Baseline Regional Cerebral Oxygen Saturation Correlates With Left Ventricular Systolic and Diastolic Function

Baseline Regional Cerebral Oxygen Saturation Correlates With Left Ventricular Systolic and Diastolic Function Catherine Paquet, MD,* Alain Deschamps, MD, PhD, FRCPC,* André Y. Denault, MD, FRCPC,* Pierre Couture, MD, FRCPC,* Michel Carrier, MD, FRCSC,† Denis Babin, MSc,* Sylvie Levesque, MSc,‡ Dominique Piquette, MD,* Jean Lambert, PhD,§ and Jean-Claude Tardif, MD, FRCPC¶ Objective: To evaluate the correlation between baseline cerebral oxygen saturation (ScO2) and cardiac function as assessed by pulmonary artery catheterization and transesophageal echocardiography (TEE). Design: A retrospective study. Setting: A tertiary care university hospital. Participants: Cardiac surgery patients. Measurements and Results: Patients undergoing cardiac surgery with bilateral recording of their baseline ScO2 using the INVOS 4100 (Somanetics, Troy, MI) were selected. A pulmonary artery catheter was used to obtain their hemodynamic profile. Left ventricular (LV) systolic and diastolic function was evaluated by TEE, after the induction of anesthesia, using standard criteria. A model was developed to predict ScO2. A total of 99 patients met the inclusion criteria. There were significant correlations between mean ScO2 values and central venous pressure (CVP) (r ⴝ ⴚ0.31, p ⴝ 0.0022), pulmonary capillary wedge pressure (r ⴝ

ⴚ0.25, p ⴝ 0.0129), mean pulmonary artery pressure (MPAP) (r ⴝ ⴚ0.24, p ⴝ 0.0186), mean arterial pressure/MPAP ratio (r ⴝ 0.33, p ⴝ 0.0011), LV fractional area change (<35, 35-50, and >50, p ⴝ 0.0002), regional wall motion score index (r ⴝ ⴚ0.27, p ⴝ 0.0062), and diastolic function (p ⴝ 0.0060). The mean ScO2 had the highest area under the receiver operating characteristic curve (0.74; confidence interval, 0.64-0.84) to identify LV systolic dysfunction. A model predicting baseline ScO2 was created based on LV systolic echocardiographic variables, CVP, sex, mitral valve surgery, and the use of ␤-blocker (r2 ⴝ 0.42, p < 0.001). Conclusion: Baseline ScO2 values are related to cardiac function and are superior to hemodynamic parameters at predicting LV dysfunction. © 2008 Elsevier Inc. All rights reserved.

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correlate with the presence of left ventricular (LV) dysfunction in patients with valvular disease during exercise testing.10 However, ScO2 has never been compared with both hemodynamic and echocardiographic assessment of cardiac function in patients undergoing cardiac surgery. The authors’ hypothesis is that the baseline mean ScO2 measured before surgery is determined by cardiac function and correlates with hemodynamic and echocardiographic parameters.

EAR-INFRARED SPECTROSCOPY (NIRS) is a technique that was developed in the 1970s1 and can be used as a noninvasive and continuous monitor of the balance between cerebral oxygen delivery and consumption.2 Several different specialties like neurology,3 neurosurgery,3 traumatology,4 vascular surgery,5 and adult2 and pediatric cardiac surgery6 have been using this monitor to measure brain and tissue perfusion. In fact, recently, some randomized controlled trials have shown the usefulness of this monitor to predict negative outcome in noncardiac7 and cardiac surgery.8 Several factors can affect oxygen delivery to the brain such as cardiac output, hemoglobin concentration, arterial oxygen saturation, and partial pressure of oxygen. However, in the awake patient, the major determinants of baseline brain oximetric signals are not clearly described. Few studies have reported the relationship between cerebral oximetry values (ScO2) and cardiac function.9,10 As cardiac performance is reduced, increased brain oxygen extraction would be encountered and lower ScO2 values would be observed.9 In addition, ScO2 has been shown to

