Association between Intraoperative Hypotension and Myocardial Injury after Vascular Surgery

Incidence and predictors of perioperative myocardial infarction in patients undergoing non-cardiac surgery in a tertiary care hospital

Background

The stress in the perioperative period is compounded by unpredictable and un-physiological changes in sympathetic tone, cardiovascular performance, coagulation and inflammatory responses, all of which in turn lead to alterations in plaque morphology predisposing to perioperative myocardial infarction (PMI). PMI has a considerable morbidity and mortality in patients undergoing not only high risk surgery, but also even with minor surgical interventions.

Objective

To study the incidence of PMI and its predictors in patients undergoing non-cardiac surgery in a tertiary care hospital.

Materials and methods

Patients undergoing non-cardiac surgery were included in this prospective single-center observational study. The revised cardiac risk index (RCRI) was used for risk stratification. ECG monitoring was done for all patients. For patients suggestive of acute myocardial ischemia, echocardiography and serum troponin were evaluated. The patient was labeled as having a PMI if there was raised troponin level along with any one evidence of myocardial ischemia (symptoms, ECG changes or imaging results) and in these patients the factors predisposing to PMI were evaluated. All patients in the study were followed up to 30 days.

Results

Of the 525 patients analyzed, 33 patients (6.28%) had a PMI. Twelve out of the 33 (36.36%) PMI patients died within 30 days following surgery. Patients undergoing high risk surgery, smokers and patients with a past history of ischemic heart disease (IHD) were found to be at higher risk of developing PMI. The ASA physical status classification and the RCRI proved to be good predictors of PMI. Most of the PMI events (72.7%) occurred within 48 hours of surgery.

Conclusion

PMI is a dreaded complication associated with a very high mortality. High risk surgery, smoking and past history of ischemic heart disease were independent predictors of PMI. The RCRI is a useful tool in pre-operative risk stratification of patients.

Physician-Directed Versus Computerized Closed-Loop Control of Blood Pressure Using Phenylephrine in a Swine Model

BACKGROUND

Vasopressors provide a rapid and effective approach to correct hypotension in the perioperative setting. Our group developed a closed-loop control (CLC) system that titrates phenylephrine (PHP) based on the mean arterial pressure (MAP) during general anesthesia. As a means of evaluating system competence, we compared the performance of the automated CLC with physicians. We hypothesized that our CLC algorithm more effectively maintains blood pressure at a specified target with less blood pressure variability and reduces the dose of PHP required.

METHODS

In a crossover study design, 6 swine under general anesthesia were subjected to a normovolemic hypotensive challenge induced by sodium nitroprusside. The physicians (MD) manually changed the PHP infusion rate, and the CLC system performed this task autonomously, adjusted every 3 seconds to achieve a predetermined MAP.

RESULTS

The CLC maintained MAP within 5 mm Hg of the target for (mean ± standard deviation) 93.5% ± 3.9% of the time versus 72.4% ± 26.8% for the MD treatment (P = .054). The mean (standard deviation) percentage of time that the CLC and MD interventions were above target range was 2.1% ± 3.3% and 25.8% ± 27.4% (P = .06), respectively. Control statistics, performance error, median performance error, and median absolute performance error were not different between CLC and MD interventions. PHP infusion rate adjustments by the physician were performed 12 to 80 times in individual studies over a 60-minute period. The total dose of PHP used was not different between the 2 interventions.

CONCLUSIONS

The CLC system performed as well as an anesthesiologist totally focused on MAP control by infusing PHP. Computerized CLC infusion of PHP provided tight blood pressure control under conditions of experimental vasodilation.

