Airway management research: a systematic review.

Recent controversy regarding the ethics of conducting airway research in patients led to disagreements concerning the value and frequency of manikin-based investigation. However, no formal examination of the methodology of airway research has been undertaken. We, therefore, performed a systematic bibliometric review of airway management research to describe the conduct, quantify the subjects (patient vs. manikin vs. other), assess the reported outcomes and map global trends. We retrieved 1505 relevant studies published between 2006 and 2017, together recruiting 359,648 subjects, of which 341,233 were patients, the remaining being volunteers or subjects managing manikins, human cadavers, animals or bench models. There were 701 randomised controlled clinical trials (46.6%), 83 non-randomised experimental clinical trials (5.5%), 298 observational studies (19.8%) and 423 non-patient studies (28.1%). A total of 1082 studies (71.9%) were patient studies and 322 were manikin studies (21.4%). The total annual number of airway management studies increased over time, as did the annual number of patient studies, but there was no significant increase in the annual number of manikin studies over time. Of the patient studies, subject baseline characteristics were most likely to be ASA status 1-2 (n = 531, 49.1%), populations were most often elective surgical patients (n = 918, 84.8%) and the most common interventions studied were tracheal intubation (n = 820, 54.4%) or supraglottic airway device insertion (n = 257, 17.1%). There was a total of 77 different primary outcomes used in the included studies, the most commonly reported being success rate and procedure time. By understanding how and what has been previously studied these data can be used to form the basis for future priority setting exercises, core outcome set development, and could inform strategy on the future directions of airway management research.

A pilot randomised trial of community-based care following discharge from hospital with a recent spinal cord injury in Bangladesh.

OBJECTIVES: To explore the feasibility of conducting a full trial designed to determine the effectiveness of a model of community-based care for people with spinal cord injury in Bangladesh. STUDY DESIGN: A pilot randomised trial. SETTING: Community, Bangladesh. SUBJECTS: Participants were 30 people with recent spinal cord injury who were wheelchair-dependent and soon to be discharged from hospital. INTERVENTION: Participants randomised to the intervention group received a package of care involving regular telephone contact and three home visits over two years. Participants randomised to the control group received usual care consisting of a telephone call and an optional home visit. MAIN MEASURES: Participants were assessed at baseline and two years after randomization. The primary outcome was mortality and secondary outcomes were measures of complications, depression, participation and quality of life. RESULTS: A total of 24 participants had a complete spinal cord injury and six participants had an incomplete spinal cord injury. Median (interquartile) age and time since injury at baseline were 31 years (24 to 36) and 7 months (4 to 13), respectively. Two participants, one in each group, died. Five participants had pressure ulcers at two years. There were no notable impediments to the conduct of the trial and no significant protocol violations. The phone calls and home visits were delivered according to the protocol 87% and 100% of the time, respectively. Follow-up data were 99% complete. CONCLUSION: This pilot trial demonstrates the feasibility of a full clinical trial of 410 participants, which has recently commenced. SPONSORSHIP: University of Sydney, Australia.

www.elearnSCI.org: a global educational initiative of ISCoS.

OBJECTIVE: To develop a web-based educational resource for health professionals responsible for the management of spinal cord injury (SCI). The resource:www.elearnSCI.org is comprised of seven learning modules, each subdivided into various submodules. Six of the seven modules address the educational needs of all disciplines involved in comprehensive SCI management. The seventh module addresses prevention of SCI. Each submodule includes an overview, activities, self-assessment questions and references. DEVELOPMENT OF THE RESOURCE: Three hundred and thirty-two experts from The International Spinal Cord Society (ISCoS) and various affiliated societies from 36 countries were involved in developing the resource through 28 subcommittees. The content of each submodule was reviewed and approved by the Education and Scientific Committees of ISCoS and finally by an Editorial Committee of 23 experts. KEY FEATURES: The content of the learning modules is relevant to students and to new as well as experienced SCI healthcare professionals. The content is applicable globally, has received consumer input and is available at no cost. The material is presented on a website underpinned by a sophisticated content-management system, which allows easy maintenance and ready update of all the content. The resource conforms to key principles of e-learning, including appropriateness of curriculum, engagement of learners, innovative approaches, effective learning, ease of use, inclusion, assessment, coherence, consistency, transparency, cost effectiveness and feedback. CONCLUSION: www.elearnSCI.org provides a cost effective way of training healthcare professionals that goes beyond the textbook and traditional face-to-face teaching.

