Resp & Anaes Flashcards
Ventilation response to PCO2
our normal reaction is that when PCO2 goes up, we have a significant response / increase in minute volume.
Most of the anaesthetic drugs reduce the response to CO2 by shifting the apnoea threshold to the right
it will also cause a decreased minute volume. Hypoventilation is thus a very high risk
Hypercarbia may result and this can have a significant effect on intracranial pressure and oxygenation.
Ventilation response to PO2
around 8 kPa, your body will start to stimulate ventilation because of the low PO2
Functional residual capacity (FRC)
the volume that remains in the lungs after normal exhalation
FRC = residual volume + expiratory reserve volume
Effect of anaesthesia on FRC:
we cause a cephalate movement of the diaphragm and the intercostal muscles start relaxing
causing the diameter of the chest to decrease
Effects of a decreased FRC:
FRC is decreased
work of breathing is higher
small change in inhalational pressure will cause a small change in volume / ventilation
Dead space:
the volume that enters the patient but doesn’t have contact with alveoli for gas exchange to happen
Dead space and ventilation
When we intubate / mask ventilate a patient, we will decrease the FRC and increase the dead space
Airway resistance in ventilation
As the lung volume decreases, the airway resistance increases
the “powers” that keep the vasculature as open as possible are
decreased decreasing the airway diameter.
work of breathing will increase due to the increased airway resistance
Effects of ventilation & anaesthesia on lungs in summary
increased airway resistance, an increased dead space, and a decreased compliance. These factors all increase the work of breathing during anaesthesia
Reflex pathways of the airways
Anaesthetics = dry and cold and foreign body tube inserted in airways
Our bronchi are made to respond to dry gases and / or foreign bodies and the reflex that controls it is mediated by irritation receptors (vagus thus parasympathetic = NB) and acetylcholine at the muscarinic receptors.
when patients are intubated there is an increase in tone and slight bronchospasm / decrease in airway diameter
V/Q discuss
Due to gravity however, the V/Q ratio in the lower lung will be low
high in the upper lobes
The effect of anaesthesia on the V/Q ratio:
if oxygen is given and it is followed by sub-optimal ventilation of the alveoli, there is nothing to keep the alveoli open and this will contribute to low V/Q units perioperatively
The treatment for this is PEEP it causes mechanical splinting of the alveoli and keeps them open
Postoperative pulmonary complications:
- Due to upper abdominal procedures and inadequate pain relief:
o Inadequate cough
o Increased work of breathing
o Tachypnoea
o Sputum retention
o Pneumonia - Due to complication of central venous catheterization
o Pneumothorax
o Haemothorax
o Effusion
