• Peripheral vasoconstriction with blood shift to central circulation

• In early hypothermia:

○ Increased inotropism and chronotropism

○ Increased cardiac output and blood pressure

• At late hypothermia:

○ Decreased chronotropism and inotropism

○ Decreased cardiac output and blood pressure

• ECG disturbances (bradycardia, heart block and prolongation of PR, QRS and QT intervals)

• Peripheral vasodilatation with blood shift from central to peripheral circulation

• Decreased blood pressure and in severe cases, shock

• Hyperdynamic circulation: Tachycardia and increased cardiac output

• ECG disturbances (prolonged QT interval, rhythm disturbances, conduction defects and ST segment changes)

• In early hypothermia:

○ Hyperventilation

• At late hypothermia:

○ Hypoventilation

• Hypercapnia and pulmonary acidosis, secondary to hypoventilation

• Decreased:

○ Ciliary motility

○ Lung compliance

○ Thorax elasticity

• Increased:

○ Bronchorrhea

○ Noncardiogenic pulmonary edema

• Alterations in diaphragm and intercostal muscles contractility

• Thermal-hyperpnea (increases in tidal volume and frequency of breathing)

• Hypocapnia and pulmonary alkalosis, secondary to hyperventilation

• Brain heat dissipation secondary to respiratory evaporation

• Great activation of sympathetic nervous system

• At first, blood flow to the brain increases but starts decreasing steadily

• Increased muscular tremor to produce heat at early stages

• Decreased nerve conduction:

○ Decreased sensitivity

○ Decreased deep tendon reflexes

• Great activation of sympathetic nervous system

• At first, blood flow to the brain increases but starts decreasing as temperature rises

• Increased blood-brain-barrier permeability

• Muscular weakness and cramps

• Neurologic dysfunction to irreversible neuronal damage

• Gastrointestinal organs injury secondary to hypoperfusion:

○ Splenic and hepatic insult. Decreased function of the last

• Decreased intestinal motility, leading to ileus and internal organs distention

• Mucosal damage and erosions in stomach, duodenum, ileum and colon

• Pancreatitis secondary to hypothermic-related serum amylase elevations

• Gastrointestinal organs injury secondary to hypoperfusion:

• Hepatic insult with consequent enzymes elevations

• Intestinal injury may lead to diarrhea

• Clinical manifestations of thrombocytopenia

• Increased disseminated intravascular coagulation

• Increased prothrombin time

• Increased hemoconcrentation and hence, hematocrit

• Spleen contraction increases circulating erythrocytes

• Increased leukopenia

• Increased bone marrow supression

• Increased blood viscosity

• Clinical manifestations of thrombocytopenia

• Increased disseminated intravascular coagulation

• Increased prothrombin time

• Early removal of red blood cells from circulation

• Increase of cold diuresis

• Mild degree of renal insufficiency due to renal vasoconstriction

• Oliguria

• Renal injury and insufficiency due to direct thermal damage and hypoperfusion (dehydration and blood shift to the skin)

• Activation of the renin-angiotensin-aldosterone system

• Increased cutaneous vasoconstriction

• Decreased sweat production by eccrine sweat glands

• Increased non-shivering thermogenesis through brown adipose tissue

• Increased cutaneous vasodilatation

• Increased sweat production by eccrine sweat glands with the consequent loss of water and electrolytes