Effect of PEP on Oxygen Saturation and Carbon Dioxide After Abdominal Surgery

Overview

Positive expiratory pressure( PEP) is routinely given to patients after surgery in order to improve lung function and oxygen saturation. There is, however, no evidence of effect on lung function, postoperative pneumonia or any other outcome (Guimarães MMF, Tyson AF). The investigators aim to test the immediate effects of PEP therapy on oxygen saturation and carbon dioxide after abdominal surgery. 80 patients will be investigated in RCT design with expiration using PEP or with expiration to a sham-PEP, a tube without resistance. At the end of the study we will also measure the effect of 10x3 deep breathing maneuvers without PEP or shamPEP. Primary outcome: Maximum and minimum levels of continuously measured oxygen saturation from pulse oximetry and transcutaneous carbon dioxide partial pressure during the trial.

Background Hypoxia, reduced lung function and atelectais are common after abdominal surgery and can be hazardous in patients with chronic hypoxia. Positive expiratory pressure (PEP) therapy or incentive spirometry are routinely given to patients after abdominal surgery to counteract atelectasis and improve oxygen saturation. Patients are instructed by a physiotherapist to take deep inspiratory breaths and expire in a PEP-device or PEP bottle. The method is used routinely in Swedish hospital and the patient breathes against 10-15 cm water resistance. This is repeated 10x3 ie 10 deep breaths and exhalation towards PEP then rest, breath, rest and another 10 breaths. This procedure should be done once an hour after surgery. The idea is that this will widen alveoli and abolish atelectasis, thus increasing the oxygen uptake and reducing the risk of postoperative complications. There is no evidence of effect of PEP and incentive spirometry on postoperative pulmonary complications after abdominal surgery (Guimarães MMF, Tyson AF). Nevertheless, PEP therapy is used in Sweden and internationally. There were no studies found reporting the immediate effect of PEP on continuous oxygen saturation and carbon dioxide partial pressure after surgery. Aims What effect does PEP have on oxygen saturation and carbon dioxide partial pressure? What is the effect of deep breathing maneuvers on oxygen saturation and carbon dioxide partial pressure? Methods Inclusion: 80 adult patients over 18 years of age who have undergone open or laparoscopic abdominal surgery. Patients receiving postoperative PEP are asked to participate in the study at one or two days after after abdominal surgery. Exclusion: Patients who cannot participate in using PEP or who do not agree to participate in the study. Power calculation:.It was estimated that 34 patients were needed to detect a mean (SD) difference in oxygen saturation of 1% (2%) and to detect a difference in transcutaneous PCO2 of 0.5 kPa (1 kPa) with a significance of p \< 0.05 and a power of 80%. Design / Randomization: RCT study with cross-over design. Patients are randomized using computer programs, handled by a person outside the study, to either start with either PEP breathing 10x3 or sham-PEP breathing 10x3. Method: Starting with lung function assessment to determine PEF (Mini Wright Clement Clarke). Then, application of continuous transcutaneous PCO2 / SaO2 (SenTec Digital Monitoring System, ResMed) and a respiratory belt around the chest detecting the respiratory rate. Data is recorded with computer equipment (Noxturnal T3, ResMed). The patients are randomized to initiate with either 10x3 breaths using PEP therapy or 10x3 breaths using Sham PEP. After a rest period, patients switch to the second treatment (cross-over). At the end of the trial, all patients take 10X3 deep breaths without PEP or sham PEP. At the start of the study, baseline level for SaO2 and TcPCO2 is recorded, and an arterial blood gas is recorded to calibrate the transcutaneous PCO2 measurement. Thereafter, the registration continues during breathing / blowing until the patient returns to its baseline values. New PEF examination is made after each study arm.