Transcutaneous carbon dioxide measurements in anesthetized apneic patients with BMI > 35 kg/m2.

Transcutaneous carbon dioxide measurement (TcCO2) offers the ability to continuously and non-invasively monitor carbon dioxide (CO2) tensions when end-tidal monitoring is not possible. The accuracy of TcCO2 has not been established in anesthetized apneic patients with obesity. In this secondary publication, we present a methods comparison analysis of TcCO2 with the gold standard arterial PCO2, in adult patients with body mass index (BMI) > 35kg/m2 who were randomized to receive high flow or low flow nasal oxygenation during post-induction apnea. Agreement between PaCO2 and TcCO2 at baseline, the start of apnea and the end of apnea were assessed using a non-parametric difference plot. Forty-two participants had a median (IQR) BMI of 52 (40-58.5) kg/m2. The mean (SD) PaCO2 was 33.9 (4.0) mmHg at baseline and 51.4 (7.5) mmHg at the end of apnea. The bias was the greatest at the end of apnea median (95% CI, 95% limits of agreement) 1.90 mmHg (-2.64 to 6.44, -7.10 to 22.90). Findings did not suggest significant systematic differences between the PaCO2 and TcCO2 measures. For a short period of apnea, TcCO2 showed inadequate agreement with PaCO2 in patients with BMI > 35 kg/m2. These techniques require comparison in a larger population, with more frequent sampling and over a longer timeframe, before TcCO2 can be confidently recommended in this setting.

Analysis of anaesthesia incidents during caesarean section reported to webAIRS between 2009 and 2022.

Anaesthesia for caesarean section occurs commonly and places specific demands on anaesthetists. We analysed 469 narratives concerning anaesthesia for caesarean section, entered by Australian and New Zealand anaesthetists into the webAIRS incident reporting system between 2009 and 2022. As expected, compared with the remaining 8978 database entries, the 469 incidents were more likely to be emergency cases (relative risk (RR) 1.95), more likely to occur between 18:00 and 22:00 hours (RR 1.81) and between 22:00 and 07:59 hours (RR 4.40) and more likely to be undertaken using neuraxial anaesthesia (RR 9.18). Most incidents involved more than one event. The most commonly reported incidents included intraoperative neuraxial anaesthesia complications (180, 38%), medication errors or issues (136, 29%), equipment issues (49, 10%), obstetric haemorrhage (38, 8%), maternal cardiac arrests (28, 6%), endotracheal tube issues (28, 6%) and neonatal resuscitation (24, 5%). Inadequate neuraxial block, reported in 95 incidents, was the most common intraoperative neuraxial complication. Allergic reactions, reported in 30 incidents, were the most common medication issue, followed by 17 associated with oxytocin and 16 syringe swaps. Thirty-eight reports included significant maternal haemorrhage, with eight of those incidents including maternal cardiac arrest. There was one maternal death and eight incidents with neonatal deaths reported, affecting nine neonates. Problems with intraoperative neuraxial anaesthesia were the most commonly reported events. Implementation of specific strategies are encouraged to enhance preparation for conversion to general anaesthesia and to mitigate medication errors, particularly those relating to oxytocic use and neuraxial anaesthesia medications.

Nitrous Oxide Use in Australian Health Care: Strategies to Reduce the Climate Impact.

Nitrous oxide is a useful inhaled analgesic. Due to its high global warming potential and ozone-depleting properties, the nitrous oxide emissions related to health care are being increasingly scrutinized. In this narrative review, we will discuss the clinical uses of nitrous oxide relevant to anesthetists, in addition to its contribution as a greenhouse gas. Using available data from Australia, we will explore potential strategies for reducing the impact of those emissions, which are likely to be applicable in other countries. These include destruction of captured nitrous oxide, minimizing nitrous oxide waste and reducing clinical use. Anesthesia clinicians are well placed to raise awareness with colleagues and consumers regarding the environmental impact of nitrous oxide and to promote cleaner alternatives. Reducing use is likely to be the most promising reduction strategy without large-scale changes to infrastructure and subsequent delay in action.

Recognized and unrecognized dural punctures in 12,981 labor epidurals: an audit of management.

