Effects of lung protective ventilation on postoperative pulmonary outcomes for prolonged oral cancer combined with free flap surgery.

The intraoperative lung protective ventilation with low tidal volume, positive end expiratory pressure (PEEP) and intermittent lungs recruitment was found to decrease postoperative pulmonary complications. In this retrospective medical records study, we investigated the effects of lung protective ventilation on postoperative pulmonary outcomes among the patients received prolonged oral cancer combined with free flap surgery.We collected the medical records of the patients received oral cancer surgery with the operation time more than 12 hours from January 2011 to December 2015. We recordedFifty nine cases were included. Thirty cases received the lung protective ventilation and 29 cases received conventional ventilation. Compared to the patients received conventional ventilation, the patients received intraoperative lung protective ventilation showedIn conclusion, for the prolonged oral cancer combined with free flap surgery, the intraoperative lung protective ventilation improves postoperative pulmonary outcomes and decreases the duration of ICU stay.

Introduction

Mechanical ventilation during general anesthesia may cause postoperative pulmonary complications.[ Setting a tidal volume higher than 10 ml/kg was used to prevent atelectasis and hypoxemia in the traditional way,[ however, many clinical studies have suggested that high tidal volume ventilation leads to alveolar over-inflation, and ventilator-induced lung injury.[ Animal experiments have also found that high tidal volume ventilation contributes to acute lung injury in healthy lungs.[ A lung protective mechanical ventilation, combination of low tidal volume, positive end-expiratory pressure (PEEP), and lungs recruitment maneuver, was initially applied in patients with acute lung injury and acute respiratory distress syndrome and it reduced morbidity and mortality.[ The lung protective ventilation was later used for surgery under general anesthesia in patients with normal lungs. Many clinical randomized controlled trials have found that the lung protective ventilation significantly decreased the postoperative pulmonary complications among abdominal, cardiovascular, and thoracic surgeries.[ However, there was no data regarding the effectiveness of lung protective ventilation on long duration operation.

The objective of this study was to examine the effect of lung protective ventilation compared with conventional ventilation on the postoperative pulmonary function and outcomes among patients receiving prolonged anesthesia for oral cancer combined with free flap reconstruction surgery.

Methods

The study protocol was approved by the Institutional Review Board of Tri-Service General Hospital (TSGHIRB No.: 1-105-15-147). Informed consent was not required because this was a retrospective medical records study. Medical records of patients who received oral cancer combined with free flap reconstruction surgery at a single medical center between January 2011 and December 2015 were collected. The lung protective ventilation for oral cancer combined with free flap surgery was started at February 2014 in our hospital. Only the cases with operation time more than 12 hours were included. The included patients were free of pulmonary morbidity, such as asthma, pneumonia, or chronic obstructive pulmonary disease. Inhalational general anesthesia with desflurane or sevoflurane was conducted. The lung protective ventilation during operation was defined as the combination of low tidal volume (6–8 ml/kg of the predicted body weight), PEEP 5 to 6 cmH2O and a lungs recruitment maneuver (inspiratory pressure maintained at 30 cmH2O for 30 seconds) in every 30 minutes. The conventional ventilation was set as 10 to 12 ml/kg of the predicted body weight for tidal volume. The respiration rates of all the patients were set as to maintain the end-tidal CO2 within 35 to 40 mmHg. Postoperatively, intravenous infusion of dexmedetomidine was administered for analgesia and sedation in ICU. Intravenous fentanyl was rescued for intolerable pain.

We recorded

the demographic data, preoperative risk index for postoperative pulmonary complications,[ past medical history, and laboratory data, preoperatively;

peak airway pressure, fluid intake, urine output, blood loss, and operation duration, intraoperatively;

PaO2/FiO2 (P/F) ratio and body temperature when arrived at intensive care unit (ICU), infiltration on Chest X-ray (CXR), duration of ventilator use, ICU and hospital stay, postoperatively.

The primary pulmonary outcomes included postoperative lung function presented as P/F ratio, incidence of infiltration on postoperative CXR, and duration of ventilator use. The secondary outcomes included the duration of ICU and hospital stays.

We compared the recorded data between the patients with and without using lung protective ventilation during anesthesia. Statistical analysis was performed by t test and Chi-Squared test for continuous and categorical variables, respectively. A P value less than .05 was considered as significant difference.

