[Subendocardial infarction on recovery from anesthesia]

A 57-year-old man without any history of coronary artery disease underwent total hip replacement for which a continuous lumbar epidural analgesia combined with general anesthesia was used. During the recovery from anesthesia, the patient developed sudden hypotension and ventricular fibrillation (Vf), followed by ST elevation (I, II, III, aVF and V2-V6) on ECG. A coronary angiography, which was performed 30 min after the onset of Vf, revealed both the total occlusion of proximal left anterior descending artery (LAD) and 25% stenosis of proximal right coronary artery. It seemed that coronary artery spasm had occurred during the emergence from anesthesia, and then the coronary spasm ceased in a minute or two, while thrombus was produced in proximal LAD. The patient recovered from the episode of myocardial ischemia after percutaneous transluminal coronary recanalization and intraaortic balloon pumping. This patient was operated again on 4th and 8th postoperative days uneventfully under general anesthesia (enflurane and nitrous oxide in oxygen).

[Midazolam as a premedicant for trigeminal nerve blocks]

Although patients with trigeminal neuralgia can be treated satisfactorily with nerve blocks, the block procedure is sometimes very painful and uncomfortable for them. To investigate the efficacy and adverse effects of midazolam as a premedicant for trigeminal nerve blocks, 19 patients were randomly assigned to receive either midazolam (0.05 mg.kg-1, n = 6), midazolam (0.1 mg.kg-1, n = 7), or saline/placebo (n = 6) before the block. The patients given midazolam (0.1 mg.kg-1) had a significantly lower incidence of recalling the block procedure and had complained of less discomfort when interviewed the following day. No serious adverse effects were observed in any patient given midazolam. Midazolam can be used safely as an effective premedicant for potentially uncomfortable procedures such as trigeminal nerve blocks.

Oral clonidine blunts the heart rate response to intravenous atropine in humans

Clonidine, recently introduced into anesthesia practice, may cause bradycardia. Whether this bradycardia is reversible with atropine is not known. Accordingly, we studied heart rate (HR) responses to intravenous atropine in 80 patients assigned randomly to either a control group, who received no medication (n = 20), or a clonidine group, who received oral clonidine of approximately 1.2 micrograms.kg-1 (n = 20), 2.5 micrograms.kg-1 (n = 20), or 5 micrograms.kg-1 (n = 20). All patients received incremental doses of atropine, 2.5, 2.5, and 5 micrograms.kg-1, at 2-min intervals (total dose 10 micrograms.kg-1). Positive chronotropic response to the cumulative atropine dose of 10 micrograms.kg-1 was attenuated significantly only in patients given clonidine 5 micrograms.kg-1 (7 +/- 1 beats per min, mean +/- standard error) when compared with those given smaller doses of clonidine (15 +/- 2, 16 +/- 2 beats per min) or no clonidine (19 +/- 2 beats per min) (P less than 0.05). To determine whether HR hyporesponsiveness to atropine induced by clonidine can be overcome by a larger dose of atropine, the authors studied 30 additional patients given clonidine 5 micrograms.kg-1 or no medication. In all patients not receiving clonidine (n = 15), HR increased by more than 20 beats per min when atropine of 15 micrograms.kg-1 was administered, whereas in only 5 patients (33%) receiving clonidine did the HR increase by 20 beats per min after atropine 15 micrograms.kg-1 (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary oedema after airway obstruction due to bilateral vocal cord paralysis

We report a case of pulmonary oedema which developed after airway obstruction due to bilateral vocal cord paralysis. The patient was a 52-yr-old woman undergoing craniotomy for an acoustic neuroma. Anaesthesia was uneventful. Spontaneous ventilation resumed after reversal of neuromuscular blockade. Following extubation she showed signs of airway obstruction and dyspnoea. The trachea was reintubated but she became hypoxic, PaO2-36 mmHg, produced pink frothy secretions and the x-ray was typical of pulmonary oedema. The oedema cleared within 24 hr. Tracheostomy was performed one week later as the cords were still fixed, but the latter had recovered by three months and the tracheostomy was closed. The cause of the cord paralysis is unknown but probably was a result of surgical trauma to the brain stem.

