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XIV, Vol.14, Number. 1/2010 57 Introduction I ntradialytic hypotension is a major complication in end stage renal disease patients on chronic intermittent hemodialysis (HD). Despite the efforts to understand its Abstract. Background Intradialytic hypotension continues to be a major problem in hemodialysis treat- ment today, despite technical improvements. Its origin is still a subject of extensive research. e aim of the study was to identify the cause of intradialytic hypotension, measuring hemodynamic parameters during a hemodialysis session. is strategy provides the opportunity of classifying the patients into different risk categories and may lead to an individualized dialysis protocol. Methods e variations in arterial blood pressure, cardiac stroke volume, heart rate, cardiac output and systemic vascular resistance were monitored during a hemodialysis session in sixty-two patients on chronic intermittent hemodialysis. Results Seventeen patients experienced an episode of intradialytic hypotension. Based on the predomi- nance of systemic vascular resistance (SVR) or stroke volume (SV) decrease at the time of hypotension, two groups could be differentiated. Six patients showed a fall in SVR (HID_svr group) whereas eleven patients showed a more pronounced decrease in cardiac output, caused by a decline in stroke volume. In the HID_sv group, Pearson's correlation revealed a predominant relationship between cardiac output variations and mean arterial pressure variations (R=0.59, p=0.001). No correlation was found between systemic vascular resistance and mean arterial pressure variations in this group. In the HID_svr group, the mean arterial pressure variations showed a strong correlation with systemic vascular resistance varia- tions (R=0.71, p=0.002) and a poor correlation with stroke volume (R=0.21, p=0.001) and cardiac output variations (R=0.11, p=0.0012). Conclusion Based on the hemodynamic response, intradialytic hypotension is due to cardiac filling failure caused by hypovolemia in one group, while in another group a fall in systemic vascular resistance, independent of cardiac function, is the cause of this complication. Different preventive strategies are proposed for the different subgroups. Keywords: intradialytic hypotension, hemodialysis, ultrafiltration, hypovolemia, systemic vascular resis- tance INTRADIALYTIC HYPOTENSION - MECHANISMS AND THERAPEUTIC IMPLICATIONS 1 Nephrology Department, "Sf. Ioan" Emergency Clinical Hospital, “Carol Davila”, University of Medicine and Pharmacy, Bucharest Mihaela-Elisabeta Stafie 1 , I. Al. Checherită 1 , A. Niculae 1 , Gabriela Lupuşoru 1 , Cristiana David 1 , Al. Ciocâlteu 1 erapeutics, Pharmacology and Clinical Toxicology Vol XIV, Number 1, March 2010 Pages 57-62 © Copyright reserved 2010 ORIGINAL PAPER Mihaela-Elisabeta Stafie, MD, Nephrology Department, "Sf. Ioan" Emergency Clinical Hospital, Vitan Bârzeşti, No. 13, Sector 4, Bucharest mstafi[email protected] causes, up to 30% of these patients still suffer frequently from hypotensive episodes that require intervention and reduce dialysis’ efficacy (1). Several factors contribute to dialysis hypotension, out of which hypovolemia has been considered to be the most important factor. Nowadays, the emphasis is shifting more and more towards failing compensatory mechanisms. e two most important compensation mechanisms are the ability of the heart to maintain cardiac output and a rise in systemic vascular resistance.

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Page 1: InTraDIalyTIc hypoTenSIon - mechanISmS anD TherapeuTIc ... fileIoan" Emergency Clinical Hospital, Vitan Bârzeşti, No. 13, Sector 4, Bucharest mstafie2003@yahoo.com. causes, up to

XIV, Vol.14, Number. 1/2010 57

Introduction

Intradialytic hypotension is a major complication in end stage renal disease

patients on chronic intermittent hemodialysis (HD). Despite the efforts to understand its

