Comparison of the characteristics in hen and quail corneas as experimental models of refractive surgery. / Comparación de las características corneales en gallina y codorniz como modelos experimentales de cirugía refractiva.

AIM: To compare the histological, morphological and the biophysical measurements between hen and quail corneas, in order to determine which of them were better suited for use as an animal model for research into corneal refractive surgery. MATERIAL AND METHODS: A study was performed using the biophysical measurements of the cornea (curvature, thickness, refraction, and axial length) of 20 animals (10 hens and 10 quails). The corneas were then prepared for histological analysis under microscopy light. RESULTS: The analysis showed that both groups have the same number of corneal layers as the human cornea and with an evident Bowman's layer. The thickness of the hen cornea and axial length of the eye, 225.3±18.4µm and 12.8±0.25mm, respectively, were larger than that of the quail (P<.01 and P<.001, respectively). The radius of curvature for the hen central cornea, 3.65±0.08mm, was greater than that for the quail (P<.001), but the refractive power of each cornea was similar. The proportion of total corneal thickness of the hen stroma, 82.6%, was more similar to that of the human than was the quail stroma, 72.5%. Within the hen stroma, the density of keratocytes, 8.57±1.49 per 5,000µm(2), was about half that in the quail stroma (P<.005). CONCLUSIONS: Because of the large size of the hen cornea, the stromal thickness and proportional similarity of the corneal layers with human cornea, the hen maybe better than the quail as an alternative species suitable for use in studies of corneal refractive surgery.

Wound healing following refractive surgery in hens.

The wound-healing response is critical to the outcome of refractive surgery and studying wound healing contributes to an understanding of the pathophysiology of other corneal injuries. Animal models allow research to be conducted with sufficient samples and under controlled parameters. We studied the hen to determine the healing process from clinical, biophysical, and biological standpoints after photorefractive keratectomy (PRK). PRK (-6.0 diopters) was performed in hen eyes. At 3, 6, 12, 24, 48, and 72 h and 5, 7, 15, 30, and 60 days postoperatively, we studied the clinical follow-up, objective measurements of light transmission (direct transmittance), apoptosis by TUNEL assay, proliferation by immunocytochemical analysis of 5-bromo-2'-deoxyuridine, and expression of alpha smooth muscle actin (SMA) in myofibroblasts in the corneas. Hen corneas reepithelialize quickly. Haze developed from 5 to 60 days after surgery and was correlated with the appearance and finalization of the expression of SMA. The direct transmittance of light was low during the first 15 days and improved at 30 and 60 days. TUNEL-positive cells were observed 3 h after surgery and the numbers decreased thereafter. Epithelial proliferation began at 12 h and was greater at 48 h, while stromal cell proliferation began at 24 h and was greater at 72 h. The hen cornea is anatomically similar to the human cornea, and the manner in which it heals is a good model for studying different surgical techniques and pharmacologic assays.

[Incidence of acute leukemia in children in Mexico City, from 1982 to 1991]. / Incidencia de las leucemias agudas en niños de la ciudad de México, de 1982 a 1991.

OBJECTIVE: To measure the incidence rate and trend of acute leukemia (AL) in political districts of Mexico City. MATERIAL AND METHODS: Descriptive longitudinal study conducted at six hospitals that care for nearly 97.5% of all cancer cases among children in Mexico City. Study data were collected in 1995 and 1996, and were analyzed in 1999, at the National Medical Center "Siglo XXI" Children's Hospital, of the Mexican Institute for Social Security. Calculations of acute leukemia annual incidence rates, standardized rates, and standardized morbidity rates (SMR) with 95% confidence intervals, were obtained for each district. Morbidity trends were assessed through average change rates. RESULTS: In this study we observed an increasing trend of acute lymphoblastic leukemia (ALL) incidence in five districts: Alvaro Obregon, Cuauhtemoc, Gustavo A. Madero, Iztacalco, and Venustiano Carranza. Acute myeloblastic leukemia (AML) showed no significantly statistic increase of incidence in any district. AML did show a significant SMR in Alvaro Obregon district (SMR = 2.91, 95% CI 1.63-4.80). Higher SMRs were found in the south and southwest areas of the city. CONCLUSIONS: Increasing incidence of ALL was observed in five districts of Mexico City. AML incidence was the highest in Alvaro Obregon district.

