Quality improvement initiative evaluating the physiological impact of 'room temperature' and 'warmed' fluid bolus therapy in cardiac surgical patients admitted to the intensive care unit

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Patients who undergo cardiac surgery are routinely cared for in the intensive care unit immediately following their operation. During part of the surgery, the patient’s circulating blood is diverted through a machine that essentially replicates the function of the heart and lungs (cardiopulmonary bypass). This occurs so that blood can be diverted from the heart so that the surgeon can operate safely. At this point the patient is cooled to prevent damage to the brain and heart that may occur whilst their blood circulation is dependent on cardiopulmonary bypass. Patients are transferred to the intensive care unit still cold (hypothermic) and warm up passively and through external warming blankets with time. However, hypothermia can last for hours, have adverse effects, such as inhibiting the blood’s normal clotting mechanisms, and causing shivering and is made worse by the common administration of room temperature fluids. Low blood pressure (hypotension) is a common problem encountered in patients during cardiac surgery and also in the intensive care unit afterward. If untreated, hypotension can lead to dysfunction of vital organs and even death. Often the first intervention to treat low blood pressure is administration of intravenous fluid into the patient’s vein. Typically, a discrete volume (e.g. 500 ml) is given rapidly as a “bolus” to improve the patient’s blood pressure. The rationale is that the intravenous fluid will increase the patient’s blood volume, leading to an increase in blood pressure and cardiac output (volume of blood pumped by the heart over one minute). It is common practice for patients to receive fluid that has been warmed to normal human body temperature (37oC) whilst in the operating theatre to prevent the adverse effects of hypothermia. However, common practice in the intensive care unit is to administer intravenous fluids that have been stored at room temperature (approximately 20 – 22oC). The use of room temperature fluids is likely to worsen hypothermia and therefore potentially increase the risk of bleeding, as well as causing shivering – which may require the administration of sedative medications. Given the above concerns, the intensive care consultant group will be introducing the use of warmed intravenous fluid bolus therapy to patients cared for in the intensive care unit following cardiac surgery. After such introduction of warm fluid therapy, we plan to systematically audit the haemodynamic impact of this practice change. Importantly, we will audit the feasibility of this practice change and ensure whether it achieves our intended aim of decreasing the time taken for patients to warm up to a normal body temperature. In addition, we wish to assess whether, as expected, a warmed bolus of fluid therapy results in a different effect on blood pressure as compared to a bolus of identical volume of room temperature fluid. This audit will take a similar path to the recent conservative oxygen therapy trial, where a practice change allowed slightly lower than usual oxygen levels to be targeted at Austin Hospital, a before and after audit was conducted and showed clear benefits in patient outcomes including an increase in earlier spontaneous ventilation thus leading to the embedding of such therapy into practice based on clear data from the quality improvement cycle. The introduction of warmed fluids will follow the same quality improvement assessment cycle.

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