Hypotension during subarachnoid anaesthesia: haemodynamic effects of colloid and metaraminol

We have studied 45 patients, aged 60-95 yr, receiving subarachnoid block for neck of femur fractures. Patient received either colloid (polygeline, Haemaccel) 8 ml kg-1 (n = 15), metaraminol 5 micrograms kg- 1 and 1.7 micrograms kg-1 min-1 (n = 15) or a combination of both treatments to maintain systolic arterial pressure (SAP) between 75 and 100% of baseline. If necessary, additional colloid 2 x 4 ml kg-1 or metaraminol 3 x 2.5 micrograms kg-1 was given. Arterial pressure was measured by automated oscillotonometry, central venous pressure (CVP) by a manometer and cardiac index (CI), stoke index (SI) and heart rate (HR) by transthoracic electrical bioimpedance. Systemic vascular resistance index (SVRI) was derived. Colloid was less effective than metaraminol (P < 0.05). In the colloid group, SAP and SVRI decreased and CVP, CI and SI increased (P < 0.001). In the metaraminol group, initial decreases in SAP, SVRI and CVP were restored after 10-15 min and HR decreased after 12 min (P < 0.001). In the combined group, initial decreases in SAP and SVRI were restored after 4 and 16 min, and CVP, CI, SI and HR increased (P < 0.001). Metaraminol was more effective than colloid because it increased SVRI, whereas colloid increased CVP without significantly increasing CI.      

A comparative study of three different methods of administering metaraminol during spinal anaesthesia in the elderly

We compared three methods of administering metaraminol during spinal (subarachnoid) anaesthesia. Fifty-two elderly patients with fractured hips were studied. Blood pressure was maintained by either intramuscular (i.m.) metaraminol (0.1 mg x kg(-1)), intravenous (i.v.) boluses (0.01 mg x kg(-1)) or an infusion (0.05 mg x kg(-1) x h(-1)). Non-invasive blood pressure was recorded every one-minute. Spinal anaesthesia initially decreased the systolic arterial pressure by 15 (14) % compared to 35 (15) % for diastolic pressure (P<0.001). I.m. metaraminol restored the systolic arterial pressure back to baseline values (-3%), but there was significant between-subject variability resulting in a very unpredictable effect. I.v. boluses and infusion had a more predictable effect and maintained systolic arterial pressure at about 20% below baseline. Range of effect, measured by inter-quartile range and variance, was greatest in the i.m. group and least in the infusion group (P<0.003). I.m. metaraminol during spinal anaesthesia has a very unpredictable effect. Infusions of metaraminol provided the best blood pressure control. Diastolic blood pressure fell significantly after spinal anaesthesia and this merits further investigation.     

Physostigmine increases the dose of propofol required to induce anaesthesia

Purpose

This prospective, randomized, double-blind study was performed to determine the effect of administration of physostigmine on the dose of propofol required to produce loss of consciousness.

Methods

Forty female unpremedicated patients were assigned in a random blind design to receive either 2 mg physostigmine or equal volume of normal salineiv, five minutes before induction of anaesthesia with propofol. All patients received general anaesthesia for breast surgery. Propofol was infused at a constant rate of 200 ml · hr^?1 while patients were breathing oxygen 100% via a face mask. In each patient the dose of propofol required to produce loss of the ability to grasp a 20 ml synnge was recorded as the end-point of loss of consciousness. At this point the protocol was terminated and, after intubation of the trachea, anaesthesia was maintained with a nitrous oxide-isoflurane or sevoflurane mixture in oxygen, increments of an opioid and a muscle relaxant. Doses of anaesthetic drugs and duration of anaesthesia vaned and depended on the type of breast surgery, determined by frozen section.

Results

The mean ± SD dose of propofol required to produce loss of consciousness was 2.4 ± 0.6 mg · kg^?1 and 2.0 ± 0.4 mg · kg^?1 in the physostigmine and in the normal saline groups respectively (P = 0.014).

Conclusion

Physostigmine pretreatment increases the dose of propofol required to produce loss of consciousness.     

