|Year : 2010 | Volume
| Issue : 1 | Page : 5-10
Clinical microbiology in the intensive care unit: Strategic and operational characteristics
S Bhattacharya1, AS Mondal2
1 Department of Microbiology, West Suffolk Hospital NHS Trust , Bury St. Edmund, United Kingdom
2 Department of Anaesthesia and Intensive Care, North Middlesex University Hospital , London, United Kingdom
|Date of Submission||11-Aug-2009|
|Date of Acceptance||28-Sep-2009|
|Date of Web Publication||6-Jan-2010|
Department of Microbiology, West Suffolk Hospital NHS Trust , Bury St. Edmund
Source of Support: None, Conflict of Interest: None
Infection is a major cause of morbidity and mortality among patients admitted in intensive care units (ICUs). The application of the principles and the practice of Clinical Microbiology for ICU patients can significantly improve clinical outcome. The present article is aimed at summarising the strategic and operational characteristics of this unique field where medical microbiology attempts to venture into the domain of direct clinical care of critically ill patients. The close and strategic partnership between clinical microbiologists and intensive care specialists, which is essential for this model of patient care have been emphasized. The article includes discussions on a variety of common clinical-microbiological problems faced in the ICUs such as ventilator-associated pneumonia, blood stream infections, skin and soft tissue infection, UTI, infection control, besides antibiotic management.
Keywords: Clinical microbiology, intensive care unit, antibiotics
|How to cite this article:|
Bhattacharya S, Mondal A S. Clinical microbiology in the intensive care unit: Strategic and operational characteristics. Indian J Med Microbiol 2010;28:5-10
|How to cite this URL:|
Bhattacharya S, Mondal A S. Clinical microbiology in the intensive care unit: Strategic and operational characteristics. Indian J Med Microbiol [serial online] 2010 [cited 2020 Jul 8];28:5-10. Available from: http://www.ijmm.org/text.asp?2010/28/1/5/58720
| ~ Introduction|| |
Infection is a major factor determining clinical outcome among patients requiring intensive care unit (ICU) support.  The causes of infection within ICU are multi-factorial, and consequences depend on source involved, organisms associated, underlying morbidity, timeliness and appropriateness of the treatment/ interventions received. Apart from the clinical and human consequences, the health economic and infection control implications of infection within ICU are huge.  This article is an attempt to summarise infection management strategies within ICUs using clinical microbiology-intensive care partnership as a standard model.
Clinical profile of patients requiring intensive care support
Any clinical event, which compromises the airway, breathing, circulation (ABC) of a patient or breaches significantly the integrity and functioning of tissues and organs (post surgery, post trauma) may result in the requirement of ICU or high dependency unit (HDU) support. These incidents can be either unexpected clinical emergencies (cerebro-vascular accidents, acute myocardial infarction, severe sepsis, fulminant hepatitis, acute pancreatitis, road traffic accidents, burns and other forms of physical trauma, intoxication), or may follow planned elective procedures (neuro-surgery, coronary artery bypass grafting, intra-abdominal surgeries). The care provided to patients within the ICU setting may include basic life support (airway, breathing, fluid-electrolyte balance, nutrition), routine or specialised organ support (artificial ventilation, intra-cardiac balloon pump, haemo-filtration, extra-corporeal membrane oxygenation-ECMO, molecular adsorbent recirculation system-MARS) besides directed therapy against infection or inflammation. Consequently, the ICU support offered in hospitals has diversified into sub-specialties such as general ICU (for patients coming with sepsis, pneumonia, pancreatitis, post trauma, post abdominal surgery), cardiothoracic ICU (post CABG, heart failure), neuro-ICU (post neurosurgery, head injury), and neonatal/paediatric ICU (for pre-term and low birth weight babies, and babies in need of specialised care for medical or surgical reasons). This life supporting system involves a continuous monitoring of the vital parameters (pulse rate, respiratory rate, temperature, blood pressure) and organ function (oxygen saturation, arterial blood gas analysis, haematological and biochemical monitoring of liver/ renal function, level of consciousness and routine physical examination). Modern intensive care is a multi-disciplinary effort of a team lead by the intensivist, but supported as and when required by associated medical/surgical specialities.
