腹腔镜手术中的生理变化【英文讲义】

Physiological Changes during Laparoscopic Surgery

                               
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Laparoscopic surgeries are commonly carried out through transperitoneal or retroperitoneal approaches with insufflation of CO2 and fewer commonly with another inert gas such as helium or argon. The working space developed by CO2 pneumoperitoneum or pneumoretroperitoneum would depend about the pressure of gas presentedto the patient. Typically, intra-abdominal pressures (intra abdominal pressure) of Ten to fifteen mm Hg are sufficient for visualization and dissection. Although higher pressures are sometimes used transiently to optimize visualization, an intra abdominal pressure of 20 mm Hg or greater for any prolonged period is considered unsafe, and pressures more than 25 mm Hg could be associated with abdominal compartment syndrome.

A physiologic effects seen with CO2 insufflation are transient and derive from the body's reaction to increases in intra abdominal pressure and CO2 absorption as it tries to achieve a new state of homeostasis. People who are otherwise healthy will tolerate laparoscopy well, while individuals with underlying cardiopulmonary or renal diseases may not tolerate prolonged CO2 insufflation. Additionally, patient positioning, for example steep Trendelenburg in prostatectomy, can exacerbate cardiovascular alterations in laparoscopy.

CARDIOVASCULAR RESPONSE

The cardiovascular response to increased intra abdominal pressure appears to be phasic. It begins with an early transient phase where venous return and cardiac filling pressures increase due to upward mechanical pressure about the dintra abdominal pressurehragm. This particular, in turn, increases intrathoracic pressure as well as intra-abdominal compression about the splanchnic venous bed and vena cava, which increases venous return. A lot more specifically, mechanical pressures on the venous vasculature result in increases in central venous pressure, pulmonary capillary wedge pressure, and right- and left-side cardiac filling pressures.

Following the transient rise in venous return with the initiation of pneumoperitoneum or pneumoretroperitoneum, a steady state of decreased blood circulation with the inferior vena cava comes after due to the compressive effects of continued intra-abdominal cava pressure. The compressive effects on the arterial vasculature and capillaries increase afterload, systemic vascular resistance (SVR), and arterial pressure, although stroke volume and cardiac output decrease.

Heart rate may rise transiently in response to increases in SVR and arterial blood pressure level to maintain cardiac output, but most studies have reported no significant long-term changes in heartbeat with laparoscopy. In a tiny subset (0.5%) of otherwise healthy patients, however, bradycardia and asystole can occur during CO2 insufflation and pneumoperitoneum. Although the exact mechanism for this response and why only certain patients experience bradycardia remain topics of continued research, it is believed that direct pressure about the vagus nerve leads to a stimulatory parasympathetic effect that leads to a decline in heart rate.

Cardiovascular changes vary with intra abdominal pressure, with higher pressures associated with more significant changes than lower pressures. In in any other case healthy patients undergoing laparoscopy, the threshold intra abdominal pressure that led to hemodynamic changes was 12 mm Hg. Those with underlying cardiac disease will likely have a lower intra abdominal pressure threshold.

Attention to patient positioning and its impact on cardiovascular response ought not to be neglected. In cases where steep or reverse Trendelenburg positions are required, hemodynamic changes are magnified, with drops within the cardiac index (CI) of as much as 50% in certain reports. In Trendelenburg position, venous return is improved with subsequent increases in cardiac filling pressures. Backwards Trendelenburg position, venous pooling in the lower extremity occurs, generating decreased venous return, ejection fraction. Due to the growing complexity of laparoscopic urologic cases and the increased duration of pneumoperitoneum required, some authors have recommended invasive hemodynamic monitoring with repetitive blood gas analysis.

RESPIRATORY RESPONSE

CO2 may be the gas of choice for laparoscopic surgeries because it is noncombustible, extremely soluble, and readily eliminated with the lungs. Other gases for example nitrous oxide have fallen out of favor. Nitrous oxide can result in bowel distension and decreased working space and is also combustible. Helium and argon, although inert and nonflammable, are a lesser amount of soluble than CO2 and therefore are hard to eliminate through ventilation. Pneumothorax caused by helium and argon resolves much slower than CO2 pneumothorax, and gas embolisms of those insoluble gases aren't well tolerated and can rapidly lead to death.

