BPT Respiratory

Question 1

Causes of left-shifted oxygen dissociation curve

Answer 1

• Decreased CO2
• Decreased H+ (raised pH)
• Decreased temperature
• Decreased 2,3-DPG
• Carboxyhemoglobin, HbF

Left-shift: increased Hb affinity for O2 for a given O2 tension, with decreased oxygen delivery to tissues.

Question 2

Diagnosis of obesity hypoventilation syndrome (OHS)

Answer 2

• Awake alveolar hypoventilation (PaCO2 > 45mmHg)
• Obese BMI (> 30kg/m2)
• Sleep disordered breathing
• No other attributable cause

Question 3

A-a gradient calculation

Answer 3

PAO2 = [FiO2 * (Pb - PH2O)] - [PaCO2 / 0.8]

Simplified version at room air (FiO2 0.21)

PAO2 = [149] - 1.25*(PaCO2)

PAO2 - PaO2 = A-a gradient

Question 4

Indications for long term oxygen therapy in COPD

Answer 4

• Resting PaO2 ≤ 55mmHg, or SaO2 ≤ 88%

* Cor pulmonate with PaO2

Question 5

Lights criteria

Answer 5

Any one of:

• Pleural / serum protein > 0.5
• Pleural / serum LDH > 0.6
• Pleural fluid LDH > 200

Question 6

Criteria for complicated parapneumonic effusion

Answer 6

Complicated parapneumonic effusion:

• Pleural fluid pH

Question 7

Indications for lung volume reduction surgery (LVRS)

Answer 7

• Age 6 months, FEV1 20%.
• Severe dyspnoea despite maximal therapy and pulmonary rehab; 6MWT > 140m
• Gas trapping (RV > 150% red, increased RV/TLC ratio)
• Upper zone predominant disease