Limiting Overdistention or Collapse when Mechanically Ventilating Injured Lungs: A Randomized Study in a Porcine Model

RATIONALE

It is unknown whether preventing overdistention or collapse is more important when titrating positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS).

OBJECTIVE

To compare PEEP targeting either minimal overdistention, minimal collapse or using a compromise between collapse and overdistention in a randomized trial, and assess the impact on respiratory mechanics, gas exchange, inflammation, and hemodynamics.

METHODS

In a porcine model of ARDS, lung collapse and overdistention were estimated by electrical impedance tomography during a decremental PEEP titration. Pigs were randomized to three groups and ventilated for 12 hours: PEEP set at ≤3% of overdistention (low overdistention); ≤3% of collapse (low collapse); and crossing point of collapse and overdistention (crossing-point).

MEASUREMENTS AND MAIN RESULTS

Thirty-six pigs (12/group) were included. Median PEEP were 7(IQR:6-8)cmH2O, 11(10-11)cmH2O, and 15(12-16)cmH2O in the three groups, p<0.001. With low overdistension, 6(50%) pigs died whereas survival was 100% in both other groups. Cause of death was hemodynamic in nature, with high transpulmonary gradient and high epinephrine requirements. Compared to the other groups, pigs surviving with low overdistension had worse respiratory mechanics and gas exchange during the entire protocol. Minimal differences existed between crossing-point and low collapse animals in physiological parameters but postmortem alveolar density was more homogeneous in crossing-point. Inflammatory markers were not significantly different.

CONCLUSIONS

PEEP to minimize overdistention resulted in high mortality in an animal model of ARDS. Minimizing collapse or choosing a compromise between collapse and overdistention may result in less lung injury, with potential benefits of the compromise approach.

Facilitating Lung Collapse for Thoracoscopic Surgery Utilizing Endobronchial Airway Occlusion Preceded by Pleurotomy and One-minute Suspension of Two-lung Ventilation

OBJECTIVES

To assess when and whether clamping the double-lumen endobronchial tube (DLT) limb of the non-ventilated lung is more conducive to a rapid and effective lung deflation than simply allowing the open limb of the DLT to communicate with the atmosphere.

DESIGN

This was a single-center, single-blind, randomized, controlled trial.

SETTING

The trial was performed in a single institutional setting.

PARTICIPANTS

The participants were 60 patients undergoing elective video-assisted thoracoscopic surgery.

INTERVENTIONS

Patients were randomized to the open-clamp airway technique (OCAT group) or control group. Patients in the control group had one-lung ventilation initiated upon being placed in the lateral decubitus position. The OCAT group had two-lung ventilation maintained until the pleural cavity was opened with the introduction of a planned thoracoscopic access port to allow the operated lung to fall away from the chest wall. Thereafter, ventilation was suspended (temporarily ceased) for 1 minute before the DLT lumen of the isolated lung was clamped. The primary outcome of the trial was the time to complete lung collapse scored as determined from video clips taken during surgery. The secondary outcomes were (1) lung collapse score at 30 minutes after pleural incision, (2) surgeon satisfaction with surgery, and (3) intraoperative hypoxemia.

MEASUREMENTS AND MAIN RESULTS

The median time to reach complete lung collapse in the OCAT group was 10 minutes (odds ratio 10.0, 95% CI 6.3-13.7), which was much shorter than that of the control group (25 minutes [odds ratio 25.0, 95% CI 13.6-36.4]). The difference in complete lung collapse at 30 minutes between the 2 groups was significant (p < 0.001). The surgeon's satisfaction with surgery was higher in the OCAT group than in the control group (8.5 ± 0.2 vs 6.8 ± 0.2; p < 0.001). There was no difference regarding intraoperative hypoxemia.

CONCLUSIONS

Suspending ventilation of both DLT limbs for 1 minute after pleural cavity opening and then clamping the DLT lumen of the isolated lung resulted in a more rapid deflation of the surgical lung. This open-clamp airway technique is an effective technique for rapid surgical lung collapse during thoracoscopic surgery.

