Complicaciones de la asistencia respiratoria mecánica en Pediatría / Complications of the mechanical ventilation in children

Objetivo: Determinar en forma prospectiva el número y tipo de complicaciones vinculados a la ventilación mecánica e intubación endotraqueal, en una Unidad de Cuidados Intensivos Pediátrica polivalente. Materiales y métodos: Se incluyeron 101 pacientes ventilados mecánicamente determinando los siguientes parámetros: sexo, edad, días de intubación, presencia de complicaciones, complicación y días de internación, presión media de la vía aérea (MAP) en el instante de la complicación, y MAP más alta si no hubo complicaciones. Se analizaron las variables dicotómicas y continuas y análisis multivariado por regresión logística; se tomó significativa una p<0,05. Resultados: La edad media de la población fue de 17,8 meses; los días de intubación y de ventilación mecánica fueron similares con una media de 8 ñ 9 días. Se observaron 99 complicaciones en 53 pacientes (52,5 por ciento). La probabilidad de complicaciones aumentó 1,07 veces (7 por ciento) por cada día con ventilación mecánica (p < 0,0015). La extubación accidental se produjo en 27 oportunidades en 23 pacientes (22,7 por ciento). El neumotórax ocurrió en 9 de 101 pacientes, y el neumomediastino en 7 de 101, no encontrándose diferencias significativas entre los que tenían MAP > de 10 versus MAP < 10. Los episodios de atelectasias fueron 31 y se observaron en 34 pacientes (24 por ciento). Otras complicaciones fueron: daño de tejido (1 por ciento), intubación en el bronquio derecho (9 por ciento), extubación accidental (22,7 por ciento), estridor postextubación (3 por ciento) y neumonía asociada al respirador (9 por ciento). Conclusiones: Observamos un número muy alto de complicaciones. Como factores de riesgo pudimos identificar la duración de la ventilación mecánica y la MAP > 8,5. Las maniobras preventivas pueden evitar muchas de las complicaciones

Adverse effects of radioprotector WR2721.

S-2-(3-Aminopropylamino)ethylphosphorothioic acid (WR2721) has radioprotective properties, but it is also toxic--in man it causes nausea and vomiting. Since radiation also causes nausea and vomiting it is important to know whether WR2721 would increase or decrease the likelihood of nausea and vomiting after radiation. This question was investigated in rats using the phenomenon of aversion to the taste of saccharin, which is readily inducible and is understood to be controlled in rats by the same pathways that control nausea and vomiting in man. The taste aversion was induced by giving 0.2 Gy60Co gamma radiation 30 min after drinking 0.1% saccharin, or WR2721 immediately after the saccharin, or giving both radiation and WR2721. There were appropriate controls. In sham-irradiated rats, WR2721 (40 or 200 mg/kg, but not 8 mg/kg) produced a significant taste aversion. When WR2721 (40 or 200 mg/kg) was given immediately after the saccharin to irradiated rats it increased the taste aversion significantly, but it did not have any effect at 8 mg/kg. It was concluded that at doses which were optimal for radioprotection (approximately 200 mg/kg) or lower, WR2721 increased in rats the taste aversion induced by radiation. By inference if conditioned taste aversion is an appropriate paradigm, WR2721 would increase nausea and vomiting in man induced by radiation.

Dexamethasone: a potent blocker for radiation-induced taste aversion in rats.

Rats, trained to drink water during a single 30-min period each day, were then given 0.1% saccharin twice a week and water on other days for 30 min. If 20 rad of radiation (0.2 Gy) were given each time 30 to 40 min after the saccharin the rats developed a profound aversion to saccharin during the course of three weeks, whereas control groups failed to do so. This paradigm was then used to test the ability of drugs, given twice weekly immediately after the saccharin, to prevent the development during three weeks of an aversion when 20 rad was given, 30 to 40 min later. Insulin, domperidone, haloperidol, acetylsalicylic acid, naloxone, chlorpheniramine, cimetidine, and dimethyl sulphoxide were tested without notable success. However dexamethasone, at doses ranging from 0.013 mg/kg to 1.3 mg/kg, significantly attenuated the conditioned taste aversion by up to 60 percent. The results are discussed in terms of a search for an antinauseant and antiemetic drug effective against radiation in man.

