Bain circuit occluded by foreign body

Canadian Journal of Anesthesia/Journal canadien d'anesthésie - The purpose of this report is to describe a potentially hypoxic event which occurred during mask induction with the Bain...     

Carbon dioxide absorption and gas exchange during pelvic laparoscopy

Twelve ASA physical status I-II patients undergoing pelvic laparoscopy for infertility were enrolled in a study to quantify the effects of CO2 insufflation and the Trendelenburg position on CO2 elimination and pulmonary gas exchange, and to determine the minute ventilation required to maintain normocapnia during CO2 insufflation. Measurements of O2 uptake (VO2), CO2 elimination (VCO2), minute ventilation (VE), FIO2, and respiratory exchange ratio (RQ) were made during three steady states: control (C) taken after 15 min of normoventilation but before CO2 insufflation, after 15 min (L1) and 30 min (L2) of hyperventilation during CO2 insufflation. The FIO2 was controlled at 0.5 and arterial blood gases were used to calculate the oxygen tension-based indices of pulmonary gas exchange. After 15 min and 30 min of CO2 insufflation, the volume of CO2 absorbed from the peritoneal cavity was estimated at 42.1 +/- 5.1 and 38.6 +/- 6.6 (SEM) ml.min-1 respectively, increasing CO2 elimination through the lungs by about 30%. Hyperventilation of the lungs by a 20-30% increase in minute ventilation maintained normocapnia. Despite the CO2 pneumoperitoneum and Trendelenburg position, there was no impairment of pulmonary oxygen exchange as estimated by (A-alpha)DO2. This study demonstrated that a 30% increase in minute ventilation, achieved by increasing tidal volume to more than 10 ml.kg-1, is sufficient to eliminate the increased CO2 load and maintain normal pulmonary O2 exchange during pelvic laparoscopy.     

Pulmonary gas exchange and ventilation-perfusion relationships during hypocapnia and thoracotomy in anaesthetized dogs

The effects of hypocapnia and thoracotomy, both individually and combined, on pulmonary gas exchange and distribution of ventilationperfusion ratio (V _a /Q) were studied in anesthetized and paralyzed mongrel dogs by the six inert gas elimination technique. Normocapnia (PaCO₂ 35 mmHg) and hypocapnia (PaCO₂ 20 mmHg) were produced sequentially by varying the inspired CO₂ concentration. Thoracotomy was performed at the fourth intercostal space. When ventilation was changed from normocapnia to hypocapnia without thoracotomy, PaO₂ decreased from 160 ± 10 to 147 ± 11 mmHg and Qs/Qt increased from 0.0 ± 0.0 to 0.6 ± 0.7%. However, no change was observed in perfusion distribution following thoracotomy during normocapnia, PaO₂ decreased from 160 ± 10 to 113 ± 15 mmHg together with a shift of perfusion toward the low V _a /Q region. However, no change was observed in Qs/Qt. When ventilation was changed from normocapnia to hypocapnia with thoracotomy, PaO₂ decreased from 113 ± 15 to 98 ± 12 mmHg and Qs/Qt increased from 0.3 ± 0.8 to 3.4 ± 2.0%. After thoracotomy, a shift of perfusion toward the low V _a /Q region was observed, which was probably responsible for the decrease in PaO₂. The decrease in PaO₂ during hypocapnia was due to an increase in the true shunt rather than the developement of low V _a /Q region. Hypocapnia combined with thoracotomy produced a further reduction of PaO₂ and a greater increase in Qs/Qt.     

