Arterial hypoxaemia following premedication in patients with coronary artery disease

Association of intravenous morphine use and outcomes in acute coronary syndromes: results from the CRUSADE Quality Improvement Initiative

BACKGROUND

Although intravenous morphine is commonly used for the treatment of chest pain in patients presenting with non-ST-segment elevation acute coronary syndromes (NSTE ACS), its safety has not been evaluated. The CRUSADE Initiative is a nonrandomized, retrospective, observational registry enrolling patients with NSTE ACS to evaluate acute medications and interventions, inhospital outcomes, and discharge treatments.

METHODS

The study population comprised patients presenting with NSTE ACS at 443 hospitals across the United States from January 2001 through June 2003 (n = 57,039). Outcomes were evaluated in patients receiving morphine versus not and between patients treated with morphine versus intravenous nitroglycerin.

RESULTS

A total of 17,003 patients (29.8%) received morphine within 24 hours of presentation. Patients treated with any morphine had a higher adjusted risk of death (odds ratio [OR] 1.48, 95% CI 1.33-1.64) than patients not treated with morphine. Relative to those receiving nitroglycerin, patients treated with morphine also had a higher adjusted likelihood of death (OR 1.50, 95% CI 1.26-1.78). Utilizing a propensity score matching method, the use of morphine was associated with increased inhospital mortality (OR 1.41, 95% CI 1.26-1.57). The increased risk of death in patients receiving morphine persisted across all measured subgroups.

CONCLUSIONS

Use of morphine either alone or in combination with nitroglycerin for patients presenting with NSTE ACS was associated with higher mortality even after risk adjustment and matching on propensity score for treatment. This analysis raises concerns regarding the safety of using morphine in patients with NSTE ACS and emphasizes the need for a randomized trial.

The effect of supplemental oxygen on the incidence of hypoxaemia after premedication in patients undergoing cardiac surgery

Opiate premedication may cause significant respiratory depression, particularly when other sedative agents such as scopolamine or benzodiazepines are added. This can cause hypoxaemia with potential for worsening myocardial ischaemia in cardiac surgery patients. The aim of this study was to investigate the incidence of hypoxaemia (SpO2 < 90%) in elective patients undergoing cardiac surgery and to assess the efficacy of supplemental oxygen in preventing it. One hundred elective patients without significant respiratory disease or cardiac failure, who received both an opiate and a sedative premedication, were prospectively randomized to receive either oxygen via a facemask at 4 l/min or no oxygen. Continuous arterial oxygen saturation was recorded using a pulse oximeter from the time of premedication until the patient arrived in theatre. An SpO2 < 90% was recorded as a significant event and oxygen was administered to the patients. Six patients were excluded because of equipment failure or protocol violations. The patient groups were comparable with respect to patient demographics, premedication type and dose or the duration of monitoring. In patients receiving oxygen (n = 48) there were no episodes of hypoxaemia (0%). In patients not receiving oxygen (n = 46) there were 14 episodes of hypoxaemia (30%, P < 0.0001). We conclude that there is a significantly high incidence of hypoxaemia in cardiac surgery patients following combined opiate and sedative premedication and that it can be reduced by the routine administration of supplemental oxygen.

A comparison of morphine-perphenazine and midazolam on preoperative sedation and arterial oxygen saturation

The effectiveness of midazolam and a mixture of morphine-perphenazine premedication to produce sedation and their effects on preoperative oxygen saturation (SaO2) were examined. Eighty-five patients whose SaO2 measured with a pulse oximeter was greater than 90% and who were not receiving narcotic sedatives or oxygen were randomized to three groups. Each patient had his SaO2 recorded before premedication with placebo (saline), midazolam 0.08 mg.kg-1 or morphine 0.15 mg.kg-1 with perphenazine 2.5-5.0 mg im. From 30-90 min later, prior to anaesthesia SaO2 was repeated, and a sedation score was obtained by a blinded observer using a seven point scale. Median sedation scores were greater for midazolam (4) than for morphine-perphenazine (2) and placebo (1) (P less than 0.0001). As well, there was a decrease in the SaO2 in the morphine-perphenazine group (1.7 +/- 2.7%, P less than 0.001) but not in the midazolam and placebo groups (0.1 +/- 2.3%, -0.8 +/- 2.1%). In conclusion midazolam produced greater sedation than morphine-perphenazine and placebo without effect on SaO2 whereas morphine-perphenazine showed a decrease in SaO2 preoperatively.

