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C Keller

Publications and source records attributed to C Keller.

At least 163 records · Page 9Linked to original sources
PubMed1999

Mucosal pressures from the cuffed oropharyngeal airway vs the laryngeal mask airway.

We tested the hypothesis that pressures exerted on the pharyngeal mucosa by the laryngeal mask airway (LMA) and cuffed oropharyngeal airway (COPA) differ, in 20 male and 20 female adult patients. Microchip pressure sensors were attached to the LMA and COPA at four similar anatomical locations (base of the tongue, lateral pharynx, posterior pharynx and distal oropharynx) and two dissimilar locations (LMA, piriform fossa and hypopharynx; COPA, middle of the tongue and proximal oropharynx). Cuff volume was adjusted until oropharyngeal leak pressure (OLP) was 10 cm H2O and mucosal pressures were recorded. This was repeated at an OLP of 15 cm H2O and at maximal OLP. Overall mucosal pressures were higher for the COPA than the LMA at 10 cm H2O (17 vs 3 cm H2O; P < 0.0001), at 15 cm H2O (21 vs 6 cm H2O; P < 0.0001) and at maximal OLP (26 vs 9 cm H2O; P < 0.0001). Mucosal pressures were always higher for the COPA at the base of the tongue, posterior pharynx and lateral pharynx, but were similar in the distal oropharynx. Maximal OLP was higher for the LMA than the COPA (27 (95% confidence intervals 25-29) vs 16 (12-19) cm H2O; P < 0.0001). We conclude that pressures acting on the mucosa were higher with the COPA compared with the LMA.

Adolescent↗
PubMed1999

Influence of neuromuscular block, mode of ventilation and respiratory cycle on pharyngeal mucosal pressures with the laryngeal mask airway.

We tested the hypothesis that the pressure exerted by the laryngeal mask airway (LMA) against the pharyngeal mucosa varied with neuromuscular block, mode of ventilation and the respiratory cycle. We studied 20 anaesthetized adult patients. Microchip sensors were attached to a size 5 LMA at locations approximately corresponding to the base of the tongue, hypopharynx, lateral pharynx, oropharynx, posterior pharynx and piriform fossa. Mucosal pressures were measured with an intracuff pressure of 60 cm H2O under four conditions during anaesthesia using 2.0 MAC of sevoflurane: (1) apnoeic, non-paralysed; (2) spontaneously breathing, non-paralysed; (3) ventilated, paralysed and (4) non-ventilated, paralysed. In conditions (2) and (3), mucosal pressures were measured at the end of inspiration and expiration. Mean mucosal pressure was less than 10 cm H2O at all locations. There were no significant changes in mucosal pressure at any location between the four conditions. There was no variation between inspiration and expiration. With an intracuff pressure of 60 cm H2O in these circumstances, mucosal pressures were much less than considered safe for prolonged tracheal intubation.

Adult↗
PubMed1999

Do laryngeal mask airway devices attenuate liquid flow between the esophagus and pharynx? A randomized, controlled cadaver study.

UNLABELLED: In this randomized, controlled cadaver study, we tested the hypothesis that the standard laryngeal mask airway (LMA) and flexible laryngeal mask airway (FLMA) attenuate liquid flow between the esophagus and pharynx. Fifty fresh cadavers were studied in four LMA groups. Ten female cadavers had a size 4 LMA and 10 had a size 4 FLMA; 10 male cadavers had a size 5 LMA and 10 had a size 5 FLMA; 5 male and 5 female cadavers functioned as controls. The chest was opened, and the infusion set of a pressure-controlled, continuous flow pump was inserted into the esophagus and ligated into place. Esophageal pressure was increased in 2-cm H2O increments. Regurgitation pressure was the esophageal pressure at which fluid was first seen with a fiberoptic scope in the hypopharynx (control group) and above the cuff or within the bowl (LMA groups). This was performed in the LMA groups at 0-40 mL cuff volume in 10-mL increments. Mean (95% confidence interval) regurgitation pressure for the control group was 7 (6-8) cm H2O and for the LMA groups combined was 19 (17-20) cm H2O at 0 mL cuff volume, 47 (41-52) cm H2O at 10 mL, 51 (44-55) cm H2O at 20 mL, 52 (45-56) cm H2O at 30 mL, and 52 (45-55) cm H2O at 40 mL. The increase in regurgitation pressure with increasing cuff volume from 0 to 10 mL was statistically significant (P < 0.0001). Regurgitation pressure was higher for the LMA groups at all cuff volumes compared with the control group (P < 0.0001). There were no differences in regurgitation pressure among the LMA groups. We conclude that the correctly placed LMA and FLMA attenuate liquid flow between the esophagus and pharynx. IMPLICATIONS: We have shown, in cadavers, that the correctly placed standard and flexible laryngeal mask airways attenuate liquid flow between the pharynx and esophagus.

