Hyponatraemia and hypernatraemia: Disorders of Water Balance in Neurosurgery.

Disorders of tonicity, hyponatraemia and hypernatraemia, are common in neurosurgical patients. Tonicity is sensed by the circumventricular organs while the volume state is sensed by the kidney and peripheral baroreceptors; these two signals are integrated in the hypothalamus. Volume is maintained through the renin-angiotensin-aldosterone axis, while tonicity is defended by arginine vasopressin (antidiuretic hormone) and the thirst response. Edelman found that plasma sodium is dependent on the exchangeable sodium, potassium and free-water in the body. Thus, changes in tonicity must be due to disproportionate flux of these species in and out of the body. Sodium concentration may be measured by flame photometry and indirect, or direct, ion-sensitive electrodes. Only the latter method is not affected by changes in plasma composition. Classification of hyponatraemia by the volume state is imprecise. We compare the tonicity of the urine, given by the sodium potassium sum, to that of the plasma to determine the renal response to the dysnatraemia. We may then assess the activity of the renin-angiotensin-aldosterone axis using urinary sodium and fractional excretion of sodium, urate or urea. Together, with clinical context, these help us determine the aetiology of the dysnatraemia. Symptomatic individuals and those with intracranial catastrophes require prompt treatment and vigilant monitoring. Otherwise, in the absence of hypovolaemia, free-water restriction and correction of any reversible causes should be the mainstay of treatment for hyponatraemia. Hypernatraemia should be corrected with free-water, and concurrent disorders of volume should be addressed. Monitoring for overcorrection of hyponatraemia is necessary to avoid osmotic demyelination.

Correlation electron cyclotron emission diagnostic and improved calculation of turbulent temperature fluctuation levels on ASDEX Upgrade.

A newly upgraded correlation electron cyclotron emission (CECE) diagnostic has been installed on the ASDEX Upgrade tokamak and has begun to perform experimental measurements of electron temperature fluctuations. CECE diagnostics measure small amplitude electron temperature fluctuations by correlating closely spaced heterodyne radiometer channels. This upgrade expanded the system from six channels to thirty, allowing simultaneous measurement of fluctuation level radial profiles without repeat discharges, as well as opening up the possibility of measuring radial turbulent correlation lengths. Newly refined statistical techniques have been developed in order to accurately analyze the fluctuation data collected from the CECE system. This paper presents the hardware upgrades for this system and the analysis techniques used to interpret the raw data, as well as measurements of fluctuation spectra and fluctuation level radial profiles.

Haemodynamic assessment in pregnancy and pre-eclampsia: A Guytonian approach.

OBJECTIVES: Hypertensive disorders of pregnancy continue to be amongst the leading causes of maternal morbidity and mortality. There is debate about the optimal monitoring and treatment for these women, particularly in regard to circulatory and fluid management. A restrictive fluid strategy is advocated, which conflicts with the prevailing view that the circulating volume is contracted in pre-eclampsia. This belief has been erroneously reinforced by use of the central venous pressure (CVP) as a measure of the volume state. METHODS: We used a Guytonian model of the circulation involving the mean systemic filling pressure (Pms) to review published data using a cohort of normal pregnant/post partum women and a pre-eclamptic cohort. The Pms is the pressure left in the circulation when the heart is stopped, arguably the true volume state measure. An analogue of the Pms (Pmsa) can be calculated using commonly measured haemodynamic variables. RESULTS: Our results show the Pmsa to be elevated in normal pregnancy versus post partum (10.79 vs. 9.58, a 12.6% difference) and elevated further in pre-eclamptic pregnancy (13.86, 29% higher than the normal pregnant group). CONCLUSIONS: There is scope to challenge the long held belief that the volume state is contracted in pre-eclampsia. This approach indicates that the maternal volume state in pre-eclampsia is often elevated. When viewed in combination with recent echocardiographic insights this model helps to explain some of the haemodynamic management paradoxes that these women present. Most importantly, it provides a sound physiological basis for the restrictive fluid strategy that is currently recommended.

Energetic ion loss detector on the Alcator C-Mod tokamak.

