Author Affiliations : Division of cardiothoracic surgery,
University of Miami
Corresponding Author:
Sandeep Sainathan, MD
Assistant Professor of cardiothoracic surgery
University of Miami
1611 NW 12TH Ave
East Tower Suit 3016F
Miami, FL 33136
sainathans@outlook.com
Sun and colleagues [1], in their retrospective analysis of 400
pediatric patients over three months undergoing first-time cardiac
surgery with cardiopulmonary bypass (CPB) in China, studied
perioperative factors which were predictive of early postoperative
adverse outcomes. The primary focus of the study was liberation from
mechanical ventilation, with patients requiring mechanical ventilation
for more than 24 hours postoperatively defined as the prolonged
mechanical ventilation (PMV) group. 23% (93/401 patients) experience
PMV. The secondary focus of the study was a composite of mortality and
morbidity (bleeding, re-exploration, reoperation, open chest, ECMO use,
etc.) outcomes.
The study collected several perioperative hemodynamics-related data. The
data most predictive of a need for PMV was the Vasoactive-Inotropic
Score (VIS) at 48 hours, followed by the operation duration. In other
words, patients who had a continuing need for the inotropic requirement
at 48 hours after surgery were likely to need extended mechanical
ventilatory support as compared to the patients that had been weaned off
inotropes by that time (VIS 48 hours: 7 (PMV) vs. 0 (non-PMV),
p<0.05). Using the ROC curves, a VIS cut-off score of 5.5 at
48 hours post-op had a sensitivity of 68% and specificity of 83% for
predicting a continued need for PMV. The PMV group tended to have more
extended operations with more prolonged cardiopulmonary bypass and
cardiac arrest times. The PMV group also had a higher amount of fluid
accumulation postoperatively despite having lower CPB prime volumes and
operative blood loss. The PMV group did not differ from the non-PMV in
the complexity of the procedure as measured by the RACHS-1 score and
demographic data such as age. Both the groups were in a similar
preoperative metabolic state as represented by serum lactate levels, but
the postoperative serum lactate was higher in the PMV group. Mortality
data was not reported independently in the study and was stated to be
low by the authors and was likely due to >90% of the cases
belonging to RACS-1 categories 2 and 3[2]. When the morbidity
metrics were composited with mortality, the incidence was three times
more common in the PMV group. As a result, the PMV group experience
twice the amount of ICU and hospital length of stay.
The continued need for inotropic support at 48 hours is likely a
surrogate marker for a protracted recovery. This is particularly true as
the groups did not differ in the complexity of the surgical procedure as
measured by the RACHS-1 system, as higher complexity procedures are
known to have a more prolonged need for mechanical ventilation [3].
Similarly, there was no age difference in the groups as neonates, and
young infants tend to have a longer recuperation time, which is another
independent predictor of prolonged mechanical ventilation [3]. As
alluded to earlier, paradoxically, the PMV group had smaller priming
volumes and less operative blood loss, which are generally associated
with better operative outcomes [4]. Thus, the underlying cause for
suboptimal outcomes in the PMV group can either be a technical
inadequacy of the repair or other underlying comorbid conditions such as
an associated chromosomal anomaly that was not captured in the database.
As defined by the Boston group and measured by the number of residual
lesions, the Technical Performance Score is known to be associated with
prolonged operative times and adverse early clinical outcomes, as
described in this study [5]. A difference in the score between the
groups may explain the difference in the outcomes. The dataset does not
delineate associated chromosomal abnormalities. Genetic abnormalities
are known to cause variation in surgical outcomes and in part may
explain the outcome difference between the cohort [6]. The type of
cardioplegia used is not available in the study, and if there was a
difference between the groups, it might explain the difference in the
spontaneous cardiac recovery rate after reperfusion in the groups.
The VIS score also appears to be a delayed predictor of a need for PMV
as its discriminatory ability was best at 48 hours post-op. In other
words, a significant inotropic requirement early in the postoperative
course as measured by the VIS was not prognostic, but the trajectory of
weaning off the inotropes was. Generally, by 48 hours postoperative, the
patient’s clinical course is apparent based on the overall clinical
picture. Patients with a poor Technical Performance Score had inferior
long-term outcomes [7]. Similarly, it would be interesting to see if
a high VIS at 48 hours has a long-term prognostic impact.
In conclusion, the VIS at 48 hours is a good surrogate marker for
adverse postoperative events in pediatric patients undergoing cardiac
surgery with cardiopulmonary bypass and is limited by its ability to
delineate the underlying cause for an unfavourable clinical course.
Thus, other predictors such as the Technical Performance Score are
likely to highlight the underlying cause and can be used to improve
outcomes. However, patients with a high postoperative VIS score at 48
hours may benefit from closer longer-term follow for outcomes such as
late survival, functional class, and need for reoperation.