120 - Pyrexial illness Flashcards
Why are UTIs common in the elderly?
Low urine flow rate and poor bladder emptying.
Risks of UTIs in patients with diabetes or underlying kidney diseases
Infection can ascend to kidneys from the bladder. Can result in pyelonephritis which can progress to septacemia.
What is pyrexia?
Fever. Common, measurable symptom/sign.
Importance of pyrexia?
Non-specific - generally limited diagnostic significance. BUT Pyrexia of Unknown Origin (PUO) can result in an emergency admission. Need to be able to distinguish between minor and major conditions.
Normal body temp
37.1 degrees Celsius. Can vary between patients.
What is an intermittent fever
Temp returns to normal at least once every 24 hours
Example of an intermittent fever
Malaria
What is a remittent fever?
Fever with peaks/troughs but is always raised and doesn’t return to normal
Example of a remittent fever
Typhoid fever
What is a sustained fever?
Temp stays above normal with only minimal variations. Also called a continuous fever.
Exampled of sustained fever
Pneumonia UTI
What is a recurring fever
Fever with one or more episodes of fever that can last several days with one or more days of normal temperature in between episodes of fever. Also known as relapsing fevers
Examples of recurring fevers
Tick bourne diseases
General rule - relationship between heart rate and temperature
For every 1 degree increase in temp, HR increases by 15bpm
What does the hypothalamus do?
Central to regulation of core body temperature. Acts as a thermostat to control thermoregulatory mechanisms and balance heat loss and heat production
How does the hypothalamus know the body temperature
Heat sensitive receptors in the pre optic area of the hypothalamus is sensitive to increases in blood temperature. Also from the temperature of blood bathing the hypothalamus.
How does the sympathetic nervous system response to an elevated core body temperature?
SNS is inhibited. Vasodilation of blood vessels in skin. Sweat glands stimulated to help loose heat through evaporation. Aiming to reduce temperature back to normal - homeostasis.
What happens when body temp falls below a set point?
SNS is activated. Vasoconstriction of blood vessels in skin. Shivering centre is activated. Sweating is inhibited. Behavioural/endocrine responses to promote heat production are triggered.
Name the 4 successive stages of fever
Prodromal phase Chill phase Flush phase Defervescence phase
What happens in the prodromal stage of fever?
Non-specific complaints Headache, fatigue, general malaise, aching.
What happens in the chill stage of fever?
Feeling chilled and shaking although core body temperature is rising. Shivering stops when temperature reaches new increased set point. Patient tries to get warmer even though temperature is already increased.
What happens in the flush phase of fever?
Vasodilation occurs - skin becomes warm, red and dry.
What happens in the defervescence stage of fever?
Sweating starts
Clinical presentations of fever
Feeling hot Rigors Excessive sweating Headache Delirium Muscle pain Increase respiration rate and heart rate Dehydration
Red flags for sepsis
Severe headache Photophobia
How does temperature normally vary?
Normally tightly controlled. 37.1 degrees Celsius mean with a normal diurnal variation of 0.5 degrees.
How is fever controlled by the body?
Mediated by exogenous and endogenous pyrogens released by cells in response to infection and non-infectious disorders
What is LPS
Lipopolysaccharide. Most studied exogenous pyrogen. Made from broken down cell walls of gram negative bacteria.
What do pyrogens to?
When presented to host cells (e.g. macrophages) - stimulates release of pyrogenic cytokines which act as pro inflammatory stimuli.
Main pyrogen involved in fever and immune responses
Interleukin-6
How do cytokines affect the hypothalamus?
Can cross the blood-brain barrier. Interact with receptors in the pre-optic region of the anterior hypothalamus. Releases prostoglandin E2 which then modifies the responsiveness of thermosensitive neurones.
What drugs can be used to reduce fevers, why?
Antipyretic drugs - NSAIDs, aspirin Affect release of prostaglandin E2 to prevent modification of the thermosensitive neurones in the hypothalamus.