consent will be obtained from the patient and/or the patient’s guardian. Patient will be kept nil per oral for 6 hours and premedicated according to standard institutional protocol. Once the patient is shifted to the operation theatre, standard monitors like electrocardiogram, pulse oximetry (SpO 2 ), non-invasive blood pressure, and end tidal capnography will be initiated. Intravenous fluid will be started after securing a suitable intravenous cannula at a rate of 100 ml/h. Patients will receive endotracheal general anaesthesia as per the institutional protocol, which includes preoxygenation for three minutes, intravenous fentanyl 2 µg/kg, propofol 2 mg/kg (or titrated to loss of verbal response, whichever is less), vecuronium 0.1 mg/kg for facilitating the endotracheal intubation and intermittent positive pressure ventilation (IPPV) for three minutes or till TOF (train of four) count becomes zero. A suitable sized endotracheal tube will be placed and its position will be confirmed. Anaesthesia will be maintained with a mixture of air and oxygen (not less than 33%) with isoflurane to maintain the required depth of anaesthesia. Dexmedetomidine (1µ/kg, intravenous, over not less than 10 min) may be used to obtund the sympathetic response to pneumoperitoneum during the procedure. Patient’s lung will be ventilated on volume control mode (VCV) with positive end expiratory pressure (PEEP) of 5 cmH 2 O, a respiratory rate of 12 to 15 breaths per minute (BPM), a tidal volume of 7 ml/kg (TV), and I:E ratio of 1:1. The respiratory rate will be adjusted to maintain the end tidal CO 2 between 30 and 35 mmHg. During the RM, the maximum limit to the PAP will be kept at 50 cmH 2 O and maximum plateau pressure at 40 cmH 2 O.
The ideal PEEP will be determined using following procedure: 1. V t will be set to 7 ml/kg body weight, respiratory rate to 12 to 15 breaths/min. 2. The initial PEEP will be set to 5 cmH 2 O, then the PEEP will be increased at steps of one cmH 2 O, and each PEEP level will be sustained for 3 min. While adjusting the PEEP, Cstat will be calculated using formula (Cstat=V t /(Pplat-PEEP) until the calculated Cstat shows a declining trend. The PEEP corresponding to the calculated maximum Cstat will be set as the optimal iPEEP for this patient. 3. The upper limit of PEEP to be tried will be 20 cmH2O. 4. A maintenance infusion of IV fluid (Ringer’s lactate or normal saline) will be infused at a rate of 100 ml/h. During RM, if any hypotension is noted (systolic blood pressure less than 90 mmHg or MAP less than 70 mmHg), a bolus of 200 ml of maintenance fluid will be infused. If hypotension persists, bolus of vasopressors like mephentermine or phenylephrine will be given to maintain the BP. The first recruitment manoeuvre (RM1) will be performed 5 min after intubation. The second recruitment manoeuvre (RM2) will be performed five minutes after establishing pneumoperitoneum. The third recruitment manoeuvre (RM3) will be performed after deflation of pneumoperitonium before extubation. |