Total spinal anaesthesia following obstetric neuraxial blockade: a narrative review.

BACKGROUND: Total spinal anaesthesia (TSA) is an emergency caused by high neuraxial blockade. It is a recognised complication of all neuraxial techniques in obstetric anaesthesia. Its incidence and outcomes have not been evaluated. There is compelling evidence that TSA continues to be a problem in contemporary practice, having the capacity to cause significant morbidity and mortality if not recognised early and promptly treated. This review based on a literature search aims to clarify the epidemiology of TSA, summarise its pathophysiology, and identify risk factors and effective treatments. METHODS: We performed a literature search using PubMed, Web of Science and Google Scholar databases using specified search terms for materials published using search terms. For each case, the type of block, the difficulty of the procedure, the dose of local anaesthetic, positivity of aspiration before and after the event, maternal outcome, Apgar score, onset of symptoms, cardiorespiratory and neurological manifestations, cardiorespiratory support employed, admission to an intensive care unit, cardiac arrest events and duration of mechanical ventilation were extracted. RESULTS: A total of 605 cases were identified, of which 51 were sufficiently detailed for analysis. Although TSA is described after all neuraxial techniques, spinal after epidural was a particular concern in recent reports. Respiratory distress was universal but apnoea was not. The onset of apnoea was variable, ranging from 1 to 180 min. Hypotension was not invariable and occurred in approximately half of cases. Multiple fatalities and neurological injuries were reported, often in under-resourced areas when providers were not skilled in airway management or when recognition and intervention were delayed. In the most recent reports good outcomes were achieved when effective treatments were rapidly provided. CONCLUSIONS: The available literature confirms that TSA remains an active clinical problem and that with prompt recognition and treatment good outcomes can be achieved. This requires anticipation and preparedness in all clinical areas where neuraxial techniques are performed.

Emergency cricothyroidotomy: an observational study to estimate optimal incision position and length.

BACKGROUND: A vertical incision is recommended for cricothyroidotomy when the anatomy is impalpable, but no evidence-based guideline exists regarding optimum site or length. The Difficult Airway Society guidelines, which are based on expert opinion, recommend an 80-100 mm vertical caudad to cephalad incision in the extended neck position. However, the guidelines do not advise the incision commencement point. We sought to determine the minimum incision length and commencement point above the suprasternal notch required to ensure that the cricothyroid membrane would be accessible within its margins. METHODS: We measured using ultrasound, in 80 subjects (40 males and 40 females) without airway pathology, the distance between the suprasternal notch and the cricothyroid membrane, in the neutral and extended neck positions. We assessed the inclusion of the cricothyroid membrane within theoretical incisions of 0-100 mm in length made at 10 mm intervals above the suprasternal notch. RESULTS: In the 80 subjects, the distance ranged from 27 to 105 mm. Movement of the cricothyroid membrane on transition from the neutral to extended neck position varied from 15 mm caudad to 27 mm cephalad. The minimum incision required in the extended position was 70 mm in males and 80 mm in females, commencing 30 mm above the suprasternal notch. CONCLUSIONS: An 80 mm incision commencing 30 mm above the suprasternal notch would include all cricothyroid membrane locations in the extended position in patients without airway pathology, which is in keeping with the Difficult Airway Society guidelines recommended incision length.

Anaesthetic management for caesarean section of a parturient with a known difficult airway and closed spinal dysraphism.

Many anaesthetists consider patients with existing neurological deficits, untreated spinal pathology or those having undergone major spinal intervention to be precluded from undergoing neuraxial anaesthesia. While this is partly rooted in fears of litigation there is also a lack of consensus of the best practice in the anaesthetic management of these patients. We present our management of a parturient who attended our institution, having a number of anaesthetic complexities including a known difficult airway, spinal fusion and persistent spinal cord tethering. She successfully underwent delivery under neuraxial blockade for the delivery of her fourth child. We believe that by undergoing a thorough multidisciplinary clinical evaluation, including the extensive use of neuroimaging and ultrasound, it may be possible to plan and perform safe neuraxial anaesthesia.

Theoretical optimal cricothyroidotomy incision length in female subjects, following identification of the cricothyroid membrane by digital palpation.

