[Safe use of cuffed tracheal tubes in children]. / Geblockte Tuben bei Kindern - Rationaler und sicherer Einsatz.

In the last 5 years the use of cuffed tracheal tubes in infants and children has become popular worldwide and is accepted by major medical authorities. The advantages of cuffed tracheal tubes in smaller children - in particular the almost 100% chance to insert the right sized tracheal tube at the first attempt and their reliable sealing characteristics within the trachea - makes tracheal intubation and ventilation considerable easier and safer. This certainly compensates for the higher cost of cuffed compared to uncuffed tracheal tubes. The fear that cuffed tracheal tubes cause increased laryngeal damage in small children could not be confirmed, if adequately designed, cuffed tracheal tubes are correctly used. Conditions for the safe use of cuffed tubes in children are the availability of an adequately designed cuffed tube with a proofed recommendation for tube size selection and cuff pressure monitoring. The following rules must be fulfiled when cuffed tubes in children using are: confirmation of an air leak < 20 cmH2O inspiratory pressure with the cuff not inflated, cuff pressure limitation at 20 cmH2O and the avoidance of negative cuff pressures, resulting in sharp, cutting edges of the cuff membrane within the trachea.

Predictors of emesis and recovery agitation with emergency department ketamine sedation: an individual-patient data meta-analysis of 8,282 children.

STUDY OBJECTIVE: Ketamine is widely used in emergency departments (EDs) to facilitate painful procedures; however, existing descriptors of predictors of emesis and recovery agitation are derived from relatively small studies. METHODS: We pooled individual-patient data from 32 ED studies and performed multiple logistic regression to determine which clinical variables would predict emesis and recovery agitation. The first phase of this study similarly identified predictors of airway and respiratory adverse events. RESULTS: In 8,282 pediatric ketamine sedations, the overall incidence of emesis, any recovery agitation, and clinically important recovery agitation was 8.4%, 7.6%, and 1.4%, respectively. The most important independent predictors of emesis are unusually high intravenous (IV) dose (initial dose of > or =2.5 mg/kg or a total dose of > or =5.0 mg/kg), intramuscular (IM) route, and increasing age (peak at 12 years). Similar risk factors for any recovery agitation are low IM dose (<3.0 mg/kg) and unusually high IV dose, with no such important risk factors for clinically important recovery agitation. CONCLUSION: Early adolescence is the peak age for ketamine-associated emesis, and its rate is higher with IM administration and with unusually high IV doses. Recovery agitation is not age related to a clinically important degree. When we interpreted it in conjunction with the separate airway adverse event phase of this analysis, we found no apparent clinically important benefit or harm from coadministered anticholinergics and benzodiazepines and no increase in adverse events with either oropharyngeal procedures or the presence of substantial underlying illness. These and other results herein challenge many widely held views about ED ketamine administration.

Predictors of airway and respiratory adverse events with ketamine sedation in the emergency department: an individual-patient data meta-analysis of 8,282 children.

STUDY OBJECTIVE: Although ketamine is one of the most commonly used sedatives to facilitate painful procedures for children in the emergency department (ED), existing studies have not been large enough to identify clinical factors that are predictive of uncommon airway and respiratory adverse events. METHODS: We pooled individual-patient data from 32 ED studies and performed multiple logistic regressions to determine which clinical variables would predict airway and respiratory adverse events. RESULTS: In 8,282 pediatric ketamine sedations, the overall incidence of airway and respiratory adverse events was 3.9%, with the following significant independent predictors: younger than 2 years (odds ratio [OR] 2.00; 95% confidence interval [CI] 1.47 to 2.72), aged 13 years or older (OR 2.72; 95% CI 1.97 to 3.75), high intravenous dosing (initial dose > or =2.5 mg/kg or total dose > or =5.0 mg/kg; OR 2.18; 95% CI 1.59 to 2.99), coadministered anticholinergic (OR 1.82; 95% CI 1.36 to 2.42), and coadministered benzodiazepine (OR 1.39; 95% CI 1.08 to 1.78). Variables without independent association included oropharyngeal procedures, underlying physical illness (American Society of Anesthesiologists class >or = 3), and the choice of intravenous versus intramuscular route. CONCLUSION: Risk factors that predict ketamine-associated airway and respiratory adverse events are high intravenous doses, administration to children younger than 2 years or aged 13 years or older, and the use of coadministered anticholinergics or benzodiazepines.

