SARS-CoV-2 Vaccine Effectiveness in Hospitalized Patients: A Multicenter Test-Negative Case-Control Study

BACKGROUND

Phase III clinical trials have documented the efficacy of the SARS-CoV-2 vaccines in preventing symptomatic COVID-19. Nonetheless, it is imperative to continue analyzing the clinical response to different vaccines in real-life studies. Our objective was to evaluate the effectiveness of five different vaccines in hospitalized patients with COVID-19 during the third COVID-19 outbreak in Mexico dominated by the Delta variant.

METHODS

A test-negative case-control study was performed in nine tertiary-care hospitals for COVID-19. We estimated odds ratios (OR) adjusted by variables related a priori with the likelihood of SARS-CoV-2 infection and its severity.

RESULTS

We studied 761 subjects, 371 cases, and 390 controls with a mean age of 53 years (SD, 17 years). Overall, 51% had a complete vaccination scheme, and an incomplete scheme (one dose from a scheme of two), 14%. After adjustment for age, gender, obesity, and diabetes mellitus, we found that the effectiveness of avoiding a SARS-CoV-2 infection when hospitalized with at least one vaccination dose was 71% (OR 0.29, 95% CI 0.19-0.45), that of an incomplete vaccination scheme, 67% (OR 0.33, 95% CI 0.18-0.62), and that of any complete vaccination scheme, 73% (OR 0.27, 95% CI 0.17-0.43).

CONCLUSIONS

The SARS-CoV-2 vaccination program showed effectiveness in preventing SARS-CoV-2 infection in hospitalized patients during a Delta variant outbreak.

Incidence of Guillain-Barré syndrome following SARS-CoV-2 immunization: Analysis of a nationwide registry of recipients of 81 million doses of seven vaccines

Background and purpose

Information on Guillain–Barré syndrome (GBS) as an adverse event following immunization (AEFI) against SARS‐CoV‐2 remains scarce. We aimed to report GBS incidence as an AEFI among adult (≥18 years) recipients of 81,842,426 doses of seven anti‐SARS‐CoV‐2 vaccines between December 24, 2020, and October 29, 2021, in Mexico.

Methods

Cases were retrospectively collected through passive epidemiological surveillance. The overall observed incidence was calculated according to the total number of administered doses. Vaccines were analyzed individually and by vector as mRNA‐based (mRNA‐1273 and BNT162b2), adenovirus‐vectored (ChAdOx1 nCov‐19, rAd26‐rAd5, Ad5‐nCoV, and Ad26.COV2‐S), and inactivated whole‐virion‐vectored (CoronaVac) vaccines.

Results

We identified 97 patients (52 males [53.6%]; median [interquartile range] age 44 [33–60] years), for an overall observed incidence of 1.19/1,000,000 doses (95% confidence interval [CI] 0.97–1.45), with incidence higher among Ad26.COV2‐S (3.86/1,000,000 doses, 95% CI 1.50–9.93) and BNT162b2 recipients (1.92/1,00,000 doses, 95% CI 1.36–2.71). The interval (interquartile range) from vaccination to GBS symptom onset was 10 (3–17) days. Preceding diarrhea was reported in 21 patients (21.6%) and mild COVID‐19 in four more (4.1%). Only 18 patients were tested for Campylobacter jejuni (positive in 16 [88.9%]). Electrophysiological examinations were performed in 76 patients (78.4%; axonal in 46 [60.5%] and demyelinating in 25 [32.8%]); variants were similar across the platforms. On admission, 91.8% had a GBS disability score ≥3. Seventy‐five patients (77.3%) received intravenous immunoglobulin, received seven plasma exchange (7.2%), and 15 (15.5%) were treated conservatively. Ten patients (10.3%) died, and 79.1% of survivors were unable to walk independently.

Conclusions

Guillain–Barré syndrome was an extremely infrequent AEFI against SARS‐CoV‐2. The protection provided by these vaccines outweighs the risk of developing GBS.

