Brendan Docherty, MSc, RN, PGCE.
Critical Care Manager, Queen Elizabeth Hospital NHS Trust, London; and Honorary Visiting Fellow, Healthcare Research Unit, City University, London
Patients whose condition deteriorates in clinical areas often become shocked or shut down because of an inability to provide oxygen and core nutrients to the tissues. Preventing shock requires an adequate cardiac output and adequate circulating volume (Hand, 2001a) otherwise organ failure will result. Often, the first organ to fail is a kidney (Adam and Osborne, 1997), resulting in fluid and electrolyte imbalances.
Nurses have to be aware of the implications of fluid management and should be empowered to advocate for the patient and for best practice within the health-care team (DoH, 1999). With reduced junior doctor hours and the advent of nurse prescribing (Pennells, 2001), nurses are not only responsible for monitoring and detecting fluid problems, but are now starting to prescribe fluid regimens in some clinical areas.
Anatomy and physiology
Body fluid is composed primarily of water and electrolytes. The water and dissolved solutes in each of the body’s fluid compartments constitute body fluid (Tortora and Grabowski, 2001). About 56% of the adult human body is fluid, with two-thirds of the fluid contained in the 75 trillion cells in the body (Tortora and Grabowski, 2001). This is called the intracellular fluid (ICF). The remaining third of the body fluid is in the spaces outside the cells and is called the extracellular fluid (ECF).
Body fluid is in constant motion and its function is to maintain healthy living conditions for the body’s cells (Methany, 1996). The ECF is in communication with the outside world and is modified by its conditions, but the ICF remains stable. Nutrients are transported by the ECF to the cells and the waste is carried away - usually through the liver or renal filtration (Metheny, 1996).
Fluid balance occurs when the amount of water a person gains each day is equal to the amount lost. The maintenance of normal fluid balance involves regulating body water content and distribution in the ECF and ICF. The digestive system is the primary source for water gains, although a small amount of water is generated by metabolic activity (Martini, 2001).
The urinary system is the primary route of water loss and renal perfusion is optimized (with a mean blood pressure of 60-70mmHg or above) by a process called autoregulation (Smith, 2000; Oh, 1996). Should hypotension occur and result in poor renal perfusion, then the initial signs will be concentrated low volumes of urine with low sodium content - the patient may also have pale and cool peripheries (Smith, 2000). In this case, a fluid bolus is recommended to increase cardiac filling pressure and circulating volume to correct the underlying cause - 250-500ml, depending on the patient’s underlying condition (Smith, 2000). Table 1 shows average daily water loss and gain.
Water movement between the ICF and ECF occurs primarily by osmosis (Toto, 1998). Osmosis is defined as the process of water movement across a semi-permeable membrane in response to osmotic pressure. Water moves from an area of low solute concentration to one of higher concentration (Tortora and Grabowski, 2001). As cells and tissues cannot transport water, fluid balance therefore reflects primarily the control of electrolyte balance (Martini, 2001).
Renal regulation of sodium and water constitutes the most important mechanism for volume regulation in the body (Toto, 1998). This is achieved through normal nephron function with numerous hormonal factors, including antidiuretic hormone, natriuretic hormone, and the renin-angiotensin aldosterone system (Toto, 1998). For a review of electrolytes and fluid balance see Oh (1996).
Hypovolaemia may be caused by blood loss, or any condition that leads to excessive reduction in plasma protein or intravascular/extracellular fluid (RCUK, 2000; Proehl, 1999). Examples of such conditions include pancreatitis, peritonitis, vomiting, diarrhoea and conditions leading to excessive nasogastric, fistular or enterostomy fluid loss (Adam and Osborne, 1997).
In the hypovolaemic patient who is hypotensive (with a systolic pressure below 90mmHg, mean blood pressure below 60mmHg) and has compensatory tachycardia (heart rate usually greater than 120bpm), if you suspect that low volume is the cause, then both the volume used and the fluid type are important (Nolan, 2001). The fluids listed on the educational handout, page 549, should be prescribed and administered.
