Physiology in Anaesthesia: Part 4 Flashcards
Define
Closing volume
RESP
Lung volume at which small airways begin to close
In health, FRC MUST exceed this
Complications of acidosis
GENERAL
- CNS: depressed LOC, raised ICP
- CVS: depression, increased catecholamines, raised calcium, dysrhythmias, vasodilation, hypovolaemia
- Pulmonary hypertension
- Hyperkalaemia
Stages of systole
two
CVS
- isovolumetric ventricular contraction
- ventricular ejection
Name and describe
Peaks of the atrial pressure wave
three
CVS
A-wave: immediately preceding systole; represents atrial contraction
C-wave: beginning of systole; represents isovolumetric ventricular contraction
V-wave: systole through early diastole; represents atrial filling
Stages of diastole
- isovolumetric ventricular relaxation
- rapid ventricular filling
- slow ventricular filling (diastasis)
- atrial contraction
Functions of diastole
- reuptake of calcium by the sarcoplasmic reticulum
- ventricular filling
- coronary artery perfusionl
Function of the cardiac papillary muscles
- contract with the ventricles during systole
- pull base of the heart towards the apex
- shortens the longitudinal axis
- increases systolic efficiency
- prevents excessive bulging of valves into the atria
What is the ejection fraction equation
EF = (EDV - ESV) / EDV
OR
EF = SV / EDV
Techniques used to measure stroke volume
- ventriculography: gold standard, but cumbersome
- echocardiography: transthoracic, transoesophageal
- thoracic impedance: non-invasive, but very inaccurate
Techniques used to measure cardiac output
- indicator-dilution techniques: thermodilution, dye dilution
- Fick method
- Doppler techniques
Determinants of stroke volume
PRELOAD: equivalent to end-diastolic volume
AFTERLOAD: intraventricular pressure during systole
CONTRACTILITY: intrinsic ability of cardiac muscle to do work
Factors that increase cardiac contractility
- raised serum calcium
- sympathetic stimulation
- parasympathetic inhibition
- inotropic drugs
Factors that decrease cardiac contractility
- reduced serum calcium
- parasympathetic stimulation
- sympathetic inhibition
- myocardial ischaemia/infarction
- hypoxia
- acidosis
- mismatched ventriculo-atrial coupling
Define wind-up
(pain physiology)
Frequency dependent increase;
spinal cord neural excitability;
additive afferent C-fibre stimulation
Systems in the body that prevent pH changes
- buffering systems: immediate
- ventilatory response: minutes
- renal response: hours to days
Specific buffering systems of the body
- HCO3 (>50%)
- Hb (35%)
- phosphates
- plasma proteins
- bone
What causes propofol infusion syndrome
Propofol infusion for greater than 48 hours;
dose greater than 5mg/kg/hr (83mcg/kg/minute).
Caused by failure of mitochondrial respiratory chain;
failure of free fatty acid transport into mitochondria
What are signs of propofol infusion syndrome
- cardiomyopathy and acute cardiac failure
- metabolic acidosis
- skeletal muscle myopathy
- hepatomegaly
- hyperkalaemia
- lipidaemia
- bradycardia (LATE SIGN)
Anion gap:
1. calculation
2. normal parameters
- Anion gap = Na - [HCO3 + Cl]
- 10-12
Causes of a high anion gap metabolic acidosis
- lactic acidosis
- ketoacidosis
- acute/chronic renal failure
- toxins: salicylates, ethylene glycol, methanol
Causes of a non-anion gap metabolic acidosis
- renal tubular acidosis
- rapid saline infusion
- gastrointestinal bicarbonate loss (vomiting, diarrhoea, nasogastric tube drainage)
- toxins: ammonium chloride
Methods to decrease central line sepsis
- cleaning with chlorhexidine over povidone
- using minocycline/rifampin catheters
- using the subclavian rather than jugular vein
- using single lumen rather than multi-lumen catheters
- using ultrasound guidance
Sarin nerve gas:
1. what is it
2. name signs of poisoning
- potent organophosphate
- DUMBELS:
Diarrhoea
Urination
Miosis
Bronchorrhoea, bronchoconstriction
Emesis
Lacrimation
Salivation
ALSO:
cardiac
CNS
Cardiac signs of sarin nerve gas poisoning
bradycardia
prolonged QT segment
ventricular dysrhythmias
Manoeuvres to maximise functional residual capacity
- early ambulation
- incentive spirometry
- deep breathing
- IPPV
Calculation of pulmonary vascular resistance
PVR = [(PAPmean - PAcp) / CO] x 80
PAPmean: mean pulmonary arterial pressure
PAcp: pulmonary wedge pressure
CO: cardiac output
What is the normal pulmonary vascular resistance
50-150 dynes/sec/cm^-5
What happens when the aorta is cross-clamped
- raised mean arterial pressure
- raised central venous pressure
- raised pulmonary artery occlusion pressure
- reduced cardiac index
What are the risks associated with aortic cross-clamping
- renal ischaemia
- colonic ischaemia
- reperfusion injury
What is the cardiac index
it relates cardiac performance to body surface area
