Effect of target-controlled pressure-controlled ventilation on percutaneous nephrolithotripsy patients under general anesthesia: a retrospective study
Highlight box
Key findings
• Pressure-controlled ventilation with end-inspiratory flow rate as the target can reduce postoperative pulmonary complications and inflammatory levels in patients undergoing percutaneous nephrolithotripsy under general anesthesia in the prone position.
What is known, and what is new?
• General anesthesia in the prone position tends to limit chest wall mobility with decreased compliance and increased airway pressure, which can increase the incidence of postoperative pulmonary complications.
• Pressure-controlled ventilation with end-inspiratory flow rate as the target can reduce postoperative pulmonary complications in patients undergoing percutaneous nephrolithotripsy under general anesthesia in the prone position.
What is the implication, and what should change now?
• Improvement of ventilation strategies for prone positioning surgery is recommended to reduce the incidence of postoperative pulmonary infection.
Introduction
The prone position is one of the most common positions for general anesthesia surgery, providing a good surgical field for percutaneous nephrolithotripsy and other procedures (1,2). However, prone position surgery tends to limit chest wall mobility, with decreased compliance and increased airway pressure. If the parameters of mechanical ventilation are not appropriately set, lung damage can be aggravated, resulting in increased circulating interleukin-6 (IL-6), macrophage-inflammatory protein-2 (MIP-2), and tumor necrosis factor-α (TNF-α) levels, leading to postoperative pulmonary complications (PPCs) (3,4). PPCs mainly include respiratory tract infection, respiratory failure, pleural effusion, atelectasis, pulmonary edema, pneumothorax, and acute lung injury, among which ventilator-related lung injury is one of the leading causes of PPCs. Volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) are commonly used ventilation modes in patients undergoing general anesthesia (5-7). VCV can ensure tidal volume, but the airway pressure changes considerably, thus increasing the potential for barotrauma. PCV can meet tidal volume requirements while maintaining low airway pressure. Studies have shown that PCV is effective in protecting the lungs, possibly because PCV produces an exponentially decreasing flow waveform so that the inhaled gas is evenly diffused and distributed in the lung tissue, promoting the expansion of the distal alveoli while avoiding local overexpansion (7,8). During PCV, the preset pressure level is reached by a higher initial inspiratory flow rate at the beginning of the inspiratory process, which decreases exponentially with the inspiratory time until the end of the inspiratory process. If the inspiratory velocity does not drop to “0” at the end of inhalation, the tidal volume can be increased by extending the inspiratory time, and the inspiratory velocity will decrease further until it reaches “0”, which we define as “zero flow rate at the end of inspiration”. It is currently unclear whether this ventilation strategy reduces the incidence of PPCs, so we designed the present study to investigate this issue. We present this article in accordance with the STROBE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-23-158/rc).
Methods
General information
From January 2020 to December 2021, a total of 154 patients admitted to Sichuan Provincial Rehabilitation Hospital of Chengdu University of TCM for percutaneous nephrolithotripsy under general anesthesia in the prone position were retrospectively enrolled. All patients received percutaneous nephrolithotripsy. According to the type of mechanical ventilation given during surgery, the patients were divided into either a fixed-respiratory-ratio-PCV group (n=78) or a target-controlled-PCV group (n=76). The inclusion criteria were as follows: (I) patients who underwent percutaneous nephrolithotripsy under general anesthesia in the prone position; (II) age ≥18 years old; (III) American Society of Anesthesiologists (ASA) grade I–II; (IV) mechanical ventilation time ≥60 minutes. Patients were excluded based on the following criteria: (I) obesity; (II) serious cardiovascular disease; (III) diabetes; (IV) hypertension; (V) smoking history; (VI) patients whose positioning required changing during surgery; (VII) patients who were lost to follow-up. This study was conducted in accordance with the Declaration of Helsinki (as revised in 2013) and was approved by the Ethics Committee of the Sichuan Provincial Rehabilitation Hospital of Chengdu University of TCM (No. c202200184). The requirement for informed consent was waived due to the study’s retrospective nature.
