Book contents
- Frontmatter
- Contents
- List of contributors
- Foreword by Professor Lord Ara Darzi KBE
- Preface
- Section 1 Perioperative care
- Section 2 Surgical emergencies
- Section 3 Surgical disease
- Section 4 Surgical oncology
- Section 5 Practical procedures, investigations and operations
- Section 6 Radiology
- Section 7 Clinical examination
- Appendices
- Pathology reference ranges
- Useful formulae
- Statistics and critical review
- Organ and tissue donation
- Eponyms in surgery
- Index
Useful formulae
Published online by Cambridge University Press: 06 July 2010
- Frontmatter
- Contents
- List of contributors
- Foreword by Professor Lord Ara Darzi KBE
- Preface
- Section 1 Perioperative care
- Section 2 Surgical emergencies
- Section 3 Surgical disease
- Section 4 Surgical oncology
- Section 5 Practical procedures, investigations and operations
- Section 6 Radiology
- Section 7 Clinical examination
- Appendices
- Pathology reference ranges
- Useful formulae
- Statistics and critical review
- Organ and tissue donation
- Eponyms in surgery
- Index
Summary
Anion gap
Is calculated as: ([Na+] + [K+]) − ([Cl−] + [HCO3−]), all units in mmol/l (Normal: 16 ± 4 mmol/l).
Increases in anion gap seen in:
▪ Diabetic ketoacidosis
▪ Uraemic acidosis
▪ Drug ingestion (e.g. salicylates)
▪ Lactic acidosis
▪ Hypokalaemia
▪ Hypocalcaemia
▪ Hypomagnesaemia
▪ Hyperalbuminaemia
▪ Laboratory error.
A decreased anion gap is less frequent but can be seen in:
▪ Hypoalbuminaemia
▪ Increased immunoglobulins (e.g. myeloma)
▪ Hyperkalaemia
▪ Hypercalcaemia
▪ Hypermagnesaemia
▪ Lithium therapy.
Body mass index (BMI)
BMI = Weight (kg)/Height (m)2.
▪ A BMI of ≤ 20 means the patient is underweight.
▪ 20–25 is desirable.
▪ 25–30 is overweight.
▪ > 30 is obese.
Body surface area (BSA)
▪ BSA (m2) = 0.20247 × Height (m)0.725 × Weight (kg) – Dubois and Dubois method.
▪ BSA (m2) = (Height (cm) ×Weight (kg)/3600) – Mosteller method.
Cardiac output (CO) (Fick method)
The cardiac output can be estimated by dividing oxygen consumption by the difference in oxygen content between arterial and venous blood. The difference between the arterial and mixed venous blood oxygen concentration correlates with oxygen uptake per unit of blood as it flows through the lungs (Fick principle). The method is cumbersome due to the need to collect expired air and arterial blood gases.
where 1.34 ml per gram is the amount of oxygen that a gram of haemoglobin can carry if 100% saturated.
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- Information
- Hospital SurgeryFoundations in Surgical Practice, pp. 784 - 788Publisher: Cambridge University PressPrint publication year: 2009