The airways and anaesthesia II. Pathophysiology

We pointed out in the first of these two articles that the commonest cause of an anaesthetic disaster in young healthy patients is a loss of airway patency then a failure to intubate occurring unexpectedly in the absence of head or neck pathology. Upper airway obstruction is a very common complication of general anaesthesia and all anaesthetists must be trained in the management of this problem. Less obvious are the changes that can occur in the lower airways which can impair gas exchange by increasing ventilation-perfusion mismatch. This article is concerned with these pathophysiological changes that occur during general anaesthesia.

The phylogenetic position and ultrastructure of the uncultured bacterium Achromatium oxaliferum

Achromatium oxaliferum is a large, morphologically conspicuous, sediment-dwelling bacterium. Nothing is known concerning its phylogeny and it has eluded all attempts at laboratory cultivation. The limited physiological description of A. oxaliferum has been based on morphological features of the bacterium such as the presence of intracellular sulphur inclusions. A. oxaliferum cells were purified from a wetland region close to Rydal Water (Cumbria, UK). Scanning and transmission electron microscopy revealed that a number of morphologically distinct A. oxaliferum cell-types, based on cell surface features and the size and abundance of calcite and sulphur inclusions within the cells, were present in a single sample of purified cells. PCR was used to amplify almost full-length 16S rRNA gene sequences from DNA extracted from A. oxaliferum cells directly purified from sediments. The PCR products were cloned and partial sequences (approx. 400 bp) were determined for seven of the clones. Three different sequence clusters were recovered from the clone libraries. A near full-length (1489 bp) 16S rRNA gene sequence was determined for a representative clone of the most dominant sequence-type (52% of the sequences). Comparative sequence analysis showed A. oxaliferum to form a deep branching lineage within the gamma-subdivision of the Proteobacteria. A. oxaliferum was related most closely to the Chromatium assemblage that includes sulphur-oxidizing symbiotic bacteria, purple sulphur bacteria, and sulphur- and iron-oxidizing thiobacilli. Phylogenetic inferences made using distance, parsimony and maximum likelihood methods all placed A. oxaliferum with this group of bacteria. Bootstrap support for a relationship with any particular lineage within the assemblage was weak. The seven clone sequences recovered from the A. oxaliferum cells however formed a monophyletic group well supported by bootstrap analysis (85-100% support depending on the analysis done). It was concluded that A. oxaliferum was related to organisms of the Chromatium assemblage but constituted a novel lineage within this group of bacteria. A. oxaliferum cells were confirmed as the source of the 16S rRNA sequence obtained, by the use of a fluorescently-labelled 16S rRNA-targeted oligonucleotide specific for the A. oxaliferum rRNA sequence.

The effects of hypoxaemia and recommendations for postoperative oxygen therapy

Hypoxaemia following surgery is common and may be prolonged and severe. The thresholds for deleterious effects of hypoxaemia on the heart and central nervous system are reviewed and the problems of assessment of the adequacy of tissue oxygenation are outlined. Recommendations for postoperative oxygen therapy are made.

Plasma antioxidant potential in severe sepsis: a comparison of survivors and nonsurvivors

OBJECTIVE

To determine the plasma antioxidant potential of patients in the intensive care unit (ICU) with severe sepsis and secondary organ dysfunction and relate these findings to outcome.

DESIGN

A prospective, cohort study.

SETTING

A nine-bed ICU in a university teaching hospital.

PATIENTS

Fifteen consecutive patients, who were within 16 hrs of development of severe sepsis and secondary organ dysfunction.

INTERVENTIONS

Plasma samples were obtained within 16 hrs of the onset of secondary organ dysfunction and subsequently on days 2, 3, 4, 6, 8, 10, and 15 until patients either left the ICU or died. Plasma antioxidant potential was determined by an ultraviolet spectrophotometric technique.

MEASUREMENTS AND MAIN RESULTS

The mean initial plasma antioxidant potential was lower than our range for healthy volunteers (p < .05). Survivors had an initial plasma antioxidant potential that was greater than nonsurvivors (p < .01), and serial subset analysis demonstrated that survivors, despite having a low initial plasma antioxidant potential rapidly attained normal or supranormal values. While plasma antioxidant potential also increased in nonsurvivors over time, values in this subset never reached the normal range and remained below values in survivors at all time points studied (p < .05).

CONCLUSIONS

Plasma antioxidant potential is initially decreased in patients with sepsis who develop organ dysfunction, and it increases over time. While we have no clear evidence to prove that this reduction has a causal relationship, failure to achieve a normal plasma antioxidant potential is strongly associated with an unfavorable outcome.