Aged↗
PubMed1999

The influence of head and neck position on oropharyngeal leak pressure and cuff position with the flexible and the standard laryngeal mask airway.

UNLABELLED: We conducted a randomized, cross-over study of 20 paralyzed anesthetized adult patients to test the hypothesis that oropharyngeal leak pressure and cuff position (assessed fiberoptically) vary with head and neck position for the flexible (FLMA) and standard laryngeal mask airway (LMA). Both devices were inserted into each patient in random order. Oropharyngeal leak pressure and fiberoptic position (including degree of rotation) were documented in four head and neck positions (neutral first, then flexion, then extension and rotation in random order) for each device. The size 5 was used for all patients, and the intracuff pressure was set at 60 cm H2O in the neutral position. All airway devices were inserted at the first attempt. Oropharyngeal leak pressure was similar for the FLMA and LMA in the neutral (22 vs 21 cm H2O), flexed (26 vs 26 cm H2O), and extended positions (19 vs 18 cm H2O) but was slightly higher for the LMA when the head was rotated (19 vs 22 cm H2O; P = 0.04). Compared with the neutral position, oropharyngeal leak pressure for the LMA was higher with flexion (26 vs 21 cm H2O; P = 0.0004) and lower with extension (18 vs 21 cm H2O; P = 0.03) but similar with rotation. Compared with the neutral position, oropharyngeal leak pressure for the FLMA was higher with flexion (26 vs 22 cm H2O; P = 0.0001) and lower with extension (19 vs 22 cm H2O; P = 0.03) and rotation (19 vs 22 cm H2O; P = 0.03). The difference in oropharyngeal leak pressure between flexion and extension was 7 and 8 cm H2O for the FLMA and LMA, respectively. Fiberoptic position was similar between devices and was unchanged by head and neck position. Rotation was not detected fiberoptically. We conclude that there are small changes in oropharyngeal leak pressure but no changes in cuff position in different head and neck positions for the FLMA and LMA. Oropharyngeal leak pressure may be improved by head and neck flexion and by avoiding extension. IMPLICATIONS: There are small changes in oropharyngeal leak pressure but no changes in cuff position in different head and neck positions for the flexible and standard laryngeal mask airways. Oropharyngeal leak pressure may be improved by head and neck flexion and by avoiding extension.

Adolescent↗
PubMed1999

The influence of the tonsillar gag on efficacy of seal, anatomic position, airway patency, and airway protection with the flexible laryngeal mask airway: a randomized, cross-over study of fresh adult cadavers.

UNLABELLED: We conducted a randomized, controlled, cross-over cadaver study to test the hypothesis that the efficacy of seal for ventilation and airway protection, anatomic position, and airway patency with the flexible laryngeal mask airway (FLMA) are altered by the application of a Boyle Davis (B-D) gag. We also determined the airway sealing pressure (ASP) at which the FLMA prevents aspiration when large volumes of fluid are placed above the cuff. We studied 20 adult cadavers (6-24 h postmortem). Efficacy of seal for ventilation and airway protection, anatomic position, and airway patency were determined with and without a B-D gag (two blade sizes: 8 and 10 cm) for the size 3, 4, and 5 FLMA in random order. Efficacy of seal for ventilation was determined by measuring the ASP at an intracuff pressure of 60 cm H2O. Efficacy of seal for airway protection was determined by flooding the mouth with 55-135 mL of water, reducing intracuff pressure until aspiration was detected fiberoptically and measuring ASP at this intracuff pressure. Anatomic position and airway patency were determined with a fiberoptic scope at an intracuff pressure of 60 cm H2O. In addition, in vivo compliance and ASP for the FLMA were measured in 10 cadavers and 10 paralyzed, anesthetized patients. Efficacy of seal for ventilation and airway protection, anatomic position, and airway patency did not change with the application of a gag for any mask size. The mean (range) ASP at which aspiration occurred when large volumes of fluid were placed above the cuff was 11 (7-15) cm H2O. The ASP for ventilation was always higher than the ASP for airway protection (P<0.0001). The FLMA had similar in vivo compliance and ASP in cadavers and anesthetized patients. We conclude that efficacy of seal for ventilation and airway protection, anatomic position and airway patency for the FLMA are unaffected by the application of a B-D gag in adults. ASP should be >15 cm H2O if there is a maximal risk of aspiration from above the cuff. IMPLICATIONS: The flexible laryngeal mask airway forms an effective seal for ventilation and protection of the airway that is unaffected by the application of a mouth gag that provides surgical access to the oropharynx. The efficacy of the seal should be >15 cm H2O if there is a maximal risk of aspiration from above the cuff.

