The pupillary light reflex for predicting the risk of hypotension after spinal anaesthesia for elective caesarean section.

INTRODUCTION: The balance between the sympathetic and parasympathetic systems could be used to predict the onset of hypotension following spinal anaesthesia. The autonomic innervation of the pupil may reflect this balance. The aim of this study was to evaluate the ability of pupillometry to predict the risk of hypotension after spinal anaesthesia for caesarean section. METHODS: Two hundred patients receiving spinal anaesthesia for caesarean section were recruited. Changes in pupillary diameter, pupillary reaction latency, pupil constriction velocity and maximum and minimum pupillary diameters were measured with a pupillometer (Neurolight®, IDMed) prior to induction of spinal anaesthesia with 10mg bupivacaine and fentanyl 30µg. Hypotension was defined as a systolic blood pressure drop of > 20% compared with the baseline value. RESULTS: A total of 141 patients (70%) presented at least one episode of hypotension. Pupillary reaction latency can poorly predict hypotension and severe hypotension after spinal anaesthesia. The areas under the receiver-operating characteristic curves were 0.654 (95% confidence interval: 0.584-0.720, P=0.0001) and 0.633 (95% confidence interval: 0.562-0.700, P=0.004) for optimal threshold values of 223 and 231ms, respectively. In multivariate analysis, a baseline systolic blood pressure > 130mmHg (odds ratio: 1.98, P=0.04) and a PRL > 223ms (odds ratio: 3.42, P=0.0002) were independently associated with the risk of spinal anaesthesia-related hypotension. CONCLUSION: Following spinal anaesthesia in patients undergoing caesarean section, though the predictive capacity pupillary reaction latency for the onset of hypotension and severe hypotension is poor, it is nevertheless the strongest predictor of hypotension identified in our study.

Pupillary reflex dilatation and analgesia nociception index monitoring to assess the effectiveness of regional anesthesia in children anesthetised with sevoflurane.

BACKGROUND: Pupillary diameter (PD) monitoring and Analgesia Nociception Index (ANI) (Metrodoloris, Lille, France), an online wavelet transform-based heart rate variability index, have been used in the assessment of pain. OBJECTIVE: The aim of this study was to evaluate the capacity of pupillary reflex dilatation and ANI to provide early assessment of regional anesthesia (RA) success following skin incision in children anesthetised with sevoflurane. METHODS: A total of 58 children, eligible for RA, were included after sevoflurane induction. The sevoflurane concentration was adjusted to maintain a MAC of 1.3 in oxygen and nitrous oxide, and a RA was performed. Pupillary diameter and ANI were recorded just prior to skin incision and then every 30 s for a period of 2 min. Regional anesthesia failure was defined by an increase in heart rate ≥ 10% occurring during the first 2 mins following incision. RESULTS: Thirty-nine and 19 subjects presented RA success and failure, respectively. In the RA failure group, skin incision induced both changes in PD (P < 0.01) and ANI (P < 0.05) within 1 min of incision. Areas under the receiver-operating curves (95% confidence interval) to identify regional anesthesia failure were 0.747 (0.613-0.881) and 0.671 (0.514-0.827) for the minimal value of ANI and the maximal value of PD recorded during the 2-min period from skin incision, respectively. CONCLUSION: Both PD and ANI rapidly change after skin incision in case of RA failure. These indices may provide a useful tool alone, or in combination with heart rate changes in the assessment of RA efficacy in children anesthetised with sevoflurane.

A randomized crossover study to determine the effect of a 30° head-up versus a supine position on the functional residual capacity of term parturients.