abstract. Background Intradialytic hypotension continues to be a major problem in hemodialysis treat-ment today, despite technical improvements. Its origin is still a subject of extensive research. The aim of the study was to identify the cause of intradialytic hypotension, measuring hemodynamic parameters during a hemodialysis session. This strategy provides the opportunity of classifying the patients into different risk categories and may lead to an individualized dialysis protocol. Methods The variations in arterial blood pressure, cardiac stroke volume, heart rate, cardiac output and systemic vascular resistance were monitored during a hemodialysis session in sixty-two patients on chronic intermittent hemodialysis. Results Seventeen patients experienced an episode of intradialytic hypotension. Based on the predomi-nance of systemic vascular resistance (SVR) or stroke volume (SV) decrease at the time of hypotension, two groups could be differentiated. Six patients showed a fall in SVR (HID_svr group) whereas eleven patients showed a more pronounced decrease in cardiac output, caused by a decline in stroke volume. In the HID_sv group, Pearson's correlation revealed a predominant relationship between cardiac output variations and mean arterial pressure variations (R=0.59, p=0.001). No correlation was found between systemic vascular resistance and mean arterial pressure variations in this group. In the HID_svr group, the mean arterial pressure variations showed a strong correlation with systemic vascular resistance varia-tions (R=0.71, p=0.002) and a poor correlation with stroke volume (R=0.21, p=0.001) and cardiac output variations (R=0.11, p=0.0012). Conclusion Based on the hemodynamic response, intradialytic hypotension is due to cardiac filling failure caused by hypovolemia in one group, while in another group a fall in systemic vascular resistance, independent of cardiac function, is the cause of this complication. Different preventive strategies are proposed for the different subgroups.Keywords: intradialytic hypotension, hemodialysis, ultrafiltration, hypovolemia, systemic vascular resis-tance

InTraDIalyTIc hypoTenSIon - mechanISmS anD TherapeuTIc ImplIcaTIonS

1Nephrology Department, "Sf. Ioan" Emergency Clinical Hospital, “Carol Davila”, University of Medicine and Pharmacy, Bucharest

mihaela-elisabeta Stafie1, I. al. checherită1, a. niculae1, Gabriela lupuşoru1, cristiana David1, al. ciocâlteu1

Therapeutics, pharmacology and clinical ToxicologyVol XIV, Number 1, March 2010Pages 57-62© Copyright reserved 2010

orIGInal paper

mihaela-elisabeta Stafie,MD, Nephrology Department,"Sf. Ioan" Emergency Clinical Hospital, Vitan Bârzeşti, No. 13, Sector 4, [email protected]

causes, up to 30% of these patients still suffer frequently from hypotensive episodes that require intervention and reduce dialysis’ efficacy (1). Several factors contribute to dialysis hypotension, out of which hypovolemia has been considered to be the most important factor. Nowadays, the emphasis is shifting more and more towards failing compensatory mechanisms. The two most important compensation mechanisms are the ability of the heart to maintain cardiac output and a rise in systemic vascular resistance.

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Therapeutics, Pharmacology and Clinical Toxicology58

materials and methods

SubjectsNinety-two of 109 patients on chronic

intermittent hemodialysis from the "Sf. Ioan" Hemodialysis Center (IHS) were investigated. Sixty-two patients were included in the study. The other patients were excluded because of aortic valvular disease - stenosis or insufficiency or left cardiac insufficiency (left ventricular ejection fraction < 45%) All patients included in the study were dialyzed 4 h per day 3 times per week using modified cellulosic membranes (TRICEA or DICEA), bicarbonate as buffer and heparin as anticoagulant. The hemodialyses were performed using the Tina Baxter machine. The blood flow volume varied from 200 to 350ml/min, whereas the dialysate flow was 500ml/min. The composition of the dialysate was Na+- 138-142 mmol/l, HCO3

--. 30-36 mmol/l , K+-2 mmol/l, Ca2+-1.5mmol/l. The temperature was between 35.5-36.5ºC. Dry weight was determined individually by the nephrologist physician on clinical grounds such as blood pressure, peripheral and/or pulmonary edema and central venous pressure. The ultrafiltration volume was based on the difference between pre-dialysis weight and dry weight.

methodsIn the present study the hemodynamic variables

monitored were: mean arterial pressure, stroke volume, heart rate, cardiac output and systemic vascular resistance.

Transthoracic echocardiography was perfor-med using an ALOKA 2D machine equipped with a 3.5MHz transducer. Stroke volume (SV) was determined by Doppler assessment of the

left ventricular outflow tract. Ecography was performed by a single person in order to prevent interobserver variability. All patients were tested right before being started on dialysis and then hourly during the hemodialysis session or at the occurrence of hypotension.

The heart rate (HR) was determined from the simultaneously recorded ECG.

Mean arterial pressure (MAP) was recorded using an automatic cuff sphygmomanometer every 30 minutes and on occurrence of symptoms of hypotension such as dizziness, muscle cramps, perspiration. The cardiac output (CO) was calculated as SV*HR. Systemic vascular resistance (SVR) was obtained using the formula: SVR=MAP/CO*80.