Tracheoscopy assisted repair of tracheo-esophageal fistula (TARTEF): a 10-year experience.

BACKGROUND: Fiberoptic tracheoscopy assisted repair of tracheoesophageal fistula (TARTEF) has been reported to be useful for the surgeon with regards to identification of the fistula and proper fistula ligation. The aim of this article is to report our 10-year experience using TARTEF with intermittent positive pressure ventilation (IPPV) during tracheoesophageal fistula (TEF) repair in newborns. METHODS: With ethical committee approval, we included all patients undergoing TARTEF from 1995-2005. Variables of interest were (1) respiratory deterioration caused by gastric inflation because of IPPV during surgery and endoscopy; (2) detection of additional airway anomalies; (3) success of intubation of the fistula; (4) other side effects or adverse events. Data are given in median and range. RESULTS: Forty-seven neonates with TARTEF were included. Mean gestational age was 37 weeks (31-42) and mean weight was 2.5 kg (1.1-3.8). The patients were intubated with tracheal tubes size 2.5-3.5 mm ID. Appropriately sized fiberoptic bronchoscopes with an outer diameter of 2.0, 2.4 and 2.8 mm were used; passed through the lumen of the tracheal tube (TT) thereby requiring the use of IPPV to ensure adequate ventilation. No respiratory deterioration was noted as a consequence of intraoperative fiberoptic manipulation within the trachea or because of gastric hyperinflation with IPPV. In all patients, the TEF was successfully penetrated with the fiberscope and this clearly helped the surgeon to rapidly identify and dissect the fistula. In two patients a tracheal bronchus was identified. In two patients accidental extubation occurred during endoscopic confirmation of successful fistula repair. CONCLUSIONS: While fiberoptic TARTEF through the tracheal tube with IPPV did expedite and facilitate surgery, it did not cause clinically relevant impairment of ventilation. Careful manipulation during fiberoptic assessment is required to avoid tube displacement.

Tracheobronchial foreign body aspiration in children - diagnostic value of symptoms and signs.

OBJECTIVE: Tracheobronchial foreign body (TFB) aspiration is a common cause of respiratory compromise in early childhood. Research indicates that a high number of children are missed with TFB aspiration. The aim of this study was to identify predictors of potential TFB aspiration. STUDY DESIGN: We analysed 370 endoscopic reports of children admitted to our emergency department who underwent explorative rigid bronchoscopy to exclude/remove a TFB (1989-2003). Patient characteristics, history, clinical, radiographic and bronchoscopic findings were noted. Sensitivities and specificities for TFB aspiration were calculated for patient history, clinical and radiographic findings. RESULTS: The median age was 1.8 years. In 59.7% of patients a TFB was found and removed. A group analysis was performed on children with symptoms less than 2 weeks (group A) and those more than 2 weeks (group B). The results showed that unilateral diminished breath sounds and unilateral overdistension on chest X-ray were the most sensitive (53-79%) and specific (68-88%) findings in both groups. The clinical triad of acute choking/coughing, wheezing and unilateral diminished breath sounds had a high specificity (96-98%) in both groups. In contrast, a positive history of acute choking/coughing in group A or a permanent cough in group B showed a low specificity (8-16%). CONCLUSION: In a paediatric respiratory compromise, the presence of unilateral diminished breath sounds, pathological chest X-ray or clinical triad is a powerful indicator for occurred TFB aspiration. Since no single or combined variables can predict TFB aspiration with full certainty, bronchoscopic exploration should be performed if TFB aspiration is suspected.

Early vs late intraoperative administration of tropisetron for the prevention of nausea and vomiting in children undergoing tonsillectomy and/or adenoidectomy.

