Ethanol monitoring of irrigating fluid absorption

Aims of the monitoring Ethanol monitoring is a non-invasive method for indicating and quantifying absorption of irrigating fluid by patients undergoing endoscopic procedures. If a tracer amount of ethanol is added to the irrigating fluid, the volume of fluid absorbed can be estimated from the amount of ethanol measued in the patients' exhaled breath. The aim of this monitoring is to enhance patient safety by allowing decisions made by the operating team to be based on accurate and updated information about intra-operative absorption events. The decisions might include the following: Further absorption can be stopped - The operation may be halted or its course modified before enough fluid is absorbed to evoke overt symptoms. Early treatment can be started - The anaesthetist can begin treatment of cardiovascular fluid overload and hyponatraemia at the earliest possible opportunity. Optimal post-operative care can be decided - The most suitable level of care for the immediate post-operative period may be chosen (surgical ward, post-operative care unit or ICU). Fluid absorption Composition of irrigating fluids The purpose of using an irrigating fluid during endoscopic procedures is to give the surgeon a clear view of the operating field by removing blood and pieces of resected tissue. The solutions must be electrolyte-free to allow cutting with a resectoscope but, because of the inherent danger that they may be absorbed into the patient through the operating field or via instrumental perforations, a solute of some kind must be added to reduce their hypo-osmolality and prevent haemolysis in the event that absorption does occur. Glycine 1.5% in sterile water is the most widely used solution for this purpose. Alternative irrigating fluids contain mannitol or sorbitol. Whatever solute is chosen to normalize their osmolality, the solutions are nevertheless grossly unphysiological, and their absorption can have serious consequences. Incidence Fluid absorption can occur in all operations where irrigating solutions are being used. However, the phenomenon is most frequently associated with transurethral resection of the prostate (TURP) and transcervical resection of the endometrium (TCRE). Several sensitive methods show that there is an uptake of small amounts of fluid during almost every one of these surgical procedures [1-4]. The median absorption during TURP is 300 mL and it exceeds 1000 mL in 8% of operations [1,5]. Absorption during TCRE is usually around 450 mL [3,6] and large-scale absorption may be even more common than during TURP. Symptoms Massive absorption of irrigating fluid gives rise to the so-called transurethral resection syndrome (TUR syndrome), which is well known from a large number of case reports. This rare but much feared complication consists of disturbances of the circulatory and central nervous systems [8]. Prospective studies have produced a wide range of estimates of the incidence of TUR syndrome (0% [9], 1% [10], 2% [11], 7% [12,13] and 10% [14,15]). The divergence of the estimates is attributable partly to poor definition of diagnostic criteria and partly to varying degrees of awareness of mild forms of the syndrome. Some urologists and anaesthetists claim they have not seen this complication in years of clinical practice, although many mild cases have probably been misinterpreted and attributed wrongly to old age, medication and excessive blood loss. Prospective symptom-oriented studies are the best way to show the association between absorption of moderate volumes of irrigant and peri- and post-operative morbidity. A disproportionate number of patients who exhibit transient deterioration of mental status after TURP show evidence of absorption [16]. Another recent report shows that nausea, vomiting, confusion and arterial hypotension occur significantly more often when between 1000 and 2000 mL of glycine solution is absorbed than when no absorption has been detected. Patients in this absorption range have a 7-fold higher risk of developing symptoms of the TUR syndrome during the early post-operative period [17]. It is generally agreed that a marked aggravation of the severity of symptoms occurs when more than 3000 mL are taken up (Fig. 1). In this absorption range, the risk of developing neurological symptoms is nearly 100 times higher than in operations without absorption [17].Fig. 1: The average number of symptoms from the circulatory (left) and neurological (right) systems alone (open circles) and after considering a severity score (closed circles) in patients undergoing TURP characterized by absorption of glycine solution. Points are placed in the middle of each analysed volume range. Data from reference 17, used with permission.Traditional methods of measuring absorption Uptake of irrigating fluid is generally more commonly known in bloody and extended operations [5], but this does not help in predicting the likelihood, timecourse or amount of absorption in any individual patient. This is why fluid absorption needs to be measured routinely in any endoscopic surgery that uses irrigating fluids. In most hospitals, the absorption of irrigating fluid is assessed at the end of the operation. In this way, symptoms can be explained more confidently and the post-operative fluid therapy can be planned more efficiently. Measurement of the serum sodium concentration is a very common but invasive way to obtain this information. Alternative approaches include volumetric and gravimetric methods. The volumetric approach measures the difference between the volume of irrigating fluid used and the volume recovered, with a correction for blood loss [1]. The gravimetric methods involves weighing patients on the operating table or in their beds. A more ambitious approach is to assess the fluid absorption repeatedly during