High concordance between expert anaesthetists' actions and advice of decision support system in achieving oxygen delivery targets in high-risk surgery patients.

BACKGROUND: Goal-directed therapy has a secure place in perioperative care. Algorithms are based on Starling's law of the heart, notwithstanding that this does not numerically define volume or heart performance variables. These have been developed based on a Guytonian view of the circulation and are implemented in a computerized decision support system (Navigator™). We studied the feasibility and performance of the graphical display of the system in an intervention and a control group of patients undergoing major abdominal surgery. METHODS: Patients were randomized to either graphically (intervention) or numerically (control) guided administration of therapy. Goals were set and treatments and concordance with guidance noted, where applicable. Anaesthesia was provided by one of three experienced anaesthetists well acquainted with Navigator™. The primary objective was to determine whether the use of graphical display decision support more efficiently enables the achievement of oxygen delivery targets. This was quantitated as percentage time in the target zone and averaged standardized distance from the target centre. RESULTS: The mean percentage time in the target zone was 36.7% for control and 36.5% for intervention. The averaged standardized difference was 1.5 in control and 1.6 in intervention. There was no significant difference in fluid balances. There was a high level of concordance between decision support recommendation and anaesthetist action (84.3%). CONCLUSIONS: In experienced hands, the addition of a graphical display for haemodynamic guidance resulted in a similar time in target and averaged standardized difference. The haemodynamic guidance system should be explored in a comparative study to anaesthesia management without guidance.

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.

Non-invasive cardiac output measurement using a fast mixing box to measure carbon dioxide elimination.

This study investigated the accuracy of a new technique for measuring cardiac output using the derivative Fick principle based on the ratio of change in the partial pressures of end-tidal and mixed expired carbon dioxide produced by short periods of partial rebreathing. A prospective clinical study involving 24 patients following cardiopulmonary bypass for coronary artery bypass grafting or valvular surgery was undertaken in the intensive care unit of a university-affiliated hospital. Haemodynamic measurements were performed after admission to the intensive care unit. Cardiac output was measured simultaneously by bolus pulmonary artery thermodilution and by a non-invasive carbon dioxide partial rebreathing technique. Cardiac output measurement using the new technique demonstrated a significant but consistent underestimate, with a bias of -0.60 +/- 0.87 l/min. This new adaptation of the partial rebreathing technique is reliable in measuring cardiac output in postoperative patients. Reasons for the consistent discrepancy between thermodilution and partial rebreathing techniques are discussed.

Acute lithium intoxication.

We present a case of acute lithium intoxication in a 51-year-old woman on chronic lithium therapy. Her serum lithium level was 10.6 mmol/l 13 hours after ingestion and 5.8 mmol/l at 24 hours. Dialysis therapy was not employed and she recovered well after fluid resuscitation. Serum lithium levels in chronic intoxication are more indicative of intracellular lithium concentration and therefore of clinical toxicity, as opposed to serum lithium levels in acute intoxication. Clinical features of toxicity are more important than a spot lithium level. A combination of clinical toxicity, the duration of exposure and a serial profile of serum lithium levels should guide dialytic therapy for removal of lithium.

Non-invasive cardiac output determination: comparison of a new partial-rebreathing technique with thermodilution.

This study compares a derivative Fick technique using carbon dioxide (CO2) with the thermodilution pulmonary artery catheter (PAC), for determination of cardiac output (CO). Subjects were sedated, mechanically ventilated adults following elective cardiac surgery Microprocessor controlled deadspace activation and side-stream capnography in a ventilator circuit enabled calculation of CO (CO(CO2)) every four minutes. Thermodilution CO (CO(TD)) was performed as clinically indicated and at 20-minute intervals. Simultaneous CO(TD)/CO(CO2) pairs were recorded from time of admission to ICU for a minimum period of two hours for each patient. There were 358 CO(TD)/CO(CO2) pairs recorded from 41 patients. Cardiac output measurements ranged from 2. 7 to 10.6 l/min. The bias (Bland-Altman) was 0.050 l/min (95% CI -0.024 to 0.125 l/min). The 95% limits of agreement were -1.354 to 1.455 l/min. This simple, non-invasive partial-rebreathing technique is a valid alternative to thermodilution for cardiac output determination in sedated, mechanically ventilated patients. There are significant implications for improved safety, reduced complexity and reduced cost in anaesthesia and intensive care.

Volume state control - a new approach.

OBJECTIVE: To describe a new approach to circulating volume control in critically ill patients. DATA SOURCES: Studies in circulatory physiology, mathematical models of the circulation and open and closed loop circulation control. SUMMARY OF REVIEW: In evaluation of the volume state it may be Wiser to consider the determinants of the systemic venous return rather than those of the cardiac output. These determinants include the mean systemic filling pressure, the right atrial pressure and the unknown resistance to venous return. A model based approach is advanced to determine a mean systemic filling pressure analogue (P(msa)) which accounts for variation in venous resistance. It is suggested that P(msa) is an appropriate object of volume control. Definition of a volume state provides insights for cardioactive therapy. CONCLUSIONS: Use of a P(msa) volume signal enables prolonged stable closed loop volume servocontrol. In global heart dysfunction the dimensionless variable (P(msa )- RAP)/P(msa )may be used to guide inotropic therapy.

