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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.55 no.5 Campinas Sept./Oct. 2005
Systemic hypertension and anesthesia*
Hipertensión arterial sistémica y anestesia
Michelle Nacur Lorentz, TSA, M.D.I; Alexandre Xavier Santos, M.D.II
IAnestesiologista do Biocor Instituto
IIME do Serviço de Anestesiologia do Hospital Julia Kubistchek/FHEMIG
BACKGROUND AND OBJECTIVES: Due to the
high incidence of systemic hypertension and the lack of consensus on pressure
levels to be accepted before inducing anesthesia for elective procedures, literature
associated to hypertension and anesthesia was reviewed. Considering that canceling
a surgery implies expenses making Medicine increasingly more expensive and that,
on the other hand, anesthesia should be induced in the safest possible manner,
this study aimed at evaluating literature evidences to orient clinical practice.
CONTENTS: Incidence and classification of systemic hypertension in addition to reports and comments on relevant studies approaching hypertension in surgical patients are presented.
CONCLUSIONS: Maximum pressure levels compatible with elective procedures are still not established and today criteria to cancel surgery of poorly controlled hypertensive patients are more based on empirical data than on evidences. There is a trend to cancel the procedure when BP is above 180/110 mmHg, but situations should be evaluated in a case-by-case basis, giving more importance to target-organs injury than to blood pressure itself.
Key Words: DISEASES: hypertension; PREANESTHETIC EVALUATION
JUSTIFICATIVA Y OBJETIVOS: Debido a la
grande superioridad de la hipertensión arterial sistémica en la población
y la falta de acuerdo sobre que niveles presóricos el anestesiologista
debe aceptar para inducir una anestesia para cirugía electiva, se realizó
una revisión en la literatura que trata de la asociación hipertensión
arterial y anestesia. Considerando que la suspensión de una cirugía
implica en gastos, lo que hace la Medicina cada vez más cara, y que, por
otro lado, el acto anestésico debe ser realizado con la mayor seguridad
posible, la finalidad de ese trabajo fue analizar las evidencias de la literatura
que puedan direccionar la práctica clínica.
CONTENIDO: El artículo presenta incidencia y clasificación de la hipertensión arterial sistémica, además de relatar y comentar trabajos relevantes a respecto de la hipertensión arterial en el paciente quirúrgico.
CONCLUSIONES: Aún no están establecidos sobre cuales niveles máximos de presión son compatibles con una cirugía electiva, siendo que, actualmente, los criterios para la suspensión de la cirugía en el paciente hipertenso mal controlado son mucho más apoyados en dados empíricos que en evidencias. Existe una inclinación en aplazar la cirugía cuando la PA es superior a 180/110 mmHg, solamente que cada caso debe ser analizado aisladamente, valorando más lesiones en órganos mira que en la presión arterial propiamente dicha.
Adequate preoperative blood pressure control as well as hypertensive patient management by the anesthesiologist has been the target for continuous discussions in the last 30 years. The decision of canceling or not an elective procedure in patients with abnormal blood pressure is probably the most frequent reason for controversies among anesthesiologists and surgeons. Considering the high incidence of systemic hypertension, especially in the elderly population, and which may be considered endemic, and the major difficulty in maintaining patients within "normal'' pressure levels, the frequency in which anesthesiologists are faced with this problem may be easily estimated. In the USA, only 54% of people considered hypertensive are treated, and just 28% of patients are able to achieve adequate blood pressure control 1.
Several questions may be posed for hypertensive patients scheduled for surgical procedures. The first is when should an elective surgery be cancelled for patients with high blood pressure. Another frequent question is whether systolic BP alone should be evaluated. Finally, it is important to check whether it is chronic hypertension or merely white-coat-hypertension, and whether intraoperative cardiovascular complications are related to inadequate BP control.
There are many controversial or even inconclusive studies on the subject. Our study aimed at reviewing the literature and evaluating evidences to orient clinical practice.
INCIDENCE AND CLASSIFICATION OF SBP
Systemic hypertension (SH) affects one out of four adults in the USA 2. It affects 10% to 15% of Caucasians and 20% to 30% of Afro-Americans in that country. Data on the number of hypertensive patients submitted to surgeries vary according to the type of surgery and the profile of the hospital (outpatient procedures, highly complex hospital). Hallen et al. 3 have reported that approximately 1.4% of all patients admitted to a general hospital received anti-hypertensive medication. Further surveys have shown a much higher incidence varying from 6% to 28% 4-6.
No etiology is found in more than 90% of cases of hypertension which are diagnosed as primary or essential SH. Secondary hypertension is responsible for 5% to 10% of cases of hypertension and may be due to renal diseases, primary hyperaldosteronism, pheochromocytoma, aortic coarctation, hormonal therapy, thyroid diseases or neurological disorders, among others. Renal vein stenosis is the most common cause of secondary SH and is present in 1% to 2% of hypertensive patients 7,8.
