The provision of surgical tracheostomies by maxillofacial surgeons in the UK: time for a dedicated tracheostomy team?

Surgical tracheostomy is a commonly provided service by surgical teams for patients in intensive care where percutaneous dilatational tracheostomy is contraindicated. A number of factors may interfere with its provision on shared emergency operating lists, potentially prolonging the stay in intensive care. We undertook a two-part project to examine the factors that might delay provision of surgical tracheostomy in the intensive care unit. The first part was a prospective audit of practice within the University Hospital Coventry. This was followed by a telephone survey of oral and maxillofacial surgery units throughout the UK. In the intensive care unit at University Hospital Coventry, of 39 referrals, 21 (53.8%) were delayed beyond 24 hours. There was a mean (standard deviation) time to delay of 2.2 days (0.9 days) and the most common cause of delay was surgeon decision, accounting for 13 (61.9%) delays. From a telephone survey of 140 units nationwide, 40 (28.4%) were regularly involved in the provision of surgical tracheostomies for intensive care and 17 (42.5%) experienced delays beyond 24 hours, owing to a combination of theatre availability (76.5%) and surgeon availability (47.1%). There is case for having a dedicated tracheostomy team and provisional theatre slot to optimise patient outcomes and reduce delays. We aim to implement such a move within our unit and audit the outcomes prospectively following this change.

Neuromedin U--a study of its distribution in the rat.

The distribution of neuromedin U, a novel peptide originally isolated from porcine spinal cord, was investigated in the rat using a recently developed radioimmunoassay. High concentrations of neuromedin U-like immunoreactivity were found in the pituitary gland and gastrointestinal tract. Significant concentrations of immunoreactivity were also found in several regions of the rat brain, spinal cord and both male and female genitourinary tracts. In the small intestine, neuromedin U-like immunoreactivity was restricted to the submucosal muscular layers, suggesting localization in neurones rather than in epithelial cells. Chromatographic analysis of pituitary, spinal cord and gut revealed a single peak of immunoreactivity which did not co-elute with either synthetic porcine neuromedin U-25 nor neuromedin U-8, indicating inter-species molecular heterogeneity.

Distribution and postprandial release of porcine peptide YY.

Peptide YY (PYY), a thirty-six amino acid intestinal hormonal peptide with a tyrosine residue at each end (hence YY as Y represents tyrosine in the new peptide nomenclature), was found throughout the gastrointestinal tract of the pig. Concentrations were very low in the foregut (antrum, 3.4 +/- 0.3 pmol/g; duodenum, 1.1 +/- 1.5 pmol/g), higher in the distal small intestine (ileum, 100 +/- 13 pmol/g) and very high in the large bowel (descending colon, 270 +/- 45 pmol/g). Peptide YY was found to circulate in plasma and concentrations rose substantially in response to eating (fasting, 138 +/- 15 pmol/l; postprandial, 263 +/- 21 pmol/l; P less than 0.001). There was a small but significant portal/arterial gradient in postprandial PYY levels. More than 90% of the immunoreactive PYY in gut extracts eluted, on gel permeation chromatography, in an identical position to pure PYY standard, but small amounts of higher molecular weight material, possibly precursors, were detected. In contrast, plasma from fasting pigs contained a large proportion (60-70%) of these large molecular forms. These findings suggest that the putative pro-PYY may be cleared more slowly from the circulation than the 36 amino acid hormonal peptide. The high concentrations of immunoreactive PYY in the circulation of the young pig may reflect a species difference between pig and man or may indicate an important role for PYY in the developing animal.

Characterization of neuromedin U like immunoreactivity in rat, porcine, guinea-pig and human tissue extracts using a specific radioimmunoassay.

Two novel bioactive peptides termed neuromedin U-8 and neuromedin U-25 have recently been isolated from porcine spinal cord but nothing is known of their occurrence and molecular forms in other species. Following gel permeation chromatography, a specific radioimmunoassay detected only a single molecular form of neuromedin U-like immunoreactivity (NmU-LI) in rat, porcine and human central nervous system and gastrointestinal tract. Only guinea pig tissue extracts revealed two molecular forms of NmU-Li. Reverse phase high performance liquid chromatographic (HPLC) analysis demonstrated that porcine NmU-LI co-eluted with synthetic neuromedin U-25 standard. Human and rat NmU-LI however, was more hydrophobic on HPLC thus indicating species differences.

Rat immunoreactive cholecystokinin (CCK): characterization using two chromatographic techniques.

Acid and neutral extracts of rat cerebral cortex and upper small intestine were prepared and the endogenous concentrations of cholecystokinin-like immunoreactivity (CCK-LI) measured by three new CCK-specific radioimmunoassays. The characterization of the immunoreactive CCK molecular forms was undertaken using gel permeation chromatography in the presence of 6 M urea to minimise problems relating to peptide adsorption or aggregation. Reverse-phase high-performance liquid chromatography (HPLC) was also performed on the rat tissue extracts. Rat cortex contained 268 +/- 12 pmol/g CCK-LI, and over 90% resembled the sulphated CCK-8, which was preferentially extracted at neutral pH. In contrast, the rat upper small intestine (97 +/- 8 pmol/g of CCK-LI) contained less than 20% CCK-8, the majority of immunoreactive CCK being of larger molecular size and being preferentially extracted at acid pH. In the small intestine the predominant molecular form(s) was intermediate in size between CCK-33 and CCK-8. Large amounts of CCK-33 and of a molecular form larger than CCK-33 were also detected. It is concluded that post-translational cleavage of CCK differs in rat brain and gut.

