ANESTHETIC CONSIDERATIONS IN ABDOMINAL SURGERY

Preoperative Evaluation

•  Fluid status: Patients often hypovolemic

•  Inadequate fluid intake (fasting, anorexia)

•  Fluid loss (emesis, bowel preps, GI bleeding, fevers = insensible loss)

•  Sequestration of fluid from intravascular space (3rd spacing)

Anesthetic Management

Technique

•  Abdominal procedures usually require muscle relaxation

• Epidural analgesia may be beneficial (↓ anesthetic requirements, blunt surgical stress response, ↑ postop pain relief, ↓ postop atelectasis, ↑ postop mobility)

Fluid Management (See Chapter 9 on Fluids, Electrolytes, and Transfusion Therapy)

•  General strategies

• Body wt-based formulas: Rough guidelines for fluid replacement

• Goal-directed strategies: Aimed at optimizing stroke volume, cardiac output, & tissue perfusion. Use mechanical ventilation or fluid bolus induced variations in pulse pressure (dPP), stroke volume (SV), or cardiac output (CO) to assess fluid responsiveness

• A more than 13% change in dPP, SV, or CO predicts fluid responsiveness

• Restrictive management: 4–8 mL/kg/hr—some evidence for ↓ postop morbidity compared with “liberal” strategies (10–15 mL/kg/hr)

•  Replacement ratio: 3 mL crystalloid per 1 mL fluid loss 1 mL colloid per 1 mL fluid loss

• Only 1/3 of crystalloid remains intravascular, 2/3 goes into interstitium

• Colloids remain intravascular longer than crystalloids & exert oncotic pressure

•  Blood products—should be given based on clinical eval of blood loss (surgical suction canister, sponges) & lab values (hematocrit)

Muscle Relaxation

•  Usually required for intra-abdominal procedures & abdominal closure

• Secondary to intraop bowel edema & abdominal distention

•  Inhalational agents may potentiate effects of muscle relaxants

•  Neuraxial blockade with local anesthetics can provide good muscle relaxation

Use of Nitrous Oxide (N₂O)

• N₂O diffuses into bowel lumen faster than nitrogen can diffuse out

•  Degree of bowel distention is a function of

• N₂O conc, blood flow to the bowel, duration of admin

•  Avoid N₂O (relative contraindication) in bowel obstruction

• May have large initial volume of bowel gas and/or difficult surgical closure

•  Causes an obligatory reduction in FiO₂

• However, ↑ FiO₂ may reduce incidence of surgical wound infection

•  May ↑ pulmonary artery pressure (esp in pts with pulmonary HTN)

•  Possible ↑ incidence of PONV (data is mixed)

Common Intraop Problems

•  ↓ FRC, atelectasis, & hypoxemia because of

• Surgical retraction of abd viscera to improve exposure

• Insufflation of gas during laparoscopy

• Trendlenburg position
(Application of PEEP may reverse those effects)

•  Hypothermia 2° to heat loss: Radiation > convection > conduction > evaporation

• Most heat loss occurs during 1st hr of anesthesia (1–1½°C)

(treat by ↑ OR temp, apply convective warming blankets, warm IV fluids)

•  Hypotension, tachycardia, & facial flushing during bowel manipulation

• 2° to mediator release (prostaglandin F1-α, aprostanoid)

•  Opioid-induced biliary tract spasm

•  May interfere with interpretation of intraop cholangiograms

(Reversed by naloxone, nitroglycerin, & glucagon)

•  Hiccups are episodic diaphragmatic spasms relieved by

↑ anesthetic depth, ↑ neuromuscular blockade, drainage of stomach to relieve gastric distention

ALCOHOL ABUSE

Preop Evaluation

•  Alcoholic cirrhosis characterized by AST/ALT ratio >2

Anesthetic Considerations

•  Acute intoxication: ↓ anesthetic requirements (2° to EtOH depressant effects)

•  Chronic intoxication: ↑ anesthetic requirements (2° to tolerance)

•  Head & cervical spine injury must be considered in intoxicated pts

Postop Considerations

•  Unrecognized alcohol abuse may present with delirium tremens

•  Often occurs 72 hrs after last drink (postop day 3)

•  Signs: Autonomic hyperactivity, tremors, hallucinations, seizures

•  Treatment: Benzodiazepines

ANESTHETIC MANAGEMENT: LIVER SURGERY

General Considerations

•  Liver resections often done for metastasis to liver or 1° hepatocellular carcinoma

