Tidal volume, PEEP, and recruitment maneuvers: 3 components of lung protective ventilation

Postoperative pulmonary complications (PPCs) have become an expected risk inside the operating room. The prevalence of PPCs in adult patients who require intraoperative ventilation ranges from 6% to over 10% in recent studies.¹ ² Patients considered at risk for PPCs is nearly a staggering quarter of all surgical patients who require anesthesia and subsequent ventilation support.²

While intraoperative ventilation and postoperative support have come a long way in regards to perioperative lung protection, there is much to improve when it comes to reducing PPC risk and subsequent events.

Lung Protective Ventilation

Lung protective ventilation (LPV) refers to creating the right balance of volume and pressure to achieve ventilation and gas exchange with minimal harm. If there’s too much pressure or volume – lung injury can occur. Too little, and issues like atelectasis, hypoventilation, and hypoxemia may happen.

Tidal volume, PEEP settings, and recruitment maneuvers are the three pillars of LPV. Achieving optimal settings of these three components is paramount to reducing PPC risk.

Tidal Volume

A major cause of ventilator-associated lung injury is volutrauma or the overstretching of the delicate alveoli due to higher tidal volume ventilation.³ When it comes to patients with acute respiratory distress syndrome (ARDS), many clinicians have transitioned to using lower tidal volumes in an effort to reduce morbidity and mortality. But even though using lower tidal volumes in higher risk patients, including those with ARDS, has been proven to reduce mortality, only about one third of physicians use a lower tidal volume as a lung protective strategy. Researchers found this is mostly due to an uncertainty if the patient truly had ARDS. ⁴

This begs the question, why don’t clinicians use lower tidal volumes for everyone, regardless of baseline lung function? A meta-analysis on 1,411 studies published in JAMA explored this question and found that using a lower tidal volume in patients without ARDS reduced the risk of developing ARDS, reduced mortality and pulmonary infections, and had less atelectasis when compared with higher tidal volumes in patients with optimal lung function.³

PEEP

Lower tidal volumes cannot be used alone when it comes to lung protective ventilation. Positive end-expiratory pressure (PEEP) must also be used to help support lung function during general anesthesia. PEEP helps restore declines in functional residual capacity (FRC) which can drop as much as 37% after the induction of anesthesia.⁵ Factors impacting a reduction in FRC include:

Muscle paralysis
Decreased chest wall recoil
Increased abdominal pressure
Atelectasis formation
Gas entrapment

When zero end-expiratory pressure (ZEEP) is utilized, there is no change in the amount of FRC reduction, meaning the lungs are receiving no help in optimizing pulmonary gas exchange. This is why utilizing PEEP levels of at least 5 cmH₂O is considered advantageous as part of a lung protective ventilation strategy – it’s been proven to increase FRC, reduce atelectasis and maintain proper oxygenation.⁵

Alveolar Recruitment Maneuvers

Alveolar recruitment maneuvers (ARMs) are the third component when striving for lung protective ventilation. Using recruitment maneuvers can reopen collapsed alveoli and improve lung function in surgical patients who require general anesthesia.⁶

Using ARMs when appropriate can help improve pulmonary function in the operating room and prevent PPCs. ARMs are helpful to reverse alveolar collapse and subsequent atelectasis but must be used thoughtfully and with proper technique.

There are two types of ARMs, manual and ventilator-driven ARMs. Manual ARMs include using the reservoir bag to set inflation pressure. Limitations of manual ARMs are

it’s difficult to control
there’s an increased risk of overpressure and
de-recruitment occurs when switching back to the ventilator circuit.6

Due to these limitations, ventilator-driven ARMs are preferred. Limiting the use of ARMs, using the lowest FIO₂ during ARMs, and using the fewest breaths and time required is recommended.⁶

Lung protective ventilation involves several patient factors, surgical factors, and mechanical factors. PPCs can’t always be prevented but following proven guidelines can improve a patient’s outcome for successful lung function in the OR and in the PACU. Following guidelines⁶ as well as using lower tidal volumes, utilizing PEEP at proper settings, and using ventilator-driven ARMs, can reduce morbidity and mortality when it comes to PPCs.

References

Canet J et al. Anesthesiology. 2010 Dec;113(6):1338-50.
The LAS VEGAS Investigators - Eur J Anaesthesiol 2017; 34:492–507.
Neto, A. et al. 2012. Association between use of lung-protective ventilation with lower tidal volumes and clinical outcomes among patients without acute respiratory distress syndrome. JAMA. 308. (16). 1651-1659.
Mikkelsen ME, Dedhiya PM, Kalhan R, Gallop RJ, Lanken PN, Fuchs BD. Potential reasons why physicians underuse lung-protective ventilation: a retrospective cohort study using physician documentation. Respir Care. 2008;53(4):455-461.
Satoh, D. et al. 2012. Impact of changes of positive end-expiratory pressure on functional residual capacity at low tidal volume ventilation during general anesthesia. J Anesth. 26:664-669. DOI 10.1007/s00540-012-1411-9 .
Young, C. et al. 219. Lung-protective ventilation for the surgical patient: international expert panel-based consensus recommendations. British Journal of Anaesthesia. doi: 10.1016/j.bja.2019.08.017.