El espacio muerto (VD/VT) como predictor de éxito en la extubación de pacientes postquirúrgicos de cirugía cardiovascular pediátrica / Dead space (VD/VT) as a predictor of successful extubation of patients after pediatric cardiovascular surgery

Introducción: La ventilación mecánica (VM) forma parte de la recuperación postoperatoria (PO) de niños con cirugía de cardiopatía congénita, pero su uso no está exento de riesgos. El fracaso de extubación (FE) se ha asociado con internaciones prolongadas, aumento de complicaciones y mortalidad. El objetivo es determinar un valor de Vd/Vt predictor de extubación exitosa (EE). Material y métodos: estudio de cohorte prospectivo y observacional realizado del 1 de Enero al 31 de Diciembre de 2016 en niños menores de 6 meses cursando PO de cirugía cardiovascular con circulación extracorpórea (CEC) con requerimientos de VM por más de 48 horas. En los mismo se analizó el éxito o fracaso de extubación. Previo a la extubación se registraron valores de mecánica respiratoria; Vd/Vt, CO2 espiratoria final, Vt/kg, etc. Otras variables registradas: edad, sexo, peso, requerimiento de VM antes de la cirugía, fisiología de ventrículo único, duración de VM, complicaciones, duración de la internación y mortalidad. Las variables continuas se describieron como mediana y rango intercuartilo (25-75) y se compararon con prueba de Wilcoxon, las categóricas como proporciones o porcentajes y se analizaron con chi2 . Se efectuó un análisis bivariado con diferentes puntos de corte de Vd/Vt pre extubación para realizar un análisis de sensibilidad del valor predictivo de EE. Resultados: Se evaluó Vd/Vt en 67 pacientes, tres se eliminaron por parálisis cordal (1) y parálisis del diafragma (2). Mediana de edad 23 días (10-55), peso 3.2 Kg (2.89- 3.88), días de VM 5 (3-7), días de internación 15 (2- 128), mortalidad 7,8%. Se extubaron con éxito 76% de los pacientes (50/64). Las características demográficas de los pacientes, la mecánica respiratoria, gases de sangre arterial y EtCO2 no tuvieron asociación significativa con EE. Un Vd/Vt pre extubación < 0,53 se asoció con EE. Conclusión: En la población estudiada un valor de Vd/Vt <0,53 se asoció con EE. Los pacientes con ventrículo único presentaron mayor FE.(AU)

Introduction: Mechanical ventilation (MV) is part of postoperative (PO) recovery of children with congenital heart disease surgery, but is not without risks. Extubation failure (EF) has been associated with prolonged hospital stays and increased complication and mortality rates. The goal is to determine the value of Vd/Vt as a predictor of successful extubation (SE). Material and methods: A prospective and observational cohort study was conducted from January 1 to December 31, 2016, in children under 6 months of age undergoing cardiovascular surgery with extracorporeal circulation (ECC) and requiring MV for more than 48 hours. Intubation success or failure was evaluated. Prior to extubation, respiratory mechanics values, such as Vd/Vt, final expiratory CO2, and Vt/kg, were recorded. Other variables, including age, sex, weight, VM requirement before surgery, single ventricle physiology, VM duration, complications, length of hospital stay, and mortality were also recorded. Continuous variables were described as median and interquartile range (25-75) and compared with the Wilcoxon test. Categorical variables were described as proportions or percentages and analyzed with chi2. Bivariate analysis was performed with different pre-extubation Vd/Vt cut-off points to analyze the sensitivity of the predictive value for SE. Results: Vd/Vt was evaluated in 67 patients; three were excluded because of vocal fold (1) and diaphragm paralysis (2). Median age was 23 days (10-55), weight 3.2 Kg (2.89- 3.88), days on MV 5 (3-7), length of hospital stay 15 (2- 128), and mortality rate 7.8%. Overall, 76% of patients (50/64) were successfully extubated. Patient demographics, respiratory mechanics, arterial blood gases, and EtCO2 were not significantly associated with SE. A pre-extubation Vd/ Vt < 0.53 was associated with SE. Conclusion: In this series of patients, a Vd/Vt value of <0.53 was associated with SE. EF was increased in patients with a single ventricle (AU)