Efectividad de las vacunas contra SARS-CoV-2 en hospitalizados con fallas vacunales en 10 hospitales de la CCINSHAE

Objetivo. Evaluar la efectividad de las vacunas contra SARS-CoV-2 para evitar muerte e intubación en pacientes hospitalizados con Covid-19. Material y métodos. Se presentó un análisis de 3 565 hospitalizaciones por SARS-CoV-2 de personas mayores de 20 años de edad, reportadas con fines de salud pública por 10 hospitales de especialidad. Se comparó a los egresados por mejoría (2 094) con los fallecidos (1 471) en modelos mixtos de regresión logística ajustados por edad, sexo, número de comorbilidades y el hospital como variable aleatoria. Resultados. Un esquema completo de vacunación, con cinco tipos de vacunas disponi­bles, tuvo un efecto protector para muerte o intubación (RM: 0.67, IC95%: 0.54,0.83, 33% de protección); y para muerte (RM: 0.80, IC95%: 0.64,0.99, 20% de protección) estos datos se compararon con los que no habían sido vacunados. Todas las vacunas aplicadas mostraron un efecto protector con un RM<0.8, con intervalos de confianza variables. Conclusio­nes. El antecedente de vacunación reduce los riesgos de ser intubado y morir, aun en pacientes previamente vacunados y hospitalizados con Covid-19 grave.

Biomarkers for Predicting Malignant Pleural Mesothelioma in a Mexican Population

Background: Diagnosis of malignant pleural mesothelioma (MPM) remains a challenge, especially when resources in pathology are limited. The study aimed to evaluate cost-effective tumor markers to predict the probability of MPM in plasma samples in order to accelerate the diagnostic workup of the tissue of potential cases. Methods: We conducted a case-control study stratified by gender, which included 75 incident cases with MPM from three Mexican hospitals and 240 controls frequency-matched by age and year of blood drawing. Plasma samples were obtained to determine mesothelin, calretinin, and thrombomodulin using enzyme-linked immunosorbent assays (ELISAs). We estimated the performance of the markers based on the area under the curve (AUC) and predicted the probability of an MPM diagnosis of a potential case based on the marker concentrations. Results: Mesothelin and calretinin, but not thrombomodulin were significant predictors of a diagnosis of MPM with AUCs of 0.90 (95% CI: 0.85-0.95), 0.88 (95% CI: 0.82-0.94), and 0.51 (95% CI: 0.41-0.61) in males, respectively. For MPM diagnosis in men we estimated a true positive rate of 0.79 and a false positive rate of 0.11 for mesothelin. The corresponding figures for calretinin were 0.81 and 0.18, and for both markers combined 0.84 and 0.11, respectively. Conclusions: We developed prediction models based on plasma concentrations of mesothelin and calretinin to estimate the probability of an MPM diagnosis. Both markers showed a good performance and could be used to accelerate the diagnostic workup of tissue samples in Mexico.

Altitude Above Sea Level and Body Mass Index as Determinants of Oxygen Saturation in Children: The SON@ Study

BACKGROUND

Altitude above sea level and body mass index are well-recognized determinants of oxygen saturation in adult populations; however, the contribution of these factors to oxygen saturation in children is less clear.

OBJECTIVE

To explore the contribution of altitude above sea level and body mass index to oxygen saturation in children.

METHODS

A multi-center, cross-sectional study conducted in nine cities in Mexico. Parents signed informed consent forms and completed a health status questionnaire. Height, weight, and pulse oximetry were recorded.

RESULTS

We studied 2,200 subjects (52% girls) aged 8.7 ± 3.0 years. Mean body mass index, z-body mass index, and oxygen saturation were 18.1 ± 3.6 kg·m-2, 0.58 ± 1.3, and 95.5 ± 2.4%, respectively. By multiple regression analysis, altitude proved to be the main predictor of oxygen saturation, with non-significant contributions of age, gender, and body mass index. According to quantile regression, the median estimate of oxygen saturation was 98.7 minus 1.7% per km of altitude above sea level, and the oxygen saturation fifth percentile 97.4 minus 2.7% per km of altitude.

CONCLUSIONS

Altitude was the main determinant of oxygen saturation, which on average decreased 1.7% per km of elevation from a percentage of 98.7 at sea level. In contrast with adults, this study in children found no association between oxygen saturation and obesity or age.