Anesthesia methods
After admission to the operating theatre, blood pressure (BP), heart rate (HR), oxygen saturation of the blood (SpO2), electrocardiogram (ECG), and bispectral index (BIS) were monitored. The midazolam (0.03 mg/kg), sufentanil citrate (0.5 µg/kg), cisatracurium besylate (0.2 mg/kg) and propofol (1.5 mg/kg) were administered for anesthesia induction. After 5 minutes of oxygen administration through the mask, endotracheal intubation was performed through the mouth using a video laryngoscope. The intubation depth was 22–24 cm, and the breath sounds of both lungs were clear and symmetrical on the lung auscultation after intubation. Finally, the anesthesia machine was connected to control the mechanical ventilation. In the fixed-respiration-ratio-PCV group, the inspiratory pressure was 8 mL/kg, the pressure rise time (Tslope) was 0 seconds, the respiration rate (RR) was 12 times/min, and the fraction of inspiration O2 (FiO2) was 50%. The PCV mode was adopted in the target-controlled-PCV Group, and the inhalation ratio was adjusted to achieve “zero flow rate at the end of inspiration”. The remaining parameters were the same as the fixed-respiratory-ratio-PCV group. A dosage of 1–5 mg/kg/h propofol + 6–12 µg/kg/h remifentanil + 2.0–8.0% desflurane was used for anesthesia inhalation maintenance, and the BIS level was maintained at 40–60 according to the depth of anesthesia. After surgery, the patients were returned to the supine position. After the patient’s spontaneous breathing had recovered, consciousness was clear, and protective reflexes had been restored, the endotracheal tube was removed.
Data collection
We collected data on gender, age, body mass index, and the American Society of Anesthesiologists (ASA) classification. The duration of surgery, duration of anesthesia, amount of blood loss, blood transfusion, fluid replacement, and PPCs (including respiratory tract infection, respiratory failure, pleural effusion, atelectasis, pulmonary edema, pneumothorax, and acute lung injury) were also recorded. The following measures were recorded at different time points [immediately after intubation (T0), immediately after prone positioning (T1), 60 minutes after prone positioning (T2), and immediately after surgery (T3)]: peak airway pressure, airway plateau pressure, end-expiratory carbon dioxide partial pressure (PET CO2), dynamic lung compliance, oxygenation index, and the incidence of hypoxemia within 72 hours after surgery (where hypoxemia was defined as oxygen saturation <90%). Preoperative and 1- and 3-day postoperative IL-6 and C-reactive protein (CRP) levels were also collected.
Statistical analysis
SPSS v.26.0 was used to complete the data analysis, with a two-sided P value <0.05 indicating a statistically significant difference. The measurement data of the two groups are expressed as means ± standard deviations, and the differences between the two groups were analyzed by independent sample t-tests. The count data of the two groups were expressed by n (%), and the chi-square test was used to analyze the difference in the count data between the two groups.
Results
Comparison of general data between the two groups
The inclusion flowchart for the study is shown in Figure 1. There were no significant differences in general data such as age, sex, body mass index, ASA grade, duration of surgery, duration of anesthesia, intraoperative blood loss, perioperative blood transfusion rate, or intraoperative fluid replacement between the two groups (P>0.05) (Table 1).
Table 1
| Groups | Target-controlled-PCV group (n=76) | Fixed-respiration-ratio-PCV group (n=78) | t value | P value |
|---|---|---|---|---|
| Age (years) | 48.49±6.96 | 48.96±7.57 | 0.405 | 0.686 |
| Gender | 0.392 | 0.531 | ||
| Male | 43 (56.58) | 48 (61.54) | ||
| Female | 33 (43.42) | 30 (38.46) | ||
| Body mass index (kg/m2) | 25.34±2.63 | 25.99±2.65 | 1.532 | 0.127 |
| ASA classification | 0.321 | 0.571 | ||
| I | 52 (68.42) | 50 (64.10) | ||
| II | 24 (31.58) | 28 (35.90) | ||
| Duration of surgery (min) | 93.70±17.93 | 89.12±19.06 | 1.536 | 0.127 |
| Duration of anesthesia (min) | 124.72±18.05 | 119.50±19.81 | 1.709 | 0.089 |
| Amount of intraoperative bleeding (mL) | 105.79±31.49 | 103.97±28.47 | 0.375 | 0.708 |
| Perioperative blood transfusion | 0.178 | 0.673 | ||
| Yes | 4 (5.26) | 3 (3.85) | ||
| No | 72 (94.74) | 75 (96.15) | ||
| Intraoperative fluid replacement (mL) | 2,241.53±275.99 | 2,315.95±270.67 | 1.689 | 0.093 |
Data are represented as n (%) or mean ± SD. ASA, American Society of Anesthesiologists; PCV, pressure-controlled ventilation; SD, standard deviation.
The incidence of PPCs between the two groups
Compared with the fixed-respiratory-PCV group, the overall incidence of PPCs was significantly reduced in the target-controlled-PCV group (3.95% vs. 14.10%, P=0.028) (Table 2).
