External Disinfection of Dialysis Monitors

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Disinfection of the hydraulic circuits of the dialysis monitors is not the sole procedure capable of guaranteeing maximum security: it is also necessary to carry out a thorough cleansing and disinfection of the external parts of the equipment before starting another dialysis session. A correct procedure includes: the operators (clothing, maneuvers, instruments) and the environment (from the dialysis room to the furnishing). Having a correctly disinfected monitor in its internal components, but operating in a contaminated environment is paradoxical.

The external surface of the equipment plays an important part in the transmissibility of infections. In the first place it is possible, and it happens frequently, that blood stains the surface of the monitors, both during the injection for vascular access and the dismantling of the hematic lines at the end of the session. Secondly, it is possible that operators use the machines (to regulate a certain parameter or to switch off an alarm) with blood-stained gloves, the consequence, for example of a preceding urgent intervention of compression of a bleeding fistula. Thirdly, it happens often that, during the disconnection of the patient, the operator, without changing gloves intervenes alternatively on the machines and on the vascular access. A very important phase is that relative to the final dismantling of the filters and of the hematic lines; a repetitive maneuver which could be carried out hurriedly without paying attention. Particular attention should be paid, therefore, to the external surface of the monitors, both at the project level (design, ergonomics, materials) and operative level (before, during and after each treatment). All buttons should be recessed and protected by a film, and knobs should not protrude, easy receptacles (especially if grained or with a rugged surface) for hematic residues or dirt. Every trace of blood should be promptly removed, and an indispensable procedure at the end of each treatment is a thorough cleansing and disinfection of all the external surfaces (in particular the support of the drip chamber) and the connections of pressure transducers) using appropriate agents. In the choice of products it is necessary to keep in mind the characteristics of the materials of which the body of the machine and relative accessories are composed to avoid irreparable damage which could range from the simple opacity of the transparent panels to the actual 'melting' of some of the plastic components. On the whole, products containing benzene, acetone, toluene, xylene or similar solvents should be avoided. Finally external detergents and disinfectants should be used with disposable paper wipes (to be changed after use on each machine) avoiding every type of cross-contamination. Other critical components, possible causes of transmission of bacteria and/or viral cross-infections from patient to patient, are constituted by the connection of the dialytic solution in the direction of and from the filter. Both the external and internal surfaces can be easily contaminated especially in the dismantling phase of the dialyzers, when the maneuver is carried out by operators wearing soiled gloves. Moreover, at the beginning of the dialytic session, before connecting the patient the connectors could be in direct contact with the filters in the presence of heated dialytic solution for some time and therefore it is clear that they could represent an ideal carrier of bacteria and/or viruses because the configuration of their internal surface is complex.

Disinfection of connectors with Amuchine® 25% for 10-15 min at the end of each dialysis treatment followed by a generous rinse could be very useful [64] (table 1).

In table 1, we report a list of the most important incompatibilities and of the dangerous associations between chemical, disinfecting, descaling, detergent normally utilized in the dialysis centers ([65] modified). We also report their characteristics and possible toxic effects [66-68].

Acetic Acid

A colorless fluid with a pungent odor. Glacial acetic acid must be stored at temperatures > 15°C to avoid crystallization. In dialysis it is used to dissolve calcium and magnesium carbonate precipitates. In a concentration of 5% it has bactericide properties (in particular against Pseudomonas aeruginosa); at lower concentrations it is bacteriostatic. It is not compatible with bases and reacts with hypochlorite. It is irritating for the skin (corrosive at a concentration of 30%: burns and necrosis), for the eyes (keratitis) and for the upper air passage (ulcerations), for the lungs (edema), and for the gastric apparatus (vomit, abdominal colic, diarrhea).

Citric Acid

An odorless white powder with an acid taste. Dissolved in water it is utilized to dissolve calcium and magnesium carbonate precipitates. This acid together with heat becomes also a descaler and disinfectant. It is incompatible with bases and with oxidant agents.

