Induced hypothermia in critical respiratory failure after lung transplantation

Design and rationale of the CHILL phase II trial of hypothermia and neuromuscular blockade for acute respiratory distress syndrome

The Cooling to Help Injured Lungs (CHILL) trial is an open label, two group, parallel design multicenter, randomized phase IIB clinical trial assessing the efficacy and safety of targeted temperature management with combined external cooling and neuromuscular blockade to block shivering in patients with early moderate-severe acute respiratory distress syndrome (ARDS). This report provides the background and rationale for the clinical trial and outlines the methods using the Consolidated Standards of Reporting Trials guidelines. Key design challenges include: [1] protocolizing important co-interventions; [2] incorporation of patients with COVID-19 as the cause of ARDS; [3] inability to blind the investigators; and [4] ability to obtain timely informed consent from patients or legally authorized representatives early in the disease process. Results of the Reevaluation of Systemic Early Neuromuscular Blockade (ROSE) trial informed the decision to mandate sedation and neuromuscular blockade only in the group assigned to therapeutic hypothermia and proceed without this mandate in the control group assigned to a usual temperature management protocol. Previous trials conducted in National Heart, Lung, and Blood Institute ARDS Clinical Trials (ARDSNet) and Prevention and Early Treatment of Acute Lung Injury (PETAL) Networks informed ventilator management, ventilation liberation and fluid management protocols. Since ARDS due to COVID-19 is a common cause of ARDS during pandemic surges and shares many features with ARDS from other causes, patients with ARDS due to COVID-19 are included. Finally, a stepwise approach to obtaining informed consent prior to documenting critical hypoxemia was adopted to facilitate enrollment and reduce the number of candidates excluded because eligibility time window expiration.

Hypermetabolism in critically ill patients with COVID-19 and the effects of hypothermia: A case series

Background

We have observed that critically ill patients with COVID-19 are in an extreme hypermetabolic state. This may be a major contributing factor to the extraordinary ventilatory and oxygenation demands seen in these patients. We aimed to quantify the extent of the hypermetabolic state and report the clinical effect of the use of hypothermia to decrease the metabolic demand in these patients.

Methods

Mild hypothermia was applied on four critically ill patients with COVID-19 for 48 h. Metabolic rates, carbon dioxide production and oxygen consumption were measured by indirect calorimetry.

Results

The average resting energy expenditure (REE) was 299% of predicted. Mild hypothermia decreased the REE on average of 27.0% with resultant declines in CO₂ production (VCO₂) and oxygen consumption (VO₂) by 29.2% and 25.7%, respectively. This decrease in VCO₂ and VO₂ was clinically manifested as improvements in hypercapnia (average of 19.1% decrease in pCO₂ levels) and oxygenation (average of 50.4% increase in pO₂).

Conclusion

Our case series demonstrates the extent of hypermetabolism in COVID-19 critical illness and suggests that mild hypothermia reduces the metabolic rate, improves hypercapnia and hypoxia in critically ill patients with COVID-19.

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COVID-19 critical illness induces an extreme hypermetabolic state.

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Hypothermia attenuates the hypermetabolic response seen in patients with COVID-19.

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Hypothermia in patients with COVID-19 may improve carbon dioxide and oxygen levels.

Is Therapeutic Hypothermia for Acute Respiratory Distress Syndrome the Future?

INTRODUCTION

Severe acute respiratory distress syndrome (ARDS) has a high mortality, and there is limited knowledge about management of severe ARDS refractory to standard therapy. Early evidence suggests that therapeutic hypothermia (TH) could be a viable treatment for acute respiratory failure. We present 2 cases where TH was successfully used to manage refractory ARDS on extracorporeal membrane oxygenation (ECMO) and a review of the literature around TH and acute respiratory failure.

RESULTS

We present 2 cases of ARDS secondary to H1N1 influenza and human metapneumovirus. Both patients were treated with the current evidence-based therapy for ARDS. Venovenous ECMO was used in both patients for refractory hypoxemia. Therapeutic hypothermia was applied for 24 hours with improved oxygenation. We did a review of the literature summarizing 38 patients in 10 publications where TH was successfully utilized in the treatment of acute respiratory failure.