Safe Brain Tumor Resection Does not Depend on Surgery Alone - Role of Hemodynamics

Aim of this study was to determine if perioperative hemodynamics have an impact on perioperative infarct volume and patients’ prognosis. 201 cases with surgery for a newly diagnosed or recurrent glioblastoma were retrospectively analyzed. Clinical data and perioperative hemodynamic parameters, blood tests and time of surgery were recorded. Postoperative infarct volume was quantitatively assessed by semiautomatic segmentation. Mean diastolic blood pressure (dBP) during surgery (rho −0.239, 95% CI −0.11 – −0.367, p = 0.017), liquid balance (rho 0.236, 95% CI 0.1–0.373, p = 0.017) and mean arterial pressure (MAP) during surgery (rho −0.206, 95% CI −0.07 – −0.34, p = 0.041) showed significant correlation to infarct volume. A rank regression model including also age and recurrent surgery as possible confounders revealed mean intraoperative dBP, liquid balance and length of surgery as independent factors for infarct volume. Univariate survival analysis showed mean intraoperative dBP and MAP as significant prognostic factors, length of surgery also remained as significant prognostic factor in a multivariate model. Perioperative close anesthesiologic monitoring of blood pressure and liquid balance is of high significance during brain tumor surgery and should be performed to prevent or minimize perioperative infarctions and to prolong survival.

The SLUScore: A Novel Method for Detecting Hazardous Hypotension in Adult Patients Undergoing Noncardiac Surgical Procedures

BACKGROUND

It has been suggested that longer-term postsurgical outcome may be adversely affected by less than severe hypotension under anesthesia. However, evidence-based guidelines are unavailable. The present study was designed to develop a method for identifying patients at increased risk of death within 30 days in association with the severity and duration of intraoperative hypotension.

METHODS

Intraoperative mean arterial blood pressure recordings of 152,445 adult patients undergoing noncardiac surgery were analyzed for periods of time accumulated below each one of the 31 thresholds between 75 and 45 mm Hg (hypotensive exposure times). In a development cohort of 35,904 patients, the associations were sought between each of these 31 cumulative hypotensive exposure times and 30-day postsurgical mortality. On the basis of covariable-adjusted percentage increases in the odds of mortality per minute elapsed of hypotensive exposure time, certain sets of exposure time limits were calculated that portended certain percentage increases in the odds of mortality. A novel risk-scoring method was conceived by counting the number of exposure time limits that had been exceeded within each respective set, one of them being called the SLUScore. The validity of this new method in identifying patients at increased risk was tested in a multicenter validation cohort consisting of 116,541 patients from Cleveland Clinic, Vanderbilt and Saint Louis Universities. Data were expressed as 95% confidence interval, P < .05 considered significant.

RESULTS

Progressively greater hypotensive exposures were associated with greater 30-day mortality. In the development cohort, covariable-adjusted (age, Charlson score, case duration, history of hypertension) exposure limits were identified for time accumulated below each of the thresholds that portended certain identical (5%-50%) percentage expected increases in the odds of mortality. These exposure time limit sets were shorter in patients with a history of hypertension. A novel risk score, the SLUScore (range 0-31), was conceived as the number of exposure limits exceeded for one of these sets (20% set). A SLUScore > 0 (average 13.8) was found in 40% of patients who had twice the mortality, adjusted odds increasing by 5% per limit exceeded. When tested in the validation cohort, a SLUScore > 0 (average 14.1) identified 35% of patients who had twice the mortality, each incremental limit exceeded portending a 5% compounding increase in adjusted odds of mortality, independent of age and Charlson score (C = 0.73, 0.72-0.74, P < .05).

CONCLUSIONS

The SLUScore represents a novel method for identifying nearly 1 in every 3 patients experiencing greater 30-day mortality portended by more severe intraoperative hypotensive exposures.

Norepinephrine reduces arterial compliance less than phenylephrine when treating general anesthesia-induced arterial hypotension

INTRODUCTION

During general anesthesia, arterial hypotension is frequent and may be an important contributor to perioperative morbidity. We assessed the effect of a 5 μg bolus of Norepinephrine (NA) when compared with 50 μg bolus of Phenylephrine (PE) administered to treat hypotension during maintenance anesthesia, on MAP, derived cardiac output and arterial stiffness parameters.

METHODS

Patients scheduled for a neurosurgical procedure under general anesthesia were prospectively included. Monitoring included invasive blood pressure, esophageal Doppler, and arterial tonometer used to estimate central aortic pressure with arterial stiffness parameters, such as augmentation index (Aix). After initial resuscitation, hypotensive episodes were corrected by a bolus administration of NA or PE in a peripheral venous line.