PURPOSE: Unintentional dural puncture (DP) and post-dural puncture headache (PDPH) continue to cause discomfort and disability in a small proportion of post-partum women. We report an audit of the management of recognized and unrecognized DP over 10 years. METHODS: Clinical data were prospectively collected for women who experienced a recognized DP or developed symptoms following a neuraxial procedure. Details were documented regarding patient characteristics, the neuraxial procedure, symptoms reported, and epidural blood patches. We reported rates of recognized DP, unrecognized DP, PDPH, and blood patches performed. Data were presented as number (percent) and proportions of interest compared using Chi square analysis. RESULTS: Between January 2009 and December 2018, 12,981 women utilized labor epidural analgesia. A recognized DP occurred in 131 (1.0%) and an unrecognized DP in 60 (0.5%), with unrecognized DPs comprising 31% of the total. Of 131 recognized punctures, 86 (66%) developed a PDPH. A total of 146 (1.1%) women experienced a PDPH. Of those, a blood patch was performed in 93 (64%). Intrathecal catheters were inserted for > 24 h in 43 (33%) women with a recognized DP. Of those, 33 (77%) developed a PDPH, compared to 53 (60%) of those without an intrathecal catheter in situ for > 24 h (P = 0.06). CONCLUSIONS: Rates of DP were consistent with those reported by others. Unrecognized DP comprised a third of all DP, and systematic post-neuraxial follow-up is essential to identify these women. Epidural blood patch was performed in most women experiencing symptoms of PDPH.

A retrospective observational study of patient analgesia outcomes when regional anaesthesia procedures are performed by consultants versus supervised trainees.

At teaching hospitals, consultants must provide effective supervision, including appropriate selection of teaching cases, such that the outcomes achieved by trainees are similar to that of consultants. Numerous studies in the surgical literature have compared patient outcomes when surgery is performed by consultant surgeons or surgical trainees but, to our knowledge, none exist in the field of anaesthesia. We aimed to compare analgesia outcomes of regional anaesthesia when performed by supervised trainees versus consultants. We designed a retrospective observational study using registry data. The primary outcome was inadequate analgesia, defined as a numerical rating scale (NRS) for pain >5 reported at any time in the post-anaesthesia care unit (PACU). Secondary outcomes included the maximum pain NRS, pain experienced in the PACU, and the requirement for systemic opioid analgesia in the PACU. Of the 1814 patients analysed, the primary proceduralist was a consultant for 514 (28.3%) patients and a trainee for 1300 (71.7%) patients. All trainees were supervised by an on-site consultant. There were no statistically significant differences between consultants and supervised trainees in terms of the primary outcome (NRS >5 in 24.9% and 24.5% of patients, respectively; P = 0.84) and secondary outcomes. Compared to trainees, consultants had a slightly higher rate of patients with a body mass index >30 kg/m2, an American Society of Anesthesiologists Physical Status Classification of 3 or 4, nerve blocks performed under general anaesthesia, paravertebral/neuraxial blocks and blocks with perineural catheter placement. Regional anaesthesia performed by supervised trainees can achieve similar analgesia outcomes to consultant-performed procedures.

Rotational thromboelastometry (ROTEM® ) in gestational diabetes mellitus and coagulation in healthy term pregnancy: A prospective observational study in Australia.

BACKGROUND: Rotational thromboelastometry (ROTEM® ) is a point-of-care test of coagulation. ROTEM® -defined hypercoagulability has been identified in pregnant women and in non-pregnant patients with diabetes mellitus. Pregnancy is known to be a hypercoagulable state, but the influence of gestational diabetes mellitus (GDM) on coagulation is unknown. AIM: The aim of this study was to assess the combined effect of pregnancy and GDM on coagulation using ROTEM® and to compare this to healthy pregnant women presenting for elective caesarean delivery. MATERIALS AND METHODS: Ethics approval was granted for recruitment of women presenting for elective caesarean delivery. Women with pre-existing conditions affecting coagulation were excluded. Group N included health pregnant women at term and Group G included pregnant women at term with GDM. Data regarding GDM management and glycaemic control were collected. Poor glycaemic control was defined by markers of accelerated fetal growth and elevated fasting or postprandial blood glucose levels. The ROTEM® parameters (extrinsically activated thromboelastometric test (EXTEM) / fibrin polymerisation test (FIBTEM) amplitude at five minutes, coagulation time, maximum clot firmness and clot formation time) were compared between the two groups using Student's t-test. RESULTS: There were 75 women in Group N and 21 women in Group G. Mean age and median body mass index values were comparable for both groups. There were no statistical differences found between the EXTEM and FIBTEM parameters analysed for the two groups. CONCLUSIONS: There was no association between GDM and increased hypercoagulability as demonstrated by ROTEM® parameters in healthy pregnant women presenting for elective caesarean delivery at term.