[Effects of enflurane on the elastic properties of frog skinned skeletal muscle fiber under relaxed and rigor conditions]

We studied the effects of enflurane on the elastic property of the mechanical skinned fiber prepared from M. Semitendinosus of bullfrog. Longitudinal and lateral elastic properties of the skinned fibers were measured under relaxed and rigor conditions to clarify the effects of enflurane on actomyosin complex. Under the rigor condition, enflurane did not change the lateral elasticity of the fibers, but enflurane decreased the longitudinal elasticity. On the other hand, under the relaxed condition, enflurane did not change the elasticity. The results suggest that enflurane probably decreases the force of binding of cross-bridges to actin, which is one of the factors to reduce the maximal force.

Detection of heat-stable enterotoxin in a cholera toxin gene-positive strain of Vibrio cholerae O1

DNA colony hybridization with a polynucleotide clonal DNA probe for heat-stable enterotoxin of Vibrio cholerae non-O1 (NAG-ST) was used to screen 197 isolates of V. cholerae O1. Under stringent hybridizing and washing conditions, one strain (GP156) reacted with the probe. The concentrated supernatant from V. cholerae O1 GP156, heated at 100 degrees C for 5 min, elicited fluid accumulation in the suckling mice and that could be completely neutralized by an anti-NAG-ST monoclonal antibody (mAb2F). The preparation from V. cholerae O1 GP156 also inhibited the binding of mAb2F to NAG-ST in a competitive ELISA. V. cholerae O1 GP156 was confirmed to possess a gene encoding cholera toxin (CT). These results indicate that a heat-stable enterotoxin is produced by certain strains of CT-producing V. cholerae O1.

Oral clonidine preanesthetic medication augments the pressor responses to intravenous ephedrine in awake or anesthetized patients

To evaluate the possible interaction between clonidine and ephedrine, the authors studied hemodynamic responses to intravenous ephedrine in 80 patients who received either clonidine pre-anesthetic medication of approximately 5 micrograms.kg-1 orally (n = 40) or no medication (n = 40). The patients were studied while they were either awake (n = 40) or anesthetized with enflurane and nitrous oxide in oxygen (n = 40). Hemodynamic measurements were made at 1-min intervals for 10 min after ephedrine 0.1 mg.kg-1 was injected as a bolus. Although the responses to ephedrine were always greater in anesthetized patients, the magnitudes of mean blood pressure increases in patients who received clonidine (10 +/- 8% for awake and 27 +/- 11% for anesthetized subjects, mean +/- standard deviation [SD]) were significantly greater (P less than 0.05) than in patients not receiving clonidine (4 +/- 5% for awake and 17 +/- 11% for anesthetized subjects). The enhanced pressor responses to ephedrine observed in both awake and anesthetized patients in the presence of clonidine may be attributed to increased catecholamine storage at sympathetic nerve endings due to clonidine, enhanced sensitivity of tissue receptors to which ephedrine binds, potentiation of alpha-adrenoceptor mediated vasoconstriction of both agents, or all of these. It is concluded that oral clonidine preanesthetic medication of 5 micrograms.kg-1 does augment rather than attenuate the pressor responses to intravenous ephedrine in patients both prior to and during general anesthesia.

