Significant exercise-induced hypoxaemia with equivocal desaturation in patients with chronic obstructive pulmonary disease.

BACKGROUND: The wide 95% confidence interval for S(a)O2 measured by pulse oximetry (S(P)O2) and the inherent characteristics of the oxyhaemoglobin dissociation curve can lead to modest but significant decreases in P(a)O2 (deltaP(a)O2 > or = 5 mmHg) that may be under-appreciated. AIM: To avoid missing potentially significant deltaP(a)O2 by using S(P)O2, this study establishes a threshold of deltaS(P)O2 to detect deltaP(a)O2 by examining the correlation between deltaS(P)O2 and deltaP(a)O2. METHODS: We enrolled 29 elderly patients with moderate to severe chronic obstructive pulmonary disease as assessed by lung function testing. Arterial blood gases and S(P)O2 measurements were carried out during maximal exercise testing. The patients were assigned to groups based on P(a)O2 measurements: group 1 had P(a)O2 at peak exercise (P(a)O2peak) > or = 60 mmHg without a deltaP(a)O2; group 2 had P(a)O2peak > or = 60 mmHg with a deltaP(a)O2; group 3 had P(a)O2peak < 60 mmHg without a deltaP(a)O2; and group 4 had P(a)O2peak < 60 mmHg with a deltaP(a)O2. RESULTS: The study population was evenly distributed between groups 1, 2 and 4. However, group 3 did not have any patients enrolled in this study that met group 3 criteria. The sensitivity of pulse oximetry required to detect S(a)O2 below 90% was 19%. DeltaS(P)O2 of 3% may increase the low sensitivity of S(P)O2 and was shown by a 92% positive predictive value for deltaP(a)O2 > or = 5 mmHg. CONCLUSION: This study suggests that important changes in oxygenation may be avoided if using deltaS(P)O2 rather than absolute values of S(P)O2 in patients with chronic obstructive pulmonary disease undergoing exercise testing to detect exercise-induced hypoxaemia.

In vitro effects of local anaesthetics on the thromboelastographic profile of parturients.

BACKGROUND: Post-dural puncture headache can be an incapacitating complication of obstetric epidural analgesia/anaesthesia and early or prophylactic epidural blood patch (EBP) is one of the treatment options. Although local anaesthetic (LA) agents have been shown to have anticoagulation effects in vitro, peri-partum women are known to be hypercoagulable. We postulated that the presence of residual LA might not result in impaired haemostasis of the EBP in parturients. METHODS: Blood samples from 10 healthy term parturients were subjected to thromboelastography after the addition of four different LA (lidocaine, bupivacaine, levobupivacaine, and ropivacaine) preparations. RESULTS: There was a significant reduction in reaction (R) and coagulation (K) time (P<0.001, P<0.05) and an increase in alpha degrees angle (P<0.01) when comparing undiluted blood with the saline control group. Maximum amplitude (MA) and clot lysis (Ly30) did not change significantly despite the 50% dilution. The thromboelastographic parameters of all four LA-treated groups were no different from their saline controls and from each other. CONCLUSION: At clinical dosages, LA did not cause any hypocoagulable changes on the thromboelastographic profile of healthy parturients.

Teaching first-year medical students physiology: does the human patient simulator allow for more effective teaching?

BACKGROUND: Although the Human Patient Simulator (HPS) is an effective teaching tool in many medical fields, literature supporting its use in the teaching of physiology to medical students is lacking. This study investigated the effectiveness of HPS-based teaching of cardiovascular physiology to first-year medical students. METHODS: Two hundred and ten first-year medical students were scheduled to our HPS laboratory with the purpose of demonstrating "physiology in action". Students were divided into groups of 19-25 each, and attended a lecture followed by a HPS session. Using a theatre-type simulator complete with mannequin, anaesthesia machine and monitors (METI, Sarasota FL), the scenarios of hypovolaemia, sepsis, and cardiac failure were run to demonstrate the physiological changes that occur with changes in preload, afterload, and cardiac contractility. Each student was given a true/false test before, and again after the HPS session, followed by a survey of their learning experience. RESULTS: There was marked improvement in test scores after the HPS session (82.1% vs. 64.6%, P < 0.001). Most of the students felt that HPS was a better teaching tool (94.5%) and raised more questions (76.5%) than lectures. They wanted more topics to be taught this way (96%), as they could apply and re-enforce textbook knowledge, and visualise real-time changes. However, they felt that their experience could have been enhanced with more time and smaller groups. DISCUSSION: HPS is an excellent teaching tool as it stimulates student curiosity and makes knowledge acquisition and understanding easier. It is highly desirable to be incorporated into the teaching of physiology.

