Single-lung ventilation with carbon dioxide hemipneumothorax: hemodynamic and respiratory effects in piglets

Objectives: Video‐assisted thoracoscopic surgery (VATS) has become a standard procedure in pediatric surgery. To facilitate surgical access, the dependent lung has to collapse using intrathoracic carbon dioxide insufflation and/or single‐lung ventilation. These procedures can induce hemodynamic deteriorations in adults. The potential impacts of single‐lung ventilation in combination with capnothorax on hemodynamics in infants have never been studied before. Aim: We conducted a randomized experimental study focusing on hemodynamic and respiratory changes during single‐lung ventilation with or without capnothorax in a pediatric animal model. Methods: Twelve piglets were randomly assigned to receive single‐lung ventilation with (SLV‐CO₂) or without (SLV) capnothorax with an insufflation pressure of 5 mmHg for a period of two hours. Before, during, and after single‐lung ventilation, hemodynamic and respiratory parameters were measured. Results: Although mean arterial pressure remained stable during the course of the study and no critical incidents were monitored, cardiac index (CI) decreased significantly with SLV‐CO₂ (baseline 3.6 ± 1.6 l·min^?1·m^?2 vs 2.9 ± 1.1 l·min^?1·m^?2 at 120 min, P < 0.05). Furthermore, global end‐diastolic volume and intrathoracic blood volume (ITBV) decreased as well significantly with SLV‐CO₂, causing a significant between‐group difference in ITBV (P < 0.05). Conclusions: Despite a decrease in CI and preload parameters, the combination of single‐lung ventilation and low‐pressure capnothorax was well tolerated in piglets and could justify further clinical studies to be performed in infants and children focusing on hemodynamic and respiratory changes during VATS.     

Adrenocorticotrophic hormone,cortisol and catecholamine concentrations during insulin hypoglycaemia in dogs anaesthetized with thiopentone

Glucose homeostasis is maintained by complex neuroendocrine control mechanisms. Increases in plasma concentrations of various glucose-raising hormones such as glucagon, catecholamines, adrenocorticotrophic hormone (ACTH), and cortisol are observed under certain conditions associated with stress (haemorrhage and hypoglycaemia). The purpose of this study was to determine the effect of thiopentone anaesthesia on the cathecholamine, ACTH and cortisol response to insulin hypoglycaemia in dogs. Blood sugar (BS), plasma cathecholamine, and ACTH, and serum cortisol concentrations were measured during the course of (1) an intravenous insulin test (ITT) and (2) an ACTH test in conscious and in anaesthetized fasted dogs. During the ITT, the anaesthetized dogs showed a moderate resistance, compared with conscious dogs, to the hypoglycaemic action induced by insulin (blood sugar concentration 30 min after insulin injection: 2.91 ± 0.25 vs 1.93 ± 0.12 mM · L^?1; P < 0.01). In addition, decreased epinephrine (220 ± 27 vs 332 ± 32 pg · ml^?1 ACTH (65 ± 6 vs 90 ± 5 pg · ml^?1) and cortisol (4.48 ± 0.3 vs 6.25 ± 0.5 μg · ml^?1) concentrations were detected 60 min after insulin injection (P < 0.01). The norepinephrine response to hypoglycaemia was not altered by anaesthesia (273 ± 33 vs 325 ± 25 pg · ml^?1). Anaesthetized dogs showed a decreased cortisol response to ACTH at 45 min (5.68 ± 0.54 vs 8.87 ± 0.47 μg · ml^?1) when compared with control dogs (P < 0.001). Haemodynamic variables during anaesthesia showed little changes (P < NS); while respiratory rate was altered (P < 0.01 between 60 and 105 min). Arterial pH was decreased (7.29 ± 0.03 vs 7.36 ± 0.04; P < 0.05) and PaCO₂ was increased (6.8 ± 0.3 vs 5.2 ± 0.3; P < 0.01) at 30 min from induction of anaesthesia but little change was seen after the beginning of the ITT and ACTH tests. We conclude that thiopentone anaesthesia provokes a moderate resistance to the hypoglycaemic action of insulin. This does not appear to be related to increases in plasma concentrations of cathecholamines, cortisol or ACTH. Since the hyperglycaemic effects of cathecholamines and glucagon are synergistic it is possible that glucagon plays an important role in the altered blood sugar response to insulin administration.     

