Cerebral ischaemia during cardiac surgery in children detected by combined monitoring of BIS and near-infrared spectroscopy

Background. Children frequently suffer transient cerebral ischaemiaduring cardiac surgery. We measured cerebral ischaemia in childrenduring cardiac surgery by combining two methods of monitoring. Methods. We studied 65 children aged between 5 months and 17yr having surgery to correct non-cyanotic heart disease usinghypothermic cardiopulmonary bypass (CPB). During surgery, wemeasured the Bispectral Index (BIS) and regional cerebral haemoglobinoxygen saturation (Sr_O2) with near-infrared spectroscopy (NIRS).Cerebral ischaemia was diagnosed if both Sr_O2 and BIS decreasedabruptly when acute hypotension occurred. In each patient, therelationship between Sr_O2 and arterial blood pressure (AP) wasindicated by a plot of mean Sr_O2 against simultaneous mean AP. Results. We noted 72 episodes of cerebral ischaemia in 38 patients.Sixty-three ischaemic events were during CPB. Cerebral ischaemiawas less frequent in older patients. Cerebral ischaemia wasmore common and more frequent in children under 4 yr old. Haematocritduring CPB was lower and Sr_O2 was more dependent on AP in childrenunder 4 yr. Conclusions. Children less than 4 yr of age are more likelyto have cerebral ischaemia caused by hypotension during cardiacsurgery. Ineffective cerebral autoregulation and haemodilutionduring CPB may be responsible. Br J Anaesth 2004: 92: 662–9     

Decreased bispectral index as an indicator of syncope before hypotension and bradycardia in two patients with needle phobia

We report two cases who exhibited a decrease in their bispectralindex (BIS^TM) score, associated with syncope during venipuncturein patients with suspected needle phobia. In case 1, the reductionin BIS score occurred during the development of hypotensionand bradycardia and may well have been caused by cerebral hypoperfusion.In case 2, the patient lost consciousness with decreasing BISscore before hypotension and bradycardia; this patient’scondition could not be completely explained by cerebral hypoperfusionas a result of a vasovagal reflex because the patient’sblood pressure and heart rate remained normal during the syncopalepisode. Br J Anaesth 2003; 91: 749–52     

Cerebral hypoperfusion in immediate postoperative period following coronary artery bypass grafting, heart valve, and abdominal aortic surgery

Perioperative levels of jugular bulb oxyhaemoglobin saturation(Sj_O2) and lactate concentration (Lj), and postoperative durationof Sj_O2<50% were compared between patients undergoing coronaryartery bypass grafting (CABG) (n=86), heart valve (n=14) andabdominal aortic (n=16) surgery. Radial artery and jugular bulbblood samples were aspirated after induction of anaesthesia,during re-warming on cardiopulmonary bypass (CPB) (36°C),on arrival in the intensive care unit (ICU) and, subsequently,at 1, 2 and 6 h after ICU admission. Most patients having heartsurgery were hypocapnic at 36°C on CPB. Following CABG andheart valve surgery, many patients were hypocapnic whereas afterabdominal aortic surgery, most were hypercapnic. During CPBand postoperatively, Sj_O2 and Lj were significantly correlatedto Pa_CO2 and the arterial concentration of lactate (La) respectively(P<0.05). After correction for arterial carbon dioxide tension(Pa_CO2) and La, there were no significant changes in Sj_O2 orLj on CPB. Postoperatively, having corrected for Pa_CO2, therewere significant effects on Sj_O2 over all groups as a resultof time from surgery (P<0.001) and its interaction with operationtype (P<0.001). Following correction for La, there were nopostoperative effects on Lj. No significant differences (P=0.2)in duration of Sj_O2<50% existed between patients undergoingCABG (1054 (82) min), abdominal aortic (893 (113) min) and heartvalve (1073 (91) min) surgery. The lack of significant reciprocaleffects on Lj combined with the frequency of hypocapnia andstrong influence of Pa_CO2on Sj_O2, suggest that Sj_O2<50% duringCPB and after cardiac surgery represents hypoperfusion as aconsequence of hypocapnia rather than cerebral ischaemia. Br J Anaesth 2001; 87: 229–36     

