Heart rate variability may identify patients who will develop severe bradycardia during spinal anaesthesia

BACKGROUND AND OBJECTIVES

The reported incidence of cardiac arrest during spinal anaesthesia is 6.4+1.2 per 10,000 patients. Many of these arrests occurred in healthy young patients during minor surgery. This raises the question of whether some of them were avoidable. We investigated the value of Heart Rate Variability (HRV) to identify patients prone to developing severe bradycardia during spinal anaesthesia.

METHODS

Eighty ASA I-II patients, 21-60 years of age, undergoing elective surgery under spinal anaesthesia were studied. The HRV was assessed for 25 min before the spinal block. Two spectral components of HRV were calculated: a low-frequency (LF) and a high-frequency (HF) component. Patients were grouped according to whether bradycardia did or did not develop during spinal anaesthesia.

RESULTS

Nineteen patients developed severe bradycardia (<45 b.p.m.). The mean value of HF before spinal anaesthesia was significantly increased in the bradycardic group (P<0.05). The correlation between baseline heart rate (HR(baseline)) and minimum heart rate and LF, HF during spinal anaesthesia was significant (P<0.01). A receiver operator curve characteristic analysis showed a sensitivity and specificity of HF and HR(baseline) of 65% and 74%, respectively, to predict bradycardia <45 b.p.m. after spinal anaesthesia.

CONCLUSIONS

The present study shows that HF and clinical factors such as patient's HR(baseline) could identify patients prone to developing severe bradycardia during spinal anaesthesia.

Hypomagnesaemia associated with diabetes mellitus may cause laryngospasm

This report describes the case of a female diabetic patient who experienced two episodes of severe laryngospasm during maintenance of anaesthesia and also 1 h post-operatively. The most probable diagnosis considered was severe hypomagnesaemia with concomitant hypocalcaemia confirmed by electrolyte measurements. The association between hypomagnesaemia and laryngospasm is discussed.

The impact of the type of anaesthesia on cognitive status and delirium during the first postoperative days in elderly patients

BACKGROUND AND OBJECTIVES

Postoperative confusion and delirium is a common complication in the elderly with a poorly understood pathophysiology. The aim of this study was to examine whether the type of anaesthesia (general or regional) plays a role in the development of cognitive impairment in elderly patients during the immediate postoperative period.

METHODS

Forty-seven patients > 60 yr of age and undergoing major surgery were randomly allocated to receive either regional or general anaesthesia. The mental status of the patients was assessed preoperatively and during the first three postoperative days with the Mini Mental State Examination. The incidence of delirium was also examined during the same period with the use of DSM III criteria.

RESULTS

Overall, during the first three postoperative days, the mean Mini Mental State Examination score decreased significantly (P < 0.001). However, this decline was very significant only in patients assigned to receive general anaesthesia (P < 0.001) compared to regional anaesthesia. Nine patients developed delirium but the type of anaesthesia did not affect its incidence. The only important factor for the development of delirium was preexisting cardiovascular disease irrespective of anaesthesia type (P < 0.025).

CONCLUSIONS

Elderly patients subjected to general anaesthesia displayed more frequent cognitive impairment during the immediate postoperative period in comparison to those who received a regional technique.

Anaesthesia and the QT interval in humans: effects of halothane and isoflurane in premedicated children

The effects of halothane and isoflurane followed by subsequent administration of vecuronium on the QT interval have been investigated during the induction of anaesthesia. Fifty-eight children, ASA I, without cardiovascular and electrolyte abnormalities and not receiving any medication were studied. Anaesthesia was induced with either halothane (n = 28) or isoflurane (n = 30), and was maintained until the end of the study with end-tidal concentrations of 2.5-3%. Recordings of ECG, heart rate and systolic arterial pressure were obtained at the following times: prior to induction of anaesthesia; 1 and 3 min after stable end-tidal concentrations of the induction agent had been reached; 1 and 3 min following vecuronium administration; at the time of tracheal intubation; 1 and 3 min later. Halothane significantly shortened the QTc interval (P < 0.05); isoflurane prolonged it (P < 0.001). Heart rate decreased significantly after halothane administration (P < 0.01); in contrast, heart rate increased after induction of anaesthesia with isoflurane (P < 0.05), increasing further after laryngoscopy and tracheal intubation (P < 0.001). Systolic arterial pressure decreased significantly (P < 0.001) in both groups after induction of anaesthesia and remained decreased until the end of the study. It is concluded that halothane may be a better choice than isoflurane for children with a long QT interval.