The ryanodine receptor type 1 gene variants in African American men with exertional rhabdomyolysis and malignant hyperthermia susceptibility.

It has been suggested that exertional rhabdomyolysis (ER) and malignant hyperthermia (MH) are related syndromes. We hypothesize that patients with unexplained ER harbor mutations in the ryanodine receptor gene type 1 (RYR1), a primary gene implicated in MH, and therefore ER patients are at increased risk for MH. Although there are reported cases of MH in individuals of African descent, there are no data available on molecular characterization of these patients. We analyzed RYR1 in six, unrelated African American men with unexplained ER, who were subsequently diagnosed as MH susceptible (MHS) by the Caffeine Halothane Contracture Test. Three novel and two variants, previously reported in Caucasian MHS subjects, were found in five studied patients. The novel variants were highly conserved amino acids and were absent among 230 control subjects of various ethnic backgrounds. These results emphasize the importance of performing muscle contracture testing and RYR1 mutation screening in patients with unexplained ER. The MHS-associated variant Ala1352Gly was identified as a polymorphism predominant in individuals of African descent. Our data underscore the need for investigating RYR1 across different ethnic groups and will contribute to interpretation of genetic screening results of individuals at risk for MH.

Effects of ryanodine on skeletal muscle lactate and pyruvate in malignant hyperthermia-susceptible and normal swine as assessed by microdialysis.

BACKGROUND: The caffeine/halothane contracture test in North America and the in vitro contracture test in Europe are currently the only validated bioassays for diagnosing malignant hyperthermia susceptibility and phenotyping families. Both tests are invasive requiring surgical muscle biopsy. Here, we report first use of the selective ryanodine receptor type I agonist ryanodine in a percutaneous microdialysis protocol designed to test whether microdialysis-induced local metabolic responses of skeletal muscle due to ryanodine receptor activation can differentiate between malignant hyperthermia-sensitive and normal pigs. METHODS: Six microdialysis catheters were implanted percutaneously into the adductor muscles of the right and left thighs of malignant hyperthermia-susceptible (n = 9) and normal (n = 8) anaesthetized (ketamine/propofol) and mechanically ventilated swine. Systemic blood gases, haemodynamic parameters and creatine kinase levels were measured before, during and after microdialysis perfusion of ryanodine. After a post-implantation equilibration period of 30 min, one catheter perfused (2 micro min-1) with 0.9% NaCl (control) and was compared with the remaining five catheters perfused with increasing concentrations of ryanodine (0.2-100 micromol). Lactate and pyruvate levels were measured enzymatically. RESULTS: Continuous perfusion with ryanodine revealed dose-dependent sigmoidal increases in the dialysate lactate and lactate-pyruvate ratio parameters; these effects were greatly augmented in malignant hyperthermia-susceptible pigs compared to normal pigs (two- to threefold): estimated EC50 greatly decreased (>19-fold) while the maximum effect increased (>twofold) in the malignant hyperthermia-susceptible group. CONCLUSION: The in vivo percutaneous microdialysis protocol for skeletal muscle, using ryanodine as the ryanodine receptor type I agonist and dialysed lactate-pyruvate parameters as metabolic index, can reproducibly differentiate between malignant hyperthermia-susceptible and normal swine.

North American malignant hyperthermia population: screening of the ryanodine receptor gene and identification of novel mutations.