Shock is defined as a life-threatening condition due to failure of the body to provide the tissues with enough oxygen and nutrients to meet cellular metabolic needs (Hand, 2001a). Hypovolaemic shock is defined in many texts by class and is outlined on the educational handout, page 549.
The Cochran Study (Alderson et al, 2001) compared the effectiveness of colloids (synthetic plasma expanders) and crystalloids in critically ill adult, such as those with trauma, burns or surgical problems. Although this meta-analysis looked at critically ill patients, we can use its information as a general approach (Cormack, 2000), although individual patient needs and physiological processes have to be considered.
Although synthetic colloids, such as gelofusin and haemaccel, gave an initial favourable result of improved blood pressure and urine output in some research studies, these colloids were later found to have leaked from the intravascular space into the tissues, creating pulmonary problems and more hypotension. The overall results of this meta-analysis did not show that synthetic colloids decreased mortality rates but demonstrated that they may even cause complications for the patient (Alderson et al, 2001; Nolan, 2001). The review also identified that synthetic colloids were more expensive than crystalloids and therefore were not cost effective and not clinically effective (Alderson et al, 2001; Nolan, 2001). Therefore, in ward patients and those who are critically ill, an isotonic crystalloid should usually be the volume replacement solution of choice unless blood products are indicated (see Blood replacement therapy, below).
Hypertonic crystalloid solutions may have potential benefits in the future and are currently being investigated (Bunn et al, 2001).
There are various crystalloid solutions available for use in intravenous fluid replacement therapy. Because blood is isotonic it is advised, where possible, to use solutions that match the blood tonicity (Alderson et al, 2001). Intravenous solutions are listed on the educational handout, page 549.
Sodium chloride - The positively charged sodium ions in sodium chloride maintain the concentration and volume of the extracellular fluid. They are necessary for maintaining nervous tissue conductivity and assist in the regulation of the blood acid-base balance (Hand, 2001c). Sodium chloride 0.9% is isotonic, will not normally alter blood tonicity and will aid fluid homeostasis. It may, however, alter electrolyte balance if given in patients with sodium abnormalities or in differing concentrations (Hand, 2001c).
Dextrose - Dextrose is also isotonic, but the sugar will be metabolised by cells, leaving the water element in the extracellular fluid without altering any electrolytes (Hand, 2001c). Sugar provides energy and one litre of 5% dextrose will result in 170 calories of energy being available - which may be useful for the undernourished patient (Hand, 2001c). Combining sodium chloride and dextrose (as dextro-saline or as alternating bags of solution) will therefore result in therapy that aids electrolyte balance, helps intracellular and extracellular fluid balance and provides energy (Hand, 2001c).
Blood replacement therapy
If hypovolaemia occurs as a result of blood loss due to trauma or occurs peri-operatively, then packed red blood cells should be replaced to ensure that hypoxaemia does not occur (Hand, 2001b). It may be a normal reaction to replace fluid loss in acute haemorrhage with fluids that are commonly available in clinical settings, but the use of crystalloid or artificial plasma expanders will further dilute the existing haemoglobin level and result in tissue hypoxia - worsening the situation (Hand, 2001b). Therefore haemodilution should be avoided where possible.
If the patient requires multiple blood transfusions, then caution should be exercised in the presence of known cardiac or renal failure. Packed cells have higher levels of sodium and potassium, which may cause fluid retention, leading to breathing problems. These patient should have diuretics prescribed with their transfusions (Edwards, 2001).
Many things can affect urine output, including drugs that affect nephron filtration (such as non-steroidal anti-inflammatory drugs and the penicillin antibiotics), glomerular filtration, fluid balance and medical disease processes (Smith, 2000). Urinary catheterisation should take place when a patient is acutely ill to monitor fluid balance more accurately (Adam and Osborne, 1997; Proehl, 1999) but this in itself may cause further problems, such as urinary tract infections, trauma and haemorrhage to the urethra, and patient discomfort (Adam and Osborne, 1997; Proehl, 1999). Causes of poor renal perfusion are many and are outlined in Table 2.
