| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
* From the Departments of Intensive Care and Neonatology,
Anaesthesia, and
Cardiology, University Children’s Hospital and
the Clinic Of Neonatology University Hospital, Zurich, Switzerland.
Dr. Markus Weiss, Department of Anaesthesia and Department of Intensive Care and Neonatology, University Children’s Hospital, Steinwiesstrasse 75, 8032 Zurich, Switzerland. Phone: +41 1 266 71 11; Fax:+41 1 266 79 94; E-mail: markus.weiss{at}kispi.unizh.ch
 |
Abstract |
|---|
 TOP Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
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-300TM. 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 (
R2 = 0.177) and the ratio of pulmonary to systemic resistance (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.
|
Introduction |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
However, hepatic vein catheters require the invasive insertion of devices. In newborns and infants particularly, the risks associated with this invasiveness would not outweigh the potential benefits of monitoring. In contrast, near-infrared spectroscopy (NIRS) is a non-invasive method for continuous, transcutaneous monitoring of tissue oxygenation.7,8 In neonates and children up to eight years, the liver represents an organ within the splanchnic region that is of homogenous tissue. Access for transcutaneous NIRS measurements can easily be obtained by placing the transducer below the right costal arch.9,10 In animal investigations, this method allowed the monitoring of hepatic vein oxygen saturation (SvhO2) as an indicator of splanchnic oxygen utilization.11 However, data systematically assessing the validity of this assumption in children are not available.
Therefore, we compared transcutaneous NIRS measured tissue oxygenation by an optode placed over the palpable liver with SvhO2 in infants and children undergoing cardiac catheterization for diagnostic assessment of congenital cardiac malformations. Due to the underlying conditions, this patient group provided a wide spectrum of systemic saturations and SvhO2.
|
Methods |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
On each patient a NIRS probe (Hamamatsu, Photonics, Japan), consisting of a near-infrared light emitter optode and a receiver optode, was placed below the right costal arch on the skin overlying the palpable liver (Figure
). Emitter and receiver optodes were secured to the body by elastic tapes and were inserted into a black probe receptacle to provide an interoptode distance of 40 mm and to shield the optodes from light. Quantitative tissue oxygenation index (TOI) representing the ratio of oxygenated hemoglobin (HbO2) to total hemoglobin [HbO2 + deoxygenated hemoglobin (HHB)] was measured and calculated using spatially resolved spectroscopy (SRS) with the NIRO-300TM device (Hamamatsu, Photonics, Japan). The underlying technical principles of SRS allow calculation of absolute tissue oxygenation values without knowledge of tissue path-length. The methods have been described in detail by Matcher et al. and Suzuki et al.12,13
|
TOI was calculated as the median value of 30 measurements (one minute) during the period of sampling from the hepatic vein for each of two repeat samples. The final values entered into the analysis were the means of the two TOI values, the two oxygen saturations and the two hemoglobin concentration measurements obtained from the paired samples. Systemic cardiac index (Qs), and systemic and pulmonary vascular resistance (Rs; Rp) were calculated using the Fick formula.
Data analysis
Data are presented as range (mean ± SD). Pearson’s correlation coefficients and P-values from linear regression analysis were calculated between TOI and hepatic vein, inferior caval vein and arterial oxygen saturation, hemoglobin concentration and calculated hemodynamic data such as Qs, Rs and Rp. Multivariable regression models with TOI as the dependent variable and the variables listed above as independent variables were performed using general linear models. These models checked for potential confounding of the possible relation between TOI and hepatic vein saturation by mean arterial blood pressure, heart rate, central venous pressure, hemoglobin concentration, temperature, and ventilator settings including expiratory gases. A P < 0.05 was considered statistically significant. Calculations were performed using SAS software (version 8.1, SAS Inc, Cary, NC, USA).
|
Results |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
TOI values ranged from 35% to 73% (58.6 ± 8.4%), SvhO2 from 32% to 80% (58.4 ± 14.4%) and arterial oxygenation saturation from 54% to 100% (90.0 ± 11.4%; Table). Fluctuations of the 30 TOI values due to the respiratory-related liver movements during the 60 sec recording period, were less than 3%. Agreement (bias/precision) between the paired TOI measurements was 0.3%/2.4% and between the two SvhO2 and hemoglobin measurements were 0.2%/8% and -0.7/11.2 g·L-1 respectively.