A comparison of bispectral index and entropy monitoring, in patients undergoing embolization of cerebral artery aneurysms after subarachnoid haemorrhage

Background. Processed EEG monitoring of anaesthetic depth couldbe useful in patients receiving general anaesthesia followingsubarachnoid haemorrhage. We conducted an observational studycomparing performance characteristics of bispectral index (BIS)and entropy monitoring systems in these patients. Methods. Thirty-one patients of the World Federation of Neurosurgeonsgrades 1 and 2, undergoing embolization of cerebral artery aneurysmsfollowing acute subarachnoid haemorrhage, were recruited tohave both BIS and entropy monitoring during general anaesthesia.BIS and entropy indices were matched to clinical indicatorsof anaesthetic depth. Anaesthetists were blinded to the anaestheticdepth monitoring indices. Analysis of data from monitoring devicesallowed calculation of prediction probability (P_K) constants,and receiver operating characteristic (ROC) analysis to be performed. Results. BIS and entropy [response entropy (RE), state entropy(SE)] performed well in their ability to show concordance withclinically observed anaesthetic depth. P_K values were generallyhigh (BIS 0.966–0.784, RE 0.934–0.663, SE 0.857–0.701)for both forms of monitoring. ROC curve analysis shows a highsensitivity and specificity for all monitoring indices whenused to detect the presence or absence of eyelash reflex. Areaunder curve for BIS, RE and SE to detect the absence or presenceof eyelash reflex was 0.932, 0.888 and 0.887, respectively.RE provides earlier warning of return of eyelash reflex thanBIS. Conclusion. BIS and entropy monitoring perform well in patientswho receive general anaesthesia after good grade subarachnoidhaemorrhage.     

Progressive changes in arterial oxygenation during one-lung anaesthesia are related to the response to compression of the non-dependent lung

Background. Arterial oxygenation can change during one-lungventilation for reasons that are not fully understood. Methods. We studied patients during anaesthesia and one-lungventilation, with an inspiratory oxygen fraction of 0.8. Arterialblood gas values were recorded every 10 s with a continuousintra-arterial sensor. The non-dependent lung was compressedseveral times during the surgical procedure, using a retractor.The change in Pa_O2 during and after compression of the non-dependentlung was measured. Results. Pa_O2 increased significantly when the non-dependentlung was compressed, and decreased when the compression wasreleased. The first compression of the non-dependent lung transientlyincreased Pa_O2, but the effect of the second compression onoxygenation was more marked and persistent. Pa_O2 increased bymore than 13 kPa at 10 min after the second compression in fourpatients (responder group). Arterial oxygenation improved markedlyin patients in this group during the surgical procedure. Conclusion. Oxygenation can improve during one-lung ventilationin some patients. This improvement is partly related to a markedincrease in Pa_O2 during compression of the non-dependent lung. Br J Anaesth 2003; 90: 21–6     

Comparison of 1% and 2% lidocaine epidural anaesthesia combined with sevoflurane general anaesthesia utilizing a constant bispectral index

Background. The authors compared the effects of epidural anaesthesiawith lidocaine 1% and lidocaine 2% on haemodynamic variables,sevoflurane requirements, and stress hormone responses duringsurgery under combined epidural/general anaesthesia with bispectralindex score (BIS) kept within the range 40–50. Methods. Thirty-three patients undergoing lower abdominal surgerywere randomly divided into two groups to receive lidocaine 1%or 2% by epidural with sevoflurane general anaesthesia. Sevofluranewas adjusted to achieve a target BIS of 40–50 during maintenanceof anaesthesia with nitrous oxide 60% in oxygen. Measurementsincluded the inspired (FI_SEVO) and the end-tidal sevofluraneconcentrations (E'_SEVO), blood pressure (BP), and heart rate(HR) before surgery and every 5 min during surgery for2 h. Plasma samples were taken immediately before and duringsurgery for measurements of catecholamines, cortisol, and lidocaine. Results. During surgery, both groups were similar for HR, BPand BIS, but FI_SEVO and E'_SEVO were significantly higher andmore variable with lidocaine 1% than with 2%. Intraoperativeplasma concentrations of epinephrine and cortisol were foundto be higher with lidocaine 1% as compared with 2%. Conclusions. To maintain BIS of 40–50 during combinedepidural/general anaesthesia for lower abdominal surgery, sevofluraneconcentrations were lower and less variable with lidocaine 2%than with 1%. In addition, the larger concentration of lidocainesuppressed the stress hormone responses better. Br J Anaesth 2003; 91: 825–9     