Aged↗
PubMed1999

Pulmonary airway resistance with the endotracheal tube versus laryngeal mask airway in paralyzed anesthetized adult patients.

BACKGROUND: The hypothesis that airway resistance is less with the laryngeal mask airway than with the endotracheal tube was tested. METHODS: Thirty-six paralyzed, anesthetized adult patients with no respiratory disease (American Society of Anesthesiologists physical status 1-3; age, 18-80 yr) were randomly allocated (9 men, 9 women in each group) to receive either a size-4 laryngeal mask airway or an endotracheal tube (men, 9-mm ID; women, 8-mm ID). A pulmonary monitor with flow transducer and esophageal balloon was used to measure peak airway pressure and mean airway resistance (device resistance plus pulmonary airway resistance) at three different tidal volumes (5, 10, and 15 ml/kg). Device resistance was measured in vitro with the distal end of the endotracheal tube or laryngeal mask airway open to the atmosphere and using the same ventilator settings. Pulmonary airway resistance was derived by subtracting the mean device resistance from the mean airway resistance. RESULTS: Peak airway pressure, mean airway resistance, device resistance, and pulmonary airway resistance were greater for the endotracheal tube (all P < 0.0001). CONCLUSIONS: The laryngeal mask airway triggers less bronchoconstriction than does the endotracheal tube in paralyzed anesthetized adult patients. This may have implications for maintaining intraoperative pulmonary function and reducing the risk for atelectasis and pulmonary infection.

Adolescent↗
PubMed1999

Pharyngeal mucosal pressures, airway sealing pressures, and fiberoptic position with the intubating versus the standard laryngeal mask airway.

BACKGROUND: The tube of the intubating laryngeal mask (ILM) is more rigid than the standard laryngeal mask airway (LMA), and the authors have tested the hypothesis that pharyngeal mucosal pressures, airway sealing pressures, and fiberoptic position are different when the two devices are compared. METHODS: Twenty anesthetized, paralyzed adults were randomly allocated to receive either the LMA or ILM for airway management. Microchip sensors were attached to the size 5 LMA or ILM at locations corresponding to the pyriform fossa, hypopharynx, base of tongue, posterior pharynx, and distal and proximal oropharynx. Mucosal pressures, airway sealing pressures, and fiberoptic positioning were recorded during inflation of the cuff from 0 to 40 ml in 10-ml increments. RESULTS: Airway sealing pressures were higher for the ILM (30 vs. 23 cm H2O), but epiglottic downfolding was more common (56% vs. 26%). Pharyngeal mucosal pressures were much higher for the ILM at five of six locations. Mean mucosal pressures in the distal oropharynx for the ILM were always greater than 157 cm H2O, regardless of cuff volume. There was no correlation between mucosal pressures and airway sealing pressures at any location for the LMA, but there was a correlation at three of six locations for the ILM. CONCLUSIONS: The ILM provides a more effective seal than the LMA, but pharyngeal mucosal pressures are higher and always exceed capillary perfusion pressure. The ILM is unsuitable for use as a routine airway and should be removed after its use as an airway intubator.

Adult↗
PubMed1999

Pharyngeal mucosal pressure and perfusion: a fiberoptic evaluation of the posterior pharynx in anesthetized adult patients with a modified cuffed oropharyngeal airway.