There was no correlation between TOI and SvhO2 (all patients r = 0.052/P = 0.752; cyanotic cardiac patients (n = 20) r = 0.171/P = 0.472; non-cyanotic cardiac patients [(n = 20) r = 0.27/0.263]. Simple linear regression analysis revealed significant associations between TOI and arterial oxygen saturation (r = 0.39, P = 0.014) and the ratio of pulmonary to systemic vascular resistance r = -0.36, P = 0.03). There was a trend towards an association between TOI and the oxygen saturation in the IVC (r = 0.30, P = 0.08), as well as with length and weight (both r = 0.28, P = 0.07), with systemic vascular resistance (r = 0.29, P = 0.07), and with systemic cardiac output (r = -0.30, P = 0.059).
Multivariable regression revealed that after considering arterial saturation and the ratio of pulmonary to systemic vascular resistance, which together explained 27.3% of the variance in TOI, no other variable significantly improved the model. Given the power of the study to detect 6% of the explained variance, the association between TOI and the primary variable of interest, SvhO2, is poor. Controlling for potential confounding variables did not change these results.
Subgroup analysis for cyanotic and non-cyanotic cardiac patients showed that most of the explained variance occurred in cyanotic patients, but there was no significant association between TOI and SvhO2 in either subgroup.
|
Discussion |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The study suggests that transcutaneous NIRS tissue oxygenation measured with an optode placed over the palpable liver did not correlate with invasively measured SvhO2 but was affected by non-hepatic variables, such as arterial oxygen saturation, systemic vascular resistance and cardiac output.
Measurement of hepatic tissue oxygenation is an upcoming technique to monitor adequacy of liver tissue oxygenation in critically ill patients. For these purposes, assessment of SvhO2 is used by some intensive care units.3 The technique is suggested to be helpful in the management of patients at risk of hepatic failure after hepatic surgery, of patients with sepsis and of patients requiring high levels of end-expiratory pressures or catecholamine therapy.14–20 SvhO2 has been shown to correlate well with gastric intramucosal pH in patients during cardiac surgery.20 However, monitoring SvhO2 is an invasive procedure and, beside problems with vessel puncture and catheter-related infections, the method increases the patients’ risk of arrhythmia from catheter dislocation and hepatic vein thrombosis, an issue particularly relevant in children. In addition, catheter placement requires bedside fluoroscopic or ultra-sonographic guidance and technical skills.21
Measurement of hepatic tissue oxygenation by NIRS represents a non-invasive approach to assess hepato- splanchnic perfusion and oxygenation. Several authors have reported on NIRS measurement of liver tissue oxygenation.9–11,22–25 Most of these studies were performed in animals, with the NIRS probe attached to the liver surface after laparotomy. The investigators mainly studied relative changes of liver tissue oxygenation during naso-gastric feeding, induced hypovolemia, low cardiac output, graded hypoxia or hepatic vascular in-flow occlusion. Of particular relevance to potential clinical applications were the data by El-Desoky and coworkers, who found a direct correlation between hepatic tissue hypoxia measured by liver surface NIRS in pigs and hepatic vein oxygen partial pressure during induced hypoxic hypoxemia.11 However, in contrast to the promising animal experiments, our data show that, in children up to eight years of age, transcutaneously measured NIRS tissue oxygenation with an optode placed over the palpable liver does not correlate at all with the invasively determined SvhO2.
We propose the following possible explanations for the failure to show any agreement between the two techniques in our study. First, in contrast to the study of El-Desoky, we did not compare intra-individual differences during induced hypoxia. Instead, we evaluated near-infrared SRS for inter-individual single point assessment of hepatic tissue oxygenation compared with SvhO2 in patients with a large range of arterial and hepatic oxygen saturation (SaO2: 54.0% to 100.0%; SvhO2: 32.1% to 80.6%). Second, measurement of tissue oxygenation by NIRS provides an average value of arterial, venous and capillary blood in the underlying tissue and includes only a small area of the liver, while SvhO2 represents the global balance between hepatic oxygen delivery and oxygen consumption in the tissue. This seems to be an important issue, when NIRS tissue oxygenation is compared with oxygen saturation in the venous outflow of a specific organ or vascular region.26 Third, it should be kept in mind that, in cyanotic cardiac patients, adaptive mechanisms regarding splanchnic blood flow and oxygen extraction may affect distribution of blood in the liver and may, therefore, be a contributing factor. Fourth, the fact that TOI was greatly influenced by systemic variables, such as arterial oxygen saturation, vascular resistances and, to a lesser extent, by inferior caval SO2 and cardiac output, implies that the NIRS method used reflects global tissue oxygenation rather than tissue oxygenation in the liver. The findings support our earlier reports on the relationship between TOI measurements over the palpable liver and invasively measured SvO2 found in another study population of 100 critically ill children.10
Fifth, transcutaneous NIRS measurement over the palpable liver below the costal arch does not always guaranty assessment of tissue oxygenation in the liver. Although the liver was palpated below the costal arch (at least 2 cm) and allowed placement of the NIRS probes in all our intubated and mechanically ventilated patients, it is likely that measurements are obtained from a thin wedge of liver and underlying other organ tissues. This represents an important limitation to the use of the method in sedated or awake, non-intubated and non-ventilated children, in whom mean projection of the liver edge has been reported to be about 1 cm below the costal margin at end-expiration.27
Sixth, it is conceivable that the probe’s measuring depth of about 4 cm is insufficient to specifically reflect liver tissue oxygenation, and that in our study NIRS actually returned a value dominated by the arterial oxygenation of the tissue between the sensor and the liver surface. If this holds true, inter-individual variation of thickness and composition of subcutaneous tissue, muscles and ascites may have affected NIRS measurements. The finding of a trend towards higher TOI values with increasing body weight and length lends support to this hypothesis.