The effect on the heart of hypoxaemia in patients with severe coronary artery disease

The aim of the study was to examine the effect of spontaneous nocturnal hypoxaemia on myocardial ischaemia in patients with severe coronary artery disease. This was a prospective study of continuously measured oxygen saturation and ECG overnight in patients prior to coronary artery bypass graft surgery. Fifteen patients with angiographically proved coronary artery disease were studied between October 1992 and September 1993. All patients had episodes of hypoxaemia with oxygen saturation < 94% and eight of the 15 patients had episodes where oxygen saturation < 85%. An episode was defined as a period of hypoxaemia not less than 2.5 min in duration, the longest total duration of hypoxaemia in one patient being 355 min. Twelve of the 15 patients showed a drop in ST segment of 1 mm or more lasting from 5-700 min. The hypoxaemic and ischaemic episodes apparently occurred at random. No causal relationship could be shown between hypoxaemia and ischaemia.

Contribution of various substrates to total citric acid cycle flux and anaplerosis as determined by 13C isotopomer analysis and O2 consumption in the heart

A simple relationship between parameters derived from a 13C NMR isotopomer analysis and O2 consumption is presented that allows measurement of the absolute rate of acetyl-CoA oxidation and anaplerotic flux in tissues oxidizing a mixture of four substrates. The method was first applied in a study of the effects of work state and beta-adrenergic stimulation on net acetate oxidation and anaplerosis in the isolated working rat heart. The results demonstrate that the anticipated ratio of 2 between O2 consumption and TCA cycle flux for hearts oxidizing only acetate holds at low workload when anaplerosis is low, but deviates toward a factor of 3 under high workload conditions when anaplerosis is increased. This analysis was also extended to hearts that oxidize a more physiological mixture of substrates including long-chain fatty acids, acetoacetate, lactate, pyruvate, and glucose. We show that the contribution each substrate makes to total TCA cycle flux can be determined by combined 13C NMR and O2 consumption measurements. The present study also demonstrates that stimulation of anaplerosis (by addition of propionate) can significantly alter the relative contribution each substrate makes to total TCA cycle flux. We conclude if 13C labeling patterns are selected appropriately, a comprehensive picture of flux through all major metabolic pathways feeding the cycle can be determined in a single experiment even when complex physiological mixtures of substrates are provided.

Effects of different oxidative insults on intermediary metabolism in isolated perfused rat hearts

13C and 31P NMR were used to evaluate exogenous substrate utilization and endogenous phosphate metabolites in perfused rat hearts exposed to tert-butylhydroperoxide (tert-BOOH) and hydrogen peroxide (H2O2). Both reagents caused a reduction in developed pressure compared to controls and, in agreement with previous 31P NMR data, had different effects on intracellular high-energy phosphates and glycolysis. 13C Isotopomer analysis of tissue extracts showed that H2O2 and tert-BOOH also had significantly different effects on substrate utilization by the citric acid cycle. The contribution of exogenous lactate and glucose to acetyl-CoA was 43% in controls and increased to over 80% in the presence of either oxidant. With tert-BOOH, exogenous glucose and lactate were both significant contributors to acetyl-CoA (44 +/- 2 and 41 +/- 3%). However, with H2O2, exogenous lactate supplied a much higher fraction of acetyl-CoA (72 +/- 2%) than glucose (9 +/- 1%). Also, when [2-(13)C] glucose was supplied, accumulation of [2-(13)C] and [5-(13)C] fructose 1,6-bisphosphate was observed in the presence of H2O2, indicating inhibition of glyceraldehyde-3-phosphate dehydrogenase. These results indicate that despite this glycolytic inhibition, H2O2 increased the utilization of pyruvate precursors when lactate was present as an alternative carbohydrate substrate.

The effects of temperature on the filtration of diluted blood through 3 mu m and 5 mu m filters

The effect of temperature on the flow of diluted blood [Hct = 0.21], through 5 mu m Nuclepore filters, is described by the Arrhenius equation with an energy of activation of 27.7 kJ/mol. Plasma, diluted with PBS, is almost three times less sensitive to temperature, with an energy of activation of 9.8 kJ/mol, while red cells are of intermediate sensitivity, with an energy of activation of 14.7 kJ/mol. The most sensitive elements to changes in temperature are leukocytes, with energies of activation of 31 kJ/mol and 35 kJ/mol for fast-flowing leukocytes (granulocytes and lymphocytes) and slow-flowing leukocytes (monocytes) respectively. Hence, the major determinants of the decline in filterability of blood through micropore filters are the leukocytes. This effect is compounded when blood is kept for 10 minutes or more at 10 degrees C due to activation of granulocytes, which leads to permanent pore blocking when the affected blood is filtered at room temperature. The combination of increased passage time of leukocytes through peripheral areas at abnormally low temperatures and subsequent activation might influence the flow of blood in non-affected tissues. The effect of temperature on the filterability of red blood cells through 3 mu m filters is not described by the Arrhenius equation and the deviations are seen as a gradual change of slope rather than a sharp break between two straight lines. The data are consistent with a gradual shift in rate limiting step away from the entry event into pores, which dominates at low temperature but becomes progressively less important at elevated temperatures. The changing parameter is probably the volume of the red cell, which is less important when flow is measured through 5 mu m pores.

