Comparison of preincisional and postincisional parasternal intercostal block on postoperative pain in cardiac surgery.

BACKGROUND: The optimum cardiac surgical pain management has known to maintain hemodynamic stability and, reduces respiratory and cardiovascular complications. Postoperative parasternal intercostal block has shown to reduce postoperative analgesic consumption after cardiac surgery. Therefore, this study sought to investigate the effectiveness of the preoperative ultrasound guided parasternal block in reducing postoperative pain after cardiac surgery. METHODS: This was a randomized, prospective, interventional, single blind study comprised of 90 adult patients scheduled for cardiac surgery involving sternotomy. Preoperatively and postoperatively, 0.25% bupivacaine administered in 4 mL aliquots into the anterior (2nd-6th) intercostal spaces on each side about 2 cm lateral to the sternal edge with a total volume of 40 mL under ultrasound guidance and direct vision, respectively. Postoperative pain was rated according to visual analogue scale. Secondary outcomes included intraoperative and postoperative fentanyl consumptions, dosages of rescue medications, and time to extubation. MAIN RESULTS: There was no significant differences in visual analogue score visual analogue score at all time points till 24 hours postoperatively. Intraoperative fentanyl requirements (microgram/kg) before cardiopulmonary bypass was significantly lower in pre-incisional group than the post-incisional group (0.16 ± 0.43 vs 0.68 ± 0.72; P = .0001). Furthermore, there were no significant difference in total fentanyl requirement (7.20 ± 2.66 vs 8.37 ± 3.13; P = .06) and tramadol requirement (0.02 ± 0.15 vs 0.07 ± 0.26; P = .28) within first 24 hours. However, time to extubation was significantly higher in the preoperative group (P = .02). CONCLUSIONS: Preoperative and postoperative parasternal intercostal block provide comparable pain relief during the postoperative period.

Assessment of upper airway dynamic properties using sternal phrenic nerve magnetic stimulation in awake subjects.

To assess upper airway (UA) dynamic properties, magnetic stimulation of the phrenic nerves (MSPN) is usually performed at cervical level or anterior-laterally at the neck base. We hypothesized that UA dynamic properties could be effectively assessed by MSPN performed at the sternal level. Instantaneous flow, pharyngeal and mask pressures were recorded in 12 healthy awake subjects. End-expiratory MSPN were applied in random order with a non-focal coil placed behind the 7th cervical vertebrae (C7-MS) and at the sternal level (a-MS). The percentage of flow-limited twitches was greater with a-MS (a-MS: 33% and C7-MS: 2%; P<0.0001). For the non flow-limited twitches, maximal inspiratory flow was 36% greater (P<0.001) and isoflow UA resistance was lower with a-MS (0.6±0.1 and 0.9±0.1 cmH2Ol(-1)s; P=0.02). Maximal inspiratory flow of flow-limited twitches was 78% greater (P=0.05) and isoflow UA resistance tended to be lesser with a-MS (0.9±0.3 and 1.8±0.7 cmH2Ol(-1)s; P=0.09). a-MS could be a practical approach for assessing UA dynamic properties in awake subjects.

Retrosternal block use in the treatment for dyspnoea.

We present a technique of retrosternal block for symptomatic treatment for dyspnoea of various aetiologies. In our experience with 20 patients, a retrosternal block using lignocaine improved symptoms within minutes. The block was easy to perform and was helpful when the patients' symptoms were not relieved by conventional therapy. Prospective controlled studies are needed to further assess this simple and promising treatment.

Characteristics of tone burst-evoked myogenic potentials in the sternocleidomastoid muscles.

HYPOTHESIS: Optimum stimulus parameters for tone burst-evoked myogenic responses can be defined. These optimized responses will be similar to those evoked by clicks in the same subjects. BACKGROUND: Loud tones give rise to myogenic responses in the anterior neck muscles, similar to click-evoked potentials, and are likely to be saccular in origin. METHODS: Tone burst-evoked and click-evoked myogenic potentials were measured from the sternocleidomastoid muscles of 12 normal subjects (6 men, 6 women) during tonic activation. The effects of tone burst frequency and duration were systematically investigated. Thresholds were measured and compared with click thresholds for the same subjects. Patients with specific lesions were studied using both stimuli. RESULTS: Tone burst-evoked responses showed frequency tuning, with the largest reflex amplitudes at either 500 Hz or 1 kHz. As the stimulus duration was increased, using a constant repetition rate, there was an increase in the reflex amplitudes followed by a decline. The overall optimum stimulus duration was 7 milliseconds. The mean tone burst threshold was 114.4-dB sound pressure level. Stimulus thresholds for click-evoked and tone burst-evoked responses were significantly correlated. Tone burst-evoked and click-evoked responses were present after stimulation of the affected ears of subjects with profound sensorineural hearing loss. Four subjects who had previously undergone vestibular neurectomy had an absence of click and tone burst-evoked responses on the side of the lesion, confirming their vestibular dependence. CONCLUSION: Tone burst-evoked myogenic responses are similar to click-evoked responses but require lower absolute stimulus intensities. To be certain of an optimum response, a stimulus duration of 7 milliseconds, an adequate intensity, and frequencies of both 500 Hz and 1 kHz should be used.

Developmental changes in the transmitter properties of sympathetic neurons that innervate the periosteum.