•  Hypoxemia → 2° hepatopulmonary shunting, atelectasis, ↓ FRC from ascites

•  Prior portosystemic shunt ↑ surgical complexity & risk of surgical bleeding

Management of Portal Hypertension

•  Pharmacologic: β-blockers

•  Endoscopic: Sclerotherapy & esophageal banding for bleeding varices

•  Transjugular intrahepatic portosystemic shunt (TIPS) have replaced surgical shunts, done percutaneously under fluoroscopy

•  Surgery: ↑ risk of encephalopathy, no evidence of better outcome

Monitoring

•  A-line & CVP

Anesthetic Technique

•  General endotracheal anesthesia

•  Thoracic epidural for postop pain control (provided no coagulopathy)

•  Aspiration precautions (nonparticulate antacids, rapid-sequence induction)

•  Avoid N₂O (risk of bowel expansion & potential ↑ pulm artery pressure)

•  Avoid histamine releasing muscle relaxants (atracurium, mivacurium) to avoid further ↓ blood pressure

•  Hyperdynamic circulation in pts with end-stage liver disease may require vasopressor therapy to ↑ systemic afterload

•  Concomitant pulmonary HTN in pts with ESLD → avoid hypoxemia, hypercarbia, & metabolic acidosis (worsen pulmonary HTN)

•  Careful NG tube placement (concern for coagulopathy + esophageal varices)

• Fluid replacement with isotonic fluids & colloids (pts have ↓ intravascular oncotic pressure)

•  Prolonged hepatic “inflow” occlusion (Pringle maneuver: Occlusion of portal vein & hepatic artery) → may lead to coagulopathy & metabolic acidosis

Postop Care

•  Bleeding: Surgical vs. coagulopathy

•  Small for size syndrome in extensive hepatic resections (remaining liver unable to support metabolic functions → ↑ lactate, ↑ liver enzymes, worsening metabolic acidosis)

ANESTHETIC MANAGEMENT: BARIATRIC SURGERY

General Considerations

•  Body mass index (BMI) = body weight in kg/(height in meters)²

•  Overweight = BMI > 25; Obesity = BMI > 30; Morbid obesity = BMI > 35

Types of Bariatric Surgery

•  Vertical band gastroplasty

• Creation of small pouch → restricts volume of food that can be ingested

•  Open Roux-en-Y gastric bypass

• Formation of small gastric pouch anastomosed to proximal jejunum

• Dumping synd.: Ingestion of energy-dense-food → nausea, diarrhea abd pain

• Pts at risk for Fe and B1₂ deficiency

•  Laparoscopic Roux-en-Y gastric bypass

• Smaller incision, ↓ postop pulm complications/pain, earlier ambulation

Preanesthetic Considerations

•  Obesity-associated comorbidities

• HTN, hyperlipidemia, obstructive sleep apnea (OSA), GERD, type II diabetes

• ↑ circulating blood volume, ↑ cardiac output → ↑ in O₂ consumption

• ↓ lung compliance, ↑ ventilation/perfusion mismatch & ↓ FRC → hypoxemia

• Long-standing hypoxemia → pulmonary HTN, & rt-sided heart failure

Anesthetic Technique

•  General endotracheal anesthesia

•  Epidural analgesia for pts undergoing open Roux-en-Y bypass

• Reduces need for systemic opioids & oversedation in pts with OSA

Airway Management

•  Specific considerations

• Predictors of difficult intubation: ↑ neck circumference (>42 cm) & Mallampati score III & IV

• Obesity = risk factor for difficult mask ventilation

• Rapid desaturation following induction 2° to ↓ FRC, ↑ O₂ consumption, & ↑ incidence of airway obstruction

•  Management strategies

• Preoxygenation for 3 min in a 25° head-up position

• Consider ramped position (horizontal alignment between auditory meatus & sternal notch) to improve laryngeal view

• Consider awake intubation if airway exam concerning

• Consider aspiration precautions (antacids + rapid-sequence induction)

• Consider use of insoluble gases (desflurane, sevoflurane)

• Consider short-acting narcotics & sedatives (↓ risk postop resp. depression)

Monitoring

•  Indications for A-line: Hypoxemia, ↓ systolic fx, moderate & severely ↑ pulm artery press, & inability to measure bp noninvasively

•  ECG: May show RBBB 2° to pulmonary HTN

•  DVT risk: ↓ risk with pneumatic compression devices and/or SC heparin

•  Equip: OR table must accommodate pt weight, capacities vary widely

Postop Complications

•  ↑ Incidence of atelectasis & hypoxemia (consider semirecumbent position, CPAP or BIPAP)