Currently it is known that PB measurement alone is not representative and SH diagnosis should be confirmed after two or more BP measurements in two or more visits after initial evaluation. BP measurement in the outpatient setting or at home by qualified non-medical professionals is more valuable than individual measurements 9-10, because it may identify cases of white-coat-hypertension and prevent unnecessary treatment.
White-coat hypertension is the measurement of persistently high BP values in the medical office, however normal in patients' daily life. It is observed in approximately 20% of patients with high BP 11 and although some studies show conflicting results, it seems to be associated to lower risk of cardiovascular events as compared to sustained hypertension 12-16. But since it might be a precursor of hypertension, it should be monitored and continuously evaluated.
After getting acquainted to different SH classifications, this study has adopted the Sixth Joint National Committee on the Detection, Evaluation and Treatment of High Blood Pressure (JNC VI) classification for being the most commonly mentioned in the studies we have evaluated. This classification is based on BP measurements without considering other risk factors and uses the mean of two or more measures taken in two or more occasions. JNC VI (Table I) has classified BP in three stages and has defined isolated systolic hypertension as SBP > 140 mmHg and DBP < 90 mmHg 17.
JNC VII 18, on the other hand, has classified hypertension in two stages:
Stage 1: Systolic BP between 140 and 159 mmHg and diastolic BP between 90 and 99 mmHg.
Stage 2: SBP equal to or above 160 mmHg and DBP equal to or above 100 mmHg.
In addition, it has established that in people above 50 years of age, SBP above 140 mmHg is more important for cardiovascular diseases than DBP. And that the risks of cardiovascular diseases starts with BP above 115/75 mmHg and double every 20/10 mmHg increase. Finally, it has defined that people with systolic BP between 120 and 139 mmHg and diastolic BP between 80 and 89 mmHg should be considered pre-hypertensive requiring changes in life style to prevent cardiovascular diseases.
Hypertensive crises are often seen with diastolic BP above 120 mmHg, although diagnosis and differentiation between urgency and emergency should be primarily based on the evaluation of the presence or not of signs of injury to target-organs than on pressure levels themselves 19,20. For example, a patient above 50 years of age with BP of 240/140 mmHg with no target-organ injury needs a less urgent treatment as compared to a pregnant patient with BP of 160/110 mmHg and seizures or to a child with acute diffuse glomerulonephritis and BP below 160/110 mmHg.
In a major study with patients scheduled for orthopedic procedures, SH was the primary medical cause for surgery cancelling, answering for 16.2% of cases 21. In another study in the UK 22 questionnaires were sent to 488 anesthesiologists with five clinical cases of patients with SH stages 2 and 3 and candidates to elective procedures; 58% of anesthesiologists have answered the questionnaire and 52.3% were used for statistical analysis (since the others have supplied inconclusive answers and could not be used in the study). A wide variability was found among anesthesiologists about which surgery should be or not cancelled, and which maximum pressure levels should be accepted, showing major confusion among colleagues in dealing with the subject.
It has already been established that poorly controlled hypertensive patients often present more severe hemodynamic changes during surgery 23. There is pronounced and relatively higher BP decrease after anesthetic induction and in general there is increased response to intubation and extubation stress. Long term SH treatment tends to reestablish vascular reactivity and brain circulation auto-regulation, and to improve hemodynamic stability. Based on these data, one may infer that preoperative hypertension management is beneficial for patients.
HYPERTENSION AND ANESTHESIA
Hypertension is a higher risk factor for coronary diseases 24, congestive heart failure 25, renal failure, progressive atherosclerosis, cerebral-vascular diseases and dementia 26. It is also associated to dyslipidemias, diabetes mellitus and obesity 27. High systolic BP is a stronger predictive factor for cardiovascular events as compared to diastolic blood pressure 28,29 and isolated systolic hypertension, very frequent in the elderly, is particularly dangerous. The higher the hypertension, the higher the risk of myocardial infarction, cardiac and renal failure, in a linear ratio30. Perioperative status, however, is much less clear, with many inconclusive or even controversial studies in the literature.
Goldman and Caldera 31, in 1979, have evaluated 676 consecutive patients submitted to general anesthesia for elective procedures and have found no association between hypertension at hospital admission and perioperative cardiac complications. Howell et al. has examined risk factors for cardiovascular death in the first 30 days after elective or urgency surgeries. For elective patients, the diagnosis of hypertension was considered risk factor. However, there has been no association between BP at admission and cardiovascular events 32. These studies, however, were limited by the fact that most patients presented hypertension stage 1 and 2, with few cases of stage 3.
Some studies have found relationship between blood pressure level, thus hypertension severity, and intra and postoperative myocardial ischemia 33-36. Another study with approximately 7 thousand vascular surgeries has failed to show SH as risk factor for perioperative myocardial infarction 37, possibly because this is a very frequent co-morbidity during vascular procedures. A recent meta-analysis with 30 studies involving 13,666 patients 38 has concluded that the relationship between SH and perioperative cardiac events is statistically significant however clinically insignificant. There is a poor association of perioperative complications and SH stages 1 and 2 (BP < 180/110 mmHg).