BACKGROUND: Malignant hyperthermia (MH) is a disorder of skeletal muscle manifested as a life-threatening hypermetabolic crisis in susceptible individuals after exposure to inhalational anesthetics and depolarizing muscle relaxants. Mutations in the gene encoding the skeletal muscle ryanodine receptor (RYR1) are considered a common cause of the disorder, and, to date, more than 20 RYR1 mutations have been reported in European and Canadian families. Some studies suggest that differences may exist in the frequencies and distribution of mutations in the RYR1 gene between European and North American MH families the frequency and distribution of mutations in the RYR1 gene. METHODS: Skeletal muscle samples from 73 unrelated individuals diagnosed as MH susceptible according to the North American MH caffeine-halothane contracture test were studied. Genomic DNA of MH-susceptible patients was investigated by polymerase chain reaction-based restriction fragment length polymorphism, single-strand conformation polymorphism, and sequencing analysis. The majority of known RYR1 mutations were analyzed using the restriction fragment length polymorphism method, whereas new mutations were searched by single-strand conformation polymorphism in exons 12, 15, 39, 40, 44, 45, and 46 of the gene. RESULTS: Seven known RYR1 mutations (Arg163Cys, Gly248Arg, Arg614Cys, Val2168Met, Thr2206Met, Gly2434Arg, and Arg2454His) were detected at frequencies of 2.7, 1.4, 1.4, 1.4, 1.4, 5.5, and 4.1%, respectively. In addition, three novel amino acid substitutions (Val2214Ile, Ala2367Thr, and Asp2431Asn) were detected at frequency of 1.4% each. These 10 mutations account for 21.9% of the North American MH-susceptible population. CONCLUSION: Three novel candidate mutations in the RYR1 gene were identified in these MH patients. The frequency and distribution of RYR1 mutations observed in this North American MH population was markedly different from that previously identified in Europe. Larger-scale studies are necessary to clarify the type and frequency of mutations in RYR1 associated with MH in North American families.

Prolonging viability of swine muscle biopsy specimens in malignant hyperthermia testing.

In North America, the caffeine halothane contracture test (CHCT) is the standard test for the diagnosis of malignant hyperthermia (MH). Current CHCT protocol recommends that the test be completed within 5 h of muscle excision. The purpose of this study was to investigate whether the period of skeletal muscle viability could be extended to 24 h. We tested the gracilis muscle from normal (n = 8) and MH-susceptible swine (n = 8). After baseline (1-2 h after excision) CHCT, the remaining muscles were placed into one of the following four treatment groups. In Groups 1 and 2, the muscles remained under tension and were stored in Krebs buffer (pH 7.4) at 23 degrees C-25 degrees C (clamped-warm) and 4 degrees C (clamped-cold), respectively. In Groups 3 and 4, the muscle strips were dissected, and the ends were tied with silk sutures, cut from the clamp, and placed in Krebs buffer at 23 degrees C-25 degrees C (free-warm) and 4 degrees C (free-cold), respectively. The responses of the treatment groups to halothane (3%) and caffeine (0.5-32 mM) were tested 22-26 h after excision. The clamped-warm storage was the only storage method to correctly diagnose MH susceptibility in all muscle strips tested. This finding was also confirmed in muscle stored under clamped-warm conditions and shipped overnight to another testing center for a parallel CHCT.

Endothelin plays a role in contractions of isolated pig pulmonary vessels induced by diaspirin cross-linked hemoglobin.

The current studies were undertaken to investigate the role of endothelin-1 (ET-1) and its receptors in contractions of isolated pulmonary vessels of the pig induced by diaspirin cross-linked hemoglobin (DCLHb). Second-order pulmonary arteries (PAs) and veins (PVs) were isolated from pigs, cut into rings (4 to 5 mm), and mounted at optimal passive tension in 37 degrees C Krebs-filled tissue baths bubbled with 95% O2/5% CO2. Isometric tension was recorded continuously. In paired rings, concentration responses to ET-1 (10(-10) to 10(-7) mol/L), DCLHb (10(-9) to 3x10(-6) mol/L), and N-nitro-L-arginine (LNA) (10(-6) to 5x10(-5) mol/L) in the presence and absence of the ET(A) receptor antagonist BQ123 (3x10(-5) mol/L) were determined. PVs and PAs with intact endothelium and rings from which the endothelium was removed (denuded) were pretreated with the ET(B) receptor antagonist BQ788 to determine the contribution of ET(B) receptors to ET-1, DCLHb, and LNA responses. ET-1, DCLHb, and LNA caused concentration-dependent increases in tension in all vessels. In the presence of BQ123, the 50% effective concentration (EC50) of ET-1 was significantly increased (by 5-fold to 10-fold) in all vessels. DCLHb concentration responses were significantly attenuated-in the PVs by 45% and in the PAs by 79%-during treatment with BQ123. BQ123 attenuated LNA responses in PVs by 35% and in PAs by 87%. Treatment with BQ788 had no effect on endothelium-intact PVs or PAs but significantly increased ET-1 EC50 (log of the molar concentration) from -9.0+/-0.22 to -7.8+/-0.05 in denuded PAs. The ET-1 EC50 was significantly decreased in denuded PAs (-9.0+/-0.22) as compared with responses in endothelium-intact PAs (-8.1+/-0.18). DCLHb concentration responses were attenuated by 71% and LNA responses by 80% during antagonism with BQ788 in the intact PAs only. These data demonstrate that ET-1 plays a role in DCLHb-induced contractions in the PA and PV. The contributions of ET are mediated by both ET(A) and ET(B) receptors in the PA but only by ET(A) receptors in the PV. These results suggest that the vasoconstrictor actions of DCLHb, which have previously been shown to depend on its interference with endothelium-generated NO, may also involve ET. This may reflect the importance of the interaction of these two endothelium-generated physiologic antagonists in the pulmonary circulation.