Lung ultrasound and mediastinal retraction in children

The authors showed a case of left mediastinal retraction associated with massive left lung collapse suspected after easy visualization of the heart on all scans of the anterolateral left hemithorax. In fact, the figure shows that the apex of the ventricle was visible at the level of the pleural line in the left hemithorax (usually not visible due to pulmonary air artifacts).

Corrigendum: Real-time effects of lateral positioning on regional ventilation and perfusion in an experimental model of acute respiratory distress syndrome

[This corrects the article DOI: 10.3389/fphys.2023.1113568.].

Pneumothorax ex vacuo: Three cases of an uncommon entity

Pneumothorax is a frequently encountered entity in pulmonary practice and can be primary or secondary. Traumatic and iatrogenic causes also account for a minority of cases presenting to the chest physician. The most common therapeutic intervention done is a tube thoracostomy in all but the mildest of cases. Pneumothorax ex vacuo is a distinctly uncommon entity that differs considerably from the rest of the pneumothorax cases in its pathogenesis, clinical manifestations, radiological findings, and management. Pneumothorax in this entity results from the sucking in of air into the pleural space caused by an exaggerated negative intrapleural pressure, which is most frequently secondary to acute lobar collapse. Symptoms attributable to pneumothorax per se are distinctly mild and the vital aspect of treatment is to relieve the bronchial obstruction. Tube thoracostomy fails to relieve the pneumothorax in such cases and should be avoided. We share three cases of pneumothorax ex vacuo encountered in our institution and alert clinicians of the presentation, radiology, and management of this uncommon condition.

Elective re-intubation to treat complete left lung collapse following Tetralogy of Fallot repair in a very young child

An 18-month-old boy weighing 6 kilograms developed complete collapse of left lung following total correction of Tetralogy of Fallot on the next day of extubation. He received extensive chest physiotherapy, along with lung recruitment maneuver by using bubble CPAP, which failed to show any improvement in lung expansion in 2 days. He was then electively intubated on 3rd postoperative day (POD3) for the purpose of suctioning tracheobronchial secretions and maintaining positive airway pressure to open up the left lung. Good results were obtained immediately after intubation, and he was extubated 9 h later. His lung showed complete aeration afterward. He was transferred out of ICU on POD5 and discharged home on POD10.

First report of an adult female patient with endobronchial inflammatory myofibroblastic tumor in Taiwan: A case report

An inflammatory myofibroblastic tumor (IMT) of the respiratory system is an uncommon disease. In Taiwan, there is a lack of previous studies on tracheobronchial IMT. The tumor is characterized by overexpression of anaplastic lymphoma receptor tyrosine kinase (ALK)‐1. Surgical resection is the standard treatment of choice nowadays.

Benign but Terminal: Cardiopulmonary Collapse from a Massive Chest Wall Lipoma

Lipomas are the most common benign soft tissue tumor. Yet, strikingly simple tumors can become problematic when compounded by odd characteristics such as size and location. We report the case of a 53-year-old male who developed complete right lung collapse secondary to a large right-sided chest wall lipoma with accelerated growth in the past 6 months. Bronchoscopy revealed extrinsic compression of the right mainstem bronchus. Histopathology of the soft tissue mass was suggestive of a lipoma. The mass was not amenable to surgery due to a high risk of mortality from his underlying comorbidities. His hospital stay was complicated by progressive end-stage restrictive lung disease necessitating intubation and eventually a tracheostomy, recurrent pneumonias, multiorgan dysfunction, and his eventual demise. We highlight a rare presentation of an unchecked lipoma, which ultimately led to the death of our patient. Simple lipomas show insidious growth and can remain asymptomatic until they reach a large size. Chest wall tumors should be considered malignant until proven otherwise by excisional biopsy. This reiterates the need to treat all chest wall tumors with wide resection in order to provide the best chance for cure.