From the Departments of *Anesthesiology, †Cardiac Surgery, and ¶Medicine, Montreal Heart Institute/Université de Montréal, Montreal, Quebec, Canada; ‡The Montreal Heart Institute Coordinating Center, Montreal, Quebec, Canada; and §Department of Preventive and Social Medicine, Université de Montréal, Montreal, Quebec, Canada. Supported by the Canadian Anesthesia Society Abbott Career Award, the Fonds de la recherche en Santé du Québec, the Canadian Institutes of Health Research, and the Fondation de l’Institut de Cardiologie de Montréal. Address reprint requests to André Y. Denault, MD, FRCPC, Department of Anesthesiology, Montreal Heart Institute, 5000 Bélanger Street, Montreal, PQ H1T 1C8, Canada. E-mail: denault@ videotron.ca © 2008 Elsevier Inc. All rights reserved. 1053-0770/08/2206-0007$34.00/0 doi:10.1053/j.jvca.2008.02.013 840

KEY WORDS: anesthesiology, cardiology monitoring, echocardiography, hemodynamics, neurology

METHODS The Department of Anesthesia of the Montreal Heart Institute has maintained a database since 1999 containing the demographic, hemodynamic, and echocardiographic data and baseline ScO2 signal (since 2002) of patients undergoing cardiac surgery. The Research and Ethics Committee approved this database. Consecutive patients undergoing cardiac surgery since 2002 in whom a complete transesophageal echocardiographic (TEE) examination was done, a pulmonary artery catheter inserted and ScO2 signal recorded bilaterally, were retained for the present study. Patients’ demographics, past medical history, and preoperative medications were collected. The presence of LV hypertrophy, defined as a ventricular mass ⬎115 g/m2 for men and ⬎95 g/m2 for women,11 or dilatation, defined as end-systolic or end-diastolic diameters above 45 and 55 mm, respectively,11 were noted from preoperative transthoracic echocardiograms and TEE examination. Surgical procedures were classified as coronary artery bypass graft (CABG) surgery with or without cardiopulmonary bypass (CPB); aortic, mitral, pulmonary, or tricuspid valve surgeries; complex surgeries; and miscellaneous procedures. A complex surgery was defined as a combination of revascularization and valvular surgery or a combination of 2 or more valvular procedures. Anesthesia was induced with 0.04 mg/kg of midazolam and 1 ␮g/kg of sufentanil, and muscle relaxation was achieved with 0.1 mg/kg of pancuronium or 0.3 mg/kg of rocuronium. After tracheal intubation, anesthesia was maintained with 1 ␮g/kg/h of sufentanil and 0.04 mg/kg/h of midazolam. No anesthetic gases were used during induction. Minute ventilation was adjusted to maintain end-tidal carbon dioxide between 30 and 40 mmHg with an infrared carbon dioxide

Journal of Cardiothoracic and Vascular Anesthesia, Vol 22, No 6 (December), 2008: pp 840-846

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analyzer. After the induction of anesthesia, during a period of hemodynamic stability defined as unchanged systemic blood pressure within 15 mmHg, before surgical incision, a cardiac hemodynamic profile was obtained with the pulmonary artery catheter (Swan-Ganz catheter 7.5F; Baxter Healthcare Corporation, Irvine, CA). Measured variables included heart rate, systolic, mean and diastolic arterial pressures, systolic, mean and diastolic pulmonary arterial pressures, central venous pressure, pulmonary capillary wedge pressure (PCWP), and cardiac output. Calculated hemodynamic indices were derived from the preceding values using standard formulas12 and included cardiac index (CI), stroke index, systemic vascular resistance index, pulmonary vascular resistance index, left and right ventricular stroke work indices, and mean arterial-to-mean pulmonary artery pressure ratio (MAP/ MPAP), an index of relative pulmonary hypertension.13 All transesophageal echocardiograms were performed online by 2 experienced cardiac anesthesiologists. The TEE examination included 2-dimensional examination in the midesophageal 4-chamber, 2-chamber, and long-axis views and transgastric short-axis and long-axis views at the midpapillary level, with additional color-flow imaging of the mitral, aortic, and tricuspid valves in order to detect any significant valvular abnormality. This was followed by a pulsed-wave Doppler examination of the pulmonary venous flow and transmitral flow ob-