Despite the proven effectiveness and protection of CO2 for insufflation in laparoscopy, the respiratory response to mechanical improves in intra abdominal pressure as well as hypercapnia from absorption should be considered. With CO2 insufflation and increases in intra abdominal pressure, the dintra abdominal pressurehragm is pushed cephalad into the thoracic cavity, constraining downward dintra abdominal pressurehragmatic excursion with respiration. All round functional respiratory capacity, vital capacity, and pulmonary compliance drop with boosts in intra abdominal pressure, and peak airway and plateau pressures can enhance up to 50% and 81%, respectively.

Despite the fact that laparoscopy is usually well tolerated, affected individuals with underlying chronic obstructive pulmonary disease (COPD) or morbid obesity are at high risk for pulmonary decompensation and could require positive end expiratory pressure for adequate gas exchange. In procedures for example prostatectomy and cystectomy, where steep Trendelenburg positioning may be required, pulmonary compliance and dintra abdominal pressurehragmatic movement are further limited.

In addition to the mechanical consequences of pneumoperitoneum, CO2 absorption in the peritoneal cavity or retroperitoneal space will result in hypercapnia and respiratory acidosis. In otherwise, healthy individuals without having pulmonary disease, CO2 is eliminated efficiently through respiration by increases in minute ventilation (increases in respiratory rate and/or tidal volume). Similar to the phasic cardiac response, CO2 excretion rises acutely, from the typical baseline degree of 125 mL/min to 200 mL/min, within approximately Quarter-hour of pneumoperitoneum then plateaus thereafter.

In patients with interstitial pulmonary disease or COPD, poor CO2 diffusion and elimination can lead to significant and catastrophic increases of PCO2 if blood gases are not supervised. End-tidal CO2 measurements are difficult to rely on and tend to underestimate the real PCO2 on this population due to impaired gas swap. Periodic arterial blood gas measurements ought to be obtained as well as in the big event that CO2 cannot be quickly eliminated, pneumoperitoneum or pneumoretroperitoneum should be relieved immediately. Once PCO2 has fallen to the acceptable range, CO2 insufflation could be resumed and also the laparoscopic procedure continuing.

RENAL RESPONSE

Oliguria is often seen otherwise expected with increases in intra abdominal pressure during laparoscopy and really should be described as a normal physiologic response. Effects are transient and reversible upon desufflation. The greater concern would be to avoid over-resuscitation, fluid overload, pulmonary edema, and exacerbation of congestive heart failure. Mechanistically, as intra abdominal pressure increases, its compressive effects on the renal vasculature, the renal parenchyma, and the IVC will reduce effective renal blood circulation (ERBF), cortical and medullary perfusion, and renal venous outflow. The renal effects are mild to negligible once the intra abdominal pressure is under 10 mm Hg, but as intra abdominal pressure reaches and exceeds 15 mm Hg, there's a pressure-dependent decrease in the glomerular filtration rate (GFR), ERBF, creatinine clearance, sodium excretion, and urinary output. In a typical intra abdominal pressure of 15 mm Hg, urinary output decreases by as much as 63% to 64%, GFR by 21%, and ERBF by 26%. Despite this drop, however, there are no long-term renal sequelae, even in patients with pre-existing renal disease, and pneumoperitoneum-induced renal failure does not occur.

Along with renal compression and decreased ERBF, a host of neurohormonal factors are freed. Among them, renin, aldosterone, endothelin, and antidiuretic hormone are elevated, resulting in systemic vasoconstriction and fluid retention. Together with desufflation, these mediators return to baseline levels, along with a post-desufflation diuresis is usually noted in the following hours. Renal homeostasis is re-established within Twenty four hours after surgery with normalization of serum and urinary creatinine and electrolytes.