Pulse dexamethasone does not impair growth and body composition of very low birth weight infants

OBJECTIVE

Evaluation of repeated pulses of dexamethasone (PDEX), given to improve cardiopulmonary outcome, on growth of very low birth weight (VLBW, < 1500 g) infants.

METHODS

In this prospective, double-blind, randomized clinical trial, VLBW infants mechanically ventilated at 1 week of age received intravenous PDEX or saline placebo (P) for 3 days, every 10 days, until no supplemental oxygen or ventilation was required or 36 weeks postmenstrual age (PMA). Weight gain, fluid intake, caloric intake, and serum glucose were monitored throughout the study. Nutritional assessment at 36 weeks PMA consisted of weight, length, head circumference, skinfold thickness measures, body composition by total body electrical conductance, and bone mineral content (BMC) by single beam photon absorptiometry.

RESULTS

37 PDEX and 31 P infants survived at least 36 days and completed the protocol. Average daily weight gain, fluid intake and caloric intake were not different between groups. The pattern of weight gain (g/kg/day, mean +/- SD) was different: PDEX infants showed significant growth delay during (3.0 +/- 11.4) and immediately after (7.8 +/- 8.7) each pulse, with subsequent growth acceleration (18.3 +/- 8.2) until the next steroid pulse. In contrast, growth rate of P infants was constant (12.6 +/- 3.7) (p = 0.04). Hyperglycemia requiring insulin therapy occurred only in the PDEX group (10/37). The catch-up growth noted between pulses in the PDEX group was explained only in part by insulin therapy. At 36 weeks PMA, there were no differences between groups in body size, composition, or BMC.

CONCLUSION

PDEX negatively affected glucose metabolism and growth patterns during and immediately after drug exposure. However, assessment near term gestational age showed similar body composition and size in both groups.

Medical management of sinusitis: educational goals and management guidelines. The International Conference on sinus Disease

The primary goal of sinusitis management is resolution of infection, leading to patency of the ostiomeatal complex. Antibiotics and decongestants are the cornerstones of therapy for acute sinusitis. Diagnosis of acute sinusitis is based on the history and physical findings. Sinusitis is considered to be acute or recurrent acute if infection resolves without residual mucosal damage. Choices for first-line antibiotic therapy include adequate dosages of trimethoprim-sulfamethoxazole, loracarbef, and amoxicillin-clavulanate. Decongestants and mucoevacuants may reduce tissue edema, facilitate drainage, and maintain ostial patency. Topical corticosteroids are useful additional therapy in allergic rhinosinusitis and as an aid in the long-term management of chronic sinusitis. Parenteral corticosteroids have no role in first-line management of acute or recurrent acute sinusitis.

The PIO2 vs. SpO2 diagram: a non-invasive measure of pulmonary oxygen exchange

A non-invasive method for measuring pulmonary oxygen exchange is described using a plot of inspired oxygen partial pressure (PIO2) vs. oxygen saturation (SpO2). This method was assessed using nine normal subjects and 35 patients undergoing major surgery, including five thoracotomies. In each patient PIO2 was varied to produce a range of values of SpO2 between 85% and 99%. A model based on the inspired to arterial oxygen difference involving the shunt equation, solved by simultaneous numerical methods, was used to show how the PIO2 vs. SaO2 relationship could be used to derive two parameters of oxygen exchange, the PIO2-Pco2 difference and the Virtual Shunt. The model allows the inspired to arterial difference in PO2 to be divided into (a) an inspired to 'ideal' alveolar difference attributable to the balance between alveolar ventilation and oxygen uptake; (b) an 'ideal' alveolar to end-capillary difference attributable to inhomogeneity in ventilation/perfusion ratios; and (c) end-capillary to arterial difference attributable to true shunt, which was termed 'virtual shunt' because of the uncertainties of assuming fixed values for haemoglobin concentration and arteriovenous oxygen content difference. The coefficient of determination showed that there was a good fit of the model to the data. Because the method is model-based it enables extrapolation to different PIO2 values as well as the study of the evolution of changes in gas exchange under varying conditions.

