Quantification of asymmetric lung pathophysiology as a guide to the use of simultaneous independent lung ventilation in posttraumatic and septic adult respiratory distress syndrome

Reverse triggering ? a novel or previously missed phenomenon?

BACKGROUND

Reverse triggering (RT) was described in 2013 as a form of patient-ventilator asynchrony, where patient's respiratory effort follows mechanical insufflation. Diagnosis requires esophageal pressure (Pes) or diaphragmatic electrical activity (EAdi), but RT can also be diagnosed using standard ventilator waveforms.

HYPOTHESIS

We wondered (1) how frequently RT would be present but undetected in the figures from literature, especially before 2013; (2) whether it would be more prevalent in the era of small tidal volumes after 2000.

METHODS

We searched PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials, from 1950 to 2017, with key words related to asynchrony to identify papers with figures including ventilator waveforms expected to display RT if present. Experts labelled waveforms. 'Definite' RT was identified when Pes or EAdi were in the tracing, and 'possible' RT when only flow and pressure waveforms were present. Expert assessment was compared to the author's descriptions of waveforms.

RESULTS

We found 65 appropriate papers published from 1977 to now, containing 181 ventilator waveforms. 21 cases of 'possible' RT and 25 cases of 'definite' RT were identified by the experts. 18.8% of waveforms prior to 2013 had evidence of RT. Most cases were published after 2000 (1 before vs. 45 after, p = 0.03). 54% of RT cases were attributed to different phenomena. A few cases of identified RT were already described prior to 2013 using different terminology (earliest in 1997). While RT cases attributed to different phenomena decreased after 2013, 60% of 'possible' RT remained missed.

CONCLUSION

RT has been present in the literature as early as 1997, but most cases were found after the introduction of low tidal volume ventilation in 2000. Following 2013, the number of undetected cases decreased, but RT are still commonly missed. Reverse Triggering, A Missed Phenomenon in the Literature. Critical Care Canada Forum 2019 Abstracts. Can J Anesth/J Can Anesth 67 (Suppl 1), 1-162 (2020). https://doi-org.myaccess.library.utoronto.ca/ https://doi.org/10.1007/s12630-019-01552-z .

Asymmetrical Lung Injury: Management and Outcome

Among mechanically ventilated patients, asymmetrical lung injury is probably extremely frequent in the intensive care unit but the lack of standardized measurements does not allow to describe any prevalence among mechanically ventilated patients. Many past studies have focused only on unilateral injury and have mostly described the effect of lateral positioning. The good lung put downward might receive more perfusion while the sick lung placed upward receive more ventilation than supine. This usually results in better oxygenation but can also promote atelectasis in the healthy lung and no consensus has emerged on the clinical indication of this posture. Recently, electrical impedance tomography (EIT) has allowed for the first time to precisely describe the distribution of ventilation in each lung and to better study asymmetrical lung injury. At low positive-end-expiratory pressure (PEEP), a very heterogeneous ventilation exists between the two lungs and the initial increase in PEEP first helps to recruit the sick lung and protect the healthier lung. However, further increasing PEEP distends the less injured lung and must be avoided. The right level can be found using EIT and transpulmonary pressure. In addition, EIT can show that in the two lungs, airway closure is present but with very different airway opening pressures (AOPs) which cannot be identified on a global assessment. This may suggest a very different PEEP level than on a global assessment. Lastly, epidemiological studies suggest that in hypoxemic patients, the number of quadrants involved has a strong prognostic value. The number of quadrants is more important than the location of the unilateral or bilateral nature of the involvement for the prognosis, and hypoxemic patients with unilateral lung injury should probably be considered as requiring lung protective ventilation as classical acute respiratory distress syndrome.

