Purpose: Epidural waveform analysis (EPWA) is a simple test to confirm the optimal placement of an epidural catheter. It relies on the transmission of the thecal pressure waveform through the epidural catheter. Little is known about the optimal volume of catheter injectate needed to optimize the EPWA test. Methods:In a randomized controlled trial we compared three different catheters: stimulating, open-ended hole [S1]; stimulating, three-hole [S3]; non-stimulating three-hole [NS3]) in 60 patients in an unblinded pilot study. After catheter insertion using a loss of resistance to air technique, we recorded the dose response curve of EPWA and the presence of epidural pressure wave transmitted through the catheter to repeated injections of 2.5 mL saline boluses in the catheter to a total volume of 10 mL. All patients were followed by the acute pain service to confirm adequacy of postoperative epidural analgesia. Results:The S3 catheters were significantly more responsive (able to transmit a pulsatile waveform) compared to the S1 [P = 0.003 (S3) and P = 0.012 (NS3)] at low injectate volume, while there was no differences between the S3 catheters in their ability to transmit a waveform for EPWA (P = 0.25). There was no increase in responsiveness after 2.5 mL injected for S3 catheters and 5 mL for the S1 catheter. Three patients had soft catheters that did not transmit an epidural pulsative waveform.Conclusions: For EPWAs, S3 epidural catheters are superior to S1 catheters for determining pulsative waveform transmission at low injectate volume. The optimal initial quantity of saline for EPWA is 5 mL regardless of the catheter type used. [P = 0,003 (S3) et P = 0,012 (NS3)

The detailed changes in the electronic charge distributions upon electronic excitation, ionization, and electron attachment are studied for selected diatomic molecules. The processes considered involve the following systems and states: O2(X 3Σg−, a 1Δg, b 1Σg+), O2+(X 2Πg), O2−(2Πg); BeH and MgH (X 2Σ+, A 2Πr); OH and SH (X 2Πi, A 2Σ+), OH+ and SH+ (X 3Σ−), and OH− and SH− (X 1Σ+). It is shown that metastable excitation in the oxygen molecule produces only a very small change in the electronic charge distribution of the system. This suggests an important role for the spin density in determining the differential behavior of these systems. The A 2Πr ← X 2Σ+ and A 2Σ+ ← X 2Πi excitations for the (BeH; MgH) and (OH; SH) pairs are examined and compared to the “active” electron approximation. The changes in binding of the system associated with these various excitations, ionization, or electron attachments is examined in terms of the partial forces exerted by the various molecular orbitals. In particular, the sharp conversion to a pronounced “ionic” molecule is evident in the BeH and MgH excitations. The A 2Πr states of BeH and MgH are as ionic as the LiH and NaH systems in their ground states. It is demonstrated that the binding ability or properties of a given orbital shows a simple graduated trend in a sequence (AB+; AB; AB−) which is not strongly dependent on the particular state symmetry of the system. The binding role assigned to a particular molecular orbital in a molecule is shown to depend on the particular state and charge situation. The implications of these results towards providing a role for the excited states and molecular ions in the theory of chemical bonding are briefly discussed.

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