Executive summary and conclusions from the European Hydration Institute Expert Conference on human hydration, health, and performance.

On April 7-8, 2014, the European Hydration Institute hosted a small group of experts at Castle Combe Manor House, United Kingdom, to discuss a range of issues related to human hydration, health, and performance. The meeting included 18 recognized experts who brought a wealth of experience and knowledge to the topics under review. Eight selected topics were addressed, with the key issues being briefly presented before an in-depth discussion. Presented here is the executive summary and conclusions from this meeting.

Visual evoked potentials in response to pattern reversal in the cat cortex.

A model of the visually evoked potential (VEP) in the cerebral cortex of the cat after binocular stimulation by means of pattern reversal is presented. The VEP is defined by four components: P1, N1, P2 and N2, which appear during the 100 ms following the stimulus. This model is repeated for the majority of recording points although N1 and P2 do not appear to be homogeneous over the entire cortex. The variability of the VEPs recorded at the same point in different cats is lower than the one observed by means of stimulation with flashes. The possible origin of the four components in the primary visual area is presented as a hypothesis and a discussion is made of the differences which exist between the models proposed for flash and pattern reversal.

Visual evoked potentials in response to flashes in the cat cortex.

A model is presented of visually evoked potentials (VEPs) in the cerebral cortex of cats after binocular stimulation by means of flashes. The VEPs consist of four components: P1, N1, P2 and N2 which appear during the first 100 ms after the stimulation is produced. This model has been found in all the animals used in the experiments and is repeated with small variations at almost all the recording points. After studying the data obtained, a hypothesis is put forward for the possible origin of the four components in the primary visual area.

Effect of stimulus intensity on visually-evoked electrical brain activity maps in rabbit.

Stimulation by means of flashes is a commonly-used method in basic research into evoked potentials. Nevertheless, the different responses obtained at different luminous intensities, to which the inter-individual and intra-individual differences are added, determine the need to control this stimulus parameter for each experimental model. Maps of visually-evoked activity in the rabbit brain, obtained after monocular stimulation with flashes at different intensities of luminosity, are presented. Variation in the intensity of the luminous stimulus does not substantially affect the distribution of the electrical potential on the surface of rabbit brain described in previous articles.

[Maps of visually evoked brain electrical activity in rabbits]. / Mapas de la actividad eléctrica cerebral evocada visualmente en conejos.

A basic model of topographic distribution of the electric response visually evoked in rabbits by means of flashes (0.69 joules/flash) has been obtained. The model is composed of four main parts--N0, P1, N1 y P2--linked to the VI visual area and displayed on a dipole shaped. The dipole turnaround time oscillates between 20 and 25 ms. The use of electrical activity brain maps on the study of the PE makes it possible to notice the phenomenon simultaneousness, thus facilitating its interpretation. A multinomial interpolation method of continuous function has been used to perform the maps.

[Brain potential mapping by a new method of polynomial interpolation]. / Mapas de potenciales cerebrales por un nuevo método de interpolación polinomial.

The mapping of evoked cerebral activity is largely determined by the choice of the interpolation system used. When the number of electrodes is very large, practically any interpolation system is valid, but the geometrical and anatomical limitations imposed by the animals normally chosen for these experiments impede the use of a large number of electrodes; hence the overriding importance of a workable interpolation system. The polynomic interpolation method on the monomial structure is presented as valid, and compared with the pseudolineal interpolation method, which is more commonly used.

[Visual evoked potentials produced by monocular flash stimuli in the cerebral cortex of the rabbit. I. Typology]. / Potenciales evocados visuales producidos por estímulos monoculares de flash, en la corteza cerebral del conejo. I. Tipología.

Visually evoked potentials obtained from the cerebral cortex of pigmented rabbits in response to monocularly applied flashes were studied. In agreement with their morphology, the VEP of the cerebral cortex of the rabbit were classified in three fundamental types: the first one is characterized by the presence of a large positive wave, (P1), followed by a negative wave, (N1), and finally, another positive wave, (P2); these last two being of quite variable amplitudes. The second one is characterized by an initial large negative wave, (N1), followed by a usually large positive wave, (P2). Should a positive, (P1), appear previous to N1 there would be little amplitude. The third one is characterized by the presentation of an early negative wave, (N0), of variable amplitude. This is usually followed by a large wave, (P1). N1 and P2 are present but their amplitude is variable.

