Changes in mucociliary activity may be used to investigate the airway-irritating potency of volatile anaesthetics

Mouse isoflurane anesthesia using the drop method

Anesthesia with isoflurane prior to carbon dioxide euthanasia is recommended as a refinement, but vaporizer access can be limited. An alternative to vaporizers is the 'drop' method, introducing a fixed volume of isoflurane into the induction chamber. Previous work suggests that isoflurane administered at a concentration of 5% via the drop method is effective but aversive to mice; lower concentrations have not been tested. We assessed mouse behavior and insensibility with induction using the drop method for isoflurane concentrations below 5%. Male Crl:CD-1 (ICR) mice (n = 27) were randomly allocated to one of three isoflurane concentrations: 1.7%, 2.7%, and 3.7%. During induction, measures of insensibility and stress-related behaviors were recorded. All mice reached a surgical plane of anesthesia, and mice exposed to higher concentrations did so more quickly; as concentrations increased from 1.7 to 2.7 and 3.7%, the time to recumbency (Least squares means ± SE: 120.5 s ± 8.1, 97.9 s ± 8.1, and 82.8 s ± 8.1, respectively), loss of righting reflex (149.1 s ± 8.5, 127.7 s ± 8.5, and 100.7 s ± 8.5, respectively), and loss of pedal withdrawal reflex (214.5 s ± 8.3, 172.2 s ± 8.3, and 146.4 s ± 8.3, respectively) all declined. Rearing was the most frequently performed stress-related behavior, and was most pronounced immediately following isoflurane administration for all treatments. Our results indicate that the drop method can be used to effectively anesthetize mice with isoflurane concentrations as low as 1.7%; future work should assess mouse aversion.

Avertin®, but Not Volatile Anesthetics Addressing the Two-Pore Domain K+ Channel, TASK-1, Slows Down Cilia-Driven Particle Transport in the Mouse Trachea

RATIONALE

Volatile anesthetics inhibit mucociliary clearance in the airways. The two-pore domain K+ channel, TASK-1, represents one of their molecular targets in that they increase its open probability. Here, we determine whether particle transport speed (PTS) at the mucosal surface of the mouse trachea, an important factor of the cilia-driven mechanism in mucociliary clearance, is regulated by TASK-1.

METHODOLOGY/RESULTS

RT-PCR analysis revealed expression of TASK-1 mRNA in the manually dissected and laser-assisted microdissected tracheal epithelium of the mouse. Effects of anesthetics (isoflurane and Avertin®) and TASK-1 inhibitors (anandamide and A293) on ciliary activity were investigated by assessment of PTS at the mucosal surface of the explanted and opened murine trachea. Neither TASK-1 inhibitors nor isoflurane had any impact on basal and ATP-stimulated PTS. Avertin® reduced basal PTS, and ATP-stimulated PTS decreased in its presence in wild-type (WT) mice. Avertin®-induced decrease in basal PTS persisted in WT mice in the presence of TASK-1 inhibitors, and in two different strains of TASK-1 knockout mice.

CONCLUSIONS/SIGNIFICANCE

Our findings indicate that TASK-1 is expressed by the tracheal epithelium but is not critically involved in the regulation of tracheal PTS in mice. Avertin® reduces PTS independent of TASK-1.

Impact of anesthesia on pathophysiology and mortality following subarachnoid hemorrhage in rats

BACKGROUND

Anesthesia is indispensable for in vivo research but has the intrinsic potential to alter study results. The aim of the current study was to investigate the impact of three common anesthesia protocols on physiological parameters and outcome following the most common experimental model for subarachnoid hemorrhage (SAH), endovascular perforation.

METHODS

Sprague-Dawley rats (n = 38) were randomly assigned to (1) chloral hydrate, (2) isoflurane or (3) midazolam/medetomidine/fentanyl (MMF) anesthesia. Arterial blood gases, intracranial pressure (ICP), mean arterial blood pressure (MAP), cerebral perfusion pressure (CPP), and regional cerebral blood flow (rCBF) were monitored before and for 3 hours after SAH. Brain water content, mortality and rate of secondary bleeding were also evaluated.

