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Biomedical subjects

C Keller

Publications and source records attributed to C Keller.

At least 145 records · Page 8Linked to original sources
PubMed1999

The intubating laryngeal mask airway in fresh cadavers vs. paralysed anesthetised patients.

PURPOSE: To compare the performance of the intubating laryngeal mask airway (ILM) between fresh cadavers and anesthetised patients in terms of ease of insertion, oropharyngeal leak pressure (OLP), in-vivo intracuff pressure, anatomical position (assessed fibreoptically) and ease of fibreoptic-guided intubation. METHODS: Twenty paralysed anesthetised patients and twenty cadavers (6-24 hr post-mortem) were studied. Groups were matched for height, weight and sex. Ease of insertion and ease of fibreoptic-guided intubation (number of insertion attempts and time to successful placement) were recorded. The OLP in-vivo intracuff pressure and anatomical position (judged fibreoptically) were measured at zero volume and after each additional 10 ml up to 40 ml. RESULTS: There were no differences in ease of insertion or ease of fibreoptic-guided intubation, OLP, in-vivo intracuff pressure or anatomic position between groups. CONCLUSIONS: We conclude that the performance of the ILM is similar for fresh cadavers and paralysed anesthetised patients. This suggests that the fresh cadaver is a suitable model for training and research.

Adult↗
PubMed1999

Comparison of the flexible and standard laryngeal mask airways.

PURPOSE: To determine mucosal pressures, ease of insertion, mask position and oropharyngeal leak pressures for the flexible (FLMA) and standard laryngeal mask airway (LMA). METHODS: Forty anesthetized, paralysed adult patients were randomly allocated to receive either the FLMA or LMA. Microchip sensors were attached to the LMA or FLMA at identical locations corresponding to the base of tongue, hypopharynx, lateral pharynx, oropharynx, posterior pharynx and pyriform fossa. Mucosal pressure, oropharyngeal leak pressure (OLP) and mask position (assessed fibreoptically) were recorded during inflation of the cuff from 0-40 ml in 10 ml increments. RESULTS: Ease of insertion and mask position were similar between devices. Mean OLP was higher for the LMA (22 vs 19 cm H2O), but the maximum OLP was similar (25 vs 24 cm H2O). Mean mucosal pressures were generally low (< 12 cm H2O) for both devices, but were higher for the LMA in the lateral pharynx (4 vs 1 cm H2O) and oropharynx (13 vs 3 cm H2O) and higher in the posterior pharynx for the FLMA (4 vs 2 cm H2O). The OLP for both devices increased with increasing intracuff volume from 0-10 ml and 10-20 ml, and from 20-30 ml for the FLMA. CONCLUSIONS: We conclude that the LMA and FLMA perform similarly in terms of ease of insertion and mask position, but OLP and mucosal pressures are slightly higher for the LMA. Pharyngeal mucosal pressures for both devices are lower than those considered safe for the tracheal mucosa. The overall clinical performance between the two devices is similar.

Adolescent↗
PubMed1999

Growth deficiency and malnutrition in Bloom syndrome.

OBJECTIVES: To describe the growth and nutritional status of a pediatric population with Bloom syndrome. STUDY DESIGN: Longitudinal growth data from 148 patients in the Bloom's Syndrome Registry (85 male, 63 female) were compiled retrospectively from physician and parent records to develop graphed statistics of weight-for-age, height-for-age, fronto-occipital circumference-for-age, and weight-for-height for both sexes with comparisons with the normal population. RESULTS: Term birth measurements confirm that the growth deficiency of Bloom syndrome has prenatal onset. Stunting persists throughout life, and an adolescent growth spurt is not apparent from the smoothed data. Growth continues by at least 1 cm/yr until age 21 years for both sexes. More than half of children with Bloom syndrome are significantly wasted until age 8 years, which is not related to early death or underlying malignancy. The mean body mass index for adults with Bloom syndrome after age 25 years is low normal (n = 22, mean = 20.2 kg/m2). CONCLUSIONS: Children with Bloom syndrome have significant growth retardation and wasting.

Adolescent↗
PubMed1999

Effects of smaller tidal volumes during basic life support ventilation in patients with respiratory arrest: good ventilation, less risk?

