Metodología de la investigación científica: capítulo III / Scientific research methodology: chapter III

En el tercer capítulo de esta serie dedicada a comentar los aspectos más relevantes del proceso de investigación científica, se revisan brevemente los diferentes diseños de estudio, la importancia de la evaluación por pares y los aspectos más relevantes que se deben considerar en la ejecución del estudio.

Metodología de la investigación científica - Parte II / Scientific research metodology - Part II

Éste es el segundo capítulo de la serie dedicada a comentar los aspectos más relevantes del proceso de investigación científica. Aquí se abordan aspectos relacionados con la formulación de objetivos e hipótesis de trabajo, los que, derivados de la identificación de una pregunta de investigación adecuada y bien formulada, son los insumos básicos para definir el diseño de la investigación.

Consumo de drogas en población escolar de Chile en alumnos de 8° básico a 4° medio, 2003 / Drug use in chilean school population ranging from 8th grade basic education to 4th year middle school, 2003

Se describe el consumo de drogas en población escolar chilena que en 2003 cursaba entre el 8° básico y el 4° año medio. Los datos corresponden al Quinto Estudio Nacional de Drogas en Población Escolar de Chile, 2003. Se determinó que la tasa de consumo reciente de cualquier droga ilícita para el grupo de estudio es de 13,66 por ciento, donde el 94 por ciento se concentra en estudiantes que usan marihuana. La tasa de consumo reciente de alcohol y cigarrillos alcanza a 61,15 por ciento y 51,54 por ciento, respectivamente. Los hombres presentan consumos recientes de drogas ilícitas más altos que las mujeres, aunque sólo las superan en 3 puntos porcentuales en marihuana; sin embargo, los usos recientes de pasta base y de cocaína se encuentran en una razón de 2:1. La tendencia del consumo en el bienio 2001-2003, de acuerdo a la prevalencia de último año, registra una disminución del consumo de marihuana y cigarrillos. La disponibilidad de drogas y la baja percepción de riesgo favorece el uso de estas sustancias.

Metodología de la investigación científica / Scientific research methodology

Este es el primer capítulo de una serie dedicada a comentar los aspectos más relevantes del proceso de investigación científica. El propósito es que esta serie ayude a los profesionales que se inician en el fascinante mundo de la investigación a precisar algunos conceptos básicos que siempre deben estar presentes en la elaboración de sus proyectos

Perfil del hipertenso adulto mayor tratado / Morbidity and mortality of treated elderly hypertensive patients

Background: There is concern about the consequences that hypertension has on the well being and mortality of elderly people. Aim: To compare the morbidity and mortality of young and old treated hypertensive subjects. Material and methods: Retrospective analysis of hypertensive subjects treated and followed for a period of 10 ñ 9 years. Subjects that started treatment at an age of less than 65 years and those that started treatment after 65 years of age, were analyzed separately. The antihypertensive drugs used for treatment and blood pressure reduction were similar in both groups. Results: Subjects that started treatment after 65 years of age (157 females and 133 males) had lower serum cholesterol levels and a higher prevalence of end organ damage than their younger counterparts. Women over 65 had a higher body mass index than women of less than 65. Males over 65 years had a higher prevalence of diabetes than younger males. Mortality and complications of hypertension were higher in subjects that started treatment after 65 years of age. Conclusions: The higher mortality of subjects that start hypertensive treatment after 65 years of age, is indicative of the need to detect and treat hypertension at the earliest possible moment

Reducción de la mortalidad por infarto del miocardio en hospitales chilenos / Reduction of acute myocardial infarction mortality in Chilean hospitals