Time required to achieve a stable cuff pressure by repeated aspiration of the cuff during anaesthesia with nitrous oxide

BACKGROUND AND OBJECTIVE: When the endotracheal tube cuff is repeatedly aspirated to avoid excessive cuff pressure during nitrous oxide anaesthesia, a stable cuff pressure is eventually achieved. We assessed the time required to achieve a stable cuff pressure after repeated cuff deflation. METHODS: During 67% nitrous oxide and oxygen anaesthesia, air-filled cuffs of a standard tracheal tube (Mallinckrodt Hi-Contour) were repeatedly deflated every 30 min for the first 3 or 4 h to inhibit excessive pressure (Groups Def-3 or Def-4, respectively, n = 10 for each); the cuff pressure was monitored for an additional 3 h. In some patients, the study was terminated at 1, 2, 3 and 4 h (n = 6 for each). RESULTS: Cuff pressure in Group Def-3, but not in Group Def-4, > 22 mmHg after stopping cuff aspiration. Intracuff nitrous oxide concentrations increased during repeated cuff deflation and increased further in Group Def-3 during an additional 3 h (from 39.8 +/- 4.7% to 44.3 +/- 3.8%; P < 0.05), whereas intracuff nitrous oxide concentrations at 4 h were not different from those in Group Def-4 at the end of the study (43.7 +/- 4.5% versus 42.3 +/- 4.8%; P = 0.579). CONCLUSIONS: When the air-filled cuff of the standard endotracheal tube is repeatedly deflated every 30 min for 4 h, but not for only 3 h, during nitrous oxide anaesthesia, a stable cuff pressure can be achieved without further deflation of the cuff. Our data also suggest that achieving an equilibrating nitrous oxide concentration in the cuff provides a subsequent stable cuff pressure.     

A comparison of the 2% and 1% formulations of propofol during anaesthesia for craniotomy

This study investigated the pharmacodynamic and pharmacokinetic equivalence of 1% and 2% propofol emulsions when used for total intravenous anaesthesia for intracranial surgery. The same infusion rate (6.7 mg.kg^-1.h^-1) of the two preparations was administered. Induction doses, recovery times, and haemodynamic profiles were identical. Similar propofol concentration profiles were produced and total body clearance of propofol was identical. Both preparations were associated with a similar incidence of injection pain but neither resulted in venous thrombosis or thrombophlebitis at 24 h. Plasma triglyceride concentrations were significantly higher with the 1% solution, but there were no differences in cholesterol concentrations. The 1% and 2% emulsions appeared to be pharmacologically equivalent with similar minor effects on arterial blood pressure and heart rate. Two percent propofol may be preferable to the 1% solution for maintenance of anaesthesia in patients in whom a large lipid load might be considered undesirable.     

Effect of controlled blood pressure increase on cerebral blood flow velocity and oxygenation in patients with subarachnoid haemorrhage

Background

Patients with aneurysmal subarachnoid haemorrhage (SAH) might have impaired cerebral autoregulation, that is, CBF – and thereby oxygen delivery – passively increase with an increase in CPP. This physiological study aimed to investigate the cerebral haemodynamic effects of controlled blood pressure increase in the early phase after SAH before any signs of delayed cerebral ischaemia (DCI) occurred.

Methods

The study was carried out within 5 days after ictus. Data were recorded at baseline and after 20 min of noradrenaline infusion to increase mean arterial blood pressure (MAP) by a maximum of 30 mmHg and to an absolute level of no more than 130 mmHg. The primary outcome was the difference in middle cerebral artery blood flow velocity (MCAv) measured by transcranial Doppler (TCD), while differences in intracranial pressure (ICP), brain tissue oxygen tension (PbtO₂), and microdialysis markers of cerebral oxidative metabolism and cell injury were assessed as exploratory outcomes. Data were analysed using Wilcoxon signed-rank test with correction for multiplicity for the exploratory outcomes using the Benjamini-Hochberg correction.

Results

Thirty-six participants underwent the intervention 4 (median, IQR: 3–4.75) days after ictus. MAP was increased from 82 (IQR: 76–85) to 95 (IQR: 88–98) mmHg (p-value: <.001). MCAv remained stable (baseline, median 57, IQR: 46–70 cm/s; controlled blood pressure increase, median: 55, IQR: 48–71 cm/s; p-value: .054), whereas PbtO₂ increased significantly (baseline, median: 24, 95%CI: 19–31 mmHg; controlled blood pressure increase, median: 27, 95%CI: 24–33 mmHg; p-value <.001). The remaining exploratory outcomes were unchanged.