The Effect of Dexmedetomidine on Postanesthesia Care Unit Discharge and Recovery: A Systematic Review and Meta-Analysis.

BACKGROUND: Current evidence on the effect of dexmedetomidine in early postoperative recovery is limited. We conducted a systematic review to evaluate the effect of dexmedetomidine on the length of stay (LOS) and recovery profile in postanesthesia care unit (PACU) patients. METHODS: The study protocol is registered on International Prospective Register of Systematic Reviews (PROSPERO; CRD42021240559). No specific funding or support was received. We conducted searches in MEDLINE, Embase, PubMed, and Cochrane Library to March 31, 2021 for peer-reviewed randomized controlled studies comparing adult patients who received intravenous dexmedetomidine and placebo undergoing noncardiac, nonneurosurgical procedures under general anesthesia. All studies reporting statistics relating to the duration of stay in the recovery ward or PACU, the primary outcome, were included. We performed individual random-effect meta-analysis on the primary and secondary outcomes (time to extubation, emergence agitation, cough, pain, postoperative nausea and vomiting, shivering, residual sedation, bradycardia, and hypotension) using Stata version 17.0. Evidence was synthesized as mean difference (MD) and risk ratio (RR) for continuous and dichotomous variables, respectively. The quality of evidence was assessed using the revised Cochrane risk-of-bias tool for randomized trials (RoB 2) tool and Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. RESULTS: Thirty-three studies including 2676 patients were eligible for analysis. All studies had low risk or some concerns of overall bias and provided low-to-high certainty evidence for all studied outcomes. Dexmedetomidine was not associated with a significantly increased PACU LOS (MD, 0.69 minute; 95% confidence interval [CI], -1.42 to 2.81 minutes). It was associated with a statistically but not clinically significant prolonged time to extubation (MD, 1 minute; 95% CI, 0.32-1.68 minutes). Dexmedetomidine was associated with significantly reduced incidence of emergence agitation (RR, 0.38; 95% CI, 0.29-0.52), cough (RR, 0.69; 95% CI, 0.61-0.79), pain (RR, 0.50; 95% CI, 0.32-0.80), postoperative nausea and vomiting (RR, 0.54; 95% CI, 0.33-0.86), and shivering (RR, 0.24; 95% CI, 0.12-0.49) in PACU. There was an increased incidence of hypotension (RR, 5.39; 95% CI, 1.12-5.89) but not residual sedation (RR, 1.23; 95% CI, 0.20-7.56) or bradycardia (RR, 5.13; 95% CI, 0.96-27.47) in the dexmedetomidine group. CONCLUSIONS: The use of dexmedetomidine did not increase the duration of PACU LOS but was associated with reduced emergence agitation, cough, pain, postoperative nausea and vomiting, and shivering in PACU. There was an increased incidence of hypotension but not residual sedation or bradycardia in PACU.

The effect of transnasal humidified rapid-insufflation ventilator exchange (THRIVE) versus nasal prongs on safe apnoea time in paralysed obese patients: a randomised controlled trial.

BACKGROUND: Evidence is lacking regarding the efficacy of Optiflow transnasal humidified rapid-insufflation ventilator exchange (THRIVE™) in obese patients. We compared the impact of this technique at 70 L min-1 with 4 L min-1 oxygen via nasal prongs on safe apnoea times of paralysed obese patients. METHODS: We randomised adults with a BMI >35 kg m-2 undergoing elective bariatric surgery. While apnoeic and paralysed, Group T received 70 L min-1 oxygen via Optiflow THRIVE™. Group N received nasal prong oxygen at 4 L min-1. The primary outcome was time to SpO2 ≤95% while apnoeic, with a 360 s cut-off. This was analysed by applying a time-to-event analysis. RESULTS: Forty-two patients were included. The median (inter-quartile range) BMI was 44.8 kg m-2 (40.0-50.0) in Group T and 42.0 kg m-2 (39.3-45.1) in Group N. Median (inter-quartile range) time to SpO2 ≤95% in Group T was 356 (165 to ≥360) s and in Group N, 210 (160-270) s. Using a survival analysis framework, median time-to-event in Group T was 356 s (95% confidence interval 165 s-upper limit not defined) and 210 s (95% confidence interval 160-242 s) (P=0.049) in Group N. CONCLUSIONS: Compared with oxygen delivered via nasal prongs at 4 L min-1, oxygen delivery via Optiflow THRIVE™ at a flow rate of 70 L min-1 can prolong safe apnoea time, however, the results are statistically inconclusive. Optiflow THRIVE™ did decrease the rate of reduction in Pao2 during apnoea. CLINICAL TRIAL REGISTRATION: ANZCTR 12618000445279.

