|Year : 2017 | Volume
| Issue : 1 | Page : 57-63
Intraoperative low tidal volume ventilation strategy has no benefits during laparoscopic cholecystectomy
Vandna Arora1, Asha Tyagi1, Surendra Kumar1, Aanchal Kakkar1, Shukla Das2
1 Department of Anaesthesiology and Critical Care, University College of Medical Sciences and GTB Hospital, New Delhi; Department of Microbiology, University College of Medical Sciences and GTB Hospital, New Delhi, India
2 Department of Microbiology, University College of Medical Sciences and GTB Hospital, New Delhi, India
|Date of Web Publication||15-Mar-2017|
Department of Anaesthesiology and Critical Care, University College of Medical Sciences and GTB Hospital, New Delhi
Source of Support: None, Conflict of Interest: None
Background and Aims: Benefits of intraoperative low tidal volume ventilation during laparoscopic surgery are not conclusively proven, even though its advantages were seen in other situations with intraoperative respiratory compromise such as one-lung ventilation. The present study compared the efficacy of intraoperative low tidal volume ventilatory strategy (6 ml/kg along with positive end-expiratory pressure [PEEP] of 10 cmH2O) versus one with higher tidal volume (10 ml/kg with no PEEP) on various clinical parameters and plasma levels of interleukin (IL)-6 in patients undergoing laparoscopic cholecystectomy.
Material and Methods: A total of 58 adult patients with American Society of Anesthesiologists physical status I or II, undergoing laparoscopic cholecystectomy were randomized to receive the low or higher tidal volume strategy as above (n = 29 each). The primary outcome measure was postoperative PaO2. Systemic levels of IL-6 along with clinical indices of intraoperative gas exchange, pulmonary mechanics, and hemodynamic consequences were measured as secondary outcome measures.
Results: There was no statistically significant difference in oxygenation; intraoperative dynamic compliance, peak airway pressures, or hemodynamic parameters, or the IL-6 levels between the two groups (P > 0.05). Low tidal volume strategy was associated with significantly higher mean airway pressure, lower airway resistance, greater respiratory rates, and albeit clinically similar, higher PaCO2and lower pH (P < 0.05).
Conclusion: Strategy using 6 ml/kg tidal volume along with 10 cmH2O of PEEP was not associated with any significant improvement in gas exchange, hemodynamic parameters, or systemic inflammatory response over ventilation with 10 ml/kg volume without PEEP during laparoscopic cholecystectomy.
Keywords: Intraoperative ventilation, laparoscopic cholecystectomy, low tidal volume
|How to cite this article:|
Arora V, Tyagi A, Kumar S, Kakkar A, Das S. Intraoperative low tidal volume ventilation strategy has no benefits during laparoscopic cholecystectomy. J Anaesthesiol Clin Pharmacol 2017;33:57-63
|How to cite this URL:|
Arora V, Tyagi A, Kumar S, Kakkar A, Das S. Intraoperative low tidal volume ventilation strategy has no benefits during laparoscopic cholecystectomy. J Anaesthesiol Clin Pharmacol [serial online] 2017 [cited 2017 Apr 27];33:57-63. Available from: http://www.joacp.org/text.asp?2017/33/1/57/202200
| Introduction|| |
Ventilation using lung protective strategy consisting of low tidal volume (6 ml/kg) along with positive end-expiratory pressure (PEEP) has well-established benefits in patients of acute respiratory distress syndrome (ARDS). It is associated with improved organ function, decreased levels of inflammatory mediators, and a reduction in mortality. Consequent to the dramatic improvement in morbidity and mortality, use of low tidal volume ventilation strategy for shorter duration during intraoperative period in patients without ARDS has also been investigated.,,,,,,,,, In certain trials, it was associated with decreased inflammatory markers and improved lung functions.,,,,
Laparoscopic cholecystectomy is a commonly performed surgery that is associated with pneumoperitoneum-induced respiratory compromise and altered pulmonary mechanics intraoperatively. As a consequence, various ventilatory strategies have been investigated for use during laparoscopic cholecystectomy. Recently, the role of lung protective ventilatory strategy using low tidal volumes was evaluated in laparoscopic gynecologic as well as urologic surgeries and showed improved gas exchange but no decrease in inflammatory markers. However, its use has not been evaluated during laparoscopic cholecystectomy, where the patient positioning varies as compared to other investigated laparoscopic surgeries.
Against this background, we aimed to evaluate and compare the efficacy of intraoperative ventilatory strategy employing low tidal volume with one using higher tidal volume in patients scheduled for elective laparoscopic cholecystectomy. The outcome measures involved parameters indicating gas exchange, pulmonary mechanics, and hemodynamic consequences as well as systemic levels of interleukin (IL)-6.
| Material and Methods|| |
This study was conducted after approval by the Institutional Ethical Committee, and obtaining informed written consent from all participants.
