Disorders in Surgical Patients

(1)

Professor of Medicine, Department of Medicine, Chief, Division of Nephrology and Hypertension, Rutgers New Jersey Medical School, Newark, NJ, USA

Keywords

Preoperative surgeryIntraoperative surgeryPostoperative surgery

Acid-base disorders are rather common in surgical patients. These disorders occur in perioperative (preoperative, intraoperative, and postoperative) periods. Disturbances in all four primary acid-base balances have been reported in surgical patients. However, these disturbances are less severe in healthy patients undergoing elective surgery compared to those who undergo emergent surgery.

Acid-Base Disorders During Preoperative Surgery

Although uncommon in a healthy subject, asymptomatic metabolic acidosis may be seen in individuals who have such diseases as diabetic ketoacidosis, diabetics with type IV RTA, chronic kidney disease stages 3 and 3A, and chronic diarrhea. Use of certain medications such as spironolactone, ACE-inhibitors, cholestyramine, and antiretroviral agents (see Chap. 15) may present with mild metabolic acidosis. Also, vigorous hydration prior to surgery may cause hyperchloremic acidosis. Interestingly, one study found metabolic acidosis in 17% of patients with elective major surgery prior to incision, which was attributed to fasting and infusion of normal saline. Thus, acid-base disorders during preoperative period are related to the patient’s preexisting disease and other conditions, as shown in Table 20.1.

Table 20.1

Pertinent causes of metabolic acidosis during preoperative surgery

High AG acidosis

Diabetic ketoacidosis

Starvation ketoacidosis

Lactic acidosis

Uremic acidosis

Normal AG acidosis

Hyperchloremic metabolic acidosis due to saline

Chronic diarrhea

Loss of alkali from gastrointestinal fistulas and drainages

Ureterosigmoidostomy

Ileal loop bladder

Renal tubular acidosis

Acetazolamide

ACE-inhibitors

Antiretroviral agents

Type IV RTA due to diabetes and hypertension

Metabolic alkalosis is commonly observed in patients on loop or thiazide diuretics for hypertension or edema. Patients who go for gastric outlet obstruction surgery may have metabolic alkalosis due to vomiting. Patients with COPD may have chronic respiratory acidosis. Respiratory alkalosis is seen infrequently unless the patient is anxious about the impending surgery.

Acid-Base Disorders During Intraoperative Surgery

Intraoperative development of acid-base disorders, particularly lactic acidosis and hyperchloremic metabolic acidosis, is rather common. Tissue hypoperfusion and cellular hypoxemia are important causes of lactic acidosis, while administration of normal saline is the cause for hyperchloremic metabolic acidosis. During surgery, loss of HCO₃ ⁻ occurs because pancreas is not stimulated in surgical crisis. Third-spacing of intestinal fluids causes hypovolemia, which requires volume replacement. Usually normal saline is used which causes hyperchloremic metabolic acidosis. This type of acidosis has been demonstrated in noncardiac and nonvascular surgery patients who underwent intraoperative procedures for more than 4 h. Increase in intraabdominal pressure during laparoscopic cholecystectomy seems to cause lactic acidosis, and low pressure pneumoperitoneum (6–8 mmHg) attenuates lactic acidosis. During liver transplantation surgery, lactic acid accumulates due to decreased hepatic clearance, low cardiac output-induced hypoperfusion, and intraoperative blood loss. Thus, lactic acidosis and hyperchloremic metabolic acidosis are the predominant acid-base disorders during intraoperative period. Mild metabolic alkalosis can occur during certain intraabdominal surgeries as a result of fluid sequestration into peritoneum and intestinal lumen, causing hypovolemia and increase in serum HCO₃ ⁻ concentration. Respiratory acid-base disturbances are uncommon with good oxygenation and mechanical ventilation.

Acid-Base Disorders During Postoperative Surgery

Anion gap (AG) metabolic acidosis and non-AG metabolic acidosis are commonly seen during immediate postoperative period. Actually these acid-base disorders are carried on from intraoperative period because of lactic acid production and administration of normal saline. Metabolic alkalosis is infrequent, unless the patient received citrated blood during intraoperative procedure. Citrate is metabolized to HCO₃ ⁻, and if the kidneys are unable to excrete excess HCO₃ ⁻, metabolic alkalosis develops. Vomiting and nasogastric suction may also lead to metabolic alkalosis. Hydration with normal saline usually improves metabolic alkalosis. Respiratory acidosis can develop postoperatively in patients with normal lungs due to inadequate ventilation. Also, excessive sedation with narcotics for pain can cause respiratory acidosis. Rarely upper abdominal or thoracic surgery can cause respiratory alkalosis due to shallow breathing by the patient.

Administration of NaHCO₃ can improve metabolic acidosis in well-oxygenated patients. NaCl or other balanced crystalloids may be necessary to improve hypovolemia and associated metabolic alkalosis. Respiratory acid-base disorders can be managed by appropriate ventilator settings.

Study Questions

Case 1

A 50-year-old woman had abdominal surgery for intestinal perforation. Postoperatively she received opiates for abdominal pain. Which one of the following primary acid-base disturbances is MOST likely to be present in the patient?