Prevention of atelectasis during general anaesthesia

exclude extended care facilities and home therapy in the community. This implies important consequences for departments of microbiology and public health. The renewed commitment of the UK health service to continuing care needs is an opportunity for the identification of this need. Furthermore, action would be in keeping with the intent of the hospital infection working group of the Department of Health and the Public Health Laboratory Service.’ Resources for infection monitoring, control, and

therapy guidance

extending beyond

boundaries will need

to

current

hospital

be found.

Clive Bowman, Jon Mitchell, Glenn Tillotson Weston General Hospital, Weston-s-Mare, Avon BS23 4TQ, UK; and Pharmaceutical Division, Bayer PLC, Newbury

Care of the elderly and physically disabled. In: Laing’s review of private healthcare 1994. Laing and Buisson, 1994: 183. Muder RR, Brennen RN, Wagener MPH, et al. Methicillin-resistant staphylococcal colonisation and infection in a long-term care facility. Ann Int Med 1991; 114: 107. Irvine PW, Van Buren N, Crossley K. Causes for hospitalisation of nursing home residents: the role of infection. J Am Ger Soc 1984; 32:

1 2

3

4

5

103-07. Thomas DR, Bennett RG, Laughon BE, et al. Postantibiotic colonisation with Clostridium difficile in nursing home patients. J Am Ger Soc 1990; 38: 415-20. Hospital infection control: guidance on the control of infection in hospitals, hospital infection working group of the DOH and Public Health Laboratory Service. London: Department of Health, 1995.

The simple isolation method used in this case, enrichment culture in modified tryptone soya broth with subculture to cefixime tellurite rhamnose sorbitol McConkey agar (CTRSMAC), has been described in detail elsewhere.2 This method has been shown to increase the isolation rate by 36% in contacts of cases and in follow-up samples. It enabled the diagnosis to be established rapidly and influenced management in this case, and subsequently has yielded an isolate of E coli 0157 in another case of haemorrhagic colitis in a 51-year-old patient. Again direct inoculation of CRT-SMAC was negative. It is common practice to use only direct plating on sorbitol McConkey agar (SMAC) for examination of clinical samples and also to restrict testing stools for E coli 0157 to a proportion of these received, the major criteria for testing being bloody diarrhoea, haemolytic uraemic syndrome, colitis, and age less than 16 years.’ Diagnosis of infection with E coli 0157 would be improved if laboratories were to test all stools submitted from patients of all ages presenting with communityacquired diarrhoea, from all outbreaks of diarrhoea, from all cases of acute colitis in addition to those from suspected or proven cases of haemorrhagic colitis, haemolytic uraemic syndrome, or thrombotic thrombocytopenic purpura, and if proven superior techniques were more widely employed. *Peter A

1

Improved detection of Escherichia coli 0157

2

SiR-Infection with verocytotoxin (VTEC), in particular E coli

3

Escherichia coli

producing 0157:H7, may cause haemorrhagic colitis, haemolytic uraemic syndrome, or

thrombotic thrombocytopenic purpura. Most serious infections have been identified in children and the elderly but cases occur at all ages.’ Routes of transmission include consumption of contaminated foods, especially those of bovine origin, water, and person-to-person spread. Although large outbreaks have been identified, many infections occur as sporadic cases and there is an increase in cases identified in summer and autumn. A previously healthy 22-year-old woman presented with a 5-day history of generalised abdominal pains, severe diarrhoea (up to 20 stools daily), and fresh rectal bleeding. She had vomited twice at the onset of symptoms. She was apyrexial, not in shock, and had generalised mild abdominal tenderness. Laboratory findings included haemoglobin 15’5 g/dL, white cells 15-5X10VL, platelets 286XlO’/L, sodium 132 mmol/L, potassium 4-1mmol/L, urea 1-9 mmol/L, creatinine 96 umol/L, and albumin 38 g/L. Colonoscopy revealed a normal rectum, scattered aphthous ulceration of the sigmoid colon, and proximally a haemorrhagic colitis extending to the splenic flexure. Appearances suggested Crohn’s colitis. A biopsy specimen showed mucosal oedema without substantial inflammation. Faecal examination was negative for pathogenic protozoa, Salmonellae, Shigellae, and campylobacters but verocytotoxin producing E coli 0157 was cultured by a novel enrichment technique. Subsequently serum showed antibodies to E coli 0157 lipopolysaccharide. She was managed conservatively and diarrhoea resolved at 3 days. However she remained unwell and on day 4 developed haemolytic uraemic syndrome (haemoglobin 8-0 g/dL with spherocytosis and schistocytes in the peripheral blood), platelets 58X10VL, urea 14-6 mmol/L, and creatinine 181 mmol/L. She made a spontaneous recovery and was discharged from hospital on day 12 with normal serum urea and creatinine and normal platelets.

