7. Summary of Intraoperative Physiologic Alterations Associated with Laparoscopic Surgery

7. Summary of Intraoperative

Physiologic Alterations Associated with Laparoscopic Surgery

Arif Ahmad, M.D., F.R.C.S. Eng., Edin.

Bruce D. Schirmer, M.D., F.A.C.S.

The physiologic impact of laparoscopic surgery, which is not synonymous with the physiology of pneumoperitoneum, includes the following:

1. Effect of the reduced tissue trauma by minimal access techniques, which is salutary.

2. Physiologic implications of CO

pneumoperitoneum, which are largely deleterious.

The laparoscopic surgeon must be aware of the physiologic consequences of laparoscopic surgery and the potential risks of pneumoperitoneum, which are traded for the benefits of minimal access techniques.

An understanding of the physiologic impact of laparoscopic surgery on the body’s various systems is necessary to accurately assess and describe the risks that prospective laparoscopic surgical patients face. This knowledge becomes even more important when considering patients with significant cardiopul- monary disease or other comorbidities.

The CO

pneumoperitoneum exerts its physiologic effects via two different mechanisms:

1. Mechanical effects relating to increased intraperitoneal pressure.

2. Chemical effect of the gas used for insufflation, which presently in most cases is CO

.

A. Neuroendocrine, Metabolic, and Immunologic Implications

Minimal access surgery aims to achieve correction of the disease process with a minimum of abdominal wall trauma in obtaining access to the site of the problem. Although not always synonymous with minimally invasive surgery, in most situations it is associated with a lesser magnitude of surgical injury than the equivalent traditional “open” procedure.

The metabolic response to trauma depends on the magnitude of the injury

and the response of the organism to it. The neuroendocrine response and the

metabolic consequences of surgery are blunted when the magnitude of injury is

curtailed by minimal access techniques. The differences between open and

minimal access methods are most obvious in cases in which the standard abdom- inal wall incision is more traumatic than the injury incurred in removing the offending organ, as in the case of cholecystectomy.

Interleukin 6 (IL-6), C-reactive protein, and leukocytosis have all been shown to be lower after laparoscopic cholecystectomy when compared to results after open cholecystectomy. This is thought to be a consequence of the limited abdominal wall injury associated with minimal access methods. Although some studies have shown lower cortisol levels after laparoscopic cholecystectomy, the majority have shown no difference in cortisol levels. Similarly, no differences in cortisol levels have been noted when patients undergoing open and laparoscopic- assisted colon resections are compared.

Immunologic implications. Systemic cell-mediated immunity is better pre- served after laparoscopic procedures; this has been attributed to diminished abdominal wall trauma and to avoidance of air exposure in the peritoneal cavity.

In laparoscopic cholecystectomy and colectomy patients, delayed-type hyper- sensitivity has been shown to be better preserved after the closed procedures than after the equivalent open procedure. Short-lived significant differences in the ratio of Th-1 and Th-2 lymphocytes have also been noted in one study of cholecystectomy patients.

Intraperitoneal cell-mediated immunity, however, appears to be impaired by pneumoperitoneum. The exact mechanism of intraperitoneal immunosuppres- sion is unclear. Some studies have implicated CO

pneumoperitoneum in the impairment of intraperitoneal immunity. Macrophages incubated in CO

produced significantly less IL-2 and tumor necrosis factor (TNF) than those incubated in air or helium.

B. Cardiovascular Implications Hemodynamic Changes

Both the mechanical (i.e., pressure-related) and the CO

absorption-related effects of CO

pneumoperitoneum impact the cardiovascular system.

1. Tachycardia is secondary to increased sympathetic discharge, hyper- carbia, and impaired venous return from the abdomen and lower extremities.

2. There is an increase in the measured central venous pressure and pul- monary artery wedge pressure. These changes are artifactual and are secondary to the transmission of increased pressure from the abdomen to the mediastinum and chest. Direct measurements actually show a decrease in cardiac chamber filling and decreased venous return. Thus, there is an increase in measured preload but a decrease in actual preload.

This causes a slight decrease in cardiac output. Preoperative hydration may attenuate the reduction in preload caused by pneumoperitoneum.

3. The afterload is also increased secondary to increased systemic vas-

cular resistance (SVR) from compensatory vasoconstriction due to

neurohumoral mechanisms and direct aortic compression from insuf-

flation. Hypercarbia also possibly contributes to the vasoconstriction.

