Influence of different PEEP levels on electrical impedance tomography findings in patients under general anesthesia ventilated in the lateral decubitus position

Regional lung ventilation during supraglottic and subglottic jet ventilation: A randomized cross-over trial

OBJECTIVE

Test the hypothesis that the center of ventilation, a measure of ventro-dorsal atelectasis, is posterior during supraglottic ventilation indicating better dependent-lung ventilation. Secondarily, we tested the hypothesis that supraglottic ventilation improves oxygenation and carbon dioxide elimination.

BACKGROUND

Supraglottic and subglottic jet ventilation are both used during laryngotracheal surgery. Supraglottic jet ventilation may better prevent atelectasis and provide superior ventilation.

DESIGN

Randomized, cross-over trial.

SETTING

Operating rooms.

PATIENTS

Patients having elective micro-laryngotracheal surgery.

INTERVENTIONS

Patients were sequentially ventilated for 5 min with one randomly selected type of jet ventilation before being switched to the alternative method.

MEASUREMENTS

Regional ventilation distribution was estimated using electrical impedance tomography, with arterial oxygenation and carbon dioxide partial pressures being simultaneously evaluated.

RESULTS

Thirty patients completed the study. There were no statistically significant or clinically meaningful differences in the center of ventilation with supraglottic and subglottic ventilation. However, ventilation with the supraglottic approach was about 4 % higher in the ventromedial lung region and about 4 % lower in the dorsal lung. Surprisingly, arterial blood oxygenation was considerably worse with supraglottic (173 [156, 199] mmHg) than subglottic ventilation (293 [244, 340] mmHg). Arterial carbon dioxide partial pressure was near 40 mmHg with each approach, although slightly lower with supraglottic jet ventilation.

CONCLUSION

The center of ventilation distribution, a measure of atelectasis, was similar with supraglottic and subglottic jet ventilation. Subglottic jet ventilation improved the dorsal-dependent lung region and provided superior arterial oxygenation. Both techniques effectively eliminated carbon dioxide, with the supraglottic approach demonstrating slightly superior efficacy.

Impact of Manual Sustained Inflation vs Stepwise PEEP on Pulmonary and Cerebral Outcomes in Carotid Endarterectomy Patients

BACKGROUND Recruitment maneuvers (RMs) are used to reduce pulmonary atelectasis in patients under general anesthesia, but they can lead to a decrease in cerebral hemodynamics. MATERIAL AND METHODS Thirty patients undergoing carotid endarterectomy were randomized to a manual sustained inflation (SI) group or a stepwise increase in PEEP (IP) group. During both RMs, the peak airway pressure (Ppeak) was maintained at 30 cmH₂O for 30 s. Electrical impedance tomography was used to evaluate pulmonary aeration changes. Mean velocity of blood flow in the middle cerebral artery (Vm) and cerebral oxygen saturation (rScO₂) was monitored intraoperatively. RESULTS IP improved lung aeration better at Ppeak=30 cmH₂O than SI (58.2±8.4% vs 46.0±8.3%, P=0.001) and this persisted until the end of surgery. Dorsal (dependent) ventilation 30 min after extubation in the SI group was lower than that before surgery (7.7±2.6% vs 9.9±3.8%, P=0.003). Vm and rScO₂ returned to baseline immediately after RM in the SI group, while it remained below baseline in the IP group (42.5±12.6 vs 50.9±18.8 cm/s, P<0.001 and 68.1±3.5% vs 70.6±3.7%, P=0.001). Heart rate declined significantly during RM only in the SI group (55.9±6.6 vs 52.2±6.9 bpm, P=0.008). CONCLUSIONS Compared with SI, IP performed better in improving lung aeration, with greater hemodynamic stability. IP resulted in slower recovery of cerebral blood flow and oxygenation.

