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Biomedical subjects

B Milne

Publications and source records attributed to B Milne.

At least 37 records · Page 2Linked to original sources
PubMed1997

Use of differential normal pulse voltammetry for the measurement of locus coeruleus catecholaminergic metabolism in an acute anaesthetized rodent model of allodynia: effect of mexiletine.

Neuropathic pain can be triggered by non-painful stimuli (e.g., light touch), a sensory abnormality termed allodynia. The acute blockade of spinal glycine receptors with intrathecal strychnine induces a reversible allodynia-like state in the rat. We describe the application of in vivo differential normal pulse voltammetry with carbon fibre micro-electrodes for monitoring the catechol oxidation current (CAOC) of the locus coeruleus (LC) in the strychnine model of allodynia. In addition, we tested the effect of mexiletine, a drug useful in the management of clinical neuropathic pain in this model. Our results show that somatosensory processing in the spinal cord of urethane-anaesthetized rats is radically altered during glycine receptor blockade such that the normally innocuous stimulus of hair deflection causes the marked activation of the LC as determined using in vivo differential normal pulse voltammetry. Mexiletine suppressed the LC and cardiovascular responses of strychnine induced allodynia. Results of this study indicate that LC CAOC, an index of LC neuronal activity: (a) is a sensitive biochemical index of strychnine-allodynia; (b) is temporally correlated with the cardiovascular and motor responses evoked by hair deflection during glycine receptor blockade; and (c) can be used to quantitate allodynia in the strychnine model.

Anesthesia↗
PubMed1997

Epidural analgesia for labour and delivery: informed consent issues.

OBJECTIVE: Many anaesthetists believe that informed consent for epidural analgesia during labour is inadequate. Patients are perceived to be poorly informed and unable to cope with the information given during labour for informed consent. We reviewed these two hypotheses: A) to define complications for which patients want clear information: B) to quantify the influence of pain, anxiety, opioid premedication, and the importance of level of education, on a patient's level of satisfaction with regard to the consent process: and C) to assess how satisfactory epidural pain relief correlates with satisfaction with the consent process. METHODS: Sixty patients were surveyed during the first two months after vaginal delivery by two interviewers. Questions related to demographics, severity of labour pain, level of satisfaction with the epidural anaesthetic, risk of complications and satisfaction with information received were either categorical or scored on a scale from 0 to 10. RESULTS: All epidural related complications were considered important to disclose (8.4/10). The level of satisfaction with the consent process was 8.1/10. Patient satisfaction was not affected by opioid premedication, anxiety, pain score, education group or level of pain relief. CONCLUSION: Patients indicated they should be informed of all possible complications associated with epidural analgesia, regardless of severity or risk. In contrast to reports in the literature, non disclosure of serious risks during labour was not acceptable to parturients.

Adult↗
PubMed1997

Cardiac output estimation by visual inspection vs thermodilution during cardiac surgery.

PURPOSE: The objectives of this study were: 1) to compare the estimated cardiac output (CO) by visual inspection with objective measurements by thermodilution: 2) to compare the estimated systemic vascular resistance (SVR) with objective measurements by thermodilution; and 3) to assess whether management of the patient, based on subjective values, would have differed from the management of the patient based on the objective values. METHODS: A non-randomized, prospective, blinded study was conducted at a tertiary care university hospital. Following institutional ethics approval, 35 patients undergoing cardiac surgery, with pulmonary artery catheter (PAC) monitoring, were studied. Prior to the measurement of CO by thermodilution, but after separation from cardiac pulmonary bypass, the CO and SVR were estimated by the anaesthetist and the surgeon. Bland and Altman's method was used for statistical analysis. RESULTS: Surgeons' estimates of CO were comparable with the objectively measured thermodilution measures: in each case (100%), the difference between the subjective estimate and the objective measurement was less than two standard deviations from the mean difference of the two methods. Anaesthetists' estimates, by visual inspection, were also comparable with the objectively measured thermodilution values; 94.6% of cases. The surgeons' and anaesthetists' estimates of SVR were also comparable with the thermodilution measures in all cases. Management based on subjective values would have differed from those based on objective values in only 8.6% of cases. CONCLUSION: An advantage of cardiac surgery is the ability to observe the heart and assess its performance visually. This study demonstrated that estimates of CO and SVR by clinical observation are comparable with the pulmonary artery catheter's derived values.

Aged↗
PubMed1997

Extreme arterial blood pressure differentials in a patient with Takayasu's arteritis.

