Neurally adjusted ventilatory assist improves respiratory mechanics in patients with intra-abdominal hypertension

doi:10.21203/rs.3.rs-1986340/v2

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Neurally adjusted ventilatory assist improves respiratory mechanics in patients with intra-abdominal hypertension

https://doi.org/10.21203/rs.3.rs-1986340/v2

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Neurally adjusted ventilatory assist (NAVA) is a new ventilator mode, which collects the electrical activity of diaphragm (EAdi) and provides proportional pressure. The relationship between intra-abdominal hypertension (IAH) and EAdi still needs to be elucidated. The aim of our study was to investigate the effect of EAdi on IAH and to assess whether NAVA is a suitable ventilation mode for patients with IAH.The patients were divided into non-IAH-NAVA (NIAH-NAVA) group (10 cases), IAH-NAVA group (10 cases), and IAH-PSV group (10 cases). The asynchrony index was also recorded for 30 minutes after enrollment. After 24 hours, the intra-abdominal pressure (IAP), EAdi, NAVA level, positive end-expiratory pressure (PEEP), static lung compliance (CSt), plateau pressure (Pplat), airway pressure (Paw), driving pressure (Pdriv), respiratory rate (RR), tidal volume (V_Ti), pH, PaO₂, PaCO₂, and oxygenation index (OI) values were monitored. We also recorded the duration of mechanical ventilation and the length of ICU stay. Patients with IAH had lower EAdi values, and there was a negative correlation between them. In patients with IAH, the NAVA level values were higher, the CSt value was lower, and the Pplat, Paw, PEEP and Pdriv values were increased. Compared with the PSV group, the CSt value was increased and the Pplat, Paw, PEEP and Pdriv values were reduced in the NAVA group. RR value was higher in patients with IAH, while V_Ti value was reduced. In the NAVA group, the asynchrony index was lower than that in the PSV group. In patients with IAH, the duration of mechanical ventilation in the NAVA group was shorter than that time in the PSV group, however, the length of ICU stay had no differences between the two groups. Our study found a negative correlation between IAP and EAdi. the NAVA level values were higher, the CSt value was lower, and the Pplat, Paw, PEEP and Pdriv values were increased in patients with IAH.However, NAVA could be used to improve respiratory mechanics and reduce the duration of mechanical ventilation in patients with IAH, also improve the asynchrony.

NAVA

IAH

EAdi

mechanical ventilation

The ventilator has been used to treat respiratory failure since the first simple breathing air bag's appearance in 19th century[1]. Use of the ventilator is essential for critical patients [2]. The primary purpose of the respirator is to provide adequate gas exchange in a patient. Presently, pressure supported ventilation (PSV) is the most commonly used assisted ventilation mode[3]. However, the use of PSV often presents the patient-ventilator asynchrony, an issue that might lead to excessive lung inflation[4] and breathing discomfort[5, 6]. Due to the patient-ventilator asynchrony, PSV increases the pressure on respiratory muscles of critically-ill patients and causes muscle fatigue as well as serious ventilator-induced injuries. Overall, the use of PSV might result in more extended hospital stays, increased mortality and higher financial burden on the health service.

NAVA is a new assisted ventilation mode of that is becoming increasingly popular in clinical practice due to its several advantages over traditional ventilator systems such as PSV[7]. The respiratory center releases nerve impulses, which propagates along the peripheral nerve (phrenic nerve) to the nerve-diaphragm junction, activates the chemically gated channel on the phrenic muscle fiber membrane, leading to Na⁺ internal flow and K⁺ external flow, and then forms endplate potential. Endplate potential propagates along the phrenic muscle fiber membrane for a distance, and then the nerve impulse converts into electrical signals, resulting in diaphragm contraction and completing a breath. NAVA collects EAdi and provides proportional pressure. In doing so, the ventilation is performed according to the patient's breath cycle, limiting the risk of patient-ventilator asynchrony. Compared with PSV, NAVA is more in line with the human respiratory physiology. NAVA can prevent excessive lung expansion, avoid ventilator-associated injuries[8], reduce the occurrence of patient-ventilator asynchrony[9] and improve gas exchange[10].

IAH, a common complication observed in critically ill patients, is a common cause of abdominal compartment syndrome (ACS). ACS can have severe effects on the respiratory and cardiovascular systems, the kidneys, the liver and the central nervous system. In its worst form, ACS can lead to multiorgan dysfunction [11]. IAH is defined by an elevated IAP, which leads to a rise in the diaphragm and a decrease in the chest and lung volumes. At the same time, elevated IAP reduces cardiac output leading to abnormal blood flow and potentially resulting in hypoxemia, hypercapnia, and respiratory failure[12].

