Understanding Physiology and Using Technology to Care for Challenging Patients

Pediatric and adult cardiac anesthesiologists are often required to take care of the most complex patients presenting for some of the highest acuity surgeries. These patients, and the planned surgical interventions, pose unique challenges, and thus, understanding the pathophysiology of these intricate conditions and appropriately utilizing technology to assist in their management is of paramount importance. In this issue of Seminars in Cardiothoracic and Vascular Anesthesia (SCVA), we present Original Research regarding clinical inquiry into using oxygen as a pulmonary vasodilator in adult patients with pulmonary hypertension due to valvular heart disease and delineating the relationship between venous-arterial carbon dioxide difference obtained from peripheral venous blood and mixed venous blood. Next, we provide a thorough review of Shone’s Complex and the perioperative challenges it presents, along with a review that delves into the perioperative considerations for modern leadless pacemakers. Finally, we present 2 case reports demonstrating perioperative dilemmas solved with clever inspiration and resourcefulness, including axillary placement of a percutaneous left ventricular assist device under monitored anesthesia care and utilization of a bronchial blocker through a double-lumen endotracheal tube to assist lung isolation.

In the first Original Research article ¹ the authors report results assessing the use of 100% fraction of inspired oxygen (FiO2) as a pulmonary vasodilator in patient with pulmonary hypertension due to valvular heart disease. Fifty-seven adult patients (>18 years) with right ventricular systolic pressure > 40 mm Hg (assessed by transthoracic echocardiography) scheduled for elective valvular heart surgery were included in the study. They observed a significant decrease of mean pulmonary artery pressure, pulmonary vascular resistance, transpulmonary gradient, and diastolic pulmonary gradient with 100% FiO2. However, cardiac output was not significantly changed, all measurements obtained prior to incision. Interestingly, patients exhibiting combined post and pre-capillary pulmonary hypertension and patients with idiopathic post-capillary pulmonary hypertension demonstrated a comparable decline in mean pulmonary artery pressure, pulmonary vascular resistance, transpulmonary gradient, and diastolic pulmonary gradient. In a prior series of adult patients with pulmonary hypertension, 100% FiO2 also led to a reduction in mean arterial pressure and pulmonary vascular resistance, regardless of etiology. ² These findings further characterize the potential of concentrated oxygen as a selective pulmonary vasodilator in patients with pulmonary hypertension due to valvular heart disease. Continued investigation is needed to determine risk-benefit relationship and evaluate effects of oxidative stress with protracted hyperoxia.

The second Original Research article ³ focuses on the relationship and agreement between venous-arterial CO2 difference obtained from peripheral venous blood (Pv-aCO2p) and mixed venous blood (Pv-aCO2) in the patients with septic shock from respiratory, abdominal, neurologic, or idiopathic sources. Pv-aCO2 has shown clinical significance in its ability to delineate between high and low cardiac output conditions.^4-6 Multiple studies have also confirmed the role of Pv-aCO2 in identifying septic patients in which tissue metabolic demands are not being met due to inadequate cardiac output.^7-9 Eighteen patients were enrolled for 38 blood gas assays over the study period. The study demonstrated a linear relationship between Pv-aCO2p and Pv-aCO2 with high correlation. This finding potentially makes the use of peripheral venous blood a substitute for mixed venous blood, negating the need of pulmonary artery catheter placement, and allowing for an individualized approach to the septic patient, if confirmed in larger populations. However, to apply this measure to clinical practice, it is crucial to evaluate the agreement between the two values. The analysis showed decent agreement, but the Giavarina Analysis was +55% showing Pv-aCO2p tends to overestimate the actual CO2 gap. This necessitates further controlled clinical trials to investigate Pv-aCO2p in different clinical environments and larger populations, until then, Pv-aCO2 obtained via pulmonary artery catheter remains the standard to determine adequate cardiac output in septic patients.

Dr John Shone and colleagues, in 1963, first described a combination of four left sided, obstructive anomalies, which would become known as Shone’s complex. The first Review Article of the issue, focuses on Shone’s complex and its’ constellation of anomalies, including parachute mitral valve, supravalvular ring of the left atrium, subaortic stenosis, and coarctation of the aorta. These anomalies produce both left ventricular inflow and outflow obstruction, resulting in complex hemodynamic difficulties requiring careful management and surgical decision making. The review focuses on the distinct anatomy, physiology, and anesthetic management of patients with this unique syndrome accounting for 0.6% of all cases of congenital cardiac anomalies.^10,11

Few things can be said to have progressed as quickly as medicine over the last few decades, in particular, pacemaker technology has evolved tremendously. The second Review Article of the current issue focuses on the perioperative considerations for modern leadless pacemakers. Leadless pacemakers have only continued to become more prevalent since 2016, when they were initially approved by the Food and Drug Administration. Their direct percutaneous implantation into the septal wall of the right ventricle obviates the need for traditional pacemaker leads and generator pocket and decreases complication risk.^12-14 Recent advances has enabled leadless synchronized atrioventricular pacing and dual chamber pacing further expanding their indications. ¹⁵ Currently, leadless pacemakers are unable to perform cardiac resynchronization therapy, anti-tachycardia pacing, or cardioverter-defibrillator therapies.^16,17 This review provides an overview of the technology, evidence base, current indications, and unique perioperative considerations for the modern leadless pacemakers. ¹⁸

Finally, this issue is completed with 2 case reports that perfectly demonstrate the ingenuity our specialty requires, when taking care of the sickest patients and facing unique perioperative dilemmas. The first case ¹⁹ demonstrates the feasibility of placing an axillary Impella 5.5 left ventricular assist device under monitored anesthesia care and local anesthetic infiltration. This technique was used to avoid general anesthesia and the sequelae of positive pressure ventilation in a patient with severe cardiopulmonary failure awaiting simultaneous heart and lung transplantation. The second case ²⁰ describes the tribulations that can often be encountered while attempting to provide adequate lung isolation for minimally invasive thoracic surgeries. Common approaches include double-lumen endotracheal tubes, or the use of an endobronchial blocker placed through a single-lumen endotracheal tube. This case exhibits the use of a unique endobronchial blocker positioned through a left-sided double-lumen endotracheal tube after failure to obtain adequate lung isolation with the tube alone.

To summarize, innovation and the advancement of medical knowledge is paramount to the goals and objectives of the Seminars in Cardiothoracic and Vascular Anesthesia. The original research, review articles, and case reports reflect the continual devotion of anesthesiologists to ultimately enhance patient outcomes and improve healthcare overall.