Isocapnic hyperventilation provides early extubation after head and neck surgery: A prospective randomized trial.

BACKGROUND: Isocapnic hyperventilation (IHV) shortens recovery time after inhalation anaesthesia by increasing ventilation while maintaining a normal airway carbon dioxide (CO2 )-level. One way of performing IHV is to infuse CO2 to the inspiratory limb of a breathing circuit during mechanical hyperventilation (HV). In a prospective randomized study, we compared this IHV technique to a standard emergence procedure (control). METHODS: Thirty-one adult ASA I-III patients undergoing long-duration (>3 hours) sevoflurane anaesthesia for major head and neck surgery were included and randomized to IHV-treatment (n = 16) or control (n = 15). IHV was performed at minute ventilation 13.6 ± 4.3 L/min and CO2 delivery, dosed according to a nomogram tested in a pilot study. Time to extubation and eye-opening was recorded. Inspired (FICO2 ) and expired (FETCO2 ) CO2 and arterial CO2 levels (PaCO2 ) were monitored. Cognition was tested preoperatively and at 20, 40 and 60 minutes after surgery. RESULTS: Time from turning off the vapourizer to extubation was 13.7 ± 2.5 minutes in the IHV group and 27.4 ± 6.5 minutes in controls (P < .001). Two minutes after extubation, PaCO2 was 6.2 ± 0.5 and 6.2 ± 0.6 kPa in the IHV and control group respectively. In 69% (IHV) vs 53% (controls), post-operative cognition returned to pre-operative values within 40 minutes after surgery (NS). Incidences of pain and nausea/vomiting did not differ between groups. CONCLUSIONS: In this randomized trial comparing an IHV method with a standard weaning procedure, time to extubation was reduced with 50% in the IHV group. The described IHV method can be used to decrease emergence time from inhalation anaesthesia.

Evaluation of a method for isocapnic hyperventilation: a clinical pilot trial.

BACKGROUND: Isocapnic hyperventilation (IHV) is a method that shortens time to extubation after inhalation anaesthesia using hyperventilation (HV) without lowering airway CO2 . In a clinical trial on patients undergoing long-duration sevoflurane anaesthesia for major ear-nose-throat (ENT) surgery, we evaluated the utility of a technique for CO2 delivery (DCO2 ) to the inspiratory limb of a closed breathing circuit, during HV, to achieve isocapnia. METHODS: Fifteen adult ASA 1-3 patients were included. After end of surgery, mechanical HV was started by doubling baseline minute ventilation. Simultaneously, CO2 was delivered and dosed using a nomogram developed in a previous experimental study. Time to extubation and eye opening was recorded. Inspired (FICO2 ) and expired (FETCO2 ) CO2 and arterial CO2 levels were monitored during IHV. Cognition was tested pre-operatively and at 20, 40 and 60 min after surgery. RESULTS: A DCO2 of 285 ± 45 ml/min provided stable isocapnia during HV (13.5 ± 4.1 l/min). The corresponding FICO2 level was 3.0 ± 0.3%. Time from turning off the vaporizer (1.3 ± 0.1 MACage) to extubation (0.2 ± 0.1 MACage) was 11.3 ± 1.8 min after 342 ± 131 min of anaesthesia. PaCO2 and FETCO2 remained at normal levels during and after IHV. In 85% of the patients, post-operative cognition returned to pre-operative values within 60 min. CONCLUSIONS: In this cohort of patients, a DCO2 nomogram for IHV was validated. The patients were safely extubated shortly after discontinuing long-term sevoflurane anaesthesia. Perioperatively, there were no adverse effects on arterial blood gases or post-operative cognition. This technique for IHV can potentially be used to decrease emergence time from inhalation anaesthesia.

Nitroglycerine and patient position effect on central, hepatic and portal venous pressures during liver surgery.

