Date post: | 14-Dec-2015 |
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Content:
1. Definitions of blood pressure, hypotension and fluid management
2. The body’s natural regulation of blood pressure and fluid content - and what can go wrong
3. Fluid management in our patients
4. Nursing priorities
Definitions
Blood pressure:
The force per unit area exerted on the walls of
the blood vessels, by the blood contained
within them.
Systolic/diastolic (mmHg)
Normal BP: 100/60 to 140/90 mmHg
(Marieb, 1998)
Definitions
Hypotension:
A systolic blood pressure of less than 100mmHg.
Reasons for hypotension:• normal variation• orthostatic• shock
Definitions
Fluid management (osmoregulation):
An important part of homeostasis that attempts
to maintain fluid volume and electrolyte
concentrations within limits that allow
necessary physiological processes to take
place.
Why does blood pressure need regulating?
Pressure difference makes blood flow.
Flow is necessary for perfusion of the tissues
(particularly the kidneys and the brain).
Hypotension - not enough flow for perfusion
Hypertension - too much pressure, possibility of damage
Mean Arterial Pressure
A ‘weighted average’ pressure that allows
estimation of effective perfusion of the tissues.
eg. MAP 65mmHg for renal perfusion
MAP = 1/3 systolic + 2/3 diastolic or
MAP = (systolic + 2 x diastolic)/3
MAP
DIASTOLIC
SYSTOLIC
Examples of Mean Arterial Pressure Values
Systolic 120 110 100 90 80 70 65Diastolic 37 42 47 53 57 62 65MAP 65 65 65 65 65 65 65
How is blood pressure regulated naturally?
Neural: stretch, vagal response, slower HR and less tone in blood vessels
Chemical: less oxygen detected, vasoconstriction, rise in BP
facilitates venous return and pulmonary perfusion
Renal: fall in BP, release of renin - angiotensin (vasoconstrictor) -
aldosterone (Na+ reabsorption)
(Age, illness, drugs, other body systems, all may
affect effective blood pressure regulation)
Why does the body need to regulate fluid?
Water is 60% of the body mass of an average man.
2/3 is ICF in cytosol in all body cells.
1/3 is ECF outside cells - interstitial and circulation.
Total: 40 litres
ICF: 28 litres
ECF: 12 litres (plasma: 2.5 litres, interstitial fluid: 9.5 litres)
Homeostasis of water and electrolytes in the fluid
compartments is essential for life and health.
How is fluid regulated?
Input: • food • drink
• (IV fluids)
Output:
• urine • faeces • sweat • expiration loss• (haemorrhage, sputum, wound exudate)
a) Input and Output
How is fluid regulated within the body?
b) Mechanisms
Water and other small molecules can pass
freely across cell and capillary membranes.
They may do this by:
• Diffusion
• Osmosis
• Filtration
• Active transport
Disorders of fluid balance
Isotonic imbalance
• Fluid volume deficit (not dehydration)
• Fluid volume excess (oedema)
Osmolar imbalance
• Hyperosmolar imbalance (dehydration)
• Hypo-osmolar imbalance (water excess)
Isotonic imbalance
a) Fluid volume deficit: (not dehydration)
• loss of water and electrolytes from circulation, in proportion, so serum levels remain const. (ICF is unchanged because [Na+] in the ECF is unchanged)
Isotonic imbalance
b) Fluid volume excess: (oedema)
• retention of water and electrolytes in proportion to the composition of the ECF.
Osmolar imbalance
a) Hyperosmolar imbalance: (dehydration)
• loss of water without loss of electrolytes
• movement of water from ICF to ECF
• impaired cell function
• thirst and lowered urine production
Osmolar imbalance
b) Hypo-osmolar imbalance: (water excess)
• diluted ECF so water moves into ICF
• caused by excessive intake or high ADH levels
Assessment of fluid and electrolyte status
a) Patient history
• normal eating and drinking patterns• recent changes • approximate daily volumes• preferred types of drinks
• oral cavity• thirst • skin turgor• oedema• sunken eyes• confusion• respiration
Assessment of fluid and electrolyte status
b) Nursing observations
• pulse rate• blood pressure• JVP• CVP• urine output• weight• bowel habit
Hypovolaemic shock
Caused by reduction in circulating blood volume due to: • external loss - haemorrhage or burns• internal loss - altered permeability of blood vessels or leakage into body cavities
Leads to inadequate tissue perfusion and generalised cellular hypoxia.
Hypotension and shock post MI
• If peripherally well-perfused, no need for drugs.
• Lie patient flat, with legs elevated if necessary, unless contra-indicated by pulmonary oedema.
• Try to correct any arrythmia, hypoxia or acidosis.
• Arrange for an echocardiogram to exclude a mechanical cause - MR, VSD, ventricular aneurysm.
• Start cautious plasma expansion and inotropes.
• Use IV nitrates and diuretics with caution.
IV fluid replacement
• For patients with excessive fluid loss or incapable of normal fluid intake.
• IV therapy - preferred method of administering fluids, electrolytes and drugs in an emergency.
• Allows accurate dosage titrations of drugs.
• Disadvantages - potential for incompatibilities, complications, adverse reactions and infection.
IV fluid replacement
• Solutions may be colloids or crystalloids.
• Crystalloids can be hypertonic, isotonic or hypotonic to the ECF.
• Tonicity of the fluid will affect the ICF content of cells.
Hypotension and nursing interventions
• Monitor any variation from baseline observations.
• IV therapy - excessive rate, increasing circulatory volume, increasing venous pressure, could lead to cardiac failure or pulmonary oedema (use flow-control devices).
• Orthostatic hypotension - supervise patient when mobilising, especially if the patient is taking anti-hypertensives.
•Maintain fluid balance charts and daily weights.
Hypotension and nursing interventions
• Monitor effects of IV nitrates and diuretics.
• Observe nature and quantity of all drainage, aspirate, faeces, etc.
• Give prescribed anti-emetics if nausea and vomiting occur.
• Encourage oral fluids and early resumption of diet, if appropriate.
• Observe the mouth for coating, furring and dryness.