Automated infusion of vasoactive and inotropic drugs to control arterial and pulmonary pressures during cardiac surgery

Drug Infusion Systems: Technologies, Performance, and Pitfalls

This review aims to broadly describe drug infusion technologies and raise subtle but important issues arising from infusion therapy that can potentially lead to patient instability and morbidity. Advantages and disadvantages of gravity-dependent drug infusion are described and compared with electromechanical approaches for precise control of medication infusion, including large-volume peristaltic and syringe pumps. This review discusses how drugs and inert carriers interact within infusion systems and outlines several complexities and potential sources of drug error. Major topics are (1) the importance of the infusion system dead volume; (2) the quantities of coadministered fluid and the concept of microinfusion; and (3) future directions for drug infusion.The infusion system dead volume resides between the point where drug and inert carrier streams meet and the patient's blood. The dead volume is an often forgotten reservoir of drugs, especially when infusion flows slow or stop. Even with medications and carriers flowing, some mass of drug always resides within the dead volume. This reservoir of drug can be accidentally delivered into patients. When dose rate is changed, there can be a significant lag between intended and actual drug delivery. When a drug infusion is discontinued, drug delivery continues until the dead volume is fully cleared of residual drug by the carrier. When multiple drug infusions flow together, a change in any drug flow rate transiently affects the rate of delivery of all the others. For all of these reasons, the use of drug infusion systems with smaller dead volumes may be advantageous.For critically ill patients requiring multiple infusions, the obligate amount of administered fluid can contribute to volume overload. Recognition of the risk of overload has given rise to microinfusion strategies wherein drug solutions are highly concentrated and infused at low rates. However, potential risks associated with the dead volume may be magnified with microinfusion. All of these potential sources for adverse events relating to the infusion system dead volume illustrate the need for continuing education of clinical personnel in the complexities of drug delivery by infusion.This review concludes with an outline of future technologies for managing drug delivery by continuous infusion. Automated systems based on physiologic signals and smart systems based on physical principles and an understanding of dead volume may mitigate against adverse patient events and clinical errors in the complex process of drug delivery by infusion.

Less Invasive and Inotrope-Reduction Approach to Automated Closed-Loop Control of Hemodynamics in Decompensated Heart Failure

We have been developing an automated cardiovascular drug infusion system for simultaneous control of arterial pressure (AP), cardiac output (CO), and left atrial pressure (PLA) in decompensated heart failure (HF). In our prototype system, CO and PLA were measured invasively through thoracotomy. Furthermore, the control logic inevitably required use of inotropes to improve hemodynamics, which was not in line with clinical HF guidelines. The goal of this study was to solve these problems and develop a clinically feasible system. We integrated to the system minimally invasive monitors of CO and pulmonary capillary wedge pressure (PCWP, surrogates for PLA) that we developed recently. We also redesigned the control logic to reduce the use of inotrope. We applied the newly developed system to nine dogs with decompensated HF. Once activated, our system started to control the infusion of vasodilator and diuretics in all the animals. Inotrope was not infused in three animals, and infused at minimal doses in six animals that were intolerant of vasodilator infusion alone. Within 50 min, our system controlled AP, CO, and PCWP to their respective targets accurately. Pulmonary artery catheterization confirmed optimization of hemodynamics (AP, from 98 ± 4 to 74 ± 11 mmHg; CO, from 2.2 ± 0.5 to 2.9 ± 0.3 L·min(-1)·m(-2); PCWP, from 27.0 ± 6.6 to 13.8 ± 3.0 mmHg). In a minimally invasive setting while reducing the use of inotrope, our system succeeded in automatically optimizing the overall hemodynamics in canine models of HF. The present results pave the way for clinical application of our automated drug infusion system.

Computer based haemodynamic guidance system is effective and safe in management of postoperative cardiac surgery patients

A circulatory guidance system, Navigator, was evaluated in a prospective, randomised control trial at six Australian university teaching hospitals involving 112 scheduled postoperative cardiac surgical patients with pulmonary artery catheters placed and receiving 1:1 nursing care. The guidance system was used to achieve and maintain physician-designated cardiac output and mean arterial pressure targets and compared these with standard post open-heart surgery care. The primary efficacy endpoint was the standardised unsigned error between the targeted and the actual values for cardiac output and mean arterial pressure, time averaged over the duration of cardiac output monitoring - the average standardised distance. This was 1.71 (SD=0.65) for the guidance group and 1.92 (SD=0.65) in the control group (P=0.202). Rates of postoperative atrial fibrillation, adverse events, intensive care unit and hospital length-of-stay were similar in both groups. There were no device-related adverse events. Guided haemodynamic therapy with the Navigator device was non-inferior to standard intensive care unit therapy. The study was registered with ClinicalTrials.gov Identifier NCT00468247.

