Cerebral perfusion and metabolism with mild hypercapnia vs. normocapnia in a porcine post cardiac arrest model with and without targeted temperature management

Aim

To determine whether targeting mild hypercapnia (PaCO2 7 kPa) would yield improved cerebral blood flow and metabolism compared to normocapnia (PaCO2 5 kPa) with and without targeted temperature management to 33 °C (TTM33) in a porcine post-cardiac arrest model.

Methods

39 pigs were resuscitated after 10 minutes of cardiac arrest using cardiopulmonary bypass and randomised to TTM33 or no-TTM, and hypercapnia or normocapnia. TTM33 was managed with intravasal cooling. Animals were stabilized for 30 minutes followed by a two-hour intervention period. Hemodynamic parameters were measured continuously, and neuromonitoring included intracranial pressure (ICP), pressure reactivity index, cerebral blood flow, brain-tissue pCO2 and microdialysis. Measurements are reported as proportion of baseline, and areas under the curve during the 120 min intervention period were compared.

Results

Hypercapnia increased cerebral flow in both TTM33 and no-TTM groups, but also increased ICP (199% vs. 183% of baseline, p = 0.018) and reduced cerebral perfusion pressure (70% vs. 84% of baseline, p < 0.001) in no-TTM animals. Cerebral lactate (196% vs. 297% of baseline, p < 0.001), pyruvate (118% vs. 152% of baseline, p < 0.001), glycerol and lactate/pyruvate ratios were lower with hypercapnia in the TTM33 group, but only pyruvate (133% vs. 150% of baseline, p = 0.002) was lower with hypercapnia among no-TTM animals.

Conclusion

In this porcine post-arrest model, hypercapnia led to increased cerebral flow both with and without hypothermia, but also increased ICP and reduced cerebral perfusion pressure in no-TTM animals. The effects of hypercapnia were different with and without TTM.(Institutional protocol number: FOTS, id 14931).

Cerebral perfusion and metabolism with mean arterial pressure 90 vs. 60 mmHg in a porcine post cardiac arrest model with and without targeted temperature management

AIM

To determine whether targeting a mean arterial pressure of 90 mmHg (MAP90) would yield improved cerebral blood flow and less ischaemia compared to MAP 60 mmHg (MAP60) with and without targeted temperature management at 33 °C (TTM33) in a porcine post-cardiac arrest model.

METHODS

After 10 min of cardiac arrest, 41 swine of either sex were resuscitated until return of spontaneous circulation (ROSC). They were randomised to TTM33 or no-TTM, and MAP60 or MAP90; yielding four groups. Temperatures were managed with intravasal cooling and blood pressure targets with noradrenaline, vasopressin and nitroprusside, as appropriate. After 30 min of stabilisation, animals were observed for two hours. Cerebral perfusion pressure (CPP), cerebral blood flow (CBF), pressure reactivity index (PRx), brain tissue pCO2 (PbtCO2) and tissue intermediary metabolites were measured continuously and compared using mixed models.

RESULTS

Animals randomised to MAP90 had higher CPP (p < 0.001 for both no-TTM and TTM33) and CBF (no-TTM, p < 0.03; TH, p < 0.001) compared to MAP60 during the 150 min observational period post-ROSC. We also observed higher lactate and pyruvate in MAP60 irrespective of temperature, but no significant differences in PbtCO2 and lactate/pyruvate-ratio. We found lower PRx (indicating more intact autoregulation) in MAP90 vs. MAP60 (no-TTM, p = 0.04; TTM33, p = 0.03).

CONCLUSION

In this porcine cardiac arrest model, targeting MAP90 led to better cerebral perfusion and more intact autoregulation, but without clear differences in ischaemic markers, compared to MAP60.

INSTITUTIONAL PROTOCOL NUMBER

FOTS, id 8442.

