Identification of myocardial injury using perioperative troponin surveillance in major noncardiac surgery and net benefit over the Revised Cardiac Risk Index.

BACKGROUND: Patients with perioperative myocardial injury are at risk of death and major adverse cardiovascular and cerebrovascular events (MACCE). The primary aim of this study was to determine optimal thresholds of preoperative and perioperative changes in high-sensitivity cardiac troponin T (hs-cTnT) to predict MACCE and mortality. METHODS: Prospective, observational, cohort study in patients ≥50 yr of age undergoing elective major noncardiac surgery at seven hospitals in Sweden. The exposures were hs-cTnT measured before and days 0-3 after surgery. Two previously published thresholds for myocardial injury and two thresholds identified using receiver operating characteristic analyses were evaluated using multivariable logistic regression models and externally validated. The weighted comparison net benefit method was applied to determine the additional value of hs-cTnT thresholds when compared with the Revised Cardiac Risk Index (RCRI). The primary outcome was a composite of 30-day all-cause mortality and MACCE. RESULTS: We included 1291 patients between April 2017 and December 2020. The primary outcome occurred in 124 patients (9.6%). Perioperative increase in hs-cTnT ≥14 ng L-1 above preoperative values provided statistically optimal model performance and was associated with the highest risk for the primary outcome (adjusted odds ratio 2.9, 95% confidence interval 1.8-4.7). Validation in an independent, external cohort confirmed these findings. A net benefit over RCRI was demonstrated across a range of clinical thresholds. CONCLUSIONS: Perioperative increases in hsTnT ≥14 ng L-1 above baseline values identifies acute perioperative myocardial injury and provides a net prognostic benefit when added to RCRI for the identification of patients at high risk of death and MACCE. CLINICAL TRIAL REGISTRATION: NCT03436238.

Lung-protective ventilation increases cerebral metabolism and non-inflammatory brain injury in porcine experimental sepsis.

BACKGROUND: Protective ventilation with lower tidal volumes reduces systemic and organ-specific inflammation. In sepsis-induced encephalopathy or acute brain injury the use of protective ventilation has not been widely investigated (experimentally or clinically). We hypothesized that protective ventilation would attenuate cerebral inflammation in a porcine endotoxemic sepsis model. The aim of the study was to study the effect of tidal volume on cerebral inflammatory response, cerebral metabolism and brain injury. Nine animals received protective mechanical ventilation with a tidal volume of 6 mL × kg-1 and nine animals were ventilated with a tidal volume of 10 mL × kg-1. During a 6-h experiment, the pigs received an endotoxin intravenous infusion of 0.25 µg × kg-1 × h-1. Systemic, superior sagittal sinus and jugular vein blood samples were analysed for inflammatory cytokines and S100B. Intracranial pressure, brain tissue oxygenation and brain microdialysis were sampled every hour. RESULTS: No differences in systemic or sagittal sinus levels of TNF-α or IL-6 were seen between the groups. The low tidal volume group had increased cerebral blood flow (p < 0.001) and cerebral oxygen delivery (p < 0.001), lower cerebral vascular resistance (p < 0.05), higher cerebral metabolic rate (p < 0.05) along with higher cerebral glucose consumption (p < 0.05) and lactate production (p < 0.05). Moreover, low tidal volume ventilation increased the levels of glutamate (p < 0.01), glycerol (p < 0.05) and showed a trend towards higher lactate to pyruvate ratio (p = 0.08) in cerebral microdialysate as well as higher levels of S-100B (p < 0.05) in jugular venous plasma compared with medium-high tidal volume ventilation. CONCLUSIONS: Contrary to the hypothesis, protective ventilation did not affect inflammatory cytokines. The low tidal volume group had increased cerebral blood flow, cerebral oxygen delivery and cerebral metabolism together with increased levels of markers of brain injury compared with medium-high tidal volume ventilation.

Lung-protective ventilation suppresses systemic and hepatic vein levels of cell-free DNA in porcine experimental post-operative sepsis.