During the development of sweat gland innervation, interactions with the target tissue induce a change from noradrenergic to cholinergic and peptidergic properties. To determine whether the change in neurotransmitter properties that occurs in the sweat gland innervation occurs more generally in sympathetic neurons, we identified a new target of cholinergic sympathetic neurons in rat, the periosteum, which is the connective tissue covering of bone, and characterized the development of periosteal innervation of the sternum. During development, sympathetic axons grow from thoracic sympathetic ganglia along rib periosteum to reach the sternum. All sympathetic axons displayed catecholaminergic properties when they reached the sternum, but these properties subsequently disappeared. Many axons lacked detectable immunoreactivities for vesicular acetylcholine transporter and vasoactive intestinal peptide when they reached the sternum and acquired them after arrival. To determine whether periosteum could direct changes in the neurotransmitter properties of sympathetic neurons that innervate it, we transplanted periosteum to the hairy skin, a noradrenergic sympathetic target. We found that the sympathetic innervation of the transplant underwent a noradrenergic to cholinergic and peptidergic change. These results suggest that periosteum, in addition to sweat glands, regulates the neurotransmitter properties of the sympathetic neurons that innervate it.

Experimental reinnervation of a strap muscle with a few roots of the phrenic nerve in rabbits.

In order to compare application of the roots of the phrenic nerve to the ansa hypoglossi for laryngeal muscle neurotization, 1 or more roots from the phrenic nerve were implanted into the right sternothyroid (RST) muscle of rabbits (n = 36). Controls were intact animals (in which RST innervation is provided by the ansa; n = 6) and denervated ones (n = 6). At 66 +/- 2 days (mean +/- SE) after neurotization, during quiet breathing, inspiratory electromyographic activity and isometric contraction force were observed in all reinnervated RST muscles (n = 24). During maximal inspiratory effort, electromyographic activity and force increased. In animals reinnervated by the C4 root alone, forces (46.22 +/- 7.8 g) were significantly higher than in intact animals (10.83 +/- 5.0 g). Retrograde labeling proved the phrenic origin of the neurotization. Electromyography of the diaphragm was recorded. We conclude that in rabbits, neurotization of a strap muscle by 1 or 2 roots of the phrenic nerve allows inspiratory contraction, even during quiet breathing. Such inspiratory activity is not observed in sternothyroid muscles of intact animals innervated by the ansa hypoglossi.

Morphometric study of the upper intercostal nerves: practical application for neurotizations in traumatic brachial plexus palsies.

UNLABELLED: The aim of the study was a morphometric evaluation of the intercostal nerves at different levels along their course in order to determine their adequacy in neurotizing the recipient nerves. The intercostal nerves were harvested from 5 cadavers. A biopsy of the nerve was obtained at 2 levels for each nerve in the parasternal region and at the level of the mid-axillary line. The musculocutaneous nerve was isolated at its origin from the lateral cord. Each harvested specimen was embedded in paraffin and sections were made using a microtome. These sections were then stained histochemically using HPS (Hematein, Phloxine, Safran). Real-time digitalisation of the video image under the microscope was performed. The sum of the different fascicular zones is the effective sensorimotor surface of the nerve at the level being studied. RESULTS: Direct suture of the upper three intercostal nerves to the musculocutaneous nerve is always possible upto the axillary fossa. The sixth intercostal nerve can be delivered upto this level in only 50% of cases without dissection of the musculocutaneous nerve upto its entry into the coracobrachialis. The musculocutaneous nerve presents a mean surface area of 2.64 mm2 while the nerve to the biceps has a mean surface area of 0.34 mm2 i.e. a ration of 1/8. The mean surface area of the intercostal nerves at the parasternal level is 0.23 mm2 while that at the axillary level is 0.34 mm2. Thus a loss of 33% in surface area occurs between the axillary and the parasternal levels. Our study confirms the insufficiency between the surface area of the intercostal nerves and the different nerve trunks to be neurotized. The relationship between the surface area of the musculocutaneous nerve and the three intercostal nerves is 26.72% with a minimum of 17.2%. If a fourth intercostal nerve is added, this ratio nerves appears to be a superior technique. We were able to deliver the sixth intercostal nerve for a direct suture to the musculocutaneous nerve in only half the cases.

Innervation of the sternalis muscle accompanied by congenital partial absence of the pectoralis major muscle.

In one case accompanied by congenital partial absence of the pectoralis major muscle the sternalis muscle was examined to confirm its innervation by means of analysis of intramuscular nerve distribution. It was proved that the sternalis muscle was supplied only by the pectoral nerves even in the case of sternalis in direct contact with the proper thoracic wall. These findings as well as the results of Ura (1937) and Morita (1944) favor the interpretation presented by Eisler (1901), in which the sternalis muscle was described as being supplied only by the pectoral nerves. However, the problem of double innervation of the sternalis requires continued discussion because the relationships between the pectoral nerves and the branches of the intercostal nerves or extramural nerves (Yamada & Mannen, 1985; Kodama et al., 1986) have not yet been resolved. The precise genesis of the sternalis muscle should be also examined though it has already been proved to be derived from the pectoralis muscle group including the subcutaneous trunci muscle.

Reduction in inspiratory activity in response to sternal vibration.

It has been shown previously that there is a reduction in tidal volume in response to longitudinal sternal vibration at 100 Hz. In the present study it was shown that the effect of such vibration is to reduce tidal volume (VT) and prolong inspiratory time (ti) in such a way that points from vibrated and non-vibrated breaths fall on the same VT:ti curve. This indicates that the normal mechanisms which terminate inspiration are unaffected by vibration. The effect of vibration is simply to reduce the rate at which inspiration proceeds. This was illustrated here when vibration reduced the rate of fall of intrapleural pressure during inspiration, and also reduced the instantaneous ventilation at any level of chemical drive. Electrophysiological recordings made here from phrenic motoneurones support these findings. It is concluded that sensory nerves in the chest wall, which can be excited by vibration, can inhibit inspiration.