surgery. On-going monitoring makes it possible to institute early treatment of vascular overload and to stop the operation before enough fluid is absorbed to result in TUR syndrome. The surgeon can sometimes see that fluid is passing into open veins, but subjective judgment is rarely accurate enough [13]. Most of the traditional methods are unnecessarily complicated and cumbersome for use in everyday clinical practice. Each has a number of shortcomings, so much so that their usefulness in routine surgery has been seriously questioned [13]. Ethanol monitoring, however, seems to overcome most of the difficulties involved in the use of the older methods (Table 1). As the bladder is impermeable to ethanol [18], any ethanol added to the irrigating fuild enters the body in direct proportion to the volume of irrigant absorbed [19-22].Table 1: Clinical methods of measuring fluid absorption. Plus signs imply advantages and minus signs disadvantages Practical aspects Choice of irrigating fluid A prerequiste for carrying out ethanol monitoring is that an ethanol-containing irrigating solution is used. Glycine 1.5% with ethanol 1% (Baxter Healthcare Ltd, UK) is available throughout Scandinavia and the UK. The regulatory authorities in the other EU countries (except France and the Netherlands) have also approved this irrigating fluid for use during TURP. In addition, mannitol 3% with ethanol 1% is marketed in Sweden and a sorbitol-mannitol-ethanol solution has recently been introduced by another pharmaceutical company (B. Braun, Melsungen, Germany). Breathalyser It is also necessary to have a breathalyser for measuring the ethanol concentration in the patients' exhaled breath. Several pocket-sized devices of good quality are available at a cost of £500 or less. The one used in most studies of the ethanol monitoring method is Alcolmeter S-D2 (Lions Laboratories Ltd, South Glamorgan, Wales), which has proved to be very reliable. However, one must be careful to press the sampling button for long enough and to avoid placing the Alcolmeter adjacent to equipment that has just been cleaned with alcohol. The calibration should be checked once a week, although recalibration is rarely necessary provided that the battery is fresh and servicing is carried out every year. Breath sampling in awake patients The awake patient is asked to breathe into the breathalyser every 10 min throughout the surgical procedure. If ethanol is detected, new samples should be taken at 5-min intervals. When irrigation is performed intermittently, the breath test is best performed when the bladder has just been evacuated. One should have the patient carry out a comfortable and moderate exhalation into the device. Forceful exhalation may be tiring and disturb the operation, and does not markedly improve the accuracy of the monitoring. An average of 96% of the maximal end-expiratory ethanol concentration is indicated if the patient exhales 70% of the forced vital capacity, and as much as 80% of it will be indicated if the patient exhales only 20% of the forced vital capacity [23]. Breath sampling during general anaesthesia Ethanol monitoring may be performed in unconscious (anaesthetised) patients [24,25]. The edge of the Alcolmeter may be tightly fitted into a hole drilled in a T-piece adapter from Capnomac equipment and the meter itself can be rested on a folded piece of cloth on the patient's forehead. Measuring should be carried out during the last part of expiration. Low-flow breathing systems may be used, but the breathalyser should be placed in the circuit directly next to the connection with the endotracheal tube because moisture exchangers and soda lime absorb ethanol. Some breathalysers interact with inhaled anaesthetics such as halothane, enflurane and isoflurane. This is not the case with the Alcolmeter S-D2, which is an electrochemical (fuel-cell) type of device. However, values obtained by thermocatalytic breathalysers are swamped by the signals generated by any volatile anaesthetic agent, although the devices work well with intravenous anaesthesia. How to interpret the ethanol data Pharmacokinetics of ethanol The principle of 'the breathalyser' is that ethanol concentrations in the exhaled gas should reflect the concentrations in the blood. In the blood 0.23 g L−1 corresponds to about 0.1 mg L−1 in the expired air - depending somewhat on whether the body load of ethanol is increasing or decreasing. The blood ethanol concentrations, in turn, reflect the balance between the rate of entry of ethanol into the circulation and its rate of removal by redistribution and elimination. Ethanol is the classic example of a substance that has zero-order elimination kinetics over practically the whole range that is of clinical interest [26], but distribution gives the overall kinetics an order greater than zero. Intravenous infusion experiments show that the exponential distribution phase in venous blood has a half-time of between 6 and 9 minutes and that the volume of the central compartment is 16 L [27,28]. The total distribution volume approximates to the total body water [28,29]. This just when absorption has the ethanol level in central of the body which the is higher than in more When absorption occurs over a a of the ethanol has at any Some of the ethanol has also been (Fig. The of ethanol in venous blood when g of ethanol by intravenous infusion at to The are with a and the breath ethanol level for Data from reference used with directly into the blood Most there is an in the exhaled ethanol concentration and a in serum sodium the period that fluid absorption occurs This is with that seen during intravenous of irrigating fluid and corresponds to an uptake of fluid directly into the vascular In these methods have been used to the breath ethanol into the volume of irrigant method the load from the exhaled ethanol