The role of point-of-care ultrasound and issues related to one-lung ventilation in neonates

We read with interest the report by Rodrigues et al.¹ on neonatal left lung upper lobectomy under One-Lung Ventilation (OLV). The authors should be commended for their management and, specifically, for the use of Point-Of-Care Ultrasound (POCUS) to confirm lung isolation. Indeed, POCUS has proven superior (95% accuracy) over auscultation (62% accuracy) in identifying tracheal versus bronchial intubation in adults.² We herein would like to briefly expand on some key lung ultrasound “signatures” and comment on some possible challenges associated with the authors’ technique.

Lung ultrasound is based primarily on artifacts:

1. “A lines”: horizontal lines/artifacts that run deeper to the pleural line, and at equidistant intervals (i.e., skin-pleural line distance = pleural line-first A-line distance, and so on). “A line pattern” is found in normal lungs and/or non-interstitial pathologies (e.g., pneumothorax, COPD/asthma exacerbation, pulmonary embolism);

2. “B lines”: vertical lines/artifacts generated by fluid (such that the more fluid the larger/more numerous the B lines) originating from pleural line and extending to bottom of the screen. “B line pattern” is found in interstitial pathologies (e.g., pulmonary edema, ARDS, pneumonia/pneumonitis);

3. “Lung-sliding”: shimmering of pleural line that moves sideways in a synchronized fashion with inspiration/expiration. The presence of lung-sliding confirms apposition of the visceral and parietal pleurae, therefore ruling out pneumothorax at that location. Similarly, the “seashore” and “barcode” signs described by the authors reflect the presence and absence, respectively, of lung-sliding using M mode. Finally, “lung-pulse” also confirms apposition of the pleurae (similar to lung-sliding), hence excluding pneumothorax.

In their report, the authors state that “In a collapsed lung, the pleural line moves with the heartbeat, originating the lung-pulse sign”. In fact, lung-pulse may or may not be present depending on the cause of lung collapse. In pneumothorax, for instance, lung-sliding/lung-pulse are absent, and other features (A line pattern + B lines absent + “lung-point”) will confirm the diagnosis. Conversely, and as alluded to earlier, the presence of lung-pulse confirms apposition of the pleurae, thus ruling out pneumothorax.

Finally, we respectfully disagree that a 3 mm ETT cannot be coupled with a Bronchial Blocker (BB). The use of an extra-luminal 3Fr Fogarty or Arndt 5Fr balloon catheter is well described³ and would mean placing it in the left mainstem bronchus in this case. Additionally, whereas the authors were able to avoid occluding the right upper lobe orifice with their ETT, what happens if the right upper lobe orifice is very close to or above the carina? In that case, we believe a BB in the left mainstem would be a superior choice.

Another point is whether the described technique is applicable in case of right lung exclusion. For the most part, it probably is, but there are certain concerns. Advancing the ETT into the smaller left (compared to right) mainstem bronchus (the ratio left mainstem/tracheal diameter is ∼0.65-0.7 in adults), as advocated by the authors, would risk excessive mucosal pressure, potentially resulting in ischemia, swelling, and/or even granuloma formation. Even a moderate period of intubation (with 3 mm ETT) of the left mainstem bronchus had resulted in tracheomalacia with subsequent collapse of the left mainstem bronchus in a premature neonate.⁴ Unlike OLV in adults with chronic lung disease, during pediatric OLV, several cycles of one-lung alternating with two-lung ventilations may be required to eventually achieve sustained adequate oxygenation. Thus, a potential (unverified) disadvantage of endobronchial intubation with a single-lumen ETT, as opposed to using a BB, is the need to repeatedly slide the ETT in and out of the mainstem bronchus. Taking into consideration the very cramped/awkward positioning of a small patient in a lateral position, most anesthesiologists will likely find that repositioning (which may require repeatedly securing/loosening the ETT) and reconfirmation of an ideal endobronchial intubation with an ETT may be more cumbersome/challenging (especially on the left side) than simply deflating/re-inflating the bronchial balloon. That said, simply advancing the ETT into the chosen mainstem bronchus for surgery that lasts a mere few hours is a simple technique that is worth trying, especially for those practitioners uncomfortable with bronchial blocker placement.

• Financial support
  Departmental and institutional resources. No external funding was acquired for the current work.

References

• ¹
  Rodrigues A, Alves P, Hipólito C, et al. Will ultrasound replace the stethoscope? A case report on neonatal one-lung ventilation. Braz J Anesthesiol. 2019;69:514-6.
• ²
  Ramsingh D, Frank E, Haughton R, et al. Auscultation versus point-of-care ultrasound to etermine endotracheal versus bronchial intubation. Anesthesiology. 2016;124:1012-20.
• ³
  Ho AMH, Karmakar MK, Critchley LAH, et al. Placing the tip of the endotracheal tube at the carina and passing the endobronchial blocker through the Murphy eye may reduce the risk of blocker retrograde dislodgement during one-lung anaesthesia in small children. Br J Anaesth. 2008;101:690-3.
• ⁴
  Ho AMH, Winthrop A, Jones EF, et al. Severe pediatric bronchomalacia. Anesthesiology. 2016;124:1395.

Publication Dates

• Publication in this collection
  14 Sept 2020
• Date of issue
  May-Jun 2020