Diagnostic Value of the Morphometric Model and Adjusted Neck Circumference in Adults with Obstructive Sleep Apnea Syndrome

BACKGROUND

Obstructive sleep apnea syndrome is a major public health problem. The morphometric model and the Sleep Apnea Clinical Score are widely used to evaluate adults; however, neither of these tools has been validated in a Mexican population.

OBJECTIVE

To determine the diagnostic value of the morphometric model and the Sleep Apnea Clinical Score and compare them with conventional clinical instruments.

METHODS

A total of 97 individuals were recruited prospectively. Initial screening excluded 36, of whom nine were subjects without apnea; the remaining 52 were consecutive patients with obstructive sleep apnea syndrome diagnosed by nocturnal polysomnography. Diagnostic values of each test were calculated.

RESULTS

Obstructive sleep apnea syndrome patients had significantly higher scores with both instruments than controls: morphometric model: 61.3 (95% CI: 45.5-75.3) vs. 41.0 (95% CI: 35.6-45.6); Sleep Apnea Clinical Score: 45.3 (95% CI: 39.5-40.3) vs. 36 (95% CI: 34.0-36.5), respectively. For severe cases, the best cutoff point for morphometric model was 46, with a sensitivity of 81% (95% CI: 62.5-92.6) and specificity of 46.7% (95% CI: 66.4-100), while for Sleep Apnea Clinical Score it was > 48, with a sensitivity of 61% (95% CI: 46.1-74.2) and specificity of 80.4% (95% CI: 66-90.6).

CONCLUSIONS

A morphometric model value of ≥ 46 or an adjusted neck circumference (Sleep Apnea Clinical Score) > 48 were adequate for diagnosing obstructive sleep apnea syndrome.

Angiogenic and inflammatory markers in acute respiratory distress syndrome and renal injury associated to A/H1N1 virus infection

Acute kidney injury (AKI) is often associated to acute respiratory distress syndrome (ARDS) due to influenza A/H1N1 virus infection. The profile of angiogenic and inflammatory factors in ARDS patients may be relevant for AKI. We analyzed the serum levels of several angiogenic factors, cytokines, and chemokines in 32 patients with A/H1N1 virus infection (17 with ARDS/AKI and 15 ARDS patients who did not developed AKI) and in 18 healthy controls. Significantly higher levels of VEGF, MCP-1, IL-6, IL-8 and IP-10 in ARDS/AKI patients were detected. Adjusting by confusing variables, levels of MCP-1 ≥150 pg/mL (OR=12.0, p=0.04) and VEGF ≥225 pg/mL (OR=6.4, p=0.03) were associated with the development of AKI in ARDS patients. Higher levels of MCP-1 and IP-10 were significantly associated with a higher risk of death in patients with ARDS (hazard ratio (HR)=10.0, p=0.02; HR=25.5, p=0.03, respectively) even taking into account AKI. Patients with influenza A/H1N1 infection and ARDS/AKI have an over-production of MCP-1, VEGF and IP-10 possibly contributing to kidney injury and are associated to a higher risk of death.

[Adult asthma in Mexico City: a population-based study]

OBJECTIVES

To determine the prevalence of asthma and the association between sociodemographic characteristics, spirometry, respiratory symptoms, quality of life and sleep in adults > 40 years.

MATERIALS AND METHODS

This report is part of our study (Latin American Research Project Obstructive Pulmonary), held in Mexico City and the metropolitan area in 2003. We used logistic regression models adjusted for study design, where asthma was the dependent and independent variable respiratory symptoms, sociodemographic and clinical characteristics among others.

RESULTS

The prevalence of physician-diagnosed asthma was: 3.3% in men and 6.2% in women. Decreased lung function in asthmatics was observed. In multivariate analysis, after adjusting for potential confounders, asthmatics had a higher risk of excessive daytime sleepiness more snoring [OR = 3.2 (95% CI 1.4-7.4), p= 0.008], and more frequent work absences due to respiratory problems [OR = 5.1 (95% CI 2.5-10.4), p<0.0001].

CONCLUSIONS

The prevalence of asthma was 5%. Asthmatics showed lower quality of life and lung function.