Validation of a prognostic index in the critically ill newborn.

OBJECTIVE: Elaborate and assess the degree of validity of a prognostic model for evaluating patients admitted to the Neonatal Intensive Care Unit (NICU). DESIGN: Cases and controls nested in a cohort. SETTING: NICU of two tertiary hospitals and another second level hospital. PATIENTS: The study was carried out in two phases. During the first phase (elaboration of a model), 336 newborns were studied; 112 belonged to the case group (dead patients) and 224 to the control group (live patients discharged). For the second phase (model validation), 300 patients were included that did not participate in the first phase, 100 cases and 200 controls. MEASUREMENTS: For each patient admitted to the study, clinical, paraclinical, perinatal and comorbidity factors were determined within the first 12 hours. Variables of statistical significance in the bivariate analysis were included in a logistic regression model with the objective of identifying a prognostic model. RESULTS: The variables that constituted the prognostic index were gestational age x birth weight, the paO2/FiO2 ratio x O2 saturation, arrest cardiac, major congenital malformations, septicemia and base excess. The model showed to have a sensitivity of 70% and a specificity of 91% during the elaboration cohort. In the validation cohort, sensitivity was 68% and specificity was 92%, a positive predictive value of 80%, negative predictive value of 85% and a correct classification rate was 84%. CONCLUSIONS: The Neonatal Mortality Prognostic Index (NMPI) developed in this study showed to be useful for the evaluation of hospital mortality for severely ill newborns admitted to NICU.

Satisfaction related factors of attendants to a medical research meeting.

OBJECTIVE: To assess satisfaction of attendants to a National Meeting on Medical Research in relation with the scientific quality and level of discussion of the research work. MATERIAL AND METHODS: An anonymous self-applied questionnaire was handed out to gather opinions about the scientific quality, level of discussion of the research work, and overall satisfaction with the meeting. The studied population included 400 physicians, all of them authors or collaborators of the research work presented. RESULTS: The rate of response was 62% (n = 249). Two hundred and twenty-four approved the scientific quality (90%), and 203 were satisfied with the level of discussion of research (88%); 239 were satisfied with the meeting as a whole (96%). The factors associated with dissatisfaction regarding the quality of the scientific meeting were the masculine gender (OR = 2.7, CI 95% = 0.8-9.l, p = 0.06), having an M.Sc. or Ph.D. degree (OR = 2.3, CI 95% = 0.9-5.5, p = 0.03), and having attending prior meetings more than twice (OR = 5.0, CI 95% = 1.5-18.4, p = 0.001). CONCLUSIONS: Most of the attendants were satisfied with the scientific quality and discussions of the research work. The masculine gender, having an M.Sc. or Ph.D. degree, and prior assistance were the factors associated with dissatisfaction of the scientific quality of the Meeting.

[Descriptive epidemiology of malignant tumors in children]. / Epidemiología descriptiva de las neoplasias malignas en niños.

The object of this study is to present the descriptive epidemiology of cancer in children at the world and national levels. The international and national literature published on cancer in children was comprehensively reviewed, with emphasis on reports treating epidemiological aspects of time, place and person. For practical reasons and with the aim of integrating the information, only the more relevant publications were included. Incidence and child mortality were analyzed. Overall incidence is between 100 and 150 (annual rates = cases x 10(6) children). Specific incidence varies according to the type of cancer, the region and the country. The Latin American pattern of neoplasms is constituted by leukemias, lymphomas, and central nervous system tumors (CNST); in the Northamerican/European pattern the CNST appear in second place and in the African pattern, lymphomas show predominance. Incidence is higher among the younger than 5 year olds, from urban environments, and there is a 1% annual increase of cancer in Northamerican children. Child mortality has diminished remarkably, mainly in developed countries, whereas in developing or underdeveloped countries, incidence remains stable or shows a slight fall. The incidence of cancer in children is greater in developed countries, but in underdeveloped countries it may be underestimated. These countries have not managed to reduce the incidence of child mortality caused by cancer, as have the United States or Great Britain. Further studies on the epidemiology of cancer in children are necessary, since many data remain unknown.

