BackgroundBolus injections of intravenous propofol and remifentanil can be used in the tracheal intubation of infants and children, but relatively large doses are needed. We hypothesised that addition of a small bolus of rocuronium would ensure good intubation conditions when modest propofol and remifentanil doses were used.MethodsSeventy infants between 3 weeks and 4 months of age were randomised to receive either placebo or rocuronium. Anaesthesia was induced with IV propofol, 3 (3–5) mg/kg [median (range)]. Rocuronium (0.2 mg/kg) or placebo was then injected, followed 15 s later by 2 μg/kg remifentanil. One anaesthetist attempted tracheal intubation 1 min after the rocuronium/placebo injection and used the ‘Copenhagen scoring system’ to assess intubation conditions. The neuromuscular effect of 0.2 mg/kg rocuronium was recorded in another eight, already intubated, infants using thumb accelerometry during train‐of‐four stimulation of the ulnar nerve.ResultsIntubation conditions were classified as ‘poor’ in 14 of 34 (41%) patients given placebo and in 10 of 36 (28%) patients given rocuronium (P = 0.32). There were four failed first attempts at intubation in the placebo group and none in the rocuronium group (P = 0.051). Maximum neuromuscular depression occurred 4 (3–8) after injection of 0.2 mg/kg rocuronium.ConclusionsIntubation conditions were poor in almost one third of the patients receiving propofol‐remifentanil. Adding a low‐dose rocuronium did not significantly improve intubation conditions.

BACKGROUNDThe relative respiratory effects of fentanyl and remifentanil, administered as i.v. bolus, have not previously been studied. We determined what remifentanil bolus dose gave the same maximum depression of ventilation as 1 µg kg(-1) of fentanyl.METHODSTwelve healthy volunteers rebreathed in a system designed to dampen variations in end-tidal carbon dioxide tension PE'CO2 so that measurements would be obtained at similar levels of CO(2) stimulation. The minute ventilation was measured before (V(preinj)) and after injection (V(nadir)) of fentanyl, 1 µg kg(-1), and remifentanil, 0.25, 0.5, and 1 µg kg(-1). The remifentanil doses were plotted against V(nadir)/V(preinj) in a log-probit diagram to determine what amount gave the same maximum ventilatory depression as the fentanyl dose.RESULTSV(nadir) was [median (inter-quartile range)] 51 (38-64)% of V(preinj) after fentanyl, and 70 (61-77), 50 (46-56), and 29 (24-38)%, respectively, after remifentanil. The nadir occurred 5.0 (4.4-7.0) min after fentanyl, and 3.8 (2.7-4.6), 2.9 (2.7-3.2), and 3.0 (2.7-3.2) min after remifentanil injection. PE'CO2 at ventilation nadir was 6.26 (5.98-6.62) kPa after fentanyl, and 6.18 (6.12-6.50), 6.11 (5.91-6.45), and 6.11 (5.93-6.45) kPa after remifentanil 0.25, 0.5, and 1 µg kg(-1), respectively. A remifentanil dose of 0.47 (0.42-0.62) µg kg(-1) was equidepressant to 1 µg kg(-1) of fentanyl. Fifteen minutes after fentanyl injection, the median minute ventilation was 30-40% less than after injection of remifentanil, 0.25 and 0.5 µg kg(-1) (P<0.05).CONCLUSIONSFentanyl, 1 µg kg(-1), and remifentanil, 0.5 µg kg(-1), gave similar maximum ventilatory depression. The onset of and recovery from ventilatory depression were faster with remifentanil.

21st Workshop on Surfactant Replacement, Oslo, June 1–4, 2006 saturated, monounsaturated and polyunsaturated components. Conclusions: RhKGF increases surfactant pools in LLF of immature lungs as BM does, but without catabolic side effects. In mature alveolarized lungs neither drug has an effect on its own, but the combination increases surfactant pools. RhKGF does not interfere with lipid homeostasis and might be useful in neonatal intensive care.

