- Email: [email protected]
Pulsed-Doppler evaluation of renal perfusion during pulsatile extracorporeal circulation. A pilot study
Rev Esp Anestesiol Reanim. 2018;65(7):380---384
Revista Española de Anestesiología y Reanimación www.elsevier.es/redar
BRIEF REPORT
Pulsed-Doppler evaluation of renal perfusion during pulsatile extracorporeal circulation. A pilot study夽,夽夽 B. Carretero de la Encarnación a , E. Mateo Rodríguez b,∗ , C.S. Romero García b , M.A. Revert Ros c a
Servicio de Anestesiología, Hospital General Universitario de Albacete, Albacete, Spain Servicio de Anestesiología, Hospital General Universitari de València, Valencia, Spain c Servicio de Radiología, Hospital General Universitari de València, Valencia, Spain b
Received 28 September 2017; accepted 27 January 2018 Available online 6 July 2018
KEYWORDS Renal perfusion; Pulsed wave Doppler; Extracorporeal circulation
Abstract Introduction: Acute renal failure (ARF) after cardiac surgery is a risk factor associated with mortality and use of resources. Some studies have reported beneficial effects of pulsatile flow on cardiopulmonary bypass (CPB) on renal function. The aim of this study is to describe the echographic morphology of the renal arterial wave modifying the parameters of pulsatile CPB. Material and method: Descriptive study was performed on 10 patients without previous AFR and undergoing cardiac surgery with CPB. Pre-, intra- and post-surgery renal ultrasound was performed. During pulsatile CPB, the amplitude and the baseline flow were modified. Recordings of pulsed Doppler in intrarenal arteries were obtained by measuring maximum systolic velocity, minimum diastolic velocity, resistance index (RI) and acceleration time (AT). Results: Statistical differences were found in ultrasounds pre-CPB between A50F50 modality (p = 0.013), A50F30 (p = 0.013) and A60F50 (p = 0.003). No statistically significance was found with A30F30 modality (p = 0.125). Conclusions: The decrease in the amplitude and the baseline flow of pulsatility during CPB shows a renal ultrasound morphology that is more similar to the physiological one. Subsequent studies using these characteristics during pulsatile CPB could thus show perfusion over the ARF that occurs after cardiac surgery. © 2018 Sociedad Espa˜ nola de Anestesiolog´ıa, Reanimaci´ on y Terap´ eutica del Dolor. Published by Elsevier Espa˜ na, S.L.U. All rights reserved.
夽 Please cite this article as: Carretero de la Encarnación B, Mateo Rodríguez E, Romero García CS, Revert Ros MA. Evaluación del flujo renal con Doppler pulsado durante la circulación extracorpórea pulsátil. Estudio piloto. Rev Esp Anestesiol Reanim. 2018;65:380---384. 夽夽 This article is part of the Anaesthesiology and Resuscitation Continuing Medical Education Program. An evaluation of the questions on this article can be made through the Internet by accessing the Education Section of the following web page: www.elsevier.es/redar ∗ Corresponding author. E-mail address: [email protected] (E. Mateo Rodríguez).
2341-1929/© 2018 Sociedad Espa˜ nola de Anestesiolog´ıa, Reanimaci´ on y Terap´ eutica del Dolor. Published by Elsevier Espa˜ na, S.L.U. All rights reserved.