[A case-control study of the impact of tuberculosis on the quality of life of patients]

A prospective study was conducted on 72 patients of pulmonary tuberculosis (TB) and 201 healthy controls in a third level hospital. The HRQoL questionnaire (12-Item Short Form Health Survey, SF-12) was used to assess the QoL at the onset of treatment DOTS. Patients with TB had significantly lower mean scores than controls for overall QoL (51.1 +/- SD 22.6) versus 75.9 (+/- SD 17.6), p < 0.0001. The most affected domains were physical and psychological. Active TB patients shown difficulties in activities of daily living and alterations of the psychological state.

Indoor pollution as an occupational risk factor for tuberculosis among women: a population-based, gender oriented, case-control study in Southern Mexico

BACKGROUND

Indoor air pollution produced by biomass cooking fuels in developing countries has been associated with acute and chronic lower respiratory diseases, but has not been identified as an occupational exposure among women.

OBJECTIVE

To examine the relationship between the use of biomass cooking fuels (mainly wood) and tuberculosis (TB) among women living in rural areas in Southern Mexico.

METHODS

We conducted a population based case-control study in the health jurisdiction of Orizaba, Mexico. Cases were all incident female pulmonary TB patients, with Mycobacterium tuberculosis in sputum, living in communities with fewer than 15,000 inhabitants, diagnosed between March 1995 and April 2003. Woodsmoke exposure was assessed by applying a standardized questionnaire (ATS-DLD-78 questionnaire). Controls were randomly selected from sex-matched neighbors. Appropriate IRB approval was obtained.

RESULTS

42 TB cases and 84 community controls were recruited. Multivariate assessment showed that more than 20 years of exposure to smoke from biomass fuels was three times more frequent among cases than among controls [Odds ratio (OR): 3.3, 95% confidence interval (CI):1.06-10.30, p = 0.03], after controlling for age, body mass, household crowding, years of formal education and tobacco use.

CONCLUSIONS

We found a strong association between the use of biomass cooking fuels and tuberculosis among women in a community-based, case-control study. Results of this study are intended to provide evidence to policy makers, community leaders and the general public on the importance of implementing gender oriented interventions that decrease the use of biomass fuels in poor communities in developing countries.

Wood smoke-associated lung disease: a clinical, functional, radiological and pathological description

BACKGROUND

Approximately half of the world's population, and up to 90% of households in rural areas of developing countries, depend on biomass for cooking and heating.

SETTING

The National Institute of Respiratory Diseases, México City.

OBJECTIVE

To describe wood smoke-associated lung disease (WSLD).

DESIGN

Description of the clinical, functional and radiological manifestations of patients with WSLD, and a comparison of pathological findings of patients who died of WSLD and smokers who died of chronic bronchitis.

RESULTS

All patients with WSLD were non-smoking women with chronic bronchitis, in whom asthma, bronchiectasis, tuberculosis, congestive heart failure, extreme obesity and alfa-1 antitrypsin deficiency had been excluded. All patients used wood for cooking and had been exposed to wood smoke for a median of 45 years. Dyspnoea, airway obstruction, air trapping, increased airway resistance, pathological evidence of anthracosis, chronic bronchitis, centrilobular emphysema and pulmonary hypertension were present in most patients with WSLD. Bronchial squamous metaplasia was a common finding. There were no significant differences in the histopathological findings between patients with WSLD and smokers. Diffuse interstitial fibrosis was absent in all patients.

CONCLUSIONS

Patients with WSLD have obstructive lung disease, chronic bronchitis, emphysema and pulmonary hypertension comparable to smokers.

[Contributions of pharmacogenomics to enhance the efficiency of randomized clinical trials]

One of the greatest advances of the modern medicine has been the report of the complete sequence of the human genome. This has brought as a consequence an evolution in the design of the clinical research, in special of the randomized clinical trials (RCTs). The pharmacogenomics, a powerful tool for the prediction of pharmacological effects based on the genotype of the studied subjects, promises to be very useful next years for the development of the pharmaceutical industry. With the present integration of the pharmacogenomical methods to the investigation and development of new medicines it may start a new era in the medical prescription producing more individualized therapies, reduction of adverse events in the patients and in addition a faster development of new medicines in a more cost-effective way. Nevertheless new methodological, ethical and social challenges appear that will have to be solved simultaneously, to allow a legal use of the vast information generated by the genetic information.

