Ventricular-Arterial Coupling: A Predictor of Post-Induction Hypotension

Overview

Post-induction hypotension (PIH) is a common occurrence during the period from induction of general anesthesia to initiation of incision. PIH has been identified as an independent risk factor for postoperative major complications. Identifying high-risk patients for PIH could potentially help prevent its occurrence. Several risk factors associated with PIH have been identified, including patient conditions and use of specific anesthetic agents. Ventricular-arterial coupling (VAC) is evaluated using the ratio Ea/Ees and represents the interaction between the left ventricle (LV) and the arterial system. It reflects how changes in LV contractility (Ees) and changes in arterial load (Ea) work together to maintain optimal LV performance. A study aims to investigate the relationship between preoperative Ea/Ees ratio and the incidence of PIH (defined as MAP \< 65 mmHg).

Post-induction hypotension (PIH) is a common event due to general anesthesia in patients undergoing surgery. It is described as hypotension occurring during the period from induction of general anesthesia to initiation of incision. A universal definition of intraoperative hypotension is lacking, leading to inconsistent rates of occurrence for PIH. According to Yoshimura et al., PIH occurs in 34% of patients using the mean arterial pressure (MAP) definition of \< 55 mmHg, whereas Maheshwari found PIH in 53% of patients using a MAP definition of \< 65 mmHg. Furthermore, Maheshwari et al. demonstrated that PIH was an independent risk factor for postoperative major complications such as myocardial injury, cerebrovascular events, and acute kidney injury. If high-risk patients for PIH could be identified we might potentially prevent PIH. In a systematic review, Chen et al. pointed out that the risk factors associated with PIH were ASA (American Society of Anesthesiologists) III-V, advanced age, emergency cases, hypovolaemia, long-term use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, use of propofol and high-dose of opioid. This study suggests that PIH may be the result of an interaction between the anesthetic agent and the cardiovascular condition of the patient. Conditions such as moderate-to-severe aortic regurgitation, moderate-to-severe mitral regurgitation, regional wall motion abnormalities, and echocardiography findings (e.g. elevated ratio of peak early diastolic transmitral flow velocity to annular velocity) have been identified as PIH-independent risk factors. End-systolic elastance (Ees) is a measure of the contractile state of the left ventricle (LV). It represents the relationship between LV end-systolic pressure (LVESP) and end-systolic volume (ESV). Effective arterial elastance (Ea) is a measure of the total arterial load on the LV and is calculated as the ratio of LVESP to stroke volume (SV). Ventricular-arterial coupling (VAC), assessed by the ratio Ea/Ees, describes the interaction between the LV and arterial system. VAC reflects the interplay between the changes in LV contractility (Ees) and changes in arterial load (Ea) to maintain optimal LV performance. Aktas et al. analyzed Ea as a predictor of PIH. The results of this study showed that pre-induction Ea had excellent predictability of hypotension. However, Ees values were not determined, thus making it speculative to conclude that pre-induction VAC is impaired in patients with high Ea. There are no studies available that assessed the role of preoperative VAC in predicting PIH. Therefore, we will investigate the relationship between the preoperative Ea/Ees ratio and the incidence of PIH (: hypotension being defined as MAP \< 65 mmHg).