Enteral versus parenteral nutrition: effects on gastrointestinal function and metabolism.

The effects of total parenteral nutrition (TPN) versus enteral nutrition (TEN) were studied in 34 patients following major neurosurgery. Measurements were made of resting energy expenditure (REE), urea production rate (UPR), visceral proteins, parameters of liver and pancreas function, as well as gastrointestinal absorption. To predict nutritional status, nutritional index (NI) was calculated. UPR revealed no significant differences between the groups. After 12 days of TEN, however, synthesis of visceral proteins increased significantly. In addition, NI improved after TEN (p < 0.05), whereas it remained unchanged after TPN. Thrombocyte and lymphocyte counts rose predominately during enteral nutrition. Only in the TEN group was REE increased by 18% and Glasgow Coma Scale (GCS) enhanced from Day 6 on. Exogenous insulin demand was enhanced in the parenterally fed group, and bilirubin (p < 0.05), amylase (p < 0.05), and lipase (p < 0.01) rose significantly, as did gamma-glutamyl-transferase (p < 0.0005) and alkaline phosphatase (p < 0.0005). After 12 d of TPN, vitamin A absorption was significantly attenuated, indicating reduced fat absorption compared to TEN. Carbohydrate absorption did not show significant changes between the groups. Only during TPN did mean values of xylose absorption remain below the normal range. Therefore, enteral nutrition following neurosurgical procedures is associated with an accelerated normalization of nutritional status and an improved substrate tolerance. TEN opposes early postoperative absorption disturbances of the small intestine.

Effects of isoflurane, fentanyl, or thiopental anesthesia on regional cerebral blood flow and brain surface PO2 in the presence of a focal lesion in rabbits.

These studies were conducted to determine the effect of anesthetic drugs on tissue perfusion and O2 supply in the brain with focal cerebral edema. Using an open cranium preparation, we studied the effects of isoflurane (I; 1 minimum alveolar anesthetic concentration), of fentanyl (F; 0.5-1 microgram.kg-1 x min-1), or of thiopental (T; 32.5 mg.kg-1 x h-1) on regional cerebral blood flow (rCBF) and regional brain tissue PO2 in albino rabbits (n = 6 per group) with a focal brain lesion (cold injury). The doses of anesthetics were sufficient to suppress nociception. rCBF (H2 clearance) and tissue PO2 (multiwire surface electrode) were studied adjacent to and distant from the lesion. Cerebral hyperemia developed immediately after trauma in all groups, although the flow increase did not attain statistical significance. rCBF was subsequently reduced by about 25% in the vicinity of the lesion. Distant from the trauma, a continuing hyperemia (+30%) was later observed in animals with isoflurane, whereas rCBF was decreased then by 10%-20% in animals with fentanyl, or was unchanged with thiopental. Brain tissue PO2 was increased with isoflurane in areas distant from the lesion, but decreased with fentanyl. However, with thiopental, the PO2 level had already been lowered before trauma with a subsequent tendency toward normalization. The heterogeneity of the tissue PO2 in fentanyl anesthesia, as well as the increased frequency of hypoxic PO2 values with thiopental, might have resulted from microcirculatory disturbances. Thus, although isoflurane seemed to facilitate hyperemia with an increased O2 supply to the brain, fentanyl tended to induce the opposite response. Although these properties suggest the potential to manipulate perfusion and O2 supply in cerebral ischemia or hyperemia after head injury, the effects of such measures on intracranial pressure, neurologic status, and outcome have yet to be proven.

Interatrial pressure difference during inflation of pneumatic antishock garments and positive end-expiratory pressure ventilation.

Since an increase in the right atrial pressure (RAP) above the left atrial pressure (LAP) may then lead to paradoxical air embolism, the efficacy of pneumatic antishock garments (PASGs) and ventilation with positive end-expiratory pressure (PEEP) in preventing increases in the RAP above the LAP was investigated during neurosurgical procedures. We examined the RAP and pulmonary capillary wedge pressure (PCWP) of 25 patients during neurosurgery of the posterior fossa. Each set of measurements of PCWP and RAP included measurements during induction of anesthesia in the supine position and the seated position prior to surgery. The PCWP and RAP were recorded during PEEP = 0 cm H2O, PEEP = 10 cm H2O, or with PASG inflation to pressures ranging from 40 to 80 mm Hg. The RAP increased from 8 +/- 6 to 20 +/- 7 mm Hg (PASG) and to 11 +/- 5 mm Hg (PEEP) in the seated position without a significant (p >0.05) change in the PCWP-RAP difference under any of the above conditions. We conclude that PASGs are a safer and more effective means of raising the RAP than PEEP ventilation during seated neurosurgical procedures without the danger of paradoxical air embolism.

Effects of anaesthetic agents on cerebral blood flow and brain oedema from a focal lesion in rabbit brain.

Anaesthetic agents reduce cerebral metabolism and may impair coupling of cerebral blood flow and metabolism. We analyzed the effects of isoflurane (I) (1 MAC), fentanyl (F), thiopental (T) (32.5 mg/kg x hr) and alpha-chloralose (C) on rCBF and brain oedema formation after a focal cerebral injury (cold lesion) in rabbits (n = 6 per group). In the isoflurane group, angiotensin II (0.15 microgram/kg x min) was given to maintain blood pressure. rCBF of cerebral cortex was measured 3 times per hr by H2-clearance with needle electrodes placed at different distances to the lesion during 6 hrs after induction of trauma. Thereafter, samples of white matter were obtained near the focal lesions and from corresponding areas of the contralateral hemisphere for measurement of specific gravity (SG) by a linear density column (Percoll R). Blood pressure was 78, 86, 72, and 88 mmHg for groups I, F, T, and C, respectively. After induction of the lesion, hyperemia of approximately 1 hr was observed in all groups. This was most pronounced distant to the lesion. Close to the lesion rCBF remained unchanged in groups C and T, but fell significantly below control in I and F. The blood flow response distant to the trauma was characterized by a moderate increase (C), or no alteration (T), while isoflurane animals had a pronounced secondary hyperemia for about 3 hrs. With fentanyl, however, rCBF was markedly reduced in this area. SG of white matter close to the lesion decreased significantly to values of 1.032 g/cm3 (I, F, T), or 1.031 (C), indicative of oedema. Specific gravity was 1.034 in the contralateral hemisphere (control).(ABSTRACT TRUNCATED AT 250 WORDS)

Selection of patients for extra-intracranial arterial bypass surgery based on rCBF measurements.

Extracranial intracranial arterial anastomosis is gaining acceptance as a form of treatment in selected cases with ischemic cerebrovascular disease. To establish indications for this operation and to provide an objective assessment of postoperative results, regional cerebral blood flow (rCBF) studies were performed in 110 patients with cerebrovascular insufficiency considered for extra-intracranial bypass surgery. The 133Xe intracarotid injection method with 16 externally placed detectors was used for measuring rCBF. Postoperatively, rCBF was measured in 40 patients. From these results our present criteria for surgery have evolved. The probability of a good postoperative result is best in patients who showed focal cerebral ischemia or a moderate general reduction of CBF with an additional ischemic focus. The operation is contraindicated in patients with either normal or severely reduced CBF values (less than 60% of normal).

Abnormal cerebral vasomotor response in patients with brain tumors.

In 37 patients with intracranial tumros, regional cerebral blood flow was measured. The typical abnormalities are described and an attempt is made to correlate the blood flow with the histologic type of tumor. Moreover, the deranged cerebral vasomotor responses are demonstrated when the flow is measured during functional tests. The practical value of the method in patients with brain tumors is discussed.