Laryngoscopy and tracheal intubation in the head-elevated position in obese patients: a randomized, controlled, equivalence trial

BACKGROUND

The proper positioning of patients before direct laryngoscopy is a key step that facilitates tracheal intubation. In obese patients, the 25 degree back-up or head-elevated laryngoscopic position, which is better than the supine position for tracheal intubation, is usually achieved by placing blankets or other devices under the patient's head and shoulders. This position can also be achieved by reconfiguring the normally flat operating room (OR) table by flexing the table at the trunk-thigh hinge and raising the back (trunk) portion of the table (OR table ramp). This table-ramp method can be used without the added expense of positioning devices, and it reduces the possibility of injury to the patient or providers that can occur during removal of such devices once tracheal intubation is achieved. In this study, we sought to determine if the table-ramp method of patient positioning was equivalent to the blanket method with regard to the time required for tracheal intubation.

METHODS

Eighty-five adults with a Body Mass Index >30 kg/m(2), scheduled for elective surgery, consented to participate in this prospective randomized equivalence study conducted in a teaching hospital. The randomization scheme used permuted blocks with subjects equally allocated to be positioned using either the blanket method or the table-ramp method. The end-point in either case was to achieve a head-elevated position, where the patient's external auditory meatus and sternal notch were in the same horizontal plane. Although all patients were positioned by the same anesthesiologist, laryngoscopy and tracheal intubation were performed by trainees with various levels of expertise. Standard i.v. induction and tracheal intubation techniques were used. The time from loss of consciousness to the time after tracheal intubation when end-tidal CO(2) was detected was recorded. The effectiveness of mask ventilation and quality of laryngeal exposure were also noted.

RESULTS

The mean time (SD) to tracheal intubation was 175 (66) s in the blanket group, as compared to 163 (71) s in the table-ramp group. Assuming the bounds for equivalence are -55,55 s, our study found a 95% confidence interval of -36.22, 13.52 s using two one-sided tests for equivalence corresponding to a significance level of 0.05. There was no difference in the number of attempts at laryngoscopy (P = 0.21) and tracheal intubation (P = 0.76) required to secure the airway between the two groups.

CONCLUSIONS

Before induction of anesthesia, obese patients can be positioned with their head elevated above their shoulders on the operating table, on a ramp created by placing blankets under their upper body or by reconfiguring the OR table. For the purpose of direct laryngoscopy and tracheal intubation, these two methods are equivalent.

Modulation of Ca2+ Channels by Heterologously Expressed Wild-Type and Mutant Human μ-Opioid Receptors (hMORs) Containing the A118G Single-Nucleotide Polymorphism

The most common single-nucleotide polymorphism (SNP) of the human μ-opioid receptor (hMOR) gene occurs at position 118 (A118G) and results in substitution of asparagine to aspartate at the N-terminus. The purpose of the present study was to compare the pharmacological profile of several opioid agonists to heterologously expressed hMOR and N-type Ca2+ channels in sympathetic neurons. cDNA constructs coding for wild-type and mutant hMOR were microinjected in rat superior cervical ganglion neurons and N-type Ca2+ channel modulation was investigated using the whole cell variant of the patch-clamp technique. Concentration–response relationships were generated with the following selective MOR agonists: DAMGO, morphine, morphine-6-glucuronide (M-6-G), and endomorphin I. The estimated maximal inhibition for the agonists ranged from 52 to 64% for neurons expressing either hMOR subtype. The rank order of potencies for estimated EC50 values (nM) in cells expressing wild-type hMOR was: DAMGO (31) ≫ morphine (76) ≅ M-6-G (77) ≅ endomorphin I (86). On the other hand, the rank order in mutant-expressing neurons was: DAMGO (14) ≫ morphine (39) ≫ endomorphin I (74) ≅ M-6-G (82), with a twofold leftward shift for both DAMGO and morphine. The DAMGO-mediated Ca2+ current inhibition was abolished by the selective MOR blocker, CTAP, and by pertussis toxin pretreatment of neurons expressing either hMOR subtype. These results suggest that the A118G variant MOR exhibits an altered signal transduction pathway and may help explain the variability of responses to opiates observed with carriers of the mutant allele.

Prevention of Postoperative Nausea and Vomiting with Granisetron and Dolasetron in Relation to CYP2D6 Genotype

We investigated the efficacy of granisetron and dolasetron in preventing postoperative nausea and vomiting. Because the metabolism of the various antiemetic 5-hydroxytryptamine type 3 (5-HT3) antagonists involves different isoforms of the hepatic cytochrome P450 system, we examined the relationship between the clinical efficacy of these drugs and polymorphic cytochrome P450 2D6 (CYP2D6) genotype. This prospective, randomized, double-blind study involved 150 adult patients with a moderate to high risk for postoperative nausea and vomiting. All subjects received dexamethasone at induction of anesthesia followed by either 12.5 mg of dolasetron or 1 mg of granisetron. We analyzed the number of complete responders (no vomiting or rescue medication) during the first 24 hours after surgery. CYP2D6 genotyping was performed using a TaqMan real-time polymerase chain reaction. A complete response was more frequent in the granisetron group (54.7%) compared with the dolasetron group (38.7%, P < 0.05). In subjects receiving dolasetron, carriers of the duplication of the CYP2D6 allele predicting ultrarapid metabolizer status had more frequent vomiting episodes (P < 0.05) than patients in the granisetron group. It is postulated that the difference in the antiemetic efficacy between two investigated 5-HT3 receptor antagonists may be associated with differences in the carrier status for the duplication of the CYP2D6 allele.