Pulsed-Doppler evaluation of renal perfusion
PALABRAS CLAVE Perfusión renal; Eco-Doppler pulsado; Circulación extracorpórea
381
Evaluación del flujo renal con Doppler pulsado durante la circulación extracorpórea pulsátil. Estudio piloto Resumen Introducción: El fracaso renal agudo (FRA) tras la cirugía cardiaca es un factor de riesgo asociado a mortalidad y consumo de recursos. Algunos estudios encuentran efectos beneficiosos del flujo pulsátil en la circulación extracorpórea (CEC) sobre la función renal. El objetivo de este estudio es describir la morfología ecográfica de la onda arterial renal modificando los parámetros de la CEC pulsátil. Material y método: Estudio descriptivo de 10 pacientes intervenidos mediante cirugía cardiaca con CEC sin FRA previo. Se realizó ecografía renal pre-, intra- y poscirugía. Durante la CEC pulsátil se modificaron la amplitud y el flujo base. Se obtuvieron registros de Doppler pulsado en arterias intrarrenales, se midió la velocidad máxima sistólica y la velocidad mínima diastólica, el índice de resistencia (IR) y el tiempo de aceleración (TAcel). Resultados: La ecografía previa a la CEC (pre-CEC) muestra que hay diferencias significativas cuando se compara con los valores obtenidos en la modalidad A50F50 (p = 0,013), A50F30 (p = 0,013) y A60F50 (p = 0,003). No las hay para la modalidad A30F30 (p = 0,125). Conclusiones: La disminución de la amplitud y del flujo base de la pulsatilidad durante la CEC permite obtener una morfología ecográfica renal más parecida a la fisiológica. Estudios posteriores utilizando estas características durante la CEC pulsátil podrían mostrar la repercusión de este modo de perfusión sobre el FRA que se produce tras la cirugía cardiaca. © 2018 Sociedad Espa˜ nola de Anestesiolog´ıa, Reanimaci´ on y Terap´ eutica del Dolor. Publicado por Elsevier Espa˜ na, S.L.U. Todos los derechos reservados.
Introduction First systolic peak
Approximately 2 million cardiac surgeries are performed each year, and acute renal failure is the major risk factor associated with mortality, longer hospital stay, and higher costs. The development of extracorporeal circulation (ECC) and technological advances over the past 30 years have enabled clinicians to deliver high amplitude intermittent flow using pulsatile pumps. In theory, pulsed flow mimics the normal haemodynamic state. For this reason, several researchers have suggested that pulsatile flow in ECC is superior to non-pulsatile flow,1---8 while others find no differences between these techniques.9---12 Intrarenal arterial waveforms observed on Doppler ultrasound have been widely used to evaluate renal dysfunction.13---15 The aim of this study is to describe the changes in renal flow waveforms caused by modifying the characteristics of pulsatile flow (amplitude and base flow) during pulsatile ECC.
Material and method Data were collected from 10 patients who underwent on-pump cardiac surgery. The study was approved by the Ethics Committee. Patients aged under 18 years and those with a history of glomerular filtration rate of less than 60 ml/min/1.73 m2 determined using the corrected Cockcroft-Gault were excluded. Demographic variables, comorbidity, characteristics of the ECC, and postoperative renal function were collected. Left-sided, subdiaphragmatic ® kidney ultrasound (Phillips HD11 ultrasound system , Bothell, WA, USA) was performed with the patient in the supine
∗
Maximum systolic peak
Systole
Diastole
∗
∗ RI measurement points Acceleration Acceleration time
Figure 1 Measurement of the resistance index (RI) and acceleration time. Normal values: Acceleration time <70 ms, resistance index ≤0.7.
position (below the surgical drapes, without interrupting surgery), and pulsed Doppler views of intrarenal arteries of the left kidney, using 3 representative proximal segmental arteries (located with colour Doppler), were viewed and recorded. The peak systolic velocity (PSV) and the minimum diastolic velocity (MDV) were determined, together with the resistance index (RI), which was defined as RI = (PSV − MDV)/PSV, and acceleration time (time to PSV, in milliseconds) (Fig. 1). All values were measured at least 3 times for each segmental artery and averaged to obtain the mean value. All measurements were made by a trained
