Lung-protective Ventilation Combined With Pressure-controlled Ventilation Volume-guaranteed in Children Undergoing One-lung Ventilation: A Randomised Controlled Trial

Abstract

The purpose of study was to evaluate the effect of lung-protective ventilation (LPV) combined with PCV-VG in children undergoing OLV. Patients were randomly assigned to the LPV combined with PCV-VG group (PCV-VG) or LPV group (volume-controlled ventilation). Both groups received tidal-volume ventilation of 8 ml kg^-1 body weight during two-lung ventilation, 6 ml kg^‑1 during OLV, with sustained 5 cmH₂O positive end-expiratory pressure.The PCV-VG group exhibited lower PIP than the LPV group at T1 (16.8±2.3 vs. 18.7±2.7, P=0.001), T2 (20.2±2.7 vs. 22.4±3.3, P=0.001), and T3 (23.8±3.2 vs. 26.36±3.7, P=0.01). Dynamic compliance was higher in the PCV-VG group at T1, T2 , and T3 (P=0.01). After anaesthesia induction, lung aeration deteriorated, but with no immediate postoperative difference in both groups. Postoperative lung aeration improved and returned to normal from 2.5 h postextubation in both groups. No differences were observed in postoperative pulmonary complications, intra-operative desaturation, hospital stay. In paediatric patients, who underwent thoracoscopic surgery, PCV-VG combined with LPV was superior to LPV in its ability to provide ventilation with lower PIP and higher dynamic compliance. However, the long-term benefits of different ventilation strategies should be further investigated.

Key Points:

1. . Evidence-based recommendations for ventilation strategies during OLV in children are lacking.

2. . Studies involving adults have demonstrated that PCV-VG potentially reduces airway pressure and improves lung compliance.

3. . The authors evaluated the effect of lung-protective ventilation combined with PCV-VG in children requiring OLV for thoracoscopic surgery.

4. . PCV-VG combined with LPV was superior to LPV in its ability to provide ventilation with lower PIP and higher dynamic compliance; however, no differences in lung aeration, postoperative pulmonary complications, and intra-operative desaturation was observed.

5. . This approach may facilitate goal-directed trials in peri-operative lung protection for children requiring OLV for thoracoscopic surgery.

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1. Introduction

One-lung ventilation (OLV) has been widely used in children; however, it is associated with increased postoperative pulmonary complications,¹ which is recognized as a risk factor for acute lung injury (ALI).² ALI and acute respiratory distress syndrome are the leading causes of death after thoracic surgery, and they significantly reduce 1-year survival.³ Paediatric patients have smaller functional residual capacities and larger closing volumes, rendering them more susceptible to lung injury during surgery.⁴ Owing to high airway pressures during OLV for pulmonary resection, children are vulnerable to ventilatorinduced barotrauma are of great concern.⁵ PCV-VG is a novel type of ventilation. The decreasing airflow of PCV-VG allows airway pressure to achieve its maximum value at the beginning of inhalation and sustains the entire inhalation phase. Continuous plateau pressure in PCV-VG is more conducive for oxygen diffusion.⁶ To date, several studies involving adults have demonstrated that PCV-VG potentially reduces airway pressure and improves lung compliance compared to VCV;⁶ however, to the best of our knowledge, no studies have investigated PCV-VG in children undergoing OLV surgery. This study aimed to compare PCV-VG combined with LPV with LPV alone in terms of airway pressure, dynamic compliance, lung aeration, postoperative pulmonary complications, intra-operative desaturation, hospital stay, and haemodynamics in children during thoracoscopic surgery.

2. Methods

The study was conducted in accordance with the principles of the Declaration of Helsinki⁷ after receiving approval from the Ethics Committee of Shanghai Children’s Hospital, Shanghai, China on 24 July 2019 (approval number: 2019R044-F01). The trial was registered in the Chinese Clinical Trial Registry at www.chictr.org.cn (trial number: ChiCTR2000035189, 02/08/2020). Confirms that informed consent was obtained from the parents or legal guardians of the children. This single-centre, prospective, randomised controlled trial was conducted at a tertiary teaching children’s hospital affiliated with Shanghai Jiao Tong University, China, from 7 August 2020. The enrolment and allocation of patients are summarised in a CONSORT flow diagram (Fig. 1).