Effect of valdecoxib pretreatment on pain and secondary hyperalgesia: a randomized controlled trial in healthy volunteers [ISRCTN05282752, NCT00260325]

Background

Induction of the COX-2 isoenzyme appears to play a major role in the genesis of central sensitization after nociceptive stimulation. This study aimed to investigate the efficacy of a single, oral dose of the specific COX-2 inhibitor-valdecoxib in attenuating the central sensitization – induced secondary hyperalgesia in a heat/capsaicin pain model in healthy volunteers.

Methods

The study was a randomized, double blind, placebo controlled, crossover, single dose efficacy trial using 20 healthy volunteers. Two hours following placebo or 40 mg, PO valdecoxib, participants underwent skin sensitization with heat/capsaicin, as well as supra-threshold pain and re-kindling measurements according to an established, validated pain model. Subjects rated pain intensity and unpleasantness on a visual analog scale and the area of secondary hyperalgesia was serially mapped.

Results

The area of secondary hyperalgesia produced after 40 mg of valdecoxib was no different than that after placebo. Furthermore, there were no significantly relevant differences when volunteers were treated with valdecoxib or placebo in relation to either cold- or hot pain threshold or the intensity of pain after supra-threshold, thermal pain stimulation.

Conclusion

We demonstrated that a single, oral dose of valdecoxib when does not attenuate secondary hyperalgesia induced by heat/capsaicin in a cutaneous sensitization pain model in healthy volunteers.

Propofol Suppresses the Cortical Somatosensory Evoked Potential in Rats

The dose-response curve for the effect of volatile anesthetics on the somatosensory evoked potential (SEP) is well described, but for propofol, the large dose segment of the curve is undefined. We describe the effect of increasing plasma concentrations of propofol on cortical SEPs in 18 rats. After surgical preparation under ketamine anesthesia, a remifentanil infusion was begun at 2.5, 5, or 10 microg x kg(-1) x min(-1). After 20 min, the propofol infusion was initiated at 20 mg x kg(-1) x h(-1) and was increased to 40, 60, and 80 mg x kg(-1) x h(-1) at 20-min intervals. SEP was recorded before remifentanil infusion, before propofol infusion rate changes, and 30 min after discontinuing propofol infusion. In six additional rats, the plasma concentrations of propofol after each 20-min infusion were measured using gas chromatography. Remifentanil did not have a significant effect, but propofol significantly depressed the SEP amplitude and prolonged the latency at infusion rates of 40 mg x kg(-1) x h(-1) and more. Propofol's effect was dose-dependent, but even at 80 mg x kg(-1) x h(-1) with an estimated plasma concentration of 31.6 +/- 3.4 microg/mL (10.8 50% effective concentration), a measurable response was present in 44.5% of rats. These results suggest that even at large doses, propofol and remifentanil provide adequate conditions for SEP monitoring.

IMPLICATIONS

Rats demonstrate dose-dependent somatosensory evoked potential (SEP) suppression with propofol but not with remifentanil. However, SEP suppression by 50% occurred only at large (1.5 EC(50)) concentrations of propofol, and a measurable SEP was present in 8 of 18 rats, even at 10.8 EC(50).

Low-dose remifentanil infusion does not impair natural killer cell function in healthy volunteers

BACKGROUND

Mu opioid agonists suppress natural killer (NK) cell activity in animal models. Studies in human volunteers, however, have yielded conflicting results, with morphine suppressing and fentanyl increasing NK cell activity. This study evaluated the effect of a constant 8-h infusion of remifentanil on NK cell number and function in human volunteers.

METHODS

After IRB approval and informed consent was obtained, 10 healthy volunteers underwent an 11 pm to 7 am infusion of saline, and at least 1 week later an infusion of 0.02-0.04 microg x kg(-1) min(-1) remifentanil. Blood was collected at 7 am for measurement of NK cell cytotoxicity using a (51)Cr release assay and measurement of NK cell number using fluorescent flow cytometry.

RESULTS

Median and range of the total NK cell cytotoxicity (KU ml(-1)) was 745.0 (498.3-1483.6) on the control morning and 818.6 (238.5-1454.5) on the morning following the remifentanil infusion. Neither the number of NK cells ml(-1) (2.5 x 10(5) (1.4 x 10(5)-4.2 x 10(5)) vs 2.7 x 10(5) (1.1 x 10(5)-4.4 x 10(5))) nor the cytotoxicity per 1000 NK cells (KU 1000 NK cells(-1)) (3.0 (1.8-5.2) vs 2.9 (0.9-6.7)) changed between the control and remifentanil conditions.

CONCLUSIONS

An 8-h infusion of remifentanil did not affect NK cell activity in normal volunteers. This result differs from previous findings of morphine-induced NK cell activity suppression and fentanyl-induced NK cell activity enhancement in normal volunteers.

Clinical Associations Between Tinnitus and Chronic Pain

OBJECTIVE: We sought to estimate the prevalence and severity of tinnitus in patients with chronic pain.

