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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.52 no.2 Campinas Mar./Apr. 2002
Arterial hypotension in myocardial revascularization surgery: influence of angiotensin-converting enzyme inhibitors*
Hipotensión arterial en cirugía de revascularización del miocardio: influencia de los inhibidores de la enzima conversora de angiotensina
Míriam Gomes Jordão, M.D.I; Ari Tadeu Lírio dos Santos, TSA, M.D.II
CET/SANE, Hospital São Lucas da PUC/RS; Hospital da Brigada Militar e Santa
Casa de Misericórdia, Porto Alegre, RS
IIAnestesiologista no Instituto de Cardiologia; Instrutor do CET/SANE, Porto Alegre, RS
BACKGROUND AND OBJECTIVES:
Angiotensin-converting enzyme inhibitors (ACEI) are widely used in hypertension
and heart failure. Their prolonged use may lead to hemodynamic instability and
hypotension during anesthetic induction. This study aimed at comparing the incidence
of hypotension in patients chronically treated and non treated with ACEI, submitted
to anesthesia for myocardial revascularization.
METHODS: Participated in this study 50 patients, physical status ASA II, III and IV, who were distributed in two groups: Group 1 - patients treated with ACEI for more than two months. Group 2 - patients not treated with ACEI. Parameters evaluated were mean blood pressure (MBP), heart rate (HR), and analysis of the ST segment in DII and V5. Systemic vascular resistance was determined during CPB.
RESULTS: The incidence of arterial hypotension in anesthetized patients under ACEI was higher than in the control group in several anesthetic moments, but was predominant during anesthetic induction. This group needed dopamine for longer periods. From the 26 patients previously treated with ACEI, 23% needed drugs to correct hypotension from induction to CPB, and 19.1% in other anesthetic periods, totaling 42.3%. No control group patient needed drug infusion to increase systemic blood pressure, from induction to CPB. However, 21% of patients in this group needed dopamine or araminol in one or more anesthetic moments.
CONCLUSIONS: In our study, patients treated whit ACEI for prolonged periods had a higher incidence of hypotension on anesthetic induction, requiring more drugs to maintain systemic pressure in adequate levels.
Key words: COMPLICATIONS: arterial hypotension; DRUGS, Cardiovascular: enalapril, captopril; SURGERY, Cardiac: myocardial revascularization
JUSTIFICATIVA Y OBJETIVOS:
Los inhibidores de la enzima conversora de la angiotensina (IECA) son drogas
muy utilizadas en estados hipertensivos e insuficiencia cardíaca. Su uso prolongado
puede ocasionar instabilidad hemodinámica con episodios hipotensivos durante
la inducción anestésica. El objetivo de este estudio es comparar la incidencia
de hipotensión arterial en pacientes crónicamente tratados con IECA con pacientes
no tratados con IECA, cuando sometidos a anestesia para cirugía de revascularización
MÉTODO: Participaron del estudio 50 pacientes, estado físico ASA II, III y IV, divididos en dos grupos: Grupo 1 - pacientes tratados con IECA por mas de dos meses y Grupo 2 - pacientes que no hacen uso de IECA. Los parámetros evaluados fueron presión arterial media (PAM), frecuencia cardíaca (FC), siendo anotados los menores valores de la PAM y FC verificados en diferentes períodos de la anestesia, y análisis del segmento ST en DII y V5. Durante la CEC, fue determinada la resistencia vascular sistémica.
RESULTADOS: La incidencia de hipotensión arterial en pacientes anestesiados en uso de IECA fue mayor de que en el grupo control en varios períodos de la anestesia, mas principalmente en la inducción anestésica. En este grupo fue necesario el uso de dopamina por tiempo más prolongado. De los 26 pacientes tratados previamente con IECA, 23% necesitaron de drogas para corrección de la hipotensión desde la inducción hasta la CEC y 19,1% en otros períodos de la anestesia, haciendo un total de 42,3%. En el grupo control ningún paciente necesitó infusión continua de drogas para aumentar la presión arterial sistémica, de la inducción hasta la CEC. Más, 21% de los pacientes de este grupo necesitaron dopamina o araminol en un o mas períodos de la anestesia.
