The laryngeal mask airway reliably provides rescue ventilation in cases of unanticipated difficult tracheal intubation along with difficult mask ventilation

In 1995, our department of anesthesiology established an airway team to assist in treating unanticipated difficult endotracheal intubations and an airway quality improvement (QI) form to document the use of emergency airway techniques in airway crises (laryngeal mask airway [LMA], flexible fiberoptic bronchoscopy, retrograde intubation [RI], transtracheal jet ventilation [TTJV], and cricothyrotomy). Over a 2-yr period, team members and staff anesthesiologists completed airway QI forms to document the smallest peripheral SpO2 during an airway crisis, the number of direct laryngoscopies (DL) performed before using an emergency airway technique, and the emergency airway technique that succeeded in rescue ventilation. Team members agreed to use the LMA as the first emergency airway technique to treat the difficult ventilation/difficult intubation scenario. A SpO2 value < or =90% during mask ventilation defined difficult ventilation. Inability to perform tracheal intubation by DL defined difficult intubation. An increase in the SpO2 value >90% defined rescue ventilation. Review of airway QI forms from October 1, 1995 until October 1, 1997 revealed 25 cases of difficult ventilation/difficult intubation. Before airway rescue, the median SpO2 was 80% (range 50%-90%), and there were four median attempts at DL (range one to nine). The LMA had a success rate of 94% (95% confidence interval [CI] 77-100). Flexible fiberoptic bronchoscopy, TTJV, RI, and surgical cricothyrotomy had success rates of 50% (95% CI 0-100), 33% (95% CI 0-100), 100% (95% CI 37-100), and 100% (95% CI 37-100), respectively. LMA insertion as the first alternative airway technique was useful in dealing with unanticipated instances of simultaneous difficulty with mask ventilation and tracheal intubation.

IMPLICATIONS

Twenty-five cases of simultaneous difficulty with mask ventilation and tracheal intubation occurred after the induction of general anesthesia during the study period. The laryngeal mask was used in 17 cases, and it provided rescue ventilation without complication in 94% of these cases (95% confidence interval 77-100).

Tests to evaluate intravenous placement of epidural catheters in laboring women: a prospective clinical study

We prospectively evaluated the diagnostic accuracy of an epinephrine-containing epidural test dose (EpiTD) as a marker of intravascular injection in 209 unmedicated laboring women. Maternal heart rate (MHR) was continuously monitored and recorded on a strip chart. A tocodynamometer monitored uterine activity. A lumbar epidural catheter was placed and aspirated. If aspiration was positive for blood or cerebrospinal fluid (CSF), the catheter was replaced. In uterine diastole and with stable MHR, 198 patients received an EpiTD (epinephrine 15 microg plus lidocaine 45 mg) via the catheter. MHR and the generated HR strip were observed. A positive EpiTD was defined as a sudden increase in MHR of 10 bpm more than the resting MHR, within one minute after the injection, with a fast acceleratory phase of more than 1 bpm. Absence of a tachycardiac response suggested a negative EpiTD. If the tachycardiac response was deemed equivocal or a uterine contraction followed the EpiTD injection within 1 min, the EpiTD was invalidated and repeated. Catheter aspiration was repeated, and the catheter was removed if aspiration was positive. All patients with negative EpiTD and aspiration received 6-12 mL of epidural bupivacaine 0.25% with or without fentanyl 50 microg. Absence of analgesia without signs or symptoms of systemic toxicity after a maximum of bupivacaine 30 mg defined failed epidural analgesia. All patients with positive EpiTD and negative aspiration received 5 mL of lidocaine 2% epidurally as a second test dose (Lido100TD). The presence of tinnitus and/or metallic taste defined a positive Lido100TD. There were 176 true negatives, 0 false negatives, 14 true positives, and 8 false positives. The sensitivity of EpiTD was 100%, the specificity 96%, the negative predictive value 100%, and the positive predictive value 63%. The prevalence of negative tests was 88%, and the prevalence of positive tests was 12%. The overall accuracy of an EpiTD was 95.5%. We conclude that EpiTD is a reliable test to identify i.v. catheters during the performance of lumbar epidural analgesia in laboring patients.

IMPLICATIONS

Catheters inserted for epidural analgesia in laboring patients may accidentally enter a blood vessel. Local anesthetics injected through these catheters may cause seizures and cardiac arrest. In this study, we concluded that injecting a small amount of epinephrine before injecting a local anesthetic frequently helps to identify these misplaced catheters. Few catheters may actually be in the correct place even after responses to epinephrine.

