Cardiopulmonary interactions in acute lung injury

Hemodynamic monitoring in the extracorporeal membrane oxygenation patient

PURPOSE OF REVIEW

Hemodynamic monitoring in ECMO patients requires familiarity with the underlying pathophysiology and circulatory mechanics of extracorporeal flow. This review discusses the various monitoring modalities relevant to the management of patients on venovenous ECMO (VV ECMO) and venoarterial (VA ECMO). We emphasize tools to judge the adequacy of perfusion, predict the response to fluid boluses, measure right ventricular function, assess left ventricular distention (for VA ECMO), and monitor the process of weaning from ECMO. We emphasize how differences between VV ECMO and VA ECMO are reflected in distinct approaches to monitoring.

RECENT FINDINGS

Point-of-care ultrasound and near-infrared spectroscopy can play a significant role in monitoring of global and regional perfusion.

SUMMARY

Recent literature in hemodynamic monitoring of ECMO patients is discussed, with comparison of VV ECMO and VA ECMO. Many common monitoring tools lack validity during ECMO: by taking into account the unique physiology of the ECMO circulation, selected methods can aid in the care of these complex patients.

Prone positioning before extracorporeal membrane oxygenation for severe acute respiratory distress syndrome: A retrospective multicenter study

OBJECTIVE

To evaluate the clinical outcomes of patients with severe acute respiratory distress syndrome (ARDS) subjected to prone positioning before extracorporeal membrane oxygenation (ECMO).

DESIGN

A retrospective analysis of a multicenter cohort was carried out.

SETTING

Patients admitted to the Intensive Care Units of 11 hospitals in Korea.

PATIENTS

Patients were divided into those who underwent prone positioning before ECMO (n=28) and those who did not (n=34).

INTERVENTIONS

None.

VARIABLES OF INTEREST

Thirty-day mortality, ECMO weaning failure rate, mechanical ventilation weaning success rate, mechanical ventilation-free days at day 60.

RESULTS

The prone group had lower median peak inspiratory pressure and lower median dynamic driving pressure before ECMO. Thirty-day mortality was 21% in the prone group and 41% in the non-prone group (p=0.098). The prone group also showed a lower ECMO weaning failure rate, and a higher mechanical ventilation weaning success rate and more mechanical ventilation-free days at day 60. In the non-prone group, median dynamic compliance marginally decreased shortly after ECMO, but no significant change was observed in the prone group.

CONCLUSIONS

Prone positioning before ECMO was not associated to increased mortality and tended to exert a protective effect.

Extended Use of Extracorporeal Membrane Oxygenation for Acute Respiratory Distress Syndrome: A Retrospective Multicenter Study

Background

Beyond its current function as a rescue therapy in acute respiratory distress syndrome (ARDS), extracorporeal membrane oxygenation (ECMO) may be applied in ARDS patients with less severe hypoxemia to facilitate lung protective ventilation. The purpose of this study was to evaluate the efficacy of extended ECMO use in ARDS patients.

Methods

This study reviewed 223 adult patients who had been admitted to the intensive care units of 11 hospitals in Korea and subsequently treated using ECMO. Among them, the 62 who required ECMO for ARDS were analyzed. The patients were divided into two groups according to pre-ECMO arterial blood gas: an extended group (n=14) and a conventional group (n=48).

Results

Baseline characteristics were not different between the groups. The median arterial carbon dioxide tension/fraction of inspired oxygen (FiO₂) ratio was higher (97 vs. 61, p<0.001) while the median FiO₂ was lower (0.8 vs. 1.0, p<0.001) in the extended compared to the conventional group. The 60-day mortality was 21% in the extended group and 54% in the conventional group (p=0.03). Multivariate analysis indicated that the extended use of ECMO was independently associated with reduced 60-day mortality (odds ratio, 0.10; 95% confidence interval, 0.02–0.64; p=0.02). Lower median peak inspiratory pressure and median dynamic driving pressure were observed in the extended group 24 hours after ECMO support.

Conclusion

Extended indications of ECMO implementation coupled with protective ventilator settings may improve the clinical outcome of patients with ARDS.

Pulse pressure variation as a guide for volume expansion in dogs undergoing orthopedic surgery

OBJECTIVE

To investigate whether pulse pressure variation (PPV) can predict fluid responsiveness in healthy dogs during clinical surgery.

STUDY DESIGN

Prospective clinical study.

ANIMALS

Thirty-three isoflurane-anesthetized dogs with arterial hypotension during orthopedic surgery.