4. Mean arterial pressure (MAP) may increase, decrease, or remain unchanged depending on the relative effect of the pneumoperitoneum on SVR and CO. The hydration status of the patient influences the magnitude of the cardiovascular changes observed during minimally invasive procedures.

Dysrhythmias

Disturbances of the heart rhythm during minimally invasive procedures are common; they occur in 25%–47% of cases. Causes include hypercarbia, acido- sis, sympathetic stimulation from decreased venous return, and vagal stimula- tion from stretching of the peritoneum. Moderate to severe hypercarbia can result in premature ventricular contractions (PVC), ventricular tachycardia (VT), and ventricular fibrillation. Bradyarrhythmias may occur from vagal stimulation.

Visceral Blood Flow

Blood flow to the viscera is reduced with intraabdominal pressures (IAP) of 15–20 mmHg, independent of the type of gas used for insufflation. The elevated intraabdominal pressure-related increase in SVR results in reduced visceral blood flow. The vasoconstrictive effect of CO

also causes reduced visceral blood flow. The clinical significance of diminished blood flow to the viscera during the procedure remains unclear.

Impact of Patient Position on Cardiopulmonary Function

Reverse Trendelenburg position:

1. Pooling of blood in the lower extremities increases hemostasis (arrest of circulation), and predisposes to deep venous thrombosis (DVT).

2. Decrease in cardiac preload occurs, due to decreased venous return secondary to the factor just mentioned. This may predispose to hypotension, especially in the setting of poor hydration or inadequate volume replacement.

3. Pulmonary function tends to improve in this position due to the caudad shift of the viscera and decreased pressure on the diaphragm. As a result, tidal volume usually increases.

Trendelenburg position:

1. Increase in preload due to increased venous return from the lower extremities and abdomen.

2. The detrimental pulmonary function changes associated with CO

pneumoperitoneum are accentuated when the patient is in this posi-

tion. The Trendelenburg position results in a cephalad migration of the viscera, which increases the pressure on the diaphragm and decreases the tidal volume.

Impact of Extraperitoneal Insufflation

Extraperitoneal CO

insufflation, which is used for inguinal hernia repair, has less of an impact on cardiopulmonary function than pneumoperitoneum.

Minimal mechanical effects are noted with this mode of exposure. Thus, in patients with limited cardiopulmonary reserve there appears to be a theoretical advantage to extraperitoneal insufflation for operations such as inguinal hernia repair where an extraperitoneal approach is feasible. However, large clinical studies have not demonstrated a significant benefit of one method over the other (Table 7.1).

Table 7.1. Cardiovascular changes.

Change Mechanism Prevention

Tachycardia Decreased venous return Pre- and intraoperative Sympathetic stimulation hydration

Hypercarbia Minimize stimulation Minimize hypercarbia, by

increasing minute ventilation Increased preload Artifactual

Actual chamber filling decreases

Increased afterload Increased systemic Minimize intraabdominal vascular resistance pressure

(SVR) from Gasless laparoscopy vasoconstriction due to: Prevent hypercarbia, by

1. Elevated increasing minute

intraabdominal ventilation pressure

2. Hypercarbia 3. Epinephrine release

Dysrhythmias Hypercarbia Minimize intraabdominal

Sympathetic stimulation pressure

Decreased venous return Gasless laparoscopy Preoperative hydration Decreased visceral Intraabdominal Reduce intraabdominal

blood flow pressure pressure

Preoperative hydration

C. Pulmonary Effects

The impact of pneumoperitoneum on pulmonary function may be divided into mechanical and chemical effects. The principal chemical effect is that the CO

gas is readily absorbed into the bloodstream, resulting in hypercarbia. The numerous physiologic repercussions of hypercarbia have, for the most part, been mentioned above.

The elevated intraabdominal pressure exerts important mechanical effects that impair pulmonary function. The increased pressure pushes the diaphragm upward, increases the intrathoracic pressure, and increases the work of breath- ing. These alterations are associated with decreased lung compliance, tidal volume, and vital capacity.

Impaired oxygenation results from reduced lung volume and atelectasis due to displacement of the diaphragm. This can be countered by increasing fractional inspiratory oxygen (FiO

). Positive end-expiratory pressure (PEEP) will also improve oxygenation, but this may be at the cost of decreasing the preload.

