Extreme value theory applied to postoperative breathing patterns.
BACKGROUND
There has been little published work on the statistical features of breath times in postoperative patients. We applied extreme value theory (a statistical method) to the variation in the timing of postoperative breathing.


METHODS
We observed 49 patients 3-6 h after a variety of surgical procedures, once they had achieved a stable breathing pattern. The breathing patterns could be one of the three types predicted by the extreme value model. 'Finite' breathing patterns (n=30) have a finite upper limit of duration for any apnoea. Patients that displayed one of the other two patterns ('standard' and 'extended') have, potentially, no limit in duration of apnoea.


RESULTS
The type of breathing pattern observed in each patient was not reliably identified by most of the commonly used risk factors (age, type of surgery, opioid type, dose, and route of administration). A finite pattern was observed in 13 of 26 patients receiving epidural (vs 17 of 23 parenteral analgesia: P=0.15), and 15 of 19 receiving morphine (vs 15 of 30 other opioids: P=0.05). The patients with 'finite' patterns were also significantly less drowsy (score 1.04 (0.92) vs 1.62 (0.62), P<0.05).


CONCLUSIONS
The breathing pattern was not related to mean breath times, suggesting that the prevalence of apnoeas cannot be reliably predicted by measurement of the respiratory rate alone.
Leong
Y P
YP
Department of Anaesthesia, Waikato Hospital, Hamilton, New Zealand.
Sleigh
J W
JW
Torrance
J M
JM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000698:Analgesia / Q000379:methods; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000009:adverse effects; D001049:Apnea / Q000209:etiology / Q000503:physiopathology*; D003627:Data Interpretation, Statistical; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D008991:Monitoring, Physiologic; D011184:Postoperative Period; D015656:Respiratory Mechanics; D012307:Risk Factors
D000701:Analgesics, Opioid