[Altitude, the ratio of PaO2 to fraction of inspired oxygen, and shunt: impact on the assessment of acute lung injury]

The ratio of PaO2 to the fraction of inspired oxygen (PaO2/FIO2) is commonly used to determine the severity of acute lung injury and acute respiratory distress syndrome (ARDS). The research presented here used computational models of the lung to analyze the effect of altitude on the PaO2/FIO2 ratio and pulmonary shunt. At a given shunt, the PaO2/FIO2 ratio is lower at higher altitudes. Therefore, when evaluating for ARDS based on a PaO2/FIO2 ratio of <200 mm Hg, patients residing at high altitudes will have less shunt and, presumably, less severe lung injury than patients at sea level. This should be taken into consideration when comparing patients from different altitudes. Shunt should more often be measured directly or be estimated assuming a constant arteriovenous oxygen content difference.

Polyurethane II catheter as long-indwelling intravenous catheter in patients with cancer

BACKGROUND

Silicone has been the standard material for indwelling devices to date. Polyurethane II exhibits properties that makes it suitable as a component of long-indwelling vascular access, with the added advantage of low cost.

OBJECTIVE

To describe the experience of an intravenous therapy team with 206 polyurethane II catheters used as long-indwelling vascular access in patients with cancer.

MATERIALS AND METHODS

All polyurethane II single- and double-lumen catheters implanted between January 1, 1994, and March 15, 1995, were analyzed, including time of stay and type and rate of infectious and noninfectious complications.

RESULTS

A total of 206 catheters were placed--164 single-lumen and 42 double-lumen catheters--in 190 patients; average stay was 101 days (range, 1-445 days). The infection incidence rate was 0.66 per 1000 catheter-days for single-lumen catheters and 1.6 per 1000 catheter-days for double-lumen catheters. Noninfectious complications included 1 thrombosis (incidence rate, 0.06 per 1000 catheter-days for single-lumen and none for double-lumen catheters), 5 catheter ruptures (2.4%), and 1 pneumothorax (0.48%). Twelve catheters (8.3%) were removed because of complications; only 1 was infectious. The remaining 17 infectious episodes (94.4%) were resolved without catheter removal. Our complication rate with single-lumen catheters in this series was similar to our previous experience with a nontunneled silicone catheter.

CONCLUSIONS

Our findings indicate that polyurethane II catheters have proven useful and safe as long-indwelling vascular access in patients with cancer at our hospital at a considerably lower cost.

Diabetes modifies the male:female ratio in pulmonary tuberculosis

SETTING

Socio-cultural factors have been invoked to explain the male predominance among patients with pulmonary tuberculosis, but there is no conclusive evidence of their role.

OBJECTIVE

To assess male predominance in a group of diabetics with pulmonary tuberculosis compared with patients with pulmonary tuberculosis alone.

DESIGN

Clinical records of in-patients with pulmonary tuberculosis and with (TBDM group, n = 202) or without (TB group, n = 226) diabetes mellitus were reviewed, and the male percentages in each of six age groups (15-29, 30-39, 40-49, 50-59, 60-69, > or = 70 years) calculated.

RESULTS

In the TB group, no gender difference (51% males) was found in the first age period, followed by a male predominance thereafter (71%, 68%, 75%, 63% and 58%). The TBDM group showed a similar pattern in the first two age groups (56% and 74%), followed by a steadily decline (r(S) = -0.90, P = 0.04) in male percentage (60%, 44%, 45%, 27%), leading to a female predominance after age 50. The association of age and gender was also corroborated by logistic regression in TBDM (P = 0.02), but not in TB (P = 0.19) patients.

CONCLUSIONS

Diabetes was associated with a progressive shift of male predominance in pulmonary tuberculosis. Because diabetes is a disease that affects social activities similarly in men and women, our results suggest that factors other than socio-cultural ones are also important for determining the male predominance in pulmonary tuberculosis.

[Epidemiology of Tuberculosis in Mexico, 1981-1998. Inconsistencies between reports of the WHO and the Ministry of health]

OBJECTIVE

To describe the tuberculosis morbidity and mortality trends in Mexico, by comparing the data reported by the Ministry of Health (MH) and the World Health Organization (WHO) between 1981 and 1998.

