Espacio muerto y destete de ventilación mecánica invasiva en residentes de la gran altitud / Dead space and weaning from invasive mechanical ventilation in high-altitude residents

RESUMEN Objetivo Determinar el valor predictivo del cálculo del espacio muerto a través de la fracción espacio muerto/volumen corriente en el destete de la ventilación mecánica invasiva en pacientes críticamente enfermos en la gran altitud. Materiales y métodos Estudio epidemiológico, observacional, analítico y prospectivo realizado en la Unidad de Terapia Intensiva Adultos del Hospital del Norte de la ciudad de El Alto, Bolivia (4090 m s. n. m. y presión barométrica de 453 mmHg) del 01 de noviembre de 2016 al 31 de marzo de 2017. Se estudiaron a los residentes de la gran altitud en ventilación mecánica invasiva. Los criterios de inclusión fueron los siguientes: a) residentes de la altitud hospitalizados en la Unidad de Terapia Intensiva en ventilación mecánica invasiva, b) pacientes con evidencia de resolución de la causa que motivó su conexión al ventilador mecánico invasivo, c) paciente con criterios e índices de destete positivos, d) prueba de respiración espontanea positivo. Las variables estudiadas fueron el espacio muerto a través de la fracción Vd/Vt y su relación con el éxito o fracaso del proceso de destete de ventilación mecánica. Se calculó la fracción Vd/Vt en los pacientes incluidos en el estudio para luego proceder al destete de la ventilación mecánica invasiva. Se dividió a los pacientes en dos grupos según la necesidad de reintubación y reconexión al ventilador mecánico dentro de las 72 horas. Resultados Se incluyeron 21 pacientes: 7 mujeres (33 %) y 14 varones (67 %). La media de edad fue 41 años con desviación estándar de 22,38 años. Dieciocho pacientes (86 %) presentaron éxito y tres (14,00 %) fracasaron en el proceso de destete de la ventilación mecánica invasiva. El valor de Vd/Vt en el grupo éxito y fracaso correspondió a 0,43 vs. 0,53 (p < 0,011109), con una sensibilidad de 0,61 y especificidad de 1; con valor predictivo positivo de 1 y valor predictivo negativo de 0,3. Conclusiones El cálculo del espacio muerto a través de la medida de la fracción espacio muerto/volumen corriente predice el éxito del destete de pacientes críticamente enfermos bajo ventilación mecánica invasiva a gran altitud.

ABSTRACT Objective To determine the predictive value of the dead space calculation through the dead space/tidal volume fraction at weaning from invasive mechanical ventilation in critically ill patients at high altitude. Materials and methods An epidemiological, observational, analytical and prospective study carried out in the Adult Intensive Care Unit of the Hospital del Norte in the city of El Alto, Bolivia (4,090 m a.s.l.; barometric pressure: 453 mm Hg) from November 01, 2016 to March 31, 2017. High-altitude residents under invasive mechanical ventilation were studied. The inclusion criteria were: a) Altitude residents hospitalized in the Invasive Mechanical Ventilation Therapy Intensive Care Unit. b) Patients with evidence of resolution of the cause that prompted their connection to the invasive mechanical ventilator. c) Patients with positive weaning criteria and rates. d) Positive spontaneous respiration test. The study variables were the dead space through the Vd/Vt fraction and its relationship with the success or failure of the weaning process from mechanical ventilation. The Vd/Vt fraction was calculated in the study patients and then weaning from invasive mechanical ventilation was performed. Patients were divided into two groups according to the need for reintubation and reconnection to the mechanical ventilator within 72 hours. Results Twenty-one (21) patients were included: 7 (33 %) women and 14 men (67 %). The mean age was 41 years with a standard deviation of 22.38 years. Eighteen (18) patients (86 %) succeeded and 3 (14 %) failed in the weaning process from invasive mechanical ventilation. The Vd/Vt values in the success and failure groups were 0.43 and 0.53 (p < 0.011109), respectively, with a sensitivity of 0.61 and specificity of 1; a positive predictive value of 1 and a negative predictive value of 0.3. Conclusions The calculation of the dead space through the measurement of the dead space/tidal volume fraction predicts the success of weaning of critically ill patients under invasive mechanical ventilation at high altitude.