Pulmonary gas exchange effects by nitroglycerin,dopamine and dobutamine during one-lung ventilation in man

The effects of nitroglycerin, dopamine and dobutamine on pulmonary gas exchange were determined in 21 adult patients during two-lung and one-lung ventilation. Nitroglycerin, in I μg·kg^?1·min^?1, decreased cardiac index (CI) andPaO₂ during both two-and one-lung ventilation, and increased in Qs/Qt during one-lung ventilation. There were no significant changes in the measured variables during infusion of dopamine, 5 μg·kg^?1·min^?1. Dobutamine, 5μg·kg^?1·min^?1, increased Cl and PaO₂ did not change during two-lung ventilation. During one-lung ventilation, PaO₂ increased from (mean value ±SD) 168 ± 46 to 201 ± 52 mmHg (P < 0.01) with dobutamine infusion. Qs/Qt decreased from 29.2 ± 7.0 to 26.0 ± 6.2 per cent (P < 0.05) without any change in pulmonary vascular resistance index during one-lung ventilation. We conclude that dobutamine has advantages over dopamine and nitroglycerin during one-lung ventilation.     

Automatic jet ventilation in children anaesthetized by the T-piece circuit

Investigation was carried out in ten children aged between one month and six years, who were anaesthetized by the T-piece circuit. The volume of the reservoir tubing of the T-piece was 250 ml. Ventilation was controlled automatically by oxygen jets which were delivered via an injector attached to the reservoir tubing. The oxygen jets were regulated by an electronically-controlled solenoid valve. The children were ventilated by a tidal volume about 12 ml±kg^?1 at a rate of 12-20 per min depending on their age, while the FGF varied between 3 and 6 l min^?1 depending on their body weight. The resulting FIO₂ ranged between 0.32 and 0.34 which was expected from the oxygen:nitrous oxide mixture (1:2), denoting no mixing of the oxygen jets with the anaesthetic mixture. The PA_co2 was ventilation-dependent, and ranged between 4±6-5±3 kPa (35-41 mmHg). The results suggest that automatic jet ventilation facilitates controlled ventilation in children anaesthetized by the T-piece circuit, while maintaining the original simplicity of the T-piece.;     

Improvement of arterial oxygenation by selective infusion of prostaglandin E1 to ventilated lung during one-lung ventilation

Background:One-lung anesthesia provides a better surgical field for thoracic procedures but also impairs the arterial oxygenation and venous admixture. During one-lung ventilation, pulmonary vasoconstriction is assumed to be present within both ventilated and collapsed lungs. We propose that arterial oxygenation could be optimized by offsetting the vasoconstriction within the microcirculation of ventilated lung. Method:In an anesthetized dog model, incremental doses of prostaglandin E₁ (PGE₁) were selectively infused into the main trunk of the pulmonary artery of the ventilated lung after one-lung ventilation for 60 min (PGE₁ group, n=9). Arterial oxygenation and calculated venous admixture (Qs/Qt) was also assessed in a time-course control group (Control group, n =5). During two-lung ventilation (FIO₂: 0.66), arterial PO₂ and venous admixture was 44.22 ± 3.5 kPa and 10.7±2.3%, respectively. One-lung ventilation (FIO₂: 0.66) with left lung collapsed reduced arterial PO₂ to 11.6±1.7 kPa and increased venous admixture to 40.7±5.8% (P<0.001). Venous O₂ tension also decreased from 6.3±0.7 kPa to 5.0±0.6 kPa with a slight increase in mean pulmonary artery pressure and pulmonary vascular resistance (P <0.05). Results: During selective infusion of PGE₁ at a dose of 0.04 to 0.2 μg kg^-1 min^-1, there was a dose-dependent improvement in arterial PO₂ with a parallel reduction of venous admixture during one-lung ventilation. Arterial PO₂ increased to a maximum of 23.0±4.3 kPa, and the venous admixture decreased significantly to a minimum of 27.4±4.2% by PGE₁ at a dose of 0.04-0.4 μg kg^-1 min^-1 (P<0.01). PGE₁ resulted in a small increase in cardiac output and decreases of pulmonary pressure and pulmonary vascular resistance at a relatively high dose of 0.4 μg kg^-1 min^-1 during selective infusion (P<0.05). Conclusion: These results suggest that a selective pulmonary artery infusion of PGE₁ to the ventilated lung within the dose range of 0.04-0.4 μg kg^-1 min^-1 is practical and effective to improve arterial oxygenation and reduce venous admixture during one-lung ventilation.     

Pharmacokinetics of doxacurium during normothermic and hypothermic cardiopulmonary bypass surgery

Purpose

To compare the pharmacokinetic behaviour of doxacurium in patients undergoing normothermic or hypothermic cardiopulmonary bypass (CPB) for coronary artery bypass graft surgery.

