Anaesthesia for gynecological endoscopy
Service de Anesthésie-Réanimation,
HU, Hôpital G. Montpied
63003 CLERMONT-FERRAND CEDEX, France
Anaesthesia for gynecological endoscopy concerns both hysteroscopic and laparoscopic procedures. These two techniques have developed in a similar manner over the past few years, from their beginnings as short and simple diagnostic procedures with little morbidity, to the present situation of true surgical operations.
This surgery requires a natural cavity such as the uterus or the peritoneum to be distended. This can result in significant physiopathological repercussions related to the re-absorption of the gas or liquid used and, at least in the case of laparoscopic surgery, repercussions on the venous return circulation and diaphragmatic kinetics due to increased intra-abdominal pressure.
These repercussions depend on the condition of the patient, which implies pre-operative selection, and also the duration and specific conditions of the operation such as insufflation pressure or the operative position (Trendelenburg, for example). So there is considerable interdependence between the surgical procedure and the anaesthetic management which requires close collaboration between the anesthetist and surgeon.
ANAESTHESIA FOR GYNECOLOGICAL LAPAROSCOPIC SURGERY
Physiologic changes related to pneumoperitoneum
A number of animal studies have been devoted to variations in cardiac output induced by the increase in intraperitoneal pressure [62, 67, 31, 46, 15, 20, 92, 7]. Despite different experimental protocols, the results are consistent (figure 1) with a fall in cardiac output proportional to the intraperitoneal pressure. Only very low intra-abdominal pressures (5 mm Hg) have no effect on cardiac output (92). The drop in right transmural auricular pressure indicates a reduction in the venous return which is demonstrated by a reduction in flow through the vena cava, the degree of which is proportional to the intra-abdominal pressure [7, 31, 46, 92]. Systemic vascular resistance is increased considerably but varies from one protocol to another [20, 31, 46, 67].
In the human, certain studies report slight haemodynamic repercussions due to the pneumoperitoneum [53, 60, 66, 74, 75]. The point in common to all these studies is the use of the Trendelenburg position before insufflation. Other studies [47, 103, 104, 105] where the insufflation is carried out with the patient lying strictly flat on the back give results much closer to the animal studies with a gradual decrease in cardiac output according to the intraperitoneal pressure.
The cardiac output is governed by the myocardial function, the post-loading and by the venous return, the latter in turn depending on venous resistance and mean systemic pressure. With an intra-abdominal pressure of 5 mm Hg, the venous return improves . Under these conditions the intraperitoneal pressure remains lower than the pressure in the vena cava which results in a flushing effect, with no obstructive phenomena in the lower vena cava. When the intraperitoneal pressure rises above the intravascular pressure, a sub-diaphragmatic narrowing of the lower vena cava slows the flow of blood. The abdominal blood volume is reduced due the pressure and a reflux into the venous system of the lower members occurs .
The increase in vascular resistance can be explained by the splanchnic vascular compression , but the persistence of high resistance after exsufflation [47, 104, 111], means a humoral factor could be suggested. During the increase in intraperitoneal pressure a considerable rise in antidiuretic hormone is found [59, 87, 110], and its vasopressive effects are well-known. This secretion would seem to be dependent on the drop in cardiac flow rate . A simultaneous rise in the level of plasma norepinephrine, whose vasoconstrictor effects are equivalent to those of vasopressin, has also been reported . The increase in vascular resistance is correlated with a rise in arterial pressure insofar as inotropism is sufficient [53, 74]. Over and beyond this, the increase in intra-abdominal pressure is accompanied by a decline in left ventricle function [52, 65, 95].
The repercussions of peritoneal insufflation on venous return explain the major role played by volemia in the disturbances caused by increased intra-abdominal pressure [31, 52]. The relative increase in volemia and the filling pressures in the Trendelenburg position are accountable for the slight haemodynamic repercussions observed in those studies where insufflation of the pneumoperitoneum takes place after installation in this position.
- Patients with cardiac pathology must be subjected to a pre-operative assessment taking the particular haemodynamic conditions imposed by laparoscopic surgery into account.
- The increase in systemic vascular resistance and the oxygen requirements of the myocardium could be the origin of poor peri-operative circulatory tolerance in coronary patients. For these patients, the post operative benefits of laparoscopic surgery must be weighed against the per- operative risks. Pre-operative investigation in these patients enables this risk to be evaluated more closely. The cardiac reserve must be assessed, in particular myocardial contractility and the ejection fraction. The data provided by these investigations will also serve to indicate whether or not specific monitoring is necessary.
- Patients presenting with decompensated congestive cardiopathy cannot be allowed the benefits of laparoscopic surgery because the haemodynamic repercussions would be too difficult to manage, even with the help of invasive monitoring techniques.
- The drop in venous return during peritoneal insufflation is one of the factors which demonstrate the drop in cardiac output during laparoscopic surgery. This drop in venous return is all the more important when the volemia is low , indicating that hypovolemia is a contra-indication, at least for as long as their circulating volume has not been restored to normal. This point is particularly important for ruptured ectopic pregnancy or during laparoscopic surgical exploration of abdominal injuries.
Monitoring of a laparoscopic surgical procedure has certain elements in common for all patients. Others are more specific to patients with cardiopathy. Ventilation monitoring is discussed in the section on re-absorption of CO2.
a. Normal monitoring
The stethoscope remains an important instrument enabling both lungs to be re-auscultated after any change in position and after insufflation of the pneumoperitoneum which, because it pushes back the tracheal carina, can deviate intubation to the right . The use of a stethoscope in the precordial position has also been recommended by certain authors in order to detect gas embolism, but requires permanent auscultation .
