1. Background
In last decade, diagnostic and therapeutic use of laparoscopy increased, due to reduced postoperative pain, better cosmetic issues, faster return to routine life, shorter hospital stay, less medical costs, lower bleeding, less postoperative pulmonary adverse effects, lower rate of postoperative wound infection, less metabolic disorders, and better respiratory function (1-4).
Postoperative pulmonary side effects (atelectasis and so on) are seen in 2 to 19 percent of patients under elective abdominal surgeries (5-8) leading to increased mortality rate and hospital stay (8). Pain, spasm, and some reflexes would result in postoperative pulmonary side effects and a restrictive pattern or even a mix pattern in pulmonary function test (PFT) (3, 9-12). These would resolve faster in laparoscopic versus in open surgeries (13-15). These alterations during laparoscopy include decreased lung volume, increased peek pulmonary pressure, and reduced pulmonary compliance secondary to increased intra-abdominal pressure and position (16).
Despite some advances, the true effects of position during laparoscopy on pulmonary complications and oxygenation are not yet clear (1). However, different positions are regarded as a possible acting factor (17, 18). Cholecystectomy and ovarian cystectomy are two main laparoscopic procedures with reverse and direct Trendelenburg positions, respectively. While, some studies demonstrated the effects of positions on pulmonary function (2, 19-21); others did not (4, 22, 23). Pulmonary function tests or arterial blood gas (4, 20, 23) are routine tests for assessment of lung function; use of SpO2 is also recommended for simple non-invasive assessment (24). Regarding few studies in this area and the relevance of the issue, this study was performed to compare the preoperative and postoperative arterial oxygen alterations before operation in comparison with after surgery between laparoscopic cholecystectomy and ovarian cystectomy.
2. Methods
In this prospective cohort, 70 consecutive women aged from 20 to 60 years with ASA class of I or II, who were candidate for laparoscopic cholecystectomy (n = 35) in reverse (20 degrees) in Sina referral university hospital and ovarian cystectomy (n = 35) in direct (30 degrees) Trendelenburg positions, in Women referral university hospital, between Feb and Sep 2016, were enrolled. The exclusion criteria were SpO2 less than 90% with room air; body weight less than 50 kg; BMI over 40 kg/m2; smoking (≥ 5 packed year); opium addiction (any kind of use or abuse); renal failure (creatinine ≥ 2 in preoperative measurements); moderate to severe heart failure (ejection fraction ≤ 45%); heart valve disease (≥ mild); lung disease (positive history or susceptive physical exam); pregnancy; breastfeeding; and sleep apnea. The study was approved by the local ethics committee and informed consent forms were obtained from all the patients. Helsinki Declaration was respected all over the study.
For all the patients, standard monitoring of ECG, noninvasive ± invasive blood pressure monitoring, pulse-oximetry, end-tidal capnography, and airway pressure monitoring were done. IV Line was inserted for all the patients. Pre-oxygenation with mask by 3 - 5 liters per minute of oxygen 100% was performed for five minutes with routine respiration. Pre-medications were intravenous midazolam 0.02 mg/kg and fentanyl 2 mcg/kg. The general anesthesia with intravenous induction was induced by sodium-thiopental 5 mg/kg and atracurium 0.5 mg/kg. bag mask ventilation was used for ventilation. After 2 - 3 minutes when muscle relaxation was initiated according to train-of-four monitoring and when bispectral index (BIS) showed optimal depth, the tracheal intubation was performed, isoflurane 0.5 to 1.2% was prescribed, and initial ventilation was started with tidal volume of 10 ml/kg, respiratory rate of 10 - 15 per minute, and positive end expiratory pressure of 3 - 5 mmHg. The expiratory CO2 was set at 35 and FiO2 was 90%. Intra-peritoneal CO2 was set at 12 mmHg. Surgical incision was finally anesthetized with bupivacaine.
After intubation and before operation (oxygen 90%) for the first time, the arterial blood gas from radial artery in supine position was obtained for laboratory assessment. Extubation was performed by applying the “Open Lung Concept” (25). After extubation, all patients received 5 liter/minutes oxygen with facemask at post-anesthesia care unit. In patients with SpO2 less than 93%, the oxygen was administered at a flow rate of 10 liter/minutes via a Venturi up to 30 minutes after surgery. Then, the second blood sample was obtained from radial artery in supine position and sent to the lab to be assessed with the same device after 30 minutes. The measured variables from arterial blood gas were PaO2, SaO2, and PaO2/FiO2 alterations.
Data analysis was performed on data of 70 subjects including 35 patients in laparoscopic cholecystectomy group and 35 subjects in ovarian cystectomy group. Data analysis was performed by SPSS (version 19.0) software [statistical procedures for social sciences; Chicago, Illinois, USA]. Independent T test, repeated measure ANOVA (univariate) and repeated measure ANOVA (multivariate) were used and considered statistically significant at P values less than 0.05.
3. Results
All participants remained in the study. Participants had statistically similar height, weight, and BMI, (Table 1) but age was different between groups of study (P = 0.000).
