Effect of PEEP and I:E ratio on cerebral oxygenation in ARDS: an experimental study in anesthetized rabbit

Mechanical Ventilation in Patients with Acute Brain Injuries: A Pathophysiology-based Approach

Applying mechanical ventilation and selecting ventilatory strategies in patients with acute brain injuries, especially those with lung damage, is challenging. Static (positive end-expiratory pressure) and dynamic (intratidal) changes in ventilator pressure, via complex pathways, influence cerebral arterial inflow and cerebral venous pressure and thus cerebral blood volume and intracranial pressure. In this process, the relationship between airway pressure and pleural and transalveolar pressures, heavily affected by elastance of the chest wall and lung, respectively, plays a central role. This relationship determines the extent to which a static and dynamic increase in airway pressure affects the cardiac function and venous return curves, which govern the static and dynamic arterial and central venous pressures. The integrity of cerebral autoregulation determines whether static changes in arterial pressure alter cerebral arterial inflow. Conversely, dynamic changes in arterial pressure during the breath are followed by corresponding changes in cerebral arterial inflow because of the inability of autoregulation to control rapid arterial pressure fluctuations. The flow dynamics in the jugular veins and the relationship between intracranial and sagittal sinus pressures determine whether static and dynamic changes in central venous pressure alter cerebral venous pressure. Setting the ventilator and planning strategies should be individualized and guided by the complex, interactive effects among central nervous, respiratory, and cardiovascular systems on cerebral blood volume and cerebral perfusion and intracranial pressures. Following a logical framework, clinicians may anticipate the likely effects of ventilator settings and strategies on cerebral hemodynamics, enabling a more individualized approach in setting the ventilator and planning ventilatory strategies.

Preliminary study: Low to moderate PEEP effects on ICP in acute neurological injury patients under mechanical ventilation

BackgroundAcute respiratory distress syndrome (ARDS) significantly impacts mortality and prognosis in acute neurological injury patients. Positive end-expiratory pressure (PEEP) is essential in mechanical ventilation to enhance oxygenation, yet its application may elevate intracranial pressure (ICP). Studies show conflicting findings regarding PEEP's effect on ICP, particularly at low to moderate levels (5-10cmH2O), warranting further investigation in acute neurological injury cases.ObjectiveTo assess the impact of low to moderate PEEP on ICP in patients with acute neurological injury who require mechanical ventilation.MethodsA retrospective analysis of 62 patients with acute neurological injury requiring mechanical ventilation at our hospital between January 2021 and September 2023 was conducted. Patients were divided into high PEEP (> 10cmH2O) and low to moderate PEEP (5-10cmH2O) groups. Parameters including PaO2, PaCO2, PaO2/FiO2, driving pressure, compliance (Cst), airway resistance, such as heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), central venous pressure (CVP), cardiac index (CI), ICP, and cerebral perfusion pressure (CPP) were recorded pre- and post-ventilation initiation, with correlation analysis performed between ICP and other parameters.ResultsPre-treatment comparisons between the high PEEP and low to moderate PEEP groups revealed no significant differences in PaO2, PaCO2, PaO2/FiO2, driving pressure, Cs, and airway resistance. However, post-treatment analysis showed significant disparities, with the high PEEP group exhibiting higher PaO2 and PaO2/FiO2 levels and lower PaCO2, driving pressure, and airway resistance levels compared to the low to moderate PEEP group. Additionally, hemodynamic parameters such as HR, SBP, DBP, CI, MAP, CVP, ICP, and CPP remained more stable in the low to moderate PEEP group post-treatment, with ICP demonstrating significant correlations with various physiological parameters.ConclusionHigh PEEP improves oxygenation and respiratory mechanics in acute neurological injury patients on mechanical ventilation but may affect hemodynamic parameters, ICP, and CPP. Conversely, low to moderate PEEP has minimal impact on these factors. Hence, personalized adjustment of PEEP levels is essential in clinical management.

