|
Downward movement of syringe
pumps reduces syringe output
H Kern, A Kuring, U Redlich, UR Döpfmer,
NM Sims, CD Spies, WJ Kox. Br J Anaesth 2001: 86: 828-31
The aim of this study was to measure the
function of different syringe pumps after lowering the height of the pumps
by the maximum distance found in clinical practice. In particular, the
effect of infusion rate on the output of the syringe pump, and the minimum
infusion rate that gave a predetermined infusion delay were measured.
Three syringe pumps with their respective infusion lines were tested.
Injectomat C (German) with its 150 cm long infusion line, Ivac 770 (USA)
with its 200 cm infusion line, and Perfusor fm (German) with its 150 cm
long infusion line. A 50 ml Injectomat syringe was used for all experiments.
In-vivo closed system simulation was achieved by using glass capillaries,
0.5 mm diameter and 1 meter long. At the end of the capillaries, a manometer
was used to simulate a central venous pressure of 8 mm Hg. The syringes
were connected to the closed system, and pumps were started with a minimum
flow rate of 1 ml/hr and kept running throughout the experiment using
a colored fluid. When the fluid reached a marked area on the capillaries,
the syringes were lowered by 80 or 130 cm for adult and neonatal settings,
respectively. The time until the marked area was reached again was recorded.
The following variables were determined: the distance of the reflux back
into the infusion system of the liquid column; the distance of the reflux
of the liquid column; the time without movement of the liquid column;
and the time for the liquid column to reach the starting position again.
The infusion volume that was not administered was calculated according
to the stopped time and flow rate. The experiment was repeated using the
flow rates of 1, 2, 3, 5, and 10 ml/hr, and repeating each measurement
8 to 10 times. The compliance of each system was caculated.
Comments: There was a significant
exponential negative correlation between flow rate and time without effective
infusion for all three systems tested. Using an exponential regression,
it was estimated that at the adult setting, where the pumps were lowered
by 80 cm, that at a minimum flow rates of 4.4 ml/hr, there would be an
effective time without infusion of 60 sec; and at a minimum of 2.6 ml/hr
the duration of time without effective infusion would be 120 sec. Likewise,
for the neonatal settings, when lowering the infusion pump by 130 cm,
a minimal infusion rate of 6 ml/hr resulted in a time of 60 sec, and 4.3
ml/hr gave a time of 120 sec without infusion. Relevant time without infusion
was found up to infusion rates of >5ml/hr. The compliance of the Injectomat-C
and Perfusor fm pump systems were similar, 81 and 85µl/mm Hg, respectively,
but that of the Ivac 770 was significantly greater, at 103 µl/mm
Hg. This compliance was positively correlated with the time without infusion.
This demonstrated that the height at which the pump is placed, the compliance
of the delivery system, and the dialed flow rate, all play a significant
role in the amount of infusion that is actually delivered.
When we transport a precariously labile infant
after surgery to the intensive care unit, there are usually several infusion
pumps attached to the patient. It is not uncommon that there is insufficient
space near the patient to secure all the pumps. Often, these pumps are
placed on a shelf below the patient. We are all very familiar with the
changes in flow rate associated with the diameter and length of an intravenous
cannula and the height of the infusion bag. Nevertheless, when an infusion
pump is used, many of us think that the pump will deliver whatever we
set, regardless of where we place the pump. If it is not possible to maintain
the height of the infusion pump at the same level during transport as
in the operating room, the flow rate should be adjusted to <5ml/hr.
An infusion system with minimum filling volume and compliance is always
preferable. With advances in technology, we tend to put too much faith
in machines and their arrogant digital readouts. This paper jogs us back
to reality.
Reviewed by: Hoshi J. Khambatta, MD
Babies & Children's Hospital
Columbia Presbyterian Medical Center, NY
American Journal of
Respiratory and Critical Care Medicine
Jobe AL, Bancalari E: NICHD/NHLBI/ORD
Workshop Summary: Bronchopulmonary Dysplasia. Am J Respir Crit Care
Med 2001; 163(7): 1723-1729
This paper is an excellent review of the
workshop sponsored by the National Institute of Child Health and Development
and the National Heart, Lung and Blood Institute to discuss recent data
about the pathology, mechanisms, interventions and epidemiology of bronchopulmonary
dysplasia (BPD). A review of this topic is particularly pertinent since
there has been a considerable change in both the epidemiology and the
pathophysiology of BPD. As more premature infants are cared for with evolving
therapies, and survive despite being born at younger gestational ages,
the disease entity itself has undergone an evolution. BPD, defined as
a need for supplemental oxygen beyond 36 weeks post-conceptual age, is
now uncommon among infants born after 30 weeks gestation, largely due
to advances in therapy (exogenous surfactant, antenatal steroids) and
to strategies that minimize ventilator induced lung injury (VALI). But
despite great improvements, BPD continues to be a common presenting co-morbid
state in many of the patients we care for in the operating room.