MATERIAL AND METHODS

The number of cases notified in the past few years, their rates, and the trends of the disease in Mexico were analyzed. The incidence of smear-positive pulmonary tuberculosis was estimated for 1997 and 1998 with the annual tuberculosis infection risk (ATIR), to estimate the percentage of bacilliferous cases in 1997-1998.

RESULTS

WHO reported more tuberculosis cases for Mexico than the MH. However, this difference has decreased throughout the years. The notification of smear-positive cases remained stable during 1993-1998. The estimated percentages of detection were 66% for 1997 and 26% for 1998 (based on ATIR of 0.5%). Tuberculosis mortality decreased gradually (6.7% per year) between 1990 and 1998, whereas the number of new cases increased, suggesting the persistence of disease transmission in the population.

CONCLUSIONS

Inconsistencies between case notifications from national data and WHO were considerable, but decreased progressively during the study period. According to ATIR estimations, a considerable number of infectious tuberculosis cases are not detected. The English version of this paper is available at: http://www.insp.mx/salud/index.html.

[Reproducibility of spirometry in Mexican workers and international reference values]

OBJECTIVE

To describe spirometric function and adjustment to foreign prediction equations in Mexican workers claiming work related disability.

MATERIAL AND METHODS

We reviewed 5771 spirometries done at the Mexican National Institute of Respiratory Diseases performed with equipment and methods proposed by the American Thoracic Society. With the spirometries we generated multiple regression equations separated for men and women based on age and height, compared to other in common use reported by Knudson and Hankinson in North America and by Quanjer in europeans.

RESULTS

80% of the tests were reproducible for FVC and FEV1 according to ATS, whereas 10% were reproducible for neither. Mean FVC in men was 12% above values reported by Quanjer, 22% above Knudson, 3% above Hankinson and 6% above Rodriguez-Reynaga, whereas similar values for women were 18%, 10%, 0% and 1%. Excluding obese and those who had less than 2 acceptable maneuvers, the numbers increase by 1-2%. FEV1 was also above predicted.

CONCLUSIONS

Most workers requesting disability are able to generate a reproducible spirometry. However for the same gender, age and height, workers had a FEV1 and a FVC above normal values reported by Knudson and Quanjer and are more similar to those reported by Hankinson in Mexican-Americans. While a set of appropriate reference values are obtained, regression equations obtained from the studied group will generate less error in the evaluation of disability in mexican workers. The English version of this paper is available at: http://www.insp.mx/salud/index.html.

[Ketotifen (Zaditen and K-Asthmal): a drug with sales disproportionate to its demonstrated effectiveness]

Ketotifen is a sedative antihistamine promoted heavily for asthma treatment. Controlled trials are inconsistent: several did not find ketotifen better than placebo or cromoglycate. We do not have published controlled trials against inhaled steroids, the comparison most important to evaluate the efficacy of ketotifen. Ketotifen is poorly effective against exercise-induced asthma, and unable to reduce bronchial hyperactivity. The sedation and delay in therapeutic effect is also bothersome. Because of the uncertainties of its effect, ketotifen is not a first line drug against asthma, according to several international guidelines. Despite this information, ketotifen represented 17% of all antiasthmatic drug sales in Mexico in 1996, clearly exaggerated for the efficacy demonstrated. Ketotifen for asthma can be substituted with advantage by inhaled cromoglycate or corticosteroids. As a sedative antihistamine it is very expensive. The authorized publicity concerning ketotifen should be reevaluated with the current information available.

[The domestic inhalation of the smoke from firewood and of other biological materials. A risk for the development of respiratory diseases]

A high proportion of the world population, especially in developing countries, is exposed to indoor pollutants produced by inefficient biomass stoves. The levels of pollutants, including toxins and carcinogens in the kitchen are usually very high. This potential pathogenic exposure has been scarcely studied. The exposure to biomass smoke has been associated to chronic bronchitis and chronic airflow obstruction in adults and to acute respiratory infections in children. At the National Institute of Pulmonary Diseases in Mexico, we have observed the entire spectrum of diseases associated with tobacco in people who never smoked and who were exposed to wood smoke. Women exposed to wood smoke had a five-fold risk of chronic bronchitis and chronic airflow obstruction, as compared to the non-exposed, according to a recent case-control study done at our Institute. The indoor levels of suspended particles smaller than 10 microns were frequently above 1,000 micrograms/m3 in a rural community in the state of Mexico. This information supports a causal role for biomass smoke for the genesis of several respiratory diseases, representing a potentially public health problem.

