Pre-oxygenation and apnoea in pregnancy: changes during labour and with obstetric morbidity in a computational simulation

Simulating high-fidelity emergency front-of-neck access: Training in an obstetric setting

Introduction

In a cannot intubate, cannot oxygenate scenario (CICO), emergency front of neck access (eFONA) is the final lifesaving step in airway management to reverse hypoxia and prevent progression to brain injury, cardiac arrest and death. The Difficult Airway Society (DAS) guidelines advise the scalpel cricothyroidotomy method for eFONA. Anatomical and physiological changes in pregnancy exacerbate the already challenging obstetric airway. We aim to assess the impact made by introducing formal eFONA training to the perioperative medicine department of an obstetric hospital.

Methods

Ethical approval and written informed consent were obtained. 17 anesthetists participated, (two consultants, one senior registrar, four registrars and eight senior house officers). Study design was as follows: Initial participant survey and performance of a timed scalpel cricothyroidotomy on Limbs & Things AirSim Advance X cricothyroidotomy training mannikin. Difficulty of the attempt was rated on a Visual Analogue Scale (VAS). Participants then watched the DAS eFONA training video. They then re-performed a scalpel cricothyroidotomy and completed a repeat survey. The primary endpoint was duration of cricothyroidotomy attempt, measured as time from CICO declaration to lung inflation confirmed visually. After a three-month period, participants were reassessed.

Results

Four anesthetists had previous eFONA training with simulation, only one underwent training in the previous year. The mean time-to-lung inflation pre-intervention was 123.6 seconds and post-intervention was 80.8 seconds. This was statistically significant (p = 0.0192). All participants found training beneficial. Mean improvement of VAS was 3. All participants' confidence levels in identifying when to perform eFONA and ability to correctly identify anatomy improved. On repeat assessment, 11/13 participants successfully performed a surgical cricothyroidotomy, mean improvement from first attempt was 12 seconds (p = 0.68) which was not statistically significant.

Conclusion

This method of training is an easily reproducible way to teach a rarely performed skill in the obstetric population.

Comparison of apnoeic oxygen techniques in term pregnant subjects: a computational modelling study

BACKGROUND

Hypoxaemia during general anaesthesia can cause harm. Apnoeic oxygenation extends safe apnoea time, reducing risk during airway management. We hypothesised that low-flow nasal oxygenation (LFNO) would extend safe apnoea time similarly to high-flow nasal oxygenation (HFNO), whilst allowing face-mask preoxygenation and rescue.

METHODS

A high-fidelity, computational, physiological model was used to examine the progression of hypoxaemia during apnoea in virtual models of pregnant women in and out of labour, with BMI of 24-50 kg m^-2. Subjects were preoxygenated with oxygen 100% to reach end-tidal oxygen fraction (FE'O₂) of 60%, 70%, 80%, or 90%. When apnoea started, HFNO or LFNO was commenced. To simulate varying degrees of effectiveness of LFNO, periglottic oxygen fraction (FgO₂) of 21%, 60%, or 100% was configured. HFNO provided FgO₂ 100% and oscillating positive pharyngeal pressure.

RESULTS

Application of LFNO (FgO₂ 100%) after optimal preoxygenation (FE'O₂ 90%) resulted in similar or longer safe apnoea times than HFNO FE'O₂ 80% in all subjects in labour. For BMI of 24, the time to reach SaO₂ 90% with LFNO was 25.4 min (FE'O₂ 90%/FgO₂ 100%) vs 25.4 min with HFNO (FE'O₂ 80%). For BMI of 50, the time was 9.9 min with LFNO (FE'O₂ 90%/FgO₂ 100%) vs 4.3 min with HFNO (FE'O₂ 80%). A similar finding was seen in subjects with BMI ≥40 kg m^-2 not in labour.

CONCLUSIONS

There is likely to be clinical benefit to using LFNO, given that LFNO and HFNO extend safe apnoea time similarly, particularly when BMI ≥40 kg m^-2. Additional benefits to LFNO include the facilitation of rescue face-mask ventilation and ability to monitor FE'O₂ during preoxygenation.