Comparative evaluation of the cerebral state index and the bispectral index during target-controlled infusion of propofol

Background. Cerebral state index (CSI) has recently been introducedas an intra-operative monitor of anaesthetic depth. We comparedthe performance of the CSI to the bispectral index (BIS) inmeasuring depth of anaesthesia during target-controlled infusion(TCI) of propofol. Methods. Twenty Chinese patients undergoing general anaesthesiawere recruited. CSI and BIS, and predicted effect-site concentrationof propofol were recorded. The level of sedation was testedby Modified Observer's Assessment of Alertness/Sedation Scale(MOAAS) every 20 s during stepwise increase (TCI, 0.5 µgml^–1) of propofol. The loss of verbal contact (LVC) andloss of response (LOR) were defined by MOAAS values of 2–3and less than 2, respectively. Baseline variability and theprediction probability (P_K) were calculated for the BIS andCSI. The values of BIS₀₅ and CSI₀₅, BIS₅₀ and CSI₅₀, BIS₉₅ andCSI₉₅ were calculated at each end-point (LVC and LOR). Results. Baseline variability of CSI was more than that of BIS.Both CSI and BIS showed a high prediction probability for thesteps awake vs LVC, awake vs LOR, and LVC vs LOR, and good correlationswith MOAAS values. Conclusion. Despite larger baseline variation, CSI performedas well as BIS in terms of P_K values and correlations with stepchanges in sedation.     

Comparability of Narcotrend index and bispectral index during propofol anaesthesia

Background. The dimensionless Narcotrend^TM (NCT) index (MonitorTechnik,Germany, version 4.0), from 100 (awake) to 0, is a new indexbased on electroencephalogram pattern recognition. Transferringguidelines for titrating the Bispectral Index^TM (BIS, AspectMedical Systems, USA, version XP) to the NCT index depends ontheir comparability. We compared the relationship between BISand NCT values during propofol anaesthesia. Methods. Eighteen adult patients about to have radical prostatectomywere investigated. An epidural catheter was placed in the lumbarspace and electrodes for BIS and NCT were applied as recommendedby the manufacturers. After i.v. fentanyl 0.1 mg, anaesthesiawas induced with a propofol infusion. After intubation, patientsreceived bupivacaine 0.5% 15 ml via the epidural catheter. Forty-fiveminutes after induction, the propofol concentration was increasedto substantial burst suppression pattern and then decreased.This was done twice in each patient, and BIS and Narcotrendvalues were recorded at intervals of 5 s. The efficacy of NCTand BIS in predicting consciousness vs unconsciousness was evaluatedusing the prediction probability (P_K). Results. We collected 38 629 artefact-free data pairs of BISand NCT values from the respective 5-s epochs. Because of artefacts,another 5008 epochs had been excluded from data analysis (3855epochs for the NCT index alone, 245 epochs for the BIS aloneand 908 epochs for both indices). Mean (SD) values in awakepatients were 94 (6) for Narcotrend and 91 (8) for BIS. Withloss of the eyelash reflex, both values were significantly reduced,to 72 (9) for NCT (P<0.001) and to 77 (11) for the BIS index(P<0.001). The P_K value for loss of eyelash reflex was similarfor BIS (0.95) and NCT (0.93). Decreasing BIS values coincidedwith decreasing NCT values. A sigmoid model [NCT index=52.8+26.8/(1+exp(–(BIS–78.3)/4.8))^0.4;r=0.52] described the correlation between BIS and NCT indexin a BIS range between 100 and 50. For BIS values lower than50, a second sigmoid model with a correlation of r=0.83 wasapplied [NCT index=6.6+45.3/(1+exp(–(BIS–29.8)/2.4))^0.6 r=0.83]. The relationship between burst suppression ratio(BSR) and NCT index was best described by the following sigmoidmodel: NCT index=265/(1+exp((–BSR+108)/–49); r=0.73. Conclusions. We found a sufficient correlation between BIS andNCT index, but deviations from the line of identity in someranges require attention. Therefore, a simple 1:1 transfer fromBIS to NCT values is not adequate. Our results might serve asa blueprint for the rational translation of BIS into NCT values.     

