Laparoscopy IV: Pneumoperitoneum

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We’re back today with Dr. Ruhotina and the next piece in our laparoscopy series. Today we’re talking all about gas and pneumoperitoneum. As before, Dr. Ruhotina made some awesome notes — take a look below!

Pneumoperitoneum Physiology 

-        Laparoscopic surgery involves insufflation of a gas (usually carbon dioxide) into the peritoneal cavity producing a pneumoperitoneum

-        Causes an increase in intra-abdominal pressure (IAP)

-        Insufflated at a rate of 4-6 L/Min to a pressure of 10-20mmHg

-        The pressure is maintained by a constant gas flow of 200-400 ml/min

Cardiovascular effects

-        Increased IAP affects venous return, systemic vascular resistance and myocardial function 

-        Increases in IAP result in compression of the vena cava decrease venous return decrease cardiac output 

-        Systemic vascular resistance is increase because of direct effects of IAP (+ increased circulating catecholamines)

o   The SVR change is usually greater than the reduction in cardiac output results in maintaining or even increasing systemic blood pressure

-        Increase SVR, systolic and diastolic pressures and tachycardia increased myocardial work load 

-        If IAP increases further decrease cardiac output further  decrease blood pressure 

Respiratory 

-        Supine position and general anesthesia decrease functional residual capacity 

-        Pneumoperitoneum + Trendelenburg cephalad shift of diaphragm further decrease FRC 

o   Can lead to atelectasis, ventilation-perfusion mismatch, potential hypoxemia, and hypercarbia 

Renal  Increased IAP increased renal vascular resistance and reduction in GFR decreased function and urine output 

 

GI Increased IAP can potential lead to regurgitation of gastric content with increased risk of pulmonary aspiration 

 

Neurological Rise in IAP increased intracranial pressure may result in decreased cerebral perfusion pressure 

 

Effects of gas absorption

-        CO2 most frequently used gas for insufflation colourless, nontoxic, nonflammable and has the greatest margin of safety in the event of a venous embolus since it is rapidly absorbed from the peritoneal cavity, additionally the  metabolic end products easily exhaled through the pulmonary alveoli. 

-        Alternatives to CO2: NO, Air, Helium, Argon

o   NO: Benefits: less acid-base disturbance, may be better for severe cardiopul disease, less post op pain, Risks: supports combustion, not flammable itself only when combustible gas present hydrogen or methane seen with bowel perforation

o   Argon/Helium(inert gases): avoids complications of hypercarbia or acidosis, although decreased solubility in blood therefore increased risk of extraperitoneal gas extravasation such as gas embolus, more expensive 

-        CO2 gas can be administered cold or heated, with or without humidification.

o   Compared with cold gas, heated gas led to only a minimal, clinically insignificant rise in core body temperature of 0.31° Celsius (95% CI 0.09-0.53), without any meaningful improvement in patient outcomes or ease of surgery extra cost of heating and/or humidifying gas used in laparoscopy cannot be justified, according to a Cochrane review of 22 randomized trials

-        Absorbed readily from peritoneum causing increase in PaCO2  increasing cardiac contractility and reduction in diastolic filling which can result in decreased myocardial oxygen supply to demand ratio and greater risk of myocardial ischemia 

-        Arrythmias  nodal rhythm, sinus bradycardia and asystole attributed to vagal stimulation that can be initiated by stretching the peritoneum 

o   Can see this effect more pronounced at the beginning of insufflation 

-        Subcutaneous emphysema, pneumomediastinum and pneumothorax

o   May occur because of incorrect positioning of the gas insufflation needle or trocars or by gas dissecting across weak tissue planes attributed to increased abdominal pressure

-        Venous gas embolism

o   Rare but fatal complication

o   May occur if carbon dioxide is insufflated directly into a blood vessel or by gas being drawn into an open vessel 

o   The physiological effect caused by CO2 are less than that with air because of its greater solubility 

o   However you can see hypotension, desaturation, and mill wheel murmur 

o   Treatment rapid deflation of the abdomen and resuscitation, place in left lateral position and the air aspirated from the central line 

 

Indicators on insufflator machines: 

Important readings of insufflator.