Results

A total of 68 medical records were collected initially. Nine cases were excluded due to not met inclusion criteria. Thus, 59 patients, 30 cases received lung protective ventilation and 29 cases received conventional mechanical ventilation, were included for further analysis. The patients’ characteristics, preoperative risk index, medical history, and preoperative laboratory data were not different between 2 groups (Table 1). Intraoperatively, the intake/output, blood loss, and duration of operation were comparable between 2 groups (Table 1). Compared to the patients received conventional mechanical ventilation, the patients received lung protective ventilation showed

Table 1

Patients’ characteristics, preoperative and intraoperative data.

lower intraoperative peak airway pressure (18.6 ± 3.9 vs 23.1 ± 2.2 cmH2O, P < .001);

higher postoperative P/F ratio (556.6 ± 115.2 vs 341.9 ± 72.7, P < .001);

lower incidence of infiltration on postoperative CXR (23.3% vs 51.7%, P = .047);

shorter duration of ventilator use (6.2 ± 4.5 vs 12.8 ± 7.5 days, P < .001); and

shorter duration of ICU stay (9.4 ± 5.3 vs 17.1 ± 8.3 days, P < .001) (Table 2). The length of hospital stay was not different between groups.

Table 2

Postoperative data.

Discussion

This study found that, compared to the conventional high tidal-volume mechanical ventilation, the protective lung ventilation during operation improved postoperative pulmonary outcomes in patients received a prolonged anesthesia for oral cancer combined with free flap surgery. Just like the abdominal, cardiovascular, and thoracic surgeries, the intraoperative lung protective ventilation may also benefit the long duration operation.

There was ample evidence from clinical and experimental studies demonstrated that conventional high tidal volume mechanical ventilation leads to lung injury for both diseased and healthy lungs.[ The possible mechanisms included direct mechanical trauma of the alveoli (barotrauma or volutrauma) and subsequent release of cytokine mediators from alveolar epithelium into the systemic circulation (biotrauma).[ The lung protective ventilation (low tidal volume with PEEP and intermittent lungs recruitment) has been applied in many kinds of surgeries and leaded to decrease postoperative pulmonary complications and improve pulmonary outcomes.[ Several meta-analyses have evaluated the effect of lung protective ventilation compared with conventional high tidal volume ventilation on surgical patients with normal lungs. Intraoperative lung protective ventilation resulted in decrease of pulmonary infections, atelectasis, acute lung injury, and the need for postoperative mechanical ventilation.[ This beneficial result of the lung protective ventilation has also been shown in experimental studies. Maria et al and Camilo et al both groups found that variable ventilation combined with lungs recruitment maneuver decreased lung tissue damage and pulmonary inflammation in rats.[

The lung protective ventilation has been used for many kinds of surgeries and resulted in an improvement of postoperative pulmonary outcomes. However, there was no report to examine the effect of intraoperative lung protective ventilation on the long duration surgery. In this study, long duration operations with more than 12 hours were investigated and an identical result as the other surgeries was obtained. Compare to the conventional mechanical ventilation, the intraoperative lung protective ventilation resulted in better postoperative pulmonary outcomes that included higher P/F ratio when the patient arrived at ICU, lower incidence of infiltration on postoperative CXR, and shorter duration of ventilator use. The results of this study are not unexpected. Based on the possible mechanisms of the conventional ventilation-induced lung injury (baro-, volu-, and bio-trauma), the longer the conventional high tidal volume ventilation use, the severer the lungs being damaged. In addition, minimal hemodynamic fluctuation occurred during the second half of the operation when free flap reconstruction was performing. Under such steady condition, a low tidal volume with PEEP and intermittent lungs recruitment supposed to be the appropriate mode to mechanical ventilation. No wonder a big difference of the duration of ventilator use and ICU stay between the 2 groups was founded in this study.

There are some limitations to this study. First, this is a retrospective observational study. Potential bias, such as patient's preoperative medical conditions, may exist. Second, the sample size is not large enough. However, statistical analysis of our data showed a significant difference between groups. A prospective randomized control trail is indicated to verify the effectiveness of lung protective ventilation on postoperative pulmonary outcomes for patients receiving prolonged surgery.

Conclusion

Compare to high tidal volume ventilation without PEEP, the intraoperative lung protective ventilation with low tidal volume, PEEP and intermittent lungs recruitment improves postoperative pulmonary outcomes and decreases the duration of ICU stay for the prolonged oral cancer combined with free flap surgery.

Author contributions

Chia-Dan Cheng contributed to the datacollection, data analysis, and manuscript preparation. Wei-Lin Lin andYuan-Wu Chen contributed to the data collection and analysis. Chen-Hwan Cherng contributed to all aspects of this manuscript, including conception and design, data analysis and interpretation, manuscript writing