BACKGROUND: Tropisetron is a long-acting 5HT3 receptor antagonist and was shown to be effective in the prevention of postoperative nausea and vomiting (PONV) after tonsillectomy. The aim of the study was to compare the effects of early vs late intraoperative administration of tropisetron with regard to prevention of PONV during the first 48 h after extubation. METHODS: In a randomized double-blind study, we investigated 120 children aged 1-12 years undergoing general anesthesia for tonsillectomy or adenotonsillectomy. Patients received 0.1 mg x kg(-1) tropisetron (maximum 2 mg) immediately after inhalational induction (early) and establishment of intravenous access or after the end of surgery before extubation (late). PONV and the need for antiemetic rescue medications were recorded within the following 48 h. Patient data were analyzed using t-test, chi-squared test (significance level of alpha = 0.05) and Spearman rank correlation test. RESULTS: The overall incidence of vomiting was 55.3%, with 60% (36/60) in the early treatment and 51.6% (31/60) in the late treatment group (P = 0.46). The observed time course 48 h postoperatively showed no difference regarding the number of vomiting episodes between the two groups and the need for antiemetic rescue medication. The incidence of nausea was higher in the late application group in the first 6 h after extubation (P = 0.001) and higher in the early application group between 24 and 48 h after extubation (P = 0.02). Morphine and the age over 3 years had a strong influence on the incidence of vomiting. CONCLUSION: The intraoperative time point (early vs late) of intravenous administration of a single prophylactic dose of tropisetron has no impact on the incidence of PONV during the first 48 h after tonsillectomy and/or adenoidectomy in children.

Anesthesia and periinterventional morbidity of rigid bronchoscopy for tracheobronchial foreign body diagnosis and removal.

BACKGROUND: Undiagnosed tracheobronchial foreign body aspiration (FBA) or delayed extraction can lead to serious morbidity. The aim of this study was to evaluate anesthetic and periinterventional morbidity of a straightforward regime using rigid bronchoscopy to rule out or remove a tracheobronchial foreign body in children with suspicion of FBA. METHODS: We retrospectively analyzed rigid bronchoscopy charts of children with suspicion of acute (< or = 24 h) and subacute (>24 h-2 weeks) tracheobronchial FBA (1990-2003). Patient characteristics, duration of fasting, technique/course of anesthesia induction, and duration/course of rigid bronchoscopy were taken. Anesthetic, periinterventional complications and length of hospital stay were noted. Data are given in median (range [interquartile range]). RESULTS: A total of 287 children were included in this study. Median age was 1.7 years (0.2-14.2 [1.2-2.5]); in 72.1% a tracheobronchial foreign body was found and removed. Fasting time before induction of anesthesia was 5 h (1-14 [4.0-7.0]). Anesthesia adverse events were seen in 0.7%, whereas periinterventional complication from rigid bronchoscopy was observed in 7.6%. Hospital discharge within 4 h after bronchoscopy was possible in 65.2%. Complications of delayed diagnosis (>24 h) were prolonged duration of rigid bronchoscopy because of severe mucosal changes or difficulties in foreign body extraction. CONCLUSIONS: General anesthesia for rigid bronchoscopy to rule out a tracheobronchial foreign body in children carries low morbidity. Most of the complications originated from the foreign body itself especially in patients with late diagnosis. The risk for serious complications caused by retained foreign bodies outweighs the low morbidity of explorative rigid bronchoscopy in children with suspected FBA or children with prolonged cough or pulmonary infection unresponsive to medical treatment.

Tissue oxygenation monitoring during major pediatric surgery using transcutaneous liver near infrared spectroscopy.

BACKGROUND: The aim of the study was to compare liver tissue oxygenation determined by near infrared spectroscopy (NIRS) with central venous oxygen saturation (SvO(2)) and intestinal perfusion as measured by gastric intramucosal pH (pHi) in pediatric surgical patients. METHODS: Twenty children undergoing craniofacial surgery with expected major intraoperative blood loss were studied. NIRS tissue oxygenation index (TOI(Liver)) and pHi values were recorded. Arterial blood gas analysis and SvO(2) were assessed from periodically taken blood samples. Data are presented as ranges (median) and were compared using linear regression analysis. Sensitivity and specificity of the intra-individual changes in TOI(Liver) to predict falling SvO(2) or pHi values were calculated. RESULTS: Patients age ranged from 0.79 to 8.27 years (1.92 years). TOI(Liver) ranged from 41.5 to 77.4% (61.5%), gastric pHi from 7.13 to 7.60 (7.37) and SvO(2) from 51 to 86% (74%). Among patients only moderate correlation was found between TOI(Liver) and SvO(2) (r = 0.594, P < 0.0001) and gastric pH(i) (r = 0.502, P < 0.0001). Intra-individual measured TOI(Liver) values, however, demonstrated close correlation with SvO(2) values (r = 0.680 to 0.976) but a varying correlation with gastric pHi values (r = 0.055 to 0.972). Sensitivity/specificity of TOI(Liver) to predict decreasing SvO(2) or gastric pHi values were 76.4/73.4% and 67.4/62.7% respectively. CONCLUSIONS: TOI(Liver) provided a better trend monitor of central venous oxygen saturation than gastric intramucosal pH. Because of its limited sensitivity and specificity to indicate deterioration of SvO(2), liver tissue oxygenation measured by transcutaneous NIRS does not provide additional practical information for clinical management.

