Overestimation of thoracic gas volume during the airway resistance maneuver: a potential error in the diagnosis of air trapping

ABSTRACT

There are no data published about the agreement between the measurement of thoracic gas volume (TGV) during the airway resistance (TGV-Raw) and the conventional technique described by Dubois. The aim of this study was to establish the agreement between both methods to measure TGV. We studied eighty consecutive subjects. Only sixty-six performed acceptable plethysmography maneuvers. The patients were measured with a constant volume plethysmograph (Medical Graphics 1085 DL). TGV was performed in the same patient with two techniques 1) during the airway resistance (Raw) measurement (TGV-Raw) and 2) during quiet breathing at the end of expiration (TGV). The panting frequency was 1 to 2 Hz with both maneuvers. The differences between both techniques were expressed in percentage (deltaTGV %) and absolute values (deltaTGV). The TGV-Raw of the whole group was higher than TGV (3.69 +/- 1.08 l vs 3.28 +/- 1.05 l, p < 0.001). Similarly, the subgroups of patients had a greater TGV-Raw than TGV (Normal 3.44 +/- 0.77 l vs 2.98 +/- 0.72 l , p < 0.001; Obstructive 4.08 +/- 1.19 l vs 3.71 +/- 1.15 l, p < 0.001; Restrictive 2.62 +/- 0.49 l vs 2.25 +/- 0.51 l, p < 0.01). There was a considerable lack of agreement between the TGV-Raw and TGV, with discrepancies of up to +0.95 l or +34%. The deltaTGV % was similar between the patients' subgroups and between the subjects with different degree of airflow obstruction (Normal 16.5 +/- 10%, Obstructive 10.8 +/- 9.4%, Restrictive 18 +/- 14.3%, p NS; mild obstruction 10.7 +/- 11%, moderate obstruction 12.3 +/- 5.7, severe obstruction 10.1+/- 6.6, p NS). In conclusion, TGV-Raw was larger than TGV. This was because the patients generally panted at a volume above FRC when performing the TGV-Raw maneuver. TGV-Raw should not be used to estimate FRC because FRC would be overestimated and the diagnosis of air trapping may be erroneous.

RESUMEN

El objetivo de este estudio fue obtener informacion postmarketing sobre el uso de infliximab en un centro reumatologico de atencion ambulatoria. Se realizo un analisis retrospectivo y prospectivode las historias clinicas de pacientes con diagnostico de artritis reumatoidea (n=37), artritis psoriasica (n=5),enfermedad mixta del tejido conectivo (n=1) y espondilitis anquilosante (n=2) que recibieron infliximab (3 mg/kg) desde agosto de 2000 a junio de 2003. El analisis descriptivo se realizo con porcentajes, media o medianay desviacion estandar o intervalo intercuartilo. La prueba de Wilcoxon se utilizo para el analisis apareado dedosis de antiinflamatorios no esteroideos y metotrexato, anterior y posterior a la administracion de infliximab. Se consideraron significativos valores de p < o = 0.05. Se incluyeron 45 pacientes a los que se les administraron un total de 207 infusiones. En 2 pacientes el infliximab se discontinuo debido a lumbalgia severa durante la infusion y en otros 2 por anafilaxia intrainfusional. Otras reacciones adversas ocurridas durante las infusiones fueron moderadas y respondieron adecuadamente al tratamiento estandar. Se presento un caso de artritis septica de rodilla por estafilococos. Un caso de artritis reumatoidea con insuficiencia renal compensada recibio infliximab en dosis de 1.9 mg/kg cada 30 dias, sin cambios en la funcion renal. Al momento, ningun paciente ha desarrollado tuberculosis activa. Debido a la mejoria clinica, se redujo la dosis de corticoides en 14/39 (35.9%) pacientes, de antiinflamatorios no esteroideos en 15/43 (34.8%) y de metotrexato en 12/34 (35.3%). En estaserie de casos se muestra el perfil de seguridad de infliximab, la posibilidad de reducir la dosis de drogas concomitantes,asi como algunos enfoques individuales sobre situaciones para las cuales no disponemos de guias basadas en la evidencia medica, y en las que los reumatologos debemos tomar decisiones segun las necesidades clinicas.