Malnutrition in childhood lymphoblastic leukemia: a predictor of early mortality during the induction-to-remission phase of the treatment.

BACKGROUND: Previous reports have shown that undernourished children with acute lymphoblastic leukemia (ALL) have a poorer long-term survival as compared with children with normal nourishment status. It has been shown that both the relapse and mortality rates of undernourished children with ALL are higher during the continuation phase of the chemotherapy and are apparently related to a poor tolerance of ablative chemotherapy. No previous articles have analyzed the early mortality rate of these patients. METHODS: We carried out a case-control study, and have studied the effect of severe malnutrition on the mortality of 17 children with ALL during the initial induction-to-remission phase of the treatment. These 17 cases were compared with 76 controls who had survived at least the phases of induction and consolidation. RESULTS: It was found that the chance of dying during the initial phase of the treatment was 2.6 times higher (confidence interval 95%: 0.55-11.89) in undernourished children with ALL than in those children with normal nourishment status. The risk of death increased with the severity of undernourishment (p = 0.04). CONCLUSIONS: These data confirm the prognostic value of malnutrition in children with ALL and suggest that undernourishment may also influence early mortality during the induction-to-remission phase of the treatment.

[Characteristics of medical care related to autopsy authorization in a pediatric hospital]. / Características de la atención médica relacionadas con la autorización de autopsias en un hospital pediátrico.

OBJECTIVE: To identify some differences of patients and medical characteristics related to autopsy authorization. DESIGN: Observational, cross-sectional study. SETTING: Third-level medical care in a pediatric hospital. METHODS: A specific mortality questionnaire was analyzed by members of the mortality staff, because they reviewed deaths which occurred between January 1994 and December 1995. Descriptive statistic and non-parametric tests (X2) were calculated to analyze data. RESULTS: A total of 408 deaths were evaluated, in which 116 autopsies were done (28.4%). Children less than 18 months of age had the highest frequencies of autopsies (33.3%-30.7%). The patients referred by other units and the autopsy application done by a medical resident, had the highest frequencies of acceptance (32.5%, 35.3%, p < 0.05). The detection of diagnostic and therapeutic problems were related with high frequencies of autopsies (37.7%, 36% p < 0.05). CONCLUSIONS: The results show us that some medical care factors are related to higher frequencies of autopsies. It is important to consider them in order to increase the capacity of teaching that a postmortem study has.

Factors associated with non-use of Pap test. A population survey.

BACKGROUND: Cervical cancer is the most important cancer in Mexican women. Early detection is possible by means of the Papanicolaou (Pap) test; however, the coverage in Mexico is low. METHODS: A cross-sectional survey was carried out in a representative sample of women from the Tlalpan area of Mexico City. Social, reproductive and health care factors associated with the lack of use of the Pap test with respect to adequate use and misuse were identified. Both bivariate and logistic regression analyses were used for the adjustment of variables. RESULTS: Of 1,215 women studied, 22.5% had never had a Pap smear, 42% had misused the test (< 90% of triennial performance), and 35.5% had adequately used the test (> or = 90% of triennial performance). The main factors related to the lack of use were the following: not knowing about the Pap test (ORa = 35.16, 95% C.I. = 17.4-70.9); having fewer than 6 years of education (ORa = 4.5, 95% C.I. = 2.5-8.4); women younger than 30 years of age (ORa = 3.4 95% C.I. = 2.3-5.1); use of contraceptives (ORa = 0.4, 95% C.I. = 0.2-0.8); history of sexually transmitted diseases (ORa = 0.3, 95% C.I. = 0.1-0.8), and the principal informant about the Pap test, i.e., the health services personnel (ORa = 0.02, 95% C.I. = 0.0008-0.05). CONCLUSIONS: The lack of use and the misuse of Pap smears vary importantly among the different social and reproductive factors. But the principal reasons for lack of use were not knowing about the Pap test and a low educational level. We propose a greater diffusion on the benefits of the test in the Mexican population, through massive means of communication and health services.

[Classification by levels of clinico-epidemiological research designs]. / Clasificación en niveles de los diseños de investigación clínico-epidemiológicos.

