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 Diastolic MAP

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?