Acute leftward septal shift by lung recruitment maneuver

Don't Drive Blind: Driving Pressure to Optimize Ventilator Management in ECMO

Introduction

Driving pressure (DP) while on ECMO has been studied in acute respiratory distress syndrome (ARDS) but no studies exist in those on ECMO without ARDS. We aimed to study association of mortality with DP in all patients on ECMO and compare change in DP before and after initiation of ECMO.

Methods

Consecutive patients placed on ECMO either veno-arterial ECMO or veno-venous ECMO between August 2010 and February 2017 were reviewed. The outcomes were compared based on DP before and after ECMO initiation.

Results

A total of 192 patients were included: 68 (35%) had ARDS while 124 (65%) did not. There were 70 individuals for whom DP was available, 33 (47%) had a decrease in DP, whereas 32 (46%) had an increase in DP and 5 (7%) had no change in DP after ECMO initiation. Those with an increase in DP had a higher initial PEEP (14 vs 9 cm H₂O, p < 0.001) and a higher PEEP decrease after ECMO (6.4 cm H₂O vs by 2.5 cm H₂O, p < 0.001). Those with an increase in DP had a significantly longer stay on ECMO than those without (p = 0.022). On multivariable analysis, higher DP 24 h after ECMO initiation was associated with an increase in 30-day mortality (OR 1.15, 75% CI 1.07–1.24, p ≤ 0.001).

Conclusion

A significant proportion of patients experienced an increase in driving pressure and decrease in compliance after initiation of ECMO. Higher driving pressure after initiation of ECMO is associated with increased adjusted 30-day mortality. Individualized ventilator strategies are needed to reduce mechanical stress while on ECMO.

Mechanical ventilation during extracorporeal membrane oxygenation

The timing of extracorporeal membrane oxygenation (ECMO) initiation and its outcome in the management of respiratory and cardiac failure have received considerable attention, but very little attention has been given to mechanical ventilation during ECMO. Mechanical ventilation settings in non-ECMO studies have been shown to have an effect on survival and may also have contributed to a treatment effect in ECMO trials. Protective lung ventilation strategies established for non-ECMO-supported respiratory failure patients may not be optimal for more severe forms of respiratory failure requiring ECMO support. The influence of positive end-expiratory pressure on the reduction of the left ventricular compliance may be a matter of concern for patients receiving ECMO support for cardiac failure. The objectives of this review were to describe potential mechanisms for lung injury during ECMO for respiratory or cardiac failure, to assess the possible benefits from the use of ultra-protective lung ventilation strategies and to review published guidelines and expert opinions available on mechanical ventilation-specific management of patients requiring ECMO, including mode and ventilator settings. Articles were identified through a detailed search of PubMed, Ovid, Cochrane databases and Google Scholar. Additional references were retrieved from the selected studies. Growing evidence suggests that mechanical ventilation settings are important in ECMO patients to minimize further lung damage and improve outcomes. An ultra-protective ventilation strategy may be optimal for mechanical ventilation during ECMO for respiratory failure. The effects of airway pressure on right and left ventricular afterload should be considered during venoarterial ECMO support of cardiac failure. Future studies are needed to better understand the potential impact of invasive mechanical ventilation modes and settings on outcomes.

Is there a place for pressure-support ventilation and high positive end-expiratory pressure combined to alpha-2 agonists early in severe diffuse acute respiratory distress syndrome?

Acute respiratory distress syndrome (ARDS) is associated with a high mortality linked primarily to co-morbidities (sepsis, cardiac failure, multiple organ failure, etc.). When the lung is the single failing organ, quick resolution of ARDS should skip some complications arising from a prolonged stay in the critical care unit. In severe ARDS (PaO2/FIO2=P/F<100 with positive end-expiratory pressure (PEEP) ≥ 5 cm H2O), current recommendations are to intubate the trachea of the patient and use mechanical ventilation, low tidal volume, high PEEP, prone positioning and possibly neuromuscular blockade in association with intravenous sedation. Another strategy is possible. Firstly, spontaneous ventilation (SV) coupled with pressure support (PS) ventilation and high PEEP is possible from tracheal intubation onwards, with the possible exception of the short period following immediately tracheal intubation. Secondly, using alpha-2 adrenergic agonists (e.g. clonidine, dexmedetomidine) can provide first-line sedation from the beginning of mechanical ventilation, as they preserve respiratory drive, lower oxygen consumption and pulmonary hypertension and increase diuresis. Alpha-2 agonists are to be supplemented, if appropriate, by drugs devoid of effect on respiratory drive (neuroleptics, etc.). The expected benefits would be to prevent acquired diaphragmatic weakness, accumulation of sedation, cognitive dysfunction, and presumably improved outcome. This hypothesis should be tested in a double blind randomized controlled trial.