Healthy paediatric patients aged 0–5 years with American Society of Anesthesiologists physical status 1 or 2 who received one lung ventilation during general anaesthesia while undergoing thoracoscopic surgery were included. The exclusion criteria severe heart disease, other lung disease, upper respiratory tract infections, difficult airway or tracheotomy.

Computer-generated, sealed-envelope randomisation was performed to assign patients to one of the following two parallel arms in a 1:1 ratio, receiving different mechanical ventilation protocols: LPV combined with PCV-VG (PCV-VG group) or LPV group (control, volume-controlled ventilation). One investigator (SZ) opened the envelopes and performed different mechanical ventilation protocols. The investigator did not participate in any other aspects of the trial. The patients as well as the Data Safety and Monitoring Board were also blinded to the random allocation.

All patients received a standardised general anaesthetic protocol, which included pre-oxygenation (without continuous positive airway pressure) and intravenous fentanyl (2 mg kg^− 1), propofol (3 mg kg^− 1), and rocuronium (0.6 mg kg^− 1). 5-Fr bronchial blocker (BB) was placed outside the endotracheal tube and placed into the target bronchi using fibre-optic bronchoscope. The pressure of the tracheal intubation cuff was maintained at 20–30 cmH₂O.⁸ All patients received ventilation using the same type of mechanical ventilator. Finally, the lungs were re-expanded manually with sustained inflation with 20–30 cmH₂O of positive airway pressure for 10–15 s under direct observation.^9,10

Anaesthesia was maintained using propofol 5–8 mg kg^− 1 h^− 1 to maintain the BIS (Philips Healthcare, Andover, MA) at 40–60 and remifentanil 0.1–0.4 ug kg^− 1 min^− 1 to maintain haemodynamic stability, and rocuronium 0.3–0.6 mg kg^− 1 h^− 1was maintained. Crystalloid solutions (6–8 ml kg^− 1 h^− 1) were used as maintenance fluids intra-operatively.

3. Results

Patient enrolment commenced on 7 August 2020. In total, 63 patients were randomly assigned to the LPV (n = 31) and PCV-VG (n = 32) groups (Fig. 1). The baseline characteristics did not differ between the groups (Table 1).

All data are presented as mean ± SD or median [IQR], unless otherwise specified.

LPV, lung-protective ventilation; PCV-VG, pressure-controlled ventilation volume-guarantee

Primary outcome

PIP at T2 and T3 were lower in the PCV-VG group than in the LPV group (T2, 20.2±2.7vs 22.4±3.3; P=0.001) (T3, 23.8±3.2vs 26.36±3.7; P=0.01) (Fig. 2A). Dynamic compliance at T2 and T3 was higher in the PCV-VG group than in the LPV group (T2, 9.1±3.7 vs 6.8±3.05 ; P=0.01) (T3, 7.1±3.3 vs 4.8±2.3; P=0.01) (Fig. 2B).

In addition,PIP was higher at T2 and T3 compared with T1(P=0.001) (Fig. 2A). Dynamic compliance was lower at T2 and T3 compared with T1(P=0.01) (Fig. 2B).

Secondary outcomes

LUS assessment

There was no difference in LUS in the dependent lung before T0. After T0, lung aeration deteriorated, but with no difference in both groups immediately after surgery [T4: 4 (2 to 6) vs. 4 (2 to 5) Z=–0.69, P=0.49] (Figure 3a and Figure 3c). Lung aeration improved in both groups after surgery and returned to normal from 2.5 h after extubation in both groups (Figure 3b and Figure 3d). Temporal ultrasound images of the lateral chest wall of the dependent lung are shown in Fig. 3.

Postoperative pulmonary complications

Five (7.9%) patients exhibited Postoperative pulmonary complications occurred in five patients, with no differences in the incidence between the two groups [LPV: 3 (9.7%) vs. PCV-VG: 2 (6.3%), P=0.97].

Intra-operative desaturation

Intra-operative desaturation was comparable in LPV group (4/31, 12.9%), compared with 3/32 (9.4%) in the PCV-VG group [OR=1.43 (0.29 to 7.0); P=0.66]. 

There was no difference in the gas exchange values between the groups. PaO₂ and PaCO₂ increased significantly at T3 compared with that at baseline (P=0.001) (Table 2).

Table 2. Gas exchange

All data are presented as mean ± SD.

