- Email: [email protected]
PERCUTANEOUS REMOVAL OF ATHEROMATOUS PLAQUES
703 AGENCY NURSES AND VIOLENCE IN A PSYCHIATRIC WARD
SIR,-Dr Fineberg and colleagues (Feb 27, p 474) have done a careful retrospective study of violent incidents in a psychiatric unit. The positive correlation between number of violent incidents and number of agency shifts worked is noteworthy: however, it may be hasty to conclude, as Fineberg et al do, that "lack of cohesion in nursing provision is reflected in patient behaviour", implying that the former determines the latter. However, another view might be that nurses may leave permanent employment because of violent incidents: the histogram in the letter indicates that a consistent rise in the employment of agency staff post-dated that of the rise of reported violent incidents. Clearly, an association exists, but the cause-and-effect conundrum can be answered through the institution of a second prospective study. It is unlikely that the characteristics of those patients within an inner-city, high-dependency psychiatric unit could be altered experimentally: perhaps, therefore, a concerted effort to recruit more permanent members of ward staff might allow resolution of this particular problem? The alternative manoeuvre-a switch to agency nurse provision alone--would seem
inadvisable.
Academic Department of Psychiatry, St Mary’s Hospital Medical School, London WC2
DAVID BALDWIN
subcutaneous tissues within hours of catheter insertion. After transcutaneous catheter insertion, a fluid exudate forms around the insertion site. Bacteria from the surrounding skin multiply within the exudate, allowing the transdermal potential to move negatively charged unattached bacteria through the exudate surrounding the catheter and into the subcutaneous tissues. This process would lead to colonisation of the intravascular component of the catheter
(figure). Coagulase-negative staphylococci
are rarely associated with human disease, but cause local infection when injected into the skin surrounding a piece ofplastic.6 Procedures which reduce or nullify the transdermal potential might reduce bacterial colonisation of intravascular catheters. Colonisation of intravascular catheters may not be the only area where the transdermal potential is important. Bacteria may colonise ’Perspex’ lens implants, peritoneal dialysis catheters, surgical sutures and drainage devices, and ventriculoperitoneal and ventriculoatrial shunts-all procedures that involve transconjunctival or transcutaneous surgical incisions in the proximity of plastic devices. The transdermal potential may move negatively charged bacteria through those lines of incision.
Department of Medical Microbiology, Old Medical School, Leeds LS2 9JT; and Department of Paediatrics, General Infirmary, Leeds
S. DEALLER M. R. MILLAR P. MACKAY
P, Pedemonte O, Zech F, Kestens-Servaye Y. Clinical use and bacteriological studies of catheter contamination sleeves. Intens Care Med 1984; 10: 297-300. Maki DG. Infection control in intravenous therapy. Ann Intern Med 1973; 79: 867-87. Barker AT, Jaffe LF, Vanable JW Jr. The glabrous epidermidis of vacies contains a powerful battery. Am J Physiol 1982; 242: R358-R366. Knowles MR, Gatzy JT, Boucher RC. Increased bioelectric potential difference across respiratory epithelia in cystic fibrosis. N Engl J Med 1981; 305: 1489-95. James AM. The electrochemistry of bacterial surfaces. Inaugurative lecture at Bedford College, University of London, 1972: 3-28. Zimmereli W. Pathogenesis of a foreign body infection: Description and characteristics of an animal model. J Infect Dis 1982, 146: 487-97.
1. Baele
TRANSDERMAL POTENTIAL AND BACTERIAL COLONISATION OF INTRAVASCULAR CATHETERS bacterial colonisation of intravascular catheters prompts us to offer a novel mechanism for such incidents-namely, transdermal potential differences. Contamination of intravenous catheters by skin bacteria is unlikely to be the whole explanation because catheters inserted through surgical incisions and needles inserted through sleeves still become colonised with bacteria.’ Furthermore, contamination of infusion fluids may be associated with catheter colonisation, but bacterial filters do not reduce this.2 The skin is electrically negative relative to the subcutaneous tissues, with a potential difference of 30-60 mV varying with body siteWe have measured the potential difference between the lumen of venous catheters and the skin surface in eleven premature babies and have found values ranging from 3 to 118 mV (mean 65-5 mV). The transdermal potential has been studied in amphibians and fish, but not much in man apart from patients with cystic fibrosis, in whom the potential difference is raised.’ Bacteria are negatively charged in a solution that has a higher pH than their isoelectric point. The isolectric point for staphylococci is between pH 2 and 3, and at physiological pH staphylococci at a potential difference of 1 V/m will have a mobility towards the anode of 10 run/s.5 At physiological voltages, unimpeded coagulasenegative staphylococci would move from the epidermis to the
SIR,-Your Jan 2/9 editorial (p 30)
on
2.