Haemodynamic and cerebral blood flow alterations after reduction of increased cerebrospinal fluid pressure in dogs

To clarify some of the mechanisms for the hypotension that may occur after cranial decompression, the authors examined alterations in cerebral blood flow (CBF) and systemic and pulmonary haemodynamic variables when cerebrospinal fluid (CSF) pressure was increased and then suddenly reduced in eight anaesthetized dogs. After CSF pressure was elevated to 50-85 mmHg for two hours, CBF decreased from 46.3 +/- 4.4 to 31.6 +/- 8.5 ml.100 g-1.min-1 (mean +/- SD, P less than 0.01). Mean systemic arterial pressure (MAP), mean pulmonary artery pressure (MPAP), pulmonary artery wedge pressure (PAWP), and systemic vascular resistance index (SVRI) increased by 20 +/- 11 mmHg, 3.9 +/- 2.5 mmHg, 5.2 +/- 3.3 mmHg, and 1448 +/- 1377 dynes.sec.cm-5.m2 from baseline values, respectively (P less than 0.01). Rapid reduction of increased CSF pressure caused CBF to increase to 61.5 +/- 19.1 ml.100 g-1.min-1, whereas MAP, MPAP, PAWP, and SVRI decreased by 22 +/- 11 mmHg, 2.4 +/- 0.9 mmHg, 2.3 +/- 2.0 mmHg, and 1289 +/- 1237 dynes.sec.cm-5.m2 from previous values (P less than 0.01) at 30 min following the decompression. However, cardiac index and pulmonary vascular resistance index remained unchanged during the study period. The present animal data indicate that the decrease in MAP after decompression is mainly a result of a reduction in systemic vascular resistance.

[Venous air embolism following repositioning from sitting to supine]

We have experienced a patient in whom venous air embolism reoccurred, when the patient's position was changed from sitting to supine. A 40 year old male with Arnold-Chiari malformation underwent suboccipital decompression and cervical laminectomy under the sitting position. During surgery, three episodes of venous air embolism were detected by high pitched sound through precordial ultrasound Doppler stethoscope, an abrupt increase in pulmonary arterial pressure, a decrease in end-tidal carbon dioxide concentration; and a small amount of bubbled air was removed from the central venous catheter. At the end of surgery when the patient was turned to supine position, the signs of venous air embolism reappeared and 3 ml of bubbled air was also removed. This case suggests that there is some remaining air in the large veins of the upper part of the body once the air embolism has occurred during sitting position and thus we need to confirm that no air is left in the large veins before repositioning. We should be cautious of reoccurrence of venous air embolism whenever patient's position is changed.

[Hemodynamic effects of lung inflation during bilateral and single lung ventilation--a clinical investigation]

Hemodynamic changes during positive airway pressure ventilation is well known. To compare changes of hemodynamic variables during one-lung inflation with those during two-lung inflation, we studied the effects of lung inflation on hemodynamic changes in 15 anesthetized patients who were intubated endobronchially. When the airway pressure was increased from 0 cmH2O to 10, 20, 30 cmH2O, systolic pressure decreased gradually and central venous pressure increased during both two-lung and one-lung inflations (P less than 0.05). During one-lung inflation, the decrease in arterial pressure relative to apneic arterial pressure was significantly less than those during two-lung inflation at each level of airway pressure (P less than 0.05). During one-lung inflation, central venous pressure which was higher relative to apneic central venous pressure, and was less than that during two-lung inflation at 30 cmH2O (P less than 0.05). Heart rate was unchanged during both two and one-lung inflations compared with apneic heart rate. We conclude that during one-lung inflation, systolic pressure and central venous pressure are influenced less by the increased airway pressure than during two-lung inflation. The results indicate that during one lung ventilation, lungs inflated with clinically accepted levels of airway pressure do not depress the systemic circulation, but when the airway pressure during one-lung inflation (like a leak test) exceeded over 30 cmH2O, a significant depression of the systemic circulation occurs.

