Effects of nicardipine and diltiazem on the bispectral index and 95% spectral edge frequency

BACKGROUND AND OBJECTIVE

Previous studies have shown that L-type voltage-sensitive Ca2+ channel blocking agents increased and the L-type Ca2+ channel activator Bay K 8644 reduced the general anaesthetic potency in animals. As the bispectral index correlates with the depth of sedation, we examined whether L-type Ca2+ channel blocking agents affect the bispectral index.

METHODS

Thirty hypertensive patients (systolic arterial pressure >160 mmHg) presenting for total intravenous anaesthesia with propofol, fentanyl and ketamine were recruited. Bispectral index monitoring was commenced directly the patients arrived in the operating theatre. All patients were given either nicardipine or diltiazem intravenously at the discretion of the anaesthesiologist in charge.

RESULTS

Twenty-three and seven patients received nicardipine or diltiazem, respectively. The bispectral index level (mean (95% confidence interval)) did not change with either drug. In the nicardipine group, the bispectral index at 0, 5, 10 and 15 min was 55 (52-58), 55 (51-59), 55 (52-59) and 56 (53-59), respectively. In the diltiazem group, values were 59 (48-71), 60 (51-70), 61 (52-71) and 61 (50-72), respectively. Both L-type Ca2+ channel blocking agents significantly decreased arterial pressure.

CONCLUSIONS

Clinical doses of nicardipine and diltiazem do not alter the bispectral index during general anaesthesia.

Differential effects of thiopental on methacholine- and serotonin-induced bronchoconstriction in dogs

BACKGROUND

Thiopental sometimes causes bronchospasm during induction of anaesthesia. In addition, we have reported previously that thiopental produced transient bronchospasm, which was blocked by atropine pretreatment, and worsened histamine-induced bronchoconstriction in dogs. Previous in vitro reports suggest that synthesis of contractile cyclooxygenase products, such as thromboxane A(2), may be involved in the mechanism of bronchospasm. However, the in vivo spastic effects have not been defined comprehensively.

METHODS

Twenty-seven mongrel dogs were anaesthetized with pentobarbital. Bronchoconstriction was elicited with methacholine (0.5 microg kg(-1)+5.0 microg kg(-1) min(-1); Mch group, n=7) or serotonin (10 microg kg(-1)+1 mg kg(-1) h(-1); 5HT group, n=20), and assessed as percentage changes in bronchial cross-sectional area (BCA, basal=100%) using a bronchoscope. In the 5HT group, dogs were subdivided into four groups of five each: S-5HT, I-5HT, 5HT-S and 5HT-A. In the S-5HT and I-5HT groups, 30 min before serotonin infusion dogs were given saline and indomethacin respectively at 5 mg kg(-1) i.v. In all groups, 30 min after bronchoconstrictor infusion started, dogs were given thiopental at doses between 0 (saline) and 20 mg kg(-1). In the 5HT-S and 5HT-A groups, dogs were given saline or atropine 0.2 mg kg(-1) i.v. 5 min after thiopental 20 mg kg(-1).

RESULTS

Methacholine and serotonin reduced BCA by about 50 and 40% respectively. Thiopental 20 mg kg(-1) increased and decreased BCA by about 20 and 10% in the Mch and 5HT groups respectively. Indomethacin and atropine did not attenuate the potentiation of serotonin bronchoconstriction produced by thiopental.

CONCLUSION

The present study indicates that thiopental may attenuate or worsen bronchoconstriction induced by muscarinic or serotonin receptor stimulation, respectively. The synthesis of contractile cyclooxygenase products and cholinergic stimulation may not be involved in the contractile effect of thiopental on serotonin bronchoconstriction.

Effects of three different L-type Ca2+ entry blockers on airway constriction induced by muscarinic receptor stimulation

BACKGROUND

The crucial role of L-type Ca(2+) channels in airway smooth muscle contraction suggests that these channels could be an important therapeutic target. There are three separate drug binding sites on this channel: those for dihydropyridines, benzothiazepines and phenyl alkylamines. In this study, we examined the effects of the dihydropyridines nifedipine and nicardipine, the benzothiazepine diltiazem, and the phenylalkylamine verapamil on airway constriction.