Table 2
| Group | Target-controlled-PCV group (n=76), n (%) | Fixed-respiration-ratio-PCV group (n=78), n (%) | χ2 value | P value |
|---|---|---|---|---|
| Respiratory infection | 1 (1.32) | 4 (5.13) | 1.781 | 0.182 |
| Respiratory failure | 0 (0.00) | 0 (0.00) | – | – |
| Pleural effusion | 0 (0.00) | 2 (2.56) | 1.974 | 0.160 |
| Atelectasis | 1 (1.32) | 2 (2.56) | 0.314 | 0.575 |
| Pulmonary edema | 0 (0.00) | 1 (1.28) | 0.981 | 0.322 |
| Pneumothorax | 1 (1.32) | 1 (1.28) | 0.000 | 0.985 |
| Acute lung injury | 0 (0.00) | 1 (1.28) | 0.981 | 0.322 |
| Overall incidence of PPC | 3 (3.95) | 11 (14.10) | 4.803 | 0.028 |
| Hypoxemia within 72 hours of surgery | 1 (1.32) | 4 (5.13) | 1.781 | 0.182 |
PPCs, postoperative pulmonary complications; PCV, pressure-controlled ventilation.
Comparison of respiratory mechanical-related indexes at different time points between the two groups
There were no significant differences between the two groups in peak airway pressure, airway plateau pressure, or dynamic lung compliance at T0 (P>0.05). However, peak airway pressure and airway platform pressure in the target-controlled-PCV group at T1, T2, and T3 were significantly reduced (P<0.05), whereas the dynamic pulmonary compliance was significantly increased compared with the fixed-respiration-ratio PCV group (P<0.05) (Table 3).
Table 3
| Group | Target-controlled-PCV group (n=76) | Fixed-respiration-ratio-PCV group (n=78) | t value | P value |
|---|---|---|---|---|
| Airway peak pressure (cmH2O) | ||||
| T0 | 15.00±2.27 | 14.42±2.13 | 1.650 | 0.101 |
| T1 | 15.33±2.12 | 16.15±2.16 | 2.358 | 0.020 |
| T2 | 15.38±2.26 | 17.93±2.53 | 6.582 | 0.000 |
| T3 | 15.29±2.25 | 16.70±2.46 | 3.718 | 0.000 |
| Airway plateau pressure (cmH2O) | ||||
| T0 | 6.44±1.20 | 6.54±1.31 | 0.469 | 0.640 |
| T1 | 7.06±1.20 | 7.77±1.31 | 3.518 | 0.000 |
| T2 | 6.84±1.18 | 7.61±1.24 | 3.956 | 0.000 |
| T3 | 6.86±1.17 | 7.47±1.36 | 3.027 | 0.003 |
| PET CO2 (mmHg) | ||||
| T0 | 38.39±4.51 | 37.85±4.63 | 0.725 | 0.470 |
| T1 | 37.61±4.54 | 38.95±4.32 | 1.880 | 0.062 |
| T2 | 38.27±4.66 | 37.54±4.49 | 0.990 | 0.324 |
| T3 | 37.93±4.77 | 38.17±4.34 | 0.333 | 0.739 |
| Pulmonary dynamic compliance (mL/cmH2O) | ||||
| T0 | 45.98±5.19 | 46.92±5.28 | 1.109 | 0.269 |
| T1 | 45.22±5.13 | 43.37±5.01 | 2.261 | 0.025 |
| T2 | 45.49±4.95 | 42.67±5.04 | 3.492 | 0.001 |
| T3 | 44.90±5.31 | 41.86±4.66 | 3.773 | 0.000 |
| Oxygenation index (mmHg) | ||||
| T0 | 415.89±34.56 | 424.73±37.43 | 1.521 | 0.130 |
| T1 | 413.67±34.78 | 424.35±35.32 | 1.889 | 0.061 |
| T2 | 522.58±36.47 | 425.33±32.33 | 0.496 | 0.620 |
| T3 | 420.33±35.35 | 426.86±33.07 | 1.184 | 0.238 |
Data are represented as mean ± SD. PCV, pressure-controlled ventilation; PET CO2, partial pressure of end-tidal carbon dioxide; SD, standard deviation.
Comparison of IL-6 and CRP levels at different time points between the two groups
There was no significant difference in preoperative interleukin 6 (IL-6) or C-reactive protein (CRP) levels between the two groups (P>0.05). However, the target-controlled-PCV group showed significantly reduced IL-6 and CRP levels at 1 and 3 days postoperatively compared with the fixed-respiration-ratio-PCV group (P<0.05) (Table 4).