BACKGROUND: Plasma levels of cell-free DNA (cf-DNA) are known to be elevated in sepsis and high levels are associated with a poor prognosis. Mechanical ventilation affects systemic inflammation in which lung-protective ventilation attenuates the inflammatory response. The aim was to study the effect of a lung protective ventilator regime on arterial and organ-specific venous blood as well as on trans-organ differences in cf-DNA levels in a porcine post-operative sepsis model. METHOD: One group of anaesthetised, domestic-breed, 9-12 weeks old, pigs were ventilated with protective ventilation (VT 6 mL x kg- 1, PEEP 10 cmH2O) n = 20. Another group, ventilated with a medium high tidal volume and lower PEEP, served as a control group (VT 10 mL x kg- 1, PEEP 5 cm H2O) n = 10. Blood samples were taken from four sources: artery, hepatic vein, portal vein and, jugular bulb. A continuous endotoxin infusion at 0.25 µg x kg- 1 x h- 1 for 5 h was started following 2 h of laparotomy, which simulated a surgical procedure. Inflammatory cytokines and cf-DNA in plasma were analysed and trans-organ differences calculated. RESULTS: The protective ventilation group had lower levels of cf-DNA in arterial (p = 0.02) and hepatic venous blood (p = 0.03) compared with the controls. Transhepatic differences in cf-DNA were lower in the protective group, compared with the controls (p = 0.03). No differences between the groups were noted as regards the transcerebral, transsplanchnic or the transpulmonary cf-DNA differences. CONCLUSIONS: Protective ventilation suppresses arterial levels of cf-DNA. The liver seems to be a net contributor to the systemic cf-DNA levels, but this effect is attenuated by protective ventilation.

Evaluating the effects of protective ventilation on organ-specific cytokine production in porcine experimental postoperative sepsis.

BACKGROUND: Protective ventilation with lower tidal volume (VT) and higher positive end-expiratory pressure (PEEP) reduces the negative additive effects of mechanical ventilation during systemic inflammatory response syndrome. We hypothesised that protective ventilation during surgery would affect the organ-specific immune response in an experimental animal model of endotoxin-induced sepsis-like syndrome. METHODS: 30 pigs were laparotomised for 2 hours (h), after which a continuous endotoxin infusion was started at 0.25 micrograms × kg(-1) × h(-1) for 5 h. Catheters were placed in the carotid artery, hepatic vein, portal vein and jugular bulb. Animals were randomised to two protective ventilation groups (n = 10 each): one group was ventilated with VT 6 mL × kg(-1) during the whole experiment while the other group was ventilated during the surgical phase with VT of 10 mL × kg(-1). In both groups PEEP was 5 cmH2O during surgery and increased to 10 cmH2O at the start of endotoxin infusion. A control group (n = 10) was ventilated with VT of 10 mL × kg(-1) and PEEP 5 cm H20 throughout the experiment. In four sample locations we a) simultaneously compared cytokine levels, b) studied the effect of protective ventilation initiated before and during endotoxemia and c) evaluated protective ventilation on organ-specific cytokine levels. RESULTS: TNF-alpha levels were highest in the hepatic vein, IL-6 levels highest in the artery and jugular bulb and IL-10 levels lowest in the artery. Protective ventilation initiated before and during endotoxemia did not differ in organ-specific cytokine levels. Protective ventilation led to lower levels of TNF-alpha in the hepatic vein compared with the control group, whereas no significant differences were seen in the artery, portal vein or jugular bulb. CONCLUSIONS: Variation between organs in cytokine output was observed during experimental sepsis. We see no implication from cytokine levels for initiating protective ventilation before endotoxemia. However, during endotoxemia protective ventilation attenuates hepatic inflammatory cytokine output contributing to a reduced total inflammatory burden.

Pre-exposure to mechanical ventilation and endotoxemia increases Pseudomonas aeruginosa growth in lung tissue during experimental porcine pneumonia.

BACKGROUND: Immune system suppression during critical care contributes to the risk of acquired bacterial infections with Pseudomonas (P.) aeruginosa. Repeated exposure to endotoxin can attenuate systemic inflammatory cytokine responses. Mechanical ventilation affects the systemic inflammatory response to various stimuli. AIM: To study the effect of pre-exposure to mechanical ventilation with and without endotoxin-induced systemic inflammation on P. aeruginosa growth and wet-to-dry weight measurements on lung tissue and plasma and bronchoalveolar lavage levels of tumor necrosis factor alpha, interleukins 6 and 10. METHODS: Two groups of pigs were exposed to mechanical ventilation for 24 hours before bacterial inoculation and six h of experimental pneumonia (total experimental time 30 h): A30h+Etx (n = 6, endotoxin 0.063 µg x kg-1 x h-1) and B30h (n = 6, saline). A third group, C6h (n = 8), started the experiment at the bacterial inoculation unexposed to endotoxin or mechanical ventilation (total experimental time 6 h). Bacterial inoculation was performed by tracheal instillation of 1x1011 colony-forming units of P. aeruginosa. Bacterial cultures and wet-to-dry weight ratio analyses were done on lung tissue samples postmortem. Separate group comparisons were done between A30h+Etx vs.B30h (Inflammation) and B30h vs. C6h (Ventilation Time) during the bacterial phase of 6 h. RESULTS: P. aeruginosa growth was highest in A30h+Etx, and lowest in C6h (Inflammation and Ventilation Time both p<0.05). Lung wet-to-dry weight ratios were highest in A30h+Etx and lowest in B30h (Inflammation p<0.01, Ventilation Time p<0.05). C6h had the highest TNF-α levels in plasma (Ventilation Time p<0.01). No differences in bronchoalveolar lavage variables between the groups were observed. CONCLUSIONS: Mechanical ventilation and systemic inflammation before the onset of pneumonia increase the growth of P. aeruginosa in lung tissue. The attenuated growth of P. aeruginosa in the non-pre-exposed animals (C6h) was associated with a higher systemic TNF-α production elicited from the bacterial challenge.