Background: The characteristics of patients with acute myocardial infarction (MI) admitted to 37 Chilean hospitals (GEMI Registry Group), have been analyzed in the periods 1993-1995 and 1997-1998. Aim: To report the changes in hospital mortality between these 2 periods, with a particular emphasis on the impact of treatment. Patients and methods: Between 1993-1995 we collected information from 2,957 patients and between 1997-1998 we registered 1,981 patients with MI. Analysis of the changes in mortality between periods was adjusted by demographic variables, coronary risk factors, MI location, Killip class on admission and the different therapeutic strategies utilized. The effects of different treatments on hospital mortality were adjusted by the previously determined mortality risk variables. Results: Hospital mortality decreased from 13.3 percent to 10.8 percent between both periods (Odds Ratio (OR) 0.78, confidence intervals (95 percent) (CI) 0.65-0.93). A significant reduction in mortality was observed among patients below 60 years of age, in men, in diabetics and in subjects with an infarction classified as Killip class over II. The use of beta blockers (OR 0.65, CI 0.42-0.99) and intravenous nitrates (OR 0.78, CI 0.61-0.99) and the lower use of calcium channel blockers (OR 0.72, CI 0.60-0.87) were significantly associated with a lower mortality. The administration of angiotensin converting enzyme inhibitors was associated with a 29.3 percent mortality reduction (OR 0.69, CI 0.47-1.02). Conclusions: There has been a significant reduction in the mortality rate for MI in Chilean hospitals during the 2 registry periods analyzed, which was significant among some high risk patients and was related to treatment changes, according to evidence based guidelines

Morbimortalidad de la hipertensión arterial esencial tratada en un seguimiento de 26 años / Mortality and morbidity of treated essential arterial hypertension: a 26 years follow up

Background: Treatment has a definitive impact on mortality in hypertension. The magnitude of blood pressure reduction, the type of drug used and the associated risk factors may modulate the effect of treatment on mortality. Aim: To report the effects of treatment of essential hypertension, in a cohort followed for up to 26 years. Patients and methods: A cohort of 1,172 essential hypertensive patients followed up to 26 years. Patients were treated with different antihypertensive drugs, alone or in combination (diuretics, beta blockers, calcium channel blockers and angiotensin converting enzyme inhibitors) according to international rules and consensus. Subjects were followed until death or loss from follow-up. Blood pressure reduction was aimed to obtain figures near 140/ 90 mm Hg. Causes of death and complications were obtained from hospital records, phone and death certificates. Survival was studied using life tables (Kaplan Meier method and intention to treat analysis) and Cox proportional hazard analysis. Results: Initial blood pressure dropped significantly from 181/109 to 154/92 mm Hg, p <0.001. Mean follow-up time was 10.6ñ6.1 years. There were 143 cardiovascular deaths, 142 acute myocardial infarctions, 101 strokes, 83 subjects had cardiac failure and 49 had renal failure. The observed rates were 0.92 percent per year for cardiovascular mortality, 1.36 percent per year for coronary heart disease, 0.94 percent per year for stroke. Conclusions: Our mortality rate is lower than that found in classical randomized studies but similar or slightly higher than the more recent ones. Morbidity rates were also very similar. Except for mortality rate, frequency of complications did not change in comparison to our previous report after 15 year of follow up. Aging did not seem to negatively influence mortality rates in adequately treated hypertensive patients

Factores predictores de riesgo de morbimortalidad en hipertensos esenciales seguidos 25 años / Risk factors for morbidity and mortality in subjects with essential hypertension, followed for 25 years

Background: Among hypertensive patients, other risk factors for mortality and morbidity, besides blood pressure, must be considered when therapeutic decisions are done. Aim: To assess the incidence and relevance of cardiovascular risk factors in a cohort of patients with essential hypertension. Material and methods: A cohort of 1.072 treated patients with essential hypertension was followed for a period up to 25 years. Four hundred eighty six were men and 586 were women, age ranged from 31 to 70 years. At entry, 56 percent of subjects did not have any organic complications associated to hypertension (stage I WHO criteria), 30 percent had mild alterations (Stage II) and 14 percent had major complications (myocardial infarction, stroke, heart failure or renal failure). Likewise, 43.8 percent had mild, 14.5 percent, moderate and 41.7 percent, severe hypertension. Patients were treated with monotherapy or combined therapy based on diuretics, beta blockers, calcium antagonists and angiotensin converting enzyme inhibitors. Goal of therapy was 140/90 mm Hg. Risk factors associated diseases and complications were registered carefully. Causes of death were obtained from hospital records and death certificates. Mortality was analyzed using life tables (intention to treat method included). Results: Blood pressure dropped significantly during follow up from a mean of 182/110 to 154/92 mm Hg. During follow up, 143 patients died and 429 complications (lethal or non lethal) were recorded. Twenty four percent of patients smoked, 24 percent reported alcohol intake, 56 percent had hypercholesterolemia, 11 percent were obese, 13 percent had diabetes and 3 percent had gout. The proportional hazard model showed that the existence of previous complications, the presence of more than 3 risk factors, and age over 60 and mean systolic and diastolic pressure during therapy, were independent and significant risk factors for mortality. Conclusions: The incidence of risk factors among our hypertensive patients is very similar to that of other national or international cohorts