Near-infrared spectroscopy in adults: effects of extracranial ischaemia and intracranial hypoxia on estimation of cerebral oxygenation

We have studied the effects of extracranial ischaemia and intracranialhypoxia on measurement of cerebral oxygenation using near-infrared,reflectance-mode, cerebral oximetry (Invos 3100 cerebral oximeter)in healthy adult subjects. Under stable systemic conditions,scalp ischaemia induced by a pneumatic tourniquet caused anapparent reduction in mean regional cerebral oxygenation (rSo₂)from mean 72 (SD 6)% to 59 (7)% (n = 8, P < 0.001). rSo₂returned to control values within 1 min of release of the tourniquet.Local scalp ischaemia induced by rapid frontalis muscle exercisecaused a significant reduction (4.5 (2)%) in rSo₂ (n = 12, P< 0.001). The effect of systemic hypoxia on rSo₂ was examinedduring controlled scalp ischaemia. A decrease in mean SpO₂ from98 (2)% to 66 (6)% was associated with a decrease in mean rSo₂from 57 (4)% to 41 (6)%. There was a significant correlationbetween the percentage reduction in rSo₂ and Sp_o2 during hypoxia(r = 0.81, P < 0.001). We conclude that the lnvos cerebraloximeter was capable of detecting tissue hypoxia deep to thescalp under carefully controlled conditions but that it alsowas affected significantly by changes in extracranial bloodflow and oxygenation which may affect its reliability in clinicalpractice. Further work is necessary to define those situationsin which cerebral oximetric monitoring is useful and valid.     

Reflex pupillary dilatation in response to skin incision and alfentanil in children anaesthetized with sevoflurane: a more sensitive measure of noxious stimulation than the commonly used variables

Background. Estimation of analgesia in anaesthetized childrenis often imprecise, and consequently, anaesthesiologists commonlyevaluate children's response to surgical stimulation by movementor haemodynamic changes. In adults reflex pupillary dilatationhas been demonstrated to be a very sensitive measure of noxiousstimulation, correlated with opioid concentrations. The autonomicnervous control changes with age, raising the hypothesis thatmechanisms involved in pupillary autonomic functions regardingboth sympathetic and parasympathetic components may also differbetween adults and children. In this pilot study, we testedthe hypothesis that the pupillary reflex dilatation might allowassessment of noxious stimulation and analgesic effect of alfentanilin children under sevoflurane anaesthesia, as an alternativeto haemodynamic and bispectral measures. Methods. After sevoflurane induction, 24 children were maintainedin steady-state conditions at 1.5 MAC of sevoflurane in O₂–N₂O(50–50). An intense noxious stimulation was provided bystandardized skin incision on the lower limb. A bolus of alfentanil(10 µg kg^–1) was administered either 1 min (n=16)or 2 min (n=8) after skin incision. Haemodynamic values, bispectralindex (BIS) and pupillary diameter (PD) were recorded just beforestimulation and at 30–60 s intervals during 4 subsequentminutes. Results. In all children PD increased significantly after noxiousstimulation [+200 (40)%, at 60 s]. In contrast, mean heart rateand blood pressure increased only 11 (7)% and 10 (8)% respectively,60 s after stimulation. BIS did not change significantly. Inall children, alfentanil injection induced a rapid decreaseof PD and restored pre-incision values in 2 min. Conclusion. PD is a more sensitive measure of noxious stimulationthan the commonly used variables of heart rate, arterial bloodpressure and BIS in children anaesthetized with sevoflurane.     