PURPOSE: To describe the extreme arterial blood pressure differentials in a patient with Takayasu's arteritis and its implications for the preservation of cerebral perfusion during anaesthesia. CLINICAL FEATURES: A 26-yr-old woman with Type III Takayasu's arteritis presented with a tentative diagnosis of mesenteric ischaemia. Determination of systolic arterial blood pressure assisted by oximetry revealed pressures of 114 mmHg in the left and 90 mmHg in the right arm while direct arterial line pressure monitoring of the left posterior tibial artery showed a pressure of 322/113 mmHg. Following induction of anaesthesia with thiopentone and succinylcholine and maintenance with N2O, isoflurane and fentanyl, posterior tibial arterial pressures were maintained (low of 213/96 mmHg) to maintain cerebral blood flow despite surgical requests to lower blood pressure. Epidural local anaesthesia was not considered for intra- or postoperative management due to the regional differences in blood pressure and the effect that sympatholysis may have had on cerebral perfusion. CONCLUSION: In patients with Takayasu's arteritis, extreme arterial blood pressure differentials may exist which may affect regional blood flow, and monitoring of both upper and lower extremity arterial blood pressure should be considered.

Adult↗
PubMed1997

The natural history of depression and the anxiety disorders in older people: the Islington community study.

BACKGROUND: This study reports the outcome of depression and anxiety disorders in older people. METHODS: Follow-up of 165 subjects age 65 or over, initially identified in a community study in inner London as depressed or having an anxiety disorder. RESULTS: 117 subjects still living in the area; 25 had died. Death was predicted only by activity limitation at first interview and not by other demographic or morbidity variables. Eighty-six subjects reinterviewed; 21 males, 65 females. Of the depressed, 34% had recovered, 39% were depressed and 27% were dead. Predictors from initial interview of continuing depression were female gender and more severe depression. Of those with phobic anxiety, 16% had recovered, 18% died and 66% were still phobic. Predictors of continuing phobic anxiety from initial interview were female gender and "stand-alone" phobic anxiety, i.e., not being depressed at initial interview. Sixty percent of those with early onset phobias had specific phobias; 82% of those with late-onset phobias had agoraphobia. Twenty-two subjects were prescribed psychotropics. The only significant predictor of psychotropic prescription was having sleep disturbance at initial interview. A low score on life satisfaction was significantly correlated with depression but not with phobic disorder. A high score was correlated with not having a current psychiatric disorder. LIMITATIONS: Some subjects were lost to follow-up. Those on psychotropics were particularly likely to refuse an interview. CONCLUSION AND CLINICAL RELEVANCE: In older people, neither depression nor the anxiety disorders generally remit spontaneously. Those with a particularly poor prognosis are women and those with a more severe depression. Agoraphobia may be precipitated in older people by stressful events and interferes with life satisfaction. There is potential for increased pharmacological treatment of older people with affective disorders.

Age Factors↗
PubMed1996

Nitric oxide synthase inhibitors attenuate acute and chronic morphine withdrawal response in the rat locus coeruleus: an in vivo voltammetric study.

Previous studies have demonstrated that activation of N-methyl-D-aspartate (NMDA) and non-NMDA receptors contributes to the hyperactivity of noradrenergic neurons of the locus coeruleus (LC) associated with opioid and non-opioid drug withdrawal syndromes. Using an in vivo voltammetric approach, we have examined the role of nitric oxide (NO), which mediates NMDA receptor function, in this withdrawal-induced LC hyperactivity. In the anaesthetized rat, acute morphine treatment (10 micrograms, i.c.v.) suppressed (55.7 +/- 4.4% of baseline) the catechol oxidation current (CA-OC) recorded from the LC using differential normal pulse voltammetry (DNPV). A subsequent intravenous injection of naloxone (2 mg/kg, i.v.) reversed the drug-induced inhibition of LC response and produced an increase (118.9 +/- 2.3% of baseline) in CA-OC above baseline, indicative of an acute withdrawal response. Systemic (100 mg/kg) and intracerebroventricular (i.c.v.) (100 micrograms) pretreatment of animals with the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) blocked the naloxone-induced LC withdrawal response without influencing the inhibitory effect of morphine on LC activity. In animals chronically infused with morphine (15 micrograms/h, i.c.v., 5 days) a naloxone challenge (2 mg/kg, i.v.) produced significant increase (253.7 +/- 19.3% of baseline) in CA-OC signal. This LC withdrawal response was significantly reduced by pretreatment with L-NAME (100 micrograms, i.c.v.) or N omega-nitro-L-arginine (L-NOARG 10 micrograms, i.c.v.). In unanaesthetized animals pretreated with chronic morphine, systemic (100 mg/kg) and central L-NAME (100 micrograms) pretreatment suppressed some of the behavioural signs of withdrawal precipitated by naloxone (10 mg/kg) injection. As doses of the NOS inhibitors used in this study have previously been reported to produce significant inhibition of brain NOS activity, their effect on opioid withdrawal response most likely is due to NOS inhibition. The results of this study indicate that NO plays an intermediary role in the LC neuronal hyperactivity associated with both acute and chronic morphine withdrawal.