OBJECTIVE: When ventilating an unintubated patient in cardiac or respiratory arrest, smaller tidal volumes of 500 ml instead of 800-1200 ml may be beneficial to decrease peak airway pressure, and to minimise stomach inflation. The purpose was to determine the effects of small (approximately 500 ml) versus large (approximately 1000 ml) tidal volumes given with paediatric versus adult self-inflatable bags and approximately 50% oxygen on respiratory parameters in patients during simulated basic life support ventilation. METHODS: While undergoing induction of anaesthesia, patients were randomised to three minutes of ventilation with either an adult (n = 40) or paediatric (n = 40) self-inflatable bag. RESULTS: When compared with an adult self-inflatable bag, the paediatric bag resulted in significantly lower mean (+/- standard deviation) exhaled tidal volume (365 +/- 55 versus 779 +/- 122 ml; P < 0.0001), peak airway pressure (20 +/- 2 versus 25 +/- 5 cm H2O; P < 0.0001), but comparable oxygen saturation (97 +/- 1% versus 98 +/- 1%; NS (nonsignificant)). Stomach inflation occurred in five of 40 patients ventilated with an adult self-inflatable bag, but in no patients who were ventilated with a paediatric self-inflatable bag (P = 0.054). CONCLUSION: Administering smaller tidal volumes with a paediatric instead of an adult self-inflatable bag in unintubated adult patients with respiratory arrest maintains good oxygenation and carbon dioxide elimination while decreasing peak airway pressure, which makes stomach inflation less likely.

Adult↗
PubMed1999

Laryngeal mask airway intracuff pressure estimation by digital palpation of the pilot balloon: a comparison of reusable and disposable masks.

Digital palpation of the pilot balloon provides information about the intracuff pressure of the laryngeal mask airway. The purpose of this in vitro study was to evaluate this technique for the reusable and disposable laryngeal mask airway. Ten anaesthetists and 10 recovery-unit nurses estimated intracuff pressures from low/high initial pressures before/after training. In the pretraining phase, the mean (95% CI) pressure was 99 (94-105) cmH2O, but this was significantly lower for the reusable laryngeal mask airway (91 vs. 103 cmH2O) and if the initial pressure was low (81 vs. 112 cmH2O). In the post-training phase, there was a significant overall improvement to 75 (66-85) cmH2O, but target pressures remained more accurate if the initial pressure was low. Subjects in the training group could estimate 95% of pressures for both devices to within +/-10 cmH2O of the target if the initial pressure was low. We conclude that anaesthetists and recovery-unit nurses are capable of accurate estimation of intracuff pressures using the digital palpation technique following a brief period of training.

Air Pressure↗
PubMed1999

The cuffed oropharyngeal airway vs. the laryngeal mask airway: a randomised cross-over study of oropharyngeal leak pressure and fibreoptic view in paralysed patients.

We conducted a randomised cross-over study of 20 patients to test the hypothesis that oropharyngeal leak pressure and the fibreoptic view differ between the cuffed oropharyngeal airway and laryngeal mask airway in paralysed patients. We also tested the design premise that inflation of the cuffed oropharyngeal airway cuff elevates the epiglottis from the posterior pharyngeal wall. Both airways were inserted into each patient in random order. Oropharyngeal leak pressure and fibreoptic view were documented at zero volume and after each additional 10 ml up to the maximum recommended volume for each device. The laryngeal mask had a higher maximum (23 vs. 16 cmH2O, p = 0.03), minimum (9 vs. 2 cmH2O, p < 0.02) and overall (17 vs. 9 cmH2O, p < 0.001) oropharyngeal leak pressure compared with the cuffed oropharyngeal airway. The glottic inlet was visible more frequently with the laryngeal mask (96 vs. 39%, p < 0.0001). There was no elevation of the epiglottis from the posterior pharyngeal wall with the cuffed oropharyngeal airway. We conclude that the laryngeal mask forms a more effective seal and provides a better fibreoptic view of the glottic inlet than the cuffed oropharyngeal airway in paralysed patients. Inflation of the cuffed oropharyngeal airway cuff does not cause elevation of the epiglottis.

Adult↗
PubMed1999

Pharmacokinetics of rocuronium bromide in obese female patients.