Patients aged between 18 and 65 years of either gender with American Society of Anesthesiologists physical status I or II and body mass index <30 kg/m2 scheduled for elective laparoscopic cholecystectomy under general anesthesia were included in the study. Those who refused consent for participation in the study, or with a history of chronic lung disease, acute respiratory tract infection, smoking, or recent exposure to mechanical ventilation (<1 year) and those having clinical signs of a systemic infection were excluded from the study. Intraoperative usage of airway device other than endotracheal tube for airway maintenance, conversion to laparotomy, and ventilation continued in the postoperative period were also defined as exclusion criteria.
A total of 58 patients were randomized to receive one of two ventilatory strategies using a computer-generated random number table (n = 29 each) [Figure 1]. The ventilatory strategies included either low tidal volume of 6 ml/kg along with PEEP of 10 cmH2O (low tidal volume group) or a higher tidal volume of 10 ml/kg with no PEEP (high tidal volume group). The tidal volumes in both groups were calculated based on the ideal body weight (IBW). Herein, IBW in males = 50 + 0.91 (height in cm – 152.4) kg and in females = 45.5 + 0.91 (height in cm – 152.4) kg.
Respiratory rate was initiated at 10 breaths/min and then titrated in increments or decrements of 2 breaths/min to maintain an end-tidal carbon dioxide of 35–40 mmHg. The ratio of inspiratory to expiratory time (1:2) and fraction of inspired oxygen concentration (FiO2) were same in both groups; the FiO2 was initiated at 0.3 and then titrated to maintain SpO2 above 97%.
The attending anesthesiologist was allowed to alter the mechanical ventilation whenever required to ensure patient safety.
Besides, the difference in ventilatory strategy, all other interventions were similar in both groups. In the operating room, routine monitoring included lead II electrocardiography, pulse oximetry, capnography, spirometry, and noninvasive oscillometric blood pressure measurements (Datex-Ohmeda®, Madison, Wisconsin, USA). An intravenous (IV) access was established and Ringer's lactate infusion initiated at 10 ml/kg/h. Radial artery was cannulated and the arterial line connected to FloTrac™ sensor and Vigileo™ monitor for invasive hemodynamic monitoring (Edwards Lifesciences®, Irvine, CA, USA). Anesthesia was induced using fentanyl 2 µg/kg IV followed by propofol 1–2.5 mg/kg IV titrated to loss of eyelash reflex. Vecuronium (0.1 mg/kg IV) was used to facilitate tracheal intubation. Anesthesia was maintained with a mixture of O2 and N2O along with isoflurane (minimal alveolar concentration = 1 ± 0.1), and further drugs and fluids were administered as clinically indicated, while maintaining patient's heart rate and blood pressure within 20% of baseline. Pneumoperitoneum was created by the surgeon, as per their routine clinical practice by insufflating carbon dioxide to achieve intra-abdominal pressure of 12 mmHg. Patients were positioned in a head-up tilt of 15–20° and the same position was maintained throughout the procedure. After completion of surgery, residual muscle relaxation was reversed using neostigmine 0.05 mg/kg IV and atropine 0.02 mg/kg IV. For prophylaxis of emesis, ondansetron 8 mg IV was administered at the end of surgery.
Patients were transferred to the recovery room after extubation of the trachea, where oxygen was supplemented at FiO2 = 0.3, titrated upward to maintain SpO2 >97% using a Venturi face mask.
The primary outcome measure of postoperative PaO2 was obtained from analysis of arterial blood sample collected just after shifting patient to the postoperative room, before initiating supplemental oxygen. The technician processing the arterial blood sample and the patient, both were unaware of the group allocation.
The intraoperative data was recorded and compared at four time intervals: following intubation and initiation of mechanical ventilation (baseline), at 15 and 30 min after beginning of laparoscopy, and at the end of surgery. These recorded variables indicating gas exchange, pulmonary mechanics, or hemodynamic consequences included tidal volume, respiratory rate, minute ventilation, peak and mean airway pressures, resistance, dynamic compliance, EtCO2, heart rate, mean arterial blood pressure, and cardiac index. Variables obtained from an arterial blood gas analysis, i.e., PaO2, PaO2/FiO2 ratio, PaCO2, and pH were recorded following intubation and initiation of mechanical ventilation (baseline), 15 min after beginning of laparoscopy, at the end of surgery following desufflation of the abdomen, and in the immediate postoperative period.
Analysis of interleukin-6
Blood samples were assessed for IL-6 at three time intervals: following induction of anesthesia (baseline), at the end of surgery following desufflation of the abdomen, and at 24 h postoperatively. The sample of 5–10 ml of blood was collected aseptically and allowed to stand at room temperature for 1 h to clot. Serum was removed and stored at −80°C till assayed on a 96-well plate using commercially available enzyme-linked immunosorbent assay (Human IL-6 ELISA Kit, Diaclone®).