514

Wright, David Bell, Alison Johnson,

Eric J Bolton

Public Health Laboratory Service and Directorate of Medicine, Royal Preston Hospital, Preston PR2 4HG, UK

Neild GH. Haemolytic uraemic syndrome in practice. Lancet 1994; 343: 398-401. Hindle MA, Bolton EJ, Wright PA, Durband CA. Improved detection of verocytotoxin producing Escherichia coli O157 in faecal samples by enrichment culture. PHLS Microbiol Dig 1995; 12: 87-89. A Working Group of the Advisory Committee on the Microbiological Safety of Food. Report on verocytotoxin-producing Escherichia coli. London: HM Stationery Office, 1995.

Prevention of atelectasis anaesthesia

during general

SiR-Rothen and colleagues (June 3, p 1387), with refined methods, provide further information about the adverse effects of ventilation with 100% oxygen. Their study suggests that breathing 100% oxygen may cause the early formation of atelectasis, thereafter impairing gas exchange within a few minutes, even while breathing spontaneously. These results and the findings of a previous study lead them to question the safety of the widespread technique of preoperative preoxygenation with 100% oxygen.’ We think this conclusion is premature. In particular, we would like to point out that no clinical criteria can predict the likelihood of difficult tracheal intubation and that an impossible be life intubation may threatening.2 Moreover, denitrogenation with 100% oxygen may allow safe apnoea, the duration of which may be close to 5 min.’We advocate that this interval duration may be useful to you seeking assistance or to implement specific management of difficult

airways.3 Furthermore, Rothen and co-workers’ conclusions are based on early refined laboratory findings, and no postoperative impairment is investigated. Blood gas measurements after 70 min cannot be compared because they were measured while breathing-30% oxygen in one group, and 100% oxygen in the other group. It is noteworthy that if the Pa02/FiO2 ratio had been calculated at 70 min no difference would have been shown between groups A (Pa02/FiO2 ratio 65) and group C (Pa02/FiO2 ratio65-5).

confirm the safety and feasibility of intraoperative mechanical ventilation with 25% oxygen.’ However, we advocate that preoperative preoxygenation with 100% oxygen may be a lifesaving technique in difficult airway management,3 and that only the demonstration of substantial postoperative impairment associated with breathing 100% oxygen, could justify questioning of this

Indeed,

we

procedure. Claude Lentschener Département d’Anesthésie-Réanimation, Hôpital Antoine Béclère, 92141 Clamart, France

1 Editorial. Preoxygenation: physiology and practice. Lancet 1992; 339: 31-32. 2 Lewis M, Keramati S, Benumof JL, Berry CC. What is the best way to determine oropharyngeal classification and mandibular space length to predict difficult laryngoscopy? Anesthesiology 1994; 81: 69-75. 3 Benumoff JL. Management of the difficult adult airway. Anesthesiology 1991; 75: 1087-110. 4 Lentschener C, Benhamou D. Is intraoperative mechanical ventilation using FiO2=1 harmful? Eur J Anesth (in press).