BACKGROUND: To reduce blood loss during liver surgery, a low central venous pressure (CVP) is recommended. Nitroglycerine (NG) with its rapid onset and offset can be used to reduce CVP. In this study, the effect of NG on portal and hepatic venous pressures (PVP and HVP) in different body positions was assessed. METHODS: Thirteen patients undergoing liver resection were studied. Cardiac output (CO), mean arterial pressure (MAP) and CVP were measured. PVP and HVP were measured using tip manometer catheters at baseline (BL) in horizontal position; during NG infusion, targeting a MAP of 60 mmHg, with NG infusion and the patient placed in 10 head-down position. RESULTS: NG infusion reduced HVP from 9.7 ± 2.4 to 7.2 ± 2.4, PVP from 12.3 ± 2.2 to 9.7 ± 3.0 and CVP from 9.8 ± 1.9 to 7.2 ± 2.1 mmHg at BL. Head-down tilt during ongoing NG resulted in increases in HVP to 8.2 ± 2.1, PVP to 10.7 ± 3 and CVP to 11 ± 1.9 mmHg. CO at BL was 6.3 ± 1.1, which was reduced by NG to 5.8 ± 1.2. Head-down tilt together with NG infusion restored CO to 6.3 ± 1.0 l/min. CONCLUSION: NG infusion leads to parallel reductions in CVP, HVP and PVP at horizontal body position. Thus, CVP can be used to guide NG dosage and fluid administration at horizontal position. NG infusion can be used to reduce HVP. Head-down tilt can be used during NG infusion to improve both blood pressure and CO without substantial increase in liver venous pressure. In head-down tilt, CVP dissociates from HVP and PVP.

Current use of nitrous oxide in public hospitals in Scandinavian countries.

BACKGROUND: The use of nitrous oxide in modern anaesthesia has been questioned. We surveyed changes in use of nitrous oxide in Scandinavia and its justifications during the last two decades. METHODS: All 191 departments of anaesthesia in the Scandinavian countries were requested by email to answer an electronic survey in SurveyMonkey. RESULTS: One hundred and twenty-five (64%) of the departments responded; four were excluded. The 121 departments provided 807.520 general anaesthetics annually. The usage of nitrous oxide was reported in 11.9% of cases, ranging from 0.6% in Denmark to 38.6% in Iceland while volatile anaesthetics were employed in 48.9%, lowest in Denmark (22.6%) and highest in Iceland (91.9%). Nitrous oxide was co-administered with volatile anaesthetics in 21.5% of general anaesthetics [2.4% (Denmark) -34.5% (Iceland)]. Use of nitrous oxide was unchanged in five departments (4%), decreasing in 75 (62%) and stopped in 41 (34%). Reasons for decreasing or stopping use of nitrous oxide were fairly uniform in the five countries, the most important being that other agents were 'better', whereas few put weight on its potential risk for increasing morbidity. Decision to stop using nitrous oxide was made by the departments except in four cases. Of 87 maternity wards, nitrous oxide was used in 72, whereas this was the case in 42 of 111 day-surgery units. CONCLUSION: The use of nitrous oxide has decreased in the Scandinavian countries, apparently because many now prefer other agents. Difference in practices between the five countries were unexpected and apparently not justified on anticipated evidence only.

Effect of patient position and PEEP on hepatic, portal and central venous pressures during liver resection.

BACKGROUND: It has been suggested that blood loss during liver resection may be reduced if central venous pressure (CVP) is kept at a low level. This can be achieved by changing patient position but it is not known how position changes affect portal (PVP) and hepatic (HVP) venous pressures. The aim of the study was to assess if changes in body position result in clinically significant changes in these pressures. METHODS: We studied 10 patients undergoing liver resection. Mean arterial pressure (MAP) and CVP were measured using fluid-filled catheters, PVP and HVP with tip manometers. Measurements were performed in the horizontal, head up and head down tilt position with two positive end expiratory pressure (PEEP) levels. RESULTS: A 10° head down tilt at PEEP 5 cm H(2) O significantly increased CVP (11 ± 3 to 15 ± 3 mmHg) and MAP (72 ± 8 to 76 ± 8 mmHg) while head up tilt at PEEP 5 cm H(2) O decreased CVP (11 ± 3 to 6 ± 4 mmHg) and MAP (72 ± 8 to 63 ± 7 mmHg) with minimal changes in transhepatic venous pressures. Increasing PEEP from 5 to 10 resulted in small increases, around 1 mmHg in CVP, PVP and HVP. There was no significant correlation between changes in CVP vs. PVP and HVP during head up tilt and only a weak correlation between CVP and HVP by head down tilt. CONCLUSIONS: Changes of body position resulted in marked changes in CVP but not in HVPs. Head down or head up tilt to reduce venous pressures in the liver may therefore not be effective measures to reduce blood loss during liver surgery.

Regional intratidal gas distribution in acute lung injury and acute respiratory distress syndrome assessed by electric impedance tomography.