Alveolar Dead Space Ventilation Ratio as an Early Predictor of Acute Respiratory Distress Syndrome in Severe Sepsis and Septic Shock Patients

PURPOSE: Examine the clinical utility of the alveolar dead space ventilation ratio (VdA/VT) as a predictor of acute respiratory distress syndrome (ARDS) in severe sepsis and septic shock patients. METHODS: A prospective observation study was done for 113 patients with severe sepsis and septic shock seen at the emergency department of a university hospital from January 2005 to June 2007. Therapies in the emergency department included central venous access, antibiotics, fluid resuscitation, mechanical ventilation, vasopressors and inotropes as required. The major outcome assessed was the development of ARDS within 3 days after admission. Hemodynamic variables, arterial blood gas values, serum lactate concentration, and estimated VdA/VT were evaluated at presentation (0 hour) and at 4 hours. Briefly the estimated VdA/VT was calculated by dividing the deference of the arterial CO2 and end-tidal CO2 by the PaCO2 value. Data were presented as median+/-SD. RESULTS: ARDS developed in twenty-two patients (<24 hours: 17 persons, 24~48 hour: 4 persons, 48~72 hour: 1 person). Patients who developed ARDS had significantly higher age, higher frequency of pneumonia, greater use of mechanical ventilation and dubutamine during ED therapy, and higher sepsis related organ failure assessment (SOFA) scores. The in-hospital mortality of patients with ARDS was significantly higher than that of patients without ARDS (54.5% vs. 15.4%, p<0.001). Pneumonia, use of dobutamine during ED therapy, and VdA/VT at 4 hours were independent predictive factors for the development of ARDS. The area under the receiving operating characteristic curve for predicting ARDS was 0.891 (95% CI; 0.808-0.980) with a value of VdA/VT at 4 hours. The cut off value of VdA/VT at 4 hours was 0.25 (sensitivity 81.8%, specificity 93.3%). At 4 hours, patients with VdA/VT equal to or greater than 0.25 under resuscitation showed a high rate of fluid and high inhospital mortality when compared with patients with VdA/VT <0.25 (CVP<10 cmH2O; 37.5% vs. 16.9%, p=0.047, mortality; 75.0% vs. 4.5%, p<0.001). In patients with VdA/VT equal to or greater than 0.25 at 0 hour, patients without ARDS showed significantly improvement of VdA/VT at 4 hours. CONCLUSION: VdA/VT was found to be an independent predictive variables for ARDS in the early in-hospital period. Improvement of VdA/VT through early goal directed therapy in emergency department may decrease the development of ARDS in severe sepsis and septic shock patients.

Changes in dead space/tidal volume ratio and pulmonary mechanics after surfactant replacement therapy in respiratory distress syndrome of the newborn infants

This study was performed to elucidate the mechanism of improved oxygenation after surfactant replacement therapy in respiratory distress syndrome (RDS) of the newborn infants. In 26 newborns with RDS, end tidal-CO2 tension (PetCO2), arterial blood gas analysis and pulmonary function tests were measured at baseline, 30 min, 2 hr and 6 hr after surfactant administration. The changes in dead space/tidal volume ratio (VD/VT ratio=(PaCO2-PetCO2)/PaCO2), oxygenation index and arterial-alveolar partial pressure difference for oxygen ((A-a)DO2) were elucidated and correlated with pulmonary mechanics. Oxygenation index and (A-a)DO2 improved, and VD/VT ratio decreased progressively after surfactant administration, becoming significantly different from the baseline at 30 min and thereafter with administration of surfactant. Pulmonary mechanics did not change significantly during the observation period. VD/VT ratio showed close correlation with OI and (A-a)DO2, but not with pulmonary mechanics. These results suggest that decreased physiologic dead space resulting from the recruitment of atelectatic alveoli rather than improvement in pulmonary mechanics is primarily responsible for the improved oxygenation after surfactant therapy in the RDS of newborn.