Guidelines for the treatment of acidaemia with THAM.

THAM (trometamol; tris-hydroxymethyl aminomethane) is a biologically inert amino alcohol of low toxicity, which buffers carbon dioxide and acids in vitro and in vivo. At 37 degrees C, the pK (the pH at which the weak conjugate acid or base in the solution is 50% ionised) of THAM is 7.8, making it a more effective buffer than bicarbonate in the physiological range of blood pH. THAM is a proton acceptor with a stoichiometric equivalence of titrating 1 proton per molecule. In vivo, THAM supplements the buffering capacity of the blood bicarbonate system, accepting a proton, generating bicarbonate and decreasing the partial pressure of carbon dioxide in arterial blood (paCO2). It rapidly distributes through the extracellular space and slowly penetrates the intracellular space, except for erythrocytes and hepatocytes, and it is excreted by the kidney in its protonated form at a rate that slightly exceeds creatinine clearance. Unlike bicarbonate, which requires an open system for carbon dioxide elimination in order to exert its buffering effect, THAM is effective in a closed or semiclosed system, and maintains its buffering power in the presence of hypothermia. THAM rapidly restores pH and acid-base regulation in acidaemia caused by carbon dioxide retention or metabolic acid accumulation, which have the potential to impair organ function. Tissue irritation and venous thrombosis at the site of administration occurs with THAM base (pH 10.4) administered through a peripheral or umbilical vein: THAM acetate 0.3 mol/L (pH 8.6) is well tolerated, does not cause tissue or venous irritation and is the only formulation available in the US. In large doses, THAM may induce respiratory depression and hypoglycaemia, which will require ventilatory assistance and glucose administration. The initial loading dose of THAM acetate 0.3 mol/L in the treatment of acidaemia may be estimated as follows: THAM (ml of 0.3 mol/L solution) = lean body-weight (kg) x base deficit (mmol/L). The maximum daily dose is 15 mmol/kg for an adult (3.5L of a 0.3 mol/L solution in a 70kg patient). When disturbances result in severe hypercapnic or metabolic acidaemia, which overwhelms the capacity of normal pH homeostatic mechanisms (pH < or = 7.20), the use of THAM within a 'therapeutic window' is an effective therapy. It may restore the pH of the internal milieu, thus permitting the homeostatic mechanisms of acid-base regulation to assume their normal function. In the treatment of respiratory failure, THAM has been used in conjunction with hypothermia and controlled hypercapnia. Other indications are diabetic or renal acidosis, salicylate or barbiturate intoxication, and increased intracranial pressure associated with cerebral trauma. THAM is also used in cardioplegic solutions, during liver transplantation and for chemolysis of renal calculi. THAM administration must follow established guidelines, along with concurrent monitoring of acid-base status (blood gas analysis), ventilation, and plasma electrolytes and glucose.

Clinical potency of calcium channel blockers in asthma may be related to their inhibition of receptor-mediated phasic responses in vitro.

The calcium channel blockers (CCB) have been clinically effective in exercise-induced asthma. The completeness of protection with the CCB might be related specifically to inhibition of Ca2+ influx or release. To examine this hypothesis, the rank order of potency of inhibition of the CCB, nicardipine, diltiazem and verapamil on the steady-state and kinetic parameters of the phasic and tonic responses to the muscarinic receptor agonist carbachol (10 microM) and KCl (40 mM) in the intact isolated guinea-pig trachea was determined. The Ca2+ channel agonist Bay K 8644 was also examined for its effects on intracellular Ca2+. Nicardipine abolished the KCl response at both 0.1 microM and 1 microM concentrations. The amplitude of the KCl response was inhibited equally by 1 microM diltiazem (61% inhibition) and 1 microM verapamil (68% inhibition). The rate constant of onset of the KCl response was similarly inhibited 60% by diltiazem and 66% by verapamil. Nicardipine abolished the carbachol phasic response at the 1 microM concentration. The amplitude of the phasic response was inhibited equally by 0.1 microM nicardipine (61.3% inhibition), 1 microM diltiazem (64.5% inhibition) and 1 microM verapamil (71% inhibition). The rate constant of decay of the phasic response was inhibited equally by 0.1 microM nicardipine (43% inhibition) and 1 microM diltiazem (29% inhibition). The rate constant of onset of the phasic response was unaffected by nicardipine, diltiazem and verapamil. Only 1 microM nicardipine inhibited the amplitude and rate constant of onset of the tonic response. The only effect of Bay K 8644 (1 microM) was to increase the phasic response amplitude. The CCB demonstrate a similar order of potency for inhibition of the phasic responses and clinical efficacy of the CCB in exercise-induced asthma (nicardipine > verapamil > diltiazem).(ABSTRACT TRUNCATED AT 250 WORDS)

Intravenous fluid therapy in neurologic injury.