The objective was to identify the characteristics of epidemiologic designs enabling their classification. A critical review of the literature in the clinical epidemiologic area was done to establish the main differences between designs. A meeting with experts to discuss this controversial topic and obtain criteria by consensus was organized. We propose an integral classification based on levels with two fundamental shafts: intervention and explanatory reasoning.

Nutritional state alterations in children with acute lymphoblastic leukemia during induction and consolidation of chemotherapy.

The objective of the study was to determine if children with high risk acute lymphoblastic leukemia (ALL) exhibit higher frequency of alterations in nutritional state during the phases of induction and consolidation of chemotherapy than children with low risk ALL, based on the arm muscle area. The design was concurrent comparative cohorts. It was performed at pediatric hematology service of the Hospital General del Centro Médico Nacional "La Raza" and hematology service of the Hospital de Pediatría del Centro Médico Nacional "Siglo XXI". One hundred-five patients were incorporated into the study: 53 with high risk (HR) ALL and 52 with low risk (LR) ALL. Basal measurements of arm circumference and tricipital skinfold were surveyed monthly (for 3 months) by standardized personnel. Altered nutritional state during follow-up was defined as the loss of 10% or more of the arm muscular area (AMA) measured at diagnosis. Statistics of proportion analysis with a significance level of 0.05 and relative risk (RR) with confidence intervals (CI) were calculated. In the first month the RR was 0.77 (CI 0.31-1.87); the LR group was the most affected. In the second month the RR was 7.31 (CI 1.41-38.03); the most affected group was the HR. In the third month the RR was 1.77 (CI 0.60-4.92); the HR group was the most affected. High-risk patients show a higher frequency of nutritional state alterations reflected in AMA during the second month after diagnosis. This may be caused by the more aggressive chemotherapy received by these patients.

[Factors associated with peritoneal dialysis catheter failure in chronic renal insufficiency]. / Factores asociados a falla del catéter de diálisis peritoneal en insuficiencia renal crónica.

AIM: To determine the frequency, time of occurrence and factors associated with the failure of the permanent peritoneal catheter during dialysis in cases of chronic renal failure (CRF). MATERIAL AND METHODS: A retrospective cohort under a nested case control design was studied at a second level health care unit of the Instituto Mexicano del Seguro Social. A total of 149 catheters, double cushion straight Tenckhoff type, were evaluated in 74 patients with CRF due to diabetic nephropathy in 36/74 patients (49%). Information concerning functionality time and causes of catheter failure as well as the clinical and technical factors concerning insertion were obtained from the clinical chart. RESULTS: The cumulated time of dialysis was 814 months. Catheter failure occurred in 101 cases (68%): 67 due to obstruction, 24 due to infection, to leakage in 6 and to other causes in 4. Those of non-infectious origin were more frequent (p < 0.01). In the first month post-insertion there was a higher number of failures than after one month, (p < 0.0005). The global functionality of the catheter at one month, one and two years was 55%, 31% and 16%, respectively. There was a greater permanence of the catheters in continuous ambulatory peritoneal dialysis than in intermittent peritoneal dialysis (p = 0.02). CONCLUSIONS: It is concluded that the frequency of the peritoneal catheter failure was high; that the most frequent cause was due to non-infectious complications during the first month of insertion; and the factor associated to catheter failure was intermittent peritoneal dialysis as compared to continuous ambulatory dialysis.

[Instrument to measure quality of life based on daily performance in pediatric patients with leukemia]. / Un instrumento para medir la calidad de vida por medio del desempeño diario en pacientes pediátricos con leucemia.

The objective of this study was to determine the validity of a questionnaire to measure daily performance as an evaluation of quality of life in pediatric leukemia patients. A questionnaire of the daily activities of a child according to Lickert's criteria was done. A pilot survey was performed in patients without a chronic or disabling disease in order to assess its validity. The impression of the medical attendance of each pediatric patient with leukemia, of their daily performance, was compared with the results of the instrument. A trained nurse applied the questionnaire to 60 mothers of patients (29 female/31 male) as outpatients during the clinical review. Fifteen questionnaires were applied twice to evaluate its consistency. According to the results, 77% of the patients were in remission. 15% in relapse, and 8% during induction to remission. The mean age of the patients was 9 = 3.6 years, ranging from 2-16 years. One hundred percent of the patients obtained a satisfactory grade greater than 35 points. In conclusion, the questionnaire identified adequately the level of the daily performance in addition to the specific affected areas of the patients with leukemia. Our findings are that their level of performance is satisfactory and is not affected because of the disease or the phase of the treatment.