Electrocardioscopic monitoring during laparoscopy enables arrhythmia, which may occur due to hypercapnia, to be rapidly detected. A sudden appearance of a microvoltage can be the sign of subcutaneous emphysema or pneumomediastinum . Automated analysis of the ST segment has yet to be validated. The changes in axes brought about by changes in position and the pneumoperitoneum make any reference trace unusable, and the use of monopolar coagulation interferes with the trace very considerably.
As in any anaesthesia, oximetry monitoring (SpO2) is essential especially because the dim lighting in the laparoscopic surgery theatre and the wearing of protective glasses if a laser is being used make it difficult to recognise cyanosis. In any case the latter is a late clinical sign of hypoxia. Variations in saturation are not specific during laparoscopic surgery. Desaturation is a late sign of complications such as gas embolism, pneumothorax, selective intubation or a shunt effect due to excessively high intraperitoneal pressure.
During laparoscopic surgery control of intraperitoneal pressure is an integral part of the anaesthesia monitoring. The insufflator must be equipped with automatic controls, even for high flow rates; it must be reliable and subjected to regular checks. Excessive intraperitoneal pressure must trigger an alert and an immediate halt in insufflation . As the majority of insufflators do not cater for a reduction in intraperitoneal pressure, this must be carried out by manual exsufflation via a trocar.
Monitoring of the neuromuscular block is especially important. Stable and deep myoresolution improves the laparoscopic surgeon's view and limits the peritoneal insufflation pressures. In addition the wide range of operating times and the rapidity with which an operation is terminated means it is essential to know exactly what the neuromuscular block situation is at any point in time. When no equipment for reading the muscular activity in the thumb is available due to the position of the upper limbs the simplest stimulation is a train of four on a temporal branch of the facial nerve and observation of the contraction of the orbicular eye muscle.
Intraperitoneal insufflation of dry and unheated gas, possibly accompanied by irrigation with cold liquids results in heat loss during laparoscopic surgery which is at least equal to that with laparotomy . Temperature monitoring associated with measures to combat heat loss are essential when procedures take several hours.
b. Cardiovascular monitoring of high-risk patients
Cardiac frequency and non invasive measurement of arterial pressure do not permit variations in cardiac flow rate nor the filling pressures induced by the pneumoperitoneum to be followed. These parameters can be important for adapting anaesthesia and per-operative intensive care of patients with limited circulatory reserve . The use of invasive monitoring can however make it worth discussing the advantages of laparoscopic surgery for these situations . The post-operative advantages for these patients [18, 24] often justifies this approach.
Measurement via the bloodstream enables arterial pressure to be monitored in real time. In addition the appearance of cyclic variations in time with ventilation is an excellent indication of drops in pre-loading which prompt the intraperitoneal insufflation pressure to be limited, to increase filling or even to accentuate the Trendelenburg position when possible . Installation of an arterial entry point also helps with blood gas measurements.
Measurement of central venous pressure is traditionally used to supervise the filling pressures in the right heart. This becomes difficult during laparoscopic surgery because of the changes in position which require continual changes at cell level, and particularly because of the increase in intrathoracic pressure transmitted from the peritoneal area via the diaphragm . What is really needed is simultaneous measurement of intrathoracic pressure which is obtained by oesophageal pressure, and to deduct this from the measured central venous pressure.
Catheterisation of the right heart using a Swan Ganz probe has been in widespread use for monitoring during laparoscopic surgery [53, 33, 102]. As for central venous pressure, the values measured need to be corrected according to the intrathoracic pressure. An increase in pulmonary arterial pressure is an early sign of gas embolism. Aspiration of the gas bubbles by the proximal orifice placed in the right atrium theoretically helps to minimise the consequences of this. The use of a Swan Ganz probe during laparoscopic cholecystectomy for patients with coronary disease helps adapt the anaesthesia protocol and therapy, for simple measurement of arterial pressure is insufficient in 80% of these cases . Measurement of oxygen levels in mixed venous blood (SvO2), which is possible on certain Swan Ganz catheters, is not essential and interpretation of the variations in these levels is sometimes difficult. Nevertheless in the course of general anaesthesia with controlled ventilation when SaO2, haemoglobin and oxygen consumption are stable, a change in SvO2 is often the sign of a change in cardiac flow rate . The invasive and potentially dangerous nature of catheterisation of the right heart mean its indications can be questioned, especially when surgery is seeking to be less aggressive. So less invasive methods have been proposed.
In this connection several studies have reported the use of cardiac flow rate monitoring by electrical bio-impedance during laparoscopic surgery [34, 69, 111, 117]. The principle is founded on continuous measurement of the blood flow rate in the thorax by analysis of the variations in conductivity relative to an electrical field. Transthoracic electrical bio-impedance brings a certain number of advantages: low risk (non invasive monitoring), easy and simple to use, continuous measurement in real time and not limited in time, and inexpensive. Finally its reliability seems to be satisfactory compared to other methods, provided that the skin is carefully prepared and the electrodes are of good quality and correctly positioned. However its use in standard monitoring is still limited due in large part to the frequent difficulties encountered in interpreting the variations.
Some studies have been made of haemodynamic monitoring during laparoscopy using trans-oesophageal ultrasound cardiography [4, 27, 72]. Whereas the advantages of this technique for monitoring and diagnosis are considerable, the cost remains an important barrier. Interpretation can also be difficult because of the variations in the viewing axis of the heart according to peritoneal pressure and the patient's position.
