Physiology
Respiratory
Regarding dead space, which of the following statements is CORRECT:
Answer:
Dead space refers to the volume of gas in the airways which does not take part in gas exchange. The anatomical dead space refers to the conducting airways, up to and including the terminal bronchioles - this is usually about 150 mL. Alveolar dead space refers to alveoli incapable of gas exchange, for example in pulmonary embolism where pulmonary capillary blood flow is blocked. Physiological dead space = anatomical dead space + alveolar dead space (in health alveolar dead space is negligible, so physiological dead space = anatomical dead space, but they are not synonymous).Dead Space
Physiology / Respiratory / Lung Volumes and Pressures
Last Updated: 11th April 2019
Total Ventilation (minute ventilation) = Tidal Volume (TV) x Respiratory Rate (RR)
With each tidal volume, about one third of the total amount of gas flowing into the airway and lung does not participate in gas exchange. This is the physiological dead space. Dead space can thus be defined as the volume of gas in the respiratory tract which does not take part in gas exchange.
Anatomical Dead Space
The anatomical dead space includes the respiratory tract down to and including the terminal bronchioles. These conducting airways have a function in warming, filtering and humidifying inspired air. The anatomical dead space is normally about 150 mL. Fowler's method is used to measure anatomical dead space.
Alveolar Dead Space
The alveolar dead space refers to alveoli incapable of gas exchange; in health, it is negligible but it may become significant in V/Q mismatch, for example in pulmonary embolism where certain alveoli lose their blood supply and no longer take part in gas exchange.
Physiological Dead Space
The physiological dead space is the sum of the anatomical and alveolar dead space (in health, all alveoli take part in gas exchange, so physiological dead space = anatomical dead space). The Bohr equation is used to measure physiological dead space.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
