Evacuated blood-collection tubes the backflow hazard Leon

Katz, eng; David L. Johnson,

Summary: Five cases of nosocomial infection caused by Serratia marcescens were traced to backflow of blood from nonsterile evacuated blood-collection tubes. The mechanism of backflow was investigated theoretically and the conditions were determined under which backflow can occur. The theory was confirmed by experiments conducted on a simulated venous system and by measurements of the venous pressure in the brachial vein of a patient during application and removal of a tourniquet. Various possible solutions to the backflow hazard include strict adherence to correct venipuncture technique, sterilization of all blood-collection tubes, improvement of the vacuum in the tubes and incorporation of a check valve into

ph

d; Philip D.

Neufeld,

ph

d; Kamlesh G.

prelevement de sang, vide plus pousse dans les tubes et incorporation d'un clapet de retenue.

tous les tubes de

Gupta, ph d and the species positively identified as S. marcescens by an independent in¬ vestigation conducted by the food mi¬ crobiology laboratory of Health and Welfare Canada in cooperation with the bureau of medical devices. In view of the large population ex¬

Although more than 500 million evacu¬ ated blood-sample collection tubes are used annually in North America, a posure to evacuated blood-collection potential hazard in their use is not tubes, the bureau of medical devices generally recognized. Under certain undertook a study to investigate the conditions blood can flow back from mechanism of backflow and to find the tube into the patient's vein and, possible solutions to the problem. because most of these tubes are not sterilized and frequently contain chem¬ ical additives, the backflow may be Theoretical considerations microbially or chemically contami¬ One might suppose that during the nated, or both. The hazard of infection due to back¬ sampling procedure the pressure in the flow of blood from hypodermic syringes vein is always greater than the pressure during venipuncture was recognized in the tube and that backflow is there¬ 30 years ago by Mendelssohn and fore impossible, but this is not the case. the system. Witts,1"3 who stressed the importance Blood flows from the vein into the of sterility of both needle and syringe. tube until the pressures in the tube Resume: Cinq cas d'infection However, when evacuated blood-col¬ and the vein have reached equilibrium. nosocomiale par Serratia marcescens lection tubes were introduced commer¬ If the pressure in the vein now de¬ ont pu etre attribues au reflux sanguin cially in 1948 it was believed that the creases for any reason, blood will flow de tubes de prelevement a vide back into the vein until equilibrium is vacuum made backflow impossible and non steriles. Le mecanisme theorique that sterility was therefore unnecessary restored. If the tube were completely du reflux sanguin a ete etudie et on and economically unjustified. filled with blood the volume of back¬ In 1972 Fust4 expressed concern flow resulting from pressure fluctua¬ a etabli les conditions responsables de ce reflux. La theorie a ete confirmee about the possible backflow hazard, but tions in the vein would be negligible Medrek5 stated that the hazard is com¬ because a liquid is practically incom¬ par des experiences sur un systeme veineux artificiel et par des mesures pletely eliminated by strict adherence pressible. However, an air bubble al¬ to proper venipuncture technique. de la pression veineuse dans la ways remains in the tube after flow In December 1974 physicians in two has ceased, and the volume of back¬ veine humerale d'un malade pendant I'application et le retrait d'un tourniquet. hospitals in Ottawa discovered within flow is directly proportional to the 4 days five cases of a rare bacteremia. volume of this bubble. Parmi diverses solutions possibles One of the physicians instituted an in¬ au probleme du reflux sont respect In analysing the factors affecting rigoureux de la technique approuvee vestigation that traced the contamina¬ backflow, let Vb represent the volume tion to evacuated blood-collection tubes of the air bubble; V., the volume of the de prelevement, sterilisation de used in the hospitals. Culture tests of needle lumen; P, the equilibrium pres¬ sample tubes from every lot that could sure when the tube is full; AP, the be located in the hospitals showed subsequent decrease in venous pres¬ From the bureau of medical devices, Health and Welfare Canada, Ottawa massive contamination by a nonpig- sure; and AVb, the increase in the vol¬ mented Serratia species in 4 of the 11 ume of the air bubble caused by AP. Reprint requests to: Mr. L. Katz, Bureau of medical devices, Environmental Health Centre, lots.6 These findings were confirmed Applying the ideal gas law to the air Tunney's Pasture, Ottawa, Ont. K1A 0L2

