Christopher W. Bryan-Brown

Nutritional aspects of body water dislocations in postoperative and depleted patients.

Measurements of plasma volume with 125I human serum albumin, extracellular water (ECW) with 82Br-minus, and total body water (TBW) with 3-H2O were made on 16 postoperative patients, 15 depleted patients, and three control subjects. Intracellular water (ICW) was calculated as the difference between TBW and ECW. The observed findings for the series as a whole showed no change in blood volume, an increase of 3.7 I in ECW, and a decrease of 1.5 I in ICW as compared to predicted values based on current weight. Compared to predicted values based on normal (pre-illness) weight, the observed body weight decreased 16% and ICW decreased 22%; this suggests that body weight consistently under-estimates the extent of nutritional depletion. Severe depletion seen in postoperative patients indicates that frequently earlier use of total parenteral nutrition would be beneficial. ICW was found to be the most reliable single index of moderate or severe nutritional depletion; errors in estimating normal values interfere with its use in mild depletion. The ratio of ECW:TBW best reflects distortion of body water composition; it is largely independent of weight, and is a more sensitive index than absolute values of ICW. Repeat measurements of body composition were made on 9 patients given total parenteral nutrition for an average period of 18 days. On the average, there was an ECW decrease of 1.8 I, a body weight increase of 2 kg, and an ICW increase of 3.2 I after parenteral nutrition. The increased ICW represents the repletion of half of the average initial deficit of 6.1 The initial ratio of ECW:TBW of 0.58 was reduced to 0.50, returning it about three-quarters of the way to the expected normal value of 0.48. Intravenous administration of 5% glucose as sole source of calories may be a factor in distortion of body water compartments.

Consumable oxygen: availability of oxygen in relation to oxyhemoglobin dissociation.

Oxygen delivery to the tissues, studied as oxygen availability, does not take account of the changes in oxyhemoglobin dissociation. Oxygen at a tension of less than 20 torr is considered relatively unavailable. This paper presents a clinical methodology for the analysis of oxyhemoglobin dissociation so that oxygen avail-ability can be mathematically modified by subtracting the calculated mixed venous content at a tension of 20 torr (consumable oxygen). Similar modification of the arterial oxygen content and oxygen utilization coefficient give more realistic indices of oxygen delivery. Examples are given to show how the use of these indices give a better understanding and quantification of the effects of changes in oxyhemoglobin dissociation characteristics on oxygen transport. The conventional estimations of oxygen avail-ability, arterial oxygen content and utilization coefficient do not change with shifts of the dissociation curve. A rightward shift of the curve gives a higher consumable oxygen, consumable arterial oxygen content, and a lower consumable oxygen coefficient, reflecting that more oxygen is available to the tissues before significant anaerobic metabolism is initiated.

Blood flow to organs: parameters for function and survival in critical illness

Tissues are usually considered as being supply-dependent (e.g., heart and brain) and supply-independent (e.g., splanchnic area, kidneys, skin, and resting muscle) for oxygen delivery. When cardiovascular function is compromised, circulatory compensations are aimed at maintaining supply-dependent tissues. In the long term, this leads to the possibility of an inadequate blood flow to supply independent tissues. The perfusion maintenance of all organs requires adequate cardiac output, blood volume, and arterial BP. When BP and cardiac output fail, regional perfusion diminishes. Although the human system tolerates anemia well, optimum Hct levels are probably between 30% to 40%. Inadequate perfusion can be supplemented partially by increasing the FIO2 on a temporary basis. Hyperoxic arterial oxygen tensions may cause maldistribution of blood flow within organs.

