Sepsis in the heart and lung transplant recipient

Heart-lung transplantation is a fairly specialised area, which makes it all the more surprising that so far two ten-mark CICM fellowship questions have asked for detailed answers about it. Question 28 from the second paper of 2016 and the identical Question 22 from the first paper of 2009 have asked the candidates to discuss the peculiarities of managing a heart-lung transplant recipient who turns up to your ICU with community-acquired pneumonia.

The bewildering array of physiological curiosities which result from the transplantation of virtually the entire thoracic contents are discussed at greater length in the Required Reading section for Cardiothoracic Intensive Care. This section focuses on the infectious complications of such a transplant. Much of the information summarised below is derived from the published experience of the Stanford University Medical Center. The specific local chapters are:

• Perioperative care of the cardiac transplant recipient
• Perioperative care of the lung transplant recipient

Risk factors for sepsis in the heart-lung transplant recipient

• Pretransplant IABP or ECMO
• Pretransplant ventilator support
• High-dose perioperative immunosuppression.
• Previous colonisation with multiresistant orgaisms
• Large-volume blood loss and transfusion
• Acute renal failure
• Prolonged pre-transplant ventilation

Infections in general

The Stanford people found the following distribution of cases:

• The majority of the infectious complications were pulmonary.
• About 25% of the infections were UTIs
• About 50% of all infections were bacterial.
• About 40% of clinically important staphylococcal infections were coagulase-negative (which means that in these people, such results should not be immediately dismissed as contaminated).
• Generally, of the bloodstream infections, the vast majority were staphylococcal.
• Of the viral agents, the most prevalent were HSV, CMV and VZV.

Specific infectious issues in heart-lung transplantation

Apart from the fact that the donated lung tends to get various pneumonias (that is discussed later) there are specific organ-transplant-related infectious complications to consider.

The heart is generally not a major problem, but the lung is the organ transplant which is most prone to infection. This is because of several features:

• Loss of cough reflex, inability to clear secretions
• Risk of silent aspiration
• Exposure of grafted organ to pathogen-rich air
• Presence of multiresistant organisms in the upper airway (due to chronic antibiotic exposure, eg. for cystic fibrosis)

Infection within the transplanted heart or lung

This is a situation where the transplanted organ acts as the vehicle of infection.

One may get some advanced warning about this if the laboratory finds something untoward in the actual transport fluid in which the organ was stored. Typically, this tends to result in mediastinitis, and case reports of this complication suggest that the prognosis may be poor.

Pneumonia

In these patients, pneumonia is the most common infection, and also the most common cause of death.

Pulmonary Pathogens in the Heart-Lung Transplant Recipient

Opportunistic: CMV (most common, 2nd month) Aspergillus Pneumocystis (4-6 months) Nocardia (1 year)

Community-acquired H.influenzae S.pneumoniae Moraxella catarrhalis

Hospital-acquired Acinetobacter Pseudomonas Stenotrophomonas Klebsiella Legionella E.Coli

Note how weirdly the range of bugs is arrayed. The community pathogens are fairly bog-standard, but the Stanford people found that gram-negatives dominated the hospital-acquired infectious lung flora. In 60% of cases, pneumonia in the heart-lung trasplant recipient is due to some sort of an opportunistic pathogen, and these tend to occur in chronological order (eg. CMV first, then Pneumocystis, then Nocardia).

Aspergillus, though common, is less common than you think - because there are still active neutrophils around with tacrolimus and mycophenolate (i.e. the immunesuppression is not as profound as it would be with some sort of bone marrow failure).