Measurement of the cardiac flow rate by pulsed Doppler velocimetry can be carried out by either the trans-oesophageal or the supra-sternum route. The basic principle is the same as with any Doppler device with a piezoelectric transducer transmitter and a transducer receiver which receives the return echoes modified by the Doppler effect when they bounce off mobile structures: wall of the heart, vessels or red blood cells. Based on the effective diameter of the aorta which can either be calculated from the cardiac flow rate measured by another method, or estimated from the patients biometric factors, the ejection volume can be deduced and thus the continuous cardiac flow rate. This slightly invasive method which is less expensive that trans-oesophageal ultrasound cardiography should become more widespread in the years to come, but its use during laparoscopic surgery is still being assessed at present [65, 75].
Management of anaesthesia
A certain number of points must be borne in mind by everyone carrying out anaesthesia for laparoscopic surgery:
- The haemodynamic modifications reach their maximum during insufflation of the pneumoperitoneum . So, however long the operation is expected to last, the same precautions must be taken.
- The haemodynamic modifications are directly connected with the degree of intra-abdominal pressure. This must therefore be as low as possible. It is, in fact, logical for the anesthetist to have access to the control of this pressure .
- The haemodynamic modifications are conditioned by the pre-loading. It is possible to improve this by prophylactic filling, but at the cost of volaemic overloading when the patient comes round. Logically the idea would be to have a moderate Trendelenburg position before insufflation of the pneumoperitoneum. In no case should a patient be tilted forwards before the intra-abdominal pressure has stabilised .
- The haemodynamic modifications depend on time. Insufflation of the pneumoperitoneum must take place gradually to enable the circulatory adaptation mechanisms to counteract the effects of the pneumoperitoneum .
- The haemodynamic modifications are more marked when the abdominal cavity is small as in the case of the new-born or small animals [62, 67, 92]. This must be taken into account when carrying out laparoscopy in children.
Repercussion of laparoscopic surgery on respiration
Peritoneal insufflation is usually accompanied by hypercapnia [36, 88]. The reason initially proposed to explain this hypercapnia was that CO2 was reabsorbed from the peritoneal cavity. This explanation was all the more plausible in that it was based on the capacity of CO2 to diffuse, and the exchange capacities of the peritoneal serosa. In fact these mechanisms need to be re-examined in the light of recent publications [14, 28, 61, 76] which reveal a two phase phenomenon, with absorption proportional to intraperitoneal pressure for low insufflation pressures, then a drop in the rate of this re-absorption probably due to the peritoneal circulation being crushed under the effect of the pressure . The variations in PaCO2 observed during the second phase with high intra-abdominal pressures which act against re-absorption essentially depend on a change in the ventilation/perfusion ratio with an increase in the dead space .
The hypercapnia mechanism is different with extra-peritoneal insufflation. In this case the pressure effect limiting re-absorption from the peritoneum no longer applies. The increase in pressure increases the diffusion space by dilaceration of the tissues, and thus the CO2 re-absorption surface. Re-absorption is thus directly proportional to the pressure and volume of CO2 insufflated . Severe hypercapnia is thus possible, if not to say frequent, in these situations [43, 84]. On the other hand, provided the hypercapnia is controlled, the circulatory repercussions of extra-peritoneal insufflation are lower than those of intraperitoneal insufflation . The same is not true of acute hypercapnia, the sudden onset of which does not allow the physiological compensation mechanisms to come into play and which is thus accompanied by severe acidosis [30, 84]. This can be at the origin of noxious haemodynamic effects.
Quite apart from accidental leakage into the subcutaneous tissues connected with poor positioning of a trocar sleeve (2.7% of cases of severe hypercapnia in a series of cholecystectomies published by Wieden ), CO2 is seen to spread outside the abdominal cavity during laparoscopic assisted hysterectomy, with or without lymphadenectomy, and during bladder neck suspensions. In laparoscopic gynecological surgery, because this effusion originates in the pelvis it mostly affects the sides and loins and generally remains hidden by the drapes until the end of the operation . Only the very abundant, rare forms can be diagnosed by the anesthetist during the operation, when they shift towards to the upper part of the thorax. In this case the capnographic signs (slow and regular increase in CO2 expired) will provide an alert during the anaesthesia .
Consequences for selection of patients
The variations in ventilation mechanics and especially the intra- thoracic pressures induced by the increase in intra-abdominal pressure can be limiting factors for laparoscopic surgery in certain patients. Insufflation of the pneumoperitoneum is accompanied by a decrease of some 30% in pulmonary compliance . The resistance of the air passages increases in the same proportions . The resulting increase in pressure in the air passages can have adverse consequences for patients with bubbles of emphysema . These patients and all those who suffer from dystrophy of the pulmonary parenchyma will find it difficult to cope with the often considerable hyperventilation required by hypercapnia, with volumes per minute sometimes reaching 2 or 3 times those used before the extra-peritoneal insufflation of CO2.
The CO2 end tidal pressure (PetCO2) provides evidence of production of carbon dioxide by the cellular metabolism, absorbed through the peritoneal cavity and pulmonary exchanges. A rapid increase in PetCO2 is a complication:
- a rapid rise of a few millimetres of mercury returning a few minutes later to the base figures can the sign of minimal CO2 gas embolism [22, 109].
- a more gradual and persistent rise is often the sign of extra-peritoneal diffusion of CO2 (pre-peritoneal, subcutaneous, retro-peritoneal, mediastinal etc.) [6, 76, 116]. This increase in expired CO2 continues after exsufflation of the pneumoperitoneum, indeed often several hours after the laparoscopic procedure, justifying a follow-up of hypercapnia in the recovery room.