Non-ventilated lung deflation during one-lung ventilation with a double-lumen endotracheal tube: a randomized-controlled trial of occluding the non-ventilated endobronchial lumen before pleural opening

PURPOSE

Lung deflation during one-lung ventilation (OLV) is thought to be faster using a double-lumen endotracheal tube (DL-ETT) than with a bronchial blocker, especially when the non-ventilated lumen is opened to allow egress of air from the operative lung. Nevertheless, ambient air can also be entrained into the non-ventilated lumen before pleural opening and subsequently delay deflation. We therefore hypothesized that occluding the non-ventilated DL-ETT lumen during OLV before pleural opening would prevent air entrainment and consequently enhance operative lung deflation during video-assisted thoracoscopic surgery (VATS).

METHODS

Thirty patients undergoing VATS using DL-ETT to allow OLV were randomized to having the lumen of the operative lung either open (control group) or occluded (intervention group) to ambient air. The primary outcome was the time to lung collapse evaluated intraoperatively by the surgeons. The T50, an index of rate of deflation, was also determined from a probabilistic model derived from intraoperative video clips presented in random order to three observers.

RESULTS

The median [interquartile range] time to lung deflation occurred faster in the intervention group than in the control group (24 [20-37] min vs 54 [48-68] min, respectively; median difference, 30 min; 95% confidence interval [CI], 14 to 46; P < 0.001). The estimated T50 was 32.6 min in the intervention group compared with 62.3 min in the control group (difference, - 29.7 min; 95% CI, - 51.1 to - 8.4; P = 0.008).

CONCLUSION

Operative lung deflation during OLV with a DL-ETT is faster when the operative lumen remains closed before pleural opening thus preventing it from entraining ambient air during the closed chest phase of OLV.

TRIAL REGISTRATION

www.clinicaltrials.gov (NCT03508050); registered 27 September 2017.

Comparison of High-Flow Humidified Oxygen With Conventional Continuous Positive Airway Pressure in Nonventilated Lungs During Thoracic Surgery: A Randomized Cross-Over Study

OBJECTIVE

This study assessed the efficacy of high-flow humidified oxygen (HFHO) as an alternative to continuous positive airway pressure (CPAP) for improving oxygenation while preserving nonventilated lung collapse during one-lung ventilation.

DESIGN

A prospective randomized cross-over trial.

SETTING

A tertiary medical center.

PARTICIPANTS

The study comprised 28 patients undergoing elective thoracotomy with one-lung ventilation using a double-lumen endobronchial tube placement.

INTERVENTIONS

The patients received prophylactic CPAP or HFHO to the nonventilated lung for 20 minutes and were then crossedover to the other oxygenation modality for 20 minutes, with a 20-minute recovery interval between the two modalities.

MEASUREMENTS AND MAIN RESULTS

Changes in respiratory parameters and lung deflation quality were recorded. Both CPAP and HFHO increased the partial pressure of arterial oxygen in either sequence in both groups, ranging from 31.8-to-66.0 mmHg. However, the increments from these two interventions were not statistically significant (95% confidence interval -12.84 to 21.87; p = 0.597). There were no differences in other parameters. Half the patients receiving CPAP experienced worsening of the surgical condition, whereas the HFHO patients experienced no change or reported a better lung deflation (p < 0.001).

CONCLUSION

HFHO could be an alternative method to CPAP for improving arterial oxygenation while preserving lung deflation during one-lung ventilation. However, additional studies are warranted in regard to its cost-effectiveness and establishment as a routine treatment.