Ventilation strategies for front of neck airway rescue: an in silico study

BACKGROUND

During induction of general anaesthesia a 'cannot intubate, cannot oxygenate' (CICO) situation can arise, leading to severe hypoxaemia. Evidence is scarce to guide ventilation strategies for small-bore emergency front of neck airways that ensure effective oxygenation without risking lung damage and cardiovascular depression.

METHODS

Fifty virtual subjects were configured using a high-fidelity computational model of the cardiovascular and pulmonary systems. Each subject breathed 100% oxygen for 3 min and then became apnoeic, with an obstructed upper airway. When arterial haemoglobin oxygen saturation reached 40%, front of neck airway access was simulated with various configurations. We examined the effect of several ventilation strategies on re-oxygenation, pulmonary pressures, cardiovascular function, and oxygen delivery.

RESULTS

Re-oxygenation was achieved in all ventilation strategies. Smaller airway configurations led to dynamic hyperinflation for a wide range of ventilation strategies. This effect was absent in airways with larger internal diameter (≥3 mm). Intrapulmonary pressures increased quickly to supra-physiological values with the smallest airways, resulting in pronounced cardio-circulatory depression (cardiac output <3 L min^-1 and mean arterial pressure <60 mm Hg), impeding oxygen delivery (<600 ml min^-1). Limiting tidal volume (≤200 ml) and ventilatory frequency (≤8 bpm) for smaller diameter cannulas reduced dynamic hyperinflation and gas trapping, preventing cardiovascular depression.

CONCLUSIONS

Dynamic hyperinflation can be demonstrated for a wide range of front of neck airway cannulae when the upper airway is obstructed. When using small-bore cannulae in a CICO situation, ventilation strategies should be chosen that prevent gas trapping to prevent severe adverse events including cardio-circulatory depression.

Effect of variable pre-oxygenation endpoints on safe apnoea time using high flow nasal oxygen for women in labour: a modelling investigation

BACKGROUND

Studies of pulmonary denitrogenation (pre-oxygenation) in obstetric populations have shown high flow nasal oxygen therapy (HFNO) is inferior to facemask techniques. HFNO achieves median end-tidal oxygen fraction (FE'O₂) of 0.87 after 3 min. As HFNO prolongs safe apnoea times through apnoeic oxygenation, we postulated that HFNO would still extend safe apnoeic times despite the lower FE'O₂ after pre-oxygenation.

METHODS

The Interdisciplinary Collaboration in Systems Medicine simulation suite, a highly integrated, high-fidelity model of the human respiratory and cardiovascular systems, was used to study the effect of varying FE'O₂ (60%, 70%, 80%, and 90%) on the duration of safe apnoea times using HFNO and facemask techniques (with the airway open and obstructed). The study population consisted of validated models of pregnant women in active labour and not in labour with BMI of 24, 35, 40, 45, and 50 kg m^-2.

RESULTS

HFNO provided longer safe apnoeic times in all models, with all FE'O₂ values. Labour and increased BMI reduced this effect, in particular a BMI of 50 kg m^-2 reduced the improvement in apnoea time to 1.8-8.5 min (depending on the FE'O₂), compared with an improvement of more than 60 min in the subject with BMI 24 kg m^-2.

CONCLUSIONS

Despite generating lower FE'O₂, HFNO provides longer safe apnoea times in pregnant subjects in labour. Care should be taken when used in patients with BMI ≥50 kg m^-2 as the extension of the safe apnoea time is limited.

A prospective, up-down sequential allocation study investigating the effectiveness of vital capacity breaths using high-flow nasal oxygenation versus a tight-fitting face mask to pre-oxygenate term pregnant women

BACKGROUND

The role of high flow nasal oxygenation (HFNO) for pre-oxygenation before obstetric general anaesthesia remains unclear. This study aimed to determine the number of vital capacity breaths using HFNO required to pre-oxygenate 90% of parturients to an end-tidal oxygen concentration fraction (F_ETO₂) of ≥0.90 (termed EN90).