Arterial to end-tidal carbon dioxide tension difference in children with congenital heart disease

In children with congenital cyanotic heart disease, right-to-leftintracardiac shunting causes an obligatory difference betweenarterial and end-tidal carbon dioxide tension (Pa_CO2–PE'_CO2)as venous blood, rich in carbon dioxide, is added to the arterialcirculation. This obligatory Pa_CO2–PE'_CO2 difference,which can be predicted from knowledge of oxygen saturation,haemoglobin concentration and Pa_CO2, increases as oxygen saturationdecreases, most markedly when the haemoglobin concentrationis high. A second possible cause of the Pa_CO2–PE'_CO2 differenceis the effect of pulmonary hypoperfusion caused by the shunt.We studied 60 children undergoing cardiac surgery and comparedthe predicted the Pa_CO2–PE'_CO2 difference with measuredvalues to investigate the extent to which additional factorsinfluence the clinically observed Pa_CO2–PE'_CO2. In manychildren, observed values were much greater than predicted,which is compatible with some degree of pulmonary hypoperfusion.However, this was not felt to represent the complete picturein all patients. Another cause of ventilation–perfusionmismatch was suspected in those children who showed a considerableimprovement in oxygen saturation during ventilation with anincreased FI_O2. We believe that pulmonary congestion causedby large left-to-right shunts may further increase the Pa_CO2–PE'_CO2difference. Br J Anaesth 2001; 86: 349–53     

Effects of propofol vs sevoflurane on arterial oxygenation during one-lung ventilation

Background: The inhibitory effect of anaesthetic agents on hypoxic pulmonaryvasoconstriction may depend upon their dose, especially whenusing a volatile agent. The aim of this randomized open studywas to compare the effects of sevoflurane and propofol, as primaryanaesthetic agents, on oxygenation during one-lung ventilation(OLV), with their administration being adjusted to maintainbispectral index (BIS) values between 40 and 60. Methods: Eighty patients scheduled for a lobectomy, receiving an epiduralmixture of ropivacaine and sufentanil, were randomly assignedto Group S (maintenance with sevoflurane) or Group P (maintenancewith propofol). After placement of a double-lumen tube, thelungs were ventilated at an inspiratory fraction of oxygen of1.0, a tidal volume of 6 ml kg^–1, and 12 bpm. Arterialblood gas samples were taken as follows: during two-lung ventilationbefore OLV, and during the first 40 min of OLV. Results: Fifteen patients were excluded (incorrect placement of the tubeor BIS outside the desired range). The two groups were comparablein terms of demographic variables, haemodynamic, and BIS levelsduring the operation. Four patients in each group had a Sp_O2<90%.Mean of the lowest Pa_O2 was 16.3 (7.5) kPa in Group S and 17.7(9.3) kPa in Group P (ns). Conclusions: Sevoflurane and propofol had similar effect on Pa_O2 during OLVwhen their administration is titrated to maintain BIS between40 and 60.     

Regional response of cerebral blood volume to graded hypoxic hypoxia in rat brain

Background. The response of cerebral blood flow to hypoxic hypoxiais usually effected by dilation of cerebral arterioles. However,the resulting changes in cerebral blood volume (CBV) have receivedlittle attention. We have determined, using susceptibility contrastmagnetic resonance imaging (MRI), changes in regional CBV inducedby graded hypoxic hypoxia. Methods. Six anaesthetized rats were subjected to incrementalreduction in the fraction of inspired oxygen: 0.35, 0.25, 0.15,and 0.12. At each episode, CBV was determined in five regionsof each hemisphere after injection of a contrast agent: superficialand deep neocortex, striatum, corpus callosum and cerebellum.A control group (n=6 rats) was studied with the same protocolwithout contrast agent, to determine blood oxygenation leveldependent (BOLD) contribution to the MRI changes. Results. Each brain region exhibited a significant graded increasein CBV during the two hypoxic episodes: 10–27% of controlvalues at 70% Sa_O2, and 26–38% at 55% Sa_O2. There wasno difference between regions in their response to hypoxia.The mean CBV of all regions increased from 3.6 (SD 0.6) to 4.1(0.6) ml (100 g)^–1 and to 4.7 (0.7) ml (100 g)^–1during the two hypoxic episodes, respectively (SchefféF-test; P<0.01). Over this range, CBV was inversely proportionalto Sa_O2 (r²=0.80). In the absence of the contrast agent, changesdue to the BOLD effect were negligible. Conclusions. These findings imply that hypoxic hypoxia significantlyraises CBV in different brain areas, in proportion to the severityof the insult. These results support the notion that the vasodilatoryeffect of hypoxia is deleterious in patients with reduced intracranialcompliance. Br J Anaesth 2002; 89: 287–93     