The clinical implication of our findings is that transcutaneous single point measurement of TOI with an optode placed over the palpable liver cannot be used to assess liver oxygenation as an alternative to measuring SvhO2. Quantitative short-time assessment of hepatic tissue oxygenation in clinical practice using NIRS seems to be limited to liver surface measurement as reported during liver surgery.28 Probably, in the future, NIRS devices with an adjustable angle of light emission-detection and an adaptable depth of measurement, combined with an ultra-sonographic imaging probe will allow the detection of underlying tissues and to focus measurement of oxygenaton to the tissue of interest.
Placing the NIRS probes in an intercostal space would provide an alternative "window to the underlying liver" even if the liver may be not palpable below the costal margin. However, air-filled lung tissue and varying distances between the NIRS probe and liver tissue during spontaneous and artificial ventilation did not further support the use of this approach. In addition, the space between the ribs is narrow in children and an initially well placed NIRS probe in an intercostal space may be easily dislodged and cover a rib if the position of the right upper arm is changed during the procedure. Finally, probes positioned on the lateral thoracic wall would impair lateral x-ray investigations during cardiac catheterization.
Recently, an alternative site for NIRS measurement of splanchnic oxygenation was reported by Petros et al. These investigators positioned the NIRS optodes on the abdomen just below the umbilicus and demonstrated that transcutaneous single point NIR measurement of splanchnic/cerebral oxygenation ratio (after an equilibration period of five minutes) was highly sensitive for detecting splanchnic ischemia in neonates.29,30 Further studies employing transcutaneous NIRS monitoring of hepato-splanchnic oxygenation will have to elucidate if these non-invasive techniques using alternative placement approaches may yield clinically useful data for monitoring systemic or splanchnic tissue oxygenation, as compared to measurements of central or mixed venous oxygen saturation, continuous cardiac output or gastric tonometry.
In conclusion, transcutaneously NIRS measured tissue oxygenation with an optode placed over the palpable liver does not correlate with SvhO2. The value is mainly determined by non-hepatic measures such as arterial saturation and vascular resistances.
|
|
Footnotes |
|---|
Revision received June 7, 2002. Accepted for publication March 28, 2002.
|
References |
|---|
|
TOPAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
2 Mythen MG, Webb AR. The role of gut mucosal hypoperfusion in the pathogenesis of post-operative organ dysfunction. Intensive Care Med 1994; 20: 203–9.[Medline]
3 De Backer D, Vincent JL. Why, when, and how to insert a hepatic vein catheter in critically ill patients. Crit Care Med 1999; 27: 1680–1.[Medline]
4 Metzler H. Continuous measurement of hepatic vein oxygen saturation with a new catheter (Letter). Intensive Care Med 1992; 18: 131–3.
5 Arnold J, Hendriks J, Ince C, Bruining H. Tonometry to assess the adequacy of splanchnic oxygenation in the critically ill patient. Intensive Care Med 1994; 20: 452–6.[Medline]
6 Kolkman JJ, Otte JA, Groeneveld ABJ. Gastrointestinal luminal PCO2 tonometry: an update on physiology, methodology and clinical applications. Br J Anaesth 2000; 84: 74–86.
7 Wahr JA, Tremper KK, Samra S, Delpy DT. Near-infrared spectroscopy: theory and applications. J Cardiothorac Vasc Anesth 1996; 10: 406–18.[Medline]
8 Owen-Reece H, Smith M, Elwell CE, Goldstone JC. Near infrared spectroscopy. Br J Anaesth 1999; 82: 418–26.
9 Teller J, Schwendener K, Wolf M, et al. Continuous monitoring of liver oxygenation with near infrared spectroscopy during naso-gastric tube feeding in neonates. Schweiz Med Wochenschr 2000; 130: 652–6.[Medline]
10 Schulz G, Weiss M, Bauersfeld U, et al. Liver tissue oxygenation as measured by near-infrared spectroscopy in in the critically ill child in correlation with central venous oxygen saturation. Intensive Care Med 2002; 28: 184–9.[Medline]
11 El-Desoky AEH, Jiao LR, Havlik R, Habib N, Davidson BR, Seifalian AM. Measurement of hepatic tissue hypoxia using near infrared spectroscopy: comparison with hepatic vein oxygen partial pressure. Eur Surg Res 2000; 32: 207–14.[Medline]
12 Matcher SJ, Kirkpatrick P, Nahid K, Cope M, Delpy DT. Absolute quantification methods in tissue near infrared spectroscopy. Proc SPIE 1995; 2389: 486–95.