Obesity, metabolic syndrome, and inflammation: An update for anaesthetists caring for patients with obesity.

Our understanding of chronic inflammation in obesity is evolving. Suggested mechanisms include hypoxia of adipose tissue and a subsequent increase in circulating cytokines. It is now known that adipose tissue, far from being an inert tissue, produces and secretes multiple peptides that influence inflammation and metabolism, including substrates of the renin-angiotensin-aldosterone system (RAAS). RAAS blocking antihypertensive medication and cholesterol-lowering agents are now being evaluated for their metabolic and inflammation-modulating effects. Surgery also has pro-inflammatory effects, which may be exacerbated in patients with obesity. This narrative review will summarise the recent literature surrounding obesity, metabolic syndrome, inflammation, and interplay with the RAAS, with evidence-based recommendations for the optimisation of patients with obesity, prior to surgery and anaesthesia.

Upper limb dimensions in adults presenting for elective surgery - implications for blood pressure measurement.

BACKGROUND: Arm conicity is associated with non-invasive blood pressure (NIBP) measurement error and may be avoided by using finger cuffs. Predicting arm conicity may help decisions regarding NIBP measurement techniques. METHODS: We obtained upper limb measurements of adults presenting to the Pre-Anesthetic Clinic to determine: the suitability of arm and finger cuff sizes; the best anthropometric predictor of arm conicity based on the right arm slant angle; the incidence of a right arm slant angle < 83 degrees. Right mid-arm circumference (MAC) was compared to recommended cuff sizes and finger circumference compared to available cuffs. Slant angle was calculated from the measurements obtained. Linear regression was used to determine the better predictor of right arm slant angle. Correlation coefficients were calculated and R2 values compared. RESULTS: Four hundred fifty-four patients participated and 453 had cone-shaped arms. One participant (0.2, 95% CI 0.0-1.2) had a MAC outside the recommended cuff range. Twenty-five participants (5.5, 95% CI 3.6-8.0) had a middle finger circumference greater than the largest ClearSight™ cuff. Body mass index (BMI), weight and right MAC all had low to moderate correlation with right arm slant angle (r = - 0.49, - 0.39, - 0.48, all p < 0.001) and regression revealed R2 values of 0.24, 0.15 and 0.23. Six participants (1.3, 95% CI 0.5-2.9) had a slant angle < 83 degrees. CONCLUSION: Current NIBP equipment caters for most patients, based on the traditional measure of MAC. The utility of finger cuffs is limited by cuff size. BMI and right MAC showed the most promise in predicting arm conicity.

Prophylactic Cefazolin Dosing in Women With Body Mass Index >35 kg·m-2 Undergoing Cesarean Delivery: A Pharmacokinetic Study of Plasma and Interstitial Fluid.

BACKGROUND: Obesity is a risk factor for surgical site infection after cesarean delivery. There is inadequate pharmacokinetic data available regarding prophylactic cefazolin dosing in obese pregnant women. We aimed to describe the plasma and interstitial fluid (ISF) pharmacokinetics of cefazolin in obese women undergoing elective cesarean delivery and use dosing simulations to predict optimal dosing regimens. METHODS: Eligible women were scheduled for elective cesarean delivery at term, with a body mass index (BMI) of >35 kg·m. Plasma and ISF samples were collected following 2 g of intravenous cefazolin. Concentrations were determined using liquid chromatography-mass spectrometry. Population pharmacokinetic modeling and Monte Carlo dosing simulations were performed using Pmetrics. Total and unbound cefazolin concentrations in plasma and ISF were compared with the minimum inhibitory concentration at which 90% of isolates are inhibited (MIC90) of cefazolin for Staphylococcus aureus, 2 mg·L. The fractional target attainment (FTA) of dosing regimens to achieve a pre-established target of 95% unbound ISF concentrations >2 mg·L throughout a 3-hour duration of the surgery was calculated. RESULTS: The 12 women recruited had a median (interquartile range [IQR]) BMI of 41.5 (39.7-46.6) kg·m and a median (IQR) gestation of 38.7 weeks (37.9-39.0). For each timepoint up to 180 minutes, the median across subjects of total and unbound plasma concentration of cefazolin remained above 2 mg·L. The minimum observed total plasma concentration was 31.7 mg·L and plasma unbound concentration was 7.7 mg·L (observed in the same participant). For each timepoint up to 150 minutes, the median across subjects of unbound ISF concentrations remained above 2 mg·L. The minimum observed unbound ISF concentration was 0.7 mg·L (observed in 1 participant). In 2 participants, the ISF concentration of cefazolin was not maintained above 2 mg·L. The mean (± standard error [SE]) penetration of cefazolin (calculated as area under the concentration-time curve for the unbound fraction of drug [fAUC]tissue/fAUCplasma) into the ISF was 0.884 ± 1.11. Simulations demonstrated that FTA >95% was achieved in patients weighing 90-150 kg by an initial 2 g dose with redosing of 2 g at 2 hours. FTA was improved to >99% when an initial 3 g dose was repeated at 2 hours. CONCLUSIONS: To maintain adequate ISF antibiotic concentrations in obese pregnant women, our results suggest that redosing of cefazolin may be required. When wound closure has not occurred within 2 hours, redosing is suggested, following either a 2 or 3 g initial bolus. These preliminary results require validation in a larger population.