Cardiopulmonary interactions during mechanical ventilation in critically ill patients

Cardiopulmonary interactions induced by mechanical ventilation are complex and only partly understood. Applied tidal volumes and/or airway pressures largely mediate changes in right ventricular preload and afterload. Effects on left ventricular function are mostly secondary to changes in right ventricular loading conditions. It is imperative to dissect the several causes of haemodynamic compromise during mechanical ventilation as undiagnosed ventricular dysfunction may contribute to morbidity and mortality.

[Peri-operative atelectasis and alveolar recruitment manoeuvres]

Respiratory complications are a significant cause of post-operative morbidity and mortality. Peri-operative atelectasis, in particular, affects 90% of surgical patients and its effects can be prolonged, due to changes in respiratory mechanics, pulmonary circulation and hypoxaemia. Alveolar collapse is caused by certain predisposing factors, mainly by compression and absorption mechanisms. To prevent or treat these atelectasis several therapeutic strategies have been proposed, such as alveolar recruitment manoeuvres, which has become popular in the last few years. Its application in patients with alveolar collapse, but without a previous significant acute lung lesion, has some special features, therefore its use is not free of uncertainties and complications. This review describes the frequency, pathophysiology, importance and treatment of peri-operative atelectasis. Special attention is paid to treatment with recruitment manoeuvres, with the purpose of providing a basis for the their rational and appropriate use.

Acute hemodynamic effects of recruitment maneuvers in patients with acute respiratory distress syndrome

BACKGROUND

The recruitment maneuver (RM) in acute respiratory distress syndrome (ARDS) can cause hemodynamic derangement. We evaluated circulatory and cardiac changes during RMs.

METHODS

We performed sustained inflation (SI) with a pressure of 40 cm H(2)O for 30 seconds as an RM on 22 patients with ARDS. Blood pressure (BP) and heart rate were recorded immediately before, every 10 seconds during, and 30 seconds after the RM. Ventricular dimensions were obtained simultaneously using M-mode echocardiography, and tissue Doppler imaging was performed on the left ventricular wall.

RESULTS

Mean, systolic, and diastolic BP decreased at 20 and 30 seconds during 30-second RMs (mean BP: 92 +/- 12 at baseline to 83 +/- 18 mm Hg at the end of the RM, P < .05) and subsequently recovered. Heart rate decreased at 10 and 20 seconds during the RM, and tended to increase afterward. Both ventricular dimensions decreased significantly during the RM. The left ventricular ejection fraction and peak velocity of the left ventricle during systole remained stable. The fractional changes in mean BP and left ventricular end-diastolic dimension during the RMs were correlated significantly with each other (r(s) = 0.59). Static compliance of the respiratory system (Crs) was lower in patients with mean BP change > or =15% than in patients in whom the change was <15% (P < .05).

CONCLUSIONS

A transient decrease in mean BP was observed during the RM, and its degree was correlated with the preload decrease, while cardiac contractility was maintained.

Respiratory and haemodynamic changes during decremental open lung positive end-expiratory pressure titration in patients with acute respiratory distress syndrome

Introduction

To investigate haemodynamic and respiratory changes during lung recruitment and decremental positive end-expiratory pressure (PEEP) titration for open lung ventilation in patients with acute respiratory distress syndrome (ARDS) a prospective, clinical trial was performed involving 12 adult patients with ARDS treated in the surgical intensive care unit in a university hospital.

Methods

A software programme (Open Lung Tool™) incorporated into a standard ventilator controlled the recruitment (pressure-controlled ventilation with fixed PEEP at 20 cmH₂O and increased driving pressures at 20, 25 and 30 cmH₂O for two minutes each) and PEEP titration (PEEP lowered by 2 cmH₂O every two minutes, with tidal volume set at 6 ml/kg). The open lung PEEP (OL-PEEP) was defined as the PEEP level yielding maximum dynamic respiratory compliance plus 2 cmH₂O. Gas exchange, respiratory mechanics and central haemodynamics using the Pulse Contour Cardiac Output Monitor (PiCCO™), as well as transoesophageal echocardiography were measured at the following steps: at baseline (T₀); during the final recruitment step with PEEP at 20 cmH₂O and driving pressure at 30 cmH₂O, (T_20/30); at OL-PEEP, following another recruitment manoeuvre (T_OLP).

