Ventilatory and metabolic changes were measured in seven patients undergoing high efficiency hemodialysis using a cuprophane dialyzer and bicarbonate-containing dialysate. At an HCO3 concentration of 35 mEq/liter and a mean in vivo urea clearance of 3.6 ml/kg/min, hypoxemia was not detected during dialysis (PaO2 was 14.00 and 13.60 kPa before and during dialysis). The new findings, related to high efficiency bicarbonate dialysis, include a sustained rise in minute ventilation (VE, 6.1 to 6.8 liter/min, P less than 0.01), an increase in CO2 excretion (VCO2, 194 to 214 ml/min, P less than 0.05), and O2 consumption (VO2, 215 to 246 ml/min, P less than 0.05). The increment in VE and VCO2 was attributed to the high flux rate of bicarbonate while the rise in VO2 is likely the result of metabolic alkalosis. Arterial pH rose from 7.40 to 7.49 mm Hg and serum HCO3 increased from 23.8 to 29.2 mEq/liter, while pCO2 remained normal at 5.07 kPa throughout the study. The acid-base status of the blood changed from that of a metabolic acidosis to that of a respiratory acidosis across the dialyzer where the pH decreased from 7.47 to 7.41 and pCO2 rose from 5.31 to 7.72 kPa. These data indicate that a healthy ventilatory response is needed to excrete the excess CO2 generated during high efficiency bicarbonate hemodialysis. The significance and etiology of the elevated O2 consumption is undetermined.
In 22 patients undergoing elective surgery, adrenal function was assessed before and on the day of surgery. Patients receiving corticosteroid therapy but with a normal cortisol response to a corticotropin stimulation tcit (group II, n = 8) were not given hydroconisone on the day of operation. Their cortisol concentration increased in a manner similar to patients (group I, n = 8) who had never had corticosteroid treatment. The plasma cortisol concentrations in these two groups were less than in subjects (group III, n = 6) with an impaired cortisol response to corticotropin stimulation, who were given hydrocortisone 25 mg at the induction of anaesthesia followed by a continuous infusion of hydrocortisone 100 mg during the next 24 h. There were no clinical signs of circulatory insufficiency in any group. The low-dose hydroconisone therapy regimen is sufficient for substitution of adrenal function during surgery and in the early postoperative phase. It could lead to mild oversubstitution in patients with impaired adrenal insufficiency undergoing major surgery.
To evaluate the reliability of capnography in identifying esophageal intubation in the presence of a carbonated beverage in the stomach, we first investigated the amount of CO2 released from different carbonated beverages and antacids in a simulated stomach; next we measured the end-expired CO2 level during esophageal ventilation with a carbonated beverage in the stomachs of six swine. CO2 levels of approximately 20% were consistently observed in all carbonated beverages. The CO2 levels obtained with sodium bicarbonate, Maalox, and sodium citrate were 19.3%, 2.0%, and 0%, respectively. CO2 waveforms were observed during esophageal ventilation in five of six animals after intragastric administration of a carbonated beverage. An end-expired CO2 level of 2.5% or more was observed in two swine. The highest end-expired CO2 level measured was 5.3%. We conclude that although capnography is convenient and effective, it lacks all the attributes of an ideal monitor for detecting esophageal intubation.
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