The measurement of rectal and testis temperature in conscious mice, with observations on the effect of direct heating.

The application of Newton's law of cooling to freshly killed mice was found not to measure accurately their rectal or testis temperature. Improvements in the fitting process gave satisfactory results for rectal temperature only. A diffusion model was applied to testis cooling but was of no avail. Finally a satisfactory correction factor was determined empirically. This method was applied to conscious mice whose hindquarters were immersed in a stirred oilbath at 34 to 42 degrees C for 1 h, and to controls. It was found that both rectal and testis temperatures increased with bath temperature, producing a graph with a slope of only 0.5, indicating a regulatory capacity. Conscious mice, but not anaesthetised, can maintain a testis temperature of 39 degrees C in a bath at 42 degrees C.

Quantitative studies of cytological damage in mouse testis produced by exposure to heat.

Damage in gonadal cells produced by exposure of the hindquarters of conscious male mice to water at temperatures up to 43 degrees C was studied by measuring the percentage of testicular cells which do not exclude trypan blue 4 h after exposure, sperm count up to ten wk later, and the percentage of morphologically abnormal sperm up to ten wk later. It was found that the percentage of cells stained with trypan blue was significantly increased by exposure for 0.5 h at 41 degrees C or 2 h at 37 degrees C. Sperm count and the percentage of abnormal sperm were affected by 0.5 h at 43 degrees C or 2 h at 40 degrees, but not by lower temperatures. Since there is a high incidence of abnormal sperm after some heat treatments, the use of this assay for mutagen screening should be approached with caution.

Dosimetry for a study of effects of 2.45-GHz microwaves on mouse testis.

In order to determine the effects of microwave radiation on the testis, it is necessary to express the physical insult in animal studies in a way that can be replicated elsewhere and ultimately used as a basis for extrapolation to man. However, there is conflict--especially in chronic experiments--between the desire for precise dosimetry and the need to minimise alteration of the normal physiological functions of the animals. The compromise arrangement used in this study was to house the mice singly, in cages with limited food and water, and to irradiate them for up to 30 days (16 h/day) in an anechoic chamber. The only measurements taken routinely were of power density in the positions normally occupied by the cages. In addition, a series of absorption measurements was made in mouse carcasses: Whole-body specific absorption rate (SAR); energy-deposition patterns (determined thermographically); and local SAR in testis (using a miniature electric (E)-field probe). It was concluded that the SAR in testis was considerably less than the whole-body SAR. Exposure for 16 h at 50 mW/cm2 elevated rectal but not testis temperature, thus demonstrating the ability of the conscious mouse to regulate the temperature of its testis.

Changes in intestinal cell kinetics in the small intestine of lactating mice.

The enlargement of the small intestine of mice during lactation is due, at least in part, to hyperplasia in the mucosal crypts and villi. The number of cells per crypt increases by 130% and the cell production rate by 63% after 15 days of lactation. These parameters were measured from crypt squashes and sections using both double-label and PLM techniques. Neither the numbers of crypts and villi in the small intestine nor the turnover time of post-mitotic cells on the villi changed. A number of factors appear to act in concert during lactation to trigger this increase in epithelial cell number in the small intestine. The experiments reported suggest a role for the increased quantity of food consumed by the lactating animal, for changing hormonal levels, and for the increased demands placed on the body by milk production.

Fission of crypts in the small intestine of the irradiated mouse.

Following 1600 R of X-rays there was a reduction in the number of crypts in the small intestine of the mouse by 77% as measured 5 days later. However, by 21 days the number had increased steadily to levels approaching normal. The number of villi did not change following irradiation. The mechanism of increase in crypt number was by budding and fission of repopulated crypts which had become larger than normal. Some aspects of crypt organization are discussed.