The terminology and definition of BPD
have been revised. The workshop decided that the term "bronchopulmonary
dysplasia" should be retained rather than the term "chronic
lung disease". The definition of BPD has been revised as described
above. The previous definition, which included the need for supplemental
oxygen at 28 days of age, did not account for the gestational age at birth,
and was felt to be a confounding factor.
Radiographic findings were believed to
be imprecise and not predictive of functional outcome, and were dropped
from the definition. The definition grades BPD as mild, moderate or severe.
The review discusses the interactions between the mechanisms of lung injury,
genetic and developmental factors, and the role of inflammation in producing
the lesions that may progress to BPD. The interactions between the airway
and the pulmonary vasculature are also discussed, and the contribution
of pulmonary hypertension to the severity of the lung lesion is described.
Many of these issues have significant application in the operating room
during the anesthetic care of the neonate, as there are ventilatory techniques
that can either contribute or ameliorate the injury to the lung. Glucocorticoid,
antioxidant, and nutritional therapeutic interventions are discussed.
Research priorities are identified to further advances in treatment and
prevention.
This paper is highly recommended for any
pediatric anesthesiologist who cares for current or former premies and
desires an up to date understanding of the pathophsiologic underpinnings
of current treatment and research about this common condition.
Reviewed by: David Polaner, MD, FAAP
Children's Hospital, Denver, CO
A Randomized
Multicenter Study of Remifentanil Compared with Halothane in Neonates
and Infants Undergoing Pyloromyotomy. I. Emergence and Recovery Profiles
Davis P, Galinkin J, McGowan F, et al.
Anesthesia & Analgesia 2001; 93:88-91.
The goal of part one of the study was
to examine the hemodynamic response and recovery profile of remifentanil
compared with that of halothane in neonates and infants. The study consisted
of 60 patients, aged less than or equal to 8 weeks old, American Society
of Anesthesiologists physical status I or II, born at term, weighing greater
than or equal to 2500gms at birth, undergoing pyloromyotomy. A preoperative
pneumocardiogram evaluation was obtained in 51 of the 60 patients.
Premedication was not administered to
the study group. An intravenous induction with atropine (10mcg/kg), propofol
(2mg/kg), succinylcholine (2mg/kg) was the technique of choice. Following
intubation, cisatracurium was used to maintain muscle relaxation, and
acetaminophen (120mg) per rectum was administered for postoperative pain
relief. Anesthesia maintenance consisted of either remifentanil with nitrous
oxide and oxygen (60%:40%) or halothane with nitrous oxide and oxygen
(60%:40%). During the surgery, end-tidal carbon dioxide was maintained
at 40 - 45 mm Hg. Those patients randomized to receive remifentanil were
given a continuous infusion that was started at 0.4mcg/kg/min. The other
patients randomized to receive halothane had an expired anesthetic concentration
of 0.4%. The need to increase the maintenance anesthetics in response
to hypertension and tacycardia with skin incision and gastric manipulation
was similar in both groups. On the contrary, a slightly higher incidence
of hypotension was observed in the halothane-anesthetized patients as
compared with remifentanil. This was not of statistical significance.
At the start of skin closure, the wound
was infiltrated with bupivacaine, and the halothane was discontinued or
the remifentanil was decreased to 0.05mcg/kg/min. At the completion of
surgery, neostigmine and glycopyrrolate were administered. Then, nitrous
oxide and remifentanil were discontinued. For the next 10 minutes no physical
stimulation was performed. The patients were then extubated and transferred
to the PACU. A blinded observer assessed several criteria: quality of
recovery scores were looked at every 15 minutes and included 1) sleeping,
2) awake / quiet, 3) crying but consolable with nonnutritive sucking,
and 4) crying and inconsolable. In addition, the time the patient met
the PACU discharge criteria was recorded, the administration of any pain
medication, as well as adverse events of vomiting, cardiovascular side
effects, and hypoxemia. A postoperative pneumocardiogram was obtained
in 56 of the 60 patients.
Following final analysis of the data,
this study showed similar hemodynamic stability and anesthetic recovery
variables with remifentanil compared to halothane. A slightly higher incidence
of hypotension was noted with halothane. Postoperative respiratory depression
was not observed with remifentanil.
Comments: This study is the first
to look at the hemodynamic response and recovery profile of remifentanil
compared with halothane in neonates and infants undergoing pyloromyotomy.