Cambios en los patrones de prescripción de medicamentos en el infarto agudo del miocardio: comparación de dos períodos / Changes in pharmacotherapy for acute myocardial infarction: comparison of 2 periods

Background: Pharmacotherapy of Chilean patients with acute myocardial infarction has been recorded in 37 hospitals since 1993. Aim: to compare pharmacotherapy for acute myocardial infarction in the period 1993 to 1995 with the period 1997-1998. Patients and methods: Drug prescription during hospital stay was recorded in 2957 patients admitted to Chilean hospitals with an acute myocardial infarction in the period 1993-1995 and compared with that of 1981 subjects admitted in the period 1997-1998. Results: When compared with the former period, in the lapse 1997-1998 there was an increase in the frequency of prescription of aspirin (93 and 96.1 percent respectively) ß blockers (37 and 55.2 percent respectively) and angiotensin converting enzyme inhibitors (32 and 53 percent). The prescription of thrombolytic therapy did not change (33 and 33.7 percent respectively). There was a reduction in the prescription of calcium antagonists and antiarrhythmic drugs. Conclusions: During the period 1997-1998, the prescription of drugs with a potential to reduce the mortality of acute myocardial infarction, increased. The diffusion of guidelines for the management of this disease may have influenced this change

Infarto agudo del miocardio en hospitales chilenos: resultados finales del estudio GEMI / Acute myocardial infarction in chilean hospitals: results of the GEMI study

Background: Acute myocardial infarction is the leading cause of death in Chile. Aim: To report the main features, hospital evolution, complications and pharmacological treatment of patients admitted to Chilean hospitals with the diagnosis of acute myocardial infarction. Patients and methods: Between 1993 and 1995, the GEMI group registered 2,957 patients admitted to 37 hospitals with the diagnosis of acute myocardial infarction. Results: Mean age of patients was 62 ñ 2 years old and 74 percent were male. Forty six percent had a history of hypertension and 40 percent were smokers. During the first five days of admission, 93 percent of patients received aspirin, 59 percent received intravenous nitrates, 59 percent intravenous heparin, 56 percent oral nitrates, 37 percent beta blockers, 32 percent angiotensin-converting enzyme inhibitors, 33 percent thrombolytic agents, 29 percent antiarrhythmics and 23 percent calcium antagonists. Coronary angiograms were performed in 28 percent of patients, angioplasty in 9 percent and 8 percent were subjected to a coronary bypass. Global hospital mortality was 13.4 percent (19.5 percent in women and 11.1 percent in men, p <0.001). Conclusions: This work gives a picture of myocardial infarction in Chilean hospitals. Pharmacological treatment is similar to that used abroad, but certainly it can be optimized

Impacto espirométrico de dos técnicas de colecistectomía / Espirometric impact of 2 cholecystectomy techniques

Diversos estudios han demostrado una disminución de los parámetros de función respiratoria en los pacientes sometidos a cirugía abdominal alta. Con el objeto de evaluar las modificaciones espirométricas en los pacientes sometidos a colecistectomía, se estudian prospectivamente 50 pacientes sometidos a colecistectomía laparoscópica y 15 pacientes operados en forma abierta. Los grupos son comparables en cuanto a sexo, edad, peso, talla y hábito tabáquico. Se les practicó espirometría mediante Espirómetro Micro Spiro HI-118, efectuándose mediciones de capacidad vital forzada (CVF) y volumen espiratorio forzado del primer segundo (VEF1) en el día preoperatorio, a las 24 y 48 h postoperatorias. Las diferencias en porcentajes de reducción de la CVF y el VEF1 entre la CL y la CA son estadísticamente significativas. La disminución de la CVF y el VEF1 son francamente menores en aquellos pacientes colecistectomizados por vía laparoscópica y la recuperación de estos parámetros es más rápida. Esto la hace recomendable en aquellos pacientes con alteraciones espirométricas y con otros factores de riesgo para complicaciones respiratorias postoperatorias