Acute Lobar Atelectasis

Lobar atelectasis (or collapse) is an exceedingly common, rather predictable, and potentially pathogenic companion to many forms of acute illness, postoperative care, and chronic debility. Readily diagnosed by using routine chest imaging and bedside ultrasound, the consequences from lobar collapse may be minor or serious, depending on extent, mechanism, patient vulnerability, abruptness of onset, effectiveness of hypoxic vasoconstriction, and compensatory reserves. Measures taken to reduce secretion burden, assure adequate secretion clearance, maintain upright positioning, reverse lung compression, and sustain lung expansion accord with a logical physiologic rationale. Both classification and logical approaches to prophylaxis and treatment of lobar atelectasis derive from a sound mechanistic knowledge of its causation.

The Diaphragm Acts as a Brake during Expiration to Prevent Lung Collapse

RATIONALE

The diaphragm is the major inspiratory muscle and is assumed to relax during expiration. However, electrical postinspiratory activity has been observed. Whether there is an expiratory diaphragmatic contraction that preserves lung patency has yet to be explored.

OBJECTIVES

We hypothesized the occurrence of an expiratory diaphragmatic contraction directed at stabilizing peripheral airways and preventing or reducing cyclic expiratory lung collapse.

METHODS

Mild acute respiratory distress syndrome was induced in 10 anesthetized, spontaneously breathing pigs. Lung volume was decreased by lowering end-expiratory airway pressure in a stepwise manner. We recorded the diaphragmatic electric activity during expiration, dynamic computed tomographic scans, and respiratory mechanics. In five pigs, the same protocol was repeated during mechanical ventilation after muscle paralysis.

MEASUREMENTS AND MAIN RESULTS

Diaphragmatic electric activity during expiration increased by decreasing end-expiratory lung volume during spontaneous breathing. This enhanced the diaphragm muscle force, to a greater extent with lower lung volume, indicating a diaphragmatic electromechanical coupling during spontaneous expiration. In turn, the resulting diaphragmatic contraction delayed and reduced the expiratory collapse and increased lung aeration compared with mechanical ventilation with muscle paralysis and absence of diaphragmatic activity.

CONCLUSIONS

The diaphragm is an important regulator of expiration. Its expiratory activity seems to preserve lung volume and to protect against lung collapse. The loss of diaphragmatic expiratory contraction during mechanical ventilation and muscle paralysis may be a contributing factor to unsuccessful respiratory support.

Reexpansion pulmonary edema: review of pediatric cases

Reexpansion pulmonary edema (RPE) is an increased permeability pulmonary edema that usually occurs in the reexpanded lung after several days of lung collapse. This condition is recognized to occur more frequently in patients under the age of 40 years, but there has been no detailed analysis of reported pediatric cases of RPE to date. For this review, PubMed literature searches were performed using the following terms: 're(-)expansion pulmonary (o)edema' AND ('child' OR 'children' OR 'infant' OR 'boy' OR 'girl' OR 'adolescent'). The 22 pediatric cases of RPE identified were included in this review. RPE was reported in almost the entire pediatric age range, and as in adult cases, the severity ranged from subclinical to lethal. No specific treatment for RPE was identified, and treatment was administered according to the clinical features of each patient. Of the 22 reported cases, 10 occurred during the perioperative period, but were not related to any specific surgical procedures or anesthetic techniques, or to the duration of lung collapse. Pediatric anesthesiologists should be aware that pediatric RPE can occur after reexpansion of any collapsed lung and that some invasive therapies can be useful in severe cases.

Acute hypoxaemia due to intraoperative lung collapse after repositioning the patient

Desaturation after induction of anaesthesia and repositioning due to mucus plug causing atelectasis (lung collapse) is a rare event. We present a case of intraoperative right lung collapse due to mucus plug in a patient undergoing left laparoscopic nephrectomy. Hypoxaemia occurred after the induction of anaesthesia and repositioning. X-ray chest revealed right lung collapse and surgery was subsequently postponed. Lung re-expanded after postural drainage and suction. Postoperatively patient was diagnosed to have retrocardiac bronchiectasis. After preoperative preparation with postural drainage, chest physiotherapy, and antibiotics, the patient underwent surgery uneventfully.