Inferior Vena Cava Diameter and Central Venous Pressure Correlation During Cardiac Surgery

Inferior Vena Cava Diameter and Central Venous Pressure Correlation During Cardiac Surgery Suraphong Lorsomradee, MD, Sratwadee Lorsomradee, MD, Stefanie Cromheecke, MD, Pieter W. ten Broecke, MD, and Stefan G. De Hert, MD, PhD Objective: The purpose of this study was to determine whether a relationship exists between the inferior vena cava diameter (IVCD) or the superior vena cava diameter (SVCD) measured at the point of entry into the right atrium using transesophageal echocardiography (TEE) and the central venous pressure (CVP) under different experimental conditions. Design: Prospective study. Setting: University hospital, single institution. Participants: Seventy patients undergoing elective cardiac surgery. Interventions: CVP, IVCD, and SVCD were measured in a 2-dimensional, long-axis midesophageal bicaval view at end-diastole with electrocardiographic synchronization. Data were recorded during suspended ventilation, before and after leg elevation, and at different levels of positive end-expiratory pressure (0, 5, and 10 cmH2O).

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AINTENANCE OF AN adequate preload is an important part of anesthetic management in major surgery. Central venous pressure (CVP) and pulmonary capillary wedge pressure derived from a pulmonary artery catheter (PAC) are the most frequently used parameters for monitoring preload.1 However, some observational studies suggested that the use of PACs to guide therapy was associated with increased morbidity and mortality.2,3 Transthoracic echocardiography (TTE) has been shown to be useful for noninvasive estimation of CVP from the diameter of the inferior vena cava (IVC) and the change in diameter with respiration.4-8 Nevertheless, the use of TTE with the subcostal view is not practical in the operating room, especially during abdominal and thoracic surgery. Transesophageal echocardiography (TEE), on the other hand, has received growing interest by anesthesiologists.9 TEE can provide information on the IVC and the superior vena cava (SVC). However, no data have been published correlating the TEE-derived inferior vena cava diameter (IVCD) or superior vena cava diameter (SVCD) with the CVP. Furthermore, the response of TEE-derived IVCD and SVCD to changes in positive end-expiratory pressure (PEEP) has not been documented. It was hypothesized that a direct relationship exists between TEE-derived IVCD measured at the point of entry into the right atrium and the CVP. To test this hypothesis, TEE-derived IVCD and SVCD, measured at the point of entry into the right atrium, were related to simultaneous CVP measurements.

From the Department of Anesthesiology, University Hospital Antwerp, Edegem, Belgium. Address reprint requests to Stefan G. De Hert, MD, PhD, Department of Anesthesiology, University Hospital Antwerp, Wilrijkstraat 10, B-2650 Edegem, Belgium. E-mail: [email protected] © 2007 Elsevier Inc. All rights reserved. 1053-0770/07/2104-0003$32.00/0 doi:10.1053/j.jvca.2006.09.009 492

Measurements and Main Results: The relationship between IVCD and CVP had 2 portions: A first (CVP <11 mmHg) in which the IVCD showed a strong correlation with the CVP (R ⴝ 0.801, p < 0.001; CVP ⴝ 2.009 ⴙ [0.312 * IVCD]) and a second (CVP >11 mmHg) in which the correlation was poor (R ⴝ 0.272, p ⴝ 0.065). No correlation between SVCD and CVP was observed. Conclusion: A strong correlation between TEE-derived IVCD measured at the point of entry into the right atrium and CVP was observed in cardiac surgical patients when CVP was <11 mmHg. © 2007 Elsevier Inc. All rights reserved. KEY WORDS: inferior vena cava, central venous pressure, superior vena cava, transesophageal echocardiography, positive end-expiratory pressure METHODS After the study was approved by the institutional ethical committee and written informed consent was obtained, 70 patients scheduled for elective cardiac surgery were studied. Exclusion criteria were patients with tricuspid valve disease and cardiac rhythm disturbances. All patients received standard premedication. In the operating room, patients received routine monitoring including 5-lead electrocardiogram, radial artery pressure, pulse oximetry, capnography, and blood and urine bladder temperature monitoring. Anesthesia was performed with sevoflurane, remifentanil, and cisatracurium. After induction of anesthesia, TEE (SONOS 5500; Philips Medical Systems, Andover, MA) and a PAC with continuous cardiac output measurement (Swan Ganz CCO/VIP; Edwards Lifesciences LLC, Irvine, CA) were placed. All pressure transducers were zeroed at the midaxillary line and fourth intercostal space. During the prebypass period, before median sternotomy, the IVCD and SVCD were measured in the 2-dimensional long-axis midesophageal bicaval view, at end-expiration and end-diastole, with electrocardiographic synchronization. During the measurements, patients were momentarily disconnected from the ventilator, and the IVCD and SVCD were measured (in millimeters) at the point of entry into the right atrium. Baseline hemodynamic data were recorded simultaneously. The lower limbs of the patients then were elevated by raising the caudal part of the table by 45°. IVCD, SVCD, and hemodynamic data were measured after stabilization of the hemodynamic parameters. The legs of the patients then were returned to the supine position. Ten minutes later, IVCD and SVCD were measured together with hemodynamic data, recorded as PEEP, 0 cmH2O. The second part of the study was the measurement during mechanical ventilation with PEEP. All patients were ventilated with PEEP, 5 cmH2O. Five minutes after PEEP application, the IVCD and SVCD together with hemodynamic data were recorded. All patients were ventilated with PEEP, 10 cmH2O. Five minutes later, the IVCD and SVCD together with hemodynamic data were measured again. A single cardiothoracic anesthesiologist was designated to take all the measurements. The reader was blinded to the CVP before measuring the IVCD and SVCD. The echocardiographic sequence was stored on tape in the video, and periodic joint reading sessions with other cardiothoracic anesthesiologists were conducted to maintain parallel reading styles. Statistical analysis was performed by using the SigmaStat 2.03 software package (SPSS, Leuven, Belgium). Echocardiographic and