RESULTS

Under baseline conditions isoflurane anesthesia resulted in deterioration of respiratory parameters (arterial pCO2 and pO2) and increased brain water content. After SAH, isoflurane and chloral hydrate were associated with reduced MAP, incomplete recovery of post-hemorrhagic rCBF (23 ± 13% and 87 ± 18% of baseline, respectively) and a high anesthesia-related mortality (17 and 50%, respectively). Anesthesia with MMF provided stable hemodynamics (MAP between 100-110 mmHg), high post-hemorrhagic rCBF values, and a high rate of re-bleedings (> 50%), a phenomenon often observed after SAH in humans.

CONCLUSION

Based on these findings we recommend anesthesia with MMF for the endovascular perforation model of SAH.

Airway responses to desflurane during maintenance of anesthesia and recovery in children with laryngeal mask airways

BACKGROUND

We sought to characterize the airway responses to desflurane during maintenance of and emergence from anesthesia in children whose airways were supported with laryngeal mask airways (LMAs).

METHODS/MATERIALS

Four hundred healthy children were randomized in a 3 : 1 ratio to either desflurane or isoflurane (reference group) during anesthetic maintenance. After induction of anesthesia, anesthesia was maintained with the designated anesthetic. The investigator chose the airway (LMA and facemask), ventilation strategy and when to remove the LMA. The incidence of airway events during maintenance, emergence and recovery was recorded.

RESULTS

Ninety percent of children received LMAs. The frequency of major airway events after desflurane (9%) was similar to that after isoflurane (4%) (number needed to harm [NNH] 20), although the frequency of major events after the LMA was removed during deep desflurane anesthesia (15%) was greater than during awake removal (5%) (NNH 10) (P < 0.006) and during deep isoflurane removal (2%) (NNH 8) (P < 0.03). The frequency of airway events of any severity after desflurane was greater than that after isoflurane (39% vs 27%) (P < 0.05). The frequencies of laryngospasm and coughing of any severity after desflurane were greater than those after isoflurane (13% vs 5% and 26% vs 14%, respectively) (P < 0.05).

CONCLUSIONS

When an LMA is used during desflurane anesthesia in children, fewer airway events occur when it is removed when the child is awake. Although the time to discharge from recovery was not delayed and no child required overnight admission, caution should be exercised when using an LMA in children who are anesthetized with desflurane.

Desflurane induces airway contraction mainly by activating transient receptor potential A1 of sensory C-fibers

We previously reported that desflurane induced airway contraction via antidromic tachykinin release from sensory C-fibers. Here, we investigated the effect of desflurane on airway lung resistance (R(L)) using specific receptor antagonists in C-fibers. Young guinea pigs were anesthetized and their tracheas were cannulated with an endotracheal tube via a tracheotomy. A Fleisch pneumotachograph and a differential transducer were used to monitor respiratory flow rate, intrapleural pressure, and airway pressure, and R(L) was calculated and recorded. A transient receptor potential A1 (TRPA1) or a transient receptor potential V1 (TRPV1) selective antagonist of sensory C-fibers, i.e., HC030031 or BCTC, was administered before the exposure to desflurane. In an additional experiment, tachykinin receptor of airway smooth muscles was antagonized only by the neurokinin-2 receptor antagonist MEN-10376 before the exposure to desflurane. HC030031 completely inhibited both the first and the second contractile responses induced by desflurane, whereas BCTC had little effect. MEN-10376 also significantly and substantially diminished the contractile response. Desflurane contracts the airway in untreated guinea pigs mainly by activating irritant gas receptor TRPA1 of afferent C-fibers, resulting in the release of contractile tachykinins such as neurokinin A.