the body and the rate of ethanol the distribution of ethanol have estimated the of ethanol absorbed from the the of of ethanol concentration This is a but only if the is exponential - which is not of ethanol have to and use that the ethanol concentration in the exhaled breath to the volumes of irrigant absorbed and to the in serum concentration during surgery. based on the are by between exhaled ethanol concentrations and measured volumes of irrigant solution absorbed every 10 min during the operation The of redistribution and elimination of ethanol with the of absorption are for by an based on an This exponential distribution kinetics on zero-order elimination kinetics The also contain the of with the in serum sodium The for direct absorption during TURP that in has recently been because of for the for the solution in the A of the old that it not enough of the absorption The new which is in is based on data from transurethral and uses the that the breath ethanol level during surgery is by the absorbed fluid volume and the distribution of ethanol. the of body on the at the very for of the volume of irrigant absorbed and the in serum sodium concentration from of the breath ethanol level at any during TURP. The for a volume based on one breath test is fluid absorption use and the of distribution and elimination of ethanol by using the the in serum sodium use of the serum sodium concentration directly with the breath ethanol level at all times during TURP Whatever the the sodium can be estimated by the from the the exhaled ethanol concentration to the the of The with which a breath can the hyponatraemia is as the and this is between and L−1 on of the In clinical practice, however, the is higher as the hyponatraemia is usually after breath of the volume of irrigant absorbed is carried out in A is made from the between known absorbed volumes of irrigant solution and the exhaled concentrations measured every 10 min during TURP. The is by for the for which absorption has been - this correction corresponds to the of distribution and elimination of the ethanol. The is used to an absorbed volume from a measured ethanol and an volume is added the that to that on the ethanol in the exhaled breath. a patient with a breath ethanol concentration of mg L−1 after min of surgery. Ethanol has been during The estimates of the fluid absorption as mL 300 mL for the The in the serum sodium concentration at min is about for TCRE The of surgery at the end of the by cases of TUR some of which The irrigating fluid is usually taken up directly into the venous during TCRE as with TURP. The of the between exhaled ethanol serum sodium and the volume of irrigant absorbed have been made during The in and are based on the patients in reference with the of a more patients with large-scale absorption. A volume of irrigant absorbed during TCRE gives about a 10% greater rise in breath ethanol concentration and a greater in sodium concentration than does TURP. can probably be explained by a difference in and body between these patient for of the volume of irrigant absorbed and the in serum sodium concentration from of the breath ethanol level at any during transcervical resection of the endometrium (TCRE). The for a volume based on one breath test is fluid absorption use and the of distribution and elimination of ethanol by using the the in serum sodium use for of the volume of irrigant absorbed by the from of the breath ethanol level during the period of at the end of The for this volume is Data from reference after instrumental A small number of absorption are by a but in the breath ethanol level which is with a of ethanol from a in the body an instrumental of the TCRE and TURP the volume of irrigant in such an can be estimated from the concentration of ethanol in the which is min after the of the fluid and usually for Data from operations allow for the into the volume of irrigant The is to it into the for direct absorption and and the result by correction for absorption needs to be used. The is to use a that has been for this purpose (Fig. unit for breath ethanol concentration The new use the measured concentration of ethanol in mg L−1 of exhaled air of the of the blood ethanol mg L−1 in exhaled air is to 0.23 g L−1 in blood. In the on the blood ethanol concentrations because these are the of on the of these exhaled ethanol concentrations are used to for who should be to blood sampling for direct of ethanol in the It is more to the of breath directly in of the measured and this is in new for the calibration of How to the of absorption The most part of ethanol monitoring is between the in which the irrigating fluid absorbed directly or into the blood. the direct of ethanol is 10 times more than that of irrigating fluid [5], but to the will the and may result in absorption is more common during TCRE than TURP probably because irrigation of some fluid through the into the A of clinical symptoms and of the timecourse of exhaled ethanol concentrations should the anaesthetist to the of a of irrigating fluid in the In the patient of in the which is arterial hypotension volume is also very common when irrigating fluid has been absorbed from an The exhaled ethanol concentration may be at the of It very does not when the irrigation or operation 6 and If in one can the operation for and a breath at the end of that If this shows a in the exhaled ethanol absorption can be but if the is the or a has taken between breath ethanol when absorption is directly and via a in the The breath ethanol concentration and the volume of irrigant absorbed as measured during one TURP. values if absorption has by the reference used with from show that the absorption in the patients is directly with small that absorption occurs via a of irrigating fluid in the The last patient is in reference new approach for the of this of absorption has