Effect of premedication on arterial blood gases prior to cardiac surgery

The effect of premedication on arterial blood gas tensions was studied in thirty adult surgical patients with valvular disease. They were divided into three groups, each group having a different premedication regimen. Blood gas tensions were compared in these patients when awake on the night before surgery, asleep, after premedication and just prior to induction of anaesthesia. Samples were taken while the patient breathed air and each patient acted as his/her own control. The patients were randomised into one of three premedication regimens: 1. intramuscular lorazepam, 2. intramuscular morphine and hyoscine (scopolamine) and 3. oral lorazepam plus intramuscular morphine and hyoscine. There was a statistically significant though not clinically significant rise in PaCO2 and fall in pH following premedication with lorazepam, morphine and hyoscine. There was also a significant fall in PaO2 associated with morphine and hyoscine premedication which was greater than that which occurred with unsedated sleep. Patients who are to undergo cardiac valvular surgery should receive supplementary oxygen following premedication and during transfer to the operating room.

The effect of a standardized premedication on oxygen saturation in the cardiac patient before transfer to the operating room

The effect of premedication with morphine and scopolamine on arterial hemoglobin oxygen saturation (SaO2) was measured continuously in 26 undisturbed patients in their hospital rooms before coronary artery bypass surgery. Two hours preoperatively each patient received morphine, 0.1 mg/kg, and scopolamine, 0.2 or 0.4 mg. SaO2 was continuously recorded using pulse oximetry from one-half hour before premedication until 1 1/2 hours after premedication. The lowest SaO2 measured both the evening before surgery and one-half hour before premedication was 95% +/- 0.5% (mean +/- SEM). After administration of premedication, the lowest SaO2 for the patient population decreased to 93% +/- 0.4% (P less than 0.001 compared with that before premedication), and occurred 52 +/- 2 minutes after premedication was given. Two patients (8%) had an SaO2 less than 90% (lowest SaO2 for both was 88%). It is concluded that the dose of morphine/scopolamine premedication used was associated with a low risk of clinically important hypoxemia in the patient population studied.

Continuous oxygen saturation monitoring during cardiac catheterization in adults

Arterial hypoxemia may contribute to morbidity during cardiac catheterization. Therefore, we measured arterial hemoglobin oxygen saturation (SaO2) continuously using pulse oximetry in 29 patients (age range, 21 to 83 years) undergoing cardiac catheterization. Baseline SaO2 was 96 +/- 0.4 percent. All patients had a decrease in SaO2 at some time during the procedure. Eleven patients (38 percent) had episodes of arterial hypoxemia, defined as a decrease in SaO2 below 90 percent. In these 11 patients, the mean number of episodes of hypoxemia was 16 +/- 7, and the mean duration of each episode was 53 +/- 25 seconds. Multiple stepwise regression analysis showed that the minimum SaO2 during catheterization for any patient was significantly associated with the baseline SaO2, duration of the procedure, and end-diastolic volume (EDV) as described by the following regression equation: minimum SaO2 = 46.8 - 0.0580 (duration of procedure in minutes) + 0.5362 (baseline SaO2) - 0.0159 (EDV). Based on our finding of arterial hypoxemia in greater than one third of our patients, we would consider continuous SaO2 monitoring or supplemental oxygen during cardiac catheterization, especially for those patients with poor ventricular function or low resting SaO2 or those expected to have long procedures.

Hypoxaemia after premedication in cardiac patients. Glycopyrronium compared with hyoscine

Arterial blood gases were analysed before and approximately one hour after premedication in two groups of 10 patients awaiting cardiac surgery. One group received intramuscular papaveretum and hyoscine, the other papaveretum and glycopyrronium. Similar, small but statistically significant reductions in mean arterial oxygen tension and oxygen saturation, and increases of arterial carbon dioxide tension occurred in both groups. Hypoxaemia in individual patients was unpredictable and in some was clinically relevant.