CONCLUSIONES: En este estudio, los pacientes tratados con IECA, por tiempo prolongado, presentaron mayor incidencia de hipotensión arterial en la inducción anestésica, necesitando, con mayor frecuencia, de drogas para mantener la presión arterial sistémica en niveles adecuados.
Angiotensin-converting enzyme inhibitors (ACEI) are widely used in hypertension and heart failure. Their major effect on the rennin-angiotensin system (RAS) is to inhibit the conversion of the relatively inactive angiotensin I to the active form angiotensin II, thus abolishing or attenuating the responses to angiotensin of the systemic vascular resistance and mean systolic and diastolic blood pressure 1.
Angiotensin II is an extremely powerful vasoconstrictor. Vasoconstriction is fast and very intense in arterioles and less intense in veins. Arterioles constriction increases peripheral vascular resistance thus increasing blood pressure. Veins constriction increases venous return. Another important mechanism to increase blood pressure is its renal action, decreasing salt and water excretion and slowly increasing extracellular volume 2. When such mechanisms are inhibited, a higher risk for hemodynamic instability in situations such as anesthetic induction is to be expected.
It is today widely accepted that hypertensive patients should undergo surgery with controlled systemic blood pressure. So, anti-hypertensive therapy should be maintained until the surgery day and restarted after it as soon as possible. This consensus results from the evidence that interactions between betablockers or calcium channel blockers and anesthesia are beneficial without increasing hypotensive response to anesthetic induction 3. However, during the Annual Meeting of the American Society of Anesthesiologists in San Diego, in 1997, drugs interaction and anesthetic consequences were discussed and ACEI were mentioned as the only group of drugs acting on the cardiovascular system which should be withdrawn in the preoperative period because cardiovascular changes are more severe when patients remain with the drug 4. Studies have shown that patients chronically treated with ACEI have more difficulty in maintaining cardiac output during an acute decrease in anesthesia-induced ventricular volume, resulting in a higher risk for arterial hypotension during induction 3,5,6. A different study has shown that ACEI do not prevent postoperative arterial hypertension 6. The subject is controversial because, for some authors, preoperative ACEI withdrawal is not justifiable 7,8.
This study aimed at comparing the incidence of arterial hypotension in patients chronically treated and not treated with ACEIs, submitted to anesthesia for myocardial revascularization.
After the Ethics Committee approval, participated in this study 50 patients of both genders, aged 33 to 78 years, physical status ASA II, III and IV, submitted to myocardial revascularization with cardiopulmonary bypass (CPB). Patients with associated aortic insufficiency were excluded from the study.
Patients were distributed in two groups. Group 1 (n = 26) - patients receiving angiotensin converting enzyme inhibitors (ACEI), enalapril or captopril for more than two months, regardless of other drugs acting on the cardiovascular system. Group 2 (n = 24) - patients not receiving ACEIs, also regardless of the use of other drugs.
All patients were premedicated with morphine (0.2 mg.kg-1) and 0.5 mg atropine 45 minutes before surgery.
Monitoring consisted of cardioscope in DII and V5, pulse oximetry, invasive mean blood pressure (MBP), central venous pressure (CVP) and urine output. Anesthesia was induced with sodium thiopental (4 mg.kg-1), fentanyl (10 µg.kg-1) and pancuronium (0.1 mg.kg-1). Anesthesia was maintained with fentanyl up to 30 µg.kg-1 and halothane up to 0.5%.
Evaluated parameters were mean blood pressure (MBP), heart rate (HR), and analysis of the ST segment in DII and V5. The lowest MBP and HR values in different anesthetic moments were recorded. Systemic vascular resistance (SVR) was determined during CPB using the formula: SVR = MBP-CVP/CO. Since during CPB, CVP equals zero, SVR = MBP/CO, where CO = cardiac output.
Data were collected in the following periods:
Period 1 - beginning of anesthesia;
Period 2 - induction;
Period 3 - tracheal intubation;
Period 4 - tracheal intubation until incision;
Period 5 - incision until heparin;
Period 6 - heparin until CPB;
Period 7 - first 10 CPB minutes.