STUDY DESIGN AND SETTING: We conducted a prospective nonrandomized study in which a survey and the Tinnitus Handicap Inventory (THI) were distributed at a tertiary chronic pain clinic.

RESULTS: Seventy-two patients participated. 50 women (mean age, 53 years) and 22 men (mean age, 47.5 years); 54.2% reported having tinnitus. There was an even distribution of patients reporting the onset of tinnitus as before versus after the onset of pain. Four patients reported a direct association between tinnitus and pain. The mean THI score was 27 (of 100) (n = 35). Fifteen subjects scored less than 16, indicating no handicap, and 4 scored over 58, indicating a severe handicap.

CONCLUSION: The study results suggest a high incidence of tinnitus within this population. There were few strong associations between pain and tinnitus. Tinnitus does not significantly handicap the majority of these patients.

SIGNIFICANCE: Tinnitus is a common symptom in the chronic pain population but is not a significant problem for these patients.

Clinical associations between tinnitus and chronic pain

OBJECTIVE

We sought to estimate the prevalence and severity of tinnitus in patients with chronic pain.

STUDY DESIGN AND SETTING

We conducted a prospective nonrandomized study in which a survey and the Tinnitus Handicap Inventory (THI) were distributed at a tertiary chronic pain clinic.

RESULTS

Seventy-two patients participated. 50 women (mean age, 53 years) and 22 men (mean age, 47.5 years); 54.2% reported having tinnitus. There was an even distribution of patients reporting the onset of tinnitus as before versus after the onset of pain. Four patients reported a direct association between tinnitus and pain. The mean THI score was 27 (of 100) (n = 35). Fifteen subjects scored less than 16, indicating no handicap, and 4 scored over 58, indicating a severe handicap.

CONCLUSION

The study results suggest a high incidence of tinnitus within this population. There were few strong associations between pain and tinnitus. Tinnitus does not significantly handicap the majority of these patients.

SIGNIFICANCE

Tinnitus is a common symptom in the chronic pain population but is not a significant problem for these patients.

Preservation of the cortical somatosensory-evoked potential during dexmedetomidine infusion in rats

Successful somatosensory-evoked potential (SEP) monitoring has been performed during the administration of dexmedetomidine to patients, but a systematic investigation of the dose response of the SEP to dexmedetomidine has not been reported. In this study, we evaluated the effect of a range of dexmedetomidine doses on the cortical SEP in rats. Twelve rats were initially anesthetized with ketamine and the lungs were mechanically ventilated. Femoral arterial and venous catheters were placed. Anesthesia was maintained with constant infusions of remifentanil (5-15 microg. kg(-1). min(-1)) and vecuronium (56 microg. kg(-1). min(-1)). Dexmedetomidine was infused at 0.1, 0.25, 0.5, 1.0, and 2.0 microg. kg(-1). min(-1) in a stepwise manner with 10-min infusion periods at each step. In eight rats, an additional large-dose infusion of dexmedetomidine at 10 microg. kg(-1). min(-1) was administered for 30 min. The cortical SEPs were recorded after stimulation of the tibial nerve. At all infusion rates, there was a statistically insignificant increase in the SEP amplitude. Dexmedetomidine consistently increased the SEP latency, but these increases were not statistically significant. These data demonstrate that dexmedetomidine maintains technically adequate conditions for SEP monitoring in rats and provides support for future studies of the effect of dexmedetomidine on SEP monitoring in humans.

IMPLICATIONS

In rats, the administration of a wide range of infusion rates of dexmedetomidine did not significantly affect the somatosensory-evoked potential. These results suggest that dexmedetomidine might be a useful adjunctive drug in patients undergoing intraoperative somatosensory-evoked potential monitoring.

Halothane constricts bovine pulmonary arteries by release of intracellular calcium

In the canine lung, when compared with the conscious state, halothane causes vasoconstriction that is independent of blood flow. However, traditionally inhalational anesthetics have been shown to attenuate hypoxic pulmonary vasoconstriction and have therefore been considered pulmonary vasodilators. We have shown, in isolated bovine pulmonary artery, that halothane produces a transient contractile response. A variety of smooth muscle cellular mechanisms could be responsible for the vasoconstriction produced by halothane. The purpose of this study was to test the hypothesis that the halothane-induced contraction was caused by the release of sarcoplasmic reticular Ca++. Isometric tension was measured in isolated rings of bovine pulmonary artery with intact endothelium. Three protocols were followed. Rings were exposed to cyclopiazonic acid or ryanodine (modulators of sarcoplasmic reticular Ca++) (protocol 1), caffeine (protocol 2) verapamil or nicardipine (protocol 3). Halothane-induced contraction was measured before, during and after exposure to drug. In nominally Ca(++)-free buffer cyclopiazonic acid and ryanodine attenuated the halothane-induced contraction. Similar responses were seen with cyclopiazonic acid and ryanodine treatment when caffeine was substituted for halothane. The calcium channel blockers nicardipine and verapamil did not significantly alter the halothane-induced contraction. Our data in bovine pulmonary artery segments are consistent with halothane effects seen in vascular smooth muscle from several other tissues and species. The results of our experiments support the conclusion that the release of intracellular Ca++ from sarcoplasmic reticular stores is responsible for the halothane-induced vasoconstriction that has been observed in this tissue.

