Non Invasive Haemodynamics in Neuraxial Anaesthesia Hypotension

Non-invasive Haemodynamic Parameters Predictive of Hypotension Induced by Neuraxial Anaesthesia During Elective Caesarean Section

Spinal (or neuraxial) anaesthesia is still considered the first choice technique for elective Caesarean section as simple, quick, reliable and cheap. However, this anaesthetic method can be burdened by maternal hypotension with significant maternal and foetal implications.

Hypotension induced by neuraxial anaesthesia (NA-induced hypotension) is defined as systolic blood pressure (SBP) less than 100 mmHg or a decrease of 20-30% from baseline values. The incidence of hypotension could exceed 71% and can cause, if serious and prolonged, nausea, vomiting, lost of consciousness, placental hypoperfusion and foetal acidosis.

There are two alternative hypotheses to explain why hypotension might be so commonly diagnosed after regional analgesia during labour: preload reduction theory and afterload reduction theory. A non-invasive continue haemodynamic monitoring could be useful in detecting pregnant women with a positive preoperative supine stress, at increased risk for clinically significant hypotension during Caesarean section under spinal anaesthesia. These women seem more likely to benefit from optimizing the administration of fluids and vasoconstrictors to maintain pressure and cardiac output at basal levels.

Predictors of clinical need of therapy to counteract symptomatic hypotension (dependant variable) will be sought by using regression logistic analysis. Putative variable to include in the model will be selected through clinical and statistical criteria. Univariate screening will be performed assuming the usual cut-off of p<0,1 and taking into account the biological relevance. The final variable to challenge in the multivariate model will be selected according to the parsimony criteria in order to avoid overfitting and multicollinearity.

Inclusion Criteria:

• Pregnant women with high bleeding risk (previous caesarean section, previous uterine surgery, placenta praevia/accrete, previous documented uterine atony, foetal macrosomia, polyhydramnios)
• Obstetric nulliparous or multiparous patients
• Spontaneous pregnancy
• Single foetus, at term
• Elective Caesarean section, fasting according to international guidelines
• At term BMI > 18 and < 35 kg/m2

Exclusion Criteria:

• Contraindications to neuraxial anaesthesia

• Previous documented maternal cardiovascular problems

• Gestational hypertension (defined as new onset systolic blood pressure ≥ 140 mmHg or diastolic blood pressure ≥ 90 mmHg on two occasions at east 4 - 6 hours apart while the patient is on bed rest, with an appropriately sized cuff, after 20 weeks gestation)

• Chronic hypertension of any causes (defined as systemic blood pressure > 140/90 mmHg)

• Preeclampsia (defined as gestational hypertension with one or more of the following de novo conditions:

  • Proteinuria (defined as the excretion of 300 mg or more of protein in a 24-hour urine collection or a protein/creatinine ratio of at least 0.3 (each measured as mg/dL) or at least 1 g/L [2+] on dipstick testing)

  • Other maternal organ dysfunction:

    1. progressive renal insufficiency (renal creatinine concentration greater than 1.1 mg/dL or a doubling of the serum creatinine concentration in the absence of other renal disease),
    2. impaired liver function as indicated by abnormally elevated blood concentrations of liver enzymes (at least twice upper limit of normal concentration), severe persistent right upper quadrant or epigastric pain unresponsive to medication and not accounted for by alternative diagnoses, or both),
    3. new-onset cerebral or visual disturbances (examples include eclampsia, altered mental status, blindness, stroke, or more commonly hyperreflexia when accompanied by clonus, severe headaches when accompanied by hyperreflexia, persistent visual scotoma),
    4. haematological complications (thrombocytopenia - platelet count below 150,000/dL, disseminated intravascular coagulation (DIC), haemolysis).

• Uteroplacental dysfunction with foetal growth restriction (less than fifth percentile)

• Reversed end-diastolic flow on umbilical artery Doppler studies (IR > 0,5 at 24 week gestation)