Journal of Cardiothoracic and Vascular Anesthesia, Vol 21, No 4 (August), 2007: pp 492-496

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Table 1. Demographic Data and Preoperative Risk Factors Demographic data Sex (male/female; % female) Age (y) Body mass index (kg/m2) Body surface area (m2) Ejection fraction (%) EuroSCORE (median [range]) Preoperative risk factor (n [%]) Diabetes IDDM NIDDM Hypertension Smoking COPD Hyperlipidemia Obesity History of stroke Renal disease Current medication (n [%]) ␤-Blockers Calcium channel blockers ACE inhibitors Nitrates Diuretics Digoxin Oral antidiabetics Insulin Acetylsalicylic acid Other

52/18 (26) 68 ⫾ 8 26.9 ⫾ 3.9 1.91 ⫾ 0.18 58 ⫾ 16 4 (0-13)

1 (1.4) 19 (27.1) 49 (70.0) 23 (32.9) 9 (12.9) 48 (68.6) 27 (38.6) 5 (7.1) 5 (7.1) 49 (70.0) 8 (11.4) 30 (42.9) 27 (38.6) 20 (28.6) 0 (0) 17 (24.3) 5 (7.1) 60 (85.7) 20 (28.6)

Figure 3 shows the linear regression lines between IVCD and CVP before and after leg elevation in patients with baseline CVP ⱕ11 mmHg. Before passive leg elevation, a strong correlation was observed (R ⫽ 0.880, p ⬍ 0.001; CVP ⫽ 0.549 ⫹ [0.371 * IVCD]). After passive leg elevation, the correlation was weaker (R ⫽ 0.686, p ⬍ 0.001; CVP ⫽ 3.924 ⫹ [0.297 * IVCD]). Passive leg elevation increased CVP of some patients to more than 11 mmHg and shifted the linear regression line between IVCD versus CVP upward and rightward to the scatter portion. However, the analysis of linear regression lines showed no significant difference in slopes and intercepts before and after passive leg elevation. The echocardiographic and hemodynamic effects of mechanical ventilation at different levels of PEEP are summarized in Table 3. Peak and mean airway pressure were significantly increased after 5 and 10 cmH2O PEEP application. PEEP, 10 cmH2O, induced significant increases in CVP and mean pulmonary artery pressure while cardiac output was significantly decreased. However, heart rate and mean arterial pressure remained unchanged. Although SVCD remained unchanged, IVCD was significantly increased after 5 and 10 cmH2O PEEP application.

NOTE. Data are presented as mean ⫾ standard deviation, unless noted otherwise. Abbreviations: ACE, angiotensin-converting enzyme; COPD, chronic obstructive pulmonary disease; EuroSCORE, European System for Cardiac Operative Risk Evaluation; IDDM, insulin-dependent diabetes mellitus; NIDDM, non–insulin-dependent diabetes mellitus.

hemodynamic parameters were compared versus baseline using the 1-way repeated-measures analysis of variance. Simple linear regressions were used to express correlation between IVCD and CVP. Comparison of 2 regression lines was performed by using the t test to compare intercepts and slopes of regression lines. Values are expressed as mean ⫾ standard deviation unless stated otherwise. Statistical significance was accepted at p ⬍ 0.05. All p values were 2-tailed. RESULTS