Study protocolThe patients were categorized according to

their intradialytic blood pressure status. Patients experiencing a decrease in systolic blood pressure during dialysis of more than 20 mmHg or below 100 mmHg associated with symptoms such as dizziness and nausea were considered hypotensive patients. Hypotensive patients were subdivided based on the most pronounced decrease in either stroke volume or systemic vascular resistance. Thus three groups were formed – a stable group (non-HID),

a group of hypotensive patients with predominant decrease in systemic vascular resistance (HID_svr) and a hypotensive group with a predominant decrease in stroke volume (HID_sv).

Statistical analysisResults were expressed as mean ± standard

deviation. Comparison between groups was performed

Intradialytic hypotension

Table I. Characteristics of the population

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XIV, Vol.14, Number. 1/2010 59

by unpaired Student’s test or by ANOVA in case of normally distributed variables and by the Kruskal-Wallis test in case of parameters that were not normally distributed. The correlation between variables was evaluated using the Pearson correlation. A p-value under 0.05 was considered to be statistically significant. The SPSS software was used for statistical analysis.

results

Hypotensive episodes occurred in 17 of 62 patients during hemodialysis session (27.4 %).

The patients’ characteristics for the three groups are described in table I.

The hypotensive episodes occurred on average at 204 minutes after initiation of HD in the HID_sv group and at 186 min in the HID_svr group (see figure 1).

The hemodynamic variables at the time of hypotension were compared with the data measured

at 3 hours in the stable group. The variations in hemodynamic parameters are detailed in tables II, III, IV and V.

Mihaela-Elisabeta Stafie et al.

figure 1. The change in mean arterial pressure during dialysis session in the two hypotensive groups (HID_sv and

HID_svr) and in the stable group

figure 2. The change in stroke volume during the dialysis session in the two hypotensive groups (HID_sv and HID_

svr) and in the stable group

figure 3. The change in systemic vascular resistance during dialysis session in the two hypotensive groups (HID_sv and

HID_svr) and in the stable group.

Table II. The changes in mean arterial pressure during dialysis in all groups

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Therapeutics, Pharmacology and Clinical Toxicology60

Intradialytic hypotension

Table III. The changes in stroke volume during dialysis in all groups

Table IV. The changes in heart rate during dialysis in all groups

Table V. The changes in cardiac output during dialysis in all groups

Table VI. The changes in systemic vascular resistance during dialysis in all groups

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Mihaela-Elisabeta Stafie et al.

Table VII. Changes in hemodynamic variables - comparison between start of treatment - 3 hours

The ultrafiltration volume at the moment of hypotension occurrence was larger in the hemodynamic unstable groups than in stable patients (table VII) – statistically significant results ANOVA, p=0.0005.

The stroke volume fell highly significant in the HID_sv group (-37.17%), but only slightly in the HID_svr group (-8.1%) and in the nonHID group (-5.10%) at the moment of hypotension (see figure 2). With Pearson’s correlation coefficient for the HID_sv group, the decrease in SV correlated moderately with the decrease in MAP (R=0.59, p=0.001). No correlation was found between systemic vascular resistance variations and mean arterial pressure variations in this group.

For the HID_svr group, CO increased at the moment of hypotension occurrence (+9.01%), but there were an abrupt decline of SVR (-30.48%) (see figure 3). The variations in SVR in the HID_svr group showed a strong correlation with the variations in MAP with Pearson’s correlation (R=0.71, p=0.002). The variations in MAP showed a poor correlation with SV (R=0.21,p=0.001) or with CO (R=0.11, p=0.0012) in the HID_svr group.

Discussion and conclusions

The main factor of intradialytic hypotension is the reduction of blood volume induced by ultrafiltration (2). Based on the hemodynamic response pattern, intradialytic hypotension is due to a cardiac filling failure in one subgroup, while in another subgroup a fall in systemic vascular resistance, independent of cardiac function, is

the cause of hypotension (3,4). The first group consists of cardiac compromised patients, with narrow margins in cardiovascular reserve capacity (5). The management of this type of hypotension might be an adjustment of the patient’s dry weight or cardiotonic medication (6). Prolonged or more frequent dialysis sessions can diminish the magnitude of variation in fluid state as well as sodium and ultrafiltration profile (7). The second group of patients experiences a decrease in systemic vascular resistance, which is inadequate during hypovolemia. The cause of this fall could not be clarified from our study. The cause of the SVR fall could be explained by a decrease in sympathetic tonus during HD (8) or by the release of nitric oxide (9). In this younger group, preventive strategies such as cool dialysate or alpha-agonists might be of benefit (10,11).

We conclude that intradialytic hypotension was not studied on an individual basis. Non-invasive monitoring of hemodynamic variables provides the opportunity to classify the individual hypotension prone patient and to apply the most effective preventive strategy.

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