Inhaled nitric oxide attenuates increased pulmonary artery pressure following diaspirin crosslinked hemoglobin (DCLHB) administration.

Intravenous administration of diaspirin crosslinked hemoglobin (DCLHb) can result in elevated pulmonary and systemic arterial pressures in some mammalian species. This study was designed to evaluate the ability of inhaled nitric oxide (INO) to attenuate elevations in pulmonary artery pressure in a closed-chested swine model. Yorkshire pigs received escalating doses of INO followed by escalating doses of DCLHb or a single dose of DCLHb followed by escalating doses of INO. Systemic and pulmonary arterial pressures were monitored continuously. Significant elevations occurred in systemic and pulmonary arterial pressure following a cumulative dose of 0.1 gm/kg DCLHb. A single dose of 0.3 gm/kg also resulted in elevations of pulmonary and systemic arterial pressure. Inhaled nitric oxide partially reversed the changes in pulmonary but not systemic pressure. These results indicate that INO might be a therapeutic option for humans who may experience increased pulmonary artery pressure following administration of DCLHb.

Inhibition by midazolam of the adrenergic function in the isolated canine mesenteric vein.

BACKGROUND: Midazolam has been reported to cause hypotension or to depress sympathetic activity following intravenous injection. However, little information is available concerning the mechanism of these effects. The aim of the present study was to determine the effects of midazolam on release of noradrenaline (NA) at nerve terminals and on receptors in the venous smooth muscle. METHODS: The effect of midazolam at nerve terminals was examined by measuring the amount of NA release from superfused canine mesenteric vein helical strips during electrical stimulation (ES; 5 Hz, 2 ms, 9 V). The NA was quantified by high-performance liquid chromatography with electrochemical detection; tension development evoked by ES was also recorded simultaneously. In a separate series of experiments, ring preparations from the isolated vein were mounted in Krebs-Ringer solution for isometric tension recording to assess the effect of midazolam on alpha-adrenoceptors. RESULTS: Application of tetrodotoxin (10(-6) M) or replacement of superfusate with Ca(2+)-free solution decreased both the release of NA and the tension development evoked by ES. Yohimbine (5 x 10(-8) M) increased the ES-evoked release of NA, whereas it decreased tension development in the vein strips. Midazolam (10(-4) M) did not affect either the basal release of NA or the basal tension, but inhibited both the NA release (P < 0.01) and the tension development (P < 0.01) during ES; midazolam at 10(-5) M inhibited the tension development (P < 0.05) but had no effect on NA release. In the ring preparations, midazolam (10(-5) and 10(-4) M) attenuated responses to NA (a mixed alpha 1- and alpha 2-adrenoceptor agonist, 10(-8) to 10(-3) M), phenylephrine (the alpha 1-adrenoceptor agonist, 10(-8) to 10(-3) M) and 5-bromo-6-[2-imidazolin-2yl-amino]-quinoxaline (UK14304; the alpha 2-adrenoceptor agonist, 10(-7) to 10(-3) M) in a dose-dependent manner. CONCLUSION: The data obtained in the present study suggest that midazolam at 10(-4) M may reduce venous tone by inhibiting the release of NA from sympathetic nerve endings and both alpha 1- and alpha 2-adrenoceptor mediated smooth muscle contractions. It is also postulated that a stage of the post-receptor transduction mechanism linked to the venous smooth muscle contraction may be more sensitive to midazolam than the NA release mechanism at nerve terminals since midazolam at the low concentration tested inhibited ES-evoked tension development with no effect on the release of NA.

Factors contributing to differences in the regulation of cGMP in isolated porcine pulmonary vessels.