Sedation caused by clonidine in patients with spinal cord injury

Background. In patients with spinal cord injury, cephalad spreadof intrathecal (i.t.) medication could be delayed. Methods. We used bispectral index and an observer scale to assesssedation after two different doses of i.t. clonidine in patientswith or without spinal cord injury. Twelve patients with neurologicaldeficit caused by trauma (Spinal Cord Injury, SCI) were comparedwith patients without neurological disease. They received 10mg of i.t. bupivacaine with clonidine, with either 50 µg(low dose, n=6) or 150 µg (high dose, n=6) at L₂–L₃.A further 12 patients, six with spinal trauma lesion and sixhealthy, received i.t. bupivacaine and 150 µg of i.m.clonidine. Results. Sedation and a decrease in BIS occurred only in patientsreceiving 150 µg of clonidine. Onset of sedation and thedecrease in BIS was delayed in most spinal cord injured patientswhatever the route of administration (P<0.001). Durationof sedation was not different between the groups. Delayed sedationand decrease of BIS after i.t. clonidine in patients with spinalcord injury are similar than those observed after i.m. clonidine. Conclusion. A systemic effect is likely to be the main reasonfor sedation. Br J Anaesth 2003; 90: 742–5     

Accuracy of feedback-controlled oxygen delivery into a closed anaesthesia circuit for measurement of oxygen consumption

Background. Oxygen consumption (V^·>O₂) is rarely measuredduring anaesthesia, probably because of technical difficulties.Theoretically, oxygen delivery into a closed anaesthesia circuit(V^·>O₂-PF; PhysioFlex^TM Draeger Medical Company, Germany)should measure V^·>O₂. We aimed to measure V^·>O₂-PFin vitro and in vivo. Methods. Three sets of experiments were performed. V^·>O₂-PFwas assessed with five values of V^·>O₂ (0–300 mlmin^–1) simulated by a calibrated lung model (V^·>O₂-Model)at five values of FI_O2 (0.25–0.85). The time taken forV^·>O₂-PF to respond to changes in V^·>O₂-Modelgave a measure of dynamic performance. In six healthy anaesthetizeddogs we compared V^·>O₂-PF with V^·>O₂ measuredby the Fick method (V^·>O₂-Fick) during ventilationwith nine values of FI_O2 (0.21–1.00). V^·>O₂-PFand V^·>O₂-Fick were also compared in three dogs whenV^·>O₂ was changed pharmacologically [102 (SD 14),121 (17) and 200 (57) ml min^–1]. In patients during surgery,we measured V^·>O₂-PF and V^·>O₂-Fick simultaneouslyafter induction of anaesthesia (n=21) and during surgery (n=17)(FI_O2 0.3–0.5). Results. Compared with V^·>O₂-Model, V^·>O₂-PFvalues varied from time to time so that averaging over 10 minis recommended. Furthermore, at an FI_O2 >0.8, V^·>O₂-PFalways overestimated V^·>O₂. With FI_O2 <0.8, averagedV^·>O₂-PF corresponded to V^·>O₂-Model andadapted rapidly to changes. Averaged V^·>O₂-PF alsocorresponded to V^·>O₂-Fick in dogs at FI_O2 <0.8.V^·>O₂ measured by the two methods gave similar resultswhen V^·>O₂ was changed pharmacologically. In contrast,V^·>O₂-PF systematically overestimated V^·>O₂-Fickin patients by 52 (SD 40) ml min^–1 and this bias increasedwith smaller arteriovenous differences in oxygen content. Conclusion. V^·>O₂-PF measures V^·>O₂ adequatelywithin specific conditions. Br J Anaesth 2003; 90: 281–90     

Randomized study comparing the effects of hydroxyethyl starch solution with Gelofusine on pulmonary function in patients undergoing abdominal aortic aneurysm surgery

