This is the second explainer in a series of eight, outlining potentially reversible causes of cardiac arrest.
The human body contains a significant volume of fluid. The typical 70 kilogram male has 42 litres of fluid, comprising 60 per cent of his body weight. The typical adult female body has slightly less – around 55 per cent – because females have a higher proportion of body fat (Brandis, n.d). Two thirds of total body fluid is intracellular. The remainder is mostly extracellular (blood, plasma, interstitial fluid), with a small amount of transcellular fluid (cerebrospinal, synovial, peritoneal, and pleural) (Shepherd, 2011)
Absolute hypovolaemia is the term used to describe loss of volume of fluid from the body, such as that which occurs during haemorrhage. Relative hypovolaemia is the term used when there is shifting or inappropriate redistribution of body fluids, as in major burn trauma. When there is significant acute volume loss or redistribution of body fluid, the patient is at risk of hypovolaemic shock (Jordan, 2000).
|Volume of fluid loss||Percentage of total volume*|
|Moderate hypovolaemia||750 – 1500ml||15 – 30%|
*Values based on a 70kg adult (Clinical Quality and Patient Safety Unit QAS, 2016)
A fluctuation in fluid volume of 5 to 10 per cent can have serious adverse effect on the patient (Shepherd, 2011). As the hypovolaemic patient deteriorates, they will become tachycardic, hypotensive, oliguric and peripherally hypoperfused, constituting a medical emergency. Acute Loss of Consciousness occurs once volume loss becomes severe. Once haemodynamic compensatory mechanisms are overwhelmed, cardiac arrest may be imminent.
Symptoms of hypovolaemia do not always present until a significant volume change has occurred (see table), however patients can become dehydrated with a negative fluid balance of as little as 1 per cent (Shepherd, 2011). Nurses should be aware of early signs of dehydration, which include:
If you suspect hypovolaemia, any source of volume loss should be identified and managed if possible. For example: apply direct pressure to bleeding wounds. Observe for any obvious fluid loss – vomiting, diarrhoea, review urine output, output from wound drains, nasogastric tube and other sources. Surgical intervention may be indicated, such as an urgent laparotomy if internal bleeding is suspected, external fixation of open fractures or surgical closure of wounds.
Close attention should be given to fluid balance monitoring, including clinical assessment, review of fluid balance charts and reviewing hydration (Scales and Pilsworth, 2008). If inappropriately managed, dehydration can lead to hypovolaemic shock.
During cardiac arrest hypovolaemia is managed by aggressive fluid resuscitation, to replace intravascular volume (Soar, Nolan, Böttiger, Perkins, et al., 2015; Frazee and Karshan, 2016). A range of intravenous fluids are used in these scenarios, including colloid or plasma expanders (for example, gelofusine or haemaccel) and crystalloids or balanced salt solutions (for example, normal saline, Hartmanns and Ringer-Lactate solutions) (O’Neill and Perrin, 2002). Glucose is not recommended, as hyperglycaemia is linked to poorer neurological outcome after cardiac arrest (Soar, Nolan, Böttiger, Perkins, et al., 2015).
The current recommendation from the Australian and New Zealand Committee On Resuscitation guidelines (ANZCOR), is that fluids should be infused if hypovolaemia is suspected, at a rate of at least 20mL/kg) (Australian Resuscitation Council and New Zealand Resuscitation Council WHAKAHAUORA AOTEAROA, 2016). Caution is advised however, as complications can occur when excessive volumes are administered, including organ failure (Frazee and Kashani, 2016). Clinicians should therefore aim to achieve normovolaemia and not overload the patient (Soar, Nolan, Böttiger, Perkins, et al., 2015).
Even in non-monitored settings, cardiac arrest is rarely a sudden unpredictable event, as most patients demonstrate slow but progressive physiological deterioration. Clinical assessment, fluid balance and blood chemistry monitoring can all give early indicators of alterations in fluid status. Where these elements are unnoticed or poorly managed, poorer outcomes are inevitable.
Early, effective recognition and response to signs of hypovoalaemia may prevent some cardiac arrests, deaths and unanticipated ICU admissions (Soar, Nolan, Böttiger et al., 2015).
Also read How to Perform a Chest Pain Assessment