Propofol sequestration within the extracorporeal circuit

Various drugs administered during cardiac anaesthesia are sequestered in the extracorporeal circuit in vitro, but it is uncertain whether this sequestration phenomenon affects plasma drug concentration in vivo. The present study was undertaken to evaluate (1) in vitro sequestration of propofol in the extracorporeal circuit and (2) whether the change in plasma propofol concentration induced by initiation of cardiopulmonary bypass in vivo can be explained by haemodilution. For the in vitro evaluation, three separate experiments with a closed circuit (membrane oxygenator, reservoir, and tubings) were performed. The pH and PCO₂ of the circulating solution (a mixture of Ringer’s acetate and whole blood) were maintained within the normal physiological range, and the temperature of the solution was 28° C. The solution was circulated at a flow of 4 L · min^?1 and propofol was added to the solution to achieve a concentration of 2 μg · ml^?1. Serial samples were taken from the circulating solution for measurement of propofol concentration by high performance liquid chromatography. In the in vivo part of the study, 14 patients received a continuous infusion of propofol, and samples for the determination of plasma propofol concentration and blood haematocrit were taken before and five and ten minutes after initiation of cardiopulmonary bypass. In vitro, at 5 and 120 min after addition of propofol into the circulating solution, approximately 65% and 25%, respectively, of the predicted propofol level was measurable in the solution. In vivo, five minutes after initiation of the cardiopulmonary bypass plasma propofol concentration decreased (P < 0.001) more (from 2.8 ±0.7 (mean ± SD) to 1.5 ± 0.5 μg · ml^?1, a 45 ± 12% decrease) than would have been predicted on the basis of acute haemodilution (a decrease in haematocrit from 0.39 ± 0.04 to 0.28 ± 0.03 is a 29 ± 4% decrease). Ten minutes after initiation of cardiopulmonary bypass, plasma propofol concentration was 1.6 ± 0.5 μg · ml^?1 (a 37 ± 27% decrease from the pre-bypass level) and haematocrit was 0.27 ± 0.04 (a 30 ± 6% decrease): the decrease in plasma propofol concentration was not different from the decrease observed in the haematocrit. In conclusion, propofol is markedly sequestered within the extracorporeal circuit in vitro. This sequestration may, to some extent, affect plasma propofol concentration in vivo.     

Pulse oximetry during ketamine anaesthesia in war conditions

Ketamine anaesthesia with spontaneous breathing of air is a common method of anaesthesia in Red Cross hospitals for war wounded. Arterial oxygen saturation of 65 patients was measured with a portable pulse oximeter during the anaesthesia and the first 30 min of recovery. The patients were young (12-47 yr), haemodynamically stable and underwent peripheral surgery. Fifty-seven measurements were free from artefacts and were analyzed. The results showed that during induction six patients (11%) had a brief period (40-420 sec) of oxygen saturation under 90%. Two of these patients showed signs of upper airway obstruction and four breathed normally. During maintenance one patient had short periods (40-80 sec) of saturation under 90%, when he snored. No periods of desaturation occurred during the recovery period. It is concluded that arterial oxygen saturation remained acceptable when patients breathed air during ketamine anaesthesia.     

Haemodynamic changes during the apnoea test for diagnosis of brain death

Haemodynamic responses to the apnoea test jor the diagnosis of brain death were investigated in nine patients with severe head injury or cerebrovascular disease. To prove apnoea, the ventilator was disconnected for ten minutes and oxygen was insufflated to avoid hypoxaemia. No respiratory movement was séen in any patient. Ten minutes after disconnecting the ventilator, PaCO₂ was increased to 78 ± 3 mmHg and pH was reduced to 7.17 ± 0.02. Adequate oxygenation was maintained in all patients. Cardiac output increased from 4.8 ± 0.7 to 5.7 ± 0.8 L · min^{? 1} (P < 0.05), and mean pulmonary artery pressure increased from 11 ± I to 17 ± 2 mmHg (P < 0.01). However, mean arterial pressure, heart rate, pulmonary artery wedge pressure and right a trial pressure did not change. Plasma catecholamines were measured in three patients. Plasma norepinephrine concentrations increased in all three patients but the changes in plasma epinephrine were minimal. These circulatory responses to acute hypercapnia were less than those reported in awake volunteers and in patients during general anaesthesia. However, since plasma norepinephrine concentration increased during the test, some sympathoadrenal response, probably of spinal origin, was present, and may have prevented the direct depressant circulatory effects of acute hypercapnia. In conclusion, the apnoea test did not produce haemodynamic disturbances when respiratory acidosis was limited toapH 7.17±0.02 and PaCO₂ 60–80 mmHg.     