The influence of obesity on coagulation in healthy term pregnancy as assessed by rotational thromboelastometry.

BACKGROUND: Rotational thromboelastometry (ROTEM® ) is a point-of-care coagulation test which has been used to demonstrate hypercoagulability in pregnant populations and obese populations. AIM: The aim of this study was to assess the combined effect of pregnancy and obesity on coagulation using ROTEM® in healthy pregnant women of varying body mass indices (BMIs) presenting for elective caesarean delivery. MATERIALS AND METHODS: Ethics approval was granted for recruitment of women presenting for elective caesarean delivery. Women with any condition affecting coagulation were excluded. The ROTEM® parameters of extrinsically activated thromboelastometric test / fibrin polymerisation test (EXTEM/FIBTEM) amplitude at five minutes (A5), coagulation time (CT), maximum clot firmness (MCF) and clot formation time (CFT) were compared between three different groups: normal weight, overweight and obese women. RESULTS: One hundred and eighty-five women presenting for elective caesarean delivery met inclusion criteria and were divided into three groups; normal weight (BMI < 25 kg/m2 , n = 86), overweight (BMI 25-29.9 kg/m2 , n = 54) and obese (BMI ≥ 30 kg/m2 , n = 45). They had a mean (SD) age of 32.7 ± 5.0 years and the median (interquartile range) BMI of 21.9 kg/m2 (20.5-23.0), 27.0 kg/m2 (26.0-28.5), 36.0 kg/m2 (32.2-41.8) for the normal weight, overweight and obese groups respectively. Forty-one (22.2%) women were nulliparous. Across the three groups for FIBTEM A5 (P = 0.018), FIBTEM MCF (P = 0.032), FIBTEM CFT (P = 0.047) and EXTEM MCF (P = 0.015) there was evidence of increasing coagulability with increasing BMI. However, following Bonferroni correction, this was no longer significant. CONCLUSIONS: There is no association between BMI and ROTEM® parameters in pregnant women presenting for elective caesarean delivery at term.

Perioperative Blood Pressure Monitoring in Patients With Obesity.

Blood pressure monitoring plays a key part in the preoperative, intraoperative, and postoperative care of all patients. In patients with obesity, hypertension indicates increased metabolic and surgical risk and may signal the presence of significant medical comorbidities, including obstructive sleep apnea. Avoidance of hypertension postoperatively is necessary to minimize bleeding risk after surgery. Hypotension in the postoperative period may be the first sign of significant complications that require urgent management. With the problem of being overweight or obese now affecting two-thirds of adults in Western countries, the proportion of patients with obesity in perioperative environments is similarly increasing. Detection of aberrations in blood pressure is contingent on the accuracy of blood pressure measurement methods. Patients with obesity tend to have a large arm circumference and "cone-shaped arms." Standard blood pressure cuffs fit such patients poorly, and this compromises the accuracy of measurements. Alternatives to arm blood pressure cuffs, some made specifically for individuals with obesity, have been evaluated but are not widely available to clinicians. This focused narrative review will discuss the relevance of hypertension management in the care of patients with obesity, highlight the currently available methods for perioperative monitoring of blood pressure, and explore the opportunities that exist to improve the perioperative blood pressure care in patients with obesity undergoing surgical procedures.