208 CMA

JOURNAL/AUGUST 9, 1975/VOL. 113

Lasix

for the long term

Composition: Each tablet containa 40 mg or 20 mg turoxemide. Each 2 ml ampoule containa 20 mg furoaemide; each 4 ml ampoule containa 40 mg. Indications - Oral: Mild to moderate hypertenaion or with other hypotenaivea in aevere caaea. Edema aaaociated with congeative heart tailure, cirrhoaia ot the liver, renal diaeaae including the nephrotic ayndrome, aa welt aa other edematoua atatea. Parenteral: Acute pulmonary, cardiac, hepatic or renal edema. Contralndlcations: Complete renal ahutdown. Diacontinue if increaaing azotemia and otiguria occur during treatment ot progreaaive renal diaeaae. In hepatic coma and electrolyte depletion, do not inatitute therapy until the baaic condition ia improved or corrected. Until turther experience haa been accumulated, do not adminiater parenterally to children. Warnings: Sulfonamide diuretica have been reported to decreaae arterial reaponaiveneaa to preaxor aminea and to enhance the effecta of tubocurarine. Exercixe caution in adminiatering curare or ita derivativea during Laaix therapy. Diacontinue 1 week prior to elective aurgery. Caaea of reveraibte deafneaa and tinnitua have been reported when Laaix Parenteral waa given at doaea exceeding aeveral timex the uaual therapeutic doae of 20 to 40 mg. Tranaient deatneex ix more likely to occur in patienta with aevere impairment of renal function and in patienta alao receiving druga known to be ototoxic. Precautions: Inject Laaix Parenteral atowly [1 to 2 minuteal when i.v. route ia uaed. Sodium intake ahould not be lexa than 3 g/day. Potaxxium aupplementa ahould be given when high doxex are uxed over prolonged periodx. Caution with potaxxium levela ix daxirable when on digitalix glycoaidex, potxaxium-depleting ateroida, or in impending hepatic coma. Potxaxium aupplementation, diminution in doxe, or dixcontinuation of Lxxix may be required. Aldoxterone antagonixta ahould be added when treating xevere cirrhoxix with axcitex. Reproduction atudiex in animala have produced no evidence of drug-induced fetal abnormatitiex. Lxxix hax had only limited uxe in pregnancy and ahould be uxed only when deemed eaxentiat. Check urine and blood glucoxe ax decreaxed glucoxe tolerance hax been obaerved. Check aerum calcium levela ax rare caxex 01 tetany have been reported. Patienta receiving high doxee of axticylatee with Lxxix may experience xaticylate toxicity at lower doxex. Adverse reactions: Ax with any effective diuretic, electrolyte depletion may occur expecially with high doxex and rextricted axlt intake. Electrolyte depletion may manifeet itxelf by weaknexx, dizzineex, lethargy, leg crampe, anorexia, vomiting and/or mental confuxion. Check aerum electrolytex, expecialty potaxalum at higher doxe levela. In edematoux hypertenaivex reduce the doxage of other antihypertenaivex xince Lxxix potentiatex their effect. Axymptomatic hyperuricemia can occur and gout may rarely be precipitated. Reveraible elevationa of BUN may be xeen axpecially In renal inaufficiency. Dermatitix, pruritux, pareethexia, blurring of vixion, poxtural hypotenxion, nauxex, vomiting, or diarrhea may occur. Anemia, leukopenia, and thrombocytopenia [with purpura] and rare caxex of agranutocytoxix have occurred. Weaknexx, fatigue, dizzineex, muacle crampe, thirat, increaxed perapiration, bladder apeam and xymptomx of urinary frequency may occur. Overdosage: Symptoma: Dehydration and electrolyte depletion. Treatment: Diecontinue drug and inxtitute water and electrolyte replacement. Dosage and administration - Oral: Hypertension: Uxual doxage ix 40 to 80 mg daily. Individualize therapy and adjuat doxage of concomitant hypotenaive therapy. Edema: Uxual initial doxage ix 40 to 80 mg. Adjuxt according to rexponxe. If diurexix hax not occurred after 6 houra, increaxe doxage by incrementa of 40 mg xx frequently xx every 6 houra if neceaxary. The effective dose can then be repeated 1 to 3 timex daily. A maximum daily dose of 200 mg ahould not be exceeded. Maintenance doxage muxt be adjuxted individually. An intermittent doxage achedule of 2 to 4 consecutive dayx each week may be utilized. With doxee exceeding 120 mg/day, clinical and laboratory observationa are advixabte. Parenteral: Uxual doxage ix 20 to 40 mg given xxx aingle doxe, injected i.m. or i.v. The i.v. injection ahould be given alowly [1 to 2 minutex]. Ordinarily, a prompt diurexix enxuex. If diurexix ix not axtixtactory, xucceeding doxee may be increased by incrementa of 20 mg 2 houra after the previoux doxe, until the required diurexix ix obtained. The maximum recommended daily doxage ix 100 mg. Acute pulmonary edema: Adminixter 40 mg immediately by alow i.v. injection. May be followed by another 40 mg ito 1 Ia houra later. Pediatric use: Inatitute Lxxix orally under cloxe observation in the hoxpital. Single oral dose ix 0.5 to 1 mg/kg. The daily oral doxe ahould not exceed 2 mg/kg in divided doxex. In newborna and prematurex, the daily oral doxe ahould not exceed 1 mg/kg. Particular caution with potaxalum leveta ix dexirable. Do not adminixter to jaundiced newborna or infanta auffering from diseaxex with the potential of cauxing hyperbilirubinemia and poaxibty kernicterux. Supply: Yellow, round, acored 40 mg tableta [Code DLII in bottlex of 50 and 500. White round 20 mg tableta [Code DLF] in bottlex of 30. Amber ampoulex of 2 ml in boxex of 5 and 50; 4 ml in boxex of SO. Complete information on requext.