- the CO2 is transported by the circulatory system from the peripheral areas towards the lungs. Any disturbance in the circulation will reduce the CO2 expired . A rapid drop in PetCO2 may be the sign of a drop in cardiac flow rate or a decreased venous return, but also pulmonary arterial obliteration. This is what happens in massive gas embolism which shows up as a drop in PetCO2 proportional in size and duration to the volume of the CO2 embolus .
Classically the PetCO2 values are 2 to 6 mm Hg lower than that of PaCO2. During anaesthesia with artificial ventilation, the ventilation/perfusion ratio of often greater than 1, so a PaCO2-PetCO2 gradient of 10 to 15 mm Hg must be expected [37, 89, 91, 120]. However, during laparoscopic surgery the change in the arterial CO2-ETCO2 gradient is very variable. Some authors find an increase [19, 70], others no gradient at all [25, 50, 79, 88], and yet others a negative gradient [17, 101], explained by the rapid changes in ventilation/perfusion ratios with a massive shunt effect, whereas perfused alveoli are better ventilated.
Changes in position such as the Trendelenburg or the lateral reclined position can modify the value of the PetCO2 [83, 99]. Furthermore Wittgen et al. have shown that in cases of cardio-vascular disease, the correlation between PetCO2 and PaCO2 was less good when compared with patients with no such pathology , and the same is true with obese patients . A recent study confirms that in patients with respiratory impairment the increases in PaCO2 are under-estimated by PetCO2 . So for these patients with respiratory or heart pathology, it is particularly useful to duplicate the PetCO2 measurement by arterial gasometry at the beginning of the operation and every time there is an important variation in PetCO2.
In view of this uncertainty, trans-cutaneous CO2 monitoring would give a better idea of PaCO2 , but this also raises a certain number of technical problems (heating of electrodes, difficulties with measurements in adults etc.).
Day case surgery
Day case surgery can be carried out under local anaesthetic, loco-regional block or under general anaesthesia.
Concerning this subject, it would be quite feasible to repeat the text of the "Practical manual of laparoscopy " by Gordon and Taylor. However a rather more differentiated attitude is necessary concerning the sedation associated with the local anaesthetic which can encourage hypercapnia because of the respiratory depression it induces.
Deeb et al  have successfully used the technique of peritoneal irrigation with 100 ml 0.5% lidocain associated with heavy sedation for laparoscopy for tubal ligation. These techniques are indeed possible but do require very quick and expert surgical technique and also a certain degree of co-operation from the patient.
Loco-regional anaesthesia enables loss of consciousness and tracheal intubation to be avoided. Its use remains reserved for certain very particular and exceptional situations
- where general anaesthesia is not recommended:
- when general anaesthesia is refused,
- when intubation is expected to be difficult,
- known and documented allergy to certain products used for general anaesthesia (especially curare),
- when the vocal cords need to be protected (singers etc.),
- in exceptional cases where the surgeon wishes to have per operative verbal contact to keep the patient informed of surgical findings and maybe make a difficult decision immediately with the patient's consent.
In all these cases a preliminary consultation concerning anaesthesia is essential to explain the particular points about the loco-regional technique, the need for good co-operation during the operation, and the possibility of general anaesthesia if the peri-medullar block is insufficient.
Apart from the risk of failure and the potential toxicity of local anaesthetics, which are common to all epidural anaesthesia, the use of this technique for laparoscopic surgery poses specific problems:
- A sensory level between T4 and S5 is usually necessary to obtain good quality anaesthesia during laparoscopy. Bowel pain connected with the peritoneal irritation has indeed been described during Caesarean sections carried out under loco-regional anaesthesia . So a high level of sensitivity really reaching T4 is required in the case of pneumoperitoneum.
- The association of a broad sympathetic T4-S5 block, the pneumoperitoneum (which can compress the lower vena cava whenever there is 10 mm Hg insufflation pressure or more), and a position with the patient tilted forward results in a drop in the venous return which in turn provokes a drop in the cardiac output.
- Loco-regional anaesthesia for laparoscopy is theoretically associated with several modifications in respiration. The T4-S5 sensory block is accompanied by a certain degree of paralysis of the intercostal muscles. In addition the pneumoperitoneum using CO2, associated with the per-operative position of the patient results in the diaphragm being pushed back. All these changes, including the sedation which is often necessary, results in hypercapnia with a theoretical risk of hypoxia. Systematic administration of oxygen with spontaneous ventilation is therefore strongly recommended. However it must be recognised, with Ciofolo and colleagues, that there are less problems in reality than in theory, at least when loco-regional anaesthesia is used in young women with no past history of respiratory problems . Under these conditions respiratory tolerance is good and the changes in respiratory parameters only slight or moderate.
- The final point concerning loco-regional anaesthesia for laparoscopy is the possibility of reconciling, from the anaesthetist's point of view, the constraints of practising these delicate techniques which require a considerable time for installation, then close monitoring and frequent contact with the patient, and the fast and repetitive rotation of laparoscopic procedures in the theatre, given that these operations take relatively little time: 30-90 minutes on average. This organisational aspect is, in Sarma's opinion  the major drawback for the use of epidural anaesthesia under day surgery conditions.