METHODS

Using up-down, sequential allocation trial design, volunteer term parturients undergoing caesarean delivery were investigated with HFNO with their mouth closed, followed by mouth open, and if F_ETO₂ ≥0.90 was not achieved after a maximum of 20 vital capacity breaths, pre-oxygenation was attempted with a face mask. The primary outcome was the number of vital capacity breaths required using HFNO (mouth open and closed) to achieve EN90. Secondary outcomes included assessment of EN90 using mouth open versus mouth closed and face mask pre-oxygenation, maternal satisfaction and evaluation of fetal cardiotocography.

RESULTS

Twenty women at term were recruited. Successful pre-oxygenation occurred in 4 (20%), 3 (15%) and 14 (70%) women with HFNO mouth closed, HFNO mouth open, and via face mask respectively. At up to 20 vital capacity breaths, face mask pre-oxygenation was more successful at achieving EN90 compared with both HFNO with a closed (P=0.006) or open (P=0.001) mouth. Closed mouth HFNO did not outperform open mouth pre-oxygenation.

CONCLUSION

Face mask pre-oxygenation is more effective at achieving EN90 compared with to HFNO within a clinically acceptable number of vital capacity breaths. Further studies are needed to determine the role of HFNO in optimising the time before desaturation and for apnoeic oxygenation in term parturients.

High oxygen fraction during airway opening is key to effective airway rescue in obese subjects

Apnea is common after induction of anesthesia and may produce dangerous hypoxemia, particularly in obese subjects. Optimal management of airway emergencies in obese, apneic subjects is complex and controversial, and clinical studies of rescue strategies are inherently difficult and ethically-challenging to perform. We investigated rescue strategies in various degrees of obesity, using a highly-integrated, computational model of the pulmonary and cardiovascular systems, configured against data from 8 virtual subjects (body mass index [BMI] 24-57 kg m^-2). Each subject received pre-oxygenation with 100% oxygen for 3 min, and then apnea with an obstructed airway was simulated until SaO₂ reached 40%. At that time, airway rescue was simulated, opening of the airway with the provision of various patterns of tidal ventilation with 100% oxygen. Rescue using tidal ventilation with 100% oxygen provided rapid re-oxygenation in all subjects, even with small tidal volumes in subjects with large BMI. Overall, subjects with larger BMI pre-oxygenated faster and, after airway obstruction, developed hypoxemia more quickly. Our results indicate that attempts to achieve substantial tidal volumes during airway rescues are probably not worthwhile (and may be counter-productive); rather, it is the assurance of a high-inspired oxygen fraction that will prevent critical hypoxemia.

Use of transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) to facilitate the management of subglottic stenosis in pregnancy

Subglottic stenosis is a rare condition. Diagnosis is often delayed as symptoms are attributed to other causes, such as asthma. This problem may be compounded in pregnancy when dyspnoea may be attributed to normal physiological changes. In respiratory compromise, surgical intervention may be required and airway management is challenging as endotracheal intubation may be traumatic or, in severe cases, impossible. Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) is a novel open-airway apnoeic technique using high-flow nasal oxygen. It does not expose the patient to the risks of jet ventilation, nor does it require the placement of an airway device to effectively oxygenate the patient. In pregnancy, elevation of maternal carbon dioxide is of particular concern as it may result in a worsening fetal acidosis. While THRIVE has been shown to provide some clearance of carbon dioxide, a patent airway is required for it to function effectively. In this case report we describe the management of a pregnant patient who underwent balloon dilatation for severe subglottic stenosis at 23 weeks' gestation using THRIVE and we summarise the evidence supporting the use of this new technique in pregnant women.

Analysis of Physiological Respiratory Variable Alarm Alerts Among Laboring Women Receiving Remifentanil

BACKGROUND

Remifentanil may be used by laboring women for analgesia, despite controversy because of potential apneas. We evaluated candidate variables as early warning alerts for apnea, based on prevalence, positive predictive rate, sensitivity for apnea event detection, and early warning alert time intervals (lead time) for apnea.