Comparison of the alteration of cardiac function by sevoflurane, isoflurane, and halothane in the isolated working rat heart

OBJECTIVES

Despite its widespread use, little is known about sevoflurane's physiologic effects. The direct myocardial effects of sevoflurane were compared with both halothane and isoflurane.

DESIGN

Administration of minimum alveolar concentration (MAC) fractions of anesthetic (0 to 3.0) was systematically varied to decrease the possibility of time-related effects on measured parameters.

SETTING

Isolated rat hearts were perfused using a working heart model where the parameters affecting myocardial work were carefully controlled and monitored.

PARTICIPANTS

To avoid confounding effects of prior anesthetic administration, hearts were removed from rats, after decapitation, in the absence of anesthetic.

INTERVENTIONS

In the first series, isolated perfused rat hearts were exposed to one of the three anesthetics in doses of 0 to 1.5 times MAC. In the second series, hearts were exposed to either sevoflurane or isoflurane in doses of 0 to 3.0 times MAC. The following variables were measured: the rate of change of left ventricular pressure; aortic flow rate; cardiac output; left ventricular end-diastolic pressure; the time constant of isovolumetric relaxation; and coronary vascular resistance. Oxygen consumption was measured during the first series.

MEASUREMENTS AND MAIN RESULTS

In the first series, all systolic variables were reduced in the presence of halothane when compared with either isoflurane or sevoflurane. Halothane affected diastolic function to a greater degree than either sevoflurane or isoflurane, as measured by the rate of relaxation and end-diastolic pressure. In the second series, at a dose of 3.0 times MAC, both sevoflurane and isoflurane decreased systolic and diastolic function, with a greater reduction in cardiac output, and peak aortic flow and higher left ventricular end-diastolic pressures observed with isoflurane. Coronary resistance and oxygen consumption were not affected by any of the anesthetics.

CONCLUSIONS

These data suggest that sevoflurane depresses cardiac function less than either halothane in doses of 1.0 and 1.5 x MAC or isoflurane at doses of 3 x MAC.

Potassium channel blockade and halothane vasodilation in conducting and resistance coronary arteries

On the basis of reports that volatile anesthetics, such as halothane, open membrane potassium channels in several tissues, it was investigated whether coronary vasodilation by halothane is mediated by a similar mechanism. The ability of glyburide, a blocker of ATP-sensitive K+ (KATP) channels, and tetraethylammonium (TEA+), a blocker of Ca(2+)-activated K+ channels, to modify halothane-induced vasodilation was assessed in two vascular preparations. First, coronary resistance vessel tone was measured in isolated rat hearts arrested with tetrodotoxin and, second, conducting vessel responsiveness was evaluated in ring segments of the porcine epicardial coronary artery contracted with prostaglandin F2 alpha. Halothane alone markedly vasodilated the perfused hearts and attenuated the agonist contraction of the coronary rings. Blockade of KATP channels with glyburide alone did not affect the base-line vascular tone or responsiveness but it inhibited cromakalim vasodilation. TEA+ alone caused vasoconstriction. In hearts perfused at constant pressure, glyburide significantly attenuated the halothane-induced increase in coronary flow by 56% and perfusion with a high K+ buffer reduced the halothane-induced vasodilation response by 94%. In endothelium-denuded coronary rings, glyburide did not affect halothane-induced relaxation but KATP channel blockade potentiated halothane-caused relaxation in endothelium-intact rings. The attenuation of halothane-induced vasodilation by TEA+ seen in the perfused hearts did not achieve statistical significance and no halothane/TEA+ interaction was evident in the coronary rings. Thus, the data from the perfused heart experiments suggest that halothane relaxes rat coronary resistance vessels, in part, by opening K+ channels.

Transvalvular left ventricular pressure measurement in the isolated working rat heart

A method of continuously measuring left ventricular (LV) pressure in an isolated buffer-perfused working rat heart is described. Transvalvular placement of a micromanometer through the aorta is the unique feature of this procedure. Advantages include catheter stability and lack of myocardial trauma. Changes in cardiac function were quantified by exposing hearts to either isoproterenol (10(-9) M) or halothane (1.5% vol/vol). To examine if any obstruction to LV outflow was caused by the micromanometer, cardiac performance was assessed during pullback from the ventricle to the aorta. Complications such as aortic insufficiency and ventricular arrhythmias were also studied. The results indicate that the transvalvular placement of a micromanometer can provide continuous, high-fidelity reproduction of LV pressure in this small-organ preparation. The presence of the micromanometer did not significantly alter cardiac performance, and proper catheter placement was achieved easily in a high percentage (> 90%) of cases.

