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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.54 no.3 Campinas May/June 2004
Continuous and bolus thermodilution cardiac output measurement during off-pump coronary artery bypass surgery*
Comparación entre la medida continua del débito cardíaco y por termodilución en bolus durante la revascularización miocárdica sin circulación extracorpórea
Sílvia M. Kim, M.D.I; Sílvia D. S. Oliveira, M.D.II; Ubirajara S. Fonseca, M.D.II; Luiz Marcelo Sá Malbouisson, TSA, M.D.III; José Otávio Costa Auler Júnior, TSA, M.D.IV; Maria José Carvalho Carmona TSA, M.D.V
IPreceptora da Disciplina de Anestesiologia
IIME do CET/SBA do HC da FMUSP
IIIDoutor em Anestesiologia pela FMUSP. Assistente do Serviço de Anestesiologia e Terapia Intensiva Cirúrgica do Instituto do Coração do HC da FMUSP
IVProfessor Titular da Disciplina de Anestesiologia da FMUSP; Diretor do Serviço de Anestesiologia e Terapia Intensiva Cirúrgica do Instituto do Coração do HC da FMUSP
VProfessora Doutora da Disciplina de Anestesiologia da FMUSP; Supervisora do Serviço de Anestesiologia e Terapia Intensiva Cirúrgica do Instituto do Coração do HC da FMUSP
BACKGROUND AND OBJECTIVES: Off-pump CABG
surgery is related to major and abrupt hemodynamic changes that may not be immediately
detected by continuous cardiac output measurement (CCO). This study aimed at
comparing results of cardiac index measurement with pulmonary artery catheter
(PAC) with thermal filament (Baxter Edwards Critical Care, Irvine, CA) versus
standard bolus thermodilution method during distal coronary anastomosis.
METHODS: Participated in this study 10 patients undergoing off-pump CABG who were monitored with PAC with thermal filament. Measurements of cardiac index were obtained in four moments: at anesthetic induction with the chest still closed (M1), after sternotomy (M2), after heart stabilization with the octopus device (M3) and at distal anastomosis completion (M4).
RESULTS: There has been significant cardiac index decrease (p < 0.05) during coronary anastomosis, detected when measurements were taken with bolus thermodilution method. Cardiac index has varied 2.8 ± 0.7 to 2.3 ± 0.8 L.min.m-2 in the beginning and 2.5 ± 0.8 L.min.m-2 at the end of anastomosis. This variation was not detected by the continuous method (from 3 ± 0.6 to 3.2 ± 0.5 to 3.1 ± 0.6 L.min.m-2 during anastomosis).
CONCLUSIONS: CCO measurement with PAC was late in detecting acute hemodynamic changes due to changes in heart position during off-pump CABG.
Key Words: MEASUREMENT TECHNIQUES: thermodilution; MONITORING: cardiac output; SURGERY, Cardiac: coronary artery bypass
JUSTIFICATIVA Y OBJETIVOS: La cirugía
de revascularización miocárdica sin uso de circulación extracorpórea
(CEC) se relaciona a importantes alteraciones hemodinámicas bruscas que
pueden no ser prontamente detectadas por la medida continua de débito cardíaco.
Este estudio compara resultados obtenidos por la medida del índice cardíaco
con el catéter de arteria pulmonar con filamento térmico (Baxter Edwards
Critical Care, Irvine, CA) con el método patrón por termodilución
con solución, durante la anastomosis coronariana distal.
MÉTODO: Diez pacientes sometidos a la cirugía de revascularización miocárdica sin CEC fueron monitorizados con el catéter de arteria pulmonar con filamento térmico. Las medidas de índice cardíaco fueron obtenidas en cuatro momentos: al inicio de la anestesia, en cuanto el tórax aun estaba cerrado (M1), después de la esternotomia (M2), después de la estabilización del corazón con el aparato octopus (M3) y al final de la anastomosis coronariana distal (M4).