BACKGROUND: Regional tidal volume distribution and end-expiratory lung volume (EELV) distribution in patients with acute lung injury and acute respiratory distress syndrome (ALI, ARDS) have previously been investigated using computed tomograpy and electric impedance tomography (EIT). In the present study, we utilized the high temporal resolution of EIT to assess intratidal gas distribution. METHODS: Sixteen ventilator patients with ALI/ARDS were studied. EIT was used for analysis of intertidal, intratidal and EELV regional distribution. Intratidal regional gas distribution (ITV) was analyzed by dividing the regional tidal impedance signal into eight iso-volume parts. Alveolar pressure/volume curves during ongoing ventilation and volume-dependent compliance during the initial inspiration (Cini) were calculated. A low-pressure (~32 cm H2O) recruitment maneuver and a decremental PEEPtrial were implemented. RESULTS: The increase in EELV was preferentially distributed to non-dependent lung regions. The intratidal gas distribution pattern was similar to the tidal volume distribution following increased PEEP; non-dependent distribution decreased and dependent distribution increased during inspiration. Cini increased, indicating successful recruitment. The distribution varied widely among individual patients. In one patient with a low EELV, the ITV pattern showed that non-dependent distribution increased and dependent distribution decreased. This coincided with minimal improvement in volume-dependent compliance. This patient probably needed higher recruitment pressure. In one patient with a high baseline EELV, there was very little change in regional ITV, and non-dependent Cini decreased. This was probably a patient with low potential recruitability, who required only moderate PEEP. CONCLUSION: On-line intratidal gas distribution monitoring offers additional information on recruitability and optimal PEEP.

Bronchoscopic suctioning may cause lung collapse: a lung model and clinical evaluation.

OBJECTIVE: To assess lung volume changes during and after bronchoscopic suctioning during volume or pressure-controlled ventilation (VCV or PCV). DESIGN: Bench test and patient study. PARTICIPANTS: Ventilator-treated acute lung injury (ALI) patients. SETTING: University research laboratory and general adult intensive care unit of a university hospital. INTERVENTIONS: Bronchoscopic suctioning with a 12 or 16 Fr bronchoscope during VCV or PCV. MEASUREMENTS AND RESULTS: Suction flow at vacuum levels of -20 to -80 kPa was measured with a Timeter(trade mark) instrument. In a water-filled lung model, airway pressure, functional residual capacity (FRC) and tidal volume were measured during bronchoscopic suctioning. In 13 ICU patients, a 16 Fr bronchoscope was inserted into the left or the right main bronchus during VCV or PCV and suctioning was performed. Ventilation was monitored with electric impedance tomography (EIT) and FRC with a modified N(2) washout/in technique. Airway pressure was measured via a pressure line in the endotracheal tube. Suction flow through the 16 Fr bronchoscope was 5 l/min at a vacuum level of -20 kPa and 17 l/min at -80 kPa. Derecruitment was pronounced during suctioning and FRC decreased with -479+/-472 ml, P<0.001. CONCLUSIONS: Suction flow through the bronchoscope at the vacuum levels commonly used is well above minute ventilation in most ALI patients. The ventilator was unable to deliver enough volume in either VCV or PCV to maintain FRC and tracheal pressure decreased below atmospheric pressure.

Positive end-expiratory pressure optimization using electric impedance tomography in morbidly obese patients during laparoscopic gastric bypass surgery.

BACKGROUND: Morbidly obese patients have an increased risk for peri-operative lung complications and develop a decrease in functional residual capacity (FRC). Electric impedance tomography (EIT) can be used for continuous, fast-response measurement of lung volume changes. This method was used to optimize positive end-expiratory pressure (PEEP) to maintain FRC. METHODS: Fifteen patients with a body mass index of 49 +/- 8 kg/m(2) were studied during anaesthesia for laparoscopic gastric bypass surgery. Before induction, 16 electrodes were placed around the thorax to monitor ventilation-induced impedance changes. Calibration of the electric impedance tomograph against lung volume changes was made by increasing the tidal volume in steps of 200 ml. PEEP was titrated stepwise to maintain a horizontal baseline of the EIT curve, corresponding to a stable FRC. Absolute FRC was measured with a nitrogen wash-out/wash-in technique. Cardiac output was measured with an oesophageal Doppler method. Volume expanders, 1 +/- 0.5 l, were given to prevent PEEP-induced haemodynamic impairment. RESULTS: Impedance changes closely followed tidal volume changes (R(2) > 0.95). The optimal PEEP level was 15 +/- 1 cmH(2)O, and FRC at this PEEP level was 1706 +/- 447 ml before and 2210 +/- 540 ml after surgery (P < 0.01). The cardiac index increased significantly from 2.6 +/- 0.5 before to 3.1 +/- 0.8 l/min/m(2) after surgery, and the alveolar dead space decreased. P(a)O2/F(i)O2, shunt and compliance remained unchanged. CONCLUSION: EIT enables rapid assessment of lung volume changes in morbidly obese patients, and optimization of PEEP. High PEEP levels need to be used to maintain a normal FRC and to minimize shunt. Volume loading prevents circulatory depression in spite of a high PEEP level.

