Distribution of capsular types and antimicrobial susceptibility of invasive isolates of Streptococcus pneumoniae in Colombian children. Pneumococcal Study Group in Colombia.

Streptococcus pneumoniae is the leading bacterial cause of childhood pneumonia in the developing world. This study describes the type distribution and antimicrobial susceptibility of invasive pneumococcal isolates from Colombian children and is part of the Sistema Regional de Vacunas (SIREVA), a PAHO regional initiative designed to determine the ideal serotype composition of a protein polysaccharide pneumococcal conjugate vaccine for use in children less than 5 years old in Latin America. In Colombia, during the study period, centres in Bogota, Medellin, and Cali collected 324 S. pneumoniae isolates from invasive diseases, 238 (73.5%) from children under the age of 2. Pneumonia was the clinical diagnosis in 41.3% cases, meningitis in 41%, and sepsis in 11.2%. The seven most frequent types included 14(21.9%), 5(10.5%), 23F(9.6%), 1(9%), 6B(9%), 19F(7.1%), and 6A(6.2%). The frequency of diminished susceptibility to penicillin (DSP) was 12%, with 8.9% of isolates showing intermediate level resistance and 3.1% showing high level resistance. Among DSP isolates, 23% were also resistant to cefotaxime, 33.3% to erythromycin, 48.7% to chloramphenicol, and 74.3% to trimethoprim/sulfamethoxazole. Multiple resistance was detected in 59% of the isolates that have DSP. Penicillin resistance was associated with types 23F (53.8%) and 14 (25.6%). These data provides information on capsular types prevalent in Colombia that will not only allow the formulation of an ideal vaccine for the region but also reinforce the need for ongoing regional surveillance.

Age-dependent vulnerability to carotid chemodenervation in piglets.

We sought to determine the age of greatest vulnerability in piglets to the loss of carotid chemoreceptor function. We studied four groups of carotid body-denervated (CBD) piglets whose carotid bodies were surgically removed at 4-5, 9-10, 12-15, and 21-22 days and who are herein referred to, respectively, as the CBD5, CBD10, CBD15, and CBD20 groups. Four intact groups, at corresponding ages, underwent a sham surgical procedure. After a postsurgery recovery of at least 7 days, we studied all animals to detect the presence of apnea and the consequences of it, if any. Two days before the experiments, we implanted in all animals a fiber-optic arterial catheter for continuous monitoring of arterial O2 saturation, and electroencephalographic electrodes for the recording of sleep states. During quiet sleep in the CBD15 group, we found numerous prolonged central apneic events accompanied by a profound desaturation, tachycardia, a rise in blood pressure, and, eventually, a flattening of the electroencephalogram. No prolonged apneic events occurred, however, in the other CBD groups nor in the intact animals. During active sleep, no prolonged apneic events occurred at all. We thus conclude that, in piglets, the absence of normally functioning carotid chemoreceptors at approximately 2 wk of age can lead to life-threatening apneic events with severe hypoxemia, events that are state specific.

Respiratory, cardiovascular, and metabolic adjustments to hypoxemia during sleep in piglets.

The influence of sleep on ventilation, metabolic rate, cardiovascular function, and regional distribution of blood flow during hypoxemia (PaO2 of 45-50 mm Hg (1 mm Hg = 133.3 Pa)) was studied in piglets at 6+/-1 and 34+/-5 days (mean+/-SD). Measurement of ventilation and metabolic rate was done in a metabolic chamber, and blood flow was measured using the microsphere technique. A subgroup of animals was instrumented for cardiac output measurement (dye-dilution technique) and continuous monitoring of the hemoglobin saturation in oxygen (SaO2). We found that although sleep did not influence the metabolic and cardiac output response to hypoxemia, it affected the ventilatory response as well as the brain and the respiratory muscle blood flows. During active sleep in the older animals, the ventilatory response to hypoxemia was smaller than in the other two states; marked drops in SaO2 occurred with changes in the breathing pattern; and that state was associated with the highest rate of brain blood flow. As well, age affected the ventilatory and metabolic response, but not the cardiovascular response to hypoxemia. The age-dependent ventilatory changes with hypoxemia (smaller ventilatory response in the young than in the older animals) were related to the different levels of oxygen consumption. In summary, active sleep was responsible for all the sleep-dependent changes in the response to a moderate degree of hypoxemia.

Effect of theophylline on metabolic and ventilatory response to hypoxemia during quiet sleep in piglets.

Theophylline, a drug frequently used in newborns, stimulates respiration and increases the metabolic rate in a sustained fashion; hypoxemia, on the other hand, decreases metabolic rate and increases ventilation slightly and, at times, only transiently. This study looked at the effect of theophylline on the metabolic and ventilatory response to hypoxemia in piglets. We studied two groups of piglets during normoxia and hypoxemia: first during a baseline period; and second, after the infusion of either theophylline or a placebo. All studies were done in quiet sleep, 2 d after instrumentation was performed to place vascular catheters and electroencephalographic electrodes. O2 consumption (VO2) and CO2 production (VCO2) were measured in a metabolic chamber, and alveolar ventilation (VA) was then derived from VCO2 and PaCO2. We found that theophylline did not abolish the small decrease in oxygen consumption brought about by hypoxemia. Nor did theophylline augment the ventilatory response to hypoxemia. In fact, the percent change in alveolar ventilation decreased slightly: going from 17 +/- 8% during the baseline period to 9 +/- 6% (p < 0.005) after theophylline administration. We found a significant increase in respiratory exchange ratio (R) in response to hypoxemia (from 0.87 +/- 0.05 to 0.97 +/- 0.04, p < 0.001). However, after the administration of theophylline, additional exposure to hypoxemia did not result in a change in R. In summary, our results show that, in sleeping newborn piglets, theophylline does not abolish the decrease in oxygen consumption observed in response to hypoxemia; nor does it enhance the ventilatory response to a moderate degree of hypoxemia.