Residual Paralysis in the PACU
Berg Study: TOF < 0.7 in Pancuronium
Berg et al. examined 691 patients who received pancuronium, atracurium, or vecuronium during abdominal, gynaecological, or orthopaedic surgery. Postoperatively, the TOF was measured mechanomyographically. The incidence of residual block (TOF < 0.7), was significantly higher in the pancuronium group (59/226, 26%) than in the atracurium/vecuronium groups (24/450, 5.3%). In the pancuronium group, significantly more patients with residual block developed post-operative pulmonary complications (10/59, 16.9%) as compared to patients without residual block (8/167, 4.8%), however this relationship did not hold for the atracurium/vecuronium groups (4.2% vs. 5.4%). Multiple regression analysis indicated that abdominal surgery, age, long-lasting surgery, and a TOF ratio < 0.7 following the use of pancuronium were potential risk factors for the development of POPC.
Murphy: TOF for Critical Respiratory Events
Murphy et al. collected data over a 1-year period in which PACU nurses identified patients with evidence of a critical respiratory event during the first 15 minutes of PACU admission, after which TOF was quantified using acceleromyography. TOF data were also collected in a control group matched by age, sex, and surgical procedure. A total of 61 of 7459 patients developed a CRE after a general anesthetic (42 were matched with controls for statistical analysis – why not all of them?). The most common CREs among matched cases were severe hypoxemia (52.4%) and upper airway obstruction (35.7%, what about the unmatched cases?). Mean (±sd) TOF ratios were 0.62 (±0.20) in the CRE cases, with 73.8% of the CRE cases having TOF ratios <0.70. In contrast, TOF values in the controls were 0.98 (p < 0.0001).
Debaene Study: Recovery from Single Intubating Dose
Debaene et al. conducted a prospective trial of 526 patients receiving a single intubating dose of intermediate acting non-depolarizing NMBDs and no reversal. They found that even after 120 minutes, > 30% had a TOF < 0.9, and ~ 10% had a TOF < 0.7 as measured with the TOF Watch acceleromyograph. Importantly, they also found that the sensitivity of the qualitative TOF was only 11% for a TOF < 0.9 (and 27% for a TOF < 0.7). Surprisingly, the sensitivity of the head lift was 11% and 19%, respectively.
Summary of Data
TOF of 0.7 is a reasonable cutoff for patients who have received pancuronium, as there is evidence that these patients have a significantly increased risk of complications – these data do not hold for vecuronium patients. Murphy’s study showed that the average TOF for patients who had a critical respiratory event was 0.72, based on TOF accelerometry (i.e., quantitative measurements). Debaene’s data establish the insensitivity of both the head lift and the qualitative TOF to detect residual paralysis; however, any conclusions on the decision to reverse must be based on complication rate data.
Rose et al. prospectively collected and analyzed data on 24,157 PACU admission, and found that critical respiratory events (RR < 8, paCO2 > 50 mm Hg, or stridor or laryngospasm requiring intervention) were related to opiate premedication (OR 1.8), preoperative sedation (OR 2.0), fentanyl > 2 ucg/kg/hr as the sole opioid (OR 1.9), fentanyl combined with morphine (OR 1.6), atracurium at > 0.25 mg/kg/hr (OR 2.2), or thiopental induction as compared to propofol (OR 2.5).