Conclusion

In this study of patients with SAH, MCAv was not significantly affected by a brief course of controlled blood pressure increase; despite this, PbtO₂ increased. This suggests that autoregulation might not be impaired in these patients or other mechanisms could mediate the increase in brain oxygenation. Alternatively, a CBF increase did occur that, in turn, increased cerebral oxygenation, but was not detected by TCD. Trial registration: clinicaltrials.gov (NCT03987139; 14 June 2019).     

Adding sufentanil to levobupivacaine or ropivacaine intrathecal anaesthesia affects the minimum local anaesthetic dose required

Background: We carried out this prospective, randomized, double-blind study in order to evaluate whether the intrathecal addition of sufentanil 3.3 mcg affects both the minimum local anaesthetic dose (MLAD) of spinal levobupivacaine and ropivacaine for a caesarean section and enhances the spinal block characteristics.
Methods: One hundred and eighty women were randomly allocated into four groups: levobupivacaine (Group L), levobupivacaine plus sufentanil (Group L+S), ropivacaine (Group R) and ropivacaine plus sufentanil (Group R+S). Each received 3 ml of the study solution intrathecally as part of a combined spinal/epidural technique. The initial dose was 12 mg for Groups L and L+S, and 15 mg for Groups R and R+S. The test solution was required to achieve a visual analogue pain score (VAPS) of 30 mm or less to be considered effective at skin incision, uterine incision, birth, peritoneal closure and at the conclusion of surgery. Effective or ineffective responses determined a 0.5 mg decrease or increase of the same drug, respectively, for the next patient in the same group, using an up–down sequential allocation.
Results: Using the Dixon and Massey formula, the MLAD was 10.65 mg [confidence interval (CI) 95%: 10.14–11.56] in Group L, 4.73 mg (CI 95%: 4.39–5.07) in Group L+S, 14.12 mg (CI 95%: 13.50–14.60) in Group R and 6.44 mg (CI 95%: 5.86–7.02) in Group R+S.
Conclusions: The addition of sufentanil reduced the MLAD of both the local anaesthetics. It did not affect their potency ratio significantly and resulted in enhanced spinal anaesthesia.     

Reduced blood pressure lability during emergence from anaesthesia in rats: a pilot study using clonidine

Background: In the post-operative setting, pressure lability is increased in hypertensive patients. α-2 agonists were shown qualitatively to reduce this lability qualitatively. Here, upon immobilization combined with emergence from anesthesia in rats and clonidine administration, pressure lability was quantitatively assessed and related to baroreflex sensitivity.
Methods: After local anesthesia of all incisions and surgical wounds and myorelaxation with metocurine, rats had halothane withdrawn for 60 min. Rats received (a) saline ( n =8), (b) clonidine 30 μg/kg i.v ( n =8) simultaneous to halothane discontinuation and (c) halothane readministration ( n =8) 20 min after halothane discontinuation. Pressure lability was quantitatively assessed using occurrence/amplitude of peaks in systolic blood pressure (SBP) and cardiac baroreflex slope.
Results: Clonidine was associated with partial blunting of hypertension, reduced standard deviation of SBP, reduced number and amplitude of peaks in systolic pressure. Clonidine was also associated with increased slope of the cardiac baroreflex upon early intervals of emergence, but not at later intervals.
Conclusion: Clonidine reduces pressure lability upon immobilization stress combined to emergence from anesthesia, via parasympathetic activation and possibly sympathetic inhibition during early emergence as opposed to sympathetic inhibition during late emergence.     

Comparison of the Finapres blood pressure monitor with intra-arterial manometry during induction of anaesthesia

The Finapres (Ohmeda, Madison, U.S.A.) is a non-invasive device which continuously measures the arterial blood pressure in a finger and produces a real-time display of the arterial pressure wave. It consists of a finger cuff with an infra-red transmission plethysmograph, a servo control box and a monitor unit. The device was compared with intra-arterial pressure monitoring in twenty patients during induction of anaesthesia for elective neurosurgical procedures. The differences between the two methods were considerable, ranging from -40 mmHg to +26 mmHg for mean pressure. While the Finapres has potential as a non-invasive continuous blood pressure monitor, the current model Finapres, as supplied, displays too great a variability for it to be used as an alternative to intra-arterial pressure monitoring.     