3. 4. 5. 6
PERCUTANEOUS REMOVAL OF ATHEROMATOUS
PLAQUES SIR,-Professor Hofling and colleagues (Feb 20, p 384) report on percutaneous removal of atheromatous plaques in peripheral arteries. However, the difficulties involved in this procedure are not all solved. Seven of the patients had rest pain and two had gangrene. It would have been more useful if an arteriogram from one of these patients had been shown rather than the clearly benign lesion in fig 1. The arteriogram presented shows that the extent of the stenosis is extremely localised and bridged by a large collateral. Such a patient would hardly be expected to have any symptoms at all and certainly not rest pain or gangrene. Hofling and colleagues state that no major complications occurred in any patient. A close examination of fig 1 shows that the collateral vessel, which was previously carrying blood beyond the stenosis, has indeed now embolised or become occluded. This confirms that the technique is not without its
dangers. While this approach may be of use in the future, Hofling et al have demonstrate that they can use the technique in vessels which are hard to deal with m other ways. In addition, the method has limitations in that several passes were required to obtain a satisfactory result in even a small stricture such as that shown in fig 1. How long did this take in each patient and what was its cost in terms of services and equipment? As Hofling et al correctly point out a randomised controlled study is required before any claims can be made. This type of study is regrettably lacking even now in the field of angioplasty, which has been used for many years. The widespread use of the Simpson type of atherectomy catheter in a variety of patients can only lead to more complications than are mentioned here. No amount of invasive or non-invasive measurements saying how good or bad the technique is can replace proper clinical trials and long-term follow up. to
Flow of electricity into skin from around skin puncture
intravenous cannula.
site,
Department of Surgery, Clinical Sciences Building, Leicester Royal Infirmary, Leicester LE2 7LX
P. R. F. BELL
SIR,-Dr Fineberg and colleagues (Feb 27, p 474) have done a careful retrospective study of violent incidents in a psychiatric unit. The positive correlation between number of violent incidents and number of agency shifts worked is noteworthy: however, it may be hasty to conclude, as Fineberg et al do, that "lack of cohesion in nursing provision is reflected in patient behaviour", implying that the former determines the latter. However, another view might be that nurses may leave permanent employment because of violent incidents: the histogram in the letter indicates that a consistent rise in the employment of agency staff post-dated that of the rise of reported violent incidents. Clearly, an association exists, but the cause-and-effect conundrum can be answered through the institution of a second prospective study. It is unlikely that the characteristics of those patients within an inner-city, high-dependency psychiatric unit could be altered experimentally: perhaps, therefore, a concerted effort to recruit more permanent members of ward staff might allow resolution of this particular problem? The alternative manoeuvre-a switch to agency nurse provision alone--would seem
inadvisable.
Academic Department of Psychiatry, St Mary’s Hospital Medical School, London WC2
DAVID BALDWIN
subcutaneous tissues within hours of catheter insertion. After transcutaneous catheter insertion, a fluid exudate forms around the insertion site. Bacteria from the surrounding skin multiply within the exudate, allowing the transdermal potential to move negatively charged unattached bacteria through the exudate surrounding the catheter and into the subcutaneous tissues. This process would lead to colonisation of the intravascular component of the catheter
(figure). Coagulase-negative staphylococci
are rarely associated with human disease, but cause local infection when injected into the skin surrounding a piece ofplastic.6 Procedures which reduce or nullify the transdermal potential might reduce bacterial colonisation of intravascular catheters. Colonisation of intravascular catheters may not be the only area where the transdermal potential is important. Bacteria may colonise ’Perspex’ lens implants, peritoneal dialysis catheters, surgical sutures and drainage devices, and ventriculoperitoneal and ventriculoatrial shunts-all procedures that involve transconjunctival or transcutaneous surgical incisions in the proximity of plastic devices. The transdermal potential may move negatively charged bacteria through those lines of incision.