Computational modelling of lung injury: is there potential for benefit?

State-of-the-art medical care of the victims of current conflicts is generating large quantities of quality clinical data as a by-product. Observational research based on these data is beginning to have a profound influence on the clinical management of both military and civilian trauma patients. Computational modelling based on these datasets may offer the ability to investigate clinical treatment strategies that are practically, ethically or scientifically impossible to investigate on the front line. This article reviews the potential of this novel technology to aid development of treatment for blast lung and other unresolved medical scenarios.

Feedback control of multiple hemodynamic variables with multiple cardiovascular drugs

The ultimate goal of disease treatment is to control the biological system beyond the native regulation to combat pathological process. To maximize the advantage of drugs, we attempted to pharmacologically control the biological system at will, e.g., control multiple hemodynamic variables with multiple cardiovascular drugs. A comprehensive physiological cardiovascular model enabled us to evaluate cardiovascular properties (pump function, vascular resistance, and blood volume) and the feedback control of these properties. In 12 dogs, with dobutamine (5+/-3 mug.kg(-1).min(-1)), nitroprusside (4+/-2 mug.kg(-1).min(-1)), dextran (2+/-2 ml.kg(-1)), and furosemide (10 mg in one, 20 mg in one), rapid, sufficient and stable control of pump function, vascular resistance and blood volume resulted in similarly quick and stable control of blood pressure, cardiac output and left atrial pressure in 5+/-7, 7+/-5, and 12+/-10 minutes, respectively. These variables remained stable for 60 minutes (RMS 4+/-3 mmHg, 5+/-2 ml.min(-1).kg(-1), 0.8+/-0.6 mmHg, respectively).

Computationally managed bradycardia improved cardiac energetics while restoring normal hemodynamics in heart failure

In acute heart failure, systemic arterial pressure (AP), cardiac output (CO), and left atrial pressure (P (LA)) have to be controlled within acceptable ranges. Under this condition, cardiac energetic efficiency should also be improved. Theoretically, if heart rate (HR) is reduced while AP, CO, and P (LA) are maintained by preserving the functional slope of left ventricular (LV) Starling's curve (S (L)) with precisely increased LV end-systolic elastance (E (es)), it is possible to improve cardiac energetic efficiency and reduce LV oxygen consumption per minute (MVO (2)). We investigated whether this hemodynamics can be accomplished in acute heart failure using an automated hemodynamic regulator that we developed previously. In seven anesthetized dogs with acute heart failure (CO < 70 mL min(-1) kg(-1), P (LA) > 15 mmHg), the regulator simultaneously controlled S (L) with dobutamine, systemic vascular resistance with nitroprusside and stressed blood volume with dextran or furosemide, thereby controlling AP, CO, and P (LA). Normal hemodynamics were restored and maintained (CO; 88 +/- 3 mL min(-1) kg(-1), P (LA); 10.9 +/- 0.4 mmHg), even when zatebradine significantly reduced HR (-27 +/- 3%). Following HR reduction, E (es) increased (+34 +/- 14%), LV mechanical efficiency (stroke work/oxygen consumption) increased (+22 +/- 6%), and MVO (2) decreased (-17 +/- 4%) significantly. In conclusion, in a canine acute heart failure model, computationally managed bradycardia improved cardiac energetic efficiency while restoring normal hemodynamic conditions.

IMPROVED TRANSFORMATION OF MORPHOMETRIC MEASUREMENTS FOR A PRIORI PARAMETER ESTIMATION IN A PHYSIOLOGICALLY-BASED PHARMACOKINETIC MODEL OF ETHANOL

Prescription of the brain's time course of exposure to experimentally administered ethanol can be achieved with intravenous infusion profiles computed from a physiologically-based pharmacokinetic (PBPK) model of alcohol distribution and elimination. Previous parameter estimation employed transformations of an individual's age, height, weight and gender inferred from the literature, with modeling errors overcome with real-time, intermittent feedback. Current research applications, such as ethanol exposures administered during fMRI scanning, require open-loop infusions, thus improved transformation of morphometric measurements.Records of human breath alcohol concentration (BrAC) clamp experiments were analyzed. Optimal, unique PBPK parameters of a model of the distribution and elimination of ethanol were determined for each record and found to be in concordance with parameter values published by other investigators. A linear transformation between the readily measurable physical characteristics or morphometrics, including gender, age, height, weight, and TBW estimates, and the model parameters were then determined in a least squares sense according to the formula theta=F(x)=F(m)x where x=(age height weight TBW)(T)inR(4) and theta =(R(C) V(P) V(B) m(max)k(AT))(T)inR(5).The transformation was then evaluated with several parameter prediction performance measures. A substantial improvement in all error statistics, in relation to an earlier affine transformation that used only body weight as the relevant morphometric was obtained. Deviation from the measured response was reduced from 27 to 20%. Error in parameter estimation was reduced from 109 to 38%. Percent alcohol provided in error was reduced from 46 to 28%. Error in infusion profile estimation was reduced from 55 to 33%.The algorithm described, which optimizes individual pharmacokinetic parameter values and then subsequent extension to a priori prediction, while not unique, can be readily be adapted to other molecules and pharmacokinetic models. This includes those used for distinct purposes, such as automated control of anesthetic agents.