Background: In animals with acquired surfactant‐deficiency, a recruitment maneuver by increased tidal volumes enhances the effect of exogenous surfactant. In contrast, in the preterm lamb model, hyperinflation early after birth impairs the effect of surfactant prophylaxis. Here we examined whether a lung recruitment maneuver just before surfactant would affect the response to rescue treatment in immature lambs with established respiratory distress syndrome (RDS). Methods: Five pairs of preterm twin lambs with gestational age 127 days were delivered by cesarean section and supported by pressure‐limited mechanical ventilation for 4 h. At 30 min of age, when all the lambs were in severe respiratory failure, they were treated with porcine surfactant, 200 mg kg −1 . One lamb in each pair was subjected to a lung recruitment maneuver consisting of five sustained inflations of 20 ml kg −1 just before surfactant instillation. Results: At 10 min after surfactant treatment, all the lambs showed a large improvement in oxygenation and an increase in inspiratory capacity and static compliance. Except for a transiently better oxygenation after surfactant therapy in the recruitment group ( P < 0.05), there was no significant between‐group differences in gas exchange or lung mechanics at any time point during the study. There was no difference in post mortem intrapulmonary air volume or alveolar expansion in histologic lung sections between groups. Conclusion: This small study does not show any positive or negative effect of a lung recruitment maneuver on the response to rescue surfactant therapy in immature animals with RDS.

To assess the hemodynamic and metabolic effects of shivering during extreme normovolemic hemodilution, we anesthetized 16 pigs with fentanyl-midazolam-pancuronium. Mild hypothermia (36.5° ± 0.1°C) was induced by surface cooling, and the animals were randomized to either a control group (hemoglobin 118 ± 3 g/L) or a hemodilution group (hemoglobin 52 ± 2 g/L). In the latter group, blood was replaced with an isotonic Ringer’s acetate/dextran 70 solution. Shivering was allowed to occur by a controlled decrease in the infusion rate of pancuronium. Shivering increased oxygen consumption (&OV0312;o2) in both groups (P < 0.001). Initially, this was predominantly compensated for by an increased oxygen extraction ratio (ER), but when &OV0312;o2 was 2.3 ± 0.2 times baseline, critical levels of mixed venous oxygenation (S&OV0456;o2 = 18% ± 2%; P&OV0456;O2 = 22.5 ± 1.5 mm Hg) and ER (82% ± 3%) were recorded in anemic animals. Control animals did not reach critical levels until &OV0312;o2 was maximal (3.7 ± 0.3 times baseline). Maximal attained &OV0312;o2 was less (2.9 ± 0.1 times baseline) in the anemic animals (P = 0.01), and at this stage two of these pigs had myocardial lactate production, one of which died in ventricular fibrillation. Coronary perfusion pressure was significantly less (P < 0.001) in the anemic animals. We conclude that in this experimental model, maximal shivering as measured by &OV0312;o2 was limited in hemodiluted animals, and left ventricular oxygen balance was marginal, as evidenced by a decreased lactate uptake and extraction.

Background: Cyclic opening and closing of lung units during tidal breathing may be an important cause of iatrogenic lung injury. We hypothesized that airway closure is uncommon in children with healthy lungs when inspiratory pressures are kept low, but paradoxically may occur when inspiratory pressures are increased. Methods: Elastic equilibrium volume (EEV) and closing capacity (CC) were measured with a tracer gas (SF 6 ) technique in 11 anesthetized, muscle‐relaxed, endotracheally intubated and artificially ventilated healthy children, aged 0.6–13 years. Airway closing was studied in a randomized order at two inflation pressures, +20 or +30 cmH 2 O, and CC and CC/EEV were calculated from the plots obtained when the lungs were exsufflated to −20 cmH 2 O. (CC/EEV >1 indicates that airway closure might occur during tidal breathing). Furthermore, a measure of uneven ventilation, multiple breath alveolar mixing efficiency (MBAME), was obtained. Results: Airway closure within the tidal volume (CC/EEV >1) was observed in four and eight children (not significant, NS) after 20 and 30 cmH 2 O inflation, respectively. However, CC 30 /EEV was >CC 20 /EEV in all children ( P ≤0.001). The MBAME was 75±7% (normal) and did not correlate with CC/EEV. Conclusion: Airway closure within tidal volumes may occur in artificially ventilated healthy children during ventilation with low inspiratory pressure. However, the risk of airway closure and thus opening within the tidal volume increases when the inspiratory pressures are increased.

