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Identifying and treating PCP

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VOL: 96, ISSUE: 37, PAGE NO: 19

Veronica Bastow, MSc, SRP, is superintendent physiotherapist, Queen Elizabeth Hospital, King’s Lynn, Norfolk

Pneumocystis carinii is a fungal organism (Mandell et al, 2000) that is not a problem in healthy people, but in those with compromised immune systems it can become an opportunistic pathogen, causing P carinii pneumonia.

PCP is a severe form of pneumonia with a high mortality rate. It is the leading cause of death in patients with HIV/AIDS and over 80% of this patient group can expect to develop at least one case of PCP (Project Inform, 1998). It also affects premature infants being cared for in hospital, patients with cancer and those being treated with immunosuppressive medications for the management of organ transplants or cancer.

Seldom diagnosed before the AIDS epidemic, PCP is now increasingly being seen in immunocompromised patients who do not have HIV/AIDS.

The vulnerability of the patient groups at risk of contracting PCP has obvious implications for nursing care, particularly in relation to those with HIV/AIDS, so local infection control guidelines should be strictly adhered to during the sputum collection procedure.

Disease process

Initially, a few scattered cysts are present along the walls of the alveoli. The P carinii then clump together and stick to or become coated with alveolar material. This makes them difficult to free from the lung host and explains why P carinii was originally identified as a parasite. This tendency to adhere to the alveoli creates problems when nurses or physiotherapists are asked to obtain a sputum specimen.

Clinical presentation

Patients usually present with increasing breathlessness, which may initially be evident only on exertion. The alveolar function is impaired by the presence of exudate and organisms, and oxygen levels fall as a result. This eventually leads to laboured and distressed breathing on talking and while at rest.

Fine crackles may be heard on auscultation, but often the breath sounds are normal. An arterial blood-gas analysis showing low PaO2 when breathing air indicates a poor prognosis. Fevers and cough are common, with the cough often being non-productive. Some patients also experience haemoptysis and tightness or pain in the chest. The latter may indicate a pneumothorax.

Examination of the chest X-ray of a patient with PCP often reveals diffuse ground-glass interstitial infiltrate, which appears as a hazy, white mottled area. Occasionally pneumatoceles, nodules, cavities or a pleural effusion may also be seen.

In children, the predominant features are an increased respiratory rate, breathlessness, cough and fever. Intercostal recession may be seen and the breath sounds are often quiet. Cyanosis may occur. Crackles are usually not audible, but wheezing may be heard.

Diagnosis

Invasive and non-invasive methods are used, with each carrying its own particular risks. In patients receiving prophylactic pentamidine isethionate, the yield of PCP from a sputum specimen is likely to be reduced as a result of the effects of the treatment on the number of P carinii organisms.

Non-invasive techniques

If patients are able to produce a good quality sputum sample spontaneously, it is usually sufficient for diagnosis (Walzer, 1994). But P carinii thrives deep in the lungs so samples may not contain the pathogen. This creates the risk of a false negative result, so sputum specimens are often obtained by induction.

Sputum induction involves the administration of ultrasonically nebulized hypertonic saline over a period of 15-20 minutes. This method of nebulization produces particles that are small enough to penetrate the smaller airways. The hyperosmolarity of the saline causes fluid to be drawn into the lung interstitium, which washes cysts and debris into the larger airways from where they can then be expectorated.

In an attempt to reduce the risk of false negative results, some hospitals require all specimens obtained for PCP examination to be collected using the hypertonic saline technique. This has been shown to significantly reduce the risk of a false specimen diagnosis, but has not eliminated it (Huang et al, 1995).

Invasive techniques

The invasive techniques used to diagnose PCP include:

- Flexible fibreoptic bronchoscopy;

- Bronchoalveolar lavage (BAL);

- Transbronchial bronchoscopy;

- Open lung biopsy.