Methods

Twenty patients in two equal groups were studied. Anaesthesia was induced with sufentanil and midazolam after a standard premedication. Doxacurium was administered at 3 × ED₉₅ (80μ·kg^?1), and anaesthesia was maintained with 0.5 μg·kg^?1 hr^?1 sufentanil, 0.05 mg·kg^?1 midazolam and isoflurane 0.5–1%. Systemic temperature for patients in the normothermic and hypothermic groups was maintained at 33–36C and 26–30C respectively. Timed blood and urine samples were collected and pharmacokinetic parameters were estimated using a non-compartmental approach.

Results

For the normothermic and hypothermie groups, terminal elimination half-life (t_1/2B) was 100.1 ± 28 and 183.8 ± 60 min (P < 0.05) respectively, elimination half-life during the CPB phase (T_1/2 CPB) 114.5 ± 10 and 183.8 ± 60 min (P < 0.05), mean residence time 108.8 ± 25 and 164.8 ± 34 min (P < 0.05) and apparent volume of distribution at steady state 0.20 ± 0.03 and 0.26 ± 0.04 L·kg^?1 (P < 0.05). Compared with the hypothermie group, the normothermic group had a higher rate of renal clearance (1.40 ± 0.4 vs 0.93 ± 0.3 ml·min^?1·kg^?1;P < 0.05) and a higher value for renal clearance as a percentage of the total clearance (76.2 ± 10 vs 58.3 ± 20%).

Conclusion

The elimination rate of doxacurium during normothermic CPB is faster than that in hypothermic CPB.     

Détermination de la courbe dose-effet du vécuronium chez l'homme anesthésié

Dose-response curves have been determined in 37 healthy subjects, after injection of a single bolus of Organon NC 45 (vecuronium or Norcuron®). The doses used were 0.0125, 0.025, 0.037 and 0.05 mg · kg^?1. The ulnar nerve was stimulated at the wrist and the force of thumb adduction measured. No premedication was used. Anesthesia was induced with thiopentone and fentanyl, and maintained by a nitrous oxide/oxygen mixture under controlled ventilation. Paco₂ was 37 ± 0.5 mmHg and temperature 36.8 ± 0.1 °C. The effective doses (ED) were : ED₅₀ at 0.024 mg · kg^?1, ED₉₀ at 0.034 mg · kg^?1 and ED₉₅ at 0.037 mg · kg^?1. At 0.05 mg · kg^?1, the degree of twitch inhibition was 99.2 ± 0.6 %, the delay of maximum effect was 7.7 ± 1.4 min, and the length of action (up to 90 % recovery) was 27.2 ± 2.3 min. Vecuronium is therefore a potent neuromuscular blocking agent with a relatively short duration of action.     

Effets hémodynamiques comparés du midazolam et du flunitrazépam chez les traumatisés crâniens en ventilation contrôlée

The haemodynamic effects of midazolam were compared with those of flunitrazepam in 10 patients with severe head injury under controlled ventilation. Right atrial pressure, pulmonary pressure, pulmonary capillary wedge pressure and cardiac output were measured using a Swan-Ganz thermodilution catheter. Arterial pressure (P?a) was recorded by radial arterial canulation. All patients in this cross-over study received midazolam (0.15 mg · kg^?1) and flunitrazepam (0.02 mg · kg^?1) intravenously randomly, with 24 h between the two injections. The measurements were first carried out before and then 5, 10, 20, 30 and 60 min after injection. The only significant variations after midazolam and flunitrazepam were a fall in P?a (from 93±12 to 81±11 mmHg for midazolam and from 89±14 to 78±20 mmHg for flunitrazepam) and in cardiac index (from 4.80±1.03 to 4.17±1.14 l · min^?1 · m^?2 for midazolam and from 5.18±1.32 to 4.54±1.03 l · min^?1 · m^?2 for flunitrazepam). The small decrease in heart rate was not significant. The cardiovascular changes after midazolam and flunitrazepam were small and similar for both drugs. It seemed that midazolam and flunitrazepam were safe for sedating head injured patients under controlled ventilation.     