Bronchial mucus transport velocity in patients receiving desflurane and fentanyl vs. sevoflurane and fentanyl

BACKGROUND AND OBJECTIVE

Sevoflurane has been shown to distinctly reduce bronchial mucus transport velocity, an essential determinant of mucociliary clearance and pulmonary complications. However, sevoflurane is regarded as one of the least irritant volatile anaesthetics, especially when compared with desflurane. Hence, the aim of this double-blind, randomized, controlled trial was to assess differences in bronchial mucus transport velocity between sevoflurane and desflurane.

METHODS

Twenty patients listed for general surgery were randomized to receive either maintenance of anaesthesia with desflurane and fentanyl, or sevoflurane and fentanyl. Thirty minutes after tracheal intubation, bronchial mucus transport velocity was assessed by fibreoptic observation of the movement of methylene blue dye applied to the dorsal surface of the right main bronchus.

RESULTS

Both agents distinctly reduced bronchial mucus transport velocity when compared with previous studies, but the degree of impairment did not significantly differ between the investigated groups (median [25%/75% percentile]): desflurane 1.5 [0.5/4.2] vs. sevoflurane 1.3 [0.3/2.9] mm min(-1), P = 0.343).

CONCLUSIONS

Desflurane is commonly regarded as more irritant to the airway, but as far as bronchial mucus transport velocity is concerned, the choice between sevoflurane and desflurane does not seem to matter.

Effects of sevoflurane on the cAMP-induced short-circuit current in mouse tracheal epithelium and recombinant Cl- (CFTR) and K+ (KCNQ1) channels

BACKGROUND

An optimal level of airway surface liquid is essential for mucociliary clearance in lungs. The cAMP-activated cystic fibrosis transmembrane conductance regulator (CFTR) and KCNQ1 channels in tracheal epithelium play key roles in luminal and basolateral membranes, respectively. The aim of this study was to examine the effects of sevoflurane on cAMP-induced chloride secretion by the mouse tracheal epithelium and the modulation of recombinant CFTR and KCNQ1 channels.

METHODS

The equivalent short-circuit current (Isc) of the mouse tracheal epithelium was measured using a flow-type Ussing chamber technique. Inhibition of Na+ absorption was achieved through the luminal application of amiloride. cAMP-dependent Cl- secretion was evoked by forskolin and isobutylmethylxanthine (Fsk/IBMX) applied to the basolateral side. The effect of sevoflurane on CFTR and KCNQ1 channels was assessed using a whole-cell patch clamp in human embryonic kidney 293T cells expressing CFTR and KCNQ1 channels.

RESULTS

Fsk/IBMX induced a sustained Isc that was suppressed by the application of sevoflurane [decreased by 49 (4.5)% at 190 microM]. The Fsk/IBMX-induced Isc was also blocked by basolateral application of chromanol 293B, a blocker of the KCNQ1 K+ channel. In KCNQ1-expressing cells, sevoflurane 190 microM reduced the outward currents to 59 (4.9)% at 80 mV. The CFTR current was not affected by sevoflurane (approximately 360 microM).

CONCLUSIONS

These results suggest that the inhibition of KCNQ1 underlies sevoflurane-induced decrease in airway secretion.

The effect of sevoflurane on ciliary motility in rat cultured tracheal epithelial cells: a comparison with isoflurane and halothane

Halothane and isoflurane potently depress airway ciliary motility. We compared the effect of sevoflurane on ciliary beat frequency (CBF) with that of halothane and isoflurane using purified and cultured rat tracheal epithelial cells. Rat tracheal epithelial cells were isolated from adult male Sprague-Dawley rats to establish an air-liquid interface culture. Apical surfaces of the cells were exposed to a fresh gas containing humidified and warmed (25 degrees C) air (vehicle) with or without sevoflurane (0%-4%), halothane (0%-2%), or isoflurane (0%-2%). The images of motile cilia were videotaped and CBF was analyzed using a computer. Baseline CBF (= 100%) and CBF 30 min after the exposure were measured. CBF 30 min after vehicle exposure was 101% +/- 4% (mean +/- sd). Exposures to 0.25%-2% sevoflurane did not change CBF significantly, although exposures to 0.25%-2% halothane or isoflurane decreased CBF dose-dependently. CBFs 30 min after exposures to 2% of sevoflurane, halothane, and isoflurane were 97% +/- 9%, 56% +/- 14%, and 47% +/- 6%, respectively (n = 5 each). Sevoflurane 4% reduced CBF significantly but slightly (84% +/- 2%, n = 5). These results show that sevoflurane has a direct cilioinhibitory action but its action is much weaker than that of halothane and isoflurane in isolated rat tracheal epithelial cells.