HOECHST Hoechst Pharwareuticals. Oivis.on of canadian Hsechst Ltd Montreal

1229/7065/E

EReg Hoechst TM

bubble we obtain the following relation: AVb/Vb = AP/P;

hence, AVb = Vb (AP/P) (1). The volume of the backflow will be equal to AVb. Since the needle is sterile, the contaminated blood will enter the vein only if AVb is greater than the volume of the needle lumen, V,,. Thus, the condition for backflow of blood is as follows: Vb (AP/P) > V,, or AP/P > Vn/Vb (2). Consider now some typical values for the variables in equation 2. The lumen volumes (½) of needles of seven commonly used gauges and two nominal lengths are listed in Table I. Values for the bubble volume (Vb) were determined by measuring the volume of the draw and the total tube volume for tubes of 2, 5, 7, 15 and 20 ml from one manufacturer. The average bubble volumes were 0.4, 1, 0.9, 2.0 and 3 ml, respectively, indicating that the bubble volumes were roughly proportional to the tube volumes and that the tubes had been evacuated to a constant pressure of about 1 0. atmospheres. To estimate the rate of deterioration of the vacuum with time, we measured the rate of leakage of gas through the stoppers of one brand of tube with a helium mass spectrometer leak detector. In all cases the leakage rate was negligible (indicating that an effective vacuum can be maintained for several years). The ambient venous pressure in the brachial vein is about 10 cm H20 but the actual value used in these calculations is not critical because P is the sum of the atmospheric pressure and the venous pressure, and the latter is never more than 7% of the total. Thus, we can consider P to be constant, within a few percent, at 1050 cm H20. By applying the above numerical values to equation 2 we can calculate the value of AP needed to produce a backflow volume exceeding the lumen volume. The results are shown in Fig. 1 for various needle sizes and bubble

volumes. For example, for a bubble volume of 1 ml and a 22-gauge, 1" needle the critical value of AP is only 6 cm H20; a decrease in venous pressure exceeding this value would produce backflow of blood from the tube. Removal of a tourniquet from the arm can cause a decrease in pressure in the brachial vein of 10 times this critical value. Experimental demonstration of backflow The theoretical description of backflow was confirmed experimentally by means of a simulated venous system in which water was circulated at a rate of about 50 ml/min through a closed loop of transparent plastic tubing by a peristaltic pump with an adjustable pressure and pulse rate. A 7-ml bloodcollection tube containing methylene blue dye solution and a bubble of about 1 ml was connected, to the simulated vein through a 20-gauge, 1½" needle. Backflow was observed when the decrease in pressure (AP) exceeded 18 cm H20. This agrees well with the theory that predicts, for these condiWMEN DIAMETER (mm) Q3 0.4 05

3

Nominal "-Length Needle p Nominal l.k"-Length Needle Vb Bubble Volume

/ p

0

Z

.Q5rnL/

a.

.-

-.