Following administration of 0.6 mg kg-1 rocuronium, the pharmacokinetics and the pharmacodynamics were studied in six obese and six control (normal weight) patients receiving balanced anaesthesia. Twelve gynaecological patients were allocated into two groups, according to body mass index (normal weight: body mass index: 20-24, obese weight: body mass index > 28). Venous plasma concentrations were determined by high-pressure liquid chromatography before administration of rocuronium, at 1, 2, 4, 6, 8, 10, 15, 20, 25, 30, 35, 40, 48, 60, 75, 120, 180, 240, 300, 360 and 420 min after administration of rocuronium and at recovery of single twitch to 25% and 75% of control twitch height. Onset time was shorter (NS) in the obese compared with normal weight (obese weight: 65 +/- 16, normal weight: 100 +/- 39 s, mean +/- SD). Duration 25% (obese weight: 29.5 +/- 5.3, normal weight: 28.4 +/- 5.3 min) and spontaneous recovery time (obese weight: 12.6 +/- 2.7, normal weight: 12.5 +/- 2.3 min) did not show any differences between the two groups. The pharmacokinetics of rocuronium were comparable in the two groups. The volume of distribution at steady state Vss (mL kg-1) was 208 +/- 56 in normal weight and 169 +/- 37 in obese weight. Distribution (T1/2 alpha) and elimination half-life (T1/2 beta) as well as mean residence time were 15.6 +/- 3.7, 70.3 +/- 23.9 and 53.2 +/- 9.8 min in normal weight and 16.9 +/- 3.8, 75.5 +/- 25.5 and 51.1 +/- 18.9 min in obese weight, respectively. Also, no differences were observed in plasma clearance (3.89 +/- 0.58 in normal weight and 3.62 +/- 1.42 mL kg-1 min-1 obese weight). This study indicates that the pharmoacodynamics and pharmacokinetics of rocuronium are in female patients not altered by obesity.

Adult↗
PubMed1999

The influence of increasing concentrations of nitrous oxide on cerebral blood flow velocity in hypocapnic patients with brain tumours.

An increase of more than 50% in cerebral blood flow velocity in the middle cerebral artery was recently reported in hypocapnic volunteers, while inhaling 50% nitrous oxide. We measured cerebral blood flow velocity in the middle cerebral artery in 10 anaesthetized hypocapnic (ETCO2 = 25 mmHg) patients with brain tumours while administering increasing concentrations of nitrous oxide. At an end-tidal concentration of 50% and 70% nitrous oxide in oxygen, neither mean arterial pressure (base-line: 84 +/- 8 mmHg vs. (50% nitrous oxide): 82 +/- 9 mmHg and (70% nitrous oxide): 80 +/- 8 mmHg) nor cerebral blood flow velocity in the middle cerebral artery (base-line: 32 +/- 7 cm s-1 vs. (50% nitrous oxide): 34 +/- 8 cm s-1 and (70% nitrous oxide): 34 +/- 9 cm s-1) changed significantly. The data from our clinical investigation indicate that administration of increasing concentrations of nitrous oxide to already anaesthetized and hypocapnic patients does not change cerebral blood flow velocity in the middle cerebral artery.

Adult↗
PubMed1999

The laryngeal mask airway in fresh cadavers versus paralysed anaesthetized patients: ease of insertion, airway sealing pressure, intracuff pressures and anatomic position.

We compared the performance of the size 5 laryngeal mask airway in 20 paralysed anaesthetized male patients and 20 male cadavers (6-24 h post-mortem). Groups were matched for height and weight. Airway sealing pressure, in vivo intracuff pressure and anatomical position (judged fibre-optically) were documented at zero volume and after each additional 10 mL up to 40 mL. All laryngeal mask airways were inserted at the first attempt and insertion times were similar. There were no differences in airway sealing pressure, in vivo intracuff pressure or fibre-optic position between the groups. We conclude that the performance of the laryngeal mask airway is similar for fresh cadavers and paralysed anaesthetized patients. This may have implications for laryngeal mask airway research and training.

Adult↗
PubMed1999

Recurrent laryngeal nerve injury with the laryngeal mask.

We report a case of recurrent laryngeal nerve injury after anesthesia with the LMA and review the published cases of major pharyngolaryngeal morbidity. Prevention of this and other pharyngolaryngeal injuries probably depends on the skilled application of the correct insertion technique and the use of low intracuff pressures and volumes.

Aged↗
PubMed1999

Pharmacology of warfarin and clinical implications.