Effects of cocaine on pial arterioles in cats

We used the closed cranial window technique to observe the responses of pial arterioles to topical application of cocaine in 29 anesthetized cats. Alterations in arteriolar diameter were dependent on the concentration of cocaine applied. Cocaine dissolved in artificial cerebrospinal fluid at concentrations of 10(-8) or 10(-7) M was without effect. Concentrations of 10(-6) and 10(-5) M produced dilation (4.9 +/- 1.5% [mean +/- SEM] and 5.9 +/- 2.0%, respectively) in large arterioles (greater than 100 microns) but no significant change in the diameter of small arterioles (less than 100 microns). A concentration of 10(-4) M dilated both large and small arterioles (20.3 +/- 3.1% and 12.0 +/- 7.1%, respectively). Pretreatment with 1 mg/kg i.v. propranolol blocked the increase in pial arteriolar diameter after application of 10(-4) M cocaine and produced significant vasoconstriction in small arterioles (-8.3 +/- 3.1%). Cocaine produces vasodilation of cat cerebral arterioles. This effect appears to be mediated, at least in part, by mechanisms that depend on stimulation of beta-adrenergic receptors.

Clinical evaluation of clonidine added to lidocaine solution for epidural anesthesia

The effects of clonidine added to lidocaine solution used for epidural anesthesia were assessed in 92 women scheduled for surgery and premedicated with diazepam 10 mg po. Patients received 18 ml 2% lidocaine with clonidine 5 micrograms.ml-1 (group C-5, n = 26), with clonidine 10 micrograms.ml-1 (group C-10, n = 20), with epinephrine 5 micrograms.ml-1 (group E, n = 26), or plain (group P, n = 20). No significant difference in the number of segments of analgesia was found at any observation period among the four groups of patients. The decreases in mean blood pressure (BP) observed 20 min after epidural injection in those given clonidine (5 +/- 8% for C-5, 10 +/- 11% for C-10, mean +/- SD) were similar to those given plain lidocaine (7 +/- 12%) but significantly less than those given epinephrine (18 +/- 12%, P less than 0.01 vs. C-5 or P). The response of BP to ephedrine given for restoring BP during anesthesia was not attenuated in patients who received epidural clonidine. Heart rate (HR) decreased significantly in patients given clonidine 10 micrograms.ml-1 (7 +/- 8%, P less than 0.01), but not in those given clonidine 5 micrograms.ml-1, whereas HR increased significantly in those given lidocaine plain or with epinephrine (10 +/- 8% and 28 +/- 14%, respectively, P less than 0.01). The incidence of sinus bradycardia was similar among the four groups of patients. Significant differences were also observed in sedation score between clonidine groups and groups P or E; sedation appeared approximately 10-20 min after epidural injection in both clonidine groups.(ABSTRACT TRUNCATED AT 250 WORDS)

End-tidal carbon dioxide monitoring during awake blind nasotracheal intubation

STUDY OBJECTIVE

To test the usefulness of the end-tidal carbon dioxide monitor in facilitating awake blind nasotracheal intubation in patients with potentially difficult airways.

DESIGN

Randomized, controlled comparison of regimen.

SETTING

Inpatient surgery clinic at a university hospital.

PATIENTS

Sixty-one consecutive patients with potentially difficult airways.

INTERVENTIONS

After airway anesthesia with 4% lidocaine was administered to all patients, either fentanyl and diazepam (n = 30) or fentanyl alone (n = 31) was given intravenously before the awake blind nasotracheal intubation procedure.

MEASUREMENTS AND MAIN RESULTS

End-tidal carbon dioxide concentration, arterial blood pressure, heart rate, and arterial oxygen saturation (by pulse oximeter) were measured in each patient during the awake blind nasotracheal intubation procedure. The day after anesthesia and surgery, each patient was asked to assess the degree of discomfort experienced during the procedure. In 54 of 61 patients, the end-tidal carbon dioxide monitor facilitated awake blind nasotracheal intubation. End-tidal carbon dioxide was significantly higher in patients given both fentanyl and diazepam than in those given fentanyl alone (7.4% +/- 1.4% vs 5.9% +/- 0.9%, respectively; p less than 0.05), but no patient in either group recalled the awake intubation as extremely uncomfortable.

