Original Article

Changes in Transcutaneous Carbon Dioxide, Oxygen Saturation, and Respiratory Rate after Interscalene Block

Authors: Joseph D. Tobias, MD, Louis Del Campo, MD, Keith Kenter, MD, Kelly Groeper, MD, Bruce Gray, MD, James Edwards, MD

Abstract

Background: We used transcutaneous (TC) carbon dioxide (CO2) monitoring to prospectively evaluate changes in respiratory status after interscalene anesthesia in 45 adults (40 successful and 5 unsuccessful blocks).


Methods: TC-CO2 oxygen saturation and respiratory rate were recorded every minute for 5 minutes before block and every 2 minutes for a total of 30 minutes (15 data sets) after injection of the local anesthetic solution.


Results: After successful block, TC-CO2 increased from 41 ± 5 mm Hg to a maximum value of 44 ± 6 mm Hg (P < 0.0001) and the respiratory rate increased from 14 ± 2 breaths/min to a maximum of 20 ± 4 breaths/min (P < 0.001). The increase in TC-CO2 was ≥5 mm Hg in 11 patients and ≥10 mm Hg in 4 patients, with a maximum increase of 12 mm Hg. Of the 600 TC-CO2 data points recorded (15 each from the 40 patients with a successful block), 62 (10.3%) showed a TC-CO2 value of 50 mm Hg or greater, with a maximum value of 57 mm Hg. No significant change in TC-CO2 or respiratory rate was seen in the five patients with unsuccessful block.


Conclusion: After interscalene blockade, we found an increase in respiratory rate and hypercarbia that resulted in no clinically significant effect.


The interscalene approach remains a popular method of providing regional anesthesia for surgical procedures of the shoulder and arm. In addition to anesthesia of the brachial plexus, phrenic nerve block and hemidiaphragmatic paralysis invariably accompany successful block. Studies using ultrasonography have shown that there is a 100% incidence of hemidiaphragmatic paralysis after interscalene (IS) block. 1 Urmey and McDonald 2 showed alterations in respiratory function resulting from the hemidiaphragmatic paralysis including a mean decrease in forced vital capacity of 27.2% and forced expiratory volume of 26.4%. They also noted a mean decrease in peak expiratory flow rate of 15.4% and a mean decrease in maximum mid-expiratory flow rate of 17.9%. Similar alterations in respiratory function have been reported by other investigators. 3–5 However, to date, there are no reports evaluating changes in arterial partial pressure of carbon dioxide (PaCO2) related to the altered respiratory function after IS anesthesia. Using transcutaneous (TC) CO2 monitoring, we prospectively evaluated changes that followed IS anesthesia in adults.

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References

1. Urmey WF, Talts KH, Sharrock NE. One hundred percent incidence of hemidiaphragmatic paresis associated with interscalene brachial plexus anesthesia as diagnosed by ultrasonography. Anesth Analg 1991; 72: 498–503.
 
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