BACKGROUND: Airway management continues to pose challenges to the obstetric anesthesiologist. Functional residual capacity (FRC), which acts as an oxygen reservoir, is reduced from the second trimester onwards and is exacerbated in the supine position. Mechanisms to increase FRC may delay the onset of hypoxemia during periods of apnea. Values for changes in FRC in term parturients in semierect positions are unknown. We hypothesized that the FRC of healthy term parturients would increase significantly in the 30° head-up position in comparison with the supine position. METHODS: Twenty-two healthy term parturients were recruited. Initial screening spirometry was performed to exclude undiagnosed respiratory disease. FRC was measured using the helium dilution technique in the supine, 30° head-up, and sitting erect positions. Subjects were randomized to sequence of position testing order. Noninvasive systolic blood pressure, heart rate, and oxygen saturation were measured twice in each testing position. RESULTS: Results from 20 subjects were analyzed. The spirometry results for all subjects were within predicted normal reference intervals. FRC measurements differed significantly (P<0.001) among all positions. FRC increased by a mean of 188 mL (95% confidence interval 18 to 358 mL) from the supine to the 30° head-up position (P=0.03). There were no significant differences in vital signs among testing positions (P>0.16). CONCLUSIONS: We have demonstrated that the FRC of healthy term parturients increases significantly in the 30° head-up position in comparison with supine.

Maternal ambulation during labor.

PURPOSE OF REVIEW: To describe the recent advances in labor epidural analgesia, which may have an impact on maternal ambulation during labor. RECENT FINDINGS: With the advent of new epidural adjuvant drugs and new epidural delivery systems, we are now able to use very low concentration local anesthetic solutions with a reduction in the total doses of local anesthetic administered. This allows a much greater preservation of lower limb motor function in the parturient, with a subsequent positive effect on maternal ambulation. Although it is well documented that maternal satisfaction scores are higher with ambulatory epidurals than with other more conventional epidural techniques, the other positive effects, such as shorter labor times, and a reduction in instrumental and cesarean delivery rates, thought to have been associated with ambulatory epidurals, have however been more difficult to prove. SUMMARY: Since the earliest 'walking epidural' was described in the early 1990s, there has been much research into finding the ideal regional technique for labor analgesia that provides excellent analgesia with high maternal satisfaction scores while having little adverse effect on obstetric outcome. This review attempts to map the journey of the 'walking epidural' from its earliest form to its more recognizable modern day appearance.

The dose-dependent effects of phenylephrine for elective cesarean delivery under spinal anesthesia.

BACKGROUND: Hypotension is the most common serious side effect of spinal anesthesia for cesarean delivery. There has been a move recently toward the use of phenylephrine as a vasopressor infusion to improve maternal cardiovascular stability and fetal outcome. Although it seems safe in the elective setting, there have been concerns about its propensity for causing an increase in afterload and a baroreceptor-mediated bradycardia in the mother, with a consequent reduction in maternal cardiac output (CO). Using a noninvasive measure of CO, our aim was to investigate whether there were any dose-dependent effects of phenylephrine on maternal cardiovascular stability and, if so, any impact on fetal outcome. METHODS: In this randomized, double-blind study, 75 women scheduled for elective cesarean delivery were allocated to receive a phenylephrine infusion at 25 µg/min, 50 µg/min, or 100 µg/min. This infusion was titrated to maintain maternal baseline systolic blood pressure (SBP), from induction of spinal anesthesia until delivery. The maternal cardiovascular variables recorded included heart rate (HR) and SBP. A suprasternal Doppler monitor measured CO and stroke volume, as well as measures of venous return (corrected flow time) and contractility, at baseline, and then every 5 minutes for 20 minutes after initiation of spinal anesthesia. Apgar scores and umbilical cord blood gases were recorded. RESULTS: SBP control was satisfactory in all groups; however, the group receiving phenylephrine 100 µg/min required significantly higher doses to achieve arterial blood pressure control compared with the lower infusion rates. There were no significant differences in the number of times SBP decreased below 80% of baseline, or the numbers of boluses of ephedrine or phenylephrine required to maintain SBP above 80% of baseline. There were significant time and dose-dependent reductions in HR and CO with phenylephrine, such that HR and CO were seen to decrease with time in each group, and also with increasing concentrations of phenylephrine. Stroke volume remained stable throughout. Apgar scores and umbilical cord blood gases were similar among groups. CONCLUSION: By infusing a higher concentration (100 µg/min), we subject the mother and fetus to a much higher dose of phenylephrine, with significant effects on maternal HR and CO (up to a 20% reduction). Future investigation is required to determine whether this reduction in maternal CO has detrimental effects when providing anesthesia for an emergency cesarean delivery for a compromised fetus.