CONCLUSIONS

Monitoring of end-tidal carbon dioxide is useful and valuable in both facilitating blind nasotracheal intubation and avoiding profound hypoventilation.

[Evaluation of noninvasive monitoring of preoxygenation]

Administration of 100% oxygen before a "rapid-sequence" induction of anesthesia is recommended to prevent hypoxemia during induction. In the present study, we used a laser scattering analyzer to study the effectiveness of nitrogen washout from the lungs with oxygen wash into the lungs under two different preoxygenation regimens; 4 times of maximal breathing of 100% oxygen in one minute and normal tidal breathing of 100% oxygen for 3 minutes. The volunteers were healthy, ASA physical status 1, 22 to 33 years of age (26 +/- 3), 167 +/- 5 cm tall, and weighing 60 +/- 5 kg. Arterial blood saturation measured by a pulse oximeter was 97 while breathing 21% oxygen, and 99% while breathing 100% oxygen. Arterial oxygen tensions were 98 mmHg while breathing 21% oxygen, and over 480 mmHg while breathing 100% oxygen. Arterial carbon dioxide and end tidal carbon dioxide concentrations indicated that 4 time of maximal breathing in a minute leads to hyperventilation. The end-tidal oxygen concentration was not significantly different between before and after oxygen administration in two different regimens. End-tidal nitrogen concentration after tidal volume ventilation was lower than that of 4 breath in a minute. These results indicate that end-tidal nitrogen and oxygen could reflect arterial nitrogen and oxygen tensions during preoxygenation.

Hemodynamic status susceptible to slowing of heart rate during thermodilution cardiac output determination in anesthetized patients

To identify hemodynamic variables that might indicate susceptibility to slowing of heart rate (HR) and to mean arterial pressure (MAP) decrease caused by cold injectate during thermodilution (TD) cardiac output determination, we measured hemodynamic variables in 32 anesthetized patients undergoing major surgery. A total of 608 cardiac output determinations were evaluated for any relationship between the magnitude of HR decreases and basal hemodynamic variables. The magnitude of HR decrease was pronounced in low cardiac index (CI), low mean pulmonary artery pressure (MPAP), and high systemic vascular resistance index (SVRI). Although there was some decrease in MAP associated with cold injectate, neither changes in SVRI nor those in the other hemodynamic variables correlated with the decreases in MAP. These results suggest that decreased CI and MPAP associated with elevated SVRI may be more susceptible to slowing of HR during cardiac output determination by TD in anesthetized patients.

[The effects of a small dose of atropine upon sinus bradycardia during spinal anesthesia]

Positive or negative chronotropic effects of atropine and their magnitude are known to be determined by its dose given, concomitant sympathetic tone, and patient's age. Thus, the aim of the present study is to investigate the small effective dose of atropine for acceleration of heart rate in sedated bradycardic patients under spinal anesthesia, and to evaluate the relationship between the heart rate response to atropine and level of analgesia or patient's age. Significant increases in heart rate were observed in patients receiving intravenous atropine 4 micrograms.kg-1 (n = 21) or 6 micrograms.kg-1 (n = 35) except 2 micrograms.kg-1 (n = 18). However, there were wide variations in cardiac responses to atropine among patients in each group. Negative chronotropic responses to atropine were elicited in 10 (56%), 2 (9%), and 1 (3%) of the patients receiving 2 micrograms.kg-1, 4 micrograms.kg-1 and 6 micrograms.kg-1, respectively. Although there was no correlation between the heart rate response to each dose of atropine and the level of spinal anesthesia, the magnitude of positive chronotropic response to atropine of 6 micrograms.kg-1 related inversely with age. The present results suggest that atropine above 4 micrograms.kg-1 is required to accelerate the heart rate in most bradycardic patients under spinal anesthesia irrespective of the level of analgesia. However, it seems appropriate to administer atropine intravenously in a cumulative fashion, because of individual's variability including age in the chronotropic response to atropine.