Direct vasodilation by sevoflurane, isoflurane, and halothane alters coronary flow reserve in the isolated rat heart

Direct vasodilation of coronary resistance vessels by anesthetics may reduce coronary flow reserve and interfere with myocardial flow-metabolism coupling. This study was performed to evaluate the potential for the halogenated anesthetic agents sevoflurane, isoflurane, and halothane to alter the regulation of coronary flow via a direct action on coronary resistance vessels. Coronary flow and flow reserve were measured in the quiescent isolated perfused rat heart at anesthetic concentrations between 0 and 3 x MAC. In order to minimize anesthetic-induced secondary changes in coronary resistance, constant coronary perfusion pressure was maintained; the left ventricular cavity was vented; and tetrodotoxin was used to achieve cardiac arrest. These conditions permitted the dissociation of direct anesthetic actions from indirect regulatory processes affecting coronary vascular resistance (CVR). Coronary flow reserve was defined as the difference between coronary flow prior to and during administration of a maximally vasodilating dose of adenosine. Each anesthetic significantly reduced the magnitude of both CVR and coronary flow reserve in a concentration-dependent manner. Sevoflurane reduced coronary flow reserve significantly less than did halothane and isoflurane. At high concentrations (3.0 x MAC), coronary flow reserve was abolished by halothane and was decreased to near zero by isoflurane; however, flow reserve was reduced only 48% from control by sevoflurane. This difference among anesthetics is explained primarily by variations in the magnitude of direct coronary vasodilation produced by each anesthetic, rather than by effects on maximal vasodilator capacity. These data show that sevoflurane's intrinsic vasodilator action on coronary resistance vessels differs substantially from that of halothane and isoflurane.

Direct effects of myocardial depressant drugs on coronary vascular tone: anesthetic vasodilation by halothane and isoflurane

Because certain vasoactive drugs also possess negative myocardial inotropic properties, it is difficult to determine their direct pharmacological actions on coronary resistance vessels in situ. Thus, a drug's myocardial effects may induce indirect physiological changes in coronary vascular tone that confound measuring its direct action. To separate the direct from indirect drug actions on vascular tone, the authors describe an experimental system utilizing the isolated perfused rat heart arrested with tetrodotoxin. The direct effects of the volatile anesthetics halothane and isoflurane on coronary vascular tone were examined in this preparation, using the concept of minimum alveolar concentration as the measure of potency. Both anesthetics demonstrated a dose-dependent direct coronary vasodilation that was reversible, with the median effective dose being 1.31 +/- 0.08 (mean +/- S.E.) for halothane, and 1.53 +/- 0.12 for isoflurane (P = 0.06; units of measure are the fraction of minimum alveolar concentration for each anesthetic). Further studies indicated that maximal vasodilation by adenosine was diminished after 90 min of perfusion, independent of anesthetic administration. Myocardial oxygen consumption was decreased significantly from the beating state by arrest, but neither anesthetic nor adenosine affected myocardial oxygen consumption further. These data indicate that halothane and isoflurane are equipotent for inducing direct dilation of coronary resistance vessels in the isolated perfused arrested rat heart.

Vascular responses to dopamine and dobutamine in the awake calf during constant aortic flow or constant aortic pressure

We investigated vascular effects of dopamine and dobutamine infusions in awake calves implanted with the Penn State total artificial heart (TAH). This preparation uniquely permits independent servo-control of cardiac output (CO) and arterial blood pressure (BP). Thirty-two studies (22 with dopamine and 10 with dobutamine) were performed in four juvenile calves from 1 to 4 months after TAH implantation. Studies were performed in one of two TAH operating conditions: (a) constant aortic flow, in which the CO is fixed and aortic BP varies with systemic vascular resistance (SVR), or (b) constant pressure, in which the CO varies to maintain a constant BP when SVR changes. During both constant flow and constant pressure studies, dopamine caused a dose-dependent increase and dobutamine caused a dose-dependent decrease in SVR. There was no difference in the SVR response between constant flow or constant pressure conditions at any dose of dopamine or dobutamine (p greater than 0.05). The infusion doses of dopamine required to raise the SVR 20 and 50% during constant flow studies were 7.2 and 12.4 micrograms.kg-1.min-1, respectively. In constant pressure studies, these doses were 7.7 and 13.5 micrograms.kg-1.min-1. The infusion dose of dobutamine resulting in a 20% reduction in SVR was 27.2 micrograms.kg-1.min-1 in constant flow studies 26.2 micrograms.kg-1.min-1 in constant pressure studies. These data suggest that baroreflex and other indirect mechanisms are less important than direct vascular drug effects in this system.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of neuromuscular blockade with vecuronium on hemodynamic responses to noxious stimuli in the rat

The effect of neuromuscular blockade with vecuronium on the hemodynamic responses to a noxious stimulus was investigated in male Sprague-Dawley rats. The rats were anesthetized with either halothane (group 1, n = 10), or isoflurane (group 2, n = 10). The maximum values for heart rate and mean arterial pressure during the noxious stimulus (base-tail clamp) were measured, and the maximum changes in these values (maximum minus prestimulation) were calculated. The responses were measured at two different anesthetic concentrations (0.6 X MAC, 0.75 X MAC), before and after vecuronium 1.0 mg.kg-1 iv. It was found that neuromuscular blockade with vecuronium did not reduce any of the hemodynamic responses measured, at either anesthetic concentration, in either the halothane or the isoflurane group. However, increasing the anesthetic concentration from 0.6 X MAC to 0.75 X MAC produced statistically significant (P less than 0.01) reductions in several of the responses measured. The inability of vecuronium to reduce hemodynamic responses to noxious stimuli in this study suggests that neuromuscular blockade does not alter anesthetic depth in the rat. A knowledge of this "absence of effect" may be important for investigators who need to induce muscle relaxation in laboratory animals prior to examining the effect of anesthetic agents on hemodynamic responses to noxious stimuli. The results also question the ability of neuromuscular blockade to reduce anesthetic requirement, and support the view that neuromuscular blockade does not contribute to the anesthetic state.