CONCLUSION

Therapeutic hypothermia may be a viable salvage therapy for ARDS refractory to the current evidence-based therapy but needs further evaluation.

Effect of therapeutic hypothermia on gas exchange and respiratory mechanics: a retrospective cohort study

Targeted temperature management (TTM) may improve respiratory mechanics and lung inflammation in acute respiratory distress syndrome (ARDS) based on animal and limited human studies. We aimed to assess the pulmonary effects of TTM in patients with respiratory failure following cardiac arrest. Retrospective review of consecutive cardiac arrest cases occurring out of hospital or within 24 hours of hospital admission (2002-2012). Those receiving TTM (n=44) were compared with those who did not (n=42), but required mechanical ventilation (MV) for at least 4 days following the arrest. There were no between-group differences in age, gender, body mass index, APACHE II, or fluid balance during the study period. The TTM group had lower ejection fraction, Glasgow Coma Score, and more frequent use of paralytics. Matched data analyses (change at day 4 compared with baseline of the individual subject) showed favorable, but not statistically significant trends in respiratory mechanics endpoints (airway pressure, compliance, tidal volume, and PaO2/FiO2) in the TTM group. The PaCO2 decreased significantly more in the TTM group, as compared with controls (-12 vs. -5 mmHg, p=0.02). For clinical outcomes, the TTM group consistently, although not significantly, did better in survival (59% vs. 43%) and hospital length of stay (12 vs. 15 days). The MV duration and Cerebral Performance Category score on discharge were significantly lower in the TTM group (7.3 vs. 10.7 days, p=0.04 and 3.2 vs. 4, p=0.01). This small retrospective cohort suggests that the effect of TTM ranges from equivalent to favorable, compared with controls, for the specific respiratory and clinical outcomes in patients with respiratory failure following cardiac arrest.

Transplantation of lungs from a non-heart-beating donor

BACKGROUND

In animals, we have previously done successful lung transplantations using organs from non-heart-beating donors. We have also developed an ex-vivo system of assessing the function of such organs before transplantation. The next stage was to try the technique in human beings. Bearing in mind the sensitive ethical issues involved, our first aim was to find out what procedures would be acceptable, and to use the results to guide a clinical lung transplantation from a non-heart-beating donor.

METHODS

The ethical acceptability of the study was gauged from the results of a broad information programme directed at the general public in Sweden, and from discussions with professionals including doctors, nurses, hospital chaplains, and judges. The donor was a patient dying of acute myocardial infarction in a cardiac intensive-care unit after failed cardiopulmonary resuscitation. The next of kin gave permission to cool the lungs within the intact body, and intrapleural cooling was started 65 min after death. Blood samples were sent for virological testing and cross matching. The next of kin then had time to be alone with the deceased. After 3 h, the body was transported to the operating theatre and the heart-lung block removed. The lungs were assessed ex vivo, and the body was transported to the pathology department for necropsy.

RESULTS

No contraindications to transplantation were found, and the right lung was transplanted successfully into a 54-year-old woman with chronic obstructive pulmonary disease. The donor lung showed excellent function only 5 min after reperfusion and ventilation, and during the first 5 months of follow-up, the function of the transplanted lung has been good.

INTERPRETATION

About half the deaths in Sweden are caused by cardiac and cerebrovascular disease. This group could be a potential source of lung donors. When all hospitals and ambulance personnel in Sweden have received training in non-heart-beating lung donation, we hope that there will be enough donor lungs of good quality for all patients needing a lung transplant.

Lung transplantation is warranted for stable, ventilator-dependent recipients

BACKGROUND

Lung transplantation for patients on ventilators is a controversial use of scarce donor lungs. We have performed 500 lung transplants in 12 years and 21 of these have been in ventilator-dependent patients.

METHODS

A retrospective review of patient records and computerized database was performed. Living patients were contacted to confirm their health and functional status.

