Delivery of future ready medical care within the Australian Defence Force (ADF) needs to consider operational environments where casualty evacuation is delayed for multiple reasons, including contested evacuation asset manoeuvre, extended evacuation distances, health resource limitations and tactical constraints.
Prolonged field care (PFC) of a casualty with a tourniquet applied for an extended duration of time in the management of catastrophic haemorrhage creates several clinical and operational management challenges. Extended tourniquet time correlates with ischaemic limb injury and is therefore associated not only with decreasing rates of limb viability and functional recovery, but also with an increasing risk of systemic metabolic effects upon tourniquet release and subsequent reperfusion.
Tourniquet Conversion (TQC) involves the control of limb haemorrhage from penetrating wounds by the application of direct pressure to enable subsequent tourniquet removal. TQC is recommended to be conducted by appropriately trained health care providers as early as possible taking into consideration factors including the pattern of limb wounding, haemodynamic status of the casualty, and tactical constraints.
From an injury management perspective, early restoration of blood circulation reduces the risk of ischaemic injury and therefore improves functional outcomes and the probability of viable limb preservation. From an operational perspective, removing an arterial tourniquet early permits potential de-escalation of triage and evacuation priorities thereby influencing the safety of retrieval service providers, allocation of local health assets and mission support.
TQC after an extended duration of application is associated with the risk of significant adverse systemic effects, thereby potentially undermining resuscitative measures in an already compromised casualty. The systemic impacts of tourniquet release are determined by the time duration of application and the volume and composition of ischaemic tissue involved.
Larger volumes of metabolically more active tissue such as muscle are associated with greater risks associated with delayed TQC. Restoring blood supply to an injured ischaemic limb after prolonged tourniquet application commonly results in immediate hypotension due to volume sequestration and a reduction in ischaemic pain mediated pressor activity.
Even without further external blood loss, immediate significant hypotension should be anticipated upon arterial torniquet removal, particularly if the duration of tourniquet application is beyond 2 hours. In addition, venous blood returning from a reperfused ischaemic limb is typically cold and acidotic with high concentrations of potassium and myoglobin due to cellular injury. Such metabolic byproducts of limb ischaemia are associated with increased risks of cardiac dysrhythmia and arrest due to electrolyte disturbance and longer-term renal injury.
TQC should therefore only be considered after suitable resuscitative conditions have been obtained in terms of both casualty stability but also in terms of suitability of the healthcare facility to manage the potential resuscitation requirements of reperfusion. If the likelihood or consequence of profound adverse systemic effects after TQC are significantly elevated, then TQC should be delayed until the patient is optimised, or the health care team is better resourced. TQC is therefore best viewed as a planned procedure that is best conducted once controlled environmental conditions have been obtained.
Current Tactical Combat Casualty Care (TCCC) Guidelines recommend TQC within 2 hours of application and an absolute contraindication to TQC beyond 6 hours. On initial inspection these guidelines appear justified in consideration of the time dependent nature of tourniquet associated limb ischaemia. Ischaemic damage by vascular wounding and tourniquet application represents a grey scale of increasing risk influenced by the pattern of wounding, tissue type, and other associated injuries.
The Tourniquet Traffic Light (TTL) provides a simplified framework for the common understanding of the time dependent ischaemic risk profiles related to tourniquet application. A tourniquet applied for less than 2 hours duration has negligible impact upon limb salvage rates with minimised systemic risk after TQC and therefore represents the optimal standard of clinical care. On the other end of the scale, a tourniquet applied for greater than 6 hours duration remains a strong predictor for unsuccessful limb preservation. As primary amputation is typically recommended after 6 hours of warm ischaemia, TQC is therefore unwarranted.
What remains unclear within current TCCC guidelines however is the optimal conduct of TQC within the 2–6-hour post-application period. During this intermediate time window there is progressive permanent ischaemic injury being sustained to the extremity, but also an associated progressive increase in the systemic risk profile associated with the conduct of TQC. Beyond 2 hours of tourniquet application, advanced medical care is increasingly required to appropriately monitor and manage the potential systemic consequences of TQC.
A minimum standard of medical capability for conducting delayed TQC in this time window ideally includes continuous electrocardiography, regular electrolyte monitoring, arrythmia management including cardioversion capability and the resources to administer infusions for the management of hyperkalaemia, renal protection, and inotropic support. Typically, this level of health care support requires a Role 2 or greater facility.
In managing penetrating extremity trauma with extended tourniquet times in austere environments, the risk of progressive limb ischaemia must be weighed against the risks of delayed TQC where suboptimal resources are available to assess and manage the systemic consequences of reperfusion. TQC within 2 hours of application is safe. TQC beyond 6 hours is unwarranted. TQC within the 2–6-hour time window is situationally dependant on the capability of the health care facility and can be safely conducted with appropriate resources; however, it is generally unsuitable within the austere pre-hospital PFC environment.