MRSA infected pseudoaneurysms of the radial artery

G. Stansby* J. Smout* R. Chalmers** P. Lintott***
*Northern Vascular Institute, Freeman Hospital, Newcastle-Upon-Tyne, NE7 7DN, U.K. ** Vascular Surgery Unit, University Department of Clinical and Surgical Sciences, Edinburgh Royal Infirmary, Edinburgh, U.K. ***Higher Surgical Trainee, Oxford Rotation, U.K.

Correspondence to: G. Stansby, Northern Vascular Institute, Freeman Hospital, Newcastle-Upon-Tyne, NE7 7DN, U.K.

Introduction Case histories

Discussion References

Keywords: Radial, catheter, pseudoaneurysm, methicillin, staphylococcus, MRSA
Surg J R Coll Surg Edinb Irel., 1 April 2003, 108-110

The use of radial artery catheters for real-time blood pressure monitoring and arterial blood gas sampling has become commonplace in both intensive care and high dependency units. Although this procedure is relatively safe, it can be complicated by local infection leading to pseudoaneurysm formation. In this report we describe three cases of pseudoaneurysm formation following prolonged radial catheter placement, with evidence of local methicillin resistant staphylococcus aureus (MRSA) infection. With the growing problem of in-hospital MRSA colonisation, the report aims to emphasize the need for vigilance for this complication and reinforce the importance of careful asepsis. In all cases the pseudoaneurysms were successfully treated with local ligation of the radial artery, without subsequent ischaemic complications. Allen’s test was performed to ensure sufficient collateral circulation prior to surgery

INTRODUCTION
Placement of radial artery catheters for both real-time blood pressure measurement, and arterial blood gas sampling has become a routine part of patient monitoring on the intensive care unit (ICU). Arterial catheter infections are infrequent; however, when they do occur they may be associated with pseudoaneurysm formation and rupture.¹ In recent years methicillin resistant staphylococcus aureus (MRSA) has become an important pathogen in the ICU setting. In this case report we describe three cases of delayed radial artery pseudoaneurysm formation associated with MRSA colonisation of the arterial line site.

CASE HISTORIES
In this case report we describe three patients who required prolonged radial artery catheters for haemodynamic monitoring on the ICU at St Mary’s Hospital, Paddington, who subsequently developed radial artery pseudoaneurysms.

Patient 1
The first patient was a 57-year-old male who was admitted via casualty with a collapse secondary to a subdural haematoma. The only significant factor in his past medical history was chronic alcohol abuse. The haematoma was managed conservatively, and a left radial artery catheter was inserted for blood pressure and arterial blood gas measurements. The arterial catheter remained in situ for 15 days, and five days following its removal the skin site appeared inflamed and a wound swab grew MRSA. The inflammation initially appeared to settle; however, eight days later an acute arterial bleed occurred from the wound site. Surgical exploration of the radial artery confirmed the presence of a 3cm pseudoaneurysm.

Patient 2
The second patient was a 76-year-old female who underwent an elective thoracoabdominal aneurysm repair. Her post-operative recovery was complicated by ischaemic colitis and subsequent enterococcus septicaemia. Bilateral radial catheters were inserted at the time of surgery, although the left was removed on admission to ICU. Over the next two weeks the patient’s general condition improved, and on post-operative day 20 was noted to have an erythematous arterial catheter site. The catheter was promptly removed and four days later a pulsatile swelling was noted. The clinical diagnosis of pseudoaneurysm was made, and at operation MRSA was cultured from the aneurysm sac as well as from the patient’s central venous pressure (CVP) catheter tip, axillae, nose and laparotomy wound. The patient subsequently made a good recovery and was eventually discharged 71 days following her primary procedure.