Laparoscopic extraperitoneal inguinal hernia repair complicated by subcutaneous emphysema

The case of a healthy 59- yr- old man who underwent elective laparoscopic extraperitoneal inguinal hernia repair and general anaesthesia is presented. After one hour of surgery, a sudden increase in theFetCO₂ from 5.0% to 9.4% in relation to a massive subcutaneous emphysema, but without any haemodynamic instability, was noticed. The acute rise ofFetCO₂ was the first sign of an abnormal event. Nevertheless, subcutaneous emphysema was diagnosed with chest wall examination and palpation. Subcutaneous emphysema and hypercarbia are potential complications of laparoscopic surgery, but are more likely to occur in extraperitoneal surgery, since insufflated CO₂ can diffuse easily into the surrounding tissues. High insufflation pressures will increase chances of this occurring and was the most likely cause of this complication. This case encouraged us to make recommendations for the management of laparoscopic extraperitoneal surgery which included: monitoring of CO₂ insufflation pressure, routine examination and palpation of chest wall, use of N₂O with caution, adjusting ventilation to physiologicalFetCO₂ and excluding other causes of subcutaneous emphysema and hypercarbia. Il s’agit du cas d’un patient de 59 ans en bonne santé opéré sous anesthésie générale pour une hernie inguinale par laparoscopie et par l’abord extrapéritonéal. Soixante minutes après le début de l’opération, on note une augmentation subite et importante de laFETCO₂ qui passe de 5% à 9,4% sans manifestations hémodynamiques. Cette montée brutale de laFETCO₂ a été le premier signal de l’incident. L’emphysème souscutané n’a été diagnostiqué qu’après l’examen et la palpation des parois abdominale et thoracique. L’emphysème souscutané et l’hypercarbie représentent des complications potentielles de la chirurgie laparoscopique et sont plus susceptibles de survenir avec l’abord extrapéritonéal, parce que le CO₂ peut diffuser plus facilement dans les tissus environnants. Une pression d’insufflation trop élevée constitue le mécanisme le plus plausible de l’incident. Ce cas clinique nous offre l’opportunité de suggérer quelques recommandations pour la prise en charge de l’opéré par laparoscopie et abord extrapéritonéal: monitorage de la pression d’insufflation du CO₂, examen et palpation fréquents des paroi thoracique et abdominale, utilisation prudente du N₂O dans le mélange de gaz inspiré, réglage de la ventilation pour uneFetCO₂ physiologique et exclusion de toutes les autres causes possibles d’emphysème souscutané et l’hypercarbie.     

Autoregulation and the CO2 responsiveness of cerebral blood flow after cardiopulmonary bypass

Cerebral blood flow (CBF) was measured by 133Xe clearance to determine whether there were any residual effects of cardiopulmonary bypass (CPB) on the CBF response to changes in arterial PCO2 or blood pressure in the early (3-8 hr) post-CPB period. During CPB, the nine patients studied were managed according to alpha-stat, temperature uncorrected, pH management. The mean +/- SD increase in CBF resulting from an increase in PaCO2 (1.35 +/- 0.5 ml.100 g-1.min-1.mmHg-1 PaCO2) was within the normal range, indicating appropriate CBF response to a change in PaCO2. There were no significant differences in CBF, being 25.7 ml.100 g-1.min-1 at a mean arterial blood pressure of 70 mmHg and 26.5 ml.100 g-1.min-1 at 110 mmHg, demonstrating intact cerebral autoregulation over this pressure range. We conclude that cerebral autoregulation and CO2 responsiveness are preserved in the immediate postoperative period after CPB using alpha-stat pH management.     

Preservation of renal blood flow during hypotension induced with fenoldopam in dogs

The introduction of drugs that could induce hypotension with different pharmacological actions would be advantageous because side effects unique to a specific drug could be minimized by selecting appropriate therapy. Specific dopamine-1, (DA1) and dopamine-2 (DA2) receptor agonists are now under clinical investigation. Fenoldopam mesylate is a specific DA1 receptor agonist that lowers blood pressure by vasodilatation. The hypothesis that fenoldopam could be used to induce hypotension and preserve blood flow to the kidney was tested. Systemic aortic blood pressure and renal blood flow were measured continuously with a carotid arterial catheter and an electromagnetic flow probe respectively, in order to compare the cardiovascular and renal vascular effects of fenoldopam and sodium nitroprusside in ten dogs under halothane general anaesthesia. Mean arterial pressure was decreased 30 +/- 8 per cent from control with infusion of fenoldopam (3.4 +/- 2.0 micrograms.kg-1.min-1) and 34 +/- 4 per cent with infusion of sodium nitroprusside (5.9 micrograms.kg-1.min-1) (NS). Renal blood flow (RBF) increased during fenoldopam-induced hypotension 11 +/- 7 per cent and decreased 21 +/- 8 per cent during sodium nitroprusside-induced hypotension (P less than 0.01). Sodium nitroprusside is a non-selective arteriolar and venous vasodilator that can produce redistribution of blood flow away from the kidney during induced hypotension. Fenoldopam is a selective dopamine-1 (DA1) receptor agonist that causes vasodilatation to the kidney and other organs with DA1 receptors and preserves blood flow to the kidney during induced hypotension.     

