Perfusion index as a predictor of hypotension following spinal anaesthesia in lower segment caesarean section

Abstract

Background and aims:
Perfusion index (PI) is a new parameter tried for predicting hypotension during spinal anaesthesia for the lower segment caesarean section (LSCS). This study aimed at investigating the correlation between baseline perfusion index and incidence of hypotension following SAB in LSCS.

Methods:
In this prospective observational study, 126 parturients were divided into two groups on the basis of baseline PI. Group I included parturients with PI of ≤3.5 and Group II, parturients with PI values >3.5. Spinal anaesthesia was performed with 10 mg of injection bupivacaine 0.5% (hyperbaric) at L3-L4 or L2-L3 interspace. Hypotension was defined as mean arterial pressure <65 mmHg. Statistical analysis was performed using Chi-square test, independent sample t-test and Mann-Whitney U-test. Regression analysis with Spearman's rank correlation coefficient was done to assess the correlation between baseline PI and hypotension. Receiver operating characteristic (ROC) curve was plotted for PI and occurrence of hypotension.

Results:
The incidence of hypotension in Group I was 10.5% compared to 71.42% in Group II (P < 0.001). There was significant correlation between baseline PI >3.5 and number of episodes of hypotension (rs0.416, P < 0.001) and total dose of ephedrine (rs0.567, P < 0.001). The sensitivity and specificity of baseline PI of 3.5 to predict hypotension was 69.84% and 89.29%, respectively. The area under the ROC curve for PI to predict hypotension was 0.848.

Conclusion:
Baseline perfusion index >3.5 is associated with a higher incidence of hypotension following spinal anesthesia in elective LSCS.

Full text

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© 2017 Indian Journal of Anaesthesia | Published by Wolters Kluwer - Medknow
Address for correspondence:
Dr. Rinita Paul,
102A, Moghal Maskan
Apartments, 6‑3‑579, Opposite
Zilla Parishad, Anand
Nagar Colony, Khairatabad,
Hyderabad ‑ 500 004,
Telangana, India.
E‑mail: dr.rinita@gmail.com
INTRODUCTION
Hypotension following spinal anaesthesia results
from the sympathetic blockade and decreased cardiac
output.[1] Pregnant women are more sensitive to local
anaesthetics, less responsive to vasopressors and
have lower mean arterial pressure (MAP) at term.[2]
Hence, parturients can develop profound hypotension
following central neuraxial blockade for the lower
segment caesarean section (LSCS).
Non-invasive blood pressure (NIBP) measurement
is the standard method of monitoring intraoperative
haemodynamics. However, beat to beat variation
in perfusion dynamics cannot be measured by this
method and limits its efficacy.
Perfusion index (PI) is defined as the ratio of pulsatile
blood flow to non-pulsatile blood flow in the peripheral
vascular tissue, measured using a pulse oximeter based
on the amount of Infrared light absorbed.[3] Hence, PI
can be used to assess perfusion dynamics and is being
considered as a non-invasive method to detect the
likelihood of development of hypotension following
Devika Rani Duggappa, MPS Lokesh, Aanchal Dixit, Rinita Paul,
RS Raghavendra Rao, P Prabha
Department of Anaesthesia, Bangalore Medical College and Research Institute, Bengaluru, Karnataka, India
Perfusion index as a predictor of hypotension
following spinal anaesthesia in lower segment
caesarean section
ABSTRACT
Background and Aims: Perfusion index (PI) is a new parameter tried for predicting hypotension
during spinal anaesthesia for the lower segment caesarean section (LSCS). This study aimed
at investigating the correlation between baseline perfusion index and incidence of hypotension
following SAB in LSCS. Methods: In this prospective observational study, 126 parturients
were divided into two groups on the basis of baseline PI. Group I included parturients with PI
of ≤3.5 and Group II, parturients with PI values >3.5. Spinal anaesthesia was performed with
10 mg of injection bupivacaine 0.5% (hyperbaric) at L3–L4 or L2–L3 interspace. Hypotension
was dened as mean arterial pressure <65 mmHg. Statistical analysis was performed using
Chi‑square test, independent sample t‑test and Mann–Whitney U‑test. Regression analysis with
Spearman’s rank correlation coefcient was done to assess the correlation between baseline PI
and hypotension. Receiver operating characteristic (ROC) curve was plotted for PI and occurrence
of hypotension. Results: The incidence of hypotension in Group I was 10.5% compared to 71.42%
in Group II (P < 0.001). There was signicant correlation between baseline PI >3.5 and number of
episodes of hypotension (rs 0.416, P < 0.001) and total dose of ephedrine (rs 0.567, P < 0.001).
