PHYSIOLOGY• Body temperature is controlled by the hypothalamus• Neurons in pre-optic ant hypothal & post hypothal • Receive two kinds of signals • Peripheral N transmit info from warmth/cold receptors of skin • Other from temp of blood bathing the region• Both signals are integrated by Temp Regulation Centre (TRC) of hypothalamus • Maintain normal temp• In neutral temp environment • Humans produces more heat than is needed • To maintain core body temp at 37°C 2
TEMPERATUREMEASUREMENT Mean oral temp = 36.8° ± 0.4°C (98.2° ± 0.7°F) Lowest at 6 A.M. and highest between 4 to 6 PM Maximum normal oral temp 37.2°C (98.9°F) at 6 AM 37.7°C (99.9°F) at 4 PM (99 %) Fever Definition ( Harrison) A.M temperature of >37.2°C (>98.9°F) or P.M. temperature of >37.7°C (>99.9°F) 3
TEMPERATUREMEASUREMENT Normal daily temp variation is 0.5°C (0.9- 1°F) During febrile illness diurnal variation is higher Daily temp variation is fixed in early childhood Elderly individuals have reduced ability to develop fever even in severe infections Rectal temp 0.4°C (0.7°F) > oral readings Lower-esophageal temp reflects core temp
TEMPERATUREMEASUREMENT Tympanic membrane (TM) thermometer Measure radiant heat from TM & ear canal TM values are 0.8°C (1.6°F) < rectal temp In women who menstruate AM temp lower in the 2 weeks before ovulation It rises by ~0.6°C (1°F) with ovulation Remains at that level until menses occur
DEFFINITION OF FEVER INICU The Society of Critical Care Medicine practice parameters define fever in the ICU as a temperature > 38.3°C ( 101°F).Unless the patient has other features of an infectious process, only a temperature > 38.3°C ( 101°F) warrants further investigation.
EPIDEMIOLOGY Fever complicates up to 70 percent of all ICU admissions and is often due to an infection In one observational study of 24,204 adult ICU admissions, fever ≥39.5ºC (103 ºF) was associated with an increase in mortality (20 versus 12 percent)
FEVER PATTERNS Most patients have remittent or intermittent fever that, when due to infection, usually follow a diurnal variation. Sustained fevers have been reported in patients with Gram-negative pneumonia or CNS damage. The appearance of fever at different time points in the course of a patient’s illness may however provide some diagnostic clues. Fevers that arise > 48 h after institution of mechanical ventilation may be secondary to a developing pneumonia. Fevers that arise 5 to 7 days postoperatively may be related to abscess formation. Fevers that arise 10 to 14 days post institution of antibiotics for intra-abdominal abscess may be due to fungal infections.
CAUSES OF FEVER IN THE ICU Any disease process that results in the release of the proinflammatory cytokines IL-1, IL-6, and TNF- will result in the development of fever Infections are the commonest cause of fever in ICU patients, many noninfectious inflammatory conditions cause the release of the proinflammatory cytokines with a febrile response. Similarly, it is important to appreciate that not all patients with infections are febrile. Approximately 10% of septic patients are hypothermic and 35% are normothermic at presentation. Septic patients who fail to develop a temperature have a significantly higher mortality than febrile septic patients The reason that patients with established infections fail to develop a febrile response is unclear; however, preliminary evidence suggests that this aberrant response is not due to diminished cytokine production.
DIFFERENTIAL DIAGNOSIS Sources of fever in the ICU may be Infectious Non infectious
NONINFECTIOUS CAUSES For reasons that are not entirely clear, most noninfectious disorders usually do not lead to a fever > 38.9°C (102°F); therefore, if the temperature increases above this threshold, the patient should be considered to have an infectious etiology as the cause of the fever. However, patients with drug fever may have a temperature > 102°F. Similarly, fever secondary to blood transfusion may be > 102°F. On the basis of the number of medications administered to patients in the ICU, one would expect drug fever to be a relatively common event. Drug fever should be considered in patients with an otherwise unexplained fever, particularly if they are receiving ß-lactam antibiotics. Drug fever is usually characterized by high spiking temperatures and shaking chills. It may be associated with a with leukocytosis and eosinophilia. Relative bradycardia, although commonly cited, is uncommon.
