The measurement of occlusion pressure during anaesthesia

Occlusion pressure (Po max) was used to indicate the depression of respiratory drive following rapid administration of methohexitone 0.5 mg/kg and etomidate 0.067 mg/kg to fourteen patients under stable light anaesthesia. Methohexitone produced considerably more respiratory depression than etomidate, the difference probably being clinically significant. Po max is the maximum sub-atmospheric pressure generated in the trachea when inspiration is prevented by occlusion of the airway, at functional residual capacity. The factors concerning the use of this simple, non-invasive technique during anaesthesia are discussed, and suggestions made for producing consistent, useful, measurements.     

A centenary of auscultatory blood pressure measurement: a tribute to Nikolai Korotkoff

In 1905, Dr. Nikolai Korotkoff (1874-1920), a Russian surgeon, discovered a simple and precise technique to measure arterial pressure. He was born on 26th February 1874 in the central Russian city of Kursk. Korotkoff graduated from the Medical Faculty of Moscow University in 1898, but he worked later in the Surgical Clinic at the Imperial Military Medical Academy in St. Petersburg (Russia). Korotkoff served as a military surgeon during the Russo-Japanese War (1904-1905) and his major efforts were to find reliable clinical signs that could predict whether limb flow would be viable after vascular surgery of traumatic aneurysm. He found that after complete compression, the aneurysm of the arm (i.e. distal pulse on a. brachialis) disappeared with Riva-Rocci cuff and then gradually decreasing the pressure, a series of sounds could be heard by stethoscope under the artery distal to the compression. Korotkoff described four distinct phases of sounds: first sound, then compression murmurs, second tone, and disappearance of sounds. Korotkoff was also able to demonstrate the same auscultatory finding in healthy persons. He failed to notice only the muffled second sound, which was demonstrated a little later. These classical observations are now well known as the five different phases of Korotkoff sounds. In November 1905, during a conference of the Imperial Military Medical Academy, he reported his discovery in a short presentation entitled 'On the issue of the methods for measuring blood pressure'. In 1939, the Joint Committee of the American Heart Association and the Cardiac Society of Great Britain and Ireland recognized officially and accepted worldwide Korotkoff's method for blood pressure determining. Copyright (c) 2005 S. Karger AG, Basel.     

Peripheral arterial injuries: a reassessment.

Ninety-four patients with peripheral arterial injuries were subjected to acute repair, negative exploration, or late repair of the complications of the arterial injury (false aneurysm, A-V fistula, and/or limb ischemia). The causes of failure after acute injury include extensive local soft tissue and bony damage, severe concomitant head, chest or abdominal wounding, stubborn reliance on negative arteriograms in patients with probable arterial injury, failure to repair simultaneous venous injuries, or harvesting of a vein graft from a severely damaged extremity. There is a positive correlation between non-operative expectant treatment and the incidence of late vascular complications requiring late arterial repair. Delayed complications of arterial injuries occurred most frequently in wounds below the elbow and knee.     

Performance of a tonometer for arterial pressure measurement during anesthesia in the elderly

We investigated performance of an arterial tonometer during anesthesia in the elderly. Thirty patients (17 men and 13 women), ranging from 70 to 86 years old, were included, and agreement between tonometric arterial pressure (TAP) and intraarterial pressure (IAP) was calculated. A total of 6487 paired points was sampled, and values for precision (mean absolute difference ± SD) were 6.8 ± 5.2 for systolic, 6.9 ± 4.6 for mean, and 9.2 ± 5.4mmHg for diastolic blood pressures. Values for bias and limits of agreement [mean difference (TAP – IAP) ± SD, mean difference (TAP – IAP) ± 2 SD, respectively] for systolic, mean, and diastolic pressure were 1.2 ± 8.4 and 1.2 ± 16.8, 5.7 ± 5.9 and 5.7 ± 11.8, and 8.6 ± 6.2 and 8.6 ± 12.4mmHg, respectively. Compared with previous data, aging is likely to affect the performance of an arterial tonometer.     