Epinephrine-induced tachycardia is different from contraction-associated tachycardia in laboring patients

Maternal tachycardic responses to the intravenous injection of epinephrine 15 micrograms were compared with tachycardic responses induced by the pain of labor in a double-blind, prospective study of 15 women in active labor. After placement of an epidural catheter, maternal heart rate was continuously recorded. Each patient received, in uterine diastole, two injections of a test dose (epinephrine 15 micrograms + lidocaine 45 mg) at 2-4 min intervals, once via the epidural catheter and once intravenously in a random fashion. From the maternal heart rate strips, the acceleratory phase (bpm) of epinephrine-induced tachycardic responses (EITRs) and contraction-associated tachycardic responses (CATRs) were calculated. The upper bound of the 99% confidence interval (CI) to discriminate between the two groups was estimated. The acceleratory phase of EITRs was 1.85 +/- 0.61 bpm. The acceleratory phase of CATRs was 0.69 +/- 0.49 (P < 0.0003). The upper bound of the 99% CI was 1.17 bpm. Using this value to discriminate between EITRs and CATRs, all EITRs would be correctly identified. We conclude that on-line analysis of maternal tachycardic responses might be used in laboring women to discriminate between EITRs and CATRs and further improve the accuracy of an epinephrine test dose during the performance of epidural analgesia.

Cervical dural puncture and lumbar extradural blood patch

The authors report the successful treatment of post-dural puncture headache, consequent to a cervical dural puncture, with a lumbar extradural blood patch. The increase in intracranial pressure generated by the injection of autologous blood in the extradural space seems to be the likely mechanism for the prompt relief of post-dural puncture headache. We conclude that extradural injection of autologous blood at the same level of the dural puncture may not be necessary.

Diagnostic accuracy of an intrathecal test dose in epidural analgesia

The authors evaluated the accuracy of an intrathecal test dose (TD) to rule out unintentional subarachnoid injection in a prospective and double-blind study. Twenty-nine unmedicated patients scheduled to receive continuous spinal analgesia for their surgical procedures entered the study. After placement of non-invasive monitoring (ECG, BP and SpO2), an intrathecal catheter was placed in the lumbar area. In the supine position 15 patients in the study group received lidocaine 45 mg + epinephrine 15 mg and 14 patients in the control group received normal saline 3 ml intrathecally. After the injection, a blinded observer assessed the presence of the following signs at one minute intervals for five minutes: sensory loss by pin-prick (P) over the lumbar and sacral dermatomes, ability to raise legs (R), and subjective feeling of warmth (W) and heaviness (H) over the lower limbs. For each sign the sensitivity (SN), specificity (SP), and negative (-) and positive (+) predictive value (PV) were calculated. At four minutes SN reached 100% (CI 78-100%) for R and H, while only R obtained a SP of 93% (CI 66-100%). Using R as detector of intrathecal injection the -PV was 100% and the +PV 25% (assuming a 2% prevalence of unintentional spinal). We conclude that, with our test dose; (a) four minutes are needed to recognize signs of intrathecal injection; (b) leg-raising is a reliable sign; and (c) inquiring about other signs may only decrease the diagnostic accuracy of this test.

Haemodynamic consequences of warm cardiac irrigation during cardiac surgery

Following cardiopulmonary bypass (CPB) and prior to closing the chest, some surgeons irrigate the heart and pericardium with warm saline. This prospective study, using each patient as his own control, evaluated the haemodynamic effects of warm (44 +/- 5 degrees C) irrigation on the heart and pericardium following CPB. Following discontinuation of CPB, a Mon-a-therm model 6500 thermocouple monitor measured the myocardial septum and the irrigating fluid temperatures. Immediately before, during and two minutes after irrigation of the heart and pericardium, we measured heart rate (HR), systemic blood pressure (BP), pulmonary artery pressure (PAP), central venous pressure (CVP), thermodilution cardiac output, and calculated systemic vascular resistance (SVR). During warm irrigation, HR increased from 93 +/- 15 to 101 +/- 13 min-1 and systolic BP increased from 111 +/- 17 to 131 +/- 27 mmHg. After irrigation, HR decreased to 96 +/- 12 min-1 with no change in systolic BP. The calculated SVR after irrigation increased to 1117 +/- 413 dynes.sec.cm-5 from the pre-irrigation value of 821 +/- 243 dynes.sec.cm-5, while cardiac index decreased to 2.4 L.min-1.m-2 from its pre-irrigation value of 2.99 L.min-1.m-2. Warm irrigation of the pericardial pouch causes tachycardic and hypertensive responses in patients undergoing cardiac surgery.

Dissociation of mixed venous oxygen saturation and cardiac index during opioid induction

STUDY OBJECTIVE

To evaluate the independent effects of opioid induction and paralysis on changes in mixed venous oxygen saturation (SvO2).

DESIGN

Prospective, with each patient serving as his or her own control.

SETTING

Cardiac operating rooms of a major U.S. teaching hospital.

PATIENTS

15 elective patients for aortocoronary bypass graft surgery.

INTERVENTIONS

Prior to induction with sufentanil 2 to 3 micrograms/kg (t1), after recovery from succinylcholine 1 to 1.5 mg/kg (t2), and after subsequent paralysis with vecuronium (t3), we recorded cardiac index (VO2), arterial oxygen saturation (SaO2), and SvO2, then calculated oxygen consumption (VO2) and arterial oxygen content (CaO2).