Guanosine 3',5'-cyclic monophosphate (cGMP) is an important second messenger in many biological systems including vascular smooth muscle where it mediates relaxation. Cellular levels of cGMP are regulated primarily by three enzymes; nitric oxide (NO) synthase, soluble guanylate cyclase, and cGMP-phosphodiesterase. Basal cGMP levels of isolated endothelium intact porcine pulmonary vein are five fold higher than in pulmonary artery. The objective of this study was to investigate possible reasons for this difference. Therefore, we compared NO synthase activity of pulmonary vein with artery and used pharmacologic approaches to compare soluble guanylate cyclase and phosphodiesterase activities in these vessels. NO synthase activities of pulmonary vein and artery were measured by monitoring the conversion of exogenous L-[14C]arginine to L-[14C]citrulline and by quantifying NO formation from endogenous L-arginine. Rates (pM/min per mg protein) of basal L-citrulline and NO formation from endothelium intact pulmonary vein (29.0 +/- 4.8 and 44 +/- 7.1, respectively) were significantly higher than from artery (8.3 +/- 2.2 and 17.1 +/- 3.3). Western blot analysis indicated higher constitutive NO synthase protein in the vein than in artery. N-nitro-L-arginine (0-100 microM), a potent inhibitor of NO synthase, induced contractions of the pulmonary vein which were significantly higher than those of the artery. N-nitro-L-arginine (5 and 20 microM) in the presence of phosphodiesterase inhibitors, decreased basal cGMP levels of endothelium intact blood vessels. In endothelium denuded pulmonary vein and artery, basal cGMP levels were not different from each other, but increased significantly following stimulation of soluble guanylate cyclase with exogenous NO. In the presence of both non-specific and specific cGMP phosphodiesterase inhibitors, exogenous NO-induced cGMP levels of endothelium denuded tissues were not significantly different from each other. However, in the absence of the phosphodiesterase inhibitors, exogenous NO-induced cGMP was significantly less in the artery than in the vein. These results suggest that (I) the intact porcine pulmonary vein contains higher levels of NO synthase activity than pulmonary artery, and that (II) the soluble guanylate cyclase activities in pulmonary vein and artery are equally responsive to NO, and finally (III) pulmonary artery expresses greater phosphodiesterase activity than vein. Higher NO synthase and lower phosphodiesterase activity may explain the greater accumulation of cGMP in the pulmonary vein compared to the artery.

Halothane attenuates nitric oxide relaxation of rat aortas by competition for the nitric oxide receptor site on soluble guanylyl cyclase.

Endothelial cells play an important role in the regulation of vascular activity through the release of endothelium derived relaxing factor (EDRF) now believed to be nitric oxide (NO). NO and the NO donor drug nitroglycerin relax vascular smooth muscle by stimulating soluble guanylyl cyclase leading to elevation of intracellular levels of cyclic guanosine 3',5'-monophosphate (cGMP). Halothane has been shown to inhibit the action of NO on blood vessels. This study was designed to further investigate the mechanisms by which halothane attenuates NO-induced vascular relaxations. This was done by examining the effects of halothane on nitroglycerin and NO-induced relaxations in the presence and absence of the inhibitors of soluble guanylyl cyclase, methylene blue and 6-anilino-5,8-quinolinedione (LY 83583). Thoracic aortas from anesthetized male Sprague-Dawley rats were excised and cut into rings and the endothelium was removed. The aortic rings were suspended in organ baths containing Krebs solution and equilibrated at their optimal passive tension. When a stable plateau of contraction was produced by EC60 concentrations of norepinephrine, increasing concentrations of nitroglycerin or NO were added to the baths to relax the rings. This contraction-relaxation procedure was repeated three or four times. In some baths halothane was administered by a calibrated vaporizer 10 min before beginning the second procedure. Either methylene blue or LY 83583 was added to the baths 20 min before the third procedure. The combination of halothane, methylene blue or LY 83583 was added before the fourth procedure. Halothane, methylene blue or LY 83583 significantly inhibited nitroglycerin-induced relaxation individually. Halothane and LY 83583 also significantly inhibited NO-induced relaxations (5 x 10(-9)-3 x 10(-8) M and 5 x 10(-9)-3 x 10(-5) M, respectively) individually. The combination of halothane and methylene blue or halothane and LY 83583 significantly inhibited nitroglycerin-induced relaxation, also, the combination of halothane and LY 83583 significantly inhibited NO-induced relaxations. Halothane, methylene blue and LY 83583 treatment led to rightward shift in the concentration-effect curves. Halothane, in combination with methylene blue or LY 83583, produced inhibition equivalent to the sum of their individual effects. The present study demonstrates that the halothane, methylene blue and LY 83583 attenuate nitroglycerin and NO-induced relaxations of endothelium-denuded rat aortic rings. This suggests that halothane, methylene blue and LY 83583 may act through competitive antagonism at a common site of action on soluble guanylyl cyclase in the EDRF/NO relaxation pathway.