Intravenous ketamine attenuates arterial pressure changes during the induction of anaesthesia with propofol

BACKGROUND AND OBJECTIVE: To investigate whether the administration of ketamine before induction with propofol produces a smaller decrease in arterial pressure. METHODS: Twenty-two patients were assigned to one of two groups to receive either propofol with ketamine (n = 11) or propofol alone (n = 11, control). Anaesthesia was induced with 2 mg kg-1 propofol and 0.5 mg kg-1 ketamine or 2 mg kg-1 propofol alone. Ketamine was administered 1 min prior to induction with propofol. Immediately after induction with propofol, vecuronium (0.15 mg kg-1) was administered. Four minutes after administration of vecuronium, tracheal intubation was performed. Anaesthesia was maintained using sevoflurane (0.5%) in 66% nitrous oxide until 3 min after intubation. Systolic, diastolic and mean arterial pressure and heart rate were recorded on arrival, directly before induction with propofol, prior to tracheal intubation, immediately after intubation and at 3 min after intubation. RESULTS AND CONCLUSIONS: Administration of ketamine before induction with propofol preserved haemodynamic stability compared with induction with propofol alone.     

Evaluation of arterial oxygenation during anaesthesia

Canadian Journal of Anesthesia/Journal canadien d'anesthésie - The clinical or physiological signs of hypoxaemia have limited value during anaesthesia. In the absence of surgical bleeding,...     

Heart rate and arterial pressure changes during fibreoptic tracheal intubation under general anaesthesia

The cardiovascular responses to fibreoptic orotracheal intubation under general anaesthesia were compared with those in a control group in whom tracheal intubation was effected with a Macintosh laryngoscope. The patients received a standard anaesthetic and were allocated randomly to either group immediately before intubation. Fibreoptic intubation took significantly longer to perform. There were significant increases in heart rate and arterial pressure in both groups compared with pre-induction values. The tachycardia in the fibreoptic group was significantly greater than that in the control group during the second minute after intubation, and the increase in systolic pressure was sustained for a longer period in the fibreoptic group. The maximum increases in systolic and diastolic pressures above pre-intubation values were significantly greater in the fibreoptic group. The cardiovascular responses associated with fibreoptic intubation under general anaesthesia appear to be more severe than those which follow intubation effected with a Macintosh laryngoscope.     

Accuracy of radial arterial pressure measurement during surgery under controlled hypotension

BACKGROUND: Radial arterial pressure underestimates the pressure in the aorta in several clinical situations. A central-to-radial pressure gradient was attributed to intense vasodilation. The aim of this study was to evaluate the accuracy of radial pressure monitoring during controlled hypotension achieved with profound arterial vasodilation. METHODS: Ten patients with ASA physical status I and II undergoing maxillofacial surgery under general anesthesia were enrolled in this prospective study. Radial and femoral arteries were cannulated and connected to a pressure monitoring system. Controlled hypotension was achieved with an infusion of nicardipine titrated to maintain MAP between 50 and 60 mmHg. Simultaneous radial and femoral systolic, mean and diastolic arterial pressures were recorded before, during and after controlled hypotension. Results were expressed as mean +/- SD. Concomitant radial and femoral pressures were compared by a paired Student's test, P < 0.05 being significant. RESULTS: In all, 150 sets of arterial pressures measurement were obtained. There were no statistically significant differences between radial and femoral arterial pressures measured before, during or after controlled hypotension. CONCLUSION: Radial arterial pressure is an accurate measure of central arterial pressure during controlled hypotension achieved with arterial vasodilation.     

Predicting arterial oxygenation during one-lung anaesthesia

Eighty patients undergoing elective thoracotomy were studied to assess the possibility of predicting arterial oxygenation (PaO2) during one-lung anaesthesia (OLA). The first 50 patients were studied retrospectively. The method of multiple linear regression was used to construct a predictive equation for PaO2 during OLA. Potential predictors of PaO2 during OLA which were considered were: age, side of operation, preoperative pulmonary flow rates, preoperative and intraoperative PaO2 during two-lung ventilation. The three most significant predictors for PaO2 during OLA were: side right of operation (P < 0.05), preoperative FEV1% (P < 0.01) and intraoperative PaO2 during two-lung ventilation (P = 0.0001). The predictive equation for PaO2 after ten minutes of OLA was: PaO2 = 100 - 72 (side) - 1.86 (FEV1%) + 0.75 (two-lung) PaO2; (for side insert 0 for left-sided thoracotomy and 1 for right-sided thoracotomy). The remaining 30 patients were studied prospectively and the predicted PaO2 correlated with the observed PaO2 after ten minutes of OLA (r = 0.73, P < 0.01). Four of 30 patients had a predicted PaO2 at ten minutes of OLA < 150 mmHg. Of these, 2/4 subsequently required abandonment of OLA for pulse oximetric saturation < 85%. We conclude that although it is not possible to predict an individual patient's PaO2 during OLA with a high degree of accuracy, it is possible, before the initiation of OLA, to identify those patients whose arterial oxygenation is likely to decrease to low levels during OLA.     

