Jerry Ingrande

Dose adjustment of anaesthetics in the morbidly obese

Anaesthesiologists must be prepared to deal with pharmacokinetic and pharmacodynamic (PD) differences in morbidly obese individuals. As drug administration based on total body weight can result in overdose, weight-based dosing scalars must be considered. Conversely, administration of drugs based on ideal body weight can result in a sub-therapeutic dose. Changes in cardiac output and alterations in body composition affect the distribution of numerous anaesthetic drugs. With the exception of neuromuscular antagonists, lean body weight is the optimal dosing scalar for most drugs used in anaesthesia including opioids and anaesthetic induction agents. The increased incidence of obstructive sleep apnoea and fat deposition in the pharynx and chest wall places the morbidly obese at increased risk for adverse respiratory events secondary to anaesthetic agents, thus altering the PD properties of these drugs. Awareness of the pharmacology of the commonly used anaesthetic agents including induction agents, opioids, inhalation agents and neuromuscular blockers is necessary for safe and effective care of morbidly obese patients.

Lean Body Weight Scalar for the Anesthetic Induction Dose of Propofol in Morbidly Obese Subjects

BACKGROUND: The unique anesthetic risks associated with the morbidly obese (MO) population have been documented. Pharmacologic management of these patients may be altered because of the physiologic and anthropometric changes associated with obesity. Unfortunately, studies examining the effects of extreme obesity on the pharmacology of anesthetics have been sparse. Although propofol is the induction drug most frequently used in these patients, the appropriate induction dosing scalar for propofol remains controversial in MO subjects. Therefore, we compared different weight-based scalars for dosing propofol for anesthetic induction in MO subjects. METHODS: Sixty MO subjects (body mass index ≥40 kg/m2) were randomized to receive a propofol infusion (100 mg · kg−1 · h−1) for induction of anesthesia based on total body weight (TBW) or lean body weight (LBW). Thirty control subjects (body mass index ⩽25 kg/m2) received a propofol infusion (100 mg · kg−1 · h−1) based on TBW. Syringe drop was used as the marker for loss of consciousness (LOC), at which point the propofol infusion was stopped. The propofol dose required for syringe drop and time to LOC were recorded. RESULTS: Total propofol dose (mg/kg) required for syringe drop and time to LOC were similar between control subjects and MO subjects given propofol based on LBW. MO subjects receiving a propofol infusion based on TBW had a significantly larger propofol dose and significantly shorter time to LOC. There was a strong relationship between LBW and total propofol dose received in all 3 groups. CONCLUSION: LBW is a more appropriate weight-based scalar for propofol infusion for induction of general anesthesia in MO subjects.

Regional anesthesia and obesity

Purpose of review Worldwide, the number of overweight and obese patients has increased dramatically. As a result, anesthesiologists routinely encounter obese patients daily in their clinical practice. The use of regional anesthesia is becoming increasingly popular for these patients. When appropriate, a regional anesthetic offers advantages and should be considered in the anesthetic management plan of obese patients. The following is a review of regional anesthesia in obesity, with special consideration of the unique challenges presented to the anesthesiologist by the obese patient. Recent findings Recent studies report difficulty in achieving peripheral and neuraxial blockade in obese patients. For example, there is an increased incidence of failed blocks in obese patients compared with similar, normal weight patients. Despite difficulties, regional anesthesia can be used successfully in obese patients, even in the ambulatory surgery setting. Summary Successful peripheral and neuraxial blockade in obese patients requires an anesthesiologist experienced in regional techniques, and one with the knowledge of the physiologic and pharmacologic differences that are unique to the obese patient.

Pharmacology and obesity.

Dosing of anesthetic agents in the morbidly obese patient differs significantly from that of the normal size patient. Until recently, obese subjects have been routinely excluded from clinical trials to obtain regulatory approval for investigational drugs. This has resulted in package insert dosage recommendations based on total body weight (TBW), valid for normal weight patients but not for the obese. Well-planned and rational management of morbidly obese patients undergoing surgery requires detailed knowledge of how morbid obesity affects drug dosing. Not only the increased body size and different body composition but also the physiological changes and comorbidities impact safe drug dosing by the anesthesiologist. The aim of this review is to provide the anesthesiologist with a practical approach to drug dosing in the morbidly obese patients.