Analysis of Variance↗
PubMed1996

Innocuous hair deflection evokes a nociceptive-like activation of catechol oxidation in the rat locus coeruleus following intrathecal strychnine: a biochemical index of allodynia using in vivo voltammetry.

Blockade of spinal glycinergic inhibition with intrathecal (i.t.) strychnine induces a reversible allodynia-like state in both conscious and lightly-anaesthetized rats. Since the locus coeruleus (LC) is activated by noxious stimuli, we determined the effect of non-noxious hair deflection (HD) on noradrenergic neuronal activity in the LC of rats treated with i.t. strychnine. Differential normal pulse voltammetry was used to measure the catechol oxidation current (CA.OC), an index of LC activity. Rats were maintained in a light plane of anaesthesia with i.v. urethane and i.t. strychnine (40 micrograms) was injected near the L1-L2 segment. HD, applied to the caudal dermatomes affected by i.t. strychnine, evoked a significant increase (max. 141 +/- 7%, n = 5, P < 0.05) in CA.OC and mean arterial pressure as compared to baseline (no strychnine). In contrast, HD had no significant effect on CA.OC or mean arterial pressure in the saline-treated rats (n = 5). Pre-treatment with i.t. MK801 (30 micrograms) significantly blocked the increase in CA.OC and mean arterial pressure evoked by HD in strychnine-treated rats. The results of this study indicated that HD, in the presence of i.t. strychnine but not saline, can evoke noradrenergic activity in the LC of lightly anaesthetized rats. This effect on the LC is: (1) comparable to that observed with noxious stimulation without i.t. strychnine; (2) segmentally localized, corresponding to the spinal site of strychnine injection; and (3) mediated by spinal NMDA receptors, consistent with the role of excitatory amino acids in sensory transmission. These data provide the first neurochemical evidence that HD, in the presence of i.t. strychnine, is a nociceptive event, supporting the use of this preparation as an experimental model of allodynia.

Animals↗
PubMed1996

Delayed bilateral spinal anaesthesia following interscalene brachial plexus block.

PURPOSE: To present a case of delayed neuraxial blockade after interscalene brachial plexus block. CLINICAL FEATURES: A 65-yr-old lady presenting for radial head excision underwent a right interscalene block using bupivacaine and lidocaine. She experienced excellent anaesthesia and had stable vital signs for the duration of surgery. However, after 65 min, she developed signs of bilateral neuraxial block, progressing over the following hour to involve the cervical to lumbar dermatomes, with sparing of the phrenic nerves. The patient remained alert and communicative throughout with haemodynamic stability. Two days following the block, the patient experienced severe frontal and occipital pain, typical of a post dural puncture headache, which responded to fluids and recumbency. CONCLUSION: This example of delayed central neural blockade complicating interscalene block is presented in contrast to other reports, which have usually occurred promptly after injection, accompanied by complete sensory and motor block requiring cardio-respiratory support. The presumed mechanism of the delayed onset of bilateral neuraxial spread was a dural cuff puncture with slow CSF spread from a plexus sheath "depot" of local anaesthetic.

Aged↗
PubMed1996

Lower body nerve stretch: a role in essential hypertension or pre-eclampsia?

Despite the relatively high incidence of essential hypertension and pregnancy-induced hypertension, the etiologies of these disorders remain enigmatic. A link between stretching of neural structures in the lower body and the induction of hypertension in these disorders is hypothesized. Hypertension has been documented in patients undergoing femoral and tibial lengthening procedures; in experimental models the stretching of lower extremity nerves appeared to be responsible for the increase in blood pressure with bone lengthening. The upright posture of humans puts an added strain on nerves and an increased pressure on lumbar disks may put increasing tension on the nerve roots. The resultant nerve stretch in pregnant women may be exacerbated by the hormone relaxin. A possible link between the stretching of neural structures and the genesis of essential hypertension or pre-eclampsia/eclampsia is hypothesized.