382 Table 1
B. Carretero de la Encarnación et al. Results of the renal pulsatile Doppler ultrasound.
Normal range (T1) Pre-ECC
PSV (cm/s)
MDV (cm/s)
RI
Acceleration time (ms)
28.2 ± 7
10.5 ± 2
<0.70 0.62 ± 0.1
<70 145 ± 10
Pulsatile ECC T2 A50F50 T3 A60F50 T4 A50F30 T5 A30F30 (T6 post-ECC 24 h)
Amplitude 50 60 50 30 36.5 ± 10
Base flow 50 50 30 30 11.4 ± 3
29.0 24.3 27.8 21.1 0.67
± ± ± ± ±
10 6 7 1 0.1
14.1 13.6 13.9 12.3 85
± ± ± ± ±
3 4 4 2 0.4
0.49 0.43 0.50 0.51
± ± ± ±
0.1 0.1 0.1 0.1
253 260 120 150
± ± ± ±
11 15 0.5 0.7
ECC: extracorporeal circulation; RI: resistance index; MDV: minimum diastolic velocity; PSV: maximum systolic velocity. Data shown as mean ± standard deviation.
Figure 2 (A) Renal Doppler T1 (pre-ECC). (B) Renal Doppler T2 ECC A50F50. (C) Renal Doppler T4 A30F30. A: amplitude; ECC: extracorporeal circulation; F: base flow.
researcher who was blinded to the subjects’ clinical data. PSV, MDV, RI and acceleration time were measured at the following time points: pre-ECC T1: before the surgical incision, after induction, with the patient anaesthetised, T2 ECC: standard pulsatile ECC with base flow 50%, amplitude 50% and 60 bpm; T3 A60: pulsatile ECC with base flow 50%, amplitude 60% and 60 bpm; T4 F30: pulsatile ECC with base flow 30%, amplitude 50% and 60 bpm; T5 A30F30: pulsatile ECC with base flow 30%, amplitude 30% and 60 bpm; and T6 24 h, with the patient extubated, 24 h after the end of surgery. Measurements were taken during ECC by asking the perfusionist to start pulsatile perfusion and maintain it for ® 5 min. Pulsatile ECC was delivered using a Stockert S5 roller pump (SorinGroup, Munich, Germany) that permits pulsatile flow (Appendix A). The statistical analysis was performed on R. After a descriptive analysis of the data, normality was tested with the Saphiro---Wilk test. Normally distributed data are expressed as mean and standard deviation, while non-normal data are expressed as median and interquartile range. The Wilcoxon signed-rank test was used to find significant differences between the variables of interest, RI and acceleration time, obtained during the renal ultrasound. In addition to the frequentist analysis, a graphic diagnosis was made using R’s ggplot2 library.
Results The descriptive analysis of the data shows that the mean age of the series was 67 years (SD 10) with a mean body mass index of 28 (SD 4). Seven patients were men, 80% presented arterial hypertension, 60% presented type 2 diabetes mellitus, and 60% dyslipidaemia. Mean Euroscore II
score was 2.7 (SD 1.8). Mean time on pump was 134 min (SD 41 min), and mean duration of aortic clamping was 102 min (SD 40 min). The median minimum temperature reached was 33 ◦ C (IQR 33.34). Mean arterial pressure during ECC was 70 mmHg (SD 7 mmHg) and 70 mmHg (8 mmHg) in the ICU. Mean urine output at 24 h was 2360 ml (940 ml). Four patients were given diuretics (furosemide 10 or 20 mg) and 7 were given nephrotoxic antibiotics (vancomycin). Eight patients required vasoactive drugs, predominantly nitroglycerin (30%). The results of the comparative analysis are shown in Table 1. Fig. 2 shows the renal pulsed Doppler waveforms observed at T1 pre-ECC, T2 ECC A50F50 and T5 A30F30. Significant differences were observed between the T1 preECC ultrasound and the values obtained at T2 A50F50 (p = 0.013), T3 A60F50 (p = 0.003) and T4 A5030 (p = 0.013). At T5 A30F30, no significant differences were found in comparison with the previous ultrasound (p = 0.125): in this modality, the RI was closer to the pre-ECC value (Fig. 3).