Differential Lung Ventilation Using a Bronchial Blocker in a Pediatric Patient on Extracorporeal Membrane Oxygenation: A Case Report

We describe a patient with acute on chronic respiratory failure after a cardiac arrest who was cannulated to venoarterial extracorporeal membrane oxygenation. The patient developed right-sided interstitial emphysema with air leak and left-sided hemothorax with secondary atelectasis. A differential lung ventilation strategy was used in which an endotracheal tube was placed in the left main stem bronchus and a bronchial blocker was placed in the right mainstem bronchus. The patient's overall pulmonary function improved, and he was successfully decannulated from extracorporeal membrane oxygenation. In conclusion, differential lung ventilation may be performed in patients on extracorporeal membrane oxygenation with disparate lung disease as an alternative ventilation strategy.

Independent lung ventilation with use of a double-lumen endotracheal tube for refractory hypoxemia and shock complicating severe unilateral pneumonia: A case report

Background

The indications for independent lung ventilation (ILV) in critical care settings have not been fully clarified, especially because extracorporeal membrane oxygenation (ECMO) is being used increasingly in cases of severe respiratory failure.

Case report

A 90-year-old man presented with severe unilateral pneumonia, and despite conventional mechanical ventilation management with use of a single lumen endotracheal tube and high positive endo-expiratory pressure (PEEP), oxygenation and hemodynamics deteriorated. We then performed ILV using a double-lumen endotracheal tube (DLT) and two ventilators, each set at a different respiratory mode. With continuous administration of a neuromuscular blocking agent, the ventilator for the left lung (non-affected lung) was set to pressure-controlled ventilation (PCV) mode, whereas the ventilator for the right lung (affected lung) was set to bi-level mode, 1 breath/min, and high PEEP. ILV and the high PEEP applied to the affected lung prevented hyperinflation of the non-affected lung and increased pulmonary blood perfusion on the non-affected side. Thus, ILV immediately improved oxygenation and hemodynamics by correcting ventilation/perfusion mismatch.

Discussion

Although ECMO is a valid treatment option for patients with severe respiratory failure, it is highly invasive intervention. ILV performed with use of a DLT is less invasive and more useful than ECMO. Thus, ILV should be kept in mind as a treatment option, especially in cases of refractory respiratory failure and circulatory failure in which the pathophysiology of the left and right lungs differs markedly.

Independent lung ventilation: Implementation strategies and review of literature

Independent lung ventilation, though infrequently used in the critical care setting, has been reported as a rescue strategy for patients in respiratory failure resulting from severe unilateral lung pathology. This involves isolating and ventilating the right and left lung differently, using separate ventilators. Here, we describe our experience with independent lung ventilation in a patient with unilateral diffuse alveolar hemorrhage, who presented with severe hypoxemic respiratory failure despite maximal ventilatory support. Conventional ventilation in this scenario leads to preferential distribution of tidal volume to the non-diseased lung causing over distension and inadvertent volume trauma. Since each lung has a different compliance and respiratory mechanics, instituting separate ventilation strategies to each lung could potentially minimize lung injury. Based on review of literature, we provide a detailed description of indications and procedures for establishing independent lung ventilation, and also provide an algorithm for management and weaning a patient from independent lung ventilation.

Differential lung ventilation for increased oxygenation during one lung ventilation for video assisted lung surgery

BACKGROUND

One lung ventilation (OLV) is the technique used during lung resection surgery in order to facilitate optimal surgical conditions. OLV may result in hypoxemia due to the shunt created. Several techniques are used to overcome the hypoxemia, one of which is continuous positive airway pressure (CPAP) to the non-dependent lung. Another technique is ventilating the non-dependent lung with a minimal volume, thus creating differential lung ventilation (DLV). In this study we compared the efficacy of CPAP to DLV during video assisted thoracoscopic lung resection.

PATIENTS AND METHOD

This is a prospective study of 30 adult patients undergoing elective video assisted thoracoscopic lung lobectomy. Each patient was ventilated in four modes: two lung ventilation, OLV, OLV + CPAP and OLV + DLV. Fifteen patients were ventilated with CPAP first and DLV next, and the other 15 were ventilated with DLV first and then CPAP. Five minutes separated each mode, during which the non-dependent lung was open to room air. We measured the patient's arterial blood gas during each mode of ventilation. The surgeons, who were blinded to the ventilation technique, were asked to assess the surgical conditions at each stage.