PaCO₂, arterial pressure of carbon dioxide; PaO₂, arterial pressure of oxygen; LPV, lung-protective ventilation; PCV-VG, pressure-controlled ventilation volume-guaranteed ventilation; T1, 10 min after induction of anaesthesia without pneumoperitoneum; T3, 5 min after complete CO₂ insufflation

Hospital stays 

The length of hospital stay did not differ between the PCV-VG (6.5 ± 2.1) and VCV (6.1 ± 1.9) groups [0.4 (95% CI -0.59 to 1.39), P=0.43].

Haemodynamic variables

There was no difference in the haemodynamic variables between the groups. MAP was higher at T3 in both groups compared with that at T1 and T2 (P=0.001). CVP was higher at T2 and T3 than that at T1 (P=0.001). The heart rate was stable throughout the operation (Fig. 4).

4. Discussion

This randomised controlled trial revealed that PCV-VG reduced airway pressure and increased dynamic compliance than VCV in children undergoing thoracoscopic surgery. After induction of anaesthesia, lung aeration deteriorated; however, there was no difference in either group immediately after surgery. Lung aeration improved in both groups after surgery and returned to normal from 2.5 h after extubation in both groups. There was no difference in postoperative pulmonary complications, oxygenation, hospital stay, or haemodynamics.

Similar results have been obtained in laparoscopic^6,13 and lumbar spine¹⁴ surgeries. High airway pressures achieved during OLV have reportedly been associated with postpneumonectomy pulmonary oedema^4,15 and acute lung injury after pneumonectomies.¹⁶ Therefore, patients undergoing OLV may benefit more from lower PIP. To the best of our knowledge, evidence-based recommendations for ventilation strategies during OLV in children are lacking and this is the first randomised controlled trial to evaluate the effect of LPV combined with PCV-VG during OLV in a paediatric population.

Patients who received PCV-VG exhibited lower PIP and higher dynamic compliance, indicating a possible association with the decreasing airflow of PCV-VG, which allows airway pressure to achieve its maximum at the beginning of inhalation and continue the entire inspiratory phase.⁶ Continuous measurement of lung compliance and volumetric pressure automatically adjusts the air supply flow rate and air pressure.⁶ Therefore, PCV-VG mode potentially reduces airway pressure to the greatest extent possible while ensuring ideal volume and improving lung compliance.¹¹

In the current study, we found no difference in PPCs between the two groups. This may be related to limited fluid input, plateau pressures remaining below 30 cmH₂O at all times,¹⁷ and lung-protective ventilation.¹⁵ Most important, the sample was too small.

We also found that lung aeration was comparable in both groups after surgery and was fully restored 2.5 h after surgery, as evaluated using LUS. This result is consistent with that of our previous study.¹² However, the influence of the ventilation mode can easily overlap because patient factors or other factors affect patient prognosis to a greater extent.¹⁸ For instance, the lungs were manually re-expanded at the time of thoracic cavity closure. Moreover, patient may exhibit compensatory adaptations, which need to be considered.¹⁸ To be more specific, patient with healthy lungs may compensate and overcome perioperative lung problems, such as lung oedema or atelectasis, but this is unlikely in patients with ALI or acute respiratory distress syndrome,

PaO₂ increased significantly in both groups at T3 compared to that at baseline, and no superiority in oxygenation was observed regardless of the mode of ventilation, a finding that corroborates with a previous study.¹⁹ This finding may be explained by the similarity in the mean values.¹³

However, this study also had certain limitations. First, blinding was not conducted in investigators who were aware of the mode of ventilation. Second, we did not enrol patients with obesity or lung injuries.

In summary, PCV-VG mode reduced the airway pressure and increased dynamic compliance in patients who underwent thoracoscopic surgery requiring OLV. However, its benefificial effects on lung aeration, postoperative pulmonary complications,

intra-operative desaturation and hospital stay remain unclear.

Declarations

Acknowledgments relating to this article

Assistance with this article: We thank our colleagues within the Department of Anesthesiology, Shanghai Children’s Hospital, Shanghai, China (Yuezhen Fu, MD, PHD and Yiru Tong, MD, PHD) for technical assistance.

Author contributions 

Study design/planning: Rong Wei and Change Zhu. Study conduct: Saiji Zhang and Change Zhu. Data collection: Shenghua Yu and Yuting Zhang. Writing the paper: Change Zhu and Rong Wei. Confrming the fnal paper: all authors.

Competing interests 

Te authors declare no competing interests.

Financial support and sponsorship: Funding from Special Clinical Research Project of Shanghai Municipal Health Commission (20204Y0470)

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