Discussion Pulsatile ECC with lower amplitude and base flow gives a renal ultrasound image that is more similar to pre-ECC morphology. This is the first time the effect of changes in amplitude or base flow on the renal artery waveform using pulsed Doppler ultrasound have been described. Intrarenal arterial waveforms observed on Doppler ultrasound are widely used to evaluate renal dysfunction. The RI correlates with renal vascular resistance, the filtration rate, and the effective renal plasma flow.13---15 It also establishes the severity of
Pulsed-Doppler evaluation of renal perfusion
383
Figure 3 Box plot of the resistance index according to ultrasound modality. A: amplitude; ECC: extracorporeal circulation; F: base flow.
tubular necrosis and evaluates renal functional recovery, since reduced RI precedes a reduction in plasma urea and creatinine levels by 24---48 h.14 The normal acceleration time is <70 ms. Longer acceleration time is indicative of renal hypoperfusion. In our patients, the average preECC acceleration time was higher than normal ranges. Performing the pre-ECC (T1) ultrasound with the patient under general anaesthesia before the surgical incision, the patient’s comorbidity (arterial hypertension and diabetes mellitus), and the abnormal renal flow during ECC could explain this finding. The lack pulsatile flow settings could have biased the results of both studies that support the use of this technique to improve renal perfusion during ECC4---8 and those that find no differences with respect to continuous flow.9---11 Studies investigating changes in amplitude and base flow (or other characteristics, such as rate) in pulsatile ECC in larger patient series could show the potential benefits of different settings on perioperative renal function. Elevated postoperative RI could show whether a particular type of ECC produces more acute renal failure than others. In our study, we show that the A30F30 mode is numerically equivalent to pre-CEC ultrasound data; however, the implications of this are unclear, since there are no studies that correlate postoperative clinical outcomes with the presence of postoperative complications. Furthermore, given the small number of patients, our results should be viewed with caution. This study is limited by its sample size which, being a pilot study, is low. Further studies in larger series are needed to confirm our preliminary results. We did not evaluate the incidence of haemolysis, ventilator-induced injury, or safety of ECC connections: further studies should take into account these side effects that increase bpm in pulsatile ECC.
Conclusions Reducing amplitude and base flow during ECC gives an ultrasound image that is more similar to pre-ECC morphology. Further studies with a larger number of patients using these characteristics during pulsatile ECC could show the effect of this perfusion mode on the incidence of acute renal failure after cardiac surgery.
Conflicts of interest The authors declare that they have no conflicts of interest.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j. redare.2018.01.021.
References 1. Koning NJ, Vonk AB, van Barneveld LJ, Beishuizen A, Atasever B, van den Brom CE, et al. Pulsatile flow during cardiopulmonary bypass preserves postoperative microcirculatory perfusion irrespective of systemic hemodynamics. J Appl Physiol. 2012;112:1727---34. 2. Alkan T, Akcevin A, Undar A. Benefits of pulsatile Perfusion on vital organ recovery during and after pediatric open heart surgery. ASAIO J. 2007;53:651---4. 3. Moazami N, Dembitsky WP, Adamson R, Steffen RJ, Soltesz EG, Starling RC, et al. Does pulsatility matter in the era of continuous-flow blood pumps? J Heart Lung Transplant. 2015;34:999---1004.
384 4. Adademir T, Ak K, Aljodi M, Elc ¸i ME, Arsan S, Isbir S. The effects of pulsatile cardiopulmonary bypass on acute kidney injury. Int J Artif Organs. 2012;35:511---9. 5. Serraino GF, Marsico R, Musolino G, Ventura V, Gulletta E, Santè P, et al. Pulsatile cardiopulmonary bypass with intra-aortic balloon pump improves organ function and reduces endothelial activation. Circ J. 2012;76:1121---9. 6. Kocakulak M, Askin G, Tarcan O, Pis¸kin E. Pulsatile flow improves renal function in high-risk cardiac operations. Blood Purif. 2005;23:263---7. 7. Sievert A, Sistino J. A meta-analysis of renal benefits to pulsatile perfusion in cardiac surgery. JECT. 2012;44:10---4. 8. Nam MJ, Lim CH, Kim HJ, Kim YH, Choi H, Son HS, et al. A meta-analysis of renal function after adult cardiac surgery with pulsatile perfusion. Artif Organs. 2015;39:788---94. 9. Saito S, Westaby S, Piggot D, Dudnikov S, Robson D, Catarino PA, et al. End-organ function during chronic nonpulsatile circulation. Ann Thorac Surg. 2002;74:1080---5. 10. Chow G, Roberts IG, Harris D, Wilson J, Elliott MJ, Edwards AD, et al. Stockert roller pump generated pulsatile flow: cerebral metabolic changes in adult cardiopulmonary bypass. Perfusion. 1997;12:113---9.