Cardiorespiratory effects of nalbuphine and morphine premedication in adult cardiac surgical patients

Premedication for cardiac surgical patients attempts to achieve relief of anxiety with minimal or no cardiorespiratory changes. Nalbuphine (NUBAIN) and morphine produced similar decreases in respiratory rate (1-3 breaths per min) and PaO2 (averaging 1.34 kPa), and increases in arterial PaCO2 (averaging 0.56 kPa). Cardiovascular changes were not seen with either agent. A similar degree of sedation and relief of anxiety was achieved with both drugs. Side effects were minimal and infrequent. Nalbuphine produces respiratory depression and sedation without cardiovascular changes which is comparable to an equivalent dose of morphine in patients with either valvular or coronary artery disease.

Diazepam sedation reduces functional residual capacity and alters the distribution of ventilation in man

We measured ventilation and static lung volumes in five fit volunteers in the right lateral decubitus position, while they were fully awake and while sedated with diazepam. We also assessed the distributions of ventilation and perfusion in the lungs, using inhalations and intravenous injections of xenon-127. Diazepam, 0.04 mg . kg-1, was administered every three to five minutes as required to induce and maintain a state of sedation which was moderately heavy. Total doses ranged from 0.16 to 0.38 mg . kg-1. Sedation did not alter minute ventilation, but reduced tidal volume, increased breathing frequency and reduced functional residual capacity slightly. Sedation also diminished the normal gradient of ventilation from non-dependent to dependent regions of the lungs. Spontaneous episodes of very small tidal volume breathing during sedation were associated with a marked reduction or cessation of ventilation of the most dependent region of the lungs. There were no sedation-related changes in the distribution of perfusion. These effects of moderately heavy sedation may contribute to the hypoxaemia and impairment of pulmonary gas exchange often present during recovery from general anaesthesia.

The effects of vascular catheterization upon heart rate and blood pressure before aorto-coronary bypass surgery

Ten patients presenting for aorto-coronary bypass surgery were premedicated with their regular dose of propranolol and nitrates and diazepam 0.15 mg x kg-1 by mouth, morphine 0.15 mg x kg-1 and scopolamine 0.4 mg intramuscularly, 60 to 90 minutes before arrival in the operating room. Venous, arterial and pulmonary artery catheterizations were done under local anaesthesia. No significant changes were noted in systolic blood pressure and rate pressure product. Heart rate was decreased after internal jugular puncture and for the remainder of the study. PaCO2 increased and PaO2 decreased from values obtained the day before operation. Cardiovascular stability during vascular catheterization was achieved by emphasizing a detailed preoperative explanation, maintenance of beta-blockade up to the time of operation, substantial sedative premedication, and the liberal use of local anaesthesia.

Mechanism of nitroglycerin-induced hypoxemia

We and others have previously demonstrated a consistent significant decline in arterial oxygen tension (PaO2) after sublingual nitroglycerin in premedicated and unpremedicated patients both with and without coronary artery disease and/or obstructive ventilatory disease. Thus, in our 19 patients, PaO2 fell by an average of 17% (12 mm Hg), mean systemic arterial pressure by 19% (17 mm Hg), pulmonary arterial pressure by 38% (6 mm Hg), pulmonary arterial occlusive pressure by 62% (5.3 mm Hg), and cardiac index by 16% (0.37 liter/min/m2) [P less than 0.001 for each] after nitroglycerin. Previous experimental studies suggest that the mechanism for the reduction of PaO2 may be relief of hypoxic pulmonary vasoconstriction with an increase in perfusion to poorly ventilated or nonventilated regions of the lungs. To examine this possibility, pulmonary vasodilatation was precluded by administration of a pulmonary vasoconstrictor (phenylephrine) simultaneously with nitroglycerin in nine patients with coronary artery disease. No significant change was observed in systemic or pulmonary arterial pressure, pulmonary arterial occlusive pressure, or systemic and pulmonary vascular resistance, and PaO2 did not decline. In ten other patients with coronary artery disease, the intrapulmonary right-to-left shunt fraction was determined before and after sublingual nitroglycerin; only a minimal increase in shunt fraction of 1.4% was observed, quantitatively insufficient to account for the observed decline in PaO2, thus excluding a predominant effect of nitroglycerin on nonventilated alveoli as a cause of the hypoxemia. We conclude that the reduction of PaO2 after nitroglycerin administration is attributable to pulmonary vasodilatation with a relative increase in perfusion of poorly ventilated lung units.