In this study, we investigated the effect of IAH on EAdi. We also assessed whether the use of NAVA, instead of PSV, would be more suitable for patients with IAH.

1 Patients

A total of 30 patients receiving mechanical ventilation in the intensive care unit (ICU) at The First People's Hospital of Lianyungang were monitored in this study. The study included ten patients without IAH (NIAH group) and 20 patients with IAH (IAH group). Patients were enrolled in the study based on the following criteria: 1) admitted to the ICU experiencing mechanical ventilation, ten patients without IAH and 20 patients with continuous increase in IAP over 12 mmHg. 2) age > 18 years and BMI between 18 and 24. Patient exclusion criteria included the following: 1) presence of neuromuscular diseases, esophageal strictures, perforation, bleeding from varicose veins in the esophagus, and gastric fundus. 2) presence of thoracic deformities and diaphragmatic hernias. 3) presence of prostatic hypertrophy or urethral strictures, history of bladder surgery, severe blood clotting disorders, multiple organ failure, pregnancy, and end-stage cancer. 4) presence of lung disease before enrollment.

All patients were treated with a Servo-i respirator produced by Maquet Of Sweden. The bedside elevation was 30°, and all patients were given light sedation (RASS score − 1 to 1). The NIAH group was kept on ventilation with the NAVA. The IAH group was divided into IAH-NAVA and IAH-PSV in a randomized manner. Therefore, the 30 patients enrolled in the study were divided into non-IAH-NAVA (NIAH-NAVA) group (10 patients), IAH-NAVA group (10 patients), and IAH-PSV group (10 patients) (Fig. 1. A). IAP was measured every 4–6 h through the bladder with a maximal instillation volume of 25 mL of sterile saline. IAP was measured in triplicate, and the average was being recorded. IAH was diagnosed with an IAP ≥ 12 mmHg.

For all patients, age, height, BMI, and APEACHE II score values were recorded (Fig. 1. A). The NAVA levels and the pressure support levels were set to achieve the V_Ti values (6–8 mL /kg, ideal weight). The PEEP and FIO₂ levels were set according to the low PEEP-FIO₂ table to make SPO₂ ≥ 95% (Fig. 1. B and C). All patients were observed for 30 minutes after enrollment, then the tasynchrony indexand we recorded. After 24 hours, IAP and EAdi values were monitored in all patients, the NAVA level, PEEP, CSt, Ppalt, Paw, Pdriv, RR V_Ti values were also recorded, and we did arterial blood gas analysis and registered the pH, PaO₂,PaCO₂ and OI values. We also recorded the duration of mechanical ventilation and the length of ICU stay. (Fig. 1. A).

2 Intubation Of The Eadi Catheter And Collecting Eadi

Intubation with a diaphragm electrode catheter (16Fr/125cm, Maquet Critical Care, Solna, Sweden) was carried out as follows. First, the distance from the patient nose (N) through the earlobe (E) to the xiphoid process (X) (i.e., NEX, cm) was measured to estimate the depth (Y) at which the catheter was placed. The depth of the catheter was calculated as Y(cm) = NEX×0.9 + 18cm. Second, the diaphragmatic electrode catheter was inserted, and the EAdi signal monitoring module was connected to the respirator. At this point, four electrocardiogram waveforms appeared in the EAdi catheter implantation preview screen. Changes in the P wave amplitudes were monitored. When the amplitude of the four-channel P wave decreased from top to bottom, the P wave of the first waveform became the most obvious, the fourth waveform disappeared, and the marked blue signal appeared in the second and third waveforms (Fig. 2). This succession of events on the preview screen indicated that the catheter had been successfully placed in the correct location.

3 Statistical Analysis

Data are shown as mean ± SD for all parameters. Statistical significance was assessed with Student’s t-test. Pearson linear correlation analysis was used to determine the correlation between EAdi and IAP. Statistical analysis was performed using GraphPad Prism 6.0 (GraphPad, SanDiego, CA, USA). P values that were < 0.05 were considered statistically significant.

1 Patient characteristics

Among the 30 patients, 14 were male, and 16 were female with age ranging between 42–84 years. 16 patients underwent gastrointestinal surgery, 7 patients were diagnosed with severe pancreatitis, 7 patients were diagnosed with multiple injuries. We recorded the age, height, BMI and APEACHE II score values for all patients, and we found no significant differences in those values (Table 1).

