Enid R. Kafer

Esmolol is more effective than sodium nitroprusside in reducing blood loss during orthognathic surgery

The goal of this study was to compare the efficacy of esmolol and sodium nitroprusside (SNP) as primary drugs for producing controlled hypotension and limiting blood loss during orthognathic surgery. Thirty ASA physical status I and II patients (mean age 22 yr) undergoing LeFort I maxillary osteotomies were randomly assigned to receive either esmolol (n = 15) or SNP (n = 15) as the primary drug to induce hypotension. All patients received a balanced anesthetic technique including isoflurane, with controlled hypotension during the down fracture of the maxilla. Patients assigned to the esmolol treatment group received boluses of 500 μg/kg of esmolol, followed by a continuous infusion of 100–300 μkg−1 ·min−1, and the SNP treatment group received a continuous infusion of SNP at 0.25--4.00 μkg−1· min−1; both infusions were nitrated to obtain a mean arterial blood pressure within the target range of 55--65 mm Hg. The mean arterial blood pressure during the hypotensive period was 58.7 ±0.7 (mean ± SEM) and 61.8 ± 0.4 mm Hg for esmolol and SNP, respectively (P < 0.001). In addition, 40% ± 4% of the observed values in the esmolol group and 53% ± 3% in the SNP group were outside the target range for mean arterial blood pressure (difference significant at P < 0.05), and a greater proportion of the deviations were above 65 mm Hg in the SNP group than in the esmolol group (0.64 vs 0.46, respectively, P < 0.05). The mean heart rate was 70 Rekha 3 beats/min (esmolol) and 100 ± 3 beats/min (SNP) (P < 0.001), and the mean blood loss was 436 ± 65 mL (esmolol) and 895 ± 101 mL (SNP) (P < 0.001). The surgical field was judged to be drier with esmolol than with SNP (P < 0.05). Plasma renin activity decreased slightly in the esmolol group, whereas in the SNP group it increased 267% (P < 0.001). The absence of the renin release may have facilitated the stability of controlled hypotension with esmolol. The advantages of esmolol over SNP for controlled hypotension during orthognathic surgery include greater control of blood pressure, reduction in blood loss, and a drier surgical field. These advantages must be weighed against the possibility of significant myocardial depression produced by intense β1-adrenergic blockade.

Biphasic Depression of Ventilatory Responses to CO2 Following Epidural Morphine

The authors examined the duration of effects of lumbar epidural morphine (0.1 mg/kg) on control of ventilation (CO2 response), pain relief, segmental analgesia (loss of pain in response to a painful stimulus) and loss of temperature discrimination, and plasma morphine concentrations in seven patient

Use of capnography and transcutaneous oxygen monitoring during outpatient general anesthesia for oral surgery

The combination of the capnograph (respired CO2 monitor) and the transcutaneous oxygen monitor was evaluated as a non-invasive system for monitoring of respiratory function in 10 ASA class I patients undergoing ultralight general anesthesia for removal of third molars. Capnography proved to be a sensitive and accurate method for detecting apnea and airway obstruction using the continuous display of the CO2 waveform. All episodes of apnea or obstruction were immediately detected as the respired CO2 level fell to zero baseline. The end-tidal CO2 (PetCO2) obtained via nasal prong sampling was not significantly different from the PaCO2. PetCO2 values served as useful indicators of hypoventilation. During steady-state conditions of respiration, transcutaneous oxygen tensions (PtcO2) correlated well with simultaneously measured PaO2 (r = 0.93). However, during any period when oxygenation was rapidly changing (step increase in FIO2, step decrease in FIO2, or apnea) the PtcO2 lagged behind changes in PaO2 even after a five-minute equilibration period, thereby not accurately reflecting the true state of oxygenation. Consequently, the transcutaneous oxygen monitor does not appear to be optimal as a respiratory monitor in the setting of ultralight general anesthesia where rapid, critical changes in oxygenation must be detected without delay.

IMPROVED OXYGENATION DURING THORACOTOMY WITH SELECTIVE PEEP TO THE DEPENDENT LUNG

In 22 patients during thoracotomy in the lateral position, the effects of selective positive end expiratory pressure (PEEP) to the dependent lung while simultaneously ventilating the non-dependent lung at zero end-expiratory pressure (ZEEP) on (1) inspired O2 concentration required to maintain adequate Pao2 during thoracotomy and (2) alveolar-arterial oxygen difference (Aao2D) while breathing 100 percent O2 at the end of thoracotomy were examined and compared to ventilation of both lungs at ZEEP. Selective PEEP to the dependent lung resulted in adequate Pao2 with a lower inspired O2 concentration (44 ± SD 6% versus 70 ± SD 21%), and a smaller Aao2D while breathing 100 percent O2 189 ± SD 31 versus 342 ± SD 69 torr) at the end of thoracotomy.

Absence of symptoms with carboxyhemoglobin levels of 16-23%.

It has been generally accepted that carboxyhemoglobin levels between 10-20% produce mild headaches, dizziness and/or nausea. Experimental double blind exposures of 18 healthy, nonsmoking young men at rest to 7,000-24,000 ppm CO, designed to elevate COHb to 15-20% in 3-5 minutes, were followed by exposure to 232 ppm CO designed to maintain COHb level for a total of 130 minutes. Resulting COHb values were 16-23%. These COHb values did not produce significantly more symptoms (as reported in an open-ended questioning) than reported in the control group (n = 23). Subjects were especially queried about headache, dizziness and nausea. The symptoms which were previously reported in clinical studies of CO poisoning may have resulted from CO exposure in combination with (a) exposure to other substances, (b) stress due to the event that precipitated medical attention or (c) higher COHb levels before the first blood sample was taken.

In vivo response time of transcutaneous oxygen measurement to changes in inspired oxygen in normal adults

Nous avons mesuré le temps de réaction de l’oxymètre trans-cutané (PtcO2) à l’augmentation en palier de l’oxygène inspiré (FiO2 1.0) et à la diminution en palier (air libre) chez cinq adultes normaux d’âge moyen de 27 ans. L’électrode était placée sur la partie supérieure du thorax. Le temps nécessaire pour obtenir 63 et 95 pour cent de la réponse maximale à une augmentation en palier d’oxygène inspiré était de 2.9 plus ou moins 0.2 min. et de 6M plus ou moins 0.2. Ces mêmes temps, pour une diminution en palier de l’oxygène inspiré étaient de 2.4, plus ou moins 0.2 et 5.J plus ou moins 03 min.Les temps nécessaires pour atteindre 63 et 95 pour cent de la dênitrogénation totale étaient de î 1.0 et 2.6 minutes. Pour la rênitrogénation ces mêmes temps étaient 0.8 et 23 min.On conclut de ces mesures que le temps de réponse de l’oxymètre trans-cutané est passablement plus long que les temps d’équilibration alvéolaire des gaz inspirés; de ce fait, l’oxymétrie transcutanée n’apparaît pas tout à fait adaptée pour déceler les changements rapides dans l’oxygénation du sang artériel durant i’anesthésie, la période péri-opératoire et même durant le sommeil.