Short- and Long-term Outcome After Interventional VSD Closure: A Single-Center Experience in Pediatric and Adult Patients

Interventional closure of congenital ventricular septal defects (VSD) is recording a continuous rise in acceptance. Complete atrioventricular block (cAVB) and residual shunting are major concerns during follow-up, but long-term data for both are still limited. We retrospectively evaluated the outcome of patients with interventional VSD closure and focused on long-term results (> 1 year follow-up). Transcatheter VSD closures were performed between 1993 and 2015, in 149 patients requiring 155 procedures (104 perimembranous, 29 muscular, 19 residual post-surgical VSDs, and 3 with multiple defects). The following devices were used: 65 × Amplatzer™ Membranous VSD Occluder, 33 × Duct Occluder II, 27 × Muscular VSD Occluder, 3 × Duct Occluder I, 24 × PFM-Nit-Occlud®, and 3 × Rashkind-Occluder. The median age at time of implantation was 6.2 (0.01-66.1) years, median height 117 (49-188) cm, and median weight 20.9 (3.2-117) kg. Median follow-up time was 6.2 (1.1-21.3) years and closure rate was 86.2% at last follow-up. Complications resulting in device explantation include one case of cAVB with a Membranous VSD occluder 7 days after implantation and four cases due to residual shunt/malposition. Six (4%) deaths occurred during follow-up with only one procedural related death from a hybrid VSD closure. Overall, our reported results of interventional VSD closure show favorable outcomes with only one (0.7%) episode of cAVB. Interventional closure offers a good alternative to surgical closure and shows improved performance by using softer devices. However, prospective long-term data in the current era with different devices are still mandatory to assess the effectiveness and safety of this procedure.

Effect of Perfusion Fluids on Recovery of Inflammatory Mediators in Microdialysis

Microdialysis is an excellent tool to assess tissue inflammation in patients, but in vitro systems to evaluate recovery of inflammatory mediators have not been standardized. We aimed to develop a reference plasma preparation and evaluate different perfusion fluids with respect to recovery of metabolic and inflammatory markers. The reference preparation was produced by incubation of human blood with lipopolysaccharide and cobra venom factor to generate cytokines and activate complement, respectively. Microdialysis with 100 kDa catheters was performed using different colloid and crystalloid perfusion fluids (hydroxyethyl starch (HES) 130/0.4, HES 200/0.5, hyperosmolar HES 200/0.5, albumin 200 g/l, T1 perfusion fluid and Ringer's acetate) compared to today's recommended dextran 60 solution. Recovery of glucose, glycerol and pyruvate was not significantly different between the perfusion fluids, whereas lactate had lower recovery in HES 200/0.5 and albumin perfusion fluids. Recovery rates for the inflammatory proteins in comparison with the concentration in the reference preparation differed substantially: IL-6 = 9%, IL-1β = 18%, TNF = 0.3%, MCP-1 = 45%, IL-8 = 48%, MIG = 48%, IP-10 = 25%, C3a = 53% and C5a = 12%. IL-10 was not detectable in microdialysis dialysate. HES 130/0.4 and HES 200/0.5 yielded a recovery not significantly different from dextran 60. Hyperosmolar HES 200/0.5 and albumin showed significantly different pattern of recovery with increased concentration of MIG, IP-10, C3a and C5a and decreased concentration of IL-1β, TNF, MCP-1 and IL-8 in comparison with dextran 60. In conclusion, microdialysis perfusion fluid dextran 60 can be replaced by the commonly used HES 130/0.4, whereas albumin might be used if specific immunological variables are in focus. The present reference plasma preparation is suitable for in vitro evaluation of microdialysis systems.

Carbon Dioxide and the Heart: Physiology and Clinical Implications

Carbon dioxide (CO2) is an end product of aerobic cellular respiration. In healthy persons, PaCO2 is maintained by physiologic mechanisms within a narrow range (35-45 mm Hg). Both hypercapnia and hypocapnia are encountered in myriad clinical situations. In recent years, the number of hypercapnic patients has increased by the use of smaller tidal volumes to limit lung stretch and injury during mechanical ventilation, so-called permissive hypercapnia. A knowledge and appreciation of the effects of CO2 in the heart are necessary for optimal clinical management in the perioperative and critical care settings. This article reviews, from a historical perspective: (1) the effects of CO2 on coronary blood flow and the mechanisms underlying these effects; (2) the role of endogenously produced CO2 in metabolic control of coronary blood flow and the matching of myocardial oxygen supply to demand; and (3) the direct and reflexogenic actions of CO2 on myocardial contractile function. Clinically relevant issues are addressed, including the role of increased myocardial tissue PCO2 (PmCO2) in the decline in myocardial contractility during coronary hypoperfusion and the increased vulnerability to CO2-induced cardiac depression in patients receiving a β-adrenergic receptor antagonist or with otherwise compromised inotropic reserve. The potential use of real-time measurements of PmO2 to monitor the adequacy of myocardial perfusion in the perioperative period is discussed.