Various anaesthetic techniques have been proposed for outpatient laparoscopic surgery . Their very number is eloquent: that there is at present no consensus concerning the anaesthesia technique to use for outpatient laparoscopic surgery. At the very most a few common-sense remarks can be made, recommending products with suitable kinetics and being wary of the possibility of bradycardia associated with the use of propofol in patients who have not usually received any pre-medication [32, 39, 40].
Intubation is the reason for many cases of sore throat during the postoperative period. It may be a relatively minor discomfort, but is more difficult to accept when the surgery itself results in little persistent pain. In the case of very short laparoscopies, ventilation with a face mask may be used . This opinion is far from being shared by everyone, if only for the risk of regurgitation due to the Trendelenburg position and raised intra-abdominal pressure (11). The same reserves are applicable to the laryngeal mask airway recently proposed for outpatient laparoscopies with spontaneous ventilation .
The pneumoperitoneum must be evacuated as completely as possible and this is particularly important for the control of post operative pain. In order to obtain correct exsufflation the supra pubic trocar sheath must be kept under direct visual control to maintain it just level with the peritoneum, with the patient in a slight Trendelenburg tilt, while gently pressing down on the abdomen. Installation of a drain for a few hours has also been suggested . Instillation of liquid into the abdominal cavity at the end of the laparoscopic operation has also proved to be an efficient technique .
When exsufflation is carried out correctly it is often possible to do without morphine-like substances which are not easy to manage for outpatients, and the risk of nausea and vomiting involved with these drugs must also be borne in mind.
Lengthy laparoscopic procedures
Laparoscopic procedures, lasting more than 4 hours, are no longer exceptional in gynecological surgery. The management of these patients needs to take certain specific constraints into consideration.
There is nothing particular to say about the pre-operative work-up for lengthy laparoscopic procedures. However they do require special precautions when installing the patient and especial care must be taken to avoid any risk of brachial plexus compression This complication which is rarely seen now, used to occur when the shoulder rests were not properly adjusted relative to the soft parts of the neck. Nevertheless elongation of the plexus remains possible due to forced abduction of an upper limb. This might happen if a poorly tightened arm-rest gradually slips downwards when the patient is in the Trendelenburg position. The increase in the number of surgeons (and onlookers) during certain delicate or spectacular operations can also result in a limb slipping upwards if it is not correctly fixed alongside the body. When the lower limbs are installed in leg sheaths or are fixed too tightly with straps, nerves can be compressed . Considerable loss in body heat due to insufflation of cold gas and copious peritoneal irrigation  justify the installation of a heated mattress. Venous stasis combined with the increase in intra-abdominal pressure means there is a significant risk of thrombo-embolism. So, even if the patient is encouraged to get up and walk soon after the operation, prophylactic heparin should be given in the same way as for operations via laparotomy.
The anaesthetic technique must be adapted to the constraints of long laparoscopic operations:
- The halogen anaesthetics and especially isoflurane have vasodilator properties which enable the increase in vascular resistance which accompany peritoneal insufflation to be controlled . This effect can be potentiated by calcium antagonists such as nicardipine . The use of halogen substances must however be reconsidered when the operation is to take place in the Trendelenburg position: changes in cerebral vaso-regulation must be avoided in a patient who is going to lie with her head low down for several hours .
- If per-operative ventilation is not used with a closed circuit, a heater-humidifier must be available on the respirator to avoid heat loss.
- Correct myoresolution makes it possible to reduce the increase in intra-abdominal pressure and its consequences on haemodynamics and ventilation. There is nothing specific to say about the use of central analgesics during the per-operative period compared with an equivalent procedure via laparotomy.
At the end of the procedure systemic vascular resistance remains high, even when intraperitoneal pressure has returned to normal [103, 111]. From the circulation point of view, this results in an increase in venous return and thus cardiac inotropism, whereas the after-load remains high. An increase in arterial pressure is thus not unusual at this stage. However, the acid embolus theory, although interesting, has not been clearly established. This would mean that when exsufflation occurs, blood blocked in the lower limbs by the abdominal hyper-pressure is liberated into the systemic circulation. In spite of all the precautions taken patients often suffer from hypothermia at the end of a lengthy laparoscopic procedure. This is due at least in part to the reduction in pressure effect of the gases insufflated . The hypothermia means an increase in myocardial effort when the patient comes round because muscular shivering uses a lot of oxygen. For all these reasons, after a long laparoscopic procedure the moment when exsufflation takes place and the period immediately after are often a time of haemodynamic instability. It is not advisable to cap this with circulatory constraints due to recovery from the anaesthetic. Recovery should thus be calm and progressive, continuing to control all the parameters. Extubation should not take place too early. Mechanical ventilation should continue in the recovery room for about 30 minutes. Extubation will then take place in a patient who is awake, recovered from the neuromuscular block, in a stable haemodynamic, ventilatory and thermal condition . Administration of high concentrations of oxygen using the high flow mask and monitoring of the various levels is then initiated.
Extra peritoneal laparoscopic surgery
Certain procedures such as Burch vaginal suspensions or pelvic lymphadenectomies mean that the operating field is extended to include the pre-peritoneal or retro-peritoneal space.
Extra-peritoneal insufflation of CO2 is usually accompanied by hypercapnia, due to the rise in pressure which increases the diffusion space and the surface through which CO2 is reabsorbed. So re-absorption is directly proportional to the pressure and volume of CO2 insufflated  Severe hypercapnia is therefore possible and may indeed be frequent in these situations . Because it occurs suddenly, the physiological compensation mechanisms do not have time to come into play, and the hypercapnia is therefore accompanied by severe acidosis , which is what make this complication so important and requires a certain number of steps to be taken :
- Auscultation of the patient to eliminate selective intubation, or a pneumothorax.
