Question 27

College comments

Syllabus topic/section: 2.1.13 Trauma Intensive Care

Discussion: 

Candidates who were able to describe the different types of necrotising fasciitis (types 1-3) in part a) were rewarded as the rationale for antibiotics is predicated by type. Answers which were not successful displayed poor synthesis of knowledge, insufficient details or did not address the question asked.

The role of surgery was well described in most cases however some candidates were unable to display an at standard knowledge of the mechanism of effects and rationale for IVIG (e.g., activation of complement, promotion for antibody dependent cytotoxicity, reduction of IL-6 and TNF-alpha production, inhibits superantigen etc) and HBOT (e.g., minimise tissue loss, decrease the number of limb amputations and reduce deaths; increases oxygen supply to the hypoxic infected tissues- generates reactive oxygen species leading to bacteriostatic or bactericidal effects, particularly on anaerobic organisms; suppresses production of cytokines and inflammatory mediators).
 

Interpretation

a)

The empirical antibiotics need to be broad, as the infection can often be polymicrobial. Gram +ve, gram -ve and anaerobic organisms may all be involved. A selection should therefore contain several agents:

• A gram+ve agent, eg. vancomycin or linezolid
• A gram-ve and anaerobe covering agent, eg. a carbapenem or extended spectrum beta-lactam
• Clindamycin, to decrease the production of bacterial toxins (most relevant for S.pyogenes)

b)

Role of surgery

• Critically important for survival
• Surgical debridement should be early and aggressive (this improves survival, as has been demonstrated in multiple studies).
• In fact, a delay in surgery of over 24 hours seems to increase the relative risk of mortality by 9.4 (i.e. the mortality is ten times greater if you wait another day).
• Surgery also assists diagnosis by retrieving deep tissue samples, and improves functional outcomes by reducing likelihood of bystander damage (eg. compartment syndrome, vascular thrombosis, etc)

Role of IV immunoglobulin

• Most important for removing superantigens in the context of toxic shock syndrome
• Secondary benefit as immunomodulator and as passive immunity
• Often well received as a large dose of hyperoncotic resuscitation fluid
• Limited data in support of its use for necrotising fasciitis

Role of hyperbaric oxygen

• Retards the growth of anaerobic pathogens involved in the milieu of necrotising deep tissue infections
• Theoretical benefits also include the survival of otherwise poorly perfused nonviable tissue and the improvement of cardiac demand during sepsis
• A difficult resource to access, as the critically ill patients who would most benefit are also those least likely to be suitable for interhospital transfer, and therefore to benefit one would need to already be admitted to a centre that does this.