Demographic data and preoperative risk factors of the patients are summarized in Table 1. Figure 1 shows the relationship between IVCD and CVP in 70 patients. The data were measured before and after leg elevation and at zero PEEP. No correlation between the SVCD and CVP was observed. The scatter plot of IVCD versus CVP shows 2 portions: in 1 (CVP ⱕ11 mmHg), the IVCD showed a strong correlation with the CVP (R ⫽ 0.801, p ⬍ 0.001; CVP ⫽ 2.009 ⫹ [0.312 * IVCD]) (Fig 2A); and in the other (CVP ⬎11 mmHg), the correlation between IVCD and CVP was poor (R ⫽ 0.272, p ⫽ 0.065) (Fig 2B). The echocardiographic and hemodynamic effects of leg elevation are presented in Table 2. Passive leg elevation induced significant increases in IVCD, SVCD, CVP, mean arterial pressure, and cardiac output. Heart rate remained unchanged.

Fig 1.

Correlation between the CVP and the IVCD and SVCD.

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Table 2. Hemodynamic and Echocardiographic Parameters Before and After Leg Elevation

HR (beats/min) MAP (mmHg) MPAP (mmHg) CO (L/min) CVP (mmHg) IVC diameter (mm) SVC diameter (mm)

Baseline

Leg Elevation

P Value

69 ⫾ 11 70 ⫾ 9 22 ⫾ 5 4.3 ⫾ 1.5 10 ⫾ 3 23.2 ⫾ 4.5 14.6 ⫾ 2.8

68 ⫾ 11 78 ⫾ 13 27 ⫾ 5 4.8 ⫾ 1.6 14 ⫾ 3 27.2 ⫾ 4.3 15.7 ⫾ 2.6

0.585 ⬍0.001* ⬍0.001* 0.006* ⬍0.001* ⬍0.001* 0.023*

NOTE. Data are presented as mean ⫾ standard deviation. Abbreviations: CO, cardiac output; CVP, central venous pressure; HR, heart rate; IVC, inferior vena cava; MAP, mean arterial pressure; MPAP, mean pulmonary artery pressure; SVC, superior vena cava. *Statistically significant (p ⬍ 0.05).

Variations in IVCD depend not only on the compliance of the vessel but also on the amount of blood contained in the vessel. Passive leg elevation is a reversible maneuver that mimics rapid fluid loading by shifting venous blood from the legs toward the intrathoracic compartment, thereby increasing right and left ventricular preloads. This results in increased blood pressure and cardiac output in coronary patients with a normal right ventricular ejection fraction.12,13 In the present study, passive leg elevation induced significant increases in IVCD, SVCD, CVP, mean arterial pressure, and cardiac output. Both SVCD and IVCD increased after passive leg elevation, however, the increase in the SVCD was lower and showed no correlation with the CVP. In contrast, IVCD versus CVP (baseline CVP ⱕ11 mmHg) still showed correlation after passive leg elevation even if the correlation was weaker. Passive leg elevation increased CVP of some patients to more than 11 mmHg and shifted the linear regression line between IVCD versus CVP upward and rightward to the more scattered portion. This is probably a reason why the correlation was weaker. Furthermore, the disparity of results when the CVP ⬎11 mmHg could Fig 2. Correlation between the IVCD and the CVP (A) <11 mmHg and (B) >11 mmHg; R ⴝ 0.801, p < 0.001 (A: CVP <11 mmHg) and R ⴝ 0.272, p < 0.065 (B: CVP >11 mmHg).

Although significant increases in both IVCD and CVP were observed, the authors could not show a correlation between IVCD and CVP during PEEP ventilation. DISCUSSION

The results of this prospective study demonstrated a strong correlation between the IVCD and the CVP when CVP was lower than 11 mmHg. This correlation was weaker after passive leg elevation. No relation between IVCD and CVP was seen during PEEP ventilation. The scatter plot of the IVCD versus the CVP showed 2 portions. The first, steep portion (CVP ⱕ11 mmHg) reflects a compliant vessel with a preload reserve, whereas the second portion (CVP ⬎11 mmHg) reflects a poorly compliant vessel without any preload reserve. These 2 portions in the plot of the IVCD versus the CVP are in accordance with previous data obtained with TTE-derived IVCD.10,11

Fig 3. Correlation between the CVP and the IVCD before and after leg elevation in patients with baseline (CVP <11 mmHg, R ⴝ 0.880, p < 0.001 [before leg elevation] and R ⴝ 0.686, p < 0.001 [after leg elevation]).