Protective ventilation reduces Pseudomonas aeruginosa growth in lung tissue in a porcine pneumonia model.

BACKGROUND: Mechanical ventilation with positive end expiratory pressure and low tidal volume, i.e. protective ventilation, is recommended in patients with acute respiratory distress syndrome. However, the effect of protective ventilation on bacterial growth during early pneumonia in non-injured lungs is not extensively studied. The main objectives were to compare two different ventilator settings on Pseudomonas aeruginosa growth in lung tissue and the development of lung injury. METHODS: A porcine model of severe pneumonia was used. The protective group (n = 10) had an end expiratory pressure of 10 cm H2O and a tidal volume of 6 ml x kg-1. The control group (n = 10) had an end expiratory pressure of 5 cm H2O and a tidal volume of 10 ml x kg-1. 1011 colony forming units of Pseudomonas aeruginosa were inoculated intra-tracheally at baseline, after which the experiment continued for 6 h. Two animals from each group received only saline, and served as sham animals. Lung tissue samples from each animal were used for bacterial cultures and wet-to-dry weight ratio measurements. RESULTS: The protective group displayed lower numbers of Pseudomonas aeruginosa (p < 0.05) in the lung tissue, and a lower wet-to-dry ratio (p < 0.01) than the control group. The control group deteriorated in arterial oxygen tension/inspired oxygen fraction, whereas the protective group was unchanged (p < 0.01). CONCLUSIONS: In early phase pneumonia, protective ventilation with lower tidal volume and higher end expiratory pressure has the potential to reduce the pulmonary bacterial burden and the development of lung injury.

Lung protective ventilation induces immunotolerance and nitric oxide metabolites in porcine experimental postoperative sepsis.

Low tidal volume ventilation is beneficial in patients with severe pulmonary dysfunction and would, in theory, reduce postoperative complications if implemented during routine surgery. The study aimed to investigate whether low tidal volume ventilation and high positive end-expiratory pressure (PEEP) in a large animal model of postoperative sepsis would attenuate the systemic inflammatory response and organ dysfunction. Thirty healthy pigs were randomized to three groups: Group Prot-7h, i.e. protective ventilation for 7 h, was ventilated with a tidal volume of 6 mL x kg(-1) for 7 h; group Prot-5h, i.e. protective ventilation for 5 h, was ventilated with a tidal volume of 10 mL x kg(-1) for 2 h, after which the group was ventilated with a tidal volume of 6 mL x kg(-1); and a control group that was ventilated with a tidal volume of 10 mL x kg(-1) for 7 h. In groups Prot-7h and Prot-5h PEEP was 5 cmH2O for 2 h and 10 cmH2O for 5 h. In the control group PEEP was 5 cmH2O for the entire experiment. After surgery for 2 h, postoperative sepsis was simulated with an endotoxin infusion for 5 h. Low tidal volume ventilation combined with higher PEEP led to lower levels of interleukin 6 and 10 in plasma, higher PaO2/FiO2, better preserved functional residual capacity and lower plasma troponin I as compared with animals ventilated with a medium high tidal volume and lower PEEP. The beneficial effects of protective ventilation were seen despite greater reductions in cardiac index and oxygen delivery index. In the immediate postoperative phase low VT ventilation with higher PEEP was associated with reduced ex vivo plasma capacity to produce TNF-α upon endotoxin stimulation and higher nitrite levels in urine. These findings might represent mechanistic explanations for the attenuation of systemic inflammation and inflammatory-induced organ dysfunction.