Dose-response relationships for edrophonium antagonism of mivacurium-induced neuromuscular block during N2O-enflurane-alfentanil anaesthesia

The purpose of this study was to determine the dose-response relationships for edrophonium antagonism of mivacuriuminduced neuromuscular block. Seventy-five ASA I or II adults were given mivacurium 0.15 mg · kg^{? 1} followed by an infusion (7 μg · kg^{? 1} · min^{? 1}) during alfentanil-propofol-N₂O-enflurane anaesthesia. Train-of-four stimulation (TOF) was applied to the ulnar nerve every 20 sec and the response of the adductor pollicis was recorded (Relaxograph NMT-100. Datex, Helsinki, Finland). Mivacurium infusion was modified at five-minute intervals in order to keep the height of the first twitch in TOF (T₁) at 5% of its control value. At the end of surgery, edrophonium (0.0. 0.125, 0.25, 0.5. or 1.0 mg · kg^{? 1}) combined with glycopyrrolate (0.0, 0.0012, 0.0025, 0.005, or 0.01 mg · kg^{? 1}) were administered by random allocation. Edrophonium doses of 0.25, 0.5 and 1.0 mg · kg^{? 1} were different from placebo with regard to time to attain a TOF ratio (fourth twitch in TOF/ T,) = 0.7 (13.8 ± 4.5, 11.1 ± 3.5, 11.4 ± 3.0 vs 19.7 ± 4.7 min P < 0.05). Doses of 0.5 and 1.0 mg · kg^{? 1} permitted faster recovery time of T₁ from 10 to 95% (T_{10– 95}) than did placebo (7.5 ± 3.8,8.9 ± 3.5 vs 14.5 ± 5.0 min P < 0.05). Edrophonium 0.5 mg · kg^{? 1} was different from placebo with regard to recovery time of T₁ from 25 to 75% (T_{25– 75}) (3.3 ± 2.0 vs 6.7 ± 2.0 min P < 0.05). Only edrophonium 0.5 mg · kg^{? 1} provided faster recovery than placebo with regard to all three indices. It is concluded that edrophonium 0.5 + glycopyrrolate 0.005 mg · kg^{? 1} allow the fastest recovery from a mivacurium-induced block during enflurane-N₂O anaesthesia.     

High–frequency jet ventilation vs continuous positive airway pressure for differential lung ventilation in patients undergoing resection of thoracoabdominal aortic aneurysm

Twenty patients, scheduled for surgical resection of thoracoabdominal aortic aneurysm were divided into two groups according to the type of differential lung ventilation used during graft replacement of the descending thoracic aorta. In the high–frequency jet ventilation (HFJV) group of ten patients, HFJV was applied to the left lung once collapsed and retracted by the surgeon, the patient lying in the right lateral decubitus and being intubated by a Carlens' tube. In the continuous positive airway pressure (CPAP) group of ten patients, CPAP was applied to the left lung at the same mean airway pressure as HFJV (1 kPa). Before anaesthetic induction, an arterial and a Swan–Ganz catheter were inserted for cardiovascular monitoring. The same anaesthetic technique using fentanyl 6 μg·kg^-1, flunitrazepam 0.02 mg kg^-1 and pancuronium 0.1 mg kg^-1 was used for each patient. Haemodynamic and respiratory measurements were made: 15 min after positioning the patients in the right lateral decubitus using two–lung ventilation; 15 min after collapse and retraction of the left lung using one–lung ventilation and 15 min after using differential lung ventilation with CPAP or HFJV. Left lung collapse with conventional one–lung ventilation induced a dramatic decrease in arterial oxygenation: Pao₂/Fio₂ ratio decreased from 43 6 kPa to 20 8 kPa, alveolo–arterial oxygen difference increased from 24 7 kPa to 72 11 kPa and pulmonary shunt increased from 17 2% to 37 3%. Whereas differential lung ventilation with CPAP did not improve any of the respiratory parameters measured, differential lung ventilation with HFJV, significantly increased Pao₂/Fio₂ ratio to 41 14 kPa. Therefore, since HFJV improves gas exchange without altering the conditions of surgical comfort, different lung ventilation with HFJV appears to be superior to differential lung ventilation with CPAP.     

Haemodynamic changes during induced hypotension — comparison of trimethaphan with prostaglandin E1 assessed using transoesophageal echocardiography

