Factors Affecting Cardiovascular Physiology in Cardiothoracic Surgery: Implications for Lumped-Parameter Modeling

A predictive patient-specific computational model of coronary artery bypass grafts for potential use by cardiac surgeons to guide selection of graft configurations

Cardiac surgeons face a significant degree of uncertainty when deciding upon coronary artery bypass graft configurations for patients with coronary artery disease. This leads to significant variation in preferred configuration between different surgeons for a particular patient. Additionally, for the majority of cases, there is no consensus regarding the optimal grafting strategy. This situation results in the tendency for individual surgeons to opt for a “one size fits all” approach and use the same grafting configuration for the majority of their patients neglecting the patient-specific nature of the diseased coronary circulation. Quantitative metrics to assess the adequacy of coronary bypass graft flows have recently been advocated for routine intraoperative use by cardiac surgeons. In this work, a novel patient-specific 1D-0D computational model called “COMCAB” is developed to provide the predictive haemodynamic parameters of functional graft performance that can aid surgeons to avoid configurations with grafts that have poor flow and thus poor patency. This model has significant potential for future expanded applications.

Hemodynamic Response to Device Titration in the Shunted Single Ventricle Circulation: A Patient Cohort Modeling Study

Clinical outcomes of ventricular assist device (VAD) support for shunted single ventricle patients trail the larger population due in part to the challenges in optimizing VAD support and balancing systemic and pulmonary circulations. We sought to understand the response to VAD titration in the shunted circulation using a lumped-parameter network modeling six patient-specific clinical cases. Hemodynamic data from six patients (mean body surface area = 0.30 m2) with a systemic-to-pulmonary shunt was used to construct simulated cases of heart failure and hemodynamic response to increasing VAD flow from 5 to 10 L/min/m2. With increasing VAD flow, the pulmonary arterial pressure stayed relatively constant in five patient cases and increased in one patient case. The mean VAD flow needed to attain an arterial-venous O2 saturation difference of 30% was 6.5 ± 1.2 L/min/m2, which is higher than that in the equivalent nonshunted scenario due to the partial diversion of flow to the pulmonary circulation. The hemodynamic responses to VAD support can vary significantly between specific patient cases; therefore hemodynamic modeling may help guide an individualized approach to perioperative VAD management in the shunted single-ventricle circulation and to understand the patients who may benefit the most from VAD support.

Contrasting effects of three breathing techniques on pulmonary function, functional capacity and daily life functional tasks in patients following valve replacement surgery- A pilot randomized clinical trial

Background

Valve replacement surgeries affect the physiological mechanisms of patients leading to various postoperative pulmonary complications. Lung expansion therapy consisting of numerous techniques is routinely used for the prevention and treatment of these complications.

Objectives

Our study aimed to compare the effects of diaphragmatic breathing (DB), flow (FS) and volume-oriented incentive spirometer (VS) in patients following valve replacement surgery.

Methods

29 patients posted valve replacement surgeries were randomly assigned to VS, FS and DB groups. Patients underwent preoperative training and seven-day rehabilitation post-surgery. Pulmonary function tests were performed before surgery and for seven days afterward. On the seventh postoperative day, patients performed a six-minute walk test and completed a functional difficulties questionnaire (FDQ).

Results

Pulmonary function test values reduced in all three groups postoperatively when compared to the preoperative values but improved by the seventh postoperative day (p < 0.05). On comparing the seventh postoperative day values to the preoperative values, the VS group had no significant difference (p = 1.00) (Forced Vital Capacity- % change: DB-37.76, VS-1.59, FS-27.98), indicating that the value had nearly returned to the baseline. As compared to the DB and FS groups, FVC showed a greater improvement in the VS group (p = 0.01 and p = 0.06 respectively). No significant differences were observed between groups for distance walked (p > 0.05), however, FDQ scores demonstrated positive changes in favor of VS when contrasted with FS or DB (p < 0.05).

Conclusion

Diaphragmatic breathing, flow or volume-oriented spirometer could improve pulmonary function in the postoperative period. The volume-oriented spirometer, however, was found to be the most beneficial among the three techniques in improving patients’ pulmonary function and daily life functional tasks. Further research is warranted to confirm these findings.

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The present pilot randomized clinical trial is the first of a kind that exhibits the effects of three breathing exercises in patients following valve replacement cardiac surgery.

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The study demonstrates the individual and contrasting effects of volume spirometry, volume spirometry and deep breathing exercise between preoperative day until postoperative day 7 in terms of pulmonary function and function activities.

Does thoracic epidural anaesthesia constitute over-instrumentation in video- and robotic-assisted thoracoscopic lung parenchyma resections?

PURPOSE OF REVIEW

Effective and sustained perioperative analgesia in thoracic surgery and pulmonary resection is beneficial to patients by reducing both postoperative pulmonary complications and the incidence of chronic pain. In this review, the indication of thoracic epidural anaesthesia in video- (VATS) and robotic-assisted (RATS) thoracoscopy shall be critically objectified and presented in a differentiated way.

RECENT FINDINGS

Pain following VATS and RATS has a negative influence on lung function by inhibiting deep respiration, suppressing coughing and secretion and favours the development of atelectasis, pneumonia and other postoperative pulmonary complications.In addition, inadequate pain therapy after these procedures may lead to chronic pain.

SUMMARY

Since clear evidence-based recommendations for optimal postoperative analgesia are still lacking in VATS and RATS, there can be no universal recommendation that fits all centres and patients. In this context, thoracic epidural analgesia is the most effective analgesia procedure for perioperative pain control in VATS and RATS-assisted surgery for patients with pulmonary risk factors.