RESULTADOS: Hubo disminución significativa (p < 0,05) del índice cardíaco durante la anastomosis coronariana, detectada por la medida con termodilución con bolus de solución. El índice cardíaco varió de 2,8 ± 0,7 para 2,3 ± 0,8 L.min.m-2 en el inicio de la anastomosis y 2,5 ± 0,8 L.min.m-2 al final de la misma. Esa variación no fue detectada por la medida continua (de 3 ± 0,6 para 3,2 ± 0,5 y 3,1 ± 0,6 L.min.m-2 durante la anastomosis coronariana).
CONCLUSIONES: La medida de débito cardíaco continuo utilizando el catéter de arteria pulmonar con filamento térmico, presentó atraso en la detección de las alteraciones hemodinámicas agudas relacionadas al cambio del posicionamiento del corazón en la cirugía de revascularización miocárdica sin CEC.
Off-pump coronary artery bypass surgery (CABG) may promote sudden and transient hemodynamic changes related to heart positioning and ischemic changes. Non-anatomic heart position to help arteries exposure may decrease cardiac output. So, hemodynamic monitoring plays an important role in identifying decreased cardiac output 1-7.
Monitors to continuously monitor cardiac output have been developed and introduced in the clinical practice. Pulmonary artery catheter with thermal filament is based on thermal energy emission to calculate cardiac output by the thermodilution principle. During internal thoracic artery anastomosis to anterior descending artery, continuous measurements have shown good correlation with actual hemodynamic conditions 8, but results obtained with the continuous method and with bolus thermodilution have differences which cannot be clinically accepted 9.
This study aimed at identifying cardiac output changes during intraoperative heart positioning and at comparing continuous and intermittent thermodilution method with solution bolus injection.
The protocol was approved by the Scientific Committee, Instituto do Coração (InCor) and by the Research Projects Analysis Committee (CAPPesq), Hospital das Clínicas, Faculdade de Medicina, USP.
Participated in this study 10 patients of both genders, aged 48 to 78 years, submitted to off-pump coronary artery bypass surgery. Surgical risk was established according to Higgin's criteria 10, being admitted low to moderate risk patients. Revascularized arteries were: anterior descending, left marginal, diagonal or circumflex. Only hemodynamic changes observed until first anastomosis were evaluated in this study.
All patients were evaluated the day before surgery and received 7.5 mg oral midazolam at referral to the operating center. After monitoring with ECG at DII and V5 leads with continuous ST segment analysis and pulse oximetry, patients were submitted to peripheral venoclysis with large catheter and radial artery catheterization. General anesthesia was induced with titrated sufentanil up to 0.5 µg.kg-1 and propofol (until loss of reflexes) or etomidate (0.2 mg.kg-1). Muscle relaxation was achieved with pancuronium (0.08 mg.kg-1) or atracurium (0.5 mg.kg-1) and tracheal intubation was performed after manual ventilation under mask. Anesthesia was maintained with variable isoflurane concentrations (0.7% to 0.9%) and intermittent sufentanil bolus.
Pulmonary artery catheter (7F) with thermal filament (CCO catheter, Baxter Edwards Critical Care, Irvine, CA) was introduced in the right internal jugular vein and connected to a Vigilance monitor (Baxter Edwards Critical Care, Irvine, CA). After catheter positioning in the pulmonary artery, mixed venous blood sample was collected for gases analysis and continuous venous saturation monitor gaging.
Hemodynamic evaluation was performed after anesthetic induction and with the chest still closed (M0), after sternotomy (M1), in the beginning of coronary anastomosis after myocardial wall stabilizing device Octopus (Medtronic, Inc., Minneapolis, Minn.) positioning (M2) and at anastomosis completion before Octopus removal (M3). Cardiac output measurements were divided by body surface measurements to obtain cardiac index value.
Cardiac output values recorded by the Vigilance monitor were considered continuous output. Then, cardiac output was measured with bolus injection of 10 mL saline solution in room temperature. Thermodilution curves were evaluated and recorded result has considered the mean of three consecutive measurements.
Data were evaluated by two-way Analysis of Variance for repetitive measurements (ANOVA), considering significant p < 0.05.
Anthropometric data relating gender, age, body surface, surgical risk and coronary anastomosis site are shown in table I. Table II shows cardiac index obtained by continuous and intermittent thermodilution technique as well as mixed oxygen venous saturation (SvO2), also represented in figure 1.