[Medical student traits associated with future success as physicians]. / Características del estudiante de medicina asociadas al éxito ulterior como médico.

OBJECTIVE: To identify the individual and family factors present during medical studies which are associated to success as a physician. RESEARCH DESIGN: Prolective case-control study. SETTING: Mexico City metropolitan area. STUDY UNITS: 120 physicians considered to be successful and 245 physicians who according to an established criteria were considered to be non-successful. MAIN MEASUREMENTS: A success-achieving index was constructed on the opinion of 134 physicians from different health-care institutions private and public. The index was composed by criteria such as being a member of prestiged academic associations; having a practice in third level institutions; having done postgraduate studies; being a professor with teaching and research activities; having obtained directive medical positions; and a high income at the moment of the interview. RESULTS: The main factors associated to success were: frequent attendance to cultural activities by the family of the subjects (OR = 5.2, IC 95% = 3.15-8.60, p = 0.00000001); the global score obtained during their medical studies, i.e. higher than 8.5 over 10 (OR = 4.43, IC 95% = 2.64-7.49, p = 0.00000001); and having been awarded recognitions, prizes or scholarships during their medical studies (OR = 4.3, IC 95% = 2.64-7.03, p = 0.00000001). A logistic regression model selected the cultural activities of the family, global score during medical studies and earning of recognitions, prizes and scholarships as independent variables associated to success achievement (p = 0.00001). CONCLUSIONS: Frequent cultural activities by the family and academic behavior were the factors present during medical studies which were associated to ulterior success as a physician.

[The utility of joint sensitivity and specificity curves applied to a diagnostic test]. / Utilidad de las curvas de sensibilidad y especificidad conjunta en la aplicación de una prueba de diagnóstico.

The aim of this study was to obtain the cut point to determine an individual's seronegativity with respect to measles using commercial reagents. To determine the test sensitivity, the serum of 22 individuals 21 years of age or older, and a positive history of measles (positive control group) was studied. For specificity, the serum of 22 children 15 to 24 months old, and no measles vaccination record nor positive history of measles (negative control group), was analyzed. The antibodies titer determination for both groups was done using the ELISA technique and the Brunell method, subsequently, as well as a ROC curve (Received Operating Curve). When the Brunell method was used, the cut points were 0.4090 (sensitivity 1.0 and specificity 0.95) and 0.5042 (sensitivity 0.95 and specificity 1.0). When a ROC curve was done the cut point was 0.4500, with a sensitivity and specificity of 100 per cent. It was also concluded that the latter is the best method to obtain this cut point, because it does not establish arbitrary values when the data distribution does not follow a normal pattern.

[Granulocytopenia and fever in children with leukemia as indicator of quality of medical care]. / Granulocitopenia y fiebre en niños con leucemia como indicador de calidad de la atención médica.

OBJECTIVES: 1. To identify the quality degree of medical care in patients with acute leukaemia who had fever and granulocytopenia during the hospitalization period. 2. To establish the relationship between the medical care process and the results in this concern. DESIGN: Retrospective survey. STUDY AREA: Children's Hospital of the Mexican Institute of Social Security. STUDY SUBJECTS: Twenty three patients with acute leukaemia were studied. Also, hospitalization episode of these patients, in which they suffered fever and granulocytopenia, was randomly selected. MAIN MEASUREMENTS: Compliance of diagnostic and therapeutic process was measured during hospitalization, according to the protocolized recommendations made by consensus of the hospital expert group. In order to identify the quality degree of medical care, it was taken into account the protocol compliance besides the results observed in the patients. Results were assessed based on patients' survival to fever and granulocytopenia episode, as well as on fever's duration. The correlation was calculated by using Spearman's coefficient. RESULTS: The medical care quality of the hospital was "adequate" (85% on average). Compliance degree, including the total process was 71%; with diagnostic process 63%, and with therapeutic process 76%. The results observed in the patients were considered as "adequate" (89%). By evaluating individual cases, the medical care quality was considered excellent or adequate in 17 patients (74%) regular in five (22%) and poor in one (4%). Diagnostic process was adequate in 6 patients (26%) regular in 12 (53%) poor in three (13%) and very bad in two (8%). On the other hand, therapeutic process was excellent in 14 patients (60%) regular in one (4%) poor in six (26%) and very bad in two (9%). Results observed in 13 cases were excellent (57%) adequate in eight (35%) regular in one (4%) and very bad in one (4%). The relationship between process and result was 0.41 (P < 0.05) between diagnostic process and result 0.14 and, between therapeutic process and result 0.34. CONCLUSIONS: The medical care quality rendered to patients with leukaemia, who suffered a granulocytopenia episode and fever, was considered as adequate. Therapeutic recommendations were followed accurately, meanwhile, diagnostic process had a lower adherence. A positive relationship between process and result was observed.