Eficacia y tolerancia de ciprofloxacina por 5 días en mujeres con infección urinaria: estudio multicéntrico / Efficacy and tolerance of a 5 days course of ciprofloxacin in the treatment of urinary tract infection in women

Background: There is no consensur about the ideal antimicrobial agent and duration of treatment for urinary tract infection in women. Aim: To assess the efficacy of a five days course of ciprofloxacion for the treatment of urinary tract infection in women. Patients and methods: Women with urinary tract infection were treated with ciprofloxacin (Baycip, Bayer) 250mg bid during 5 days. Patients were evaluated three to four days after treatment start, two to seven days and one month after treatment end. Results: Of 101 eligible women, 96 aged 18 to 65 years old, coming from three major Chilean cities, participated in the study and 80 completed the follow up period. There was a 95 percent clinical success, 2.5 percent partial improvement and 2.5 percent treatment failure. The causal microorganism was erradicated in 90 percent of cases, in 1.2 percent treatment failed and in 8.7 percent a re-infection occurred. Adverse effects attributable to the drug were observed in 12 patients (headache in 3, gastrointestinal disturbances in 8, somnolence in 1 and irritability in 1). Conclusions: Ciprofloxacin is an useful antimicrobial for the treatment of lower urinary tract infection in women

Experiencia clínica con un inhibidor de la alfa glucosidasa (acarbosa) en el tratamiento de la diabetes no insulinodependiente: estudio multicéntrico / Multicentric study on the effect of an alpha glucosidase inhibitor in the treatment of non insulin dependent diabetes

Diabetic patients received acarbose, 150 mg/day durign four weeks and this dose was increased to 300 mg/day durign 3 months. Afterwards, patients were followed for a period of 12 weeks without acarbose. Fasting and post-prandial blood glucose and glycosilated hemoglobin were measured sequentially durign the study. Results: Eighty five patients were recruited for the study but 64 complied with the treatment protocol. The age of these patients was 56 ñ 8.8 years old, their diabetes duration was 7.8 ñ 8.8 years and their body mass index was 27.6 ñ 3.6 kg/m². During acarbose treatment, glycosilated hemoglobin decreased from 8.36 ñ 1.33 to 7.71 + 1.7 percent (p < 0.001), fasting blood glucose decreased from 173 ñ 48 to 159 ñ 59 mg/dl (p < 0.03) and post-prandial blood glucose decreased from 254 ñ 80 to 241 ñ mg/dl (NS). After discontinuing acarbose glycosilated hemoglobin and blood glucose levels returned to basal levels. Body weight and blood pressure did not change during the treatment period. Fifty nine patients bad gastrointestinal symptoms (meteorism, flatulence and abdominal distention) that were mild in 59 percent and moderate in 39 percent. Episodes of hypoglycemia were not observed. Conclusions: Acarbose, associated to sylphonylureas is an effective drug to reduce blood glucose and glycosilated hemoglobin levels in patients with non insulin dependent diabetes

Endocarditis infecciosa: factores pronósticos de mortalidad en 131 casos / Infectious endocarditis: prognostic factors of mortality in 131 cases

We followed during their hospital stay, 129 patients aged 14 to 74 years old, who had 131 episodes of infective endocarditis. Clinical assessment, echocardiography and microbiological study was done to all patients. Surgical indications were those derived from complications. Thirty three patients died during hospital stay (25.2 percent). There were no differences between survivors and deceased patients in the lapse between onset of symptoms and hospital admission, presence of fever, dyspnea or heart murmurs. Skin and mucosal septic manifestations occured with higher frequency in deceased patients (57.1 and 24.3 percent respectively). Blood cultures were positive in 55 percent in survivors and 48 percent in those who died. The most frequent infecting organisms were staphilococci and streptococci. Vegetations were found with greater frequency in aortic position in both groups of patients. Deceased patients had a higher frequency of cardiac failure (84 and 65 percent respectively) and embolic episodes (77 and 46 percent respectively) than survivors. Antimicrobial treatment was successfull in 94 percent of survivors and 15 percent of those who died. Forty percent of survivors and 54 percent of deceased patients were subjected to surgical procedures. The most important predictor of hospital mortality in this series of patients with infective endocarditis was antimicrobial treatment failure

