Better Protection of Pulmonary Surfactant Integrity With Deep Hypothermia and Circulatory Arrest

The dynamic changes in autophagy activity and its role in lung injury after deep hypothermic circulatory arrest

Deep hypothermic circulatory arrest (DHCA) can cause acute lung injury (ALI), and its pathogenesis mimics ischaemia/reperfusion (I/R) injury. Autophagy is also involved in lung I/R injury. The present study aimed to elucidate whether DHCA induces natural autophagy activation and its role in DHCA‐mediated lung injury. Here, rats were randomly assigned to the Sham or DHCA group. The sham group (n = 5) only received anaesthesia and air intubation. DHCA group rats underwent cardiopulmonary bypass (CPB) followed by the DHCA procedure. The rats were then sacrificed at 3, 6 and 24 h after the DHCA procedure (n = 5) to measure lung injury and autophagy activity. Chloroquine (CQ) was delivered to evaluate autophagic flux. DHCA caused lung injury, which was prominent 3–6 h after DHCA, as confirmed by histological examination and inflammatory cytokine quantification. Lung injury subsided at 24 h. Autophagy was suppressed 3 h but was exaggerated at 6 h. At both time points, autophagic flux appeared uninterrupted. To further assess the role of autophagy in DHCA‐mediated lung injury, the autophagy inducer rapamycin and its inhibitor 3‐methyladenine (3‐MA) were applied, and lung injury was reassessed. When rapamycin was administered at an early time point, lung injury worsened, whereas administration of 3‐MA at a late time point ameliorated lung injury, indicating that autophagy contributed to lung injury after DHCA. Our study presents a time course of lung injury following DHCA. Autophagy showed adaptive yet protective suppression 3 h after DHCA, as induction of autophagy caused worsening of lung tissue. In contrast, autophagy was exaggerated 6 h after DHCA, and autophagy inhibition attenuated DHCA‐mediated lung injury.

The Expression of CD34(+)/C-kit(+) Stem Cells in Peripheral Blood in Infants After Deep Hypothermia Circulatory Arrest

To investigate the effect of deep hypothermic circulatory arrest (DHCA) on the expression of a CD34(+)/C-kit(+) progenitor cell population in peripheral blood in infants. The expression of CD34(+)/C-kit(+) stem cells in peripheral blood of 10 patients after DHCA was measured before institution of cardiopulmonary bypass (CPB) (T0), at 12-24 hours (T1) and 4-5 days (T2) after cessation of CPB, respectively. The level of CD34(+)/C-kit(+) stem cells in peripheral blood was significantly higher in the DHCA group at T1 and T2 (p<0.01). Our data show that DHCA may cause the increase of CD34(+)/C-kit(+) stem cells in peripheral blood after surgery. The role of increase of CD34(+)/C-kit(+) stem cells in peripheral blood on the beneficial effects of DHCA needs to be studied.

Hypothermic versus normothermic cardiopulmonary bypass in patients with valvular heart disease

OBJECTIVE

The aim of this study was to test the hypothesis that normothermic cardiopulmonary bypass (CPB) is as effective as hypothermic CPB in terms of cardiac protection (cTnI level) and outcome in patients with valvular heart disease.

DESIGN

Prospective randomized study.

SETTING

A tertiary cardiothoracic referral center.

PARTICIPANTS

140 patients who had valvular heart disease, with/without coronary artery disease, surgically treated under CPB.

INTERVENTIONS

The patients were allocated randomly to undergo either hypothermic (temperature [T], 31 °C-32 °C) or normothermic CPB (T>36 °C).

MEASUREMENTS AND MAIN RESULTS

The primary endpoint was the dynamics of troponin I. The secondary endpoints were ventilation time, the need for inotropic support, intensive care unit (ICU) and hospital stay durations, complications, and mortality. There were no significant intergroup differences in dynamics of troponin I. Ventilation time was significantly lower in the hypothermic group (6 (5-9) and 8 (5-12); p = 0.01).

CONCLUSIONS

Normothermic CPB in patients with valvular heart disease was as effective as hypothermic perfusion in terms of myocardial protection after the surgery assessed by cTnI release. The short ventilation duration in patients who underwent hypothermic CPB needs to be confirmed in a future investigation.

Continuous pulmonary infusion of L-arginine during deep hypothermia and circulatory arrest improves pulmonary surfactant integrity in piglets

BACKGROUND

The integrity of pulmonary surfactant (PS) is impaired during deep hypothermia and circulatory arrest (DHCA), a preferred bypass strategy for infants undergoing complex cardiac operations, due mainly to bypass-induced systemic inflammation. The requirement of L-arginine, a precursor of nitric oxide, is elevated during acute pulmonary inflammation. We hypothesized that continuous intrapulmonary supplementation of L-arginine during DHCA can maintain the integrity of PS metabolism and thus protect the pulmonary function.

METHODS

Sixteen piglets underwent 90-minute circulatory arrest at 18 degrees C before rewarming. During circulatory arrest, antegrade infusion of Ringer's lactate solution alone (n = 8) or containing L-arginine (1 mg/kg/min, n = 8) was initiated into the pulmonary circulation. Disaturated phosphatidylcholine, total phospholipids, and total proteins from tracheal aspirates were measured serially until the experiment ended (4 hours after rewarming). Various variables of pulmonary function were also monitored.

RESULTS

L-arginine led to less decrement of disaturated phosphatidylcholine/total phospholipids and disaturated phosphatidylcholine/total proteins after DHCA. At 4 hours after rewarming, L-arginine had significantly mitigated the deterioration of pulmonary static compliance (3.6 +/- 0.5 vs 3.3 +/- 0.3 mL/cm H2O) and partial pressure of arterial oxygen/fraction of inspired oxygen (330 +/- 48 vs 296 +/- 32 mm Hg). Pulmonary retention of water (6.2 +/- 1.0 vs 5.5 +/- 1.2) was significantly reduced. The L-arginine-treated group showed an increase in NO metabolites (NO2-/NO3-) from the pulmonary circulation, the extent of which is correlated to PS content.

CONCLUSIONS

Continuous L-arginine supplementation during DHCA attenuated PS depletion and, therefore, ameliorated postoperative pulmonary dysfunction.