The sensitivity and specicity of baseline PI of 3.5 to predict hypotension was 69.84% and
89.29%, respectively. The area under the ROC curve for PI to predict hypotension was 0.848.
Conclusion: Baseline perfusion index >3.5 is associated with a higher incidence of hypotension
following spinal anesthesia in elective LSCS.
Key words: Hypotension, perfusion index, pregnancy, spinal anaesthesia
Access this article online
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DOI: 10.4103/ija.IJA_429_16
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How to cite this article: Duggappa DR, Lokesh M, Dixit A, Paul R,
Raghavendra Rao RS, Prabha P. Perfusion index as a predictor of
hypotension following spinal anaesthesia in lower segment caesarean
section. Indian J Anaesth 2017;61:649-54.
This is an open access article distributed under the terms of the Creative
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Original Article
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Duggappa, et al.: Perfusion index ‑ Predictor of hypotension
650 Indian Journal of Anaesthesia | Volume 61 | Issue 8 | August 2017
subarachnoid block (SAB).[4-6] Various studies carried
out previously have employed perfusion index to
assess haemodynamic parameters. However, there
are limited data regarding its use for prediction of the
incidence of hypotension occurring as a result of the
central neuraxial blockade. We conducted this study
to determine whether a baseline PI >3.5 predicts the
development of hypotension after spinal anaesthesia
in parturients.
METHODS
The prospective observational study was conducted
from June 2014 to October 2014. Approval for the
study was obtained from the Institutional Ethics
Committee. Informed written consent was obtained
from every participant in the study.
The study included parturients between 20 and 35 years
of age posted for elective caesarean section. We
hypothesised that parturients with higher baseline
PI would have a higher incidence of hypotension.
Anticipating equal distribution of baseline PI on
either side of cut-off point of 3.5 suggested in a
study by Toyama et al.,[7] we conducted a pilot
study in 15 parturients and found a difference in
the incidence of hypotension to be 20% when those
15 patients were divided into two groups based on
cut-off point of 3.5 (Group I PI ≤3.5 [eight patients]
and PI >3.5 [seven patients]). Keeping the confidence
interval at 95%, a minimum of 120 parturients would be
required, to achieve a power of 80%, if the same result
had to be reproduced. We enrolled 126 parturients
for the study. Parturients involved in the pilot study
were not considered for final analysis. Parturients
with placenta praevia, preeclampsia, cardiovascular
or cerebrovascular disease, gestational diabetes, body
massindex≥40,gestationalage<36or >41 weeks,
contraindications to spinal anaesthesia and those
requiring emergency LSCS were excluded from the
study. Standard monitoring with electrocardiography,
automated NIBP, and pulse oximetry (SpO2) was
performed for baseline values and intraoperative
monitoring. The perfusion index was measured in
the supine position using a specific pulse oximeter
probe (Masimo Radical 7®; Masimo Corp., Irvine, CA,
USA) which was attached to the left index finger of
all parturients to ensure uniformity in measured PI
values.