RESULTS

Oxygenation during OLV+ CPAP was significantly lower that OLV + DLV (p = 0.018). There were insignificant alterations of pH, PCO2 and HCO3 during the different ventilating modes. The surgeons' assessments of interference in the field exposure between OLV + CPAP or OLV + DLV was found to be insignificant (p = 0.073).

CONCLUSIONS

During OLV, DLV is superior to CPAP in improving patient's oxygenation, and may be used where CPAP failed.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03563612 . Registered 9 June 2018, retrospectively (due to clerical error).

Can differential regional ventilation protect the spared lung in acute respiratory distress syndrome?

Acute respiratory distress syndrome (ARDS) is a common clinical problem prevalent in intensive care settings. It can complicate many critical illnesses. The general treatment is mainly supportive. Mechanical ventilation, low tidal volume strategy, and control of plateau pressure form the basis of current management. No specific treatment exists for ARDS. Various interventions have been tested for the lethal condition including steroids, fluid restriction, statins, high-frequency ventilation, nitric oxide, and prone ventilation strategy. However, none has shown improvement apart from prone positioning and low tidal volume ventilation. We report our observation in a patient with ARDS, which may potentially show a new mechanism to protect normal alveoli in ARDS lung and thereby may improve survival.

A new method of securing the airway for differential lung ventilation in intensive care

Differential lung ventilation to achieve optimised ventilation for each lung is a procedure rarely used in the intensive care unit, to treat select cases of severe unilateral lung disease in intensive care. However, existing techniques both for securing the airway and ventilating the lungs are challenging and have complications. We present the use of differential lung ventilation in the intensive care setting, securing the airway with a technique not previously described, using endotracheal tubes inserted through a tracheotomy and orally. In the course of 1 month, we treated three patients with unilateral atelectatic and consolidated lungs by differential lung ventilation. The left lung was ventilated through an endotracheal tube inserted into the left main stem bronchus through a tracheotomy. The right lung was ventilated through an endotracheal tube with the cuff positioned immediately under the vocal cord. In patient 1, the diseased lung remained consolidated after 24 h of differential lung ventilation. In the two other patients, the diseased lungs responded to differential lung ventilation by increased compliance and radiographic increased aeration. Differential ventilation of the lungs with this novel technique is feasible and may increase the likelihood of successful treatment of atelectatic lungs refractory to conventional ventilator strategies.

Ventilation in chest trauma

Chest trauma is one important factor for total morbidity and mortality in traumatized emergency patients. The complexity of injury in trauma patients makes it challenging to provide an optimal oxygenation while protecting the lung from further ventilator-induced injury to it. On the other hand, lung trauma needs to be treated on an individual basis, depending on the magnitude, location and type of lung or chest injury. Several aspects of ventilatory management in emergency patients are summarized herein and may give the clinician an overview of the treatment possibilities for chest trauma victims.

A novel technique of differential lung ventilation in the critical care setting

Background

Differential lung ventilation (DLV) is used to salvage ventilatory support in severe unilateral lung disease in the critical care setting. However, DLV with a double-lumen tube is associated with serious complications such as tube displacement during ventilatory management. Thus, long-term ventilatory management with this method may be associated with high risk of respiratory incidents in the critical care setting.

Findings

We devised a novel DLV technique using two single-lumen tubes and applied it to five patients, two with severe unilateral pneumonia and three with thoracic trauma, in a critical care setting. In this novel technique, we perform the usual tracheotomy and insert two single-lumen tubes under bronchoscopic guidance into the main bronchus of each lung. We tie the two single-lumen tubes together and suture them directly to the skin. The described technique was successfully performed in all five patients. Pulmonary oxygenation improved rapidly after DLV induction in all cases, and the three patients with thoracic trauma were managed by DLV without undergoing surgery. Tube displacement was not observed during DLV management. No airway complications occured in either the acute or late phase regardless of the length of DLV management (range 2-23 days).