Duplex PCR system for simultaneous detection of Neisseria gonorrhoeae and Chlamydia trachomatis in clinical specimens.

AIMS: To evaluate the use of a duplex polymerase chain reaction (PCR) assay for the simultaneous detection of Neisseria gonorrhoeae and Chlamydia trachomatis in clinical samples. METHODS: Genital swab specimens were obtained from both China (203 swabs) and Hong Kong (202 swabs). N gonorrhoeae and C trachomatis were detected in each specimen with a number of tests including enzyme immunoassays (IDEIA) and PCR assays using both single and double primer pairs. The primer pair for N gonorrhoeae was derived from the cppB gene on its cryptic plasmid and the PCR product was 390 base pairs long. For C trachomatis, the PCR product was 473 base pairs long, resulting from amplification of a sequence in the common 7.4 kilobase plasmid present in all serovars. For N gonorrhoeae, PCR results were also compared with those obtained by culture and Gram's smear of the discharges. RESULTS: For the 203 specimens collected in China, similar numbers of positive results (177) were obtained by both Gonozyme and duplex PCR for the detection of N gonorrhoeae. No discrepant results were found among the cultured specimens when Gonozyme and duplex PCR were compared. C trachomatis was detected in 47 specimens by duplex PCR, but was detected in only 28 by IDEIA. Of the 202 Hong Kong specimens, 46 were positive for N gonorrhoeae, detected by both Gonozyme and duplex PCR; 34 were positive for C trachomatis, 25 of which were detected by IDEIA and the remainder by duplex PCR. CONCLUSIONS: The duplex PCR assay is a satisfactory diagnostic tool for the simultaneous detection of N gonorrhoeae and C trachomatis in clinical swab samples. Further evaluation is suggested.

Diagnosis of urogenital gonorrhoea: evaluation of an enzyme immunoassay and use of urine as a non-invasive specimen.

Urethral swabs and urine samples were collected from 42 male patients attending a social hygiene clinic in Hong Kong and used for gonococcal culture and detection of antigens by enzyme immunoassay. Of the patients, 21 were suffering from gonorrhoea as indicated by positive gonococcal culture from both urethral swabs and urine. Twenty of the positive cases were detected by both swab and urine specimens using Gonozyme, an enzyme immunoassay kit. One culture-positive case failed detection by both swab and urine specimens. Gonozyme showed sensitivity and specificity of 95.2% and 100% respectively. With male patients, the use of urine as an alternative specimen to urethral swabs appears to have potential value for both culture and Gonozyme testing. Genital swabs and urine samples were subsequently collected from 108 patients (89 male, 19 female) attending the sexually transmitted disease monitoring centre in Guangzhou, China. Gonozyme tests were performed on both types of specimen, while only swabs were cultivated. When compared with swab culture, Gonozyme had sensitivity and specificity of 100% and 89.2% for males, and 100% and 90.9% for females, respectively. When urine was compared with swabs in the Gonozyme test, urine had sensitivity and specificity of 83.6% and 89.2% for males, and 62.5% and 81.8% for females, respectively. Hence, Gonozyme merits further investigation as an acceptable rapid diagnostic method for detection of Neisseria gonorrhoeae, especially when using urine as an alternative non-invasive specimen from male patients.

Development of a specific probe for the aminoglycoside-(3)-N-acetyltransferase resistance gene.