When catheterised, the urine output should be related to the patient’s weight for estimation of adequate renal filtration by using the equation 0.5ml/kg/hour (Adam and Osborne 1997; Smith, 2000). However, if urine volume falls below the predicted output level on two consecutive hours, then this condition should be managed and treated (Smith, 2000). Options include fluid input, inotropic therapy, if fluid balance is adequate, and consideration of urinary flow - for example, is the catheter blocked or is there renal disease, such as glomerulonephritis (Smith, 2000)? However, it would be considered unwise to consider diuretic therapy such as frusemide unless the patient had definite signs of fluid overload (Smith, 2000; Adam and Osborne, 1997).
Physical assessment is a critical element of assessing and treating disorders of fluid balance (Toto, 1998). The physical assessment of a patient can often be more meaningful than relying on the use of monitoring equipment. The advanced assessment of a patient’s fluid status requires a review of the patient’s history and laboratory results as well as careful clinical observations (Proehl, 1999). There are many clinical manifestations of fluid deficit, which may be seen in the assessment of your patient (Table 3).
Fluid balance assessment is a fundamental aspect of caring for the critically ill patient with hypovolaemia. The management of fluid balance requires the nurse to have a complex mixture of skills, including an understanding of the principles of fluid balance in the body and of the different intravenous fluids. The nurse must also have an understanding of the body’s responses to fluid depletion and be able to recognise those signs and respond appropriately.
For those patients in the ward setting, if problems occur and physical symptoms develop, then a senior practitioner should be called and this will depend on local arrangements. For example, some hospitals may have a patient-at-risk scoring system and a team of specialists that can be called to assist; or they may have a medical emergency team that functions as a pre-emergency critical event team (Goldhill et al, 1999; Salamonson et al, 2001).
It is important that the nursing roles and responsibilities are identified in fluid management (Edwards, 2001; Happ, 2000). With this in mind, nurses can have a very real impact on the quality of patient care and can positively improve the nursing contribution to the overall patient experience (DoH, 1999).
- This educational hand-out can be photocopied and used in teaching sessions on this subject.
Medline and Cinahl databases were searched for the years 1995 to 2001 as an indication of the most contemporary evidence base (Cormack, 2000). The literature was critiqued for robustness and application to ward-based patients using the Benton and Cormack (2000) critique tool, and the evidence is presented through the text.
Review the anatomy and physiology of the kidneys. Following that, review and indicate the actions of the following hormones and their effect on fluid balance:
- Antidiuretic hormone
- Renin-angiotensin system
- Natriuretic hormone
Consider a patient who you have recently admitted with fluid balance problems, such as pulmonary oedema or dehydration. Relate and reflect on these questions in relation to your history and nursing assessment.
- Is there a disease process or injury state present that can disrupt fluid and electrolyte balances? In what type of imbalance does this condition usually result?
- Is the patient receiving any medication or treatment that can disrupt fluid and electrolyte balance? If so, how might the therapy upset fluid balance?
- Is there an abnormal loss of body fluids and, if so, from what source? What types of imbalances are usually associated with the loss of these fluids?
- Have any dietary restrictions been imposed? If so, how might fluid balance be affected?
- Has the patient taken adequate amounts of water and other nutrients orally or by some other route? If not, how long has the inadequate intake been present?
- How does the total intake of fluids compare with the total output of fluid?
Source: Methany (1996)
Here are some clinical manifestations of volume depletion that you may encounter in your patients. Describe how the patient with these symptoms will present and how you would detect such symptoms.
- Thready Pulse
- Jugular venous pulsation decreased or not visible
- Central venous pressure < 3cm water
- Muscle cramps
- Decreased skin turgor
- Decreased sweat
- Blue and cold
- Weight loss
- Dry mucous membranes
- Anorexia, nausea
- Increased thirst
- Sunken eyes
- Decreased body temperature
- Lungs clear
- Decreased urine output
- Concentrated urine
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