Clinical evaluation of a partial CO2 rebreathing technique for cardiac output monitoring in critically ill patients.

BACKGROUND: Monitoring central hemodynamics is essential in critically ill patients and less invasive techniques are needed. In this study, the clinical and technical performance of a new non-invasive cardiac output monitor (NICO) based on partial CO2 rebreathing technique and a modified Fick equation were evaluated. The various sources of possible errors in measurement of cardiac output (CO), carbon dioxide production (VCO2) and pulmonary shunt were also assessed. METHODS: Simultaneous measurements of CO with partial CO2 rebreathing technique (CO(nico)) and thermodilution (CO(td)) were performed in 15 patients during major surgery or in the ICU. Pulmonary shunt was estimated from this device and compared to values obtained by standard shunt formula. The accuracy of VCO2 measurements was assessed in a mechanical lung model. RESULTS: A good correlation was found between CO(nico) and CO(td) (r = 0.96, within-subject correlation r = 0.88) with a small underestimation of cardiac output by the NICO of 0.04 L/min, limits of agreement (+/- 2 SD) being - 1.68 and 1.76 L/min. In hemodynamic unstable patients the method closely tracked changes in CO. Pulmonary shunt was underestimated by approximately 11%-units compared to standard shunt calculations using arterial and mixed venous blood gases. We also observed an underestimation in VCO2 measurements. CONCLUSION: Clinical evaluation shows that partial CO2 rebreathing technique provides a useful and accurate non-invasive estimate of cardiac output. Although this technique cannot fully replace the pulmonary artery catheter, it may be used to monitor central hemodynamics in a large number of critically ill patients.

[Liver transplantation--from experiment to routine care. Experiences from the first 500 liver transplantations in Gothenburg]. / Levertransplantation--från experiment till rutinsjukvård. Erfarenheter från de första 500 levertransplantationerna i Göteborg.

During a fifteen-year period, 500 liver transplantations have been performed at Sahlgrenska University Hospital in Göteborg. The results have improved, and factors influencing outcome are discussed. A one-year survival rate over 90% and a 5-year survival rate close to 80% can now be expected for most indications. Long-term complications as well as special problems occurring in different groups of recipients are discussed. New indications for liver transplantation such as liver metastasis of endocrine tumors are described. This article also describes our experience of in situ splitting and living-related liver transplantation as well as other innovations such as cavoportal hemitransposition and multivisceral transplantation.

Oxygen consumption in patients with hyperthyroidism before and after treatment with beta-blockade versus thyrostatic treatment: a prospective randomized study.

OBJECTIVE: To evaluate randomly the effect of thyrostatic treatment (tiamazole) versus selective (metoprolol) and nonselective beta-blockade (propranolol) on whole-body energy metabolism in women with hyperthyroidism. SUMMARY BACKGROUND DATA: beta-blockade is used as an alternative to thyrostatic drugs in the preoperative treatment of patients with hyperthyroidism. beta-blockers have well-established symptomatic effects, but in contrast to antithyroid drugs beta-blockade is thought to lack direct effects on the increased metabolism in hyperthyroidism. METHODS: Whole-body oxygen consumption and carbon dioxide production was measured in a semiopen canopy system with paramagnetic O2 and infrared CO2 sensors. A constant flow generator and the gas-dilution method for calculation of gas flow were used. Anabolic parameters were body weight, triceps skinfold, and arm muscle circumference. RESULTS: Tiamazole normalized oxygen consumption and induced signs of anabolism with improved nutritional state. Metroprolol did not affect oxygen consumption. Propranolol reduced elevated oxygen consumption by 54%. Body weight and other anthropometric assessments were stable after specific and nonspecific beta-blockade, which also led to symptomatic relief in approximately 90% of the patients. CONCLUSION: Tiamazole was the most effective drug to oppose the adverse effects of hyperthyroidism. Therefore, thyrostatic agents are recommended for preoperative treatments of patients with severe catabolic hyperthyroidism. Whenever beta-blockers are chosen for treatment of hyperthyroidism, propranolol (beta 1 + beta 2) has an advantage because it reduces the metabolic rate, whereas selective beta 1-blockade seemed to provide only symptomatic relief, related to the normalization of heart rate.