Background. Restoring blood flow to ischaemic tissue can causelung damage with pulmonary oedema. Hydroxyethyl starch (HES)solution, when used for volume replacement, may modify and reducethe degree of ischaemia–reperfusion injury. We comparedthe effects of HES solution with those of Gelofusine solutionon pulmonary function, microvascular permeability and neutrophilactivation in patients undergoing elective infrarenal abdominalaortic aneurysm surgery. Methods. Forty patients were randomized into two groups. Theanaesthetic technique was standardized. Lung function was assessedwith the PO₂/FI_O2 ratio, respiratory compliance, chest x-rayand a score for lung injury. Microvascular permeability wasdetermined by measuring microalbuminuria. Neutrophil activationwas determined by measurement of plasma elastase. Results. Four hours after surgery, the median (quartile values)PO₂/FI_O2 ratio was 40.3 (37.8, 53.1) kPa for the HES-treatedpatients compared with 33.9 (31.2, 40.9) kPa for the Gelofusine-treatedpatients (P<0.01, Mann–Whitney test). The respiratorycompliance was 80 (73.5, 80) ml cm^–1 H₂O inthe HES-treated patients compared with 60.1 (50.8, 73.3) mlcm^–1 H₂O in the Gelofusine-treated patients (P<0.01,Mann–Whitney test). The lung injury score 4 h after surgerywas less for the patients treated with HES compared with thepatients treated with Gelofusine (0.33 vs 0.71, P=0.01, Wilcoxonrank sum test). Mean (SD) plasma elastase was less in the HES-treatedpatients on the first postoperative day (1.96 (0.17) vs 2.08(0.24), P<0.05). The log mean microalbuminuria was less inthe HES-treated patients (0.41 vs 0.91 mg mmol^–1,P<0.05). This difference in microvascular permeability wasassociated with different volumes of colloid required to maintainstable cardiovascular measurements in the two groups of patientsstudied (3000 vs 3500 ml, P<0.01, Mann–Whitney test). Conclusion. Compared with Gelofusine, the perioperative pulmonaryfunction of patients treated with HES after abdominal aorticaneurysm surgery was better. Br J Anaesth 2004; 92: 61–6     

Liver tissue partial pressure of oxygen and carbon dioxide during partial hepatectomy

Background. Data on tissue oxygen partial pressure (Pt_O2) andcarbon dioxide partial pressure (Pt_CO2) in human liver tissueare limited. We set out to measure changes in liver Pt_O2 andPt_CO2 during changes in ventilation and a 10 min period of ischaemiain patients undergoing liver resection using a multiple sensor(Paratrend^® Diametrics Medical Ltd, High Wycombe, UK). Methods. Liver tissue oxygenation was measured in anaesthetizedpatients undergoing liver resection using a sensor insertedunder the liver capsule. Pt_O2 and Pt_CO2 were recorded with FI_O2values of 0.3 and 1.0, at end-tidal carbon dioxide partial pressuresof 3.5 and 4.5 kPa and 10 min after the onset of liver ischaemia(Pringle manoeuvre). Results. Data are expressed as median (interquartile range).Increasing the FI_O2 from 0.3 to 1.0 resulted in the Pt_O2 changingfrom 4.1 (2.6–5.4) to 4.6 (3.8–5.2) kPa, but thiswas not significant. During the 10 min period of ischaemia Pt_CO2increased significantly (P<0.05) from 6.7 (5.8–7.0)to 11.5 (9.7–15.3) kPa and Pt_O2 decreased, but not significantly,from 4.3 (3.5–12.0) to 3.3 (0.9–4.1) kPa. Conclusion. Pt_O2 and Pt_CO2 were measured directly using a Paratrend^®sensor in human liver tissue. During anaesthesia, changes inventilation and liver blood flow caused predictable changesin Pt_CO2. Br J Anaesth 2004; 92: 735–7     

Exhaled nitric oxide as a marker of lung injury in coronary artery bypass surgery