Actions of diaspirin cross-linked hemoglobin on isolated rat and dog vessels.

The objectives of these studies were to investigate the responses of isolated blood vessels from rats and dogs to the administration of diaspirin cross-linked hemoglobin (DCLHb) and to determine the mechanisms of these responses. Isolated vascular rings (3 to 5 mm) were suspended at optimal passive tension in Krebs-filled (37 degrees C) tissue baths and bubbled with 95% O2-5% CO2, and isometric tension was recorded. With the vessels under basal conditions increasing concentrations of DCLHb (10(-8)-3 x 10(-6) mol/L) were added. DCLHb addition was repeated during a submaximal contraction with norepinephrine and again during acetylcholine relaxation. The effects of the nitric oxide synthase inhibitor L-nitro arginine (10(-5) mol/L) on the responses to DCLHb were also determined. Dog vessels developed very little tension (1% to 5% of norepinephrine maximum), whereas rat arteries contracted between 9% and 15% when exposed to DCLHb under basal conditions. However, both the dog and rat vessels developed significant tension to DCLHb when they were precontracted (5% to 54%) and also when they were relaxed with acetylcholine (21% to 93%). L-nitro arginine eliminated the contractile responses to DCLHb but did not cause contraction of any of the vessels under basal conditions. We conclude that in this model the mechanism of DCLHb-induced contractions of in vitro dog and rat vessels is dependent on interference with nitric oxide. This is similar to the mechanism of DCLHb action in isolated pig vessels reported previously. Differences in responses of dog, rat, and pig vessels under basal conditions in vitro are the result of active generation of nitric oxide by pig but not by dog or rat vessels.

Hemoglobin-induced contraction of pig pulmonary veins.

The effects of hemoglobin Ao (HbAo), alpha alpha cross-linked hemoglobin (alpha alphaHb), cyanomet alpha alpha cross-linked hemoglobin (cyanomet alpha alphaHb), and human serum albumin (HSA) were compared under basal conditions and during relaxation with acetylcholine (ACh), sodium nitroprusside (SNP), and papaverine (PAP) in porcine pulmonary veins. Isometric tension changes were recorded in isolated rings (3 to 4 mm) that were suspended in Krebs solution bubbled with 95% O2/5% CO2. Increasing concentrations of HbAo and alpha alphaHb (10(-9) - 3 x 10(-6) mol/L) caused concentration-dependent increases in tension that reached a maximum of 4.20 +/- 0.3 gm and 3.78 +/- 0.6 gm, respectively. Cyanomet alpha alphaHb and HSA (10(-9) - 3 x 10(-6) mol/L) did not cause significant increases in tension. The maximum responses to HbAo and alpha alphaHb were significantly increased during relaxation with ACh and SNP but not with PAP. In contrast, SNP (10(-4) mol/L) and PAP (10(-5) mol/L), but not ACh, reversed contractions induced by HbAo and alpha alphaHb. These studies support the concept that hemoglobin-induced vascular contraction is primarily mediated by inactivation of the vasodilator nitric oxide in vitro. We suggest that this mechanism is common to acellular hemoglobins in which the ligand binding site is unimpaired and in which the heme iron is in the ferrous (+2) state.

Diaspirin cross-linked hemoglobin does not alter isolated human umbilical artery or vein tone.