MEASUREMENTS AND MAIN RESULTS

SvO2 increased from 75% at t1 to 82% at t2 (p = 0.03) and to 83% at t3 (p = 0.006). CI decreased from 3.1 L/min/m2 at t1 to 2.5 L/min/m2 at t2 (p = 0.023) and to 2.1 L/min/m2 at t3 (t1 vs. t3, p = 0.019; t2 vs. t3, p = NS). Calculated VO2 decreased from 2.88 ml O2/min/kg at t1 to 2.09 ml O2/min/kg at t2 (p = 0.03) and to 1.87 ml O2/min/kg at t3 (t1 vs. t3, p = 0.002; t2 vs. t3, p = 0.027). CaO2 remained unchanged.

CONCLUSIONS

Opioid anesthesia, not paralysis, increases SvO2. Most of the decrease in VO2 occurs from anesthesia, not paralysis. The direct relationship between CI and SvO2 no longer holds upon induction of anesthesia. Parallel changes in CI cannot be inferred based on SvO2 alone.

Epidural test dose: lidocaine 100 mg, not chloroprocaine, is a symptomatic marker of i.v. injection in labouring parturients

The authors studied the sensitivity (SN) and specificity (SP) of an epidural test dose containing either lidocaine 100 mg or 2-chloroprocaine 100 mg as symptomatic markers of intravascular injection in labouring parturients. In a prospective, double-blind and randomized fashion 48 unmedicated and labouring parturients were equally divided into three groups. After placement of a lumbar epidural catheter the normal saline group (NS) received 5 ml normal saline i.v., the lidocaine group (LD) received lidocaine 100 mg i.v., and the 2-chloroprocaine group (CH) received 2-chloroprocaine 100 mg i.v. All injections were given during uterine diastole. Within the next one to two minutes a blinded observer recorded the patient's perception of the presence of metallic or funny taste, dizziness, and tinnitus. We then calculated SN and SP of each symptom (alone and in combination) along with their positive (+) and negative (-) predictive value (PV). In both groups no symptom alone reached clinically acceptable levels of SN (< 87%). Only in the LD group, tinnitus+taste and dizziness+taste reached a SN of 100% with a SP of 81% and 69% respectively. While the -PV was 100% for both groups of symptoms, the +PV reached 42% for tinnitus+taste and 30% for dizziness+taste. We conclude that lidocaine 100 mg is a sensitive marker of intravascular injection in labouring parturients, and that tinnitus+taste is the most reliable indicator of intravenous injection.

Vomiting after alfentanil anesthesia: effect of dosing method

This double-blind study correlated the association of nausea and vomiting after alfentanil with its method of administration (bolus dose vs continuous infusion). Of 40 women undergoing lower abdominal gynecologic or laparoscopic surgery, 20 received an intravenous alfentanil (30 micrograms/kg) bolus dose for induction of anesthesia, with subsequent bolus doses of 10 micrograms/kg every 10 min, and 20 received the same induction dose delivered over 1 min, followed by an intravenous infusion at 1.0 micrograms.kg-1.min-1. The infusion group experienced more frequent nausea and vomiting than the bolus dose group (50% vs 30%, respectively; P = 0.0001). Laparoscopic surgery affected the incidence of nausea and vomiting independently of the method of alfentanil administration (75% for laparoscopic vs 17% for incisional procedures; P = 0.0001). Laparoscopy and alfentanil infusion combined synergistically to worsen the incidence of nausea and vomiting. We conclude that alfentanil infusion for laparoscopic surgery entails a high risk for nausea and vomiting.

Epidural test dose and intravascular injection in obstetrics: sensitivity, specificity, and lowest effective dose

The authors studied the sensitivity and specificity of several epidural test doses as markers of intravascular injection in laboring patients in a prospective double-blind, randomized study. Fifty-nine parturients were assigned randomly to receive an intravenous injection of either normal saline solution (3 mL, NS group) or 1.5% lidocaine with epinephrine 1:200,000 (1 mL, EPI-5 group; 2 mL, EPI-10 group; or 3 mL, EPI-15 group). The EPI-5 and EPI-10 doses were diluted to 3 mL volume with normal saline solution. All injections were given during uterine diastole. Maternal heart rate was monitored with a pulse oximeter. An observer who was unaware of the study treatment recorded the baseline and the peak maternal heart rate within the first minute after the injection and questioned the patient about tinnitus, dizziness, metallic taste, and palpitations. He then recorded his opinion as to whether the patient had received the saline or the test solution. Analysis of the maternal heart rate showed an average increase (baseline-to-peak criterion) of 8 +/- 10 beats/min (mean +/- SD) in the NS group. In the other groups, the increase was 21 +/- 8 (EPI-5 group), 31.5 +/- 13 (EPI-10 group), and 29 +/- 9 beats/min (EPI-15 group). A baseline-to-peak criterion of greater than 10 beats/min identified all intravascular injections in the EPI-15 (by design) and EPI-10 groups (15 of 15 and 14 of 14, respectively) with a sensitivity of 100%. Specificity was 73% (11 of 15 true negatives).(ABSTRACT TRUNCATED AT 250 WORDS)