The effects of positive end-expiratory pressure on cardiac function: a comparative echocardiography-conductance catheter study

Development of a framework for the hemodynamic impact of positive end-expiratory pressure in normal and heart failure conditions

Positive end-expiratory pressure (PEEP) improves respiratory conditions. However, the complex interaction between PEEP and hemodynamics in patients with heart failure makes it challenging to determine appropriate PEEP settings. In this study, we developed a framework for the impact of PEEP on hemodynamics considering cardiac function, by integrating the impact of PEEP in the generalized circulatory equilibrium framework, and validated the framework by assessing its ability to accurately predict PEEP-induced hemodynamics. In eight dogs, PEEP was increased stepwise, and hemodynamic responses were measured under normal, volume-loaded, and myocardial infarction (MI)-induced heart failure conditions. For predicting hemodynamics under PEEP using the proposed framework, the PEEP-intrathoracic pressure (ITP) relationship was empirically established in dogs. Hemodynamic parameters were estimated at each PEEP level based on the hemodynamics recorded without PEEP. The parameters were then used to predict hemodynamics under various heart conditions. The predicted and measured values were compared. A stepwise increase in PEEP decreased arterial pressure (AP) and cardiac output (CO). Left atrial pressure (LAP) decreased in normal hearts but increased in MI hearts. Predicted AP [R2, 0.92; root mean-squared error (RMSE), 6.3 mmHg], CO (R2, 0.96; RMSE, 7.9 mL·min-1·kg-1), and LAP (R2, 0.92; RMSE, 2.3 mmHg) matched measured values with high accuracy, irrespective of volume status or heart condition. In conclusion, we developed a framework for the hemodynamic impact of PEEP considering cardiac function and demonstrated its validity. The results indicate that the effects of PEEP on hemodynamics can be explained primarily by ITP and are modulated by cardiac function.NEW & NOTEWORTHY Positive end-expiratory pressure (PEEP) has both the benefit of improving respiratory status and the disadvantage of deteriorating hemodynamics. As the effects of PEEP vary depending on cardiac function, optimizing PEEP setting remains challenging. This study is the first to systematically elucidate the impact of PEEP on hemodynamics with consideration of cardiac function and establish a validated framework. This novel framework provides a comprehensive understanding of the hemodynamic effects of PEEP.

Tailoring the Best Positive End-Expiratory Pressure Through Invasive Right Ventricular Pressure-Volume Loops in a Patient Supported by Veno-Arterial Extracorporeal Membrane Oxygenation

Patients undergoing veno-arterial extracorporeal membrane oxygenation (VA-ECMO) typically suffer from cardiogenic pulmonary edema and lung atelectasis, which can exacerbate right ventricular (RV) dysfunction through an increase in lung elastance and RV afterload. Invasive mechanical ventilation settings, and positive end-expiratory pressure (PEEP) in particular, can help to improve RV performance by optimizing lung recruitment and minimizing alveolar overdistention. In this report, we present a VA-ECMO supported patient in whom in vivo RV pressure-volume (PV) loops were measured during a decremental PEEP trial, leading to the identification of an optimum PEEP level from a cardio-respiratory viewpoint. This innovative approach of tailoring mechanical ventilation settings according to cardio-respiratory physiology through in vivo RV PV loops may provide a novel way to optimize hemodynamics and patient outcomes.

Mechanisms maintaining right ventricular contractility-to-pulmonary arterial elastance ratio in VA ECMO: a retrospective animal data analysis of RV-PA coupling

BACKGROUND

To optimize right ventricular-pulmonary coupling during veno-arterial (VA) ECMO weaning, inotropes, vasopressors and/or vasodilators are used to change right ventricular (RV) function (contractility) and pulmonary artery (PA) elastance (afterload). RV-PA coupling is the ratio between right ventricular contractility and pulmonary vascular elastance and as such, is a measure of optimized crosstalk between ventricle and vasculature. Little is known about the physiology of RV-PA coupling during VA ECMO. This study describes adaptive mechanisms for maintaining RV-PA coupling resulting from changing pre- and afterload conditions in VA ECMO.

METHODS

In 13 pigs, extracorporeal flow was reduced from 4 to 1 L/min at baseline and increased afterload (pulmonary embolism and hypoxic vasoconstriction). Pressure and flow signals estimated right ventricular end-systolic elastance and pulmonary arterial elastance. Linear mixed-effect models estimated the association between conditions and elastance.

RESULTS

At no extracorporeal flow, end-systolic elastance increased from 0.83 [0.66 to 1.00] mmHg/mL at baseline by 0.44 [0.29 to 0.59] mmHg/mL with pulmonary embolism and by 1.36 [1.21 to 1.51] mmHg/mL with hypoxic pulmonary vasoconstriction (p < 0.001). Pulmonary arterial elastance increased from 0.39 [0.30 to 0.49] mmHg/mL at baseline by 0.36 [0.27 to 0.44] mmHg/mL with pulmonary embolism and by 0.75 [0.67 to 0.84] mmHg/mL with hypoxic pulmonary vasoconstriction (p < 0.001). Coupling remained unchanged (2.1 [1.8 to 2.3] mmHg/mL at baseline; - 0.1 [- 0.3 to 0.1] mmHg/mL increase with pulmonary embolism; - 0.2 [- 0.4 to 0.0] mmHg/mL with hypoxic pulmonary vasoconstriction, p > 0.05). Extracorporeal flow did not change coupling (0.0 [- 0.0 to 0.1] per change of 1 L/min, p > 0.05). End-diastolic volume increased with decreasing extracorporeal flow (7.2 [6.6 to 7.8] ml change per 1 L/min, p < 0.001).