Results

The ratio of partial pressure of arterial oxygen (PaO₂) to fraction of inspired oxygen (FiO₂) increased from T₀ to T_OLP (120 ± 59 versus 146 ± 64 mmHg, P < 0.005), as did dynamic respiratory compliance (23 ± 5 versus 27 ± 6 ml/cmH₂O, P < 0.005). At constant PEEP (14 ± 3 cmH₂O) and tidal volumes, peak inspiratory pressure decreased (32 ± 3 versus 29 ± 3 cmH₂O, P < 0.005), although partial pressure of arterial carbon dioxide (PaCO₂) was unchanged (58 ± 22 versus 53 ± 18 mmHg). No significant decrease in mean arterial pressure, stroke volume or cardiac output occurred during the recruitment (T_20/30). However, left ventricular end-diastolic area decreased at T_20/30 due to a decrease in the left ventricular end-diastolic septal-lateral diameter, while right ventricular end-diastolic area increased. Right ventricular function, estimated by the right ventricular Tei-index, deteriorated during the recruitment manoeuvre, but improved at T_OLP.

Conclusions

A standardised open lung strategy increased oxygenation and improved respiratory system compliance. No major haemodynamic compromise was observed, although the increase in right ventricular Tei-index and right ventricular end-diastolic area and the decrease in left ventricular end-diastolic septal-lateral diameter during the recruitment suggested an increased right ventricular stress and strain. Right ventricular function was significantly improved at T_OLP compared with T₀, although left ventricular function was unchanged, indicating effective lung volume optimisation.

Appropriate Ventilatory Settings for Thoracic Surgery: Intraoperative and Postoperative

Mechanical ventilation of patients undergoing thoracic surgery is often challenging. These patients frequently have significant underlying comorbidities, including cardiopulmonary disease, and often must undergo 1-lung ventilation. Perioperative respiratory complications are common and are multifactorial in etiology. Increasing evidence suggests that mechanical ventilation is associated with, and may even cause, lung damage in both sick and healthy patients. Gas exchange to provide acceptable end-organ oxygenation remains a primary goal but so too is minimization of risks for acute lung injury. Every ventilator strategy is associated with potential beneficial and adverse side effects. Understanding the impact of various ventilation strategies allows clinicians to provide optimal care for patients.

Heart-lung interactions

PURPOSE OF REVIEW

Assessment of cardiovascular stability using ventilation-induced changes in measured physiological variables, referred to as functional hemodynamic monitoring, usually requires measurement of ventilation-induced changes in venous return. Thus, it is important to understand the determinants of these complex heart-lung interactions.

RECENT FINDINGS

Several animal and human studies have recently documented that ventricular interdependence plays an important role during positive-pressure breathing, causing acute cor pulmonale. With the use of lower tidal volume ventilation in patients with acute respiratory failure, the incidence of acute cor pulmonale is decreasing proportionally. When present, however, it induces a stroke volume variation that is 180 degrees out of phase with that seen in hypovolemic states, such that left ventricular stroke volume increases during inspiration rather than decreasing as seen in hypovolemia. Further, when either tidal volume or positive end-expiratory pressure levels are varied, both stroke volume variation and pulse pressure variation are affected in a predictable manner. The greater the swing in intrathoracic pressure, the greater the change in venous return.

SUMMARY

Functional hemodynamic monitoring is becoming more prevalent. For it to be used effectively, the operator needs to have a solid understanding of how ventilation induces both pulse pressure variation and stroke volume variation in that specific patient.

Echocardiographic measurement of ventricular function

PURPOSE OF REVIEW

We review new findings concerning ventricular function in patients in intensive care units with shock or unexplained respiratory distress syndrome analyzed using echocardiography.

RECENT FINDINGS

Bedside echocardiography is not only an imaging technique but should be considered as a hemodynamic method. Left-ventricular systolic function can be assessed in daily clinical practice by measuring shortening fraction, fraction area change and ejection fraction. But these indices are dependent on load conditions. Index of myocardial performance can be also used. Rate of left-ventricular pressure increase may be measured from mitral regurgitation. Other indices such a maximal elastance and preload-adjusted maximal power were developed to evaluate myocardial systolic function but are not still used in clinical practice in patients in intensive care. Cardiac output measurement can be calculated easily from aortic annulus diameter and the velocity time integral of aortic blood flow. To complete the assessment of ventricular function, left-ventricular diastolic function and pressure as well as right ventricular size, septal movement and right pressures should be analyzed.

SUMMARY

Using echocardiography the intensivist can examine both the mechanism and the cause of shock or pulmonary edema. It is time to increase the use of this technique in intensive care units.