Diaspirin cross-linked hemoglobin (DCLHbTM; Baxter Healthcare Corp., Round Lake, IL, USA) is undergoing clinical trials as a blood substitute. Administration of DCLHb is associated with an increase of mean arterial pressure in vivo and contraction of selected adult isolated blood vessels of from certain species in vitro. The mechanisms of these pressor effects may be due to scavenging of the endothelium derived relaxing factor, nitric oxide (NO), by hemoglobin. Unlike adult blood vessels, prostacyclin (PGI2) rather than EDNO is the important relaxing agent in human umbilical vessels. In this study, we examined if DCLHb had vasoconstrictor effects on isolated human umbilical vessels. Human umbilical veins and arteries were excised, cut into rings and placed in organ chambers filled with 25 ml Krebs-Ringer solution (37 degrees C). 5-hydroxytryptamine (5-HT, 0.01-10 microM) increased the tension of human umbilical arteries (HUA, from 0.4 +/- 0.2 g to 2.6 +/- 0.4g) and veins (HUV, from 0.8 +/- 0.4g to 2.5 +/- 0.4g) in a dose-dependent manner. DCLHb (0.01-10 microM) did not have a significant effect on HUA and HUV. Substance P (1 microM, via prostanoid synthesis) and nitroglycerin (NG, 1 microM) but not acetylcholine (ACh, 1 microM) caused relaxation of both HUA and HUV. The NO synthase inhibitor L-NA did not have significant effects on HUA and HUV. DCLHb did not alter 5-HT preconstricted tension of HUA and HUV. The basal cGMP contents of HUA and HUV were low. These results support our previous finding that DCLHb-induced vasoconstriction in isolated vessels is dependent primarily on the binding of NO by hemoglobin.

Effects of halothane and isoflurane on carbon monoxide-induced relaxations in the rat aorta.

BACKGROUND: Halothane and isoflurane previously were reported to attenuate endothelium-derived relaxing factor/nitric oxide-mediated vasodilation and cyclic guanosine monophosphate (cGMP) formation in isolated rat aortic rings. Carbon monoxide has many chemical and physiologic similarities to nitric oxide. This study was designed to investigate the effects of halothane and isoflurane on carbon monoxide-induced relaxations and cGMP formation in the isolated rat aorta. METHODS: Isometric tension was recorded continuously from endothelium denuded rat aortic rings suspended in Krebs-filled organ baths. Rings precontracted with submaximal concentrations of norepinephrine were exposed to cumulative concentrations of carbon monoxide (26-176 microM). This procedure was repeated three times, with anesthetics delivered 10 min before the second procedure. Carbon monoxide responses of rings contracted with the same concentration of norepinephrine (10(-6) M and 2 x 10(-6) M) used in the anesthetic-exposed preparations also were examined. The concentrations of cGMP were determined in denuded rings using radioimmunoassay. The rings were treated with carbon monoxide (176 microM, 30 s) alone, or carbon monoxide after a 10-min incubation with halothane (0.34 mM or 0.72 mM). To determine whether the sequence of anesthetic delivery influenced results, vascular rings pretreated with halothane were compared with nonpretreated rings. RESULTS: Carbon monoxide (26-176 microM) caused a dose-dependent reduction of norepinephrine-induced tension, with a maximal relaxation of 1.51 +/- 0.07 g (85 +/- 7% of norepinephrine-induced contraction). Halothane (0.34 mM and 0.72 mM) significantly attenuated the carbon monoxide-induced relaxations, but only the highest concentration of isoflurane (0.53 mM) significantly attenuated the carbon monoxide-induced relaxations. Carbon monoxide (176 microM) significantly increased cGMP content (+88.1 +/- 7.1%) and preincubation of the aortic rings with halothane (0.34 mM and 0.72 mM) inhibited this increase (-70.7 +/- 6.8% and -108.1 +/- 10.6%, respectively). When aortic rings and carbon monoxide were added simultaneously to Krebs solution equilibrated with halothane (0.72 mM), no inhibition of cGMP formation occurred. CONCLUSION: Carbon monoxide-induced endothelium-independent relaxations of rat aortic rings were decreased by clinically relevant concentrations of halothane and isoflurane. The carbon monoxide-induced elevations of cGMP were attenuated by halothane only when the anesthetic was incubated with aortic rings before carbon monoxide treatment. The possible clinical significance of the actions of the anesthetics on this endogenous vasodilator is yet to be determined.

Intravenous lecithin-coated microcrystals of dantrolene are effective in the treatment of malignant hyperthermia: an investigation in rats, dogs, and swine.