Valor preditivo da razão entre espaço morto e volume corrente fisiológicos no processo de desmame da ventilação mecânica em crianças / Predictive value of the physiological deadspace/tidal volume ratio in the weaning process of mechanical ventilation in children

OBJETIVO: Avaliar a razão entre espaço morto e volume corrente fisiológicos (V D/V T) como preditor do fracasso na extubação em 42 crianças ventiladas (idade média: 4,75 anos). MÉTODO: Prontidão para extubação foi determinada usando os critérios propostos pela 6ª Conferência Internacional de Consenso em Medicina Intensiva adaptados a crianças. RESULTADOS: A ventilação não invasiva (VNI) foi usada em quatro pacientes que desenvolveram insuficiência respiratória após a extubação; nenhum foi reintubado. Crianças que precisaram de VNI para evitar a reintubação tiveram razão V D/V T significativamente maior do que as que foram extubadas sem VNI (p < 0,001). O valor de corte da razão V D/V T foi 0,55, e a área sob a curva ROC foi 0,86. CONCLUSÃO: Nossos achados confirmam o bom valor preditivo do sucesso/fracasso do desmame pela razão V D/V T e sugere seu papel como preditor da necessidade de VNI após extubação.

OBJECTIVE: To evaluate the physiological deadspace/tidal volume ratio (V D/V T) as a predictor of extubation failure in 42 ventilated children (median age: 4.75 years). METHOD: Extubation readiness was determined using the criteria proposed by the 6th International Consensus Conference on Intensive Care Medicine adapted to children. RESULTS: Non-invasive ventilation (NIV) was used in four patients who developed respiratory failure after extubation; none was reintubated. Children who needed NIV to avoid reintubation had a significantly higher V D/V T ratio than those who were extubated without NIV (p < 0.001). The cut-off value of V D/V T ratio was 0.55 and the area under the receiver operating characteristic curve was 0.86. CONCLUSION: Our findings confirm the good predictive value of weaning success/failure of the V D/V T ratio and suggest its role for predicting the need for NIV after extubation.

Avaliação da relação entre espaço morto e volume corrente como índice preditivo de falha de extubação / Evaluation of the dead space to tidal volume ratio as a predictor of extubation failure

OBJETIVO: O objetivo do estudo foi avaliar a relação entre espaço morto e volume corrente (VD/VT) como preditivo de falha na extubação de crianças sob ventilação mecânica. MÉTODOS: Entre setembro de 2001 e janeiro de 2003, realizamos uma coorte, na qual foram incluídas todas as crianças (1 dia-15 anos) submetidas a ventilação mecânica na unidade de terapia intensiva pediátrica em que foi possível realizar a extubação e a ventilometria pré-extubação com a medida do índice VD/VT. Considerou-se falha na extubação a necessidade de reinstituição de algum tipo de assistência ventilatória, invasiva ou não, em um período de 48 horas. Para a análise dos pacientes que foram reintubados, definiu-se como sucesso-R a não reintubação. Para as análises estatísticas, utilizou-se um corte do VD/VT de 0,65. RESULTADOS: No período estudado, 250 crianças receberam ventilação mecânica na unidade de terapia intensiva pediátrica. Destas, 86 compuseram a amostra estudada. Vinte e uma crianças (24,4 por cento) preencheram o critério de falha de extubação, com 11 (12,8 por cento) utilizando suporte não-invasivo e 10 (11,6 por cento) reintubadas. A idade média foi de 16,8 (±30,1) meses, e a mediana, de 5,5 meses. A média do índice VD/VT de todos os casos foi de 0,62 (±0,18). As médias do índice VD/VT para os pacientes que tiveram a extubação bem sucedida e para os que falharam foram, respectivamente, 0,62 (±0,17) e 0,65 (±0,21) (p = 0,472). Na regressão logística, o índice VD/VT não apresentou correlação estatisticamente significativa com o sucesso ou não da extubação (p = 0,8458), nem para aqueles que foram reintubados (p = 0,5576). CONCLUSÕES: Em uma população pediátrica submetida a ventilação mecânica, por etiologias variadas, o índice VD/VT não possibilitou predizer qual a população de risco para falha de extubação ou reintubação.