Conclusions

This novel DLV technique appears to be efficacious and safe in the critical care setting.

Clinical review: Independent lung ventilation in critical care

Independent lung ventilation (ILV) can be classified into anatomical and physiological lung separation. It requires either endobronchial blockade or double-lumen endotracheal tube intubation. Endobronchial blockade or selective double-lumen tube ventilation may necessitate temporary one lung ventilation. Anatomical lung separation isolates a diseased lung from contaminating the non-diseased lung. Physiological lung separation ventilates each lung as an independent unit. There are some clear indications for ILV as a primary intervention and as a rescue ventilator strategy in both anatomical and physiological lung separation. Potential pitfalls are related to establishing and maintaining lung isolation. Nevertheless, ILV can be used in the intensive care setting safely with a good understanding of its limitations and potential complications.

Ventilation in the patient with unilateral lung disease

Severe ULD presents a challenge in ventilator management because of the marked asymmetry in the mechanics of the two lungs. The asymmetry may result from significant decreases or increases in the compliance of the involved lung. Traditional ventilator support may fail to produce adequate gas exchange in these situations and has the potential to cause further deterioration. Fortunately, conventional techniques can be safely and effectively applied in the majority of cases without having to resort to less familiar and potentially hazardous forms of support. In those circumstances when conventional ventilation is unsuccessful in restoring adequate gas exchange, lateral positioning and ILV have proved effective at improving and maintaining gas exchange. Controlled trials to guide clinical decision making are lacking. In patients who have processes associated with decreased compliance in the involved lung, lateral positioning may be a simple method of improving gas exchange but is associated with many practical limitations. ILV in these patients is frequently successful when differential PEEP is applied with the higher pressure to the involved lung. In patients in whom the pathology results in distribution of ventilation favoring the involved lung, particularly BPF, ILV can be used to supply adequate support while minimizing flow through the fistula and allowing it to close. The application of these techniques should be undertaken with an understanding of the pathophysiology of the underlying process; the reported experience with these techniques, including indications and successfully applied methods; and the potential problems encountered with their use. Fortunately, these modalities are infrequently required, but they provide a critical means of support when conventional techniques fail.

Combined differential lung ventilation and inhaled nitric oxide therapy in the management of unilateral pulmonary contusion

Unilateral pulmonary contusion after blunt thoracic trauma can prove to be a devastating injury. Regional disturbances in blood flow and alveolar ventilation can significantly alter pulmonary function. We present a case report of unilateral pulmonary contusion that resulted in significant pulmonary dysfunction. This patient was successfully managed with multimodality therapy consisting of differential lung ventilation and inhaled nitric oxide. The effect of nitric oxide applied to the "normal" lung, the "injured" lung, and both lungs is described. The use of inhaled nitric oxide was associated with an increase in oxygenation when applied to the normal or both lungs. The use of nitric oxide in conjunction with differential lung ventilation appeared to offer benefit in this patient with severe unilateral pulmonary contusion.

Independent lung ventilation

Situations in which independent lung ventilation may be of use include massive hemoptysis, pulmonary alveolar proteinosis, risk of interbronchial aspiration, unilateral lung injury, single lung transplant, and BPF. Any decision to attempt independent lung ventilation should take into consideration the many technical difficulties associated with the procedure. They include difficulties in the placement of DLTs and monitoring tube position, the risk of tube displacement, and the risk of airway trauma. The clinician also must consider the costs in terms of available manpower and resources. Maintaining a patient on independent lung ventilation requires highly skilled nursing care, specialized monitoring devices, and readily available FOB. Even with these limitations, independent lung ventilation may be of use in certain clinical situations when standard methods have failed.

The critical care of the severely injured patient--II. Pulmonary and renal support

The management of pulmonary support in trauma patients is a balance of risk versus benefit. Decisions must be based upon the patient's physiologic needs, with constant attention to the potential complications of the therapy. The avoidance of renal failure by volume replacement, careful attention to the use of potentially nephrotoxic agents, and close monitoring of renal function can reduce the incidence and severity of this serious complication of trauma. If renal failure does occur, aggressive renal replacement therapy with either intermittent hemodialysis or CRRT should be tailored to the clinical situation.