Hypotension was considered as MBP below 70 mmHg and severe hypotension when MBP dropped below 60 mmHg, requiring drugs such as dopamine and araminol.
Statistical analysis was performed with chi-square and Students t tests for independent samples being considered significant p a £ 0.05.
Demographics data, physical status and characteristics such as hematocrit, hemoglobin, ejection fraction, in addition to associated drugs are shown in table I and II. Both groups were similar as to these preoperative data, thus maintaining the homogeneity of the sample.
MBP and HR in different anesthetic periods are shown in table III. Note p < 0.05 for MBP in period 3 and for HR in period 2.
Hypotension is shown in table IV-A, where it is observed that 50% of patients treated with ACEI showed hypotension (< 70 mmHg) in period 2, which corresponds to anesthetic induction, as compared to 20.8% of non-users. So, the first group had a 2.4 relative risk for hypotension in this period (1.01 - 5.73) with p = 0.032, thus statistically significant. Table IV-B shows the number of patients with MBP £ 60 mmHg, comparing the incidence of hypotension between groups. When MBP £ 60 mmHg, dopamine infusion (5 mg.kg-1) and/or single araminol injection (0.5 mg) were started.
Table V shows all anesthetic periods where drugs were needed to control hypotension. From all ACEI-treated patients, 23% received dopamine from induction to CPB or araminol in certain periods. No control group patient needed drugs for normal blood pressure maintenance, for such prolonged period of time.
Figure 1 shows medians for both groups during different anesthetic periods, where the median is equivalent to mean pressures in mmHg, varying between percentiles 25-75. Lower values are seen in Group 1.
No ST segment changes were observed in both groups during the procedure. There were no statistically significant differences in SVR calculated during the first 10 CPB minutes for both groups.
This study has shown that the incidence of arterial hypotension in anesthetized patients using ACEI was higher as compared to the control group during several anesthetic periods, but especially during induction (Table IV). However, the most relevant data from this study was the more prolonged use of dopamine in those patients (Table V). From the 26 ACEI-treated patients, 23% needed drugs to correct hypotension from induction until CPB and 19.1% in other anesthetic periods, totaling 42.3%. In control group no patient needed drugs to continuously increase systemic blood pressure, from induction to CPB. However, 21.9% of patients in this group needed dopamine or araminol in one or more anesthetic periods (Table V). This greater need for drugs to correct blood pressure was already observed by other authors 3-5.
Severe hypotension treatment in anesthetized patients under ACEI is a concern. Angiotensin II 2.4 µg bolus was effective to restore systemic blood pressure in ACEI-treated patients with severe hypotension during anesthetic induction. An increase in preload and afterload and a transient decrease in ventricular function was observed in this study with the use of this drug 9. A different study has achieved good results with terlipressin (Vasopressin agonist) without impairing ventricular function in ACEI-treated patients not responding to epinephrine or phenylephrine in intraoperative hypotensive episodes 10. A study has shown that responses to norepinephrine infusions are significantly attenuated during and immediately after cardiopulmonary bypass in patients treated with ACEI for a long time 7. In our study, there was no hypotension refractory to dopamine or araminol.
A classic study 2 has shown that the rennin-angiotensin system efficiently contributes to increase blood pressure to normal values after severe hemorrhage. In our study, we have observed the greater difficulty of the patient with chronic rennin-angiotensin system inhibition to compensate an abrupt systemic blood pressure decrease.
The hypovolemic status of such patients is also related to an increased risk for hypotension and should be adequately treated and prevented with fluid replacement 5,6,11,12. Paradoxically, HR does not increase with blood pressure decrease. A parasympathetic tonus increase was described to explain such fact in ACEI-treated patients 5. Our study has not shown HR increase, but it should be reminded that most patients investigated were under betablockers.
The conclusion was that patients treated with ACEI for long periods show a higher incidence of arterial hypotension during anesthetic induction with the need of drugs to maintain systemic blood pressure in adequate levels.
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Submitted for publication May 09, 2001
Accepted for publication August 28, 2001