This was a double-blinded study. The baseline
haemodynamic values including PI were recorded in
the supine position by an anaesthesiologist who was
not involved in the further intraoperative monitoring
of the patient. Those with a baseline perfusion index
of≤3.5fellintoGroup I and those withaperfusion
index of >3.5 fell into Group II.[7]
Intravenous (IV) access was established in the left upper
limb. Each parturient was prehydrated with 500 ml of
Ringer lactate over 20 min. After prehydration, the
baseline values were recorded. While administering
neuraxial blockade, the Masimo® pulse oximeter
was disconnected to prevent observer bias and SpO2
was recorded using a different pulse oximeter. Spinal
anaesthesia was performed by an anaesthesiologist
blinded to the baseline PI values, using Quincke’s
25-gauge spinal needle in left lateral decubitus position
with 10 mg of injection bupivacaine 0.5% (hyperbaric)
at the L3–L4 or L2–L3 interspace. The parturient was
returned to the supine position with a left lateral
tilt of 15° to facilitate left uterine displacement. The
Masimo® pulse oximeter was reconnected to monitor
the patient till the end of surgery. Oxygen was given
through face mask at 4 L/min.
Ringer’s lactate was administered at a rate of
100 ml/10 min. The level of sensory block was checked
5 min after the spinal injection with a cold swab. If a T6
sensory block level was not achieved, these parturients
were excluded from the study and managed according
to institutional protocol. Maximum cephalad spread
was checked 20 min after SAB. NIBP, heart rate (HR),
respiratory rate (RR), SpO2 and PI were recorded at
2 min intervals after the SAB up to 20 min and then
at 5 min intervals by the same anaesthesiologist who
administered SAB till the end of surgery. Hypotension
was defined as a decrease in MAP <65 mm of Hg and
treated with IV bolus of 6 mg injection ephedrine and
100 ml of Ringer lactate. The first 60 min following spinal
anaesthesia was considered for anaesthesia-induced
hypotension. Bradycardia was defined as HR <55
beats/min and treated with injection atropine 0.6 mg
IV bolus. Following extraction of the baby, Apgar score
was recorded at 1st and 5th min. Injection oxytocin 10
units was given as uterotonic following baby extraction
at a rate of 200 mU/min as a separate infusion. Patients
requiring additional oxytocics and/or additional
surgical interventions excluded from the study. The
incidence of other side effects such as nausea, vomiting
if observed were recorded.
Categorical and discrete data are presented as tables,
and continuous data represented by graphs. Discrete
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Duggappa, et al.: Perfusion index ‑ Predictor of hypotension
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Indian Journal of Anaesthesia | Volume 61 | Issue 8 | August 2017
and continuous data were analysed for normal
distribution using Shapiro–Wilk test. Chi-square
test was applied to assess statistical significance for
discrete and categorical data. Independent sample
t-test and Mann–Whitney U-test were applied for
continuous data which showed normal and skewed
distribution, respectively. Regression analysis with
Spearman’s rank correlation coefficient was done to
assess the correlation between baseline PI with other
parameters. A Receiver Operating Characteristic (ROC)
curve was obtained for baseline PI compared with
the hypotension episodes of 126 patients. Data
were analysed using SPSS (Statistical Package for
Social Sciences) version 20. (IBM SPSS Statistics for
Windows, version 20.0, IBM Corp., Armonk, NY, USA)
P < 0.05 was considered statistically significant.
RESULTS
A total of 126 patients were included in the study.
Two parturients were excluded from the study due to
an inadequate level of the spinal blockade, and four
parturients had to be excluded due to the requirement
of additional oxytocics, as the drugs administered could
influence the HR and blood pressure of the patients.
Fifty-seven patients were in Group I and 63 patients
were in Group II for final analysis [Figure 1]. The
demographic parameters such as age, weight and height
were comparable between the two groups [Table 1].
The average duration of surgery in both groups
was comparable (Group I - 45.87 ± 11.14 min and
Group II - 47.93 ± 9.78 [P = 0.2]).
The median level of cephalad spread of sensory block
achieved in both groups was T6. (interquartile range
[IQR] - T4–T6).