Differential lung ventilation with a double-lumen tracheostomy tube in unilateral refractory atelectasis

Two patients with refractory hypoxemia due to unilateral lung atelectasis were treated with differential lung ventilation (DLV) through a Robertshaw-type, double-lumen tracheostomy tube. DLV was applied using two non-synchronized ventilators and maintained for 6 and 3 days, respectively. Ventilator settings were chosen in accord to the clinical, laboratory and chest X-rays results. Particularly, tidal volume and PEEP were set to avoid excessively high alveolar pressure and to obtain the highest possible value of compliance. We investigated the mechanical properties of the two lungs separately by measuring airway pressure and compliance of each lung before the beginning of DLV and at 0, 5, 24, and 48 h after. Initially we observed in both patients very low values of compliance (7-9 cm H2O/l) and a significant level of PEEPi (12-8 cm H2O) of the diseased lung, whereas PEEPi in the healthy lung was negligible. The clinical improvement was assessed by sequential chest X-rays and by significant improvement of arterial blood gas and PaO2/FiO2 ratios and was associated with a progressive increase of compliance (24-22 cm H2O/l) and by a fall of PEEPi levels (5-4 cm H2O) of the diseased lung. We also observed an improvement of SvO2, O2AVI, PVRI and Qva/Qt values (Case 1). The tracheostomy tube used to apply DLV was very reliable, allowing easy nursing care and selective bronchial aspirations. We conclude that DLV is a very useful technique in unilateral lung pathology, and it can be a life saving procedure in selected patients, by supplying volume and PEEP more efficiently to the affected lung.

Advanced techniques in thoracic trauma

Technologic aid is available for the three central problems of hemorrhage, lung damage, and cardiac damage. Autotransfusion, new modes of ventilator support, extracorporeal oxygenation, balloon pumping, and left ventricular assist are available for the trauma patient. The author explains these new devices and their role in thoracic trauma cases.

Selective decontamination of the digestive tract improves survival in patients receiving differential lung ventilation

In a review of the literature on differential lung ventilation (DLV) the average mortality was found to be 47%. The major cause of death (66%) was infection. The effect of a novel infection prevention regimen on the colonisation and infection rate of the respiratory tract and on outcome was studied in polytrauma patients. Nineteen patients who presented with asymmetric pulmonary contusion were treated with DLV (103 +/- 72 h) and conventional mechanical ventilation (CMV) (16 +/- 10 days). They were treated with selective decontamination of the digestive tract with topical non-absorbable antibiotics in combination with systemic antibiotic prophylaxis starting immediately after admission. In one patient colonisation of the respiratory tract was found with Staphylococcus aureus. This disappeared after continued systemic antibiotic prophylaxis. Colonisation with hospital-acquired Gram-negative bacteria or yeasts was not observed. No patient developed pneumonia throughout the period on conventional mechanical ventilation or on DLV. One patient died from cerebral injury. It is concluded that prolonged endobronchial intubation for DLV can be used without increased risk for pneumonia with this antibiotic regimen and that the very low mortality in this study may be attributed to the prevention of infectious complications.

Differential lung ventilation: a review and 2 case reports

The respiratory parameters of some of the patients with acute respiratory failure deteriorates while using conventional ventilation. These patients suffer unilateral lung disease and the failure to respond favourably to therapy is due to increased intrapulmonary shunt. There is a reflex vasodilation in the injured lung. Functional residual capacity is reduced in the injured lung and the compliance decreases. Gas flow is then deviated to the other lung, thus increases alveolar collapse and decreases regional compliance in the injured lung. These events cause severe hypoxemia. We present here two cases with unilateral lung disease that failed to respond to conventional mechanical ventilation. Asynchronized differential lung ventilation was found to be the therapeutic answer to the problem. We discuss the pathophysiology of unilateral lung injury and the physiology of differential lung ventilation.