METHODS

We performed a secondary analysis of respiratory physiological data that had been collected during a prospective IRB-approved study of laboring women receiving IV patient-controlled boluses of remifentanil 20 to 60 μg every 1 to 2 minutes. Analyzed data included the respiratory rate (RR), end-tidal CO2 (EtCO2), pulse oximetry (SpO2), heart rate (HR), and the Integrated Pulmonary Index (IPI; Capnostream 20; Medtronic, Boulder, CO) that had been recorded continuously throughout labor. We defined immediate early warning alerts as any drop in a variable value below a prespecified threshold for 15 seconds: RR < 8 breaths per minute (bpm), EtCO2 < 15 mm Hg, and SpO2 < 92%. We defined alerts as "sustained" when the value remained below the threshold for ≥ 10 further seconds. The IPI value (1 to 10; 10 = healthy patient, ≤4 = immediate attention required, 1 = dire condition) was generated from a proprietary algorithm using RR, EtCO2, SpO2, and HR parameters. Apnea was defined as maximal CO2 < 5 mm Hg for at least 30 consecutive seconds.

RESULTS

We counted 62 apneas, among 10 of 19 (52.6%) women who received remifentanil (total dose 1725 ± 1392 μg, administered over 160 ± 132 minutes). We counted 331 immediate early warning alerts for the variables; 271 (82%) alerts were sustained for ≥10 seconds. The positive predictive value of alerts for apnea was 35.8% (99% confidence interval [CI]: 27.1-45.6), 28.9% (99% CI: 20.8-38.7), 4.3% (99% CI: 1.9-9.6), and 24.6% (99% CI: 18.3-32.2) for RR, EtCO2, SpO2, and IPI, respectively. The sensitivity for apnea event detection was 100% (99% CI: 90.3-100) for RR (<8 bpm) and IPI (≤4); 75.8% (99% CI: 59.8-86.9) for EtCO2 <15 mm Hg; and 14.5% (99% CI: 6.5-29.4) for SpO2 <92%. We found a statistically significant difference in the timing of RR, EtCO2, SpO2, and IPI alerts for apnea; Friedman's Q = 33.53; P < .0001. The EtCO2 had a median (interquartile range) lead time of -0.2 (-12.2 to 0.7) seconds, and SpO2 had a median (interquartile range) lead time of 40.0 (40.0 to 40.0) seconds.

CONCLUSIONS

The majority of women receiving IV remifentanil for labor analgesia experienced apneas. Alerts for EtCO2 (<15 mm Hg), RR (<8 bpm), and IPI (≤4) detected most apneas, whereas SpO2 alerts missed the majority of apneas. All variables had a low positive predictive rate, demonstrating the limitations of the respiratory monitors utilized as early warning surveillance for apneas in this setting.

Investigating the effect of cardiac oscillations and deadspace gas mixing during apnea using computer simulation

Gaseous mixing in the anatomical deadspace with stimulation of respiratory ventilation through cardiogenic oscillations is an important physiological mechanism at the onset of apnea, which has been credited with various beneficial effects, e.g. reduction of hypercapnia during the use of low flow ventilation techniques. In this paper, a novel method is proposed to investigate the effect of these mechanisms in silico. An existing computational model of cardio-pulmonary physiology is extended to include the apneic state, gas mixing within the anatomical deadspace, insufflation into the trachea and cardiogenic oscillations. The new model is validated against data published in an experimental animal (dog) study that reported an increase in arterial partial pressure of carbon dioxide (PaCO₂) during apnea. Computational simulations confirm that the model outputs accurately reproduce the available experimental data. This new model can be used to investigate the physiological mechanisms underlying clearance of carbon dioxide during apnea, and hence to develop more effective ventilation strategies for apneic patients.

Apnoeic oxygenation in pregnancy: a modelling investigation

Recent studies have shown that nasal oxygen delivery can prolong the time to desaturation during apnoea in the non-pregnant population. We investigated the benefits of apnoeic oxygenation during rapid sequence induction in the obstetric population using computational modelling. We used the Nottingham Physiology Simulator, and pre-oxygenated seven models of pregnancy for 3 min using Fi O2 1.0, before inducing apnoea. We found that increasing Fi O2 at the open glottis increased the time to desaturation, extending the time taken for Sa O2 to reach 40% from 4.5 min to 58 min in the average parturient model (not in labour). Our study suggests that a small increase in time to desaturation could be achieved at Fi O2 0.4-0.6, which could be delivered by standard nasal cannulae. The greatest increases in time to desaturation were seen at Fi O2 1.0, which could be delivered by high-flow nasal cannulae under ideal conditions.