Continuous ventilation technique for laryngeal mask airway (LMA) removal after fiberoptic intubation in children.

BACKGROUND: Fiberoptic tracheal intubation through the laryngeal mask airway (LMA) is a simple technique to establish a safe airway in neonates and infants with a difficult airway. The technique, however, is complicated by the removal of the laryngeal mask from the patient's mouth because of the similarity in length of the LMA and the tracheal tube. METHODS: Several solutions have been presented to stabilize the tracheal tube within the trachea during withdrawal of the LMA. With all these techniques ventilation of the patient is interrupted. RESULTS: We present a modified technique, using a double tube assembly, which allows uninterrupted ventilation of the patient during withdrawal of the LMA from the patient's mouth. CONCLUSIONS: The technique is simple and safe, can be performed without hurry and carries potential advantages for neonates and children with limited cardiorespiratory reserve.

Tracheal sealing characteristics of pediatric cuffed tracheal tubes.

BACKGROUND: The aim of the study was to compare sealing characteristics of the new Microcuff pediatric tracheal tube featuring a high volume-low pressure (HVLP) cuff with ultrathin membrane with three conventional pediatric cuffed tracheal tubes. METHODS: After obtaining approval of the local ethical committee, 80 children aged 2-4 years were tracheally intubated with the following tubes (i.d. 4.0 mm) in random order: Microcuff P-HVLP, Mallinckrodt Hi-Contour P, Rüschelit Super Safety Clear, and Sheridan CF. Cuff pressure to prevent air leakage at standardized ventilator setting (PIP 20 cm H2O/PEEP 5 cm H2O/RR 20 min(-1)) was assessed within 5 min after intubation by auscultation of audible sounds at the mouth. Cuff pressures required with each group were compared with Kruskall-Wallis test (P < 0.05). Values are median and range. RESULTS: No significant differences in patient characteristics were found between the four groups. The Microcuff tube required significantly lower sealing pressures [11 cm H2O (6-26)] compared with the other tracheal tube brands [Mallinckrodt: 36 cm H2O (18-48); Rüschelit: 21 cm H2O (8-46); Sheridan: 26 cm H2O (18-60), (P < 0.0001)]. CONCLUSION: This preliminary investigation suggests that the new Microcuff pediatric tracheal tube with ultrathin high volume-low pressure cuff membrane allows effective tracheal sealing at very low cuff pressures. This represents a benefit for children with regard to their lower mucosal perfusion pressures compared with adult patients.

Latex allergy in children with urological malformation and chronic renal failure.

PURPOSE: Children with spina bifida, bladder exstrophy and anorectal anomalies are at risk for latex allergy. Severe intraoperative anaphylaxis in a boy treated with kidney transplantation prompted this study to evaluate the prevalence of latex allergy in a cohort of children with chronic renal failure (CRF). MATERIALS AND METHODS: Between 1996 and 2002, 57 boys and 28 girls were investigated at a median age of 10.5 years (range 1.3 to 22.9). Urological malformations were the underlying cause of CRF in 33 patients (39%). Of the patients 39 were on conservative treatment, 20 were on dialysis and 26 had a functioning renal graft. Latex reaction was assessed by a careful history, specific serum latex IgE and skin prick test. RESULTS: A total of 19 patients (22%) showed latex reaction, of whom 8 had allergy (clinical symptoms included severe intraoperative anaphylaxis in 1) and 11 had sensitivity (positive IgE or prick test without symptoms). Of these 19 patients 11 had urological malformations. The number of surgical procedures, young age at operation and atopy were significant risk factors. When operations were analyzed separately, ie urological vs nonurological surgery, only urological surgery was significantly associated with latex reaction. A significant correlation was also found between the overall number of operations and latex radioallergosorbent class. CONCLUSIONS: All children with CRF who undergo early and multiple urological surgery are at high risk for latex reaction. Primary latex prevention, ie the routine use of latex-free gloves, tubes and catheters, should be implemented in all children with complex urological malformations.