CONCLUSIONS

The right ventricle dilates with increased preload and increases its contractility in response to afterload changes to maintain ventricular-arterial coupling during VA extracorporeal membrane oxygenation.

Increasing Levels of Positive End-expiratory Pressure Cause Stepwise Biventricular Stroke Work Reduction in a Porcine Model

BACKGROUND

Positive end-expiratory pressure (PEEP) is commonly applied to avoid atelectasis and improve oxygenation in patients during general anesthesia but affects cardiac pressures, volumes, and loading conditions through cardiorespiratory interactions. PEEP may therefore alter stroke work, which is the area enclosed by the pressure-volume loop and corresponds to the external work performed by the ventricles to eject blood. The low-pressure right ventricle may be even more susceptible to PEEP than the left ventricle. The authors hypothesized that increasing levels of PEEP would reduce stroke work in both ventricles.

METHODS

This was a prospective, observational, experimental study. Six healthy female pigs of approximately 60 kg were used. PEEP was stepwise increased from 0 to 5, 7, 9, 11, 13, 15, 17, and 20 cm H2O to cover the clinical spectrum of PEEP. Simultaneous, biventricular invasive pressure-volume loops, invasive blood pressures, and ventilator data were recorded.

RESULTS

Increasing PEEP resulted in stepwise reductions in left (5,740 ± 973 vs. 2,303 ± 1,154 mmHg · ml; P < 0.001) and right (2,064 ± 769 vs. 468 ± 133 mmHg · ml; P < 0.001) ventricular stroke work. The relative stroke work reduction was similar between the two ventricles. Left ventricular ejection fraction, afterload, and coupling were preserved. On the contrary, PEEP increased right ventricular afterload and caused right ventriculo-arterial uncoupling (0.74 ± 0.30 vs. 0.19 ± 0.13; P = 0.01) with right ventricular ejection fraction reduction (64 ± 8% vs. 37 ± 7%, P < 0.001).

CONCLUSIONS

A stepwise increase in PEEP caused stepwise reduction in biventricular stroke work. However, there are important interventricular differences in response to increased PEEP levels. PEEP increased right ventricular afterload leading to uncoupling and right ventricular ejection fraction decline. These findings may support clinical decision-making to further optimize PEEP as a means to balance between improving lung ventilation and preserving right ventricular function.

EDITOR’S PERSPECTIVE

Cardiopulmonary interactions-which monitoring tools to use?

Heart-lung interactions occur due to the mechanical influence of intrathoracic pressure and lung volume changes on cardiac and circulatory function. These interactions manifest as respiratory fluctuations in venous, pulmonary, and arterial pressures, potentially affecting stroke volume. In the context of functional hemodynamic monitoring, pulse or stroke volume variation (pulse pressure variation or stroke volume variability) are commonly employed to assess volume or preload responsiveness. However, correct interpretation of these parameters requires a comprehensive understanding of the physiological factors that determine pulse pressure and stroke volume. These factors include pleural pressure, venous return, pulmonary vessel function, lung mechanics, gas exchange, and specific cardiac factors. A comprehensive knowledge of heart-lung physiology is vital to avoid clinical misjudgments, particularly in cases of right ventricular (RV) failure or diastolic dysfunction. Therefore, when selecting monitoring devices or technologies, these factors must be considered. Invasive arterial pressure measurements of variations in breath-to-breath pressure swings are commonly used to monitor heart-lung interactions. Echocardiography or pulmonary artery catheters are valuable tools for differentiating preload responsiveness from right ventricular failure, while changes in diastolic function should be assessed alongside alterations in airway or pleural pressure, which can be approximated by esophageal pressure. In complex clinical scenarios like ARDS, combined forms of shock or right heart failure, additional information on gas exchange and pulmonary mechanics aids in the interpretation of heart-lung interactions. This review aims to describe monitoring techniques that provide clinicians with an integrative understanding of a patient's condition, enabling accurate assessment and patient care.

Echocardiographic assessment of pulmonary capillary wedge pressure by E/e' ratio: A systematic review and meta-analysis

BACKGROUND

The reliability of echocardiographic methods for the assessment of pulmonary capillary wedge pressure (PCWP) is still a matter of debate. Since its first description, the E/e' ratio has been regarded as a suitable method. The aim of this study is to evaluate the evidence of how E/e' effectively estimates PCWP and its diagnostic accuracy for elevated PCWP.

METHODS

We systematically searched MEDLINE and Embase databases for studies investigating the agreement between E/e' and PCWP, from inception to July 2022. We limited our research to studies published from 2010 to date. Retrospective studies and studies on non-adult population were excluded.

RESULTS

Twenty-eight studies, involving a total of 1964 subjects, were included. The pooled analysis of the studies showed a modest correlation between E/e' and PCWP. The weighted average correlation (r) is 0.43 (95% CI 0.37-0.48). We found no significant differences between reduced and preserved ejection fraction groups. Thirteen studies analysed the diagnostic accuracy of E/e' for elevated PCWP. The AUC of receiver operating characteristic curves for PCWP >15 mmHg was estimated in the interval 0.6-0.91.

DISCUSSION

E/e' appears to have a modest correlation with PCWP and an acceptable accuracy for elevated PCWP. (PROSPERO number, CRD42022333462).