Efficacy of adaptive ventilation support combined with lung recruitment maneuvering for acute respiratory distress syndrome

OBJECTIVE

This study was designed to evaluate the efficacy of adaptive support ventilation (ASV) and lung recruitment maneuvering (LRM) on the hemodynamics and respiratory mechanics of patients with acute respiratory distress syndrome (ARDS).

METHODS

A total of 100 patients with ARDS admitted to the intensive care unit (ICU) of our hospital from July 2016 to October 2019 were randomly divided into the control group (n=50) receiving synchronized intermittent mandatory ventilation (SIMV) and the study group (n=50) receiving ASV + LRM. The hemodynamics, respiratory mechanics, oxygen metabolism parameters, pulmonary index of microcirculatory resistance and prognosis were compared between the two groups.

RESULTS

No significant difference was observed between the two groups in terms of baseline data (P > 0.05). Positive end-expiratory pressure (PEEP), mean arterial pressure (MAP), central venous pressure (CVP), heart rate (HR), systemic vascular resistance index (SVRI), pulmonary arterial pressure (PAP), and cardiac output index (CI) were not significantly different between the two groups (P > 0.05). PEEP, peak inspiratory pressure (PIP), pulmonary vascular resistance index (PVRI), and extravascular lung water (EVLW) were lower, and arterial oxygen pressure (PaO₂), global oxygen delivery (DO₂), oxygen-uptake (VO₂), and dynamic compliance (Cdyn) were higher in the study group than in the control group (P < 0.05). Time to withdrawal, APACHE II score, and length of stay in ICU were lower in the study group than in the control group (P < 0.05).

CONCLUSION

ASV + LRM can improve respiratory mechanics, oxygen metabolism, reduce microcirculatory resistance, shorten ICU stay and alleviate the conditions of ARDS patients, but has no significant effect on hemodynamics.

Wavelet Transform Image Enhancement Algorithm-Based Evaluation of Lung Recruitment Effect and Nursing of Acute Respiratory Distress Syndrome by Ultrasound Image

This study aimed to analyze the application of ultrasound images of lung recruitment (LR) nursing treatment guided by positive-end expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS). An ultrasound image enhancement algorithm (UIEA) wavelet transform (WT) was constructed, and the soft threshold (ST) and adjacent region average (ARA) were introduced for simulation comparison. In addition, the signal-to-noise ratio (SNR), peak signal-to-noise ratio (PSNR), and running time were undertaken as the evaluation indexes. The WT algorithm was applied to the ultrasound images of 85 ARDS patients before and after PEEP recruitment. The mean artery pressure (MAP), heart rate (HR), and central venous pressure (CVP), peak inspiratory pressure (Ppeak), mean inspiratory pressure (Pmean), dynamic lung compliance (DLC), PCO₂, and PaO₂/FiO₂ of the patients were recorded before and after the LR. The results showed that the signal-to-noise ratio (SNR) (19.67 ± 3.15 dB) and PSNR (23.08 ± 2.08 dB) of the images enhanced by the WT algorithm were much higher than those of ST (13.88 ± 2.74 dB and 14.62 ± 1.76 dB, respectively) and ARA (14.96 ± 3.06 dB and 15.11 ± 1.94 dB, respectively), while the running time was in adverse (P < 0.05); the HR and CVP of patients after LR nursing treatment were increased greatly, while the MAP was in the opposite case (P < 0.05); after LR nursing treatment, Ppeak, Pmean, DLC, PCO₂, and PaO₂/FiO₂ of the patient were significantly greater than those before the LR, and the difference was statistically significant (P < 0.05). In short, the WT algorithm not only enhanced the quality of ultrasound images but also shortened the running time and improved the processing efficiency. PEEP LR nursing treatment could effectively improve the vascular patency, cardiac ejection capacity, and DLC in patients with ARDS, thereby increasing the airway pressure and maintaining the unobstructed expiration.