The problem was SH stage 3 patients since their status is well less clear. Although there is a trend toward higher hemodynamic instability, ischemic events and arrhythmias in severe hypertension patients, it was impossible to conclude that cancelling the procedure would improve perioperative cardiac behavior. Recent American Heart Association protocols have classified SH as minor risk factor not primarily interfering with perioperative events 39.
Another interesting point is isolated systolic pressure. For a long time, diastolic pressure was more valued than systolic pressure, being isolated systolic hypertension considered a benign disease for the elderly since most hypertensive patients above 60 years of age have only high systolic BP. More recent studies have shown that there is increased risk of cardiovascular events and death for this group of patients 40-42, in addition to mild increase in perioperative morbidity. In a different study with 2767 patients, borderline isolated systolic hypertension was the most common type of untreated hypertension among adults above 60 years of age and has progressed to permanent hypertension in 80% of cases. In addition, it could progress to more severe types and to cardiovascular complications 43. So, currently it is recognized that isolated systolic hypertension should also be treated.
EVALUATION OF HYPERTENSIVE PATIENTS
Hypertensive patients should be thoroughly evaluated before surgery. In addition to the underlying disease, co-morbidities 44 and possible target-organ injuries, especially coronary ischemia and ventricular dysfunction, should also be investigated. Attention should always be paid to the possibility of secondary SH when there are suggestive clinical signs. It is also important to differentiate SH from white-coat hypertension, having in mind that sometimes multiple blood pressure measurements are needed.
Among routine preoperative tests, especial attention should be given to ECG, serum potassium glycemia, erythrogram, urea and creatinine.
Anti-hypertensive drugs taken by patients should be carefully evaluated, reminding that most hypertensive patients are under some type of drug treatment and that drug combination is currently more common than single therapy, especially for stages 2 and 3 45. Potential hypokalemia due to diuretics should be evaluated and inadequacy of fast ionic correction should be considered. In patients needing potassium replacement, it preferable to do this within days than within hours.
Patients receiving angiotensin-converting enzyme inhibitors may present exacerbated response to anesthetic induction and perioperative hypotension 46,47. So, many authors recommend withdrawing the drug in the morning or the day before surgery.
Angiotensin II antagonists should also be withdrawn before surgery for the risk of refractory hypotension 48.
Confirmation of all drugs being used, which is done for every surgical patient, is here especially important since in this population, in general old, where the presence of one or more diseases being treated is common, physiological reserves to respond to certain situations are lower and drug associations may be more noxious.
Thirty years after initial Prys-Roberts et al. studies there is still no consensus on when to cancel surgery for hypertensive patients. The American Heart Association and the American College of Cardiology suggest that SH stage 3 (SBP > 180 mmHg and DBP > 110 mmHg) should be controlled before elective procedures 39. In spite of this recommendation, many authors suggest that target-organ injuries should be preferably considered as compared to isolated pressure levels, since canceling a surgery means several economic, bureaucratic and emotional problems and there is no certainty that canceling the surgery will benefit patients, that is, if in a future intervention, these same patients will be free from complications.
Some authors argue that with technical anesthetic evolution and control, the procedure and the treatment of possible intercurrences are safer nowadays. Undoubtedly, anesthesia as well as patients' intra and postoperative management have evolved and today through adequate monitoring, new anesthetic agents and especially new drugs, there is better perioperative pressure control 49. Nitroglycerin, sodium nitropruside and fenoldopam are drugs used to control intraoperative and immediate postoperative hypertensive crises. Sublingual nifedipine should be totally discouraged due to difficult titration and associated complications 50. Beta-blockers are particularly beneficial for patients with SH and coronary disease 51,52.
For major anesthetic-surgical procedures and faced to the need for more accurate BP measures, invasive blood pressure monitoring is recommended, avoiding pressure variations 20% above baseline.
However, in spite of all these cares and concepts the question about canceling surgery remains 53-55. All patients presenting for elective surgeries should be in their best possible conditions for the procedure. Currently, with the increasing concern with lawsuits, the situation of the anesthesiologist has become even more delicate. On the other hand, when canceling a procedure for adequate BP control, one must be aware that this may take 3 to 4 weeks and, in some cases, up to two months. There is no benefit in postponing the procedure for one or two days, which would only bring inconveniences for patients and the hospital. Last but not least, it is worth reminding that each case should be individually evaluated. One thing is to face a poorly controlled hypertensive patient candidate to cosmetic surgery and the other is an oncologic patient waiting for surgery results to start the treatment.
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Dra. Michelle Nacur Lorentz
Address: Rua Marquês de Maricá, 181/1502 Santo Antônio
ZIP: 30350-070 City: Belo Horizonte, Brazil
Submitted for publication January 12, 2005
Accepted for publicati May 10, 2005
* Received from BIOCOR Hospital de Doenças Cardiovasculares, Nova Lima, MG