Bone Development↗
PubMed1995

Involvement of excitatory amino acid pathways in the expression of precipitated opioid withdrawal in the rostral ventrolateral medulla: an in vivo voltammetric study.

Previous studies have shown that catecholaminergic neurons in the rostral ventrolateral medulla (RVLM) become hyperactive during opioid withdrawal. In the present study, the role of excitatory amino acid pathways in the expression of opioid withdrawal in the RVLM was examined by using differential pulse voltammetry (DNPV) to measure changes in the catecholamine oxidation current (CA.OC) following naloxone challenge in rats treated with acute or chronic morphine. Acute morphine (10 micrograms i.c.v.) significantly reduced the CA.OC signal in the RVLM and the mean arterial pressure to 37.1 +/- 6.6% and 21.1 +/- 3.5% below baseline, respectively. Naloxone (1 mg kg-1 i.v.) reversed the morphine effect and produced a significant increase in the CA.OC signal to 25.6 +/- 15.2% above baseline. In animals treated with chronic morphine (10 micrograms h-1 i.c.v., 5 days), naloxone (1 mg kg-1 i.v.) produced a significant increase in the CA.OC signal to 54.2 +/- 16.5% above baseline. Both the nonselective excitatory amino acid antagonist, gamma-D-glutamylglycine (DGG, 200 micrograms i.c.v.) and the selective NMDA antagonist, D(-)-amino-7-phosphonoheptanoic acid (D-APH, 25 micrograms i.c.v.) attenuated the naloxone-induced increase in the CA.OC by 50.7% and 46.0% respectively. In morphine naive animals, DGG and D-APH depressed the CA.OC by 42.8 +/- 8.7% and 17.7 +/- 9.8%, respectively. To the extent that the CA.OC is an index of neuronal activity, these results suggest that RVLM hyperactivity during morphine withdrawal is dependent, in part, upon activation of NMDA receptors.

Animals↗
PubMed1995

Prophylaxis against the systemic hypotension induced by propofol during rapid-sequence intubation.

The objective of this study was to determine the effectiveness of two prophylactic approaches against the anticipated hypotension induced by propofol during rapid-sequence intubation. Thirty-six male or female nonpremedicated ASA class I-II patients aged 21-60 yr undergoing elective outpatient surgery were included in the study. Patients were randomly allocated to receive pre-induction ephedrine sulphate (70 micrograms x kg(-1)iv), pre-induction volume loading (12 ml x kg(-1) Ringer's lactate) or no treatment. Rapid-sequence intubation with cricoid pressure was then performed with propofol (2.5 mg. x kg(-1)) and succinylcholine (1.5 mg x kg(-1). The lungs were subsequently ventilated with 0.25-0.5% isoflurane in a 2:1 N2O/O2 mixture. Vecuronium was given once neuromuscular function had recovered from the succinylcholine. Heart rate and systemic arterial blood pressure were measured non-invasively before induction, after propofol administration and every minute for ten minutes after intubation. Pre-induction volume loading prevented the hypotension observed before surgical stimulation in control and ephedrine groups. Moreover, pre-induction volume loading was not associated with increases in heart rate after intubation as was ephedrine administration. The intubating conditions were excellent to satisfactory in most patients and the overall incidence of adverse events during intubation was mainly due to pain during injection of propofol. The present study showed that preoperative volume loading is more efficacious than pre-induction administration of ephedrine sulphate in maintaining haemodynamic stability during rapid-sequence induction with propofol and succinylcholine. In addition, propofol in combination with succinylcholine provides excellent conditions for rapid-sequence intubation.

Adult↗
PubMed1994

The role of excitatory amino acids in the expression of precipitated acute and chronic clonidine withdrawal: an in vivo voltammetric study in the rat locus coeruleus.