Table 1. Toxicity and incompatibility of the chemical agents normally utilized for detersion, descaling and internal and external disinfection of the dialysis monitors

Agent

Incompatibility

Risk with

Acids (generic)

Bases (generic)

Hypochlorite

Hydrogen peroxide

Aldehydes

Acids (generic)

Hypochlorite

Ammonia

Hydrogen peroxide

Phenols

Hydrochloric acid

Chlorhexidine

Alcohols

Oxidant agents

Oxidant agents

Phenols

Potassium

Chlorhexidine

Soaps

Iodine

Anionic materials

Aldehydes

Citric acid

Hypochlorite

Hydrogen peroxide

Bases (generic)

Ether

Oxidant agents

Hypochlorite

Alogens

Hydrogen peroxide

Oxygen

Phenols

Alkalis

Oxidant agents

Aldehydes

Hydrogen peroxide +

Concentrated alkalis

Hypochlorite

Peracetic acid

Iodine

Phenols

Aldehydes

Alcohols

Hypochlorite

Acids (generic)

Acids

Nitrites

Aldehydes

Phenols

Hydrogen peroxide

Alkalis

Iodine

Phenols

Chlorhexidine

Alkalis

Tensioactive agents

Chlorhexidine

Alcohols (Ethanol, Methanol)

These are highly inflammable colorless fluids with a characteristic odor, utilized in combination with iodine or chlorhexidine. They are incompatible and can give violent reactions with oxidant agents and potassium. They are irritant to the eyes and cause corneal damage. Ingestion of methanol is toxic and the maximal concentration tolerated is 200 ppm. Inhaling its vapor causes a violent irritation of mucosa.

Chlorhexitine

An odorless and colorless or yellow fluid. Utilized mainly as gluconate but also as acetate, it is used with alcohol for disinfecting or with water for cleansing. It is efficacious against bacteria both gram positive and negative but some of these have been described as resistant to chlorhexidine in water solution (Pseudomonas Maltophila). It is incompatible with soaps and with other anionic materials. It cannot be used together with iodine and aldehydes because it can produce carcinogenic products.

Diethylic Ether

A colorless fluid with characteristic odor. Very volatile and inflammable, it has a very low boiling point (35°C) and it has to be stored at cold temperatures away from the light. Its vapors are inflammable in contact with air starting from 1.8% and in oxygen it can explode starting from a concentration of 2%. For these reasons it cannot be utilized near flame or electrical devices that can produce sparks. It reacts with oxidant agents and with halogens. Diethylic ether vapors if inhaled are rapidly absorbed through the alveolar membranes. Successively it passes into the circulation and easily through cellular membranes spreading in all the tissues with accumulation in lipids. Its most important action is the depression of the nervous system: inhalation at a concentration of 1% causes analgesia, at 3% loss of consciousness and over this concentration anesthesia. It has an irritating effect on the mucosa causing hypersecretion.

Phenol

In the crystalline phase it is pink. Soluble in water it can be mixed with ether, alcohol and fats. It has to be stored at cold temperatures away from the light. Phenol is bacteriostatic at the concentrations of 0.2%, bactericide over 1% and fungicide over 1.3%. Many derivates of phenol have a better bactericide action compared to phenol itself (halogenate phenols, biphenols, alkylic derivates, resocinols). Phenolic solutions are incompatible with alkalis and with aldehydes and react strongly with oxidant agents. Phenol is rapidly absorbed and so intoxication can happen after inhalation, contact and ingestion. If there is contact it can cause burns on the skin or in the eyes in a concentration of 1%; at a concentration of 10% it causes corrosions similar to those caused with caustic agents. Inhalation of pure phenol vapors even in small quantities can cause serious lesions with edema of the glottis, hemorrhagic tracheo-bronchitis and bron-copneumonia. Whatever way it is absorbed, symptoms appear very rapidly. Exposure for long periods must be avoided because it can cause: cutaneous eruptions, digestive disturbances, nervous disturbances and myocardial hepatic and renal pathologies.

Formaldehyde

A colorless fluid with a characteristic pungent and irritant odor. Formaline is formaldehyde in solution with water at a concentration of 35-40%, it has to be stored at a temperature >15°C. It cannot be mixed with ammonia, phenol or acids and reacts with anti-oxidant agents. If it reacts with hydrochloric acid it produces carcinogenic substances. For the cells, it is a poison which combines covalently with various protoplasmatic groups and when it comes into contact with hepatic cells it becomes formic acid. It is toxic when inhaled and can cause eye damage (keratitis) upper breathing passage edema and pulmonary edema. Skin contact can cause burns and ulcerations on the hands, it can also cause sensitization. A theratogenic effect is not proved but is suspected, a carcinogenic effect is proven in animals and suspected in humans.