Table 1

The age, height, BMI and APEACHE II score values of all patients.
	NIAH-NAVA	IAH-NAVA	IAH-PSV
Age values (year)	65.20 ± 3.73	64.90 ± 3.98	66.50 ± 3.14
Heigh values (cm)	165.30 ± 3.71	167.80 ± 3.50	166.90 ± 3.40
BMI values (Kg/m²)	21.60 ± 1.07	20.50 ± 1.00	19.50 ± 1.05
APEACHE II values (score)	18.70 ± 1.55	17.30 ± 1.04	18.80 ± 1.41

2 The Indexes Of Arterial Blood Gas Analysis

PSV and NAVA were used in the patients for 24 hours. After this timeframe, we performed arterial blood gas analysis and recorded the pH, PaO_2, PaCO₂ and OI values inorder to assess whether the two modes of mechanical ventilation could ensure normal gas exchange. We found that there were no significant differences in those values (Table 2).

Table 2

The pH, PaO₂, PaCO₂ and OI values of all patients.
	NIAH-NAVA	IAH-NAVA	IAH-PSV
pH values	7.39 ± 0.02	7.40 ± 0.02	7.39 ± 0.02
PaO₂ values (mmHg)	98.28 ± 3.81	102.80 ± 4.02	100.10 ± 3.01
PaCO₂ values (mmHg)	37.30 ± 1.48	39.00 ± 1.31	38.60 ± 1.19
OI values (mmHg)	324.60 ± 13.29	329.50 ± 13.31	335.50 ± 10.80

3 The Relationship Between Iap And Eadi

To investigate the relation between IAH and EAdi, we recorded the IAP and EAdi values of 30 patients after 24 hours. We found that the IAP values in the IAH group were significantly higher compared with the NIAH group (Fig. 3. A), while EAdi values were significantly lower in the IAH group compared to the NIAH group (Fig. 3. B). There was a significant negative correlation observed between EAdi and IAP (Fig. 3. C).

4 The Parameters Of Respiratory Mechanical

In order to compare the effects of PSV and NAVA on respiratory mechanical in patients with IAH, we recorded the NAVA level, CSt, Pplat, Paw, PEEP, Pdriv, RR and V_Ti values after administering the NAVA and PSV for 24 hours. We found that in patients with IAH, the NAVA level value (Fig. 4. A) was higher and the CSt value ( Fig. 4. B) was lower, but NAVA could increase the CSt value ( Fig. 4. B) compared to the PSV. The Pplat ( Fig. 4. C), Paw (Fig. 4. D), PEEP (Fig. 4. E) and Pdriv (Fig. 4. F) values were increased in patients with IAH, however, NAVA could decrease those values( Fig. 4. C-F). The RR (Fig. 4. H) values were higher in patients with IAH, while the V_Ti values (Fig. 4. G) were decreased.

5 The indexes of patient-machine synchronization, the duration of mechanical ventilation and the length of ICU stay

In order to compare the asynchrony index in patients with IAH, we recorded the times after administering the NAVA and PSV for 30 minutes. An asynchrony index was calculated. This index corresponds to the total number of asynchrony events, including auto-triggering (Fig. 5. D), double triggering (Fig. 5. E), ineffective effort (Fig. 5. F), divided by the total respiratory rate (which corresponds to the total Eadi signals) × 100. The asynchrony index was expressed as a percentage. In patients with IAH, the asynchrony index (Fig. 5. A) in the NAVA group was significantly lower than that in the PSV group. We also recorded the duration of mechanical ventilation, length of ICU stay. In patients with IAH, the duration of mechanical ventilation (Fig. 5. B) in the NAVA group was shorter than that time in the PSV group, however, the length of ICU stay (Fig. 5. C) had no differences between the two groups.

The elevation of IAP can result in IAH and even ACS, which can have detrimental effects on the respiratory and cardiovascular system, the kidneys, the liver, and the central nervous system, potentially leading to multiple organ dysfunction syndrome (MODS) [13]. NAVA provides ventilation by monitoring EAdi signals and fully synchronizes with the physiological instructions of the respiratory center. Therefore, since it is tailored to the patient’s needs, NAVA is less likely to cause diaphragmatic atrophy due to excessive ventilator support or increased respiratory muscle activity due to insufficient support. Studies on the feasibility and safety of NAVA in patients have been conducted for various clinical indications, including severe acute respiratory distress syndrome (ARDS) and acute exacerbations of chronic obstructive pulmonary disease (AECOPD) [14]. However, a study investigating the feasibility of NAVA in patients with IAH was still lacking.

In our study, we found that the EAdi values of the IAH group were lower than those of the NIAH group, and there was a significant negative correlation between EAdi and IAP values: the higher IAP, the lower EAdi. The RR value was higher in patients with IAH, and the V_Ti value was decreased, which might be related to IAH. After an increase in IAP, the diaphragm muscles passively lifted, IAP was transmitted to the thorax, meanwhile, the thoracic volume was decreased, and then the V_Ti value was lower, while the RR value was higher to ensure normal gas exchange in patients. NAVA uses EAdi, which is the best available signal to estimate the respiratory drive, to trigger on and cycle off the ventilatory assist. The respiratory center received those informations after an increase in IAP and then reduced the EAdi values to ensure the lower V_Ti values and the higher RR values in patients.