Table 4
| Group | Target-controlled-PCV group (n=76) | Fixed-respiration-ratio-PCV group (n=78) | t value | P value |
|---|---|---|---|---|
| IL-6 (ng/L) | ||||
| Preoperatively | 1.86±0.63 | 1.93±0.64 | 0.691 | 0.491 |
| 1 day postoperatively | 1.81±0.55 | 2.02±0.56 | 2.393 | 0.018 |
| 3 days postoperatively | 1.12±0.40 | 1.33±0.47 | 2.887 | 0.004 |
| CRP (mg/L) | ||||
| Preoperatively | 12.19±2.30 | 12.68±2.27 | 0.585 | 0.193 |
| 1 day postoperatively | 11.83±2.17 | 12.79±2.10 | 0.894 | 0.006 |
| 3 days postoperatively | 8.92±2.30 | 10.24±2.46 | 0.574 | 0.001 |
Data are represented as mean ± SD. PCV, pressure-controlled ventilation; CRP, C-reactive protein; IL-6, interleukin 6; SD, standard deviation.
Discussion
Prone position surgery tends to limit chest wall mobility, with decreased compliance and increased airway pressure. It can exacerbate lung injury if the mechanical ventilation parameters are not correctly set, leading to an increased incidence of PPCs (9-11). PCV is the most commonly used ventilation strategy in prone position surgery and is beneficial in reducing lung injury, but the incidence of PPCs remains high (12,13). We designed this study to investigate whether pressure-controlled ventilation aiming for “zero flow rate at the end of inspiration” improves the prognosis of patients undergoing prone position surgery. Our results showed that pressure-controlled ventilation aiming for “zero flow rate at the end of inspiration” significantly improved intraoperative respiratory mechanics and reduced the incidence of PPCs and postoperative inflammation.
PCV allows the ventilator to maintain pressure at the airway opening for a specified period of time (14-17). As such, the final tidal volume and flow rate are affected by compliance, airway resistance, and spontaneous breathing. The main advantages of PCV ventilation are variable flow, better synchronization, reduced respiratory work, limited intra-alveolar pressure, more uniform gas distribution, and improved patient oxygenation levels. Recent studies of prone position surgery have demonstrated that PCV ventilation strategies can reduce the severity of lung injury (5,6). However, the PCV ventilation strategy also has shortcomings; for instance, tidal volume is difficult to control, and it is relatively challenging to judge respiratory mechanical changes (18-20). During PCV, the preset pressure level is reached at a higher initial inspiratory flow rate at the beginning of the inspiratory process, which decreases exponentially with the inspiratory time until the end of the inspiratory process. If the inspiratory velocity does not drop to “0” at the end of inhalation, it can lead to prolonged inspiratory time and increased tidal volume, which can lead to excessive expansion of the alveoli. In contrast, shortened inspiratory time and reduced tidal volume can lead to atelectasis. To regulate the ventilation strategy more precisely during PCV ventilation, we adjusted the end-inspiratory flow rate to “0” by adjusting the inspiration-to-exhalation ratio. The “zero flow rate at the end of inspiration” indicates that the inhalation time is appropriate and slightly longer. Under this ventilation strategy, atelectasis caused by hypoventilation can be effectively reduced, and hyperinflation of the alveoli caused by hyperventilation can also be avoided. Additionally, the respiratory mechanical-related indexes were improved, and the incidence of PPCs and postoperative inflammation was reduced. Moreover, reduced peak airway pressure and airway platform pressure were also found in the target-controlled-PCV group when compared with the fixed-respiration-ratio-PCV group. High peak airway pressure and airway platform pressure will affect the ratio of ventilation blood flow, finally resulting in decreased dynamic pulmonary compliance and PPCs. Increased IL-6 and CRP have been proved to be association with postoperative complication by a previous study (21). In the present study, IL-6 and CRP were also found to be reduced in the target-controlled-PCV group when compared with the fixed-respiration-ratio-PCV group, indicating that target-controlled-PCV may reduce lung injury during the operation.
Limitations
The present study was a single-center retrospectively clinical study with limited patients.
Conclusions
Prognosis and related indicators of different diseases are the focus of current research (22-25). The present study was the first study looking into pulmonary complications associated with ventilation in percutaneous nephrolithotripsy patients. The present study found that the pressure-controlled ventilation with end-inspiratory flow rate as the target can reduce postoperative pulmonary complications and inflammatory levels in patients undergoing percutaneous nephrolithotripsy under general anesthesia in the prone position. Improvements in ventilation strategies for prone position surgery are recommended to reduce the incidence of postoperative pulmonary infection.
Acknowledgments
Funding: The study was supported by the Medical Research Project in Chengdu, Sichuan Province, China (No. 2022001).
Footnote
Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-23-158/rc
Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-23-158/dss
Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-23-158/prf
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-23-158/coif). The authors have no conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki (as revised in 2013) and was approved by the Ethics Committee of the Sichuan Provincial Rehabilitation Hospital of Chengdu University of TCM (No. c202200184). The requirement for informed consent was waived due to the study’s retrospective nature.
Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
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(English Language Editor: D. Fitzgerald)