- Hyperventilation to correct the hypercapnia
- Reduction of insufflation pressure. Good myoresolution usually enable this problem to be solved without reducing the surgeon's visibility . If surgical exposure is insufficient, the use of an abdominal wall suspension device must be considered .
- Conversion to laparotomy if, despite all these steps, the patient's capnia cannot be kept at acceptable levels (in practice, below 50 mm Hg).
Laparoscopic surgery and neoplastic pathology
Laparoscopic surgery has not yet proved to be satisfactory from the oncological point of view for the excision of neoplasms [12, 63]. However the technique has a special place in the follow-up assessment of ovarian cancer which has previously been the subject of surgery, radiation therapy or chemotherapy . These a second-look laparoscopy is not restricted to simple inspection of the peritoneal cavity because adhesiolysis and multiple biopsies are often needed and suspicious areas may require identification using clips. The pre-, per- and postoperative management of these patients gives rise to a certain number of specific problems.
In the case of follow-up laparoscopy, generally speaking the spread of the neoplasm is simply assessed without there being any necessity to complete the procedure by a search for lung, liver or lymph node metastasis. The chemotherapy regimen used for these neoplasms often includes cis-platinum with cyclophosphamide. These two products are both toxic for the heart (myocarditis, conduction and rhythm problems), so it is necessary to carry out an electrocardiogram and echocardiography during the pre-operative work-up. Cyclophosphamide can cause lung problems which means that a functional respiratory investigation should be carried out. Investigation of liver and kidney function should also be requested in the case of treatment using cis-platinum. An empty bowel will make exposure and the surgeon's procedures easier. This is obtained using a bowel preparation based on senna extracts (X-prepù) or polyethylene glycol. These products must not be used when the small intestine has been subjected to radiation. In other patients the drastic effects of these preparations are often accompanied by hypovolemia which needs to be compensated for immediately the patient arrives in theatre. These patients have scanty and precious venous reserves. Prior to the operation the possibility of a peripheral approach should be checked. If this is going to be difficult, then plans should be made to install a central catheter from the outset, either under local anaesthesia or after induction by inhalation, depending on what the patient prefers.
The per-operative phase brings with it the problem of vascular loading : certain chemotherapy products (bleomycin, cyclophosphamide) result in pulmonary pathology which can be aggravated by excess vascular loading with crystalloids and by ventilation with high concentrations of oxygen [23, 41, 107] Although oxygen has not been found to have a toxic effect by all authors , it is best to be prudent. Other anti-tumoural agents used for chemotherapy for ovarian cancers such as cis-platinum can have adverse effects on liver function, thus contra-indicating in principle the use of high doses of halogen agents such as halothane.
In the postoperative period, control of nausea and vomiting is particularly important for these patients who dread them all the more when they have already suffered the side effects of chemotherapy. Various techniques have been proposed to prevent and treat this nausea and vomiting including, for example, trans-dermal scopolamine which almost halves the severity of these symptoms. It is however accompanied by a certain number of side effects (dry mouth, discomfort for the eyes) which should be taken into account . Dropideridol is efficient  but does have side effects on vigilance . Ephedrine (0.5 mcg/kg IM) is often very efficient and has no disagreeable side effects . The use of propofol as an anti emetic has also been proposed . The same applies to the anti 5HT3 substances which are efficient both when used as a cure  and for prevention . Their high cost should be set against their efficacy and absence of side effects . The menstrual period considerably increases the risk of nausea and vomiting . There is nothing very specific to say about postoperative analgesia except for patients under treatment with opiates for chronic pain due to the development of the neoplasm. In these cases the morphine-like substances must be relayed parenterally until bowel function returns to normal, and the doses adapted to cover the pain due to the operation as well.
Gas embolism is an unfamiliar subject to many due to its low incidence, estimated at between 0 and 0.6% of laparoscopic surgical procedures depending on the publications. In fact it is likely that the primitive forms which give rise to non specific neurological problems or a simple delay in coming round, are far more frequent. They can also be mistaken for the various other haempamic complications of laparoscopic surgery such as acute obstacles to venous return or cardiac arrhythmia, not forgetting the delayed forms which occur at the end of the operation when exsufflation of the pneumoperitoneum releases bubbles of CO2 trapped in the mesenteric or portal circulation .
The entry point is most often in a large vein (iliac vein, inferior vena cava) punctured during insertion of the Veress' needle at the beginning of insufflation. Another entry point is the peri-umbilical venous plexus. Per- operative vascular injuries only lead to gas embolism if the pneumoperitoneum pressure is very close to venous pressure. If it is greater, as is most often the case in laparoscopic surgery, the vessels collapse stopping any entry of gas. In the rare situations where the venous pressure is greater than the pneumoperitoneum pressure, the vascular opening results in haemorrhage and not in entry of gas.
Pollution of the intra-abdominal CO2 by nitrous oxide from the anaesthetic circuit or by carbon monoxide from the diathermy probe worsens the repercussions of gas embolism because these gases are less soluble than CO2. Similarly the permeability of the foramen ovale in 30% of young subjects accounts for the high frequency of systemic embolus and neurological complications. In the same way the lower solubility of nitrous oxide and air explain that these two gases are far more dangerous than CO2 in case of gas embolism
The volume of the gas embolus is the main factor governing the clinical symptoms. Only small flow rate emboli (less than 0.3 ml/kg/min in the dog) are accompanied by an increase in the PETCO2 which shows the elimination of intravascular CO2 via the pulmonary route. When the volume of the gas embolus increases, the PETCO2 drops due to the decrease in exchanges at the pulmonary capillary bed and/or by circulatory arrest.