Anaesthesia, recovery and postoperative nausea and vomiting after breast surgery. A comparison between desflurane, sevoflurane and isoflurane anaesthesia.

BACKGROUND: Whereas induction and recovery will occur more rapidly with the new low soluble anaesthetics than with isoflurane, the quality of anaesthesia and recovery with special emphasis on postoperative nausea and vomiting (PONV) is not well known. METHODS: In an open (peroperatively), double-blinded (postoperatively), randomised controlled study, we assessed anaesthesia characteristics, recovery and 24 h PONV after breast surgery comparing isoflurane, desflurane and sevoflurane. RESULTS: There were no significant quality differences between the three agents during anaesthesia and recovery except for the incidence of PONV in the postanaesthesia care unit (PACU). The PONV rate (24 h in PACU and ward) was higher in the desflurane group (67%) than in the isoflurane group (22%), (P<0.01). The corresponding PONV rate for sevoflurane was 36%. CONCLUSION: The quality of anaesthesia, time to opening of eyes and influence on respiration was similar with all three anaesthetics. As the emergence from anaesthesia did not differ significantly between the three agents, the choice of agent could be based on PONV rate and price. Desflurane had a significantly higher 24 h PONV rate than isoflurane. Early PACU PONV rate was significantly (P<0.05) lower for the more soluble isoflurane (4%) than for the low soluble gases, desflurane and sevoflurane together (28%). The result of this study does not give a rationale for a transition to the new low soluble agents in breast cancer surgery.

Intestinal perfusion during pneumoperitoneum with carbon dioxide, nitrogen, and nitric oxide during laparoscopic surgery.

OBJECTIVE: To find out what effect insufflation pressure and type of gas have on intestinal perfusion during pneumoperitoneum. DESIGN: Randomized, controlled, prospective, experimental study. SETTING: University affiliated animal experimental laboratory, Sweden. ANIMALS: Fasted, anaesthetised, domestic pigs of both sexes operated on laparoscopically (n = 7, weight 26-31 kg). INTERVENTIONS: Insufflation of carbon dioxide (CO2), nitric oxide (NO), or nitrogen (N2) at intra-abdominal pressures of 0, 5, 10, 15 and 20 mm Hg. MAIN OUTCOME MEASURES: Cardiac output, portal blood flow, and jejunal mucosal perfusion. RESULTS: Cardiac output decreased during N2 and NO (15, 20 mm Hg) but not during CO2 insufflation because of an accompanying tachycardia. Portal flow decreased during insufflation with N2 and NO (15, 20 mm Hg) and CO2 (20 mm Hg). Jejunal perfusion was reduced during N2 and NO insufflation (5-20 mm Hg) but remained unchanged during CO2 insufflation (5-20 mm Hg). CONCLUSIONS: Insufflation with CO2 maintained jejunal mucosal perfusion, probably as a result of hypercarbia as N2 at equal pressures reduced mesenteric flow. The vasodilator NO provided no haemodynamic benefit.

Intraoperative glucose administration influences respiratory quotient during paediatric anaesthesia.