Selection of baseline blood pressure to guide management of hypotension during spinal anaesthesia for caesarean section

IntroductionRecommendations on vasopressor management during caesarean section under spinal anaesthesia suggest maintaining systolic arterial pressure ≥90% of an accurately measured baseline value. The baseline is often taken as the first reading in the operating room. We hypothesise that this reading may not reflect an accurate baseline value.MethodsA retrospective case note review of 300 non-hypertensive women undergoing caesarean section with neuraxial anaesthesia, including spinal anaesthesia for elective delivery (n=100), and spinal (n=100) and epidural top-up anaesthesia (n=100) for emergency delivery. Systolic arterial pressure values recorded at various time points between the last antenatal visit and the first blood pressure value recorded in the operating room were compared.ResultsThere was a stepwise and significant increase in systolic arterial pressure over three time points (last antenatal clinic, morning of surgery, operating room) before elective caesarean section (all P <0.001). In women having emergency caesarean under spinal anaesthesia, a stepwise increase over four time points (last antenatal clinic, first reading in labour, final reading in labour, operating room) was observed. A similar trend was seen over these time points for women having emergency caesarean under epidural top-up, although the systolic blood pressure did not rise during labour.ConclusionsUsing the initial blood pressure reading in the operating room as the baseline value may lead to unnecessary vasopressor use and hypertension. Prospective research is required to clarify which reading represents the most accurate baseline to maintain homeostasis and reduce the hypotensive sequelae of neuraxial anaesthesia for both the mother and fetus.     

Dual blockade of the renin-angiotensin system compared with a 50% increase in the dose of angiotensin-converting enzyme inhibitor: effects on proteinuria and blood pressure.

BACKGROUND: Several publications in the past 2 years have demonstrated that combined angiotensin-converting enzyme inhibitors (ACEI) and angiotensin-II receptor antagonist (AIIRA) are more effective in reducing blood pressure and proteinuria in patients with chronic renal disease than ACEI or AIIRA alone. This study compares the effect of increasing the ACEI dose by 50% with that of adding an AIIRA to a standard ACEI dose. METHODS: This study was designed as part of a previous comparison of ACEI with ACEI plus candesartan. Directly after completion of the randomized intervention periods of that study, the dose of ACEI was increased by 50% in all patients. Proteinuria and blood pressure were compared in both groups of patients in the three periods, on standard ACEI, on ACEI plus candesartan and on a dose of ACEI increased by 50%. RESULTS: No significant differences in the primary end-point proteinuria or secondary end-points were observed when the ACEI dose was increased by 50%. Proteinuria was 1.8 g in 24 h on candesartan and ACEI and 2.4 g in 24 h when the ACEI dose was increased by 50% (P<0.02). Systolic blood pressure was 126.6 mmHg on candesartan and ACEI and 134.47 mmHg when the ACEI dose was increased by 50% (P<0.002). Diastolic blood pressure, serum creatinine, urea and potassium were not different between groups. CONCLUSIONS: Standard ACEI plus candesartan is more effective in reducing systolic blood pressure and proteinuria than a 50% increase in ACEI dose. This has implications for the prevention of renal failure in chronic renal disease.     

Comparative study between 5% prilocaine and 2% mepivacaine by the subarachnoid route in transurethral resections

OBJECTIVE: To compare the duration of spinal block with 5% prilocaine and 2% mepivacaine in short procedures for transurethral resection and to assess possible complications in the immediate postoperative period. MATERIAL AND METHODS: Fifty-seven patients scheduled for transurethral resection of the prostate or a vesical tumor. Patients were ASA I-III, over 55 years of age and randomly assigned to two groups to receive 5% prilocaine (1 mg/kg, n = 27) or 2% mepivacaine (0.8 mg/kg, n = 30). We collected data on anesthetic technique, levels of extension of motor and sensory blockades, duration of blockades and complications within the first 24 hours after surgery. RESULTS: Demographic data, ASA classification and duration of surgery were similar in both groups. We found statistically significant differences (p < 0.05) in duration of sensory blockade (120.92 +/- 36.21 min with prilocaine and 145.83 +/- 35.81 min with mepivacaine) and in motor blockade (106.29 +/- 38.16 min with prilocaine and 133.16 +/- 42.21 min with mepivacaine). Five cases of hypotension and 4 of bradycardia occurred in each group and one patient in the mepivacaine group suffered slight postoperative cephalea. CONCLUSIONS: Both local anesthetics offer good surgical conditions with hemodynamic stability and few complications. The duration of sensory and motor blockade is shorter with prilocaine than with mepivacaine, making prilocaine more appropriate for short interventions.     

