Malnutrition

Learning objectives

Define malnutrition
Describe how malnutrition affects different body systems
Anesthetic management of the malnourished patient

Definition and mechanisms

Malnutrition or nutritional deficiency occurs when there is a negative balance between nutritional supply and demand
- Reduced supply states are caused by mechanical obstruction, poor absorption, and psychogenic eating disorders (e.g., anorexia nervosa)
- Increased demand occurs in hypermetabolic states (e.g., sepsis, trauma, and cancer)
It is a deficiency, excess, or imbalance of energy, protein, and other nutrients, which adversely affects the body’s tissues and form
Malnutrition occurs in approximately half of the surgical patients, resulting in an increased incidence of postoperative complications
The main symptoms are unintentional weight loss (≥5-10% over 3-6 months) and a low body weight (BMI <18.5 kg/m2)

Note: Malnutrition involves both undernutrition and overnutrition, however, this article will only discuss undernutrition, for overnutrition the reader is referred to the obesity considerations

Signs and symptoms

Body systems affected by malnutrition

System	Features
Central nervous system	Impaired mental ability Mental depression Depressed cognitive function Fatigue and generalized weakness
Musculoskeletal	Reduced muscle mass and strength Histologically confirmed myopathy in severe anorexia nervosa patients Reduced bone mass, osteopenia, and osteoporosis with secondary fractures Impaired thermoregulation Impaired wound healing
Cardiovascular	Reduction in cardiac output Hypotension and bradycardia Increased risk of arrhythmia due to vitamin and electrolyte disturbance Mitral valve prolapse Loss of cardiac muscle mass with associated reduced left ventricular function and ejection fraction Increased vagal tone Peripheral vasoconstriction Sinus arrest and wandering atrial pacemakers ECG changes: Prolonged QTc, ST depression and T-wave inversion
Respiratory	Reduced respiratory muscle strength and function Spontaneous pneumothorax Pneumomediastinum from persistent vomiting Decreased respiratory compliance (due to decreased elasticity of lung tissues)
Renal	Reduced glomerular filtration rate Total body water proportionally higher Proteinuria High urea due to dehydration
Gastrointestinal	Decreased enteral feeding leading to gut atrophy, bacterial translocation, and impaired immune function Esophagitis and Mallory-Weiss tear from purging Gastric dilatation Paradoxical decrease in gastric emptying time
Micronutrient disturbances	Vitamin A insufficiency - blindness (xerophthalmia due to corneal ulceration is the leading cause of childhood blindness), immunosuppression Reduced iron, ferritin, and iron deficiency anemia Low folic acid and zinc levels
Electrolyte disturbances	Hypokalemia (due to repeated purging and vomiting) Hypocalcemia (prolonged nondepolarizing muscle relaxation action) Hypoglycemia and hypoglycemic coma Metabolic alkalosis (more likely in patients who purge) Increased cortisol and corticotrophin-releasing hormone levels with blunted response
Hematological	Leucopenia Often normal immune function until 50% drop in normal expected body weight Elevated liver transaminases Anemia Pancytopenia
Pharmacological	Delayed or reduced absorption of drugs Hypoalbuminemia increases free fraction of drugs, decreased protein binding occurs Pseudocholinesterase deficiency in severe malnutrition (severe albumin <2 g/dL) → prolonged treatment with nondepolarizing muscle relaxants Lower total body mass means reduced drug doses required and lowered thresholds for toxicity Neostigmine, edrophinium, and catecholamines can cause life-threatening arrhythmias

Risk factors

Lack of breastfeeding
Anorexia nervosa
Bulimia nervosa
Bariatric surgery
Gastroenteritis
Pneumonia
Malaria
Measles
HIV/AIDS
Hyperemesis
Abnormal nutrient loss due to diarrhea or chronic small bowel illnesses (e.g., Crohn’s disease, untreated celiac disease)
Poverty
Homelessness
Social isolation

Treatment

Improve nutrition
Supplementation
Ready-to-use therapeutic foods
Treat underlying cause

Management

Keep in mind

Malnutrition affects all systems, organs, and cells
Treat all malnourished patients as if they have a full stomach (increased aspiration risk)
Careful adjustment of drug dosing and understanding of the pharmacokinetics specific to the malnourished patient is vital