METHODS

Tension of guinea-pig tracheal strips was measured isometrically in vitro with a force displacement transducer. Strips were precontracted with carbachol 10(-7) M with or without 4-aminopyridine 10(-3) M, a voltage-sensitive K(+ )channel blocker. Then, nifedipine 10(-8)-10(-4) M, diltiazem 10(-8)-3 x 10(-4) M or verapamil 10(-8)-3 x 10(-4) M was added cumulatively to the organ bath (n=6 each). The bronchial cross-sectional area of pentobarbital-anaesthetized dogs was assessed using a bronchoscopy method. Bronchoconstriction was elicited with methacholine 0.5 micro g kg(-1) plus 5 micro g kg(-1) min(-1), and then nicardipine 0-1000 micro g kg(-1), diltiazem 0-3000 micro g kg(-1) or verapamil 0-3000 micro g kg(-1) were given i.v. (n=7 each).

RESULTS

In the in vitro experiments, nifedipine and diltiazem fully reversed carbachol-mediated tracheal contraction with logIC(50) values of 4.76 (SEM 0.22) (mean 17.5 micro M) and 4.60 (0.33) (mean 24.8 micro M), respectively. Although verapamil 10(-6)-10(-4) M reversed the contraction by 87.2%, strip tension re-increased by 18.1% following maximal relaxation with verapamil 3 x 10(-4 )M. This re-increase was almost fully abolished by pretreatment with 4-aminopyridine. In the in vivo experiments, nicardipine and diltiazem dose-dependently reversed methacholine-induced bronchoconstriction, with logID(50) values of 3.22 (0.05) (mean 0.60 mg kg(-1)) and 1.85 (0.32) (mean 14.0 mg kg(-1)), respectively. Verapamil worsened methacholine-induced bronchoconstriction.

CONCLUSIONS

Although supraclinical doses of dihydropyridines and benzothiazepines can produce airway relaxant effects, these agents are unlikely to be used in the treatment of bronchoconstriction. In addition, verapamil may aggravate airway constriction.

Spasmolytic effects of colforsin daropate on serotonin-induced pulmonary hypertension and bronchoconstriction in dogs

BACKGROUND

We have previously found that agents increasing intracellular cAMP levels of smooth muscles, such as PDE3 inhibitors, aminophylline and prostaglandin E1, produce both bronchodilation and pulmonary vasodilation in serotonin-induced pulmonary hypertension and bronchoconstriction models. In the present study we have simultaneously evaluated the spasmolytic effects of colforsin daropate, a novel forskolin derivative, on serotonin-induced pulmonary hypertension and bronchoconstriction.

METHODS

Ten mongrel dogs were anesthetized with pentobarbital. The pulmonary hypertension and bronchoconstriction were elicited with serotonin (10 microg/kg + 1 mg x kg(-1) x h(-1)) and assessed as percentage changes in pulmonary vascular resistance (PVR) and bronchial cross-sectional area (BCA) (basal = 100%). Initially, the relaxant effects of colforsin daropate (0-300 microg/kg) were determined. The PVR and BCA were assessed before and 30 min after serotonin infusion began and 5 min after each dose of colforsin daropate. To determine whether colforsin daropate-induced relaxation is independent of plasma catecholamine, propranolol 0.4 mg/kg was given following colforsin daropate 300 microg/kg i.v.

RESULTS

Colforsin daropate reversed both pulmonary hypertension and bronchoconstriction dose-dependently: -logED50 (95% confidence intervals, mean ED50) for pulmonary hypertension and bronchoconstriction 5.44 (5.08-5.80, 3.6 microg/kg) and 4.90 (4.06-5.20, 12.5 microg/kg), respectively. However, colforsin daropate (>or= 30 microg/kg) produced a more pronounced systemic than pulmonary vasodilation. Although colforsin daropate (>or= 30 microg/kg) significantly increased plasma catecholamines, propranolol did not reverse the relaxant effects.

CONCLUSIONS

Colforsin daropate may attenuate bronchoconstriction and pulmonary hypertension. In addition, as beta-blockade did not change the attenuation, the relaxant effects may be independent of plasma catecholamines.

Unventilated airway is time-dependently constricted in paralyzed dogs

BACKGROUND

Apnea has been reported to produce bronchoconstriction and to cause hypoxia, hypercapnia, and modulation of vagal afferent nerves, which also change airway tone. In this study, the authors determined the mechanism of apnea-induced bronchoconstriction.

METHODS

Twenty-eight dogs anesthetized and paralyzed were assigned to four groups (n = 7 each): apnea after artificial ventilation with 50% and 100% O2 groups (apnea-50% O2 and apnea-100% O2 groups, respectively), an apnea plus vagotomy group (fraction of inspired oxygen [FiO2] = 1.0), and a one-lung ventilation group (FiO2 = 1.0). The trachea was intubated with a single- or double-lumen tube in the three apnea groups or the one-lung ventilation group, respectively. The bronchial cross-sectional area (BCA) was assessed by the authors' bronchoscopic method. In the apnea-100% O2 and apnea plus vagotomy groups, a respirator was turned off for 5 min to produce apnea. In the apnea-50% O2 group, apnea was produced for 3 min. In the one-lung ventilation group, the right lumen was blocked for 5 min, and 15 min later, the left lumen was blocked for 5 min. BCA, arterial oxygen tension (PaO2), and arterial carbon dioxide tension (PaCO2) were assessed every minute.