Three dimensional closed loop control of the human circulation.

In the control of the circulation it is suggested there is merit in describing states which are the object of each therapy. Considering the determinants of venous return rather than those of cardiac output, we suggest that the mean systemic filling pressure is a parsimonious description of the volume state. A method is described of deriving a mean systemic filling pressure analogue based on stopping the flow in a notional regional systemic circulation. The mean systemic filling pressure (PM) forms a quantitative link between volume therapy and circulatory dynamics. The systemic vascular resistance is a conventional measure of the state of arteriolar resistance. We suggest that the ratio (PM - PRA)/PM (where PRA is the right atrial pressure) is a global measure of the effect of cardioactive drugs. Studies are reported in which the mean blood pressure, right atrial pressure and cardiac output are simultaneously controlled within desired tolerances using state based control.

The use of electrical conductivity measurement in the calculation of ion-free water loss in urine.

The urine electrical conductivity is a practical guide to the ion-to-water ratio of urine. It may be used to assess the influence of urinary loss upon the total body ion-to-water ratio. It is suggested that the total body ion-to-water ratio is the object of control in water therapy, commonly administered as 5% dextrose. The total body ion-to-water ratio closely accords with the ratio in the extracellular fluid. Since sodium is the predominant extracellular cation, the plasma sodium concentration closely reflects the extracellular and total body ion-to-water ratio. As a consequence the urine electrical conductivity may be used as a continuous signal in the open or closed loop control of water balance as reflected by the plasma sodium concentration.

Charcoal hemoperfusion treatment of severe theophylline toxicity.

A 38 year old man was admitted eight hours after taking ten grams of theophylline. The plasma concentration of theophylline on admission was 732 mumol/l. In view of the patient's continuing clinical deterioration, charcoal hemoperfusion was undertaken. This led to a rapid fall in plasma theophylline concentrations and improvement in clinical signs. It is suggested that charcoal hemoperfusion has a role in the severely theophylline toxic patient in whom standard conservative measures are failing. The patient's hyperglycemia, metabolic acidosis, and hypokalemia are discussed.

The patient/computer interface--a problem area.

In disease states, loss of homeostatic control may be countered by the provision of external inputs or therapy. Where the variables of interest may change rapidly and respond predictably to therapy, a patient/computer interface may be used to enhance data collection and/or in the formation of appropriate therapeutic responses. Ultimately, if appropriate dynamic responses are achieved, the patient therapy loop may be closed. Realisation of problem-free interfaces requires careful design of input transducers, computing hardware and software, output therapeutic devices and their integration. This process will require ingenuity, engineering competence and a thorough understanding of medicine and the clinical environment. In addition to sound technological solutions, the designer must be cognisant of the human aspects, for both patient and user of interface operation.

An 8-year prospective experience with balloon tamponade in emergency control of bleeding esophageal varices.

The use of balloon tamponade in the emergency control of bleeding from esophageal varices is controversial. This paper reports a prospective study over an 8-year period in which balloon tamponade has been the sole means employed for the early control of bleeding varices. During 1972-1980 all patients referred to Prince Henry's Hospital with upper gastrointestinal bleeding were admitted to a special unit. Ninety-one had bleeding esophageal varices, and 17 were admitted on one or more occasions for bleeding for a total of 132 admissions. After early endoscopy, balloon tamponade was used during 103 of these admissions with failure to control bleeding on six occasions; five of these patients died from hemorrhage and the sixth recovered after emergency portacaval shunt. Another patient died from rebleeding not treated by tamponade. Reinsertion of the balloon for rebleeding was necessary on 28 occasions with successful control in all cases. Balloon tamponade was not used during 29 admissions because bleeding had ceased or the patient was considered to have terminal liver disease. In this group there were four deaths from severe liver disease and hemorrhage. Balloon tamponade was used in 78% of admissions and controlled bleeding in more than 90% of patients. This suggests that tamponade may be the method of choice early control of bleeding from esophageal varices.

Successful treatment of ergotamine poisoning with sodium nitroprusside.

A case of ergotamine overdosage which produced vascular insufficiency in a 26-year-old female is described. She was treated successfully with the intravenous infusions of sodium nitroprusside and low molecular weight dextran, and anticoagulation with heparin. It is suggested that sodium nitroprusside may represent the drug of first choice in this condition.

Use of a microprocessor in the control of malignant hypertension with sodium nitroprusside.

In a malignant hypertensive, steady control of blood pressure at a pre-determined level has been achieved with the continuous intravenous infusion of sodium nitroprusside. A microprocessor was programmed to assess the patient's blood pressure and adjust the rate of nitroprusside infusion so that a mean pressure of 106 mmHg was achieved. Brief interruption of the nitroprusside infusion allowed the effectiveness of changes in oral therapy to be evaluated. Thiocyanate concentrations were measured throughout as an index of potential nitroprusside toxicity. After six days, blood pressure control was maintained with oral therapy alone and papilloedema had almost resolved.