B. Carretero de la Encarnación et al. 11. Abramov D, Tamariz M, Serrick CI, Sharp E, Noel D, Harwood S, et al. The influence of cardiopulmonary bypass flow characteristics on the clinical outcome of 1820 coronary bypass patients. Can J Cardiol. 2003;19:237---43. 12. Baraki H, Gohrbandt B, del Bagno B, Haverich A, Boethig D, Kutschka I. Does pulsatile perfusion improve outcome after cardiac surgery? A propensity-matched analysis of 1959 patients. Perfusion. 2012;27:166---74. 13. Naesens M, Heylen LM, Lerut E, Claes K, de Wever L, Claus F, et al. Intrarrenal resistance index after renal transplantation. NEJM. 2013;369:1797---806. 14. Ninet S, Schnell D, Dewitte A, Zeni F, Meziani F, Darmon M. Doppler-based renal resistive index for prediction of renal dysfunction reversibility: a systematic review and meta-analysis. J Crit Care. 2015;30:629---35. 15. Iwashima Y, Yanase M, Horio T, Seguchi O, Murata Y, Fujita T, et al. Effect of pulsatile left ventricular assist system implantation on Doppler measurements of renal hemodynamic. Artificial Organs. 2012:353---8.
Revista Española de Anestesiología y Reanimación www.elsevier.es/redar
BRIEF REPORT
Pulsed-Doppler evaluation of renal perfusion during pulsatile extracorporeal circulation. A pilot study夽,夽夽 B. Carretero de la Encarnación a , E. Mateo Rodríguez b,∗ , C.S. Romero García b , M.A. Revert Ros c a
Servicio de Anestesiología, Hospital General Universitario de Albacete, Albacete, Spain Servicio de Anestesiología, Hospital General Universitari de València, Valencia, Spain c Servicio de Radiología, Hospital General Universitari de València, Valencia, Spain b
Received 28 September 2017; accepted 27 January 2018 Available online 6 July 2018
KEYWORDS Renal perfusion; Pulsed wave Doppler; Extracorporeal circulation
Abstract Introduction: Acute renal failure (ARF) after cardiac surgery is a risk factor associated with mortality and use of resources. Some studies have reported beneficial effects of pulsatile flow on cardiopulmonary bypass (CPB) on renal function. The aim of this study is to describe the echographic morphology of the renal arterial wave modifying the parameters of pulsatile CPB. Material and method: Descriptive study was performed on 10 patients without previous AFR and undergoing cardiac surgery with CPB. Pre-, intra- and post-surgery renal ultrasound was performed. During pulsatile CPB, the amplitude and the baseline flow were modified. Recordings of pulsed Doppler in intrarenal arteries were obtained by measuring maximum systolic velocity, minimum diastolic velocity, resistance index (RI) and acceleration time (AT). Results: Statistical differences were found in ultrasounds pre-CPB between A50F50 modality (p = 0.013), A50F30 (p = 0.013) and A60F50 (p = 0.003). No statistically significance was found with A30F30 modality (p = 0.125). Conclusions: The decrease in the amplitude and the baseline flow of pulsatility during CPB shows a renal ultrasound morphology that is more similar to the physiological one. Subsequent studies using these characteristics during pulsatile CPB could thus show perfusion over the ARF that occurs after cardiac surgery. © 2018 Sociedad Espa˜ nola de Anestesiolog´ıa, Reanimaci´ on y Terap´ eutica del Dolor. Published by Elsevier Espa˜ na, S.L.U. All rights reserved.
