Since 1932, when Cuthbertson first described the systemic response to lower-limb injury, our understanding of surgical physiology has grown significantly, resulting in improved perioperative management, decreased complications, more efficacious analgesia, and faster recovery times. Better control of the sympathoadrenal pathway, endocrine response, and fluid management results in less patient fatigue, shorter functional recovery, and decreased hospital stays. In this chapter we will review the surgical stress response, fluid and electrolyte balance, and organ-specific responses to surgery.
Surgical stress response is the physiologic response to surgery and the name given to the hormonal and metabolic changes that follow surgery. This stress response has three key components: (1) sympathetic nervous system activation, (2) endocrine response with pituitary hormone secretion and insulin resistance, and (3) immunologic and hematologic changes including cytokine production, acute phase reaction, neutrophil leuokocytosis, and lymphocyte proliferation.
The surgical stress response has three key components:
Sympathetic nervous system activation
Endocrine response with pituitary hormone secretion and insulin resistance
Immunologic and hematologic changes including cytokine production, acute phase reaction, neutrophil leukocytosis, and lymphocyte proliferation
Sympathetic Nervous System
The sympathoadrenal response results from an increased secretion of catecholamines from the adrenal medulla. Circulating norepi-nephrine and epinephrine result in tachycardia and hypertension, and directly modify the function of numerous organs, including the liver, pancreas, and kidney. Gluconeogenesis is increased, glucagon production is stimulated, and water is retained to maintain fluid volume and cardiovascular homeostasis.
The endocrine response includes changes in pituitary secretion with secondary effects on hormone secretion from target organs. The overall metabolic effect is increased catabolism, which mobilizes substrate to provide energy, and retention of salt and water to maintain fluid volume and cardiovascular homeostasis. Specifically, corticotrophin stimulates cortisol secretion from the adrenal cortex resulting in increased blood glucose levels, arginine vasopressin stimulates the kidney to retain water, and insulin secretion by the pancreas is often diminished (Table 44-1).
Table 44-1 Principal Hormonal Responses to Surgery |Favorite Table|Download (.pdf)
Table 44-1 Principal Hormonal Responses to Surgery
|Endocrine Gland||Hormone||Change in Secretion|
|TSH||May increase or decrease|
|FSH and LH||May increase or decrease|
|Glucagon||Usually small increases|
Cortisol secretion increases rapidly following the start of surgery. It results in protein breakdown, gluconeogenesis in the liver, and in-creased lipolysis. Blood glucose concentrations increase and are related to the intensity of the surgical injury. Consequently, longer and more drastic elevations in blood glucose are seen in cardiac surgery than in minor surgical procedures such as herniorrhaphy. The usual mechanisms that maintain glucose homeostasis are ineffective in the postoperative period; cortisol promotes glucose production, there is ...