There are very few instances in which a specific technique actually has demonstrated superiority [Anaesthesia 56: 1141, 2001; Chan et al. Anesth Analg 93: 1181, 2001 FREE Full-text at Anesthesia & Analgesia], thus patient satisfaction may be of paramount importance when choosing a technique. There are two randomized, controlled studies comparing general anesthesia to neuraxial analgesia in patients predisposed to cardiac events, the largest of which included 423 patients and showed a non-significant trend towards reduced risk in general anesthesia [Bode RH et al. Anesthesiology 84: 3, 1996] – importantly, this study was stopped after it was determined that, based on the complication rates at interim analysis, it would be impossible to find a statistically significant difference even if one did in fact exist [Go AS et al. Anesthesiology 84: 1, 1996]. The smaller trial, of 100 high risk patients, similarly showed no change in morbidity at 6 or 12 months [Christopherson R et al. Anesthesiology 79: 422, 1993]. As MACE are rare, even in high risk patients, both studies were underpowered.
Preoxygenation should always precede “rapid sequence induction” if possible. In healthy patients, 8 vital capacity breaths of 100% oxygen over 60 seconds is equivalent to 3 minutes of normal breathing of 100% oxygen [Brake et. al. Anesthesiology 91: 612, 1999]. Four vital capacity breaths in 30 seconds, however, is inadequate as it does lead to decreased desaturation time
Rapid Sequence Induction (RSI)
The rationale for RSI is a perceived reduction in the risk of pulmonary aspiration in patients considered “at risk,” however the evidence behind this has recently (and appropriately) been questioned [Neilipovitz DT. Can J Anaesth 54: 748, 2007].
A traditional RSI includes fentanyl (1-2 ucg/kg, although remifentanil or alfentanil may be more reliable in terms of blunting response to DL [Jhaveri et. al. Anesthesiology 87: 253, 1997]) » Preoxygenation for 1-3 mins » defasiculating (panc 1-2 mg IV) » IV induction agent not followed by mask ventilation » SCh (1-2 mg/kg) » cricoid pressure » DL/ETT 45-90 seconds after SCh » OG/NG tube
The major concern regarding RSI is the potential for loss of airway (because paralysis is induced prior to establishment of ventilation, and given this risk it must be justified based on a dual assessment of the airway and aspiration risk (for a thorough discourse on the risk of pulmonary aspiration, see [Warner MA et al. Anesthesiology. 78: 56, 1993]). Neilipovitz and Crosby recommend application of low pressure ventilation by face mask, and suggest that this does not increase the risk for gastric insufflation / aspiration. Preoxygenation for a full 3-5 minutes is key, with a focus on complete exhalation. 0.6 mg/kg succinylcholine may provide adequate relaxation but allow for return of spontaneous ventilation should the airway not be secured.
Sevoflurane is the ideal inhaled anesthetic, and can be used with or without nitrous oxide. It has enjoyed a resurgence in adult use as it allows the maintenance of spontaneous ventilation and allows patients to regulate their own depth of anesthesia, thus preventing excess sevoflurane [Muzi M et al. Anesthesiology 85: 536, 1996; Muzi M et al. Anesth Analg 85: 1143, 1997]. The “awake look” that traditionally relied on short acting IV agents has been expanded to sevoflurane
When mask-inducing with sevoflurane, LOC occurs within 1 minute of breathing 8% gas. In order to deliver 8% immediately, the circuit must be primed – reservoir bag is emptied, “pop-off” valve is opened, vaporizer is set at 8% and fresh gas maxed. Note that an LMA can be placed within 2 minutes if sevoflurane is given at 7% [Muzi M et al. Anesthesiology 85: 536, 1996]. Prior benzodiazepines may facilitate inhalational induction, whereas opiates will complicated it by increasing the likelihood of apnea [Muzi M et al. Anesth Analg 85: 1143, 1997].
Goals are amnesia, analgesia, muscular relaxation, and autonomic attenuation. Volatile anesthetics blunt SNS responses and can be used alone, but have the disadvantage of causing dose-dependent cardiac depression. Often they are combined with N2O, presumably to preserve cardiac function, however this data is mostly from isoflurane, the worst cardiac depressant of the three (sevo, des, iso)
Opiates, by contrast, do not cause cardiopulmonary depression and can often be combined with nitrous oxide for maintenance. Disadvantages of an opiate/N2O anesthetic include hypertension (as opiates do not blunt SNS responses) and frequent requirement of non-depolarizing NMBDs, because patient movement is more of a problem with opiates than with inhaled anesthetics. Another disadvantage of opiates are that they cannot be titrated as rapidly as volatile anesthetics
|Faster||Lower risk of dural puncture headache|
|Better motor and sensory analgesia||Less risk of systemic hypotension (equalized by E)|
|Associated with less pain during surgery||Can significantly extend duration with a catheter|
Significant disadvantages of regional anesthesia include failure of the block and the potential for severe hypotension. The only true contraindication is patient refusal
IV Regional Anesthesia
For procedures lasting 20-90 minutes, IV regional anesthesia (IVRA, aka “Bier block”) may also be considered – double tourniquets help relieve the pain, as may the additional use of ketorolac
Peripheral Nerve Block
Appropriate for superficial extremity procedures. Attractive in patients with chronic pulmonary disease, severe cardiac disease, or impaired renal function. The major disadvantage is unpredictable response ie the potential for failure by the anesthesiologist
Monitored Anesthetic Care
Defined as a procedure in which an anesthesiologist is requested to provide anesthetic services. Same standard of care as any other anesthetic technique. Opiate administration is often used but requires careful monitoring. Inhaled anesthetics can be used if kept below the threshold of LOC.