BACKGROUND: Oxidation of carbohydrates and fat yields respiratory quotients (RQ) of 1.0 and 0.7 respectively. Maintained or increased blood glucose concentrations are usually seen during paediatric anaesthesia and surgery even without glucose administration. The aim of the present study was to evaluate whether an intraoperative glucose infusion influences the RQ as an indication of a different metabolic preference in comparison to a glucose-free fluid regime. METHODS: Eighteen children between 0.5 and 24 months of age were studied during anaesthesia with controlled ventilation, oxygen in air, isoflurane, thiopentone, atracurium and fentanyl. Oxygen consumption and carbon dioxide production were measured using indirect calorimetry All children received Ringer acetate as needed; in addition, nine children were given glucose 10%, 3 ml.kg-1.h-1, corresponding to 300 mg.kg-1.h-1. Blood samples for analyses of glucose, lactate, free fatty acids and ketones were taken before and during surgery. RESULTS: RQ was significantly higher in the children given glucose 0.92 +/- 0.08, compared to 0.81 +/- 0.06 in the children without glucose (P < 0.01). Oxygen consumption tended to be higher, although not significantly so, in patients without glucose infusion. Energy expenditure was 1.70 +/- 0.29 kcal.kg-1.h-1, without significant group differences. Higher blood glucose concentrations during surgery were found in the children given glucose. CONCLUSIONS: Our results indicate a higher glucose oxidation rate in patients given glucose during surgery.

Respiration during emergence from anaesthesia with desflurane/N2O vs. desflurane/air for gynaecological laparoscopy.

BACKGROUND: The complications related to anaesthesia usually occur in the early postoperative period. Hypercapnia and hypoxaemia may result from any persistent depression of the respiratory drive relative to the metabolic demand. The purpose of this study was to compare the respiratory effects of desflurane anaesthesia with or without nitrous oxide during the period of emergence. METHODS: Twenty patients scheduled for a standardised surgical procedure, laparoscopic hysterectomy, were randomly allocated to anaesthesia with 1.3 MAC of desflurane/N2O (Group 1) or desflurane alone (Group 2), with 10 patients in each group. Times of resumption of spontaneous breathing and extubation were recorded and elimination rates of carbon dioxide, end-tidal concentrations of desflurane and N2O, and blood gases were measured. RESULTS: Spontaneous breathing was resumed in both groups when pH had decreased by about 0.07 and PaCO2 increased by about 1.4 kPa compared with the values at the end of 1.3 MAC anaesthesia with controlled normoventilation. There were no significant differences between the groups with regards to extubation time, 6 vs. 13 min, or total MAC value at extubation, 0.20 vs. 0.19 in Group 1 and 2, respectively. Neither did the groups differ in minute ventilation, end-tidal carbon dioxide, oxygen concentrations, or blood gases. CO2 elimination decreased in both groups from about 220 ml 70 kg-1 min-1 at the end of anaesthesia to a lowest value of about 160 ml 70 kg-1 min-1. CONCLUSION: The respiratory profiles during recovery from gynaecological laparoscopy with either desflurane/N2O or desflurane anaesthesia were similar with fast resumption of spontaneous breathing, short time to extubation, and no signs of CO2 retention.

A retrospective analysis of nitric oxide inhalation in patients with severe acute lung injury in Sweden and Norway 1991-1994.

BACKGROUND: Patients with severe acute lung injury (ALI) have been treated compassionately on doctors' initiative with inhaled nitric oxide (INO) in Sweden and Norway since 1991. In 1994 the previously used technical grade nitric oxide was replaced by medical grade nitric oxide. METHODS: We have carried out a retrospective data collection on all identified adult patients treated with INO for >4 h during the period 1991-1994 focusing on safety aspects and patient outcome. We used the following exclusion criteria (1) Age <18 years, (2) Simultaneous treatment with extracorporeal removal of CO2 (3) NO inhalation period <4 h, (4) Incomplete or missing patient charts, (5) Use of INO in order to treat pulmonary hypertension following cardiac surgery, with little or no acute lung injury. RESULTS: Inclusion criteria were met by 56 out of 73 identified patients. Mean age was 48+/-19 years and the median duration of INO treatment was 102 h. PaO2/FIO2 ratio at start of treatment was 85 +/- 33 mm Hg with a lung injury score (LIS) of 3.2+/-0.8. The aetiology of the lung injury was pneumonia (n= 27), sepsis (n=12) and trauma (n=8). Survival to hospital discharge was 41% and survival after 180 d was 38%. Three serious adverse events were identified, two from technical failures of the INO delivery device and one withdrawal reaction necessitating slow weaning from INO. No methaemoglobin values >5% were reported during treatment. CONCLUSION: The overall mortality did not differ dramatically from historical controls with high mortality. Only a randomised study may determine whether INO as an adjunct to treatment alters the outcome in severe ALI. One cannot at present advocate the routine use of INO in patients with ALI outside such studies.

Should nitrous oxide be discontinued before desflurane after anaesthesia with desflurane/N2O?