The impact of blood pressure cuff location on the accuracy of noninvasive blood pressure measurements in obese patients: an observational study

Purpose Obesity presents many challenges to the anesthesiologist, including poorly fitting blood pressure (BP) cuffs due to the conical shape of the upper arm. The aim of this study was to determine the accuracy of noninvasive BP readings, obtained from a noninvasive BP cuff using various cuff locations and wrapping techniques, compared with invasive intra-arterial BP readings. Methods Thirty American Society of Anesthesiologists physical status I-III obese (body mass index[30 kgm -2 ) individuals undergoing non-cardiac surgery were enrolled in this observational study. Serial oscillometric noninvasive BP (NIBP) measurements were taken in the patients’ forearm and upper arm with two different wrapping formations (one following the contour of the upper arm, the other keeping cuff edges parallel). These NIBP measurements were compared with invasive arterial blood pressure (ABP) measurements taken from the ipsilateral radial artery. The precision and bias of the NIBP and ABP measurements were determined using Bland-Altman analysis. Analysis of variance and Welch’s t test were used to determine between-group differences inPurposeObesity presents many challenges to the anesthesiologist, including poorly fitting blood pressure (BP) cuffs due to the conical shape of the upper arm. The aim of this study was to determine the accuracy of noninvasive BP readings, obtained from a noninvasive BP cuff using various cuff locations and wrapping techniques, compared with invasive intra-arterial BP readings.MethodsThirty American Society of Anesthesiologists physical status I-III obese (body mass index > 30 kg·m−2) individuals undergoing non-cardiac surgery were enrolled in this observational study. Serial oscillometric noninvasive BP (NIBP) measurements were taken in the patients’ forearm and upper arm with two different wrapping formations (one following the contour of the upper arm, the other keeping cuff edges parallel). These NIBP measurements were compared with invasive arterial blood pressure (ABP) measurements taken from the ipsilateral radial artery. The precision and bias of the NIBP and ABP measurements were determined using Bland-Altman analysis. Analysis of variance and Welch’s t test were used to determine between-group differences in bias.ResultsThere was poor agreement between the ABP measurements and all types of NIBP measurements. Each of our study participants had a least one NIBP parameter (mean arterial pressure, systolic BP, or diastolic BP) that was > 10 mmHg different than the corresponding ABP parameter. Upper arm BP measurements showed a statistically insignificant trend toward underestimating ABP. For all cuff positions and wrapping techniques, systolic BP offered the best agreement between NIBP and ABP measurements.ConclusionsAll the forms of NIBP cuff orientation studied had unacceptable precision and bias compared with invasive ABP measurements. When patient and/or surgical conditions necessitate accurate BP monitoring, direct arterial measurement should be considered over NIBP measurements in obese patients.RésuméObjectifL’obésité pose de nombreux défis à l’anesthésiologiste, notamment des brassards pneumatiques difficiles à ajuster en raison de la forme conique du bras. L’objectif de cette étude était de déterminer la précision des mesures non invasives de la tension artérielle (TA) obtenues à l’aide d’un brassard pneumatique non invasif placé à différents niveaux et ajusté différemment, et de les comparer à des mesures invasives intra-artérielles de la TA.MéthodeTrente personnes obèses de statut physique I-III selon la classification de l’American Society of Anesthesiologists (indice de masse corporelle > 30 kg·m−2) subissant une chirurgie non cardiaque ont participé à cette étude observationnelle. Des mesures de la TA non invasives (TA-NI) réalisées par oscillométrie en série ont été prises au niveau de l’avant-bras et du bras des patients en plaçant le brassard de deux façons différentes (l’une en suivant le pourtour du bras, l’autre en gardant parallèles les bords du brassard). Ces mesures TA-NI ont été comparées aux mesures intra-artérielles de la tension artérielle invasives (TA-I) prises au niveau de l’artère radiale ipsilatérale. La précision et le biais des mesures TA-NI et TA-I ont été déterminés à l’aide d’une analyse de Bland-Altman. L’analyse de la variance et le test t de Welch ont été utilisés pour déterminer les différences de biais entre les groupes.RésultatsLes mesures TA-I et TA-NI, tous types confondus, concordaient peu. Chacun des participants à l’étude avait au moins un paramètre de TA-NI (tension artérielle moyenne, TA systolique ou TA diastolique) qui était différent de plus de 10 mmHg au paramètre TA-I correspondant. Lors des mesures de TA au niveau du bras, on a observé une tendance non significative d’un point de vue statistique vers une sous-estimation de la TA-I. Quelle que soit la position du brassard et la technique de placement, la TA systolique était celle affichant le plus de concordance entre les mesures TA-NI et TA-I.ConclusionToutes les méthodes de positionnement du brassard pour mesurer la TA de façon non invasive étudiées ont donné des mesures dont la précision et le biais étaient inacceptables par rapport aux mesures invasives de la TA. Lorsque les conditions liées au patient et/ou à la chirurgie nécessitent un monitorage précis de la TA, une mesure artérielle directe doit être envisagée plutôt que des mesures non invasives chez les patients obèses.

