Specimen Collection

BLOOD CULTURES Postmortem blood cultures are frequently obtained but they rarely provide useful information. A recent study (5) from a general hospital showed that in 54% of patients with negative antemortem blood cultures, positive blood cultures were obtained postmortem although the patients had no infectious disease that could be considered a cause of death. Of patients with confirmed antemortem bacteremia/fung-emia, only 34% had a postmortem blood culture from which the same organisms were isolated. Moreover, of patients without cultures or with negative or contaminated antemortem blood cultures, all had positive postmortem cultures; 76% of the isolates were considered contaminants and 22% of the isolates were of indeterminate significance (5). Thus, the decision to obtain a postmortem blood culture should rely on a strong clinical suspicion of sepsis in the absence of a pathogen-isolated ante-mortem. Because the results of in vivo blood cultures generally are quite reliable, a known bloodstream pathogen rarely needs to be isolated again at autopsy.

Hospitalized patients commonly receive antibiotics prior to phlebotomy for blood cultures. This is frequently prompted by new fever spikes or acute deterioration in clinical status. Despite such treatment, organisms may still be isolated at autopsy from these patients (1).

Blood may be obtained from the right atrium, inferior vena cava, or from the aorta. In patients in whom thoracic dissection is not possible, as with a restricted autopsy permission, blood may be obtained from the femoral vein. Although the theory of bacterial transmigration through the bowel wall is largely dismissed, traditional autopsy protocol recommends that blood be obtained prior to manipulation or removal of the bowel. Searing the area with a hot spatula will sterilize the site of needle entry. In cases requiring a femoral stick, sterilize the skin with povidone iodine. In fetuses and neonates, a portion of liver may be submitted in place of blood, since searing of the heart or great vessels may damage the thoracic organs.

LUNG CULTURES The lungs' gross appearance should direct the pathologist to the best site for culture. The most common evidence of acute infectious pneumonia is pleural fibrin-ous exudate and parenchymal consolidation. Palpation of the lungs while they are still in situ is the best method for detecting this change. The surface of the lungs may be sterilized by searing with a heated spatula. Four stabbing motions, 90o to each other with a sterile blade, will mobilize a cube of tissue that can then be lifted up with a sterile forceps. The blade can then make the final cut to free the tissue block. The tip of the forceps should not be too hot as the tissue will stick, making it difficult to drop the specimen into the container. Providing that the lung has not been perfused with formalin, areas of consolidation may still be cultured after the lung is sliced. Again, the surface should be sterilized by searing. In patients with moderate to severe emphysema, pneumonia may be more difficult to visualize grossly. Thus, in these patients, the prosector's index of suspicion should be raised.

It is standard practice in most microbiology laboratories that with all cultures of tissues a Gram stain is performed as well. If the prosection occurs in the morning, the results of the Gram stain may be available to be included in the preliminary autopsy report. Any Gram stains performed and read by the pathologist may also provide other valuable information for the preliminary autopsy report—for example, the presence of a coexisting lymphoma.

Oral and gastric contents may enter the bronchial tree ago-nally or during transit of the body to the autopsy room. This contamination may change the gross appearance of the pulmonary cut surface as well as add more bacteria to the lung parenchyma. However, the lack of consolidation will help the pathologist to conclude that the discoloration is not pneumonia. Should the pathologist obtain a lung culture of such an area, the Gram stain will yield the correct interpretation.

ABSCESSES During evisceration or dissection of organs, abscesses may be found unexpectedly. In such a case, the prosector should immediately aspirate some of the pus with a needle and syringe. An attempt should be made to take material from the center of the abscess. Even though the abscess is contaminated at this time, the specimen is still acceptable since any organisms in the abscess will likely far outnumber those introduced during the course of the dissection. The Gram stain will aid in this interpretation.

There is no reason to culture acute perforations of bowel since both Gram stain and culture will point to fecal flora. Only when a host response is seen, such as an abscess, should the lesion be cultured.