Halothane induces depressor responses to noxious stimuli in the rat

The effect of halothane on hemodynamic responses to noxious stimuli was investigated in anesthetized male Sprague-Dawley rats. It was found that increasing the end-tidal halothane concentration from sub-MAC to supra-MAC levels was frequently associated with a reversal of the mean arterial pressure response to a noxious stimulus from a pressor response to depressor response. The depressor responses could be produced by noxious stimuli at several sites but were of greatest frequency (100%) and magnitude (up to -80 mmHg) after clamp application at the base of the tail. The depressor responses were often, but not always, accompanied by decreases in heart rate. The correlation coefficient between the changes in heart rate and the changes in mean arterial pressure caused by noxious stimuli was +0.61 (n = 9). The authors further characterized the depressor responses in an additional 18 rats. The depressor responses were not influenced by vagotomy or muscarinic cholinergic blockade and were associated with concurrent decreases in both cardiac output and systemic vascular resistance. The hemodynamic changes associated with the depressor responses were consistent with a centrally mediated withdrawal of sympathetic tone. Knowledge of this effect of halothane on the arterial blood pressure and heart rate responses to noxious stimuli may be important for correctly interpreting animal responses to noxious stimuli in the presence of general anesthetic agents, particularly because animals are frequently used to characterize both the potency and the hemodynamic effects of anesthetic agents. The presence of depressor responses also indicates that mean arterial pressure responses to noxious stimuli cannot be used as a linear index of anesthetic depth in rats anesthetized with halothane.

Mechanisms of differential growth of heart ventricles in newborn pigs

The left ventricular free wall (LVFW) grew approximately three times faster than the right ventricular free wall (RVFW) during the first 10 days of life in neonatal pigs. Faster growth was associated with proportional increases in total RNA and messenger RNA. These findings indicated that greater capacity for protein synthesis was a major factor in accelerated growth. Despite faster growth, heart content of ribosomal subunits was higher in piglets than in 60-day-old pigs or adult rats, suggesting a relatively slower rate of peptide chain initiation than elongation. When hearts from 5-day-old pigs were perfused in vitro, protein synthesis was more rapid in the LVFW than in the RVFW. In the absence of added insulin, the higher rate was due to both greater efficiency and greater capacity for protein synthesis. In the presence of the hormone, greater capacity was responsible for the increased rate of protein synthesis in the LVFW as compared with the RVFW.

Palmitate oxidation by isolated working fetal and newborn pig hearts

Palmitate oxidation and the effect of palmitate on glucose and lactate utilization were investigated in isolated, perfused, fetal (0.9 gestation), and neonatal (2 day old) pig hearts. Hearts were perfused under working conditions, developing a mean aortic pressure of 50-55 mmHg, paced at 180 beats/min for 30 min, with Krebs-Henseleit buffer containing 3% albumin, glucose (5 mM), and insulin (100 microU/ml). Palmitate (1 mM) and lactate (5 mM), either individually or in combination, were added to the perfusion buffer. Palmitate oxidation was assessed from 14CO2 production from [U-14C]-palmitate, glucose uptake as 3H2O production from D-[2-3H]-glucose, and lactate metabolism from changes in buffer lactate content. After perfusion, ATP, creatine phosphate, triglycerides, and glycogen were measured. Substantial palmitate oxidation was observed at both ages but was greater in neonatal hearts. Nevertheless, palmitate inhibited lactate utilization and glucose uptake similarly in fetal and neonatal hearts. Lactate also reduced palmitate uptake and oxidation by 40-60% in both fetal and neonatal hearts. During perfusions with palmitate, tissue concentrations of triglycerides increased approximately threefold in fetal hearts and were unaffected by lactate. Thus both palmitate and lactate can act as major energy substrates for the immature heart. Both substrates significantly (P less than 0.01) suppress glucose utilization, and each has suppressive effects on the other's metabolism.

Mass spectrometry for monitoring respiratory and anesthetic gas waveforms in rats

A method is presented for real-time monitoring of airway gas concentration waveforms in rats and other small animals. Gas is drawn from the tracheal tube, analyzed by a mass spectrometer, and presented as concentration vs. time waveforms simultaneously for CO2, halothane, and other respiratory gases and anesthetics. By use of a respiratory simulation device, the accuracy of mass spectrometric end-tidal CO2 analysis was compared with both the actual gas composition and infrared spectrophotometry. The effects of various ventilator rates and inspiration-to-expiration ratios on sampling accuracy were also examined. The technique was validated in male Sprague-Dawley rats being ventilated mechanically. The difference between the arterial PCO2 (PaCO2) and the end-tidal PCO2 (PETCO2) was not significantly different from zero, and the correlation between PETCO2 and PaCO2 was strong (r = 0.97, P less than 0.0001). Continuous gas sampling for periods up to 5 min did not affect PaCO2, PETCO2, or airway pressures. By use of this new method for measuring end-tidal halothane concentrations in rats approximately 6.5 mo of age, the minimum alveolar concentration of halothane that prevented reflex movement in response to tail clamping was 0.97 +/- 0.04% atmospheric (n = 14). This mass spectrometric technique can be used in small laboratory animals, such as rats, weighing as little as 250 g. Gas monitoring did not distort either PETCO2 or PaCO2. Under the defined conditions of this study, accurate and simultaneous measurements of phasic respiratory concentrations of anesthetic and respiratory gases can be achieved.