The invasive nature of these techniques increase the risk of haemorrhage and pneumothorax, but results obtained from bronchoscopy and bronchoalveolar lavage are more reliable than those from induced sputum samples (Miller and O’Doherty, 1997; Huang et al, 1995).

Mucolytic agents have also been reported to increase the yield of sputum (Walzer, 1994).

Treatments

The following drug therapies are available for the treatment of patients with PCP:

- Co-trimoxazole;

- Pentamidine isethionate;

- Atovaquone;

- Trimetrexate;

- Corticosteroids.

Co-trimoxazole

High doses of co-trimoxazole, a combination of sulphamethoxazole and trimethoprim, are administered orally to treat PCP. The drug can also be used prophylactically.

It has several unpleasant side-effects, such as fever, rash, pruritis, vomiting and headache. It also suppresses bone marrow activity, which can result in neutropenia, risking further complications in patients who are already immunodeficient.

Regular blood tests are required to monitor the effect of the drug. If it is being used prophylactically and there is any indication of neutropenia, treatment may be stopped immediately.

Pentamidine isethionate

Pentamidine isethionate is a broad-spectrum anti-protozoan compound. When administered intramuscularly or intravenously it causes minor adverse reactions in almost all patients and is associated with serious toxicity in 47% of those who take it (Walzer, 1994).

However, administering pentamidine via a nebulizer reduces these risks as it limits systemic absorption and therefore decreases toxicity.

A pilot study carried out by Walzer (1994) showed a 70-100% response to treatment among patients with mild to moderate PCP who were treated with nebulized pentamidine.

Adverse effects such as bronchospasm and coughing may occur, even when the drug is administered this way. The side-effects of treatment include coughing, tightness in the chest and an unpleasant metallic taste in the mouth, which can cause increased salivation.

Administering smaller particles via a nebulizer that produces an aerosol with a low-mass median aerodynamic diameter can minimise these side-effects and achieve a more effective deposit of the drug in the alveoli (Miller and O’Doherty, 1997).

The action of pentamidine and the effects it may have on those exposed to it remain largely unexplained, so those administering this treatment should take caution.

To prevent bronchosconstriction, patients should be given bronchodilators before nebulized pentamidine is administered.

The British Thoracic Society (1997) guidelines recommend that patients being treated with pentamidine are cared for in a room with an air extraction unit so that airborne particles can be removed from the environment.

Atovaquone

Atovaquone has recently become available as a treatment for mild to moderate PCP in patients who cannot tolerate co-trimoxazole. It should be taken with fatty foods and has several side-effects, including diarrhoea, nausea, vomiting, headache, fever and neutropenia.

Trimetrexate

Intravenous infusions of trimetrexate are used to treat moderate to severe PCP in patients with HIV/AIDS who cannot tolerate or fail to respond to other drug therapies.

To prevent toxicity the drug must be administered with calcium folinate, but these should never be given at the same time. The calcium folinate should be administered daily during treatment and for 72 hours after the last dose of trimetrexate.

A full blood count and renal and hepatic function tests should be carried out twice a week and treatment should be interrupted if these show significant changes.

Corticosteroids

In moderate to severe PCP, corticosteroids may be used to reduce the pulmonary inflammatory response. When administered intravenously and within 72 hours of onset, this form of treatment has been shown to halve the mortality rate (Bozzette et al, 1990).

The use of corticosteroids is recommended in patients who are hypoxic when breathing air and those with a PaO2 of less than 9.3kPa or a pulse oximetry reading of less than 92% at rest. The drug dosage should be reduced gradually, usually over a period of 21 days.

There are few reported side-effects, including herpetic infection and oral thrush (Lipman and Johnson, 1997).

Conclusion

PCP is life-threatening in immunodeficient and immunosuppressed patients. Safe, effective treatment relies on an accurate diagnosis using a quality sputum specimen from the lower respiratory tract.

Before initiating treatment, patients and staff should be informed about all known side-effects and should consult both the hospital’s guidelines and those of the British Thoracic Society (1997).

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