腹腔镜手术中的麻醉

Anaesthesia in Laparoscopy

Dr. R.K. Mishra.

                               
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Introduction:

Minimal access surgery has been proved to be a useful surgical technique.  New standards have been established for various indications.  Patient comfort is a greater consideration in the 21stcentury.  The acquisition of recent technology and skills now affords a better choice of the mode of surgery.  

The anaesthetic problems during minimal access surgery are related to the cardiopulmonary effects of pneumoperitoneum, carbon dioxide absorption, extraperitoneal gas insufflation, venous embolism and inadvertent injuries to intra-abdominal organs. Optimal anaesthetic care of patients undergoing laparoscopic surgery is very much important. A good anaesthetic techniques facilitate risk free surgery and allow early detection and reduction of complications.

The general anaesthesia and the pneumoperitoneum required as part of the laparoscopic procedure do increase the risk in certain groups of patients. Patients with Cardiac diseases and COPD should not be considered a good candidate for laparoscopic anaesthesia in inexperienced hand. The laparoscopy may also be more difficult in patients who have had previous lower abdominal surgery. The elderly may also be at increased risk for complications with general anaesthesia combined with pneumoperitoneum.

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Effect of pneumoperitoneum on body:

Pneumoperitoneum at the time of laparoscopic surgery causes upward displacement of the diaphragm, resulting in the reduction in lung volumes including functional residual capacity. Pulrnonary compliance is reduced and airway resistance is increased due to high intra-abdominal pressure.  The anaesthetist often uses high airway pressure to overcome the intra-abdominal pressure for a given tidal volume, which increases the risk of haemodynamic changes and barotrauma.

The impaired diaphragmatic mobility gives rise to uneven distribution of ventilation to the nondependent part of the lung, resulting in ventilation-perfusion mismatch with hypercarbia and hypoxaemia. The ventilatory impairment is even more severe if there is associated airway and alveolar collapse. Increased intra-abdominal pressure also predisposes to regurgitation of gastric contents and pulmonary aspiration.

Venous gas embolism is a  fatal complication of pneumoperitoneum. Verres needle or the trocar, may directly puncture the arteries or blood flow across an opening in an injured vessel may sometimes draw gas into the vessel  and leads to gas embolism.

A slow infusion of air less than 1 litre/minute is absorbed across the pulmonary capillary-alveolar membranes without causing any damage. At higher infusion rates, the gas bubbles lodging in the peripheral pulmonary arterioles provoke neutrophil clumping, activation of the coagulation cascade and platelet aggregation. This may leads to pulmonary vasoconstriction, bronchospasm, pulmonary oedema and some times pulmonary haemorrhage. Gas bubbles attached to fibrin deposits and platelet aggregates mechanically obstruct the pulmonary vasculature and increases the pulmonary vascular resistance.

The increased right heart after load leads to acute right heart failure with arrhythmias, ischaemia, hypotension and elevated central venous pressure. Some time paradoxical embolism is seen through a patent foramen ovale.

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Elevated intra-abdominal pressure produces physiological changes in the haemodynamics by its effects on systemic vascular resistance, venous return and myocardial performance. Systemic venous return  increases when intra-abdominal pressure is elevated. Effects on venous return and cardiac output depend on the magnitude of the intra-abdominal pressure. Venous return initially increases  with intra-abdominal pressure below 10 mmHg, this paradox is due to reduction in the blood volume sequestrated in the splanchnic vasculature which increases cardiac output and arterial pressure.  When intra-abdominal pressure exceeds 20 mmHg, the inferior vena cava is compressed. Venous return from the lower half of the body is impeded resulting in a fall in cardiac output.

The circulation of kidney becomes much compromised with increased intra-abdominal pressure. Renal blood flow and glomerular filtration rate decreases because of increase in renal vascular resistance, reduction in glomerular filtration gradient and decrease in cardiac output. The increase in systemic vascular resistance  impairs left ventricular function and cardiac output. Arterial pressure however remains relatively unchanged, which conceal the fall in cardiac output. High intra-thoracic pressure during intermittent positive pressure ventilation add in impairment of  venous return and cardiac output, particularly if positive end expiratory pressure (PEEP) is also applied. The elevation in intra abdominal pressure produces lactic acidosis, probably by severely lowering cardiac output and by impairing hepatic clearance of blood lactate.

Stretching of the peritoneum some time leads to stimulation of vagus nerve and can provoke arrhythmias such as AV dissociation, nodal rhythm, sinus bradycardia and asystole. This shock is more commonly seen with rapid stretching of the peritoneum at the beginning of peritoneal insufflation.

Faulty pneumoperitoneum may give rise to subcutaneous emphysema, pneumomediastinum, pneumopericardium and pneumothorax. However, gas  can also dissect through existing defects in the diaphragm or along surgically traumatised tissue planes in the retroperitoneum, the diaphragm or the falciform ligament.

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Anaesthetist's role in laparoscopy:

The role of anaesthetist in laparoscopic surgery is vital. The laparoscopic surgery should never be performed if anaesthetist has no experience in minimal access surgical anaesthesia. It is up to anaesthetist to identify whether he is capable of performing, realistically and with its structures and without compromising the safety of the patients. It is only on these clearly established bases that safe laparoscopy can be contemplated.