What to do
Prophylactic measures are essential and must be applied systematically. These include not only the aspiration tests carried out when the Veress' needle is inserted, but also the use of open laparoscopy when a problem with insufflation can be expected (multiple abdominal operations). Generally speaking it is important to limit the insufflation flow rate to one litre per minute for as long as the procedure remains blind. The use of oesophageal or precordial Doppler, or failing this a simple stethoscope is useful for early detection of gas embolism in high risk situations. In view of the pressures used specifically for laparoscopic surgery (cf. fig. 1) there is no indication for the use of anti-G suit or positive end expiratory pressure (PEP), unlike with anesthesia for neurosurgery.
What needs to be done in the presence of a gas embolism largely depends on the volume and thus the systemic effects (fig. 1). Whereas certain gestures must be systematic in the presence of massive gas embolism, installation of a central catheter in the right atrium to aspirate the CO2 bubbles wastes time better spent on other symptomatic revival procedures and is of limited benefit, because only low volumes of gas are usually collected under these conditions.
The other treatments which follow the initial resuscitation are more debatable. Neuro-protection using barbiturates or hyperthermia is not always beneficial, makes neurological monitoring more complicated and risks inducting noxious haemodynamic repercussions. The same is true for hyperbaric oxygen therapy, which is less useful than in cases of air embolism because CO2 is more soluble and there is a high pressure gradient between the blood and CO2 bubbles (over 600 mm Hg) which encourages re-absorption. Use of this technique is only justified if the chamber is available within a short space of time and if it is possible to continue reviving the patient during the oxygen therapy session.
A sudden drop in arterial pressure may occur during any of the various phases of laparoscopic surgery, indicating various aetiologies:
- The first possibility of gas embolism is at the beginning of the procedure by direct insufflation of CO2 into a vein during insufflation of the pneumoperitoneum (c.f. supra). The second possible aetiology is injury to a major vessel by the Veress' needle or a trocar. These injuries are often obvious but may also go undiagnosed immediately due to the retro-peritoneal situation of the major vessels. A third cause of collapse at the time of insufflation is preoperative hypovolemia which magnifies the repercussions of the pneumoperitoneum on venous return .
- During laparoscopic surgery, apart from gas embolism, cardiovascular collapse may result from faulty surgical haemostasis. This may be particularly difficult to achieve, especially in case of injury to the major vessels because not all the vascular surgery instruments have yet been adapted for laparoscopic surgery. Sudden heart failure in a patient with coronary disease, for example, may also be a reason for this hypo-tension. This situation is becoming more common as laparoscopic surgery progresses to include older patients with past history of circulatory problems .
- At the end of the operation, the two main causes of cardiovascular collapse are vascular injury which has been overlooked and delayed gas embolism.
This is an unexceptional complication which has two very different aetiologies. There may be passage of CO2 through the pleura from the abdominal cavity. This effusion takes place gradually during the laparoscopy, is not usually suffocating and, in the moderately abundant forms, resorbs spontaneously. The usual explanation given to explain the mechanism of this complication is an anatomical malformation connecting the pleura and the peritoneal cavity . However, attempts to obtain hard evidence concerning this malformation once a pneumothorax occurring during laparoscopy has abated seem so far to have been in vain . There is another objection to this hypothesis also in that the intra-thoracic pressure in patients under controlled ventilation during laparoscopy is higher than the intraperitoneal pressure each time the respirator insufflates. It is thus difficult to see how CO2 could accumulate in the pleural cavity, even if there is an anatomical malformation.
Pneumothorax due to high pressure trauma is quite different. Abdominal insufflation is accompanied by an increase in intrathoracic pressures which can have detrimental effects in patients with bubbles of emphysema or a past history of recurring pneumothorax. In these cases the pneumothorax can be suffocating and must be drained immediately (fig 3).
ANAESTHESIA FOR HYSTEROSCOPY
Whereas diagnostic hysteroscopy can take place under simple sedation, or with a para-cervical block in the gynaecologist's consulting rooms, anaesthetic management is necessary when a surgical procedure is to be carried out by the endo-uterine route. This should be adapted to the patient's preoperative condition and how the procedure is to be carried out, this often being on a day surgery basis. General anesthesia or loco-regional anaesthesia may be used. The anesthetist taking charge of these patients must also bear potential complications in mind, such as vascular overloading or glycine intoxication connected with re-absorption of the liquid used to distend and irrigate the uterine cavity.
Installation and Monitoring
Care must be taken when installing the patients that the external popliteal sciatic nerve is not compressed in the leg restraints.
Monitoring includes non invasive measurement of arterial pressure, ECG, pulse oxymetry and capnography. Given the considerable heat loss which can occur with copious irrigation, temperature monitoring is also useful. When loco-regional anaesthesia is used, regular supervision of the patient's state of consciousness is also required.
Monitoring of the input and output of irrigation liquid is indispensable. If a deficit of 500 ml between input and output of irrigation liquid is noted, blood investigation for electrolyte levels is indicated. If this deficit reaches 1,000 ml, 20 mg fusemide should be administered intravenously and plasma electrolytes checked at the same time. If the deficit reaches 2,000 ml, the procedure must be interrupted immediately. Similarly the anesthetist must pay careful attention to intra uterine pressure and check that this never exceeds 70 mm Hg.