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tained at the midesophageal level. Global LV systolic function was evaluated by determining the fractional area change (FAC). The FAC was analyzed as a categoric variable (above 50%, 35%-50%, and below 35%) and was not measured if less than 80% of the perimeter of the ventricular image being defined by contiguous endocardial echoes was seen.14 To assess regional LV systolic function, the regional wall motion score index (RWMSI), using the 16 segments recommended by the American Society of Echocardiography11 and the FAC, was measured using the transgastric view. Normal cardiac function was defined as an LV FAC more than 50 and a RWMSI equal to 1. The classification of LV diastolic dysfunction (DD) was based on the Canadian consensus guidelines,15 to which were added the use of more recent criteria16 and a validated algorithm.17 Abnormal diastolic profiles were separated into 2 groups: normal or relaxation abnormalities were classified as normalto-mild DD and pseudonormal and restrictive patterns were classified as moderate-to-severe DD. Patients with a pacemaker, atrial fibrillation, nonsinus rhythm, severe mitral regurgitation, or stenosis or aortic insufficiency were not evaluated for diastolic function. The interobserver variability for the assessment of global left ventricular systolic function (end-diastolic area coefficient of variation 3.4% ⫾ 1.4%),18 regional left ventricular wall motion score index (96% ⫾ 0.5% agree-

Fig 1. NIRS: the light source provides 2 continuous wavelengths of near-infrared light on the forehead, at the area corresponding to the junction between the anterior and middle cerebral artery. Two detectors, respectively, having a source-detector spacing of 3 and 4 cm, are also present to distinguish the extracerebral from the intracerebral tissue signal. A subtraction of the superficial signal from the deeper signal is made by the monitor to obtain the regional hemoglobin oxygen saturation in the frontal cortex.

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ment)19 and diastolic function (kappa 0.76 ⫾ 0.12)17,20 have been reported. The NIRS technology is based on the principle that each substance has its characteristic absorbance and has been previously described.2 Two probes attached to the forehead contain the light sources, each providing 2 continuous wavelengths of near-infrared light (730 and 810 nm) that reach a brain area corresponding to the junction between the anterior and middle cerebral artery vascularization territory (Fig 1). The authors used the INVOS 4100 system (Somanetics, Troy, MI) according to the manufacturer’s instructions in all these patients. The baseline preinduction ScO2 values obtained over 5 minutes, defined as the mean left and right ScO2 values, were used for data analysis. To document the absence of an effect of anesthesia on the evaluation of LV function, 71 patients in whom a preoperative transthoracic echocardiogram was performed by a cardiologist, and a postinduction TEE examination was obtained from 2 clinical studies,18,20 were analyzed. Of these 71 patients, 50 patients (37 men; mean age, 68 ⫾ 7 years) underwent CABG surgery. The LV FAC was 48% ⫾ 13% using transthoracic echocardiography before the induction of anesthesia and 49% ⫾ 12% using TEE after the induction of anesthesia (p ⫽ 0.68). In 21 patients undergoing valvular surgery, there were 8 men, and the mean age was 71 ⫾ 6 years; the LV FAC was 36% ⫾ 4% using transthoracic echocardiography and 38% ⫾ 9% using TEE (p ⫽ 0.59). No changes in RWMSI were observed in either group after the induction of anesthesia. Continuous variables are presented as mean ⫾ standard deviation if distributed normally or median (minimum ⫺ maximum) if not distributed normally. Categoric variables are presented as number and percentage. The relations between mean ScO2 and demographic and surgical procedure variables were evaluated with a Pearson correlation coefficient and a Student t test. The link among mean ScO2 and LV FAC, age groups (⬍35, 35-50, and ⱖ50), and diastolic dysfunction was evaluated with an analysis of variance followed by the pairwise comparisons of the 3 categories when the global analysis of variance was significant. The area under the receiver operating characteristic curve was calculated for each absolute value of the hemodynamic variables in relationship with normal or abnormal cardiac function to determine the best predictor. A model to predict the mean ScO2 was developed by using multiple linear regression analysis using a stepwise approach. Only variables with a p ⬍ 0.25 in univariate analysis were considered as potential predictors. Residual analysis was performed to evaluate the model. A post hoc analysis revealed the power of the present study to be 97% to distinguish an 8% difference in the ScO2 value between patients having a normal versus an abnormal cardiac function. Analyses were performed with SAS release 8.2 (SAS Institute Inc, Cary, NC); p values ⬍0.05 were considered to be statistically significant. RESULTS

