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Abstract
Severe hypothermia is a medical emergency and requires active and occasionally rapid core rewarming to prevent cardiac arrhythmias and death. In the accident and emergency department rewarming is often limited to warmed intravenous fluids, heated blankets, gastric and bladder lavage. Extracorporeal methods, which rewarm core blood directly, for example haemodialysis and cardiopulmonary bypass, require expertise and equipment not always found in a district general hospital. Venovenous haemofiltration is now commonly found in district general hospitals around the country and can be used safely for core rewarming. A case is reported of a severely hypothermic elderly patient successfully rewarmed using venovenous haemofiltration, in an accident and emergency department, when other conventional methods had failed.
- hypothermia
- venovenous haemofiltration
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Hypothermia is defined as a core body temperature below 35°C.1 Patients presenting with severe hypothermia (<28°C)2 are at high risk of serious arrhythmias and asystole.1
Rewarming severely hypothermic patients in the accident and emergency (A&E) department initially requires non-invasive methods, which are usually successful. However, if these methods fail, or the patient is in circulatory arrest, then invasive methods are needed. Extracorporeal rewarming is an invasive method, which can rapidly and safely rewarm core blood.3–5
Venovenous haemofiltration is readily available now in most district general hospitals where it can be used as an alternative to arteriovenous haemofiltration in treating patients with acute renal failure. It is an extracorporeal circulation that is an efficient rewarmer of core blood and thus, can be used to rewarm severely hypothermic patients who need more invasive measures.
Case history
A 77 year old woman found collapsed at home was admitted to hospital with a Glasgow Coma Scale (GCS) of 8 and rectal temperature of 26°C. Blood pressure was 93/55 and heart rate 89 in sinus rhythm. While rewarming with a heated blanket and warmed intravenous fluids she had a prolonged ventricular fibrillation (VF) arrest with episodes of other serious arrhythmias. Defibrillation was used while conventional rewarming methods continued, together with gastric lavage and bladder catheter irrigation, but with no success.
Even after five hours the core temperature was still only 30°C and she was continuing to have episodes of VF arrest that responded to defibrillation. As the cause of her obtunded conscious was not clear (GCS remained 7/15), and adrenaline (epinephrine) was maintaining her blood pressure, we intended to warm her efficiently to normothermia using venovenous haemofiltration in the A&E department. A temperature of 34°C was reached after one hour, her blood pressure was now 120/73 with adrenaline and her heart rate 111 in sinus rhythm.
As her GCS remained the same with mild hypothermia, she was referred to the medical team for further investigations towards a working diagnosis of a cerebral vascular accident, which caused her to collapse two days before admission. She died a day later.
Haemofiltration
Haemofiltration was performed using the Gambro AK-10 “Low flow” haemofiltration machine with BMM 10–1 Blood Monitor and HFM 10–1 Fluid Monitor. A vascath was inserted into the right femoral vein. The haemofiltration fluid was Normosol with 60 mmol of potassium added and the exchange volume was set to 27 litres with a filtration rate of 84 ml/min. Heparin was used as the anticoagulant (10 000 units in 40 ml normal saline run at 4 ml per hour). The Haemofilter was a polysulfone filter made by Link Medical/Bellco.
Because of the previous large warmed fluid transfusions, the machine was set to take off one litre of fluid to prevent overload. Haemofiltration was stopped after one hour having reached the desired temperature of 34°C.
Discussion
This case shows a practical and safe method of warming severely hypothermic patients using venovenous haemofiltration in the A&E department.
Venovenous haemofiltration is one form of extracorporeal rewarming. Successful outcomes with rewarming hypothermic patients have been reported with cardiopulmonary bypass,3, 4 haemodialysis6 and peritoneal dialysis .7
For severe hypothermia with circulatory arrest, rewarming with cardiopulmonary bypass is the most efficient by being rapid and providing adequate and immediate circulatory support.4, 5, 8 However, it requires considerable time to set up (sometimes, exceeding one hour) and technical support. Its use is therefore often limited to operating theatres.
Continuous arteriovenous haemofiltration has also been successfully used to rewarm hypothermic patients.9 However, at our district general hospital, venovenous haemofiltration, involving insertion of a single large double lumen central venous catheter has been found to be more practical. A roller pump is used instead of the patient's blood pressure, to circulate the blood through the filtration unit before it is warmed and returned to the patient. Continuous venovenous rewarming has been successfully used in both a juvenile animal model,10 and in adult intensive care patients.5
Extracorporeal venovenous rewarming warms core blood directly and thus is more efficient than standard rewarming techniques (for example, warming blankets, warmed intravenous fluids, gastric, bladder and peritoneal lavage).5
Haemofiltration is now commonly used across the country in treating acute renal failure patients and in intensive care units. The haemofiltration machine is mains driven, easy to operate and very portable. It can be set up and ready to use in 20 minutes.
The experienced operator (intensivist/nephrologist/haemofiltration nurse) needs to set the fluid volume to be exchanged, the required fluid loss and the filtration rate (ml/min). The machine will then automatically carry out the treatment when activated, with the nurse supervising all data and checking the results. In our case, minimal filtration was required as the primary use was for rewarming. Treatment was terminated early as the desired temperature was reached.
Complications of haemofiltration are rare. For example air embolism, hypotension, infections, leaks in the filter or anticoagulation problems.
This case report shows the effectivess and simplicity of using venovenous haemofiltration in the A&E setting.