Infections among patients in the intensive care unit
Infection among ICU patients might be community acquired (viral encephalitis, bacterial meningitis, pneumonia, endocarditis, intra-visceral abscesses, urinary tract infections-UTIs) or hospital and health care associated infections (surgical site infections- SSIs, hospital acquired pneumonia-HAP, catheter related blood stream infections - CR-BSI, catheter associated UTI).  The consequence and complications of infection might have variable clinical (sepsis, organ failure, death), health economic (bed utilisation, hospital stay, cost of care, antibiotic utilisation), infection control impact (spread of infection to patient/ staff/ visitor). A sustained partnership between the intensivist and the clinical microbiologist is essential for improving clinical outcomes and optimising resource utilisation.
Typical microbiological challenges within ICUs
- Limited time and narrow window of opportunity to diagnose, treat or intervene because of critical illness. The cost of delay or failure is often death or grievous organ damage to the patient
- Single or multiple organ failure in the patient leading to inadequate tissue penetration of antimicrobial agents or suboptimal drug metabolism and elimination (altered pharmaco-kinetics and pharmacodynamics)
- High antimicrobial usage leading to increased cost, anti-microbial resistance, CDAD (Clostridium difficile associated diarrhoea)
- Lack of side room or isolation facilities leading to greater infection control risks
| ~ Common Health Care Associated Infections in intensive care unit Patients|| |
Ventilator associated pneumonia
Patients requiring artificial mechanical ventilation are susceptible to infection due to micro-aspiration of oropharyngeal or gastric secretions leading to lower respiratory tract infection. Common pathogens include organisms present in patient's own upper respiratory tract (Staphylococcus spp., Streptococci., Haemophilus influenzae, oral anaerobes) as well as those present in the hospital environment (mainly aerobic Gram negative bacilli such as Eschericia coli, Klebsiella spp., Pseudomonas spp., Acinetobacter spp.). The patient may manifest with local (coarse crackles on auscultation, increased oxygen requirement manifested as increase in FiO 2 , new chest X ray infiltration) usually along with systemic manifestations of infection. Specific identification of causative organism is often difficult because of the paucity of good quality samples, which often require invasive sampling (bronco- alveolar lavage, protected bronchial brush or non-directed bronchial lavage). The presence of bacteria in the sample, do not necessarily signify infection (colonisation of upper respiratory tract with Gram-negative bacilli or Candida is common in hospitalised/antibiotic treated patients). Hence in most cases antibiotic choice is empirical and based on circumstantial, epidemiological and clinical evidence. Therapy generally involves giving broad-spectrum antibiotics to cover putative Gram positive and Gram-negative pathogens (Piperacillin-Tazobactum, Carbapenems such as Imipenem or Meropenem). In specific situations, depending on positive microbiology specific directed therapy may have to be added (such as Vancomycin or Linezolid for MRSA; Fluconazole, Caspofungin or Amphotericin B for Candida albicans or other Candida species). The duration of therapy depends on clinical response, pathogens involved, underlying risk factors and co-morbidities. In recent years VAP care bundles consisting of elevation of the head of the bed to 30-45 degrees, daily 'sedation vacation' and daily assessment of readiness to extubate, peptic ulcer disease prophylaxis, and deep venous thrombosis prophylaxis have been shown to improve outcome. ,
Skin and soft tissue infection
This may either take the form of surgical site infection (SSI), vascular catheter induced phlebitis (VIP) with or without adjoining infection of skin and soft tissues, and pressures sores (decubitus/pressure ulcers and stress ulcers). While appropriate peri-operative antibiotics have a role in prevention of SSI it is no substitute for good surgical techniques. Prevention is the mainstay in the management of VIP and pressure ulcers, because once developed the treatment could not only be difficult (e.g. pressure sores), and prolonged (leading to increased hospital stay and its consequences) but also life threatening through the development of sepsis. The evidence regarding the efficacy of antibiotic prophylaxis in preventing post-operative infections is highly variable. Although there are clearly areas where the benefit of peri-operative antibiotics is fairly well established, ,, there are areas where there either no evidence that prophylaxis has any effect,  or the evidence on either side of the argument does not exist because of lack of adequate studies.  