Navigating the depths: USG for safe spinal in super obese parturient

Arasu G1, Senthil Kumar K2

1Final year DNB Post Graduate, Department of Anesthesiology, Kauvery Hospital, Trichy

2HOD – Department of Anaesthesiology, Kauvery Hospital, Trichy

Introduction

Obesity in pregnancy poses a growing challenge for anaesthesiologists. The WHO classifies obesity as: Class I (BMI 30–34.9 kg/m²), Class II (BMI 35–39.9 kg/m²), and Class III (BMI ≥40 kg/m²). Class III is further stratified into morbid obesity (40–49.9 kg/m²), super-obesity (50–59.9 kg/m²), and super-super obesity (≥60 kg/m²).

Anaesthetic management in these patients is complicated by a higher incidence of difficult airway, altered respiratory mechanics, rapid desaturation, and comorbidities such as hypertension and diabetes. Technical difficulties in administering neuraxial anaesthesia also arise due to poorly palpable surface landmarks and increased depth to the intrathecal space.

Ultrasound (USG) guidance has been shown to improve success rates of neuraxial blocks by facilitating localisation of intervertebral spaces and estimation of skin-to-dura depth. We report the successful use of USG-guided spinal anaesthesia in a super-obese parturient undergoing elective caesarean section.

Case Presentation

A 36-year-old super-obese woman (weight 149 kg, height 1.57 m, BMI 60.5 kg/m²), gravida 2 para 1, was scheduled for an elective caesarean section at 37 weeks of gestation. She had a history of pregnancy-induced hypertension and moderately controlled gestational diabetes mellitus. Her medications included Labetalol 100 mg BD and mixed insulin. Fasting blood glucose on the morning of surgery was 134 mg/dL. Other laboratory results were within normal limits.

The patient and relatives were counselled regarding anaesthetic options, risks, and possible complications, and appropriate preparations were undertaken. Obstetric ultrasound at 34 weeks confirmed a breech presentation of a singleton foetus with normal anatomy.

On admission, her vitals were: Blood pressure 122/72 mmHg, heart rate 104/min, respiratory rate 19/min, SpO₂ 98% on room air, and temperature 36.6°C. Laboratory investigations, electrocardiography, and echocardiography were normal. She was classified as ASA Physical Status III due to her BMI. Airway examination revealed Mallampati class II, adequate mouth opening, normal neck extension, and upper lip bite test class I. Spinous processes and interspaces were not palpable.

A pre-procedural neuraxial ultrasound was performed in sitting position in the pre-operative hold area, identified and marked the interspinous spaces, particularly L3-4 space. The estimated skin-to-dura distance was 8.0 cm.

In the operating room, ASA-standard monitoring was applied. Initial vitals: BP 150/75 mmHg, HR 103/min, RR 19/min, SpO₂ 98% on room air. After aseptic preparation and infiltration with 2% lignocaine, spinal anaesthesia was administered at the L3–L4 interspace using a 25G Quincke spinal needle (90 mm), guided by the ultrasound markings. Clear CSF was obtained at a depth of 8.5 cm, and 2.4 mL of 0.5% Hyperbaric Bupivacaine was injected intrathecally on the first attempt.

The patient was positioned supine with left uterine displacement facilitated with a wedge. Sensory blockade reached T4–T6. A single episode of hypotension was treated with phenylephrine 100 mcg.

Ten minutes after skin incision, a male baby weighing 3.6 kg was delivered, with Apgar scores of 3 and 7 at 1 and 5 min respectively. 10 Units of Oxytocin infusion was started. The neonate was managed and resuscitated by the paediatric team.

Surgery lasted 85 minutes with an estimated blood loss of 700 ml. Misoprostol 800 mcg per rectum was administered for primary postpartum haemorrhage prophylaxis. The patient received 1500 mL crystalloids and IV paracetamol 1 g. Thromboprophylaxis included compression stockings, enoxaparin 80 mg SC daily, and early ambulation within 24 hr.

The intraoperative course was otherwise uneventful. She was monitored with continuous pulse oximetry for 24 hr due to hypoventilation risk and patient was discharged on postoperative day 5 in a stable state.

Discussion

Morbidly obese parturient face increased risks of comorbidities, prolonged labour, caesarean delivery, and higher maternal morbidity and mortality due to anaesthesia-related complications. Early anaesthetic involvement, meticulous planning, and vigilant postoperative care are essential.

Spinal anaesthesia is generally the technique of choice for caesarean section, providing dense block, rapid onset, and favourable surgical conditions while avoiding complications of general anaesthesia. General anaesthesia in super-obese parturient is associated with difficult mask ventilation, rapid desaturation, difficult intubation, increased aspiration risk, thromboembolism, obstructive sleep apnoea, and postoperative respiratory failure.

Neuraxial techniques, although technically challenging in obese women, remain preferable as they avoid airway manipulation, reduce foetal exposure to volatile anaesthetics, and lower the risk of postpartum haemorrhage. Challenges include positioning difficulties, identifying spinal spaces, failed or high blocks, hypotension, and post-dural puncture headache.

In our case, additional difficulties included securing IV access, patient transfer, the need for longer spinal needles, and dose considerations. The required bupivacaine dose in pregnancy is reduced due to decreased CSF volume and increased sensitivity to local anaesthetics.

Conclusion

Ultrasound-guided spinal anaesthesia is invaluable in obese parturient when anatomical landmarks are poorly defined. Pre-procedural ultrasound increases the success rate, decreases complications, and avoids the risks of general anaesthesia in high-risk obstetric patients. This case demonstrates that even in super-super obese parturient, USG-guided spinal anaesthesia can be safely, swiftly and effectively performed, ensuring favourable maternal and neonatal outcomes.

References

  • Chin KJ, Perlas A, Chan V, Brown-Shreves D, Koshkin A, Vaishnav V. Ultrasound imaging facilitates spinal anesthesia in adults with difficult surface anatomic landmarks. Anesthesiology 2011; 115:94–101
  • Sahin T, Balaban O, Sahin L, Solak M, Toke K. A randomized controlled trial of preinsertion ultrasound guidance for spinal anaesthesia in pregnancy: outcomes among obese and lean parturients: ultrasound for spinal anesthesia in pregnancy. J Anesth 2014; 28:413–419.
  • M Balki, Y Lee, S Halpern, JC Carvalho. Ultrasound imaging of the lumbar spine in the transverse plane: the correlation between estimated and actual depth to the epidural space in obese parturients. Anesth Analg
  • A Bilge, B Basaran. Ultrasound-assisted technique versus the conventional landmark location method in spinal anesthesia for cesarean delivery in parturients with class 3 obesity: a randomized controlled trial.BJA –June2025
  • Chin KJ, Perlas A, Chan V, Brown-Shreves D, Koshkin A, Vaishnav V. Ultrasound imaging facilitates spinal anesthesia in adults with difficult surface anatomic landmarks.
  • Young B, Onwochei D, Desai N. Conventional landmark palpation vs. preprocedural ultrasound for neuraxial analgesia and anaesthesia in obstetrics– a systematic review and meta-analysis with trial sequential analyses.

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