-

\.lml..3ml

o.2625

2423

22

21

20

NEEDLE GAUGE

FIG. 1-Calculated values of decrease in venous pressure necessary to cause backflow of a volume greater than lumen volume of needle. Vb is volume of air left in blood-collection tube after blood flow ceases.

Table I-Lumen volumes of needles of various sizes Lumen volume (ml) Nominal 1' Nominal 1½' Gauge Lumen diameter (mm)* lengtht lengtht 20 0.559 0.01250 0.01560 21 0.495 0.00979 0.01223 22 0.394 0.00618 0.00773 23 0.318 0.00402 0.00508 24 0.292 0.00340 0.00425 25 0.241 0.00232 0.00290 26 0.216 0.00186 0.00233 *Obtainetj from Canadian Government Specifications Board standard 41-GP-2b for syringe needles. tNominal length is the length of the needle distal to the hub; the overall lengths for these sizes are 2' and 2½', resDeCtivelY. CMA JOURNAL/AUGUST 9, 1975/VOL. 113

211

tions, the

onset of backflow

when AP

has been shown to be

as

much

as

10

times the critical decrease needed to equals 16 cm H20 (Fig. 1). The occurrence of backflow de- produce backflow of blood from the pended only on the magnitude of AP tube. It is therefore essential that the and not on the rate of the pressure tourniquet be removed well before the decrease or on the direction in which blood flow into the tube has stopped the needle was pointing with respect and preferably even before the tube to the flow of water in the simulated stopper is completely punctured. Al¬ vein. This is in disagreement with the though the instructions supplied with theory of Mendelssohn and Witts,1 who some brands of tube mention the latter attributed the backflow only to the dy- point, users are not sufficiently aware namic effect of the blood flowing past of its importance. Most manufacturers the point of the needle. They postulated state that the tourniquet should be re¬ that the effect could be avoided by moved after blood flow has begun, and inserting the needle in the upstream this appears to be common clinical direction. Our experiments demon¬ practice. In some cases the tourniquet is strate that the decrease in static pres¬ left on until the tube draw is complete sure is the major factor apart from in order to prevent occlusion; this prac¬ any dynamic effects that may also tice appears to be hazardous. exist. One method of preventing backflow It was also possible to produce back¬ of blood is to hold the tube with the flow by pressing on the end of the needle uppermost so that the proximal tube, thereby compressing the stopper, end of the needle is not immersed. and by tilting the tube up wards, there¬ However, many clinicians find this by increasing the hydrostatic head. This awkward, and when this would be dif¬ suggests that backflow could be caused ficult one might guard against back¬ by other minor manipulations such as flow by withdrawing the needle or tube movement of the patient's arm, or brief before the draw is complete, while pressure of the technician's thumb on there is still a partial vacuum in the the vein near the site of puncture. tube. The somewhat higher concentra¬ To determine the relevance of these tion of additives in the sample might results to the actual pressures in a pa¬ not be of concern in many situations. tient's vein durine the sampling pro¬ One should avoid exerting any pres¬ cedure, we measured these pressures sure on the end of the collection tube with a transducer-catheter system after puncturing the stopper because (Statham model P23 De transducer- this compresses the stopper and might amplifier system) in a 37-year-old man cause backflow. with normal blood pressure. The re¬ Care should be taken not to move cording was made with the catheter in¬ the patient's arm during sampling, for serted into the brachial vein at the elevation of the arm a few centimetres usual site of venipuncture. The patient after the tube draw is complete can was supine with the arm at heart level. lower the venous pressure sufficiently The basal venous pressure was about to produce backflow. 10 cm H20, with fluctuations of roughIt has been suggested6 that the simly 4 cm. The pressure increased to 63 plest and the essential technologic cm H20 within 20 seconds of applica¬ tion of the tourniquet and decreased again to the basal level 1 or 2 seconds ioq after removal of the tourniquet (Fig. 2). This decrease of 53 cm H2O would, according to our calculations (equation

