Intraoperative Hypotension and Myocardial Infarction Development Among High-Risk Patients Undergoing Noncardiac Surgery

A Nested Case-Control Study

Linn Hallqvist, MD, PhD Student, DESA; Fredrik Granath, PhD; Michael Fored, MD, PhD; Max Bell, MD, PhD

Disclosures

Anesth Analg. 2021;133(1):6-15. 

In This Article

Results

Study Participants

In total, 326 cases met the inclusion criteria and were successfully matched with 326 controls (Figure 1). Table 1 shows baseline and perioperative characteristics. Cases had more DM and more frequently previous MI, even though cardiovascular disease was a matching criterion and cases with a MI within 30 days before surgery were excluded. MI cases had significantly higher preoperative BP (150 vs 133 mm Hg) than controls. Preoperative laboratory status (Hb and creatinine) were equal, as were intraoperative anesthetic procedures and duration of surgery. Intraoperative events—blood loss, low Hb levels, excessive fluid balance—were more frequent in MI cases than in controls (P < .001). MI cases more commonly developed AKI, fulfilling the Kidney Disease: Improving Global Outcomes (KDIGO) criteria[23] stage 1 within 2 postoperative days; 109 (39%) vs 34 (12%) among controls (P < .001). The distribution of MI type among cases was 59 (18%) type 1 and 267 (82%) type 2. Median time from surgery to MI diagnosis was 2 days; 75% were diagnosed within a week of surgery.

Outcomes

Presented in Table 2 and Figure 2, risk estimates increased gradually with increasing intraoperative BP drop. An intraoperative hypotensive reduction of 41–50 mm Hg, from individual baseline systolic arterial pressure (SAP), was associated with more than tripled MI risk, OR = 3.42 (95% CI, 1.13–10.3), and a hypotensive event >50 mm Hg with considerable increased odds, OR = 22.6 (95% CI, 7.69–66.2). These risk estimates are derived after adjustment for preoperative covariates: high BP (SAP ≥140 mm Hg), DM, and IHD and intraoperative risk events: blood loss (>1800 mL), Hb <85 g/L, hypoxia (SaO 2 <90%), and fluid balance (>2000 mL).

Figure 2.

Odds ratios (log scale) of MI in relation to intraoperative hypotension. *Decrease in SBP (mm Hg) from baseline for >5 min. Adjusted for preoperative risk factors: SBP, IHD, and DM. Further adjusted for intraoperative risk factors: blood loss (>1800 mL), Hb <85 g/L, hypoxia (SaO2 <90%), and fluid balance (>2000 mL). DM indicates diabetes mellitus; Hb, hemoglobin; IHD, ischemic heart disease; MI, myocardial infarction; SaO2, arterial oxygen saturation; SBP, systolic blood pressure.

The right panel of Table 3 displays absolute risks of MI in relation to IOH together with estimated incidence of IOH in different risk groups. High absolute excess risks were observed among patients with a SBP drop >50 mm Hg as compared to patients with a SBP drop ≤40 mm Hg; patients with very high baseline risk increased their risk from 3.6 to 68 per 1000 operations, patients with high risk increased from 0.5 to 10 and the corresponding increase in lower-risk patients was 0.1 to 1.8. The incidence of high-risk hypotensive events (ie, SBP drop >50 mm Hg) decreased with increasing risk factor burden (P = .005). The left panel of Table 3, displaying Orbit study results,[18] shows that 19% of surgeries are characterized as very high risk, with 76% of MI's occurring in these patients. The corresponding fraction among cases in this study was 75%.

Absolute decrease in mm Hg, from individual preoperative BP baseline, was selected as main IOH definition. Multivariable comparison of the 3 final models based on different IOH definitions yielded similar odds estimates. The AIC test favored the models with IOH defined as a relative to baseline measure, ahead of the model with absolute BP thresholds (AIC value 226), while data do not clearly support discrimination between the models based on absolute and relative change from baseline BP (AIC value 214 vs 210); results are shown in Supplemental Digital Content 3, Table 2, http://links.lww.com/AA/D363.

Results From Sensitivity Analyses

There was no evidence of effect modification between preoperative BP or intraoperative tachycardia and IOH. Although not significant, a more pronounced effect of IOH in higher-risk patients compared to lower-risk patients was observed, as in MI development on postoperative days 1–2 compared to later diagnosed MI cases; results are detailed in Supplemental Digital Content 3, Table 1, http://links.lww.com/AA/D363. None of the interaction tests involving these covariates were significant.

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