  • Preset Insufflation pressure,

  • Actual Pressure

  • Gas flow rate and

  • Volume of gas consumed

 

Preset Pressure

-        Pressure adjusted by surgeon before starting insufflation

-        The preset pressure ideally should be 12 mmhg- 15mmhg

-        Fifteen mmHg is used as the standard insufflation pressure. 

o   multiple reasons for the use of a 15 mmHg threshold most importantly it is a function of basic cardiovascular physiology

o   Elevated IAP exerts its effects primarily on the cardiovascular system and secondarily on the pulmonary and renal systems. It is well known that the cardiopulmonary, renal and abdominal affects are minimal and still reversible at an insufflation pressure of less then or equal to 15mmHg

o   Animal studies have shown that an intra-abdominal pressures of 20 mmHg has the following effects:

§  markedly impairs renal function, reducing GFR and RBF to 21% and 23% of their baseline values

§  Adverse cardiac and pulmonary effects for prolonged intra-abdominal pressures of 20mmHg lasting over three hours

§  Brief increases to a pressure of 20mm are tolerable

-        Whenever intra abdominal pressure decreases due to leak of gas outside, insufflator eject some gas inside to maintain the pressure equal to preset pressure and if intra-abdominal pressure increases due to external pressure, insufflator sucks some gas from abdominal cavity to again maintain the pressure to preset pressure.

 

Actual Pressure

-        Actual intra-abdominal pressure sensed by insufflator

-        With veress needle is attached there is some error in actual pressure reading because of resistance of flow of gas through small caliber of veress needle. Many microprocessor controlled good quality insufflator deliver pulsatile flow of gas when veress needle is connected, in which the low reading of actual pressure measures the true intra-abdominal pressure.

-        If there is any major gas leak actual pressure will be less and insufflator will try to maintain the pressure by ejecting gas through its full capacity.

 

Flow rate

-        Rate of flow of CO2 though the tubing of insufflator

-        Some information suggests that when you attach the veress needle the flow rate should be adjusted for 1 liter per minute. 

o   Experiment were performed on animals where direct I.V. CO2 were administered and it was found that risk of air embolism is less if rate is within 1 liter/minute.

o   At the time of access using veress needle technique sometime veress needle may be inadvertently enter inside a vessel but if the flow rate is 1 liter/minute there is less chance of serious complication

-        When initial pneumoperitoneum is achieved and canulla is inside abdominal cavity the insufflators flow rate may be set at maximum

 

Total Gas used

-        Fourth indicator of insufflator

-        Normal size human abdominal cavity need 1.5 liter CO2 to achieve intra-abdominal actual pressure of 12 mm Hg. In some big size abdominal cavity and in multipara patients sometime we need 3 liter of CO2 (rarely 5 to 6 liters) to get desired pressure of 12mm Hg. Whenever there is less or more amount of gas is used to inflate a normal abdominal cavity, surgeon should suspect some error in pneumoperitoneum technique. These errors may be leak or may be pre-peritoneal space creation or extravasations of gas.

 

Prior to starting your case: 

-        Turn the insufflator on and check the carbon dioxide (CO2) cylinder to make sure it contains sufficient gas to complete the procedure

o   Have extra CO2 container in room if needed

-        Check the insufflator to assure it is functioning properly

o   After  connecting sterile insufflation tubing  Turn the insufflator to high flow the actual pressure indicator should register 0 

o   Kink the tubing to shut off the flow of gas The pressure indicator should rapidly rise to 30mmHg and flow indicator should go to zero (Fig. 2.2). The pressure/flow shutoff mechanism is essential to the performance of safe laparoscopy. These simple checks verify that it is operating properly. 

 

Closed entry abdominal technique opening abdominal pressure

-        several prospective studies have demonstrated that the initial intra- abdominal pressure (IAP) 8 mmHg provides a reliable confirmation of appropriate Veress needle tip placement through the umbilicus or Palmer’s point [48–50]. 

o   In obese women IAP may be higher than in non-obese women, and can be up to 10 mmHg when the Veress needle is correctly inserted. 

 

TROUBLESHOOTING 

  • Loss of working space → ACTUAL PRESSURE HIGHER THAN SET PRESSURE, FLOW RATE = 0

    • Check actual and set pressure of pneumoperitoneum

    • Check status of relaxation of the patient (look for intraabdominal muscle contractions or firmness of abdomen, this is different than anesthesia checking neuromuscular twitch as diaphragm relaxation is different than intraabdominal)

    • Check valve on for connection insufflator tubing

    • Check insufflator tubing along the entire path, make sure it is not kinked

    • Mechanical obstruction- kinking of tubing, someone standing on tubing, closed valve 

  • Loss of working space→ ACTUAL PRESSURE LOWER THAN SET PRESSURE, FLOW RATE= HIGH indicates a leak 

    • Check insufflator tubing to make sure tubing is connected to insufflator and port

    • Check all ports and make sure the valves are closed

    • Check all ports for leaking co2 

    • Check for distention of bowel and bladder catheter as CO2 can escape into hollow organ (bladder or bowel)

  • Loss of working space→ ACTUAL PRESSURE IS LOWER THAN SET PRESSURE, FLOW RATE=0 (no flow)

    • Ensure power is on 

    • Check tank gas level

  • If screen blank

    • Most likely = disconnected power cords, disconnected cables, blown light source, disconnected light cable