CPGs- Value, time critical, clinical approach Flashcards
How does pulse oximetry work?
- emits 2 light waveforms, red and infrared.
- detector on other side of probe measures amount of light passing through vascular bed.
- both lights pulsate rapidly each second.
- Hb absorbs more light than oxyHb therefore greater concentration of oxyHb, greater amount of red light received by detector.
- both oxyHb and Hb absorb infrared equally which determines amount of Hb in arterial blood flow
- infrared = total amount of available Hb
- red light = saturated Hb
Limitations of Spo2
- anaemia or hypovolaemia may give normal readings
- poor perfusion can cause inaccuracy incl., cardiac arrest, shock, burns, PVD, oedema/hypothermia
- movement
- nail polish
- skin pigmentation
Oxy-Hb Dissociation curve - explain
Represents affinity of Hb for o2 at different levels of partial pressure. As Pao2 reduces from 100, initially little effect on spo2
Leftward shift: increased pH, reduced paco2, increased temp
Rightward shift: decreased pH, increased paco2, increased exercise, increased altitude, catecholamine release
Ventilation - explain inspiration and expiration
Movement of air into and out of lungs due to pressure differences
Inspiration: air into lungs, pressure in lungs must be lower than atmospheric pressure. Pressure in lungs is lowered by increased volume. Muscles contract, expanding lungs.
Expiration: at end of resp phase, intrapulmonary pressure is already higher than atmospheric pressure causes air to follow pressure gradient = passive expiration
Why is intrapleural space negative?
Parietal pleura (attached to chest wall), pulled outward. Visceral pleura pulled inward by elastic recoil therefore constant pull in opposite directions caused 0 sub-atmospheric pressure hence preventing collapsed lung.
Types of hypoxia?
Stagnant - good oxygenation but decreased blood flow eg. cardiac arrest, shock, haemorrhage
Anaemia - decreased o2 carrying capacity, decreased Hb levels e.g. hypovolaemia
Histotoxic - good oxygenation of blood but o2 unable to dissociate due to cellular blocking agent e.g. cyanide
Hypoxic - decreased o2 in pulmonary vascular system e.g. atmospheric changes, APO
Assessment of Oxygen requiring patient
Acute/chronic Respiratory status Spo2 Causes Bleomycin and paraquat poisoning
Management of Adequate Spo2
greater than or equal to 92%
No O2 required, reassure pt
Management of Mild-mod hypoxaemia
85-91%
2-6L via nasal prongs or 5-10L via face mask
titrate to 92-96%
Management of severe hypoxaemia
less than 85% or critical illness:
-Arrest
-Trauma (head/major)
-Epilepsy
-Ketamine sedation
-Anaphylaxis
-Shock
-Sepsis
Non rebreather 10-15L/min - BVM if inadequate TV
Once pt haemodynamically stable, titrate to 92-96%
If deteriorates or Spo2 less than 85%, BVM 100%, consider SGA
Management of Chronic Hypoxaemia
Kyphoscoliosis Neuromuscular disorders Obesity COPD Cystic fibrosis Bronchiecstasis -high concentration o2 may be harmful in COPD pts at risk of hypercapnic resp failure -titrate Spo2 88-92%
Management regardless of SPo2
PPH Inhalation (toxic) Cord prolapse Cluster headache Decompression illness Dystocia - shoulder -o2 via NRB 10-15l/min
Unwell patients include
unconscious/altered conscious
SOB
pale/sweaty
Definition of perfusion
The ability of the cardiovascular system to provide tissues with an adequate oxygenated blood supply to meet their functional demands at that time and to effectively remove associated metabolic waste products.
Perfusion can be affected by:
temp
anxiety
altered consciousness
When assessing perfusion, take into context:
presenting problem
pts meds
trends
response to mx
Adequate perfusion
Warm, pink, dry skin
Pulse 60-100
BP over 100
Alert
Borderline perfusion
Cool, pale, clammy
Pulse 50-100
BP 80-100
Alert
Inadequate perfusion
Cool, pale, clammy
Pulse less than 50 greater than 100
BP 60-80
Alert or altered