Automated drug delivery system to control systemic arterial pressure, cardiac output, and left heart filling pressure in acute decompensated heart failure

Pharmacological support with inotropes and vasodilators to control decompensated hemodynamics requires strict monitoring of patient condition and frequent adjustments of drug infusion rates, which is difficult and time-consuming, especially in hemodynamically unstable patients. To overcome this difficulty, we have developed a novel automated drug delivery system for simultaneous control of systemic arterial pressure (AP), cardiac output (CO), and left atrial pressure (Pla). Previous systems attempted to directly control AP and CO by estimating their responses to drug infusions. This approach is inapplicable because of the difficulties to estimate simultaneous AP, CO, and Pla responses to the infusion of multiple drugs. The circulatory equilibrium framework developed previously (Uemura K, Sugimachi M, Kawada T, Kamiya A, Jin Y, Kashihara K, and Sunagawa K. Am J Physiol Heart Circ Physiol 286: H2376-H2385, 2004) indicates that AP, CO, and Pla are determined by an equilibrium of the pumping ability of the left heart (SL), stressed blood volume (V), and systemic arterial resistance (R). Our system directly controls SL with dobutamine, V with dextran/furosemide, and R with nitroprusside, thereby controlling the three variables. We evaluated the efficacy of our system in 12 anesthetized dogs with acute decompensated heart failure. Once activated, the system restored SL, V, and R within 30 min, resulting in the restoration of normal AP, CO, and Pla. Steady-state deviations from target values were small for AP [4.4 mmHg (SD 2.6)], CO [5.4 ml x min(-1) x kg(-1) (SD 2.4)] and Pla [0.8 mmHg (SD 0.6)]. In conclusion, by directly controlling the mechanical determinants of circulation, our system has enabled simultaneous control of AP, CO, and Pla with good accuracy and stability.

Information technology and acute dialysis

The careful application of information technology to the field of acute dialysis may result in both a better understanding of the disease as well as an improvement in patient outcomes. Often these applications increase costs and complexity with little change in understanding or quality of care. To avoid this common trap, a targeted assessment of needs and possible solutions is mandatory. Our group was assembled to provide balanced perspectives and recommendations that address how information technology should be assessed and applied to acute dialysis therapy, with the intent to increase the understanding of the current practice and to improve patient care. To achieve these goals, five areas of focus were identified: patient safety, current practice pattern assessment, practice variation, patient assessment, and dialysis machine technology. To facilitate the assessment, we formulated five specific questions and developed answers based on the available literature and group consensus.

Automated information systems in anesthesiology

The current state of the art of anesthesia information systems remains primitive. Currently, available commercial systems focus only at automating the charting process and not the care process. Until systems are available that integrate these two functions, anesthesiologists will not truly benefit from such systems.

Computer control versus manual control of systemic hypertension during cardiac surgery

BACKGROUND

We recently demonstrated the feasibility of computer controlled infusion of vasoactive drugs for the control of systemic hypertension during cardiac surgery. The objective of the current study was to investigate the effects of computer controlled blood pressures on hemodynamic stability when compared to conventional manual control.

METHOD

Systemic artery blood pressures were managed either by computer (80 patients) or by a well-trained anesthesiologist (80 patients). The vasodilator drugs sodium nitroprusside and nitroglycerin were used. Hemodynamic stability was determined from the standard deviation of the mean arterial pressure samples and from the percentages of time that arterial pressure was hypertensive or hypotensive.

RESULTS

The average standard deviation of the mean arterial pressure samples was smaller for the computer controlled than for the manually controlled group: 7.5+/-2.2 (mean+/-SD) versus 8.9+/-2.3 mmHg (P<0.0001). The systemic artery pressure was less hypertensive and less hypotensive in the computer controlled than in the manually controlled group: 9.4+/-5.7 versus 13.1+/-6.0% (P<0.0001) and 8.0+/-5.9 versus 11.8+/-7.4% (P<0.0001), respectively.

CONCLUSION

We conclude that, compared with manual control, computer control of systemic hypertension significantly improved hemodynamic stability during cardiac surgery.