From the technical point of view, general anesthesia for hysteroscopy presents no specific problems. The choice of drugs will depend on the patient's preoperative condition, the expected duration of the procedure and whether it is on a day surgery basis or not. For a short procedure ventilation can be provided by a face or by a laryngeal mask. For lengthy procedures or those which require an accentuated Trendelenburg position, tracheal intubation and controlled ventilation are indicated. The same applies to obese patients and those presenting hiatus hernia.
General anesthesia has often been accused of causing early signs of massive re-absorption of irrigation liquids to disappear (variations in levels of consciousness). On the other hand this technique does not require much vascular filling, unlike loco-regional anaesthesia. It thus results in less overloading for these patients who are already exposed to the risk of re-absorption of irrigation liquid.
In order to ensure complete anaesthesia during hysteroscopy, a block of the sensory levels from T8 to S5 is required. This can be achieved using epidural anesthesia or spinal anaesthesia.
The use of conical tipped needles (Witacre type, for example) limits the incidence of headache due to puncture of the dura mater during spinal anesthesia. Reducing the gauge of the needles has the same effect. The choice of local anaesthetic drug (5% lidocaine or 0.5% bupivicaine) depends on how long the surgical procedure is expected to last.
Rapid installation of the sensory block enables surgery to commence quickly. The sympathetic nervous system block which takes place just as quickly sometimes poses problems with respect to circulatory tolerance with sudden onset vaso-paralysis. This is particularly true in older patients with doubtful circulatory conditions or in women presenting with preoperative hypovolemia. It is possible to ward off the effects of this vaso-paralysis by prophylactic vascular filling (for example 1,000 ml crystalloids) and/or by using a vasoconstrictor agent such as ephedrine (30 mg in 250 ml 5 % glucose solution, with the flow rate adapted to the patient's blood pressure.
The main advantage of epidural anesthesia as compared with spinal anesthesia is the installation of a catheter which enables local anaesthetics to be re-injected if the surgical procedure is prolonged. The fact that the dura mater is not punctured also reduces the risk of post operative headache. Finally, the epidural catheter can be left in place at the end of the operation in order to manage postoperative analgesia.
In fact, a hysteroscopic surgical procedure rarely lasts longer than the duration of the effects of a local anaesthetic injected during spinal anesthesia and the postoperative pain is usually easy to manage with non morphine-type analgesics administered systemically. So it is rarely justified to install an epidural catheter. Similarly, the argument of post-spinal anesthesia headache has lost in importance since the arrival of the new conical tipped needles (see above). All this considerably limits the indications for epidural anesthesia for hysteroscopy, and all the more so in that this anaesthetic technique is longer and more complex than spinal anesthesia to use, and is thus difficult to reconcile with the quick rotation of patients in a day surgery program.
Although still perhaps acceptable for diagnostic hysteroscopy, the use of CO2 to distend the uterine cavity is no longer considered for endo-uterine surgery. The various solutions used for this surgery can induce non specific complications linked with re-absorption of the liquid. Some of them and more particularly glycine can be the origin of specific manifestations.
Non specific complications
Endo-uterine surgery results in re-absorption of liquids by the broaching of endometrial or myometrial vessels, by a mechanism close to that described for prostate surgery [73, 80, 81]. It would seem logical to carry out hystero-resection at the beginning of the cycle in order to limit re-absorption when the vessels are broached. This absorption can also take place via the peritoneal cavity when the solution injected into the uterus flows out through the tubes .
Supervision of the patient's weight before and after the hysteroscopy together with follow-up of input and output enable this re-absorption to be monitored (see above). Monitoring of intra uterine pressure and limiting it to 700 mm Hg is also essential. Massive re-absorption of dextran or glycine results in a drop in natremia, made evident by postoperative plasma electrolyte studies.
The clinical symptoms of massive re-absorption are associated with oedema of the face, increase in diuresis and problems with consciousness after the patient has come round from the anaesthetic which can go as far as coma. Acute pulmonary oedema can also complicate the situation. In this case the central venous pressure will be high. Symptomatic treatment of acute circulatory failure associating diuretics, inotropic support, oxygen and possibly controlled ventilation must be initiated.
Acute intoxication with glycine is well documented during prostatic resection (TURP syndrome) and is seen after large quantities of glycine have been reabsorbed. The toxicity is of dual nature:
- intracellular hyper-hydration and hypo-natremia occurring when a hypo-osmolar and hypo-tonic liquid, i.e. 1.5 % glycine, penetrates the internal environment. This hyper-hydration explains the majority of the circulatory signs seen ;
- the neurological symptoms would appear to be directly linked with neurological toxicity of glycine or one of its metabolites for the central nervous system . This amino acid which crosses the haemato-encephalic barrier is also an inhibiting neurotransmitter at central level.
The clinical manifestations are neurological to begin with: problems with consciousness which range from simple confusion syndrome with agitation to coma. Signs are sometimes localised such as a focal convulsive attack, or visual symptoms such as a drop in visual acuity or even temporary blindness . The cardiovascular symptoms range from bradycardia to collapse with a broadening of the QRS complexes and modifications to the ST segment.
If these complications are to be prevented, the intra-uterine pressure and volume of fluid injected must be respected (see above). Treatment of the circulatory problems is the same as that for acute heart failure. The neurological signs can require intubation with controlled ventilation, combined with specific treatment for the epileptic manifestations.
Gynecological surgery, which saw the birth of laparoscopy, is still today, as in the past, a field of tremendous changes where indications and new techniques continue to appear and develop. As anaesthetists, we are called upon to accompany these changes whilst preserving the safety and well-being of the patients entrusted to us.
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