Valor pronóstico de los índices no invasivos de reperfusión coronaria en pacientes con infarto agudo del miocardio tratados con trombólisis / Prognostic value of non invasive indexes of coronary reperfusion in patients with acute myocardial infarction treated with trombolysis

In 807 consecutive patients from the Chilean National Registry of Acute Myocardial Infarction we analyzed the resolution of chest pain and ST segment elevation over 50 percent within the first 90 min, abrupt CK rise within 8 h and T wave inversion in infarct related EKG leads within the first 24 h after thrombolysis. Global in-hospital mortality was 12.1 percent. Mortality of patients with the presence of 3 or 4 markers of coronary artery patency was 5.1 percent, in those with resolution of ST elevation and abrupt CK rise was 6.25 percent and in those with T wave inversion it was 3.9 percent (p<0.001). Multivariate analysis, adjusted by age, gender, risk factors, Killip class and infarct location showed that early T wave inversion was the better predictor of a low in-hospital mortality and its combination with other markers of coronary artery patency did not increase its prognostic power. Early CK rise and the presence of 3 out of 4 reperfusion criteria were also independent predictors of a low mortality. Non invasive markers of coronary artery patency are associated with a lower in-hospital mortality and may serve as surrogate end points in clinical trials

Evaluación de utilización de los métodos estadísticos en la investigación en salud / Assessment of statistical methods useful in health research

Two hundred sixty four papers appeared in Revista Médica de Chile and Revista Chilena de Pediatría between 1983 and 1993 were reviewed. Student's T, Fisher's, and X2 test are the most frequently used statistical methods in 67 percent of papers. Correlation coefficients are used in 10 percent of papers. Multivariate methods are seldom used. Statistical analysis of papers published in Chilean medical journals is restricted to very few methods

Infarto agudo del miocardio en Chile: diferencias entre hombres y mujeres en su evolución y pronóstico / Myocardial acute infarction in Chile: diferences between male and female in its evolution and prognostic

Gender may be prognostic factor for the evolution of acute myocardial infarction and women may have higher mortality and complication rates. To study if there are differences in the evolution of acute myocardial infarction between men and women, we have recorded information on risk factors, clinical evolution, treatment and complications of 2052 patients hospitalized for acute myocardial infarction in 36 chilean hospitals. The odds ratio for female sex and mortality was calculated using a logistic regression analysis adjusted for risk factors, treatment, invasive procedures and complications. Twenty six percent of analyzed patients were female. Mortality rates among females and males were 11,8 and 20,2 percent respectively (p<0.01). Women had higher frequency of smoking, diabetes, obesity and hypertension. Blood lipid levels were similar in both sexes. Compared to men, a lesser proportion of women were treated with thrombolytic agents (25 and 35 percent respectively) intravenous heparin (54 and 61 percent respectively), beta blockers (31 and 42 percent respectively) and intravenous nitrates (53 and 61 percent respectively). Also, women were subjected to less invasive procedures. The odds ratio for mortality and sex was 1.72 (confidence interval from 1.13 to 2.62). Female sex is an independent risk factor for acute myocardial infarction mortality

Dicotomización de variables continuas en modelos de regresión logística / Dichotomization of continuous variables in logistic regression models

It is highly to observe in the biomedical literature that the continuous variables such as systolic blood pressure and cholesterol are dichotomized and used in such manner in a given statistical analysis. The consequences of such transformation can be very varied. In this article, how the dichotomization of a continuous exposure variable affects the quality of the prediction of a response using the logistic regression is examined. One can conclude that, in almost all the studied simulation, the percentages of misclassification can increase deastically, reaching over there times the probability of misclassification of the ones using the original variable. Therefore, we recommended to avoid dichotomization