Individualized PEEP without Recruitment Maneuvers Improves Intraoperative Oxygenation: A Randomized Controlled Study

Individualized positive end-expiratory pressure (PEEP) combined with recruitment maneuvers improves intraoperative oxygenation in individuals undergoing robot-assisted prostatectomy. However, whether electrical impedance tomography (EIT)-guided individualized PEEP without recruitment maneuvers can also improve intraoperative oxygenation is unknown. To test this, fifty-six male patients undergoing elective robot-assisted laparoscopic prostatectomy were randomly assigned to either individualized PEEP (Group PEEPIND, n = 28) or a control with a fixed PEEP of 5 cm H2O (Group PEEP5, n = 28). Individualized PEEP was guided by EIT after placing the patients in the Trendelenburg position and performing intraperitoneal insufflation. Patients in Group PEEPIND maintained individualized PEEP without intermittent recruitment maneuvers, and those in Group PEEP5 maintained a PEEP of 5 cm H2O intraoperatively. Both groups were extubated in a semi-sitting position once the extubation criteria were met. The primary outcome was arterial oxygen partial pressure (PaO2)/inspiratory oxygen fraction (FiO2) prior to extubation. Other outcomes included intraoperative driving pressure, plateau pressure and dynamic, respiratory system compliance, and the incidence of postoperative hypoxemia in the post-operative care unit (PACU). Our results showed that the intraoperative median for PEEPIND was 16 cm H2O (ranging from 12 to 18 cm H2O). EIT-guided PEEPIND was associated with higher PaO2/FiO2 before extubation compared to PEEP5 (71.6 ± 10.7 vs. 56.8 ± 14.1 kPa, p = 0.003). Improved oxygenation extended into the PACU with a lower incidence of postoperative hypoxemia (3.8% vs. 26.9%, p = 0.021). Additionally, PEEPIND was associated with lower driving pressures (12.0 ± 3.0 vs. 15.0 ± 4.4 cm H2O, p = 0.044) and better compliance (44.5 ± 12.8 vs. 33.6 ± 9.1 mL/cm H2O, p = 0.017). Our data indicated that individualized PEEP guided by EIT without intraoperative recruitment maneuvers also improved perioperative oxygenation in patients undergoing robot-assisted laparoscopic radical prostatectomy, which could benefit patients with the risk of intraoperative hemodynamic instability caused by recruitment maneuvers. Trial registration: China Clinical Trial Registration Center Identifier: ChiCTR2100053839. This study was registered on 1 December 2021. The first patient was recruited on 15 December 2021.

Effect of driving pressure on early postoperative lung gas distribution in supratentorial craniotomy: a randomized controlled trial

BACKGROUND

Neurosurgical patients represent a high-risk population for postoperative pulmonary complications (PPCs). A lower intraoperative driving pressure (DP) is related to a reduction in postoperative pulmonary complications. We hypothesized that driving pressure-guided ventilation during supratentorial craniotomy might lead to a more homogeneous gas distribution in the lung postoperatively.

METHODS

This was a randomized trial conducted between June 2020 and July 2021 at Beijing Tiantan Hospital. Fifty-three patients undergoing supratentorial craniotomy were randomly divided into the titration group or control group at a ratio of 1 to 1. The control group received 5 cmH₂O PEEP, and the titration group received individualized PEEP targeting the lowest DP. The primary outcome was the global inhomogeneity index (GI) immediately after extubation obtained by electrical impedance tomography (EIT). The secondary outcomes were lung ultrasonography scores (LUSs), respiratory system compliance, the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO₂/FiO₂) and PPCs within 3 days postoperatively.

RESULTS

Fifty-one patients were included in the analysis. The median (IQR [range]) DP in the titration group versus the control group was 10 (9-12 [7-13]) cmH₂O vs. 11 (10-12 [7-13]) cmH₂O, respectively (P = 0.040). The GI tract did not differ between groups immediately after extubation (P = 0.080). The LUS_S was significantly lower in the titration group than in the control group immediately after tracheal extubation (1 [0-3] vs. 3 [1-6], P = 0.045). The compliance in the titration group was higher than that in the control group at 1 h after intubation (48 [42-54] vs. 41 [37-46] ml·cmH₂O^-1, P = 0.011) and at the end of surgery (46 [42-51] vs. 41 [37-44] ml·cmH₂O^-1, P = 0.029). The PaO₂/FiO₂ ratio was not significantly different between groups in terms of the ventilation protocol (P = 0.117). At the 3-day follow-up, no postoperative pulmonary complications occurred in either group.