RESULTS

The BCA in intact dogs time-dependently decreased by approximately 20% and 40% at 3 and 5 min after apnea started, respectively, whereas they did not in vagotomized dogs. In the apnea-50% O2 and apnea-100% O2 groups, bronchoconstriction could occur without hypoxemia, although hypercapnia was observed in all dogs. In the one-lung ventilation group, despite the fact that PaCO2 increased by only 2 mmHg without hypoxemia, unventilated BCA time-dependently decreased by 33.6 +/- 10.3%, whereas ventilated BCA did not.

CONCLUSION

The current study suggests that the unventilated airway may constrict spontaneously. In addition, the airway constriction could be vagally mediated but not due to hypoxia and hypercapnia.

The relationship between pneumatic tourniquet time and the amount of pulmonary emboli in patients undergoing knee arthroscopic surgeries

Near-fatal pulmonary embolism can occur immediately after tourniquet release after orthopedic surgeries. In this study, we determined the relationship between tourniquet time and the occurrence of pulmonary emboli in 30 patients undergoing arthroscopic knee surgeries, by using transesophageal echocardiography. The right atrium (RA) was continuously monitored by transesophageal echocardiography, and the number of emboli present was assessed with the following formula: Amount of emboli = 100 x [(total embolic area in the RA after tourniquet release) - (total area of emboli or artifact in the RA before tourniquet release)]/(RA area). The area was assessed 0-300 s after tourniquet release by using image-analysis software. The peak amount of emboli appeared approximately 50 s after tourniquet release. In addition, there was a significant correlation between amount of emboli (Ae [%]) and tourniquet time (Ttq [min]): (Ae = 0.1 x Ttq - 1.0, r = 0.795, P < 0.01). This study suggests that acute pulmonary embolism may occur within 1 min of tourniquet release and that the number of emboli is dependent on Ttq.

A comparison of the relaxant effects of olprinone and aminophylline on methacholine-induced bronchoconstriction in dogs

IV aminophylline, a nonselective phosphodiesterase (PDE) inhibitor, is often used to treat an asthma attack during anesthesia. However, in some instances, aminophylline-resistant attacks are observed. Selective PDE3 inhibitors are now clinically available and have been reported to produce bronchodilation. Thus, we compared the relaxant effects of olprinone, a novel PDE3 inhibitor, and aminophylline on methacholine-induced bronchoconstriction. Dogs were anesthetized with pentobarbital. Bronchoconstriction was elicited with methacholine (0.5 microg/kg + 5.0 microg. kg(-1). min(-1)) and assessed as percentage of changes in the bronchial cross-sectional area (BCA; basal = 100%) monitored by bronchoscope. Initially, the relaxant effects of olprinone (n = 8; 0-1000 microg/kg) and aminophylline (n = 8; 0-50 mg/kg) were compared. The bronchial cross-sectional areas were assessed before and 30 min after methacholine infusion began and 5 min after each dose of olprinone or aminophylline. We then determined whether propranolol (0.4 mg/kg) reversed the relaxation induced by olprinone (1000 microg/kg) and aminophylline (50 mg/kg). Olprinone and aminophylline dose-dependently antagonized bronchoconstriction by 56.2% +/- 21.3% (SD) and 68.0% +/- 30.3% with -log 50% effective dose (mean) of 4.80 +/- 0.38 (15.8) microg/kg and 1.96 +/- 0.42 (10.9) mg/kg, respectively. Aminophylline 50 mg/kg significantly increased plasma epinephrine, whereas olprinone did not. In addition, propranolol significantly reduced aminophylline-induced relaxation, but not olprinone-induced relaxation. Therefore, the relaxant effects of olprinone are independent of plasma epinephrine, whereas aminophylline effects may partially result from increased circulating concentrations of epinephrine.

IMPLICATIONS

We compared the relaxant effects of olprinone and aminophylline on methacholine-induced bronchoconstriction in dogs. The relaxant effects of olprinone are independent of plasma epinephrine, whereas the aminophylline effects may be partly caused by an increase in plasma epinephrine.