Haemodynamic changes during induced hypotension depend upon the hypotensive agent used. We investigated if, using transoesophageal echocardiography (TEE), we could identify the haemodynamic differences between trimethaphan and prostaglandin E₁. Twenty-nine patients undergoing total hip replacement were selected for study. Hypotension was induced to a mean arterial pressure of 8.0– 9.3 kPa with either trimethaphan (5–20 μg · kg^?1 min^?1) or prostaglandin E₁ (0.5–2.0 μg · kg^?1 min^?1). The left atrial dimension, cardiac output, fractional shortening, pulmonary venous flow and mitral valve flow were evaluated using TEE. During induced hypotension, left atrial dimension decreased in both trimethaphan and prostaglandin E₁ groups (P < 0.05). In the trimethaphan-treated patients systolic velocity in pulmonary venous flow decreased from 41.9 ± 4.8 cm · sec^?1 before induced hypotension to 27.8 ± 4.2 cm · sec^?1 by 30 min after stable hypotension had been established (P < 0.01). The late/early ratio of peak velocity in mitral blood flow decreased in prostaglandin E₁ treated patients. Cardiac output increased from 4.2 ± 0.5 L · min^?1 to 5.3 ± 0.4 L · min^?1 during 30 min hypotension with prostaglandin E₁ administration (P < 0.05), but cardiac output decreased from 5.0 ± 0.5 to 3.5 ± 0.4 L · min^?1 with trimethaphan (P < 0.01). The differences in haemodynamic variables could be attributed to the venule dilatation effect of trimethaphan. We conclude that it was possible to detect the haemodynamic differences between trimethephan and prostaglandin E₁ using TEE.     

Pressure support ventilation vs spontaneous ventilation via ProSeal™ laryngeal mask airway in pediatric patients undergoing ambulatory surgery: a randomized controlled trial

Aim: To investigate the advantages of using pressure support ventilation (PSV) vs spontaneous ventilation via ProSeal? laryngeal mask airway in children undergoing ambulatory surgery. Background: In our ambulatory surgical unit, the use of unassisted spontaneous breathing via laryngeal mask airway is a common anesthetic technique during general anesthesia. However, this may be associated with inadequate ventilation. PSV is a ventilatory mode that is synchronized with the patient’s respiratory effort and may improve gaseous exchange under general anesthesia. Materials and methods: After the approval from the ethics committee, a randomized controlled trial involving 24 pediatric patients was conducted in our ambulatory surgical unit. They were randomized into two groups, namely Group PSV (receiving PSV) and Group SV (unassisted spontaneous ventilation). Outcome measures included intraoperative respiratory and hemodynamic parameters as well as recovery room data. Results: There were no significant differences in baseline characteristics between the two groups. Patients in Group PSV had lower ETCO₂ (42.8 ± 5.8 vs 50.4 ± 4.0, P = 0.001) and higher expiratory tidal volume per kg bodyweight (8.3 ± 1.8 ml kg^?1 vs 5.8 ± 0.8 ml kg^?1, P = 0.001) compared with patients in Group SV. There were no significant differences in other respiratory and hemodynamic parameters or recovery room data between the two groups. Conclusion: Pressure support ventilation via ProSeal? laryngeal mask airway during general anesthesia improves ventilation in pediatric patients undergoing ambulatory surgery. However, this did not translate to a difference in clinical outcome among our study patients.     

Protective ventilation to reduce inflammatory injury from one lung ventilation in a piglet model

Objectives: To test the hypothesis that protective ventilation strategy (PVS) as defined by the use of low stretch ventilation (tidal volume of 5 ml·kg^?1 and employing 5 cm of positive end expiratory pressure (PEEP) during one lung ventilation (OLV) in piglets would result in reduced injury compared to a control group of piglets who received the conventional ventilation (tidal volume of 10 ml·kg^?1 and no PEEP). Background: PVS has been found to be beneficial in adults to minimize injury from OLV. We designed the current study to test the beneficial effects of PVS in a piglet model of OLV. Methods: Ten piglets each were assigned to either ‘Control’ group (tidal volume of 10 ml·kg^?1 and no PEEP) or ‘PVS’ group (tidal volume of 5 ml·kg^?1 during the OLV phase and PEEP of 5 cm of H₂O throughout the study). Experiment consisted of 30 min of baseline ventilation, 3 h of OLV, and again 30 min of bilateral ventilation. Respiratory parameters and proinflammatory markers were measured as outcome. Results: There was no difference in PaO₂ between groups. PaCO₂ (P < 0.01) and ventilatory rate (P < 0.01) were higher at 1.5 h OLV and at the end point in the PVS group. Peak inflating pressure (PIP) and pulmonary resistance were higher (P < 0.05) in the control group at 1.5 h OLV. tumor necrosis factor‐alpha (P < 0.04) and IL‐8 were less (P < 0.001) in the plasma from the PVS group, while IL‐6 and IL‐8 were less (P < 0.04) in the lung tissue from ventilated lungs in the PVS group. Conclusions: Based on this model, PVS decreases inflammatory injury both systemically and in the lung tissue with no adverse effect on oxygenation, ventilation, or lung function.     

