Respiratory-Cardiovascular Interactions During Mechanical Ventilation: Physiology and Clinical Implications

Intubation and Mechanical Ventilation in Patients with Acute Pulmonary Embolism: A Scoping Review

OBJECTIVES

High-risk acute pulmonary embolism (PE) is associated with significant mortality and may require emergency endotracheal intubation and mechanical ventilation. Intubation and ventilation are thought to exacerbate cardiorespiratory instability. Our purpose was to conduct a systematic literature review to identify studies investigating peri-intubation events in acute PE.

METHODS

A systematic search of Medline, Embase, Web of Science, Cumulative Index to Nursing and Allied Health Literature, and Cochrane Library was performed. Results were screened by two independent observers. Studies reporting on intubation and positive pressure ventilation in acute PE patients were included. The primary outcome was adverse events during the peri-intubation period. Data was synthesized and an assessment of risk of bias was conducted. The review was registered on PROSPERO (CRD42023444483).

RESULTS

4100 unique articles were screened. Three retrospective studies comprising 104 patients with acute PE met criteria and were included. Peri-intubation, hemodynamic collapse was observed in 19%-28% of cases. Patients with hemodynamic collapse exhibited higher rates of echocardiographic RV dysfunction.

CONCLUSIONS

Peri-intubation adverse events are common in patients with acute PE. Current evidence is limited and highlights the need for further research to optimize management of respiratory failure in acute PE and patient selection for intubation to improve patient outcomes.

Association of point-of-care lung ultrasound findings with 30-day pulmonary complications after cardiac surgery: A prospective cohort study

Background

Several studies have shown that bedside lung ultrasound findings in postanaesthesia care units (PACUs) and intensive care units (ICUs) correlate with postoperative pulmonary complications(PPCs) after noncardiac major surgery. However, it remains unclear whether lung ultrasound findings can be used as early predictors of PPCs in patients undergoing cardiac surgery. The main aim of our study was to evaluate the relationship between early postoperative point-of-care lung ultrasound findings and PPCs after cardiac surgery.

Methods

Two board-certified physicians performed a point-of-care pulmonary ultrasound on cardiac surgery patients approximately 2 h after the patient was admitted to the ICU. Pulmonary complications occurring within 30 days postoperatively were recorded. Logistic regression modeling was used to analyze the relationship between lung ultrasound findings and PPCs.

Results

PPCs occurred in 61 (30.9 %) of the 197 patients. Lung ultrasound scores(LUS), number of lung consolidation(NLC), and depth of pleural effusion(DPE) were more significant in patients who developed PPCs (P < 0.001). According to the multivariate analysis, NLC≥3(aOR 2.71,95%CI 1.14-6.44; p = 0.024)and DPE >0.95(aOR 3.79,95%CI 1.60-8.99; p = 0.002) were found to be independently associated with PPCs during this study.

Conclusions

Our study demonstrated that DPE >0.95 and NLC ≥3 were associated with PPCs after cardiac surgery based on bedside lung ultrasound findings in the ICU. When these signs manifest perioperatively, the surgeon should be alerted and the necessary steps should be taken, especially if they present simultaneously.

How Would I Treat My Own Chronic Thromboembolic Pulmonary Hypertension in the Perioperative Period?

Chronic thromboembolic pulmonary hypertension (CTEPH) results from an incomplete resolution of acute pulmonary embolism, leading to occlusive organized thrombi, vascular remodeling, and associated microvasculopathy with pulmonary hypertension (PH). A definitive CTEPH diagnosis requires PH confirmation by right-heart catheterization and evidence of chronic thromboembolic pulmonary disease on imaging studies. Surgical removal of the organized fibrotic material by pulmonary endarterectomy (PEA) under deep hypothermic circulatory arrest represents the treatment of choice. One-third of patients with CTEPH are not deemed suitable for surgical treatment, and medical therapy or interventional balloon pulmonary angioplasty presents alternative treatment options. Pulmonary endarterectomy in patients with technically operable disease significantly improves symptoms, functional capacity, hemodynamics, and quality of life. Perioperative mortality is <2.5% in expert centers where a CTEPH multidisciplinary team optimizes patient selection and ensures the best preoperative optimization according to individualized risk assessment. Despite adequate pulmonary artery clearance, patients might be prone to perioperative complications, such as right ventricular maladaptation, airway bleeding, or pulmonary reperfusion injury. These complications can be treated conventionally, but extracorporeal membrane oxygenation has been included in their management recently. Patients with residual PH post-PEA should be considered for medical or percutaneous interventional therapy.

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

Acute dyspnea in the emergency department: a clinical review

Acute dyspnea represents one of the most frequent symptoms leading to emergency room evaluation. Its significant prognostic value warrants a careful evaluation. The differential diagnosis of dyspnea is complex due to the lack of specificity and the loose association between its intensity and the severity of the underlying pathological condition. The initial assessment of dyspnea calls for prompt diagnostic evaluation and identification of optimal monitoring strategy and provides information useful to allocate the patient to the most appropriate setting of care. In recent years, accumulating evidence indicated that lung ultrasound, along with echocardiography, represents the first rapid and non-invasive line of assessment that accurately differentiates heart, lung or extra-pulmonary involvement in patients with dyspnea. Moreover, non-invasive respiratory support modalities such as high-flow nasal oxygen and continuous positive airway pressure have aroused major clinical interest, in light of their efficacy and practicality to treat patients with dyspnea requiring ventilatory support, without using invasive mechanical ventilation. This clinical review is focused on the pathophysiology of acute dyspnea, on its clinical presentation and evaluation, including ultrasound-based diagnostic workup, and on available non-invasive modalities of respiratory support that may be required in patients with acute dyspnea secondary or associated with respiratory failure.