Fluid Management in the Hypotensive Patient

Steven Roberts

Cardiac Course 6 May 2008

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)

Fluid balance in a tomato

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.

Questions?