BACKGROUND: The appearance of hypoxaemia immediately after anaesthesia with nitrous oxide may be partially explained by diffusion hypoxia. This study was undertaken to evaluate circulatory and respiratory variables during emergence after desflurane/nitrous oxide anaesthesia, and whether there are any differences depending on which gas is discontinued first. METHODS: 20 patients were studied after gynaecological laparoscopic surgery. The depth of anaesthesia was reduced 10 min prior to the emergence by stopping the administration of one of the two inhalational agents. Desflurane was discontinued first in Group 1, nitrous oxide in Group 2. Ventilation was controlled with E'CO2 maintained at 5% until the administration of the second anaesthetic gas was discontinued. Thereafter, the patients breathed spontaneously. RESULTS: The PaCO2 at which the respiratory drive reappeared after controlled normoventilation was similar in both groups, 6.1-6.5 kPa, and extubation was performed after 10-11 min. At extubation, the end-tidal CO2 and total MAC were similar in the groups, about 6.2 vol% and 0.16, respectively. Mean arterial blood pressure was significantly higher in Group 1. The cardiac output increased in both groups from about 6 l/min at the conclusion of anaesthesia to 9.0 and 7.6 l/min at 15 min in the recovery period. End-tidal O2 decreased and CO2 increased in both groups during the first 10 min in the recovery period. pH was reduced at 15 and 30 min in both groups. CONCLUSION: Irrespective of which agent was discontinued first there was an increase in cardiac output decrease in oxygenation and a modest acidosis in the first 30-min recovery period. The only significant difference between the groups was in mean arterial blood pressure in the early emergence phase with a greater MAP when N2O had been used until the conclusion of anaesthesia.

Gas kinetics during nitrous oxide analgesia for labour.

Hypoxaemia may occur after hyperventilation with nitrous oxide during labour. The purpose of this study was to assess whether diffusion hypoxia is a contributory factor. Twenty-four parturients were randomly allocated to receive 50 or 70% nitrous oxide in oxygen. The median nitrous oxide inhalation time per contraction was 58 s and 33 s, respectively. The end-tidal carbon dioxide and the minute ventilation remained unchanged. The end-tidal oxygen concentration was lowest at 120 s, reaching 15.4% in both groups. The oxygen saturation did not differ between the groups with a lowest median value of 96% before the start of nitrous oxide inhalation. Two parturients had episodes of desaturation. Both had low end-tidal oxygen concentrations in association with the desaturation but, as the end-tidal nitrous oxide concentrations were low, the desaturations could not be attributed to diffusion hypoxia.

Conversion of inhaled nitric oxide to nitrate in man.

1. Nitric oxide (NO) is potentially useful as a selective vasodilator drug in infants and adults with pulmonary hypertension. In vitro and in vivo observations demonstrate that NO may be converted to nitrate in the blood, to be further excreted into the urine. The aim of the present study was to assess quantitatively the importance of this pathway for inhaled NO in human subjects. 2. Healthy subjects inhaled 15NO (25 p.p.m.) for 1 h. The plasma and urine levels of 15NO3- were followed for 2 and 48 h, respectively. 3. The measured retention of 15NO in the lungs was 224 +/- 13 mumol, corresponding to 90 +/- 2% of the inhaled amount. Plasma 15NO3- increased during the inhalation of 15NO, to about 15 mumol l-1, and fell when inhalation of 15NO was terminated. 4. Urinary excretion of 15NO3- during the first 24 h after inhalation was 154 +/- 12 mumol. During the following 24 h another 8 +/- 2 mumol of 15NO3- appeared in the urine. 5. We conclude that conversion of inhaled NO to nitrate is a major metabolic pathway in man, covering more than 70% of its inactivation. The metabolic fate of the remaining NO inhaled requires further study.

Nitrous oxide uptake during spontaneous and controlled ventilation.

The rate of uptake of nitrous oxide was studied in 40 orthopaedic patients anaesthetised with either enflurane or isoflurane in nitrous oxide and with either spontaneous or controlled ventilation. A variant of the Douglas bag method was used in combination with low fresh gas flows to a circle system. There were no significant differences in nitrous oxide uptake between the groups and the uptake rates followed 'the square root of time concept', with an overall best fit curve of 1080.t-0.505 ml.70 kg-1 x min-1. During spontaneous ventilation, the nitrous oxide uptake rate was similar or even higher than the corresponding rate during controlled ventilation, in spite of lower minute volumes.