The optimal fluid managing of physiologic oliguria is much more controversial in laparoscopic live donor nephrectomy. Despite animal model data that suggest no adverse renal histologic changes with prolonged pneumoperitoneum, optimizing ERBF during laparoscopy would seem reasonable.

In order to preserve renal perfusion and minimize possible deleterious effects on graft function, some investigators have suggested using isotonic and hypertonic intravascular volume expansion for transplant cases. As donors are typically healthy and at safe for cardiopulmonary complications, volume expansion and slight fluid overload in the course of surgery might not be unreasonable as long as the surgical team understands the possible unwanted effects. An alternative choice to volume expansion is to decrease intra abdominal pressure around visualization will allow.

METABOLIC RESPONSE

Metabolic acidosis from CO2 absorption is the primary derangement with laparoscopy. Systemic CO2 absorption and resultant metabolic consequences differ depending on the patient's underlying respiratory status since the lung eliminates absorbed CO2 buffered by the blood. In otherwise healthy patients, an increase in minute ventilation is enough, but for individuals with COPD, removal of CO2 is less capable, causing them to are afflicted by more major and extended derangements in acid-base balance. As stated earlier, desufflation might be necessary during a long laparoscopic procedure in patients with COPD or interstitial lung condition.

Even though clinical implications might be minimal, immune and cytokine responses to laparoscopic surgery have been noted. Cortisol, C-reactive protein, tumor necrosis factor-a, interleukin (IL)-6, IL-10, granulocytic elastase, catecholamines, and leukocytes are one of the factors released during laparoscopy that could impact your body's metabolic demand and rest energy expenditure within the postoperative setting.

PEDIATRIC CONSIDERATIONS

Laparoscopy within the pediatric population is generally nicely tolerated. From a cardiac perspective, a similar intra abdominal pressure-dependent physiologic response could be anticipated. When intra abdominal pressure is maintained at 10 to 12 mm Hg or less, clinically significant hemodynamic compromise is generally not observed; although increases in SVR (162%) and decreases in cardiac performance (67%) have been reported at pressures of 10 mm Hg. Thus, it is advisable to minimize intra abdominal pressure if visibility allows just because a lower intra abdominal pressure is associated with fewer cardiac effects. As with adults, bradycardia and asystole may appear during gas insufflation from vagal nerve stimulation. Children routinely have a higher resting vagal tone, and initiating pneumoperitoneum in a lower insufflation rate might be warranted.

In youngsters, the respiratory reaction to increased intra abdominal pressure and CO2 insufflation are magnified compared with adults. From the mechanical standpoint, inhaling the pediatric population is more determined by diphragmatic movement than on expansion from the thoracic cavity as in adults. In addition, thoracic compliance is higher in the immature chest cavity.

With increases in intra-abdominal pressure, the diaphragm is pushed relatively more cephalad, thereby decreasing functional respiratory capacity. Equally respiratory rate and peak airway pressures increases, and also the respiratory changes appear to be more significant with intraperitoneal than extraperitoneal insufflation. From a metabolic standpoint, CO2 absorption is a lot more efficient in youngsters due to a relatively greater absorptive surface-to-weight ratio. To avoid hypercarbia, minute ventilation ought to be increased, with close monitoring of end-tidal CO2 and arterial oxygenation in longer cases.

CONCLUSION

With increasing laparoscopic applications, surgeons should view the basic physiologic principles of the cardiac, respiratory, renal, and metabolic response in laparoscopy. As the complexity of urologic cases performed laparoscopically increases, for a longer time durations of CO2 insufflation and elevated intra abdominal pressure are required, further magnifying physiologic modifications in patients. Thus, the laparoscopist must be mindful from the each patient's fundamental cardiopulmonary status and anticipate the hemodynamic reaction to non-invasive surgery. Adequacy of ventilation should be assessed by serial arterial blood unwanted gas in affected individuals with pulmonary condition, and prevention of overhydration for physiologic oliguria is essential for patient safe practices.