The PI values in both groups on assessment showed
skewed distribution and the median PI in Group I
was 2.45 (IQR [1.8–2.8]), and in Group II was
5.4 (IQR [4.25–7.1]). The skewed distribution to the
right around the PI value of 3.5, was observed when
baseline PI values of both groups were combined and
assessed for normal distribution.
Intraoperatively, the HR was comparable between the
two groups.
Excluded (n = 0)
•Not meeting inclusion criteria (n = 0)
•Declined to participate (n = 0)
•Other reasons (n = 0)
Included in Study (n = 126)
Analysis
Follow-Up
Group I (Perfusion Index ≤ 3.5)
Given Spinal Anaesthesia (n = 61)
Perfusion Index > 3.5
Given Spinal Anaesthesia (n = 65)
Discontinued intervention (n = 1)
Inadequate level of block (n = 1) Discontinued intervention (n = 1)
Inadequate level of block (n = 1)
Excluded from analysis (received additional
oxytocics) (n = 3)
Included for final analysis (n = 57)
Excluded from analysis (received additional
oxytocics) (n = 1)
Included for final analysis (n = 63)
Analysed (n = 57) Analysed (n = 63)
Enrolment Assessed for eligibility (n = 126)
Figure 1: CONSORT Flow Diagram
Table1:Comparisonofdemographiccharacteristics
betweentwo groups
Demographicparameter Group I(n=57)
PI≤ 3.5
GroupII (n=63)
PI> 3.5
Age in years, median
(IQR range)
24 (21‑27.5) 25 (22‑28)
Height in cm, median
(IQR range)
156 (154‑157) 157 (156‑158)
Weight in kg, median
(IQR range)
68.0 (64.5‑70) 67.0 (62.5‑70)
Datapresentedasmedian,IQR,range.Therewasnosignicantstatistical
differenceinthedemographicdatabetweenthetwogroups.PI–Perfusion
Index;IQR–Interquartilerange
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Duggappa, et al.: Perfusion index ‑ Predictor of hypotension
652 Indian Journal of Anaesthesia | Volume 61 | Issue 8 | August 2017
The difference between the two groups with respect to
systolic blood pressure (SBP), diastolic blood pressure
(DBP) and MAP was statistically significant for the
first 25 min [Figure 2]. The difference in SBP was most
significant during the 2nd, 4th, 6th, 10th and 15th min with
values being lower in Group II than Group I, whereas
difference in DBP was most significant during the 4th,
10th, 15th, 20th and 25th min and the difference in MAP
was most significant during the 2nd, 4th, 6th, 10th, 15th,
20th and 25th min. The DBP and MAP were also lower
in Group II than Group I.
The ROC curve yielded 3.85 as a more appropriate
cut-off with a well balanced 76% sensitivity and
specificity. The area under the ROC curve (AUC) was
0.848 [Figure 3].
The incidence of hypotension in Group I was
10.5% (6/57) compared to 71.42% (45/63).
This was clinically and statistically highly
significant (P < 0.001, odds ratio –0.07). In Group I,
four patients had one episode of hypotension, one
patient had two episodes, and one patient had three.
In Group II, twenty-four patients had one episode
of hypotension, 16 patients had two episodes, four
patients had three episodes, and one patient had four
episodes [Table 2]. Eighty-nine percent of patients
in Group I had no hypotension. Thirty-two percent
of patients in Group II had multiple episodes of
hypotension (P < 0.001).
Median ephedrine usage in Group I was 0 mg
(IQR 0–0 mg) and 6 mg (IQR 6–12) in Group II
(P < 0.001) The amount of IV fluids required in Group I
was also lower than Group II (P < 0.001) [Table 2]. One
patient belonging to Group II developed bradycardia
which was treated with injection atropine 0.6 mg IV.
