1Department of Anesthesiology and Intensive Care and the 2Institute of Cardiology, Sheba Medical Center, Sackler School of Medicine, Tel-Aviv University, Tel Hashomer, Israel*Corresponding author
Accepted for publication: November 22, 2001
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Abstract |
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Methods. Systolic pressure variation (SPV), delta up (dUp), and delta down (dDown), which are the changes in the arterial blood pressure (BP) during mechanical ventilation, were measured during graded haemorrhage and retransfusion in seven pigs under light halothane anaesthesia, and compared with changes in cardiac filling pressures and left ventricular end-diastolic volume (LVEDV), measured by echocardiography.
Results. Significant changes in preload parameters and stroke volume (SV) but not in BP and heart rate occurred. SPV, dDown, and cardiac filling pressures correlated significantly with LVEDV. Following retransfusion, LVEDV returned to baseline values but the SV and left ventricular ejection fraction were significantly low. This deterioration in myocardial performance was associated with elevated dUp.
Conclusions. During mechanical ventilation, dDown and the SPV may serve as minimally invasive indicators of preload. The retransfusion stage that follows significant blood loss may be associated with deterioration in LV function.
Br J Anaesth 2002; 88: 71618
Keywords: arterial pressure, measurement; blood, loss; heart, echocardiography; pig
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Introduction |
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The aim of our study was to examine the correla tion between parameters of arterial pressure waveform analysis to echocardiographic estimates of cardiac preload and function during graded haemorrhage and retransfusion.
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Methods and results |
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Haemodynamic measurements were made at baseline and 23 min after each change in blood volume. SPV was calculated as a mean over five consecutive mechanical breaths. dUp and dDown were measured as the difference between the value of systolic BP during 5 s of apnoea and its maximal and minimal values, respectively, during the respiratory cycle immediately preceding the apnoeic period. SPV, dUp, and dDown were expressed as percentages of systolic BP during apnoea.
Echocardiographic measurements were performed by a cardiologist who was blinded to the haemodynamic data. More details of the echocardiographic methods used in the study may be found elsewhere.8 Changes in the variables during the experiment were evaluated by analysis of variance for repeated measures. Coefficients of linear correlation between the LV end-diastolic volume (LVEDV) and the SPV, dDown, central venous pressure (CVP), and pulmonary artery occlusion pressure (PAOP) for each animal were derived by calculation of the mean r-values by reversed Fisher transformation.
Changes in the haemodynamic variables during the experiment are presented in Table 1. The gradual nature of the haemorrhage caused no significant changes in the arterial BP, and a significant decrease in the mean SV occurred only after 20% haemorrhage. CVP, PAOP, and LVEDV decreased, and %SPV and %dDown increased from the very early stages of haemorrhage. Following retransfusion, LVEDV returned to its baseline value. SV and left ventricular ejection fraction (LVEF) significantly decreased. dUp increased significantly, as did left ventricular end-systolic wall stress (ESWS). Changes of PAOP, CVP, and %SPV and %dDown correlated significantly with LVEDV (r values of 0.76, 0.77, 0.77, and 0.82, respectively).
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Comment |
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The retransfusion stage was associated with a global deterioration in LV function, which was reflected by the sharp decrease in LVEF. This phenomenon may have been caused by an elevation of afterload and/or by myocardial depression. Indeed, although no significant changes of systemic vascular resistance (SVR) occurred, ESWS, a more precise characteristic of myocardial afterload,9 was significantly increased after retransfusion. The decrease of myocardial performance was accompanied by a prominent increase of dUp, as was shown previously in a model of heart failure.3
The physiologic responses to blood loss and rapid volume restoration in our experiment may have been influenced by the anaesthetic agent and muscular relaxant used, as halothane was shown to reduce SVR and blunt the cardiovascular response to acute haemorrhage,10 whereas pancuronium bromide possesses vagolytic and sympathomimetic properties.11 However, a lack of changes in BP and elevation in heart rate in response to haemorrhage suggest a relatively superficial plane of anaesthesia in our experiment.
In conclusion, during graded haemorrhage and rapid blood volume restoration parameters of arterial pressure waveform analysis correlate with echocardiographic estimates of LV preload. The combination of a small dDown and a prominent dUp reflects the possible myocardial depression that can occur following haemorrhage and retransfusion. These results suggest that the changes in the arterial pressure waveform may be used as readily available monitoring tools in the haemodynamic assessment of mechanically ventilated patients.
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References |
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