1), cause 0.05 ml of backflow from a tube with a 1-ml bubble. An accidental "short draw" caused by insufficient vacuum in the tube is particularly hazardous. Furthermore, some manufacturers supply tubes de¬ signed to take only a partial draw. In both cases the bubble volume is much larger than usual and hence the critical decrease in pressure will be small. Furthermore, the blood flow into the tube may stop before the technician has a chance to loosen the tourniquet, so that subsequent removal of the tourniquet will cause a large volume of backflow. Discussion The decrease in venous pressure re¬ sulting from removal of the tourniquet 212 CMA

solution to the problem would be to sterilize all blood-collection tubes. This would eliminate the hazard of bacterial infection. It would not, however, be a complete solution. The majority of evacuated blood-collection tubes con¬ tain various liquid or powdered addi¬ tives for specific preservative or diag¬ nostic purposes and these can also be carried into the vein during backflow. There are many such additives in use and the effects of infusion have been investigated for only a few. Further¬ more, the sterilization process may have a deleterious effect on the addi¬ tives. All these factors require further

study. Another possible solution might be to improve the vacuum in the collec¬ tion tube. The decrease in pressure necessary to produce backflow is in¬ versely proportional to the volume of air in the tube after the blood draw is complete. This volume is in turn di¬ rectly proportional to the initial pres¬ sure in the tube before the stopper is punctured. Evacuated blood-collection tubes do not contain a high vacuum; the pressure in the tube is typically 10"1 atmospheres. Reducing this pressure by a factor of 10 (to 102 atmospheres) would raise by a factor of 10 the de¬ crease in venous pressure necessary to produce backflow. In conjunction with proper technique this would effectively eliminate the backflow problem. Even 10~2 atmospheres is not a high vacuum. Relatively inexpensive, commercially available vacuum pumps are routinely used to evacuate large chambers quick¬ ly to 10"4 atmospheres. As was de¬ termined by the helium leakage tests, there should be no difficulty in main¬ taining the improved vacuum with cur¬ rently used stoppers. Improving the

100,

501

1

D

IM FIG. 2.Venous pressure measured by transducer catheter inserted into brachial vein at usual site of venipuncture. Vertical lines at 1-second intervals. Basal pressure is 10 cm H20 (A). Pressure increases to 63 cm H20 after application of tourniquet (C). Signal at B is an artefact caused by tying the tourniquet. Pressure decreases to basal value within 2 seconds of removing tourniquet (D).

JOURNAL/AUGUST 9, 1975/VOL. 113

vacuum would not alter appreciably the speed of the draw, nor would it increase hemolysis of the blood or the probability of vein occlusion, for these effects depend upon the pressure difference between the vein and the unfilled tube and this would increase by only about 10%. Still another approach might be to incorporate a check valve into the system to permit flow in one direction only. Such a mechanism would be effective even if the sampling technique were faulty. Various designs of check

valve could serve the purpose. The valve could be located in the needle, on the inner surface of the stopper, or in the tube itself. Pending a technologic solution, it is hoped that this analysis of the backflow problem will alert clinicians to the hazards of evacuated blood-collection tubes and the necessity for strict adherence to proper technique in their use. We thank Drs. R.H. Elder and B.C. Morton of Ottawa Civic Hospital, Mr. Nelson Dune of the National Research Council and Dr. H.A. Pivnik of the microbial

hazards bureau, Health and Welfare Canada. The valued assistance of Dr. A.K. DasGupta, director, bureau of medical devices, is gratefully acknowledged. References 1. MENDELSSOHN K, Wsrrs LI: Transmission of infection during withdrawal of blood. Br Med 1 1: 625, 1945 2. SHACKLE JW: Technique of venepuncture. Ibid, p 749 3. MENDELSSOHN K, Wsrrs U: Technique of venepuncture. Ibid, p 852 4. FUST JA: letter. A SCP Summary Rep 9: Jan 1972 5. MEDREK TJ: Eliminating vacutainer hazard. ASCP Summary Rep 10: Apr 1973 6. MCLEISH WA, CORRIGAN EN, ELDER RH, et al: Contaminated vacuum tubes. Can Med Assoc 1 112: 682, 1975

Beclomethasone dipropionate in asthma PAUL CHAMPIQN,* MB, PH D. LONIA MACLEAN; MOIRA CHAN-YEUNG, MB, MRCP, FRCP[C], FACP