recently been to the breathalyser by equipment which data on the fluid absorption every and of the of uptake When absorption occurs from a in the the ethanol monitoring does not give the the early of absorption as when fluid is taken up directly the fluid to with the patient's body fluids when a has been detected, the surgeon can prevent the of TUR syndrome by a surgical or by an intravenous infusion of The treatment the post-operative in but is if more than 2000 mL of fluid have been absorbed and the patient circulatory symptoms and safety Ethanol as a tracer to the or of absorption by the clinical in the early The for some years but known as a the who fluid absorption at the The surgeon most and in a of in which the fluid absorption indicated by ethanol The clinical of a irrigating fluid started in This patients and that ethanol can be the of a method by which the volume of irrigant absorbed can be estimated and throughout TURP The only that the ethanol concentration of this fluid at and rise to signs of mild A irrigating solution glycine 1.5% and ethanol 1% used in a of patients This clinical and a the between absorbed fluid, serum sodium and breath ethanol of the ethanol the that patients symptoms of TUR syndrome. the 1% ethanol solution to be suitable for routine Several other have the of ethanol monitoring that during the An early who used the 2% ethanol solution and estimated the absorbed volume by method that the ethanol monitoring with the method of measuring fluid absorption The and of the ethanol method have also been in experiments based on intravenous of irrigating It has been to that the of fluid absorption and hyponatraemia are the of which solute is used to the osmolality, and that the of ethanol does not itself the of the that it is to studies show that solutions with glycine and mannitol give rise to and that blood volume and are the in patients glycine 1.5% alone or in with ethanol 1% operations in the early of the ethanol monitoring performed or but studies that ethanol monitoring can also be used during general anaesthesia [24,25]. Breath also proved to be as accurate in patients with as in The with which ethanol monitoring can be used has made it a for fluid absorption in samples of patients and for studies of the of irrigating systems and of a on fluid absorption. How does the monitoring Ethanol monitoring does more than allow the absorption to be indicated and with and should be with this information must be decided by the The most have been well decided than the in of the monitoring However, information about much fluid is being absorbed is to the anaesthetist in the fluid may to be to prevent cardiovascular The post-operative fluid therapy should be modified in of the absorbed water load and the risk of [17]. Ethanol monitoring can also be used to out fluid absorption as the of symptoms. The of information absorption is also of in the of the and anaesthetists to TURP and The for using ethanol monitoring is that an early of fluid absorption makes it possible to the course of the operation so that absorption is the number and severity of the symptoms of TUR syndrome with increasing volume of irrigant absorbed a of the of surgery is when some absorption has been detected. The patient should have a risk of developing symptoms than if is the fluid by a has to absorption but this has not been even if such devices are being used, any signs of an absorption of irrigant should be an to the operation. The with the ethanol method so that the of surgery should be when 1000 mL of fluid have been absorbed and the operation should be stopped as as possible when 2000 mL have been taken up In for are prevent moderate and more serious symptoms of TUR syndrome from developing at the cost of with the course in between 2% and of the performed The which on ethanol monitoring of fluid can be used to prevent the TUR syndrome It has been that carry a risk of than glycine of the blood level has not been during infusion or absorption of However, studies are necessary to this of the ethanol The of ethanol is well in who are and are not used to patients who are used to the amount of ethanol that is absorbed with the irrigating fluid is enough to only with such as a The blood ethanol concentration for and is g L−1 ethanol mg This corresponds to an absorption of 1000 mL of and is when the surgeon should be that absorption is The absorption that should be corresponds to a blood ethanol concentration of g at which patients can sometimes of but from ethanol does not usually occur the serum concentration g and should be an during ethanol monitoring with irrigating fluids that contain 1% of ethanol. However, patients who are not used to ethanol may show signs of ethanol when the blood ethanol concentration is as as g in these the risk of from absorption of the irrigating fluid the associated with the ethanol Ethanol is known to the blood concentration in patients The amounts to 10% during ethanol monitoring in TURP patients an intravenous infusion of should be during the operation and early post-operative Ethanol the and blood and a mild or in may be seen after of However, intravenous infusion experiments have to show that to be by a of and there is an in the total vascular in using irrigating fluids ethanol is necessary in of such as with to with and in patients with a of or Ethanol monitoring is a method for non-invasive and of fluid absorption that has been well for use during TURP. have also been obtained during TCRE but the are based on The equipment necessary to carry out this monitoring is an irrigating fluid 1% of a breathalyser and for of the ethanol data into of fluid absorption. It is that the has about to between the ethanol of direct absorption and that of a of irrigating fluid in the patient. However, an is whether can be to stop fluid absorption other than surgery.