[Normal ventilatory response to hypoxia and hypercapnia at an altitude of 2240 meters]

OBJECTIVE

To evaluate the ventilatory response to hypoxia and hypercapnia in healthy residents of Mexico City at 2240 m above sea level.

METHODS

15 healthy subjects, 10 women and 5 men, were studied (mean age 38; range 26-76). All completed one or two tests of ventilatory response to hypoxia and hypercapnia as described by Rebuck-Campbell and Read, respectively. The results were analyzed by linear regression using the minute ventilation as the dependent variable and SaO2 (hypoxia) or PCO2 (hypercapnia) as the independent variables.

RESULTS

Seven subjects had very low or no response to hypoxia. The mean hypoxia slope was 0.7 +/- 0.6 L/min/% (+/- SD) and the hypercapnia slope was 3.0 +/- 1.4 L/min/mmHg. The intercepts were 176 +/- 278 for SaO2 and 3.0 +/- 7 for PCO2.

CONCLUSIONS

A low respiratory response to hypoxia was found in Mexico City Healthy residents. The response to hypercapnia was similar in slope to other studies but had an intercept shifted to lower values. The Mexico City residents showed a behavior typical of patients with chronic hypoxemia or of dwellers at high altitudes.

[Gasometric values reported in healthy subjects from the Mexican population: review and analysis]

We do not know the normal relationship between altitude and PaCO2 in Mexico. We collected and analyzed the reports of reference values for gasometry in Mexico City (2240 m above sea level and a mean barometric pressure of 585 Torr) and other places in the country. The reports include arterial, capillary and expired gases in children and adults, with measurements done in resting and exercising subjects, breathing room air and 100% oxygen. In Mexico City we found 18 studies in normal subjects reporting a mean PaCO2 ranging from 25.5 to 38.4 Torr. Averaging arterial studies from children and adults, adjusting for the number of subjects studied, and discarding data with mean pH below 7.37 or above 7.43 (suggesting non steady state), 10 studies with a total of 581 subjects have the following average values (Torr, means and SD): PaCO2 = 31.1 +/- 2.6, PaO2 = 67.7 +/- 2.6, calculated PAO2 and P(A-a)O2 73.6 +/- 3.3 y 6.1 +/- 3.7 respectively. The PaCO2 found was much lower than that reported for native Peruvians in the Andes who have a mean PaCO2 of 37.8 Torr at an altitude of 2390 m, and a mean PaCO2 of 33.0 Torr only at 4860 m above the sea level. On the other hand, the average values in Mexico are similar to those found in North Americans who have a mean PACO2 of 33.1 Torr at 2131 m of altitude, a mean PACO2 of 30.7 at 2371 m and a mean PaCO2 of 31 Torr at 2238 m. Normal values for gasometry in Mexico are scarce and some of the existing ones are erroneous probably due to lack of adequate calibrations and to poor quality control. Values of PaCO2 in Mexico are more similar to those found in the USA than to those found in Peruvian natives.

[The challenge of evaluating clinical competence]

The study is divided in two parts. The first one deals with theoretical aspects of evaluation. In the second part, the development of an instrument intended to explore clinical competence is presented. The importance of considering evaluation as part of a research process is emphasized in the first part. The diverse theoretical and action trends in the field of education are synthetized in two main tendencies: the active-participating and the passive-receptive. The influence of these two tendencies in the selection the objects for evaluation is also discussed. An evaluation instrument developed by us to explore clinical competence is placed within the active-participating tendency of education; the present state of this instrument is given in the second part. The instrument consists of multiple choice options of the true, false, don't know type. The instrument in its present version is the result of a long validation process. It explores particularly iatrogenic behaviors by omission or commission. The sample studied were 457 applicants for specialization courses in medicine. Of these, 127 were foreign applicants. The instrument was applied to the whole sample in one single session. The results showed a low general clinical competence, with similar results in mexican and foreign applicants. A clear difference was found in commission iatrogenia which was significantly more frequent than omission iatrogenia. The theoretical superiority of our test in relation the others is discussed.