Perioperative management of a morbidly obese pregnant patient undergoing cesarean section under general anesthesia - case report

BACKGROUND AND OBJECTIVES

The increased prevalence of obesity in the general population extends to women of reproductive age. The aim of this study is to report the perioperative management of a morbidly obese pregnant woman, body mass index >50kg/m(2), who underwent cesarean section under general anesthesia.

CASE REPORT

Pregnant woman in labor, 35 years of age, body mass index 59.8kg/m(2). Cesarean section was indicated due to the presumed fetal macrosomia. The patient refused spinal anesthesia. She was placed in the ramp position with cushions from back to head to facilitate tracheal intubation. Another cushion was placed on top of the right gluteus to create an angle of approximately 15° to the operating table. Immediately before induction of anesthesia, asepsis was carried out and sterile surgical fields were placed. Anesthesia was induced in rapid sequence, with Sellick maneuver and administration of remifentanil, propofol, and succinilcolina. Intubation was performed using a gum elastic bougie, and anesthesia was maintained with sevoflurane and remifentanil. The interval between skin incision and fetal extraction was 21min, with the use of a Simpson's forceps scoop to assist in the extraction. The patient gave birth to a newborn weighing 4850g, with Apgar scores of 2 in the 1st minute (received positive pressure ventilation by mask for about 2min) and 8 in the 5th minute. The patient was extubated uneventfully. Multimodal analgesia and prophylaxis of nausea and vomiting was performed. Mother and newborn were discharged on the 4th postoperative day.

Advanced airway management for pre-hospital trauma patients

The need for timely and appropriate airway management for trauma patients is widely recognised. There are a small number of severely injured patients who cannot be adequately supported with basic airway manoeuvres, and require early advanced airway management. The way in which this care is provided remains highly controversial. Whilst it is clear that effective airway management remains a priority for all patients and poorly performed pre-hospital anaesthesia may be detrimental to patient outcome, debate remains over exactly which patients will benefit from early advanced airway interventions, and how it should be provided. The evidence base is small and inconsistent, with significant heterogeneity in the reported data, making it impossible to draw meaningful conclusions. Current practice is not standardised, and care is delivered by providers of different abilities using a range of equipment and techniques. Standards of care provided during in-hospital practice relating to these issues of provider competence, equipment, and monitoring should be directly translated into delivery of care outside the hospital, but this is not always the case. The aim of this review is to evaluate the current evidence surrounding pre-hospital advanced airway management.

[Perioperative management of a morbidly obese pregnant patient undergoing cesarean section under general anesthesia - case report]

BACKGROUND AND OBJECTIVES

The increased prevalence of obesity in the general population extends to women of reproductive age. The aim of this study is to report the perioperative management of a morbidly obese pregnant woman, body mass index > 50 kg/m(2), who underwent cesarean section under general anesthesia.

CASE REPORT

Pregnant woman in labor, 35 years of age, body mass index 59.8 kg/m(2). Caesarean section was indicated due to the presumed fetal macrosomia. The patient refused spinal anesthesia. She was placed in the ramp position with cushions from back to head to facilitate tracheal intubation. Another cushion was placed on top of the right gluteus to create an angle of approximately 15° to the operating table. Immediately before induction of anesthesia, asepsis was carried out and sterile surgical fields were placed. Anesthesia was induced in rapid sequence, with Sellick maneuver and administration of remifentanil, propofol, and succinilcolina. Intubation was performed using a gum elastic bougie, and anesthesia was maintained with sevoflurane and remifentanil. The interval between skin incision and fetal extraction was 21 minutes, with the use of a Simpson's forceps scoop to assist in the extraction. The patient gave birth to a newborn weighing 4850 g, with Apgar scores of 2 in the 1(st) minute (received positive pressure ventilation by mask for about 2 minutes) and 8 in the 5(th) minute. The patient was extubated uneventfully. Multimodal analgesia and prophylaxis of nausea and vomiting was performed. Mother and newborn were discharged on the 4(th) postoperative day.