A total of 99 consecutive patients were selected from the database. These patients were recruited between June 2002 and November 2004. Demographic variables and types of surgical procedures are found in Table 1. The population mean ScO2 value was 65% ⫾ 11%. The patient population was comprised of a total of 65 men and 34 women, with a mean age of 65 ⫾ 13 years and a mean Parsonnet score of 18 ⫾ 13. Male patients had higher mean ScO2 than women (67 ⫾ 10 v 61 ⫾ 11, p ⫽ 0.0033). ScO2 correlated negatively with the Parsonnet score (r ⫽ ⫺0.348, p ⫽ 0.0004) and age (r ⫽ ⫺0.1248, p ⫽ 0.2185). The mean ScO2 of patients aged less than 35 (n ⫽ 4), between 35 and 50 (n ⫽ 6), and above 50 (n ⫽ 89) was 67% ⫾ 17%, 74% ⫾ 13%, and 64% ⫾ 10% (p ⫽ 0.0659), respectively. Lower ScO2 values were observed in patients with diabetes (61% ⫾ 11% [23 diabetics] v 66% ⫾ 11% [76 nondiabetics],

Table 1. Description of Demographic Variables, Medications and Surgical Procedures With Mean ScO2 Variables

Frequency (%)

ScO2 (%), Mean ⫾ SD

p Value

Hypertension Diabetes mellitus* Atherosclerotic vascular disease LV dilatation† Unstable angina Myocardial infarction LV hypertrophy Medications ACE inhibitor ␤-blockers‡ Calcium channel blockers ARA IABP presurgery CABG with CPB CABG, no CPB Reoperation AVR MVR§ PVR Mitral valve repair Tricuspid valve repair¶ Complex surgeries Aortic surgery Mediastinal exploration VSD repair LV remodeling Miscellaneous

61 (62.2) 23 (23.2)

Yes 64 ⫾ 10 61 ⫾ 11

0.2183 0.0413

23 (23.2) 22 (22.5) 43 (43.9) 33 (33.3) 47 (48.0)

64 ⫾ 11 58 ⫾ 8 65 ⫾ 9 62 ⫾ 10 65 ⫾ 12

0.5213 0.0002 0.9158 0.1099 0.7006

46 (46.5) 61 (61.6) 33 (33.3) 2 (2.3) 7 (7.1) 60 (60.6) 5 (5.1) 8 (8.1) 31 (31.3) 8 (8.1) 1 (1.0) 10 (10.1) 5 (5.1) 33 (33.3) 11 (11.1) 1 (1.0) 1 (1.0) 3 (3.0) 6 (6.1)

63 ⫾ 10 63 ⫾ 11 64 ⫾ 11 58 ⫾ 7 69 ⫾ 9 64 ⫾ 9 66 ⫾ 10 63 ⫾ 13 65 ⫾ 13 54 ⫾ 11 92 64 ⫾ 10 52 ⫾ 11 63 ⫾ 2 64 ⫾ 9 80 92 62 ⫾ 8 62 ⫾ 8

0.2510 0.0258 0.4047 0.3092 0.3334 0.6794 0.8043 0.5951 0.9312 0.0019 0.9074 0.0040 0.3166 0.9036

0.6271 0.5608

Abbreviations: ACE inhibitor, angiotensin-converting enzyme inhibitor; AVR, aortic valve replacement; ARA, antagonist of receptor AT1 of angiotensin 2; IABP, intra-aortic counterpulsation balloon pump; PVR, pulmonary valve replacement; VSD, ventricular septal defect; SD, standard deviation. *In patients without diabetes mellitus, the ScO2 value was 66 ⫾ 11. †In patients without LV dilatation, the ScO2 value was 67 ⫾ 11. ‡Patients not receiving ␤-blockers had an ScO2 value of 68 ⫾ 11. §Patients not undergoing MVR had higher ScO2 values (66 ⫾ 10). ¶Patients not undergoing tricuspid valve repair had higher ScO2 values of 66 ⫾ 10.