Authors’ reply SiR-We

wholly agree with Lentschener that preoxygenation be abandoned. We did not suggest it. However, should the breathing of 100% oxygen during induction of anaesthesia causes atelectasis and shunt in most patients. We believe this to be a reason to review the procedure of inducing anaesthesia. Will 80% oxygen in nitrogen be as safe as 100% oxygen without causing atelectasis? Should inflation of the lungs to a high airway pressure (40 cm of water) be added as a standard procedure after induction? Is there another approach to prevent atelectasis or to reopen collapsed lung tissue? We hope that comparative studies between different preoxygenation procedures will be not

undertaken. Hans U Rothen, *Göran Hedensterna Department of Anaesthesiology and Intensive Care University Hospital, Bern, Switzerland; and *Department of Clinical Physiology University Hospital, S 75185 Uppsala, Sweden

Hypertension is defined by systolic blood pressure >160 mm Hg, diastolic pressure >95 mm Hg, or on antihypertensive therapy. +, present; -, absent. Table: Distributions of genotypes and allele frequencies for the T235/M235 polymorphism among CHD patients and controls

other

with

genotypes (homozygotes for M235 and for T235/M235) was 1.00 (95% CI 0’65-1’53) heterozygotes in analyses adjusted for several risk factors for CHD (ie, age, sex, cholesterol, systolic and diastolic blood pressure, and body mass index) with logistic regression methods. The corresponding odds ratio for MI alone among homozygotes for T235 was 1-11 (95% CI 0-69-1-77). Thus we failed to detect the association of the T235 allele with CHD. AGT has been of interest as a contributor to human essential hypertension since the AGT gene marker is linked to a gene responsible for the condition in affected siblings.’°2 Furthermore, the T235 allele was reported to occur more frequently in hypertensive populations in the USA, France, and Japan." In our study, we did not find significant differences in the frequency for the T235 allele between subjects with and without hypertension in either CHD patients or controls, by contrast with Katsuya and colleagues’ findings. Our study cannot exclude the possibility of association of other mutations in the AGT gene with hypertension or CHD; therefore we need to further search for variants in the AGT gene that might be causal factors for hypertension or CHD in the Japanese population. Kimiko *Hideo

Yamakawa-Kobayashi, Tadao Arinami, Hamaguchi

*Department of Medical Genetics, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba 305, Japan

Absence of association of angiotensinogen gene T235 allele with increased risk of coronary heart disease in Japanese and colleagues (June 24, p 1600) describe an association between the angiotensinogen (AGT) gene T235 variant and coronary heart disease (CHD), and suggest that the T235 variant is an independent risk factor for CHD. The renin-angiotensin system could be involved in the pathogenesis of cardiovascular disease because it plays an important part in the regulation of blood pressure and other biological responses through generation of angiotensin II, which is a potent vasoconstrictor and also stimulates smooth-muscle cell proliferation. We have examined the T235/M235 polymorphism of the AGT gene in 315 patients with CHD (80% male, 65% myocardial infarction [MI], mean age 56-7 [SD 75] years) in whom the age of onset was before 65 years and at least one 75% stenosis was recorded in coronary arteries by coronary angiography. 380 apparently healthy unrelated Japanese adults (79% male, mean age 51-4 [7’7]) were controls. Genotypes were determined by hybridisation with

SiR-Katsuya

allele-specific

oligonucleotide

described.’ The distributions frequencies for the T235/M235 in CHD patients and controls CHD among homozygotes for

probes,

as

of genotypes

previously

allele similar polymorphism (table). The odds ratio for T235 compared with those and

were

1

2

3

et al. Molecular basis of human hypertension: role of angiotensinogen. Cell 1992; 71: 169-80. Caulfield M, Lavender P, Farrall M, et al. Linkage of the angiotensinogen gene to essential hypertension. N Engl J Med 1994; 330: 1629-33. Hata A, Namikawa C, Sasaki M, et al. Angiotensinogen as a risk factor for essential hypertension in Japan. J Clin Invest 1994; 93: 1285-87.

Jeunemaitre X, Soubrier F, Kotelevtsev YV,

Influenza types and

patient population

SiR-Claas and colleagues (July 15, p 180) report the distribution of types and subtypes of influenza virus from two surveillance systems in The Netherlands during recent influenza activity. They show that 73% of the isolates derived from sentinel general practitioner (GP) surveillance were of influenza B virus, whereas only 34% of isolates from the network of diagnostic virological laboratories of municipal health services and hospitals were of this type. They suggested that this difference was "in agreement with the generally more severe clinical outcome of infections of influenza A viruses in comparison with those of influenza B" and concluded that "isolates obtained via GPs are a better reflection of the type of viruses circulating in the population at

large".

Data from similar surveillance schemes in England and Wales do not support this conclusion. In the 3 months

515