Oxidation/reduction of methionine residues in CCK: a study by radioimmunoassay and isocratic reverse phase high pressure liquid chromatography.

The study was undertaken to investigate the oxidation and reduction of cholecystokinin (CCK) both as pure standards and as endogenous porcine peptides. Furthermore an attempt was made to prevent oxidation of the endogenous porcine peptides in the extraction procedure. CCK-8 and CCK-33 standards were always oxidized in weak solutions, CCK-8 varying from 26% to 67% oxidized and CCK-33 from 18% to 70%. Similarly, tissue extracts of porcine brain and duodenum contained oxidized forms of the peptide. CCK standards were readily oxidized in the presence of hydrogen peroxide. Oxidized CCK-8 standard and CCK-8 in porcine brain was 90% reduced and oxidized CCK-33 standard and in duodenal extracts was reduced by 70% by a 40 hour incubation with 0.725 mol/l dithiothreitol at 37 degrees C. Extraction of CCK peptides in the presence of 65 mmol/l dithiothreitol resulted in almost complete prevention of oxidation with over 95% of the peptides being obtained in the reduced state. This additive is therefore recommended for all tissue quantitation studies.

Changes in the anti-lipolytic action and binding to plasma membranes of N6-L-phenylisopropyladenosine in adipocytes from starved and hypothyroid rats.

The anti-lipolytic effect of the adenosine analogue N6-L-phenylisopropyladenosine was studied with rat adipocytes incubated with a high concentration of adenosine deaminase (0.5 unit/ml, approx. 2.5 micrograms/ml) and concentrations of noradrenaline that were equieffective in different physiological states. These studies were performed to compare the fed and starved (24h) states and to compare a hypothyroid state (induced by feeding propylthiouracil + a low-iodine diet) with the euthyroid state. Starvation increased sensitivity of the cells to the lipolytic action of noradrenaline, while decreasing sensitivity to the antilipolytic action of phenylisopropyladenosine. Hypothyroidism resulted in decreased sensitivity to noradrenaline and increased sensitivity to phenylisopropyladenosine. Studies of the binding of [3H]phenylisopropyladenosine to adipocyte plasma membranes indicated heterogeneity of binding sites or negative co-operativity in the binding. Starvation did not change [3H]phenylisopropyladenosine binding to membranes, whereas hypothyroidism caused an unexpected decrease in both the number and affinity of the binding sites. These observations are discussed in terms of the dual regulation of adipose-tissue lipolysis by lipolytic and anti-lipolytic agents.

Lipoprotein lipase activity of rat cardiac muscle. Changes in the enzyme activity during incubations of isolated cardiac-muscle cells in vitro.

1. Isolated cardiac-muscle cells from the hearts of adult rats were shown to retain a high amount of viability during 4 h of incubation when viability was assessed by Trypan Bue stain exclusion and intracellular enzyme leakage. 2. The cells also retained their ability to take up O2 and utilize added substrates over the period of incubation at both 25 and 30 degrees C. 3. When cells from the hearts of fed rats were incubated in a buffered-salts solution at pH 7.4 in the presence of amino acids and heparin, lipoprotein lipase activity in the medium increased progressively. 4. During these incubations the intracellular activity of the enzyme remained constant and the total activity of lipoprotein lipase in the system (cells plus medium) increased by 80% over the 4 h of incubation at 25 degrees C. 5. In the absence of heparin only low amounts of enzyme activity were detectable in the medium and the total lipoprotein lipase activity in the system remained constant. 6. The measurement of lipoprotein lipase activity in either fresh homogenates of the cells or in homogenates of acetone/diethyl ether-dried powders of the cells had no effect on the overall pattern of activity change during the incubations, although as reported previously the total activity detected with acetone/diethyl either-dried preparations was approx. 3-fold higher than with fresh cell homogenates. 7. The observations were compared with published data on lipoprotein lipase activity changes in neonatal heart cell cultures maintained in vitro.

Lipoprotein lipase activity of rat cardiac muscle. The intracellular distribution of the enzyme between fractions prepared from cardiac muscle and cells isolated from the hearts of fed and starved animals.

1. Subcellular fractions, characterized by using morphological, compositional and enzymic markers, were prepared from rat heart tissue and cells isolated from the hearts of fed and 24 h-starved rats. 2. The lipoprotein lipase activity of fractions from whole tissue and isolated cells was determined in either fresh fractions or in acetone/diethyl ether powders of the fractions. 3. Lipoprotein lipase activity was present in all the fractions from tissue and cells, but was found to be of highest relative specific activity in the microsomal () fractions. 4. In fractions prepared from the isolated cells of hearts from starved rats the proportion of the total lipoprotein lipase present and its relative specific activity in the microsomal fraction were greater than in the equivalent fractions from fed animals. 5. The enhancement of lipoprotein lipase activity as a result of the acetone/diethyl ether powder preparation of fractions was most extensive in the microsomal fractions. 6. Investigation of the microsomal fraction showed that the lipoprotein lipase activity present was in two pools, one of which was within endoplasmic-reticulum vesicles. 7. The observations were consistent with the possibility that the cardiac-muscle cell could be the origin of the lipoprotein lipase activity functional in triacylglycerol uptake by the heart.

The lipoprotein lipase (clearing-factor lipase) activity of cells isolated from rat cardiac muscle.

The total lipoprotein lipase activity recovered in suspension of cells prepared from adult rat hearts was unaffected by the nutritional state of the animals used. The enzyme activity present in the cell suspensions was almost exclusively associated with the cardiac muscle cells present as the major cell type.