Anesthetic Pharmacology and the Morbidly Obese Patient.

Anesthesiologists are increasingly being faced with treating obese patients. Physiologic and anthropometric changes associated with obesity—most notably increases in cardiac output, changes in tissue perfusion and increases in total body weight, lean body weight, and fat mass affect the pharmacokinetics (PK) of anesthetic agents. In addition, redundancy of airway tissue, obstructive and central sleep apnea and CO2 retention affect the pharmacodynamics (PD) of anesthetics and narrow the therapeutic window of numerous anesthetic drugs. Safe and effective pharmacologic management of the obese patient requires a thorough understanding of how obesity affects the PK and PD of anesthetics.

Perioperative management of the morbidly obese adolescent with heart failure undergoing bariatric surgery

The incidence and prevalence of adolescent obesity and adolescent heart failure are increasing, and anesthesiologists increasingly will encounter patients with both conditions. A greater understanding of the physiologic challenges of adolescent heart failure as they relate to the perioperative stressors of anesthesia and bariatric surgery is necessary to successfully manage the perioperative risks faced by this growing subpopulation. Here, we present a representative case of a morbidly obese adolescent with heart failure who underwent a laparoscopic bariatric operation and review the limited available literature on perioperative management in this age group. Specifically, we review evidence and offer recommendations related to preoperative evaluation, venous thromboembolism prophylaxis, positioning, induction, airway management, monitoring, anesthetic maintenance, ventilator management, and adverse effects of the pneumoperitoneum, rhabdomyolysis, and postoperative care.

Medical devices for the anesthetist: current perspectives

Anesthesiologists are unique among most physicians in that they routinely use technology and medical devices to carry out their daily activities. Recently, there have been significant advances in medical technology. These advances have increased the number and utility of medical devices available to the anesthesiologist. There is little doubt that these new tools have improved the practice of anesthesia. Monitoring has become more comprehensive and less invasive, airway management has become easier, and placement of central venous catheters and regional nerve blockade has become faster and safer. This review focuses on key medical devices such as cardiovascular monitors, airway equipment, neuromonitoring tools, ultrasound, and target controlled drug delivery software and hardware. This review demonstrates how advances in these areas have improved the safety and efficacy of anesthesia and facilitate its administration. When applicable, indications and contraindications to the use of these novel devices will be explored as well as the controversies surrounding their use.

Intraoperative fluid management and bariatric surgery.

Perioperative fluid management is always important. The potential short-term or long-term complications of giving too little fluid during surgery must be balanced with the risks of administering too much. In addition to the amount, the type of fluid (colloid or crystalloid) must also be considered. These concerns are relevant for every surgical patient, but are even more important for the obese patient. Obesity is associated with increases in total and lean body weights, but intracellular, extracellular, and absolute total body water contents are each relatively decreased compared with normal weight subjects. Although both aggressive and restrictive fluid strategies have been advocated, there is sparse evidence to support one approach over another. This review will discuss perioperative fluid management, especially as it pertains to the morbidly obese patient undergoing bariatric surgery.

Anesthesia and Intraoperative Management of Renal Transplantation

The global epidemic of diabetes and hypertension has resulted in a dramatic increase of chronic kidney disease. For patients with end-stage renal disease, a transplant provides better survival and health-related quality of life than dialysis and is less resource intensive and more cost effective. Renal transplantation is the most commonly performed organ transplantation in the world, but because of organ shortages, the number of transplants is not increasing significantly. In an attempt to alleviate the organ shortage, expanded criteria for donors and donation after cardiac death are alternative strategies to increase the cadaveric donor pool.