Propofol anaesthesia reduces early post-operative emesis after paediatric strabismus surgery

Propofol anaesthesia may reduce postoperative emesis. The purpose of this study was to compare the incidence of emesis after propofol anaesthesia with and without nitrous oxide, compared with thiopentone and halothane anaesthesia, in hospital and up to 24 hr postoperatively, in outpatient paediatric patients after strabismus surgery. Seventy-five ASA class I or II, unpremedicated patients, aged 2–12 yr were randomly assigned to one of three groups: Thiopentone, 6.0 mg · kg^{? 1} iv induction followed by halothane and N₂O/O₂ for maintenance (T/H); propofol for induction, followed by propofol and oxygen for maintenance (P/O₂); and propofol for iv induction, followed by propofol infusion and N₂O/O₂ for maintenance (P/N₂O). All received vecuronium, controlled ventilation, and acetaminophen pr. Morphine was given as needed for postoperative analgesia. There were no differences in age, weight, number of eye muscles operated upon, duration of anaesthesia or surgery. The P/N₂O group (255 ± 80 μg· kg^{? 1}· min^{? 1}) received less propofol than the P/O₂ group (344 ± 60 μg · kg^{? 1}· min^{? 1}) (P ≤ 0.0001) and had shorter extubation (P < 0.001) and recovery (P < 0.01) times. Emesis in the hospital, in both the P/N₂O (4.0%) and P/O₂ group (4.0%) was less than in the T/H group (32%) (P < 0.01). Antiemetics were required in four patients in the T/H group (16.0%). Overall emesis after surgery was not different among the groups: T/H (48%), P/O₂ (28%) and P/N₂O (42%). The use of propofol anaesthesia with and without N₂O decreased only early emesis. This supports the concept of a short-acting, specific antiemetic effect of propofol.     

Auswirkungen von Dopexamin Transpulmonales Shuntvolumen bei thorax- chirurgischen Eingriffen mit Ein-Lungen-Beatmung

Objective: To study the influence of dopexamine on pulmonary shunt and hypoxic pulmonary vasoconstriction during major thoracic surgery with one-lung ventilation (OLV). Design: Prospective, randomised, placebo-controlled study. Setting: University hospital. Patients: Twenty adult patients undergoing elective pulmonary resection. Anaesthesia: General anaesthesia was performed using propofol, fentanyl, N₂O and vecuronium.Volume-controlled ventilation was performed to maintain normocapnia over the whole investigation period. During OLV, the tidal volume was reduced and the respiratory rate was increased to avoid a peak airway pressure exceeding 40 cm H₂O. Furthermore the FiO₂ was increased to 1,0 and the external PEEP was removed during OLV. Interventions: The patients received either dopexamine at 2 µg/kg/min (group A, n=10) or 0,9% saline as control (group B, n=10) after assessing the baseline values. Measurement and results: The following cardiorespiratory variables were recorded: Heart rate, mean arterial pressure and mean pulmonary arterial pressure. Cardiac output was measured by thermodilution using a continuous cardiac output thermodilution catheter. Arterial and mixed venous blood gas analysis were measured from simultaneously drawn samples. Cardiac index (CI), systemic vascular resistance index, pulmonary vascular resistance index, oxygen delivery index (DO₂I), oxygen consumption index and the venous admixture were calculated using standard formula. Furthermore, pressure-flow-curves were constructed to analyse flow independent changes in the pulmonary vascular resistance. Data were recorded at the following times: After induction of anaesthesia in stable haemodynamics during two-lung ventilation (baseline values, T0), intraoperatively during one-lung ventilation (T1) and postoperatively after re-establishing two-lung ventilation (T2). Patients characteristics, data from the preoperative lung function testing and surgical procedures did not differ significantly between the groups. CI increased in the dopexamine group from 2,5±1,2 l·min^?1·m^?2 (T0) to 3,6±0,9 l·min^?1·m^?2 (T1) and 4,0±1,3 l·min^?1· m^?2 (T2). The course of the intrapulmonary right-to-left shunting did not differ between the groups. In the dopexamine-treated group the DO₂I increased from 430±143 ml·min·m^?2 (T0) to 652±255 ml·min·m^?2 (T1) and 653±207 ml·min·m^?2 (T2). Regarding the pressure-flow-curves there was no difference during OLV between the two groups indicating no major blocking effect of dopexamine on hypoxic pulmonary vasoconstriction. Conclusion: It is concluded that dopexamine can be used to improve haemodynamics and oxygen delivery during thoracic surgery without increasing venous admixture during one-lung ventilation.     

Glucose intolerance during prolonged sevoflurane anaesthesia

Purpose

The effects of prolonged sevoflurane anaesthesia on insulin sensitivity were investigated by two successive intravenous glucose tolerance tests (IVGTT) in eight patients who underwent prolonged surgery.

