Ventilation

Question 1

Describe the respiratory failure

Answer 1

Hypercapnic >45 mmhg co2

Hypoxic <55-60mmhg O2

Question 2

What is the alveolar Gas equation

Answer 2

PAO2 = pio2 -Paco2/R

Question 3

Describe ventilatory capacity

Answer 3

the maximal sustainable ventilation a person can sustain without fatigue of the respiratory muscle (approx 50% of maximum voluntary ventilation)

The demand for ventilation is the spontaneous minute ventilation required to achieve the paco2 set by the CNS controller

Question 4

What can increase ventilation demand

Answer 4

Increase in the VT/VD ratio
Increase CO2
decrease in Pco2 set point by CNS controller

Question 5

Describe the four components of the respiratory system that can cause failure

Answer 5

CNS control – drugs, trauma
Bellow – neuromuscular, trauma
Airway – COPD, asthma
alveolar

Question 6

Describe the progression of ABGs in asthma

Answer 6

Initially hypocapnic due to limited airway obstrucion and cns stimulation by vagul afferents in the lung (irritant and J)

Second phase: obstruction is worsening fatigue of resp muscles beginning CO2>40 normpocapnia in status asthmatic should be considered abnormal and close monitoring for hypercapnic failure should be monitored

Third phase: extreme obstruction leading to muscle fatigue and hypercapnic failure. Elevated serum HCO3 is rare

Question 7

Discuss A/C ventilation mode

Answer 7

Arises from two traditional modes assist and control

• Assist mode allows the patient to spontaneously breath and then sync support to achieve desired tidal volume
• Control mode provide machine breaths without regard for patient initiation

Control is obsolete as because it locks the patient out if making spontaneous breaths. Also complete disuses of resp muscles leads to atrophy

Question 8

Discuss setting used in A/C mode

Answer 8

Setting that can be set are resp rate and tidal volume
The ventilator detects patient inspiratory effort by detecting -ve pressure deflection from baseline, when the inspiratory effort exceeds a threshold the ventilatory begins to deliver preset tidal volume . The timing of the next vent depends on resp rate set and the resp rate of the patient.

For example if resp rate set at 10 the ventilator will deliver a breath every 6 seconds however if patient initates sooner it will reset the till the next 6 seconds

Patient can also inspire from the ventilator demand vlave. This occurs if inspiratory flow rates exceed those generated by the machine or if patient continues to inspire after volume has been delivered