A scintillator-based energetic ion loss detector has been successfully commissioned on the Alcator C-Mod tokamak. This probe is located just below the outer midplane, where it captures ions of energies up to 2 MeV resulting from ion cyclotron resonance heating. After passing through a collimating aperture, ions impact different regions of the scintillator according to their gyroradius (energy) and pitch angle. The probe geometry and installation location are determined based on modeling of expected lost ions. The resulting probe is compact and resembles a standard plasma facing tile. Four separate fiber optic cables view different regions of the scintillator to provide phase space resolution. Evolving loss levels are measured during ion cyclotron resonance heating, including variation dependent upon individual antennae.

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.

Outbreak of adenoviral infections in a long-term paediatric facility, New Jersey, 1986/87.

During an 8-week period in the winter of 1986-87, there were 11 deaths from an adenovirus infection (case fatality rate = 39%, 11/28) in a long-term care paediatric facility in southern New Jersey. Among the 61 resident children, all with severe congenital and/or acquired disabilities, 28 developed a febrile respiratory illness compatible with adenovirus infection [attack rate (AR) = 46%]. Patients with tracheostomies were three times as likely to become ill [relative risk (RR) = 3.2, 95% confidence intervals (CI) = 1.8-5.6]. Twenty-three members of the staff had a similar febrile illness (AR = 22%, 23/106); nurses were more likely to be ill than other staff (RR = 3.0, 95% CI = 1.1-11.4). Adenovirus 7 was isolated from four of the case patients and adenovirus 1 from one. The findings suggest prolonged transmission between patients and nursing staff with lack of cohorting of ill patients probably contributing to the prolongation of the outbreak. This investigation indicates that adenoviral outbreaks, although rare, can have a high mortality in severely disabled children, and that future outbreak investigations should examine the use of vaccines or antiviral agents to reduce mortality and for outbreak control.

Use of surveillance for invasive pneumococcal disease to estimate the size of the immunosuppressed HIV-infected population.

We used population-based surveillance in New Jersey in 1986 to quantify the risk of invasive pneumococcal disease in persons with the acquired immunodeficiency syndrome (AIDS) and in those who went on to develop AIDS. Using pneumococcal surveillance, we also devised a method to estimate the size of the immunosuppressed population infected with the human immunodeficiency virus (HIV), the so-called pre-AIDS population. From rates of pneumococcal disease that occurred in areas with a low incidence of AIDS, we calculated the number of patients expected to contract pneumococcal disease in areas with a high incidence of AIDS. There were 59 more cases of pneumococcal disease observed than expected; 14 of these patients had AIDS by the time of pneumococcal infection. We attributed the remaining 45 cases to the increased risk of pneumococcal infection in pre-AIDS. The pre-AIDS pneumococcal cases and the attack rate of pneumococcal disease in pre-AIDS were used to estimate the size of the 1986 pre-AIDS New Jersey population as 8823 pre-AIDS cases (95% confidence interval, 7377 to 10,714) or 0.37% of the adult New Jersey population. Surveillance for marker diseases may provide a simple, independent method of estimating the pre-AIDS population.

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.

Food-borne outbreak of Giardia lamblia.

An outbreak of giardiasis occurred following a family party for 25 persons. Nine who had eaten fruit salad became ill, compared with one who had not eaten the salad (Relative Risk = 7.4, 95% CI = 1.4, 169.3). The fruit salad preparer had a diapered child and a pet rabbit at home who were both positive for Giardia lamblia. This outbreak emphasizes the importance of good hygienic practices in food preparation and the possibility of domestic-animal-to-person transmission in Giardia outbreaks.

Lyme disease in New Jersey.

Lyme disease is a spirochetal infection endemic throughout New Jersey. Case reports from 1984 through 1986 suggest different high-risk groups and different disease severity than had been observed in earlier cases in the state. Both sexes now appear equally at risk, while younger age groups, particularly children less than ten years old, appear to be at increased risk. Mild disease is usual, although classic rheumatologic and neurologic complications can occur. Informal surveys suggest Lyme disease is under-reported by a factor of five- to tenfold in New Jersey. Early recognition by physician and patient is necessary for prompt treatment to reduce complications.

Epidemiology of congenital syphilis.

Between 1984 and 1987, the number of reported cases of congenital syphilis in New Jersey tripled. Findings indicate an increase in early syphilis among females of childbearing age living in areas of high syphilis morbidity, reflecting, possibly, lifestyle changes within populations already at risk for the disease. Future studies and interventions are needed.