Determinación de la relación R/I mediante la técnica de la respiración única

Artículo

Autor: Giorgio lotti, Caroline Brown

Fecha: 29.04.2025

Cómo determinar la relación reclutamiento/insuflación a partir de los valores de monitorización del respirador.

Gracias a la relación reclutamiento/insuflación (R/I), los médicos disponen de un medio a pie de cama para evaluar la capacidad de reclutamiento de un paciente a fin de establecer la PEEP según corresponda. Al utilizar la técnica de la respiración única como describen Chen et al. (Chen L, Del Sorbo L, Grieco DL, et al. Potential for Lung Recruitment Estimated by the Recruitment-to-Inflation Ratio in Acute Respiratory Distress Syndrome. A Clinical Trial. Am J Respir Crit Care Med. 2020;201(2):178-187. doi:10.1164/rccm.201902-0334OC1, Chen L, Chen GQ, Shore K, et al. Implementing a bedside assessment of respiratory mechanics in patients with acute respiratory distress syndrome. Crit Care. 2017;21(1):84. Published 2017 Apr 4. doi:10.1186/s13054-017-1671-82), la relación R/I se puede calcular a partir de los datos disponibles en la pantalla de monitorización del respirador.

En los siguientes pasos, le mostraremos cómo llevar a cabo la técnica en un respirador HAMILTON-C6.

El paciente debe recibir ventilación en modo (S)CMV con una PEEP de 15 cmH2O durante 30 minutos (consulte la figura 1). La pausa para inspirar debe establecerse en el mínimo del 5 %. Le recomendamos que utilice una escala de tiempo de 30 segundos para garantizar que la parte relevante de las curvas no desaparezca antes de que se congele la pantalla.

Transcurridos 30 minutos, defina Frec. en 6 c/min (consulte la figura 2).
A continuación, configure PEEP en 5 cmH2O (consulte la figura 3).
Mientras la PEEP va bajando a 5 cmH2O, restablezca rápidamente Frec. al valor anterior, ajuste la PEEP en 15 cmH20 y congele la pantalla (consulte la figura 4).

Captura de pantalla de formas de onda en el modo (S)CMV con una PEEP de 15 — Figura 1

Captura de pantalla que muestra Frec. reducida a 6 — Figura 2

Captura de pantalla que muestra PEEP reducida a 5 cmH2O — Figura 3

Captura de pantalla que muestra la pantalla congelada con un cursor al comienzo de la última inspiración antes de que cambie la PEEP — Figura 4

Paso 1: PEEP, alta

Coloque el cursor al final de la última espiración en el nivel máximo de PEEP (consulte la figura 5).

Pva = PEEP, alta = 15 cmH2O

Captura de pantalla del cursor colocado correctamente y Pva de 15 — Figura 5

Paso 2: Diferencia en PEEP

Mueva el cursor hasta el extremo de la primera espiración en el nivel mínimo de PEEP (consulte la figura 6). Ahí, se mide el valor real de PEEP,baja y el volumen al final de la espiración en relación con la medición de referencia (End-exp Vol, no está visible en la curva pero se puede leer con el cursor). El Vt espiratorio adicional debido al desinflado y el desreclutamiento (VTe,plus) es lo opuesto al End-exp Vol.

Pva = PEEP, baja = 4,9 cmH2O
V = End-exp Vol (volumen al final de la espiración) = -429 ml
VTe,plus = 429 ml

Ahora, puede calcular la diferencia en PEEP:

PEEP,alta = 15 cmH2O
PEEP,baja = 4,9 cmH2O
ΔPEEP = 10,1 cmH2O

Captura de pantalla del cursor colocado correctamente y los valores correspondientes — Figura 6

Paso 3: Presión de trabajo y compliance en el nivel mínimo de PEEP

Coloque el cursor al final de la primera meseta inspiratoria en el nivel mínimo de PEEP (consulte la figura 7). En este punto, mida la presión meseta (Pmeseta,baja) y el VT inspiratorio (VTI,bajo).

Pva = Pmeseta,baja = 17 cmH2O
V = VTi,bajo = 467 ml

Ahora ya puede calcular la presión de trabajo y la compliance en el nivel mínimo de PEEP:

ΔP,baja = Pmeseta,baja – PEEP,baja = 17 – 4,9 = 12,1
C,baja = VTi,bajo/ΔP,baja = 467/12,1 = 38,6

Después de tomar nota de las mediciones del cursor como se describe en los pasos 1, 2 y 3, no olvide comprobar el ajuste de PEEP. La medición de la relación requiere solamente una respiración en el nivel mínimo de PEEP. Si se prolonga la ventilación en el nivel mínimo de PEEP, puede producirse un colapso alveolar generalizado, lo que conllevaría un empeoramiento grave de los intercambios gaseosos.