On Spearman’s rank correlation we found highly
significant correlation between baseline PI >3.5 and
number of episodes of hypotension (rs 0.416, P < 0.001),
total dose of ephedrine used (rs 0.567, P < 0.001) and
total IV fluids used (rs 0.249, P =−0.019).
Post hoc power analysis comparing the incidence
of hypotension and vasopressor use between the
two groups showed a power of more than 90%, at
Table2:Requirementofephedrineand intravenousuids
andnumber ofepisodesofhypotension
Parameter GroupI (n=57)
PI≤ 3.5
GroupII (n=63)
PI> 3.5
P
Dose of ephedrine
in mg, median (IQR,
minimum–maximum)
0.00 (0‑0, 0‑18) 6.0 (0‑12, 0‑24) <0.001
Fluidrequirement in
mL, median (IQR)
1000 (900‑1100) 1100 (1000‑1150) <0.001
Episodes of
hypotension
0 51 18 <0.001
1 4 24
2 1 16
3 1 4
4 0 1
Datarepresentingmeanephedrineanduidrequirementpresentedasmedian
withIQR,assessedforsignicanceusingMann–WhitneyU‑test.Numberof
episodesofhypotensioncomparedbetweenthetwogroupsofpatientsusing
Chi‑squaretest.PI–P:erfusionIndex;IQR–Interquartilerange
AreaUnder theCurve
TestResultVariable(s): PIbaseline
Area Std.Error PAsymptotic 95%Condence
Interval
LowerBound Upper Bound
0.848 0.036 <0.001 0.779 0.918
Figure 3: ROC curve depicting baseline PI against incidence of
hypotension
Figure 2: Comparison of systolic blood pressure, diastolic blood
pressure and mean arterial pressure between the two groups
intraoperatively. Systolic, diastolic and mean arterial pressure values
presented as mean ± standard deviation. Statistical analysis done
using independent t-test P > 0.05
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Indian Journal of Anaesthesia | Volume 61 | Issue 8 | August 2017
confidence intervals of 95%. The sensitivity and
specificity of baseline PI with a cut-off of 3.5 was
69.84% and 89.29% respectively.
The RR and SpO2 were comparable between the
two groups throughout the study period. There was
no significant difference in Apgar scores between
the groups at 1st and 5th min. The incidence of
nausea and vomiting was similar in both groups
(Group I – 4/57 (7.01%), Group II 9/63 (14.28%),
P = 0.20).
DISCUSSION
In the present study, the incidence and severity of
hypotension, vasopressor requirement was higher in
parturients whose baseline PI values were greater than
3.5. The ROC curve revealed that PI discriminated well
between patients who developed hypotension versus
those who did not; it yielded a new baseline PI value
of 3.85 as the cut off point for predicting hypotension
in parturients undergoing caesarean section under sub
arachnoid block.
Hypotension following administration of spinal
anaesthesia for caesarean delivery is common.[8] There
is no definite monitoring system which may predict
the likelihood of developing hypotension so that
additional precautions may be taken. Studies have
tried to evaluate the usefulness of perfusion index in
predicting hypotension following spinal anaesthesia
in casearean section.[7]
The principle of SpO2 is based on two light sources
with different wavelengths 660 nm and 940 nm,
emitted through cutaneous vascular bed of finger or
earlobe.[6] The absorbance of both wavelengths has a
pulsatile component, which represents fluctuations in
the volume of arterial blood between the source and
the detector. The non-pulsatile component is from
connective tissue, bone and venous compartment.
The perfusion index (PI) is the ratio of the pulsatile
component (arterial) and non-pulsatile component of
light reaching the detector.
Healthy pregnancy is characterised by a decrease in
systemic vascular resistance, increased total blood
volume and cardiac output.[9] The reduction of
systemic vascular resistance may vary in parturients
depending on various factors.[9-13] This decrease
in tone will correspond to higher perfusion index
values due to increase in pulsatile component due to
vasodilatation. Induction of a sympathectomy by spinal
anaesthesia will cause a further decrease peripheral
vascular tone and increase pooling and hypotension.