[Visual evoked potentials produced by monocular flash stimuli in the cerebral cortex of the rabbit. I. Typography]. / Potenciales evocados visuales producidos por estímulos monoculares de flash, en la corteza cerebral del conejo. II. Topografía.

The visually evoked potentials in the hemisphere contralateral to the stimulated eye in rabbit, can be described topographically as follows. While a positive wave (P1) begins forming in the anterior zones and in the V I binocular zone, the N0 wave, at times very large, is produced in a more occipital zone, which corresponds to the visual streak. Immediately afterwards, the positivity, P1, practically invades the whole of the hemisphere. After this, the N1 wave which is produced in the most posterior parts of the V I, begins forming. The whole phenomenon comes to an end when the P2 wave is generated in the most occipital zones.

The eyes as a portal of entry for hepatitis and other infectious diseases.

Surgeons who are exposed to cardiac, vascular and dialysis access, as well as the operating room staff, are at high risk for becoming infected with hepatitis. The virulence of this disease warrants maximum protection for these individuals. The eye is an exposed and documented portal of entry for blood and other potentially infectious debris. We strongly recommend the use of optically clear glasses or goggles in the operating room in order to minimize the danger of contacting a disabling and potentially lethal illness.

Massive symptomatic cystic hygroma confined to the thorax in early childhood.

A case of massive symptomatic cystic hygroma confined to the left hemithorax and mediastinum in a 21-month-old boy is reported. The symptoms were of increasing respiratory distress and cough with fever. The mass surrounded all of the major vascular and nervous structures of the mediastinum and left hemithorax and was attached to the pericardium. It was excised, and the postoperative course was complicated by prolonged chylothorax and malfunction of the left hemidiaphragm. Seven other reported symptomatic cases of cystic hygroma confined to the thorax in early childhood are reviewed. The hygromas tend to be large and their care typically is complex and complicated. Hemorrhage into the cysts is a frequent finding and likely contributes to the acute and progressive symptoms.

Hemodynamic and oxygen transport patterns in surviving and nonsurviving postoperative patients.

Invasive hemodynamic monitoring was performed on 220 critically ill surgical patients judged by clinical evaluation to have a high likelihood of surgical complications or death. Patients with markedly abnormal preoperative hemodynamic values were excluded from analysis. Data were separated into preoperative, intraoperative and postoperative time intervals and the mean value of each variable for each patient at each time period was computed. In comparison to survivors, the nonsurvivors generally had: (a) reduced myocardial performance as judged by lower cardiac index and left ventricular stroke work in the presence of high right and left ventricular filling pressures, (b) reduced pulmonary function (increased alveolar-arterial oxygen content difference and pulmonary shunt fraction), (c) pulmonary vasoconstriction (increased pulmonary artery pressure and pulmonary vascular resistance), and (d) decreased oxygen delivery despite maintenance of normal arterial blood gases and comparable hemoglobin values. Both survivors and nonsurvivors had vital signs usually within the normal range (until the terminal state of nonsurvivors).

Cardiorespiratory effects of pneumatic trousers in critically ill patients.

Although pneumatic antishock trousers (PT) are widely used in prehospital and emergency care, little is known about their cardiorespiratory effects in critically ill patients. To examine this issue, we measured hemodynamic and oxygen metabolism variables in ten critically ill patients. All patients were studied with PTs uninflated, after five minutes of PT inflation to 40 mm Hg, and five minutes after PT deflation. Significant increase in mean arterial pressure, systemic vascular resistance, and pulmonary artery pressures were present after PT inflation. No significant changes in cardiac index, stroke index, arterial or mixed venous blood gas values, or oxygen delivery were found. There was a downward trend in VO2 that was on the border of statistical significance. Regression analysis of cardiorespiratory variables on blood volume demonstrated no physiologic effects of external counterpressure in hypovolemic, hypervolemic, or normovolemic patients. We concluded that PT inflation increases BP through its effects on peripheral resistance. No significant autotransfusion effect was present, and there was a suggestive impairment in oxygen metabolism.