All observed continuous variables were normal in distribution, except the plasma levels of IL-6. Log-transformation was done for IL-6 values to convert them to a normal distribution. Comparison of continuous variables between both groups was done using unpaired t-test or repeated measure ANOVA followed by Tukey's test as appropriate. Categorical variables were compared using Chi-square or Fisher's exact test. P < 0.05 was considered statistically significant.
Taking into account previously published postoperative oxygenation following varying intraoperative tidal volumes, 29 patients were required in each group to detect an effect size of 30% in the postoperative PaO2 at an alpha error of 5% and a power of 80%.
| Results|| |
A total of 58 patients were included in the study. The two groups were statistically similar with respect to the demographic profile, baseline hemodynamic parameters before induction, as well as the surgical characteristics including duration of surgery, volume of carbon dioxide insufflated, and IV fluids infused intraoperatively (P > 0.05) [Table 1].
|Table 1: Baseline and intraoperative data for patients undergoing laparoscopic cholecystectomy|
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The primary outcome measure, i.e., postoperative PaO2 was statistically similar between low tidal volume and high tidal volume group (80  mmHg vs. 79  mmHg) (P = 0.326).
The PaO2/FiO2 ratio was statistically similar between both groups at all observed intraoperative and postoperative time points (P = 0.998) [Table 2]. It was clinically better with a medium effect size (standard error of mean [SEM] = 0.5) intraoperatively. Significantly higher PaCO2 and lower pH were seen with low tidal volume group as compared to high tidal volume group at initiation of ventilation, intraoperative time points as well as the end of surgery (P < 0.001), but became statistically similar in postoperative period [Table 2].
|Table 2: Blood gas results in patients undergoing laparoscopic cholecystectomy|
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Intraoperatively, the respiratory rate required for maintaining eucapnia was significantly higher for the low tidal volume as compared to high tidal volume group (P < 0.001), but minute ventilation was statistically similar (P = 0.363) [Table 3]. The EtCO2 was maintained in eucapnic range of 35–40 mmHg in both groups, but it was significantly higher with the low tidal volume group at all time points (P < 0.001) [Table 3].
|Table 3: Intraoperative respiratory and hemodynamic data at four different time points in patients undergoing laparoscopic cholecystectomy|
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The peak airway pressure (Ppeak) and dynamic compliance were statistically similar between both groups (P = 0.472 and P = 0.451, respectively). The effect size for Ppeak and dynamic compliance was 0.6 and 0.7, respectively, at 30 min intraoperatively. The mean airway pressure (Pmean) was significantly higher, and resistance lower, with the low tidal volume group at all times (P < 0.001) [Table 3].
There was no significant difference in intraoperative heart rate (P = 0.926), mean arterial pressure (P = 0.8), and cardiac index (P = 0.090) between both groups [Table 3].
The median plasma IL-6 values were statistically similar between both groups at initiation of ventilation, end of surgery, and 24 h later (P = 0.341) [Table 4].
|Table 4: Comparison of plasma interleukin-6 levels in patients undergoing laparoscopic cholecystectomy|
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The protocol of both ventilatory strategies could be adhered to in all patients without any untoward consequences.
| Discussion|| |
This study evaluated the effect of intraoperative low tidal volume ventilation on gas exchange, pulmonary mechanics, and hemodynamic consequences, supplemented with levels of IL-6 as a marker of ventilation-induced systemic inflammatory response, as compared to high tidal volume ventilation in patients scheduled for elective laparoscopic cholecystectomy. While there was no significant difference in the oxygenation associated with its use as compared to high tidal volume ventilation, the pulmonary mechanics were better maintained. This advantage was negated by the higher systemic IL-6 levels in postoperative period, albeit statistically similar, as compared to those following higher tidal volume ventilation.
Although there are previous studies regarding the use of various mechanical ventilation strategies during laparoscopic cholecystectomy,,,, there are none evaluating the use of low tidal volume strategy. The use of low tidal volume ventilation is firmly established for long-term usage in critically ill patients, and recently benefits have been shown following intraoperative use as well.,,,
We chose 6 ml/kg as a “low tidal volume” and 10 ml/kg as “high tidal volume”. Although tidal volumes as high as 15 ml/kg have been suggested for intraoperative use to prevent atelectasis, conventionally used volumes seldom exceed 10 ml/kg. Previous studies evaluating “high” versus “low” tidal volumes during short-term intraoperative ventilation have compared volumes ranging from 9 to 12 ml/kg versus reduced volumes of 5–8 ml/kg, respectively.,,,,,,,,, Thus, 10 and 6 ml/kg tidal volumes were chosen by us to represent a “high” and “low” volume. A PEEP of 10 cmH2O was added along with low tidal volume of 6 ml/kg, whereas no PEEP was added with the higher tidal volume of 10 ml/kg. In routine anesthetic practice, conventionally used high tidal volumes of 10 ml/kg do not require the addition of PEEP to maintain gas exchange. On the other hand, low tidal volumes may result in alveolar derecruitment and atelectasis as a result of minimal expansion,, and it is thus recommended to add PEEP along with lowered volumes. A PEEP of 10 cmH2O minimizes tidal recruitment and derecruitment during anesthesia, whereas lower levels of PEEP may paradoxically increase regional shear stress and lung injury due to repeated opening and closing of the alveoli. Thus, we used the lowered tidal volume of 6 ml/kg along with a PEEP of 10 cmH2O.