Arm and finger measurements in the third trimester: Implications for blood pressure measurement.

OBJECTIVES: To obtain arm and finger measurements of women ≥32 weeks gestation to determine: the requirement for different arm cuff sizes; the suitability of available finger cuffs in this population; the best predictor of arm conicity; the frequency of cuff placement on the forearm or leg. STUDY DESIGN: Prospective observational pilot study. MAIN OUTCOME MEASURES: Right and left mid-arm circumference (MAC) and to compare these to the recommended cuff sizes; right and left finger circumference; right and left arm conicity; the responses of women to a three-point Likert scale regarding cuff placement. RESULTS: Measurements were obtained for 450 women at an Australian tertiary hospital with a median (IQR) gestation of 35.7 (34.0-37.0); 299 (66.4%) were Caucasian and 35 (7.8%) had gestational hypertension. The median (IQR) body mass index (BMI) was 29.6 kg/m2 (26.2-33.4), range 18.0-62.2. Median (IQR) right MAC was 29.9 cm (27.4-33), range 19.6-53.2. Based on right MAC, 58 (12.9%) required a large cuff and 6 (1.3%) a thigh cuff. Maximum right finger circumference was 7.0 cm. BMI, weight and right MAC were positively correlated with right arm conicity: r = 0.51, 0.42 and 0.45, p < 0.001 for all. R2 for each were 0.26, 0.17 and 0.20. Fourteen (3.1%) reported cuff placement on the forearm or leg. CONCLUSIONS: A small percentage of women are likely to be unsuited to traditional arm cuffs. Available finger-cuffs would suit this population. BMI could potentially be used to select women with cone-shaped arms for future studies of alternative devices.

Successful Resuscitation of Maternal Cardiac Arrest With Disseminated Intravascular Coagulation Guided by Rotational Thromboelastometry and Transesophageal Echocardiography: A Case Report.

We present a case of maternal cardiac arrest during an elective cesarean delivery. Transesophageal echocardiography identified a large pulmonary artery mass, and guided resuscitation efforts. After return of spontaneous circulation, the patient developed disseminated intravascular coagulation with massive hemorrhage. Blood product selection and volume replacement were guided by rotational thromboelastometry and transesophageal echocardiography, respectively. Correction of coagulopathy was observed clinically and confirmed by rotational thromboelastometry. The patient fully recovered without neurological deficit.

What is the failure rate in extending labour analgesia in patients with a body mass index ≥ 40 kg/m(2)compared with patients with a body mass index < 30 kg/m(2)? a retrospective pilot study.

BACKGROUND: Early utilisation of neuraxial anaesthesia has been recommended to reduce the need for general anaesthesia in obese parturients. The insertion and management of labour epidurals in obese women is not straight-forward. The aim of this pilot study was to compare the failure rate of extension of epidural analgesia for emergency caesarean section, in pregnant women with a body mass index (BMI) ≥ 40 kg/m(2), to those with a BMI < 30 kg/m(2). The results will be used to calculate the sample size of a planned prospective study. METHODS: In this retrospective, (1:1) case-control pilot study, obese subjects and control subjects were selected from the obstetric database, if they delivered between January 2007 and December 2011. All subjects used epidural analgesia during labour and subsequently required anaesthesia for Category 1 or 2 Caesarean Section. Data was extracted from the patient medical record. Failure to extend was analysed using liberal and restrictive definitions. Chi-square or Fisher's exact tests were used to detect differences between groups. Multiple logistic regression was used to examine variables predictive of extension failure. RESULTS: There were 63 subjects in each group. The mean BMI of the obese group was 45.4 (5.8) kg/m(2) and 23.9 (3.0) kg/m(2) in the control group. The odds ratio for failure to extend the existing epidural blockade (liberal definition) was 2.48 (95 % CI:1.02 - 6.03) for the obese group compared with the control group (adjusted for age, parity and gestation). Using the restrictive definition, the odds ratio for failure in the obese group was 6.78 (95 % CI:1.43 - 32.2). The combination of respiratory co-morbidity and gestational diabetes significantly predicted extension failure. Surgical time and epidural complications on labour ward were significantly greater in the obese group. CONCLUSIONS: In this small retrospective cohort, patients with a BMI ≥ 40 kg/m(2) were significantly more likely to fail epidural extension for caesarean section. The presence of respiratory co-morbidity and gestational diabetes were significant predictors of extension failure; their clinical relevance requires further evaluation.