Laryngeal damage due to an unexpectedly large and inappropriately designed cuffed pediatric tracheal tube in a 13-month-old child.

PURPOSE: To present a case of laryngeal damage in an infant caused by a too large and inappropriately designed cuffed tracheal tube. CLINICAL FEATURES: A 13-month-old child undergoing cardiac surgery was intubated with an uncuffed endotracheal tube with an internal diameter (ID) of 4.0 mm. Because of an important air leak around the tracheal tube during mechanical ventilation, a cuffed endotracheal tube ID 4.0 mm was inserted. The air leak with the tube cuff not inflated was acceptable at 25 cm H2O airway pressure. After extubation on the third postoperative day, the patient showed increasing stridor and respiratory deterioration. Fibreoptic laryngoscopy of the spontaneously breathing patient showed a large intra-laryngeal web. After surgical removal of the web, the child rapidly recovered and was discharged from the hospital on the 12th postoperative day. Inspection of the 4.0 mm (ID) cuffed tracheal tube revealed a cuff positioned inappropriately high and an increase of 0.7 mm in outer tube diameter compared to the 4.0 mm (ID) uncuffed tracheal tube from the same manufacturer. The tube cuff is likely to be situated within the larynx when placed in accordance to insertion depth formulas or radiological criteria, as used for uncuffed tracheal tubes in children. CONCLUSION: The larger than expected tracheal tube with its intra-laryngeal cuff position in a 13-month-old child likely caused mucosal damage and an inflammatory reaction within the larynx resulting in granulation tissue formation and fibrous healing around the tracheal tube.

Evaluation of a new combined SpO2/PtcCO2 sensor in anaesthetized paediatric patients.

BACKGROUND: The recently introduced TOSCA monitor (Linde Medical Sensors AG, Basel, Switzerland) combines pulse oximetry (SpO2) and transcutaneous PCO2 (PtcCO2) monitoring in a single ear sensor. The aim of the present study was to evaluate accuracy of the TOSCA monitor to estimate SaO2 and PaCO2 in anaesthetized children. METHODS: With approval of the hospital ethical committee and after obtaining informed parental consent, the TOSCA sensor was attached to one ear lobe of anaesthetized children in whom arterial access was established for cardiac catheterization or invasive blood pressure monitoring. SpO and PtcCO2 as well as SpO and PECO2 values from the anaesthesia monitoring (AS5; Datex-Ohmeda, Helsinki, Finland) were compared with SaO2 and PaCO2 values from arterial blood gas analysis. Corresponding data were compared using Bland Altman bias analysis. RESULTS: A total of 111 blood samples were taken from 60 children (median age: 4.41 years; 0.35-16.13 years). SaO2 values ranged from 63 to 100% (median: 98.7%), PaCO2 ranged from 3.8 to 7.3 kPa (median: 4.6 kPa). Mean difference (+/-2 sd) between PaCO2 and PtcCO2 was -0.035 kPa (+/-0.74 kPa), between PaCO2 and PECO2 0.002 kPa (0.73 kPa), respectively (1 kPa = 7.3 mmHg). Bias and precision between SaO2 and SpO was -0.63% (+/-2.77%) and 0.13% (+/-4.52%) between SaO2 and SpO. CONCLUSIONS: In anaesthetized children, the TOSCA ear sensor allows estimation of SaO2 and PaCO2, comparable in accuracy to endtidal capnometry and finger pulse oximetry. This makes the TOSCA monitor a helpful add-on to respiratory monitoring in anaesthetized children, in situations, in which endtidal capnometry is unreliable or difficult to establish.

Awake spinal or caudal anaesthesia in preterms for herniotomies: what is the evidence based benefit compared with general anaesthesia?