Methods

The first IVGTT was administered (25 g glucose as 20% dextrose in water iv) over two minutes 35 min after initiation of surgery. Arterial blood samples were obtained at 0, 5, 10, 30, 60, and 120 min after glucose administration for blood glucose and plasma insulin determination. A second IVGTT was performed six hours following the initiation of surgery.

Results

The disappearance rate of glucose (k-value) for the first IVGTT was 0.887 ± 0.436 (mean ± SD) % · min^?1, and 0.784 ± 0.289 for the second IVGTT. Both k-values are lower than the normal value. The maximum insulin response to glucose (ΔIRI · ΔBS^?1) of the second IVGTT was lower than the first IVGTT (0.124 ± 0.092 vs 0.071 ± 0.056, P < 0.05). The total insulin output of the first IVGTT was higher than the second IVGTT (1,161 ± 830 vs 568 ± 389 μU · min · ml^?1, P < 0.05).

Conclusion

Glucose intolerance is enhanced by diminished insulin output in response to blood glucose elevation during prolonged anaesthesia and surgery.     

Impact of caudal block on functional residual capacity and ventilation distribution in anaesthetized preschool children

Introduction: In children, general anaesthesia is often performed in combination with regional anaesthesia and caudal block (CB) is probably the most commonly used central neuroaxial blockade. The administration of local anaesthetics results in a motor blockade. The impact of this motor blockade induced by CB on the functional residual capacity (FRC) and ventilation distribution is unknown. The aim of this study was to determine the impact of CB versus control on FRC and ventilation distribution in preschool children. We hypothesized that an effective CB would lead to an increase of FRC and ventilation distribution while these parameters would remain unchanged in the control group. Methods: After approval from the local Ethics Committee, 52 preschool children (15–30 kg, 3–8 years) without cardiopulmonary disease who were to undergo elective surgery requiring combined general/regional anesthesia with a CB, were randomly allocated into two groups: CB (n = 26) or control (n = 26). Anesthesia was standardized using a propofol TCI for children. All children were breathing spontaneously via a laryngeal mask airway. FRC and lung clearance index (LCI), a measure of ventilation distribution, were calculated using a sulfur‐hexafluoride gas (SF₆) multibreath washout technique. A blinded reviewer performed off‐line analyses of the data. Following the first measurement in the supine position (baseline), all children were turned into the left‐lateral position. The CB group received a CB (0.2 ml·kg^‐1 bupivacaine 0.25% + epinephrine 1: 200 000 test dose and 0.8 ml·kg^‐1 bupivacaine 0.175%), while in the control group no intervention took place. After 5 min in the lateral position, all children were turned back to the supine position. After 15 min, the effectiveness of the CB was tested by pinching the skin at the L1 level with any movement being taken as a noneffective block (n = 0), and the second FRC assessment was performed in both groups. Results: At baseline, FRC and LCI were similar for the two groups. In the CB group, FRC (mean ± SD) increased from 17.0 ± 4.3 ml·kg^‐1 to 20.5 ± 5.1 ml·kg^‐1 (P < 0.0001) after an effective CB while FRC in the control group remained unchanged (17.2 ± 4.9 ml·kg^‐1 to 17.1 ± 4.8 ml·kg^‐1 (P = 0.0757). At the same time, the LCI decreased from 12.0 ± 2.5 to 9.37 ± 1.7 (P < 0.0001) in the CB group, while it remained constant in the control group (10.8 ± 2.7 vs 10.7 ± 2.6, P = 0.1515). Conclusions: CB resulted in a significantly increased FRC and ventilation distribution, whereas these parameters did not change in the control group. This indicates that a CB could have a major impact on respiratory function in anaesthetized, spontaneously breathing children. Additionally, the constant values for FRC and LCI in the control group showed that there was no ‘over‐time’ effect on these two parameters during the assessed study period. Acknowledgement: The study was funded by the Department of Anaesthesia, University of Basel, Switzerland and by the Swiss Association of Anaesthesia and Reanimation (SGAR).     