13 Suzuki S, Takasaki S, Ozaki T, Kobayashi Y. A tissue oxygenation monitor using NIR spatially resolved spectroscopy. Proc SPIE 1999; 3597: 582–92.
14 Dahn MS, Lange P, Lobdell K, Hans B, Jacobs LA, Mitchell RA. Splanchnic and total body oxygen consumption differences in septic and injured patients. Surgery 1987; 101: 69–80.[Medline]
15 Dahn MS, Lange MP, Jacobs LA. Central mixed and splanchnic venous oxygen saturation monitoring. Intensive Care Med 1988; 14: 373–8.[Medline]
16 Ruokonen E, Uusaro A, Alhava E, Takala J. The effect of dobutamine infusion on splanchnic blood flow and oxygen transport in patients with acute pancreatitis. Intensive Care Med 1997; 23: 732–7.[Medline]
17 Trager K, Radermacher P, Georgiff M. PEEP and hepatic metabolic performance in septic shock. Intensive Care Med 1996; 22: 1274–5.[Medline]
18 Takano H, Matsuda H, Kadoba K, et al. Monitoring of hepatic venous oxygen saturation for predicting acute liver dysfunction after Fontan operations. J Thorac Cardiovasc Surg 1994; 108: 700–8.
19 Kainuma M, Nakashima K, Sakuma I, et al. Hepatic venous hemoglobin oxygen saturation predicts liver dysfunction after hepatectomy. Anesthesiology 1992; 76: 379–86.[Medline]
20 Landow L, Phillips DA, Heard SO, Prevost D, Vandersalm TJ, Fink MP. Gastric tonometry and venous oximetry in cardiac surgery patients. Crit Care Med 1991; 19: 1226–33.[Medline]
21 Dahn MS, Ballerstadt R, Lange MP, Schultz J. Development of a percutaneous fiberoptic hepatic venous localization catheter. Crit Care Med 1999; 27: 1598–1602.[Medline]
22 Kitai T, Tanaka A, Tokuka A, et al. Quantitative detection of hemoglobin saturation in the liver with near-infrared spectroscopy. Hepatology 1993; 18: 926–36.[Medline]
23 El-Desoky AEH, Seifalian AM, Davidson BR. Effect of graded hypoxia on hepatic tissue oxygenation measured by near infrared spectroscopy. J Hepatol 1999; 31: 71–6.
24 Rhee P, Langdale L, Mock C, Gentilello LM. Near-infrared spectroscopy: continuous measurement of cytochrome oxidation during hemorrhagic shock. Crit Care Med 1997; 25: 166–70.[Medline]
25 Beilman GJ, Groehler KE, Lazaron V, Ortner JP. Near-infrared spectroscopy measurement of regional tissue oxyhemoglobin saturation during hemorrhagic shock. Shock 1999; 12: 196–200.[Medline]
26 Ali MS, Harmer M, Vaughan RS, Dunne JA, Latto IP. Spatially resolved spectroscopy (NIRO-300) does not agree with jugular bulb oxygen saturation in patients undergoing warm bypass surgery. Can J Anesth 2001; 48: 497–501.
27 McNicholl B. Palpability of the liver and spleen in infants and children. Arch Dis Child 1957; 32: 438–40.[Medline]
28 Kitai T, Tanaka A, Tokuka A, et al. Intraoperative measurement of graft oxygenation state in living related liver transplantation by near infrared spectroscopy. Transpl Int 1995; 8: 111–8.[Medline]
29 Petros AJ, Heys R, Tasker RC, Fortune PM, Roberts I, Kiely E. Near infrared spectroscopy can detect changes in splanchnic oxygen delivery in neonates during apnoeic episodes (Letter). Eur J Pediatr 1999; 158: 173.[Medline]
30 Fortune PM, Wagstaff M, Petros AJ. Cerebro-splanchnic oxygenation ratio (CSOR) using near infrared spectroscopy may be able to predict splanchnic ischaemia in neonates. Intensive Care Med 2001; 27: 1401–7.[Medline]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