All patients had decreased cardiac index during coronary anastomosis, detected both by continuous and intermitted thermodilution. Difference between mean values detected by both methods in different surgical times was statistically significant (p < 0.001). There have been no statistically significant differences between values of both methods in moments M0 (after anesthetic induction) and M1 open chest). However, there have been differences between values (p < 0.05) at sudden cardiac output decrease during coronary anastomosis, both in beginning and end of procedure. SvO2 decrease has shown statistically significant interaction with cardiac output decrease detected by bolus thermodilution.
Off-pump coronary artery bypass surgery is becoming increasingly frequent, in an attempt to decrease the pump's adverse effects and having a less invasive option with lower morbidity 7. Coronary artery bypass (CAB) may promote several changes, such as systemic inflammatory response syndrome, coagulation disorders, hemodilution and risk for air embolism, in addition to postoperative pulmonary function changes. Factors such as coronary reoperation, older age, female gender and left ventricular dysfunction are independent forecasters for high mortality risk during coronary artery bypass surgery. Off-pump surgery is a potential alternative for these high risk patients 11,12. Currently, there are devices to stabilize and immobilize myocardial wall to be manipulated, which help surgical technique and decrease the need for heart rate-decreasing drugs 13. The incidence of complications, such as CAB conversion, myocardial infarction and coronary re-intervention is low, suggesting that Octopus tissue stabilizer is a safe device 14. However, there may be major hemodynamic changes directly related to changes in heart position and ventricular manipulation for coronary anastomosis.
Hemodynamic fluctuations may be minimized by preload adjustment and vasoactive drugs. It is important to early detect changes to orient therapy. Table position changes, volume administration or even drug support may be needed to manage sudden cardiac output decrease.
Continuous cardiac output measurement through Edwards CCO catheter thermal filament catheter (Baxter Edwards Critical Care, Irvine, CA) is an interesting monitoring means which uses the thermodilution principle of blood warmed by heat pulses emitted by the filament positioned in the right ventricle 8.
Clinical and experimental studies have shown a good correlation between cardiac output values obtained by continuous measurement and intermittent measurements with cold solution bolus 8. Other studies, however, have shown a delay in acute hemodynamic changes detection 15.
As observed in our study, there has been good correlation between cardiac index values obtained by the standard bolus thermodilution method and by continuous measurements with pulmonary artery catheter with thermal filament in moments of hemodynamic status maintenance. However, in moments where there has been sudden cardiac function changes, such as during ventricular wall stabilizer device placement and at anastomosis completion, there has been continuous measurement delay. With brief cardiac output decrease there is no changes in monitor values, which represent mean values obtained in three to six previous minutes. For this reason, some centers suggest the term semi- continuous cardiac output to define the technique. Measurement recorded in the STAT mode is more accurate, however slower than MBP and SvO2 response during acute hemodynamic changes 16. Nevertheless, massive heart manipulation during measurement could further interfere with the technique.
This continuous cardiac output monitoring disadvantage could be minimized by bolus thermodilution cardiac output measurements whenever there are acute hemodynamic changes by severe bleeding or major SvO2 decrease. As SvO2 during acute hemorrhage decreases in parallel with cardiac output decrease 15, continuous SvO2 monitoring directly follows cardiac output changes, provided that oxygen arterial saturation and hemoglobin levels remain constant. This way, sudden hemodynamic changes of off-pump coronary artery bypass could justify the loss of correlation of both cardiac output measurement techniques.
In conclusion, continuous cardiac output measurement with pulmonary artery catheter with thermal filament was late in detecting acute hemodynamic changes related to changes in heart position during off-pump coronary artery bypass surgery. So, for this type of surgery, in initial and final anastomosis moments, it is recommended to complement continuous cardiac output measurement with bolus injections or with oxygen mixed venous saturation monitoring.
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Dra. Maria José Carvalho Carmona
Rua Rodésia, 161/82 Vila Madalena
05435-020 São Paulo, SP
Submitted for publication May 12, 2003
Accepted for publication August 20, 2003
* Recebido do Serviço de Anestesiologia e Divisão de Cirurgia do Instituto do Coração do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HC FMUSP), SP