Cerebral blood flow distribution during induced hypotension with haemorrhage, trimetaphan or nitroprusside in rats

Local cerebral blood flow (CBF) during three types of profound hypotension were compared using the quantitative autoradiographic [14]-C iodo-antipyrine method. Rats were rendered hypotensive to a mean arterial pressure of 30 mm Hg for 30 min by haemorrhage, trimetaphan or nitroprusside during 0.8% halothane anaesthesia. During haemorrhagic hypotension, mean local CBF was reduced significantly in all except two pontine regions. This reduction in flow ranged from 83% to 41% compared with the normotensive control group, with the neocortex and telencephalon most affected. During trimetaphan-induced hypotension, local CBF was reduced to the same degree and in the same pattern as that during haemorrhagic hypotension. In contrast, during nitroprusside-induced hypotension, local CBF in many regions of the brain was well maintained (57-101%); although local CBF was significantly below control in all cortical and telencephalic regions, it was significantly greater in the majority of these regions than in the other two hypotensive groups. We conclude that local CBF was significantly reduced in the neocortex and telencephalon by hypotension of this degree induced by all three methods, but nitroprusside preserved local CBF significantly better than the other methods, in these, as in most other regions.

Effect of pulse dexamethasone therapy on the incidence and severity of chronic lung disease in the very low birth weight infant

We conducted a prospective, randomized, double-blind trial to assess the efficacy and safety of pulse doses of dexamethasone on survival without supplemental oxygen in very low birth weight infants at high risk of having chronic lung disease. Seventy-eight infants with birth weights < or = 1500 gm who were ventilator dependent at 7 days of postnatal age were randomly assigned to receive pulse doses of dexamethasone, 0.5 mg/kg per day, divided twice daily (n = 39), or an equivalent volume of saline solution placebo (n = 39), for 3 days at 10-day intervals until they no longer required supplemental oxygen or assisted ventilation, or reached 36 weeks of postmenstrual age. At study entry, the groups did not differ by birth weight, gestational age, or severity of lung disease. At 36 weeks of postmenstrual age, there was both a significant increase in survival rates without oxygen supplementation (p = 0.03) and a significant decrease in the incidence of chronic lung disease (p = 0.047) in the group that received pulse therapy. Supplemental oxygen requirements were less throughout the study period in the group that received repeated pulse doses of dexamethasone (p = 0.013). The total numbers of deaths and the durations of supplemental oxygen, ventilator support, and hospital stay did not differ between groups. Recorded side effects in the pulse therapy group were minimal and included an increase in the use of insulin therapy for hyperglycemia (p < 0.05). We conclude that in this population of very low birth weight infants, treatment with pulse doses of dexamethasone resulted in improvement in pulmonary outcome without clinically significant side effects.

The role of colony-stimulating factor 1 and its receptor in the etiopathogenesis of endometrial adenocarcinoma

Colony-stimulating factor 1 (CSF-1) is a homodimeric growth factor that humorally regulates the growth and differentiation of mononuclear phagocytes, and locally regulates maternal-fetal interactions during pregnancy. It exerts these actions through a transmembrane tyrosine kinase receptor, colony-stimulating factor 1 receptor (CSF-1R), the product of the c-fms proto-oncogene. Recent studies have demonstrated overexpression of CSF-1 and its receptor in breast, ovarian, and endometrial adenocarcinomas. To further investigate the possible role of CSF-1 and its receptor in the pathogenesis of endometrial adenocarcinoma, a prospective study was undertaken to study CSF-1 expression in benign and neoplastic endometrial epithelium and to compare serum CSF-1 levels in endometrial adenocarcinoma patients with healthy perimenopausal women. The mean serum levels of CSF-1 in 71 patients with endometrial cancer (4.9 +/- 1.8 microgram/liter) were significantly elevated compared with levels found in the 32 controls (3.5 +/- 1.1 microgram/liter). Within the endometrial adenocarcinoma group, circulating CSF-1 levels were significantly elevated in patients with large tumor volume, high grade, myometrial invasion, residual disease, and circulating CA-125 levels. High serum levels of serum CSF-1 were associated with elevated serum CA19-9 and CA-125 levels. Immunohistochemistry results revealed in tumor epithelium intense staining for CSF-1R (27 of 54 cases, 50%) and elevated staining for CSF-1 (41 of 54 cases, 75.9%), with intense staining of CSF-1 in 16 of 54 cases (29.6%). Staining was significantly greater in intensity and number of cells involved in malignant compared with benign epithelium for CSF-1R and CSF-1 (P = 0.05 and <0.0001, respectively). A positive correlation between amount and intensity of CSF-1 and CSF-1R staining in endometrial adenocarcinoma tissue was also demonstrated (P = 0.007). CSF-1 and CSF-1R mRNA was also detected in the tumor samples, confirming the expression of the protein in these tissues. Reverse transcription-PCR demonstrated the presence of mRNA for both the transmembrane and secreted forms of CSF-1 in all tumors analyzed. These results therefore support the hypotheses that CSF-1 and CSF-1R are overexpressed in endometrial adenocarcinoma, that levels of expression significantly correlate with clinicopathological risk factors for poor outcome, and that CSF-1 in association with its receptor via autocrine, juxtacrine, and/or paracrine interactions has a causal role in endometrial adenocarcinoma development and proliferation.