夽 Please cite this article as: Carretero de la Encarnación B, Mateo Rodríguez E, Romero García CS, Revert Ros MA. Evaluación del flujo renal con Doppler pulsado durante la circulación extracorpórea pulsátil. Estudio piloto. Rev Esp Anestesiol Reanim. 2018;65:380---384. 夽夽 This article is part of the Anaesthesiology and Resuscitation Continuing Medical Education Program. An evaluation of the questions on this article can be made through the Internet by accessing the Education Section of the following web page: www.elsevier.es/redar ∗ Corresponding author. E-mail address: [email protected] (E. Mateo Rodríguez).
2341-1929/© 2018 Sociedad Espa˜ nola de Anestesiolog´ıa, Reanimaci´ on y Terap´ eutica del Dolor. Published by Elsevier Espa˜ na, S.L.U. All rights reserved.
Pulsed-Doppler evaluation of renal perfusion
PALABRAS CLAVE Perfusión renal; Eco-Doppler pulsado; Circulación extracorpórea
381
Evaluación del flujo renal con Doppler pulsado durante la circulación extracorpórea pulsátil. Estudio piloto Resumen Introducción: El fracaso renal agudo (FRA) tras la cirugía cardiaca es un factor de riesgo asociado a mortalidad y consumo de recursos. Algunos estudios encuentran efectos beneficiosos del flujo pulsátil en la circulación extracorpórea (CEC) sobre la función renal. El objetivo de este estudio es describir la morfología ecográfica de la onda arterial renal modificando los parámetros de la CEC pulsátil. Material y método: Estudio descriptivo de 10 pacientes intervenidos mediante cirugía cardiaca con CEC sin FRA previo. Se realizó ecografía renal pre-, intra- y poscirugía. Durante la CEC pulsátil se modificaron la amplitud y el flujo base. Se obtuvieron registros de Doppler pulsado en arterias intrarrenales, se midió la velocidad máxima sistólica y la velocidad mínima diastólica, el índice de resistencia (IR) y el tiempo de aceleración (TAcel). Resultados: La ecografía previa a la CEC (pre-CEC) muestra que hay diferencias significativas cuando se compara con los valores obtenidos en la modalidad A50F50 (p = 0,013), A50F30 (p = 0,013) y A60F50 (p = 0,003). No las hay para la modalidad A30F30 (p = 0,125). Conclusiones: La disminución de la amplitud y del flujo base de la pulsatilidad durante la CEC permite obtener una morfología ecográfica renal más parecida a la fisiológica. Estudios posteriores utilizando estas características durante la CEC pulsátil podrían mostrar la repercusión de este modo de perfusión sobre el FRA que se produce tras la cirugía cardiaca. © 2018 Sociedad Espa˜ nola de Anestesiolog´ıa, Reanimaci´ on y Terap´ eutica del Dolor. Publicado por Elsevier Espa˜ na, S.L.U. Todos los derechos reservados.
Introduction First systolic peak
Approximately 2 million cardiac surgeries are performed each year, and acute renal failure is the major risk factor associated with mortality, longer hospital stay, and higher costs. The development of extracorporeal circulation (ECC) and technological advances over the past 30 years have enabled clinicians to deliver high amplitude intermittent flow using pulsatile pumps. In theory, pulsed flow mimics the normal haemodynamic state. For this reason, several researchers have suggested that pulsatile flow in ECC is superior to non-pulsatile flow,1---8 while others find no differences between these techniques.9---12 Intrarenal arterial waveforms observed on Doppler ultrasound have been widely used to evaluate renal dysfunction.13---15 The aim of this study is to describe the changes in renal flow waveforms caused by modifying the characteristics of pulsatile flow (amplitude and base flow) during pulsatile ECC.
