Anesthetic modulation of the cardiovascular response to microlaryngoscopy. A comparison of propofol and methohexital with special reference to leg blood flow, catecholamines and recovery.

The modulating effects of propofol versus methohexital on the cardiovascular response to microlaryngoscopy were studied in 35 patients divided into four equal groups (one patient participated twice). Heart rate (HR), mean arterial blood pressure (MAP, cardiac output (CO; impedance cardiography), leg blood flow (LBF; occlusion plethysmography) and concentrations of arterial catecholamines were measured. After administration of atropine and fentanyl (2 micrograms.kg-1), anesthesia was induced by either an injection of propofol (2.0 mg.kg-1) followed by a low (6 mg.kg-1.h-1; n = 9) or a high (12 mg.kg-1.h-1; n = 9) dose propofol infusion or an injection of methohexital (1.5 mg.kg-1) followed by a low (5 mg.kg-1.h-1; n = 9) or a high (10 mg.kg-1.h-1; n = 9) dose methohexital infusion. The low methohexital infusion dose was insufficient to control MAP, which increased 41% during microlaryngoscopy compared to the awake state. The HR increased in all groups but the increase was most prominent in the low dose methohexital group. There were no statistically significant changes in CO in any group, whereas LBF increased consistently in all groups except in patients anesthetized with the low dose of methohexital. The increases of LBF in the propofol groups were intermediate and not dose dependent. The methohexital low dose group showed increases in norepinephrine levels compared to awake values and in epinephrine levels compared to the other groups. Propofol seems to differ from methohexital in modulation of peripheral vascular tone.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic gas exchange during aortocoronary bypass surgery using a double pump system and mechanical ventilation. A comparison between indirect calorimetry and invasive blood gas measurements using Fick's principle.

Oxygen uptake and carbon dioxide excretion during aorto-coronary bypass surgery were studied in seven patients by indirect calorimetry and compared to blood-gas based measurements. Medium-high dose fentanyl, droperidol and midazolam were used for maintaining anaesthesia. During the period of extracorporeal circulation no external oxygenator was used. Circulation was maintained by two pumps by-passing the left and right heart respectively and the patient's lungs were ventilated with O2/N2 using a Servo 900C ventilator. For indirect calorimetric measurements gas concentrations were analysed by Beckman instruments and gas volumes were measured by the Servo 900C ventilator. Oxygen uptake and carbon dioxide excretion decreased by 31% and 39%, respectively. For invasive measurements during extracorporeal circulation, arterial and venous blood gases and pump flow were used. Using pump flow instead of cardiac output when calculating oxygen uptake circumvented errors in thermodilution measurements. There was a good correlation (r = 0.88) between the invasive and the indirect calorimetric measurements. Further, there was a good correlation between naso-pharyngeal temperature and indirect calorimetric measurements of oxygen uptake (r = 0.87).

Validation of a system for measurement of metabolic gas exchange during anaesthesia with controlled ventilation in an oxygen consuming lung model.

An oxygen consuming lung model was used for evaluation and validation of a technique for metabolic gas exchange measurements during controlled ventilation. The technique comprised a Servo 900 C ventilator (Siemens) and separate oxygen and carbon dioxide analysers (Beckman). Measurements of oxygen consumption and carbon dioxide production were made either by measuring inspired and expired ventilation and gas fractions in these volumes or by measuring gas fractions and calculating expired ventilation from inspired by transformation (Haldane). Irrespective of the FIO2, measured values correlated well with lung model settings: measured values were within +/- 2% of simulated. When Haldane transformation was used with an FIO2 of 0.5 there was a significant underestimation of oxygen consumption. Carbon dioxide production values correlated well irrespective of the FIO2 used or method of measurement of ventilation volume. Metabolic gas exchange measurements by measuring both inspired and expired ventilation volumes may be used when inert gases are not in equilibrium, for example during nitrous oxide anaesthesia.

Methohexitone anaesthesia for microlaryngoscopy: circulatory modulation with metoprolol and dihydralazine.

Anaesthesia for microlaryngoscopy was induced and maintained with fentanyl 3 micrograms kg-1 and methohexitone (initial bolus of 1-1.5 mg kg-1 plus subsequent infusion of 4 mg kg-1 h-1). Suxamethonium was used to induce neuromuscular blockade. Twenty minutes before induction of anaesthesia, previously normotensive patients (n = 35), and patients with hypertension well controlled by beta-receptor antagonists (n = 16) were pretreated with metoprolol (M) 0.2 mg kg-1 i.v. and dihydralazine (DH) 0.2 mg kg-1 i.v., dihydralazine 0.2 mg kg-1 i.v. alone, or saline. Arterial pressure (AP) and heart rate (HR) were monitored: any arrhythmia and ST60-T changes were noted. After the methohexitone infusion was stopped, the times for emergence and full recovery were short (median 2 min 15 s and 5 min later, respectively). Pretreatment with M + DH abolished increases in AP and HR during endoscopy. Arrhythmias were observed in fewer pretreated patients than in controls (P less than 0.05). ST60-T changes in the ECG indicating myocardial ischaemia were found in two of 19 M + DH and in six of 21 saline-pretreated patients. One of these six patients developed a myocardial infarction. Pretreatment with dihydralazine alone attenuated the pressor response to microlaryngoscopy, but was associated with consistently high HR and an incidence of arrhythmias as well as ST60-T changes similar to that found after saline.