Richard M Kaplan

The safety of prehospital naloxone administration by paramedics

We performed a retrospective review to investigate the safety of prehospital naloxone administration by paramedics as part of a protocol for all patients presenting with an acutely depressed level of consciousness (LOC). The prevalence of naloxone-induced vomiting, seizures, hypotension, hypertension, and cardiac arrest was sought from the prehospital records of 813 patients treated during a 12-month period. The mean age of the treated patients was 42.4 +/- 9.7 years. The initial dose of naloxone was 0.4 to 0.8 mg, and the mean total dose was 0.9 +/- 0.6 mg. No patients lost a pulse within ten minutes of receiving naloxone. Two patients (0.2%) experienced a significant drop in systolic blood pressure, and one patient (0.1%) demonstrated a significant rise in systolic blood pressure within five minutes of naloxone administration. Vomiting occurred in two patients (0.2%), and one patient (0.1%) suffered a tonic-clonic seizure within five minutes of naloxone administration. Of the 813 patients treated, 60 patients (7.4%: mean age, 32.3 +/- 6.7 years) were judged to have an improved LOC after naloxone, with 27 (3.3%) regaining a normal LOC. We conclude that in the above doses, naloxone is safe as part of prehospital protocols for paramedics treating patients with an acutely depressed LOC. However, the vast majority of patients treated empirically with naloxone in the field demonstrated no benefit.

Success rates of blind orotracheal intubation using a transillumination technique with a lighted stylet

The technique of guided orotracheal intubation using a lighted stylet depends on the transillumination of the soft tissues of the neck to direct the tube through the glottis and into the trachea. We conducted an operating room study of this technique, recording success rates and intubation times of 50 patients undergoing elective surgery. All patients were intubated successfully, 35 of 50 (70%) on the first attempt, 12 of 15 (80%) on the second attempt, and three of three (100%) on the third attempt. The average time for intubation was 37 seconds. A new design of the lighted stylet method resulted from the experience gained. Intubator training and experience influenced initial success rates, and the cadaver laboratory was of particular value in teaching the technique.

Correct positioning of an endotracheal tube using a flexible lighted stylet

Endotracheal intubation is not without complications, among the most serious of these being misplacement of the endotracheal (ET) tube. Unrecognized esophageal placement is a lethal complication, but even when placed in the trachea, ET tubes can be displaced distally and enter a mainstem bronchus. Correct positioning of an ET tube is usually defined as the placement of the tube within the trachea approximately 5 cm above the carina. Chest x-ray is the most common and a reliable method of demonstrating correct positioning, particularly in ICU patients. Using transillumination by means of a flexible stylet (lightwand), we investigated whether transillumination could position an ET tube consistently within 5 ± 2 cm of the carina. Ten human cadavers of varied weight and body habitus were intubated under direct vision and 10 ml of a radiopaque dye was injected down the tube as a marker for the carina. A premeasured flexible lighted stylet was then inserted into the inplace tube so that the bulb was positioned at the tubes distal opening. The brightest transilluminated glow produced by the bulb was then positioned at the sternal notch. A chest x-ray was taken and the distance of the tube tip from the carina was calculated. In each case the tube tip could be placed consistently at a level 5 ± 1 cm from the carina by observing the maximal transilluminated glow at the sternal notch. We conclude that transillumination of the neck using a flexible lighted stylet can accurately and consistently position an ET tube at an appropriate distance above the carina. Use of this method by nurses, paramedical personnel, and physicians could reduce the need for routine radiographic confirmation of ET tube position in the critically ill and injured.

Myths and pitfalls in emergency translaryngeal ventilation: correcting misimpressions

Translaryngeal jet ventilation has been proven an effective emergency airway alternative. However, confusion exists as to the proper cannulae and oxygen sources for this technique. Our study was designed to determine the delivered volumes of gas using cannulae and oxygen sources recommended in previous reports on translaryngeal jet ventilation. From this, we hope to clarify the proper technique of translaryngeal jet ventilation. Using a variety of oxygen sources and cannulae, peak flow rates were measured using a digital flowmeter. Delivered volumes of gases generated with each combination were then calculated. All of the cannulae tested (standard 16-gauge IV cannulae and larger) provided peak flow rates high enough so that predicted tidal volumes would be adequate to maintain adequate ventilation in apneic adults when a 50-psi source was used. Only a 4-mm tracheal cannula provided comparable values when a bag-valve device was used. No cannulae provided sufficient flow rates to ensure adequate ventilation in apneic adults when a demand-valve mechanism of 60 cm H2O driving pressure served as the source. Our observations were consistent with previous clinical studies and suggest that standard translaryngeal jet ventilation cannulae (12 to 16 gauge) must be connected to an oxygen source of 50 psi in apneic adults. Demand-valve devices do not provide sufficient driving pressures for these cannulae. A cannula of 4 mm ID should be placed if only a bag-valve device is available for ventilation.

Transcutaneous pacing for bradyasystolic cardiac arrests in prehospital care

To test the efficacy of transcutaneous pacing in prehospital bradyasystolic arrest, we applied an external transcutaneous pacing device to patients with asystole, pulseless idioventricular rhythms (PIVR), and pulseless bradycardias. Pacemaker units were carried by emergency medical services (EMS) physicians and specially trained EMS personnel. Patients were followed to determine hospital course and outcome. Of the 112 patients evaluated, information to adequately document the presence or absence of electrical capture was available in 105 cases. Fifty-five (52%) of these cases demonstrated electrical capture; 9 of 112 patients (8%) recovered pulses. Of those in asystole, 26 of 50 (52%) showed electrical capture, while the rate was 60% for those with PIVR (24 of 40 patients) and complete heart block (CHB) (3 of 5 patients), and 25% for other pulseless bradycardias (2 of 8 patients). Pulses developed following capture in five of 55 patients (9%) in asystole and in four of 44 patients (9%) with PIVR. No patient with CHB or other bradycardias developed a pulse. No patients survived to be discharged from the hospital. The average time to application of the pacing device was 29 minutes after loss of pulse. Our data strongly suggest that delayed use of the transcutaneous pacing device does not improve the dismal survival rates of patients who suffer bradyasystolic cardiac arrest. Further studies should be directed toward investigating survival rates in patients paced immediately after the onset of cardiac arrest.