•  ↑ Postop. hypercarbia esp in pts with baseline retention and periop opioid use → CO2 narcosis → hypercapnic resp. failure

•  Negative-pressure pulmonary edema 2° to inspiration against closed glottis

•  Accidental stapling of NG tube to pt stomach (prevent by keeping close communication with surgical team)

•  DVT prophylaxis & early ambulation ↓ risk of thromboembolism

ANESTHESTIC MANAGEMENT: LAPAROSCOPIC SURGERY

General Considerations

•  Advantages include smaller incision, ↓ surgical trauma, ↓ postop pain, ↓ pulmonary dysfx, ↓ postop ileus, faster recovery, & ↓ hospital stay

•  3 ports typically inserted into abdomen: (subumbilical port used for CO₂ insufflation to 12–15 mm Hg)

Anesthetic Technique: Laparoscopic Surgery

•  General anesthesia with endotracheal intubation and controlled ventilation

•  Muscle relaxation to avoid further increase in intrathoracic pressure

•  Rapid-sequence induction for antireflux procedures and patients with full stomach

• Persistent ↑ ETCO₂ despite adequate minute volume may signal subcutaneous emphysema

•  Attenuation of hemodynamic changes to peritoneal insufflation:

• Bradycardia → glycopyrrolate or atropine

• Decreased CO & hypertension → use volume loading and/or vasopressor

• Hypertension → use vasodilators

Monitoring

•  Large-bore peripheral IV access (limited access to tucked arms during case)

•  Orogastric tube to aspirate gas from stomach prior to trocar placement

•  Acute ↑ in peak airway pressure may signal:

• Endobronchial migration of tube (esp. with bed change to Trendlenburg)

• Pneumothorax (usually accompanied by ↓ SpO₂)

•  Avoid ↑ peak airway pressure: Use pressure-control ventilation and ↓ exp time (e.g., I/E ratio 1:1.5)

• Minute volume usually must be ↑ by 20% to maintain normocarbia

•  Bradycardia following CO₂ insufflation likely vagally mediated

• May also be 2° to hypercarbia & respiratory acidosis

•  Avoid ↑ in insufflation pressure that can compromise venous return (max 12–15 mm Hg)

Postop Care

•  Shoulder pain (suprascapular nerve irritation)—treat with NSAIDs

•  Unrecognized intra-abdominal visceral/vascular injury → progressive hypotension, ↑ abdominal girth, ↓ hematocrit

•  ↑ incidence of PONV

•  Extensive subcutaneous emphysema may require mechanical ventilation

LARGE INTESTINAL SURGERY

Indications

•  Colon cancer, diverticulitis, ulcerative colitis, Crohn’s dz, ischemic colitis, reversal of colostomy

Preop Evaluation

•  Preop fasting + bowel prep = large fluid deficit

•  Bowel obstruction can ↑ risk for gastric aspiration during induction

•  Thoracic epidural analgesia (T8–12) ↓ atelectasis, ↑ early ambulation (may contribute to hypotension in presence of hypovolemia)

Anesthetic Management: Large Intestinal Surgery

•  Consider aspiration precautions if pt is obstructed

•  Consider stress dose steroids if pt on preop steroids

•  Fluid replacement must account for evaporative losses of exposed viscera

•  Mesenteric traction syndrome: Hypotension during bowel surgery from bowel-associated mediator release (vasoactive intestinal peptide)

→ Hypovolemia, surgical bleeding, sepsis 2° to peritoneal fecal spillage

Postop Complications

•  Prokinetic agents (metoclopramide) can cause anastomotic dehiscence after colonic surgery

•  Postop ileus caused by bowel manipulation, opioids, immobility, lack of enteral feeding, & bowel edema from fluid overload (epidural analgesia may ↓ incidence of ileus)

•  Prolonged NG tube placement can lead to ischemic necrosis of nasal septum

SMALL INTESTINAL SURGERY

Indications

•  Small bowel obstruction, neoplasms, intussusception, intestinal bleed, resection of carcinoid tumor, Crohn’s dz

Carcinoid Tumors/Carcinoid Syndrome

•  Carcinoid tumors typically asymptomatic

→ May present with abd pain, diarrhea, & intermittent obstruction

•  Metastatic carcinoid tumors (hepatic, pulm metastases) systemic symptoms

→ Carcinoid syndrome: Cutaneous flushing, bronchoconstriction, hypotension, diarrhea, & rt-sided valvular lesions