CARDIAC VALVULAR VEGETATIONS The microbiologic examination of endocarditis is a special challenge for the pathologist, because it competes with the other components of a complete examination, that is, photography and histology. If a vegetation is suspected clinically, the task is easier. In the

Fig. 9-2. Aseptic exposure of aortic valve vegetation. The aorta has been trimmed away to allow good visualization of the aortic valve. Photography and collection of a portion of the vegetation (center of field) for culture and Gram stain was easily accomplished. (Courtesy Dr. W.D. Edwards.)

case of an aortic or pulmonic valve vegetation, the ascending aorta or main pulmonary artery may be cut carefully away so as to visualize the valve leaflets (Fig. 9-2). Following photography, a portion of the vegetation may be removed with sterile forceps and scalpel or scissors and sent for culture. Enough material should be collected to allow for an adequate Gram stain to be prepared as well. Since the amount of tissue is usually scant, it should be sent to the microbiology laboratory as soon as possible to prevent drying.

In suspected infective endocarditis with mitral or tricuspid vegetation, the outside of the heart need not be seared as this would cause disfigurement of the heart. Rather, the ventricle is incised along the acute or obtuse margin (right and left ventricles, respectively) with a sterile scalpel until the ventricular chamber is entered (Fig. 9-3). The cut across the atrial-ven-tricular groove is then extended so that it will be easier to splay open the valve ring. It may be necessary to have an assistant to keep the ventricle open. After taking photographs, a portion of the vegetation is obtained for culture and Gram stain.

If the suspected endocarditis appears to be accompanied by coronary atherosclerosis and myocardial infarctions, the prosector may find it more appropriate to examine (or remove) the coronary arteries prior to addressing the valve pathology. Manipulation of the heart should be minimized. The pathologist may then begin to breadloaf the heart, keeping the slices at 1-cm thickness. When the slices have reached the tip of the papillary muscles, the valve may be viewed from below and specimens may be procured for Gram stain and culture.

Fig. 9-3. Aseptic exposure of mitral valve from left ventricle. With an incision into the left ventricle along the obtuse margin, the mitral valve is readily available for photography and collection of a vegetation for culture and Gram stain.

When infective vegetations are encountered unexpectedly, the pathologist should submit tissue for culture and Gram stain, despite the expected contamination. Important information can still be obtained because the repertory of expected pathogens is limited and the Gram stain will be very helpful in interpreting the culture results.

DRAINING SINUSES Since draining sinuses are usually continuous with the skin surface, they may be heavily contaminated with skin flora. Thus, the material closest to the skin surface should be wiped away with sterile gauze. The purulent material that is present in the deeper sections of the sinus will be much more informative. This material may be aspirated with a large bore needle and syringe, a scalpel or, as a last resort, a swab. The Gram stain is critically important in the interpretation of the organisms isolated. The presence of acute inflammation will differentiate true infection from colonization. When the clinical history suggests Actinomyces, the prosector should examine a portion of the pus for "sulfur granules." If they are found, they may be pressed between two slides and then the two slides may be pulled apart, as with the "pull-prep." Since sulfur granules are more solid and require more force to spread out, it is safer to press the two slides together on a counter top, to avoid breaking the slides.

CEREBROSPINAL FLUID (CSF) When infectious meningitis is suspected but not confirmed prior to death, the pro sector may find it necessary to procure CSF. This is most easily accomplished by performing a cisternal tap. The procedure entails placing the body in a prone position making sure that there is adequate padding under the face so as to avoid disfigurement. After vigorous cleansing of the skin with iodine and then alcohol (the alcohol must be allowed to evaporate), a 12-gauge needle is inserted at the midline below the base of the occipital bone and directed slightly superiorly, toward the eyes. The needle is pushed forward slowly and carefully, with frequent attempts to aspirate fluid. Unnecessary movement of the syringe should be avoided so as to prevent bleeding. (As stated in Chapter 2, aspiration of blood, together with CSF, is common, even among experienced prosectors.) If no or only blood-tinged CSF is aspirated, it is still possible to collect a satisfactory specimen after removal of the calvarium. For that purpose, a needle may be inserted in the subarachnoid space. Should this fail, a tissue specimen of meninges and a small amount of underlying brain may be taken. Pus tends to collect in the inferior aspect of the brain, thus making collection of material possible.

If a brain abscess is suspected, the prosector can try to localize the lesion by palpation. Should the site be determined, the brain surface can be sterilized by searing and aspiration can be attempted with a long, large-bore needle. In certain situations, hemisection of the brain (see Chapter 6) and fresh cutting of one half may be indicated.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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