Background: In mature animals with surfactant deficiency induced by lung lavage, the therapeutic effect of exogenous surfactant is enhanced by a lung recruitment maneuver. We then tested whether a lung recruitment maneuver at birth immediately before surfactant treatment would improve lung function also in preterm lambs with surfactant deficiency due to immaturity.Methods: Ten newborn lambs with a gestational age of 127 days were randomized to receive surfactant either before the first breath or immediately after a lung recruitment maneuver consisting of five sustained inflations of 8, 16 or 32 ml/kg. Functional residual capacity was measured by sulfur hexafluoride washout, and inspiratory capacity as well as maximal compliance were obtained from a static expiratory pressure–volume curve after the lungs had been inflated to 35 cm H2O. In addition, blood gases were obtained. Measurements were made at 15, 45, 175, 135, 170 and 230 min after birth. Post mortem histological examinations of the lungs were performed in a blinded fashion.Results: The lung recruitment maneuvers did not improve oxygenation. Inspiratory capacity, static compliance and functional residual capacity at 4 h, as well as post mortem intrapulmonary air volume, had an inverse relation to the size of inflations given at birth. There was also a negative correlation between size of inflations at birth and response to surfactant therapy, as assessed by lung microscopy.Conclusion: Lung recruitment at birth does not improve the response to surfactant in immature lambs, but may instead have an adverse effect on lung function and morphology.

BACKGROUND:The lower inflexion point (LIP) on the inspiratory part of the pressure-volume (PV) loop has been suggested to be related to the pressure at which air spaces collapse. Our hypothesis is that airway collapse might instead be assessed from the upper inflexion point on the expiratory part of the PV-loop (UIPexp), where lung volume starts to decrease significantly. We therefore examined whether there was a relation between LIP and UIPexp in premature surfactant-treated lambs.METHODS:Ten lambs, at 119-141 days of gestational age, were delivered by cesarean section and given 200 mg/kg modified natural porcine surfactant before the first breath. The lambs were then connected to a ventilator and PV-loops using airway pressures of 0-35-0 (ZEEP-loop) and 5-35-5 cmH2O (PEEP-loop) were obtained after lung recruitment at 15, 60 and 120 min after birth. From the loops, LIP, UIPexp, upper inflexion point of the inspiratory part of the loop (UIP insp), inspiratory capacity (IC) as well as inspiratory and expiratory maximal compliance of the respiratory system (Crs(insp) and Crs(exp)) were calculated.RESULTS:The ZEEP-loop showed a substantial hysteresis with a distinct LIP at 19+/-2 cmH2O (mean+/-SD), which was different (P<0.001) from UIPexp (9+/-2 cmH2O). The pressures at LIP and UIPexp were unrelated (r2=0.06). UIPinsp was located at 28+/-2 cmH2O. Crs(insp) was 2.1+/-0.6 ml x cmH2O(-1) x kg(-1), which was lower (P<0.001) than Crs(exp) (2.8+/-0.6 ml x cmH2O(-1) x kg(-1)). IC was 26+/-6 ml/kg. The PEEP-loop had a minimal hysteresis with an expiratory part coinciding with that of the ZEEP-loop.CONCLUSION:In surfactant-treated premature lambs the pressures at LIP and UIPexp are not related, showing that LIP does not indicate the pressure at which airways collapse.

Anaesthesia systems that minimize the use of volatile anaesthetics to reduce cost and pollution are of interest. Closed circuit anaesthesia is the ideal solution, but requires continuous adjustment of fresh gas flow and composition and thus is demanding in routine practice. We describe an alternative system, the Reflector system, which is open in regard to oxygen, nitrogen and N2O, and semiclosed in regard to volatile anaesthetics. The Reflector system is a circle system with a carbon dioxide absorber and an automatic vapour delivery device placed in the inspiratory limb of the circle. A zeolite filter, the Reflector, is placed between the ventilator and the circle. The Reflector functions as a molecular sieve, preventing the volatile anaesthetic from leaving the circle. Isoflurane consumption using the Reflector system in bench tests and an animal study was compared with that of an open system. In bench tests consumption was reduced by 79% and 82%, at a respiratory frequency of 10 and 20 min-1, respectively. The corresponding mean figures from the animal experiment were 65% and 77%.