The history of oral anticoagulants started in the 1920s in North Dakota and Alberta when a new type of hemorrhagic disease struck cattle in these areas. The group of Karl Paul Link finally succeeded in isolating the causative agent, dicumarol. It was not before the 1940s, that dicumarol or its derivatives were introduced to medicine. Acenocoumarol, phenprocoumon, and warfarin are the most commonly used oral anticoagulants. There is no known difference in the pharmacodynamic activity of these agents on the vitamin K metabolism. They are completely absorbed from the gastrointestinal tract and are firmly bound to plasma albumin and metabolized in the liver. The different elimination half-lives of the coumarins have several implications for patient management. Absorption, protein binding, and anticoagulant activity of oral anticoagulants are affected in many different ways. Also the different pharmacological properties of coumarins require different strategies in the clinical management of patients.

Animals↗
PubMed1999

Comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients.

We have compared four tests for assessing airway sealing pressure with the laryngeal mask airway (LMA) to test the hypothesis that airway sealing pressure and inter-observer reliability differ between tests. We studied 80 paralysed, anaesthetized adult patients. Four different airway sealing pressure tests were performed in random order on each patient by two observers blinded to each other's measurements: test 1 involved detection of an audible noise; test 2 was detection of end-tidal carbon dioxide in the oral cavity; test 3 was observation of the aneroid manometer dial as the pressure increased to note the airway pressure at which the dial reached stability; and test 4 was detection of an audible noise by neck auscultation. Mean airway sealing pressure ranged from 19.5 to 21.3 cm H2O and intra-class correlation coefficient was 0.95-0.99. Inter-observer reliability of all tests was classed as excellent. The manometric stability test had a higher mean airway sealing pressure (P < 0.0001) and better inter-observer reliability (P < 0.0001) compared with the three other tests. We conclude that for clinical purposes all four tests are excellent, but that the manometric stability test may be more appropriate for researchers comparing airway sealing pressures.

Adolescent↗
PubMed1999

Liability of laryngeal mask airway devices to thermal damage from KTP and Nd:YAG lasers.

We have compared the liability of four laryngeal mask airway (LMA) devices (standard, flexible, intubating and reusable) and a tracheal tube to thermal damage from KTP and Nd:YAG lasers at two power densities used commonly in airway surgery: 570 W cm-2 and 1140 W cm-2. Eighty-five airway devices were tested: 24 standard LMA (silicone-based), 12 flexible LMA (silicone-based, metal wires), 24 disposable LMA (PVC-based), one intubating LMA (silicone and steel-based) and 24 PVC-based tracheal tubes. Comparisons were made during laser strike to eight different targets: the unmarked and marked part of the airway device tube; the unmarked part of the airway device tube after application of blood; the cuff filled with air or methylene blue dye; the unmarked flexible LMA tube on or between the metal wires; and the epiglottic elevator bar of the intubating LMA. The laser strike was continued for 30 s and each target was tested three times. Three different, but identical, impact sites were used for each target. There was no ignition of any airway device with either power density or laser type. The silicone-based LMA were generally more resistant to flaring and penetration than the PVC-based LMA and tracheal tube, but the intubating LMA tube flared more rapidly with the KTP laser, and the disposable LMA cuff was more resistant to penetration. Print markings, blood and the metal wires of the flexible LMA reduced the thermal resistance of the tube. Filling the cuff with methylene blue dye increased the thermal resistance of all airway devices. We conclude that the silicone-based LMA devices were more thermal resistant to KTP and Nd:YAG laser strike than PVC-based devices with the exception of the disposable LMA cuff and the intubating LMA tube.

Equipment Failure↗
PubMed1999

Calculated vs measured pharyngeal mucosal pressures with the laryngeal mask airway during cuff inflation: assessment of four locations.

We have compared calculated with measured pharyngeal mucosal pressures at four different locations on the surface of the laryngeal mask airway (LMA) during cuff inflation in 10 anaesthetized, paralysed adult patients. Microchip sensors were attached to a size 5 LMA at the following locations: the anterior and lateral side, tip and backplate. Pressures were recorded during inflation of the cuff from 0 to 40 ml in 5-ml increments. Calculated pressures were determined by subtracting in vivo from in vitro intracuff pressures. Calculated pressures were greater than measured pressures at cuff volumes of 5 ml or greater at all locations (P < or = 0.003). The greatest mean calculated the measured pressures were 118 and 14 cm H2O, respectively. We conclude that measured mucosal pressures at the four locations tested were less than calculated pressures and less than capillary perfusion pressure.

