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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.