Nasotracheal intubation using a flexible lighted stylet.

Nasotracheal intubation is an essential skill for clinicians involved in the care of acutely ill or injured patients. Unfortunately, it has the dangers and difficulties of any blind technique. Although usually performed in the awake patient, nasotracheal intubation has also been used in the apneic patient. Transillumination of the soft tissues of the neck with a lighted stylet has been shown to be a reliable method of orotracheal intubation. The usefulness of a longer, flexible lighted stylet as an aid to nasotracheal intubation in the apneic patient has been examined. Eighty patients, who were paralyzed, apneic, and about to undergo nasotracheal intubation for elective ear, nose, and throat or maxillofacial surgery were randomized to be nasotracheally intubated blindly or with a stylet by an emergency medicine resident or anesthesiologist. Sixty-three percent intubated in the lighted-stylet group and 41% in the blind nasotracheal intubation group were successfully intubated. There were no significant differences in the time needed to intubate or the number of attempts. There were notable differences in the success rates of individual intubators with each technique. Although not statistically significant, our results suggest a useful role for the lighted stylet in nasotracheal intubation in the apneic patient.

Methemoglobin levels following intravenous lidocaine administration

Methemoglobin levels were obtained before and after administration of IV lidocaine in 40 cardiac patients. Patients were given a 1-mg/kg bolus of IV lidocaine hydrochloride, started on a maintenance infusion at 2.0 mg/min, and given a second bolus of lidocaine of 0.5 mg/kg 15 minutes after the initial bolus. The maintenance infusion was adjusted from 1 to 4 mg/min according to clinical needs. Methemoglobin levels were drawn at zero, one, and six hours, and lidocaine levels were drawn at one and six hours after the initial bolus. Elevation of methemoglobin levels after lidocaine administration was statistically significant (P less than .05), but not clinically significant. The highest methemoglobin level obtained was 1.2%. Only one other patient had a level above 1%. No patient developed either signs of lidocaine toxicity or toxic levels of methemoglobin. Routine determination of methemoglobin levels is not clinically indicated following routine lidocaine administration. It may have some as-yet-undetermined value in lidocaine-toxic patients.

Oxygen enrichment of bag-valve-mask units during positive-pressure ventilation: A comparison of various techniques

Bag-mask devices are used frequently to provide patients with positive-pressure-assisted ventilation. To increase the percentage of oxygen delivered (FDO2) from the bag, supplemental oxygen must be provided by way of an oxygen inlet nipple attached to the unit. Using ten medical volunteers and a test lung with oxygen analyzer, we studied the effect of several variables on the FDO2 and determined the most effective reservoir that would provide the highest consistent FDO2 from the ventilating port of the bag. An FDO2 of 1.00 was consistently provided by the 2.5-L bag reservoir and a demand-valve set-up attached to the reservoir port of the ventilating bag. Bag refill time significantly affected the FDO2 when no reservoir or corrugated tube reservoirs were used. Corrugated tube reservoirs were found to be more sensitive to all variations in ventilatory technique and to oxygen flow rates. From our findings we recommend that corrugated tube reservoirs not be used for oxygen supplementation, as they are sensitive to variations in ventilatory technique and cannot alert clinicians to problems with oxygen flow. While both the 2.5-L bag reservoir and demand-valve provide a consistent FDO2 of 1.00, the demand valve has the advantage of audible filling of the ventilating bag as well as being compact and independent of ventilatory technique.

A Comparative Study of Five Transcutaneous Pacing Devices in Unanesthetized Human Volunteers

Transcutaneous Pacing (TCP) is a rapidly applied “non-invasive” technique that can be used successfully in the hospital, emergency department or field setting (1–9). Although the technique has been studied for three decades (7), it is only in the last few years that commercial units have been widely available. Improvements in pad design (particularly the development of non-metallic electrodes) and pulse characteristics (a pulse width of greater than 20 msec.) have allowed the development of units which may provide high capture rates with a level of discomfort which is tolerable in the conscious patient. Transcutaneous pacing may obviate the need for emergency transvenous pacing; further, it is easily adaptable to the field setting although early application appears to be needed for success (1,2). No study has compared the relative effectiveness of different TCP units, and there are no published data on some of the devices. The purpose of this investigation was to compare the functions of five different external pacemaker units on ten volunteers, in order to determine: 1) what percent of subjects could be captured within the limits of tolerability (the capture rate); 2) how much current was required by each unit to capture (the capture threshold); and 3) the degree of discomfort produced by each pacemaker at the capture threshold.

Methemoglobin levels following sublingual nitroglycerin in human volunteers

Sublingual nitroglycerin 0.8 mg every five minutes for a total of 4.8 mg was administered to 11 healthy volunteers. One volunteer had to withdraw due to a hypotensive bradycardic reaction after 2.4 mg. In the remaining subjects, methemoglobinemia over the next hour never significantly increased from baseline levels, reaching a peak of only 0.71%. We conclude that commonly used doses of sublingual nitroglycerin do not induce significant methemoglobinemia and that nitroglycerin would not be useful in the treatment of cyanide poisoning.