Captura de pantalla del cursor colocado correctamente mostrando los valores según se indica arriba — Figura 7

Paso 4: Volumen insuflado y reclutado

Con los valores que ha anotado, ya puede calcular (para el cambio de PEEP que ha analizado) el cambio de volumen debido justo a la insuflación alveolar (Vinsuflado) y el cambio debido al reclutamiento alveolar (Vreclutado).

Vinsuflado = C,baja x ΔPEEP = 38,6 x 10,1 = 390 ml
Vreclutado = VTe,plus – Vinsuflado = 429 – 390 = 39 ml

Estos dos valores le proporcionan la relación reclutamiento/insuflación.

R/I = Vreclutado/Vinsuflado = 39/390 = 0,10 ml

¿Qué nos dice?

Los valores de R/I inferiores a 0,3–0,4 indican una capacidad de reclutamiento baja. Tal como sucede en este caso, un ajuste de PEEP baja (de entre 5 y 8 cmH2O) puede ser la opción más apropiada. Por otro lado, se recomienda aplicar un nivel mínimo de PEEP de 12 cmH2O si los valores de R/I son superiores a 0,6–0,7, lo que indica una capacidad de reclutamiento alta. Se recomiendan niveles de PEEP intermedios cuando el valor de R/I se encuentra en torno a 0,5 (Rosà T, Bongiovanni F, Michi T, et al. Recruitment-to-inflation ratio for bedside PEEP selection in acute respiratory distress syndrome. Minerva Anestesiol. 2024;90(7-8):694-706. doi:10.23736/S0375-9393.24.17982-53).

Pva: presión de las vías aéreas
V: volumen
End-exp Vol: volumen al final de la espiración
VTe,plus: volumen tidal espiratorio adicional asociado a la disminución brusca de PEEP
Pmeseta,baja: presión meseta en el nivel mínimo de PEEP
VTI,bajo: volumen inspiratorio en el nivel mínimo de PEEP
C,baja: compliance en el nivel mínimo de PEEP

Notas al pie

Referencias

1. Chen L, Del Sorbo L, Grieco DL, et al. Potential for Lung Recruitment Estimated by the Recruitment-to-Inflation Ratio in Acute Respiratory Distress Syndrome. A Clinical Trial. Am J Respir Crit Care Med. 2020;201(2):178-187. doi:10.1164/rccm.201902-0334OC
2. Chen L, Chen GQ, Shore K, et al. Implementing a bedside assessment of respiratory mechanics in patients with acute respiratory distress syndrome. Crit Care. 2017;21(1):84. Published 2017 Apr 4. doi:10.1186/s13054-017-1671-8
3. Rosà T, Bongiovanni F, Michi T, et al. Recruitment-to-inflation ratio for bedside PEEP selection in acute respiratory distress syndrome. Minerva Anestesiol. 2024;90(7-8):694-706. doi:10.23736/S0375-9393.24.17982-5

Potential for Lung Recruitment Estimated by the Recruitment-to-Inflation Ratio in Acute Respiratory Distress Syndrome. A Clinical Trial.

Chen L, Del Sorbo L, Grieco DL, et al. Potential for Lung Recruitment Estimated by the Recruitment-to-Inflation Ratio in Acute Respiratory Distress Syndrome. A Clinical Trial. Am J Respir Crit Care Med. 2020;201(2):178-187. doi:10.1164/rccm.201902-0334OC

Link to article

Rationale: Response to positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome depends on recruitability. We propose a bedside approach to estimate recruitability accounting for the presence of complete airway closure.Objectives: To validate a single-breath method for measuring recruited volume and test whether it differentiates patients with different responses to PEEP.Methods: Patients with acute respiratory distress syndrome were ventilated at 15 and 5 cm H2O of PEEP. Multiple pressure-volume curves were compared with a single-breath technique. Abruptly releasing PEEP (from 15 to 5 cm H2O) increases expired volume: the difference between this volume and the volume predicted by compliance at low PEEP (or above airway opening pressure) estimated the recruited volume by PEEP. This recruited volume divided by the effective pressure change gave the compliance of the recruited lung; the ratio of this compliance to the compliance at low PEEP gave the recruitment-to-inflation ratio. Response to PEEP was compared between high and low recruiters based on this ratio.Measurements and Main Results: Forty-five patients were enrolled. Four patients had airway closure higher than high PEEP, and thus recruitment could not be assessed. In others, recruited volume measured by the experimental and the reference methods were strongly correlated (R2 = 0.798; P < 0.0001) with small bias (-21 ml). The recruitment-to-inflation ratio (median, 0.5; range, 0-2.0) correlated with both oxygenation at low PEEP and the oxygenation response; at PEEP 15, high recruiters had better oxygenation (P = 0.004), whereas low recruiters experienced lower systolic arterial pressure (P = 0.008).Conclusions: A single-breath method quantifies recruited volume. The recruitment-to-inflation ratio might help to characterize lung recruitability at the bedside.Clinical trial registered with www.clinicaltrials.gov (NCT02457741).