Summary: Beclomethasone dipropionate aerosol therapy can replace or diminish systemic corticosteroid therapy in the majority of asthmatics. In a clinical trial of 41 patients with perennial asthma, the 10 who had not required long-term corticosteroid therapy improved symptomatically and in pulmonary function. Of the 31 who had required prolonged systemic corticosteroid therapy 12 were able to discontinue oral prednisone therapy, 15 were able to decrease the maintenance dose of prednisone and only 4 were unable to decrease the dose; all maintained satisfactory lung function and some showed improvement. Discontinuation of systemic corticosteroid therapy was accomplished more readily in patients whose daily maintenance dose was less than 15 mg and who had been taking the drug for less than 3 years. Side effects consisted of a "dry throat" in seven patients, two of whom had throat infections with Candida albicans. Recurrence of rhinitis after discontinuation or reduction of systemic corticosteroid therapy was noted in 11 patients. R6sum6: La dipropionate de b6cIom.thasone dans I'asthme Chez Ia majoritA des asthmatiques le dipropionate de b6clom6thasone donne en a6rosol peut remplacer ou diminuer Ia posologie de Ia corticoth6rapie par voie g6n6rale. Au cours d'un essai clinique sur 41 From the University of British Columbia, department of medicine, Vancouver General Hospital This work was supported by the Canadian Thoracic Society. *Re.arch fellow, BC Tuberculosis and Christmas Seal Society Reprint requests to: Dr. M. Chan-Yeung, UBC department of medicine, Vancouver General Hospital, Vancouver, BC V5Z 1M9

malades souffrant d'asthme chronique, los 10 malades dont l'6tat n'avait pas exige une corticoth6rapie prolong6e ont vu leur 6tat s'am6lioror au point de vue symptomatique ainsi que leur fonction pulmonaire. Chez los 31 autres qui avaient d. rocevoir une corticoth6rapie do longue dur6e par voje g6n6ralo, 12 ont Pu abandonner Ia prednisone orale, 15 sont parvenus a r6duire Ia dose d'ontretien do prednisone ot 4 seulemont n'ont Pu r6duire cette dose; chez tous, Ia fonction pulmonaire s'est maintonue do fa9on satisfaisante et cortains malades ont 6t6 am6lior6s. L'abandon do Ia corticoth6rapie par vole gbn6ralo a pu so faire plus facilement chez los malados dont Ia posologie d'entretion quotidionne 6tait inf6rioure a 15 mg ot qui avalont pris lo medicament pendant moms do 3 ans. Chez sept malades los r6actions secondairos consistajent on "gorge s.che", mais ii faut remarquor quo deux do coux-ci souffraient d'infections do Ia gorge causee par Candida albicans. Chez 11 malades on a not6 do Ia rhinite apres abandon ou r6duction do Ia corticoth6rapie par voie g6n6rale.

Beclomethasone dipropionate has recently been used as an aerosol in the treatment of patients with chronic perennial asthma, particularly as a replacement for oral corticosteroid therapy. Several studies14 have shown that the drug is effective and has few side effects. The following is a report of a clinical trial of beclomethasone dipropionate aerosol therapy in 41 patients with asthma. The major aim of this trial was to study the extent to which this therapy could replace systemic corticosteroid therapy.

Patients and methods

Patients Two groups of patients with perennial asthma were studied: a non-steroiddependent group - 10 patients who had never received, or only occasionally required, intermittent courses of systemic corticosteroids; and a steroiddependent group - 31 patients who had received systemic corticosteroids for a long period. Six of the 41 patients were using disodium cromoglycate at the time of the study; another 21 had tried it in the past but had not found it helpful. Methods The patients were observed for 4 to 6 weeks before the commencement of aerosol beclomethasone therapy, during which period they were stabilized on their usual medication and baseline measurements of respiratory function were made. In steroid-dependent patients the lowest dose of steroids required to keep them free from symptoms and maintain satisfactory lung function was established. Patients were instructed to record on special diary cards the severity of symptoms relating to asthma, cough and sputum volume for each day and night (scores are shown in Appendix 1) and the frequency with which they used oral (Tedral, Amesec or Choledyl) or aerosol (Ventolin or Alupent) bronchodilators and other medications. Beclomethasone dipropionate therapy was then begun. The drug was administered as a metered aerosol delivering 50 ,.tg per puff. Patients were asked to inhale 100 p.g four times daily. After 1 week of beclomethasone therapy those who were steroid-dependent were asked to reduce their prednisone dosage at a maximum rate of 1 mg/d. The six

CMA JOURNAL/AUGUST 9, 1975/VOL. 113 213

Evacuated blood-collection tubes--the backflow hazard.

Five cases of nosocomial infection caused by Serratia marcescens were traced to backflow of blood from nonsterile evacuated blood-collection tubes. Th...
947KB Sizes 0 Downloads 0 Views