Justification of empiric methodology to determine dexmedetomidine dose for the TREX study

Introduction

Dexmedetomidine is the sedative agent administered in combination with remifentanil and low dose of sevoflurane in the interventional arm of the ongoing TREX trial ( T rial R emifentanil DE xmedetomidine). The TREX pilot study (published in Paediatr Anaesth 2019;29:59–67) established infusion rates higher than those initially proposed. This could be attributed to an inappropriate target concentration for sedation or incorrect initial pharmacokinetic parameter estimates.

Methods

The TREX study is a Phase III, randomized, active controlled, parallel group, blinded evaluator, multicenter, superiority trial comparing neurological outcome after standard sevoflurane anesthesia with dexmedetomidine/remifentanil, and low dose sevoflurane anesthesia in children aged less than 2 years undergoing anesthesia of 2 h or longer. In this report, dexmedetomidine pharmacokinetics were analyzed in the interventional arm of the Italian population.

Results

There were 162 blood samples from 32 infants (22 male and 10 female). The median (IQR) age was 12 (5.2–15.5) months, weight 9.9 (7.3–10.8) kg. Duration of anesthesia ranged from 2 to 6 h. None of the children were born premature (median postnatal age 39 weeks, IQR 38–40 weeks). A 3-compartment PK model that incorporated allometric scaling and a maturation function demonstrated plasma concentration observations from the current Italian arm of the TREX study were consistent with those predicted by a “universal” model using pooled data obtained from neonates to adults.

Conclusions

This current PK analysis from the Italian arm of the TREX study confirms that plasma concentration of dexmedetomidine is predictable using known covariates such as age and size. The initial target concentration (0.6 μg.L⁻¹) used to sedate children cared for in the intensive care after cardiac surgery was inadequate for infants in the current TREX study. A target concentration 1 mcg.L⁻¹, corresponding to a loading dose of 1 mcg.kg⁻¹ followed by an infusion of 1 mcg.kg⁻¹.h⁻¹, provided adequate sedation.     

Defining intra-operative hypotension--a pilot comparison of blood pressure during sleep and general anaesthesia

The scientific justification for particular values of intra-operative hypotension is poorly substantiated. To provide a rationale for appropriate values we recorded blood pressure measurements at home for 24 h using an automated non-invasive ambulatory blood pressure measurement device. These blood pressures were compared with blood pressure measured before and during general anaesthesia in 18 subjects undergoing elective day surgery. We confirmed that a pre-operative reading taken upon admission to hospital is significantly elevated compared to a usual daytime blood pressure in the same patient. The median (IQR [range]) increases in systolic and mean arterial pressures were 10 (2-15 [-5 to 59]) mmHg, p = 0.003 and 10 (5-14 [-5 to 35]) mmHg, p = 0.002, respectively. When using this admission blood pressure measurement as a 'baseline', systolic and mean arterial pressures decreased during sleep by 41 (30-46 [6-83]) mmHg and 34 (26-36 [6-58]) mmHg, respectively (p = 0.001). This decreased even further intra-operatively: systolic blood pressure by 49 (36-64 [15-96]) mmHg and mean arterial pressure by 36 (26-46 [8-66]) mmHg (p = 0.001).     

The influence of esmolol on the dose of propofol required for induction of anaesthesia

Cardiac output may be an important determinant of the induction dose of intravenous anaesthetic. Esmolol is known to reduce cardiac output, and we examined its effect on the propofol dose required for induction of anaesthesia. The size of the effect seen with esmolol was compared with midazolam co-induction. Sixty patients were randomly allocated to placebo (saline), esmolol (1mg x kg(-1) bolus, followed by an infusion at 250 microg x kg(-1)min(-1)) or midazolam (0.04 mg x kg(-1)) groups. Induction of anaesthesia commenced 3 min following the administration of the study drug, using a Diprifusor set to achieve plasma propofol concentrations of 10 microg x ml(-1) at 5 min. The primary end point used was the propofol dose per kg at loss of response to command. The mean (SD) propofol dose for each group was 2.38 (0.48) mg x kg(-1) for placebo, 1.79 (0.36) mg x kg(-1) for esmolol and 1.34 (0.35) mg x kg(-1) for midazolam (all means significantly different; p < 0.0005). We found that predosing with esmolol reduces the propofol requirements for induction of anaesthesia by 25%.