Venous thromboembolism (VTE) is one of the most preventable complications in hospitalised patients. Critically ill patients are at risk of VTE due to coexisting of multiple risk factors but, at the same time, often at risk of bleeding. Though not common, fatal pulmonary embolism (PE) continues to occur [1] – due to the alignment of failures (or 'holes') in each defensive layer according to the Swiss cheese model [2]. Tackling this is not easy because the pattern of the 'holes' in each layer of the cheese is different between patients and, to complicate the matter further, both the size and location of the 'holes' also change with time in each individual patient.

In brief, fatal PE occurs due to one of the three failures – failure to prevent, failure to diagnose and failure to treat (aggressively). It is well established that anticoagulants are very effective in reducing VTE. The golden rule to reduce the size of the 'holes' in prevention is to use a multimodal approach, with anticoagulants as a key player. The bottom line is that any anticoagulants, even at a reduced dose, is better than no anticoagulant. Judging bleeding risk to determine when anticoagulant prophylaxis can be safely initiated solely based on INR or aPTT is a last century practice. As for diagnosing PE in the critically ill, computed tomography pulmonary angiography (CTPA) is the practical gold standard. While contrast-induced-nephropathy (CIN) is real and critically ill patients are certainly at risk, the benefits of a CTPA will almost always outweigh the risk of CIN when intensivists suspect their patients may have PE (or when the pre-test probability is >10-15%)[3,4]. Immediate aggressive systemic anticoagulation is pivotal in confirmed PE. It is better to aim at a higher aPTT (80-100s) target than a lower one (e.g. 60-80s) as soon as possible to avoid clot propagation which may lead to requiring even higher risk therapies, such as thrombolysis, extracorporeal membrane oxygenation (ECMO) or surgical embolectomy. For those unfortunate few individuals who continue to deteriorate despite systemic anticoagulation, the options 'to lyse, suck, use ECMO, or remove' are endless; but in reality the choice is often limited by what expertise is most available at the time of crisis.

Finally, the controversial issue of using inferior vena cava filters as a primary VTE prophylaxis in patients with contraindications to anticoagulants will be discussed, including the results of our recently completed randomized controlled trial [5].

References:

[1] Ho KM, Burrell M, Rao S, Baker R. Incidence and risk factors for fatal pulmonary embolism after major trauma: a nested cohort study. Br J Anaesth 2010;105:596-602.

[2] Reason J. Human error: models and management. BMJ 2000; 320: 768-70.

[3] Ho KM. Balancing the risks and benefits of using emergency diagnostic radiocontrast studies to diagnose life-threatening illness in critically ill patients: a decision analysis. Anaesth Intensive Care 2016;44:724-8.

[4] Ho KM, Harahsheh Y. Predicting contrast-induced nephropathy after CT pulmonary angiography in the critically ill: a retrospective cohort study. J Intensive Care 2018;6:3.

[5] Ho KM, Rao S, Honeybul S, Zellweger R, Wibrow B, Lipman J, Holley A, Kop A, Geelhoed E, Corcoran T. Detailed assessment of benefits and risks of retrievable inferior vena cava filters on patients with complicated injuries: the da Vinci multicentre randomised controlled trial study protocol. BMJ Open 2017;7:e016747.

How to prevent fatal pulmonary embolism

Neuro Resus