The difficult airway with recommendations for management--part 1--difficult tracheal intubation encountered in an unconscious/induced patient

Background

Previously active in the mid-1990s, the Canadian Airway Focus Group (CAFG) studied the unanticipated difficult airway and made recommendations on management in a 1998 publication. The CAFG has since reconvened to examine more recent scientific literature on airway management. The Focus Group’s mandate for this article was to arrive at updated practice recommendations for management of the unconscious/induced patient in whom difficult or failed tracheal intubation is encountered.

Methods

Nineteen clinicians with backgrounds in anesthesia, emergency medicine, and intensive care joined this iteration of the CAFG. Each member was assigned topics and conducted reviews of Medline, EMBASE, and Cochrane databases. Results were presented and discussed during multiple teleconferences and two face-to-face meetings. When appropriate, evidence- or consensus-based recommendations were made together with assigned levels of evidence modelled after previously published criteria.

Conclusions

The clinician must be aware of the potential for harm to the patient that can occur with multiple attempts at tracheal intubation. This likelihood can be minimized by moving early from an unsuccessful primary intubation technique to an alternative “Plan B” technique if oxygenation by face mask or ventilation using a supraglottic device is non-problematic. Irrespective of the technique(s) used, failure to achieve successful tracheal intubation in a maximum of three attempts defines failed tracheal intubation and signals the need to engage an exit strategy. Failure to oxygenate by face mask or supraglottic device ventilation occurring in conjunction with failed tracheal intubation defines a failed oxygenation, “cannot intubate, cannot oxygenate” situation. Cricothyrotomy must then be undertaken without delay, although if not already tried, an expedited and concurrent attempt can be made to place a supraglottic device.

Optimization of mechanical ventilator settings for pulmonary disease states

The selection of mechanical ventilator settings that ensure adequate oxygenation and carbon dioxide clearance while minimizing the risk of ventilator-associated lung injury (VALI) is a significant challenge for intensive-care clinicians. Current guidelines are largely based on previous experience combined with recommendations from a limited number of in vivo studies whose data are typically more applicable to populations than to individuals suffering from particular diseases of the lung. By combining validated computational models of pulmonary pathophysiology with global optimization algorithms, we generate in silico experiments to examine current practice and uncover optimal combinations of ventilator settings for individual patient and disease states. Formulating the problem as a multiobjective, multivariable constrained optimization problem, we compute settings of tidal volume, ventilation rate, inspiratory/expiratory ratio, positive end-expiratory pressure and inspired fraction of oxygen that optimally manage the tradeoffs between ensuring adequate oxygenation and carbon dioxide clearance and minimizing the risk of VALI for different pulmonary disease scenarios.

In silico modelling of physiologic systems

In silico modelling, in which computer models are developed to model a pharmacologic or physiologic process, is a logical extension of controlled in vitro experimentation. It is the natural result of the explosive increase in computing power available to the research scientist at continually decreasing cost. In silico modelling combines the advantages of both in vivo and in vitro experimentation, without subjecting itself to the ethical considerations and lack of control associated with in vivo experiments. Unlike in vitro experiments, which exist in isolation, in silico models allow the researcher to include a virtually unlimited array of parameters, which render the results more applicable to the organism as a whole. In silico modelling is best known for its extensive use in pharmacokinetic experimentation, the best-known example of which is the development of the three-compartment model. In addition, complex in silico models have been applied to pathophysiological problems to provide information which cannot be obtained practically or ethically by traditional clinical research methods. These experiments have led to the development of significant insights in subject matters ranging from pure physiology to congenital heart surgery, obstetric anaesthesia airway management, mechanical ventilation and cardiopulmonary bypass/ventricular support devices. The utility of these models is based on both the validity of the model framework as well as the corresponding assumptions. In vivo experimentation has validated some, but not all of the in silico strategies employed. We present a review illustrating by example how in silico modelling has been applied to a number of cardio-respiratory problems in states of health and disease, the purpose of which is to give the reader a sense of the complexity and assumptions which underlie this diverse and underappreciated research strategy, as well as an introduction to a research strategy that will likely continue to grow in importance.