p ⫽ 0.0413) and those with LV dilatation (58% ⫾ 8% [n ⫽ 22] v 67% ⫾ 11% [n ⫽ 77 without LV dilatation], p ⫽ 0.0002). There were a total of 60 CABG surgeries with CPB, 5 CABG surgeries without CPB, 31 aortic valve replacements, 8 mitral valve replacements, 1 pulmonic valve replacement, 10 mitral valve repairs, 5 tricuspid valve repairs, 11 aortic surgeries, 1 mediastinal exploration, 1 ventricular septal defect repair, 3 LV remodelings, and 6 miscellaneous surgeries. Included in these patients was a total of 33 patients who underwent complex coronary artery bypass surgery or complex valvular surgery. The miscellaneous surgeries included the MAZE procedure and tricuspid valve replacement, aortic and pulmonic valve repair, closure of fistula, and aortic enlargement with septal myomectomy. Patients undergoing mitral valve replacement (n ⫽ 8, ScO2 ⫽ 54% ⫾ 11% v 66% ⫾ 10%, p ⫽ 0.0019) or tricuspid valve repair (n ⫽ 5, ScO2 ⫽ 52% ⫾ 11% v 66% ⫾ 10%, p ⫽

BASELINE REGIONAL CEREBRAL OXYGEN SATURATION

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Table 2. Correlation of ScO2 With Hemodynamic and Echocardiographic Variables Variables

Mean ⫾ SD or Median (min-max)

Correlation Coefficient With ScO2

p Value

Hemodynamic and echocardiographic variables HR (mmHg) CVP (mmHg) PCWP (mmHg) MAP (mmHg) MPAP (mmHg) CO (L/min) CI (L/min/m2) SV (mL) SI (mL/m2) LVSWI (g/m/m2) RVSWI (g/m/m2) SVRI (dynes · sec · cm⫺5/m2) PVRI (dynes · sec · cm⫺5/m2) MAP/MPAP MAP-CVP (mmHg) RWMSI

55 ⫾ 14 12 ⫾ 5 16 ⫾ 6 73 ⫾ 11 23 ⫾ 8 3.5 ⫾ 0.8 1.9 ⫾ 0.4 65 ⫾ 16 36 ⫾ 8 28 ⫾ 10 5.1 ⫾ 2.8 2,662 ⫾ 727 307 ⫾ 223 3.5 ⫾ 1.2 61 ⫾ 12 1.0 (1.0-2.5)

⫺0.01 ⫺0.31 ⫺0.25 0.09 ⫺0.24 ⫺0.03 ⫺0.12 0.03 ⫺0.04 0.09 ⫺0.13 0.24 ⫺0.12 0.33 0.20 ⫺0.27

0.8926 0.0022 0.0129 0.3713 0.0186 0.7726 0.2603 0.7476 0.7196 0.3855 0.2253 0.0248 0.2612 0.0011 0.0489 0.0062

Group

LV FAC

⬍35 35-50 ⱖ50

(n ⫽ 16) (n ⫽ 20) (n ⫽ 63)

Mean ScO2

p Value

62 ⫾ 10 58 ⫾ 9 68 ⫾ 10

0.0002

⬍35 v ⱖ50 ⬍35 v 35-50 35-50 v ⱖ50 DD

Normal or RA (n ⫽ 47) PN or RE (n ⫽ 25) NE (n ⫽ 27) Normal⫹RA v NE Normal⫹RA v PN⫹RE

68 ⫾ 10 63 ⫾ 11 61 ⫾ 11

0.0229 0.2524 0.0001 0.0060

0.0032 0.0251

Abbreviations: HR, heart rate; CO, cardiac output; LVSWI, left ventricular stroke work index; NE, nonevaluable diastolic function; PCWP, pulmonary capillary wedge pressure; PN, pseudonormal diastolic dysfunction; PVRI, pulmonary vascular resistance index; RA, relaxation abnormality; MAP/MPAP, ratio of mean arterial pressure/mean pulmonary arterial pressure; RE, restrictive diastolic dysfunction; RVSWI, right ventricular stroke work index; RWMSI, regional wall motion score index; SI, stroke index; SD, standard deviation; SV, stroke volume; SVRI, systemic vascular resistance index; DD, diastolic dysfunction.