Material and method Data were collected from 10 patients who underwent on-pump cardiac surgery. The study was approved by the Ethics Committee. Patients aged under 18 years and those with a history of glomerular filtration rate of less than 60 ml/min/1.73 m2 determined using the corrected Cockcroft-Gault were excluded. Demographic variables, comorbidity, characteristics of the ECC, and postoperative renal function were collected. Left-sided, subdiaphragmatic ® kidney ultrasound (Phillips HD11 ultrasound system , Bothell, WA, USA) was performed with the patient in the supine
∗
Maximum systolic peak
Systole
Diastole
∗
∗ RI measurement points Acceleration Acceleration time
Figure 1 Measurement of the resistance index (RI) and acceleration time. Normal values: Acceleration time <70 ms, resistance index ≤0.7.
position (below the surgical drapes, without interrupting surgery), and pulsed Doppler views of intrarenal arteries of the left kidney, using 3 representative proximal segmental arteries (located with colour Doppler), were viewed and recorded. The peak systolic velocity (PSV) and the minimum diastolic velocity (MDV) were determined, together with the resistance index (RI), which was defined as RI = (PSV − MDV)/PSV, and acceleration time (time to PSV, in milliseconds) (Fig. 1). All values were measured at least 3 times for each segmental artery and averaged to obtain the mean value. All measurements were made by a trained
382 Table 1
B. Carretero de la Encarnación et al. Results of the renal pulsatile Doppler ultrasound.
Normal range (T1) Pre-ECC
PSV (cm/s)
MDV (cm/s)
RI
Acceleration time (ms)
28.2 ± 7
10.5 ± 2
<0.70 0.62 ± 0.1
<70 145 ± 10
Pulsatile ECC T2 A50F50 T3 A60F50 T4 A50F30 T5 A30F30 (T6 post-ECC 24 h)
Amplitude 50 60 50 30 36.5 ± 10
Base flow 50 50 30 30 11.4 ± 3
29.0 24.3 27.8 21.1 0.67
± ± ± ± ±
10 6 7 1 0.1
14.1 13.6 13.9 12.3 85
± ± ± ± ±
3 4 4 2 0.4
0.49 0.43 0.50 0.51
± ± ± ±
0.1 0.1 0.1 0.1
253 260 120 150
± ± ± ±
11 15 0.5 0.7
ECC: extracorporeal circulation; RI: resistance index; MDV: minimum diastolic velocity; PSV: maximum systolic velocity. Data shown as mean ± standard deviation.
Figure 2 (A) Renal Doppler T1 (pre-ECC). (B) Renal Doppler T2 ECC A50F50. (C) Renal Doppler T4 A30F30. A: amplitude; ECC: extracorporeal circulation; F: base flow.
researcher who was blinded to the subjects’ clinical data. PSV, MDV, RI and acceleration time were measured at the following time points: pre-ECC T1: before the surgical incision, after induction, with the patient anaesthetised, T2 ECC: standard pulsatile ECC with base flow 50%, amplitude 50% and 60 bpm; T3 A60: pulsatile ECC with base flow 50%, amplitude 60% and 60 bpm; T4 F30: pulsatile ECC with base flow 30%, amplitude 50% and 60 bpm; T5 A30F30: pulsatile ECC with base flow 30%, amplitude 30% and 60 bpm; and T6 24 h, with the patient extubated, 24 h after the end of surgery. Measurements were taken during ECC by asking the perfusionist to start pulsatile perfusion and maintain it for ® 5 min. Pulsatile ECC was delivered using a Stockert S5 roller pump (SorinGroup, Munich, Germany) that permits pulsatile flow (Appendix A). The statistical analysis was performed on R. After a descriptive analysis of the data, normality was tested with the Saphiro---Wilk test. Normally distributed data are expressed as mean and standard deviation, while non-normal data are expressed as median and interquartile range. The Wilcoxon signed-rank test was used to find significant differences between the variables of interest, RI and acceleration time, obtained during the renal ultrasound. In addition to the frequentist analysis, a graphic diagnosis was made using R’s ggplot2 library.