Telematics in prehospital emergency care: the Hector Pilot of Crete

Emergency Medicine is considered the neglected specialty of contemporary medicine, although it is widely acknowledged that improvement in the outcome of the acutely and critically ill depends on its timely and effective management during the critical first hour [1], the so called "golden hour". The crucial question therefore is whether Telematics can affect this outcome and in particular how they can assist the existing models of Prehospital Emergency Medical Services (EMS) to meet this goal. The Hector Pilot of Crete tries to give a convincing answer to this question, taking into account the concept and some of the requirements of Emergency Medicine.

Epidemiology of road traffic accidents during pleasure travelling: the evidence from the Island of Crete

During the six-month period April to September 1995, all 730 road traffic injury victims who contacted any of the three hospitals of the Heraklion District in the island of Crete, directly or through the Medical Emergency Transportation Network, were recorded. A special form was completed containing information about selected characteristics of the victims, nature of the injuries and conditions of the accident. All 39 fatalities owing to road traffic accidents were also registered. In the absence of data concerning the person-time at risk only proportional analyses could be performed. On the basis of Greek hospital discharge statistics in Heraklion District during 1992, one foreigner visitor was discharged owing to injuries of any type for every 18 Greeks. The corresponding ratio for road traffic accidents is close to 1:3, underlying the importance of road traffic accidents as the major health hazard during pleasure travelling. Left-side driving country nationals were at an increased risk for traffic accident when they drove a rented rather than an owned vehicle (p = 0.02), possibly on account of maladaptation during the adjustment period in the country of visit. Moreover, road traffic victims from left-side driving countries compared with foreigners from right-side driving countries were involved 2.5 times more frequently in accidents in which overpassing or other driving maneuvers require reflexes conditioned on reverse directionality (p = 0.02). Alcohol abuse was reported as a primary cause of accident in a significantly higher proportion of foreign nationals (p < 10(-6)) reflecting the fact that the latter group was on vacation. Alcohol intoxication was more common among Eastern European victims than among victims from European Union countries (p < 10(-5)). The likelihood of death following hospitalization ranged from 0% among those with a Glascow Coma Scale (GCS) score of 8 or higher, to 90% among those with GCS less than 8. After adjustment for exact GCS score there was no difference in the probability of death or the likelihood for admission to intensive care unit between Greek and foreign nationals. Road traffic accidents are a major hazard during pleasure travelling and victims of such accidents among travellers have a distinct epidemiologic profile compared with accidents of a similar nature among locals.

Hemodynamic effects of intravenous somatostatin administered in the postoperative period

OBJECTIVE

To evaluate the hemodynamic effects of intravenous somatostatin administration in patients during the early postoperative period.

DESIGN

Prospective, case-controlled trial.

SETTING

Postanesthesia care unit.

PATIENTS

Ten postoperative, noncirrhotic, American Society of Anesthesiologists physical status II patients, after resection of nonsecretory (i.e., non-neuroendocrine) tumors. No patient received any vasoactive medication perioperatively.

INTERVENTIONS

Three hours after the end of surgery, normal saline or somatostatin was intravenously administered in two phases: a) in phase 1, patients received a 20-mL bolus of normal saline within 1 min, followed by a continuous infusion of 20 mL of normal saline for the next 30 mins. Patients were left undisturbed for the subsequent 30 mins. b) in phase 2, patients received somatostatin (3.5 micrograms/kg, 20-mL bolus) over 1 min, followed by a continuous infusion of somatostatin (3.5 micrograms/kg/hr) for 72 hrs.