Myocardial tissue CO2 tension detects coronary blood flow reduction after coronary artery bypass in real-time†

BACKGROUND

Coronary stenosis after coronary artery bypass grafting (CABG) may lead to myocardial ischaemia and is clinically difficult to diagnose. In a CABG model, we aimed at defining variables that detect hypoperfusion in real-time and correlate with impaired regional ventricular function by monitoring myocardial tissue metabolism.

METHODS

Off-pump CABG was performed in 10 pigs. Graft blood flow was reduced in 18 min intervals to 75, 50, and 25% of baseline flow with reperfusion between each flow reduction. Myocardial tissue Pco2 (Pt(CO2)), Po2, pH, glucose, lactate, and glycerol from the graft supplied region and a control region were obtained. Regional cardiac function was assessed as radial strain.

RESULTS

In comparison with baseline, myocardial pH decreased during 75, 50, and 25% flow reduction (-0.15; -0.22; -0.37, respectively, all P<0.05) whereas Pt(CO2) increased (+4.6 kPa; +7.8 kPa; +12.9 kPa, respectively, all P<0.05). pH and Pt(CO2) returned to baseline upon reperfusion. Lactate and glycerol increased flow-dependently, while glucose decreased. Regional ventricular contractile function declined significantly. All measured variables remained normal in the control region. Pt(CO2) correlated strongly with tissue lactate, pH, and contractile function (R=0.86, R=-0.91, R=-0.70, respectively, all P<0.001). New conductometric Pt(CO2) sensors were in agreement with established fibre-optic probes. Cardiac output was not altered.

CONCLUSIONS

Myocardial pH and Pt(CO2) monitoring can quantify the degree of regional tissue hypoperfusion in real-time and correlated well with cellular metabolism and contractile function, whereas cardiac output did not. New robust conductometric Pt(CO2) sensors have the potential to serve as a clinical cardiac monitoring tool during surgery and postoperatively.

Hepatic and abdominal carbon dioxide measurements detect and distinguish hepatic artery occlusion and portal vein occlusion in pigs

Hepatic artery (HA) occlusion and portal vein (PV) occlusion are the most common vascular complications after liver transplantation with an impact on mortality and retransplantation rates. The detection of severe hypoperfusion may be delayed with currently available diagnostic tools. Hypoperfusion and anaerobically produced lactic acid lead to increases in tissue carbon dioxide. We investigated whether the continuous assessment of the intrahepatic and intra-abdominal partial pressure of carbon dioxide (PCO(2) ) could be used to detect and distinguish HA and PV occlusions in real time. In 13 pigs, the HA and the PV were fully occluded (n = 7) or gradually occluded (n = 6). PCO(2) was monitored intrahepatically and between loops of small intestine. The hepatic and intestinal metabolism was assessed with microdialysis and PV as well as hepatic vein blood samples, and the results were compared to clinical parameters for the systemic circulation and blood gas analysis. Total HA occlusion led to significant increases in hepatic PCO(2) and lactate, and this was accompanied by significant decreases in the partial pressure of oxygen and glucose. PV occlusion induced a significant increase in intestinal PCO(2) (but not hepatic PCO(2) ) along with significant increases in intestinal lactate and glycerol. Gradual HA occlusion and PV occlusion caused steady hepatic and intestinal PCO(2) increases, respectively. Systemic clinical parameters such as the blood pressure, heart rate, and cardiac output were affected only by PV occlusion. In conclusion, even gradual HA occlusion affects liver metabolism and can be reliably identified with hepatic PCO(2) measurements. Intestinal PCO(2) increases only during PV occlusion. A combination of hepatic and intestinal PCO(2) measurements can reliably diagnose the affected vessel and depict the severity of the occlusion, and this may emerge as a potential real-time clinical monitoring tool for the postoperative course of liver transplantation and enable early interventions.