In patients with IAH, the NAVA level values were higher, the CSt value was lower, and The Pplat, Paw, PEEP and Pdriv values were increased, which also might be related to IAH. IAP was transmitted to the thorax, then the intrathoracic pressure was increased. In order to ensure normal gas exchange, the ventilator needed a higher NAVA level and PEEP values, then the Pplat, Paw and Pdriv values were also increased, the CSt value was lower. Compared with the PSV group, the CSt value was increased and the Pplat,Paw, PEEP and Pdriv values were reduced in the NAVA group, which minimizes barometric lung injury. Studies on AECOPD[15] and ARDS [16] showed that NAVA is safe and feasible, also improved the synchronization between the patient and ventilator. We compared the asynchrony index within 30 minutes between PSV and NAVA, and the results showed that the asynchrony index was significantly reduced in the NAVA group, indicating that NAVA achieved more excellent patient-ventilator synchronization.This indicated that NAVA provides lower airway pressure in patients with IAH, which may because that the commands of NAVA come directly from the respiratory center that needed a lower target V_Ti in patients with IAH, and NAVA also improved synchrony. We also recorded the duration of mechanical ventilation and the length of ICU stay. In patients with IAH, we found that the duration of mechanical ventilation in the NAVA group was shorter than that time in the PSV group, however, the length of ICU stay had no differences between the two groups. This indicated that NAVA may reduce the duration of mechanical ventilation in patients with IAH which was due to improved synchrony.

However, our study did not grade abdominal pressure, and the number of patients enrolled in the study is quite small.The duration of the study intervention, at 24 hours, is short. For future studies, we plan to increase patients' numbers and further explore the difference between NAVA and PSV based on abdominal pressure.We will also extend the duration of the study intervention.

Compared with regular IAP patients, patients with IAH require a different ventilation mode, which is closer to human physiology. NAVA may be more suitable for patients with IAH. Patients with IAH had lower EAdi values. Both NAVA and PSV may provide sufficient oxygen metabolism for patients. Compared with PSV, NAVA can improve respiratory mechanics and reduce the duration of mechanical ventilation of patients with IAH. NAVA can also improve synchronicity between the ventilator and the patient.

NAVA

neurally adjusted ventilatory assist

EAdi

electrical activity of diaphragm

IAH

intra-abdominal hypertension

IAP

intra-abdominal pressure

PEEP

positive end-expiratory pressure

CSt

static lung compliance

Pplat

plateau pressure

Paw

airway pressure

Pdriv

driving pressure

respiratory rate

V_Ti

tidal volume

oxygenation index.

Ethics approval and consent to participate

The study protocol was in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines and approved by the Ethics Committee of The First' People’s Hospital of Lianyungang, protocol number ky20180520001. Written informed consent was taken from all the patients and their legal guardians. This study was registered in Clinical Trials （NO. ChiCTR1900022218）where the trial protocol could be accessed.

Consent for publication

Not applicable.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no competing interests.

Funding

This study was supported by the Health Science and Technology Project of Lianyungang (201812).

Author contributions

Xiuwen Kang, Chenying Zhang and Huiling Xu collected the data, performed the analyses, interpreted the data, and drafted the manuscript. Wan Wang, Rong Hu, Zhifang Mu, Yong Li, Yeju Shen, Suxia Liu, Caihong Gu collected the data, supervised the analyses and reviewed the manuscript. All authors contributed to manuscript revision and have read and approved the submitted version.

Acknowledgements

The authors would like to thank all the patients,their families, the investigators, research nurses and all staffs of the First People's Hospital of Lianyungang.

Guidelines statement

All methods in our manuscripts were carried out in accordance with relevant guidelines and regulations.

Author details

¹ Department of Critical Care Medicine, The First People's Hospital of Lianyungang, 6 Zhenhua Road, Lianyungang, Jiangsu 222002, China. ² Department of Respiratory and Critical Care Medicine, The First People's Hospital of Lianyungang, 6 Zhenhua Road, Lianyungang, Jiangsu 222002, China

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No competing interests reported.

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You are reading this latest preprint version

Neurally adjusted ventilatory assist improves respiratory mechanics in patients with intra-abdominal hypertension

Status:

Version 2

Abstract

Figures

Background

Materials And Methods

1 Patients

2 Intubation Of The Eadi Catheter And Collecting Eadi

3 Statistical Analysis

Results

1 Patient characteristics

2 The Indexes Of Arterial Blood Gas Analysis

3 The Relationship Between Iap And Eadi

4 The Parameters Of Respiratory Mechanical

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

Status:

Version 2