[Ethical attitudes related to problems of managing patients with acquired immunodeficiency syndrome]

We evaluated, with a questionnaire, ethical attitudes towards the clinical attention of patients with AIDS in 88 physicians. Most of the surveyed were residents and all were working in two mexican hospitals with experience managing patients with AIDS: The National Institute of Nutrition and the National Institute of Respiratory Diseases. None of the questions was answered similarly by all physicians and some of them considered ethically unquestionable, behaviours that traditionally are immoral or even illegal. Reproducibility of the results, evaluated in 10 doctors 5 months later, was acceptable. Ethical attitudes were heterogeneous and inconsistent in the surveyed. This can be the results of a poor or absent training in Medical Ethics in medical schools and during residencies. We believe this deficiency helps maintaining discriminatory attitudes against patients with AIDS and may decrease the quality of medical services to the group.

[Method for calculating the distribution of randomly expected scores in a false-true-do not know-type of test]

Multiple choice tests have been used widely in the evaluation of knowledge. The lowest passing limit is generally chosen arbitrarily. Better and more objective criteria may arise from analyzing the distribution of correct and incorrect answers as expected by chance. In order to calculate the distribution of correct answers and the difference between correct and incorrect answers (core) we propose the use of a method based on a gaussian distribution. The distribution of scores expected by chance is approximated by a gaussian distribution with a mean of zero and a standard deviation SD = square root of n(pA + pE), and the distribution of the total number of correct answers has a mean of npA and SD = square root of npApE, where n is the total number of questions, and pA and pE are the probabilities of having a correct and an incorrect answer, respectively. The formulae are applicable to questions type false/true/do not know and to the more common type of one correct in five options. Once the chance distribution is known, it can be compared with the distribution of scores or correct answers obtained, which can then be used to separate people in two groups: those that answer the test as expected or worse than expected by chance, and those that answer the test better than expected by chance. The first group should not be passed. The passing of individuals in the second group can be decided by additional criteria.

[Accuracy of an the ear oximeter Biox-III and its sensitivity to carboxyhemoglobin in Mexico City]

Ear oximeters estimate arterial oxygen saturation (Sa02) measuring the characteristics of light transmission through the ear lobe. We tested the accuracy of a new ear oximeter (Biox-III) in Mexico City comparing its estimates (Sa02OXI) with Sa02 measured by a Co-Oximeter, in a simultaneously taken arterial blood sample. We used two indexes in the arterial sample: Sa02 of the total hemoglobin (Sa02T) given directly by the Co-Oximeter and Sa02 of the hemoglobin available for oxygenation (Sa02A) which corrects for the presence of carboxyhemoglobin and metahemoglobin. We studied 21 subjects with a total of 100 simultaneous samples with a Sa02T ranging from 36.2% to 97.2%. The samples were obtained with the subjects resting, during light exercise, during rebreathing and increasing the Fi02. Spearman and Pearson's correlation coefficients between Sa02OXI and Sa02A were 0.97, and between Sa02OXI and Sa02T were 0.96. Lineal regression equations were: Sa02T = 2.047 (Sa02OXI) -8.5 and Sa02A = 1.102 (Sa02OXI) -9.32. Slopes of the equations and correlation coefficients were statistically significant (P less than 0.001). Mean error of Sa02OXI compared with Sa02T (Sa02T-Sa02OXI) was -4.4% and compared with Sa02A (Sa02A-Sa02OXI) was -0.4%, with a standard deviation of 3.4% and 3.5% respectively. In the presence of carboxyhemoglobin the ear oximeter overestimates Sa02T but not Sa02A. Measurement error increases during rebreathing maybe because error increases at low Sa02 and because of the delay in oximeter's response in a situation of a continuously falling Sa02. Ear oximeter Biox-III estimates Sa02 in Mexico City as accurately as the Biox-IIA at sea level. Sa02 measurement is quick, easy, continuous and non-invasive, which increase its potential clinical and research application.