BACKGROUND: Pharyngeal airway devices can exert substantial pressures against the pharyngeal mucosa. The authors assess the relation between pharyngeal mucosal perfusion and directly measured mucosal pressure (MP) in the posterior pharynx using a fiberoptic technique with a modified cuffed oropharyngeal airway (COPA). The authors also measure in vivo intracuff pressure (CP), airway sealing pressure and MP at four locations using an unmodified COPA. METHODS: Twenty adult patients, American Society of Anesthesiologists status I or II, undergoing general anesthesia were allocated randomly to receive either (1) a COPA with a millimeter microchip sensor fixed on the external cuff surface to record distal posterior pharyngeal MP or (2) a COPA with a fiberoptic scope inserted inside the cuff to record digitized images of the distal posterior pharyngeal mucosa. MP and digitized images were obtained at the same location over an in vivo CP range of 10-160 cm H2O in 10- to 20-cm H2O increments. The digitized images were scored according to blood vessel caliber and mucosal color by two investigators blinded to MP and CP. In an additional 20 matched patients, in vivo CP, airway sealing pressure, and MP was measured at four different cuff locations (corresponding to the anterior, lateral, and posterior pharynx and the distal oropharynx) with increasing cuff volume. RESULTS: Blood vessel caliber and mucosal color was normal in all patients when the mean mucosal pressure was 17 cm H2O. Blood vessel caliber was first reduced when the mean mucosal pressure was 34 cm H2O. There was a progressive incremental reduction in blood vessel caliber and mucosal color when the mean mucosal pressure increased from 34 to 80 cm H2O (P < or = 0.05). Complete blood vessel collapse and mucosal paling first occurred with the mean mucosal pressure was 73 cm H2O and was present in 90% of patients when the mean mucosal pressure was 80 cm H2O. Mean MP was always higher in the posterior pharynx compared with the other locations when the cuff volume was 20 ml or greater (P < 0.001). In vivo CP is an excellent predictor of mucosal pressure. Mean (95% confidence interval [CI]) MP in the posterior pharynx was 35 (5-67) and 78 (50-109) cm H2O when the airway sealing pressure was 10 (6-16) and 17 (13-21) cm H2O respectively. CONCLUSION: Pharyngeal mucosal perfusion is reduced progressively in the posterior pharynx when MP is increased from 34 to 80 cm H2O with the COPA. CP provides reliable information about MP and should be less than 120 cm H2O to prevent mucosal ischemia.

Adult↗
PubMed1999

Effect of fluvoxamine on sufentanil antinociception and tolerance under chronic intravenous infusion in rats.

Fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), significantly potentiates analgesia when administered in animals together with opioids. The aim of the present study was to investigate the effects of fluvoxamine on sufentanil antinociception and tolerance. Following animal care committee approval, the effects of continuous infusions of fluvoxamine and sufentanil were studied in behavioural tests (hot-plate test, tail-flick test, catalepsy test) in Sprague-Dawley rats with a jugular vein catheter. Saline was administered as a control. The time-effect curves for continuous intravenous sufentanil indicate dose-related antinociception and rapid development of tolerance in the hot-plate and tail-flick tests. Co-administration of fluvoxamine with continuous sufentanil enhances antinociception and attenuates development of tolerance, most clearly seen in the tail-flick test. Fluvoxamine alone and saline were not effective. No animal showed catalepsy. As a side effect we observed a marked loss of body weight. The IC50 values of sufentanil binding with and without fluvoxamine addition are 0.56+/-0.17 nM and 0.3+/-0.15 nM, respectively, indicating no direct effect on the occupancy of sufentanil on the mu-receptor by this serotonin reuptake inhibitor. In conclusion, we were able to show that the combination of an opioid with an SSRI at low doses improves analgesia and decreases development of tolerance in nociceptive tests in rats. The clinical implications of these promising results in an animal model, however, await further investigation.

Analgesics, Opioid↗
PubMed1999

Supplemental and complementary alternatives to hormone replacement therapy.

Tables 1 and 2 offer a summary of information currently available on the sources, dosages, and proposed health benefits of the supplemental and complementary nutritional therapies that can be suggested as alternatives to hormone replacement therapy. These therapies have the additional benefit of being broadly available to women of all socioeconomic strata, and should be acceptable to women of various ethnicities and cultures. Adequate intakes (AI) of vitamins are recommended based on observational or experimentally determined approximations of the average nutrient intake, by a defined population or group, that appears to sustain a defined nutritional state (Food and Nutrition Boar, Institute of Medicine, 1997). Reviewing the empirical evidence concerning the use of vitamin supplements leads to the conclusion that doses higher than AI or recommended daily requirements is not warranted. For those individuals who choose to supplement, counseling should be provided to caution about tolerable upper limits, those maximum levels of nutrient intake judged unlikely to pose a risk for adverse health effects (Food and Nutrition Boar, Institute of Medicine). Supplemental and complementary therapy directed at ameliorating symptoms or reducing the risk of menopause related illness (osteoporosis and CHD) becomes a decision balance of the woman's preferences, risk and health history, and personal and financial resources. There appears to be some protection of morbidity and mortality from CHD with antioxidant dietary intake. Osteoporosis appears to be delayed with calcium supplementation. Menopausal symptoms, CHD risk, and osteoporosis risk appears to be reduced with phytoestrogen supplementation, although doses have not been established. Research concerning the safety and efficacy of these therapies continues. Findings from current clinical trials, such as the Women's Health Initiative may render these and additional alternative therapies to HRT more precise in the near future.