MEASUREMENTS AND MAIN RESULTS

Anesthesia was managed according to a prospectively designed protocol. Patients' hemodynamic profiles and pressure waveforms were recorded immediately before the bolus injections of normal saline and somatostatin, and at every minute thereafter for 30 mins. Bolus doses of somatostatin produced a transient, nonsignificant decrease in heart rate, along with short-lived increases in systolic arterial pressure, diastolic arterial pressure, systolic pulmonary arterial pressure, diastolic pulmonary arterial pressure, and central venous pressure.

CONCLUSION

Bolus intravenous somatostatin administered postoperatively after tumor resection in patients produced transient cardiovascular changes that were not sustained during a subsequent continuous infusion.

Anaesthesia and the QT interval in humans. The effects of isoflurane and halothane

Prolongation of the QT interval may cause potentially hazardous arrhythmias. The effects on the QT interval (QTc, corrected for heart rate) of isoflurane and halothane followed by vecuronium have been investigated during induction of anaesthesia in 51 patients. All patients were ASA 1 or 2, without cardiovascular problems or electrolyte abnormalities and were not receiving medication. Midazolam 0.08 mg.kg-1 was administered intramuscularly for premedication. Anaesthesia was induced with either isoflurane (n = 26) or halothane (n = 25), and the inspired concentration increased to reach an end-tidal concentration of 2.5% to 3%. Recordings of ECG, heart rate, systolic and diastolic arterial pressure were obtained at the following times: prior to induction of anaesthesia; 1 min and 3 min after a stable end-tidal concentration had been reached; 1 min and 3 min following vecuronium administration, at the time of tracheal intubation and 1 min and 3 min later. Halothane significantly shortened QTc (p < 0.05 to p < 0.001), in contrast to isoflurane which prolonged it (p < 0.01). The heart rate decreased (p < 0.01 to p < 0.001) after induction of anaesthesia with halothane and returned to pre-induction values after tracheal intubation. In contrast, heart rate increased after induction with isoflurane and increased further after laryngoscopy and tracheal intubation (p < 0.001). In the isoflurane group, ST depression was noticed in seven patients and nodal rhythm in two, while in the halothane group seven patients developed nodal rhythm and, in two patients, ventricular ectopics were recorded. There were no sequelae. In both groups, systolic and diastolic arterial pressure decreased after induction of anaesthesia (p < 0.01 to p < 0.001), increasing again after intubation.

Acute tolerance to fentanyl during anesthesia in dogs

The effect of fentanyl on increases in heart rate and mean arterial pressure elicited by electric stimulation of a branch of the radial nerve was studied in anesthetized, paralyzed, and artificially ventilated dogs. In one group, a bolus of 100 micrograms/kg of fentanyl depressed the evoked changes in heart rate and arterial pressure by 82 and 75%, respectively, by 5 min, and recovery occurred within 90 min. A second group was given increasing bolus doses of fentanyl from 1.5 to 100 micrograms/kg every 20 min for 200 min. The doses and intervals were chosen to give a logarithmic increase in plasma concentration of fentanyl to include a final bolus dose of 100 micrograms/kg and were predicted by a two-compartment pharmacokinetic model derived from data of the first group. In the second group, the bolus dose of 100 micrograms/kg after 5 min had no significant effect on evoked cardiovascular responses. Over the following 2 h, the evoked changes in heart rate and arterial pressure increased above those preceding the 100 micrograms/kg dose. An additional bolus dose of 100 micrograms/kg given 2 h after the first did not depress the evoked reflexes below the control values. It was concluded that tolerance to the effects of fentanyl can occur within 3 h and that for evoked responses to arterial pressure, rebound withdrawal effects can be seen within an additional 90 min.

Failure of large tidal volumes to improve oxygen availability during anaesthesia

Eight patients undergoing peripheral vascular surgery were ventilated with small (5.3 ml/kg) and large (16.3 ml/kg) tidal volumes at a constant respiratory rate. Carbon dioxide was added to the inspired gases to maintain normal end-tidal levels. The use of large tidal volumes resulted in a significant increase in arterial oxygen tension and content, but, due to a reduction in cardiac output, failed to improve oxygen availability.

