1 Introduction
Mechanical ventilation during general anesthesia may cause postoperative pulmonary complications.[1] [2] [3,4] [5] [6,7] [8–11]
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.
2 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 cmH2 O and a lungs recruitment maneuver (inspiratory pressure maintained at 30 cmH2 O 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
1. the demographic data, preoperative risk index for postoperative pulmonary complications,[12]
2. peak airway pressure, fluid intake, urine output, blood loss, and operation duration, intraoperatively;
3. 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.
3 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
1. lower intraoperative peak airway pressure (18.6 ± 3.9 vs 23.1 ± 2.2 cmH2 O, P < .001);
2. higher postoperative P/F ratio (556.6 ± 115.2 vs 341.9 ± 72.7, P < .001);
3. lower incidence of infiltration on postoperative CXR (23.3% vs 51.7%, P = .047);
4. shorter duration of ventilator use (6.2 ± 4.5 vs 12.8 ± 7.5 days, P < .001); and
5. 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 1: Patients’ characteristics, preoperative and intraoperative data.
Table 2: Postoperative data.
4 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.[3,5,13] [14–18] [8–11] [19–21] [22,23]
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.
5 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
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