Difficult intubation in pregnancy

PURPOSE OF REVIEW

This review focuses on difficult intubation in pregnant patients, particularly during the late pregnancy when physiological, patho-physiological and psychological factors may cause or aggravate difficulties with providing sufficient oxygenation and securing the airway. It is intended to highlight the methodological approach to the difficult airway in this particular patient population and to draw relevant principles in dealing with this problem.

RECENT FINDINGS

There are strong indications for improvement in the outcome of airway management in pregnant patients; however, this is obscured by the growing frequency of caesarean sections and connected to this by more tracheal intubations. Various new airway devices have been suggested as alternative techniques for laryngoscopic intubation if the latter becomes difficult or failed.

SUMMARY

A scenario-oriented approach to the problem of difficult intubation in pregnant patients leads to the recognition of the unpredicted difficult or failed intubation as the main concern. The appropriate means to cope with this rare but life-threatening complication lies in a gradual employment of principles beginning with preferential application of regional anaesthesia techniques, followed by proceeding according to locally adapted simple and comprehensive failed intubation algorithms, design of a suitable difficult airway cart that contains only a few but well chosen items and by implementation of a continuous and mandatory training program to which all personnel are subjected to participate in regular intervals.

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.

Obesity and Obstetric Anaesthesia

Obesity is increasing in the population as a whole, and especially in the obstetric population, among whom pregnancy-induced physiological changes impact on those already present due to obesity. In particular, changes in the cardiovascular and respiratory systems during pregnancy further alter the physiological effects and comorbidities of obesity. Obese pregnant women are at increased risk of diabetes, hypertensive disorders of pregnancy, ischaemic heart disease, congenital malformations, operative delivery, postpartum infection and thromboembolism. Regional analgesia and anaesthesia is usually preferred but may be challenging. Obese pregnant women appear to have increased morbidity and mortality associated with caesarean delivery and general anaesthesia for caesarean delivery in particular, and more anaesthesia-related complications. This article summarises the physiological and pharmacological implications of obesity and pregnancy and describes the issues surrounding the management of these women for labour and delivery.

Does position of the patient adversely affect successful intubation whilst wearing CBRN-PPE?

INTRODUCTION

Following a CBRN incident attending medical personnel will be required to instigate life saving airway interventions whilst wearing CBRN-PPE. CBRN-PPE is known to adversely affect fine motor skill but little is known about whether the position of the patient compounds this problem.

METHODS

Seventy-five clinicians were recruited and performed intubation and insertion of a LMA in to a manikin whilst wearing CBRN-PPE. Both skills were completed twice with the manikin positioned on a bench and once on the floor. Following completion of the study 25 participants (a minimum of 2 participants from each professional group) were interviewed to ascertain their experiences. The recruitment of a non-homogenous group allowed for subgroup analysis with regards the potential impact of professional background on skill performance.

RESULTS

9.33% first attempts at intubation at waist height ended in failure but this reduced to 4% on the second attempt. This improvement was reversed with the manikin on the floor where the failure rate was 26.67%. Intubation on the floor took significantly longer to perform, being 45.9 s slower than the first attempt at intubation in the optimal position [95% CI (30.7 s, 61.1 s); p<0.001] and 62.4 s longer than the second [95% CI (48.4 s, 76.3 s); p<0.001]. LMA insertion was successful at all attempts, regardless of the manikins position. LMA placement on the floor was no slower than the second attempt at waist height (p=0.231) and faster than the first attempt at waist height (by 4.8 s [95% CI (3.4 s, 6.1 s); p<0.001]). Anaesthetists were consistently the fastest at performing all airway skills regardless of the position of the manikin but previous exposure to wearing CBRN-PPE had no statistically significant impact on skill performance. All 25 clinicians interviewed had difficulty in viewing the larynx with the manikin positioned on the floor regardless of being an experienced 'on floor' intubator with the movement of the CBRN-PPE hood being the principle reason. This is in contrast to only three participants noting issues with vision whilst standing-up.

CONCLUSION

the position of the patient is likely to be an independent factor when choosing to either intubate or insert a LMA whilst wearing the current NHS CBRN-PPE.