Increased body mass index and ASA physical status IV are risk factors for block failure in ambulatory surgery - an analysis of 9,342 blocks.
OBJECTIVE
Regional anesthesia can be the technique of choice for selected ambulatory surgery procedures, but in spite of its benefits, it has an inherent failure rate even in experienced hands. We examine the efficacy and factors associated with failure of ambulatory regional anesthesia techniques.


METHODS
This study included 9,342 blocks performed on 7,160 patients at the Duke University Ambulatory Surgery Center. Blocks were classified as interscalene, supraclavicular, axillary, lumbar plexus, femoral, sciatic, ankle, paravertebral, spinal, and other (frequency less than 100). A block was considered surgical if a single attempt at placing the block resulted in a complete sensory, motor, and sympathetic nerve block. Multiple logistic regression analyses were used to assess the risk-adjusted association between patient characteristics and block failure.


RESULTS
Paravertebral blocks and those considered in the "other" category had significantly higher failure rates (P < 0.001), while spinal and lumbar plexus blocks had lower than average rates of failure (P < 0.001 and P = 0.03, respectively). In multiple logistic regression analyses excluding paravertebral blocks, body mass index (BMI) scores greater than 25 (P values: BMI 25-29: < 0.001; BMI 30-34: P < 0.001; BMI 35: P < 0.001) and ASA physical status IV (P < 0.001) were significantly associated with higher block failure rates.


CONCLUSIONS
High BMI and ASA IV are independent risk factors for block failure in ambulatory surgery patients.
University of North Carolina School of Medicine, USA.
Juliann T
JT
Cotter
Karen C
KC
Nielsen
Ulrich
U
Guller
Susan M
SM
Steele
Stephen M
SM
Klein
Roy A
RA
Greengrass
Ricardo
R
Pietrobon
D000556:Ambulatory Surgical Procedures / Q000379:methods*; D000765:Anesthesia, Conduction / Q000009:adverse effects* / Q000379:methods; D015992:Body Mass Index; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000009:adverse effects* / Q000379:methods; D011446:Prospective Studies; D012044:Regression Analysis; D012307:Risk Factors; D016896:Treatment Outcome