Pneumothorax during laparoscopic Nissen fundoplication

We present a case of 100% pneumothorax in a 41-yr-old man with a history of gastritis and gastroesophageal reflux scheduled for Nissen fundoplication. The patient was anaesthetized, and insufflation of the abdominal cavity with carbon dioxide was performed uneventfully. There was an increase in the peak inspiratory pressure and wheezing was noted with a decrease in the arterial oxygen saturation to 91%. An obstructive pattern was noted on the end tidal carbon dioxide monitor. The patient also had decreased breath sounds in the left lung field. The endotracheal tube was withdrawn 1.5 cm with equal breath sounds noted in both lung fields, but the wheezing persisted. At the end of the case the trocars were removed and the abdomen was deflated. The arterial oxygen saturation increased to 94% while breathing FIO₂ of 1.0. A chest roentgenogram showed a 100% left pneumothorax. A left chest tube was placed with immediate improvement of the arterial oxygen saturation to 100%. We recommend monitoring of arterial oxygen saturation, peak inspiratory pressures, and excursion of the chest for early diagnosis and prompt treatment of pneumothorax during laparoscopic procedures.     

Ventilatory failure due to an improperly placed nasogastric tube

A case is described of a 35-yr-old patient who was transferred to the operating room for the repair of a right ventricular laceration. Prior to transfer a nasogastric tube was placed unknowingly beyond the tracheal tube cuff into the trachea. During the surgery, the patient's head was turned to insert a central venous line at which time the ventilator low pressure alarm sounded and effective ventilation ceased. The problem was corrected by turning off the nasogastric tube suction. It is postulated that the nasogastric tube became unkinked when the head was turned and this led to the evacuation of gas from the lungs and breathing circuit through the nasogastric tube suction. Identification of the problem was complicated by the lack of a temporal relationship between the insertion and connection to suction of the nasogastric tube, and the episode of ventilatory failure.     

Butorphanol compared with fentanyl in general anaesthesia for ambulatory laparoscopy

Butorphanol was compared with fentanyl as the narcotic component of general anaesthesia for ambulatory laparoscopic surgery. This double-blind, randomized study enrolled 60 healthy women who received equianalgesic doses of fentanyl 1 microgram.kg-1 (F, n = 30) or butorphanol 20 micrograms.kg-1 (B, n = 30) prior to induction of anaesthesia. Tracheal anaesthesia was maintained with nitrous oxide/oxygen, isoflurane, and succinylcholine by infusion. Intraoperatively, patients who received B demonstrated lower pulse rate before and after intubation (P less than 0.05, P less than 0.01) and lower diastolic blood pressure after intubation (P less than 0.01). Anesthesiologists judged the maintenance phase as satisfactory more often with B (P less than 0.05). Postoperatively, there were no differences in analgesic need. No major side-effects occurred in either group. Among minor side-effects, patients who received B reported postoperative sedation more often, 77% vs 37% (P less than 0.01), which occurred during the first 45 min of recovery (P less than 0.05). Discharge times were not different. On the first postoperative day, more subjects who received B were satisfied with their anaesthesia experience (P less than 0.05). Butorphanol 20 micrograms.kg-1 is an acceptable alternative analgesic in general anaesthesia for ambulatory laparoscopy.     