Implementing a bedside assessment of respiratory mechanics in patients with acute respiratory distress syndrome.

Chen L, Chen GQ, Shore K, et al. Implementing a bedside assessment of respiratory mechanics in patients with acute respiratory distress syndrome. Crit Care. 2017;21(1):84. Published 2017 Apr 4. doi:10.1186/s13054-017-1671-8

Link to article

BACKGROUND Despite their potential interest for clinical management, measurements of respiratory mechanics in patients with acute respiratory distress syndrome (ARDS) are seldom performed in routine practice. We introduced a systematic assessment of respiratory mechanics in our clinical practice. After the first year of clinical use, we retrospectively assessed whether these measurements had any influence on clinical management and physiological parameters associated with clinical outcomes by comparing their value before and after performing the test. METHODS The respiratory mechanics assessment constituted a set of bedside measurements to determine passive lung and chest wall mechanics, response to positive end-expiratory pressure, and alveolar derecruitment. It was obtained early after ARDS diagnosis. The results were provided to the clinical team to be used at their own discretion. We compared ventilator settings and physiological variables before and after the test. The physiological endpoints were oxygenation index, dead space, and plateau and driving pressures. RESULTS Sixty-one consecutive patients with ARDS were enrolled. Esophageal pressure was measured in 53 patients (86.9%). In 41 patients (67.2%), ventilator settings were changed after the measurements, often by reducing positive end-expiratory pressure or by switching pressure-targeted mode to volume-targeted mode. Following changes, the oxygenation index, airway plateau, and driving pressures were significantly improved, whereas the dead-space fraction remained unchanged. The oxygenation index continued to improve in the next 48 h. CONCLUSIONS Implementing a systematic respiratory mechanics test leads to frequent individual adaptations of ventilator settings and allows improvement in oxygenation indexes and reduction of the risk of overdistention at the same time. TRIAL REGISTRATION The present study involves data from our ongoing registry for respiratory mechanics (ClinicalTrials.gov identifier: NCT02623192 . Registered 30 July 2015).

Recruitment-to-inflation ratio for bedside PEEP selection in acute respiratory distress syndrome.

Rosà T, Bongiovanni F, Michi T, et al. Recruitment-to-inflation ratio for bedside PEEP selection in acute respiratory distress syndrome. Minerva Anestesiol. 2024;90(7-8):694-706. doi:10.23736/S0375-9393.24.17982-5

Link to article

In acute respiratory distress syndrome, the role of positive end-expiratory pressure (PEEP) to prevent ventilator-induced lung injury is controversial. Randomized trials comparing higher versus lower PEEP strategies failed to demonstrate a clinical benefit. This may depend on the inter-individually variable potential for lung recruitment (i.e. recruitability), which would warrant PEEP individualization to balance alveolar recruitment and the unavoidable baby lung overinflation produced by high pressure. Many techniques have been used to assess recruitability, including lung imaging, multiple pressure-volume curves and lung volume measurement. The Recruitment-to-Inflation ratio (R/I) has been recently proposed to bedside assess recruitability without additional equipment. R/I assessment is a simplified technique based on the multiple pressure-volume curve concept: it is measured by monitoring respiratory mechanics and exhaled tidal volume during a 10-cmH2O one-breath derecruitment maneuver after a short high-PEEP test. R/I scales recruited volume to respiratory system compliance, and normalizes recruitment to a proxy of actual lung size. With modest R/I (<0.3-0.4), setting low PEEP (5-8 cmH2O) may be advisable; with R/I>0.6-0.7, high PEEP (≥15 cmH2O) can be considered, provided that airway and/or transpulmonary plateau pressure do not exceed safety limits. In case of intermediate R/I (≈0.5), a more granular assessment of recruitability may be needed. This could be accomplished with advanced monitoring tools, like sequential lung volume measurement with granular R/I assessment or electrical impedance tomography monitoring during a decremental PEEP trial. In this review, we discuss R/I rationale, applications and limits, providing insights on its clinical use for PEEP selection in moderate-to-severe acute respiratory distress syndrome.

Herramientas a pie de cama para evaluar la capacidad de (des)reclutamiento

¿Qué es la capacidad de reclutamiento y cómo podemos medirla?