Optimal individual positive end expiratory pressure during mechanical ventilation in patients undergoing laparoscopic surgery: A clinical study

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.