CONCLUSIONS

Driving pressure-guided ventilation during supratentorial craniotomy did not contribute to postoperative homogeneous aeration, but it may lead to improved respiratory compliance and lower lung ultrasonography scores.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT04421976.

Dexmedetomidine improves lung compliance in patients undergoing lateral decubitus position of shoulder arthroscopy: A randomized controlled trial

BACKGROUND

The improvement of oxygenation and pulmonary mechanics in patients under general anesthesia can be achieved by dexmedetomidine (DEX) infusion. However, its role in patients undergoing lateral supine shoulder arthroscopy has not been thoroughly studied. This study aimed to evaluate the effect of DEX on lung compliance in patients undergoing shoulder arthroscopic surgery in a lateral decubitus position.

METHODS

The patients who underwent lateral recumbent shoulder arthroscopy under general anesthesia were randomly divided into the DEX group (group D) and the control group (group N). At the start of the trial, group D was given 0.5 μg/kg/hours continuous pumping until 30 minutes before the end of anesthesia; Group N was injected with normal saline at the same volume. The patients were recorded at each time point after intubation: supine position for 5 minutes (T0), lateral position for 5 minutes (T1), lateral position for 1 hour (T2), lateral position for 2 hours (T3), airway peak pressure, platform pressure, dynamic lung compliance, and static lung compliance, etc.

RESULTS

At the end of the drug infusion, the DEX group showed significant improved pulmonary mechanics and higher lung compliance than the control group. Compared with group N, group D's heart rate and mean arterial pressure were lower at all time points; there was no statistical difference in Tidal volume and Pressure end-tidal carbon dioxide data at each time point in Group D.

CONCLUSION

DEX can improve lung compliance and reduce airway pressure and platform pressure of patients undergoing shoulder arthroscopy in the lateral position under general anesthesia.

Lung regions identified with CT improve the value of global inhomogeneity index measured with electrical impedance tomography

Background

The global inhomogeneity (GI) index is a functional electrical impedance tomography (EIT) parameter which is used clinically to assess ventilation distribution. However, GI may underestimate the actual heterogeneity when the size of lung regions is underestimated. We propose a novel method to use anatomical information to correct the GI index calculation.

Methods

EIT measurements were performed at the level of the fifth intercostal space in six patients with acute respiratory distress syndrome. The thorax and lungs were segmented automatically from serial individual CT scans. The anatomically derived lung regions were calculated in EIT images from simulating a homogeneous ventilation distribution in a finite element model. The conventional approach (GI_meas,func ), analyzes images in functionally-defined lung regions, while our proposed measure (GI_meas,anat ) is based on analysis in anatomically-defined regions. We additionally define a simulated comparison (GI_sim,anat ) to determine the lower limit of the GI measure for a homogenous distribution of ventilation.

Results

As expected, the conventional GI_meas,func [0.382 (0.088), median (interquartile range)] were significantly lower than the proposed GI_meas,anat [0.823 (0.152), P<0.05], and were much closer to the lower limit GI_sim,anat [0.343 (0.039)]. Both GI_meas,anat and GI_meas,func were strongly correlated with arterial oxygen partial pressure to fractional inspired oxygen ratio (R=-0.88, P<0.05), whereas GI_sim,anat (R=0.23) was not. GI_meas,anat had a linear-regression slope 3.2 times that of GI_meas,func suggesting a higher sensitivity to the changes in lung condition.

Conclusions

The proposed GI_meas,anat (or shortened as GI_anat ) is an improved measure of ventilation inhomogeneity over GI, and better reflects portion of non-ventilated regions due to alveolar collapse or overdistension.