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Table 3. Airway Pressure, Hemodynamic, and Echocardiographic Parameters During Mechanical Ventilation With Different Levels of PEEP

Peak airway pressure (cmH2O) Mean airway pressure (cmH2O) HR (beats/min) MAP (mmHg) MPAP (mmHg) CO (L/min) CVP (mmHg) IVC diameter (mm) SVC diameter (mm)

PEEP 0 cmH2O

PEEP 5 cmH2O

PEEP 10 cmH2O

18 ⫾ 3

21 ⫾ 3*

25 ⫾ 3*

6⫾1

9 ⫾ 1*

14 ⫾ 1*

71 ⫾ 11 72 ⫾ 11 23 ⫾ 5 4.6 ⫾ 1.6 11 ⫾ 3 23.9 ⫾ 4.2 14.7 ⫾ 2.6

70 ⫾ 11 74 ⫾ 11 24 ⫾ 4 4.7 ⫾ 1.6 12 ⫾ 3 25.0 ⫾ 4.0* 14.6 ⫾ 2.4

70 ⫾ 12 72 ⫾ 11 25 ⫾ 4* 4.4 ⫾ 1.7* 14 ⫾ 3* 26.5 ⫾ 4.2* 14.7 ⫾ 2.8

NOTE. Data are presented as mean ⫾ standard deviation. Abbreviations: CO, cardiac output; CVP, central venous pressure; HR, heart rate; IVC, inferior vena cava; MAP, mean arterial pressure; MPAP, mean pulmonary artery pressure; PEEP, positive end-expiratory pressure; SVC, superior vena cava. *Different compared with PEEP 0 cmH2O (p ⬍ 0.05).

also be explained by interfering factors such as the compliance of the right atrium and ventricle and right ventricular systolic function. However, the present study did not include right ventricular function. The uppermost IVC, just below its entry into the right atrium, is within the thorax. During mechanical insufflation, the pressure inside the thorax increases more than the pressure outside the thorax. Therefore, the pressure gradient to venous return is reduced, and the systemic venous return decreases during mechanical insufflation.14 As a consequence, mechanical insufflation increases the volume of extrathoracic venous blood and hence the endoluminal diameter of the distensible IVC, as observed in previous studies.15 Although IVCD in the present study was measured intrathoracically, the response to PEEP ventilation was still in accordance with a recent study that measured extrathoracic TTE-derived IVCD.16 Unlike the IVC, the route of SVC is purely intrathoracic and carries about 20% of the venous return to the right atrium. As in hypovolemia, cyclic increases in intrathoracic pressure, the pressure surrounding the SVC, can induce partial or even complete collapse of the vessel. Indeed, it can reduce the distending pressure of the SVC (ie, its intravascular pressure minus the intrathoracic pressure to below its closing pressure). The SVC collapsibility index is perhaps more reliable than the

IVC distensibility index in predicting fluid responsiveness.17 However, the present study observed only the end-expiration SVCD and IVCD and did not include the end-inspiration SVCD and IVCD. Therefore, no comment is made on the SVC or IVC distensibility index. Both CVP and the respective diameters of the IVC and SVC are influenced by many important physiologic and pathophysiologic issues. Central venous pressure is only a measure of cardiac preload when utilized as a dynamic parameter and related to cardiac output or a surrogate of it. In addition, CVP is assessed relative to the surrounding cardiac pressure, or transmural pressure. This suggests that the transmural pressure may be overestimated when applying PEEP, even in apnea. Exception can be made when low lung compliance is present, which often occurs after cardiac surgery. However, these patients were evaluated before surgery. In addition, the problem is whether the diameter of the IVC and SVC will alter much at the inlet point into the right atrium. A more sensitive parameter, the pulsed-wave Doppler flow through the IVC and SVC, is able to tell much more about right atrial pressures, compliance of right atrium and ventricle and function, respectively. Several groups of authors showed a good correlation between the noninvasive TTE-derived IVCD and the CVP.18-21 However, both subxiphoid and parasternal approach TTE are inconvenient to perform during major abdominal or thoracic surgery. In contrast, perioperative TEE can be performed routinely in high-risk patients undergoing noncardiac surgery.22 The data of the present study were obtained in cardiac surgical patients before sternotomy. Although it can be expected that similar data will be obtained in noncardiac patients, it is not yet defined if these indices, as validated in the present study, may apply for all patients. In addition, the only positive correlation was found between IVCD and CVP during apnea at endexpiration. With positive-pressure ventilation and various PEEP applications, no correlations between IVCD/SVCD and CVP were shown. Clinically, it is therefore unlikely that vena cava measurements can be used as surrogates for invasively measured loading pressures. Furthermore, unless a baseline relationship has been established with the use of an invasive method, the mere measurement of IVCD is unlikely to be useful as a surrogate for an absolute (numerical) CVP measurement in the operative setting. Thus, the measurement of IVCD can only be used as a trend monitor of right heart filling pressures after it is calibrated against an invasive pressure reading.

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