It is important that evidence based recommendations for surgical prophylaxis is adhered to not only in the choice and dose of agent but also for the duration. Various evidence based guidelines from Cochrane and other sources (e.g. Scottish Intercollegiate Guideline Network-SIGN)  are available. Prolonged antibiotic use in the peri-operative period not only lack justification but also contribute to subsequent problems (selection of resistant strains, C. difficile associated diarrhoea) besides unnecessarily increasing cost of care. For the prevention of VIP and associated SSTI, adherence to the three-day rule is important so that the need for intravenous access is seriously reviewed on a daily basis, and no peripheral venous catheters are left for more than 72 hours. , This requires documentation (with time, date, site, name of the person responsible for insertion and assessment) so that regular audits could be conducted as and when required.  Although the pathogenesis of pressure ulcers appears to be multi-factorial,  scrupulous attention to the integrity of skin is paramount in the prevention of decubitus ulcers in debilitated and critically ill patients because once established these lesions especially if they involve deeper tissues are notoriously difficult to manage and may cost not only the well being and potentially the life of the patient but also the reputation of institution and health care workers (physicians and nurses) responsible for the patient care. Good hygiene, adequate nutrition, patient mobility, special bed mattress, and adequate nurse patient ratio is critical if this condition is to be avoided. ,,,,
Blood stream infections (BSIs) including catheter related
This constitutes an important cause of morbidity and mortality among patients in critical care settings and other clinical areas. BSIs that accompany primary diseases such as infective endocarditis, community acquired pneumonia, uro-sepsis and meningitis are not being discussed here. This section is only dealing with BSIs that may result from health care interventions such as a vascular catheter insertion, secondary bacteremia following urinary catheter related sepsis, infection of surgical sites or infection arising out of hospital acquired or ventilator related pneumonia. Vascular access devices are inserted in critically ill patients for the maintenance of fluid-electrolyte balance, administration of therapeutic agents (vasoactive drugs, antibiotics, etc.), maintain nutritional requirements (TPN- total parenteral nutrition), monitoring vital parameters (e.g. central venous pressure, arterial pressure), providing vital organ support (e.g. haemo-filtration), and doing essential investigations (blood gas monitoring, besides routine haematological and biochemical tests). Again, the only way to avoid infections from these essential interventions include strict and meticulous attention to asepsis during insertion of vascular access devices, regular mapping and review of each vascular channel so that they are kept only as long as essential. There is evidence that the use of chlorhexidine-based preparations and insertion of central line through the sub-clavian access (in contrast to internal jugular or femoral access) reduce infection rates.  Most patients with BSIs are likely to manifest clinically with systemic signs of infection (fever, leucocytosis, raised inflammatory markers) and blood cultures both peripheral and through the vascular access device need to be taken within 15 minutes of each other detect CR-BSI. Empirical therapy should constitute glycopeptide antibiotics such as Vancomycin to cover common Gram-positive pathogens (Methicillin sensitive and resistant Staphylococcus aureus and S. epidermidis) but in most cases CR-BSI removal of the vascular access device remains the mainstay to prevent future episodes or complications (e.g. endocarditis). 
Urinary tract infection
Urinary catheters are used in the ICU setting to monitor urine output, relieve retention and facilitate nursing care. However, each episode of urinary catheter insertion constitutes an infection risk and the catheter need should be reviewed on a day-to-day basis and should be present only as long as clinically indicated. Most catheters get colonised by bacteria within a few days, therefore the presence of bacteria in catheterised specimen of urine (CSU) is common and does not necessarily warrant antibiotic therapy.  Therefore, the decision to initiate antibiotic therapy has to be individualised and systemic and local signs of infection are more important than CSU microbiology and cytology. During the process of change of catheter a single shot of gentamicin (2 mg/kg body weight iv) or other appropriate antibiotics with a good urinary excretion can help prevent sepsis during the catheter change in sensitive strains. Finally, flushing of blocked catheters might actually be harmful because of chance of developing ascending infection of the upper urinary tract (e.g. pyelonephritis). 
| ~ Key Clinical Microbiology Strategies for Infection Management within Intensive Care Units|| |
Regular ICU rounds by Clinical Microbiologists with bed-side discussion with Intensivists regarding infection management
In many institutions (for example in the UK) where clinical microbiology as opposed to laboratory centred approach is the mode of practice ICU rounds by microbiologists on a regular basis is common.  The objectives of this bedside round are multi-focal and have been elaborated in the subsequent points. This round is crucial for efficient management of infection in critical care and is based on partnership and mutual understanding of microbiological and intensive care perspectives.