NONINFECTIOUS CAUSES ATELECTASIS is commonly implicated as a cause of fever. Standard ICU texts list atelectasis as a cause of fever, although they provide no primary source. FEBRILE REACTIONS complicate about 0.5% of blood transfusions More common following platelet transfusion. Antibodies against membrane antigens of transfused leukocytes and/or platelets are responsible for most febrile reactions to cellular blood components. Febrile reactions usually begin within 30 min to 2 h after a blood-product transfusion is begun. The fever generally lasts between 2 h and 24 h and may be preceded by chills. An acute leucocytosis lasting up to 12 h commonly occurs following a blood transfusion.
NONINFECTIOUS CAUSES ARDS may progress to a "chronic" stage characterized by pulmonary fibroproliferation and fevers ACALCULOUS CHOLECYSTIS occurs in approximately 1.5% of critically ill patients. An important "noninfectious" cause of fever in critically ill patients, as it is frequently unrecognized and therefore potentially life threatening The pathophysiology of acalculous cholecystitis is related to the complex interplay of a number of pathogenetic mechanisms, including gallbladder ischemia, bile stasis with inpissation in the absence of stimuli for emptying of the gallbladder, positive-end expiratory pressure, and parenteral nutrition. Bacterial invasion of the gallbladder appears to be a secondary phenomenon. The diagnosis of acalculous cholecystitis is often exceedingly difficult and requires a high index of suspicion. Pain in the right upper quadrant is the finding that most often leads the clinician to the correct diagnosis, but it may frequently be absent.
NONINFECTIOUS CAUSES The most difficult patients are those recovering from abdominal sepsis who deteriorate again, misleadingly suggesting a flare-up of the original infection. Rapid diagnosis is essential because ischemia may progress rapidly to gangrene and perforation, with attendant increase in the already high morbidity and mortality The diagnosis should therefore be considered in every critically ill patient who has clinical findings of sepsis with no obvious source Ultrasound is the most common radiologic investigation used in the diagnosis of acalculous cholecystitis Features include increased wall thickness, intramural lucencies, gallbladder distension, pericholecystic fluid, and intramural sludge. Wall thickness 3 mm is reported to be the most important diagnostic feature on ultrasound examination, with a specificity of 90% and a sensitivity of 100%. Percutaneous cholecystostomy may be the procedure of choice Posterative fever upto 48 Hrs.
VENTILATOR-ASSOCIATEDPNEUMONIA occurs in approximately 25% of patients undergoing mechanical ventilation Fagon and colleagues reported an attributable mortality of 27%. Diagnosis of VAP remains one of the most difficult clinical dilemmas in critically ill patients receiving mechanical ventilation initial empiric antibiotic regimen must be broad and cover both Gram- positive and negative organisms,
DIAGNOSTIC APPROACH A thorough review of the medical history and a full physical examination should be performed whenever a patient develops an unexplained fever in the ICU. Blood cultures are the only mandatory diagnostic tests in patients with a new fever SPUTUM.. indicated for febrile patients with any of the following findings new sputum production; a change in the color, amount, or thickness of their sputum. a new or progressive pulmonary infiltrate. an increased respiratory rate. an increased minute volume; a decreased tidal volume; decreased oxygenation. needing more ventilatory support; or requiring more inspired oxygen.
DIAGNOSTIC APPROACH URINE . Urinalysis and urine culture are indicated for febrile patients with ○ a urethral catheter. ○ urinary obstruction. ○ renal calculi. ○ recent genitourinary surgery or trauma, or neutropenia.