It has been previously shown that activation of excitatory amino acid (EAA) pathways contributes to hyperactivity of the locus coeruleus (LC) in antagonist precipitated opioid withdrawal. In this study, using differential normal pulse voltammetry to monitor catechol oxidation as an index of the activity of the LC, the role of EAA pathways in antagonist precipitated withdrawal after acute and chronic clonidine treatment was examined. Intracerebroventricular clonidine (10 micrograms i.c.v.) significantly reduced LC activity to 54.4 +/- 3.1% of baseline 45 minutes following the injection. Subsequent systemic injection of the selective alpha 2 receptor antagonist atipamezole (0.2 mg/kg i.v.) or yohimbine (0.5 mg/kg i.v.) resulted in a rapid reversal of the depressant effects and a significant increase in LC activity above baseline. Pretreatment with the non-selective EAA receptor antagonist gamma-D-glutamylglycine (DGG) (50 micrograms i.c.v.) attenuated the atipamezole-induced rebound response of the LC but not the reversal of clonidine action. However, both the yohimbine-induced rebound and reversal of clonidine effects were attenuated by DGG treated animals. In chronic clonidine treated animals (2, 5, 7, 10 micrograms/h i.c.v., 5 days), a challenge with atipamezole (0.2 mg/kg i.v.) produced an immediate increase in LC activity, blood pressure and heart rate. The magnitude of these responses was dependent on the dose of clonidine. The atipamezole-induced increase in LC activity and blood pressure was significantly attenuated by pretreatment with DGG (200 micrograms i.c.v.). These findings suggest that LC hyperactivity and blood pressure increases elicited during clonidine withdrawal are mediated in part by activation of EAA receptors. In this regard, the mechanisms underlying clonidine withdrawal closely resembles those underlying opioid withdrawal.

Acute Disease↗
PubMed1994

The effects of hypothermic and normothermic cardiopulmonary bypass on glyceryl trinitrate activity.

Glyceryl trinitrate (GTN) is used to control arterial blood pressure during cardiopulmonary bypass (CPB) procedures, but its effects are often decreased during the period of extracorporeal support. The plasma and urine concentrations of GTN and glyceryl-1,2-dinitrate (1,2-GDN) and glyceryl-1,3-dinitrate (1,3-GDN) for male and female patients who received GTN during hypothermic CPB, and male and female patients who were given GTN during normothermic CPB, were measured by gas-liquid chromatography. During hypothermic CPB, the male and female subjects experienced significant decreases in GTN clearance (P < 0.05), 66% and 52%, respectively. Neither the males nor the females who underwent normothermic CPB experienced any significant change in GTN clearance. These results suggest that the lower core temperature during hypothermic CPB may decrease the biotransformation of GTN to GDNs and nitric oxide, thereby resulting in less dilation of blood vessels. Furthermore, the males in the hypothermic CPB group had significantly greater urinary concentrations of 1,3-GDN and 1,2-GDN than the females (P < 0.05), and the normothermic CPB males had a significantly greater urinary concentration of 1,2-GDN than the females in that group. The normothermic CPB males also had significantly higher plasma concentration of GTN at two time points, and 1,3-GDN at one time point, than the females. These data suggest that there may be a gender difference in GTN biotransformation.

Aged↗
PubMed1993

Evidence for the involvement of excitatory amino acid pathways in the development of precipitated withdrawal from acute and chronic morphine: an in vivo voltammetric study in the rat locus coeruleus.

Previous studies have demonstrated that activation of excitatory amino acid (EAA) pathways projecting to the locus coeruleus may be involved in the increased firing of locus coeruleus (LC) neurons during opioid withdrawal. Using differential normal pulse voltammetry to monitor catechol oxidation current (CA.OC), an index of neuronal activity in the LC, the role of EAA pathways in naloxone precipitated withdrawal after acute and chronic morphine treatment was examined. Acute morphine treatment (10 micrograms i.c.v.) significantly reduced the CA.OC signal in the LC to 54.3 +/- 3.1% of baseline. Naloxone challenge (1 mg/kg i.v.) completely reversed the morphine effect and produced a significant increase in the CA.OC signal above baseline, peak 145.4 +/- 10.1% of baseline. This naloxone-induced rebound response was attenuated by pretreatment with the EAA receptor antagonists gamma-D-glutamylglycine (DGG) (2, 20, 200 micrograms i.c.v.) and (-)-2-amino-7-phosphonoheptanoic acid (D-APH), but not L-APH (25 micrograms i.c.v.). In chronically morphine-treated rats (25 micrograms/h i.c.v., 5 days), naloxone challenge (1 mg/kg i.v.) produced a significant increase in CA.OC signal, peak 466.5 +/- 112.7% of baseline. This naloxone-induced response was attenuated by pretreatment with DGG (200 micrograms i.c.v.) or D-APH (25 micrograms i.c.v.). To the extent that CA.OC reflects locus coeruleus neuronal activity, the present findings further suggest that increases in locus coeruleus activity during naloxone precipitated withdrawal after both acute and chronic morphine treatment are mediated at least in part by activation of EAA pathways.