Dantrolene effectively treats malignant hyperthermia (MH) hut the current form, Dantrium, must be dissolved to a 0.33 mg/mL, pH 9.5 solution. This study describes lecithin-coated microcrystal formulations of sodium dantrolene (MC-NaD) and neutral dantrolene (MC-D) which reconstitute to 200 mg/mL within 1 min. In rats, the pharmacokinetics and pharmacodynamics of MC-NaD and Dantrium were similar: half-lives of 3.1 h, volume distributions of 0.54 and 0.59 L/kg, and 95% effective dose (ED95) values for depression of skeletal muscle twitch height (ED95T) of 2.6 +/- 0.7 and 2.8 +/- 0.5 mg/kg. In swine, the ED95T values for MC-NaD and Dantrium were also similar (2.8 +/- 0.4 vs 2.7 +/- 0.6 mg/kg), but MC-D and Dantrium were only similar at doses more than 2.5 mg/kg (ED95T: 3.5 +/- 0.4 vs 2.7 +/- 0.5 mg/kg). In susceptible swine, MC-NaD successfully treated five of six MH episodes and prevented MH in three of four swine. However, MC-NaD caused marked pulmonary hypertension in swine, while MC-D caused only a mild response that was eliminated by filtration. Likewise, MC-D caused no pulmonary response in dogs. These observations suggest that MC-D has potential to improve the treatment of MH.

Effect of halothane on phenylephrine-induced vascular smooth muscle contractions in endotoxin-exposed rat aortic rings.

OBJECTIVES: a) To determine the response of endotoxin-exposed vascular smooth muscle to exogenous vasoconstrictors during concomitant exposure to an inhaled anesthetic (halothane); and b) to determine if excess nitric oxide production is responsible for any altered response. DESIGN: In vitro, prospective, repeated-measures, dose-response study. SETTING: University/medical school experimental physiology laboratory. SUBJECTS: Adult male Sprague-Dawley rats, whose aortae were studied in an in vitro preparation. INTERVENTIONS: Thoracic aortae were excised from anesthetized animals and cut into 3-mm rings. After incubation in aerated organ baths containing a modified essential medium with or without Escherichia coli lipopolysaccharide (100 micrograms/mL) at 37 degrees C for 5 hrs, the rings were removed and suspended in separate baths for isometric tension recording. Phenylephrine dose-response data (10(-10) to 10(-5) M) were determined for lipopolysaccharide- and nonlipopolysaccharide-treated rings. After washout and equilibration, two vessels (one each lipopolysaccharide- and nonlipopolysaccharide-treated) were additionally exposed to 2% halothane and phenylephrine dose-response determinations were repeated for all vessels. This procedure was repeated for 1% halothane in a separate experiment. In some experiments, the nitric oxide synthase inhibitor, N omega-nitro-L-arginine (3 x 10(-4) M), was added to the bath after the washout from the second phenylephrine dose-response determination. Then, a third phenylephrine dose-response determination was performed, with and without 2% halothane. MEASUREMENTS AND MAIN RESULTS: Dose-response curves were evaluated using a logistic regression analysis. In addition, absolute and percentage changes in tension were compared between the first and second contractions. Exposure to lipopolysaccharide resulted in a decrease in the maximum tension from 2.07 +/- 0.03 (controls) to 1.24 +/- 0.04 g/mg of vessel dry weight and an increase in the dose at which the contraction is 50% of maximum (ED50) from 3.78 x 10(-8) to 2.05 x 10(-7) M (p < .05). Exposure to 2% halothane produced significant reductions in the maximum tensions in both groups. The lipopolysaccharide-treated vessels showed not only a proportionately larger decrease (-51 +/- 5% vs. -18 +/- 2% in the control plus halothane group), but also a significantly greater absolute decrease (0.59 +/- 0.09 vs. 0.34 +/- 0.04 g/mg in the control plus halothane group). The addition of 1% halothane produced less pronounced decreases in tension, with only an additive effect in the lipopolysaccharide-treated vessels. The addition of N omega-nitro-L-arginine resulted in a reversal of the lipopolysaccharide-induced decrease in tension. However, 2% halothane still had a significantly greater effect on the lipopolysaccharide-exposed rings. CONCLUSIONS: Exposure of rat aortic rings to lipopolysaccharide in vitro decreased the contractile response to phenylephrine. The addition of 2% halothane resulted in a more than additive decrease in tension in the lipopolysaccharide-treated vessels. Patients in septic or endotoxic shock are sensitive to most anesthetic regimens, and some of this sensitivity may be due to an altered vasoconstrictive response induced by lipopolysaccharide exposure. The inability of nitric oxide synthase inhibition to reverse this response completely suggests that induction of nitric oxide synthase and increased production of nitric oxide are not solely responsible for this finding.