RESULTS

Patients included 13 men and 8 women with a mean age of 43 years. Sixteen patients were considered stable awaiting lung transplant, whereas 5 patients were unstable with acute graft failure after prior lung transplantation. Stable patients had been ventilated for a mean of 57 +/- 46 days whereas unstable patients had been supported for 10 +/- 9 days. Half of the patients required cardiopulmonary bypass support during the transplant, and there was no statistical difference in the frequency of CPB in stable and unstable patients (p = 0.61). Three hospital deaths included 0 of 16 of the stable patients and 3 of 5 of the unstable patients (p = 0.01). Long-term actuarial survival was significantly better in stable versus unstable patients (p = 0.02), with 5-year survival 40% for stable patients and 0% for unstable patients.

CONCLUSIONS

Lung transplantation can be successfully conducted in stable patients who have become ventilator dependent after listing for transplantation. Acute retransplantation for early lung dysfunction is high risk and has produced poor long-term results.

Selective use of extracorporeal membrane oxygenation is warranted after lung transplantation

OBJECTIVES

Early allograft dysfunction after lung transplantation ranges from subclinical x-ray abnormalities to pulmonary edema, hypoxemia, hypercarbia, and pulmonary hypertension. Management may include extracorporeal circulation to allow recovery of the acute lung injury. We reviewed our experience with extracorporeal membrane oxygenation after lung transplantation to assess the utility of this therapy.

METHODS

A retrospective chart review was performed. Single or bilateral lung transplantation was performed in 444 adults from July 1988 to July 1998. Twelve (2.7%) patients experienced allograft dysfunction severe enough to require extracorporeal membrane oxygenation after failure of conventional therapy, including sedation, paralysis, and inhaled nitric oxide.

RESULTS

Seven of 12 patients requiring extracorporeal membrane oxygenation were discharged from the hospital. Mean and median times to extracorporeal membrane oxygenation support were 1.2 days and 0 days, respectively. Mean length of support was 4.2 days. Four patients died while receiving extracorporeal membrane oxygenation support. One patient was weaned from extracorporeal membrane oxygenation but died during the hospitalization. Two patients required acute retransplantation while receiving extracorporeal membrane oxygenation, and one survived to discharge. Three patients continued to receive extracorporeal membrane oxygenation support for more than 4 days, and all 3 died. All survivors had begun receiving extracorporeal membrane oxygenation support by post-transplantation day 1. Three of 7 patients discharged from the hospital died 12 months, 13 months, and 72 months after transplantation because of bronchiolitis obliterans syndrome (n = 2) or lymphoma (n = 1). Four patients are alive 2, 12, 25, and 54 months after transplantation.

CONCLUSIONS

Extracorporeal membrane oxygenation provides effective therapy for acute post-transplantation lung dysfunction. The frequency and pattern of our extracorporeal membrane oxygenation use reflects bias toward early extracorporeal membrane oxygenation support for isolated graft failure in otherwise intact and uninfected recipients.

Cardiovascular effects of induced hypothermia after lung transplantation

BACKGROUND

Induced hypothermia may be used to reduce metabolism in acute respiratory failure. Hypothermia is accompanied by an increase in pulmonary vascular resistance, as also seen in the early period after lung transplantation. It was our concern that the combination of the two would lead to an increased workload on the right ventricle.

METHODS

To test this hypothesis we induced hypothermia to 32 degrees C in two groups of pigs. In one group we performed left single-lung transplantation combined with right pulmectomy (TRANSP group); in the other group, only right pulmectomy was performed (PULMEC group).

RESULTS

During hypothermia, there was a significant increase in both groups in pulmonary vascular resistance (TRANSP group, 77%, p<0.05; PULMEC group, 54%, p<0.05) and a significant decrease in cardiac output (TRANSP group, 41%, p<0.05; PULMEC group, 34% p<0.05). Mean pulmonary artery pressure was unchanged, and the work done by the right ventricle was reduced (TRANSP group, 39%, p<0.05; PULMEC group, 31%).

CONCLUSIONS

Induced hypothermia to 32 degrees C after lung transplantation resulted in a significant decrease in the work done by the right ventricle despite a significant increase in pulmonary vascular resistance.