The pharmacokinetic behaviour of opioids administered during cardiac surgery

Cardiac surgery with hypothermic cardiopulmonary bypass (CPB) is among the most commonly performed operations in Canada today. The potential effects of hypothermia and CPB on the disposition of certain opioids are reviewed. Reasons for prolongation of the elimination half-time of the opioids used during cardiac surgery are explored. The roles that age, hypothermia, protein binding and drug sequestration may play in changing opioid pharmacokinetic behaviour are examined and suggestions for future research are made.     

pH adjustment of mepivacaine decreases the incidence of tourniquet pain during axillary brachial plexus anaesthesia

The effect of pH adjustment of mepivacaine on the incidence of tourniquet pain during axillary brachial plexus anaesthesia was studied. Thirty-nine patients scheduled for hand surgery, during which use of pneumatic tourniquet for longer than 60 min was planned, were randomized into two groups. Both received axillary brachial plexus block with 40 ml, 1.4% mepivacaine, 1:200,000 epinephrine. The study group had 4 ml sodium bicarbonate (1 mEq · ml^{? 1}) added (final pH 7.31), and the control group had 4 ml saline added (final pH 5.6). The incidence of tourniquet pain was determined from cases for which tourniquet inflation lasted longer than 60 min. Tourniquet; pain was defined as poorly localized and distinct from an inadequate axillary block by a blinded observer. More tourniquet pain occurred in the control group. The authors conclude that alkalinization of mepivacaine for axillary brachial plexus anaesthesia may be indicated in cases where use of pneumatic tourniquet for long periods is planned.     

Pressure controlled-inverse ratio ventilation and pulmonary gas exchange during lower abdominal surgery

Although pressure controlled-inverse ratio ventilation (PC-IRV) has been used successfully in the treatment of respiratory failure, it has not been applied to the treatment of respiratory dysfunction during anaesthesia. With PC-IRV the inspiratory wave form is fundamentally altered so that inspiratory time is prolonged (inverse I:E), inspiratory flow rate is low, and the peak inspiratory pressure is limited. Positive end-expiratory pressure (PEEP) can be applied and the mean airway pressure is higher than with conventional ventilation. To assess the clinical efficacy of this new mode of ventilation we studied ten patients having lower abdominal gynaecologic surgery in the Trendelenburg position under general anaesthesia. Pulmonary O2 exchange was determined during four steady states: awake control (AC), after 30 and 60 min of PC-IRV during surgery, and at the end of surgery. Patients' lungs were ventilated with air/O2 by a Siemens 900C servo ventilator in the PC-IRV mode with an I:E ratio of 2:1 and 5 cm H2O of PEEP. The FIO2 was controlled at 0.5 and arterial blood gases were used to calculate the oxygen tension-based indices of gas exchange. There were significant increases of (A-a) DO2 at 30 and 60 min (41 and 43%). These changes were less than those reported in a previous study using conventional tidal volume ventilation (7.5 ml.kg-1) and were similar to those in patients whose lungs were ventilated with high tidal volumes (12.7 ml.kg-1). Thus, in this clinical model of compromised gas exchange, arterial oxygenation was better with PC-IRV than with conventional ventilation, but not better than with large tidal volume ventilation.     

Electrocautery-induced pacemaker malfunction during surgery

We report a case of electrocautery-induced pacemaker failure that resulted in asystole in a 15-year-old girl scheduled for cardiac surgery. Her pacemaker was converted to the asynchronous mode the night before surgery. Electromagnetic interference from the unipolar electrocautery caused a reduction in the battery voltage, which allowed the digital circuitry, but not the voltage control oscillator (VCO), to work properly. Eventually the battery current drain caused VCO "lock-out," and pacemaker and battery failure. This report demonstrates that electrocautery-induced pacemaker failure can occur, even after conversion to asynchronous mode.     

Uterine and umbilical blood flow velocity during epidural anaesthesia for Caesarean section

The purpose of this study was to use colour Doppler to determine the effect of epidural anaesthesia on the uterine and umbilical blood flow velocities. After determining the precision of the technique, Doppler insonation of the uterine and umbilical arteries was performed in consenting non-labouring patients requesting epidural anaesthesia for Caesarean section. Patients in Group I were normal and those in Group II were at high risk for uteroplacental blood flow abnormalities. The pulsatility indexes (PI) of both uterine and umbilical arteries were compared at the following times: control, after fluid and after anaesthesia using repeated measure analysis of variance. In Group I (n = 30) the PI increased from 0.72 to 0.82 in the left uterine artery and from 0.71 to 0.85 in the right uterine artery (P < 0.05). In Group II (n = 10) the PI increased from 0.67 to 0.85 in the left uterine artery (NS) and from 0.98 to 1.38 in the right uterine artery (P < 0.05). There was no change in the PI in the umbilical artery. We conclude that the PI of the uterine arteries increases after epidural anaesthesia with lidocaine, epinephrine and fentanyl but there is no change in the umbilical PI. While these changes do not appear to be clinically important in the low-risk population, further studies are required to determine the impact on fetuses at high risk for in utero hypoxaemia.     