DIAGNOSTIC APPROACH CHEST IMAGING A chest radiograph is worthwhile in many patients with respiratory symptoms or signs. It may detect a new or progressive pulmonary infiltrate. distinguish pneumonia from tracheobronchitis, or identify a respiratory source of fever other than pneumonia or tracheobronchitis Computed tomography (CT) should be reserved for the clarification of abnormal chest radiographic findings.
DIAGNOSTIC APPROACH S.CHEMISTRY Done for LFT, Urine fucntions, electrolyte imbalance TFT(THYROID FUCTION TEST) Done if thyroid storm is suspected
Blood Cultures B/C should be obtained in patients with a new fever when clinical evaluation does not strongly suggest a noninfectious cause Skin Preparation The site of venipuncture should be cleaned with either 2% chlorhexidine gluconate in 70% isopropyl alcohol (2% alcoholic chlorhexidine), or 1–2% tincture of iodine (iodine in alcohol). Povidone iodine (10%), although acceptable, is a less efficient agent. When blood is to be inoculated into a culture or transport tube, the needle used for venipuncture should not be replaced by a sterile needle. The risk of a needle stick injury during the switch in needles is currently thought to outweigh the risk of contamination
Blood CulturesBlood Volume and Collection System One blood culture is defined as a sample of 20–30 mL of blood drawn at a single time from a single site, regardless of how many bottles or tubes the laboratory may use to process the specimen. The sensitivity of B/C → obtaining the cultures before the initia-tion of anti-infective therapy and the volume of blood drawn
Blood CulturesNumber of Cultures and Sites 3-4 B/C with adequate volume (20–30 mL each) are drawn within the first 24 hrs of suspected bacteremia or fungemia Each culture should be drawn by separate venipuncture or through a separate intravascular device but not through multiple ports of the same intravascular catheter There is no evidence that the yield of cultures drawn from an artery is different from the yield of cultures drawn from a vein. Culture from the device (+) and from venipuncture (-); the positive culture may represent a contaminant or a catheter-related infection, but clinical judgment rather than any rigid criteria is needed to interpret the significance of discordant results
Blood Cultures Labeling Blood cultures should be clearly labeled with the exact time, date, and anatomic site or catheter lumen from which blood is drawn and also include other information (concomitant antimicrobial therapy) that may be appropriate.
Recommendations forObtainingBlood Cultures 1. 3-4 B/C within the first 24 hrs of the onset of fever (level 2) 2. Additional B/Cx2: suspicion of continuing or recurrent bacteremia or fungemia or 48–96 hrs after initiation of appropriate therapy for bacteremia/fungemia. (level 2). 3. P’ts without an indwelling vascular catheter, obtain at least two blood cultures using strict aseptic technique from peripheral sites by separate venipunctures after appropriate disinfection of the skin (level 2). 4. 2% chlorhexidine gluconate in 70% isopropyl alcohol, but tincture of iodine is equally effective. 30 secs of drying time before proceeding with the culture procedure. Povidone iodine is an acceptable alternative, but it must be allowed to dry for 2 mins (level 1)
Recommendations forObtainingBlood Cultures 5. The injection port of the blood culture bottles should be wiped with 70–90% alcohol before injecting the blood sample into the bottle to reduce the risk of introduced contamination (level 3) 6. P’t with intravascular catheter→one B/C from venipuncture and at least one culture from intravascular catheter. Obtaining blood cultures exclusively through intravascular catheters yields slightly less precise information than information obtained when at least one culture is drawn by venipuncture (level 2). 7. Label the blood culture with the exact time, date, and anatomic site from which it was taken (level 2). 8. Draw 20–30 mL of blood per culture (level 2).
Fever diagnostic algorithmMarik, P. E. Chest 2000;117:855-869
REFERRENCES Critical Care medicine 2008 UPtoDate 2012 Harrison book of Medicine Guidelines for evaluation of new fever in critically ill adult patients: 2008 update from the American College of Critical Care Medicine and the Infectious Disease Society of America.