Cardiac surgery does not lead to loss of oscillatory components in circulatory signals.

The circulatory system is oscillatory in its nature. Oscillatory components linked to physiological processes and underlying regulatory mechanisms are identifiable in circulatory signals. Autonomic regulation is essential for the system's ability to deal with external exposure, and the integrity of oscillations may be considered a hallmark of a healthy system. Loss of complexity is seen as a consequence of several diseases and aging. Heart rate variability is known to decrease after cardiac surgery and remain reduced for up to 6 months. Oscillatory components of circulatory signals are linked to the system's overall complexity. We therefore hypothesize that the frequency distributions of circulatory signals show loss of oscillatory components after cardiac surgery and that the observed changes persist. We investigated the development of the circulatory frequency distributions of eight patients undergoing cardiac surgery by extracting three time series from conventional blood pressure and electrocardiography recordings: systolic blood pressure, heart rate, and amplitude of the electrocardiogram's R-wave. Four 30-min selections, representing key events of the perioperative course, were analyzed with the continuous wavelet transform, and average wavelet power spectra illustrated the circulatory frequency distributions. We identified oscillatory components in all patients and variables. Contrary to our hypothesis, they were randomly distributed through frequencies, patients, and situations, thus, not representing any reduction in the overall complexity. One patient showed loss of a 25-s oscillation after surgery. We present a case where noise is misclassified as an oscillation, raising questions about the robustness of such analyses.

Post cardiac surgery stunning reduces stroke work, but leaves cardiac power output unchanged in patients with normal ejection fraction.

This study assesses positional changes in cardiac power output and stroke work compared with classic hemodynamic variables, measured before and after elective coronary artery bypass graft surgery. The hypothesis was that cardiac power output was altered in relation to cardiac stunning. The study is a retrospective analysis of data from two previous studies performed in a tertiary care university hospital. Thirty-six patients scheduled for elective coronary artery bypass graft surgery, with relatively preserved left ventricular function, were included. A pulmonary artery catheter and a radial artery catheter were placed preoperatively. Cardiac power output and stroke work were calculated through thermodilution both supine and standing prior to induction of anesthesia and again day one postoperatively. Virtually all systemic hemodynamic parameters changed significantly from pre- to postoperatively, and from supine to standing. Cardiac power output was maintained at 0.9-1.0 (±0.3) W both pre- and postoperatively and from supine to standing on both days. Stroke work fell from pre- to postoperatively from 1.1 to 0.8 J (P < 0.001), there was a significant fall in stroke work with positional change preoperatively from 1.1 to 0.9 J (P < 0.001). Postoperatively the stroke work remained at 0.8 J despite positional change. Cardiac power output was the only systemic hemodynamic variable which remained unaltered during all changes. Stroke work appears to be a more sensitive marker for temporary cardiovascular dysfunction than cardiac power output. Further studies should explore the relationship between stroke work and cardiac performance and whether cardiac power output is an autoregulated intrinsic physiological parameter.

Swedish-Norwegian co-operation in the treatment of three hypothermia victims: a case report.

BACKGROUND: Accidental hypothermia with cardiac arrest represents a challenge for pre-hospital rescuers as well as in-hospital staff. For pre-hospital personnel, the main focus is to get the patient to the correct destination without unnecessary delay. For in-hospital personnel early information is vital to assess the possibility for resuscitation with extracorporeal re-warming. The challenge is augmented when rescuers must cross national borders to reach and/or deliver the patients. We present a case where three adolescent boys suffered severe hypothermia after a canoeing accident in Sweden. CASE PRESENTATION: Three 14-year-old boys were canoeing a mountain lake close to the Norwegian border when their boat capsized and they all fell into the cold water. The rescue operation was hampered by rough weather conditions, and immersion times spanned from 63 to 125 min. Flight times from the scene of accident to the nearest ECMO center in Norway (Trondheim) and Sweden (Umeå) were about 30 and 90 min respectively. Two of the victims showed no vital signs after retrieval from the water and had extremely low body temperatures. They were brought to Trondheim University Hospital where they were resuscitated successfully with extracorporeal re-warming. Unable to be weaned from ECMO in the initial phase, both patients were retrieved by mobile ECMO teams to Karolinska University Hospital, from where they were discharged to their homes with good outcomes, although with some sequelae. A third victim with moderate to severe hypothermia without cardiac arrest was treated at a local hospital, from where he after a short stay was discharged without physical sequelae. CONCLUSION: These cases are a reminder of the traditional mantra that «no one is dead until warm and dead¼. Good communication between pre- and in-hospital staff can be vital for optimizing patient treatment when handling victims of severe hypothermia, and especially when there is multiple victims. Communication between neighboring countries, but even neighboring regions within the same country, can be challenging. We encourage regions similar to ours to review protocols regarding hypothermia management, making them more robust before incidents like this take place.