0.004) had lower ScO2 values (Table 1). The hemodynamic and echocardiographic results are shown in Table 2. There were significant correlations between mean ScO2 values and CVP (r ⫽ ⫺0.31, p ⫽ 0.0022), PCWP (r ⫽ ⫺0.25, p ⫽ 0.0129), MPAP (r ⫽ ⫺0.24, p ⫽ 0.0186), systemic vascular resistance index (r ⫽ 0.24, p ⫽ 0.0248), MAP/MPAP ratio (r ⫽ 0.33, p ⫽ 0.0011), MAP-CVP difference (r ⫽ 0.20, p ⫽ 0.0489), RWMSI (r ⫽ ⫺0.27, p ⫽ 0.0062), FAC (p ⫽ 0.0002), and diastolic function (p ⫽ 0.0060). An FAC greater than 50% was associated with higher ScO2 values (68% ⫾ 10%) than an FAC lower than 35% (62% ⫾ 10%) or between 35% and 50% (58% ⫾ 9%) (p ⫽ 0.0229 and p ⫽ 0.0001, respectively). Normal or mild diastolic dysfunction was associated with higher ScO2 than moderate-to-severe diastolic dysfunction (68% ⫾ 10% v 63% ⫾ 11%, p ⫽ 0.0251). There was no correlation between ScO2 and either CI or stroke index. Fifty-seven patients (58%) were considered to have normal cardiac function as defined previously. Patients with abnormal cardiac function (n ⫽ 42) had higher PCWP (p ⫽ 0.0053), MPAP (p ⫽ 0.0167), right ventricular stroke work index (p ⫽ 0.0009), lower MAP/MPAP ratio (p ⫽ 0.0098), and a lower mean ScO2 value (60% ⫾ 10% v 68% ⫾ 10%, p ⫽ 0.0001). The mean hemodynamic values for patients with normal versus

abnormal cardiac function and the areas under receiver operating characteristic curves for each variable are shown in Table 3. The mean ScO2 value had the highest area under the curve to identify patients with abnormal cardiac function (0.74; confidence interval, 0.64-0.84). An ScO2 value of 64% had the best global accuracy to detect abnormal cardiac function, with sensitivity and specificity of 75% and 67%, respectively. The model to predict baseline mean ScO2 is shown in Table 4. The key variables identified in the model were the presence of normal LV systolic function, which tended to raise the mean ScO2 value, and LV dilatation, mitral valve replacement, female sex, CVP, and the use of ␤-blockers that contributed to lower the value (r2 ⫽ 0.42, p ⬍ 0.0001). DISCUSSION

In this cohort of patients undergoing cardiac surgery, the major determinants of the baseline ScO2 values have been identified. The authors observed that ScO2 is significantly influenced by several cardiac variables. Furthermore, the awake baseline mean ScO2 value obtained before the induction of anesthesia had a better sensitivity and specificity to predict the

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Table 3. Comparison of Hemodynamic Variables Between Patients With Normal Cardiac Function Versus Abnormal Cardiac Function as Defined With TEE Variables

Normal Cardiac Function (n ⫽ 57)

Abnormal Cardiac Function (n ⫽ 42)

p Value

Area Under ROC Curve (95% Confidence Interval)

HR (mmHg) CVP (mmHg) PCWP (mmHg) MAP (mmHg) MPAP (mmHg) CO (L/min) CI (L/min/m2) SV (mL) SI (mL/m2) LVSWI (g/m/m2) RVSWI (g/m/m2) SVRI (dynes · sec · cm⫺5/m2) PVRI (dynes · sec · cm⫺5/m2) MAP/MPAP MAP-CVP (mmHg) Mean baseline oximetry (%)