METHODS

Fluid challenge with lactated Ringer's solution (15 mL kg^-1 in 15 minutes) was administered in mechanically ventilated dogs (tidal volume 10 mL kg^-1) with hypotension [mean arterial pressure (MAP) < 65 mmHg]. The volume expansion was considered effective if cardiac output (CO; transesophageal Doppler) increased by ≥ 15%. Cardiopulmonary data were analyzed using two-way ANOVA, receiver operating characteristics (ROC) curves and Spearman coefficient; p < 0.05 was considered significant.

RESULTS

Effective volume expansion, mean ± standard deviation 42 ± 4% increase in CO (p < 0.0001) was observed in 76% of the dogs, resulting in a decrease in PPV (p < 0.0001) and increase in MAP (p < 0.0001), central venous pressure (CVP; p = 0.02) and ejection fraction (p < 0.0001) compared with before the fluid challenge. None of these changes occurred when volume expansion resulted in a nonsignificant CO increase of 4 ± 5%. No significant differences were observed in blood gas analysis between responsive and nonresponsive dogs. The increase in CO was correlated with the decrease in PPV (r = -0.65; p < 0.0001) but absolute values of CO and PPV were not correlated. The PPV performance (ROC curve area: 0.89 ± 0.06, p = 0.0011) was better than that of CVP (ROC curve area: 0.54 ± 0.12) and MAP (ROC curve area: 0.59 ± 0.13) to predict fluid responsiveness. The best cut-off for PPV to distinguish responders and nonresponders was 15% (50% sensitivity and 96% specificity).

CONCLUSIONS AND CLINICAL RELEVANCE

In mechanically ventilated, healthy, isoflurane-anesthetized dogs, PPV predicted fluid responsiveness to volume expansion, and MAP and CVP did not show such applicability.

Venovenous extracorporeal membrane oxygenation in adult respiratory failure: Scores for mortality prediction

Despite a potentially effective therapy for adult respiratory failure, a general agreement on venovenous extracorporeal membrane oxygenation (VV-ECMO) has not been reached among institutions due to its invasiveness and high resource usage. To establish consensus on the timing of intervention, large ECMO organizations have published the respiratory extracorporeal membrane oxygenation survival prediction (RESP) score and the ECMOnet score, which allow users to predict hospital mortality for candidates with their pre-ECMO presentations. This study was aimed to test the predictive powers of these published scores in a medium-sized cohort enrolling adults treated with VV-ECMO for acute respiratory failure, and develop an institutional prediction model under the framework of the 3 scores if a superior predictive power could be achieved. This retrospective study included 107 adults who received VV-ECMO for severe acute respiratory failure (a PaO2/FiO2 ratio <70 mm Hg) in a tertiary referral center from 2007 to 2015. Essential demographic and clinical data were collected to calculate the RESP score, the ECMOnet score, and the sequential organ failure assessment (SOFA) score before VV-ECMO. The predictive power of hospital mortality of each score was presented as the area under receiver-operating characteristic curve (AUROC). The multivariate logistic regression was used to develop an institutional prediction model. The surviving to discharge rate was 55% (n = 59). All of the 3 published scores had a real but poor predictive power of hospital mortality in this study. The AUROCs of RESP score, ECMOnet score, and SOFA score were 0.662 (P = 0.004), 0.616 (P = 0.04), and 0.667 (P = 0.003), respectively. An institutional prediction model was established from these score parameters and presented as follows: hospital mortality (Y) = -3.173 + 0.208 × (pre-ECMO SOFA score) + 0.148 × (pre-ECMO mechanical ventilation day) + 1.021 × (immunocompromised status). Compared with the 3 scores, the institutional model had a significantly higher AUROC (0.779; P < 0.001). The 3 published scores provide valuable information about the poor prognostic factors for adult respiratory ECMO. Among the score parameters, duration of mechanical ventilation, immunocompromised status, and severity of organ dysfunction may be the most important prognostic factors of VV-ECMO used for adult respiratory failure.

Extracorporeal life support for severe acute respiratory distress syndrome

PURPOSE OF REVIEW

To provide a summary of the recent literature on extracorporeal membrane oxygenation (ECMO) in adults with severe acute respiratory distress syndrome (ARDS), focusing on advances in equipment, current conventional and unconventional indications, complications, and future applications.

RECENT FINDINGS

ECMO use has increased during the past 5 years. Advances in cannulation, circuit design, and patient selection have made it a safer therapeutic option in severe ARDS, and its use has become more widespread for nonconventional indications.

SUMMARY

High-quality evidence for the routine use of ECMO for management of adult patients with severe ARDS is still lacking. An ongoing randomized controlled trial (ECMO to rescue lung injury in severe ARDS) will contribute valuable data to guide clinical decisions to opt for this supportive therapy.