Antioxidants↗
PubMed1999

Amblyopia and visual acuity in children with Down's syndrome.

BACKGROUND/AIMS: Amblyopia in people with Down's syndrome has not been well investigated. This study was designed to determine the prevalence and associated conditions of amblyopia in a group of home reared children with Down's syndrome. METHODS: All children in the study group underwent an evaluation of visual acuity. In addition, previous ophthalmological records were reviewed, and a subgroup of children was examined. For the purposes of this study, amblyopia was defined quantitatively as a difference of two Snellen acuity lines between eyes or if unilateral central steady maintained (CSM) vision and a clear fixation preference was observed. A high refractive error was defined as a spherical equivalent more than 3 dioptres and astigmatism more than 1.75 dioptres. Anisometropia was defined as a difference of at least 1.5 dioptres of sphere and/or 1.0 dioptre of cylinder between eyes. 68 children with Down's syndrome between the ages of 5 and 19 years were enrolled in the final study group. RESULTS: Amblyopia was observed in 15 (22%) of 68 patients. An additional 16 (24%) patients had bilateral vision less than 20/50. Strabismus, high refractive errors, and anisometropia were the conditions most commonly associated with decreased vision and amblyopia CONCLUSION: This study suggests that the prevalence of amblyopia is higher than previously reported. Fully 46% of these children with Down's syndrome had evidence of substantial visual deficits. These patients may be at higher risk for visual impairment and should be carefully examined for ophthalmological problems.

Adolescent↗
PubMed1999

A comparison of the reinforced and standard laryngeal mask airway: ease of insertion and the influence of head and neck position on oropharyngeal leak pressure and intracuff pressure.

We conducted a randomized, crossover study of 60 paralysed anaesthetized adult patients to compare ease of insertion for the reinforced (RLMA) and standard laryngeal mask airway (LMA). We also test the hypothesis that oropharyngeal leak pressure (OLP) and intracuff pressure (ICP) vary with head and neck position for the two devices. OLP and ICP were documented in four head and neck positions (neutral first, then flexion, extension and rotation in random order) for each device. The size 5 was used for all patients and the ICP was set at 60 cm H2O in the neutral position. The first time insertion success rates were similar (LMA: 60/60 v RLMA; 59/60), but insertion time was slightly less for the LMA (6 v 8 s, P = 0.004). Compared with the neutral position, OLP for the LMA was higher in flexion (21 v 28 cm H2O, P < 0.0001) and rotation (21 v 23 cm H2O, P < 0.0001), but lower in extension (21 v 14 cm H2O, P < 0.0001). Compared with the neutral position, OLP for the RLMA was higher in flexion (19 v 27 cm H2O, P < 0.0001), similar in rotation (20 v 19 cm H2O), but lower in extension (27 v 14 cm H2O, P < 0.0001). The difference in OLP between flexion and extension was 13 and 14 cm H2O for the RLMA and LMA respectively. OLP was slightly higher for the LMA compared with the RLMA when the head was in neutral (P < 0.0001) and rotation (P < 0.0001), but was similar during flexion and extension. There was a significant positive correlation between ICP and OLP for the LMA (P < 0.0001) and RLMA (P < 0.0001). We conclude that ease of insertion is similar for the RLMA and LMA. OLP is higher with head/neck flexion and lower with extension for both devices and is associated with a similar change in ICP. We recommend assessing the efficacy of seal for all head and neck positions likely to be encountered prior to the start of surgery.

Adolescent↗
PubMed1999

The obese patient as a surgical risk.

Obesity has become a serious problem in the United States. The increasing prevalence of obesity makes the likelihood of clinicians caring for these individuals high. Several considerations for the preoperative care of these patients include appropriate assessment, particularly of the cardiopulmonary systems, and a thorough clinical examination. Intraoperative concerns include appropriate equipment, medication, positioning, and cardiopulmonary monitoring. Postoperative care for the obese patient requires special concern regarding oxygenation and wound healing.

Humans↗