Flow cytometric determination of pre-transfusion red cell volume in fetuses and neonates requiring transfusion based on RhD+ dilution by transfused D- red cells

We report a case of feto-maternal haemorrhage and describe a new flow-cytometric method of determining a fetus's or infant's pre-transfusion red cell volume (RCV). We validate this method against an established technique, employing fetal haemoglobin (HbF) dilution, for determining the RCV in fetuses and neonates requiring intravascular transfusion. We discuss advantages and other potential applications of this new method.

Visualisation of changes in regional cerebral blood flow (rCBF) produced by ketamine using long TE gradient-echo sequences: preliminary results

Autoradiographic studies have shown that low dose ketamine produces increases in regional glucose utilisation and blood flow in the hippocampus, cerebral cortex, and olfactory lobe in the rat brain, probably due to antagonism at the NMDA receptor. Functional MRI using deoxyhaemoglobin contrast can be used to study changes in regional cerebral blood flow (rCBF). Long TE gradient-echo sequences were used to study changes in rCBF produced by low dose ketamine in rats anaesthetised with nitrous oxide, supplemented with either halothane (HAL) or fentanyl/fluanisone/midazolam (FFM) combination. Images from rats in the FFM group showed a 10-14% increase in signal intensity in the hippocampus, cerebral cortex, and olfactory lobe following either a single bolus or a low dose infusion of ketamine (p < .05). These changes were significantly reduced in the HAL group (p < .005). Halothane is known to attenuate the changes in regional glucose utilisation produced by the noncompetitive NMDA antagonist dizocilpine (MK-801), and its effects on ketamine-induced changes in rCBF seen in this study may be due to a similar effect. The potential use of functional MRI in studying the effect of pharmacological interventions on rCBF is discussed.

A method of costing anaesthetic practice

This paper identifies the main factors involved in the cost of elective general anaesthetic practice. The costs of anaesthesia were divided into overheads and running costs, which are sensitive to the duration of anaesthesia, and fixed costs which are incurred by each patient but are not sensitive to the duration of anaesthesia. The overhead costs consisted of salaries, capital equipment and maintenance costs. The overhead cost of a consultant anaesthetist combined with a technical assistant's salary, monitoring equipment and anaesthetic machine was estimated at 45.05.h-1 pounds (using 1993 salary scales and prices). The fixed costs of pre-operative assessment and nursing care in recovery were the same for all patients, 20.60 pounds per patient. For the majority of anaesthetics the combined cost of the anaesthetist, overheads and postoperative care was about 70% of the total cost, the remainder being the running costs which included drugs, anaesthetic gases, vapours, intravenous fluids, sterile equipment and other disposable items. Four sample anaesthetics were costed in two ways: both methods used the same overhead and fixed cost per patient but one added the cost of all the individual drugs and consumables used, whereas the other grouped these together using a charge sheet which can be computerised and used prospectively to cost anaesthesia. There was close agreement between the costs derived with the two methods. The cost of a 30 min delay in the start of an operating session was 27.30 pounds (anaesthetist, assistant and nurse salary (9.50.h-1 pounds)) which is more than the cost of 2 h of propofol infusion anaesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Free radicals in anaesthesia and intensive care

This review aims to outline the nature and origin of free radicals, or oxidants, in biological systems and to summarise their involvement in diseases of interest to anaesthetists, with particular reference to reperfusion injury (of the gut, brain, myocardium and transplanted organs), shock/trauma, inflammation/sepsis and halothane hepatitis. In-vitro and animal studies examining the role of free radicals and antioxidants in the pathophysiology and treatment of these conditions are presented. Some of the evidence from clinical studies supporting the use of antioxidant therapy in patients is also presented.