BACKGROUND: Misidentification of the cricothyroid membrane is frequent in females, placing them at risk of difficult or failed cricothyroidotomy in the event of failed oxygenation. If anatomy is impalpable, the current guidelines of the Difficult Airway Society, based on expert opinion, recommend an 8-10 cm vertical incision to facilitate access to the cricothyroid membrane. At present no evidence-based guideline exists regarding optimum site or length. We investigated the likelihood of inclusion of the cricothyroid membrane, within hypothetical vertical midline incisions, in a female population. METHODS: We asked clinicians to identify the cricothyroid membrane in both the neutral and extended head positions using palpation, the point identified acting as the theoretical midpoint of a cricothyroidotomy incision. We then identified the cricothyroid membrane using ultrasound. We determined the minimum incision length that would be required to ensure that the cricothyroid membrane lay within its boundaries, if clinician digital palpation was the method of cricothyroid membrane localisation. RESULTS: Ninety female subjects were recruited. Theoretical incisions of 7 and 8 cm were required for successful cricothyroidotomy in the neutral and extended head positions respectively. This was necessary because of the high failure rate of cricothyroid membrane identification (80.9%) and the wide range of error (7.2 cm in a vertical plane). CONCLUSIONS: Based on clinical estimation of the location of the cricothyroid membrane, an incision length of 8 cm, using the clinician's best estimate as its midpoint, would overlie all cricothyroid membrane locations. Our data support the current Difficult Airway Society guidelines for cricothyroidotomy incision length.

Laryngeal handshake technique in locating the cricothyroid membrane: a non-randomised comparative study.

BACKGROUND: Evaluation of the anterior neck anatomy is used to identify the cricothyroid membrane (CTM) before front of neck airway access. This has been traditionally performed using palpation which results in misidentification of the CTM in a high proportion of subjects. The 'laryngeal handshake' is currently advocated by the Difficult Airway Society as the method to identify the CTM. We sought to investigate the accuracy of this technique in females. METHODS: Five clinicians were asked to identify the CTM using the 'laryngeal handshake' technique in a total of 45 anaesthetised females (Group L) and by conventional palpation in 45 controls (Group P). We measured and analysed the distance to actual CTM using ultrasound, the time to identification, and perceived difficulty using a visual analogue scale. RESULTS: Successful identification of the CTM occurred in 28/45 (62%) patients in Group L vs 15/45 (33%) in Group P [P=0.006; mean difference, 29%; 95% confidence interval (CI), 21-39%]. Distance to the CTM (P=0.012) and visual analogue scale (P=0.012) were significantly reduced in Group L. Mean time to CTM identification was greater in Group L at 31 (5.6) s, compared with Group P, which took 18 (5.5) s (P<0.001). The midline was accurately identified more frequently in Group L than in Group P (39/45 vs 28/45, P=0.008). CONCLUSIONS: The 'laryngeal handshake' method of palpation is more accurate but takes longer than conventional palpation technique in locating the CTM and the midline. This is of particular relevance if a vertical incision is required to perform front of neck access when anatomy is indistinct.

Ultrasonographic evaluation of gastric contents in term pregnant women fasted for six hours.

BACKGROUND: Current fasting guidelines suggest six hours are adequate to minimise the aspiration risk after a light meal consumed by pregnant women undergoing elective caesarean section. We assessed gastric contents in non-labouring pregnant women, using ultrasonographic analysis. METHODS: In a prospective study, pregnant women ≥36 weeks' gestation, without conditions likely to influence gastric emptying, underwent ultrasonographic analysis of their gastric antrum, after six hours of fasting following a standardised light meal. The primary outcome was solid food content in the antrum. Other outcomes included fluid in the supine and right lateral positions, antral cross-sectional area and estimated residual gastric fluid volume. Antral grades were classified: grade 0 = absence of fluid in both supine and right lateral positions: grade 1 = fluid present in the right lateral position only: grade 2 = fluid in both positions. RESULTS: Complete data were available in 46/51 (90%) women. No woman had solid food visible. Antral grades 0, 1 and 2 were seen in 6 (13%), 36 (78%) and 4 (9%) women respectively. Eighteen of 48 women (37.5%) had a residual volume greater than 1.5 mL/kg. Of those with a grade 1 antrum, 13/36 (36%) had residual volumes in excess of 1.5 mL/kg. For grade 2, this was 4/4 (100%). CONCLUSIONS: Our cohort of pregnant women fasted for six hours had no solid food visible in the antrum, but many had both qualitative and quantitative ultrasonographic evidence of gastric volumes potentially associated with aspiration risk. This suggests that pregnancy-specific fasting guidelines may be required.

Spinal dysraphisms in the parturient: implications for perioperative anaesthetic care and labour analgesia.