Aminoglycoside-(3)-N-acetyltransferase isoenzyme V (AAC(3)V) is produced by > 90% of aminoglycoside-resistant Escherichia coli isolates from Hong Kong. A gentamicin resistance determinant from a conjugative plasmid carried by one of these E. coli strains producing AAC(3)V was cloned as a 6-kb fragment in the PstI site of the Bluescript II KS-phagemid vector. A 0.8-kb SphI-SalI fragment from the cloned insert was used as a probe in an epidemiological study. The specificity of this probe was evaluated by colony hybridization with 17 control strains producing different known aminoglycoside resistance enzymes. Hybridization was observed only with strains producing AAC(3)V. The probe demonstrated the presence of the AAC(3)V gene in 95.5% to 133 gentamicin-resistant E. coli isolates. This result agreed with the earlier data on the distribution of this enzyme that were based on the susceptibility profile.

Use of PCR in routine diagnosis of treated and untreated pulmonary tuberculosis.

AIMS: To assess the routine use of a polymerase chain reaction (PCR) assay for the direct detection of Mycobacterium tuberculosis in expectorated sputum specimens. METHODS: A pair of primers (20-mer) were designed to amplify the 38 kilodalton protein of M tuberculosis. The specificity of the assay was evaluated in 31 M tuberculosis strains, 15 atypical mycobacterium species, and several commensal bacteria of the upper respiratory tract. The assay was subsequently applied to 519 sputum specimens from 85 inpatients of a chest hospital in Hong Kong. RESULTS: An amplified product of 239 base pairs was found in all M tuberculosis strains, standard strains of M bovis, and M africanum but not in the other bacterial strains tested. For the 51 patients with pulmonary radiographic lesions, the diagnosis of pulmonary tuberculosis was subsequently confirmed by both culture and PCR in 41 of them. Five patients who were treated before admission were positive by PCR alone. All but one patient in the control group (patients with acute exacerbation of chronic obstructive airway diseases) or those with atypical mycobacterial diseases were PCR negative. The PCR remained positive after four weeks of anti-tuberculosis treatment in 29 patients, 16 of whom had become culture negative. CONCLUSION: This PCR assay is a useful technique for the diagnosis of untreated and recently treated cases of pulmonary tuberculosis.

Polymerase chain reaction for the detection of Neisseria gonorrhoeae in clinical samples.

AIMS: To evaluate the use of a cppB gene derived polymerase chain reaction (PCR) assay for direct detection of Neisseria gonorrhoeae in clinical samples. METHODS: A PCR assay was performed on 33 N gonorrhoeae strains and 12 other Neisseria species and other normal genital flora to evaluate the specificity of the chosen cppB primers. The assay was subsequently evaluated with 52 clinical swab samples collected from China. RESULTS: An amplified product of 390 base pairs (bp) was observed with all the N gonorrhoeae strains, each of these products on digestion with the restriction enzyme MspI produced two bands of 250 bp and 140 bp respectively. This set of primers did not produce any amplified product of the expected length with the other non-gonococcal strains tested. For the 52 clinical swabs, 34 were culture positive and PCR successfully detected all these positives. In addition the PCR was positive for two swabs which were culture negative but positive for N gonorrhoeae antigens when tested with the ELISA method (Gonozyme). CONCLUSIONS: This PCR assay is a promising diagnostic tool for detection of gonococci directly from clinical swab samples. Further evaluation is necessary.

A one-year survey of campylobacter enteritis and other forms of bacterial diarrhoea in Hong Kong.

The following enteropathogens were isolated from the faeces of 769 (10.2%) of 7,545 patients of whom 5,704 had diarrhoea or abdominal pain, attending a teaching hospital in Hong Kong during one year: salmonellae 458 (6.1%); Vibrio parahaemolyticus 125 (1.7%); campylobacters 108 (1.4%); shigellae 83 (1.1%); others 19 (0.3%). Further identification of the campylobacter isolates showed that 63 (58%) were Campylobacter jejuni biotype 1, 44 (41%) were C. coli and only one was C. jejuni biotype 2. Seventy-five (69%) of the 108 campylobacters were isolated from children under two years of age, mostly during the second year of life. Faecal specimens from 1,841 children under the age of two years without gastrointestinal symptoms yielded almost the same percentages of salmonellae, campylobacters and shigellae as children with diarrhoea. Salmonellae, shigellae and vibrios were isolated most often in the hot late summer months (August to October), but, contrary to the pattern in Europe and North America, both C. jejuni and C. coli were most prevalent in the coolest months of the year (January to March). The reasons for this "reversed' trend are unknown.