The following monitoring device should routinely used at the time of minimal access surgical general anaesthesia:

• Electrocardiogram,
• Sphygmomanometer,
• Airway pressure monitor,
• Pulse oximeter,
• Endtidal CO2 concentration (PETCO2) monitor,
• Peripheral nerve stimulator
• Body temperature probe.
  
  

Anaesthesia for laparoscopy can be achieved with a variety of agents and techniques. General anaesthesia using balanced anaesthesia technique including intravenous induction agents like: Thiopentone, propofol, etomidate, and inhalational agents like: Nitrous oxide, isoflurane can be used.

A variety of muscle relaxants including succinyl choline, mivacurium, atracurium, vecuronium is available for rapid recovery and cardiovascular stability. Total intravenous anaesthesia using agents like propofol, midazolam and ketamine, alfentanil and vecuronium has been reported  for outpatient laparoscopy.

A balanced anaesthesia using appropriate amount of  muscle relaxant, intravenous and epidural narcotics and artificial ventilation is essential to combat the insult and the effects of pneumoperitoneum, namely the resorption of carbon dioxide, diaphragmatic movement impairment and the reduction in lung volumes. The direct arterial pressure monitoring and records of blood pressure and the blood gases estimation is needed. The CVP monitoring helps in assessing the preload status. The ECG monitoring demonstrates the rhythm status continuously.

The prophylactic heparin should be used is in accordance with prevention of deep venous thrombosis and subsequent pulmonary embolism. The use of intermittent inflated pneumatic cast compression helps in maintaining circulation in the legs during the operation.

Now a days epidural anaesthesia is also considered as a safe alternative to general anaesthesia for outpatient laparoscopy without associated respiratory depression.

A good anaesthetist should keep following points in mind at the time of laparoscopic surgery:

• All patients undergoing laparoscopy should have a empty bowel. In the unlikely event of bowel damage, there is much less risk of contamination if the bowel is empty.
• Good muscle relaxation reduces the intra-abdominal pressure required for adequate working room in abdominal cavity.
• The  inflation of stomach should be avoid during artificial ventilation using mask as this increases the risk of gastric injury during trocar insertion or instrumentation.
• The distended stomach also hamper the visibility of calots triangle at the time of laparoscopic Cholecystectomy or laparoscopic bile duct surgery.
• Tracheal intubation and intermittent positive pressure ventilation should be routinely used. This ensures airway protection and controls pulmonary ventilation to avoid hypocarbia.
• The ventilatory pattern should be adjusted according to respiratory and haemodynamic performance of the individual patient.
• Ventilation with large tidal volumes (12-15 ml/kg) prevents alveolar atelectasis and hypoxaemia and allows adequate alveolar ventilation and CO2 elimination.
• Halothane increases the incidence of arrhythmia during laparoscopic surgery especially in the presence of hypercarbia so use of halothane should be avoided.
• Isoflurane is the preferred volatile anaesthetic agent in minimal access surgery as it has less arrhythmogenic and myocardial depressant effects.
• Patients should receive adequate airway humidification and protection against unintentional hypothermia because generally the duration of operation is more in laparoscopic surgery.
• Excessive intravenous sedation should be avoided because it diminishes airways reflexes against pulmonary aspiration in the event of regurgitation.
• Monitoring of PET CO2 is mandatory during laparoscopic surgery. The continuous monitoring of PET CO2 allows adjustment of the minute ventilation to maintain normal concentration of carbon dioxide and oxygen.
• Airway pressure monitor is mandatory for anaesthetised patients receiving intermittent positive pressure ventilation.
  
  

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Postoperative complains to be considered by anaesthetist:

At the end of the procedure, antagonism of the residual muscle relaxation should be reversed by appropriate dose of neostigmine. When patient is awake he or she should be extubated and transferred to the recovery room in a semi recumbent position. During the next five hours in the post operative period, analgesia should be achieved. The urine output should be at rate of 100 ml/h and that should continue for 18 hours post operatively. The nursing management included oxygen therapy, early mobilization, incentive spirometry and chest physiotherapy. These should repeated at 2 hour interval. On the morning of the second post operative day the patient should be mobile, pain free, and should start soft diet. She or he should be transferred to the surgical ward and may be discharged home next day if everything is alright.

It is very common to expect some pain after the procedure. Shoulder pain may occur as a result of distension of the abdomen with gas. As the gas absorbs into the blood stream and is exhaled through the lungs the pain will gradually disappear, usually over 24 or 48 hours. Depending on the surgery carried out, there may be some interference in bowel function leading to abdominal distension and colicky discomfort. Tramadol hydrochloride is effective for these types of pain. Vomiting is also common after recovery from anaesthesia. Ondem or vomiset if given half an hour before reversal agent is very helpful in preventing postoperative nausea and vomiting.

All procedures under anaesthesia carry small but inherent risks and patient should understand these before agreeing to undergo the procedure. However, the risks of anaesthesia for elective surgery under modern conditions are very small indeed.

Prof. Dr. R. K. Mishra.