Abstract and Introduction
Background: Hemodynamic instability during anesthesia and surgery is common and associated with cardiac morbidity and mortality. Information is needed regarding optimal blood pressure (BP) threshold in the perioperative period. Therefore, the effect of intraoperative hypotension (IOH) on risk of perioperative myocardial infarction (MI) was explored.
Methods: A nested case-control study with patients developing MI <30 days postsurgery matched with non–MI patients, sampled from a large surgery cohort. Study participants were adults undergoing noncardiac surgery at 3 university hospitals in Sweden, 2007–2014. Matching criteria were age, sex, American Society of Anesthesiologists (ASA) physical status, cardiovascular disease, hospital, year-, type-, and extent of surgery. Medical records were reviewed to validate MI diagnoses and retrieve information on comorbid history, baseline BP, laboratory and intraoperative data. Main exposure was IOH, defined as a decrease in systolic blood pressure (SBP), in mm Hg, from preoperative individual resting baseline lasting at least 5 minutes. Outcomes were acute MI, fulfilling the universal criteria, subclassified as type 1 and 2, occurring within 30 days and mortality beyond 30 days among case and control patients. Conditional logistic regression assessed the association between IOH, decrease in SBP from individual baseline, and perioperative MI. Mortality rates were estimated using Cox proportional hazards. Relative risk estimates are reported as are the corresponding absolute risks derived from the well-characterized source population.
Results: A total of 326 cases met the inclusion criteria and were successfully matched with 326 controls. The distribution of MI type was 59 (18%) type 1 and 267 (82%) type 2. Median time to MI diagnosis was 2 days; 75% were detected within a week of surgery. Multivariable analysis acknowledged IOH as an independent risk factor of perioperative MI. IOH, with reduction of 41–50 mm Hg, from individual baseline SBP, was associated with a more than tripled increased odds, odds ratio (OR) = 3.42 (95% confidence interval [CI], 1.13–10.3), and a hypotensive event >50 mm Hg with considerably increased odds in respect to MI risk, OR = 22.6, (95% CI, 7.69–66.2). In patients with a very high-risk burden, the absolute risk of an MI diagnosis increased from 3.6 to 68 per 1000 surgeries.
Conclusions: In patients undergoing noncardiac surgery, IOH is a possible contributor to clinically significant perioperative MI. The high absolute MI risk associated with IOH, among a growing population of patients with a high-risk burden, suggests that increased vigilance of BP control in these patients may be beneficial.
Hypotension is common after the anesthetic induction, and may result from blood loss, fluid shifts, and cytokine release perioperatively. Hemodynamic instability is associated with perioperative cardiac, kidney and cerebral injury, and increased mortality in high-risk surgical patients.[2–6] Consensus is lacking regarding optimal blood pressure (BP) thresholds to maintain adequate organ perfusion and oxygenation during anesthesia and surgery. Various definitions of perioperative hypotensive events exist. Multiple studies with binary cut-offs show associations with increased risk of organ damage and mortality.[2–4] Individualized intraoperative hypotension (IOH) definitions are theoretically better when investigating the risk of perioperative myocardial[5,7] and kidney injury. Higher BP may be beneficial for certain high-risk patients.[2,3,7,9]
Perioperative myocardial infarction (MI) diagnosing is challenging since ischemic symptoms often are disguised.[6,10,11] MI is traditionally divided into different types: MI type 1 from occlusive coronary artery disease, plaque rupture, and thrombosis, and MI type 2, characterized by a supply-demand imbalance resulting in myocardial ischemia. Isolated cardiac troponin elevation, without other features of infarction, that is, ischemic electrocardiogram (ECG) changes to the ST segment and T-wave or symptoms, is termed myocardial injury. Perioperatively, hemodynamic instability is a presumed mechanism.[2,4–6] Perioperative myocardial injury and infarction are associated with increased mortality.[11,14–16]
We investigated whether IOH is an independent risk factor for acute perioperative MI, defined according to the third universal definition, in a noncardiac high-risk surgical population. Data on the frequency of MI type 1 versus type 2, and on intraoperative events possibly associated with the development of MI; tachycardia, hypoxia, loss of blood, and hemoglobin (Hb) were retrieved.
Anesth Analg. 2021;133(1):6-15. © 2021 International Anesthesia Research Society