Sequential hemodynamic and oxygen transport abnormalities in patients with acute pancreatitis.

Physiologic abnormalities were evaluated by sequential hemodynamic and oxygen transport measurements in 33 patients with acute pancreatitis. The hypotensive crisis, which was defined as the lowest mean arterial pressure (MAP), was used as the common temporal reference point to align the data in a coherent fashion. The data of the 48-hour periods before and after the hypotensive crisis then were evaluated. The patients were divided into normotensive and hypotensive groups and the latter were divided into survivors and nonsurvivors to evaluate the severity of the disorder and to identify the patterns representative of survival and death. The physiologic abnormalities of the hypotensive patients include decreased systemic vascular resistance index (SVRI) and compromised cardiac function. The latter was demonstrated during the hypotensive episode by significantly reduced left ventricular stroke work index (LSWI), despite increases in heart rate (HR), central venous pressure (CVP), pulmonary capillary wedge pressure (WP), and cardiac index (CI). The normotensive group had increased oxygen consumption (Vo2), oxygen delivery (Do2), pulmonary shunt (Qsp/Qt), LSWI, normal SVRI, and high CI. The hypotensive nonsurvivors had lower MAP, LSWI, SVRI, Do, and hematocrit as well as higher pulmonary vascular resistance index (PVRI) and Qsp/Qt than did the survivors. These findings do not support myocardial depression as the primary cardiovascular abnormality in acute pancreatitis, but rather suggest the decreased vascular tone from flow maldistribution in the peripheral microcirculation limits tissue oxygenation in the face of increased metabolic requirements of the hypercatabolic state.

Sequential cardiorespiratory patterns associated with outcome in septic shock.

Sequential hemodynamic and oxygen transport monitoring was performed in 33 patients with septic shock to define physiologic patterns associated with outcome. Measurements taken over a 24-hour period prior to the hypotensive crisis, defined as the lowest initial mean arterial pressure (MAP) after a decrease of at least 30 mm Hg from initial normal values, were compared to those taken during the 24 hours thereafter. In the 24-hour period prior to the hypotensive crisis, the 19 survivors demonstrated significantly greater cardiac index (CI), left cardiac work index (LCWI), oxygen delivery (DO2), and oxygen consumption (VO2) than the 14 patients who died. No other significant differences were found between the two patient groups. When sequential cardiorespiratory patterns were examined, significant increases in CI, LCWI, left ventricular stroke work index (LVSWI), DO2, and VO2 were present in survivors as early as eight hours before the hypotensive crisis. The results presented in this study suggest that patterns of survival may be determined in critically-ill septic patients before shock, as defined by the initial hypotensive episode, develops.

Sequential cardiorespiratory patterns in septic shock.

Sequential hemodynamic and oxygen transport monitoring was performed in 33 patients with septic shock to define the temporal pattern of physiologic events. Measurements taken over a 24-h period before the hypotensive crisis, defined as the lowest initial mean arterial pressure (MAP), were compared to those taken during the 48 h thereafter. In the 24-h period before the hypotensive crisis, there were increases in cardiac index (CI), central venous pressure (CVP), pulmonary capillary wedge pressure (WP), pulmonary vascular resistance index (PVRI), and pulmonary shunt (Qsp/Qt), but decreases in MAP, systemic vascular resistance index (SVRI) and oxygen delivery (Do2). When sequential cardiorespiratory patterns were examined, oxygen consumption (VO2) fell transiently to significantly low values 12 h before as well as at the time of the hypotensive crisis. SVRI fell and CI rose to values significantly different from normal in the 4 h before the low MAP. During the subsequent 48 h after the hypotensive crisis, CI, CVP, WP, PVRI and Qsp/Qt remained elevated. Values for MAP, SVRI, DO2, and VO2 were significantly reduced. These results demonstrate the existence of antecedent cardiorespiratory alterations that precede the hypotensive episode in septic shock and suggest that flow maldistribution in the systemic circulation is an early event with possible pathogenic significance.