Lung recruitment during anesthesia

Hello again, this is Dr Robert Bilkovski and we continue on our next installment in the podcast series on perioperative safety, where we look at lung recruitment during anesthesia. This podcast will help you get a grounding on the negative effects general anesthesia has on the lungs and the importance alveolar recruitment maneuvers can provide. 

[note: basis for this podcast leverages Alveolar Recruitment Maneuvers to Help Improve Lung Function During General Anesthesia https://clinicalview.gehealthcare.com/white-paper/alveolar-recruitment-…]

When a patient is undergoing surgery, they undergo a transition from standing to a supine position along with the induction of general anesthesia which may negatively affect lung function. Specifically, the collapse of alveolar units can result in the development of atelectasis and as a result may make ventilation and oxygenation more difficult. There are multiple additional factors that can contribute to lung collapse and include: the high FiO2 used during induction, diaphragm dysfunction during anesthesia and the central anesthetic effects on respiratory muscle tone.^[1]  In addition, changes in abdominal pressure, chest wall compliance, and neuromuscular blockade all produce additive effects that can further compromise lung function, notably reduction in the functional residual capacity which represents the end-expiratory lung volume.  As a result of these changes, the lung has a smaller volume and can require greater pressures in order to support the patient's ventilatory needs. 

For more information on oxygen exchange and the alveolar unit, I suggest revisiting a podcast from the   series on end-tidal oximetry, specifically podcast #1 of the series that looked at the principles of oxygen exchange.

Of note, up to 90% of patients undergoing general anesthesia may develop hypoxemia due to progressive atelectasis. Early studies found that the use of a tidal volume of 12 – 15 mL/kg body weight was effective in reducing atelectasis and restoring compliance for normal pulmonary gas exchange in the operating room. [2] Since then, researchers have turned their focus to lower tidal volumes for the adverse effects of high tidal volume ventilation has been recognized both in patients with acute respiratory distress syndrome and those with healthy lungs undergoing anesthesia. This has shifted recommendations away from high tidal volume to low tidal volume ventilation, where now the tidal volume goal is between 6 to 8 ml per kg body weight.^[3]

The basis for lung protective strategies is to minimize the burden of volutrauma and barotrauma. Volutrauma refers to the damage that can be imposed to the lungs as a result of high tidal volumes which causes excessive inflation of the alveoli, whereas barotrauma is the result of excessive tranpulmonary pressure which is the difference between pressures inside and outside the lungs.^[4]

During surgery, an approach by which the anesthesiologist can reduce the incidence of atelectasis is to conduct a recruitment maneuver. The basis of recruitment maneuvers is to bring a collapsed alveolus back to normal function via the application of sufficient positive pressure ventilation. The opening pressure of an alveolus or terminal airway is the specific amount of positive pressure that results in their reopening; but the opening pressure will vary from one alveolus to another. Most collapsed alveoli can be opened during general anesthesia with an alveolar recruitment maneuver that consists of peak inspiratory pressure of 40 cm H2O being applied for 7-10 seconds. ^[5] However, there are different ways to perform a recruitment maneuver: 

1. Pressure can be delivered manually, but this approach is ill-advised for it may be associated with a paradoxical increased rate of post-operative complications^[6]
2. What is preferred is to conduct a step-wise changes in volume settings on the ventilator component of the anesthesia delivery device. In this setting, the delivered volume and/or pressure can be increased every 3 – 6 breaths until the target opening pressure is achieved. After delivering several breaths at the target pressure one can return to the previous low tidal volume ventilation. 

The importance of alveolar recruitment maneuvers was summarized by an international expert panel which published a consensus statement in 2019 and in it the panel concluded that recruitment maneuvers should be used:^[7]

1. Whenever the patient is disconnected from the breathing circuit and whenever the patient’s hemoglobin saturation is consistently ≤94%;
2. One should evaluate change in respiratory system compliance and driving pressure after an alveolar recruitment maneuver and repeat maneuver with a longer inspiratory hold or higher pressure if recruitment is assessed as ineffective; and
3. Alveolar recruitment maneuvers should be performed using the lowest effective peak inspiratory pressure and shortest effective time or fewest number of breaths

 

In closing a meta-analysis published in 2019 showed that the effect of alveolar recruitment maneuvers from 12 selected studies had a statistically significant reduction in postoperative pulmonary complications, especially when lung-protective ventilation strategies were also deployed,^[8] thereby stressing the clinical utility of recruitment maneuvers during general anesthesia.

This concludes this podcast on lung recruitment strategies during general anesthesia. Thank you for listening and be sure to listen in again on future topics pertaining to perioperative safety.

References:

[1]     Tusman, G. and Belda, J.F., 2010. Treatment of anesthesia-induced lung collapse with lung recruitment maneuvers. Current anaesthesia & critical care, 21(5-6), pp.244-249.

[2]     The Acute Respiratory Distress Syndrome Network: Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000, 342:1301–1308.

[3]     Futier, E., Constantin, J. M., Paugam-Burtz, C., Pascal, J., Eurin, M., Neuschwander, A., ... & Jaber, S. (2013). A trial of intraoperative low-tidal-volume ventilation in abdominal surgery. New England Journal of Medicine, 369(5), 428-43

[4]     Beitler JR, Malhotra A, Thompson BT. Ventilator-induced Lung Injury. Clin Chest Med. 2016 Dec;37(4):633-646.

[5]     Hartland BL, Newell TJ, Damico N. Alveolar recruitment maneuvers under general anesthesia: a systematic review of the literature. Respiratory care. 2015 Apr 1;60(4):609-20.

[6]     Ball, L., Hemmes, S. N. T., Neto, A. S., Bluth, T., Canet, J., Hiesmayr, M., ... & Pelosi, P. (2018). Intraoperative ventilation settings and their associations with postoperative pulmonary complications in obese patients. British Journal of Anaesthesia, 121(4), 899-908.

[7]     Young, C. C., Harris, E. M., Vacchiano, C., Bodnar, S., Bukowy, B., Elliott, R. R. D., ... & Sprung, J. (2019). Lung-protective ventilation for the surgical patient: international expert panel-based consensus recommendations. British Journal of Anaesthesia, 123(6), 898-913.

[8]     Cui, Y., Cao, R., Li, G., Gong, T., Ou, Y. and Huang, J., 2019. The effect of lung recruitment maneuvers on post-operative pulmonary complications for patients undergoing general anesthesia: a meta-analysis. *PLoS One*, *14*(5), p.e0217405.

 

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Dr. Bilkovski is a paid consultant of GE HealthCare. GE is a trademark of General Electric Company used under trademark license. Reproduction in any form is forbidden without prior written permission from GE HealthCare. Nothing in this material should be used to diagnose or treat any disease or condition. Readers must consult a healthcare professional.

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