Effect of frequency of ventilation, positive end-expiratory pressure, PaO2 and PaCO2 on phrenic nerve activity. A study using a new valveless all-purpose ventilator

The effect of changing the frequency of ventilation from 12 b.p.m. (NFV) to 80 b.p.m. (HFV) and applying PEEP on phrenic nerve activity (PNA) has been examined in anaesthetized dogs. HFV did not cause a greater decrease in PNA than the application of 0.5 kPa of PEEP. When the PEEP generated by HFV was removed by applying NEEP, PNA returned to control values. At a low normal PaCO2 (less than 5.3 kPa) and high PaO2 (greater than 30 kPa), HFV and PEEP (0.5 kPa) totally abolished PNA in some preparations. With a high normal PaCO2 (greater than 6.0 kPa) and high PaO2 (greater than 30 kPa), HFV and PEEP (0.5 kPa) decreased PNA by a mean of only 30%. When PaO2 was decreased to physiological values (less than 13.3 kPa), with a low normal PaCO2 (less than 5.3 kPa), the decrease in PNA by HFV and PEEP (0.5 kPa) was decreased to 25%. It was concluded that the frequency of ventilation per se has little or no effect on PNA in the range of frequencies studied.

A new valveless all-purpose ventilator. Clinical evaluation

Preliminary clinical evaluation of a new ventilator, which embodies a new valveless design principle and a circuit which is open to atmosphere, has been performed on adult patients undergoing surgery. Using normal respiratory fresh gas flows (100 ml kg-1 min-1) PaCO2 and PaO2 were the same as with a conventional ventilator. High frequency ventilation (HFV) up to 100 b.p.m. caused no statistically significant changes in PaCO2 and PaO2. The peak airway pressures were 30% less than with a Manley ventilator and decreased by a further 40% during HFV, PEEP, NEEP, CPAP and IMV were easily applied.

Dissociation between the effects of fentanyl and alfentanil on spontaneous and reflexly evoked cardiovascular responses in the dog

Observations were made for 3 h in 10 anaesthetized dogs on the effects of alfentanil 500 micrograms kg-1 and fentanyl 100 micrograms kg-1 on resting heart rate (HR) and mean arterial pressure (MAP), and on the changes evoked in heart rate and mean arterial pressure (delta HR and delta MAP) by stimulation of a cutaneous nerve. Both drugs caused similar decreases in the resting HR (43-44%) and MAP (28-31%), which returned to baseline within 180 min following alfentanil but not fentanyl. Fentanyl decreased the somato-cardiovascular reflexes by 73% and 82% compared with a significantly smaller reduction of 54% and 55% (P less than 0.05) with alfentanil. Following alfentanil, delta MAP had recovered by 15 min and delta HR by 70 min compared with 70 and 90 min respectively for fentanyl. In conclusion, there was a dissociation between the maximum effect of alfentanil and fentanyl on the resting circulation and on the evoked cardiovascular reflexes. With both drugs a dissociation was observed between the durations of their effect on the resting cardiovascular system and on the evoked cardiovascular responses.

Haemodynamic effects of midazolam and thiopentone during induction of anaesthesia for coronary artery surgery

The cardiovascular effects of thiopentone 3 mg kg-1 and midazolam 0.3 mg kg-1 were observed during induction of anaesthesia in 16 premedicated patients about to undergo myocardial revascularization. There were no significant changes in either group in cardiac output or central venous pressure. The heart rate in both groups showed an increase at 3 min and thereafter returned to control values. After 3 min, there was a significant decrease in both arterial pressure and peripheral resistance by 12% and 15% (mean values) respectively from control values in the group receiving midazolam, whereas after thiopentone the peripheral resistance increased by approximately 13% and was not affected by a further dose of thiopentone 1 mg kg-1.

Cardiorespiratory effects of increased airway pressure during controlled and spontaneous breathing after cardiac surgery

The cardiorespiratory effects of intermittent positive pressure ventilation with zero end-expiratory pressure (IPPV), continuous positive airway pressure breathing (CPAP) and spontaneous breathing (SR) were studied in 11 patients 3--20 h after open-heart surgery. The transition from IPPV to CPAP resulted in a significant reduction in tidal volume and significant increases in respiratory frequency, PaCO2, oxygen transport and mean arterial pressure, but there were no significant changes in cardiac output or PaO2. There were no significant differences in any of the measurements between CPAP and SR.