Decreased lung compliance increases preload dynamic tests in a pediatric acute lung injury model / Una compliance pulmonar disminuida incrementa los test dinámicos de precarga en un modelo pediátrico de lesión pulmonar aguda

Background: Preload dynamic tests, pulse pressure variation (PPV) and stroke volume variation (SVV) have emerged as powerful tools to predict response to fluid administration. The influence of factors other than preload in dynamic preload test is currently poorly understood in pediatrics. The aim of our study was to assess the effect of tidal volume (V T) on PPV and SVV in the context of normal and reduced lung compliance in a piglet model. Material and method: Twenty large-white piglets (5.2 ± 0.4 kg) were anesthetized, paralyzed and monitored with pulse contour analysis. PPV and SVV were recorded during mechanical ventilation with a V T of 6 and 12 mL/kg (low and high V T, respectively), both before and after tracheal instillation of polysorbate 20. Results: Before acute lung injury (ALI) induction, modifications of V T did not significantly change PPV and SVV readings. After ALI, PPV and SVV were significantly greater during ventilation with a high V T compared to a low V T (PPV increased from 8.9 ± 1.2 to 12.4 ± 1.1%, and SVV from 8.5 ± 1.0 to 12.7 ± 1.2%, both P < 0.01). Conclusions: This study found that a high V T and reduced lung compliance due to ALI increase preload dynamic tests, with a greater influence of the latter. In subjects with ALI, lung compliance should be considered when interpreting the preload dynamic tests.

Introducción: Test dinámicos de precarga, variación de presión de pulso (PPV) y variación de volumen sistólico (SVV) han emergido como herramientas poderosas para predecir respuesta a la administración de fluidos. Actualmente la influencia de factores distintos a la precarga en la determinación de los test dinámicos de precarga es pobremente conocida en pediatría. Nuestro objetivo fue medir el efecto del volumen tidal (V T) sobre PPV y SVV en un contexto de compliance pulmonar normal y disminuida en un modelo porcino. Material y método: Veinte cerditos Large-White anestesiados y paralizados (5,2 ± 0,4 kg). PPV y SVV fueron medidos por análisis de contorno de pulso durante ventilación con V T de 6 y 12 mL/kg (V T bajo y alto, respectivamente), ambos previo y posterior a lesión pulmonar aguda (ALI) químicamente inducida con instilación traqueal de polisorbato 20. Resultados: Previo a inducción de ALI, PPV y SVV no tuvieron cambios significativos al modificar el V T. Sin embargo, después de ALI, PPV y SVV fueron significativamente mayores durante ventilación con V T alto, respecto a V T bajo (PPV aumentó de 8,9 ± 1,2 a 12,4 ± 1,1%, y SVV de 8,5 ± 1,0 a 12,7 ± 1,2%, ambos P < 0,01). Conclusiones: Este estudio encontró que un V T alto y una compliance pulmonar disminuida debido a ALI incrementan los test dinámicos de precarga, con una mayor influencia de esta última. En sujetos con ALI la compliance pulmonar debiera ser considerada al interpretar los test dinámicos de precarga.

Diferencia veno-arterial de dióxido de carbono como predictor de gasto cardiaco disminuido en modelo pediátrico experimental / Veno-arterial difference of carbondioxide as a predictor of low cardiac output in an experimental pediatric model

Background: Cardiac output (CO) measurement is not a standard of care for critically ill children, but it can be estimated by indirect methods such as veno-arterial pCO2 difference (ΔVACO2). Aim: To determine the correlation between CO and ΔVACO2 and evaluate the usefulness of ΔVACO2 in the diagnosis of low CO in an experimental pediatric model. Materials and Methods: Thirty piglets weighing 4.8 ± 0.35 kg were anesthetized and monitored with transpulmonary thermodilution. Lung injury was induced with tracheal instillation of Tween 20®. Serial measurements of central venous and arterial blood gases, as well as CO, were obtained at baseline, 1, 2 and 4 h after lung injury induction. Low cardiac output (LCO) was defined as CO lower than 2.5 Llminlm². Results: There was an inverse correlation between CO and ΔVACO2 (r = -0.36, p < 0.01). ΔVACO2 was 14 ± 8 mmHg in LCO state and 8 ± 6 mmHg when this condition was not present (p < 0.01). Area under the receiver operating characteristic (ROC) curves of ΔVACO2 and LCO state was 0.78 (0.68-0.86). The best cut-point was 8.9 mmHg to determine LCO with a sensibility 0.78, specificity 0.7, positive predictive value 0.27 and negative predictive value 0.96. Conclusions: In this model there was an inverse correlation between ΔVACO2 and CO. The best cutoff value to discard LCO was ΔVACO2 of 8.9 mmHg, indicating that under this value the presence of LCO is very unlikely.

Variación de presión de pulso en ventilación mecánica / Variation of pulse pressure in mechanical ventilation

La condición hemodinámica de los pacientes críticos puede presentar una amplia variedad de volumen circulante efectivo y función miocárdica. La insuflación de un volumen corriente es capaz de interferir en forma cíclica sobre la hemodinámica, emergiendo la monitorización hemodinámica funcional -reflejo directo de la interacción corazón-pulmón- como una valiosa herramienta para predecir la respuesta a fluidos y como fuente de información dinámica de la condición fisiológica de cada individuo.En el siguiente artículo se revisa en forma resumida los sustentos del empleo de la variación de presión de pulso en ventilación mecánica para la predicción de respuesta a volumen, como también sus limitaciones actualmente aceptadas.

Hemodynamic condition of critically ill patients may present a wide variation of effective circulating volume and miocardic function. The insufflation of an ordinary volume may interfere cyclically on hemodynamics, and functional hemodynamic monitoring (direct reflex of heart-lung interaction) emerges as a valuable tool for predicting the response to fluids and as a dynamic source of information concerning the physiological condition of each individual. In the current article, support for the use of pulse pressure variation in mechanical ventilation for predicting response to volume, and its currently accepted limitations are dealt with in an abridged review.