Comparative Study of Haemodynamic Changes After Spinal Anaesthesia in Non-obese and Pregnant Women
Comparative Study of Haemodynamic Changes After Spinal Anaesthesia in Non-obese and Pregnant Women
Obesity has become one of the most common risk factors in obstetric practice with serious
 anaesthetic implications. Obese pregnants have limited physiological reserves and
 cardiovascular co- morbidities when compared to non-obese pregnant women. Spinal anaesthesia
 is the anaesthetic technique of choice for caesarean section. The haemodynamic changes
 associated with spinal anaesthesia pose the greatest hazard to the mother and the foetus and
 are exaggerated in obese pregnant women. However differences in the changes in haemodynamic
 variables such as cardiac output (CO), stroke volume (SV) and systemic vascular resistance
 (SVR) between obese and non-obese pregnant women having caesarean section (CS) under spinal
 anaesthesia have not been studied before. This study compares the haemodynamic changes after
 spinal anaesthesia for CS in non-obese and obese parturients in a single centre, prospective
 case control study, using LiDCOrapidV2. This LiDCOrapidV2 device is a noninvasive method of
 measuring haemodynamic variables. It is a single centre, prospective, case control study. The
 primary outcome compares the differences and variability in CO, SV and SVR between obese and
 non-obese parturients. The secondary outcomes include comparison of the correlation between
 changes in blood pressure (BP) and CO in each patient and the difference in BP between
 conventional intermittent oscillometric device and continuous LiDCORapidV2in each patient
 with a view to assess the need for measurement of cardiac output in obstetric anaesthesia
Pregnancy is a state of physiological alteration as a result of increased oxygen demand and
 involves significant haemodynamic changes including sustained rises in cardiac output (CO)
 (by up to 30- 60%) and stroke volume (SV) (up to 30%) by virtue of increase in the blood
 volume This is associated with decrease in the systemic vascular resistance (SVR) and
 enhanced myocardial performance. When pregnancy is associated with obesity the cardiovascular
 system is further stressed. Obese pregnant women with a body mass index (BMI) more than
 35kg/m2 pose significant health issue and are at risk for anaesthesia related maternal
 mortality. Several cases of sudden cardiac arrests of unexplained cause in obese pregnants
 have been reported. Obesity induced pathological changes have profound effects on cardiac
 endothelial and vascular function. Thus in pregnancy, obesity leads to further increase in
 blood volume and cardiac output proportionate to the amount of fat thus causing further
 volume overload of the heart. A study conducted with transthoracic echo showed a mean
 increase of around 550mls in cardiac output between obese and non-obese parturients in the
 third trimester. In contrast to the decrease in SVR that occurs in normal pregnancy, obesity
 by itself is associated with increased SVR by virtue of the increased sympathetic activity
 due to the effects of hormones including leptin, insulin and inflammatory mediators. This
 causes an increase in afterload 6, 8 thus offsetting the advantage of reduced afterload of
 normal pregnancy affecting the CO further. This combination of volume and pressure overload
 leads to systolic dysfunction. Furthermore the increase in heart rate of pregnancy in line
 with elevated cardiac output will decrease the diastolic interval and time for myocardial
 perfusion causing diastolic dysfunction. Thus obese pregnant patients may present with a
 systolic, diastolic or both systolic and diastolic dysfunction of the left ventricle.
 Associated obstructive sleep apneoa (OSA) and pulmonary hypertension may lead to right
 ventricular failure. These changes are further compromised in the third trimester due to
 aortocaval compression thus reducing cardiac output and placental perfusion. The large
 abdominal panniculus in obesity will further add to the uterine and vascular compression. It
 is thus evident that obese parturient women pose an increase in risk for cardiovascular
 compromise. As obesity is considered a global health care problem especially in women,
 anaesthetists are increasingly faced with the care of this high risk group of
 patients.9However there is paucity of evidence to quantify this cardiovascular compromise on
 obese pregnant women and guide provision of best care.

 Regional anaesthesia has been the preferred technique of anaesthesia, especially in obese
 pregnant patients. Induction of spinal anaesthesia will cause profound haemodynamic changes
 that represent the greatest hazard to the mother and the foetus. Evidence suggests these
 haemodynamic changes are common after spinal anaesthesia and results in hypotension causing
 unconsciousness, maternal nausea and vomiting, dizziness including deleterious effects on the
 foetus like neonatal acidaemia and lower APGAR score. However because of the changes in
 peripheral vascular resistance, changes in maternal arterial pressure do not necessarily
 reflect changes in maternal cardiac output. These changes in cardiac output and associated
 oxygen delivery pose the greatest risk to the foetus.

 A recent review of cardiovascular alterations in the parturient undergoing caesarean delivery
 with neuraxial anaesthesia showed that induction of spinal anaesthesia will lead to decrease
 in CO by 10-35% as measured by various invasive techniques. Although the patho-physiology of
 pregnancy and obesity and echocardiography findings gives us an understanding that these
 patients are more prone for severe hypotension and cardiovascular compromise the extent of
 alteration of haemodynamic variables in obese pregnant patients during spinal anaesthesia has
 not been studied previously. Our primary aim therefore is to investigate the haemodynamic
 alterations in obese parturient during spinal anaesthesia and compare it with those in
 non-obese parturient.

 Traditionally clinicians and researchers have used heart rate (HR)and BP as surrogate markers
 of cardiac output during spinal anaesthesia. Managing maternal BP was considered as safe
 optimization of foetal wellbeing. Recent publications have emphasized that keeping BP at
 baseline is not an optimal strategy and maintaining CO is superior in maintaining uterine
 blood flow. In addition the correlation of the foetal compromise in the form of umbilical
 artery pH and umbilical artery pulsatality index was better related to SV and CO than BP and
 heart rate. 19 Thus measurement of CO is considered a better approach than BP in optimising
 oxygen delivery to the foetus.

 Although pulmonary artery catheterization is a gold standard for measuring cardiac output it
 is not desirable to use routinely because of its invasiveness, patient compliance and its
 potential complications. Minimally invasive CO monitors like LiDCO plus has been validated
 and successfully used for this purpose, but still require an arterial line and is complex for
 routine use.

 LiDCOrapidV2(LiDCO Group plc, LiDCO Limited, United Kingdom), incorporates the CNAPTM
 (continuous noninvasive arterial pressure) module that derives CO, SV, and SVR from a
 continuous noninvasive arterial waveform and analysed by the PulseCOTM algorithm avoiding
 invasive blood pressure measurements. This study studies the clinical application of the
 LIDCOrapidV2 and compares the haemodynamic variables in obese and non-obese pregnant women
 having CS under spinal anaesthesia.
Inclusion Criteria:

 1. Pregnant patients with BMI of less than 30 undergoing elective CS.

 2. Obese pregnant patients with BMI of more than 35 undergoing elective CS

 Exclusion Criteria:

 1. Patients with other comorbidities like pre-eclampsia, eclampsia, essential
 hypertension, respiratory disease and compromised renal function.

 2. Patients on long-term medication.

 3. Patients having CS under epidural.

 4. Patients having general anaesthesia.

 5. Patients on antihypertensive medication.

 6. Patients with BMI of 31-34.

 7. Patients less than 36 weeks of gestation