Selective Recruitment Maneuvers for Lobar Atelectasis: Effects on Lung Function and Central Hemodynamics: An Experimental Study in Pigs

Selective Recruitment of Large Lower Lobe Atelectasis on Donor Back Table in Rejected Donor Lungs

Background

Large atelectatic areas in donor lungs are frequently resistant to standard recruitment maneuvers, producing a tenaciously low PO₂/FiO₂ ratio. The aim of this study is to investigate the optimal protocol for the recruitment of large atelectatic areas in the context of ex vivo lung perfusion (EVLP).

Methods

Seventeen rejected lungs with large lower lobe atelectasis (≥40%) were divided into 2 groups: manual resuscitation (n = 5) and selective recruitment (n = 12). Transplant suitability was then evaluated in cellular EVLP. In the manual resuscitation group, following bronchoscopy, if the conventional recruitment maneuver was not successful, a bagging technique was utilized to resolve atelectasis in EVLP. In the selective recruitment group, a pediatric endotracheal tube was introduced to the lower lobe bronchus on the back table of the donor hospital. Selective recruitment of the lower lobe was accomplished while keeping peak inspiratory pressure <30 cm H₂O for 30 seconds.

Results

The average atelectasis size and lung weight in 17 donor lungs was 75.4 ± 20.6% and 960 ± 221 g, respectively. There were no significant differences between the 2 groups in all donor variables, except cold ischemic time (P = 0.001, 5.2 ± 0.5 versus 6.4 ± 0.7 hours). The selective recruitment group was associated with better transplant suitability (P = 0.035, 75% versus 20%), better PO₂/FiO₂ ratio (P = 0.186, 324 ± 89 versus 258 ± 87 mm Hg), lower lung weight (P = 0.057, 997.9 ± 229.2 versus 1377.2 ± 452.9 g), and better pathological score (P < 0.05, 1.0 ± 1.3 versus 2.8 ± 0.8) than the manual resuscitation group.

Conclusion

A selective recruitment procedure is a safe and effective method of eliminating large atelectasis before EVLP.

Haemodynamic Effects of Lung Recruitment Manoeuvres

Atelectasis caused by lung injury leads to increased intrapulmonary shunt, venous admixture, and hypoxaemia. Lung recruitment manoeuvres aim to quickly reverse this scenario by applying increased airway pressures for a short period of time which meant to open the collapsed alveoli. Although the procedure can improve oxygenation, but due to the heart-lung and right and left ventricle interactions elevated intrathoracic pressures can inflict serious effects on the cardiovascular system. The purpose of this paper is to give an overview on the pathophysiological background of the heart-lung interactions and the best way to monitor these changes during lung recruitment.

Paediatric lung recruitment: a review of the clinical evidence

Lung recruitment is used as an adjunct to lung protective ventilation strategies. Lung recruitment is a brief, deliberate elevation of transpulmonary pressures beyond what is achieved during tidal ventilation levels. The aim of lung recruitment is to maximise the number of alveoli participating in gas exchange particularly in distal and dependant regions of the lung. This may improve oxygenation and end expiratory levels. Restoration of end expiratory levels and stabilisation of the alveoli may reduce the incidence of ventilator induced lung injury (VILI). Various methods of lung recruitment have been studied in adult and experimental populations. This review aims to establish the evidence for lung recruitment in the pediatric population.

Measurements of functional residual capacity during intensive care treatment: the technical aspects and its possible clinical applications

Direct measurement of lung volume, i.e. functional residual capacity (FRC) has been recommended for monitoring during mechanical ventilation. Mostly due to technical reasons, FRC measurements have not become a routine monitoring tool, but promising techniques have been presented. We performed a literature search of studies with the key words 'functional residual capacity' or 'end expiratory lung volume' and summarize the physiology and patho-physiology of FRC measurements in ventilated patients, describe the existing techniques for bedside measurement, and provide an overview of the clinical questions that can be addressed using an FRC assessment. The wash-in or wash-out of a tracer gas in a multiple breath maneuver seems to be best applicable at bedside, and promising techniques for nitrogen or oxygen wash-in/wash-out with reasonable accuracy and repeatability have been presented. Studies in ventilated patients demonstrate that FRC can easily be measured at bedside during various clinical settings, including positive end-expiratory pressure optimization, endotracheal suctioning, prone position, and the weaning from mechanical ventilation. Alveolar derecruitment can easily be monitored and improvements of FRC without changes of the ventilatory setting could indicate alveolar recruitment. FRC seems to be insensitive to over-inflation of already inflated alveoli. Growing evidence suggests that FRC measurements, in combination with other parameters such as arterial oxygenation and respiratory compliance, could provide important information on the pulmonary situation in critically ill patients. Further studies are needed to define the exact role of FRC in monitoring and perhaps guiding mechanical ventilation.

Appropriate Ventilatory Settings for Thoracic Surgery: Intraoperative and Postoperative

Mechanical ventilation of patients undergoing thoracic surgery is often challenging. These patients frequently have significant underlying comorbidities, including cardiopulmonary disease, and often must undergo 1-lung ventilation. Perioperative respiratory complications are common and are multifactorial in etiology. Increasing evidence suggests that mechanical ventilation is associated with, and may even cause, lung damage in both sick and healthy patients. Gas exchange to provide acceptable end-organ oxygenation remains a primary goal but so too is minimization of risks for acute lung injury. Every ventilator strategy is associated with potential beneficial and adverse side effects. Understanding the impact of various ventilation strategies allows clinicians to provide optimal care for patients.

Are Selective Lung Recruitment Maneuvers Hemodynamically Safe in Severe Hypovolemia? An Experimental Study in Hypovolemic Pigs with Lobar Collapse

BACKGROUND

We have previously shown, in normovolemic pigs, that a selective lung recruitment maneuver (S-LRM), i.e., insufflation of air-oxygen via a balloon catheter with its tip located in the bronchus of a collapsed lung lobe, effectively improves oxygenation and lung volume without affecting hemodynamics negatively. In this study, we examined the respiratory and circulatory effects of S-LRM during hypovolemia with compromised circulation.

METHODS

In eight ventilated (fraction of inspired oxygen, Fio2 1.0) and anesthetized pigs a balloon catheter was inserted in the bronchus of the right lower lung lobe. The lobe was selectively lavaged to create a dense lobar collapse. The pigs were then subjected to S-LRM (40 cm H2O airway pressure for 30 s) at normovolemia, after venesection of 20% and 40% of the blood volume, respectively. Blood gases, compliance of the respiratory system (Crs), vascular pressures, and cardiac output were registered before, during, and after the S-LRM.

RESULTS

Pao2, venous admixture, and Crs improved significantly with S-LRM at all three volume levels. No change in hemodynamics with S-LRM occurred in normovolemia and 20% hypovolemia. For 40% hypovolemia, cardiac output was unchanged by S-LRM, whereas minor decreases in mean arterial blood pressure were seen: 48 (37-52) mm Hg (median, 25th and 75th percentiles) 3 min before S-LRM, 40 (35-44) mm Hg at the end of S-LRM (P = 0.0207), and 47 (39-54) mm Hg 3 min after S-LRM.

CONCLUSION

A S-LRM effectively improved oxygenation and Crs and had only minor circulatory side effects, even in severe hypovolemia in this animal model of lobar collapse.