53 ⫾ 12 12 ⫾ 5 14 ⫾ 4 74 ⫾ 12 21 ⫾ 6 3.3 ⫾ 0.6 1.8 ⫾ 0.3 65 ⫾ 14 36 ⫾ 7 30 ⫾ 11 4.2 ⫾ 2.1 2,767 ⫾ 700 296 ⫾ 171 3.8 ⫾ 1.3 62 ⫾ 13 68 ⫾ 10

58 ⫾ 15 12 ⫾ 5 18 ⫾ 7 72 ⫾ 10 25 ⫾ 9 3.6 ⫾ 1.0 2.0 ⫾ 0.4 66 ⫾ 19 36 ⫾ 8.6 26 ⫾ 9 6.3 ⫾ 3.3 2,521 ⫾ 749 321 ⫾ 279 3.1 ⫾ 1.0 59 ⫾ 11 60 ⫾ 10

0.0624 0.8312 0.0053 0.3700 0.0167 0.0991 0.0914 0.6818 0.8786 0.1089 0.0009 0.1115 0.6158 0.0098 0.3052 0.0001

0.60 (0.49-0.71) 0.50 (0.40-0.61) 0.64 (0.54-0.74) 0.55 (0.44-0.66) 0.63 (0.53-0.73) 0.57 (0.48-0.66) 0.58 (0.49-0.67) 0.52 (0.43-0.61) 0.51 (0.42-0.60) 0.60 (0.50-0.69) 0.67 (0.59-0.75) 0.61 (0.51-0.70) 0.49 (0.39-0.58) 0.65 (0.54-0.75) 0.55 (0.43-0.66) 0.74 (0.64-0.84)

Abbreviations: HR, heart rate; CO, cardiac output; LVSWI, left ventricular stroke work index; PCWP, pulmonary capillary wedge pressure; PVRI, pulmonary vascular resistance index; ROC curve, receiver operating characteristic curve, RVSWI, right ventricular stroke work index; SI, stroke index; SV, stroke volume; SVRI, systemic vascular resistance index; TEE, transesophageal echocardiography.

presence of abnormal cardiac function compared with any of the hemodynamic variables obtained with the pulmonary artery catheter. Alteration in LV function is associated with reduced cerebral oxygen delivery, leading to increased oxygen extraction and decreased mean cerebral oximetry value (Fig 2). The other cardiac variables associated with baseline ScO2 were LV dilatation, MVR, and CVP. LV dilatation is a feature of cardiomyopathy, and a correlation between the evolution of heart failure patients (n ⫽ 8) and ScO2 has been observed.9 In the present study, MVR was performed in symptomatic patients, and typically this population will have abnormal cardiac function. CVP was found to be the best hemodynamic variable in the final model. An increase in CVP is associated with a reduction in the cerebral brain perfusion pressure usually estimated by the MAP ⫺ CVP difference in the absence of intracranial pressure monitoring. This difference correlated positively with ScO2 values. The baseline ScO2 value of 65% was the same as observed by Edmonds21 in a series of cardiac surgical patients. Female sex was associated with lower ScO2 as previously observed,22 but other investigators did not observe any differences between sexes.23,24 A negative correlation between ScO2 and age has previously been described.24 The authors observed a similar trend, but there were only 10 pa-

tients younger than 50 years of age and this was not normally distributed. Finally, patients on ␤-blockers had lower ScO2 values. This could be explained by the hemodynamic effect of this class of drug. Few studies have been published on the relationship between brain oximetry and cardiac function. Madsen et al9 compared ScO2 values of 39 normal patients with 8 patients with heart failure. First, they noticed that patients with heart failure had lower baseline values (34% v 65%). Second, those who clinically improved had an increase in ScO2 up to 50%. Koike et al10 studied exercise testing in normal patients and in those with valvular disease. They observed that cerebral oxygenation during exercise is dependent on the cardiovascular and pulmonary systems. In addition, the presence of cerebral hypoperfusion appeared during exercise in cardiac patients whose cardiac output failed to increase normally. In an observational study of defibrillators, de Vries et al25 observed that the onset of fibrillation is associated with an acute reduction in both ScO2 and retrograde jugular venous O2. These studies support the association between cardiac function and brain oxygenation, but so far this aspect has not been studied in the operating room environment and with the use of hemodynamic and echocardiographic monitoring.

