Schwartz's Principles of Surgery ABSITE and Board Review, 9th Ed.

CHAPTER 14. Minimally Invasive Surgery, Robotics, and Natural Orifice Transluminal Endoscopic Surgery

BASIC SCIENCE QUESTIONS

1. Pneumoperitoneum results in which of the following?

A. Decreased plasma rennin

B. Decreased antidiuretic hormone (ADH)

C. Decreased glomerular filtration rate

D. Decreased free water absorption in the distal tubules

Answer: C

Increased intra-abdominal pressure decreases renal blood flow, glomerular filtration rate, and urine output. These effects may be mediated by direct pressure on the kidney and the renal vein. The secondary effect of decreased renal blood flow is to increase plasma renin release, thereby increasing sodium retention. Increased circulating antidiuretic hormone levels also are found during the pneumoperitoneum, increasing free water re-absorption in the distal tubules. (See Schwartz 9th ed., p 362.)

2. When compared to open procedures, laparoscopic procedures

A. Result in greater immune suppression

B. Result in greater stress hormone production

C. Result in higher serum cortisol levels

D. Result in slower normalization of cytokine levels

Answer: C

Endocrine responses to laparoscopic surgery are not always intuitive. Serum cortisol levels after laparoscopic operations are often higher than after the equivalent operation performed through an open incision. The greatest difference between the endocrine response of open and laparoscopic surgery is the more rapid equilibration of most stress-mediated hormone levels after laparoscopic surgery. Immune suppression also is less after laparoscopy than after open surgery. There is a trend toward more rapid normalization of cytokine levels after a laparoscopic procedure than after the equivalent procedure performed by celiotomy. (See Schwartz 9th ed., p 362.)

3. Which of the following does NOT require an electrical current to coagulate tissue?

A. Monopolar cautery

B. Bipolar cautery

C. Mixed current cautery

D. Ultrasonic shears device

Answer: D

A third means of using ultrasonic energy is to create rapidly oscillating instruments that are capable of heating tissue with friction; this technology represents a major step forward in energy technology. An example of its application is the laparoscopic coagulation shears device (Harmonic Scalpel), which is capable of coagulating and dividing blood vessels by first occluding them and then providing sufficient heat to weld the blood vessel walls together and to divide the vessel. This nonelectric method of coagulating and dividing tissue with a minimal amount of collateral damage has facilitated the performance of numerous endosurgical procedures. It is especially useful in the control of bleeding from medium-sized vessels that are too big to manage with monopolar electrocautery and require bipolar desiccation followed by cutting. (See Schwartz 9th ed., p 370.)

CLINICAL QUESTIONS

1. Which of the following statements concerning N2O pneumoperitoneum is true

A. N2O is flammable, therefore, electrosurgery should not be used

B. Minute ventilation is increased in patients with N2O pneumoperitoneum when compared to CO2

C. N2O pneumoperitoneum is more analgesic than CO2 pneumoperitoneum

D. N2O is the gas of choice to use for oncologic procedures

Answer: C

N2O had the advantage of being physiologically inert and rapidly absorbed. It also provided better analgesia for laparoscopy performed under local anesthesia when compared with CO2 or air. Despite initial concerns that N2O would not suppress combustion, controlled clinical trials have established its safety within the peritoneal cavity. In addition, N2O has been shown to reduce the intraoperative end-tidal CO2and minute ventilation required to maintain homeostasis when compared to CO2 pneumoperitoneum. The effect of N2O on tumor biology and the development of port site metastasis are unknown. As such, caution should be exercised when performing laparoscopic cancer surgery with this agent. Finally, the safety of N2O pneumoperitoneum in pregnancy has yet to be elucidated. (See Schwartz 9th ed., p 361.)

2. Hypercarbia from a CO2 pneumoperitoneum can cause

A. Bradycardia

B. Increased myocardial oxygen demand

C. Metabolic acidosis

D. Hypocalcemia

Answer: B

CO2 is rapidly absorbed across the peritoneal membrane into the circulation. In the circulation, CO2 creates a respiratory acidosis by the generation of carbonic acid. Body buffers, the largest reserve of which lies in bone, absorb CO2(up to 120 L) and minimize the development of hypercarbia or respiratory acidosis during brief endoscopic procedures. Once the body buffers are saturated, respiratory acidosis develops rapidly, and the respiratory system assumes the burden of keeping up with the absorption of CO2 and its release from these buffers.

In patients with normal respiratory function, this is not difficult; the anesthesiologist increases the ventilatory rate or vital capacity on the ventilator. If the respiratory rate required exceeds 20 breaths per minute, there may be less efficient gas exchange and increasing hypercarbia. Conversely, if vital capacity is increased substantially, there is a greater opportunity for barotrauma and greater respiratory motion-induced disruption of the upper abdominal operative field. In some situations, it is advisable to evacuate the pneumoperitoneum or reduce the intra-abdominal pressure to allow time for the anesthesiologist to adjust for hypercarbia. Although mild respiratory acidosis probably is an insignificant problem, more severe respiratory acidosis leading to cardiac arrhythmias has been reported. Hypercarbia also causes tachycardia and increased systemic vascular resistance, which elevates blood pressure and increases myocardial oxygen demand. (See Schwartz 9th ed., p 361.)

3. The most common arrhythmia seen with CO2 pneumoperitoneum is

A. Ventricular tachycardia

B. Superventricular tachycardia

C. Sinus tachycardia

D. Sinus bradycardia

Answer: D

The pressure effects of the pneumoperitoneum on cardiovascular physiology also have been studied. In the hypovolemic individual, excessive pressure on the inferior vena cava and a reverse Trendelenburg position with loss of lower extremity muscle tone may cause decreased venous return and decreased cardiac output. This is not seen in the normovolemic patient. The most common arrhythmia created by laparoscopy is bradycardia. A rapid stretch of the peritoneal membrane often causes a vagovagal response with bradycardia and, occasionally, hypotension. The appropriate management of this event is desufflation of the abdomen, administration of vagolytic agents (e.g., atropine), and adequate volume replacement. (See Schwartz 9th ed., p 361.)

4. A patient undergoing laparoscopic colon resection is noted to have a decreased urine output during the last hour of the case. A bolus is given at the end of the case. One hour later, there is still very poor urine output. The appropriate treatment is

A. Repeat the bolus

B. IV furosemide

C. Check urine electrolytes

D. None of the above

Answer: D

Low urine output is a normal physiologic response to increased intra-abdominal pressure for up to 1 hour after surgery. Although the effects of the pneumoperitoneum on renal blood flow are immediately reversible, the hormonally mediated changes such as elevated antidiuretic hormone levels decrease urine output for up to 1 hour after the procedure has ended. Intraoperative oliguria is common during laparoscopy, but the urine output is not a reflection of intravascular volume status; IV fluid administration during an uncomplicated laparoscopic procedure should not be linked to urine output. (See Schwartz 9th ed., p 362.)

5. Laser therapy restores luminal patency in a blood vessel by

A. Coring out the obstructive lesion

B. Fracturing the obstructive lesion

C. Chemically dissolving the obstructive lesion

D. None of the above

Answer: A

Photodynamic therapy works by coring out the obstructive lesion. (See Schwartz 9th ed., p 372, and Table 14-1.)

TABLE 14-1 Modalities and techniques of restoring luminal patency

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