Department of Medical Microbiology, Old Medical School, Leeds LS2 9JT; and Department of Paediatrics, General Infirmary, Leeds
S. DEALLER M. R. MILLAR P. MACKAY
P, Pedemonte O, Zech F, Kestens-Servaye Y. Clinical use and bacteriological studies of catheter contamination sleeves. Intens Care Med 1984; 10: 297-300. Maki DG. Infection control in intravenous therapy. Ann Intern Med 1973; 79: 867-87. Barker AT, Jaffe LF, Vanable JW Jr. The glabrous epidermidis of vacies contains a powerful battery. Am J Physiol 1982; 242: R358-R366. Knowles MR, Gatzy JT, Boucher RC. Increased bioelectric potential difference across respiratory epithelia in cystic fibrosis. N Engl J Med 1981; 305: 1489-95. James AM. The electrochemistry of bacterial surfaces. Inaugurative lecture at Bedford College, University of London, 1972: 3-28. Zimmereli W. Pathogenesis of a foreign body infection: Description and characteristics of an animal model. J Infect Dis 1982, 146: 487-97.
1. Baele
TRANSDERMAL POTENTIAL AND BACTERIAL COLONISATION OF INTRAVASCULAR CATHETERS bacterial colonisation of intravascular catheters prompts us to offer a novel mechanism for such incidents-namely, transdermal potential differences. Contamination of intravenous catheters by skin bacteria is unlikely to be the whole explanation because catheters inserted through surgical incisions and needles inserted through sleeves still become colonised with bacteria.’ Furthermore, contamination of infusion fluids may be associated with catheter colonisation, but bacterial filters do not reduce this.2 The skin is electrically negative relative to the subcutaneous tissues, with a potential difference of 30-60 mV varying with body siteWe have measured the potential difference between the lumen of venous catheters and the skin surface in eleven premature babies and have found values ranging from 3 to 118 mV (mean 65-5 mV). The transdermal potential has been studied in amphibians and fish, but not much in man apart from patients with cystic fibrosis, in whom the potential difference is raised.’ Bacteria are negatively charged in a solution that has a higher pH than their isoelectric point. The isolectric point for staphylococci is between pH 2 and 3, and at physiological pH staphylococci at a potential difference of 1 V/m will have a mobility towards the anode of 10 run/s.5 At physiological voltages, unimpeded coagulasenegative staphylococci would move from the epidermis to the
SIR,-Your Jan 2/9 editorial (p 30)
on
2.
3. 4. 5. 6
PERCUTANEOUS REMOVAL OF ATHEROMATOUS
PLAQUES SIR,-Professor Hofling and colleagues (Feb 20, p 384) report on percutaneous removal of atheromatous plaques in peripheral arteries. However, the difficulties involved in this procedure are not all solved. Seven of the patients had rest pain and two had gangrene. It would have been more useful if an arteriogram from one of these patients had been shown rather than the clearly benign lesion in fig 1. The arteriogram presented shows that the extent of the stenosis is extremely localised and bridged by a large collateral. Such a patient would hardly be expected to have any symptoms at all and certainly not rest pain or gangrene. Hofling and colleagues state that no major complications occurred in any patient. A close examination of fig 1 shows that the collateral vessel, which was previously carrying blood beyond the stenosis, has indeed now embolised or become occluded. This confirms that the technique is not without its
dangers. While this approach may be of use in the future, Hofling et al have demonstrate that they can use the technique in vessels which are hard to deal with m other ways. In addition, the method has limitations in that several passes were required to obtain a satisfactory result in even a small stricture such as that shown in fig 1. How long did this take in each patient and what was its cost in terms of services and equipment? As Hofling et al correctly point out a randomised controlled study is required before any claims can be made. This type of study is regrettably lacking even now in the field of angioplasty, which has been used for many years. The widespread use of the Simpson type of atherectomy catheter in a variety of patients can only lead to more complications than are mentioned here. No amount of invasive or non-invasive measurements saying how good or bad the technique is can replace proper clinical trials and long-term follow up. to
Flow of electricity into skin from around skin puncture
intravenous cannula.
site,
Department of Surgery, Clinical Sciences Building, Leicester Royal Infirmary, Leicester LE2 7LX
P. R. F. BELL