Background. Exhaled nitric oxide (NO) concentrations have beensuggested as a marker of disease onset and severity in a numberof inflammatory conditions such as acute asthma. Known markersof the onset of acute lung injury require invasive tests andlaboratory based analysis and have limited clinical applicability.We performed a study of the use of exhaled NO as a marker ofdeveloping acute lung injury during and after coronary arterybypass grafting in patients requiring cardiopulmonary bypass. Methods. Mixed expired air samples were taken from the patientbreathing system and analysed for exhaled NO using chemiluminescenceanalysis. Results. Exhaled nitric oxide concentrations in expired gascorrelated with the Pa_O2/FI_O2 ratio (r=0.23, P<0.01). Therewas a non-significant trend towards a reduction in exhaled NOlevels from after induction of anaesthesia to post-bypass timepoints, with the lowest exhaled NO concentrations occurringat this time (P=0.07). There was no correlation between meanarterial pressure (r=–0.1, P=0.54) or mean pulmonary arterypressure (r=–0.1, P=0.67) and expired NO levels. Conclusions. Further work is required to test whether exhaledNO concentration may be useful in diagnosing the onset of acutelung injury in patients undergoing coronary artery bypass grafting. Br J Anaesth 2002; 89: 247–50     

Haemodynamic, acid-base and blood volume changes during prolonged low pressure pneumoperitoneum in rabbits

Background. The anaesthetic management of small infants duringadvanced laparoscopic surgery can be complicated by the majorpathophysiological effects of increased intra-abdominal pressure.In this study haemodynamic, acid–base and blood volumechanges were investigated during pneumoperitoneum in a smallanimal model. Methods. Ten fasted, anaesthetized, mechanically ventilatedand multi-catheterized New Zealand rabbits were randomized tocarbon dioxide pneumoperitoneum (PP, duration 210 min, pressure8 mm Hg) or control group. Cardiac index was determined usingtrans-cardiopulmonary thermodilution and total blood volumewas measured by thermal-dye dilution with indocyanine greenusing a fibreoptic monitor system. Results. In PP cardiac index (CI), central venous oxygen saturation(SCV_O2), total blood volume (TBV) and base excess (BE) decreasedsignificantly during the study whereas all variables remainedconstant in the control group. After release of PP the measuredvariables did not return to baseline within 30 min [PP, baselinevs study end: CI 108 (22) vs 85 (14) ml kg^–1 min^–1,SCV_O2 81.4 (8.9) vs 56.7 (9.8)%, TBV 318 (69) vs 181 (54) ml,BE –1.9 (2.7) vs –8.7 (1.8) mmol litre^–1;P<0.01]. Conclusion. Our animal model suggests that a decrease in CI,metabolic acidosis and hypovolaemia could occur after prolongedlow pressure pneumoperitoneum in small infants, which is possiblynot detectable by the standard monitor setting. Therefore, theroutine use of an extended monitoring including measurementof central venous oxygen saturation and acid–base parametersshould be considered during and soon after operation, when pneumoperitoneumwill last longer than 2 h.     

Remifentanil and nitrous oxide reduce changes in cerebral blood flow velocity in the middle cerebral artery caused by pain

Background. Cerebral blood flow is affected by painful stimuli,and analgesic agents may alter the response of cerebral bloodflow to pain. We set out to quantify the effects of remifentaniland nitrous oxide on blood flow changes caused by experimentalpain. Methods. We simulated surgical pain in 10 conscious volunteersusing increasing mechanical pressure to the tibia. We measuredchanges in cerebral blood flow velocity in the middle cerebralartery (CBFV_MCA) caused by the pain, using transcranial Dopplersonography. We gave increasing doses of remifentanil (0.025,0.05 and 0.1 µg kg^–1 min^–1)or nitrous oxide [20%, 35% and 50% end-tidal concentration (FE'_N2O)]and compared these effects on blood flow changes. Results. Nitrous oxide increased CBFV_MCA only when given at50% FE'_N2O. Remifentanil did not affect CBFV_MCA. Pain increasedCBFV_MCA. Both agents attenuated this pain-induced change inCBFV_MCA with the exception of nitrous oxide at 20% FE'_N2O. Conclusions. Inhalation of nitrous oxide or adminstration ofremifentanil attenuated pain-induced changes in CBFV_MCA. Br J Anaesth 2003: 90: 296–9