Blood glucose control using a novel continuous blood glucose monitor and repetitive intravenous insulin boluses: exploiting natural insulin pulsatility as a principle for a future artificial pancreas.

The aim of this study was to construct a glucose regulatory algorithm by employing the natural pulsatile pattern of insulin secretion and the oscillatory pattern of resting blood glucose levels and further to regulate the blood glucose level in diabetic pigs by this method. We developed a control algorithm based on repetitive intravenous bolus injections of insulin and combined this with an intravascular blood glucose monitor. Four anesthetized pigs were used in the study. The animals developed a mildly diabetic state from streptozotocin pretreatment. They were steadily brought within the blood glucose target range of 4.5-6.0 mmol/L in 21 to 121 min and kept within that range for 128 to 238 min (hypoglycemic values varied from 2.9 to 51.1 min). The study confirmed our hypotheses regarding the feasibility of this new principle for blood glucose control, and the algorithm was constantly improved during the study to produce the best results in the last animals. The main obstacles were the drift of the IvS-1 sensor and problems with the calibration procedure, which calls for an improvement in the sensor stability before this method can be applied fully in new studies in animals and humans.

Comparison of arterial and mixed venous blood glucose levels in hemodynamically unstable pigs: implications for location of a continuous glucose sensor.

One of several unsolved challenges in the construction of an artificial endocrine pancreas (a system for automatically adjusting the blood glucose level) is the positioning of the glucose sensor. We believe the best positioning to be either intraarterial or in a central vein. It is therefore important to know whether the glucose content in these blood locations is the same. We conducted a post hoc analysis of previously collected data from pigs exposed to gross inflammatory and circulatory stress. Paired arterial and mixed venous glucose values were compared with a mixed effects model. We found the blood glucose values from the arterial and mixed venous blood to be the same.

Pharmacology of intravenous insulin administration: implications for future closed-loop glycemic control by the intravenous/intravenous route.

BACKGROUND: Our group is attempting to construct an artificial pancreas based on intravenous glucose monitoring and intravenous insulin delivery. To do so, the pharmacology of intravenous insulin administration must be studied. We used a pig model to determine the inherent lag time in the insulin/blood glucose system. The goal was to suggest a method that reduces the blood glucose level in a rapid and yet predictable manner. METHODS: Six pigs received continuous intravenous insulin infusions at 0.04, 0.08, or 0.4 IU/kg/h for 60 min. Two pigs received short-term intravenous infusions at 0.4 IU/kg/h for 2 min, repeated five times at 60-min intervals. Four animals received five intravenous insulin bolus injections at 60-min intervals, two at 0.01 IU/kg and two 0.02 IU/kg, with a final dose of 0.04 IU/kg. The blood glucose level was measured every 1-5 min. RESULTS: A high rate of intravenous insulin infusion led to rapid declines in blood glucose levels. The same rapid decline was achieved when the infusion was halted after 2 min. Using the latter method and with intravenous insulin boluses, blood glucose levels started to rise again after approximately 15-20 min. Insulin boluses led to a first detectable decrease in blood glucose level after 2-6 min and to a maximum rate of decrease shortly thereafter. CONCLUSIONS: We found that intravenous bolus injections of insulin lowered blood glucose levels rapidly and predictably. Repetitive small intravenous insulin boluses together with an accurate and fast-responding intravascular continuous glucose monitor should be studied as a method of closed-loop glycemic control.

Continuous measurement of blood glucose: validation of a new intravascular sensor.

BACKGROUND: Tight blood glucose control is used extensively in perioperative and critically ill patients. Several studies, however, have shown contradictory effects on patient outcomes. A major problem of these studies has been inadequate control of the prime variable, blood glucose. This paper describes the validation of a new intravascular continuous blood glucose sensor. METHODS: The glucose sensor was placed in the superior caval vein of seven anesthetized pigs. Sensor readings were compared with arterial blood gas readings. Fluctuations in blood glucose were created using intravenous glucose and insulin. A total of 807 paired sensor and blood gas readings were obtained. RESULTS: The sensor was tested with a range of blood glucose values (0.63-15.75 mM [mean bias, 0.0131 mM]). Analysis using Bland-Altman plots yielded 95% limits of agreement at -0.908 and 0.934 mM. There were 121 paired measurements with a mean value below 2.2 mM, yielding 95% limits of agreement at -0.553 and 0.466 mM. CONCLUSIONS: The performance of the sensor was in agreement with blood gas measurements in a wide range of glucose values. For the clinician, it is noteworthy that performance was equally good in the hypoglycemic area.