2-Amino-5-phosphonovalerate↗
PubMed1993

Diazepam's effect on systemic vascular resistance during cardiopulmonary bypass is not caused by its vehicle (alcohol-propylene glycol).

Control of hemodynamic parameters during cardiopulmonary bypass (CPB) is a desirable goal of the anesthesiologist. Diazepam is known to reduce systemic vascular resistance (SVR) during CPB. This study tested the hypothesis that diazepam reduces SVR during CPB through the action of its vehicle, alcohol-propylene glycol (APG). The study protocol was approved by the Institution's Human Experimentation Review Board and all patients gave informed consent. Premedication, induction, and maintenance of anesthesia were standardized. Thirty consecutive patients undergoing nonemergent cardiac surgical procedures were randomized to receive a standardized amount of diazepam, diazemuls, or alcohol-propylene glycol during stable CPB. SVR in the diazepam group decreased significantly (1,242 to 968 dyne.s.cm-5, P < 0.05) compared to baseline; whereas there was no significant change in SVR in the diazemul group, and a statistically significant increase in SVR (1,217 to 1,537 dyne.s.cm-5, P < 0.05) in the APG group. It is concluded that diazepam reduces SVR during CPB. Diazepam's vehicle does not reduce SVR during CPB, and is in fact associated with an increase in SVR.

Aged↗
PubMed1992

Stereoselective effects of central alpha 2-adrenergic agonist medetomidine on in vivo catechol activity in the rat rostral ventrolateral medulla (RVLM).

The stereoselective central effects of a novel, highly potent and selective alpha 2-agonist medetomidine on adrenergic neuronal activity, reflected by changes in catechol oxidation current, in the rostral ventrolateral medulla of the halothane-anesthetized rat were examined using in vivo differential normal pulse voltammetry. Dexmedetomidine, the active isomer, significantly decreased catechol oxidation current to 33.4 +/- 4.5% of baseline when given centrally (1 microgram, i.c.v.) and to 10.3 +/- 3.9% of baseline when given systemically (50 micrograms/kg, i.v.). Dexmedetomidine also significantly reduced mean arterial blood pressure by 19.9% following central administration but significantly increased mean arterial blood pressure by 59.9% following systemic administration. Levomedetomidine, the inactive isomer, had no effect on catechol oxidation current or blood pressure. The depressant effects of dexmedetomidine on catechol oxidation current were reversed by the selective alpha 2-adrenoceptor antagonist atipamezole (2 micrograms, i.c.v. or 200 micrograms/kg, i.v.). The results of the present study demonstrate, to our knowledge, for the first time the central stereoselective effects of medetomidine and antagonism by atipamezole on rostral ventrolateral medulla activity in the anesthetized rat.

Adrenergic alpha-Agonists↗
PubMed1992

Balloon flotation is more important than flow direction in determining the position of flow-directed pulmonary artery catheters.

Pulmonary artery catheters (PAC) inserted using pressure monitoring usually advance into a branch of the right pulmonary artery (PA). However, in some clinical situations it may be desirable to locate the tip of the PAC in a branch of the left PA. A two-part study was undertaken to explore factors that determine the ultimate location of the tip of a PAC. In the clinical study, 33 patients were randomized to supine or right-side down patient positioning during insertion of the PAC. Five patients were excluded because of withdrawal of the PAC during surgery. Seven of 14 PACs inserted in right-side down position were located in a branch of the left PA, while all 14 inserted with the patients supine went to a branch of the right PA (P less than 0.005). This suggests that the effect of upward flotation of the air-filled balloon in the column of blood predominates over movement with the current of maximal blood flow. Using a cardiac bypass pump and a plexiglass model of the pulmonary arterial bifurcation, the effects of lateral positioning on the direction of travel of balloon-tipped catheters were studied. The tip floated upward preferentially, even when flow was obstructed to the upward limb (P less than 0.005). Varying the flow rate in the system between 0.5 and 3.0 L/min and changing the direction of the natural curve of the PAC tip had no impact on this tendency to float upward. The authors conclude that balloon flotation in the column of blood strongly influences PAC tip location, and that this fact can assist in preferentially directing its placement.

Catheterization↗