Gluteraldehyde

As a disinfectant agent it is superior to formaldehyde and is active against all microorganisms, also spores and viruses. It is less volatile compared to formaldehyde and for this reason it has a less aggressive odor and is less irritant when inhaled. Incompatibilities and toxic effects are similar to those of formaldehyde, although less severe for skin and mucosa but can cause sensiti-zation phenomena. A carcinogenic effect is suspected both in animals and in humans.

Iodine

It is crystalline in shape, the color is green-violet, and it has an acrid and irritant odor. Normally, it is diluted in alcohol obtaining a dark brown-solution. It is incompatible with phenol and alkali. Iodine has a direct toxic effect on cells because it causes denaturation of proteins, similar to acids and caustics. It has a powerful action against all microorganisms and viruses. Diluted at a concentration of 1:20,000 it can destroy the majority of bacteria in 1 min and at the same concentration in 15 min can kill bacterial spores. Iodine and its derivates can cause allergic reactions resulting in anaphylactic shock: cutaneous, ocular, mucosa and upper breathing passage, lung hypersensitivity. Inhaling iodine vapors can cause symptoms similar to the ones caused by chlorine inhaling.

Sodium Hypochlorite

A colorless or slightly yellow fluid, it has the characteristic odor of chlorine. It has to be stored at cold temperatures and away from the light. Sodium hypochlo-rite concentration decreases during storage and for this reason solutions have to be used in short time. There are many solutions where chlorine is present in hypochlorite form. Elementary chlorine, also in the indissociated chlorine acid form, is a very powerful biocide. At a pH of 7, the concentration necessary to kill most of the microorganisms in 15-30 s is between 0.10 and 0.25 ppm. Mycobacterium Tuberculosis is the only resistant microorganism: concentrations 500 times higher are needed to destroy it (50-125 ppm). It is also viricidal and amebicidal. It is a highly reactive agent and for this reason it can be bound to an organic material and if this is present its bactericide action decreases. It is incompatible with acids, and if it comes in contact with them it converts to highly toxic chlorine gas. It is not compatible with nitrites (risk of explosion), reacts with aldehydes, phenol, alkali and hydrogen peroxide. Maximum concentration of chlorine tolerated in the air is 0.5 ppm: it is a very aggressive substance and can cause acute pulmonary edema. Symptoms are burning of the eyes and of the upper breathing passage, dry cough, retrosternal pain sensation of suffocation. Concentrated hypochlorite causes damage to the skin (irritation, eczema, necrosis), eyes (irritation keratitis) lungs (edema) digestive apparatus (vomiting, abdominal colic), kidney (nephrotoxicity).

Hydrogen Peroxide

It is colorless and odorless and decomposes producing oxygen. One liter of pure hydrogen peroxide can produce 1201 of oxygen. As a disinfectant agent it is used as a solution in a concentration of 3% which produces 10 volumes of oxygen. Hydrogen peroxide is normally used mixed with peracetic acid. It has a light germicide action and is incompatible with alkali and with iodine. It can react strongly with hypochlorite, alcohols, phenol and aldehydes. Hydrogen peroxide causes burns in a concentration of 5% on the mucosa and of 10% on the skin with hyperemia, and penetrates in the lower layers of the derma. The worst burns (higher concentration of hydrogen peroxide or longer time) are similar to the ones caused by corrosive acids.

Tensioactive Agents

These agents can reduce the surface tension of interface with greasy substances; they permit the detachment and removal; they are detergents. They dissociate in water depending on the activity of the anion or of the cation; they are called anionic or cationic. The anionic ones include soaps and the cationic ones come from quaternary ammonium (the 4 atoms of hydrogen of the ammonium are substituted by radicals; at least one of these is paraffinic with high molecular weight). Anionic tensioactives are incompatible with chlorhexidine and have an antagonist action compared to the cationic ones. They are scarcely toxic (if ingested) and harmful with the only exception of potassium soaps, but they can cause sensitization and pathologic alteration of the skin after prolonged exposure. The aggressiveness is caused by alkaline pH (between 10 and 11) and by the solvent action on the skin lipids. Cationic tensioactives are often utilized in dialysis for skin disinfection and for disinfection of the monitors. They are toxic if ingested causing inhibition of the endoglobular cholinhesterase, and have a ganglioplegic action similar to curare. Solutions with concentrations < 10% can cause necrosis of the mucosa.

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