Consequences of fluid absorption during transurethral resection of the prostate using distilled water or glycine 1.5 per cent

This prospective and randomized study compared the consequences of two irrigating fluids, distilled water and glycine for transurethral prostatectomy. Forty-nine consecutive unselected patients undergoing transurethral resection of the prostate with spinal anaesthesia were investigated. The irrigating fluid was either distilled water (group A, 24 patients) or glycine 1.5 per cent (group B, 25 patients). The absorption of irrigating fluid was measured, all surgical events and any clinical signs of TURP syndrome during and after surgery were recorded. Early signs of TURP syndrome were observed in one patient in group A and in four in group B without further consequence. From all the biological variables, only plasma protein concentration, haematocrit, free plasma haemoglobin and free bilirubin concentrations were found to have changed. Plasma protein concentration and haematocrit decreased significantly during and after surgery in the two groups. Free plasma haemoglobin increased significantly with time: a significantly higher concentration was observed in group A than group B. Free bilirubin concentration increased with time in the two groups and was statistically greater in group A. With the two irrigating fluids, we observed a significant amount of haemolysis and haemodilution without clinical consequences. A low irrigating fluid pressure, a short resection time, and the use of spinal anaesthesia seems to us to be essential. Close observation of patients following transurethral prostatectomy is needed but the choice of the irrigating fluid does not seem to be important. Cette étude prospective et randomisée a comparé les conséquences de deux liquides d’irrigation, l’eau distillée et le glycocolle au cours de la chirurgie prostatique par voie basse. Quarante-neuf patients consécutifs, non sélectionnés, bénéficiant d’une résection transuréthrale de prostate sous rachianesthésie, sont étudiés. Le liquide d’irrigation est soil l’eau distillée (groupe A, 24 patients), soit le glycocolle à 1.5 pour cent (groupe B, 25 patients). L’absorption des liquides d’irrigation, les incidents chirurgicaux et les signes cliniques du syndrome de réabsorption sont systématiquement notés. Des signes caractéristiques du syndrome de réabsorption sont observés dans un cas dans le groupe A et dans quatre cos dans le groupe B sans conséquence ultérieure. Seuls la protidémie, l’hématocrite, l’hémoglobine plasmatique libre et la bilirubine libre changent significativement. L’hémoglobine plasmatique libre augmente significativement dans les deux groupes, avec un taux plasmatique significativement plus élevé dans le groupe A. Avec les deux liquides d’irrigation, on observe une hémolyse et une hémodilution sans conséquence clinique. Un temps de résection court, un faible niveau de pression d’irrigation, l’utilisation de l’anesthésie rachidienne nous semblent trés importants. Une surveillance clinique et biologique attentive pendant et après la résection transuréthrale de prostate sont nécessaires; en revanche, le choix du liquide d’irrigation ne semble pas l’élément essentiel.     

Exposure of operating room personnel to nitrous oxide during paediatric anaesthesia

This study was undertaken to quantify the exposure of operating room staff to nitrous oxide during routine paediatric otolaryngeal surgery and to determine the influence of the method of induction of anaesthesia on this exposure. The nitrous oxide exposure of the anaesthetist, the surgeon and the circulating nurse were measured, using body-worn passive atmospheric samplers, during twelve routine paediatric otolaryngeal surgical lists. During six of the lists an inhalational technique, with nitrous oxide, oxygen and halothane, was used for the induction of anaesthesia. During the other six lists anaesthesia was induced using intravenous thiopentone. In all cases, anaesthesia was maintained using nitrous oxide, oxygen and halothane. Regardless of the induction technique used, the mean nitrous oxide exposures of the anaesthetist, the surgeon and the nurse all exceeded the maximum level of 25 ppm.hr-1 recommended by the United States National Institute for Occupational Safety and Health (NIOSH). The use of an intravenous technique for the induction of anaesthesia reduced the nitrous oxide exposure of the anaesthetist and the circulating nurse. This suggests that, although the use of an intravenous induction may reduce exposure to nitrous oxide, the NIOSH recommendations for maximum exposure of operating room personnel to nitrous oxide are currently unattainable in practice.