RESULTS

There were 269 bolus administrations of vasopressors (149 NA, 120 PE) in 47 patients with no adverse effects detected. A decrease in stroke volume (SV) was observed with PE compared with NA (-18 ± 9% vs. -14 ± 7%, P < 0.001). This decrease was associated with an increase in Aix, which was greater for PE than for NA (+10 ± 8% vs. +6 ± 6%, P < 0.0001), and a decrease in total arterial compliance greater for PE compared to NA (Ctot = SV/Central Pulse Pressure) (-35 ± 9% vs. -29 ± 10%, P < 0.001).

DISCUSSION

This study suggests that 5 μg of NA administered as a bolus in a peripheral venous line could treat general anesthesia-induced arterial hypotension with a smaller decrease in SV and arterial compliance when compared to PE.

Relationship between Intraoperative Hypotension, Defined by Either Reduction from Baseline or Absolute Thresholds, and Acute Kidney and Myocardial Injury after Noncardiac Surgery: A Retrospective Cohort Analysis

BACKGROUND

How best to characterize intraoperative hypotension remains unclear. Thus, the authors assessed the relationship between myocardial and kidney injury and intraoperative absolute (mean arterial pressure [MAP]) and relative (reduction from preoperative pressure) MAP thresholds.

METHODS

The authors characterized hypotension by the lowest MAP below various absolute and relative thresholds for cumulative 1, 3, 5, or 10 min and also time-weighted average below various absolute or relative MAP thresholds. The authors modeled each relationship using logistic regression. The authors further evaluated whether the relationships between intraoperative hypotension and either myocardial or kidney injury depended on baseline MAP. Finally, the authors compared the strength of associations between absolute and relative thresholds on myocardial and kidney injury using C statistics.

RESULTS

MAP below absolute thresholds of 65 mmHg or relative thresholds of 20% were progressively related to both myocardial and kidney injury. At any given threshold, prolonged exposure was associated with increased odds. There were no clinically important interactions between preoperative blood pressures and the relationship between hypotension and myocardial or kidney injury at intraoperative mean arterial blood pressures less than 65 mmHg. Absolute and relative thresholds had comparable ability to discriminate patients with myocardial or kidney injury from those without.

CONCLUSIONS

The associations based on relative thresholds were no stronger than those based on absolute thresholds. Furthermore, there was no clinically important interaction with preoperative pressure. Anesthetic management can thus be based on intraoperative pressures without regard to preoperative pressure.

Femoral nerve block with propofol sedation versus general anesthesia in patients with severe cardiac dysfunction undergoing autologous myoblast sheet transplantation

PURPOSE

Regional anesthesia is more favorable than general anesthesia in patients with severe comorbidity; however, data on the superiority of peripheral nerve blocks over general anesthesia in patients with severe cardiac dysfunction are lacking. We aimed to demonstrate that peripheral nerve blocks reduce perioperative analgesic requirements and promote faster recovery compared to general anesthesia.

METHODS

We retrospectively evaluated intraoperative blood pressure, perioperative medications, and postoperative recovery in patients who underwent skeletal muscle harvesting for autologous myoblast sheet transplantation. We compared patients who received general anesthesia (group G, n = 27) to those who received femoral nerve block with propofol sedation (group B, n = 22).

RESULTS

Left ventricular ejection fraction was 24% on average, with no significant difference between groups. Compared with group G, a lower dose of propofol was used intraoperatively (1.25 versus 2.0 µg/mL, respectively; P < 0.001) and fewer patients required opioids (13.6 versus 100%, P < 0.01) in group B. Additionally, the lowest intraoperative mean blood pressure was higher (54 versus 48 mmHg, respectively; P = 0.02) in group B. More patients received postoperative analgesic drugs (51.9 versus 13.6%, P = 0.01) and they received them more frequently (1 [0-3] versus 0 [0-1], P = 0.02) in group G. The length of heart care unit stay was shorter in group B than group G (0 [0-18.5] versus 17 [0-47] h, respectively; P < 0.0001).

