Changes in Ventilation Inhomogeneity and Respiratory Function Following Elective Caesarean Section Under Regional Anaesthesia

Study Overview
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Brief Summary
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Pregnancy is associated with physiological changes affecting the cardiorespiratory system as a consequence of an increase in both cardiac output and intra-abdominal pressure. The aim of this prospective observational study is to examine the perioperative changes in ventilation inhomogeneity and respiratory function measured by the non-invasive nitrogen multiple breath washout and forced oscillation techniques.

Detailed Description
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Pregnancy is associated with physiological changes affecting the cardiorespiratory system as a consequence of an increase in both cardiac output and intra-abdominal pressure. These alterations lead to a ventilation/perfusion mismatch which is potentiated by a decrease in functional residual capacity (FRC). These effects explain why pregnant women are more prone to the occurrence of hypoxemia, particularly in the third trimester of their pregnancy. The importance of the ventilation inhomogeneity can be estimated from the lung clearance index (LCI) measured by the non-invasive nitrogen multiple breath washout (N2 MBW) technique. Moreover the loss in lung volume is associated with reduction in respiratory system compliance, which can also be assessed non-invasively by the forced oscillation technique (FOT). To our knowledge, there is no existing data on LCI or FRC using the aforementioned techniques in pregnant women. Furthermore, existing data on respiratory function in pregnant women is largely restricted to spirometric and body plethysmographic measurements taken primarily in the 1970s-1980s. As such, the important roles of lung ventilation inhomogeneity as well as the potential changes following birth after caesarean section have yet to be completely characterised.

Official Title
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Changes in Ventilation Inhomogeneity and Respiratory Function Following Elective Caesarean Section Under Regional Anaesthesia: a Prospective Observational Study

Conditions
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Pregnancy

Intervention / Treatment
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* Other: Physiologic measures of lung function


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Written informed consent Pregnant woman in the third trimester (37-40 weeks gestational age) Scheduled for elective caesarean section under regional (spinal or combined spinal-epidural) anaesthesia Exclusion Criteria: Pregnant women outside 37-40 weeks gestational age Non-singleton pregnancy Previous history of ≥2 caesarean sections History or clinical signs of cardiopulmonary disease in the last 12 months (chronic hypertension, gestational hypertension, preeclampsia, asthma, acute or chronic bronchitis, others) Positive current smoking status Pre-pregnant body mass index (BMI) >30 kg/m2 (based on booking records) Respiratory infection <2 weeks prior to surgery Inability to perform the respiratory function tests

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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Female

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Intervention/Treatment |
| --- |
|Other: Physiologic measures of lung function|Respiratory function tests: Nitrogen multiple breath washout (N2MBW) measured with an ultrasonic flowmeter (Exhalyzer D with ICU insert, Eco Medics, Duernten, Switzerland) Forced oscillation technique (FOT) measured with a tremoFlo device (Thorasys, Montreal, Canada)|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Perioperative changes in ventilation inhomogeneity (LCI) following delivery by caesarean section | Nitrogen multiple breath washout technique | 1-3 days prior to caesarean section until 5 days postoperative | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Alterations in FRC throughout the postpartum period | Nitrogen multiple breath washout technique | 1-3 days prior to caesarean section until 5 days postoperative | 
| Changes in respiratory mechanics: respiratory system compliance (Crs) | Forced oscillation technique | 1-3 days prior to caesarean section until 5 days postoperatively | 
| Changes in respiratory mechanics: airway resistance (Raw) | Forced oscillation technique | 1-3 days prior to caesarean section until 5 days postoperatively | 
| Perioperative respiratory complications | Apnoea/bradypnoea, oxygen desaturation <90%/hypoxemia, hypoventilation/atelectasis, pulmonary embolism, incoercible cough | During caesarean section until 5 days postoperatively | 
| Perioperative respiratory interventions | Intubation, oxygen therapy, bronchodilator, adrenaline, continuous positive airways pressure (CPAP), respiratory physiotherapy | During caesarean section until 5 days postoperatively | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Lung volume, Lung Clearance Index, Functional Residual Capacity, Respiratory function