Adult↗
PubMed1999

Laryngeal mask airway size selection in males and females: ease of insertion, oropharyngeal leak pressure, pharyngeal mucosal pressures and anatomical position.

We have compared ease of insertion, oropharyngeal leak pressure, directly measured pharyngeal mucosal pressure and anatomical position (assessed fibreoptically) for the size 4 and size 5 laryngeal mask airway (LMA) in 20 male and 20 female patients. Microchip pressure sensors were attached to the LMA at locations corresponding to the piriform fossa, hypopharynx, base of the tongue, lateral and posterior pharynx, and the oropharynx. Oropharyngeal leak pressure, mucosal pressure and fibreoptic position were recorded during inflation of the cuff from 0 to 30 ml in 10-ml increments. In males, oropharyngeal leak pressure over the inflation range was higher for size 5 (21 vs 17 cm H2O; P = 0.01); mucosal pressure over the inflation range was higher in the posterior pharynx for size 4 (7 vs 2 cm H2O; P = 0.007), and higher in the piriform fossa (8 vs 5 cm H2O; P = 0.003) and hypopharynx (9 vs 5 cm H2O; P = 0.003) for size 5. In females, oropharyngeal leak pressure over the inflation range was the same (21 vs 21 cm H2O), but mucosal pressure over the inflation range was higher in the piriform fossa (21 vs 8 cm H2O; P = 0.003) and posterior pharynx (4 vs 2 cm H2O; P = 0.004) for size 4, and higher in the lateral pharynx (5 vs 1 cm H2O; P = 0.01) and oropharynx (11 vs 5 cm H2O; P = 0.009) for size 5. The distribution of mucosal pressure was different for size 4 between males and females, but not for size 5. For both males and females, fibreoptic position was similar. We conclude that the size 5 LMA is optimal in males, but either size is suitable for females. The shape of the pharynx may be different between males and females.

Adult↗
PubMed1999

Direct measurement of mucosal pressures exerted by cuff and non-cuff portions of tracheal tubes with different cuff volumes and head and neck positions.

We measured directly mucosal pressures against the cuff and non-cuff portions of the tracheal tube in different head-neck positions and tested the reliability of calculated mucosal pressures, in vivo intracuff pressures and cuff volume as determinants of directly measured mucosal pressures. We studied 10 anaesthetized, paralysed adult patients. An 8.5-mm, high volume, low pressure PVC tracheal tube was used. Microchip sensors were attached to three cuff locations (anterior, lateral and posterior) and two non-cuff locations (anterior tip and anterior aspect of the tube, 5 cm proximal to the cuff). Directly measured mucosal pressures, in vivo intracuff pressures and calculated mucosal pressures (in vivo minus in vitro intracuff pressures) were determined after brief inflation (< 15 s) to 0, 5, 10 and 15 ml. In vivo intracuff pressures were then set at 30 mm Hg and the measurements repeated, first in the neutral position and then with the head-neck extended, flexed and rotated. Cuff mucosal pressures were highest anteriorly and lowest posteriorly. Non-cuff mucosal pressures did not vary with cuff volume and were approximately 15 mm Hg. Compared with the neutral position, in vivo intracuff pressures were higher in the rotated, extended and flexed positions. Compared with the neutral position, mucosal pressure increased on the anterior aspect of the tube in the flexed position by 22 mm Hg (P = 0.003), at the anterior tip in the extended position by 11 mm Hg (P = 0.002) and at the anterior tip (5 mm Hg, P = 0.05) and lateral aspect of the cuff (5 mm Hg, P = 0.03) in the rotated position. In vivo intracuff pressures and calculated mucosal pressures were moderate predictors of measured mucosal pressures; cuff volume was a poor predictor. We conclude that tracheal mucosal pressures were highest anteriorly, that non-cuff portions of the tube exerted substantial mucosal pressures and that the rotated position caused a greater increase in tracheal mucosal pressure than the extended or flexed position. Indirect methods of measuring mucosal pressure were of moderate predictive value.

Adult↗