CONCLUSIONS

Femoral nerve block with sedation was more beneficial than general anesthesia in patients with severe cardiac dysfunction who underwent skeletal muscle harvesting for autologous myoblast sheet transplantation.

Update on Finger-Application-Type Noninvasive Continuous Hemodynamic Monitors (CNAP and ccNexfin): Physical Principles, Validation, and Clinical Use

The CNAP HD Monitor (CNSystems, Graz, Austria) and the ccNexfin (The ClearSight System: Edwards Lifesciences Corporation, Irvine, CA) are continuous, noninvasive blood pressure monitors using a finger-application device. These devices show a promising ability to allow for rapid detection of hemodynamic derangement when compared with oscillometry. The accuracy and precision of these devices as blood pressure monitors has been evaluated when compared with intra-arterial catheters. Additionally, they can be used to measure beat-to-beat cardiac output (CO). As CO monitors, they are capable of trending changes in CO when compared with a transpulmonary thermodilution monitor. Difficulty with use in critically ill and awake patients has been encountered because of altered microvascular physiology and patient movement. The principles of operation and clinical validation of these devices are presented. The clinicians who are interested in using these devices in their clinical setting should be aware of the relatively large bias and CIs in the hemodynamic measurements.

Experimental assessment of oxygen homeostasis during acute hemodilution: the integrated role of hemoglobin concentration and blood pressure

Background

Low hemoglobin concentration (Hb) and low mean arterial blood pressure (MAP) impact outcomes in critically ill patients. We utilized an experimental model of “normotensive” vs. “hypotensive” acute hemodilutional anemia to test whether optimal tissue perfusion is dependent on both Hb and MAP during acute blood loss and fluid resuscitation, and to assess the value of direct measurements of the partial pressure of oxygen in tissue (P_tO₂).

Methods

Twenty-nine anesthetized rats underwent 40% isovolemic hemodilution (1:1) (or sham-hemodilution control, n = 4) with either hydroxyethyl starch (HES) (n = 14, normotensive anemia) or saline (n = 11, hypotensive anemia) to reach a target Hb value near 70 g/L. The partial pressure of oxygen in the brain and skeletal muscle tissue (P_tO₂) were measured by phosphorescence quenching of oxygen using G4 Oxyphor. Mean arterial pressure (MAP), heart rate, temperature, arterial and venous co-oximetry, blood gases, and lactate were assessed at baseline and for 60 min after hemodilution. Cardiac output (CO) was measured at baseline and immediately after hemodilution. Data were analyzed by repeated measures two-way ANOVA.

Results

Following “normotensive” hemodilution with HES, Hb was reduced to 66 ± 6 g/L, CO increased (p < 0.05), and MAP was maintained. These conditions resulted in a reduction in brain P_tO₂ (22.1 ± 5.6 mmHg to 17.5 ± 4.4 mmHg, p < 0.05), unchanged muscle PO₂, and an increase in venous oxygen extraction. Following “hypotensive” hemodilution with saline, Hb was reduced to 79 ± 5 g/L and both CO and MAP were decreased (P < 0.05). These conditions resulted in a more severe reduction in brain P_tO₂ (23.2 ± 8.2 to 10.7 ± 3.6 mmHg (p < 0.05), a reduction in muscle P_tO₂ (44.5 ± 11.0 to 19.9 ± 12.4 mmHg, p < 0.05), a further increase in venous oxygen extraction, and a threefold increase in systemic lactate levels (p < 0.05).

Conclusions

Acute normotensive anemia (HES hemodilution) was associated with a subtle decrease in brain tissue P_tO₂ without clear evidence of global tissue hypoperfusion. By contrast, acute hypotensive anemia (saline hemodilution) resulted in a profound decrease in both brain and muscle tissue P_tO₂ and evidence of inadequate global perfusion (lactic acidosis). These data emphasize the importance of maintaining CO and MAP to ensure adequacy of vital organ oxygen delivery during acute anemia. Improved methods of assessing P_tO₂ may provide an earlier warning signal of vital organ hypoperfusion.