The above mechanical factors will also make it more difficult to adequately ventilate the patient, especially in light of the CO

pneumoperitoneum-related hypercarbia. Elevating the minute ventilation by increasing tidal volume and/or the respiratory rate should improve ventilation and lower the CO

levels in the blood.

As mentioned earlier, the Trendelenburg position results in further embar- rassment of pulmonary function by increasing the pressure on the diaphragm.

Reverse Trendelenburg improves pulmonary function by decreasing the pressure on the diaphragm (Table 7.2).

D. Gastrointestinal and Hepatic Impact

As mentioned, pneumoperitoneum diminishes visceral blood flow. The risk of aspiration increases during laparoscopic procedures done under pneumoperi- toneum due to the increased IAP, especially when the patient is in the Trende- lenburg position or if the patient has a history of gastroesophageal reflux.

Pneumoperitoneum also decreases hepatic blood flow although the clinical significance of this temporary alteration is uncertain. Impairment or derange- ments in liver function have not been noted after advanced laparoscopic proce- dures, thus far.

E. Renal Effects

Pneumoperitoneum results in decreased renal blood flow. The clinical impli-

cations of decreased renal perfusion are likely to be most significant in patients

with previously impaired renal function. In a study of patients undergoing

laparoscopic cholecystectomy, renal blood flow, glomerular filtration rate, and

urine output were reduced compared to open cholecystectomy. A drop in urine

output is anticipated during laparoscopic cases.

F. Body Temperature Changes

The factors responsible for intraoperative hypothermia in open cases are also applicable to laparoscopic cases. However, heat exchange from the open abdominal cavity and exposed intestines that occurs in open cases is replaced by the cooling effect of gas insufflation in laparoscopic cases.

The cooling effect of nonheated gas insufflation is significant, and laparo- scopic methods have a potential of inducing greater heat loss than open cases.

The carbon dioxide in the gas tank is at high pressure in the range of 3000 mmHg. When the gas enters the abdomen at a pressure of 15 mmHg, the fall in pressure is associated with significant cooling. It has been estimated that there is a drop of 0.3°C for every 50 mL CO

delivered. It is apparent that the cooling is more pronounced at higher flow rates and when gas leakage from the abdomen necessitates continuous insufflation of gas.

Warmed CO

reduces the cooling but is associated with tissue desiccation and thus requires further study.

To offset the cooling associated with pneumoperitoneum, other controllable factors should be minimized as in open surgery. Additionally, it is important to minimize gas leaks.

Table 7.2. Pulmonary changes.

Change Mechanism Prevent/treat

Impaired Reduced lung volume, Increase oxygenation oxygenation vital capacity, and With increased FiO

and

atelectasis secondary to PEEP cephalad displacement

of the diaphragm

Impaired ventilation As above Increase minute ventilation on respirator

Respiratory acidosis Hypercarbia Avoid/rule out inadvertent preperitoneal insufflation Increase minute ventilation Decreased tidal Decreased compliance Minimize intraabdominal

volume due to an increased pressure

intraabdominal pressure Gasless laparoscopy, reverse Trendelenburg position

Increased work of Decreased compliance Minimize intraabdominal

breathing pressure

Gasless laparoscopy Reverse Trendelenburg

position

G. Selected References

1. Schauer P. Physiologic consequences of laparoscopic surgery. In: Eubanks S, Swanstrom L, Soper N (eds). Mastery of Endoscopic and Laparoscopic Surgery.

Baltimore: Lippincott Williams & Wilkins, 2000:22–37.

2. Chekan E, Pappas T. Minimally invasive surgery. In: Townsend CM Jr, Evers KM, Beauchamp D, Mattox K (eds). Sabiston Textbook of Surgery, 16th edition. Philadel- phia: Saunders, 2004. pp. 292–310.

3. Bannenberg JJ, Rademaker BM, Froeling FM. Hemodynamics during laparoscopic extra- and intraperitoneal insufflation; an experimental study. Surg Endosc 1997;

11:911–914.

4. Joris JL, Noirot DP, Legrand MJ, et al. Hemodynamic changes during laparoscopic cholecystectomy. Anesth Analg 1993;76:1067–1071.

5. Iwase K, Takenaka H, Ishizaka T, et al. Serial changes in renal function during laparo- scopic cholecystectomy. Eur Surg Res 1994;25:203.

6. Safran DB, Orlando R. Physiological effects of pneumoperitoneum. Am J Surg 1994;

167:281.