Results The descriptive analysis of the data shows that the mean age of the series was 67 years (SD 10) with a mean body mass index of 28 (SD 4). Seven patients were men, 80% presented arterial hypertension, 60% presented type 2 diabetes mellitus, and 60% dyslipidaemia. Mean Euroscore II
score was 2.7 (SD 1.8). Mean time on pump was 134 min (SD 41 min), and mean duration of aortic clamping was 102 min (SD 40 min). The median minimum temperature reached was 33 ◦ C (IQR 33.34). Mean arterial pressure during ECC was 70 mmHg (SD 7 mmHg) and 70 mmHg (8 mmHg) in the ICU. Mean urine output at 24 h was 2360 ml (940 ml). Four patients were given diuretics (furosemide 10 or 20 mg) and 7 were given nephrotoxic antibiotics (vancomycin). Eight patients required vasoactive drugs, predominantly nitroglycerin (30%). The results of the comparative analysis are shown in Table 1. Fig. 2 shows the renal pulsed Doppler waveforms observed at T1 pre-ECC, T2 ECC A50F50 and T5 A30F30. Significant differences were observed between the T1 preECC ultrasound and the values obtained at T2 A50F50 (p = 0.013), T3 A60F50 (p = 0.003) and T4 A5030 (p = 0.013). At T5 A30F30, no significant differences were found in comparison with the previous ultrasound (p = 0.125): in this modality, the RI was closer to the pre-ECC value (Fig. 3).
Discussion Pulsatile ECC with lower amplitude and base flow gives a renal ultrasound image that is more similar to pre-ECC morphology. This is the first time the effect of changes in amplitude or base flow on the renal artery waveform using pulsed Doppler ultrasound have been described. Intrarenal arterial waveforms observed on Doppler ultrasound are widely used to evaluate renal dysfunction. The RI correlates with renal vascular resistance, the filtration rate, and the effective renal plasma flow.13---15 It also establishes the severity of
Pulsed-Doppler evaluation of renal perfusion
383
Figure 3 Box plot of the resistance index according to ultrasound modality. A: amplitude; ECC: extracorporeal circulation; F: base flow.
tubular necrosis and evaluates renal functional recovery, since reduced RI precedes a reduction in plasma urea and creatinine levels by 24---48 h.14 The normal acceleration time is <70 ms. Longer acceleration time is indicative of renal hypoperfusion. In our patients, the average preECC acceleration time was higher than normal ranges. Performing the pre-ECC (T1) ultrasound with the patient under general anaesthesia before the surgical incision, the patient’s comorbidity (arterial hypertension and diabetes mellitus), and the abnormal renal flow during ECC could explain this finding. The lack pulsatile flow settings could have biased the results of both studies that support the use of this technique to improve renal perfusion during ECC4---8 and those that find no differences with respect to continuous flow.9---11 Studies investigating changes in amplitude and base flow (or other characteristics, such as rate) in pulsatile ECC in larger patient series could show the potential benefits of different settings on perioperative renal function. Elevated postoperative RI could show whether a particular type of ECC produces more acute renal failure than others. In our study, we show that the A30F30 mode is numerically equivalent to pre-CEC ultrasound data; however, the implications of this are unclear, since there are no studies that correlate postoperative clinical outcomes with the presence of postoperative complications. Furthermore, given the small number of patients, our results should be viewed with caution. This study is limited by its sample size which, being a pilot study, is low. Further studies in larger series are needed to confirm our preliminary results. We did not evaluate the incidence of haemolysis, ventilator-induced injury, or safety of ECC connections: further studies should take into account these side effects that increase bpm in pulsatile ECC.
Conclusions Reducing amplitude and base flow during ECC gives an ultrasound image that is more similar to pre-ECC morphology. Further studies with a larger number of patients using these characteristics during pulsatile ECC could show the effect of this perfusion mode on the incidence of acute renal failure after cardiac surgery.
Conflicts of interest The authors declare that they have no conflicts of interest.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j. redare.2018.01.021.
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