The mechanical behavior of the lung and chest wall has not been determined in preschool children. We therefore obtained static expiratory pressure-volume (P-V) curves of the respiratory system, partitioned into lung and chest wall components using esophageal (Pes) and airway pressure (Paw) registration in 17 anesthetized children (0.2 to 15.5 yr) in the supine and lateral position. From the P-V curves the inspiratory capacity (IC), the chest wall elastance (Ecw), and the maximal compliance of the respiratory system (Crs) and lungs (C(lung)) were calculated and related to growth. At IC (Paw = 30 cm H(2)O), Pes was the same in the two positions: 11 +/- 3 cm H(2)O. In contrast, at end-expiration (Paw = 0), Pes was close to zero in the lateral position, but markedly positive in the supine position (7 +/- 2 cm H(2)O). C(lung) was similar in both positions and increased with growth. Thus, C(lung) in the lateral position (ml/cm H(2)O) = 0.0017 x length(2.26) (cm), r(2) = 0.90. Crs and IC were approximately 20% greater (p = 0.001) in the supine position than in the lateral, and correlated strongly (r(2) >/= 0.93) with power functions of length in both positions. Ecw expressed as a fraction of total respiratory system elastance (Ecw/Ers) was 33 +/- 12% in the lateral position and 12 +/- 16% supine (p < 0.001). We conclude that the respiratory mechanics in children correlated closely with body size and showed important differences between the supine and lateral positions.

Lung Trauma From Five Moderately Large Manual Inflations Immediately After Surfactant Instillation in Newborn Immature Lambs † 1678

Clinically, hemodilution to a hematocrit of 9% has been studied, but the effects of hypovolemia during this degree of hemodilution have not been elucidated.We studied the response to blood loss during extreme hemodilution and evaluated indicators of hypovolemia. Systemic and myocardial hemodynamics, oxygen transport, and blood lactate concentrations were measured in 12 anesthetized pigs exposed to a graded blood loss of 10, 20, 30, and 40 mL/kg. Six animals were hemodiluted (hematocrit 10.8% +/- 1.4%, mean +/- SD), and six animals served as controls (hematocrit 34.6% +/- 1.5%). Hemodilution decreased systemic oxygen delivery to 9.5 +/- 0.6 mL [center dot] kg-1 [center dot] min-1 (controls 21.7 +/- 3.9 mL [center dot] kg-1 [center dot] min (-1)) (P < 0.01) despite a 31% increase in cardiac output. Systemic oxygen uptake was unchanged. Arterial lactate increased to 3.3 +/- 1.1 mM/L (controls 1.6 +/- 0.6 mM/L) (P < 0.05), and mixed venous oxygen saturation (SvO2) decreased to 38.2% +/- 4.8% (controls 68.6% +/- 2.9%) (P < 0.01). At a blood loss of 10 mL/kg, cardiac output continued to be greater in the hemodiluted animals (P < 0.01). Arterial blood pressure decreased to 61 +/- 8 mm Hg (controls 84 +/- 18 mm Hg) (P < 0.05), whereas heart rate was unchanged. Systemic oxygen delivery decreased to 8.8 +/- 1.2 mL [center dot] kg-1 [center dot] min-1 (controls 14.1 +/- 2.5 mL [center dot] kg (-1) [center dot] min-1) (P < 0.01). Systemic oxygen uptake was maintained by a further increase in oxygen extraction, and SvO2 decreased to 29.7% +/- 7.3%, compared with 55.3% +/- 9.0% in controls (P < 0.01). Arterial lactate increased to 4.9 +/- 1.4 mM/L (controls 1.8 +/- 0.8 mM/L) (P < 0.01). Myocardial oxygen delivery and lactate uptake were unchanged. When the blood loss equaled 30 mL/kg, myocardial lactate production occurred, and two hemodiluted animals died of circulatory failure. Central venous and capillary wedge pressures changed minimally during the blood loss and did not differ between groups. We conclude that a decrease in arterial blood pressure and SvO2 were early signs of hypovolemia during hemodilution, whereas central venous pressure and pulmonary capillary wedge pressure were insensitive indicators. Implications: Anesthetized pigs with extremely low hemoglobin levels (one third of normal) showed poor tolerance to blood loss >10 mL/kg. A decreasing arterial blood pressure, a decreasing oxygen saturation in the venous blood, and an increase in arterial blood lactate concentration were useful indicators of blood loss. (Anesth Analg 1998;87:786-94)