Table 1.Independent Variables in Groups of the Study
| Cholecystectomy | Ovarian Cystectomy | Total | ||
|---|---|---|---|---|
| Mean (SD) | Mean (SD) | Mean (SD) | Range | |
| Height (centimeters) | 164.31 (7.69) | 162.38 (7.88) | 163.34 (5.78) | 152 - 175 |
| Weight (kg) | 69.31 (9.17) | 65.94 (10.39) | 67.83 (10.37) | 50 - 86 |
| BMI (kg.m-2) | 27.96 (3.97) | 24.39 (4.02) | 25.68 (3.27) | 19.4 - 31.8 |
| Age (years) | 41.45 (8.87) | 31.20 (6.36) | 44.0 (7.53) | 22 - 60 |
Abbreviation: SD, standard deviation
Mean (SD) duration of surgery was 152.0 (± 21.37) ranging from 90.0 to 220.0 minutes. The duration of surgery was similar across the groups. Total PaO2 was higher in the first measurement. In addition, it was higher in cholecystectomy (upward) than in ovarian cystectomy (downward) without any significant difference in repeated measure ANOVA (univariate) by considering the confounding effect preoperative PaO2 (P = 0.060), and by assessing the combined effects preoperative PaO2, position, age and duration of surgery in a multivariate analysis model (P = 0.654).
Total SpO2 was higher in first measurement. Also it was higher in cholecystectomy (upward) compared with ovarian cystectomy (downward) without significant difference in repeated measure ANOVA (univariate) by considering the confounding effect preoperative SpO2 (P = 0.412) and by assessing the combined effects of preoperative SpO2, position, age and duration of surgery in a multivariate analysis model (P = 0.984). (Table 2)
Table 2.Comparison PaO2 and SpO2 Between Groups of Study
| Cholecystectomy | Ovarian cystectomy | Total | P valuea | P valueb | P valuec | |
|---|---|---|---|---|---|---|
| Mean (SD) | Mean (SD) | Mean (SD) | ||||
| PaO2 | ||||||
| Preoperative | 288.94 (65.32) | 257.71 (64.54) | 273.33 (66.35) | 0.048 | 0.060 | 0.654 |
| postoperative | 257.49 (80.22) | 201.05 (65.74) | 229.27 (78.16) | 0.002 | ||
| SpO2 | ||||||
| Preoperative | 99.17 (1.32) | 98.56 (1.83) | 98.86 (1.61) | 0.111 | 0.412 | 0.984 |
| postoperative | 98.26 (2.11) | 97.27 (2.51) | 97.76 (2.35) | 0.080 |
Abbreviations: SD, standard deviation; PaO2, arterial partial pressure of oxygen; SpO2, Oxygen saturation
aComparison of groups of the study based on independent T test
bInteraction between groups of the study and time (preoperative vs. postoperative) based on repeated measure ANOVA (univariate)
cInteraction between groups of the study and time (preoperative vs. postoperative) based on repeated measure ANOVA (multivariate) (after adjusting age and duration of operation)
4. Discussion
This prospective cohort was performed to compare PaO2, SpO2, and PaO2/FiO2 before operation and 30 minutes after surgery across the laparoscopic cholecystectomy versus ovarian cystectomy with upward and downward positions, respectively. This study was solely performed among women to eliminate the confounding role of gender. In addition, the confounding roles of age, height, weight, BMI, and duration of surgery were removed by multivariate analysis. Variation in age range in other studies is due to background disease leading to operation. It’s seems that we should expect more hypoxemia and shunt development after head down laparoscopic surgeries. But, if we look at literature it is not proved yet (1, 26). Furthermore, considering the lung biomechanical rules it’s could be more complicated; in head down position the zone I in the lung tolerates the highest direct compression by upward pushed diaphragm. But, in head up the maximum pressure is transferred to the zone III which is more vulnerable to pressure induced atelectasis.
Total PaO2 was higher in the first measurement. In addition, it was higher in cholecystectomy (upward) than in ovarian cystectomy (downward) without any significant difference in univariate and multivariate analysis. Sprung et al. reported that PaO2 was significantly different by body weight and pneumoperitoneum in patients with morbid obesity; however, the effect of position was not significant but with smaller amounts in downward position, which are similar to our results (26).
Total SpO2 was higher in the first measurement. In addition, it was higher in cholecystectomy (upward) than in ovarian cystectomy (downward) without any significant difference in univariate and multivariate analysis. In general, the position had no effect on PaO2, SpO2, and PaO2/FiO2 ratio in our study. SaO2 has been introduced as a good tool for assessment of perioperative lung function in different studies (27, 28). Despite search in Ovid, Pubmed, Pubmed Central, Science Direct, and Elsevier, there were no similar studies in this area to be compared for discussion and usually, PFT, PaO2, and arterial blood gas analysis are used.
4.1. Limitations
In our study, the confounding role of gender was eliminated. Regarding some neglected variables, assessment of more variables in future studies is suggested. This study could not recognize any significant difference in oxygenation between two different positions in laparoscopic surgery in healthy- ASA I or II- patients, but the minor differences in oxygenation could be important in special groups of patients i.e. overweight individuals, patients with preexisting lung disease or chronic abstractive pulmonary disease (COPD), weak or old people, or others who are at risk of developing pulmonary complications. Our study has low power to reveal these minor but important differences in these selected groups of patients. It seems that larger sample sizes are necessary to develop more evidence in selected groups of patients.