Anaesthetists may encounter parturients with a spectrum of anatomical and functional abnormalities secondary to spinal dysraphisms, which are among the most common neurodevelopmental anomalies. These range from surgically corrected open dysraphisms to previously undiagnosed closed dysraphisms. Both bony and neural structures may be abnormal. In true bony spina bifida, which occurs in up to 50% of the population, failure of fusion of the vertebral arch is seen and neural structures are normal. Ninety percent of such cases are confined to the sacrum. In open dysraphisms, sensory preservation is variable and may be present even in those with grossly impaired motor function. Both epidural and spinal blockade have been described for labour analgesia and operative anaesthesia in selected cases but higher failure and complication rates are reported. Clinical assessment should be performed on an outpatient basis to assess neurological function, evaluate central nervous system shunts and determine latex allergy status. Magnetic resonance imagining is recommended to clarify anatomical abnormalities and to identify levels at which neuraxial techniques can be performed. Of particular concern when performing neuraxial blockade is the possibility of a low-lying spinal cord or conus medullaris and spinal cord tethering. Previous corrective de-tethering surgery frequently does not result in ascent of the conus and re-tethering may be asymptomatic. Ultrasound is not sufficiently validated at the point of care to reliably detect low-lying cords. Epidurals should be performed at anatomically normal levels but spread of local anaesthetic may be impaired by previous surgery.

Evaluation of the effect of intra-operative intravenous fluid on post-operative pain and pulmonary function: a randomized trial comparing 10 and 30 ml kg(-1) of crystalloid.

BACKGROUND: Existing evidence suggests that administration of intravenous fluids has been shown to improve outcomes including pain in gynecological laparoscopic surgery but the optimum fluid dose has not been determined. AIMS: To determine the effect of administration of intravenous fluids on post-operative pain and pulmonary function after gynecological laparoscopy. METHODS: In a prospective randomized double-blinded study 100 ASA 1 and 2 elective patients undergoing gynecological laparoscopy were randomized to receive intravenous compound sodium lactate 10 ml kg(-1) (CSL10-restrictive) or 30 ml kg(-1) (CSL30-liberal) administered intra-operatively. The primary outcome measure was the post-operative pain score at 24, 48 and 72 h, assessed by 0-10 verbal rating scale (VRS). Pulmonary function (FEV1, FVC, PEFR) and oxygen saturation were also measured. RESULTS: Patients who received CSL 30 had lower post-operative pain scores than CSL 10 (ANCOVA-mean difference = 0.47, 95 % CI 0.11-0.83, P = 0.01). Post-operative pain VRS was lower in CSL30 than CSL10 at 48 h (mean difference 0.56, 95 % CI 0.04-1.09, P = 0.036). Patients in CSL30 reported shoulder tip pain less frequently than those in CSL10 (30.4 vs. 43.9 % of assessments, P = 0.03, OR 0.58) but reported wound pain more frequently 39.0 vs. 24.2 %, P = 0.01, OR 2.0). Indices of pulmonary function did not differ between groups at any time. CONCLUSIONS: Liberal compared to restrictive administration of i.v. crystalloid is associated with a clinical modest reduction in pain. Pulmonary dysfunction was not increased with liberal fluid administration.

Comparison of transversus abdominis plane block vs spinal morphine for pain relief after Caesarean section.

BACKGROUND: Transversus abdominis plane (TAP) block is an alternative to spinal morphine for analgesia after Caesarean section but there are few data on its comparative efficacy. We compared the analgesic efficacy of the TAP block with and without spinal morphine after Caesarean section in a prospective, randomized, double-blinded placebo-controlled trial. METHODS: Eighty patients were randomized to one of four groups to receive (in addition to spinal anaesthesia) either spinal morphine 100 µg (S(M)) or saline (S(S)) and a postoperative bilateral TAP block with either bupivacaine (T(LA)) 2 mg kg(-1) or saline (T(S)). RESULTS: Pain on movement and early morphine consumption were lowest in groups receiving spinal morphine and was not improved by TAP block. The rank order of median pain scores on movement at 6 h was: S(M)T(LA) (20 mm)

Anaesthetic management of a patient with Liddle's syndrome for emergency caesarean hysterectomy.

We describe the anaesthetic management of a patient with Liddle's syndrome during caesarean section and emergency hysterectomy for placenta accreta associated with significant intrapartum haemorrhage. Liddle's syndrome is a rare autosomal dominant disorder characterised by early onset arterial hypertension and hypokalaemic metabolic alkalosis. Additional issues were the presence of short stature, limb hypertonicity and preeclampsia. Initial management with a low-dose combined spinal-epidural technique was subsequently converted to general anaesthesia due to patient discomfort. The management of Liddle's syndrome in the setting of neuraxial and general anaesthesia in a patient undergoing caesarean section is discussed.

Management of a parturient with thrombocytopenia-absent-radius syndrome undergoing urgent caesarean section.

Thrombocytopenia-absent-radius syndrome is a rare congenital condition characterised by a low platelet count and limb abnormalities. There may be airway difficulties and cardiac disease is frequently associated. We present a case of successful general anaesthesia for urgent caesarean section. The major anaesthetic difficulties encountered were severe thrombocytopenia with a platelet count 30x10(9)/L, which precluded regional anaesthesia, and extensive limb abnormalities resulting in difficulty with vascular access and cardiovascular monitoring. Platelet transfusion was required but airway difficulties were not encountered.