PURPOSE OF REVIEW: Postoperative apnoea is known to threaten preterm and ex-preterm infants undergoing surgery for inguinal hernia. Awake regional anaesthesia, initially spinal and later caudal anaesthesia have been suggested as effective techniques to avoid these complications. However, most herniotomies in this group of patients are still performed under general anaesthesia without deleterious consequences. Whereas some experts continue to claim advantages for awake regional over general anaesthesia for preterm infants, others consider awake regional anaesthesia to be an exclusive, technically difficult and unreliable technique of unconfirmed benefit. RECENT FINDINGS: It is appropriate to weigh the scarce available evidence that has been accumulated since 1984, and put it into perspective with new developments in paediatric general anaesthesia. The actual clinical significance of postoperative apnoea and improvements in neonatal and perioperative care and monitoring must also be reconsidered. SUMMARY: The available evidence does not allow unequivocal conclusions to be drawn or recommendations to be made. Awake regional anaesthesia for herniotomies in preterm infants has been found to be superior in most studies; however, it requires technical expertise and dedication on the part of the anaesthetist and surgeon. When light general anaesthesia with modern anaesthetic agents such as sevoflurane or desflurane is combined with a caudal block, postoperative apnoea is very rare, and can easily be recognized and managed with good postoperative monitoring and therapy.

The Panomat P-10 micro-volumetric infusion pump is suitable for continuous drug administration at minimal flow rates.

PURPOSE: To evaluate the performance of the Panomat P-10 micro-volumetric infusion pump for its use in drug administration at minimal flow rates (microL x hr(-1); e.g., intrathecal application). METHODS: Fluid delivery at steady state conditions, and after vertical displacement of the syringe pump by -50 cm was determined gravimetrically. The Panomat P-10 infusion pump was evaluated at 4, 10, 20, 50 and 100 microL x hr(-1), and compared to a conventional syringe pump assembly at 100, 200, 500 and 1000 microL x hr(-1). Measurements were repeated twice with two different devices of each syringe pump system, and with two syringes. Data are reported as mean +/- SD. RESULTS: Steady state fluid delivery of the Panomat P-10 infusion pump revealed less than 5% deviation to set flow rate at 10, 20, 50 and 100 microL x hr(-1), and 12% deviation at 4 microL x hr(-1). Mean zero-drug delivery time (ZDDT) after lowering the pump by 50 cm at 4 microL x hr(-1) flow rate was 38.4 +/- 7.3 min. At 100 microL x hr(-1) and with original infusion line ZDDT was almost 20 times shorter when compared to the conventional syringe pump assembly (1.5 +/- 0.5 min vs 28.5 +/- 5.0 min). CONCLUSION: The tested Panomat P-10 micro-volumetric pump shows an acceptable flow accuracy as well as a low susceptibility to vertical displacement, and is therefore suitable for continuous drug administration at minimal flow rates. The technology used in this pump carries potential implications for a new generation of syringe pumps.

Transcutaneously measured near-infrared spectroscopic liver tissue oxygenation does not correlate with hepatic venous oxygenation in children.

PURPOSE: To compare transcutaneous near-infrared spectroscopic (NIRS) measured liver tissue oxygenation with hepatic vein oxygen saturation (SvhO2) in children undergoing cardiac catheterization. METHODS: A NIRS optode (containing an emitter and a receiver of near-infrared light) was placed directly below the right costal arch above the palpable liver in 40 children aged 0.02 to 7.28 yr (median: 1.8 yr). Spatially resolved spectroscopic measured tissue oxygenation index (TOI) was recorded using the NIRO-300. Paired blood samples from the hepatic vein were taken under radiological control for determination of SvhO2 in a co-oxymeter. TOI values were compared with hepatic vein oxygenation, with simultaneously obtained arterial oxygen saturation (SaO2), inferior vena cava SO2 and hemoglobin concentration using simple linear and multi-regression analysis. RESULTS: TOI values ranged from 35% to 73% (58.6 +/- 8.4%); SvhO2 from 32% to 80% (58.4 +/- 14.4%), and arterial SO2 from 54% to 100% (90.0 +/- 11.4%). TOI and hepatic vein oxygen saturation failed to correlate (r = 0.052/P = 0.752). A regression model containing arterial saturation (Delta R2 = 0.177) and the ratio of pulmonary to systemic resistance (Delta R2 = 0.095) explained 27.3% of the observed variance in TOI. In this model, hepatic vein oxygen saturation was no longer significant; explaining only 3.4% of the variance. No other variable retained a significant association. CONCLUSION: Transcutaneously measured NIRS tissue oxygenation with an optode placed over the palpable liver does not correlate with SvhO2. The value is dominated by non-hepatic variables such as arterial saturation and vascular resistances.