ARTICLE REVIEW
The use of ultrasound is growing exponentially in critical care. It is well established its utility for cardiopulmonary evaluation, but its potential uses in the weaning process are not yet well defined.
This review performed by Mayo et al. (1) describes differing ultrasound possibilities that could help in the weaning process. The authors divided these options into four categories:
Cardiac function
Weaning may be considered an exercise requiring an elevation in cardiac index, oxygen demand and consumption (2). Some measures that could predict failure of an spontaneuous breathing trial (SBT) are: Left ventricle ejection fraction (LVEF) <40%, evaluation of diastolic funtion in the mitral diastolic inflow depending on the LVEF: if normal E/e’>12,if reduced E/A>2, cardiac output measured before and after a manouvre of passive leg raise without change.
Diaphragmatic function
We may measure the diaphragmatic excursion and the diaphragmatic muscle thickening during inspiration, also the thickening fraction (TF) is reported in most studies (3). During SBT: diaphragmatic excursion < 11mm, TF< 30% or bilateral absence of diaphragmatic excrusion may increase likelihood of failure.
Pleural effusion
Pleural fluid drainage may not improve gas exchange or respiratory mechanics, despite large effusions that cause lobar atelectasis. Ultrasound can accurately estimate the volume of the effusion and can guide in its drainage. Authors suggest that a removal of a moderate and large effusion may increase the success of a SBT.
Lung aeration
Soummer et al. demostrated that lung ultrasound (LUS) predicts weaning failure with some accuracy and a LUS score has been validated. LUS score <13 increases the likelihood of success and > 17 increases the possibility of failure, while between 13 and 17 the effect is unknown (4). In spite of the fact that LUS score may be a little complicated to be done in our daily work, it is a useful bedside tool.
In conclusion, there is not a reliable tool to predict the success in the weaning process and in most cases, there is more than a single cause of failure. Ultrasound may help to diagnose and treat most of this causes. All this measures explained above can help to predict the success, despite not all of them has been validated. Future research is needed to determine the role of ultrasonography in the weaning process.
Article review submitted by Laura Galarza Barrachina on behalf of the NEXT committee.
References
(1) Mayo P, Volpicelli G, Lerolle N, Schreiber A, P. Doelken P, Vieillard-Baron A. Ultrasonography evaluation during the weaning process: the heart, the diaphragm, the pelura and the lung. ICM 2016 DOI 10.1007/s00134-016-4245-3
(2) De Backer D, El Haddad P, Preiser JC, Vincent JL (2000) Hemodynamic response to a successful weaning from mechanical ventilation after cardiovascular surgery. Intensive Care Med 26:1201–1206
(3) Matamis D, Soilemezi E, Tsagourias M, Akoumianaki E, Dimassi S, Boroli F et al (2013) Sonographic evaluation of the diaphragm in critically ill patients. Technique and clinical applications. Intensive Care Med 39(5):801–810
(4) Soummer A, Perbet S, Brisson H, Arbelot C, Constantin JM, Lu Q, Rouby JJ, The Lung Ultrasound Study Group (2012) Ultrasound assessment of lung aeration loss during a successful weaning trial predicts postextubation distress. Crit Care Med 40:2064–2072