Halothane selectively attenuates alpha 2-adrenoceptor mediated vasoconstriction, in vivo and in vitro

The mechanism by which halothane interferes with catecholamine-induced vasoconstriction was examined, utilizing specific agonists at postjunctional alpha 1- and alpha 2-adrenoceptors on vascular smooth muscle. Stimulation of either adrenoceptor subtype normally produces vasoconstriction. Two experimental models of drug-induced vasoconstriction were used: in vivo blood pressure response in pithed rats, and in vitro isometric tension development in canine saphenous vein rings. These models were then utilized to examine the anti-vasoconstriction properties of halothane. In vivo, halothane (1 MAC) produced a significant depression in the vascular response to azepexole (an alpha 2-adrenoceptor agonist), but halothane did not alter vasoconstriction by phenylephrine (an alpha 1-adrenoceptor agonist). Halothane caused a 24% reduction of maximal response (P less than 0.0001) to azepexole in pithed rats, and a 3.2-fold rightward shift of the log dose-response curve (P less than 0.0001). Similarly, in vitro, halothane significantly attenuated alpha 2- but not alpha 1-adrenoceptor responsiveness. Halothane (4%) depressed maximal vein contraction to azepexole by 26% (P less than 0.0001), and shifted the log concentration-response curve 2.4-fold to the right (P less than 0.0001). The observed selective interference with alpha 2-mediated vasoconstriction by halothane is unlikely to represent drug antagonism at the receptor level. Our observations may suggest, indirectly, that halothane interferes with Ca+2 entry into vascular smooth muscle. The phenomenon of selective anti-vasoconstriction at alpha 2-adrenoceptors by halothane may explain why alpha 1-adrenergic agonists often appear to retain their vasopressor activity during halothane anesthesia. The mechanism of halothane-induced vasodilation thus includes attenuation of alpha 2- but not alpha 1-adrenergic vasoconstriction; this further demonstrates the multifactorial nature of halothane-induced vasodilation.

Cardiac dysfunction during status epilepticus in the neonatal pig

Cardiovascular complications frequently occur during status epilepticus. To determine the changes in systemic and pulmonary arterial pressure, cardi output, and left ventricular contractility during seizures, 1-week-old pigs were intubated, paralyzed, mechanicall entilated, and catheterized with a Swan-Ganz catheter. Seizures were induced with intravenous bicuculline. Early changes consisted of significant systemic and pulmonary arterial hypertension. After 2 hours of seizures, the animals developed progressive systemic hypotension and decreased cardiac output. M-mode echocardiography disclosed a decrease in left ventricular contractility. Cardiac tissue frozen in situ showed a significant increase in lactate and reductions in glucose, triglyceride, and adenosine triphosphate levels. Prolonged seizures in the neonatal pig result in cardiac dysfunction, which may play a role in the development of epileptic brain damage.

Acute myocardial effects of chloramphenicol in newborn pigs: a possible insight into the gray baby syndrome

Mechanical function and mitochondrial respiration were observed in newborn pig hearts in the presence of chloramphenicol. Isolated perfused hearts exposed to chloramphenicol (25, 50, or 100 micrograms/ml) demonstrated acute reductions in pressure development and cardiac output accompanied by elevated left atrial filling pressure. The effects of chloramphenicol and chloramphenicol succinate (25, 50, 100, or 200 micrograms/ml) on oxidative activity of isolated mitochondria were also investigated. With unesterified chloramphenicol, inhibition of state 3 respiration was most apparent when glutamate and palmitylcarnitine were supplied as substrates. Inhibition of mitochondrial oxidation of succinate or glutamate was only detectable at 200 micrograms/ml. Inhibition of alpha-ketoglutarate oxidation was not seen at any concentration of antibiotic studied. Chloramphenicol succinate most strongly inhibited state 3 oxidation of succinate and alpha-ketoglutarate and had relatively mild effects on oxidation of glutamate and palmitylcarnitine. Succinate oxidation by submitochondrial particles was unaffected by chloramphenicol succinate, a result suggesting interference with succinate transport.

Aerobic capacity, obesity, and atherosclerotic risk factors in male adolescents

Correlations between aerobic capacity, obesity, and atherosclerotic risk factors were evaluated in adolescents with low-to-moderate levels of physical fitness. Subjects with higher levels of fitness had a more favorable risk profile with decreased body mass index, lower systolic and diastolic blood pressure and plasma triglyceride levels, and higher plasma high-density lipoprotein-cholesterol levels. Simple linear regression analysis revealed an association between body mass index and blood pressure, plasma triglyceride and plasma high-density lipoprotein-cholesterol. The level of aerobic fitness as determined by exercise duration was also associated with the same atherosclerotic risk factors. However, multiple linear regression analysis demonstrated that body mass index provided the largest explanation, by those variables examined, of the interindividual variance in blood pressure, plasma triglyceride, and high-density lipoprotein-cholesterol. Aerobic fitness contributed only minimally to the variation in these risk factors. These findings suggest that if aerobic conditioning is used to modify atherosclerotic risk factors, it should be accompanied by a reduction in weight in adolescents with low-to-moderate levels of physical fitness.