Determination of the pharmacodynamic interaction of propofol and dexmedetomidine during esophagogastroduodenoscopy in children

Objectives: Propofol is a sedative‐hypnotic drug commonly used to anesthetize children undergoing esophagogastroduodenoscopy (EGD). Dexmedetomidine is a highly selective alpha‐2 adrenergic receptor agonist that has been utilized in combination with propofol to provide anesthesia. There is currently no information regarding the effect of intravenous dexmedetomidine on the propofol plasma concentration–response relationship during EGD in children. This study aimed to investigate the pharmacodynamic interaction of propofol and dexmedetomidine when used in combination for children undergoing EGD. Methods: A total of 24 children undergoing EGD, ages 3–10 years, were enrolled in this study. Twelve children received dexmedetomidine 1 μg·kg^?1 given over 10 min as well as a continuous infusion of propofol delivered by a computer‐assisted target‐controlled infusion (TCI) system with target plasma concentrations ranging from 2.8 to 4.0 μg·ml^?1 (DEX group). Another group of 12 children undergoing EGD also received propofol administered by TCI targeting comparable plasma concentrations without dexmedetomidine (control group). We used logistic regression to predict plasma propofol concentrations at which 50% of the patients exhibited minimal response to stimuli (EC₅₀ for anesthesia). Results: The EC₅₀ ± se values in the control and DEX groups were 3.7 ± 0.4 μg·ml^?1 and 3.5 ± 0.2 μg·ml^?1, respectively. There was no significant shift in the propofol concentration–response curve in the presence of dexmedetomidine. Conclusion: The EC₅₀ of propofol required to produce adequate anesthesia for EGD in children was unaffected by a concomitant infusion of dexmedetomidine 1 μg·kg^?1 given over 10 min.     

Changes inPetCO2 and pulmonary blood flow after bronchial occlusion in dogs

The use ofPetCO₂ in detecting accidental bronchial intubation was investigated. ThePetCO₂ was measured in six mongrel dogs after occluding the left mainstem bronchus in three conditions; pentobarbital anaesthesia, 0.8% halothane insufflation together withpentobarbital anaesthesia, and simultaneous left pulmonary artery and bronchial airway occlusion with intravenous pentobarbital anaesthesia. An external flow probe measured left pulmonary artery blood flow. ThePetCO₂ decreased after bronchial occlusion during pentobarbital (35 ± 3 vs 30 ± 5 mmHg) and halothane-pentobarbital (30 ± 6 vs 25 ± 6 mmHg) conditions (P < 0.05). However, within three minutes of bronchial occlusion, the values ofPetCO₂ had returned to their pre-occlusion values. After five minutes of bronchial occlusion pulmonary artery blood flow in the non-ventilated lung decreased (P < 0.05) during pentobarbital (770 ± 533 ml · min^?1 vs 575 ± 306 ml · min^?1) and halothane-pentobarbital (495 ± 127 ml · min^?1 vs 387 ± 178ml · min^?1) conditions. Simultaneous bronchial and pulmonary artery occlusion prevented any changes inPetCO₂. It was concluded that accidental one- lung ventilation results in small and transient decreases inPetCO₂. A redistribution of blood flow from the nonventilated to ventilated lung occurs which restoresPetCO₂ to the original values observed with twolung ventilation.     

Ventilatory requirements during laparoscopic cholecystectomy

The purpose of this clinical study was to determine: (1) the increase in minute ventilation required to maintain preinsufflation arterial carbon dioxide tension (PaCO₂) during laparoscopic cholecystectomy, and (2) whether end-tidal PCO₂ (PetCO ₂) can be used as an index of PaCO₂ and, therefore, of the adequacy of minute ventilation during the pneumoperitoneum. We measured PaCO₂,PetCO ₂, expired minute volume (V_exp) standardized for body surface area (SA), airway and intra-abdominal pressure (Paw, Pabd) during general anaesthesia for laparoscopic cholecystectomy just before and 30 min after the creation of a CO₂ pneumoperitoneum in 28 healthy (ASA class 1 and 2) consenting adults. They were in the reverse Trendlenburg position (20°) with a 5° lateral tilt. Expired minute volume was increased from 3.75 (SEM ± 0.12) to 4.19 (0.15) L·min^?1·m^?2 to maintain PaCO₂ close to control levels: 38.9 (0.8) vs 40.1 (0.6) mmHg 5.19 (0.1) vs 5.35 (0.08) kPa). In most of the patients (23/28),PetCO ₂ was less than 41 mmHg with a correlation between PaCO₂ andPetCO ₂. In ten of these patients, (Pa-Pet)CO₂ was greater than the normal range. In 5/28, (Pa-Pet)CO₂ was negative. The “driving pressure” (Paw-Pabd) increased from 8.7 (1.0) to 10.4 (1.1) cm H₂O, without any correlation between the increase in Paw-Pabd and that in \(\dot Vexp\) . The results indicate the need for extra ventilatory requirement during laparoscopy and thatPetCO ₂ is an imperfect index of PaCO₂ under these circumstances.