[Usefulness of residuals in clinical research]. / Utilidad de los residuales en la investigación clínica.

The simple linear regression analysis, multiple linear regression and logistic regression constitute powerful statistical analysis tools widely used in clinical research. These kinds of analyses are based upon mathematical models which at the same time are established on certain basic assumptions. The regression analysis assumptions are basically: a) that the model is really linear, b) that the distribution of data is normal (from a statistical point of view), c) that the variances of the employed data are homogeneous (homocedastics) and that the included data are independent. The regression diagnostic has become popular as a form to evaluate if the assumptions have been accomplished, one of its most important techniques is the residual analysis. A residual can be defined as the value which measures the distance between the regression line and the corresponding value of the variable "y". Among these kinds of residuals used to evaluate the assumptions of regression are: the crude residual, the standardized, of student and the jackknife. The most useful among them is the jackknife residual. The usefulness and limitations of the residuals in the evaluation of the regression analysis assumptions are described, basically referring to the identification and handling of extreme values (outliers).

[Risk factors associated with the development of leukemia in children]. / Factores de riesgo asociados al desarrollo de leucemia en niños.

INTRODUCTION: Leukemia is the most frequent neoplasia in children; in our country it is the main cause of medical attention in children with cancer. The are different risk factors associated with the development of this kind of cancer. OBJECTIVE: To identify which of the already known factors described in the literature associated with the development of leukemia are most frequent in the pediatric population of Mexico City. MATERIAL AND METHODS: A protective case-control study was carried out using prevalent and incident cases. In two third level hospitals of Mexico City, a total of 81 children who had been diagnosed as suffering from different kind of leukemia, confirmed by biopsy of bone marrow, were select and studied. The control were 154 children from two different sources: 77 of them came from the same hospital where the cases received medical care, the selection criteria was not to have any kind of neoplasia; and 77 came from the same community where those diagnosed children cases lived, the selection criteria for this group was that they were healthy children. Both cases and community controls were visited at home and interview to complete precoded questionnaire with the different variables of the study. The information from the hospital controls was obtained during the time they stayed in the hospital. Odds ratio (OR's) for the different associations were calculated, as well as its confidence intervals at 95% (IC) accord to Cornfield and unconditioned logistic regression was carried out to control confounding variables. RESULTS: OR greater than 1 was found in those with familiar cancer background 1.93 (1.2-3.63); the mother being exposed to X-ray during pregnancy 1.89 (0.84-4.22); previous abortions before the child with leukemia was born 2.44 (1-06-5.68); being born from full term birth 2.42 (0.47-16.65); being born with weight greater that 3500 g 2.21 (1.04-4.33); being exposed to fertilizers 4.73 (1.04-24.14) and insecticides 1.93 (1.05-3.56). OR smaller than 1 was found in those who have been in a hospital because of an infectious disease during the first year of life 0.57 (0.17-1.74); to have suffered from chicken pox 0.59 (0.32-1.08). No association to parent's age or job was found. Multivariated analysis shows that the exposure to insecticide is the most important risk factor associated with the development of leukemia in children. CONCLUSIONS: We obtained positive associations to different risk factors described in the literature, having found that exposure to fertilizers is the most important risk factor and finding no association with the parent's occupation. This leads to the need of carrying out further studies to investigate, in more detail, the occupation of the father to confirm whether or not this is a risk factor.