PREDICTIVE VALUE OF FRC AND RESPIRATORY COMPLIANCE ON PULMONARY GAS EXCHANGE INDUCED BY HIGH FREQUENCY JET VENTILATION IN HUMANS

To determine if functional residual capacity (FRC), complianceof the respiratory system (C), or underlying pulmonary diseaseare predictive for the efficacy of high frequency jet ventilation(HFJV) on pulmonary gas exchange, we investigated six adultpatients within 4 h of abdominal surgery and six patients withsevere adult respiratory distress syndrome. Gas exchange duringintermittent positive pressure ventilation (IPPV) was comparedwith that during HFJV at frequencies of 100 b.p.m. (HFJV₁₀₀)and 200 b.p.m. (HFJV₂₀₀), resulting in a minute ventilationof about 400 ml kg^–1 with both ventilatory frequencies,and in both groups of patients. Baseline FRC and C were measuredduring IPPV with the multiple-breath nitrogen washout methodand from expiratory pressure-volume curves, respectively. Changesin the alveolar-arterial oxygen difference (PA_O2–Pa_O2):FlO2 ratio induced by HFJV correlated negatively with C (HFJV₁₀₀:r = –0.78, P <0.005; HFJV200: r = –0.84, P <0.005); that is, greater oxygenation was obtained in patientswith a better compliance. Similarly, changes in arterial partialpressure of carbon dioxide (Pa_co2) induced by HFJV correlatednegatively with C (HFJV₁₀₀: r = –0.77, P < 0.001; HFJV₂₀₀:r = —0.61, P < 0.05). In contrast, there was no significantcorrelation between FRC measured during IPPV and changes in(PA_O2–Pa_O2): Fl_O2 ratio or Pa_co2 induced by HFJV, as thesechanges were influenced more by the patient's pulmonary diseasethan by baseline FRC. These results should be interpreted inthe context of different underlying pathophysiological mechanismsreducing FRC in both groups of patients.     

DOSE REQUIREMENTS AND PLASMA CONCENTRATIONS OF PIPECURONIUM DURING BILATERAL RENAL EXCLUSION AND ORTHOTOPIC LIVER TRANSPLANTATION IN PIGS

We have studied five pigs undergoing bilateral clamping of therenal pedicles, seven pigs undergoing orthotopic liver transplantationand three control animals without surgery in order to examinethe roles of the kidney and liver in the plasma clearance ofpipecuronium. An i.v. infusion of pipecuronium was controlledto maintain a constant 90–95 % twitch depression throughoutthe investigation. The right sciatic nerve was stimulated continuouslywith supra-maximal stimuli at 0.1 Hz and the force of the correspondingevoked isometric muscle contraction was recorded continuously.Control pigs needed an infusion rate of pipecuronium 8–10.7µg kg^–1 min^–1. In the renal group, it wasnecessary to reduce the infusion rate of pipecuronium by about25% after clamping both renal vascular pedicles (P < 0.05compared with controls); in pigs undergoing liver transplantation,it was necessary to reduce the rate by approximately 80% afterclamping hepatic vessels (P < 0.05 compared with controlsand from the period after clamping of renal vessels). Afterhepatic recirculation, the infusion rate of pipecuronium wasincreased progressively to a rate which corresponded to 50%of baseline values (P < 0.05 compared with the anhepaticphase and from controls). Plasma concentrations of pipecuroniumwere comparable in the three animal groups and did not changesignificantly during the study. These data suggest that theliver plays a more important role than the kidney in the plasmaclearance of pipecuronium in pigs.     

The occurrence of intra-operative hypotension varies between hospitals: observational analysis of more than 147,000 anaesthesia

Background: Hypotension, a common intra-operative incident, bears an important potential for morbidity. It is most often manageable and sometimes preventable, which renders its study important. Therefore, we aimed at examining hospital variations in the occurrence of intra-operative hypotension and its predictors. As secondary endpoints, we determined to what extent hypotension relates to the risk of post-operative incidents and death.
Methods: We used the Anaesthesia Databank Switzerland, built on routinely and prospectively collected data on all anaesthesias in 21 hospitals. The three outcomes were assessed using multi-level logistic regression models.
Results: Among 147,573 anaesthesias, hypotension ranged from 0.6% to 5.2% in participating hospitals, and from 0.3% up to 12% in different surgical specialties. Most (73.4%) were minor single events. Age, ASA status, combined general and regional anaesthesia techniques, duration of surgery and hospitalization were significantly associated with hypotension. Although significantly associated, the emergency status of the surgery had a weaker effect. Hospitals' odds ratios for hypotension varied between 0.12 and 2.50 ( P ≤0.001), even after adjusting for patient and anaesthesia factors, and for type of surgery. At least one post-operative incident occurred in 9.7% of the procedures, including 0.03% deaths. Intra-operative hypotension was associated with a higher risk of post-operative incidents and death.
Conclusion: Wide variations remain in the occurrence of hypotension among hospitals after adjustment for risk factors. Although differential reporting from hospitals may exist, variations in anaesthesia techniques and blood pressure maintenance may also have contributed. Intra-operative hypotension is associated with morbidities and sometimes death, and constant vigilance must thus be advocated.