Prompt communication of urgent microbiology/virology results
Delay in communication of clinically significant microbiology results and consequently the delay in initiating the appropriate anti-infective therapy or intervention can adversely affect the clinical outcome of a patient in ICU. Clinical microbiology ward round achieves this objective through early communication of even preliminary results so that therapy can be initiated at the earliest opportunity.
Assessment of infection
This constitutes the central objective of the clinical microbiology round in ICU so that diagnostic, therapeutic and infection control interventions can be initiated at the earliest. Assessment of infection is and has to be a broad based approach relying on an entire gamut of historical, epidemiological, clinical, diagnostic parameters (physical examination, haematological, biochemical, radiological) and not just based on microbiology results (positive or negative).
Change, stoppage, optimisation and augmentation of antimicrobial therapy
This constitutes one of the most important interventions offered by clinical microbiologists in ICU, and a consensual approach in consultation with the intensivists is taken with regard to change of any anti-infective therapy. What is required to make this intervention from microbiologists effective is not just the knowledge of resistance mechanisms and antibiotic spectrum but also a detailed understanding of acute physiology, pharmacokinetic-pharmacodynamic effects, and the ability to see the patient as a whole and not just from a microbiological point of view. The [Table 1] provides a general guide for selection of anti-infective therapy in various important infective syndromes seen in ICUs.
Infection prevention and control
In the ICU setting achieving the objective of preventing the spread of infection from patient/staff/visitor to patient/ staff/visitor can be challenging because of the need to balance the lack resource and information availability with the clinical need of the patient. Universal precautions and scrupulous attention to the adherence of best practice guidelines is the way to prevent hospital-acquired infections. The risk of transmission of infection is real and several interventions such as endo-tracheal intubation (e.g. swine flu, tuberculosis, meningococcal meningitis), vascular catheter insertion (e.g. risk of sharps injury or splash and consequent risk of blood borne viruses) can affect the health care workers (HCWs). Transmission of multi-resistant pathogens (MRSA, , ESBL, , multi-resistant Acinetobacter baumannii, ) has been reported in ICU besides posing significant infection control problems with regard to varicella , and tuberculosis ,, (especially in neonatal intensive care units).
Microbiology result interpretation and feedback to intensive care unit team regarding antimicrobial resistance, audit and policy implementation
With the training and knowledge base, microbiologists during intensive care rounds are in a unique position to directly interact with clinicians or patients to explain clinical significance of test results (e.g. infection versus colonisation, predictive value of test results, significant titres of serology tests, meaning of a PCR result). This may translate not only to better understanding of the significance of microbiology test results but more judicious use of diagnostic tests and anti-infective therapy.
Rational utilisation of diagnostic, therapeutic and infection prevention/control resources
One of the challenges in clinical microbiology is to optimise and rationalise the use of sparse resources so as to deliver the greatest good for the maximum number of patients keeping in mind the limitations of resource availability (diagnostic test, therapeutic option, infection control facilities). Each ICU is different from the other in terms of the patient/staff profile and resource availability so development of local guidelines in consultation with all relevant departments is essential to optimise patient care.
| ~ Conclusions|| |
Microbiology has already made a transition from pathological subspecialty to an essential clinical support service. It is important that we accelerate this transition of microbiology to the frontline of direct patient care, viz., the ICU. Many lives are either saved or lost in the ICU setting of every major hospital. Infection is a major contributor to adverse patient outcome. Close partnership between microbiologists and intensive care physicians can save many more lives. "Care bundles," used in ICU setting either for management of sepsis or management of patients requiring ventilation, are setting the standards of care. ,, There is no reason why a number of "infection service bundles"  comprising of appropriate uses of diagnostic-therapeutic-infection control resources, which are monitored and tailored by clinical microbiologists and supported by intensivists cannot become an integral part of ICU package.
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