Fatty acid and glucose utilization in isolated, working fetal pig hearts

Fatty acid uptake and the effects of long- and short-chain fatty acids on glucose utilization were assessed in isolated perfused fetal pig hearts (0.9 gestation) in which oxygenated nutrient buffer was pumped from both ventricles at controlled pressure (55 mmHg, mean arterial pressure) and heart rate (180 beats/min). When either 1.5 mM palmitate or 1.0 mM octanoate was added to buffer containing 10 mM glucose and insulin (100 microU/ml), glucose uptake, as measured by 3H2O production from D-[2-3H]glucose, was suppressed when compared with glucose uptake in the absence of fatty acid. Increased tissue concentrations of glucose 6-phosphate, fructose 6-phosphate, and citrate in hearts perfused with buffer containing octanoate indicated active beta-oxidation and inhibition of phosphofructokinase activity when compared with hearts perfused with glucose alone. In contrast, hearts perfused with buffer containing palmitate showed no increases in these metabolic intermediates. These results suggest that suppression of glucose uptake in the presence of long-chain fatty acid was not the result of phosphofructokinase inhibition but may result from inhibition of glucose transport by palmitate. Determinations of tissue concentrations of free carnitine and carnitine derivatives indicated that, although palmitate underwent esterification to long-chain acyl carnitine in the fetal heart, it failed to undergo extensive beta-oxidation.

Fatty acid and glucose utilization in isolated, working newborn pig hearts

The effects of exogenous fatty acids on glucose uptake were assessed in isolated, working newborn pig hearts in which great vessel pressures were controlled (mean 55 mmHg) and oxygenated nutrient buffer was recirculated through the heart for 30 or 60 min. When palmitate (1.5 mM) or octanoate (1.0 mM) were added to buffer containing 10 mM glucose and 100 mU insulin/ml, glucose uptake, as measured by 3H2O production from D-[2-3H]glucose, was suppressed to less than one-half that observed when glucose alone was present. Increased tissue levels of glucose 6-phosphate, fructose 6-phosphate, and citrate following perfusion in the presence of exogenous fatty acids were consistent with decreased glycolytic activity due to inhibition of phosphofructokinase. Measurements of carnitine in perfused and unperfused hearts indicated that total carnitine levels in neonatal hearts are similar to those of adult pigs. Increased tissue levels of long-chain acyl carnitine, acetyl carnitine, and citrate in hearts perfused with palmitate and glucose in combination with extensive fatty acid uptake and marked suppression of glycolysis indicated that the newborn pig heart is capable of utilizing fatty acids as a primary energy source.

Perinatal changes in mitochondrial respiration of the rabbit heart

Oxidative metabolism and citrate synthase activity during the perinatal period were assessed in isolated rabbit heart mitochondria at 27 days' gestation (27 dpc), 1 day postpartum (1 dpp) and 10 dpp. Oxygen consumption was measured during state 3 and state 4 respiration using the following substrates: glutamate, alpha-ketoglutarate, pyruvate/malate, succinate/rotenone, acetate, palmitylcarnitine, and palmityl CoA/carnitine. Results obtained from fetal and neonatal animals were compared to values obtained from adult left and right ventricles. Rates of state 3 oxygen consumption per milligram mitochondrial protein using tricarboxylic acid cycle intermediates or palmitylcarnitine were higher in both 1 and 10 dpp animals than in either left or right ventricles. Respiratory activity per milligram mitochondrial protein using these substrates was similar in 27 dpc fetuses and adult left ventricles. The rate of oxidation of palmityl CoA was lower in fetal mitochondria than in adult left ventricle, indicating that the capacity for conversion of long-chain fatty acyl CoA to acylcarnitine necessary for transport of fatty substrates into the mitochondria is decreased in fetal hearts. Increases in myocardial citrate synthase corresponded to increases in mitochondrial mass reported by other investigators.

Carbohydrate metabolism in isolated, working newborn pig heart

Metabolic activity of the newborn pig heart was observed by means of a preparation that allowed isolated hearts to perform a physiologic work load. A 10-min period of retrograde aortic perfusion was followed by 60 min of recirculating perfusion in which bicarbonate buffer was infused into the right atrium and ejected from both ventricles at measured pressures and flow rates. The buffer was supplemented with either glucose (10 mM), lactate (20 mM), or pyruvate (20 mM), or was unsupplemented. Pressure development and ventricular outputs were stable through 60 min of perfusion with glucose, pyruvate, or lactate supplementation. Myocardial high-energy phosphate and glycogen contents were also stable. In hearts perfused without substrate supplementation, mechanical performance deteriorated after 30 min. Rates of substrate uptake and oxygen consumption indicated that either glucose, lactate, or pyruvate could serve as a primary source of metabolic energy. Minimal lactate production was observed when either glucose or pyruvate were present. These findings indicate that, despite recent emergence from the relatively hypoxic intrauterine environment, the well-oxygenated newborn pig heart did not depend on anaerobic metabolism of glucose for energy production at physiologic work loads.