↑ 5-hydroxy-indole-acetic acid (>30 mg in 24-hr urine)

•  Epidural analgesia may exacerbate intraop hypotension (consider use of dilute local anesthetics/narcotics + volume loading)

Monitoring

•  Consider TEE for carcinoid (eval rt-sided heart lesions & guide fluid therapy)

Anesthetic Management

•  Consider aspiration precautions/rapid-sequence induction for obstruction

•  Carcinoid tumors

• Avoid agents that release histamine (thiopental, succinylcholine, atracurium, morphine)

• Octreotide (synthetic somatostatin) effective in relieving hypotension (subcutaneous dose 50–500 mcg—half-life of 2.5 hrs)

Postop Care

•  50% of carcinoid deaths result from cardiac involvement

•  Similar considerations as in large intestine surgery

PANCREATIC SURGERY

Indications

•  Pancreatic adenocarcinoma resection (Whipple: Pancreatojejunostomy with gastrojejunostomy & choledochojejunostomy)

•  Treatment of complications of pancreatitis: Infected pancreatic necrosis, hemorrhagic pancreatitis, drainage of pancreatic pseudocyst

Monitoring

•  Pancreatic surgery can be assoc with significant blood loss & fluid shifts (consider A-line, CVP depending on pt comorbidities)

Anesthetic Management

•  Consider thoracic epidural analgesia (T6–T10) for postop pain control

•  Often feeding tube tip will be adjusted by surgeon during procedure

•  Pancreatic surgery for infection may be complicated by sepsis & ARDS
requires aggressive fluid resuscitation, vasopressor support (α-agonist, e.g., norepinephrine) & postop mechanical ventilation

Postop Care

•  Significant pancreatic resection → insulin insufficiency & new-onset diabetes

SPLENIC SURGERY

Indications

•  Splenic injury (blunt or penetrating trauma)

•  Idiopathic thrombocytopenic purpura with splenic sequestration of platelets

Preop Preparation

•  Periop platelet transfusion not warranted (unless platelet count is <50,000/μL or clinical evidence of coagulopathy)

Anesthetic Management

•  Avoid drugs that interfere with platelet function (NSAIDs)

Postop Care

•  Pts should receive pneumococcal, Haemophilus influenzae, & meningococcal vaccines

HEMORRHOIDECTOMY & DRAINAGE OF PERIRECTAL ABSCESS

Anesthetic Management

•  Procedures usually short, often in lithotomy/prone position

•  Usually general anesthesia (consider LMA for lithotomy cases)

•  Spinals may be used (hypobaric soln for prone case, hyperbaric for lithotomy)

•  Deep plane of anesthesia provides sphincter relaxation

Postop Care

•  Postop pain can be severe → consider use of narcotics & NSAIDs

INGUINAL HERNIORRHAPHY

Anesthetic Management

•  Commonly done as an outpatient procedure

•  Spermatic cord traction may initiate a vagally mediated bradycardia

• MAC + local anesthesia most common approach

• Paravertebral block (T10–L2) increasingly used

• Spinal or general anesthesia may also be used

VENTRAL HERNIORRHAPHY

Preop Considerations

•  Staged ventral hernia repair may ↓ incidence of postop respiratory failure (closure of large abd defects → pulm restriction)

Monitoring

•  Obtain large-bore IV access to replace evaporative fluid losses in large cases

Anesthetic Management

•  Consider epidural analgesia (T10–T12) or transversus abdominis plane block (bilateral for midline incisions, unilateral for one-sided hernias)

•  Usually done with general endotracheal anesthesia + muscle relaxation

•  Smooth emergence impt. (no coughing/bucking) to avoid disruption of repair

APPENDECTOMY

Preop Evaluation

•  Consider preop IV hydration to replace fluid deficits (vomiting, poor intake)

Anesthetic Management

•  Performed via open or laparoscopic approach

•  Consider taking aspiration precautions (rapid-sequence induction)

Postop Care

•  IV opioids usually sufficient for postop pain management

CHOLECYSTECTOMY

Anesthetic Management

•  Performed via open or laparoscopic approach with general endotracheal anesthesia

•  Opioid-induced biliary tract spasm

• May interfere with interpretation of intraop cholangiograms

• Can be reversed by naloxone, nitroglycerin, & glucagon

•  Minimal blood loss unless abdominal vessel injury occurs

Postop Care

•  Lap cholecystectomy → less postop pain & earlier discharge (usually same day)

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