The results appear promising. However, keep in mind that the study group
was small and it is questionable whether the doses used of remifentanil
and halothane is comparable. Further studies have to be done regarding
the use of remifentanil in neonates and infants.
Reviewed by: Cheryl K. Gooden,
MD
Mount Sinai Medical Center
New York, NY
Cross-validation of a composite
pain scale for preschool children within 24 hours of surgery.
Suraseranivongse S, Santawat U, Kraiprasit K, Petcharatana S, Prakkamodom
S and Muntraporn N. British Journal of Anaesthesia 2001; 87: 400-405.
In this prospective study of 167 Thai children undergoing surgical procedures,
the authors compared the scores of four previously validated postoperative
pain scores (Children's Hospital of Eastern Ontario Pain Scale (CHEOPS),
Objective Pain Scale (OPS), Toddler Preschool Postoperative Pain Scale
(TPPPS), Face, Legs, Activity, Cry and Consolability (FLACC)) to an anesthesiologist's
decision to treat a child for pain, and to each other. The evaluations,
initially made by the nurse, would trigger videotape for later evaluation
of the child's behavior, and consultation with a blinded anesthesiologist
who would make an independent decision to treat the child for pain. The
videotapes were evaluated and scored on all four scales by four nurse
anesthetists trained in the scoring systems. Categorization was based
upon patient age, evaluation in the PACU and later on the ward. Inter-
and intra-rater reliability, as well as correlation between the different
scoring systems was determined. The results showed satisfactory correlation
between the scores, and good reliability of the raters (intra- and inter-rater).
The CHEOPS yielded the best agreement with the physician's decision to
treat, both in the PACU and on the ward. In terms of ease of use, the
CHEOPS and FLACC were the most practical.
Comment: This is a well-done study that demonstrates the universal
application of some of the English language based pain scales after translation.
The study validates the scoring systems for use in Thai children, and
the translation made of the scoring systems for the purposes of the study.
The correlation between these systems is also reassuring. The ability
of a non-physician trained in these scoring systems to be able to predict
a decision to treat may be useful in the effective allocation of resources,
but the sensitivity and specificity are probably not adequate to completely
eliminate the need for evaluation by trained and experienced personnel.
How do anesthesiologists
treat malignant hyperthermia in a full-scale anaesthesia simulator?
Giardi Ti, Christensen UC, Jacobsen J, Jensen PF and þrding H.
ACTA Anaesthesiologica Scandinavica 2001; 45:1032-1035
In this study, the design involved evaluation of 32 anesthesia teams
(anesthesiologist and nurse anesthetist) being videotaped in an operating
room outfitted with an anesthesia simulator. The teams were videotaped
during a simulated anesthetic, which recreated an episode of malignant
hyperthermia. Team members were evaluated in their performance including
the diagnosis and initial treatment of MH. The authors outline eight goals
of initial treatment: termination of surgery and calling for additional
manpower, hyperventilation with 100% oxygen and increased fresh gas flow,
elimination of triggering agents, dantrolene administration, treatment
of acidosis with bicarbonate, treatment of hyperkalemia with glucose/insulin
infusion, administration of diuretics to preserve renal function, cooling
to control body temperature.
Within the 25-30 minutes of the scenario, all teams succeeded in terminating
surgery, eliminating triggering agents, instituting dantrolene and initiating
specific symptomatic treatments. Teams failing to return to mechanical
ventilation were frequently not hyperventilating the patients effectively,
although reporting the intention to do so. In fact, more than half the
teams inadequately hyperventilated the patient. The authors comment upon
the probability of enhanced preparation by the participants in knowing
that the host hospital was a MH center, and by the non-random pairing
of the teams, as possible factors affecting the results.
Comment: Task specific simulator training is a widely accepted
teaching and evaluation tool in medicine (ACLS, CPR), but full-scale simulation
has not been widely employed in the U.S. With adaptation of personnel
management principles developed for flight crews, and growing recognition
of the educational value of realistic simulation, evaluation by simulator
scenario may be on the horizon. The authors of this study have shown that
standard training in Denmark is likely adequate for recognition and initiation
of therapy for MH. It would be interesting to have epidemiologic data
about the actual incidence and morbidity/mortality of MH in Denmark to
permit evaluation of the validity of the conclusion. The finding that
hyperventilation is more successful using the mechanical ventilator freeing
the anesthesia provider to attend to other tasks is well received.
Reviewed by: Scott Markowitz, MD
Fellow in Pediatric Anesthesia, and
Jeffrey L. Galinkin, MD
Children's Hospital of Philadelphia
|