Tissue Blood Flow and Oxygen Transport in Critically Ill Patients

The theoretical and practical solutions to the problems of increasing oxygen transport are well understood. Unfortunately the quantitation of hypoxia, both as an absolute deficit and as a precise method of prognosis is not yet available. This may well be because regional hypoxia in a vital tissue cannot be mirrored in a total body measurement.In the low-flow state, oxygen delivery can be maintained by redistribution of cardiac output, reduction of oxygen uptake by ischemic tissue by reducing work load, by increasing oxygenation of the blood, or by decreasing the affinity of oxygen for hemoglobin. The latter provides for more oxygen to be delivered by a given amount of oxyhemoglobin before the tension falls to deleterious regions (about 20 torr). There is some evidence that pharmacologic doses of methylpredniso-lone may be beneficial in this respect.

Relationship of therapy to prognosis in critically ill patients.

A prognostic classification system was developed to help define overall therapeutic goals in critically ill patients with rapidly changing clinical status, in order: a) to force the conscious decision as to use or omission of heroic measures (including cardiopulmonary resuscitation); b) to promote dialogue between the primary physician, ICU staff and the family with respect to the treatment goals and likelihood of success; c) to prevent confusion in those charged with the overall care of the ICU; d) to encourage the development of a treatment plan based on a frequent reassessment of the patient which does not ask the ICU staff to render extraordinary care to a patient who has no reasonable hope for survival as a person; e) to minimize the medical legal risks; f) to dignify the entire ICU operation for the patient, his family, and the staff; and most importantly, g) to guarantee continual reassessment of each individual case with respect to the goals of treatment and the determination of that point in time when treatment should be stopped, when the goals are no longer attainable.

Cerebral edema unresponsive to conventional therapy in neurosurgical patients with unsuspected nutritional failure.

Three patients went into a neurasthenic decline during a prolonged recovery period following craniotomy. Consistent with the accepted therapy for cerebral edema, they were initially treated with osmotic diuretics, steroids, and fluid restriction. Body composition studies demonstrated expanded extracellular fluid and an intracellular deficit proportionally greater than weight loss. There was also hyponatremia, hypoalbuminemia, low blood volume, and intestinal malabsorption. Subsequent therapy was directed at reversal of nutritional failure. With return of the fluid compartment measurements to normal, patients made appropriate neurological recoveries. The rationale for postoperative treatment of chronic cerebral edema and generalized neural dysfunction by hyperalimentation is presented.

Toward a unified approach to psychological factors in the ICU.

The traditional mind-body distinctions are not appropriate in the ICU setting. Manifestations of psychological disturbance cannot be properly assessed or treated as a disorder of a single organ. The therapy of such behavioral symptoms should involve a multisystem failure approach.Each component system: external environment, sensory, response (motor), central nervous system and the pathophysiologic state of the patient himself (internal environment) is interdependent. Failure of one component can compromise the whole. It also seems clinically evident that treatment directed to-ward strengthening other components may enable the patient in failure to function adequately. Examples are given of how treatment of other systems enables the central nervous system to function more efficiently.With the therapeutic approach described, behavioral problems have been ameliorated and psychological disturbances are seldom a threat to medical management.

Cardiorespiratory Response to a New Isoquinoline Derivative in Critically III Patients

NC 7197, a new N-substituted tetrahydroisoquinoline derivative, was given in doses of 0.2 mg/kg body weight on 26 occasions to a series of 23 critically ill postoperative and posttraumatic patients who had been in moderate or severe degrees of shock. This agent was observed to improve pressure-flow and oxygen-transport variables, including increases in cardiac index, mean arterial pressure, central venous pressure, both left and right ventricular stroke work, central blood volume, systemic vascular resistance, oxygen availability, arteriovenous oxygen content difference, and oxygen consumption, and decreases in mean transit time and pulmonary vascular resistance. Previous studies on critically ill patients have suggested that these are the most commonly desired therapeutic actions for this type of patient. The agent has pronounced inotropic effect with minimal chronotropic effects, but with higher doses, chronotropic effects as well as alpha blocking effects may occur. The optimal effects may be obtained by adjusting the dose to an appropriate therapeutic range. It is concluded that, in the dose used, this agent produced both alpha and beta adrenergic actions in critically ill patients.