Parturients with high baseline perfusion index are
expected to have lower peripheral vascular tone and
hence are at higher risk of developing hypotension
following spinal anaesthesia. PI has been used in
the study by Mowafi et al. to detect intravascular
injection of the epinephrine-containing epidural test
dose, hence its reliability to detect vasoconstriction
has been demonstrated successfully.[4] Ginosar et al.
demonstrated that increase in PI following epidural
anaesthesia was a clear and reliable indicator of
sympathectomy.[5]
In contrast, a recent study performed by Yokose
et al.[14] demonstrated that PI had no predictive value
for hypotension in parturients undergoing LSCS
following SAB. This discrepancy was attributed
to various methodological differences, such as the
definition of hypotension, co-loading with colloids
and method of calculation of baseline PI.
The cut-off value of baseline perfusion index for
prediction of hypotension following spinal anaesthesia
was chosen as 3.5 based on a study conducted by
Toyama et al.[7] who did regression analysis and ROC
curve analysis and concluded that a baseline perfusion
index cut-off point of 3.5 could be used to identify
parturients at risk for such hypotension. An attempt
was made to explore the predictive ability of this value
in the Indian population, in this study. Further, only the
baseline value was considered for analysis, since we
did not try to explore the correlation between changes
in serial PI values with the incidence of hypotension.
In this study, the baseline PI >3.5 and probability of
hypotension were significantly correlating, a finding
similar to study by Toyama et al.
On Spearman rank correlation, a highly significant
correlation was found between baseline PI >3.5 and
number of episodes of hypotension, the total dose
of ephedrine used and total IV fluids used. A higher
requirement of vasopressor was seen in parturients
with baseline PI >3.5.
Toyama et al. found a sensitivity and specificity of 81%
and 86%, respectively, for baseline PI with a cut-off of
3.5 to predict hypotension, whereas in this study, the
specificity was comparable, 89.29%, but sensitivity
was lower, 69.84%.
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654 Indian Journal of Anaesthesia | Volume 61 | Issue 8 | August 2017
In this study, the consumption of IV fluid was higher
than that in the study by Toyama et al. As we used
injection ephedrine and fluid bolus to treat hypotension
while they used only injection phenylephrine to treat
hypotension.
Uterotonics such as prostaglandin F2 alpha,
methylergometrine are powerful vasoconstrictors
and would have influenced the observations and
hence patients receiving these drugs were excluded
from analysis, as they received these drugs between
20 and 25 min after spinal anaesthesia.
There are many limitations in this study. Patient
movement and any stimulus increasing sympathetic
activity like anxiety could easily change the PI values.
In this study, we recorded baseline PI values with
utmost care to avoid patient movement, especially
while recording baseline values and all patients were
counselled before taking them up for surgery to allay
anxiety. The baseline value of PI could have been
affected due to aortocaval compression in supine
position while recording baseline values. Systemic
vascular resistance was not measured, but it would
be invasive and unnecessary for the uncomplicated
caesarean section. Arterial blood gas analysis for both
the mother and foetus was not done which could have
ruled out hypoxia resulting from hypoperfusion.
Since PI is dependent on the vascular tone of digital
vessels, its role in predicting hypotension in conditions
where the tone of these vessels is affected is questionable
and more studies regarding its use in other patients
needs to be done before it can be accepted as a universal
non-invasive tool to predict hypotension following spinal
anaesthesia. In addition, further studies comparing PI
with invasive and accepted tools of haemodynamic
monitoring may throw more light regarding its utility.
CONCLUSION
Perfusion Index (PI) can be used as a tool for predicting
hypotension in healthy parturients undergoing
elective caesarean section under SAB. Parturients
with baseline PI >3.5 are at higher risk of developing
hypotension following SAB compared to those with
baselinePI≤3.5.
Financial support and sponsorship
Nil.
Conicts of interest
There are no conflicts of interest.
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