Table 4. Modeling Mean Brain Oximetry Values Variable

Parameter Estimate

Standard Error

95% Confidence Limits

p Value

Normal systolic function LV dilatation MVR CVP Sex ␤-blockers

4.83 ⫺6.74 ⫺8.64 ⫺0.46 ⫺5.61 ⫺4.37

1.94 2.29 3.20 0.19 1.85 1.83

0.97, 8.70 ⫺11.29, ⫺2.19 ⫺15.01, ⫺2.28 ⫺0.84, ⫺0.07 ⫺9.28, ⫺1.95 ⫺8.00, ⫺0.75

0.0148 0.0041 0.0083 0.0200 0.0031 0.0187

NOTE. Normal LV systolic function: 1 if FAC ⬎50% or RWMSI ⫽ 1 (else ⫽ 0), LV dilatation if end-systolic and end-diastolic diameter ⬎45 mm and 55 mm; MVR: mitral valve replacement: 0 if none, 1 if present; sex: 0 if male and 1 if female; and ␤-blockers: 0 if none, 1 if present.

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Fig 2. Brain-heart interaction: relationship between reduced cerebral oxygen saturation (ScO2) and cardiac systolic/diastolic function. Because systolic cardiac function is reduced through a reduction in the LV FAC or an increase in the RWMSI, MAP will be reduced. Cardiac performance can also result from LVDD that can be present with or without systolic dysfunction. In this case, the left atrial pressure (LAP), PCWP, and, consequently, the MPAP will increase; the MAP/MPAP ratio decreases, and this may lead to increased CVP. Because the CVP is used to estimate the intracranial pressure, the cerebral perfusion pressure (MAP-CVP) will be reduced. The result will be a reduction in cerebral blood flow (CBF). This will lead to an increase in the oxygen extraction of the brain. This explains why reduced cardiac function is associated with reduced ScO2. LA, left atrium; RA, right atrium; RV, right ventricle.

Therefore, brain oximetry could represent a noninvasive technology that could potentially be advocated as a surrogate to invasive central venous oximetry26 because both techniques

will be influenced by cardiac function. It also could be considered as a tool to screen patients with cardiac disease, particularly in settings in which history and physical examination are limited. However, because ScO2 reflects the balance between oxygen transport and cerebral metabolic rate of oxygen, cardiac pathology associated with hyperdynamic state, such as acute aortic regurgitation, could be associated with normal or elevated ScO2 values despite altered LV function. There are several limitations to the present study. This is a retrospective study with inherent bias. The number of patients was small; however, so far, it represents the largest cohort in which the relationship between brain oximetry and cardiac function has been addressed. The number of patients was still sufficient to have an adequate power analysis to support the authors’ hypothesis. The anesthesiologists performing the TEE were not blinded to the ScO2 values, which could theoretically introduce a bias. However, the relationship in cardiac surgical patients between echocardiographic results that include both systolic and diastolic function, hemodynamic parameters, and ScO2 was unknown at the time of the study. Preinduction baseline cerebral oximetry values were used, as recommended in previous trials.7,8,27 TEE is usually not performed in awake patients before the induction of anesthesia for cardiac surgery. In addition, the authors usually inserted the pulmonary artery catheter after the induction of anesthesia. This is why the authors decided to analyze the effect of general anesthesia in a series of patients in which a transthoracic echocardiogram was obtained before the induction of anesthesia in 2 studies. The induction of anesthesia was not associated with any significant change in left ventricular function and RWMSI. The authors also had previously documented no change in cardiac index and mild but not clinically significant changes in central venous pressure after the induction of anesthesia.28 The authors also chose to study only baseline ScO2 in the pre-CPB period because several confounding factors influence the post-CPB period, such as hypothermia, anemia from hemodilution, and vasoactive support. Further studies will be required to explore these issues. In conclusion, in a population of cardiac surgical patients, it was observed that ScO2 correlates with cardiac performance and is significantly influenced by several cardiac factors. NIRS could potentially be used as a noninvasive tool to evaluate cardiac performance. Further studies with larger numbers of patients will be required to explore the cardiac application of this promising noninvasive monitoring modality.

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