Patient 3
The third patient was a 65-year-old male smoker who was admitted for an elective resection of an oesophageal carcinoma. His post-operative recovery was complicated by recurrent episodes of respiratory failure, each requiring admission to ICU. During his ICU stays radial arterial catheters were sequentially inserted in the left, right and finally the left radial arteries. Although, local signs of radial artery infection were not obvious, MRSA was found to colonise his sputum, groins and CVP catheter tip. Following topical treatment his MRSA swabs became clear. However, on day 72 post-surgery, 23 days following the removal of the most recent radial line, a swelling was noted over his left radial artery at the wrist which duplex scanning confirmed to be a small pseudoaneurysm.

All three patients underwent urgent surgical exploration of the radial artery catheter site. Both ends of the radial artery were identified and oversewn, after ensuring sufficient collateral hand circulation using Allen’s test. All patients had MRSA cultured from the aneurysm clot and one patient developed a post-operative MRSA wound infection. None of the patients developed subsequent circulatory insufficiency in the hand. All patients had a prolonged course of vancomycin following their pseudoaneurysm surgery.

DISCUSSION
Radial artery pseudoaneurysm formation is rare and may occur following accidental trauma, local surgery or arterial catheterisation. Unlike ‘true’ arterial aneurysms, pseudoaneurysms are not bounded by the three layers of the arterial wall, but are collections of blood in continuity with the arterial system. Following arterial puncture the combination of the coagulation processes and arterial vasoconstriction act to seal the defect and allow vessel repair. When arterial wall defects are large, or when infection hampers the healing process continuity between the arterial lumen and interstitial tissue may remain.

Delayed radial artery pseudoaneurysm formation has only been reported in association with infection, and less than 20 of these cases have been reported in the English literature.² Where an organism was identified in association with a pseudoaneurysm it has usually been staphylococcus(s) aureus, and only recently has the methicillin resistant strain of S. aureus been identified as a causative pathogen.^2,3 Studies suggest that colonisation occurs in around 20% of radial arterial catheters, although S. aureus is only isolated in around 3% of cases.¹

Radial arterial pseudoaneurysms can present locally with tenderness, oedema, purulent discharge and erythema, or systemically with fever, leucocytosis and bacteraemia.² Ischaemic complications such as distal emboli are rare, particularly, as blood supply to the hand tends to be ulnar dominant. Previous reports have shown that radial catheter-related pseudoaneurysms are associated with fever and or bacteraemia for more than 48 hours in the majority of cases.⁴ Most catheter infections resolve with catheter removal and intravenous antibiotics for 10-21 days. It is suggested that patients with persistent S. aureus infection 48 hours after line removal should be followed-up closely for pseudoaneurysm formation and receive a prolonged course of antibiotics (10-21 days).²

Infected thrombus is thought to be the source of lytic enzymes causing localised destruction of the arterial wall, with eventual aneurysm formation. Staphylococcus aureus produces enzymes such as hyaluronidase that are important in arterial wall degradation. However, it is unclear whether MRSA infection is associated with a different virulence than methicillin sensitive strains. Some animal models and patients studies suggest that this is not the case.^5,6 A study on bacterial products, on the other hand, showed that MRSA strains tested had a more consistent and significantly greater production of coagulase.⁷ This enzyme allows the bacteria to activate thrombin causing local coagulation and assists in evasion of host leucocytes. It may be hypothesised that this could favour the organism’s initial colony formation when associated with local blood vessel injury.

It is important that all arterial lines are placed with strict attention to aseptic technique. All three of the cases described were associated with prolonged catheter placement (mean 18 days in-situ), and a significant time lag may occur before the aneurysm becomes clinically evident; this is similar to that seen in other reports.¹ Prompt surgical management is recommended, as there is a risk of rupture. If the ulnar artery is patent, over-sewing the ends of the radial artery is appropriate.

Methicillin resistant staphylococcus aureus is an increasing problem worldwide, and our experience would suggest that patients found to have catheter sites colonised with MRSA should have the radial catheter removed at the earliest opportunity, be prescribed appropriate antibiotics, and for the site to be followed-up for evidence of pseudoaneurysm formation. With the rising incidence of MRSA colonisation we may see this complication with increasing frequency in the future.

REFERENCES
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Copyright: 19 December 2002