Cerebral autoregulation and the blood-brain barrier are two important mechanisms that attempt to preserve brain homeostasis. The function of either may be disrupted by injury. When autoregulation is impaired, blood pressure and hematocrit determine cerebral oxygen delivery. Injury to the blood-brain barrier impairs brain volume regulation and may contribute to cerebral edema. The choice of intravenous fluid influences cerebral blood flow, cerebral oxygen delivery, brain metabolism, and brain volume.

Deep venous thrombosis revealed during ultrasound-guided femoral nerve block.

Ultrasound imaging used to facilitate performance of a femoral nerve block also affords imaging of adjacent anatomical structures. Following a fracture of the femur, an ultrasound guided femoral nerve block (UGFNB) was performed to provide analgesia; this led to the incidental finding of a previously undiagnosed femoral vein thrombosis (DVT), resulting in a change in patient management before surgery. An inferior vena cava (IVC) filter was placed before intramedullary nailing of the fracture.

Chest radiograph interpretation skills of anesthesiologists.

OBJECTIVE: To assess the skills of anesthesiologists in the interpretation of chest radiographs. DESIGN: Randomized evaluation conducted among anesthesiologists and radiologists. SETTING: Postgraduate Assembly of the New York State Society of Anesthesiologists in 1999, and the Department of Radiology, New York University Medical Center. PARTICIPANTS: A total of 61 anesthesiologists (48 attending physicians; 13 residents); control group of 8 radiology residents (all participants volunteered). INTERVENTIONS: After completing a demographic survey, participants were asked to review a series of 10 chest radiographs. A brief clinical scenario accompanied each radiograph. No time limit was set for these interpretations. MEASUREMENTS AND MAIN RESULTS: The demographic characteristics of the anesthesiology participants included university faculty (46%), private group practitioners (41%), independent practitioners (11%), and 1 participant with an unspecified type of practice. Additional training among the participants included internal medicine (31%), surgery (19%), and pediatrics (3%); 34% did not specify any additional training. Of the participants, 92% were involved in cases requiring general anesthesia; 96% managed patients in the recovery room; and 34% managed patients in the intensive care unit. Of participants, 80% usually order chest radiographs, but only 42% interpret the films themselves. Misdiagnosed radiographs included pneumothorax by 11% of participants, free air under the diaphragm by 41%, bronchial perforation from a nasogastric tube by 28%, right mainstem intubation by 20%, superior vena cava perforation from a central venous catheter by 31%, normal film by 75%, negative pressure pulmonary edema by 16%, left lower lobe collapse by 80%, pulmonary infarction from a pulmonary artery catheter by 29%, and tension pneumothorax by 41%. Overall scores of the attending physicians were not significantly different from that of residents (p > 0.05). The control group of radiology residents scored significantly better (mean, 83.7; p = 0.009) than the anesthesia residents (mean, 62.8) and anesthesia attending physicians (mean, 62.5). CONCLUSION: Anesthesiologists are deficient in skills for the interpretation of chest radiographs. The skill level of university-based physicians is not greater than physicians in private practice, and skill level does not improve with level of training or experience. Most anesthesiologists rely on radiologists for interpretative results. Further training during the residency years may help improve diagnostic skills.

A rat sciatic nerve model for independent assessment of sensory and motor block induced by local anesthetics.

The purpose of this study was to develop a reliable model to independently quantify motor and sensory block produced by local anesthetics. The sciatic nerve was blocked in 52 rats by injecting 0.2 mL of 0.125%, 0.25%, 0.5%, or 0.75% bupivacaine (n = 13 for each concentration). Accurate needle placement was achieved using a nerve stimulator at 0.2 mA and 1 Hz. Ten control rats received 0.9% saline (n = 5) or sham nerve stimulation (n = 5). Motor block was assessed by measuring hindpaw grip strength with a dynamometer. Sensory block was determined by measuring hindpaw withdrawal latency from radiant heat. The intensity of both motor and sensory block measured at 30-min intervals was plotted against time until full recovery to obtain the area under the curve. Intergroup comparisons using analysis of variance showed increasing area under the curve with increasing concentrations of bupivacaine for motor blocks (P < 0.05 for all intergroup comparisons except 0.5% vs 0.75%) and sensory blocks (P < 0.05 for all intergroup comparisons). Normal saline or sham nerve stimulation did not result in any motor or sensory block.