Authors: Mark A Law, MD; Alexis L. Benscoter, DO; Santiago Borasino, MD, MPH; Maya Dewan, MD, MPH; A. K. M. Fazlur Rahman, Ph.D.; Rohit S. Loomba, MD; Kristal M. Hock, MSN, RN, CNL; Jeffrey A. Alten, MD
Pediatric Critical Care Medicine 23(7): p e347-e355, July 2022.
Commentary by: Dr. Christopher Smith, and Dr. Wenyu Bai. Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, MI
Take home points
- There was a correlation between inferior vena cava saturation and superior vena cava saturation (IVC O2 and SVC O2) obtained upon arrival to ICU following cardiac surgery in neonates.
- IVC O2 had a strong correlation with the concurrent flank near-infrared spectroscopy (rNIRS) value and SVC O2 had a weak correlation with the concurrent forehead near-infrared spectroscopy (cNIRS) value at the time of admission to ICU
- Lower IVC O2, rNIRS, and cNIRS were associated with an increased likelihood of a patient experiencing an adverse event including cardiac arrest within 48 hours of ICU admission, in-hospital death, or states of low cardiac output in neonates following cardiac surgery
Early identification and treatment of low cardiac output syndrome (LCOS) has great potential to improve outcomes for children following surgery for congenital cardiac defects with cardiopulmonary bypass (CPB)[1-3]. Traditionally, SVC O2 has been considered an estimate of mixed venous oxygen saturation, and monitoring SVC O2 is commonly used for the detection of LCOS and hemodynamic deterioration in children with or without cardiac surgery  [5-7].
In patients with inadequate oxygen delivery, there is likely a redistribution of blood flow away from splanchnic and renal beds, while perfusion to the cerebral and coronary circulations is preserved. A decreased IVC O2 may be an earlier indicator of LCOS and adverse outcomes in children following congenital cardiac surgery. The authors tested this hypothesis by comparing IVC O2 and SVC O2 simultaneously in the immediate postoperative period in a heterogenic neonatal congenital cardiac surgery population. The primary aim of the study was to correlate admission IVC O2 and SVC O2. Secondary aims were to correlate flank or cerebral near-infrared spectroscopy with IVC O2 and SVC O2, respectively, and to explore associations between oximetry data and a composite adverse outcome defined as any of the following: increasing serum lactate or vasoactive support at 2 hours post-admission, cardiac arrest within 48 hours of ICU admission, or mortality.
The single-center, retrospective study included a total of 118 neonates (<30 days) who had cardiac surgery with CPB, and 52 (44%) of the cohort had single ventricle physiology. All patients had concurrent IVC and SVC catheters and were admitted to the pediatric ICU postoperatively. The patients were mechanically ventilated, sedated, and under neuromuscular blockade at the time of admission. Catheter positions were confirmed by postoperative chest radiographs. Institutional standard practice including vasoactive medication administration, intravenous fluid bolus, and packed RBC transfusion applied to all the neonates being enrolled, and data collection included hemoglobin, arterial oxygen saturation (Sao2), IVC O2, SVC O2, cNIRS, and rNIRS immediately upon arrival to ICU. Arterial serum lactate and modified vasoactive inotropic score (VIS) were collected at ICU admission and 2 hours after admission, respectively.
The authors demonstrated the following findings from the study:
- IVC O2 measurements were significantly lower than paired SVC O2
- IVC O2 and SVC O2 correlated moderately (r = 0.54; p < 0.001)
- Admission IVC O2 had a strong correlation with concurrent rNIRS value, while SVC O2 had a weak association with cNIRS value
- Postoperative adverse outcomes were common; 36 of 118 patients (30%) had at least one adverse event and 18 of 118 (15%) experienced at least two adverse events of the composite adverse outcome. The presence of the composite outcome was associated with lower IVC O2, higher arteriovenous oxygen difference between SaO2 and IVC O2, lower cNIRS and rNIRS values, but not SVC O2
- Logistic regression showed that each 12% decrease in IVC O2 was associated with 12-fold greater odds of the composite adverse outcome; but no association between SVC O2 and increased odds of the composite adverse outcome
The authors concluded that admission IVC O2 correlated with SVC O2 and rNIRS in the early postoperative period in neonates immediately following cardiac surgery. IVC O2 desaturation was independently associated with an increase in lactate value, vasoactive-inotropic support, and cardiac arrest within 48 hours. The findings suggested lower admission IVC O2 may identify a cohort of postsurgical neonates at risk for low cardiac output and associated morbidity.
What does this mean for our practice?
The use of SVC O2 to guide the management of critically ill patients is a well-established practice and has been shown to be predictive of mortality or the need for ECMO . Early identification of neonates at risk for adverse outcomes after cardiac surgery may allow for earlier intervention and decrease the likelihood of a serious adverse event. This study showed that there was a correlation between SVC O2 and IVC O2 measurements in neonates admitted to ICU after cardiac surgery. IVC O2 measurements were found to be consistently lower than simultaneous SVC O2 measurements and the difference between these two measurements increased as the average venous saturation decreases. This increasing difference may be due to the redistribution of blood flow away from the splanchnic and renal circulations towards the brain and heart during states of low oxygen delivery.
The decision of where to obtain central venous access is often driven by institutional norms and provider preference. The results of this retrospective cohort study added some evidence that following IVC O2 obtained from a central venous catheter may provide useful information and help identify patients at risk for low cardiac output, cardiac arrest, or in-hospital mortality, either with or without monitoring SVC O2, following cardiac surgery in neonates. The strong correlation between IVC O2 and rNIRS and the association of both cNIRS and rNIRS with adverse events supported the use of NIRS for the early identification of patients at risk for adverse outcomes. The sample size and heterogeneity of the study patients may have contributed to the fact that low SVC O2 did not correlate with rates of adverse events even though this correlation has been previously demonstrated by multiple studies[4, 6, 7].
In conclusion, this single-center retrospective cohort study was aimed at validating the use of IVC O2 and NIRS for the identification of neonates at risk for adverse events following cardiac surgery. The results of the study showed that low IVC O2, cNIRS, and rNIRS measurements at the time of admission to the ICU following cardiac surgery were all associated with an increased risk of experiencing low cardiac output, cardiac arrest, or in-hospital mortality. These data support the potential use of IVC O2 monitoring after neonatal cardiac surgery and could be considered for the early identification of patients at risk for LCOS and adverse outcomes. Combining IVC O2 and NIRS data may lead to earlier identification and intervention of at-risk patients. Future investigations should determine if there is an IVC O2 threshold that would require intervention or if IVC O2, cNIRS, and rNIRS can be used to guide goal-directed treatment. This study was limited to evaluating a single point value in time of postoperative ICU admission, this may not be the time of greatest hemodynamic compromise during the perioperative period. Following central venous saturation and NIRS throughout the perioperative period may give better insight into which subset of neonates are at the greatest risk of experiencing an adverse event after cardiac surgery.
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Drs. Smith and Bai wish to acknowledge the help for guiding the review writing from Dr. Bishr Haydar, Department of Anesthesiology, University of Michigan Medical School. Ann Arbor, MI