OBJECTIVE: The objective of this study was to evaluate the ratio of dead space to tidal volume (VD/VT) as a predictor of extubation failure of children from mechanical ventilation. METHODS: From September 2001 to January 2003 we studied a cohort consisting of all children (1 day-15 years) submitted to mechanical ventilation at a pediatric intensive care unit who were extubated and for whom pre-extubation ventilometry data were available, including the VD/VT ratio. Extubation success was defined as no need for any type of ventilatory support, invasive or otherwise, within 48 hours. Patients who tolerated extubation, with or without noninvasive support, were defined as success-R and compared with those who were reintubated. Statistic analysis was based on a VD/VT cutoff point of 0.65. RESULTS:During the study period 250 children received mechanical ventilation at the pediatric intensive care unit. Eighty-six of these children comprised the study sample. Twenty-one children (24.4 percent) met the criteria for extubation failure, with 11 (12.8 percent) of these requiring non-invasive support and 10 (11.6 percent) reintubation. Their mean age was 16.8 (±30.1) months (median = 5.5 months). The mean VD/VT ratio for all cases was 0.62 (±0.18). Mean VD/VT ratios for patients with successful and failed extubations were 0.62 (±0.17) and 0.65 (±0.21) (p = 0.472), respectively. Logistic regression failed to reveal any statistically significant correlation between VD/VT ratio and success or failure of extubation (p = 0.8458), even for patients who were reintubated (p = 0.5576). CONCLUSIONS: In a pediatric population receiving mechanical ventilation due to a variety of etiologies, the VD/VT ratio was unable to predict the populations at risk of extubation failure or of reintubation.

Dead space ventilation in volume controlled versus pressure controlled mode of mechanical ventilation.

Dead space ventilation (VD) is one of the important measurements that indicates the ventilatory efficiency of a patient who requires mechanical ventilation. However, VD is not constant and can change according to the pathology in the lungs, ventilatory patterns, perfusion and ventilation-perfusion matching. The objective of this study was to measure and compare the dead space in pediatric patients who were using pressure controlled and volume controlled modes of mechanical ventilatory by measuring the difference between arterial PCO2 and end-tidal PCO2 [P(a-ET)CO2]. From November 1996 to March 1997, 12 patients who were admitted to the pediatric intensive care unit and needed ventilator support for various reasons, were enrolled in the study. Their ages ranged from 2 to 15 years. The mechanical ventilator (Benett 7200 or Servo 900C) setting during VD measurement i.e. tidal volume, inspiratory time and positive end expiratory pressure were kept constant between changing from pressure controlled to volume controlled mode or vice versa for twenty minutes in order to allow adequate time for equilibration. The P(a-ET)CO2 between volume controlled and pressure controlled mode were 3.1 and 2.6 torr (p = 0.5) and peak inspiratory pressure were 20.0 and 17.3 torr (p = 0.01), respectively; whereas mean airway pressure, PaO2, O2 saturation and heart rate revealed no significant difference between these two modes. The authors concluded that VD in pressure controlled mode from the present study was not significantly different from VD when using volume controlled mode of mechanical ventilation in the same patient. However, VD will change according to the pathophysiologic change in respiratory system and can be used for monitoring of ventilatory pattern of patients in the pediatric intensive care unit.