The lack of improved oxygenation with low tidal volume as compared to high tidal volume ventilation is in contrast to the benefit observed during laparoscopic urologic surgeries. However, laparoscopic cholecystectomy may involve less respiratory compromise as compared to urologic surgeries consequent to variations in patient positioning. This inference of benefit of low tidal volume ventilation in the presence of greater respiratory compromise is also proven by the improved oxygenation associated with its use during one-lung ventilation. At the same time, there was an insignificant trend toward better oxygenation intraoperatively, toward the end of surgery, with the use of low tidal volume strategy. Although statistically insignificant, the effect size is not small (SEM = 0.5). This could demand further studies powered to detect intraoperative oxygenation indices as the primary outcome.
Low tidal volume ventilation resulted in significantly higher PaCO2 and lower pH values. However, in the low tidal volume group, the baseline values of PaCO2 measured just following the initiation of mechanical ventilation were also significantly higher than in high tidal volume group. This would likely be a reflection of the period of manual ventilation using a face mask and breathing system during induction of anesthesia before intubation and not the ventilation strategy per se. Following initiation of mechanical ventilation, the respiratory rate was titrated to maintain ETCO2 between 35 and 40 mmHg. As a result, the values of PaCO2 and pH though statistically different were clinically similar between both groups and within normal physiologic range (35–45 mmHg and 7.35–7.45, respectively). Thus, the intraoperative higher PaCO2 and lower pH cannot be used to conclude a lesser efficacy of low tidal volume ventilation for CO2 elimination.
Similar to earlier evidence from nonlaparoscopic surgeries, the requirement of minute ventilation to maintain EtCO2 in the normal physiologic range was statistically similar with the low and high tidal volume strategies.,, However, the respiratory rates required to maintain eucapnia with both strategies of ventilation were higher in our study as compared to earlier trials conducted in nonlaparoscopic surgeries,,, as a consequence of the carbon dioxide insufflation. The trial exploring consequences of low versus high tidal volume ventilation in laparoscopic urologic surgery used predetermined, similar minute volumes in both groups rather than a titrated to maintain eucapnia, making a comparison with our study inappropriate.
A trend toward improvement in respiratory mechanics, i.e., clinically lower peak airway pressure, higher dynamic compliance, and a significantly decreased resistance was seen with low tidal volume ventilation. Although the Ppeak and compliance were statistically similar, and with a small effect size, they do appear to be clinically better with the use of low tidal volume ventilation. The significantly lesser resistance is a result of the lower inspiratory flow requirement consequent to decreased tidal volume delivery with low tidal volume ventilation, and it has been evidenced earlier also., 3, ,,, In contrast, when combined with recruitment maneuver or used in patients with preexisting lung pathology undergoing thoracic surgery, low tidal volume ventilation is associated with significantly higher peak airway pressures.,
There was no significant difference in the mean arterial pressure or cardiac index between both ventilation strategies despite higher mean airway pressures with low tidal volume ventilation., Previous trials noting blood pressure or cardiac index with these two ventilatory strategies have also suggested a lack of any appreciable difference in the hemodynamics.,
We chose IL-6 as a marker to estimate the mechanical ventilation-induced pro-inflammatory systemic response. Several inflammatory mediators have been previously measured to evaluate ventilation-induced inflammatory response and of these IL-6 appear very commonly studied and correlate with the clinical outcome following various modalities of ventilation.,,,,, The serum levels of pro-inflammatory IL-6 increased over time with both ventilatory strategies. There was, however, no significant difference between the two groups although the level was clinically higher in postoperative period with low tidal volume ventilation. Most of the earlier studies have also noted a lack of significant difference in IL-6 following low and high tidal volume ventilation.,,,,
| Conclusion|| |
Thus, the strategy using 6 ml/kg tidal volume along with 10 cmH2O of PEEP was not associated with any significant improvement in gas exchange, hemodynamic parameters, or systemic inflammatory response over ventilation with 10 ml/kg volume without PEEP during laparoscopic cholecystectomy.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]