Use of olprinone, a phosphodiesterase III inhibitor, in an asthmatic patient

Phosphodiesterase (PDE) III exists in airway smooth muscles. In addition, PDEIII inhibitors have been suggested to relax airway smooth muscle by increasing intracellular cAMP concentrations. We report a successful use of olprinone, a PDEIII inhibitor, for treatment of an asthmatic attack. A 15-year-old male patient treated with oral theophylline 400 mg x d(-1) was anesthetized with propofol, fentanyl and ketamine for knee joint surgery. Immediately after tracheal intubation, an asthma attack occurred with peak airway pressure (Paw)>40 cmH2O. Thus, propofol 20 mg was additionally given to increase anesthetic depth, and Paw gradually decreased to 30 cmH2O. In addition, we started monitoring bronchial cross-sectional area using a superfine fiberoptic bronchoscopic method previously reported. However, as Paw did not further decrease for 30 min, olprinone was intravenously infused (10 microg x kg(-1) x 10 min(-1) + 0.3 microg x kg(-1) x min(-1), total 5 mg). Olprinone infusion rapidly decreased peak Paw from 30 cmH2O to 24 cmH2O and increased bronchial cross-sectional area by 50%. These findings suggest that olprinone produced bronchodilation.

[Combination of acute normovolemic hemodilution technique with preoperative autologous blood donation prevented allogeneic blood transfusion against 4000 g surgical blood loss in a patient undergoing left partial nephrectomy]

A 41-year-old male patient with well-controlled hypertension underwent a partial nephrectomy under total intravenous anesthesia with propofol, fentanyl and ketamine. To avoid allogeneic blood transfusion, preoperative autologous blood donation (400 g) a week before the surgery and acute normovolemic hemodilution (800 g) after induction of anesthesia were performed. As surgical blood loss was more than 4000 g, blood hemoglobin (Hb) level decreased to 6.4 g.dl-1. However, as intraoperative hemodynamics was relatively stable with no ischemic changes in ECG and arterial blood gas analysis did not show metabolic acidosis, autologous blood transfusion was withheld till hemostasis had been done. After returning the autologous blood, Hb increased to 9.4 g.dl-1. On the 2nd postoperative day, Hb decreased to 7.6 g.dl-1. As the patient's vital signs did not show any severe complications, blood transfusion was not performed. Then, the Hb level increased gradually to 13.9 g.dl-1, 3 month later without allogenic blood transfusion. In addition, any postoperative complications by low Hb level were not recognized so far. This case suggests that combination of autologous transfusion techniques may be effective to avoid allogeneic blood transfusion even against massive hemorrhage. However, to avoid disadvantage of these technique, we should always evaluate preoperative patient conditions.

Comparison of relaxant effects of propofol on methacholine-induced bronchoconstriction in dogs with and without vagotomy

Propofol has been suggested to have in vivo airway relaxant effects, although the mechanism is still unclear. In this study, we determined whether propofol could antagonize methacholine-induced bronchoconstriction and determined whether vagotomy modifies this relaxant effect. Fourteen mongrel dogs anaesthetized with pentobarbital and pancuronium were assigned to a control group (n=7) and a vagotomy group (n=7). The trachea was intubated with a special endotracheal tube that had a second lumen for insertion of the bronchoscope. Bronchial cross-sectional area, which was monitored continuously through the bronchoscope, was measured with image analysis software. Bronchoconstriction was elicited with methacholine (0.5 microg kg(-1) + 5.0 microg kg(-1) min(-1)) until the end of the experiment. Thirty minutes after the start of methacholine infusion, propofol 0, 0.2, 2.0 and 20 mg kg(-1) was administered. Changes in bronchial cross-sectional area were expressed as percentages of the basal area. Plasma concentrations of propofol and catecholamine were measured by high-performance liquid chromatography. Maximal inhibition (bronchoconstriction = 0%, baseline = 100%) and IC50 (concentration producing 50% inhibition of maximal effect) produced by propofol was obtained from each concentration-response curve using a curve-fitting program. Methacholine decreased bronchial cross-sectional area to 49.3% (95% confidence interval 38.5-60.1%) and 45.3% (34.8-55.7%) of the baseline value. Propofol 20 mg kg(-1) significantly reversed this effect: bronchial cross-sectional area was reduced to 77.8% (66.2-89.6%) and 75.9% (64.0-87.9) in the control and vagotomy groups respectively. The two groups did not differ significantly in the maximal inhibitory effect of propofol [control group, 61.1% (46.3-75.9%), vagotomy group, 64.2% (40.1-88.3%)] or pIC50 [control group 5.03 (4.55-5.51), vagotomy group 4.86 (4.49-5.24)]. Therefore, the relaxant effects of propofol on methacholine-induced bronchoconstriction may not be mediated centrally. Propofol may relax airway smooth muscles directly or through the peripheral vagal pathway.