Interaction between intravenous lidocaine and epinephrine on hemodynamics and plasma potassium homeostasis in dogs anesthetized with halothane

To delineate some clinical features of an accidental intravascular injection of local anesthetic solution containing epinephrine during the attempt of regional block, the interaction between intravenous lidocaine and epinephrine on hemodynamics and potassium homeostasis was investigated in halothane-anesthetized dogs using three types of combination of lidocaine and epinephrine. These included 1% plain lidocaine (10 mg/kg), 1% lidocaine-epinephrine solution (10 mg/kg-5 micrograms/kg) and epinephrine-normal saline solution (1:200,000, 5 micrograms/kg). Although lidocaine did not produce any changes in systemic or pulmonary hemodynamics, epinephrine and lidocaine-epinephrine solution produced transient multifocal premature ventricular contractions associated with huge hemodynamic changes. Lidocaine-epinephrine solution caused a 43% increase in mean arterial pressure, a 107% increase in mean pulmonary artery pressure and a 244% increase in pulmonary capillary wedge pressure (p less than 0.05). These changes did not differ from those observed following epinephrine. In contrast, stroke volume decreased significantly to 70% of control after lidocaine-epinephrine, while neither epinephrine nor lidocaine produced a significant change. Lidocaine did not affect plasma potassium concentration, whereas both epinephrine and lidocaine-epinephrine produced significant increase in plasma potassium concentration (K+; 2.0 +/- 0.7 mEq/l with epinephrine and 1.8 +/- 1.2 mEq/l with lidocaine-epinephrine), which subsequently decreased to below control.

Comparison of arterial baroreflex function in humans anesthetized with enflurane or isoflurane

To compare the depressive effects of isoflurane and enflurane on the arterial baroreflex function, we examined baroreflex control of heart rate during the entire course of clinical anesthesia. Isoflurane and enflurane were found to have similar depressive effects on the baroreflex control of heart rate when used in combination with N2O and O2. Suppression in the baroreflex sensitivity, defined by the slopes of regression line (change in msec of RR interval per mm Hg increase or decrease in systolic blood pressure) was from 7.1 +/- 3.9 to 1.8 +/- 0.7 msec/mm Hg in patients given isoflurane and from 7.8 +/- 4.3 to 3.0 +/- 1.9 msec/mm Hg in those given enflurane when evaluated by a pressor test (bolus IV phenylephrine). The slope of the depressor test (bolus IV nitroglycerin) also decreased from 4.7 +/- 2.8 to 1.9 +/- 1.5 msec/mm Hg with isoflurane and from 5.6 +/- 3.2 to 2.3 +/- 1.2 msec/mm Hg with enflurane. During surgery in which anesthetic concentration invariably needed to be increased, the suppression of the baroreflex sensitivity remained unchanged in both groups of patients. During recovery, the arterial baroreflex function in patients given isoflurane recovered more rapidly than that in patients given enflurane. This difference may be related to a more minor degree of suppression of isoflurane on the autonomic nervous system compared to enflurane.

Alteration of pulmonary oxygenation by pulmonary artery occluded pressure measurements in mechanically ventilated patients

A significant decrease in PaO2 occurs in some patients during PAOP measurements. To examine the incidence and the types of patients whose PaO2 decreases during PAOP measurements, we studied the changes of PaO2 in 101 anesthetized, mechanically ventilated adult patients. During a 2-min inflation of a PAC balloon, seven patients (6.9 percent) developed marked decrease in PaO2/FIo2 (more than 100 mm Hg). Neither age nor size of patients, decrease in end-tidal CO2, nor baseline value of PAP correlated with the decreases in PaO2. A decrease in PaO2/FIo2 (more than 50 mm Hg) was observed more frequently in female patients and in patients with cardiac disease, especially those whose PAP values were above normal. Although a significant decrease in PaO2 during PAOP measurements does not appear to occur often, our results suggest that the changes in PaO2 should be evaluated in patients with severely compromised pulmonary oxygenation.