Maintenance of anaesthesia with sevoflurane or isoflurane effects on adverse airway events in smokers

Patients who smoke are at risk of coughing and other adverse airway events during induction of anaesthesia. We have studied the incidence of adverse airway events in smokers under isoflurane or sevoflurane anaesthesia after induction with propofol. Smokers inhaling isoflurane had a 45% incidence of adverse airway events compared to 10% in those inhaling sevoflurane (p = 0.013).

Respiratory reflexes in response to upper-airway administration of sevoflurane and isoflurane in anesthetized, spontaneously breathing dogs

OBJECTIVE

To evaluate the respiratory effects occurring during administration of sevoflurane or isoflurane to the upper airway in dogs.

STUDY DESIGN

A prospective, randomized study.

ANIMALS

Twelve healthy adult beagles (6 males, 6 females).

METHODS

At least 2 weeks after undergoing permanent tracheostomy, dogs were premedicated with acepromazine-buprenorphine, and anesthesia was induced with thiopental and maintained with alpha-chloralose. The upper airway was functionally isolated so that the inhalant could be administered to the upper airway while dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to the administration of sevoflurane or isoflurane at concentrations of 1.2, 1.8, and 2.4 times the minimal alveolar concentration (MAC) (administered in 100% O2 at a flow rate of 5 L/min) were recorded. Reflexes in response to administration of each anesthetic were also recorded following upper-airway administration of lidocaine.

RESULTS

Respiratory reflexes elicited by upper-airway administration of each anesthetic were characterized by a dose-dependent increase in expiration time, with a resultant decrease in respiratory minute ventilation and increase in end-tidal PCO2. The magnitude of these responses was greater with isoflurane than with sevoflurane at 1.8 and 2.4 MAC. These reflexes were abolished after lidocaine nebulization into the upper airway.

CONCLUSION

Isoflurane induces greater reflex inhibition of breathing than does sevoflurane when the anesthetic is inhaled into the upper airway at concentrations used for mask induction.

Respiratory reflexes in response to nasal administration of halothane to anesthetized, spontaneously breathing dogs

OBJECTIVE

To characterize and determine the sensory innervation of respiratory reflexes elicited by nasal administration of halothane to dogs.

ANIMALS

10 healthy Beagles.

PROCEDURE

Dogs underwent permanent tracheostomy and, 2 to 3 weeks later, were anesthetized with thiopental and alpha-chloralose administered IV. The nasal passages were functionally isolated so that halothane could be administered to the nasal passages while dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to administration of halothane at concentrations of 1.25, 1.75, and 2.5 times the minimum alveolar concentration (MAC), and 5% (administered in 100% O2 at a flow rate of 5 L/min) were recorded. Reflexes in response to administration of 5% halothane were also recorded following transection of the infraorbital nerve, transection of the caudal nasal nerve, and nasal administration of lidocaine.

RESULTS

Nasal administration of halothane induced an inhibition of breathing characterized by a dose-dependent increase in expiratory time and a resultant decrease in expired volume per unit time. Effects were noticeable immediately after the onset of halothane administration and lasted until its cessation. Reflex responses to halothane administration were attenuated by transection of the caudal nasal nerve and by nasal administration of lidocaine, but transection of the infraorbital nerve had no effect.

CONCLUSIONS AND CLINICAL RELEVANCE

Nasal administration of halothane at concentrations generally used for mask induction of anesthesia induces reflex inhibition of breathing. Afferent fibers in the caudal nasal nerve appear to play an important role in the reflex inhibition of breathing induced by halothane administration.