Dopamine stabilizes milrinone-induced changes in heart rate and arterial pressure during anaesthesia with isoflurane

BACKGROUND AND OBJECTIVE: Phosphodiesterase-III inhibitors and dobutamine effectively improve cardiac function in patients with cardiac failure, but they are limited by possible hypotensive effects. We tested the hypothesis that dopamine contributes to stabilizing milrinone-induced haemodynamic changes. METHODS: Nine patients undergoing major surgery were anaesthetized using nitrous oxide and oxygen supplemented with isoflurane 1-2%. After baseline haemodynamics were recorded, milrinone (25 or 50 microg kg(-1)) was administered over 10min, followed by a continuous infusion (0.5 microg kg(-1) min(-1). The second set of haemodynamic values was measured 50 min after beginning the continuous infusion of milrinone. Dopamine (4 microg kg(-1) min(-1)) was then administered with milrinone. RESULTS: Milrinone significantly increased the heart rate from 81 +/- 8 to 102 +/- 16beats min(-1), but it decreased the mean arterial pressure from 83 +/- 10 to 66 +/- 10 mmHg and systemic vascular resistance (P < 0.05 for each). The pulmonary capillary wedge pressure, cardiac index and pulmonary vascular resistance did not change significantly. The addition of dopamine to the milrinone infusion significantly decreased the heart rate (94 +/- 12 beats min(-1)) and increased the mean arterial pressure (82 +/- 11 mmHg). Dopamine and milrinone, but not milrinone alone, significantly increased the cardiac index and the rate-pressure product. CONCLUSIONS: The combination regimen of milrinone and dopamine improved cardiac function, and changes in heart rate and mean arterial pressure induced by milrinone were attenuated by dopamine. The results suggest that a combination regimen of milrinone and dopamine rather than milrinone alone should be used to maintain arterial pressure.     

Prospective evaluation of systolic arterial pressure control with a phenylephrine infusion regimen during spinal anaesthesia for caesarean section

BackgroundHypotension and nausea occur frequently during spinal anaesthesia for caesarean section. The aim of this evaluation was to assess systolic arterial pressure control with our routine prophylactic intravenous phenylephrine infusion regimen. We audited a local standard for an incidence of hypotension of ?25% during the first 15 min of anaesthesia.MethodsOne hundred healthy women undergoing elective caesarean section were assessed. Following intravenous preload with 10 mL/kg Hartmann’s solution, 0.5% hyperbaric bupivacaine 2.8 mL combined with diamorphine 400 μg was given intrathecally in the sitting position. Intravenous phenylephrine was then started at 67 μg/min (the maximum rate). Systolic arterial pressure was recorded every 2 min. The infusion was titrated, according to local guidelines, to maintain systolic arterial pressure close to baseline.ResultsThe median dose of phenylephrine given by infusion was 1000 [interquartile range 670–1000] μg, with 51 patients not requiring any change to the infusion rate. Eleven patients (11%, 95% CI 6–19) developed hypotension, defined as a systolic arterial pressure <80% of baseline. A further four patients were given a bolus of phenylephrine for suspected hypotension. The incidence of hypotension or suspected hypotension was therefore 15% (95% CI 9–24). Thirteen patients (13%, 95% CI 7–21) developed nausea. No patient vomited.ConclusionsOur routine phenylephrine infusion regimen was effective at minimizing hypotension and nausea during relatively high-dose spinal anaesthesia. This was achieved with a low intervention rate, in conjunction with a 2-min rather than a 1-min non-invasive blood pressure cycle time and a relatively low volume of intravenous fluid.